A corrosion-resistant and heat-resistant steel co-doped with ternary trace elements and a preparation method thereof

Abstract

The present invention belongs to the technical field of austenitic heat-resistant steel, and provides a corrosion-resistant heat-resistant steel with ternary trace elements co-doped therein and a preparation method thereof, wherein the preparation method comprises: using pure iron, ferrosilicon alloy, ferrochromium alloy, ferronickel alloy, ferromolybdenum alloy, ferrotungsten alloy and cobalt powder as raw materials, and sequentially performing molten steel smelting, refining and purification, casting and molding, quenching and tempering heat treatment and nitriding treatment to obtain the corrosion-resistant heat-resistant steel with ternary trace elements co-doped therein. The present invention prepares an austenitic heat-resistant steel with excellent mechanical properties and corrosion resistance by doping molybdenum, cobalt and tungsten into a steel matrix and combining different carburizing treatment processes.

Description

Technical Field

[0001] The invention belongs to the technical field of austenitic heat-resistant steel, and relates to a corrosion-resistant heat-resistant steel co-doped with ternary trace elements and a preparation method thereof. Background Art

[0002] The matrix structure of austenitic heat-resistant steel is austenite with a face-centered cubic structure, and a small amount of carbides are distributed in the austenitic matrix. It has the ability to resist creep and fracture, oxidation, and medium corrosion when working for a long time at high temperature. Austenitic heat-resistant steel has a low carbon content. The main alloying elements are Cr and Ni. Some steels also contain Si, Mo, V, Ti, Al, W and other elements to form a dense oxide film, which improves the heat resistance temperature of the material. At this stage, the newly developed austenitic heat-resistant steels include HR3C, Super304H, TP347HFG, etc. Because austenitic heat-resistant steel has good organizational and performance characteristics, it plays an important role in many fields such as petroleum, chemical, electric power, and automobile industries.

[0003] Among them, austenitic heat-resistant steel has good high-temperature mechanical properties and oxidation resistance, corrosion resistance and structural stability, and is increasingly used in automotive exhaust manifolds, turbocharger housings and other parts. However, the coarse dendrites in the cast alloy cause serious segregation, which cannot be eliminated even by heat treatment, resulting in a decrease in alloy performance and a shortened service life. Therefore, it is urgent to optimize and improve the preparation process of austenitic heat-resistant steel. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a corrosion-resistant and heat-resistant steel co-doped with ternary trace elements and a preparation method thereof. The present invention prepares an austenitic heat-resistant steel with excellent mechanical properties and corrosion resistance by adding molybdenum, cobalt and tungsten elements into a steel matrix and combining different carburizing treatment processes.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements, the preparation method comprising:

[0007] Pure iron, ferrosilicon alloy, ferrochrome alloy, ferronickel alloy, ferromolybdenum alloy, ferrotungsten alloy and cobalt powder are used as raw materials, and the corrosion-resistant and heat-resistant steel doped with the ternary trace elements is obtained after molten steel smelting, refining and purification, casting, tempering heat treatment and nitriding treatment in sequence;

[0008] Wherein, the nitriding treatment process includes:

[0009] Sandblasting the surface of the heat-resistant alloy casting obtained by quenching and tempering heat treatment, and cleaning and drying the heat-resistant alloy casting after the sandblasting is completed;

[0010] uniformly mixing hydrated lanthanum nitrate, hydrated ferric nitrate and ionized water to obtain a reaction solution, adding citric acid to the reaction solution to obtain a mixed solution, heating the mixed solution in a water bath to obtain a precursor solution, and spraying the precursor solution on the sandblasted surface of the heat-resistant alloy casting;

[0011] Pre-filling a nitriding-promoting filler in an air inlet pipe of a nitriding furnace, wherein the nitriding-promoting filler comprises an inorganic carrier and cerium oxide and cobalt oxide supported on the surface of the inorganic carrier;

[0012] The heat-resistant alloy casting sprayed with the precursor solution is transferred to the nitriding furnace, and the heat-resistant alloy casting is heated in an air atmosphere, so that the precursor solution on the surface of the heat-resistant alloy casting is crystallized to form a lanthanum ferrite film during the heating process;

[0013] When the temperature in the nitriding furnace rises to the nitriding temperature, ammonia gas is introduced into the nitriding furnace, and the furnace is kept at the nitriding temperature to perform nitriding treatment to obtain the corrosion-resistant and heat-resistant steel.

[0014] The present invention first alloys austenitic heat-resistant steel, and after introducing molybdenum, cobalt and tungsten elements, the steel matrix can produce solid solution strengthening, dislocation strengthening and precipitation strengthening effects, thereby greatly improving the mechanical properties and corrosion resistance of the corrosion-resistant heat-resistant steel. Subsequently, through modulated heat treatment, the metallographic structure and performance are improved, and more uniform, fine and uniformly distributed austenite grains are obtained, thereby further improving the mechanical properties of the corrosion-resistant heat-resistant steel. Finally, during the nitriding process, through the synergistic effect of the nitriding-promoting filler and the lanthanum ferrite film, the purpose of cleaning the workpiece surface and accelerating the diffusion rate of nitrogen atoms can be achieved, thereby reducing the nitriding temperature, shortening the nitriding time, and improving the nitriding efficiency.

[0015] During the quenching and tempering heat treatment process, the alloy castings are subjected to rapid temperature annealing and two high-temperature quenchings, which can greatly improve the tensile strength of the alloy castings. During the annealing process, rapid temperature rise is conducive to the formation of fine and uniform austenite grains. The reduction in the size of austenite grains can reduce the martensite area, making the martensite bundles smaller, and its toughness and plasticity are improved. During the first quenching and heat preservation, molybdenum, cobalt and tungsten elements are dissolved in the steel matrix. After the second quenching treatment, on the one hand, a large amount of lath martensite is formed in the alloy casting. The main deformation mode of lath martensite is slip. Under the action of external force, a large number of dislocations in the lath martensite will move along the slip plane, and its stripe boundaries and domain boundaries will play a role in preventing crack propagation, while the laths in the martensite bundle are roughly parallel, which can avoid the generation of microcracks, and thus exhibit good toughness; in addition, the lath martensite contains a high density of dislocations, and the carbides that are segregated or preferentially precipitated at the dislocations are relatively small and evenly distributed, which will hinder the movement of dislocations. The pinning effect of carbon atoms on dislocations enables the lath martensite to obtain a higher tensile strength. On the other hand, after the second quenching treatment, more uniform and fine original austenite grains can be obtained, the crystal structure of the corrosion-resistant and heat-resistant steel is refined, resulting in an increase in the grain boundary length, which in turn makes the crack propagation path of the corrosion-resistant and heat-resistant steel longer and more tortuous; at the same time, the secondary quenching treatment also reduces the carbon content dissolved in the steel matrix, making the precipitated carbides finer and more dispersed, and the carbides in the alloy castings can gather and form near the microcracks, hindering the initiation and expansion of the microcracks, and can also eliminate the high stress areas where the microcracks are formed, preventing further microcracks, thereby greatly improving the fracture toughness of the alloy castings.

[0016] The present invention adopts two different nitriding promotion methods during the nitriding treatment process. First, the nitriding promotion filler is pre-filled in the air inlet pipe of the nitriding furnace. When ammonia is introduced through the air inlet pipe, it can fully contact with the nitriding promotion filler. The contact area between ammonia and cerium oxide and cobalt oxide is increased through the inorganic carrier with a porous structure. Cerium oxide and cobalt oxide can reduce the activation energy required for the breaking of ionic bonds, accelerate the decomposition of ammonia, increase the number of active nitrogen ions, and quickly establish a higher nitrogen potential, so as to achieve the purpose of improving the nitriding rate; second, the present invention sprays a precursor solution on the surface of the heat-resistant alloy casting, and crystallizes the precursor solution to form a lanthanum ferrite film by heating, thereby improving the catalytic decomposition activity of the heat-resistant alloy casting surface to ammonia at low temperature, and can effectively adsorb the decomposed free nitrogen to form a nitrogen adsorption layer on the surface of the lanthanum ferrite film; in addition, the rare earth element lanthanum can penetrate into the surface layer of the steel matrix to form a solid solution during the nitriding process, causing serious distortion of the surrounding lattice, thereby promoting the diffusion and penetration of active nitrogen atoms. The present invention can improve the nitriding efficiency and reduce the nitriding temperature through the synergistic effect of the nitriding-promoting filler and the lanthanum ferrite film, and can also significantly improve the hardness of the nitriding layer and improve the wear resistance, contact fatigue and bending fatigue life of the nitriding layer.

[0017] The present invention prefabricates a layer of lanthanum ferrite film on the surface of corrosion-resistant and heat-resistant steel, which not only catalytically promotes the nitriding process, but also significantly improves the nitriding efficiency; it can also improve the surface hardness of the carburized layer formed after carburizing treatment, and obtain a thicker effective hardened layer. This is because, on the one hand, the Fe-O octahedral oxygen atom in the lanthanum ferrite crystal is easy to be missing, thereby forming an oxygen vacancy defect. The missing oxygen can be adsorbed on the surface of the lanthanum ferrite film during the nitriding process, accelerating the decomposition and dehydrogenation of ammonia to produce more active nitrogen atoms; at the same time, lanthanum ferrite is more likely to adsorb active nitrogen atoms after the anion is missing, thereby increasing the active nitrogen atom concentration on the surface of the nitriding layer; in addition, the atomic radius of oxygen atoms and nitrogen atoms is comparable, so active nitrogen atoms can enter the oxygen vacancy defect. In order to maintain overall electrical neutrality, the lanthanum ferrite film can be used as a diffusion channel for active nitrogen atoms, which is beneficial to improving the nitriding efficiency. On the other hand, the lanthanum ferrite film formed by crystallization forms a nano-scale rough structure on the surface of the heat-resistant alloy casting, which not only increases the adsorption capacity of the heat-resistant alloy casting surface for nitrogen and lanthanum, but also provides a permeation channel for the infiltration of nitrogen and lanthanum. Since the atomic radius of lanthanum is large, the infiltration of lanthanum will inevitably cause lattice distortion around it, further accelerating the diffusion of nitrogen, thereby greatly increasing the nitriding rate. On the other hand, during the heating and crystallization process of the precursor solution in the air atmosphere, the surface of the heat-resistant alloy casting will also have a pre-oxidation effect. The carbon element on the surface of the heat-resistant alloy casting combines with the oxygen in the air to generate CO or CO 2 The escape reduces the carbon content on the surface of the heat-resistant alloy casting. Both carbon and nitrogen occupy the interstitial positions in the face-centered cubic crystals of the alloy. The reduction of carbon will lead to a decrease in the diffusion resistance of nitrogen, which is beneficial to increase the diffusion rate of nitrogen.

[0018] As a preferred technical solution of the present invention, the blasting medium used in the sandblasting process is white corundum.

[0019] In some optional examples, the particle size of the sandblasting medium used in the sandblasting treatment is 1 to 3 mm, for example, it can be 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm or 3.0 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In some optional instances, the blasting pressure of the sandblasting treatment is 0.2-0.3 MPa, for example, it can be 0.2 MPa, 0.21 MPa, 0.22 MPa, 0.23 MPa, 0.24 MPa, 0.25 MPa, 0.26 MPa, 0.27 MPa, 0.28 MPa, 0.29 MPa or 0.3 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] In some optional examples, the blasting distance between the nozzle and the surface of the heat-resistant alloy casting during the sandblasting process is 100-150 mm, for example, it can be 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm or 150 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In some optional examples, the angle between the nozzle axis and the surface of the heat-resistant alloy casting during the sandblasting process is 60 to 70°, for example, it can be 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In some optional instances, the sandblasting time is 3 to 8 minutes, for example, it can be 3.0 minutes, 3.5 minutes, 4.0 minutes, 4.5 minutes, 5.0 minutes, 5.5 minutes, 6.0 minutes, 6.5 minutes, 7.0 minutes, 7.5 minutes or 8.0 minutes, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, the molar ratio of the lanthanum element in the hydrated lanthanum nitrate to the iron element in the hydrated ferric nitrate is 1:(0.8-1.2), for example, it can be 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1.0, 1:1.05, 1:1.1, 1:1.15 or 1:1.2, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In some optional examples, the total concentration of the hydrated lanthanum nitrate and the hydrated ferric nitrate in the reaction solution is 0.3-0.5 mol / L, for example, it can be 0.3 mol / L, 0.32 mol / L, 0.34 mol / L, 0.36 mol / L, 0.38 mol / L, 0.4 mol / L, 0.42 mol / L, 0.44 mol / L, 0.46 mol / L, 0.48 mol / L or 0.5 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional examples, the molar ratio of the hydrated lanthanum nitrate to the citric acid in the reaction solution is 1:(3-5), for example, 1:3.0, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4.0, 1:4.2, 1:4.4, 1:4.6, 1:4.8 or 1:5.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In some optional embodiments, the water bath heating temperature is 80-90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In some optional examples, the water bath heating time is 12 to 24 hours, for example, it can be 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours or 24 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional examples, the spraying amount of the precursor solution is 3 to 4 mL / min, for example, it can be 3.0 mL / min, 3.1 mL / min, 3.2 mL / min, 3.3 mL / min, 3.4 mL / min, 3.5 mL / min, 3.6 mL / min, 3.7 mL / min, 3.8 mL / min, 3.9 mL / min or 4.0 mL / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In some optional examples, the spraying time of the precursor solution is 4 to 5 minutes, for example, it can be 4.0 minutes, 4.1 minutes, 4.2 minutes, 4.3 minutes, 4.4 minutes, 4.5 minutes, 4.6 minutes, 4.7 minutes, 4.8 minutes, 4.9 minutes or 5.0 minutes, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] As a preferred technical solution of the present invention, the penetration-enhancing filler is prepared by the following method:

[0032] Dispersing soluble cerium salt and soluble cobalt salt in anhydrous ethanol, and mixing them evenly to form a penetration-enhancing dispersion; adding an inorganic carrier to the penetration-enhancing dispersion, performing magnetic stirring and ultrasonic dispersion to obtain a suspension; filtering and drying the suspension in sequence to obtain a penetration-enhancing precursor; and calcining the penetration-enhancing precursor to obtain the penetration-enhancing filler.

[0033] In some optional examples, the molar ratio of the cerium element in the soluble cerium salt to the cobalt element in the soluble cobalt salt is 1:(0.8-1.3), for example, it can be 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1.0, 1:1.05, 1:1.1, 1:1.15, 1:1.2, 1:1.25 or 1:1.3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In some optional examples, the total concentration of the soluble cerium salt and the soluble cobalt salt in the penetration-enhancing dispersion is 0.5-1.5 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] In some optional examples, the ratio of the total mass of the soluble cerium salt and the soluble cobalt salt in the penetration-enhancing dispersion to the mass of the inorganic carrier is (0.2-0.3):1, for example, it can be 0.2:1, 0.21:1, 0.22:1, 0.23:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1, 0.28:1, 0.29:1 or 0.3:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In some optional examples, the inorganic carrier includes any one of montmorillonite, diatomaceous earth, fly ash, and hydroxyapatite, or a combination of at least two of them.

[0037] In some optional instances, the rotation speed of the magnetic stirring is 300-400 r / min, for example, it can be 300 r / min, 310 r / min, 320 r / min, 330 r / min, 340 r / min, 350 r / min, 360 r / min, 370 r / min, 380 r / min, 390 r / min or 400 r / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional examples, the magnetic stirring time is 30 to 40 min, for example, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In some optional examples, the ultrasonic power of the ultrasonic dispersion is 500-600 W, for example, it can be 500 W, 510 W, 520 W, 530 W, 540 W, 550 W, 560 W, 570 W, 580 W, 590 W or 600 W, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In some optional examples, the calcination process of the penetration-enhancing precursor includes:

[0041] The penetration-enhancing precursor is heated to 300-400°C at a heating rate of 10-20°C / min, and kept warm for 1-2h; wherein the heating rate may be 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min or 20°C / min, the heating temperature may be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, and the holding time may be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h;

[0042] Subsequently, the infiltration-enhancing precursor is further heated to 700-800°C at a heating rate of 5-15°C / min, and kept warm for 3-4 hours to complete calcination to obtain the infiltration-enhancing filler, wherein the heating rate can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min or 15°C / min, and the infiltration-enhancing filler is obtained. The heating temperature can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C or 800°C and the holding time can be 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h or 4.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] As a preferred technical solution of the present invention, the heat-resistant alloy casting is heated at a heating rate of 10 to 15°C / min in the air atmosphere of a nitriding furnace, for example, 10°C / min, 10.5°C / min, 11°C / min, 11.5°C / min, 12°C / min, 12.5°C / min, 13°C / min, 13.5°C / min, 14°C / min, 14.5°C / min or 15°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] In some optional examples, the nitriding temperature is 450-500°C, for example, 450°C, 455°C, 460°C, 465°C, 470°C, 475°C, 480°C, 485°C, 490°C, 495°C or 500°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] The present invention specifically limits the nitriding temperature to 450-550°C. The nitriding temperature changes the diffusion coefficient of nitrogen atoms in each nitriding phase on the one hand; on the other hand, it also changes the phase structure of the nitriding layer. When the nitriding temperature increases, the phase region expands, the phase thickness increases, and the depth of the nitriding layer increases. When the nitriding temperature is lower than 450°C, the nitriding treatment time needs to be extended to achieve a certain nitriding layer thickness. At this time, the number of active nitrogen atoms adsorbed on the surface of the lanthanum ferrite film will be reduced, and the hardness of the nitriding layer finally formed will be lower.

[0046] In some optional examples, the flow rate of ammonia gas is 5 to 8 L / min, for example, it can be 5.0 L / min, 5.2 L / min, 5.4 L / min, 5.6 L / min, 5.8 L / min, 6.0 L / min, 6.2 L / min, 6.4 L / min, 6.6 L / min, 6.8 L / min, 7.0 L / min, 7.2 L / min, 7.4 L / min, 7.6 L / min, 7.8 L / min or 8.0 L / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In some optional examples, the nitriding treatment time is 3 to 5 hours, for example, it can be 3.0h, 3.2h, 3.4h, 3.6h, 3.8h, 4.0h, 4.2h, 4.4h, 4.6h, 4.8h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] As a preferred technical solution of the present invention, the molten steel smelting process specifically comprises the following steps:

[0049] Pure iron is put into a smelting furnace, heated to a smelting temperature and kept warm to form molten iron; then, alloy materials are put into the molten iron in batches, first, ferrosilicon alloy is added to the molten iron and kept warm, during the insulation process, argon gas is introduced from the bottom of the molten iron and a slag-forming agent is added to remove scum on the liquid surface; then, the molten iron is heated to a first temperature, ferrochromium alloy, ferronickel alloy and ferromolybdenum alloy are added to the molten iron and kept warm at the first temperature, during the insulation process, argon gas is introduced from the bottom of the molten iron and a slag-forming agent is added to remove scum on the liquid surface; finally, the molten iron is further heated to a second temperature, ferrotungsten alloy and cobalt powder are added to the molten iron and kept warm at the second temperature, during the insulation process, argon gas is introduced from the bottom of the molten iron and a slag-forming agent is added to remove scum on the liquid surface, and alloyed steel liquid is obtained.

[0050] In some optional instances, the melting temperature is 1560-1570°C, for example, it can be 1560°C, 1561°C, 1562°C, 1563°C, 1564°C, 1565°C, 1566°C, 1567°C, 1568°C, 1569°C or 1570°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In some optional examples, the melting temperature is kept for 50 to 60 minutes, for example, 50 minutes, 51 minutes, 52 minutes, 53 minutes, 54 minutes, 55 minutes, 56 minutes, 57 minutes, 58 minutes, 59 minutes or 60 minutes, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] In some optional examples, after adding ferrosilicon alloy to the molten steel, the temperature is kept for 20 to 30 minutes, for example, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes or 30 minutes, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] In some optional instances, the first temperature is 1580-1600°C, for example, it may be 1580°C, 1582°C, 1584°C, 1586°C, 1588°C, 1590°C, 1592°C, 1594°C, 1596°C, 1598°C or 1600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] In some optional instances, the first temperature is kept warm for 20 to 30 minutes, for example, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes or 30 minutes, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] In some optional instances, the second temperature is 1650-1670°C, for example, it can be 1650°C, 1652°C, 1654°C, 1656°C, 1658°C, 1660°C, 1662°C, 1664°C, 1668°C or 1670°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] In some optional examples, the second temperature is kept warm for 20 to 30 minutes, for example, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes or 30 minutes, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] In some optional examples, the slag-forming agent includes any one of lime, fluorite, alumina or calcium carbide, or a combination of at least two of them.

[0058] In some optional examples, the amount of the slag forming agent added each time the alloy material is added is: 15 to 20 kg of slag forming agent per ton of molten steel, for example, 15 kg, 15.5 kg, 16 kg, 16.5 kg, 17 kg, 17.5 kg, 18 kg, 18.5 kg, 19 kg, 19.5 kg or 20 kg, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0059] In some optional embodiments, during the heat preservation process, the flow rate of argon gas introduced into the molten steel is 15-20 Nm 3 / h, for example, it can be 15Nm 3 / h、15.5Nm 3 / h、16Nm 3 / h、16.5Nm 3 / h、17Nm 3 / h、17.5Nm 3 / h、18Nm 3 / h、18.5Nm 3 / h、19Nm 3 / h、19.5Nm 3 / h or 20Nm 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] As a preferred technical solution of the present invention, the refining and purification process specifically includes the following steps:

[0061] The alloyed steel liquid obtained after smelting the steel liquid is adjusted to the refining temperature and then injected into the refining furnace, oxygen and nitrogen are introduced into the alloyed steel liquid to perform the first stage of decarburization on the alloyed steel liquid; when the carbon content in the alloyed steel liquid is reduced to the first content, the flow rate of oxygen is reduced and the flow rate of nitrogen is increased, and the alloyed steel liquid is decarburized in the second stage; when the carbon content in the alloyed steel liquid is reduced to the second content, the flow rate of oxygen is reduced again and the flow rate of nitrogen is increased, and the alloyed steel liquid is decarburized in the third stage; when the carbon content in the alloyed steel liquid is reduced to the third content, the introduction of oxygen and nitrogen is stopped; subsequently, a purifier is added to the alloyed steel liquid, and argon is blown into the bottom of the alloyed steel liquid to remove scum on the liquid surface to obtain refined steel liquid.

[0062] In some optional examples, the refining temperature is 1600-1620°C, for example, it can be 1600°C, 1602°C, 1604°C, 1606°C, 1608°C, 1610°C, 1612°C, 1614°C, 1616°C, 1618°C or 1620°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0063] In some optional examples, during the first stage of carbon removal, the oxygen feed rate is 350-400 Nm 3 / h, for example, it can be 350Nm 3 / h、355Nm 3 / h、360Nm 3 / h、365Nm 3 / h、370Nm 3 / h、375Nm 3 / h、380Nm 3 / h、385Nm 3 / h、390Nm 3 / h、395Nm 3 / h or 400Nm 3 / h; the nitrogen intake is 50~100Nm 3 / h, for example, 50Nm 3 / h、55Nm 3 / h、60Nm 3 / h、65Nm 3 / h、70Nm 3 / h、75Nm3 / h、80Nm 3 / h、85Nm 3 / h、90Nm 3 / h、95Nm 3 / h or 100Nm 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0064] In some optional examples, the first content is 0.5-0.6wt%, for example, it can be 0.5wt%, 0.51wt%, 0.52wt%, 0.53wt%, 0.54wt%, 0.55wt%, 0.56wt%, 0.57wt%, 0.58wt%, 0.59wt% or 0.6wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0065] In some optional examples, during the second stage of carbon removal, the oxygen feed rate is 280-320 Nm 3 / h, for example, it can be 280Nm 3 / h、285Nm 3 / h、290Nm 3 / h、295Nm 3 / h、300Nm 3 / h、305Nm 3 / h、310Nm 3 / h、315Nm 3 / h or 320Nm 3 / h; the nitrogen intake is 120~180Nm 3 / h, for example, it can be 120Nm 3 / h、125Nm 3 / h、130Nm 3 / h、135Nm 3 / h、140Nm 3 / h、145Nm 3 / h、150Nm 3 / h、155Nm 3 / h、160Nm 3 / h、165Nm 3 / h、170Nm 3 / h、175Nm 3 / h or 180Nm 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0066] In some optional examples, the second content is 0.3-0.4wt%, for example, it can be 0.3wt%, 0.31wt%, 0.32wt%, 0.33wt%, 0.34wt%, 0.35wt%, 0.36wt%, 0.37wt%, 0.38wt%, 0.39wt% or 0.4wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] In some optional examples, during the third stage of carbon removal, the oxygen feed rate is 200-250 Nm 3 / h, for example, it can be 200Nm 3 / h、205Nm 3 / h、210Nm 3 / h、215Nm 3 / h、220Nm 3 / h、225Nm 3 / h、230Nm 3 / h, 235Nm 3 / h、240Nm 3 / h、245Nm 3 / h or 250Nm 3 / h; the nitrogen intake is 200~250Nm 3 / h, for example, it can be 200Nm 3 / h、205Nm 3 / h、210Nm 3 / h、215Nm 3 / h、220Nm 3 / h、225Nm 3 / h、230Nm 3 / h, 235Nm 3 / h、240Nm 3 / h、245Nm 3 / h or 250Nm 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0068] In some optional examples, the third content is 0.1-0.2wt%, for example, it can be 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt% or 0.2wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0069] In some optional examples, the purifier is composed of lime, fluorite and aluminum powder, wherein 8-10 kg of lime, 2.5-3.2 kg of fluorite powder and 1.3-1.7 kg of aluminum powder are added to each ton of alloyed steel liquid, and the amount of lime added can be 8.0 kg, 8.2 kg, 8.4 kg, 8.6 kg, 8.8 kg, 9.0 kg, 9.2 kg, 9.4 kg, 9.6 kg, 9.8 kg or 10.0 kg; the amount of fluorite powder added can be 2.5 kg, 2.6 kg, 2.7 kg, 2.8 kg, 2.9 kg, 3.0 kg, 3.1 kg or 3.2 kg; the amount of aluminum powder added can be 1.3 kg, 1.35 kg, 1.4 kg, 1.45 kg, 1.5 kg, 1.55 kg, 1.6 kg, 1.65 kg or 1.7 kg, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0070] In some optional examples, after adding the purifier, the time for introducing argon into the alloyed steel liquid is 10 to 20 minutes, for example, it can be 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0071] In some optional embodiments, after adding the purifier, the flow rate of argon gas introduced into the alloyed steel liquid is 50-60 Nm 3 / h, for example, 50Nm 3 / h、51Nm 3 / h、52Nm 3 / h、53Nm 3 / h、54Nm 3 / h、55Nm 3 / h、56Nm 3 / h、57Nm 3 / h、58Nm 3 / h、59Nm 3 / h or 60Nm 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0072] In some optional examples, based on the mass fraction of the refined steel liquid being 100wt%, the mass fraction of each element in the refined steel liquid is controlled within the following range:

[0073] Carbon 0.1-0.2wt%, silicon 1.5-2wt%, chromium 23-25wt%, nickel 19-20wt%, molybdenum 0.3-0.4wt%, tungsten 0.5-0.6wt% and cobalt 1.6-1.8wt%, the balance is iron; wherein the mass fraction of carbon can be 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt% or 0.2wt%; the mass fraction of silicon can be 1 %. The mass fraction of chromium can be 23wt%, 23.2wt%, 23.4wt%, 23.6wt%, 23.8wt%, 24wt%, 24.2wt%, 24.4wt%, 24.6wt%, 24.8wt% or 25wt%; the mass fraction of nickel can be 19wt%, 19.1wt%, 19.6wt%, 19.8wt% or 25wt%. The mass fraction of molybdenum can be 0.3wt%, 0.31wt%, 0.32wt%, 0.33wt%, 0.34wt%, 0.35wt%, 0.36wt%, 0.37wt%, 0.38wt%, 0.39wt% or 0.4wt%; the mass fraction of tungsten can be 0.5wt%, 0.51wt%, 0.52wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 10wt%; the mass fraction of molybdenum can be 0.31wt%, 0.32wt%, 0.33wt%, 0.34wt%, 0.35wt%, 0.36wt%, 0.37wt%, 0.38wt%, 0.39wt% or 0.4wt%; the mass fraction of tungsten can be 0.5wt%, 0.51wt%, 0.52 wt%, 0.53wt%, 0.54wt%, 0.55wt%, 0.56wt%, 0.57wt%, 0.58wt%, 0.59wt% or 0.6wt%; the mass fraction of cobalt can be 1.6wt%, 1.62wt%, 1.64wt%, 1.66wt%, 1.68wt%, 1.7wt%, 1.72wt%, 1.74wt%, 1.76wt%, 1.78wt% or 1.8wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0074] Silicon is a beneficial element for high temperature corrosion resistance in corrosion-resistant heat-resistant steel. At the same time, it is also a ferrite forming element, which plays a role of deoxidation in the process of alloy smelting. In addition, silicon can also form a dense silicon dioxide film on the surface of corrosion-resistant heat-resistant steel, thereby enhancing the passivation ability of the surface of corrosion-resistant heat-resistant steel, preventing corrosive gases such as oxygen, sulfur, and nitrogen from diffusing into the steel, and improving the corrosion resistance of corrosion-resistant heat-resistant steel. The present invention specifically limits the content of silicon to 1.5-2wt%. When the content of silicon exceeds 2wt%, the amount of delta ferrite will increase, and the tendency of intermetallic compound formation will also increase, resulting in reduced mechanical properties of corrosion-resistant heat-resistant steel.

[0075] Chromium is a ferrite-forming element that can reduce the austenite phase region and is one of the important alloying elements in corrosion-resistant and heat-resistant steel. When the chromium content is within the numerical range specified in the present invention, the chromium element can combine with oxygen to form a dense chromium oxide film, which can prevent corrosive gases such as oxygen, sulfur, and nitrogen from diffusing into the steel to a certain extent, and can also hinder the diffusion of metal ions outward. In addition, the addition of chromium will promote the formation of intermetallic compounds in the alloy, such as σ phase, and will also promote the formation of carbides M 23 C 6 The formation of these precipitates will hinder the grain boundary sliding and thus improve the tensile strength of corrosion-resistant and heat-resistant steel.

[0076] Nickel is an alloying element that expands the γ phase region in corrosion-resistant and heat-resistant steel, and can ensure the γ phase structure in corrosion-resistant and heat-resistant steel. The present invention specifically limits the content of nickel to 19-20wt%. When the content of nickel is within this numerical range, the high-temperature γ phase can be retained to room temperature, thereby obtaining an austenite structure at room temperature. When the content of nickel exceeds 20wt%, the solubility of carbon in the steel matrix will be reduced, thereby increasing the tendency of carbide precipitation.

[0077] Molybdenum is an element that forms and stabilizes ferrite and expands the ferrite phase region. Its ability to form ferrite is comparable to that of chromium, and its ability to expand the ferrite phase region is higher than that of chromium. The main function of the present invention of adding molybdenum to the molten steel is to improve the corrosion resistance of the corrosion-resistant heat-resistant steel, such as the resistance to reducing medium corrosion, pitting corrosion, crevice corrosion, and intergranular corrosion. The molybdenum element has a corrosion inhibition effect after forming molybdate. However, the molybdenum element will also promote the precipitation of the intermetallic phase in the corrosion-resistant heat-resistant steel, and its excessive addition will also have an adverse effect on the corrosion resistance and mechanical properties of the steel. In order to keep the corrosion-resistant heat-resistant steel with a single austenite structure, as the molybdenum content in the molten steel increases, the content of the austenite-forming element nickel should also be increased accordingly to maintain the balance between the ferrite and austenite-forming elements in the steel. As the molybdenum content increases, the tensile strength of the corrosion-resistant and heat-resistant steel at high temperatures also increases, and the high-temperature deformation resistance is enhanced, but along with it, the hot working properties of the corrosion-resistant and heat-resistant steel will also deteriorate. Therefore, in order to balance the high-temperature deformation resistance and hot working properties of the corrosion-resistant and heat-resistant steel, the present invention specifically limits the content of the molybdenum element to 0.3-0.4wt%.

[0078] Tungsten is a strong carbide-forming element. The invention adds tungsten to the molten steel to greatly improve the comprehensive mechanical properties of corrosion-resistant and heat-resistant steel. This is because, on the one hand, tungsten is a typical substitutional solid solution strengthening element. It can be dissolved into austenite at high temperature to strengthen the steel matrix, improve the stability of the structure, and play a role in solid solution strengthening. On the other hand, tungsten is also a strong carbide-forming element, which helps the tungsten-containing carbide M 23 C 6 and Laves phase precipitation and improve its stability, thereby playing a second phase strengthening role, among which the carbide M 23 C 6 It can be used as a heterogeneous nucleation core to increase the number of austenite nuclei and achieve the purpose of refining austenite grains. After grain refinement, the number of grain boundaries will increase, and dislocation movement is easy to accumulate at the grain boundaries, resulting in the slip band in the grain terminating at the grain boundary; Laves phase is a strengthening phase widely used in corrosion-resistant and heat-resistant steels. The addition of tungsten elements will reduce the particle size of Laves phases, slow down its coarsening rate, and enhance the precipitation hardening effect. On the other hand, the addition of tungsten elements can also significantly reduce the stacking fault energy of austenite, help the appearance of stacking faults, increase the width of stacking faults, prevent cross-slip, and facilitate the formation of twins. The appearance of twins can hinder the precipitation of precipitated phases at grain boundaries, thereby extending the service life of corrosion-resistant and heat-resistant steels.

[0079] In addition, adding a small amount of tungsten can further improve the corrosion resistance of corrosion-resistant and heat-resistant steel. When the corrosion-resistant and heat-resistant steel is immersed in a corrosive solution, the tungsten element will be in the form of WO 4 2- Dissolved in the corrosion solution in the form of WO 42- It is adsorbed on the surface of corrosion-resistant heat-resistant steel to form a protective layer, which inhibits the further dissolution and shedding of corrosion-resistant heat-resistant steel, thus having a corrosion-inhibiting effect. However, when the amount of tungsten added is too high, the corrosion resistance of corrosion-resistant heat-resistant steel will also decline. This is because non-metallic inclusions, intermetallic precipitation phases and grain boundaries are sensitive areas for grain boundary corrosion of corrosion-resistant heat-resistant steel, and σ phase is the most sensitive phase for grain boundary corrosion of corrosion-resistant heat-resistant steel. Therefore, the higher the precipitation amount of σ phase, the worse the corrosion resistance of corrosion-resistant heat-resistant steel. As the content of tungsten increases, the precipitation amount of σ phase increases accordingly. Therefore, the addition amount of tungsten should not be too high, otherwise it will affect the corrosion resistance of corrosion-resistant heat-resistant steel; in addition, tungsten is a typical ferrite-forming element. Excessive addition of tungsten will also lead to an increase in the content of residual ferrite, which is not conducive to the high-temperature mechanical properties of corrosion-resistant heat-resistant steel. Therefore, the present invention specifically limits the content of tungsten to 0.5-0.6wt%.

[0080] Cobalt is an important alloying element and austenite stabilizer in austenitic heat-resistant steel. The complete dissolution of cobalt in the steel matrix will increase the solubility of chromium, tungsten and carbon, reduce the precipitation phase at the grain boundary and in the grain, and reduce the diffusion rate of chromium and carbon, thereby inhibiting the M 23 C 6 coarsening; in addition, the addition of cobalt can reduce the stacking fault energy of Fe-Cr-Ni alloy, and the formation of twins is closely related to the stacking fault energy. Generally speaking, grains with higher stacking fault energy are not easy to produce twins. With the increase of cobalt content, the stacking fault energy of grains gradually decreases, which is conducive to the appearance of stacking faults, preventing the progress of cross slip, and ultimately conducive to the formation of twins. The appearance of twins can hinder the precipitation of precipitated phases at grain boundaries. Due to the coherence of twin boundaries, the incident dislocations can be selectively blocked or transmitted according to the dislocation characteristics, thereby improving the tensile strength of corrosion-resistant and heat-resistant steels. However, the cobalt content cannot exceed 1.8wt%, because excessive addition of cobalt will have an adverse effect on the corrosion resistance of corrosion-resistant heat-resistant steel. When the chromium content is in the range of 1.6-1.8wt%, the metallographic structure contains a large amount of delta ferrite, which is often distributed along the austenite grain boundaries. Due to the high chromium content in delta ferrite, the chromium-poor phenomenon at the austenite grain boundaries is alleviated, which is beneficial to prevent intergranular corrosion; when the chromium content exceeds 1.8wt%, the amount of delta ferrite in the metallographic structure decreases, (Cr, Fe) 23 C 6Carbides are easily precipitated at grain boundaries, resulting in rapid consumption of chromium in the grain boundary area, while the chromium element in the matrix austenite cannot diffuse to the grain boundary in time, resulting in the appearance of chromium-poor areas at the grain boundaries. Under the action of the potential difference generated at the grain boundary and inside the grain, the chromium-poor areas are closely connected to the carbides. Under the action of the corrosive medium, intergranular corrosion cracking of the steel matrix is ​​caused, and the intergranular corrosion rate is increased, which ultimately affects the corrosion resistance of the corrosion-resistant and heat-resistant steel.

[0081] As a preferred technical solution of the present invention, it is characterized in that the casting process specifically includes the following steps:

[0082] Preheating the steel mold, injecting the refined molten steel obtained after refining and purification into the steel mold when it reaches the casting temperature, naturally cooling to a first temperature after all the refined molten steel is injected into the steel mold, then adjusting the cooling rate, intermittently ultrasonically vibrating the steel mold, stopping the ultrasonic vibration and keeping the steel mold warm when the temperature drops to a second temperature, then naturally cooling to room temperature, and demolding to obtain an alloy casting;

[0083] In some optional instances, the preheating temperature of the steel mold is 380-400°C, for example, it can be 380°C, 382°C, 384°C, 386°C, 388°C, 390°C, 392°C, 394°C, 396°C, 398°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0084] In some optional instances, the casting temperature is 1580-1600°C, for example, it can be 1580°C, 1582°C, 1584°C, 1586°C, 1588°C, 1590°C, 1592°C, 1594°C, 1596°C, 1598°C or 1600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0085] The present invention specifically limits the casting temperature to 1580-1600°C. When the casting temperature is within this temperature range, the refined steel liquid has a higher cooling rate during the solidification process, the austenite nucleation rate is higher, and the solute atoms are continuously discharged to the surrounding liquid phase during the growth of the austenite grains, resulting in the enrichment of the solute atoms at the front of the solid-liquid interface, the grains grow along a specific crystal direction, the branching tendency is reduced, and the formed austenite grains are relatively small and evenly distributed; at the same time, the carbon atoms precipitated from the austenite will react with the alloy in the refined steel liquid. Elements combine to form carbides. When casting is carried out in the temperature range of 1580-1600℃, high-melting-point carbides such as tungsten carbide are first formed in the refined steel liquid and exist in the refined steel liquid in the form of hard particles. High-melting-point hard particles are difficult to aggregate and grow. Therefore, during the solidification process, these hard particles will be wrapped by the rapidly growing austenite grains and dispersed in the austenite, resulting in a smaller carbide particle size, a relatively dispersed and discontinuous distribution, which helps to produce a dispersion strengthening effect on the steel matrix.

[0086] When the pouring temperature is lower than 1580℃, the austenite grains will be relatively small. During the solidification process of the refined steel liquid, due to the redistribution of solute, more alloy elements or fine carbide micro-clusters will be pushed to the vicinity of the austenite grain boundaries, resulting in an increase in the number of carbides near the grain boundaries and a coarsening of the morphology. These coarse carbides concentrated at the grain boundaries will produce stress concentration, which is prone to defects such as cracks, thereby reducing the strength of the alloy casting. In addition, when the pouring temperature is too low, it will lead to too fast cooling speed, increase the growth rate of dendrites, and when the dendrites overlap, the solidification shrinkage between the dendrites cannot be compensated in time, thereby increasing the probability of shrinkage, causing the density of the alloy casting to decrease, and ultimately leading to a decrease in the tensile strength of the corrosion-resistant and heat-resistant steel.

[0087] When the pouring temperature exceeds 1600°C, the carbide content will decrease and the formed austenite grains will be coarse. This is because, on the one hand, when the pouring temperature is too high, the steel mold absorbs too much heat, the alloy elements in the refined steel liquid are fully mixed, and during the solidification process, the alloy elements dissolved in the austenite are not easy to precipitate, so that a large amount of alloy elements are dissolved in the austenite, thereby reducing the content of carbides formed with the alloy elements. The carbide content has a significant effect on the tensile strength of the heat-resistant alloy casting. Since it is difficult for dislocations to enter the interface between carbides and the steel matrix, carbides can effectively hinder the slip of dislocations. When the alloy casting is deformed, dislocations cause serious blockage at the interface between carbides and the steel matrix. Therefore, when the carbide dispersion is discontinuous, a too low carbide content will directly lead to a decrease in the tensile strength of the heat-resistant alloy casting. On the other hand, when the pouring temperature is too high, the viscosity of the refined steel liquid decreases, and the tendency of the grains to grow along a specific crystal direction to form dendrites increases, resulting in relatively developed dendrites. At the same time, due to the high pouring temperature, the diffusion rate is faster, and the diffusion ability of atoms is enhanced, which accelerates the growth rate of austenite grains. The solute atoms discharged during the growth of austenite grains can diffuse quickly and evenly in the refined steel liquid. Therefore, austenite can grow to the surrounding area, making the austenite dendrites developed and coarse.

[0088] In some optional examples, the speed of injecting the refined molten steel into the steel mold is 5 to 6 t / min, for example, it can be 5.0 t / min, 5.1 t / min, 5.2 t / min, 5.3 t / min, 5.4 t / min, 5.5 t / min, 5.6 t / min, 5.7 t / min, 5.8 t / min, 5.9 t / min or 6.0 t / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0089] In some optional instances, the first temperature is 1100-1200°C, for example, it can be 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, 1190°C or 1200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0090] In some optional instances, after naturally cooling to the first temperature, the cooling rate is adjusted to 3-5°C / min, for example, 3.0°C / min, 3.2°C / min, 3.4°C / min, 3.6°C / min, 3.8°C / min, 4.0°C / min, 4.2°C / min, 4.4°C / min, 4.6°C / min, 4.8°C / min or 5.0°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0091] In some optional examples, the intermittent ultrasonic vibration is 10 to 15 minutes of ultrasonic vibration with a pause of 2 to 3 minutes, wherein the ultrasonic vibration time can be 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 13.5 minutes, 14 minutes, 14.5 minutes or 15 minutes; the pause time can be 2.0 minutes, 2.1 minutes, 2.2 minutes, 2.3 minutes, 2.4 minutes, 2.5 minutes, 2.6 minutes, 2.7 minutes, 2.8 minutes, 2.9 minutes or 3.0 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0092] In some optional instances, the ultrasonic power of the intermittent ultrasonic vibration is 2000-3000 W, for example, it can be 2000 W, 2100 W, 2200 W, 2300 W, 2400 W, 2500 W, 2600 W, 2700 W, 2800 W, 2900 W or 3000 W, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0093] In some optional instances, the ultrasonic frequency of the intermittent ultrasonic vibration is 20 to 30 kHz, for example, it can be 20 kHz, 21 kHz, 22 kHz, 23 kHz, 24 kHz, 25 kHz, 26 kHz, 27 kHz, 28 kHz, 29 kHz or 30 kHz, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0094] In some optional instances, the second temperature is 900-1000°C, for example, it may be 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C or 1000°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0095] In some optional examples, the second temperature is kept warm for 8 to 10 hours, for example, 8.0 hours, 8.2 hours, 8.4 hours, 8.6 hours, 8.8 hours, 9.0 hours, 9.2 hours, 9.4 hours, 9.6 hours, 9.8 hours or 10.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0096] As a preferred technical solution of the present invention, the quenching and tempering heat treatment process specifically includes the following steps:

[0097] The alloy casting obtained by casting is heated to an annealing temperature at a first heating rate and kept warm. After the insulation is completed, the alloy casting is taken out of the furnace and air-cooled to room temperature to complete the annealing treatment; the alloy casting after the annealing treatment is heated to a first quenching temperature at a second heating rate and kept warm. After the insulation is completed, the alloy casting is taken out of the furnace and oil-quenched. After the alloy casting is cooled to room temperature, it is heated to a second quenching temperature at a third heating rate and kept warm. After the insulation is completed, the alloy casting is taken out of the furnace and oil-quenched. After cooling to room temperature, the quenching treatment is completed to obtain a heat-resistant alloy casting.

[0098] In some optional instances, the first heating rate is 10 to 20°C / min, for example, it can be 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min or 20°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0099] In some optional instances, the annealing temperature is 700-800°C, for example, it can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C or 800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0100] In some optional examples, the annealing temperature is kept for 1 to 3 hours, for example, 1.0 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2.0 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h or 3.0 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0101] In some optional instances, the second heating rate is 10 to 20°C / min, for example, it can be 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min or 20°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0102] In some optional instances, the first quenching temperature is 1080-1100°C, for example, it may be 1080°C, 1082°C, 1084°C, 1086°C, 1088°C, 1090°C, 1092°C, 1094°C, 1096°C, 1098°C or 1100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0103] Increasing the quenching temperature can accelerate the formation and homogenization process of austenite, which is conducive to the formation of fine and uniform austenite grains. However, when the quenching temperature exceeds 1100°C, it will also promote the growth of austenite grains to a certain extent, thereby reducing the tensile strength of the heat-resistant alloy castings. In addition, when the quenching temperature exceeds 1100°C, the solubility of metal elements, carbides, nitrides and carbonitrides in the steel matrix will increase, which will improve the stability of austenite and increase the amount of residual austenite, which is not conducive to the improvement of the tensile strength of heat-resistant alloy castings.

[0104] In some optional examples, the first quenching temperature is kept for 0.5 to 1.5 hours, for example, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours or 1.5 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0105] The present invention specifically limits the first quenching temperature to 1080-1100°C and the holding time to 0.5-1.5h. Within this parameter range, it is not only beneficial to improve the mechanical properties of corrosion-resistant heat-resistant steel at room temperature and high temperature; at the same time, it is also beneficial to improve the corrosion resistance of corrosion-resistant heat-resistant steel. The corrosion types of austenitic heat-resistant steel include pitting corrosion, stress corrosion and intergranular corrosion, among which intergranular corrosion is the most important corrosion mode in austenitic heat-resistant steel, and the corrosion mechanism is the chromium-poor theory. Under the action of the external medium, the chromium element forms a dense and firm oxide film to prevent the external corrosive medium atoms from diffusing to the inside, thereby achieving the anti-corrosion effect of protecting the steel matrix. Quenching treatment is the most important heat treatment method to improve intergranular corrosion. Its purpose is to make the precipitated carbide and other second phases dissolved in the steel matrix at high temperature and continue to diffuse. The quenching temperature and holding time will affect the size of the austenite grains and the precipitation of carbides at the grain boundaries, thereby affecting the intergranular corrosion resistance of corrosion-resistant heat-resistant steel. When the quenching temperature is too high or the holding time is too long, the austenite grain size will increase and the grain boundaries will decrease, affecting the formation rate of the surface passivation film. In addition, the supersaturated carbon element in the steel matrix diffuses to the grain boundaries, precipitates and combines with the nearby chromium element to form chromium carbides, which absorb more chromium. The chromium diffusion rate inside the steel matrix is ​​slow, and there is no time to replenish the chromium at the grain boundaries, resulting in the formation of "chromium-poor" areas at the grain boundaries. When the chromium content is reduced to below the corrosion resistance limit, the passivation ability of the surface passivation film is reduced, and intergranular corrosion will occur under the action of the corrosive medium.

[0106] In some optional instances, the third heating rate is 10 to 20°C / min, for example, it can be 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min or 20°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0107] In some optional examples, the second quenching temperature is 980-1050°C, for example, it can be 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C or 1050°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0108] In some optional examples, the second quenching temperature is maintained for 0.5 to 1.5 hours, for example, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours or 1.5 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0109] In a second aspect, the present invention provides a corrosion-resistant and heat-resistant steel co-doped with ternary trace elements prepared by the preparation method described in the first aspect.

[0110] Compared with the prior art, the present invention has the following beneficial effects:

[0111] The invention prepares austenitic heat-resistant steel with excellent mechanical properties and corrosion resistance by adding molybdenum, cobalt and tungsten into a steel matrix and combining different carburizing treatment processes.

[0112] In the nitriding process of the present invention, the inlet pipe of the nitriding furnace is pre-filled with a nitriding-promoting filler, and the ammonia gas can fully contact with the nitriding-promoting filler when entering through the inlet pipe. The contact area between the ammonia gas and the cerium oxide and the cobalt oxide is increased by the inorganic carrier with a porous structure. The cerium oxide and the cobalt oxide can reduce the activation energy required for breaking the ionic bond, accelerate the decomposition of the ammonia gas, increase the number of active nitrogen ions, and quickly establish a higher nitrogen potential, thereby achieving the purpose of improving the nitriding rate.

[0113] The present invention sprays a precursor solution on the surface of a heat-resistant alloy casting, and heats the precursor solution to crystallize and form a lanthanum ferrite film, thereby improving the catalytic decomposition activity of the heat-resistant alloy casting surface to ammonia at low temperature, and can effectively adsorb the decomposed free nitrogen to form a nitrogen adsorption layer on the surface of the lanthanum ferrite film; in addition, the rare earth element lanthanum can penetrate into the surface of the steel matrix to form a solid solution during the nitriding process, causing serious distortion of the surrounding lattice, and promoting the diffusion and penetration of active nitrogen atoms. The present invention can not only improve the nitriding efficiency and reduce the nitriding temperature through the synergistic effect of the penetration-promoting filler and the lanthanum ferrite film, but also significantly improve the hardness of the nitriding layer, and improve the wear resistance, contact fatigue and bending fatigue life of the nitriding layer.

[0114] The invention can achieve the purpose of cleaning the surface of the workpiece and accelerating the diffusion rate of nitrogen atoms through the synergistic effect of the nitriding-promoting filler and the lanthanum ferrite film, thereby reducing the nitriding temperature, shortening the nitriding time and improving the nitriding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] Figure 1 A process flow chart of the preparation of corrosion-resistant and heat-resistant steel provided in Examples 1-5 of the present invention;

[0116] Figure 2 This is a micrograph of the metallographic structure of the heat-resistant alloy casting prepared in Example 1 of the present invention;

[0117] Figure 3 This is a micrograph of the metallographic structure of the heat-resistant alloy casting prepared in Comparative Example 1 of the present invention;

[0118] Figure 4 This is a micrograph of the metallographic structure of the heat-resistant alloy casting prepared in Comparative Example 2 of the present invention;

[0119] Figure 5 This is a micrograph of the metallographic structure of the heat-resistant alloy casting prepared in Comparative Example 3 of the present invention;

[0120] Figure 6 This is a micrograph of the metallographic structure of the heat-resistant alloy casting prepared in Comparative Example 4 of the present invention;

[0121] Figure 7 This is a micrograph of the metallographic structure of the heat-resistant alloy casting prepared in Comparative Example 5 of the present invention;

[0122] Figure 8 This is a micrograph of the metallographic structure of the heat-resistant alloy casting prepared in Comparative Example 6 of the present invention;

[0123] Fig. 9 This is a scanning electron microscope image of the metallographic structure of the corrosion-resistant and heat-resistant steel prepared in Example 1 of the present invention after the corrosion resistance test;

[0124] Fig.10This is a scanning electron microscope image of the metallographic structure of the corrosion-resistant and heat-resistant steel prepared in Comparative Example 10 of the present invention after the corrosion resistance test. DETAILED DESCRIPTION

[0125] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments recorded herein.

[0126] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products, and their brands, specifications and manufacturer information are as follows:

[0127] Ferrosilicon alloy: FeSi75, purity ≥99%, purchased from Shanghai Gelin Technology Co., Ltd.;

[0128] Ferrochrome alloy: containing 50-70% chromium, purity ≥99%, purchased from Shanghai Gelin Technology Co., Ltd.;

[0129] Nickel-iron alloy: FeNi40, containing 35-45% nickel, purity ≥99%, purchased from Shanghai Gelin Technology Co., Ltd.;

[0130] Molybdenum iron alloy: Fe40Mo60, purity ≥99%, purchased from Shanghai Gelin Technology Co., Ltd.;

[0131] Tungsten-iron alloy: containing 70-80% tungsten, purity ≥99%, purchased from Shanghai Gelin Technology Co., Ltd.;

[0132] Cobalt powder: purity ≥99%, purchased from Shanghai Gelin Technology Co., Ltd.;

[0133] Alumina: industrial grade, purchased from Hubei Dechao Chemical Co., Ltd.;

[0134] Calcium carbide: purity ≥99%, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.;

[0135] Lime: purity ≥99%, purchased from Shenyang Ketuo Chemical Co., Ltd.;

[0136] Fluorite: S50691-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0137] Aluminum powder: purity ≥99%, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.;

[0138] Hydrated lanthanum nitrate: purity ≥99%, purchased from Shanghai Haohong Biopharmaceutical Technology Co., Ltd.;

[0139] Hydrated ferric nitrate: industrial grade, purchased from Hubei Chengfeng Chemical Co., Ltd.;

[0140] Cerium nitrate: N001, purchased from Shandong Desheng New Materials Co., Ltd.;

[0141] Cobalt nitrate: purity ≥99%, purchased from Hubei Chengfeng Chemical Co., Ltd.;

[0142] Montmorillonite: S42017-100g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0143] Diatomaceous earth: purity ≥99%, purchased from Jinan Jinhao Chemical Co., Ltd.;

[0144] Fly ash: industrial grade, purchased from Wuhan Jiyesheng Chemical Co., Ltd.;

[0145] Hydroxyapatite: S14126-25g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0146] Example 1

[0147] This embodiment provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0148] S1. Molten steel smelting: pure iron is put into a smelting furnace, heated to 1560°C and kept warm for 60 minutes to form molten iron;

[0149] Add ferrosilicon alloy to the molten iron and keep it warm for 20 minutes. During the heat preservation process, 15Nm 3 / h of argon and add lime, 15kg of lime per ton of molten iron, to remove scum on the liquid surface;

[0150] The molten iron was heated to 1580℃, and ferrochromium, ferronickel and ferromolybdenum were added to the molten iron and kept warm for 30 minutes. During the warming process, 15Nm 3 / h of argon and add lime, 15kg of lime per ton of molten iron, to remove scum on the liquid surface;

[0151] The molten iron was heated to 1650℃, and ferrotungsten alloy and cobalt powder were added to the molten iron and kept warm for 30 minutes. During the warming process, 15Nm 3 / h of argon and lime, 15kg of lime per ton of molten iron, remove scum on the liquid surface to obtain alloyed steel liquid;

[0152] S2, refining and purification: the alloyed steel liquid obtained in step S1 is adjusted to 1600°C and then injected into a refining furnace, oxygen and nitrogen are introduced into the alloyed steel liquid to perform the first stage of decarburization of the alloyed steel liquid, wherein the oxygen introduction amount is 350Nm 3 / h, the nitrogen flow rate is 50Nm 3 / h;

[0153] When the carbon content in the alloyed steel liquid is reduced to 0.5wt%, the oxygen flow rate is adjusted to 280Nm 3 / h, the nitrogen flow rate was adjusted to 120Nm 3 / h, to carry out the second stage of decarburization of alloyed steel liquid;

[0154] When the carbon content in the alloyed steel liquid is reduced to 0.3wt%, the oxygen flow rate is adjusted to 200Nm 3 / h, the nitrogen flow rate was adjusted to 200Nm 3 / h, the alloyed steel liquid is subjected to the third stage of decarbonization; when the carbon content in the alloyed steel liquid is reduced to 0.1wt%, the introduction of oxygen and nitrogen is stopped;

[0155] Add a purifier to the alloyed steel liquid. The purifier consists of lime, fluorite and aluminum powder. For every ton of alloyed steel liquid, add 8kg lime, 3.2kg fluorite powder and 1.7kg aluminum powder. After adding the purifier, a 50Nm 3 Argon gas was introduced at a flow rate of / h for 20 min, and the scum on the liquid surface was removed to obtain refined molten steel;

[0156] The mass fraction of each element in the refined steel liquid is controlled within the following ranges: carbon 0.1wt%, silicon 1.5wt%, chromium 25wt%, nickel 19wt%, molybdenum 0.4wt%, tungsten 0.5wt% and cobalt 1.8wt%, with the remainder being iron;

[0157] S3, casting: preheat the steel mold to 380°C, and when the refined molten steel obtained in step S2 reaches 1580°C, inject it into the steel mold at a speed of 5t / min. After all the refined molten steel is injected into the steel mold, naturally cool it to 1100°C, then adjust the cooling rate to 3°C / min, and perform intermittent ultrasonic vibration on the steel mold, with each ultrasonic vibration lasting 15min and stopping for 3min, with an ultrasonic power of 2000W and an ultrasonic frequency of 20kHz; when the steel mold is cooled to 900°C, stop the ultrasonic vibration and keep it warm for 10h, then naturally cool it to room temperature, and obtain the alloy casting after demoulding;

[0158] S4, quenching and tempering heat treatment: heating the alloy casting obtained in step S3 to 700°C at a heating rate of 10°C / min and keeping the temperature for 3 hours. After the insulation is completed, the alloy casting is taken out of the furnace and air-cooled to room temperature to complete the annealing treatment;

[0159] The annealed alloy casting is heated to 1080°C at a heating rate of 10°C / min and kept at this temperature for 1.5 hours. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After the alloy casting is cooled to room temperature, it is heated to 980°C at a heating rate of 10°C / min and kept at this temperature for 1.5 hours. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After cooling to room temperature, the quenching treatment is completed to obtain a heat-resistant alloy casting;

[0160] S5, nitriding treatment: using white corundum with a particle size of 1 mm to sandblast the surface of the heat-resistant alloy casting obtained in step S4, the sandblasting pressure is 0.3 MPa, the sandblasting distance is 100 mm, the sandblasting angle is 60°, the sandblasting time is 8 min, and after the sandblasting, the heat-resistant alloy casting is cleaned and dried;

[0161] Hydrated lanthanum nitrate, hydrated ferric nitrate and ionized water are uniformly mixed to obtain a reaction solution, wherein the molar ratio of lanthanum element to iron element in the reaction solution is 1:0.8, and the total concentration of hydrated lanthanum nitrate and hydrated ferric nitrate in the reaction solution is 0.3 mol / L; citric acid is added to the reaction solution to obtain a mixed solution, wherein the molar ratio of hydrated lanthanum nitrate to citric acid in the reaction solution is 1:3, and the mixed solution is heated in a water bath at 80° C. for 24 hours to obtain a precursor solution; and the precursor solution is sprayed on the sandblasted surface of the heat-resistant alloy casting, wherein the spraying amount of the precursor solution is 3 mL / min, and the spraying time is 5 minutes;

[0162] Disperse cerium nitrate and cobalt nitrate in anhydrous ethanol, mix well to form a penetration-enhancing dispersion, the molar ratio of cerium element to cobalt element in the penetration-enhancing dispersion is 1:0.8, and the total concentration of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion is 0.5 mol / L; add montmorillonite to the penetration-enhancing dispersion, the ratio of the total mass of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion to the mass of montmorillonite is 0.2:1, magnetic stirring is performed at a speed of 300 r / min, and ultrasonic dispersion is performed at an ultrasonic power of 500 W for 40 minutes to obtain a suspension; the suspension is filtered and dried in sequence to obtain a penetration-enhancing precursor; the penetration-enhancing precursor is heated to 300°C at a heating rate of 10°C / min and kept warm for 2 hours; then, the penetration-enhancing precursor is continued to be heated to 700°C at a heating rate of 5°C / min and kept warm for 4 hours to obtain a penetration-enhancing filler;

[0163] The air inlet pipe of the nitriding furnace is pre-filled with the prepared nitriding-promoting filler; the heat-resistant alloy casting sprayed with the precursor solution is transferred to the nitriding furnace, and the heat-resistant alloy casting is heated at a heating rate of 10°C / min in an air atmosphere, so that the precursor solution on the surface of the heat-resistant alloy casting is crystallized to form a lanthanum ferrite film during the heating process; when the temperature in the nitriding furnace is increased to 450°C, ammonia is introduced into the nitriding furnace at a flow rate of 5L / min, and the furnace is kept warm for 5h to carry out nitriding treatment to obtain the corrosion-resistant and heat-resistant steel.

[0164] Example 2

[0165] This embodiment provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0166] S1. Molten steel smelting: pure iron is put into a smelting furnace, heated to 1562°C and kept warm for 58 minutes to form molten iron;

[0167] Add ferrosilicon alloy to the molten iron and keep it warm for 22 minutes. During the warming process, 16Nm 3 / h of argon and add fluorite, 16kg of fluorite per ton of molten iron, and remove scum on the liquid surface;

[0168] The molten iron was heated to 1585°C, and ferrochromium, ferronickel and ferromolybdenum were added to the molten iron and kept warm for 28 minutes. During the warming process, 16Nm 3 / h of argon and add fluorite, 16kg of fluorite per ton of molten iron, and remove scum on the liquid surface;

[0169] The temperature of the molten iron was further raised to 1655°C, tungsten-iron alloy and cobalt powder were added to the molten iron and the temperature was kept for 28 minutes. During the temperature keeping process, 16Nm 3 / h of argon and adding fluorite, 16kg of fluorite per ton of molten iron, removing scum on the liquid surface to obtain alloyed steel liquid;

[0170] S2, refining and purification: the alloyed steel liquid obtained in step S1 is adjusted to 1605°C and then injected into a refining furnace, oxygen and nitrogen are introduced into the alloyed steel liquid to perform the first stage of decarburization on the alloyed steel liquid, wherein the oxygen introduction amount is 360Nm 3 / h, the nitrogen flow rate is 60Nm 3 / h;

[0171] When the carbon content in the alloyed steel liquid is reduced to 0.52wt%, the oxygen flow rate is adjusted to 290Nm 3 / h, the nitrogen flow rate was adjusted to 140Nm 3 / h, to carry out the second stage of decarburization of alloyed steel liquid;

[0172] When the carbon content in the alloyed steel liquid is reduced to 0.32wt%, the oxygen flow rate is adjusted to 210Nm 3 / h, the nitrogen flow rate was adjusted to 210Nm 3 / h, the alloyed steel liquid is subjected to the third stage of decarbonization; when the carbon content in the alloyed steel liquid is reduced to 0.12wt%, the introduction of oxygen and nitrogen is stopped;

[0173] Add a purifier to the alloyed steel liquid. The purifier consists of lime, fluorite and aluminum powder. For every ton of alloyed steel liquid, add 8.5kg lime, 3kg fluorite powder and 1.6kg aluminum powder. After adding the purifier, the bottom of the alloyed steel liquid is purified at a speed of 52Nm 3 Argon gas was introduced at a flow rate of / h for 18 minutes, and the scum on the liquid surface was removed to obtain refined molten steel;

[0174] The mass fraction of each element in the refined steel liquid is controlled within the following ranges: carbon 0.12wt%, silicon 1.6wt%, chromium 24.5wt%, nickel 19.2wt%, molybdenum 0.38wt%, tungsten 0.52wt% and cobalt 1.75wt%, with the remainder being iron;

[0175] S3, casting: preheat the steel mold to 385°C, and when the refined molten steel obtained in step S2 reaches 1585°C, inject it into the steel mold at a speed of 5.2t / min. After all the refined molten steel is injected into the steel mold, naturally cool it to 1120°C, then adjust the cooling rate to 3.5°C / min, and perform intermittent ultrasonic vibration on the steel mold, each ultrasonic vibration lasts for 14min, with a pause of 2.8min, the ultrasonic power is 2200W, and the ultrasonic frequency is 22kHz; when the steel mold is cooled to 920°C, stop the ultrasonic vibration and keep it warm for 9.5h, then naturally cool it to room temperature, and obtain the alloy casting after demoulding;

[0176] S4, quenching and tempering heat treatment: the alloy casting obtained in step S3 is heated to 720°C at a heating rate of 12°C / min and kept at this temperature for 2.5 hours. After the end of the heat preservation, the alloy casting is taken out of the furnace and air-cooled to room temperature to complete the annealing treatment;

[0177] The annealed alloy casting is heated to 1085°C at a heating rate of 12°C / min and kept at this temperature for 1.2 hours. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After the alloy casting is cooled to room temperature, it is heated to 1000°C at a heating rate of 12°C / min and kept at this temperature for 1.2 hours. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After cooling to room temperature, the quenching treatment is completed to obtain a heat-resistant alloy casting.

[0178] S5, nitriding treatment: using white corundum with a particle size of 1.5 mm to sandblast the surface of the heat-resistant alloy casting obtained in step S4, the sandblasting pressure is 0.28 MPa, the sandblasting distance is 110 mm, the sandblasting angle is 62°, the sandblasting time is 7 min, and the heat-resistant alloy casting is cleaned and dried after the sandblasting is completed;

[0179] Hydrated lanthanum nitrate, hydrated ferric nitrate and ionized water are uniformly mixed to obtain a reaction solution, wherein the molar ratio of lanthanum element to iron element in the reaction solution is 1:0.9, and the total concentration of hydrated lanthanum nitrate and hydrated ferric nitrate in the reaction solution is 0.35 mol / L; citric acid is added to the reaction solution to obtain a mixed solution, wherein the molar ratio of hydrated lanthanum nitrate to citric acid in the reaction solution is 1:3.5, and the mixed solution is heated in a water bath at 82° C. for 22 h to obtain a precursor solution; and the precursor solution is sprayed on the sandblasted surface of the heat-resistant alloy casting, wherein the spraying amount of the precursor solution is 3.2 mL / min, and the spraying time is 4.8 min;

[0180] Disperse cerium nitrate and cobalt nitrate in anhydrous ethanol, mix well to form a penetration-enhancing dispersion, the molar ratio of cerium element to cobalt element in the penetration-enhancing dispersion is 1:0.9, and the total concentration of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion is 0.8 mol / L; add diatomaceous earth to the penetration-enhancing dispersion, the ratio of the total mass of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion to the mass of diatomaceous earth is 0.22:1, magnetic stirring is performed at a speed of 320 r / min, and ultrasonic dispersion is performed at an ultrasonic power of 520 W for 38 minutes to obtain a suspension; the suspension is filtered and dried in sequence to obtain a penetration-enhancing precursor; the penetration-enhancing precursor is heated to 320°C at a heating rate of 12°C / min and kept warm for 1.8 hours; then, the penetration-enhancing precursor is continued to be heated to 720°C at a heating rate of 8°C / min and kept warm for 3.8 hours to obtain a penetration-enhancing filler;

[0181] The air inlet pipe of the nitriding furnace is pre-filled with the prepared nitriding promoting filler; the heat-resistant alloy casting sprayed with the precursor solution is transferred to the nitriding furnace, and the heat-resistant alloy casting is heated at a heating rate of 11°C / min in an air atmosphere, so that the precursor solution on the surface of the heat-resistant alloy casting is crystallized to form a lanthanum ferrite film during the heating process; when the temperature in the nitriding furnace is increased to 460°C, ammonia is introduced into the nitriding furnace at a flow rate of 6L / min, and the furnace is kept warm for 4.5h to carry out nitriding treatment to obtain the corrosion-resistant heat-resistant steel.

[0182] Example 3

[0183] This embodiment provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0184] S1. Molten steel smelting: pure iron is put into a smelting furnace, heated to 1565°C and kept warm for 55 minutes to form molten iron;

[0185] Add ferrosilicon alloy to the molten iron and keep it warm for 25 minutes. During the heat preservation process, 17Nm 3 / h of argon and add alumina, 17kg of alumina per ton of iron melt, and remove scum on the liquid surface;

[0186] The molten iron was heated to 1590℃, and ferrochromium, ferronickel and ferromolybdenum were added to the molten iron and kept warm for 25 minutes. During the warming process, 17Nm 3 / h of argon and add alumina, 17kg of alumina per ton of iron melt, and remove scum on the liquid surface;

[0187] The temperature of the molten iron was further raised to 1660°C, tungsten-iron alloy and cobalt powder were added to the molten iron and the temperature was kept for 25 minutes. During the temperature keeping process, 17Nm 3 / h of argon and adding alumina, 17kg of alumina is added per ton of molten iron, and the scum on the liquid surface is removed to obtain alloyed steel liquid;

[0188] S2, refining and purification: the alloyed steel liquid obtained in step S1 is adjusted to 1610°C and then injected into a refining furnace, oxygen and nitrogen are introduced into the alloyed steel liquid to perform the first stage of decarburization of the alloyed steel liquid, wherein the oxygen introduction amount is 370Nm 3 / h, the nitrogen flow rate is 70Nm 3 / h;

[0189] When the carbon content in the alloyed steel liquid is reduced to 0.55wt%, the oxygen flow rate is adjusted to 300Nm 3 / h, the nitrogen flow rate was adjusted to 150Nm 3 / h, to carry out the second stage of decarburization of alloyed steel liquid;

[0190] When the carbon content in the alloyed steel liquid is reduced to 0.35wt%, the oxygen flow rate is adjusted to 220Nm 3 / h, the nitrogen flow rate was adjusted to 220Nm 3 / h, performing the third stage of decarbonization on the alloyed steel liquid; when the carbon content in the alloyed steel liquid is reduced to 0.15wt%, stopping the introduction of oxygen and nitrogen;

[0191] Add a purifier to the alloyed steel liquid. The purifier consists of lime, fluorite and aluminum powder. For every ton of alloyed steel liquid, add 9kg lime, 2.8kg fluorite powder and 1.5kg aluminum powder. After adding the purifier, the bottom of the alloyed steel liquid is purified at a speed of 55Nm 3Argon gas was introduced at a flow rate of / h for 15 minutes, and the scum on the liquid surface was removed to obtain refined molten steel;

[0192] The mass fraction of each element in the refined steel liquid is controlled within the following ranges: carbon 0.15wt%, silicon 1.7wt%, chromium 24wt%, nickel 19.5wt%, molybdenum 0.35wt%, tungsten 0.55wt% and cobalt 1.7wt%, with the remainder being iron;

[0193] S3, casting: preheat the steel mold to 390°C, and when the refined molten steel obtained in step S2 reaches 1590°C, inject it into the steel mold at a speed of 5.5t / min. After all the refined molten steel is injected into the steel mold, naturally cool it to 1150°C, then adjust the cooling rate to 4°C / min, and perform intermittent ultrasonic vibration on the steel mold, each ultrasonic vibration lasts for 13min, with a pause of 2.5min, an ultrasonic power of 2500W, and an ultrasonic frequency of 25kHz; when the steel mold is cooled to 950°C, stop the ultrasonic vibration and keep it warm for 9h, then naturally cool it to room temperature, and obtain an alloy casting after demoulding;

[0194] S4, quenching and tempering heat treatment: heating the alloy casting obtained in step S3 to 750°C at a heating rate of 15°C / min and keeping the temperature for 2h. After the insulation is completed, the alloy casting is taken out of the furnace and air-cooled to room temperature to complete the annealing treatment;

[0195] The annealed alloy casting is heated to 1090°C at a heating rate of 15°C / min and kept at that temperature for 1 hour. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After the alloy casting is cooled to room temperature, it is heated to 1010°C at a heating rate of 15°C / min and kept at that temperature for 1 hour. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After cooling to room temperature, the quenching treatment is completed to obtain a heat-resistant alloy casting;

[0196] S5, nitriding treatment: using white corundum with a particle size of 2 mm to sandblast the surface of the heat-resistant alloy casting obtained in step S4, the sandblasting pressure is 0.25 MPa, the sandblasting distance is 120 mm, the sandblasting angle is 65°, the sandblasting time is 5 min, and the heat-resistant alloy casting is cleaned and dried after the sandblasting is completed;

[0197] Hydrated lanthanum nitrate, hydrated ferric nitrate and ionized water are uniformly mixed to obtain a reaction solution, wherein the molar ratio of lanthanum element to iron element in the reaction solution is 1:1, and the total concentration of hydrated lanthanum nitrate and hydrated ferric nitrate in the reaction solution is 0.4 mol / L; citric acid is added to the reaction solution to obtain a mixed solution, wherein the molar ratio of hydrated lanthanum nitrate to citric acid in the reaction solution is 1:4, and the mixed solution is heated in a water bath at 85° C. for 20 h to obtain a precursor solution; and the precursor solution is sprayed on the sandblasted surface of the heat-resistant alloy casting, wherein the spraying amount of the precursor solution is 3.5 mL / min, and the spraying time is 4.5 min;

[0198] Disperse cerium nitrate and cobalt nitrate in anhydrous ethanol, mix them evenly to form a penetration-enhancing dispersion, the molar ratio of cerium element to cobalt element in the penetration-enhancing dispersion is 1:1, and the total concentration of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion is 1 mol / L; add fly ash to the penetration-enhancing dispersion, the ratio of the total mass of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion to the mass of fly ash is 0.25:1, magnetic stirring is performed at a speed of 350 r / min, and ultrasonic dispersion is performed at an ultrasonic power of 550 W for 35 minutes to obtain a suspension; the suspension is filtered and dried in sequence to obtain a penetration-enhancing precursor; the penetration-enhancing precursor is heated to 350°C at a heating rate of 15°C / min and kept warm for 1.5 hours; then, the penetration-enhancing precursor is continued to be heated to 750°C at a heating rate of 10°C / min and kept warm for 3.5 hours to obtain a penetration-enhancing filler;

[0199] The air inlet pipe of the nitriding furnace is pre-filled with the prepared nitriding promoting filler; the heat-resistant alloy casting sprayed with the precursor solution is transferred to the nitriding furnace, and the heat-resistant alloy casting is heated at a heating rate of 12°C / min in an air atmosphere, so that the precursor solution on the surface of the heat-resistant alloy casting is crystallized to form a lanthanum ferrite film during the heating process; when the temperature in the nitriding furnace is increased to 480°C, ammonia is introduced into the nitriding furnace at a flow rate of 7L / min, and the furnace is kept warm for 4h to carry out nitriding treatment to obtain the corrosion-resistant and heat-resistant steel.

[0200] Example 4

[0201] This embodiment provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0202] S1. Molten steel smelting: pure iron is put into a smelting furnace, heated to 1568°C and kept warm for 52 minutes to form molten iron;

[0203] Add ferrosilicon alloy to the molten iron and keep it warm for 28 minutes. During the heat preservation process, 18Nm 3 / h of argon and add alumina, 18kg of alumina per ton of iron molten liquid, and remove scum on the liquid surface;

[0204] The molten iron was heated to 1595°C, chromium-iron alloy, nickel-iron alloy and molybdenum-iron alloy were added to the molten iron and kept warm for 22 minutes. During the warming process, 18Nm 3 / h of argon and add alumina, 18kg of alumina per ton of iron molten liquid, and remove scum on the liquid surface;

[0205] The temperature of the molten iron was further raised to 1665°C, tungsten-iron alloy and cobalt powder were added to the molten iron and the temperature was kept for 22 minutes. During the temperature keeping process, 18Nm3 / h of argon and adding alumina, 18kg of alumina per ton of molten iron, removing scum on the liquid surface to obtain alloyed steel liquid;

[0206] S2, refining and purification: the alloyed steel liquid obtained in step S1 is adjusted to 1615°C and then injected into a refining furnace, oxygen and nitrogen are introduced into the alloyed steel liquid to perform the first stage of decarburization on the alloyed steel liquid, wherein the oxygen introduction amount is 380Nm 3 / h, the nitrogen flow rate is 80Nm 3 / h;

[0207] When the carbon content in the alloyed steel liquid is reduced to 0.58wt%, the oxygen flow rate is adjusted to 310Nm 3 / h, the nitrogen flow rate was adjusted to 160Nm 3 / h, to carry out the second stage of decarburization of alloyed steel liquid;

[0208] When the carbon content in the alloyed steel liquid is reduced to 0.38wt%, the oxygen flow rate is adjusted to 230Nm 3 / h, the nitrogen flow rate was adjusted to 230Nm 3 / h, the alloyed steel liquid is subjected to the third stage of decarbonization; when the carbon content in the alloyed steel liquid is reduced to 0.18wt%, the introduction of oxygen and nitrogen is stopped;

[0209] Add a purifier to the alloyed steel liquid. The purifier consists of lime, fluorite and aluminum powder. For every ton of alloyed steel liquid, add 9.5kg lime, 2.6kg fluorite powder and 1.4kg aluminum powder. After adding the purifier, the bottom of the alloyed steel liquid is purified at a speed of 58Nm 3 Argon gas was introduced at a flow rate of / h for 12 minutes, and the scum on the liquid surface was removed to obtain refined molten steel;

[0210] The mass fraction of each element in the refined steel liquid is controlled within the following ranges: carbon 0.18wt%, silicon 1.8wt%, chromium 23.5wt%, nickel 19.8wt%, molybdenum 0.32wt%, tungsten 0.58wt% and cobalt 1.65wt%, with the remainder being iron;

[0211] S3, casting: preheat the steel mold to 395°C, and when the refined molten steel obtained in step S2 reaches 1595°C, inject it into the steel mold at a speed of 5.8t / min. After all the refined molten steel is injected into the steel mold, naturally cool it to 1180°C, then adjust the cooling rate to 4.5°C / min, and perform intermittent ultrasonic vibration on the steel mold, each ultrasonic vibration lasts for 12min, with a pause of 2.2min, an ultrasonic power of 2800W, and an ultrasonic frequency of 28kHz; when the steel mold is cooled to 980°C, stop the ultrasonic vibration and keep it warm for 8.5h, then naturally cool it to room temperature, and obtain an alloy casting after demoulding;

[0212] S4, quenching and tempering heat treatment: heating the alloy casting obtained in step S3 to 780°C at a heating rate of 18°C / min and keeping the temperature for 1.5 hours. After the insulation is completed, the alloy casting is taken out of the furnace and air-cooled to room temperature to complete the annealing treatment;

[0213] The annealed alloy casting is heated to 1095°C at a heating rate of 18°C / min and kept at this temperature for 0.8h. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After the alloy casting is cooled to room temperature, it is heated to 1030°C at a heating rate of 18°C / min and kept at this temperature for 0.8h. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After cooling to room temperature, the quenching treatment is completed to obtain a heat-resistant alloy casting.

[0214] S5, nitriding treatment: using white corundum with a particle size of 2.5 mm to sandblast the surface of the heat-resistant alloy casting obtained in step S4, the sandblasting pressure is 0.22 MPa, the sandblasting distance is 130 mm, the sandblasting angle is 68°, the sandblasting time is 4 min, and the heat-resistant alloy casting is cleaned and dried after the sandblasting is completed;

[0215] Hydrated lanthanum nitrate, hydrated ferric nitrate and ionized water are uniformly mixed to obtain a reaction solution, wherein the molar ratio of lanthanum element to iron element in the reaction solution is 1:1.1, and the total concentration of hydrated lanthanum nitrate and hydrated ferric nitrate in the reaction solution is 0.45 mol / L; citric acid is added to the reaction solution to obtain a mixed solution, wherein the molar ratio of hydrated lanthanum nitrate to citric acid in the reaction solution is 1:4.5, and the mixed solution is heated in a water bath at 88° C. for 15 h to obtain a precursor solution; and the precursor solution is sprayed on the sandblasted surface of the heat-resistant alloy casting, wherein the spraying amount of the precursor solution is 3.8 mL / min, and the spraying time is 4.2 min;

[0216] Disperse cerium nitrate and cobalt nitrate in anhydrous ethanol, mix well to form a penetration-enhancing dispersion, the molar ratio of cerium element to cobalt element in the penetration-enhancing dispersion is 1:1.2, and the total concentration of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion is 1.2 mol / L; add hydroxyapatite to the penetration-enhancing dispersion, the ratio of the total mass of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion to the mass of hydroxyapatite is 0.28:1, magnetic stirring is performed at a speed of 380 r / min, and ultrasonic dispersion is performed at an ultrasonic power of 580 W for 32 minutes to obtain a suspension; the suspension is filtered and dried in sequence to obtain a penetration-enhancing precursor; the penetration-enhancing precursor is heated to 380°C at a heating rate of 18°C / min and kept warm for 1.2 hours; then, the penetration-enhancing precursor is continued to be heated to 780°C at a heating rate of 12°C / min and kept warm for 3.2 hours to obtain a penetration-enhancing filler;

[0217] The air inlet pipe of the nitriding furnace is pre-filled with the prepared nitriding promoting filler; the heat-resistant alloy casting sprayed with the precursor solution is transferred to the nitriding furnace, and the heat-resistant alloy casting is heated at a heating rate of 14°C / min in an air atmosphere, so that the precursor solution on the surface of the heat-resistant alloy casting is crystallized to form a lanthanum ferrite film during the heating process; when the temperature in the nitriding furnace is increased to 490°C, ammonia is introduced into the nitriding furnace at a flow rate of 7L / min, and the furnace is kept warm for 3.5h to carry out nitriding treatment to obtain the corrosion-resistant heat-resistant steel.

[0218] Example 5

[0219] This embodiment provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0220] S1. Molten steel smelting: pure iron is put into a smelting furnace, heated to 1570°C and kept warm for 50 minutes to form molten iron;

[0221] Add ferrosilicon alloy to the molten iron and keep it warm for 30 minutes. During the heat preservation process, 20Nm 3 / h of argon and add calcium carbide, 20kg of calcium carbide per ton of molten iron, and remove the scum on the liquid surface;

[0222] The molten iron was heated to 1600°C, and ferrochromium, ferronickel and ferromolybdenum were added to the molten iron and kept warm for 20 minutes. During the warming process, 20 Nm of 3 / h of argon and add calcium carbide, 20kg of calcium carbide per ton of molten iron, and remove the scum on the liquid surface;

[0223] The molten iron was heated to 1670℃, and tungsten-iron alloy and cobalt powder were added to the molten iron and kept warm for 20 minutes. During the warming process, 20Nm3 / h of argon and calcium carbide, 20kg of calcium carbide per ton of molten iron, remove scum on the liquid surface to obtain alloyed steel liquid;

[0224] S2, refining and purification: the alloyed steel liquid obtained in step S1 is adjusted to 1620°C and then injected into a refining furnace, oxygen and nitrogen are introduced into the alloyed steel liquid to perform the first stage of decarburization of the alloyed steel liquid, wherein the oxygen introduction amount is 400Nm 3 / h, the nitrogen flow rate is 100Nm 3 / h;

[0225] When the carbon content in the alloyed steel liquid is reduced to 0.6wt%, the oxygen flow rate is adjusted to 320Nm 3 / h, the nitrogen flow rate was adjusted to 180Nm 3 / h, to carry out the second stage of decarburization of alloyed steel liquid;

[0226] When the carbon content in the alloyed steel liquid is reduced to 0.4wt%, the oxygen flow rate is adjusted to 250Nm 3 / h, the nitrogen flow rate was adjusted to 250Nm 3 / h, the alloyed steel liquid is subjected to the third stage of decarbonization; when the carbon content in the alloyed steel liquid is reduced to 0.2wt%, the introduction of oxygen and nitrogen is stopped;

[0227] Add a purifier to the alloyed steel liquid. The purifier consists of lime, fluorite and aluminum powder. For every ton of alloyed steel liquid, add 10kg lime, 2.5kg fluorite powder and 1.3kg aluminum powder. After adding the purifier, the bottom of the alloyed steel liquid is purified with a pressure of 60Nm 3 Argon gas was introduced at a flow rate of / h for 10 minutes, and the scum on the liquid surface was removed to obtain refined molten steel;

[0228] The mass fraction of each element in the refined steel liquid is controlled within the following ranges: carbon 0.2wt%, silicon 2wt%, chromium 23wt%, nickel 20wt%, molybdenum 0.3wt%, tungsten 0.6wt% and cobalt 1.6wt%, with the balance being iron;

[0229] S3, casting molding: preheat the steel mold to 400°C, and when the refined molten steel obtained in step S2 reaches 1600°C, inject it into the steel mold at a speed of 6t / min. After all the refined molten steel is injected into the steel mold, naturally cool it to 1200°C, then adjust the cooling rate to 5°C / min, and perform intermittent ultrasonic vibration on the steel mold, with each ultrasonic vibration lasting 10min and stopping for 2min, with an ultrasonic power of 3000W and an ultrasonic frequency of 30kHz; when the steel mold is cooled to 1000°C, stop the ultrasonic vibration and keep it warm for 8h, then naturally cool it to room temperature, and obtain an alloy casting after demoulding;

[0230] S4, quenching and tempering heat treatment: heating the alloy casting obtained in step S3 to 800°C at a heating rate of 20°C / min and keeping the temperature for 1 hour. After the insulation is completed, the alloy casting is taken out of the furnace and air-cooled to room temperature to complete the annealing treatment;

[0231] The annealed alloy casting is heated to 1100°C at a heating rate of 20°C / min and kept at this temperature for 0.5h. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After the alloy casting is cooled to room temperature, it is heated to 1050°C at a heating rate of 20°C / min and kept at this temperature for 0.5h. After the insulation is completed, the alloy casting is taken out of the furnace and oil quenched. After cooling to room temperature, the quenching treatment is completed to obtain a heat-resistant alloy casting.

[0232] S5, nitriding treatment: using white corundum with a particle size of 3 mm to sandblast the surface of the heat-resistant alloy casting obtained in step S4, the sandblasting pressure is 0.2 MPa, the sandblasting distance is 150 mm, the sandblasting angle is 70°, the sandblasting time is 3 min, and after the sandblasting, the heat-resistant alloy casting is cleaned and dried;

[0233] Hydrated lanthanum nitrate, hydrated ferric nitrate and ionized water are uniformly mixed to obtain a reaction solution, wherein the molar ratio of lanthanum element to iron element in the reaction solution is 1:1.2, and the total concentration of hydrated lanthanum nitrate and hydrated ferric nitrate in the reaction solution is 0.5 mol / L; citric acid is added to the reaction solution to obtain a mixed solution, wherein the molar ratio of hydrated lanthanum nitrate to citric acid in the reaction solution is 1:5, and the mixed solution is heated in a water bath at 90° C. for 12 h to obtain a precursor solution; and the precursor solution is sprayed on the sandblasted surface of the heat-resistant alloy casting, wherein the spraying amount of the precursor solution is 4 mL / min, and the spraying time is 4 min;

[0234] Disperse cerium nitrate and cobalt nitrate in anhydrous ethanol, mix them evenly to form a penetration-enhancing dispersion, the molar ratio of cerium element to cobalt element in the penetration-enhancing dispersion is 1:1.3, and the total concentration of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion is 1.5 mol / L; add hydroxyapatite to the penetration-enhancing dispersion, the ratio of the total mass of cerium nitrate and cobalt nitrate in the penetration-enhancing dispersion to the mass of hydroxyapatite is 0.3:1, magnetic stirring is performed at a speed of 400 r / min, and ultrasonic dispersion is performed at an ultrasonic power of 600 W for 30 minutes to obtain a suspension; the suspension is filtered and dried in sequence to obtain a penetration-enhancing precursor; the penetration-enhancing precursor is heated to 400°C at a heating rate of 20°C / min and kept warm for 1 hour; then, the penetration-enhancing precursor is continued to be heated to 800°C at a heating rate of 15°C / min and kept warm for 3 hours to obtain a penetration-enhancing filler;

[0235] The air inlet pipe of the nitriding furnace is pre-filled with the prepared nitriding-promoting filler; the heat-resistant alloy casting sprayed with the precursor solution is transferred to the nitriding furnace, and the heat-resistant alloy casting is heated at a heating rate of 15°C / min in an air atmosphere, so that the precursor solution on the surface of the heat-resistant alloy casting is crystallized to form a lanthanum ferrite film during the heating process; when the temperature in the nitriding furnace is increased to 500°C, ammonia is introduced into the nitriding furnace at a flow rate of 8L / min, and the furnace is kept warm for 3h to carry out nitriding treatment to obtain the corrosion-resistant and heat-resistant steel.

[0236] Comparative Example 1

[0237] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S1, the molybdenum content in the alloyed steel liquid is adjusted to 0.2wt%, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0238] Comparative Example 2

[0239] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S1, the molybdenum content in the alloyed steel liquid is adjusted to 0.5wt%, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0240] The metallographic structures of the heat-resistant alloy castings after quenching and tempering heat treatment prepared in Example 1, Comparative Example 1 and Comparative Example 2 were observed using a metallographic microscope, and the following results were obtained: Figure 2 (Example 1), Figure 3 (Comparative Example 1) and Figure 4 The metallographic micrograph shown in (Comparative Example 2) is Figure 2 , Figure 3 and Figure 4 By comparison, it can be seen that Figure 2 , Figure 3 and Figure 4 The metallographic structure is composed of austenite grains of different sizes, and granular materials are evenly distributed on the matrix. There are a small amount of black dot inclusions on the grain boundaries and inside the grains. Figure 2 The austenite grains in the metallographic structure are relatively fine. Figure 3 and Figure 4 The austenite grains in the metallographic structure shown are relatively coarse. This is because, Figure 3 The molybdenum content in the corresponding comparative example 1 is too low, and Figure 4 The molybdenum content in the corresponding comparative example 2 is too high, which indicates that adjusting the molybdenum content in the molten steel can directly affect the size of the austenite grains in the heat-resistant alloy casting, thereby affecting the tensile strength of the corrosion-resistant and heat-resistant steel finally prepared.

[0241] Comparative Example 3

[0242] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S1, the tungsten content in the alloyed steel liquid is adjusted to 0.4wt%, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0243] Comparative Example 4

[0244] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S1, the tungsten content in the alloyed steel liquid is adjusted to 0.7wt%, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0245] The metallographic structures of the heat-resistant alloy castings after quenching and tempering heat treatment prepared in Example 1, Comparative Example 3 and Comparative Example 4 were observed using a metallographic microscope, and the following results were obtained: Figure 2 (Example 1), Figure 5 (Comparative Example 3) and Figure 6 The metallographic micrograph shown in (Comparative Example 4) is Figure 2 , Figure 5 and Figure 6 By comparison, it can be seen that Figure 2 , Figure 5 and Figure 6 The metallographic structure is composed of austenite grains of different sizes, and granular materials are evenly distributed on the matrix. There are a small amount of black dot inclusions on the grain boundaries and inside the grains. Figure 2 The austenite grains in the metallographic structure are relatively fine. Figure 5 and Figure 6 The austenite grains in the metallographic structure shown are relatively coarse. This is because, Figure 5 The corresponding tungsten content in Comparative Example 3 is too low, Figure 6 The tungsten content in the corresponding comparative example 4 is too high, which indicates that adjusting the tungsten content in the molten steel can directly affect the size of the austenite grains in the heat-resistant alloy casting, thereby affecting the tensile strength of the corrosion-resistant and heat-resistant steel finally prepared.

[0246] Comparative Example 5

[0247] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S1, the cobalt content in the alloyed steel liquid is adjusted to 1.5wt%, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0248] Comparative Example 6

[0249] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S1, the cobalt content in the alloyed steel liquid is adjusted to 1.9wt%, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0250] The metallographic structures of the heat-resistant alloy castings after quenching and tempering treatment prepared in Example 1, Comparative Example 5 and Comparative Example 6 were observed using a metallographic microscope, and the following results were obtained: Figure 2 (Example 1), Figure 7 (Comparative Example 5) and Figure 8 The metallographic micrograph shown in (Comparative Example 6) is Figure 2 , Figure 7 and Figure 8 By comparison, it can be seen that Figure 2 , Figure 7 and Figure 8 The metallographic structure is composed of austenite grains of different sizes, and granular materials are evenly distributed on the matrix. There are a small amount of black dot inclusions on the grain boundaries and inside the grains. Figure 2 The austenite grains in the metallographic structure are relatively fine. Figure 7 and Figure 8 The austenite grains in the metallographic structure shown are relatively coarse. This is because, Figure 7 The cobalt content in the corresponding comparative example 5 is too low, and Figure 8 The cobalt content in the corresponding comparative example 6 is too high, which indicates that adjusting the cobalt content in the molten steel can directly affect the size of the austenite grains in the heat-resistant alloy casting, thereby affecting the tensile strength of the corrosion-resistant and heat-resistant steel finally prepared.

[0251] Comparative Example 7

[0252] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that the second quenching treatment in step S4 is omitted, and only the first quenching treatment is performed on the alloy casting. The other process parameters and operating steps are exactly the same as those in Example 1.

[0253] Comparative Example 8

[0254] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S5, no nitriding-promoting filler is filled into the air inlet pipe of the nitriding furnace, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0255] Comparative Example 9

[0256] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S5, the precursor solution is not sprayed on the surface of the heat-resistant alloy casting, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0257] Comparative Example 10

[0258] This comparative example provides a method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements. The difference from Example 1 is that in step S5, no nitriding-promoting filler is filled into the air inlet pipe of the nitriding furnace, and no precursor solution is sprayed on the surface of the heat-resistant alloy casting. The other process parameters and operating steps are exactly the same as those in Example 1.

[0259] For the application safety of austenitic heat-resistant steel, intergranular corrosion is currently a widely existing and extremely harmful form of local corrosion. This type of corrosion often occurs at the grain boundary or nearby areas, which can greatly reduce the mutual bonding force between grains, resulting in a decrease in the mechanical properties of austenitic heat-resistant steel and may further induce stress cracking. The metallographic structure of the corrosion-resistant heat-resistant steel prepared in Example 1 and Comparative Example 10 after the corrosion resistance test was completed was observed by scanning electron microscopy, and the following was obtained: Fig. 9 and Fig.10 The scanning electron micrograph shown, Fig. 9 and 10 Corrosion pits appeared at the grain boundaries in Fig. 9 The number and size of corrosion pits in Fig.10 , only slight corrosion marks appeared at some grain boundaries, which indicates Fig. 9 The corrosion-resistant and heat-resistant steel prepared in the corresponding embodiment 1 has better corrosion resistance.

[0260] The corrosion resistance and high temperature mechanical properties of the corrosion-resistant and heat-resistant steels provided in Examples 1-5 and Comparative Examples 1-10 were tested, and the specific test steps are as follows:

[0261] (1) Corrosion resistance

[0262] The corrosion-resistant and heat-resistant steel provided in Examples 1-5 and Comparative Examples 1-10 was prepared into a test steel with a size of 10mm×10mm×8mm, a working area of ​​1mm×10mm, and the non-working surface was sealed with epoxy resin. The electrochemical test was carried out on a Swiss Metrohm Autolab electrochemical workstation. The electrode system adopted a traditional three-electrode test system, the reference electrode was a saturated calomel electrode, and the auxiliary electrode was a platinum electrode. The test medium was a 3.5wt% NaCl solution, and the open circuit potential was measured. After the open circuit potential was stabilized, a dynamic potential scan was performed, with a scan rate of 0.001V / s and a scan step of 0.01V.

[0263] The potentiodynamic polarization curve of the sample was measured, and the corrosion potential and corrosion current density of the sample steel were calculated from the potentiodynamic polarization curve. The corrosion resistance of the corrosion-resistant high-temperature steel composite material was evaluated by the corrosion potential and the corrosion current density. The higher the corrosion potential, the lower the corrosion current density, indicating that the corrosion resistance of the corrosion-resistant high-temperature steel composite material is better.

[0264] (2) High temperature mechanical properties

[0265] The tensile strength of the corrosion-resistant and heat-resistant steels provided in Examples 1-5 and Comparative Examples 1-10 was tested by using a microcomputer-controlled universal testing machine in accordance with the national standard GB / T4338-2006 "Metallic Material High-Tension Test Method", the test temperatures were room temperature and 700°C, the tensile rate was set to 2 mm / min, when the test steel was heated to 700°C, it was kept warm for 20 minutes to ensure uniform heating, and the test steel was sprayed with water for cooling after being broken. Three groups of test steels were tested for each example and each comparative example, and the measured tensile strengths were averaged.

[0266] The test results are shown in Table 1.

[0267] Table 1 Test data of corrosion-resistant and heat-resistant steel

[0268]

[0269]

[0270] It can be seen from the data in Table 1 that the corrosion potential of the corrosion-resistant and heat-resistant steels prepared in Examples 1-5 is higher than that in Comparative Examples 1-10, and the corrosion current density is also lower than that in Comparative Examples 1-10, which indicates that the corrosion-resistant and heat-resistant steels prepared by the preparation method provided by the present invention have excellent corrosion resistance. In addition, the tensile strength of the corrosion-resistant and heat-resistant steels prepared in Examples 1-5 at room temperature and high temperature is higher than that in Comparative Examples 1-10, which indicates that the corrosion-resistant and heat-resistant steels prepared by the preparation method provided by the present invention have excellent high-temperature mechanical properties.

[0271] It can be seen from the test data of Example 1, Comparative Example 1 and Comparative Example 2 that the corrosion potential of Comparative Example 1 and Comparative Example 2 is lower than that of Example 1, while the corrosion current is higher than that of Example 1, which indicates that the corrosion resistance of the corrosion-resistant and heat-resistant steels prepared in Comparative Example 1 and Comparative Example 2 is inferior to that of Example 1. In addition, the tensile strength of Comparative Example 1 and Comparative Example 2 at room temperature and high temperature is lower than that of Example 1, which indicates that the high-temperature mechanical properties of the corrosion-resistant and heat-resistant steels prepared in Comparative Example 1 and Comparative Example 2 are inferior to those of Example 1. This is because the molybdenum content in Comparative Example 1 is too low, while the molybdenum content in Comparative Example 2 is too high, which affects the size of the austenite grains in the heat-resistant alloy casting, thereby affecting the corrosion resistance and high-temperature mechanical properties of the corrosion-resistant and heat-resistant steel finally prepared.

[0272] It can be seen from the test data of Example 1, Comparative Example 3 and Comparative Example 4 that the corrosion potential of Comparative Example 3 and Comparative Example 4 is lower than that of Example 1, while the corrosion current is higher than that of Example 1, which indicates that the corrosion resistance of the corrosion-resistant and heat-resistant steels prepared in Comparative Example 3 and Comparative Example 4 is inferior to that of Example 1. In addition, the tensile strength of Comparative Example 3 and Comparative Example 4 at room temperature and high temperature is lower than that of Example 1, which indicates that the high-temperature mechanical properties of the corrosion-resistant and heat-resistant steels prepared in Comparative Example 3 and Comparative Example 4 are inferior to those of Example 1. This is because the tungsten content in Comparative Example 3 is too low, while the tungsten content in Comparative Example 4 is too high, which affects the size of the austenite grains in the heat-resistant alloy casting, thereby affecting the corrosion resistance and high-temperature mechanical properties of the corrosion-resistant and heat-resistant steel finally prepared.

[0273] It can be seen from the test data of Example 1, Comparative Example 5 and Comparative Example 6 that the corrosion potential of Comparative Example 5 and Comparative Example 6 is lower than that of Example 1, while the corrosion current is higher than that of Example 1, which indicates that the corrosion resistance of the corrosion-resistant and heat-resistant steels prepared in Comparative Example 5 and Comparative Example 6 is inferior to that of Example 1. In addition, the tensile strength of Comparative Example 5 and Comparative Example 6 at room temperature and high temperature is lower than that of Example 1, which indicates that the high-temperature mechanical properties of the corrosion-resistant and heat-resistant steels prepared in Comparative Example 5 and Comparative Example 6 are inferior to those of Example 1. This is because the cobalt content in Comparative Example 5 is too low, while the cobalt content in Comparative Example 6 is too high, which affects the size of the austenite grains in the heat-resistant alloy casting, thereby affecting the corrosion resistance and high-temperature mechanical properties of the corrosion-resistant and heat-resistant steel finally prepared.

[0274] It can be seen from the test data of Example 1 and Comparative Example 7 that the corrosion potential of Comparative Example 7 is lower than that of Example 1, while the corrosion current is higher than that of Example 1, which indicates that the corrosion resistance of the corrosion-resistant and heat-resistant steel prepared in Comparative Example 7 is inferior to that of Example 1. In addition, the tensile strength of Comparative Example 7 at room temperature and high temperature is lower than that of Example 1, which indicates that the high-temperature mechanical properties of the corrosion-resistant and heat-resistant steel prepared in Comparative Example 7 are inferior to those of Example 1. This is because the secondary quenching treatment is omitted in Comparative Example 7, which affects the corrosion resistance and high-temperature mechanical properties of the corrosion-resistant and heat-resistant steel finally prepared.

[0275] It can be seen from the test data of Example 1, Comparative Example 8, Comparative Example 9 and Comparative Example 10 that the corrosion potential of Comparative Example 8, Comparative Example 9 and Comparative Example 10 is lower than that of Example 1, and the corrosion current is higher than that of Example 1, which indicates that the corrosion resistance of the corrosion-resistant heat-resistant steel prepared by Comparative Example 8, Comparative Example 9 and Comparative Example 10 is inferior to that of Example 1. In addition, the tensile strength of Comparative Example 8, Comparative Example 9 and Comparative Example 10 at room temperature and high temperature is slightly lower than that of Example 1, which indicates that the high-temperature mechanical properties of the corrosion-resistant heat-resistant steel prepared by Comparative Example 8, Comparative Example 9 and Comparative Example 10 are inferior to those of Example 1. This is because in Comparative Example 8, the inlet pipe of the nitriding furnace is not filled with a permeation-promoting filler, in Comparative Example 9, a lanthanum ferrite film is not formed on the surface of the heat-resistant alloy casting, and in Comparative Example 10, neither the inlet pipe of the nitriding furnace is filled with a permeation-promoting filler nor a lanthanum ferrite film is formed on the surface of the heat-resistant alloy casting, which affects the formation of the nitriding layer, and further affects the corrosion resistance and high-temperature mechanical properties of the corrosion-resistant heat-resistant steel finally prepared.

[0276] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing corrosion-resistant and heat-resistant steel co-doped with ternary trace elements, characterized in that: The preparation method comprises: Pure iron, ferrosilicon alloy, ferrochrome alloy, ferronickel alloy, ferromolybdenum alloy, ferrotungsten alloy and cobalt powder are used as raw materials, and the corrosion-resistant and heat-resistant steel doped with the ternary trace elements is obtained after molten steel smelting, refining and purification, casting, tempering heat treatment and nitriding treatment in sequence; After molten steel is smelted and refined and purified, refined molten steel is obtained. Taking the mass fraction of the refined molten steel as 100wt%, the mass fraction of each element in the refined molten steel is controlled within the following range: Carbon 0.1-0.2wt%, silicon 1.5-2wt%, chromium 23-25wt%, nickel 19-20wt%, molybdenum 0.3-0.4wt%, tungsten 0.5-0.6wt% and cobalt 1.6-1.8wt%, the balance is iron; The quenching and tempering heat treatment process includes a first quenching step and a second quenching step; The first quenching temperature is 1080-1100°C; Keeping at the first quenching temperature for 0.5 to 1.5 hours; The second quenching temperature is 980-1050°C; The second quenching temperature is kept for 0.5 to 1.5 hours; the nitriding process comprises: Sandblasting the surface of the heat-resistant alloy casting obtained by quenching and tempering heat treatment, and cleaning and drying the heat-resistant alloy casting after the sandblasting is completed; uniformly mixing hydrated lanthanum nitrate, hydrated ferric nitrate and ionized water to obtain a reaction solution, adding citric acid to the reaction solution to obtain a mixed solution, heating the mixed solution in a water bath to obtain a precursor solution, and spraying the precursor solution on the sandblasted surface of the heat-resistant alloy casting; Pre-filling a nitriding-promoting filler in an air inlet pipe of a nitriding furnace, wherein the nitriding-promoting filler comprises an inorganic carrier and cerium oxide and cobalt oxide supported on the surface of the inorganic carrier; The heat-resistant alloy casting sprayed with the precursor solution is transferred to the nitriding furnace, and the heat-resistant alloy casting is heated in an air atmosphere, so that the precursor solution on the surface of the heat-resistant alloy casting is crystallized to form a lanthanum ferrite film during the heating process; When the temperature in the nitriding furnace rises to the nitriding temperature, ammonia gas is introduced into the nitriding furnace, and the furnace is kept at the nitriding temperature to perform nitriding treatment to obtain the corrosion-resistant and heat-resistant steel.

2. The preparation method according to claim 1, characterized in that: The sandblasting medium used in the sandblasting process is white corundum; The particle size of the sandblasting medium used in the sandblasting treatment is 1 to 3 mm; The blasting pressure of the blasting treatment is 0.2-0.3 MPa; During the sandblasting process, the sandblasting distance between the nozzle and the surface of the heat-resistant alloy casting is 100 to 150 mm; During the sandblasting process, the angle between the nozzle axis and the surface of the heat-resistant alloy casting is 60-70°; The sandblasting time is 3 to 8 minutes.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the lanthanum element in the hydrated lanthanum nitrate to the iron element in the hydrated ferric nitrate is 1:(0.8-1.2); The total concentration of the hydrated lanthanum nitrate and the hydrated ferric nitrate in the reaction solution is 0.3-0.5 mol / L; The molar ratio of the hydrated lanthanum nitrate to the citric acid in the reaction solution is 1:(3-5); The water bath heating temperature is 80-90°C; The water bath heating time is 12 to 24 hours; The spraying amount of the precursor solution is 3-4 mL / min; The spraying time of the precursor solution is 4 to 5 minutes.

4. The preparation method according to claim 1, characterized in that: The penetration-promoting filler is prepared by the following method: Dispersing a soluble cerium salt and a soluble cobalt salt in anhydrous ethanol, and mixing them evenly to form a penetration-enhancing dispersion; adding an inorganic carrier to the penetration-enhancing dispersion, performing magnetic stirring and ultrasonic dispersion to obtain a suspension; filtering and drying the suspension in sequence to obtain a penetration-enhancing precursor; and calcining the penetration-enhancing precursor to obtain the penetration-enhancing filler; The molar ratio of the cerium element in the soluble cerium salt to the cobalt element in the soluble cobalt salt is 1:(0.8-1.3); The total concentration of the soluble cerium salt and the soluble cobalt salt in the penetration-enhancing dispersion is 0.5 to 1.5 mol / L; The ratio of the total mass of the soluble cerium salt and the soluble cobalt salt in the penetration-enhancing dispersion to the mass of the inorganic carrier is (0.2-0.3):1; The inorganic carrier includes any one of montmorillonite, diatomaceous earth, fly ash, and hydroxyapatite, or a combination of at least two thereof; The rotation speed of the magnetic stirring is 300-400 r / min; The magnetic stirring time is 30 to 40 minutes; The ultrasonic power of the ultrasonic dispersion is 500-600W; The calcination process of the penetration-promoting precursor comprises: The penetration-enhancing precursor is heated to 300-400° C. at a heating rate of 10-20° C. / min and kept at this temperature for 1-2 hours; Subsequently, the penetration-enhancing precursor is further heated to 700-800° C. at a heating rate of 5-15° C. / min, and kept at this temperature for 3-4 hours to complete calcination to obtain the penetration-enhancing filler.

5. The preparation method according to claim 1, characterized in that: Heating the heat-resistant alloy casting in an air atmosphere of a nitriding furnace at a heating rate of 10 to 15° C. / min; The nitriding temperature is 450-500°C; The ammonia gas flow rate is 5 to 8 L / min; The nitriding treatment time is 3 to 5 hours.

6. The preparation method according to claim 1, characterized in that: The molten steel smelting process specifically comprises the following steps: Put pure iron into a smelting furnace, heat it to a smelting temperature and keep it warm to form molten iron; then, put alloy materials into the molten iron in batches, first, add ferrosilicon alloy to the molten iron and keep it warm, during the insulation process, introduce argon gas from the bottom of the molten iron and add a slag-forming agent to remove scum on the liquid surface; then, heat the molten iron to a first temperature, add ferrochromium alloy, ferronickel alloy and ferromolybdenum alloy to the molten iron and keep it warm at the first temperature, during the insulation process, introduce argon gas from the bottom of the molten iron and add a slag-forming agent to remove scum on the liquid surface; finally, continue to heat the molten iron to a second temperature, add ferrotungsten alloy and cobalt powder to the molten iron and keep it warm at the second temperature, during the insulation process, introduce argon gas from the bottom of the molten iron and add a slag-forming agent to remove scum on the liquid surface to obtain alloyed steel liquid; The smelting temperature is 1560-1570°C; Keeping the smelting temperature at the temperature for 50 to 60 minutes; Add ferrosilicon alloy to the molten steel and keep the temperature for 20 to 30 minutes; The first temperature is 1580-1600° C.; Keeping the temperature at the first temperature for 20 to 30 minutes; The second temperature is 1650-1670°C; Keeping the temperature at the second temperature for 20 to 30 minutes; The slag-making agent includes any one of lime, fluorite, bauxite, and calcium carbide, or a combination of at least two of them; The amount of the slag-forming agent added each time the alloy material is added is: 15-20 kg of slag-forming agent per ton of molten steel; During the heat preservation process, the flow rate of argon gas introduced into the molten steel is 15-20 Nm 3 / h.

7. The preparation method according to claim 6, characterized in that: The refining and purification process specifically includes the following steps: The alloyed steel liquid obtained after smelting the steel liquid is adjusted to the refining temperature and then injected into the refining furnace, oxygen and nitrogen are introduced into the alloyed steel liquid to perform the first stage of decarburization on the alloyed steel liquid; when the carbon content in the alloyed steel liquid is reduced to the first content, the flow rate of oxygen is reduced and the flow rate of nitrogen is increased, and the alloyed steel liquid is decarburized in the second stage; when the carbon content in the alloyed steel liquid is reduced to the second content, the flow rate of oxygen is reduced again and the flow rate of nitrogen is increased, and the alloyed steel liquid is decarburized in the third stage; when the carbon content in the alloyed steel liquid is reduced to the third content, the introduction of oxygen and nitrogen is stopped; subsequently, a purifier is added to the alloyed steel liquid, and argon is blown into the bottom of the alloyed steel liquid to remove the scum on the liquid surface to obtain a refined steel liquid; The refining temperature is 1600-1620°C; In the first stage of carbon removal, the oxygen intake is 350-400 Nm 3 / h, the nitrogen intake is 50~100Nm 3 / h; The first content is 0.5-0.6wt%; In the second stage of carbon removal, the oxygen intake is 280-320 Nm 3 / h, the nitrogen intake is 120~180Nm 3 / h; The second content is 0.3-0.4wt%; In the third stage of carbon removal, the oxygen intake is 200-250 Nm 3 / h, the nitrogen intake is 200-250Nm 3 / h; The third content is 0.1-0.2 wt %; The purifier is composed of lime, fluorite and aluminum powder, wherein 8-10 kg of lime, 2.5-3.2 kg of fluorite powder and 1.3-1.7 kg of aluminum powder are added to each ton of alloyed steel liquid; After adding the purifier, the time for passing argon gas into the alloyed steel liquid is 10 to 20 minutes; After adding the purifier, the flow rate of argon gas introduced into the alloyed steel liquid is 50-60 Nm 3 / h.

8. The preparation method according to claim 7, characterized in that: The casting process specifically comprises the following steps: Preheating the steel mold, injecting the refined molten steel obtained after refining and purification into the steel mold when it reaches the casting temperature, naturally cooling to a first temperature after all the refined molten steel is injected into the steel mold, then adjusting the cooling rate, intermittently ultrasonically vibrating the steel mold, stopping the ultrasonic vibration and keeping the steel mold warm when the temperature drops to a second temperature, then naturally cooling to room temperature, and demolding to obtain an alloy casting; The preheating temperature of the steel mold is 380-400°C; The casting temperature is 1580-1600°C; The speed of injecting the refined molten steel into the steel mold is 5-6 t / min; The first temperature is 1100-1200° C.; After naturally cooling to the first temperature, the cooling rate is adjusted to 3-5°C / min; The intermittent ultrasonic vibration is performed for 10 to 15 minutes with a pause of 2 to 3 minutes. The ultrasonic power of the intermittent ultrasonic vibration is 2000-3000W; The ultrasonic frequency of the intermittent ultrasonic vibration is 20 to 30 kHz; The second temperature is 900-1000° C.; Keep at the second temperature for 8 to 10 hours.

9. The preparation method according to claim 8, characterized in that: The quenching and tempering heat treatment process specifically includes the following steps: The alloy casting obtained by casting is heated to an annealing temperature at a first heating rate and kept warm. After the insulation is completed, the alloy casting is taken out of the furnace and air-cooled to room temperature to complete the annealing treatment; the alloy casting after the annealing treatment is heated to a first quenching temperature at a second heating rate and kept warm. After the insulation is completed, the alloy casting is taken out of the furnace and oil-quenched. After the alloy casting is cooled to room temperature, it is heated to a second quenching temperature at a third heating rate and kept warm. After the insulation is completed, the alloy casting is taken out of the furnace and oil-quenched. After cooling to room temperature, the quenching treatment is completed to obtain a heat-resistant alloy casting; The first heating rate is 10-20°C / min; The annealing temperature is 700-800° C. Keeping the temperature at the annealing temperature for 1 to 3 hours; The second heating rate is 10-20°C / min; The third heating rate is 10-20°C / min.

10. A corrosion-resistant and heat-resistant steel prepared by the preparation method according to any one of claims 1 to 9 and doped with ternary trace elements.

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