A y-nb binary rare earth alloy microalloyed high strength and toughness steel and a preparation method thereof

Abstract

The present application belongs to the technical field of low-temperature high-strength and high-toughness steel, and more particularly to a Y-Nb binary rare earth alloy microalloyed high-strength and high-toughness steel and a preparation method; the purpose is to add a specific rare earth binary alloy in a low-carbon low-alloy steel to form a composite carbide with high thermal stability during solidification, and to inhibit the growth of austenite grains; and the appropriate deformation temperature and deformation amount during final forging, through double coupling measures, create a microalloy composition design and create a crystal defect nucleation basis for eliminating the banding segregation and coarse mixed crystal structure of the subsequent forgings. Through multiple measures, the forged state of the high-strength steel of the present application is refined and homogenized, and then the final strengthening and toughening of the high-strength steel parts after quenching and tempering is realized, and the yield strength and impact toughness are significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-temperature high-strength high-toughness steel, and more particularly to a Y-Nb binary rare earth alloy micro-alloyed high-strength high-toughness steel and a preparation method thereof. BACKGROUND

[0002] Ultra-high strength and toughness steel has a wide range of needs in the fields of aerospace, advanced transportation, high-end equipment manufacturing, new energy and deep sea, especially in coal machinery, the large-scale and specialization degree is continuously improved, and it is urgent to produce high-quality and large-diameter ring chains. The 23MnNiMoCr54 alloy steel is the preferred material for large and high-end mine conveying chains. The conventional 23MnNiMoCr54 alloy element has a high cost, a tensile strength of 1200MPa-1300MPa, and a low yield strength, which cannot meet the design requirements of long-distance scraper conveyors. There is an urgent need for mine machinery manufacturers to develop new lightweight high-strength steel for chain rings. Moreover, the existing high-strength steel has insufficient plasticity and toughness, and thus has insufficient fatigue life, which is a common problem. In particular, the high-strength wear-resistant steel forging has the problems of mixed crystal and coarse grains after forging.

[0003] Meanwhile, in the conventional technology, the low-carbon low-alloy steel has a serious composition segregation during solidification, so that the banded structure of the rolled bar is more obvious, and the banded structure is a main factor affecting the toughness of the low-carbon low-alloy high-strength steel. In the prior art, the banded structure is eliminated by refining the grain structure after forging, specifically by heating to Ac3+(30℃-50℃) temperature normalizing. However, the grain coarsening temperature is 930℃, and when normalizing is higher than 930℃, the original austenite grains of the high-strength steel are further coarsened and grown, which significantly affects the strength and toughness of the high-strength steel. Therefore, how to inhibit the growth of austenite grains during heating is the key to solving the toughness of the low-carbon low-alloy steel. SUMMARY

[0004] In order to solve the technical problems mentioned in the background art, the present application provides a Y-Nb binary rare earth alloy micro-alloyed high-strength high-toughness steel and a preparation method thereof, which aims to add a specific rare earth binary alloy in the low-carbon low-alloy steel to form a composite carbide with high thermal stability during solidification, and to inhibit the growth of austenite grains; and to create a micro-alloy composition design and create a crystal defect nucleation basis for eliminating the banded segregation and coarse mixed crystal structure of the subsequent forging by using appropriate deformation temperature and deformation amount during finish forging. Through multiple measures, the grain structure of the high-strength steel in the forged state is refined and homogenized, and then the final strengthening and toughening of the high-strength steel part after quenching and tempering is realized, the yield strength and impact toughness are significantly improved, and the fatigue life of the high-strength steel part is significantly improved.

[0005] As an aspect of the present application, a Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel is provided, which is composed of the following elements in mass percentage: carbon: 0.18% to 0.21%, silicon: 1.35% to 1.50%, manganese: 0.8% to 1.0%, chromium: 0.7% to 1.0%, molybdenum: 0.10% to 0.40%, nickel: 0.9% to 3.0%, sulfur: 0% to 0.01%, phosphorus: 0% to 0.01%, aluminum: 0.015% to 0.035%, niobium: 0.2% to 0.6%, yttrium: 0.1% to 0.4%, and the rest is Fe and inevitable impurities.

[0006] As another aspect of the present application, a method for preparing the Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel is also provided, which comprises a smelting process, and the specific smelting process is as follows: smelting the molten iron by using an electric furnace or a converter or an induction furnace to obtain a molten steel; sequentially performing LF refining and VD furnace or RH furnace vacuum treatment on the molten steel; wherein, during the refining, alloying elements except for niobium and yttrium and Fe-Nb and Fe-Y binary rare earth alloys are added according to mass ratio; the Fe-Nb alloy contains 20% to 30% of Nb, and the Fe-Y alloy contains 10% to 20% of Y; the tapping temperature is 1530°C to 1570°C; and the molten steel after the above treatment is poured into an ingot mold to obtain an ingot, or is poured into a continuous casting crystallizer to obtain a continuous casting billet.

[0007] The method for preparing the Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel also comprises a hot rolling forming and stress relief annealing process, which specifically comprises the following steps: using a hot rolling forming process on the ingot or the continuous casting billet, wherein, when the hot rolling forming process is used: the starting rolling temperature is 1200°C±50°C, and the final rolling temperature is 850°C±30°C; the rod material is hot rolled with a rolling ratio of ≥8; and after the hot rolling, the stress relief annealing is performed, the rod material is heated to 680°C for annealing, the annealing time is 4 hours, the furnace is cooled to 450°C to be discharged and cooled to room temperature, thereby becoming the finished product of the steel plant and the raw material for the downstream user die forging.

[0008] The method for preparing the Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel also comprises a cutting, heating and die forging process on the rod material after the stress relief annealing, wherein, in the cutting process: the rod material is cut according to the structural size of the die forging piece; in the heating and die forging process: the starting forging temperature is 1200°C±50°C, the forming fluidity of the high strength and wear-resistant steel during die forging is ensured, the holding time is 0.5h to 1.0h, and the heart of the rod material is ensured to be hot penetrated; and the final forging temperature is 840°C to 880°C, and after the forging, the forged piece is rapidly air-cooled to store a large amount of dislocations in the forged piece.

[0009] The method for preparing the Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel further comprises a preliminary heat treatment process for eliminating the mixed crystal structure of the die forging: heating the die forging to 800-930 DEG C, maintaining for a preset time of 1.0-2.0 hours, and then cooling to room temperature in air to obtain the normalized forging.

[0010] The method for preparing the Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel further comprises a quenching and secondary low-temperature tempering process; wherein, in the quenching process, the forging after the preliminary heat treatment is heated to 880 DEG C ± 10 DEG C and maintained for 0.5-1 hour, then heated to 910 DEG C ± 30 DEG C and maintained for 0.5-1 hour; the forging after the heat treatment is placed in a cooling medium, which is water or PAG cooling liquid; when the cooling medium is PAG cooling liquid, the concentration of the PAG cooling liquid is 4-12%; in the primary low-temperature tempering process, the forging after the primary quenching is subjected to low-temperature tempering treatment, the tempering temperature is 200-300 DEG C, the tempering time is 1.5-4 hours, and the forging after the tempering is cooled in water or PAG quenching liquid; the secondary low-temperature tempering process is repeated once using the primary low-temperature tempering process.

[0011] In the quenching process, the forging after the preliminary heat treatment is heated to 880 DEG C ± 10 DEG C and maintained for 0.5-1 hour, which is a very critical step, and sufficient maintaining time is required to precipitate sufficient NbC particles, which, together with the composite carbide Y3C / Cr 23 C6 precipitated during solidification, hinders the growth of austenite grains during the next higher-temperature quenching heating.

[0012] The high strength and toughness steel obtained by the above preparation method has a tensile strength of 1300-1520 MPa, a yield strength of 1200-1380 MPa, an elongation of 13-16%, a reduction of area of 50-60%, a room temperature impact energy of 100-130 J, a -50 DEG C impact energy of 60-100 J, and a hardness of HRC 42-47; the parts prepared from the high strength and toughness steel have a microstructure of lath martensite and a small amount of lath carbide-free bainite complex phase structure, and the thickness or width of the lath substructure is 20-200 nm.

[0013] In the quenching process of the method for preparing the Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel, the maintaining time after the forging is heated to 910 DEG C ± 30 DEG C is 1-2 min / mm according to the cross-sectional size of the forging.

[0014] As another aspect of the present application, a method for high-strength chain ring steel is also provided, comprising the following steps: cutting, heating and die forging of the bar after stress relief annealing after hot rolling by the above method, and normalizing, quenching and twice tempering processes, wherein the cutting process: cutting the bar according to the structural size of the chain ring die forging piece by using a saw blade cutting machine; the heating and die forging process: feeding the bar with a designed length size into an induction heating furnace, with an initial forging temperature of 1200℃±50℃ and a holding time of 0.5h-1.0h; a final forging temperature of 870℃±30℃, and air cooling after forging to store a large amount of dislocations in the forging piece; normalizing: heating the die forging piece chain ring to 800℃-930℃, holding for a preset time of 1.0h-2.0h, and then cooling to room temperature in air to obtain the normalized chain ring; quenching: heating the normalized chain ring forging piece to 910℃±30℃ and holding for a preset time, calculated according to the cross-sectional size of the chain ring, 1min / mm-2min / mm; placing the heated and held chain ring into a cooling medium, the cooling medium being PAG cooling liquid with a concentration of 4%-12%; and then twice tempering at a temperature of 240℃-280℃ and cooling to room temperature in the PAG cooling liquid after tempering.

[0015] The tensile strength of the prepared chain ring is 1450MPa-1520MPa, the yield strength is 1350MPa-1430MPa, the elongation is 11%-13%, the reduction of area is 50%-55%, the normal temperature impact energy is 100J-130J, the-50℃ impact energy is 80J-100J, and the hardness is HRC42-47; the microstructure of the chain ring is a complex phase structure of lath martensite and carbide-free bainite, and the thickness of the lath substructure is 50nm-300nm.

[0016] The technical effects of the present application are as follows: by adding the above-mentioned rare earth binary alloy in low-carbon low-alloy steel, a complex carbide with high thermal stability is formed during solidification, Y3C is the core growth Cr 23 C6 complex carbide; the growth of austenite grains is inhibited; and the deformation temperature and deformation amount during final forging are appropriate, and sufficient dislocations are stored after deformation to become the nucleation zone of recrystallization; and NbC is precipitated at a lower temperature before the quenching heating temperature, hindering the grain growth during quenching heating. Through the double coupling measures, the micro-alloy composition design and the creation of crystal defects are created for the elimination of the banded segregation and coarse mixed crystal structure of the subsequent forging piece. Through multiple measures, the forged state structure of the high-strength steel of the present application is refined and homogenized, and then the final strengthening and toughening of the high-strength steel part after quenching and tempering of the present application is realized, and the yield strength, impact toughness and fatigue performance are significantly improved.

[0017] The mine conveying chain as an important transmission device in the coal conveying process, serves in a bad environment, bears various complex loads, and high requirements are put forward to its strength, toughness, fatigue resistance and other performances. The high strength and toughness wear-resistant steel can be used for manufacturing the mine conveying chain, has remarkable mechanical properties, that is, by improving the strength and toughness, the length of the scraper is increased.

[0018] The high strength and toughness wear-resistant steel manufactured by the manufacturing method has high strength and toughness, and the high strength and toughness steel parts fundamentally solve the contradiction between the existing strength and toughness. Compared with the high strength steel of the same level in the current literature report or steel manual, the toughness of the high strength and toughness wear-resistant steel is at least 1 times higher than that of the steel with the highest toughness in the 1400MPa level high strength steel. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0020] Figure 1 Y3C particles as M 23 Electron microscope image of the composite carbide particle whose core grows C6 type carbide;

[0021] Figure 2 X-ray energy spectrum analysis diagram of the brighter part marked 1 in Figure 1

[0022] Figure 3 X-ray energy spectrum analysis diagram of the darker part marked 2 in Figure 1

[0023] High strength steel without rare earth binary alloy, grain structure after die forging; Figure 4

[0024] High strength steel containing rare earth binary alloy, grain structure after die forging; Figure 5

[0025] High strength steel containing rare earth binary alloy, grain structure of the die forging part after 840℃ holding for 1 hour preheat treatment. Figure 6 DETAILED DESCRIPTION

[0026] ​​In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0027] As an aspect of the present application, a Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel is provided, which is composed of the following elements in percentage by mass: carbon: 0.18% to 0.21%, silicon: 1.35% to 1.50%, manganese: 0.8% to 1.0%, chromium: 0.7% to 1.0%, molybdenum: 0.10% to 0.40%, nickel: 0.9% to 3.0%, sulfur: 0% to 0.01%, phosphorus: 0% to 0.01%, aluminum: 0.015% to 0.035%, niobium: 0.2% to 0.6%, yttrium: 0.1% to 0.4%, and the rest is Fe and inevitable impurities.

[0028] In the conventional technology, after adding La and Ce rare earth metals in the molten steel, the rare earth metals are easily oxidized and exist in the form of LaO and Ce2O3 rare earth compounds as fine solid particles, which can provide heterogeneous nucleation sites for the solidification process of the molten steel, increase the number of crystal nuclei in the liquid, and reduce the crystallization supercooling degree of the molten steel, thereby significantly refining the grains. After the solidification grains are refined, a smaller grain basis is provided for subsequent processing. However, it is difficult to operate in production by adding La and Ce rare earth metals, which is easy to block the casting nozzle and form large inclusions.

[0029] The role of the rare earth yttrium adopted in the present application is different from the above-mentioned mechanism. In order to reduce the burning loss of the rare earth element yttrium in the smelting process and form oxide inclusions in the alloy, and improve the yield, yttrium is added in the form of intermediate alloy Fe4Y2Si9.

[0030] The molecular formula of the intermediate alloy is Fe4Y2Si9, pure yttrium, Fe-Si alloy and iron powder are mixed uniformly according to the mass ratio, and then melted in a vacuum carbon tube furnace to obtain Fe4Y2Si9 alloy after solidification.

[0031] 0.3% of the rare earth element Y is added in the alloy, which is dissolved in the austenite at high temperature during the solidification of the molten steel. Since the atomic radius of Y is much larger than that of Fe, if it is dissolved in the austenite matrix, a larger lattice distortion energy will be generated. According to the solute atom equilibrium segregation theory, it will be segregated on the austenite grain boundary, tend to occupy the area between the austenite dendrites, and form Y3C phase. Y3C has very high stability at high temperature, and Y3C / Cr 23The complex carbide of C6 has higher high-temperature stability, and does not dissolve into high-temperature austenite when being forged to high temperature, but exists on the austenite grain boundary, which pins the migration and growth of the austenite grain boundary, and hinders the growth of the austenite grain.

[0032] Therefore, the grain refinement is different from the conventional technology. The conventional technology provides heterogeneous crystal nuclei, increases the number of crystal nuclei, and increases the crystalline grain during solidification, thereby refining the grain, but the obvious disadvantage is that a small amount of addition does not work, and a large amount of addition forms new inclusions, which deteriorates the performance, and therefore it is difficult to popularize and apply in production. In the present application, Y3C is first precipitated in the solid phase as the temperature decreases after solidification, and then Cr 23 C6 is subsequently precipitated with Y3C to form a complex carbide. Since the complex carbide is precipitated in situ and has a crystallographic orientation relationship with the parent phase austenite, it will not form inclusions, and has higher high-temperature stability. When being forged to a temperature of about 1200℃, it will not dissolve into austenite, has a pinning inhibition effect on the growth of the austenite grain, and prevents the forging structure from being coarsened and forming a mixed structure of fine grains and coarse grains. As shown in FIG. 2, Y3C particles serve as the core of the growth of M Figure 1 C6 type carbide. 23 FIG. 3 is an electron microscope image of a complex carbide particle with Y3C particles as the core of the growth of M

[0033] As another aspect of the present application, a method for preparing a Y-Nb binary rare earth alloy microalloyed high-strength and high-toughness steel is also provided, which comprises a smelting process, and the specific smelting process adopts the following steps: smelting by using an electric furnace or a converter or an induction furnace to obtain a molten steel; sequentially performing LF refining and VD furnace or RH furnace vacuum treatment on the molten steel; wherein, during the refining, alloying elements except for niobium and yttrium and Fe-Nb and Fe-Y binary rare earth alloys are added according to the mass ratio; the Fe-Nb alloy contains 20% to 30% of Nb, and the Fe-Y alloy contains 10% to 20% of Y; the tapping temperature is 1530℃ to 1570℃; and the molten steel after the above treatment is poured into an ingot mold to obtain an ingot, or is poured into a continuous casting crystallizer to obtain a continuous casting billet.

[0034] Among them, Nb is a strong carbide forming element, which will significantly segregate at the grain boundary during the solidification of the alloy liquid, and combine with carbon to generate NbC with high temperature stability and high strength, which hinders the migration of the grain boundary. At the same time, after adding niobium in the alloy, due to the segregation of niobium at the grain boundary, eutectic NbC is formed, which breaks the continuous network of Cr23C6, preventing it from precipitating in a continuous network. It is because of this distribution of grain boundary carbide that the phase boundary becomes more tortuous, which is not conducive to the connection and expansion of cracks, thereby improving the toughness of the alloy, and also improving the resistance to grain boundary sliding and the strength.

[0035] In some embodiments, the method for preparing Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel further comprises a hot rolling forming and stress relief annealing process, specifically comprising the following steps: using a hot rolling forming process on the ingot or continuous casting billet, wherein when the hot rolling forming process is used: the starting rolling temperature is 1200℃±50℃, and the final rolling temperature is 850℃±30℃; the hot rolling is performed to form a rod, and the rolling ratio is ≥8; after the hot rolling, the stress relief annealing is performed, the rod is heated to 680℃ for annealing, the annealing time is 4 hours, the furnace is cooled to 450℃, and the cooling is performed to room temperature to become the raw material of the die forging.

[0036] In some embodiments, the method for preparing Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel further comprises a cutting, heating and die forging process on the rod after the stress relief annealing, wherein the cutting process: the rod is cut according to the structural size of the die forging; the heating and die forging process: including holding at the initial forging temperature; wherein the initial forging temperature is 1200℃±50℃, and the forming fluidity of the high strength and wear-resistant steel during die forging is ensured, and the holding time is 0.5h-1.0h. As shown in Figure 4 As shown in

[0037] As shown in Figure 1 , the complex carbide particles with Y3C particles as the core and M 23 C6 type carbide are precipitated on the austenite grain boundary. The complex carbide has higher high-temperature stability, and does not dissolve at the die forging heating temperature, but still exists as a complex carbide particle, thereby being able to hinder the growth of austenite grains and refine the austenite grains. X-ray energy spectrum analysis shows that the brighter part of the particle center marked as 1 (white particle) is a yttrium-rich phase, and the black part marked as 2 (black particle) is a chromium-rich phase, and the yttrium-rich phase is the core of the chromium-rich phase.

[0038] The Figure 1 brighter part of the particle center in the figure is the yttrium-rich phase (white particle-1), and the energy spectrum analysis is performed on the composition to obtain Figure 2 the energy spectrum, which is a Y and Cr containing carbide.

[0039] The Figure 1 dark part of the black color in the figure is the chromium-rich phase (black particle-2), and the energy spectrum analysis is performed on the composition to obtain Figure 3 the energy spectrum, which shows that the Y3C core is surrounded by Cr-rich carbide.

[0040] Due to the structure of the die forging, the deformation amount of each part is greatly different, which will produce a serious mixed crystal structure, and must be eliminated before quenching and tempering.

[0041] In some embodiments, the method for preparing the Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel further comprises a preliminary heat treatment process for eliminating the mixed crystal structure of the die forging: heating the die forging to 800-930°C, holding for a preset time of 1.0-2.0 hours, and then cooling to room temperature in air to obtain the normalized forging.

[0042] The lower finish forging temperature results in a higher dislocation density remaining in the die forging, especially around the inter-situ complex carbide, and a high-density dislocation wall or substructure exists, which is prone to form recrystallization nuclei at the dislocation wall during normalizing, thereby causing recrystallization of the mixed crystal and coarse grains and grain refinement and homogenization.

[0043] As another aspect of the application, a method for preparing a Y-Nb binary rare earth alloy micro-alloyed high-strength steel for chain links is also provided, which comprises the following steps: a cutting, heating and die forging process for the hot-rolled and stress-relieved rod prepared by the above method, and a normalizing, quenching and twice tempering process, wherein the cutting process: cutting the rod according to the structural dimensions of the chain link die forging using a saw blade cutting machine; the heating and die forging process: feeding the rod with a designed length into an induction heating furnace, with a start forging temperature of 1200°C±50°C and a holding time of 0.5-1.0 hours; a finish forging temperature of 870°C±30°C, and rapid air cooling after forging to store a large amount of dislocations in the forging; normalizing: heating the die forging chain link to 800-930°C, holding for a preset time of 1.0-2.0 hours, and then cooling to room temperature in air to obtain the normalized chain link; quenching: heating the normalized chain link forging to 910°C±30°C and holding for a preset time, which is calculated according to the cross-sectional dimensions of the chain link, 1-2 min / mm; placing the heated and held chain link into a cooling medium, which is a PAG cooling liquid with a concentration of 8-12%, and then performing twice tempering at a temperature of 240-280°C and cooling to room temperature in the PAG cooling liquid.

[0044] The prepared chain link has a tensile strength of 1450-1520 MPa, a yield strength of 1350-1430 MPa, an elongation of 11-13%, a reduction of area of 50-55%, a room temperature impact energy of 100-130 J, a -50°C impact energy of 80-100 J, and a hardness of HRC 42-47; and the microstructure of the chain link is a complex structure of lath martensite and carbide-free bainite, with a lath substructure thickness of 50-300 nm.

[0045] The high-strength chain ring prepared by the above method is superior to the existing high-strength chain ring material 23MnNiMoCr54 steel. The 23MnNiMoCr54 steel has a tensile strength of about 1300 MPa, a yield strength of 1000 MPa, and a high content of alloy elements Ni and Mo, and has a low cost performance. After using the material of the application, the yield strength and fatigue life are significantly improved.

[0046] Example 1: Manufacturing of high-strength steel chain ring.

[0047] (1) Special steel plant smelting according to composition: chemical composition: carbon: 0.18%~0.21%, silicon: 1.35%~1.50%, manganese: 0.8%~1.0%, chromium: 0.7%~1.0%, molybdenum: 0.10%~0.40%, nickel: 0.9%~3.0%, sulfur: 0%~0.01%, phosphorus: 0%~0.01%, aluminum: 0.015%~0.035%, niobium: 0.2%~0.6%, yttrium: 0.1%~0.4%, the rest is Fe and inevitable impurities.

[0048] The smelting process includes the following steps: smelting raw materials by electric arc furnace or intermediate frequency induction furnace to obtain molten steel; the molten steel is sequentially subjected to LF refining and VD vacuum treatment; wherein the tapping temperature is 1530~1570℃; the refined molten steel is poured into a continuous casting crystallizer to obtain a continuous casting billet.

[0049] (2) Hot rolling of continuous casting billet: heat the continuous casting billet to 1150℃ and hot roll it to the required size round steel bar; the final rolling temperature is 870℃.

[0050] (3) Stress relief and hardness reduction annealing: reheat the hot-rolled round steel bar to 680℃ for annealing, the holding time is 4 hours, the furnace is cooled to 450℃ and then cooled to room temperature.

[0051] (4) Cutting and die forging: cutting with a saw blade cutting machine, feeding the bar of designed length into an induction heating furnace, heating to 1200℃, holding time 0.5 hours, then feeding into a die forging machine to forge and shape. The chain ring forging is air cooled to room temperature.

[0052] (5) Normalizing: preliminary heat treatment for eliminating mixed crystal structure. Place the chain ring forging in a heating furnace, heat to 840℃ and hold for 2 hours, then take out and air cool. After normalizing, the grain size is about 18µm, corresponding to 9.5 grade grain size.

[0053] (6) Quenching and tempering heat treatment. The quenching temperature is 920℃, the holding time is 1.0 hour, then quenching in 8% PAG cooling liquid. Quenching is followed by tempering, the tempering temperature is 260℃, the tempering time is 3 hours. Tempering twice.

[0054] (7) Mechanical properties.

[0055] Table 1 Mechanical properties of the link

[0056] Mechanical properties Rm / MPa Rp0.2 / MPa A / ％ Z / ％ [Ku2 / J] HRC 1530 1380 13.5 55 115 46.5

[0057] The grain structure of the high-strength steel obtained in Example 1 after die forging is shown in Figure 1, which is a high-strength steel containing a rare earth binary alloy. Figure 5

[0058] Comparative Example 1: High-strength steel without Y-Nb binary rare earth alloy micro-alloying.

[0059] Comparative Example 1 does not contain Y-Nb binary rare earth alloy in its composition, and the grain structure obtained is shown in Figure 2, which has a serious mixed crystal structure, with an average grain size of about 80 pm, equivalent to a grain size of 4. Figure 4

[0060] The high-strength steel link manufactured by the method of Example 1 has a grain structure as shown in Figure 3, with uniform and fine grain size, all being equiaxed grains, with a maximum grain diameter of about 20 pm. Figure 6

[0061] The mechanical parameters of the high-strength steel links prepared in Example 1 and Comparative Example 1 are shown in Table 2.

[0062] Table 2 Effect of rare earth alloy element addition on impact absorption energy

[0063] Heat treatment Rm / MPa Rp0.2 / MPa A / ％ Z / ％ [Ku2 / J] HRC Non-rare earth binary alloy 1345 1176 12.2 49 76 43.56 Rare earth binary alloy 1481 1316 14 60 126 45.68

[0064] Conclusion: The impact absorption energy of the high-strength and tough steel is significantly improved by about 65% by the rare earth binary alloy in Example 1.

[0065] Comparative Example 2: Variation of dislocation density stored in the forging with final forging temperature.

[0066] Comparative Example 2 differs from Example 1 only in that the final forging temperature is increased, the composition remains unchanged, and the rest of the process flow is consistent. The experimental results obtained are shown in Table 3.

[0067] Table 3 Effect of final forging temperature on dislocation density and impact absorption energy

[0068] Finish forging temperature (°C) 840 850 860 880 900 dislocation density (m -2 ) 8.2 x 10 16 ]] 3.1 x 10 16 ]]> 7.4 x 10 15 ]] 3.7 x 10 15 ]]> 2.8 x 10 15 ]]> Grain size (pm) 15 20 26 35 40 Impact absorption energy (Ku2 / J) 135 128 122 113 102

[0069] Figure 6 The grain structure of the high-strength steel containing a rare earth binary alloy after die forging and pre-treatment at 860°C for 1 hour.

[0070] ​​​In view of the decrease of the final forging temperature, the dislocation density increases, which creates favorable conditions for recrystallization nucleation, thereby refining the grains. However, the forged piece is prone to cracking at a low final forging temperature, thereby negatively affecting the strength of the material. The final forging temperature is preferably 850-880°C.

[0071] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for producing a Y-Nb binary rare earth alloy microalloyed high strength and toughness steel, characterized in that, The Y-Nb binary rare earth alloy micro-alloyed high strength and toughness steel is composed of the following elements with mass percentage: Carbon: 0.18%~0.21%, silicon: 1.35%~1.50%, manganese: 0.8%~1.0%, chromium: 0.7%~1.0%, molybdenum: 0.10%~0.40%, nickel: 0.9%~3.0%, sulfur: 0%~0.01%, phosphorus: 0%~0.01%, aluminum: 0.015%~0.035%, niobium: 0.2%~0.6%, yttrium: 0.1%~0.4%, and the rest is Fe and inevitable impurities; The smelting process in the preparation method is as follows: The molten iron is smelted by an electric furnace, a converter or an induction furnace to obtain a molten steel; The molten steel is sequentially subjected to LF refining and VD furnace or RH furnace vacuum treatment; during the refining, alloying elements except niobium and yttrium and Fe-Nb and Fe-Y binary rare earth alloys are added according to the mass ratio; the Fe-Nb alloy contains 20%~30% of Nb and the Fe-Y alloy contains 10%~20% of Y; the tapping temperature is 1530°C~1570°C; The molten steel after the above treatment is poured into a ingot mold to obtain a ingot or a continuous casting mold to obtain a continuous casting billet; It also includes a hot rolling forming and stress relief annealing process, specifically including the following steps: The ingot or continuous casting billet is subjected to a hot rolling forming process, wherein, When the hot rolling forming process is used: the opening rolling temperature is 1200°C±50°C and the final rolling temperature is 850°C±30°C; the rod material is hot rolled with a rolling ratio of ≥8; After hot rolling, the stress relief annealing is performed, the rod material is reheated to 680°C for annealing, the annealing time is 4 hours, the furnace is cooled to 450°C and then cooled to room temperature to become the finished product of the steel plant, which is the raw material for the downstream user die forging.

2. The method of claim 1, wherein, It also includes a process of cutting, heating and die forging the rod material after the stress relief annealing, wherein, The cutting process: the rod material is cut according to the structure size of the die forging part; The heating and die forging process: the initial forging temperature is 1200°C±50°C to ensure the forming fluidity of the high-strength wear-resistant steel during die forging, the holding time is 0.5h~1.0h to ensure the heat penetration of the core of the rod material; the final forging temperature is 840°C~880°C, and the forged part is rapidly air-cooled after forging to store a large amount of dislocations in the forged part; It also includes a preliminary heat treatment process for eliminating the mixed crystal structure of the die forging part: the die forging part is heated to 800°C~930°C, and then cooled to room temperature in the air after being kept for a preset time of 1.0h~2.0h to obtain the forged part after normalizing; It also includes a quenching and secondary low-temperature tempering process, wherein, Quenching: the forged part after the preliminary heat treatment is heated to 880°C±10°C, kept for 0.5h~1h, continuously heated to 910°C±30°C and kept for 0.5h~1h; the heated and kept forged part is placed in a cooling medium, and the cooling medium is a PAG cooling liquid with a concentration of 4%~12%; Primary low-temperature tempering: the forged part after the primary quenching is subjected to low-temperature tempering treatment, the tempering temperature is 200°C~300°C, the tempering time is 1.5h~4h, and the forged part is cooled in the PAG quenching liquid after tempering; The secondary low-temperature tempering is repeated by using the primary low-temperature tempering process; In the quenching process, the forged piece is heated to 910 DEG C + 30 DEG C and then kept for a preset time, and the keeping time is set according to the cross-sectional size of the forged piece, 1 min / mm to 2 min / mm.

3. The method of claim 1, wherein, The process also comprises a cutting, heating and die forging process of the bar after stress relief annealing after hot rolling, and a normalizing, quenching and twice tempering process, wherein, The cutting process: the bar is cut according to the structural size of the chain ring die forging by using a saw blade cutting machine; The heating and die forging process: the bar with the designed length size is sent into an induction heating furnace, the initial forging temperature is 1200 DEG C + 50 DEG C, the keeping time is 0.5 h to 1.0 h, the final forging temperature is 870 DEG C + 30 DEG C, and the forged piece is rapidly air-cooled after forging so as to store a large amount of dislocations in the forged piece; The normalizing: the die forged chain ring is heated to 800 DEG C to 930 DEG C and kept for a preset time of 1.0 h to 2.0 h, and then cooled to room temperature in air to obtain the normalizing chain ring; The quenching: the normalizing chain ring is heated to 910 DEG C + 30 DEG C and kept for a preset time, and the keeping time is set according to the cross-sectional size of the chain ring, 1 min / mm to 2 min / mm; The chain ring after keeping is placed into a cooling medium, and the cooling medium is PAG cooling liquid, and the concentration of the PAG cooling liquid is 4% to 12%; Then, twice tempering is carried out at a tempering temperature of 240 DEG C to 280 DEG C, and the chain ring is cooled to room temperature in the PAG cooling liquid after tempering.

4. A high toughness steel produced by the method of claim 2, characterized in that, The high-toughness steel has a tensile strength of 1300 MPa to 1520 MPa, a yield strength of 1200 MPa to 1380 MPa, an elongation of 13% to 16%, a reduction of area of 50% to 60%, a normal temperature impact energy of 100 J to 130 J, a-50 DEG C impact energy of 60 J to 100 J, and a hardness of HRC 42 to 47; The microstructure of the chain ring is a lath martensite and a small amount of lath carbide-free bainite complex phase structure, and the thickness or width of the lath substructure is 20 nm to 200 nm.

5. A chain link produced by the method of claim 3, wherein The chain ring has a tensile strength of 1450 MPa to 1520 MPa, a yield strength of 1350 MPa to 1430 MPa, an elongation of 11% to 13%, a reduction of area of 50% to 55%, a normal temperature impact energy of 100 J to 130 J, a-50 DEG C impact energy of 80 J to 100 J, and a hardness of HRC 42 to 47; The microstructure of the chain ring is a lath martensite and a small amount of lath carbide-free bainite complex phase structure, and the thickness or width of the lath substructure is 20 nm to 200 nm.

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