0Cr17Ni2 Series Low-P Steel Ingot and Forgings, Preparation Method and Application

Abstract

The present invention provides a 0Cr17Ni2-based low-P steel ingot and forging, as well as a preparation method and application thereof, belonging to the field of metal materials technology. The preparation method of the 0Cr17Ni2-based low-P steel ingot provided by the present invention comprises the following steps: smelting, refining, casting, and first annealing the raw materials for preparing the 0Cr17Ni2-based low-P steel ingot in sequence to obtain the 0Cr17Ni2-based low-P steel ingot; the elemental composition of the 0Cr17Ni2-based low-P steel ingot, calculated by mass fraction, comprises: C 0.11-0.18%, Mn ≤ 0.80%, Si ≤ 0.80%, Cr 16.00-18.00%, Ni 1.50-2.50%, P ≤ 0.012%, S ≤ 0.010%, and the balance is Fe. The present invention controls specific smelting and refining conditions to obtain the 0Cr17Ni2-based low-P steel ingot, and forgings prepared using the 0Cr17Ni2-based low-P steel ingot have excellent high-temperature mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to 0Cr17Ni2 series low-P steel ingots and forgings, as well as preparation methods and applications. Background Art

[0002] 0Cr17Ni2 steel is an austenitic heat-resistant stainless steel containing ferrite. It has a good combination of strength and toughness and excellent corrosion resistance. It is widely used in the production of nitric acid, acetic acid and textile industries for shafts, piston rods, pumps and other parts that require both strength and toughness and corrosion resistance.

[0003] At present, the mechanical properties of 0Cr17Ni2 steel, especially its high-temperature mechanical properties, still need to be further improved in order to expand its application in high-end equipment such as aerospace, marine equipment, ship power equipment, and power generation turbines, compressors, and air compressors. Summary of the Invention

[0004] The purpose of the present invention is to provide 0Cr17Ni2 series low-P steel ingots and forgings, as well as preparation methods and applications. The forgings prepared using the 0Cr17Ni2 series low-P steel ingots provided by the present invention have excellent high-temperature mechanical properties.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a 0Cr17Ni2 series low-P steel ingot, comprising the following steps:

[0007] The raw materials for preparing the 0Cr17Ni2 series low-P steel ingot are sequentially smelted, refined, cast and first annealed to obtain the 0Cr17Ni2 series low-P steel ingot;

[0008] The element composition of the 0Cr17Ni2 series low-P steel ingot includes, by mass fraction, C 0.11-0.18%, Mn≤0.80%, Si≤0.80%, Cr 16.00-18.00%, Ni 1.50-2.50%, P≤0.012%, S≤0.010%, and the balance is Fe;

[0009] The smelting includes a melting stage, an oxidation stage and a reduction stage in sequence;

[0010] The conditions of the melting stage include: a molten pool temperature of 1550-1570°C; FeO is added, the mass of the FeO is 2-3% of the mass of the molten steel; the basicity R is 2.0-2.5; and the oxygen blowing pressure is 0.25-0.30 MPa;

[0011] The conditions of the oxidation stage include: oxygen blowing pressure ≥ 1.5 MPa; molten pool temperature 1660-1680°C; molten steel boiling time 6-10 minutes; adding Mn, the mass of which is 0.1-0.3% of the mass of the molten steel;

[0012] The conditions of the reduction stage include: adding thin slag material after slag discharge, adjusting the carbon content to 0.8-1.1%, adding silicon manganese iron alloy, manganese iron alloy and chromium iron alloy to make thin slag, and then adding reducing agent to make white slag;

[0013] The refining includes sequentially performing a VOD stage, a VCD stage, a VOH stage and a VD stage;

[0014] The conditions of the VOD stage include: vacuum degree of 90-110 mbar, vacuuming time of 1-1.5 hours, oxygen blowing volume of 530-570 m 3 / h, Ar flow rate is 4~7m 3 / h;

[0015] The conditions of the VCD stage include: vacuum degree of 15-20 mbar, vacuum pumping time of 13-18 min, Ar flow rate of 4-7 m 3 / h;

[0016] The conditions of the VOH stage include: adding aluminum, CaO, CaF2 and FeSi, heating to 1650-1670°C, and Ar flow rate of 4-7m 3 / h;

[0017] The conditions of the VD stage include: vacuum degree of 0.8~1.5mbar, vacuum time ≥20min, Ar flow rate of 4~7m 3 / h.

[0018] Preferably, the casting conditions include: molten steel calming time of 6-10 min, argon blowing volume of 4-7 L / min, casting temperature of 1550-1570° C., and casting speed of 5-7 mm / s.

[0019] Preferably, the temperature of the first annealing is 840-860° C., and the holding time is 8-10 hours.

[0020] The present invention provides a 0Cr17Ni2 series low-P steel ingot prepared by the preparation method described in the above technical solution.

[0021] Preferably, the average grain size of the 0Cr17Ni2 low-P steel ingot is ≤ grade 3.

[0022] The present invention provides a forging, which is prepared from the 0Cr17Ni2 series low-P steel ingot described in the above technical solution.

[0023] The present invention provides a method for preparing the forging described in the above technical solution, comprising the following steps:

[0024] The 0Cr17Ni2 series low-P steel ingot is subjected to forging, second annealing, rough machining, third annealing and solution treatment in sequence to obtain the forging.

[0025] Preferably, the forging conditions include: initial forging temperature of 1150-1170° C., final forging temperature of 860-890° C., forging ratio ≥3.0, extension ratio ≥2.0, and total forging ratio ≥4.0.

[0026] Preferably, the temperature of the second annealing is 820-840°C, and the holding time is 8-10 hours;

[0027] The third annealing temperature is 820-850° C., and the holding time is 8-10 hours;

[0028] The solution treatment includes sequentially performing a first solution treatment and a second solution treatment;

[0029] The temperature of the first solution treatment is 1180-1200°C, and the holding time is 1.5-2.5h;

[0030] The temperature of the second solution treatment is 780-800° C., and the holding time is 8-10 hours.

[0031] The present invention provides the use of the 0Cr17Ni2 series low-P steel ingot described in the above technical solution, the forging described in the above technical solution, or the forging prepared by the preparation method described in the above technical solution in marine equipment, ship power equipment or power stations.

[0032] Beneficial effects: Compared with 0Cr17Ni2, by controlling specific smelting and refining conditions, the present invention optimizes the S content from ≤0.030wt% to ≤0.010wt%, which is beneficial to reducing sulfide inclusions and improving pitting corrosion resistance; the present invention optimizes the P content from ≤0.040wt% to ≤0.012wt%, which is beneficial to reducing P segregation brittleness and improving toughness and fatigue resistance. The 0Cr17Ni2 series low-P steel ingot provided by the present invention belongs to austenitic heat-resistant stainless steel. The forgings prepared using it have excellent high-temperature mechanical properties, overcome the disadvantage of 0Cr17Ni2 steel having high-temperature temper brittleness, and can be used in the manufacture of marine equipment, ship power equipment, and steam turbines, compressors, and air compressors for power generation, ensuring the reliability and safety of the operation of these high-end equipment. In addition, the 0Cr17Ni2 series low-P steel ingots and forgings provided by the present invention also have excellent corrosion resistance, stress resistance, fatigue resistance and good welding performance. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing a 0Cr17Ni2 series low-P steel ingot, comprising the following steps:

[0034] The raw materials for preparing the 0Cr17Ni2 series low-P steel ingot are sequentially smelted, refined, cast and first annealed to obtain the 0Cr17Ni2 series low-P steel ingot;

[0035] The element composition of the 0Cr17Ni2 series low-P steel ingot includes, by mass fraction, C 0.11-0.18%, Mn≤0.80%, Si≤0.80%, Cr 16.00-18.00%, Ni 1.50-2.50%, P≤0.012%, S≤0.010%, and the balance is Fe;

[0036] The smelting includes a melting stage, an oxidation stage and a reduction stage in sequence;

[0037] The conditions of the melting stage include: a molten pool temperature of 1550-1570°C; FeO is added, the mass of the FeO is 2-3% of the mass of the molten steel; the basicity R is 2.0-2.5; and the oxygen blowing pressure is 0.25-0.30 MPa;

[0038] The conditions of the oxidation stage include: oxygen blowing pressure ≥ 1.5 MPa; molten pool temperature 1660-1680°C; molten steel boiling time 6-10 minutes; adding Mn, the mass of which is 0.1-0.3% of the mass of the molten steel;

[0039] The conditions of the reduction stage include: adding thin slag material after slag discharge, adjusting the carbon content to 0.8-1.1%, adding silicon manganese iron alloy, manganese iron alloy and chromium iron alloy to make thin slag, and then adding reducing agent to make white slag;

[0040] The refining includes sequentially performing a VOD stage, a VCD stage, a VOH stage and a VD stage;

[0041] The conditions of the VOD stage include: vacuum degree of 90-110 mbar, vacuuming time of 1-1.5 hours, oxygen blowing volume of 530-570 m 3 / h, Ar flow rate is 4~7m 3 / h;

[0042] The conditions of the VCD stage include: vacuum degree of 15-20 mbar, vacuum pumping time of 13-18 min, Ar flow rate of 4-7 m 3 / h;

[0043] The conditions of the VOH stage include: adding aluminum, CaO, CaF2 and FeSi, heating to 1650-1670°C, and Ar flow rate of 4-7m 3 / h;

[0044] The conditions of the VD stage include: vacuum degree of 0.8~1.5mbar, vacuum time ≥20min, Ar flow rate of 4~7m 3 / h.

[0045] The present invention first describes the elemental composition of the 0Cr17Ni2 series low-P steel ingot.

[0046] In the present invention, the element composition of the 0Cr17Ni2 series low-P steel ingot includes C 0.11-0.18% by mass, specifically 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17% or 0.18%.

[0047] In the present invention, the element composition of the 0Cr17Ni2 series low-P steel ingot includes Mn≤0.80%, calculated by mass fraction, and specifically can be 0.50%, 0.55%, 0.60%, 0.61%, 0.62%, 0.63%, 0.64%, 0.65%, 0.66%, 0.68%, 0.70%, 0.75% or 0.80%.

[0048] In the present invention, the element composition of the 0Cr17Ni2 series low-P steel ingot includes Si≤0.80% by mass, and specifically can be 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75% or 0.80%.

[0049] In the present invention, the element composition of the 0Cr17Ni2 series low-P steel ingot includes Cr 16.00-18.00%, specifically 16.00%, 16.20%, 16.40%, 16.60%, 16.80%, 16.91%, 17.05%, 17.12%, 17.20%, 17.40%, 17.60%, 17.80% or 18.00%, calculated by mass fraction.

[0050] In the present invention, the element composition of the 0Cr17Ni2 series low-P steel ingot includes Ni 1.50-2.50%, specifically 1.50%, 1.70%, 1.90%, 2.10%, 2.30%, 2.38%, 2.39%, 2.41% or 2.50%, by mass fraction.

[0051] In the present invention, the element composition of the 0Cr17Ni2 series low-P steel ingot includes P≤0.012% by mass, specifically 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.010%, 0.011% or 0.012%.

[0052] In the present invention, the element composition of the 0Cr17Ni2 series low-P steel ingot includes S≤0.010% by mass, specifically 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009% or 0.010%.

[0053] In the present invention, the element composition of the 0Cr17Ni2 low-P steel ingot includes the balance Fe by mass fraction.

[0054] The preparation method of the 0Cr17Ni2 low-P steel ingot of the present invention is described in detail below. In the present invention, unless otherwise specified, the raw materials and reagents used are commercially available products well known to those skilled in the art.

[0055] The present invention smelts the raw materials for preparing the 0Cr17Ni2 low-P steel ingot. In this invention, the raw materials preferably include scrap steel and alloying materials. The scrap steel is preferably pure scrap steel with a sulfur mass fraction of ≤0.020% and a phosphorus mass fraction of ≤0.020%. Control and detection of harmful elements in the scrap steel facilitates subsequent smelting, refining, casting, and first annealing to produce the 0Cr17Ni2 low-P steel ingot. The alloying materials preferably include Cr alloys and Ni alloys, preferably high-grade alloys with low sulfur and low phosphorus content. In an embodiment of the present invention, the pure scrap steel with a sulfur content of ≤0.020wt% and a phosphorus content of ≤0.020wt% and the alloying materials are smelted in an electric arc furnace (EAF). The smelting process sequentially includes a melting stage, an oxidation stage, and a reduction stage. In this embodiment, the raw materials and slag-forming materials used in the smelting process are pre-baked to ensure sufficient dryness. The present invention preferably adopts the "three highs" method for removing phosphorus during the smelting process, specifically including high basicity, high oxygen potential and high slag volume, which will be explained in detail below.

[0056] In the present invention, the conditions in the melting stage include: a molten pool temperature of 1550-1570°C, preferably 1560°C; FeO addition, the mass of which is 2-3% of the molten steel mass, preferably 2.2-2.5%; a basicity R of 2.0-2.5, preferably 2.2-2.3; and an oxygen blowing pressure of 0.25-0.30 MPa, preferably 0.28 MPa. The present invention preferably conducts the melting stage under the above conditions to ensure high basicity and high oxygen potential. During the melting stage, the present invention reduces the phosphorus content to ≤0.008wt%, entering the oxidation stage.

[0057] In the present invention, the conditions of the oxidation stage include: oxygen blowing pressure ≥1.5 MPa, preferably 1.6-2.5 MPa; molten pool temperature 1660-1680°C, preferably 1670°C; carbon removal ≥40%, and sampling analysis satisfies the C content of 0.8wt%, P content ≤0.010wt%, and S content ≤0.020wt%; Mn is added after the molten steel is boiled for 6-10 minutes (more preferably 7-8 minutes), and the mass of Mn is 0.1-0.3% of the mass of the molten steel, preferably 0.15-0.25%, and more preferably 0.2%; and the reduction stage is entered when the C content is 0.80-1.0wt%, the P content is ≤0.010wt%, and the S content is ≤0.020wt% and the molten steel temperature is 1670-1720°C (preferably 1700°C). The present invention preferably carries out the oxidation stage under the above conditions, which is conducive to ensuring a high oxygen potential and a high slag amount. The slag production amount in the oxidation stage is high, and the P content is reduced to ≤0.010wt% by continuous slag production and continuous slag discharge. Specifically, the P content can be reduced to 0.008~0.010wt%.

[0058] In the present invention, the reduction stage conditions include: removing the slag produced in the oxidation stage, adding a thin slag material, adjusting the carbon content to 0.8-1.1 wt% (preferably 1.0 wt%), then adding a ferrosilicomanganese alloy, a ferromanganese alloy, a ferrochromium alloy, and a ferronickel alloy. After the thin slag is formed, a reducing agent is added to form a white slag, and the white slag is preferably maintained for 18-23 minutes (more preferably 20 minutes). When the molten steel temperature is preferably 1670-1720°C (more preferably 1700°C), the molten steel is transferred to a ladle, the slag is skimmed until the residual amount is preferably ≤1 kg / t, and the molten steel temperature is preferably 1630-1680°C (more preferably 1650°C), and the material is discharged for subsequent processes. In the present invention, the thin slag material is preferably lime and fluorite; the amount of lime added is preferably 180-220 kg / t, more preferably 200 kg / t; and the amount of fluorite added is preferably 60-80 kg / t, more preferably 70 kg / t. In the present invention, the addition amount of the silicon manganese iron alloy is preferably 4~5kg / t, more preferably 4.5~5kg / t; the addition amount of the manganese iron alloy is preferably 4~7kg / t, more preferably 5kg / t; the addition amount of the chromium iron alloy is preferably 160~170kg / t, more preferably 165kg / t; the addition amount of the nickel iron alloy is preferably 18~20kg / t, more preferably 19.5kg / t. In the present invention, the reducing agent preferably includes a first reducing agent and a second reducing agent. In the present invention, the first reducing agent preferably includes ferrosilicon powder or calcium carbide; the amount of the ferrosilicon powder is preferably 4~7kg / t, more preferably 5kg / t; the amount of the calcium carbide is preferably 2~3kg / t, more preferably 2.3kg / t. In the present invention, the second reducing agent preferably includes carbon powder or AD powder; the amount of the carbon powder is preferably 0.8-1.5 kg / t, more preferably 1 kg / t; the amount of the AD powder is preferably 5-8 kg / t, more preferably 6.6 kg / t.

[0059] After smelting, the present invention refines the resulting molten steel. In an embodiment of the present invention, the molten steel is transferred to a vacuum refining furnace (VODC) for refining. In the present invention, the refining includes a VOD stage, a VCD stage, a VOH stage, and a VD stage.

[0060] In the present invention, the conditions of the VOD stage include: vacuum degree of 90-110 mbar, preferably 100 mbar; oxygen blowing volume of 530-570 mbar; 3 / h, preferably 550m 3 / h; Ar flow rate is 4~7m 3 / h, preferably 5m 3 / h; the C content is 0.70~0.90wt%, preferably 0.80wt%; the vacuum time is 1~1.5h, preferably 1.25h.

[0061] In the present invention, the conditions of the VCD stage include: vacuum degree of 15-20 mbar, preferably 18 mbar; vacuum pumping time of 13-18 min, preferably 15 min; Ar flow rate of 4-7 m 3 / h, preferably 5m 3 / h.

[0062] In the present invention, the conditions of the VOH stage include: adding aluminum, CaO, CaF2 and FeSi, then heating to 1650-1670°C (preferably 1660°C), Ar flow rate of 4-7m 3 / h, preferably 5m 3 / h. In the present invention, the addition amount of aluminum is preferably 1-2 kg / t, more preferably 1.5 kg / t; the addition amount of CaO is preferably 1-4 kg / t, more preferably 2 kg / t; the addition amount of CaF2 is preferably 6-10 kg / t, more preferably 8 kg / t; and the addition amount of FeSi is preferably 4-7 kg / t, more preferably 5 kg / t.

[0063] In the present invention, the conditions of the VD stage include: vacuum degree of 0.8~1.5mbar, preferably 1.0mbar; vacuum time ≥20min, preferably 25min; Ar flow rate of 4~7m 3 / h, preferably 5m 3 / h.

[0064] After the VD stage is completed, the present invention preferably pre-adds CaSi powder to the bottom of the tundish, then passes Ar through the bottom to completely expel the air inside, and discharges the material under an Ar protective atmosphere for subsequent steps. Discharging the material under an Ar protective atmosphere prevents secondary oxidation. In the present invention, the amount of CaSi powder added is preferably 0.8-1.5 kg / t, more preferably 1 kg / t.

[0065] After the refining is completed, the present invention casts the obtained molten steel. The casting of the present invention is preferably carried out in an argon protective atmosphere. Before performing the casting, the present invention preferably pre-checks the casting system and the steel mold to ensure that they are dry, free of moisture, clean and pollution-free. In the present invention, the conditions for the casting include: the molten steel calming time is preferably 5~10min, more preferably 7min; the argon blowing amount is preferably 4~7L / min, more preferably 5L / min; the casting temperature is preferably 1550~1570℃, more preferably 1560℃; the casting speed is preferably 5~8mm / s, more preferably 6mm / s. The present invention casts in an Ar protective atmosphere to prevent secondary oxidation and ensure the purity of the vacuum molten steel. In the present invention, after the casting is completed, it is preferably cooled in the mold, and the cooling time in the mold is preferably according to the formula T (h) = 35R 2(m) × 1.2, where R is the mold radius, and the mold is demoulded after the mold is cooled.

[0066] After casting, the present invention performs a first annealing on the resulting steel ingot to obtain the 0Cr17Ni2-based low-P steel ingot. In the present invention, the first annealing temperature is preferably 840-860°C, more preferably 850°C; the holding time is preferably 8-10 hours, more preferably 9 hours; and after the holding period, the ingot is preferably cooled to ≤200°C before being removed from the furnace. The present invention preferably performs the first annealing quickly after demolding to prevent an excessive drop in the ingot temperature.

[0067] After the first annealing, the present invention preferably performs surface inspection and composition inspection on the obtained steel ingot to obtain a qualified product.

[0068] The present invention provides a 0Cr17Ni2 low-P steel ingot prepared by the preparation method described in the above technical solution. In the present invention, the average grain size of the 0Cr17Ni2 low-P steel ingot is preferably ≤ grade 3, specifically grade 1 or grade 2.

[0069] The present invention provides a forging, which is prepared from the 0Cr17Ni2 series low-P steel ingot described in the above technical solution.

[0070] The present invention provides a method for preparing the forging described in the above technical solution, comprising the following steps:

[0071] The 0Cr17Ni2 series low-P steel ingot is subjected to forging, second annealing, rough machining, third annealing and solution treatment in sequence to obtain the forging.

[0072] In the present invention, the 0Cr17Ni2 low-P steel ingot is preferably subjected to blanking and heat treatment prior to forging. In an embodiment of the present invention, the 0Cr17Ni2 low-P steel ingot is blanked, then heat treated, and then forged. In the present invention, the heat treatment temperature is preferably 1170-1190°C, more preferably 1180°C, and the holding time is preferably 8-10 hours, more preferably 9 hours.

[0073] In the present invention, the forging conditions include: the initial forging temperature is preferably 1150~1170℃, more preferably 1160℃, the final forging temperature is preferably 860~890℃, more preferably 870℃; the cooling method is preferably furnace cooling to ≤200℃ and air cooling after leaving the furnace; the forging ratio is preferably ≥3.0, specifically 3.0; the extension ratio is preferably ≥2.0, more preferably 2.2~2.5; the total forging ratio is preferably ≥4.0, specifically 4.0.

[0074] After forging, the workpiece is subjected to a second annealing process. The temperature for the second annealing process is preferably 820-850°C, more preferably 830°C; the holding time is preferably 8-10 hours, more preferably 9 hours; the heating rate to the second annealing temperature is preferably 70-90°C / h, more preferably 80°C / h; and after the holding period, the workpiece is preferably furnace-cooled to ≤200°C before being air-cooled.

[0075] After annealing, the workpiece is subjected to rough machining and preferably ultrasonic testing before undergoing a third annealing. In the present invention, the third annealing temperature is preferably 820-850°C, more preferably 830°C; the holding time is preferably 8-10 hours, more preferably 9 hours; and after the holding period, strong air cooling is preferably used.

[0076] After annealing is completed, the present invention performs a solution treatment on the workpiece. In the present invention, the solution treatment preferably includes performing a first solution treatment and a second solution treatment in sequence. In the present invention, the temperature of the first solution treatment is preferably 1180~1200℃, more preferably 1190℃; the holding time is preferably 1.5~2.5h, more preferably 2h; and water cooling is preferably performed after the holding is completed. In the present invention, the temperature of the second solution treatment is preferably 780~800℃, more preferably 790℃; the holding time is preferably 8~10h, more preferably 9h; and strong wind rapid cooling is preferably performed after the holding is completed.

[0077] After the solution treatment, the present invention preferably performs physical and chemical property testing, dimensional testing, and non-destructive testing (NDT testing) on the obtained workpiece to obtain a qualified product.

[0078] The present invention provides the use of the 0Cr17Ni2 low-P steel ingots described in the above technical solution, the forgings described in the above technical solution, or the forgings produced by the preparation method described in the above technical solution in marine equipment, ship power equipment, or power plants. In the present invention, the 0Cr17Ni2 low-P steel ingots or forgings can be used to produce components for steam turbines, compressors, or air compressors, for example, turbine stators, compressor rotors, or air compressor blades. In the present invention, the operating temperature of the forgings is preferably no more than 550°C, and more preferably between 538°C and 550°C.

[0079] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0080] The testing methods in the following experimental process include: the allowable deviation of the chemical composition of finished steel products adopts GB / 222, the chemical composition analysis method of steel and alloy adopts GB / T223, the macrostructure and defect acid etching test method of steel adopts GB / T226, the sampling location and sample preparation of mechanical properties of steel and steel products adopt GB / T2975, the metal average grain size test method adopts GB / 16394, the determination of the content of non-metallic inclusions in steel by standard rating chart microscopic inspection method adopts GB / T10561, the measurement of multi-element content of stainless steel by spark atomic emission spectrometry (conventional method) adopts GB / T11170; the metallographic determination method of delta ferrite content in martensitic stainless steel adopts GB / T4402.

[0081] The mechanical properties test methods in the following experimental process include: room temperature tensile test method adopts GB / T228.1, specifically using Φ5mm standard specimen, using WE-300 tensile testing machine, test temperature is 25℃, and measuring the tensile strength Rm and yield strength R P0.2 , elongation after fracture A and cross-sectional shrinkage Z; the impact performance adopts the Charpy pendulum impact test method for metal materials in accordance with GB / T 229-2020; the hardness requirement test HBW adopts the GB5310-2008 standard; the hardness test method adopts GB / T231.1; the forgings are subjected to high-temperature mechanical properties, compressive resistance and endurance strength MPa tests in accordance with GB / T8732-2014 standard, the strength grades QT1 and QT2 are graded according to EN10269-2006, and the high-temperature performance data are quoted from EN10269-2006 and DIN17240-1976.

[0082] Comparative Example 1

[0083] The chemical composition of the steel ingot is shown in Table 1.

[0084] Example 1

[0085] The chemical composition of the steel ingot in this embodiment is shown in Table 1, and the specific preparation method is as follows:

[0086] (1) preparing raw materials by selecting pure scrap steel and high-grade Cr alloy and Ni alloy with a S content of ≤0.020wt% and a P content of ≤0.020wt%; placing the prepared raw materials in an electric arc furnace (EAF) for smelting, wherein the smelting includes a melting stage, an oxidation stage, and a reduction stage in sequence;

[0087] The conditions in the melting stage include: a molten pool temperature of 1560° C.; FeO is added, the mass of the FeO being 2.5% of the mass of the molten steel; a molten pool basicity R of 2.2; an oxygen blowing pressure of 0.28 MPa, reducing the P content to ≤0.008 wt%.

[0088] The conditions of the oxidation stage include: an oxygen blowing pressure of 2.5 MPa, a molten pool temperature of 1670° C., a high oxygen potential, a carbon removal amount of ≥40%, and sampling analysis meeting a carbon content of 0.8wt%, a phosphorus content of ≤0.010wt%, and a sulfur content of ≤0.020wt%; adding manganese after the molten steel is boiled for 7 minutes, wherein the mass of manganese is 0.2% of the mass of the molten steel, a high slag production amount, and continuous slag production and slag discharge; and entering the reduction stage when the carbon content is 0.80-1.0wt%, the phosphorus content is ≤0.010wt%, and the sulfur content is ≤0.020wt% and the molten steel temperature is 1700° C.;

[0089] The reduction stage comprises the following conditions: after removing the slag produced in the oxidation stage, adding thin slag material (specifically, 200 kg / t of lime and 70 kg / t of fluorite), adjusting the carbon content to 1.0 wt%, then adding 5 kg / t of ferrosilicon manganese alloy, 5 kg / t of ferromanganese alloy, 165 kg / t of ferrochrome alloy, and 19.5 kg / t of ferronickel alloy; after the thin slag is produced, adding a reducing agent (specifically, 5 kg / t of ferrosilicon powder and 1 kg / t of carbon powder) to produce white slag; maintaining the white slag for 20 minutes; transferring the molten steel into a ladle when the temperature reaches 1700° C.; skimming the slag in the ladle until the residual slag is ≤1 kg / t; and discharging the molten steel when the temperature reaches 1650° C.;

[0090] (2) transferring the molten steel having a temperature of 1650° C. obtained after smelting into a vacuum refining furnace (VODC) for refining, wherein the refining includes sequentially performing a VOD stage, a VCD stage, a VOH stage, and a VD stage;

[0091] The conditions of the VOD stage include: vacuum degree of 100 mbar, vacuuming time of 1.5 h, oxygen blowing volume of 550 m 3 / h, Ar flow rate is 5m 3 / h, C content is 0.80wt%;

[0092] The conditions of the VCD stage include: vacuum degree of 18 mbar, vacuum time of 15 min, Ar flow rate of 5 m 3 / h;

[0093] The conditions of the VOH stage include: adding aluminum 1kg / t, CaO 2kg / t, CaF28kg / t and FeSi 5kg / t, then heating to 1660°C, Ar flow rate of 5m 3 / h;

[0094] The conditions of the VD stage include: vacuum degree of 1.0 mbar, vacuum time of 25 min, Ar flow rate of 5 m 3 / h;

[0095] After the VD stage is completed, 1kg / t of CaSi powder is pre-added to the bottom of the tundish, and then Ar is passed through the bottom of the tundish to exhaust the air inside the tundish. The vacuum molten steel at a temperature of 1620℃ is poured into the tundish, and the final deoxidation is completed under the protection of Ar to complete the discharge.

[0096] (3) Pre-check the casting system and steel mold to ensure that they are dry, free of moisture, clean and pollution-free, and cast the molten steel obtained after refining. The casting conditions include: molten steel cooling time of 7 minutes, casting in Ar protective atmosphere, argon blowing volume of 5L / min, casting temperature of 1560℃, casting speed of 6mm / s; after casting, the mold is cooled, and the cooling time in the mold is calculated according to the formula T(h)=35R 2 (m) × 1.2, where R is the mold radius, and the mold is demoulded after the mold is cooled;

[0097] (4) Annealing the steel ingot obtained after demoulding, wherein the annealing conditions include: heating from room temperature to 850°C at a heating rate of 80°C / h and keeping the temperature for 9 hours; cooling the furnace to ≤200°C after the end of the heat preservation, and then taking the furnace out of the furnace and air cooling to obtain the steel ingot.

[0098] Example 2

[0099] The chemical composition of the steel ingot in this embodiment is shown in Table 1. The specific preparation method is shown in Example 1.

[0100] Example 3

[0101] The chemical composition of the steel ingot in this embodiment is shown in Table 1. The specific preparation method is shown in Example 1.

[0102] Table 1 Chemical composition of the steel ingots in Examples 1 to 3 and Comparative Example 1

[0103]

[0104] Example 4

[0105] The steel ingot in Example 1 was used to prepare forgings. The specific preparation method is as follows:

[0106] (1) blanking the steel ingot, heating it to 1180°C, holding it for 9 hours, and then forging it. The forging conditions include: a starting forging temperature of 1160°C, a final forging temperature of 870°C, cooling it to ≤200°C and then air cooling it out of the furnace, a forging ratio of 3.0, an elongation ratio of 2.5, and a total forging ratio of 4.0.

[0107] (2) annealing the workpiece obtained after forging, wherein the annealing conditions include: heating from room temperature to 830°C at a heating rate of 80°C / h, and holding the temperature for 9 hours; cooling the furnace to ≤200°C after the holding period, and then air cooling the workpiece out of the furnace;

[0108] (3) The workpiece obtained after annealing is rough-machined and inspected using ultrasonic testing;

[0109] (4) The workpieces that have passed the ultrasonic flaw detection are subjected to annealing and solution treatment in sequence;

[0110] The annealing temperature is 830°C, the holding time is 9 hours, and after the holding time is completed, the annealing is performed by strong wind rapid cooling;

[0111] The solution treatment includes a first solution treatment and a second solution treatment in sequence; the temperature of the first solution treatment is 1190°C, the holding time is 2 hours, and water cooling is performed after the holding is completed; the temperature of the second solution treatment is 790°C, the holding time is 9 hours, and strong wind rapid cooling is performed after the holding is completed to obtain the forging.

[0112] Example 5

[0113] The steel ingot in Example 2 was used to prepare forgings. The specific preparation method is as described in Example 4.

[0114] Example 6

[0115] The steel ingot in Example 3 was used to prepare forgings. The specific preparation method is as described in Example 4.

[0116] Test Example 1

[0117] The average grain sizes of the steel ingots in Comparative Example 1 and Examples 1 to 3 were tested, and the specific results are shown in Table 2.

[0118] Table 2 Average grain size metallographic grade of the steel ingots in Comparative Example 1 and Examples 1 to 3

[0119]

[0120] The steel ingots in Comparative Example 1 and Examples 1 to 3 were subjected to room temperature mechanical property tests, and the specific results are shown in Table 3.

[0121] Table 3 Room temperature mechanical properties test results of the steel ingots in Comparative Example 1 and Examples 1 to 3

[0122]

[0123] Test Example 2

[0124] The forgings in Examples 4 to 6 were subjected to high temperature mechanical property tests, and the specific results are shown in Table 4.

[0125] Table 4 High temperature mechanical properties test results of forgings in Examples 4 to 6

[0126]

[0127] The test results above demonstrate that the 0Cr17Ni2 low-P steel ingot provided by the present invention, compared to the original 0Cr17Ni2 steel ingot, optimizes the S content from ≤0.030wt% to ≤0.010wt%, which helps reduce sulfide inclusions and eliminates sulfide banding. The P content is optimized from ≤0.040wt% to ≤0.012wt%, which helps reduce phosphorus segregation and, in turn, improves mechanical properties such as elongation after fracture and reduction of area. Furthermore, the present invention utilizes an EAF (electric arc furnace) + VODC (vacuum refining furnace) + argon-shielded casting process, which minimizes non-metallic inclusions, improves molten steel purity and steel quality, and significantly increases the average grain size metallographic grade of the steel ingot from ≤4 to ≤3. Forgings produced using this steel ingot exhibit stable high-temperature resistance, fully meeting the operating requirements of high-end equipment forgings such as turbine stators, compressor rotors, and compressor blades for aerospace, ship propulsion, and power generation.

[0128] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing forgings using 0Cr17Ni2 low-P steel ingots, characterized in that: Follow these steps: The raw materials for preparing the 0Cr17Ni2 series low-P steel ingot are sequentially smelted, refined, cast and first annealed to obtain the 0Cr17Ni2 series low-P steel ingot, wherein the average grain size of the 0Cr17Ni2 series low-P steel ingot is level 2; The element composition of the 0Cr17Ni2 low-P steel ingot is calculated by mass fraction as follows: C 0.16%, Mn 0.64%, Si 0.55%, Cr 17.12%, Ni 2.41%, P 0.006%, S 0.003%, and the balance is Fe; The raw materials for the preparation are pure scrap steel with an S content of ≤0.020wt% and a P content of ≤0.020wt% and high-grade Cr alloy and Ni alloy; The smelting includes a melting stage, an oxidation stage and a reduction stage in sequence; The conditions in the melting stage include: a molten pool temperature of 1560° C.; FeO is added, the mass of the FeO being 2.5% of the mass of the molten steel; a molten pool basicity R of 2.2; an oxygen blowing pressure of 0.28 MPa, reducing the P content to ≤0.008 wt%. The conditions of the oxidation stage include: an oxygen blowing pressure of 2.5 MPa, a molten pool temperature of 1670° C., a carbon removal amount of ≥40%, and sampling analysis meeting a carbon content of 0.8wt%, a phosphorus content of ≤0.010wt%, and a sulfur content of ≤0.020wt%; adding Mn after the molten steel is boiled for 7 minutes, wherein the mass of Mn is 0.2% of the mass of the molten steel, a high slag production amount, and continuous slag production and slag discharge; and entering the reduction stage when the carbon content is 0.80-1.0wt%, the phosphorus content is ≤0.010wt%, and the sulfur content is ≤0.020wt% and the molten steel temperature is 1700° C.; The conditions of the reduction stage include: after removing the slag produced in the oxidation stage, adding a thin slag material, wherein the thin slag material comprises 200 kg / t of lime and 70 kg / t of fluorite, and the carbon content is adjusted to 1.0 wt%, and then adding 5 kg / t of ferrosilicon manganese alloy, 5 kg / t of ferromanganese alloy, 165 kg / t of ferrochrome alloy, and 19.5 kg / t of ferronickel alloy. After the thin slag is produced, a reducing agent is added to produce white slag, wherein the reducing agent comprises 5 kg / t of ferrosilicon powder and 1 kg / t of carbon powder. The white slag is maintained for 20 minutes. When the molten steel temperature reaches 1700° C., the molten steel is transferred into a ladle, the slag in the ladle is skimmed until the residual amount is ≤1 kg / t, and the molten steel is discharged when the temperature reaches 1650° C. The refining includes sequentially performing a VOD stage, a VCD stage, a VOH stage and a VD stage; The conditions of the VOD stage include: vacuum degree of 100 mbar, vacuuming time of 1.5 h, oxygen blowing volume of 550 m 3 / h, Ar flow rate is 5m 3 / h, C content is 0.80wt%; The conditions of the VCD stage include: vacuum degree of 18 mbar, vacuum time of 15 min, Ar flow rate of 5 m 3 / h; The conditions of the VOH stage include: adding 1kg / t of aluminum, 2kg / t of CaO, 8kg / t of CaF2 and 5kg / t of FeSi, then heating to 1660°C, with an Ar flow rate of 5m 3 / h; The conditions of the VD stage include: vacuum degree of 1.0 mbar, vacuum time of 25 min, Ar flow rate of 5 m 3 / h; After the VD stage is completed, 1kg / t of CaSi powder is pre-added to the bottom of the tundish, and then Ar is passed through the bottom of the tundish to exhaust the air in the tundish. The vacuum molten steel at a temperature of 1620°C is poured into the tundish, and the final deoxidation is completed under Ar protection; The casting conditions include: molten steel cooling time of 7 minutes, casting in Ar protective atmosphere, argon blowing volume of 5L / min, casting temperature of 1560℃, casting speed of 6mm / s; after casting, mold cooling is performed, and the mold cooling time is calculated according to the formula T=35R 2 ×1.2, where T is in h, R is the mold radius in m, and the mold is demoulded after the cooling is completed; The first annealing conditions include: heating from room temperature to 850°C at a heating rate of 80°C / h, holding for 9 hours; cooling the furnace to ≤200°C after the holding is completed, and then taking the furnace out of the furnace for air cooling; The 0Cr17Ni2 low-P steel ingot is blanked, heated to 1180° C., held at that temperature for 9 hours, and then forged. The forging conditions include: an initial forging temperature of 1160° C., a final forging temperature of 870° C., furnace cooling to ≤200° C. and air cooling after exiting the furnace, a forging ratio of 3.0, an elongation ratio of 2.5, and a total forging ratio of 4.

0. The workpiece obtained after forging is subjected to a second annealing, wherein the conditions of the second annealing include: heating from room temperature to 830°C at a heating rate of 80°C / h, holding for 9 hours; cooling the furnace to ≤200°C after the holding is completed, and then taking the furnace out of the furnace for air cooling; The workpiece obtained after the second annealing is rough-machined and inspected using ultrasonic testing; The workpieces that have passed the ultrasonic flaw detection are subjected to the third annealing and solution treatment in sequence; The third annealing temperature is 830°C, the holding time is 9 hours, and strong wind cooling is performed after the holding period. The solution treatment includes a first solution treatment and a second solution treatment in sequence; the temperature of the first solution treatment is 1190°C, the holding time is 2 hours, and water cooling is performed after the holding is completed; the temperature of the second solution treatment is 790°C, the holding time is 9 hours, and strong wind rapid cooling is performed after the holding is completed to obtain the forging.

2. A forging produced by the method of claim 1.

3. Use of the forging according to claim 2 in marine equipment, ship power equipment or power stations.

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