Method for improving purity of stainless steel, 21Cr12MoV stainless steel ingot, 21Cr12MoV stainless steel forge piece and preparation method and application of 21Cr12MoV stainless steel ingot and 21Cr12MoV stainless steel forge piece

Abstract

The invention provides a method for improving the purity of stainless steel, a 21Cr12MoV stainless steel ingot, a 21Cr12MoV stainless steel forge piece and a preparation method and application of the 21Cr12MoV stainless steel ingot and the 21Cr12MoV stainless steel forge piece, and belongs to the technical field of smelting. The method provided by the invention comprises the following steps: smelting raw materials to obtain molten steel; the molten steel is subjected to VD refining under the argon blowing condition, and refined molten steel is obtained; mixing the refined molten steel with a deoxidizing agent, and deoxidizing under the protection of argon to obtain deoxidized molten steel; the deoxidized molten steel is subjected to protective pouring, and a steel ingot is obtained; and the steel ingot is subjected to electroslag remelting, and the stainless steel ingot is obtained. According to the method, VD refining is adopted, argon blowing is conducted at the same time, then the deoxidizing agent is adopted, protective pouring and electroslag remelting are matched, the inclusion content can be reduced to the maximum extent, the purity of molten steel is improved, and then the mechanical property and heat resistance of the forge piece are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting, and in particular relates to a method for improving the purity of stainless steel, a 21Cr12MoV stainless steel ingot and a 21Cr12MoV stainless steel forging, and a preparation method and application thereof. Background Art

[0002] 21Cr12MoV is a martensitic heat-resistant stainless steel that is widely used in the manufacture of key components in industries such as energy, petrochemicals, and aerospace. In the field of steam turbines, it is used as a material for core components such as blades, disks, and impeller shafts. It can withstand the complex stresses caused by high temperature, high pressure, and high-speed rotation, ensuring the long-term stable operation of the unit.

[0003] At present, the preparation method of 21Cr12MoV stainless steel is mainly induction furnace smelting. The prepared 21Cr12MoV stainless steel has many inclusions, resulting in poor mechanical properties and heat resistance of forgings. Summary of the invention

[0004] The object of the present invention is to provide a method for improving the purity of stainless steel, a 21Cr12MoV stainless steel ingot and a 21Cr12MoV stainless steel forging, and a preparation method and application thereof. The method provided by the present invention can improve the purity of stainless steel.

[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 improving the purity of stainless steel, comprising the following steps:

[0007] (1) smelting the raw materials to obtain molten steel;

[0008] (2) subjecting the molten steel obtained in step (1) to VD refining under argon blowing conditions to obtain refined molten steel;

[0009] (3) mixing the refined molten steel obtained in step (2) with a deoxidizer, and deoxidizing the molten steel under argon protection to obtain deoxidized molten steel;

[0010] (4) performing protective pouring on the deoxidized molten steel obtained in step (3) to obtain a steel ingot;

[0011] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting to obtain a stainless steel ingot.

[0012] Preferably, the blowing time of argon gas in step (2) is 6 to 10 minutes.

[0013] Preferably, the amount of the deoxidizer used in step (3) is 1-1.5 kg / t.

[0014] Preferably, in step (5), the voltage of the electroslag remelting is 60-66V, the current of the electroslag remelting is 12-14kA, and the time of the electroslag remelting is 6.5-7.0h.

[0015] The present invention also provides a 21Cr12MoV stainless steel ingot prepared by the method described in the above technical solution, wherein the O content in the 21Cr12MoV stainless steel ingot is ≤15ppm; the A-type inclusion rating in the 21Cr12MoV stainless steel ingot is ≤1.0, the B-type inclusion rating is ≤1.0, the C-type inclusion rating is ≤1.5, and the D-type inclusion rating is ≤1.5.

[0016] The present invention also provides a 21Cr12MoV stainless steel forging, which is prepared from the 21Cr12MoV stainless steel ingot described in the above technical solution.

[0017] The present invention also provides a method for preparing the 21Cr12MoV stainless steel forgings described in the above technical solution, comprising: forging, rough machining and heat treating the 21Cr12MoV stainless steel ingot in sequence to obtain the 21Cr12MoV stainless steel forgings.

[0018] Preferably, the initial forging temperature of the forging is 1000-1200°C, the final forging temperature of the forging is ≥850°C, the forging ratio of the forging is ≥3.0, the extension ratio of the forging is ≥2.0, and the total forging ratio is ≥4.0.

[0019] Preferably, the heat treatment comprises annealing and solution treatment performed sequentially.

[0020] The present invention also provides the application of the 21Cr12MoV stainless steel forgings described in the above technical scheme or the 21Cr12MoV stainless steel forgings prepared by the preparation method described in the above technical scheme in aerospace, ship power, medical equipment and 300-350MW compressed air energy storage power stations.

[0021] The present invention provides a method for improving the purity of stainless steel, comprising the following steps: smelting raw materials to obtain molten steel; performing VD refining on the molten steel under argon blowing conditions to obtain refined molten steel; mixing the refined molten steel with a deoxidizer, deoxidizing under argon protection to obtain deoxidized molten steel; performing protective casting on the deoxidized molten steel to obtain an ingot; and performing electroslag remelting on the ingot to obtain a stainless steel ingot. The present invention performs VD (vacuum degassing) refining on the molten steel obtained by smelting, and vacuuming can improve the oxygen removal rate. At the same time, blowing argon during the refining process will increase the volume of inclusions in the molten steel and quickly float up, thereby removing the inclusions and further purifying the molten steel. Subsequently, a deoxidizer is used to further remove oxygen under argon protection, and protective casting can reduce the content of inclusions to the maximum extent and improve the purity of the molten steel; then electroslag remelting is performed to further reduce the content of inclusions, thereby improving the purity of the stainless steel ingot, and further improving the mechanical properties and heat resistance of the forging. Experimental results show that the B-type inclusion rating in the 21Cr12MoV stainless steel ingot prepared by the method provided by the present invention is 0.4-0.5; the room temperature mechanical properties of the 21Cr12MoV stainless steel forging are as follows: longitudinal tensile strength is 880-895MPa, and transverse tensile strength is 895-910MPa; longitudinal yield strength is 719-730MPa, and transverse yield strength is 720-735MPa; longitudinal elongation after fracture is 17-19%, and transverse elongation after fracture is 13-15%; longitudinal impact absorption energy is 58-68J, and transverse impact absorption energy is 22-25J; high temperature mechanical properties are as follows: 400°C yield strength is 435-525MPa; 500°C yield strength is 335-350MPa; 550°C creep strength is 113-213MPa; 550°C endurance strength is 137-260MPa. DETAILED DESCRIPTION

[0022] The present invention provides a method for improving the purity of stainless steel, comprising the following steps:

[0023] (1) smelting the raw materials to obtain molten steel;

[0024] (2) subjecting the molten steel obtained in step (1) to VD refining under argon blowing conditions to obtain refined molten steel;

[0025] (3) mixing the refined molten steel obtained in step (2) with a deoxidizer, and deoxidizing the molten steel under argon protection to obtain deoxidized molten steel;

[0026] (4) performing protective pouring on the deoxidized molten steel obtained in step (3) to obtain a steel ingot;

[0027] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting to obtain a stainless steel ingot.

[0028] Unless otherwise specified, the present invention has no particular limitation on the sources of the raw materials used, and the raw materials may be prepared using commercially available products or well-known preparation methods known to those skilled in the art.

[0029] The method provided by the invention is applicable to stainless steel of any chemical composition, and is preferably applicable to 21Cr12MoV stainless steel.

[0030] The invention smelts raw materials to obtain molten steel.

[0031] In the present invention, the mass percentage of S in the raw material is preferably ≤0.020%; the mass percentage of P in the raw material is preferably ≤0.020%. The present invention can further improve the inclusion level by using pure raw materials with S≤0.020wt% and P≤0.020wt%.

[0032] The present invention has no special limitation on the composition of the raw materials, and the raw materials can be selected according to the actual steel type.

[0033] In the present invention, the smelting is preferably carried out in an electric arc furnace; the smelting preferably includes a melting period, an oxidation period and a reduction period carried out in sequence. The present invention has no special limitation on the model of the electric arc furnace, and instruments and equipment familiar to those skilled in the art can be used.

[0034] In the present invention, a slag-forming agent is preferably added during the melting period; the slag-forming agent is preferably FeO; the mass of the slag-forming agent is preferably 2-4% of the mass of the raw material. As an embodiment, the mass of the slag-forming agent can be 2-3% of the mass of the raw material. In the present invention, the slag-forming agent is beneficial to dephosphorization, promotes the floating of inclusions and gas and removes them with the slag flow.

[0035] In the present invention, the temperature in the melting period is preferably 1540-1560° C. As an embodiment, the temperature in the melting period may be 1545-1555° C., or may be 1550° C.

[0036] In the present invention, the melting period is preferably carried out under oxygen blowing conditions; the pressure of the oxygen blowing is preferably 0.25-0.30 MPa. As an embodiment, the pressure of the oxygen blowing can be 0.26-0.28 MPa. In the present invention, oxygen blowing during the melting period can cause a strong carbon-oxygen reaction, causing the melt to boil, and the impurities in the melt to fully float up, further achieving a purification effect.

[0037] The present invention has no particular limitation on the duration of the melting period. The P content in the melt may be reduced to below 0.012 wt % by using operations well known to those skilled in the art.

[0038] In the present invention, the basicity of the melt after the melting period is preferably 2 to 2.5.

[0039] In the present invention, the temperature of the oxidation period is preferably 1650-1670°C; the oxidation period is preferably carried out under oxygen blowing conditions; the oxygen blowing pressure is preferably 1-2MPa, more preferably 1.5MPa; the melting time during the oxidation period is preferably 5-7min. The present invention adopts an oxygen-enriched dephosphorization process during the oxidation period, and performs oxidative decarburization when the melt is boiling to remove gas and inclusions.

[0040] As an implementation manner, the temperature during the oxidation period may be 1655-1665° C., or 1660° C.; and the melting point may be boiled for 6 minutes.

[0041] In the present invention, the decarburization amount of the oxidation period melt is preferably ≥40%; the P content of the oxidation period melt is preferably ≤0.010wt%, and the S content of the melt is preferably ≤0.010wt%.

[0042] In the present invention, after the oxidation period, the melt is preferably deslagging; the deslagging temperature is preferably 1690-1710° C., more preferably 1700° C. The present invention has no particular limitation on the deslagging operation, and operations well known to those skilled in the art can be used.

[0043] In the present invention, the thin slag material, alloy raw material, reducing agent and composite deoxidizer are preferably added in sequence during the reduction period.

[0044] In the present invention, when the temperature of the melt is greater than 1650°C, thin slag is preferably added; the thin slag preferably includes lime and fluorite. The present invention has no particular limitation on the amount of the thin slag, and the C content can be adjusted to less than 1.0wt%.

[0045] As an implementation mode, the amount of lime used can be 3-8 kg / t, and can also be 6 kg / t; the amount of fluorite used can be 3-8 kg / t, and can also be 6 kg / t.

[0046] In the present invention, the alloy raw materials preferably include ferrosilicon manganese, ferromanganese and ferrochrome. The present invention has no special limitation on the amount of the alloy raw materials, as long as the raw material composition meets the composition requirements of the prepared stainless steel.

[0047] As an implementation mode, the usage of ferrosilicomanganese, ferromanganese and ferrochrome can be independently 7-9 kg / t, and can also be 8 kg / t.

[0048] In the present invention, the reducing agent preferably includes at least one of ferrosilicon powder, calcium carbide and carbon powder; the amount of ferrosilicon powder is preferably 3-8 kg / t, more preferably 5-7 kg / t; the amount of calcium carbide is preferably 2-3 kg / t; the amount of carbon powder is preferably 0.5-2 kg / t, more preferably 1-1.8 kg / t. In the present invention, ferrosilicon powder, calcium carbide and carbon powder are used to make white slag for deoxidation.

[0049] In the present invention, the retention time of the white slag after adding the reducing agent to make the white slag is preferably 15 to 25 minutes, more preferably 20 minutes. In the present invention, the retention time of the white slag after making the white slag is limited to the above range to fully perform reduction and deoxidation.

[0050] In the present invention, the composite deoxidizer preferably includes the following components in mass percentage: C 0.02-0.07%, Mn 10-30%, Si 5-15%, Al 0.4-1.2%, Ca 0.3-1% and Fe 54-75%. The composite deoxidizer is added during the reduction period to further improve the deoxidation effect and reduce the inclusion content.

[0051] In the present invention, the amount of the composite deoxidizer is preferably 8-10 kg / t. As an embodiment, the amount of the composite deoxidizer can be 9-10 kg / t. The present invention can further improve the deoxidation effect by limiting the amount of the composite deoxidizer to the above range, thereby further reducing the inclusion content.

[0052] In the present invention, the temperature of the melt when the composite deoxidizer is added is preferably 1580-1620° C. As an embodiment, the temperature of the melt when the composite deoxidizer is added can be 1590-1610° C., or can be 1600° C.

[0053] In the present invention, 6 to 15 minutes after the composite deoxidizer is added to the melt, when the melt composition meets the required requirements and the melt temperature is 1690 to 1710°C, the melt is preferably transferred into a ladle, and then the slag is removed from the ladle and then the temperature is lowered to 1650 to 1700°C to obtain molten steel.

[0054] As an implementation method, after adding the composite deoxidizer into the melt for 10 to 15 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt can be transferred into a ladle, and then the slag is removed from the ladle and then the temperature is lowered to 1660 to 1680°C to obtain molten steel.

[0055] The present invention has no particular limitation on the operation of transferring the melt into the ladle, and the operation well known to those skilled in the art may be adopted.

[0056] In the present invention, the slagging in the ladle is preferably performed until the residue amount is ≤1.5kg / t.

[0057] After obtaining the molten steel, the present invention performs VD refining on the molten steel under the condition of blowing argon gas to obtain refined molten steel. The present invention performs VD (vacuum degassing) refining, and vacuuming can improve the removal rate of oxygen. At the same time, blowing argon gas during the refining process will increase the volume of inclusions in the molten steel and quickly float up, thereby removing the inclusions and further purifying the molten steel.

[0058] In the present invention, the VD refining is preferably carried out in a VD / VOD vacuum refining furnace. The present invention has no particular limitation on the model of the VD / VOD vacuum refining furnace, and any equipment well known to those skilled in the art can be used.

[0059] In the present invention, the blowing time of argon is preferably 6 to 10 minutes; the flow rate of argon is preferably 4 to 6 m 3 / h; the argon blowing is preferably bottom blowing. As an embodiment, the argon blowing time can be 7 to 9 minutes, or 8 minutes; the argon flow rate can be 4 to 6m 3 / h, can also be 5m 3 In the present invention, by limiting the blowing time and flow rate of argon gas to the above range, inclusions can be further removed.

[0060] In the present invention, the vacuum degree of the VD refining is preferably ≤1.0 mbar; the time of the VD refining is preferably ≥20 min; and the temperature of the VD refining is preferably 1600-1700°C. As an embodiment, the vacuum degree of the VD refining can be 0.1-0.8 mbar, or 0.3-0.5 mbar; the time of the VD refining can be 25-30 min; and the temperature of the VD refining can be 1620-1680°C, or 1640-1660°C. The present invention limits the vacuum degree, temperature and time of VD refining within the above ranges, which can further remove inclusions.

[0061] After obtaining the refined molten steel, the present invention mixes the refined molten steel with a deoxidizer and performs deoxidation under the protection of argon gas to obtain deoxidized molten steel.

[0062] In the present invention, the temperature of the refined molten steel is preferably 1610-1620°C, more preferably 1615°C.

[0063] In the present invention, the deoxidizer is preferably CaSi powder; the amount of the deoxidizer is preferably 1-1.5 kg / t. As an embodiment, the amount of the deoxidizer can be 1.2-1.4 kg / t.

[0064] In the present invention, the mass ratio of Ca to Si in the CaSi powder is preferably 1:(2-4), more preferably 1:3; the particle size of the CaSi powder is preferably 3-5 mm. In the present invention, the CaSi powder is preferably dried before use. The present invention has no special limitation on the drying operation, and the operation well known to those skilled in the art can be used.

[0065] In the present invention, the mixing of the refined steel liquid and the deoxidizer is preferably carried out in a tundish. In the present invention, the tundish is preferably bottom-blown with argon before use. The present invention can exhaust the air in the tundish by blowing argon at the bottom of the tundish to avoid the presence of oxygen; the use of a deoxidizer in the tundish for final deoxidation of the tundish can further reduce the oxygen content in the refined steel liquid, thereby reducing the content of inclusions.

[0066] The present invention has no special limitation on the model of the tundish, and any instrument or equipment familiar to those skilled in the art may be used.

[0067] The present invention has no special limitation on the operation of mixing the refined molten steel and the deoxidizer, and the technical scheme for preparing the mixed material well known to those skilled in the art can be adopted.

[0068] In the present invention, the deoxygenation time is preferably 5 to 10 minutes, more preferably 8 minutes. The present invention can further improve the deoxygenation effect by limiting the deoxygenation time within the above range.

[0069] After deoxidation, the present invention preferably performs sedation on the deoxidized melt to obtain deoxidized molten steel. In the present invention, the sedation time is preferably 6 to 7 minutes. The sedation of the present invention can remove gas and inclusions in the deoxidized molten steel and improve purity.

[0070] After obtaining the deoxidized molten steel, the present invention performs protective pouring on the deoxidized molten steel to obtain a steel ingot.

[0071] In the present invention, the protective pouring system is preferably inspected before the protective pouring. The present invention has no special limitation on the operation of inspecting the protective pouring system, as long as it is ensured to be dry, free of moisture, and the runner and steel mold are clean and free of pollution.

[0072] In the present invention, the temperature of the protective pouring is preferably 1550-1570°C, more preferably 1560°C; the flow rate of the protective pouring is preferably 5-7 mm / s, more preferably 6 mm / s; the atmosphere of the protective pouring is preferably argon; the flow rate of the argon is preferably 4-6 L / min, more preferably 5 L / min. The present invention adopts argon protective pouring to prevent secondary oxidation of deoxidized molten steel.

[0073] After the protective pouring is completed, the present invention preferably cools and demoulds the product obtained by the protective pouring in sequence to obtain a steel ingot.

[0074] In the present invention, the cooling time is preferably calculated according to Formula I:

[0075] T=35R 2 (M)×1.2Formula I;

[0076] Wherein, T is the cooling time, the unit is h; R is the mold radius, the unit is m.

[0077] The present invention has no particular limitation on the demoulding operation, and any operation well known to those skilled in the art may be used.

[0078] After obtaining the steel ingot, the present invention performs electroslag remelting on the obtained steel ingot to obtain a stainless steel ingot. The present invention adopts electroslag remelting to further reduce the inclusion content, thereby improving the purity of the stainless steel ingot, and further improving the mechanical properties and heat resistance of the forging.

[0079] In the present invention, the voltage of the electroslag remelting is preferably 60-66V; the current of the electroslag remelting is preferably 12-14kA; and the time of the electroslag remelting is preferably 6.5-7.0h. As an embodiment, the voltage of the electroslag remelting can be 62-64V; the current of the electroslag remelting can be 13-14kA; and the time of the electroslag remelting can be 6.6-6.8h.

[0080] In the present invention, the slag system used in the electroslag remelting is preferably CaF 2 -Al 2 O 3 -MgO ternary slag system. 2 -Al 2 O 3 The -MgO ternary slag system is not particularly limited, and any ternary slag system well known to those skilled in the art may be used.

[0081] In the present invention, the mass of the slag system is preferably 5 to 15% of the mass of the steel ingot.

[0082] The present invention has no particular limitation on the melting rate of the electroslag remelting, and it can be carried out at a uniform speed.

[0083] In the present invention, the electroslag remelting is preferably direct slag smelting of consumable electrodes; Si-Mn alloy powder is preferably added during the slag smelting period of the electroslag remelting; the amount of the Si-Mn alloy powder is preferably 2-3 kg / t. In the present invention, the Si-Mn alloy powder is a deoxidizer, which can improve the deoxidation effect.

[0084] In the present invention, the mass ratio of Si to Mn in the Si-Mn alloy powder is preferably 1: (9-11), more preferably 1: 10. The present invention has no particular limitation on the particle size of the Si-Mn alloy powder, and any particle size known to those skilled in the art may be used.

[0085] After electroslag remelting, the present invention preferably sequentially cools and anneals the product obtained by electroslag remelting to obtain a stainless steel ingot.

[0086] The present invention has no particular limitation on the cooling operation, and any cooling operation well known to those skilled in the art may be used.

[0087] In the present invention, the holding temperature of the annealing treatment is preferably 820-840° C.; the holding time of the annealing treatment is preferably 8-10 hours; the cooling method of the annealing treatment is preferably furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is preferably ≤300° C. The present invention has no special limitation on the operation of the furnace cooling and air cooling, and the operation well known to those skilled in the art can be adopted.

[0088] The present invention first adopts smelting and then performs vacuum degassing and refining. Vacuuming can improve the oxygen removal rate. At the same time, blowing argon during the refining process will increase the volume of inclusions in the molten steel and quickly float them up, thereby removing the inclusions and further purifying the molten steel. Subsequently, a deoxidizer is added to further remove oxygen under the protection of argon. In combination with protective pouring, inclusions can be reduced to the maximum extent and the purity of the molten steel can be improved. Subsequently, electroslag remelting is performed to further reduce inclusions, thereby improving the purity of the stainless steel ingot, and further improving the mechanical properties and heat resistance of the forging.

[0089] The present invention also provides a 21Cr12MoV stainless steel ingot prepared by the method described in the above technical solution.

[0090] In the present invention, the O content in the 21Cr12MoV stainless steel ingot is ≤15ppm; the A-type inclusion rating in the 21Cr12MoV stainless steel ingot is ≤1.0, the B-type inclusion rating is ≤1.0, the C-type inclusion rating is ≤1.5, and the D-type inclusion rating is ≤1.5.

[0091] In the present invention, the chemical composition of the 21Cr12MoV stainless steel ingot preferably includes, by mass percentage, C 0.18-0.23%, Mn 0.30-0.80%, Si≤0.50%, Cr 11.00-12.50%, Mo0.80-1.20%, Ni0.30-0.80%, V 0.25-0.35%, Cu≤0.30%, P≤0.030%, S≤0.020%, O≤15ppm and the balance Fe.

[0092] The 21Cr12MoV stainless steel ingot provided by the present invention is a low-O stainless steel ingot, which is a martensitic heat-resistant stainless steel with corrosion resistance, high strength, high hardness and good welding performance. It is suitable for major engineering structure fields such as aerospace, ship power, medical equipment and 300-350MW compressed air energy storage power stations.

[0093] The present invention also provides a 21Cr12MoV stainless steel forging, which is prepared from the 21Cr12MoV stainless steel ingot described in the above technical solution.

[0094] The present invention also provides a method for preparing the 21Cr12MoV stainless steel forgings described in the above technical solution, comprising: forging, rough machining and heat treating the 21Cr12MoV stainless steel ingot in sequence to obtain the 21Cr12MoV stainless steel forgings.

[0095] In the present invention, the initial forging temperature of the forging is preferably 1000-1200°C; the final forging temperature of the forging is preferably ≥850°C; the forging ratio of the forging is preferably ≥3.0; the extension ratio of the forging is preferably ≥2.0; and the total ratio of the forging is preferably ≥4.0.

[0096] As an embodiment, the initial forging temperature of the forging may be 1050-1100°C; the final forging temperature of the forging may be 900-1000°C; the forging ratio of the forging may be 3.5-4.5; the extension ratio of the forging may be 2.5-3.5; and the total forging ratio may be 4.5-5.5.

[0097] The present invention has no special limitation on the rough machining operation, and operations well known to those skilled in the art may be adopted.

[0098] In the present invention, the heat treatment preferably includes annealing and solution treatment performed sequentially.

[0099] In the present invention, the annealing holding temperature is preferably 860-950°C; the annealing holding time is preferably 12-20h, further 15-20h, and more preferably 18h. As an embodiment, the annealing holding temperature can be 880-920°C, and can also be 900°C. The present invention adopts annealing to remove the residual stress of forging and improve the mechanical properties of the forging.

[0100] In the present invention, the holding temperature of the solution treatment is preferably 1020-1070° C.; the holding time of the solution treatment is preferably 1-18 h; and the cooling method of the solution treatment is preferably water cooling, oil cooling or air cooling.

[0101] The present invention has no special limitation on the operation of water cooling, oil cooling or air cooling, and operations well known to those skilled in the art may be adopted.

[0102] The present invention also provides the application of the 21Cr12MoV stainless steel forgings described in the above technical scheme or the 21Cr12MoV stainless steel forgings prepared by the preparation method described in the above technical scheme in aerospace, ship power, medical equipment and 300-350MW compressed air energy storage power stations.

[0103] The present invention has no special limitation on the application of the 21Cr12MoV stainless steel forgings in aerospace, ship power, medical equipment and 300-350MW compressed air energy storage power stations, and the application operations familiar to those skilled in the art can be adopted.

[0104] The invention adopts EAF (electric arc furnace) smelting + VD refining + argon protection pouring + electroslag remelting during smelting, which can reduce non-metallic inclusions to the maximum extent, improve the purity of molten steel, enhance the quality of steel, and make the high-temperature performance of forgings stable and significantly improved; wherein, compared with the original 2Cr12MoV, the chemical composition is: the O element is optimized to O≤15ppm; the non-metallic inclusions are optimized from A, B, C, D≤2 levels to A≤1.0, B≤1.0, C≤1.5, D≤1.5, ensuring that the machine base made of 2Cr12MoV stainless steel will no longer cause stress cracks and stress corrosion caused by B-type inclusions in high-stress and high-fatigue operation, thereby reducing durability and reliability.

[0105] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part 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 creative work are within the scope of protection of the present invention.

[0106] Example 1

[0107] The preparation method of 21Cr12MoV stainless steel ingot is:

[0108] (1) 20 steel with S≤0.020wt% and P≤0.020wt% is subjected to electric arc furnace smelting to obtain molten steel; the electric arc furnace smelting consists of a melting period, an oxidation period and a reduction period carried out in sequence;

[0109] Among them, slag-forming agent FeO is added during the melting period, and the mass of the slag-forming agent is 2% of the mass of the scrap steel; the temperature of the melting period is 1550°C; the melting period is carried out under oxygen blowing conditions; the pressure of the oxygen blowing is 0.28MPa; after the melting period is completed, the basicity of the melt is 2.3, and P is removed to less than 0.012wt%;

[0110] The temperature of the oxidation period is 1660°C; the oxidation period is carried out under oxygen blowing conditions; the oxygen blowing pressure is 1.5MPa; the melting time of the melt during the oxidation period is 6min; the decarburization amount of the melt during the oxidation period is ≥40%, the P content is ≤0.010wt%, and the S content is ≤0.010wt%; after the oxidation period, the melt is deslagging at 1700°C;

[0111] During the reduction period, when the temperature of the melt is greater than 1650°C, thin slag is added, and then 6kg / t lime and 6kg / t fluorite are added to adjust the C content to less than 1.0wt%, and then 8kg / t ferrosilicon manganese, 8kg / t ferromanganese and 8kg / t ferrochrome are added, and then a reducing agent is added. After the white slag is made, the white slag is kept for 20 minutes, and then 9kg / t composite deoxidizer is added when the melt temperature is 1600°C. After 13 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt is transferred to a ladle, and then the ladle is skimmed until the residue amount is ≤1.5kg / t, and then the temperature is lowered to 1680°C; the reducing agent is a mixture of ferrosilicon powder, calcium carbide and carbon powder: the amount of ferrosilicon powder is 7kg / t; the amount of calcium carbide is 3kg / t; the amount of carbon powder is 2kg / t; the composite deoxidizer is composed of the following components in mass percentage: C 0.055%, Mn 20%; Si 13%, Al 1.0%, Ca 0.8% and Fe 65.145%;

[0112] (2) subjecting the molten steel obtained in step (1) to VD refining in a VD / VOD vacuum refining furnace under argon blowing conditions to obtain refined molten steel; wherein the argon blowing time is 8 minutes; the argon flow rate is 5m 3 / h; the vacuum degree of VD refining is 0.8mbar; the time of VD refining is 25min; the temperature of VD refining is 1650℃;

[0113] (3) First, add 1.5kg / t dry CaSi powder to the bottom of the tundish, then blow argon at the bottom of the tundish to exhaust the air in the tundish, then pour the refined molten steel at 1620°C into the tundish for deoxidation for 10 minutes under argon protection, and then calm for 7 minutes to obtain deoxidized molten steel; wherein the mass ratio of Ca to Si in the CaSi powder is 1:3, and the particle size is 3-5 mm;

[0114] (4) Before pouring, the pouring system is checked to ensure that it is dry and free of moisture, and the runner and steel mold are clean and free of pollution. Then, the deoxidized molten steel obtained in step (3) is subjected to protective pouring, and then cooled and demolded in sequence to obtain a steel ingot. The protective pouring temperature is 1560° C., the protective pouring flow rate is 6 mm / s, the protective pouring atmosphere is argon, and the argon flow rate is 5 L / min. The cooling time is calculated according to formula I:

[0115] T=35R 2(M)×1.2Formula I;

[0116] Where, T is the cooling time, in h; R is the mold radius (ingot mold specification size), in m;

[0117] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting, cooling and annealing treatment in sequence to obtain a 21Cr12MoV stainless steel ingot; wherein the electroslag remelting adopts CaF 2 -Al 2 O 3 -MgO ternary slag system, CaF 2 、Al 2 O 3 The mass ratio of Si to Mn is 1:2:3, the mass of the ternary slag system is 5% of the mass of the steel ingot, a 3 t crystallizer, a crystallizer diameter of 610 mm, a consumable electrode is used for direct slagging, the consumable electrode diameter is 450 mm, the voltage is 65 V, the current is 13 kA, 3 kg / t of Si-Mn alloy powder is added during the slagging period, the mass ratio of Si to Mn in the Si-Mn alloy powder is 1:10, the melting rate of the whole electroslag remelting process is uniform, and the electroslag remelting time is 7.0 h; the holding temperature of the annealing treatment is 830°C; the holding time of the annealing treatment is 10 h; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300°C.

[0118] Example 2

[0119] The preparation method of 21Cr12MoV stainless steel ingot is:

[0120] (1) 20 steel with S≤0.020wt% and P≤0.020wt% is subjected to electric arc furnace smelting to obtain molten steel; the electric arc furnace smelting consists of a melting period, an oxidation period and a reduction period carried out in sequence;

[0121] Among them, slag-forming agent FeO is added during the melting period, and the mass of the slag-forming agent is 2% of the mass of the scrap steel; the temperature of the melting period is 1550°C; the melting period is carried out under oxygen blowing conditions; the pressure of the oxygen blowing is 0.28MPa; after the melting period is completed, the basicity of the melt is 2.4, and P is removed to less than 0.012wt%;

[0122] The temperature of the oxidation period is 1660°C; the oxidation period is carried out under oxygen blowing conditions; the oxygen blowing pressure is 1.5MPa; the melting time of the melt during the oxidation period is 7min; the decarburization amount of the melt during the oxidation period is ≥40%, the P content is ≤0.010wt%, and the S content is ≤0.010wt%; after the oxidation period, the melt is deslagging at 1700°C;

[0123] During the reduction period, when the temperature of the melt is greater than 1650°C, 6kg / t of lime and 6kg / t of fluorite are added to adjust the C content to less than 1.0wt%, then 8kg / t of ferrosilicon manganese, 8kg / t of ferromanganese and 8kg / t of ferrochrome are added, and then a reducing agent is added. After white slag is produced, the white slag is kept for 20 minutes, and then 9.5kg / t of a composite deoxidizer is added when the melt temperature is 1590°C. After 13 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt is transferred to a ladle, and then the ladle is skimmed until the residue amount is ≤1.5kg / t, and then the temperature is lowered to 1650°C; the reducing agent is a mixture of ferrosilicon powder, calcium carbide and carbon powder; the amount of ferrosilicon powder is 7kg / t; the amount of calcium carbide is 3kg / t; the amount of carbon powder is 1.8kg / t; the composite deoxidizer is composed of the following components in mass percentage: C 0.06%, Mn 25%, Si 13%, Al 1.1%, Ca 0.9% and Fe 59.94%;

[0124] (2) subjecting the molten steel obtained in step (1) to VD refining in a VD / VOD vacuum refining furnace under argon blowing conditions to obtain refined molten steel; wherein the argon blowing time is 9 minutes; the argon flow rate is 5m 3 / h; the vacuum degree of VD refining is 0.95mbar; the time of VD refining is 30min; the temperature of VD refining is 1650℃;

[0125] (3) First, add 1.38kg / t dry CaSi powder to the bottom of the tundish, then blow argon at the bottom of the tundish to exhaust the air in the tundish, then pour the refined molten steel at 1615°C into the tundish for deoxidation under argon protection for 10 minutes, followed by sedation for 7 minutes to obtain deoxidized molten steel; wherein the mass ratio of Ca to Si in the CaSi powder is 1:3, and the particle size is 3-5 mm;

[0126] (4) Before pouring, the pouring system is checked to ensure that it is dry and free of moisture, and the runner and steel mold are clean and free of pollution. Then, the deoxidized molten steel obtained in step (3) is subjected to protective pouring, and then cooled and demolded in sequence to obtain a steel ingot. The protective pouring temperature is 1560° C., the protective pouring flow rate is 6 mm / s, the protective pouring atmosphere is argon, and the argon flow rate is 5 L / min. The cooling time is calculated according to formula I:

[0127] T=35R 2 (M)×1.2Formula I;

[0128] Where, T is the cooling time, in h; R is the mold radius, in m;

[0129] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting, cooling and annealing treatment in sequence to obtain a 21Cr12MoV stainless steel ingot; wherein the electroslag remelting adopts CaF 2 -Al 2 O 3 -MgO ternary slag system, CaF 2 、Al 2 O 3 The mass ratio of Si to Mn is 1:2:3, the mass of the ternary slag system is 5% of the mass of the steel ingot, a 3 t crystallizer, a crystallizer diameter of 610 mm, a consumable electrode is used to directly slag, the diameter of the consumable electrode is 450 mm, the voltage is 65 V, the current is 13 kA, 2.5 kg / t of Si-Mn alloy powder is added during the slag-melting period, the mass ratio of Si to Mn in the Si-Mn alloy powder is 1:10, the melting rate of the whole electroslag remelting process is uniform, and the electroslag remelting time is 7.0 h; the holding temperature of the annealing treatment is 830°C; the holding time of the annealing treatment is 10 h; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤500°C.

[0130] Example 3

[0131] The preparation method of 21Cr12MoV stainless steel ingot is:

[0132] (1) 20 steel with S≤0.020wt% and P≤0.020wt% is subjected to electric arc furnace smelting to obtain molten steel; the electric arc furnace smelting consists of a melting period, an oxidation period and a reduction period carried out in sequence;

[0133] Among them, slag-forming agent FeO is added during the melting period, and the mass of the slag-forming agent is 2% of the mass of the scrap steel; the temperature of the melting period is 1550°C; the melting period is carried out under oxygen blowing conditions; the pressure of the oxygen blowing is 0.28MPa; after the melting period is completed, the basicity of the melt is 2.4, and P is removed to less than 0.012wt%;

[0134] The temperature of the oxidation period is 1660°C; the oxidation period is carried out under oxygen blowing conditions; the oxygen blowing pressure is 1.5MPa; the melting time of the melt during the oxidation period is 7min; the decarburization amount of the melt during the oxidation period is ≥40%, the P content is ≤0.010wt%, and the S content is ≤0.010wt%; after the oxidation period, the melt is deslagging at 1700°C;

[0135] During the reduction period, when the temperature of the melt is greater than 1650°C, thin slag is added, and then 7kg / t lime and 7kg / t fluorite are added to adjust the C content to less than 1.0wt%, and then 7kg / t ferrosilicon manganese, 7kg / t ferromanganese and 7kg / t ferrochrome are added, and then a reducing agent is added to make white slag, and the white slag is kept for 25 minutes. Then, when the melt temperature is 1600°C, 10kg / t composite deoxidizer is added. After 15 minutes, when the melt composition meets the required requirements and the melt temperature is 1700°C, the melt is transferred to a ladle, and then the ladle is skimmed until the residue amount is ≤1.5kg / t, and then the temperature is lowered to 1680°C; the reducing agent is a mixture of ferrosilicon powder, calcium carbide and carbon powder: the amount of ferrosilicon powder is 7.5kg / t; the amount of calcium carbide is 3kg / t; the amount of carbon powder is 2kg / t; the composite deoxidizer is composed of the following components in mass percentage: C 0.06%, Mn 28%, Si 15%, Al 1.2%, Ca 1% and Fe 54.75%;

[0136] (2) subjecting the molten steel obtained in step (1) to VD refining in a VD / VOD vacuum refining furnace under argon blowing conditions to obtain refined molten steel; wherein the argon blowing time is 10 min; the argon flow rate is 5 m 3 / h; the vacuum degree of VD refining is 1.0 mbar; the time of VD refining is 28 min; the temperature of VD refining is 1650°C;

[0137] (3) First, add 1.5kg / t dry CaSi powder to the bottom of the tundish, then blow argon at the bottom of the tundish to exhaust the air in the tundish, then pour the refined molten steel at 1610°C into the tundish for deoxidation for 10 minutes under argon protection, and then calm for 7 minutes to obtain deoxidized molten steel; wherein the mass ratio of Ca to Si in the CaSi powder is 1:3, and the particle size is 3-5 mm;

[0138] (4) Before pouring, the pouring system is checked to ensure that it is dry and free of moisture, and the runner and steel mold are clean and free of pollution. Then, the deoxidized molten steel obtained in step (3) is subjected to protective pouring, and then cooled and demolded in sequence to obtain a steel ingot. The protective pouring temperature is 1560° C., the protective pouring flow rate is 6 mm / s, the protective pouring atmosphere is argon, and the argon flow rate is 5 L / min. The cooling time is calculated according to formula I:

[0139] T=35R 2 (M)×1.2Formula I;

[0140] Where, T is the cooling time, in h; R is the mold radius (ingot mold specification size), in m;

[0141] (5) The steel ingot obtained in step (4) is subjected to electroslag remelting, cooling and annealing treatment in sequence to obtain a 21Cr12MoV stainless steel ingot; wherein the electroslag remelting adopts CaF 2 -Al 2 O 3 -MgO ternary slag system, CaF 2 、Al 2 O 3 The mass ratio of Si to Mn is 1:2:3, the mass of the ternary slag system is 5% of the mass of the steel ingot, a 3 t crystallizer, a crystallizer diameter of 610 mm, a consumable electrode is used to directly slag, the consumable electrode diameter is 450 mm, the voltage is 66 V, the current is 13 kA, 3 kg / t of Si-Mn alloy powder is added during the slag-melting period, the mass ratio of Si to Mn in the Si-Mn alloy powder is 1:10, the melting rate of the whole electroslag remelting process is uniform, and the electroslag remelting time is 7.0 h; the holding temperature of the annealing treatment is 830°C; the holding time of the annealing treatment is 10 h; the cooling method of the annealing treatment is furnace cooling and air cooling in sequence; the terminal temperature of the furnace cooling is ≤300°C.

[0142] The chemical composition of the 21Cr12MoV stainless steel ingots prepared in Examples 1 to 3 is shown in Table 1; wherein the chemical composition analysis method of the 21Cr12MoV stainless steel ingots in Table 1 is GB / T223.

[0143] Table 1 Chemical composition of 21Cr12MoV stainless steel ingots prepared in Examples 1 to 3

[0144]

[0145] It can be seen from Table 1 that, compared with the original 21Cr12MoV, the S content of the 21Cr12MoV stainless steel ingot prepared by the preparation method provided by the present invention is optimized from ≤0.020wt% to ≤0.005; and the P content is optimized from ≤0.030wt% to ≤0.015wt%.

[0146] The non-metallic inclusion content of the 21Cr12MoV stainless steel ingots prepared in Examples 1 to 3 was measured using the standard rating chart microscopic inspection method according to GB / T10561. The results are shown in Table 2.

[0147] Table 2 Non-metallic inclusion data of 21Cr12MoV stainless steel ingots prepared in Examples 1 to 3

[0148]

[0149] It can be seen from Table 2 that the preparation method provided by the present invention can reduce the content of inclusions and improve the grade of inclusions.

[0150] Example 4

[0151] A preparation method of a 21Cr12MoV stainless steel forging is as follows: the 21Cr12MoV stainless steel ingot prepared in Example 1 is forged, rough-machined, annealed and solution treated in sequence to obtain a 21Cr12MoV stainless steel forging; wherein the initial forging temperature of the forging is 1180°C, the final forging temperature is 880°C, the forging ratio is 3.2, the elongation ratio is 2.3, and the total ratio is 4.3; the holding temperature of the annealing is 930°C, and the holding time is 18 hours; the holding temperature of the solution treatment is 1050°C, and the holding time is 18 hours, and the cooling method is oil cooling.

[0152] Example 5

[0153] A preparation method of a 21Cr12MoV stainless steel forging is as follows: the 21Cr12MoV stainless steel ingot prepared in Example 2 is forged, rough-machined, annealed and solution treated in sequence to obtain a 21Cr12MoV stainless steel forging; wherein the initial forging temperature of the forging is 1180°C, the final forging temperature is 880°C, the forging ratio is 3.3, the elongation ratio is 2.3, and the total ratio is 4.4; the holding temperature of the annealing is 930°C, and the holding time is 18h; the holding temperature of the solution treatment is 1050°C, and the holding time is 18h, and the cooling method is water cooling.

[0154] Example 6

[0155] A preparation method of a 21Cr12MoV stainless steel forging is as follows: the 21Cr12MoV stainless steel ingot prepared in Example 3 is forged, rough-machined, annealed and solution treated in sequence to obtain a 21Cr12MoV stainless steel forging; wherein the initial forging temperature of the forging is 1180°C, the final forging temperature is 860°C, the forging ratio is 3.2, the elongation ratio is 2.2, and the total ratio is 4.2; the holding temperature of the annealing is 940°C, and the holding time is 18h; the holding temperature of the solution treatment is 1050°C, and the holding time is 18h, and the cooling method is air cooling.

[0156] The 21Cr12MoV stainless steel forgings prepared in Examples 4 to 6 were subjected to mechanical property and high temperature creep tests. The results are shown in Tables 3 and 4. The room temperature tensile test used a Φ5 mm standard specimen, a WE-300 tensile testing machine, and a test temperature of 25 ° C to measure the tensile strength Rm, yield strength R P0.2 , elongation after fracture A and cross-sectional shrinkage rate Z; the impact performance adopts the Charpy pendulum impact test method for metal materials in accordance with GB / T 229-2020; the high-temperature mechanical properties endurance strength test refers to GB / T8732-2014 standard, the grading method of strength grades QT1 and QT2 refers to EN10269-2006, and the high-temperature performance data is cited from EN10269-2006 and DIN17240-1976.

[0157] Table 3 Room temperature mechanical properties of 21Cr12MoV stainless steel forgings prepared in Examples 4 to 6

[0158]

[0159]

[0160] It can be seen from Table 3 that the 21Cr12MoV stainless steel forgings prepared by the present invention have excellent room temperature mechanical properties.

[0161] Table 4 High temperature mechanical properties of 21Cr12MoV stainless steel forgings prepared in Examples 4 to 6

[0162]

[0163]

[0164] It can be seen from Table 4 that the 21Cr12MoV stainless steel forgings prepared by the present invention have excellent high-temperature mechanical properties.

[0165] It can be seen from the above examples that the 21Cr12MoV stainless steel ingot prepared by the preparation method provided by the present invention has low inclusion content, and the 21Cr12MoV stainless steel forging has excellent mechanical properties and heat resistance.

[0166] 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for improving the purity of stainless steel, comprising the following steps: (1) smelting the raw materials to obtain molten steel; (2) subjecting the molten steel obtained in step (1) to VD refining under argon blowing conditions to obtain refined molten steel; (3) mixing the refined molten steel obtained in step (2) with a deoxidizer, and deoxidizing the molten steel under argon protection to obtain deoxidized molten steel; (4) performing protective pouring on the deoxidized molten steel obtained in step (3) to obtain a steel ingot; (5) The steel ingot obtained in step (4) is subjected to electroslag remelting to obtain a stainless steel ingot.

2. The method according to claim 1, characterized in that The time of blowing argon in step (2) is 6 to 10 minutes.

3. The method according to claim 1, characterized in that The amount of the deoxidizer used in step (3) is 1-1.5 kg / t.

4. The method according to claim 1, characterized in that In the step (5), the voltage of the electroslag remelting is 60-66V, the current of the electroslag remelting is 12-14kA, and the time of the electroslag remelting is 6.5-7.0h.

5. A 21Cr12MoV stainless steel ingot prepared by the method according to any one of claims 1 to 4, wherein the O content in the 21Cr12MoV stainless steel ingot is ≤15ppm; the A-type inclusion rating in the 21Cr12MoV stainless steel ingot is ≤1.0, the B-type inclusion rating is ≤1.0, the C-type inclusion rating is ≤1.5, and the D-type inclusion rating is ≤1.

5.

6. A 21Cr12MoV stainless steel forging, prepared from the 21Cr12MoV stainless steel ingot according to claim 5.

7. The method for preparing the 21Cr12MoV stainless steel forging according to claim 6, comprising: The 21Cr12MoV stainless steel ingot is forged, rough-machined and heat-treated in sequence to obtain a 21Cr12MoV stainless steel forging.

8. The preparation method according to claim 7, characterized in that: The initial forging temperature of the forging is 1000-1200° C., the final forging temperature of the forging is ≥850° C., the forging ratio of the forging is ≥3.0, the extension ratio of the forging is ≥2.0, and the total ratio of the forging is ≥4.

0.

9. The preparation method according to claim 7, characterized in that: The heat treatment includes annealing and solution treatment performed sequentially.

10. Application of the 21Cr12MoV stainless steel forging according to claim 6 or the 21Cr12MoV stainless steel forging prepared by the preparation method according to any one of claims 7 to 9 in aerospace, ship power, medical equipment and 300-350MW compressed air energy storage power station.

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