A precipitation hardening stainless steel and a method for producing the same

Abstract

The present application relates to a kind of precipitation hardening type stainless steel and its preparation method, the preparation method includes by the selection of raw material and smelting technology to prepare precipitation hardening type martensitic stainless steel, using vacuum induction furnace, electroslag remelting and vacuum consumable remelting combined three smelting processes, improve the purity of steel, reduce the content of impurity element in steel.The chemical composition of the stainless steel includes: C≤0.05%;Mn 1.50~2.50%;Si1.00~1.30%;S≤0.001%;P≤0.003%;Ni 6.00~6.50%;Cr 14.00~15.50%;Mo 0.30~0.50%;Nb 0.30~0.50%;Al≤0.015%;Ti≤0.015%;H≤0.00005%;O≤0.0008%;N 0.040~0.060%;The balance is Fe and unavoidable impurities.The precipitation hardening type stainless steel of the present application makes the precipitation of martensitic structure more effective by optimizing heat treatment process, significantly improves the strength and plasticity of material, and has good mechanical properties and processing performance, suitable for aerospace, ocean engineering, chemical and medical instrument field, with wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal processing, in particular to a precipitation hardening stainless steel and a preparation method thereof. BACKGROUND

[0002] The precipitation hardening stainless steel is a kind of stainless steel that can improve the strength and hardness by means of heat treatment to make alloying elements precipitate out of the matrix. The precipitation hardening stainless steel has the following characteristics: high strength, after precipitation hardening treatment, its strength can be comparable to high-strength alloy steel; good corrosion resistance, inheriting the corrosion resistance of stainless steel, it can be used in various corrosive environments; good weldability, it can be welded under certain conditions, but attention should be paid to the welding process; processing performance, it has certain processing performance, but it may be slightly more complex than ordinary stainless steel. The application fields of the precipitation hardening stainless steel are as follows: aerospace field, used for manufacturing high-strength and corrosion-resistant parts, such as aircraft structural parts and engine parts; marine engineering, suitable for corrosion in marine environment, used for key parts of offshore platforms and ships; chemical industry, excellent in corrosive medium, can be used for chemical equipment and pipelines; medical devices, meeting the requirements of biocompatibility and corrosion resistance, used for manufacturing medical devices. The precipitation hardening stainless steel is classified according to the structure:

[0003] Martensitic precipitation hardening stainless steel: taking martensite as the matrix, improving the strength by precipitation hardening; semi-austenitic precipitation hardening stainless steel, having certain austenitic and martensitic structure, the performance can be adjusted by heat treatment; austenitic precipitation hardening stainless steel, precipitation hardening treatment on the austenitic matrix. The precipitation hardening martensitic stainless steel is prepared by adding C, Ni, Cr, Si, Nb, Cu, Mo and other chemical elements in the steel, reasonably matching the chemical elements, forming a large amount of martensitic structure after solid solution and cooling, and using aging treatment to make the precipitated phase precipitate, playing a pinning effect in the martensitic dislocation structure, greatly improving the strength, plasticity and toughness.

[0004] According to the above design criteria and organizational requirements, various ultra-high strength steels have been developed in the prior art, as shown in Table 1. Table 1 shows a precipitation hardening martensitic stainless steel 17-4PH (GB / T1220), and the mass percentage of the chemical elements is shown in Table 1:

[0005] Table 1 Chemical composition (wt%)

[0006]

[0007] The steel grade shown in Table 1 is 17-4PH, which is used to manufacture aircraft engine parts, landing gears, fasteners and the like in the field of aviation and aerospace; is used to manufacture valve, pump shaft, pressure vessel and the like in the field of petroleum and chemical industry, and has good reliability in harsh corrosion environment; is used to manufacture surgical instruments, implants and the like in the field of medical instruments, and its biocompatibility and corrosion resistance make it one of the ideal materials in the field of medical instruments; is used to manufacture various high-strength mechanical parts such as gears, shafts, couplings and the like in the field of mechanical manufacturing. The manufacturing process is: electric furnace + secondary refining pouring into ingot → fast forging machine into material → annealing → turning.

[0008] The steel has the following problems:

[0009] (1) Poor hot plasticity, the chemical composition determines the organization in the steel, and due to the high content of Cr and the small amount of Ni, the ferrite content is high, which is easy to produce crack defects during hot working deformation.

[0010] (2) The steel is smelted by electric furnace + secondary refining process, and the gas elements oxygen, nitrogen and hydrogen are high, which causes the finished forging to have more oxides, and due to the high hydrogen content, the risk of white spots increases, which leads to the decrease of strength and toughness of the material, and even the scrap.

[0011] (3) Due to the Nb and C elements in the steel, the steel ingot produced by electric furnace + secondary refining is easy to form CNNb type inclusions, which reduces the plasticity and yield of the steel.

[0012] In summary, the existing precipitation hardening stainless steel has high strength and corrosion resistance in many application fields, but still has significant defects. First, due to the high chromium and low nickel chemical composition configuration, the hot plasticity is poor, which is easy to produce cracks in the processing process, which limits the processing efficiency and quality of the finished product. Secondly, the smelting process of traditional electric furnace and secondary refining makes the gas element content high, and the risk of oxide and white spot increases, which seriously affects the mechanical properties of the material. Finally, the formation of inclusions further reduces the plasticity and yield strength of the steel. SUMMARY

[0013] The technical problem to be solved by the present application is to provide a preparation method of precipitation hardening stainless steel, to solve the problems of high impurity content, strong crack sensitivity and difficult effective control of gas elements in the conventional preparation method in the prior art. The existing preparation method limits the mechanical properties of the precipitation hardening stainless steel, especially in high stress and corrosion environment, the material shows poor plasticity, crack resistance and corrosion resistance.

[0014] In order to solve the above technical problems, the present application provides a preparation method of precipitation hardening stainless steel, comprising the following steps:

[0015] S1: Vacuum Induction Furnace Smelting: High-purity raw materials are smelted in a vacuum induction furnace. The raw materials are melted and degassed, and the gas content and the mass percentage of chemical elements are controlled as follows: C≤0.05%, Mn: 1.50~2.50%, Si: 1.00~1.30%, S≤0.001%, P≤0.003%, Ni: 6.00~6.50%, Cr: 14.00~15.50%, Mo: 0.30~0.50%, Nb: 0.30~0.50%, Al≤0.015%, Ti≤0.015%, H≤0.00005%, O≤0.0008%, N: 0.040~0.060%, with the balance being Fe and other unavoidable impurities, to produce electrode rods.

[0016] S2: Electroslag remelting: The electrode rod obtained in step S1 is subjected to electroslag remelting using a slag material composed of CaF2, Al2O3, and MgO. The melting rate is adjusted to reduce chemical element segregation and improve the purity of the steel to obtain an electroslag ingot.

[0017] S3: Forging vacuum consumable electrode: The electroslag ingot obtained in step S2 is heat-treated and then forged to obtain a vacuum consumable electrode.

[0018] S4: Vacuum self-consumable remelting: The vacuum self-consumable electrode obtained in step S3 is subjected to vacuum self-consumable remelting, and further degassed under the condition of vacuum degree ≤0.5Pa to obtain steel ingot;

[0019] S5: Forging process: The steel ingot obtained in step S4 is forged: before forging, it is gradually heated to 800°C and held for 1 to 4 hours, then heated to 1100 to 1180°C and held for 1 to 7 hours, and forging is carried out in the temperature range of 950 to 1100°C. After forging, it is cooled slowly. Within this temperature range, the steel can be formed in the optimal thermoplasticity zone, thereby avoiding forging cracks.

[0020] S6: Heat treatment: The forged steel is subjected to heat treatment, which includes solution treatment and aging treatment.

[0021] Compared with existing technologies, the preparation method of precipitation-hardening stainless steel disclosed in this application has the following advantages: The preparation method of this application replaces the difficulty in controlling impurity elements in existing technologies with precise control through a vacuum induction furnace smelting process. Induction melting and multiple degassing treatments (such as argon protection) are performed under vacuum conditions, effectively reducing the content of gaseous impurities such as oxygen, nitrogen, and hydrogen, optimizing the chemical composition, and eliminating the problems of numerous inclusions, hydrogen embrittlement, and oxidation tendency in traditional processes. Through smelting and multiple refining under vacuum conditions, impurity control is significantly improved, the strength and plasticity of the steel are significantly enhanced, and the risks of hydrogen embrittlement and white spots are significantly reduced. Furthermore, by employing a triple process combining vacuum induction furnace, electroslag remelting, and vacuum arc remelting, combined with precise temperature and vacuum control, the purity of the steel is further improved during degassing, eliminating harmful impurities and resulting in a significant improvement in the final material performance. Since Mn volatilizes during vacuum arc remelting, the amount of Mn added generally exceeds the standard value. Regarding nitrogen addition, nitrogen is also denitrified during the reaction, thus requiring excessive addition as nitrogen is also added.

[0022] The preparation method described in this application significantly reduces the content of gaseous impurities such as oxygen and hydrogen through multi-stage vacuum degassing and the use of high-purity raw materials, thereby reducing the crack sensitivity of precipitation-hardening stainless steel during processing and application. By reducing the S and P content in the refined steel, the purity of the raw materials is greatly improved. This invention employs a smelting process of vacuum induction + electroslag + vacuum consumable remelting, which reduces the gas content while also lowering the residual S content, significantly reducing inclusions, and further purifying the molten steel through the slag system. This method further enhances the purity of the steel through multiple remelting processes, resulting in steel with higher strength and toughness, and better overall performance in high-stress and corrosive environments. The final technical effect is a significant improvement in the plasticity, crack resistance, and corrosion resistance of the steel, thereby extending its service life and expanding its application areas.

[0023] In one possible implementation, in step S1, the conditions for smelting in the vacuum induction furnace are as follows: the temperature after the raw material is fully melted is 1520-1600℃, the temperature during the refining period of the raw material is 1500-1570℃, the refining time is ≥60 minutes, and the vacuum degree is ≤5Pa; the temperature for casting the electrode rod is 1540-1580℃.

[0024] Compared with existing technologies, the above-mentioned possible implementation methods control the temperature during the refining period. If the temperature is too low, the refining effect will not be achieved, and if the temperature is too high, Al and Ti in the crucible will be reduced into the molten steel. Therefore, the temperature is generally controlled at 1500-1580℃, and the temperature range is further subdivided to ensure the optimal retention and reaction of chemical elements during refining. In particular, refining in the range of 1520-1570℃ can minimize oxides and inclusions in the molten steel, while effectively improving the purity and uniformity of the steel, and ensuring the improvement of the material's mechanical properties and corrosion resistance.

[0025] In one possible implementation, step S1 further includes an argon injection step during the refining period, comprising: when the gas content in the furnace reaches O≤15ppm, N≤15ppm, and H≤1ppm, argon gas at 8000Pa is introduced into the furnace and CrN is added, and after stirring for 5-10 minutes, a Mn source is added.

[0026] Compared with existing technologies, the above-mentioned possible implementation methods can refine steel under vacuum conditions by injecting argon gas multiple times, eliminating more gaseous impurities. Combined with the reasonable addition of CrN and Mn sources, it can effectively reduce impurity segregation, enhance the uniformity of steel, and effectively avoid the formation of gas inclusions, resulting in steel with higher toughness and stronger crack resistance, making it suitable for use under high temperature and high stress conditions.

[0027] In one possible implementation, in step S2, the current for electroslag remelting is 3KA to 19KA, the power is 60kW to 800kW, the melting rate is 3.5 to 10.5kg / min, and after obtaining the electroslag ingot, the slow cooling time is not less than 24 hours.

[0028] Compared with existing technologies, the above-mentioned possible implementation methods can optimize the current, power and melting speed of electroslag remelting, so that the chemical composition of the material is uniform during the melting process, reducing element segregation, and significantly improving the purity and mechanical properties of the steel. This results in a significant reduction in impurity content, improved steel purity and more stable material properties.

[0029] In one possible implementation, in step S2, the mass ratio of CaF2, Al2O3, and MgO in the slag is 65:30:5.

[0030] Compared to existing technologies, the above-described possible implementation methods can further reduce impurities and inclusions during the electroslag remelting process by adjusting the slag ratio, significantly improving the purity of the electroslag ingot and enhancing the material's strength and toughness. The ultimate technical effect is the production of high-purity steel with excellent crack resistance, suitable for more demanding environmental applications.

[0031] In one possible implementation, step S3 includes the following steps:

[0032] Initial heating phase: The initial temperature is controlled below 600℃, and then the temperature is increased to 800℃ at a steady rate. The entire heating process lasts for more than 2 hours.

[0033] 800℃ heat preservation stage: When the temperature reaches 800℃, maintain this temperature for at least 1 hour.

[0034] Further heating stage: After holding at 800℃, continue heating until the temperature reaches between 1140℃ and 1210℃, with a heating time of no less than 2 hours to ensure gradual heating;

[0035] High-temperature insulation stage: Maintain the temperature for at least 2 hours within the range of 1140℃ to 1210℃;

[0036] The forging process includes the following steps:

[0037] Reheating stage: The electroslag ingot is heated to 1120-1160℃; within this temperature range, the steel can be formed in the optimal thermoplastic zone, and the grain size can be effectively controlled.

[0038] Forging stage: Forging is carried out within a temperature range of ≥1000℃ for the initial forging temperature and ≥850℃ for the final forging temperature;

[0039] Slow cooling stage: After forging, slow cooling treatment is carried out. The slow cooling method is cover cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0040] Finishing: After slow cooling, the forging is finished by machining to ensure that it meets the electrode size requirements matched by the vacuum consumable crystallizer.

[0041] Compared with existing technologies, the above-described possible implementation methods can achieve homogenization of the steel's microstructure during forging by gradually heating, uniformly raising the temperature, and precisely controlling the forging temperature. This significantly improves the material's comprehensive mechanical properties, ensuring the final product has excellent plasticity and crack resistance. The material's microstructure is more refined, its mechanical properties are superior, it can adapt to more demanding working conditions, reduces internal stress, and significantly improves its toughness and crack resistance, ultimately resulting in a more stable and high-strength finished material. The reheating temperature range allows the material to maintain good plasticity during forging and reduces the risk of cracks and other defects during processing. At the same time, the chemical composition of the material is homogenized during reheating, further improving the steel's machinability.

[0042] In one possible implementation, in step S4, the melting rate of the vacuum consumable remelting is 2.5 to 6.5 kg / min, and helium cooling technology is used to accelerate the cooling of the molten steel ingot.

[0043] Compared with existing technologies, the above-mentioned possible implementation methods can effectively prevent material component segregation and gas residue by controlling the melting rate and introducing helium cooling technology, ultimately improving the hardness and durability of the material.

[0044] In one possible implementation, in step S5, the slow cooling after forging is performed by cover cooling, sand cooling, pit cooling, or furnace cooling, and the slow cooling time is not less than 24 hours.

[0045] Compared with existing technologies, the above-described possible implementation methods can reduce the tendency of thermal stress and structural stress caused by phase transformation during hot working and cooling through a slow cooling process, thereby significantly improving the plasticity and crack resistance of steel.

[0046] In one possible implementation, the heat treatment process in step S6 includes the following specific steps:

[0047] Solution treatment: The treatment temperature is 950~1080℃, the holding time is 2.5mm / min+60min, and the cooling method is rapid cooling;

[0048] Aging treatment: The treatment temperature is 550±10℃, the holding time is 2.5mm / min+240min, and the cooling method is air cooling.

[0049] Compared with existing technologies, the above-mentioned possible implementation methods can stabilize the martensitic structure in the material and release internal stress through precise heat treatment processes, thereby obtaining better strength and toughness. By improving the microstructure of the steel through solution treatment and aging treatment, the mechanical properties of the material are significantly improved, especially exhibiting higher performance stability in high-strength and corrosion-resistant application environments.

[0050] Another technical problem to be solved by the present invention is to provide a precipitation-hardening stainless steel to solve the problems of poor mechanical properties and poor corrosion resistance caused by the high impurity content and general purity of conventional precipitation-hardening stainless steel in the prior art.

[0051] To address the aforementioned technical problems, this invention also provides a precipitation-hardening martensitic stainless steel, which is prepared by the aforementioned preparation method. The composition of the precipitation-hardening martensitic stainless steel includes: C ≤ 0.05%, Mn: 1.50–2.50%, Si: 1.00–1.30%, S ≤ 0.001%, P ≤ 0.003%, Ni: 6.00–6.50%, Cr: 14.00–15.50%, Mo: 0.30–0.50%, Nb: 0.30–0.50%, Al ≤ 0.015%, Ti ≤ 0.015%, H ≤ 0.00005%, O ≤ 0.0008%, N: 0.040–0.060%, with the balance being Fe and other unavoidable impurities.

[0052] Compared with the prior art, the preparation method of precipitation-hardening stainless steel proposed in this application has the following advantages: The precipitation-hardening martensitic stainless steel of this application solves the problem of difficult control of impurity content in the prior art by using a three-stage smelting process of vacuum induction furnace, electroslag remelting and vacuum arc remelting to precisely control the impurity content. It enables narrow-range point control of the composition of stainless steel, ensuring batch stability of steel. Furthermore, it effectively reduces the content of gaseous impurities and non-metallic inclusions through precise temperature and vacuum control, improves the purity of the material, makes its mechanical properties more superior, and significantly enhances the corrosion resistance of the material.

[0053] Compared with the existing 17-4PH steel, the steel described in this invention has optimized chemical composition, significantly reduced residual element content, and reduced ferrite content, giving it high strength while maintaining good plasticity, as well as good toughness and plasticity. At the same time, its transverse and longitudinal mechanical properties tend to be consistent. By adjusting the chemical composition, it has more martensitic structure at room temperature, which improves its strength. Attached Figure Description

[0054] Figure 1 Heating curve of electrode forging for electroslag ingots;

[0055] Figure 2 This diagram illustrates the role of nickel in steel. Detailed Implementation

[0056] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0057] This invention provides a method for preparing precipitation-hardening stainless steel, comprising the following steps:

[0058] S1: Vacuum Induction Furnace Smelting: High-purity raw materials are smelted in a vacuum induction furnace. The raw materials are melted and degassed, and the gas content and the mass percentage of chemical elements are controlled as follows: C≤0.05%, Mn: 1.50~2.50%, Si: 1.00~1.30%, S≤0.001%, P≤0.003%, Ni: 6.00~6.50%, Cr: 14.00~15.50%, Mo: 0.30~0.50%, Nb: 0.30~0.50%, Al≤0.015%, Ti≤0.015%, H≤0.00005%, O≤0.0008%, N: 0.040~0.060%, with the balance being Fe and other unavoidable impurities, to produce electrode rods.

[0059] S2: Electroslag remelting: The electrode rod obtained in step S1 is subjected to electroslag remelting using a slag material composed of CaF2, Al2O3, and MgO. The melting rate is adjusted to reduce chemical element segregation and improve the purity of the steel to obtain an electroslag ingot.

[0060] S3: Forging vacuum consumable electrode: The electroslag ingot obtained in step S2 is heat-treated and then forged to obtain a vacuum consumable electrode.

[0061] S4: Vacuum self-consumable remelting: The vacuum self-consumable electrode obtained in step S3 is subjected to vacuum self-consumable remelting, and further degassed under the condition of vacuum degree ≤0.5Pa to obtain steel ingot;

[0062] S5: Forging process: Forging the steel ingot obtained in step S4: Before forging, gradually heat to 800°C and hold for 1 to 4 hours, then raise the temperature to 1100 to 1180°C and hold for 1 to 7 hours, forging in the temperature range of 950 to 1100°C, and then slowly cool after forging.

[0063] S6: Heat treatment: The forged steel is subjected to heat treatment, which includes solution treatment and aging treatment.

[0064] As a preferred embodiment, in step S1, the conditions for smelting in the vacuum induction furnace are as follows: the temperature after the raw material is fully melted is 1520-1600℃, the temperature during the refining period of the raw material is 1500-1570℃, the refining time is ≥60 minutes, and the vacuum degree is ≤5Pa; the temperature for casting the electrode rod is 1540-1580℃.

[0065] As a preferred embodiment, in step S1, the refining period further includes an argon injection step, which includes: when the gas content in the furnace reaches O≤15ppm, N≤15ppm, and H≤1ppm, 8000Pa of argon gas is introduced into the furnace and CrN is added, and after stirring for 5-10 minutes, a Mn source is added.

[0066] As a preferred embodiment, in step S2, the current of the electroslag remelting is 3KA to 19KA, the power is 60kW to 800kW, the melting rate is 3.5 to 10.5kg / min, and after obtaining the electroslag ingot, the slow cooling time is not less than 24 hours.

[0067] As a preferred embodiment, in step S2, the mass ratio of CaF2, Al2O3, and MgO in the slag is 65:30:5.

[0068] As a preferred embodiment, step S3, the forging heat treatment includes the following steps:

[0069] Initial heating phase: The initial temperature is controlled below 600℃, and then the temperature is increased to 800℃ at a steady rate. The entire heating process lasts for more than 2 hours.

[0070] 800℃ heat preservation stage: When the temperature reaches 800℃, maintain this temperature for at least 1 hour.

[0071] Further heating stage: After holding at 800℃, continue heating until the temperature reaches between 1140℃ and 1210℃, with a heating time of no less than 2 hours to ensure gradual heating;

[0072] High-temperature insulation stage: Maintain the temperature for at least 2 hours within the range of 1140℃ to 1210℃;

[0073] The forging process includes the following steps:

[0074] Re-firing stage: Heat the electroslag ingot to 1120-1160℃;

[0075] Forging stage: Forging is carried out within a temperature range of ≥1000℃ for the initial forging temperature and ≥850℃ for the final forging temperature;

[0076] Slow cooling stage: After forging, slow cooling treatment is carried out. The slow cooling method is cover cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0077] Finishing: After slow cooling, the forging is finished by machining to ensure that it meets the electrode size requirements matched by the vacuum consumable crystallizer.

[0078] As a preferred embodiment, in step S4, the melting rate of the vacuum consumable remelting is 2.5 to 6.5 kg / min, and helium cooling technology is used to accelerate the cooling of the molten steel ingot.

[0079] As a preferred embodiment, in step S5, the slow cooling after forging is carried out by cover cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0080] As a preferred embodiment, the heat treatment process in step S6 includes the following specific steps:

[0081] Solution treatment: The treatment temperature is 950~1080℃, the holding time is 2.5mm / min+60min, and the cooling method is rapid cooling;

[0082] Aging treatment: The treatment temperature is 550±10℃, the holding time is 2.5mm / min+240min, and the cooling method is air cooling.

[0083] The present invention also provides a precipitation-hardening martensitic stainless steel, which is prepared by the aforementioned preparation method. The composition of the precipitation-hardening martensitic stainless steel includes: C ≤ 0.05%, Mn: 1.50~2.50%, Si: 1.00~1.30%, S ≤ 0.001%, P ≤ 0.003%, Ni: 6.00~6.50%, Cr: 14.00~15.50%, Mo: 0.30~0.50%, Nb: 0.30~0.50%, Al ≤ 0.015%, Ti ≤ 0.015%, H ≤ 0.00005%, O ≤ 0.0008%, N: 0.040~0.060%, with the balance being Fe and other unavoidable impurities.

[0084] The following is a detailed analysis of the elements in the high-purity, high-strength steel of the present invention, and further explains the composition configuration and rationale for the high-purity, high-strength steel of the present invention:

[0085] As a precipitation-hardening martensitic stainless steel, extremely low residual elements and the interaction between alloying elements and the matching of their addition amounts are very important.

[0086] The role of nickel in this steel is manifested in the following ways: Nickel can push the chromium content of martensitic chromium stainless steel to a higher level, improving the steel's corrosion resistance, thus solving the problem that martensitic chromium stainless steel sacrifices hardness to improve its corrosion resistance. In martensitic chromium-nickel stainless steel, nickel has a dual effect of expanding the austenite phase region and lowering the Ms temperature (e.g., Figure 1 As shown, nickel will cause the steel to become a single-phase austenitic stainless steel and lose its quenching ability. At the same time, nickel also reduces the ferrite content, with the best effect among all alloying elements. Under specific carbon and chromium content conditions, this effect can enable the steel to achieve satisfactory phase transformation effects and maximum hardness values. Nickel can also improve the hardenability of steel. Nickel can promote martensitic transformation, and along with this effect, nickel improves the mechanical properties of steel. 6-8% nickel can still give the steel a martensitic structure in the solution-treated state, but the impact toughness is too low at 5% nickel. As the nickel content increases, the strength and toughness of the steel improve. Above 8% nickel, due to the formation of a complex mixed structure of martensite and austenite, the strength and toughness actually decrease.

[0087] The role of molybdenum in this steel is manifested in: increasing tempering stability and enhancing the secondary hardening effect, while simultaneously increasing the steel's strength without reducing its toughness. The addition of molybdenum can improve both the strength and tempering stability of the steel. This is mainly because molybdenum forms a fine close-packed cubic phase, which exhibits extremely high stability under over-aging conditions, thus mitigating the degradation of molybdenum. 23 The C6 carbide substitution process increases the tempering stability of steel. In martensitic chromium-nickel stainless steel, the molybdenum content typically fluctuates between 0.5% and 4%. Excessive molybdenum will promote ferrite formation, which will have an adverse effect on the steel. Molybdenum can also improve corrosion resistance, low-temperature mechanical properties, high-temperature strength, and tempering stability.

[0088] Copper plays a crucial role in steel by being an austenite-forming element, but its ability to form austenite is far less than that of nickel, approximately 30% of nickel's. It can improve the corrosion resistance of steel, especially in reducing media. However, the addition of copper increases the difficulty of hot working deformation. Copper can also induce a secondary hardening effect, without significantly affecting the hardness of martensite. This secondary hardening effect results in the formation of fine, dispersed phases.

[0089] The roles of carbon and nitrogen in steel are as follows: With increasing carbon content, the strength and hardness of the steel increase, but this leads to decreased corrosion resistance, reduced toughness, and increased welding difficulty. To achieve good overall performance in terms of strength, toughness, and corrosion resistance, the carbon content of precipitation-hardening stainless steel should be <1%. When the carbon content is below 0.03%, martensitic aging stainless steel exhibits good corrosion resistance, and high strength can be obtained through aging hardening. The effect of nitrogen is similar to that of carbon, but it does not have a detrimental effect on corrosion resistance; in fact, nitrogen can improve corrosion resistance under certain conditions. Nitrogen has a stronger strengthening effect on martensitic chromium-nickel stainless steel than carbon and is an inexpensive strengthening element.

[0090] The role of niobium in steel is reflected in the following aspects: niobium is a ferrite-forming element. Adding niobium can cause carbon in steel to form carbon-niobium compounds, which refines the grain size of the steel and improves its corrosion resistance.

[0091] In summary, harmful elements such as P, S, Al, and Ti, as well as gases such as H, O, and N, are all considered impurities and are minimized. Raw materials are selected from intermediate alloys and metals of the same or similar steels. High-purity medium-alloy ultra-high-strength steel is achieved through vacuum induction remelting, electroslag remelting, and vacuum arc remelting. Accordingly, this invention also provides a method for manufacturing the aforementioned medium-purity high-alloy ultra-high-strength steel, which includes the following steps:

[0092] The smelting process of vacuum induction furnace + electroslag remelting + vacuum arc remelting melts the raw materials into steel ingots, controlling the mass percentage content of each chemical element as follows: C: ≤0.05%; Mn: 1.50~2.50%; Si: 1.00~1.30%; S≤0.001%; ​​P≤0.003%; Ni: 6.00~6.50%; Cr: 14.00~15.50%; Mo: 0.30~0.50%; Nb: 0.30-0.50%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00005%; O: ≤0.0008%; N: 0.040~0.060%; with the balance being Fe and other unavoidable impurities.

[0093] In step S1: (1) Requirements for raw materials for the vacuum induction furnace:

[0094] ① Add high-purity pure iron, which requires S≤0.002% and P≤0.005%, or refined steel smelted by electric furnace + LF + VOD + VD, where the residual elements S, P, and Al are all ≤0.001%.

[0095] ② Add high-purity molybdenum, nickel, chromium, niobium, manganese, or electrolytic manganese. Before charging the furnace, inspect the surface of the raw materials; rust, oil, and oxidation are not allowed, and any such defects must be removed.

[0096] (2) Vacuum induction furnace smelting process:

[0097] ① Slow and low temperature melting during the melting period, with a temperature of 1520~1600℃ after full melting; Vacuum induction furnace smelting can improve the degassing effect by increasing the steel liquid surface, so slow and low power melting can achieve a good degassing effect.

[0098] ② The vacuum degree during the refining period should be ≤5Pa, the holding time during the refining period should be ≥60min, and the temperature during the refining period should be 1500~1570℃. If the temperature is too low, it will not play a refining role, and if the temperature is too high, Al and Ti in the crucible will be reduced into the molten steel.

[0099] ③ After the refining period, when the gas meets the requirements, i.e. O≤15ppm, N≤15ppm, H≤1ppm, start adding CrN by charging Ar≥8000Pa, and add metallic Mn or electrolytic Mn after stirring for 5-10 minutes.

[0100] ④ Pouring temperature: 1540~1580℃. If the pouring temperature is too low, the molten steel will solidify and the pouring process cannot be completed; if the pouring temperature is too high, the electrodes will easily crack.

[0101] ⑤ The electrodes require slow cooling (including sand cooling, hood cooling, pit cooling, and slow cooling in the furnace), polishing, and flattening before electroslag remelting. This effectively reduces the content of the chemical element sulfur in the steel and improves non-metallic inclusions, ensuring the purity of the steel and preparing for improved strength and toughness.

[0102] In step S2: (3) Preparation for electroslag remelting:

[0103] ① Each electrode corresponds to one steel ingot, and the shrinkage cavity should face downwards with the end of the shrinkage cavity cut flat.

[0104] ② Slag ratio: CaF2:Al2O3:MgO=70:30; slag weight 36-230kg (select the appropriate amount of slag weight according to the type of electroslag ingot).

[0105] ③ Slag baking temperature: 600-1000℃; baking time for a single hopper: 3-10h. If there are other slag materials in the heating furnace, the baking time should be ≥5h.

[0106] ④ Arc igniter: Benxi steel bell or carbon steel conductive block.

[0107] (4) Electroslag remelting process parameters (argon-protected electroslag furnace)

[0108] ① Arc initiation stage: Current and power control; different parameters are selected for different ingot types. The parameter range given below applies to 1-ton to 6-ton steel ingots. Parameters are as follows:

[0109] Current: 3KA-19KA; Power: 60kW-800kW; Arc ignition time: ≥30min.

[0110] ② Melting Stage: The melting process is controlled by the melting rate. Different melting rates are specified according to different ingot types. The melting period is based on the melting rate, and the melting rate should be kept as low as possible to improve the segregation of chemical elements. Melting rate: 3.5-10.5 kg / min.

[0111] ③ Hot capping stage: Hot capping is controlled by the melting rate. The starting weight for starting hot capping varies depending on the ingot type. To achieve the shrinkage compensation effect, hot capping requires sufficient weight support. Starting weight for hot capping: 100kg-550kg; melting rate gradually decreases, 10.5-2.0kg / min.

[0112] ④ After the steel ingot is demolded, it should be slowly cooled (including hood cooling, sand cooling, pit cooling, and furnace cooling) for ≥24 hours; or it should be sent for forging in a hot state.

[0113] In step S3: (5) Electroslag ingot forging vacuum consumable electrode process

[0114] ① Reference for heating curve of electroslag ingot forging Figure 2 As shown:

[0115] ② The reheating temperature is 1120℃, the initial forging temperature is ≥1000℃, and the final forging temperature is ≥850℃. Within this temperature range, the steel can be formed in the optimal thermoplasticity zone, and the grain size can be effectively controlled.

[0116] ③ Allows for direct forging of the required electrode dimensions in a single firing process.

[0117] ④ Slow cooling after forging (including cover cooling, sand cooling, pit cooling, and furnace cooling) ≥ 24h.

[0118] ⑤ After slow cooling, perform finishing by machining according to the electrode size matched to the vacuum consumable crystallizer.

[0119] In step S4: (6) Vacuum arc furnace smelting process:

[0120] ① The vacuum degree requirement for vacuum self-consuming furnace smelting is ≤0.5Pa, to achieve remelting and degassing.

[0121] ② Vacuum arc remelting furnace smelting specifies different melting rates according to different ingot types. The melting period is based on the melting rate. The lower the melting rate, the better the chemical element segregation.

[0122] Parameters: Initial stage current 4.0 (KA), melting stage melting speed 2.5 kg / min, feeding stage: 2.5 (KA) control, which can effectively prevent segregation.

[0123] ③ Vacuum arc furnace smelting requires the use of helium cooling to accelerate cooling, melting and solidifying simultaneously. The use of droplet pulse technology is beneficial to improve chemical composition segregation and ingot shape segregation, thereby increasing the purity of the steel ingot.

[0124] ④ After the steel ingot is remelted in a vacuum arc remelting furnace, it needs to be slowly cooled (including hood cooling, sand cooling, pit cooling, and furnace cooling) for ≥24 hours. The surface of the steel ingot needs to be ground or machined.

[0125] In step S5: (7) Forging: The vacuum consumable steel ingot is heated with the furnace temperature. The furnace temperature is required to be ≤600℃. The temperature is increased with the furnace at a rate of ≤200℃ / h. The ingot is heated to 800℃ and held for 1 hour. Then the temperature is increased slowly at a rate of ≤200℃ / h. When the temperature reaches 1100℃, it is held for 1 hour. The initial forging temperature is required to be 950℃ and the final forging temperature is 800℃. Within this temperature range, the steel can be formed in the optimal thermoplastic zone, thereby avoiding forging cracks.

[0126] (8) Solution treatment at 950℃, heat treatment at 2.5mm / min + 60min, and rapid cooling.

[0127] (9) Aging is performed at 540℃, followed by heat preservation at 2.5mm / min + 240min, and then air cooling.

[0128] The following specific embodiments, which incorporate the above-mentioned data range, are provided to further elaborate on the present invention:

[0129] Example 1:

[0130] This embodiment provides a precipitation-hardening stainless steel and its preparation method. The precipitation-hardening stainless steel is obtained by the following preparation method:

[0131] A method for preparing precipitation-hardening stainless steel includes the following steps:

[0132] S1: Vacuum Induction Furnace Smelting: High-purity raw materials are used. Smelting is performed in a vacuum induction furnace, melting and degassing the raw materials, and controlling the gas content and the mass percentage of chemical elements as follows: C: 0.03%, Mn: 1.90%, Si: 1.05%, S≤0.001%, P≤0.003%, Ni: 6.05%, Cr: 14.03%, Mo: 0.31%, Nb: 0.32%, Al≤0.015%, Ti≤0.015%, H≤0.00005%, O≤0.0008%, N: 0.073%, with the balance being... The electrode rod is prepared by mixing Fe and other unavoidable impurities. The conditions for smelting in the vacuum induction furnace are as follows: the temperature after the raw material is fully melted is 1560℃, the temperature during the refining period of the raw material is 1535℃, and the refining period also includes the step of injecting argon gas, including: when the gas content in the furnace reaches O≤15ppm, N≤15ppm, and H≤1ppm, 8000Pa of argon gas is introduced into the furnace and CrN is added. After stirring for 5-10 minutes, Mn source is added, and the refining time is ≥60 minutes and the vacuum degree is ≤5Pa. The temperature of casting the electrode rod is 1560℃.

[0133] S2: Electroslag remelting: The electrode rod obtained in step S1 is subjected to electroslag remelting. The current of the electroslag remelting is 11KA, the power is 430kW, the melting rate is 7kg / min, and after obtaining the electroslag ingot, the slow cooling time is not less than 24 hours. The slag material is a mixture of CaF2, Al2O3 and MgO with a mass ratio of 65:30:5, the amount of slag is 123kg, and the melting rate is adjusted to reduce the segregation of chemical elements and improve the purity of the steel to obtain the electroslag ingot.

[0134] S3: Forging vacuum consumable electrode: The electroslag ingot obtained in step S2 is heat-treated and then forged to obtain a vacuum consumable electrode.

[0135] The forging heat treatment includes the following steps:

[0136] Initial heating phase: The initial temperature is controlled below 600℃, and then the temperature is increased to 800℃ at a steady rate. The entire heating process lasts for more than 2 hours.

[0137] 800℃ heat preservation stage: When the temperature reaches 800℃, maintain this temperature for at least 1 hour.

[0138] Further heating stage: After holding at 800℃, continue heating until the temperature reaches 1175℃, with a heating time of no less than 2 hours to ensure gradual heating;

[0139] High-temperature insulation stage: Maintain the temperature at 1175℃ for at least 2 hours;

[0140] The forging process includes the following steps:

[0141] Re-firing stage: Heat the electroslag ingot to 1140℃;

[0142] Forging stage: Forging is carried out within a temperature range of ≥1000℃ for the initial forging temperature and ≥850℃ for the final forging temperature;

[0143] Slow cooling stage: After forging, slow cooling treatment is carried out. The slow cooling method is cover cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0144] Finishing: After slow cooling, the forging is finished by machining to ensure that it meets the electrode size requirements matched by the vacuum consumable crystallizer.

[0145] S4: Vacuum self-consumable remelting: The vacuum self-consumable electrode obtained in step S3 is subjected to vacuum self-consumable remelting. The melting rate of the vacuum self-consumable remelting is 4.5 kg / min, and helium cooling technology is used to accelerate the cooling of the molten steel ingot. Under the condition of vacuum degree ≤ 0.5 Pa, the gas is further degassed to obtain the steel ingot.

[0146] S5: Forging process: The steel ingot obtained in step S4 is forged: before forging, it is gradually heated to 800°C and held for 1 to 4 hours, then heated to 1140°C and held for 4 hours, and forged at 1025°C. After forging, it is slowly cooled. The slow cooling after forging is achieved by cover cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0147] S6: Heat treatment: The forged steel is subjected to heat treatment, which includes solution treatment and aging treatment.

[0148] The heat treatment process includes the following specific steps:

[0149] Solution treatment: The treatment temperature is 1000℃, the holding time is 2.5mm / min + 60min, and the cooling method is rapid cooling;

[0150] Aging treatment: The treatment temperature is 550℃, the holding time is 2.5mm / min + 240min, and the cooling method is air cooling.

[0151] Example 2:

[0152] This embodiment provides a precipitation-hardening stainless steel and its preparation method. The precipitation-hardening stainless steel is obtained by the following preparation method:

[0153] A method for preparing precipitation-hardening stainless steel includes the following steps:

[0154] S1: Vacuum Induction Furnace Smelting: High-purity raw materials are used. Smelting is performed in a vacuum induction furnace, melting and degassing the raw materials, and controlling the gas content and the mass percentage of chemical elements as follows: C: 0.04%, Mn: 2.30%, Si: 1.16%, S≤0.001%, P≤0.003%, Ni: 6.25%, Cr: 14.75%, Mo: 0.40%, Nb: 0.40%, Al≤0.015%, Ti≤0.015%, H≤0.00005%, O≤0.0008%, N: 0.098%, balance. The electrode rod is made of Fe and other unavoidable impurities. The conditions for smelting in the vacuum induction furnace are as follows: the temperature after the raw material is fully melted is 1520℃, the temperature during the refining period of the raw material is 1500℃, and the refining period also includes the step of injecting argon gas, including: when the gas content in the furnace reaches O≤15ppm, N≤15ppm, and H≤1ppm, 8000Pa of argon gas is introduced into the furnace and CrN is added. After stirring for 5 minutes, Mn source is added, and the refining time is ≥60 minutes and the vacuum degree is ≤5Pa. The temperature of casting the electrode rod is 1540℃.

[0155] S2: Electroslag remelting: The electrode rod obtained in step S1 is subjected to electroslag remelting. The current of the electroslag remelting is 3KA, the power is 60kW, the melting rate is 3.5kg / min, and after obtaining the electroslag ingot, the slow cooling time is not less than 24 hours. The slag material is a mixture of CaF2, Al2O3 and MgO with a mass ratio of 65:30:5, the slag amount is 36kg, and the melting rate is adjusted to reduce the segregation of chemical elements and improve the purity of the steel to obtain the electroslag ingot.

[0156] S3: Forging vacuum consumable electrode: The electroslag ingot obtained in step S2 is heat-treated and then forged to obtain a vacuum consumable electrode.

[0157] The forging heat treatment includes the following steps:

[0158] Initial heating phase: The initial temperature is controlled below 600℃, and then the temperature is increased to 800℃ at a steady rate. The entire heating process lasts for more than 2 hours.

[0159] 800℃ heat preservation stage: When the temperature reaches 800℃, maintain this temperature for at least 1 hour.

[0160] Further heating stage: After holding at 800℃, continue heating until the temperature reaches 1140℃, with a heating time of no less than 2 hours to ensure gradual heating;

[0161] High-temperature insulation stage: Maintain the temperature at 1140℃ for at least 2 hours;

[0162] The forging process includes the following steps:

[0163] Re-firing stage: Heat the electroslag ingot to 1120℃;

[0164] Forging stage: Forging is carried out within a temperature range of ≥1000℃ for the initial forging temperature and ≥850℃ for the final forging temperature;

[0165] Slow cooling stage: After forging, slow cooling treatment is carried out. The slow cooling method is cover cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0166] Finishing: After slow cooling, the forging is finished by machining to ensure that it meets the electrode size requirements matched by the vacuum consumable crystallizer.

[0167] S4: Vacuum self-consumable remelting: The vacuum self-consumable electrode obtained in step S3 is subjected to vacuum self-consumable remelting. The melting rate of the vacuum self-consumable remelting is 2.5 to 6.5 kg / min, and helium cooling technology is used to accelerate the cooling of the molten steel ingot. Under the condition of vacuum degree ≤ 0.5 Pa, the gas is further degassed to obtain the steel ingot.

[0168] S5: Forging process: The steel ingot obtained in step S4 is forged: before forging, it is gradually heated to 800°C and held for 1 hour, then heated to 1100-1180°C and held for 1 hour, and forged at 950°C. After forging, it is slowly cooled. The slow cooling after forging is achieved by cover cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0169] S6: Heat treatment: The forged steel is subjected to heat treatment, which includes solution treatment and aging treatment.

[0170] The heat treatment process includes the following specific steps:

[0171] Solution treatment: The treatment temperature is 950℃, the holding time is 2.5mm / min + 60min, and the cooling method is rapid cooling;

[0172] Aging treatment: The treatment temperature is 540℃, the holding time is 2.5mm / min + 240min, and the cooling method is air cooling.

[0173] Example 3:

[0174] This embodiment provides a precipitation-hardening stainless steel and its preparation method. The precipitation-hardening stainless steel is obtained by the following preparation method:

[0175] A method for preparing precipitation-hardening stainless steel includes the following steps:

[0176] S1: Vacuum Induction Furnace Smelting: High-purity raw materials are used. Smelting is performed in a vacuum induction furnace, melting and degassing the raw materials, and controlling the gas content and the mass percentage of chemical elements as follows: C: 0.05%, Mn: 2.50%, Si: 1.28%, S≤0.001%, P≤0.003%, Ni: 6.50%, Cr: 15.50%, Mo: 0.50%, Nb: 0.50%, Al≤0.015%, Ti≤0.015%, H≤0.00005%, O≤0.0008%, N: 0.113%, with the balance being... The electrode rod is prepared by mixing Fe and other unavoidable impurities. The conditions for smelting in the vacuum induction furnace are as follows: the temperature after the raw material is fully melted is 1600℃, the temperature during the refining period of the raw material is 1570℃, and the refining period also includes the step of injecting argon gas, including: when the gas content in the furnace reaches O≤15ppm, N≤15ppm, and H≤1ppm, argon gas of 8000Pa is introduced into the furnace and CrN is added, and after stirring for 5-10 minutes, Mn source is added, and the refining time is ≥60 minutes and the vacuum degree is ≤5Pa; the temperature of casting the electrode rod is 1580℃.

[0177] S2: Electroslag remelting: The electrode rod obtained in step S1 is subjected to electroslag remelting. The current of the electroslag remelting is 19KA, the power is 800kW, the melting rate is 10.5kg / min, and after obtaining the electroslag ingot, the slow cooling time is not less than 24 hours. The slag material is a mixture of CaF2, Al2O3 and MgO with a mass ratio of 65:30:5, the slag amount is 182kg, and the melting rate is adjusted to reduce the segregation of chemical elements and improve the purity of the steel to obtain the electroslag ingot.

[0178] S3: Forging vacuum consumable electrode: The electroslag ingot obtained in step S2 is heat-treated and then forged to obtain a vacuum consumable electrode.

[0179] The forging heat treatment includes the following steps:

[0180] Initial heating phase: The initial temperature is controlled below 600℃, and then the temperature is increased to 800℃ at a steady rate. The entire heating process lasts for more than 2 hours.

[0181] 800℃ heat preservation stage: When the temperature reaches 800℃, maintain this temperature for at least 1 hour.

[0182] Further heating stage: After holding at 800℃, continue heating until the temperature reaches 1210℃, with a heating time of no less than 2 hours to ensure gradual heating;

[0183] High-temperature insulation stage: Maintain the temperature at 1140℃ for at least 2 hours;

[0184] The forging process includes the following steps:

[0185] Re-firing stage: Heat the electroslag ingot to 1160℃;

[0186] Forging stage: Forging is carried out within a temperature range of ≥1000℃ for the initial forging temperature and ≥850℃ for the final forging temperature;

[0187] Slow cooling stage: After forging, slow cooling treatment is carried out. The slow cooling method is cover cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0188] Finishing: After slow cooling, the forging is finished by machining to ensure that it meets the electrode size requirements matched by the vacuum consumable crystallizer.

[0189] S4: Vacuum self-consumable remelting: The vacuum self-consumable electrode obtained in step S3 is subjected to vacuum self-consumable remelting. The melting rate of the vacuum self-consumable remelting is 6.5 kg / min, and helium cooling technology is used to accelerate the cooling of the molten steel ingot. Under the condition of vacuum degree ≤ 0.5 Pa, the gas is further degassed to obtain the steel ingot.

[0190] S5: Forging process: The steel ingot obtained in step S4 is forged: before forging, it is gradually heated to 800°C and held for 4 hours, then heated to 1180°C and held for 7 hours, and forged at 1100°C. After forging, it is slowly cooled. The slow cooling after forging is achieved by cover cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0191] S6: Heat treatment: The forged steel is subjected to heat treatment, which includes solution treatment and aging treatment.

[0192] The heat treatment process includes the following specific steps:

[0193] Solution treatment: The treatment temperature is 1080℃, the holding time is 2.5mm / min + 60min, and the cooling method is rapid cooling;

[0194] Aging treatment: The treatment temperature is 560℃, the holding time is 2.5mm / min + 240min, and the cooling method is air cooling.

[0195] The finished steel materials prepared by the preparation methods of Examples 1-3 of this invention were sampled from two different furnaces and subjected to low-magnification testing according to ASTM A604. The results are shown in Table 1.

[0196] Table 1. Results of low-magnification inspection

[0197]

[0198] The finished steel materials prepared by the preparation methods of Examples 1-3 of this invention were sampled from two different furnaces and tested for non-metallic inclusions according to GB / T10561 and ferrite according to AMS2315. The test results are shown in Table 2.

[0199] Table 2 Non-metallic inclusions

[0200]

[0201] The above embodiments further demonstrate that this invention provides a method for preparing high-purity, low-impurity precipitation-hardening stainless steel. The method employs a triple-smelting process combining vacuum induction furnace smelting, electroslag remelting, and vacuum arc remelting, effectively controlling the content of gaseous elements and impurities in the steel, particularly significantly reducing the content of harmful gases such as hydrogen, oxygen, and nitrogen. Simultaneously, this invention optimizes the chemical composition ratio and improves the strength, plasticity, and corrosion resistance of the steel through precise control of the forging and heat treatment processes. The test results in the embodiments show that the content of non-metallic inclusions and ferrite in the steel is controlled at low levels, and the material exhibits good quality performance in low-magnification testing, without defects such as dark spots, white spots, or radial segregation, further verifying the effectiveness and reliability of the process described in this invention. Ultimately, this invention can prepare precipitation-hardening stainless steel with high strength, good toughness, and excellent corrosion resistance, suitable for applications in demanding fields such as aerospace, chemical, and medical industries.

[0202] In the description of the embodiments of this application, it should be noted that the terms "inner" and "outer" and other terms indicating direction or positional relationship are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this application.

[0203] In the description of this application, the references to terms such as "an embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0204] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for producing a precipitation hardening type stainless steel, characterized by, The method comprises the following steps: S1: Vacuum induction furnace smelting: high-purity raw materials are used to smelt through a vacuum induction furnace, the raw materials are degassed, and the mass percentage of the gas content and chemical elements is controlled to be C≤0.05%, Mn: 1.50-2.50%, Si: 1.00-1.30%, S≤0.001%, P≤0.003%, Ni: 6.00-6.50%, Cr: 14.00-15.50%, Mo: 0.30-0.50%, Nb: 0.30-0.50%, Al≤0.015%, Ti≤0.015%, H≤0.00005%, O≤0.0008%, N: 0.040-0.060%, and the balance is Fe and other inevitable impurities, to obtain an electrode rod; S2: Electroslag remelting: the electrode rod obtained in the step S1 is electroslag remelted, CaF2, Al2O3 and MgO mixed slag is used, and the melting speed is adjusted to reduce chemical element segregation and improve the purity of the steel, to obtain an electroslag ingot; S3: Forging a vacuum consumable electrode: the electroslag ingot obtained in the step S2 is subjected to heat treatment and then is forged, to obtain a vacuum consumable electrode; S4: Vacuum consumable remelting: the vacuum consumable electrode obtained in the step S3 is subjected to vacuum consumable remelting, and is further degassed under the condition that the vacuum degree is less than or equal to 0.5 Pa, to obtain a steel ingot; S5: Forging treatment: the steel ingot obtained in the step S4 is subjected to forging: gradually heated to 800 DEG C and kept for 1-4 hours before forging, then heated to 1100-1180 DEG C and kept for 1-7 hours, forged at the temperature of 950-1100 DEG C, and slowly cooled after forging; S6: Heat treatment: the steel after forging is subjected to heat treatment, and the heat treatment comprises solid solution treatment and aging treatment; In the step S1, the conditions of the vacuum induction furnace smelting are as follows: the temperature of the fully melted raw materials is 1520-1600 DEG C, the temperature of the raw materials during refining is 1500-1570 DEG C, the refining time is greater than or equal to 60 minutes, and the vacuum degree is less than or equal to 5 Pa; and the temperature of the electrode rod pouring is 1540-1580 DEG C; In the step S3, the forging heating treatment comprises the following steps: Initial heating stage: the initial temperature is controlled to be lower than 600 DEG C, then heated to 800 DEG C at a stable rate, and the whole heating process lasts for more than 2 hours; 800 DEG C keeping stage: when the temperature reaches 800 DEG C, kept at the temperature for at least 1 hour; Further heating stage: after the 800 DEG C keeping, continuously heated until the temperature reaches between 1140 DEG C and 1210 DEG C, and the heating time is not less than 2 hours to ensure gradual heating; High-temperature keeping stage: kept at the temperature between 1140 DEG C and 1210 DEG C for at least 2 hours; The forging comprises the following steps: Reburning stage: the electroslag ingot is heated to 1120-1160 DEG C; Forging stage: forged at the temperature range that the open forging temperature is greater than or equal to 1000 DEG C and the final forging temperature is greater than or equal to 850 DEG C; Slow cooling stage: after forging, slow cooling treatment is carried out, and the slow cooling mode is cover cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours; Polishing treatment: after slow cooling, the forged piece is polished to ensure that it meets the electrode size requirements matched by the vacuum self-consumption crystallizer; In the step S2, the mass ratio of CaF2, Al2O3 and MgO in the slag is 65:30:

5. The heat treatment process in the step S6 comprises the following specific steps: Solution treatment: the treatment temperature is 950-1080 DEG C, the holding time is 2.5 mm / min+60 min, and the cooling mode is fast cooling; Aging treatment: the treatment temperature is 550±10 DEG C, the holding time is 2.5 mm / min+240 min, and the cooling mode is air cooling.

2. The method of producing a precipitation hardening stainless steel according to claim 1, characterized by, In the step S1, the refining period further comprises the step of injecting argon, which comprises: when the gas content in the furnace reaches O≤15 ppm, N≤15 ppm and H≤1 ppm, 8000 Pa of argon is filled into the furnace, CrN is added, and stirring is carried out for 5-10 minutes, and then Mn source is added.

3. The method of producing a precipitation hardening stainless steel according to claim 1, characterized by, In the step S2, the electric current for electroslag remelting is 3-19 KA, the power is 60-800 kw, the melting speed is 3.5-10.5 kg / min, and after the electroslag ingot is obtained, the slow cooling time is not less than 24 hours.

4. The method of producing a precipitation hardening stainless steel according to claim 1, characterized by, In the step S4, the melting speed of the vacuum self-consumption remelting is 2.5-6.5 kg / min, and the molten steel ingot is accelerated cooled by using helium cooling technology.

5. The method of producing a precipitation hardening stainless steel according to claim 1, characterized by, In the step S5, the slow cooling after forging adopts cover cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

6. A precipitation hardening martensitic stainless steel, characterized by, The precipitation hardening martensitic stainless steel is prepared by the preparation method in any one of claims 1 to 5, and the composition of the precipitation hardening martensitic stainless steel comprises: C≤0.05%, Mn: 1.50-2.50%, Si: 1.00-1.30%, S≤0.001%, P≤0.003%, Ni: 6.00-6.50%, Cr: 14.00-15.50%, Mo: 0.30-0.50%, Nb: 0.30-0.50%, Al≤0.015%, Ti≤0.015%, H≤0.00005%, O≤0.0008%, N: 0.040-0.060%, and the balance is Fe and other inevitable impurities.

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