Inclusion control methods for martensitic stainless steels with high fatigue and corrosion resistance

Abstract

This invention discloses a method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance. The overall process flow is as follows: molten iron pretreatment → K-OBM-S → slag removal station → VD → LF → ingot casting → electroslag remelting (ESR). Through molten iron detitanium removal and three-stage deoxidation, deoxidation and nitrogen alloying, vacuum treatment and slag system control, micro-alloying inclusion modification treatment, and electroslag remelting under a protective atmosphere, the method achieves special control of inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance. The main inclusions in the stainless steel, Al2O3, CaO-Al2O3, CaS, and TiN, are controlled into dispersed Mg-Al-RE-O type inclusions, which are tightly bonded to the steel matrix and are not easily deformed. At the same time, the method avoids the formation of rare earth oxide sulfide agglomerates, reduces the harm of inclusions to fatigue performance and corrosion resistance, and meets the requirements of special industries for martensitic stainless steel in terms of fatigue performance, corrosion resistance, and processing performance.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and specifically relates to a method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance. Background Technology

[0002] Non-metallic inclusions in steel are a key factor affecting its fatigue performance, corrosion resistance, and machining accuracy. Under conventional smelting processes, the main types of inclusions in stainless steel include Al₂O₃, CaO-Al₂O₃, CaS, and TiN, all of which significantly impair fatigue performance. Therefore, preventing the formation of such inclusions and promoting their removal or transformation into inclusions with less impact on fatigue performance are crucial for effective control.

[0003] Taking martensitic stainless steel as an example, its applications in oil well pipes, precision blades, and compressor valve plates require not only long-term high fatigue life under high-frequency vibration and high pressure, but also long-term operation in stress corrosion environments. Therefore, high requirements are placed on the material's fatigue performance, corrosion resistance, and processing precision.

[0004] Stainless steel cold-rolled sheets are thin (0.1-1.5mm). After multiple processes such as hot rolling and cold rolling, inclusions undergo elongation deformation and create pores with the steel matrix, which aggravates the impact on fatigue performance, corrosion resistance and processing accuracy. Therefore, there are higher and more special requirements for the particle size, type and quantity of inclusions.

[0005] Adding rare earth elements to steel can significantly refine inclusions and improve the fatigue properties of steel, and many researchers and inventors have disclosed related technologies. However, rare earth oxides and sulfides tend to aggregate, and their specific gravity is close to that of molten steel, making them difficult to float. Parameters such as deoxidation and slag system control, molten steel composition, rare earth addition amount, addition method, homogenization method, and electroslag remelting process all affect the morphology and distribution of rare earth inclusions.

[0006] Chinese invention patents with application numbers 202310314450.7 and 201910656623.7 disclose rare earth steel and methods for modifying inclusions using rare earth alloys, both targeting the smelting of bearing steel. During the refining stage, rare earth alloys are used to treat the molten steel, transforming Al2O3 inclusions in the steel into RE-oxygen-sulfides, thus controlling the type, distribution, and size of inclusions and improving the steel's performance and quality. However, due to differences in product requirements and process routes between bearing steel and stainless steel, their compositions and control processes differ. Furthermore, the aforementioned patents do not address TiN inclusion control, the impact of inclusions on stress corrosion cracking, or the influence of electroslag on inclusion types.

[0007] Chinese invention patent application number 201910656623.7 discloses a method for refining inclusions in high-purity rare earth electroslag steel. By adding rare earth during the electroslag remelting process to generate new inclusions, the problem of large inclusion size in rare earth electroslag steel is solved. However, this method does not involve the control of the electroslag system and cannot guarantee the uniformity of rare earth in the steel.

[0008] Chinese invention patent application number 202210243115.8 discloses a corrosion-resistant steel with high rare earth cerium content and its refining control method, which solves the problems of low rare earth cerium element yield and easy formation of cerium oxide and cerium sulfide in the production of existing corrosion-resistant steel. The main control of inclusions is cerium sulfide. However, cerium sulfide also has the problem of aggregation, which will affect fatigue performance and processing performance. Moreover, this method is applicable to high rare earth steel, and rare earth is used as an alloying element rather than an inclusion modification. Summary of the Invention

[0009] To address the technical problems existing in the prior art, the present invention provides a method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, comprising the following steps:

[0010] S1. First remove S in the molten iron ladle until w(S) < 0.01%, then remove Si after slag removal until w(Si) < 0.005%, then remove P until w(P) < 0.015%, and control the Ti content at w(Ti) < 0.003%;

[0011] In the S2 and K-OBM-S converter blowing process, nitrogen is first used for bottom blowing. After the oxidation period, the C content is controlled at w(C) = 0.2-0.7%, and the Ti content in the added alloy is controlled at w(Ti) < 0.05%. During the reduction period, bottom blowing argon is used to stir and control the nitrogen content. 20-28 kg of silicon-aluminum-iron alloy is added per ton of steel for reduction. The slag basicity is controlled at 2.0-2.2. The C content of the tapped molten steel is controlled at w(C) = 0.2-0.7%, the Si content at w(Si) = 0.2-0.3%, the Al content at w(Al) = 0.008-0.03%, the S content at w(S) < 0.01%, the P content at w(P) < 0.02%, the N content at w(N) = 0.03-0.05%, and the Ti content at w(Ti) < 0.005%. The tapped molten steel temperature is controlled above 1650℃.

[0012] Before the S3 and VD are introduced into the station, the top slag of the ladle is removed, and the amount of slag is controlled to be less than 10 kg per ton of steel. The temperature of the VD entering the station is controlled to be greater than 1630℃. Before the VD enters the station and is evacuated, lime is added at 1-6 kg per ton of steel and fluorite is added at 0-3 kg per ton of steel. Then, the first and second stage vacuum pumps are turned on to evacuate the station. During the evacuation, Ar is blown through the bottom through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled to be 6-10 Nl / min per ton of steel. After the vacuum degree is stable, the bottom blowing is turned off and maintained for 10-20 minutes.

[0013] S4. Add aluminum shot at 2-5 kg / ton of steel, lime at 5-10 kg / ton of steel, and fluorite at 2-5 kg / ton of steel. Gradually increase the volume until the vacuum pump is used to evacuate the system and maintain the ultimate vacuum level <0.1 mBar. Blow Ar through two bottom blow holes, with the bottom blow flow rate of each bottom blow hole controlled at 6-10 Nl / min / ton of steel. Stir for 10-25 min.

[0014] After S5 and LF enter the station, add lightly calcined magnesia balls at a rate of 1-2 kg per ton of steel and aluminum powder at a rate of 10-100 kg per ton of steel to adjust the slag color, so that the slag is white.

[0015] S6 and LF do not undergo calcium treatment. The single heating time should not exceed 10 minutes. After the temperature is properly adjusted, Ar is blown through two bottom blowing holes for intermediate stirring. The intermediate stirring time should be controlled at ≥5 minutes, and the bottom blowing flow rate of each bottom blowing hole should be controlled at 2-3 Nl / min per ton of steel. Then, Ar is blown through two bottom blowing holes for weak stirring. The weak stirring time should be controlled at ≥20 minutes, and the bottom blowing flow rate of each bottom blowing hole should be controlled at 0.5-2 Nl / min per ton of steel. After entering the weak stirring stage, heating and adding other alloy auxiliary materials other than rare earth are prohibited.

[0016] S7. After the weak stirring is completed, add high-purity rare earth aluminum-magnesium-iron alloy at a rate of 0.2-1.5 kg per ton of steel for micro-alloying. Stir by bottom blowing Ar through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 1-2 Nl / min per ton of steel. Stir for 3-15 minutes and then leave the station.

[0017] The calming time from the exit of S8 and LF to the start of casting is controlled to be >25min. Argon sealing protection is used during the ingot casting process to prevent secondary oxidation of molten steel.

[0018] S9. Electroslag remelting under a protective Ar atmosphere, the chemical composition of the protective slag is: w(CaO) = 35-40%, w(SiO2) < 2%, w(Al2O3) = 25-30%, w(MgO) = 5-10%, w(RE2O3) = 3-8%, w(CaF2) = 10-25%, w(moisture) < 0.01%, and the rest are unavoidable impurities.

[0019] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the chemical composition of the silicon-aluminum-iron alloy is controlled as follows: w(Si) = 35-40%, w(Al) = 25-55%, w(Ti) < 0.05%, the total mass percentage content of other impurities such as O, P, and S is less than 0.1%, and the remainder is Fe.

[0020] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the mass percentage content of active CaO in lime is controlled to be greater than 90%, and the mass percentage content of CaF2 in fluorite is controlled to be greater than 85%.

[0021] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the MgO mass percentage content in the lightly calcined magnesium balls is controlled to be greater than 85%.

[0022] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the Al mass percentage content in the aluminum powder is controlled to be greater than 98%, and the particle size of the aluminum powder is controlled to be less than 1 mm.

[0023] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the chemical composition of the high-purity rare earth aluminum-magnesium-iron alloy is controlled as follows: w(RE) = 25-32%, w(Al) = 15-25%, w(Mg) = 3-8%, w(O) < 100ppm, w(Ti) < 0.05%, the total mass percentage content of other impurities such as P and S is less than 0.1%, and the remainder is Fe.

[0024] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the rare earth element RE in the high-purity rare earth aluminum-magnesium-iron alloy is one or more of La, Ce, and Y.

[0025] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, after step S9, step S10 is also included: further purification by vacuum arc remelting furnace (VAR).

[0026] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, during the slag conditioning process in step S5, the content of w(SiO2) in the slag is controlled to be less than 3%, CaO / Al2O3 = 1.2-2, and w(MgO) = 8-10%.

[0027] The method for controlling inclusions in high-fatigue-performance and corrosion-resistant martensitic stainless steel of the present invention, through hot metal pretreatment, K-OBM-S smelting, reduction and nitrogen alloying, VD vacuum treatment, deep deoxidation and two slag formations, inclusion microalloying modification treatment, and electroslag remelting with a special slag system under a protective atmosphere, achieves special control of inclusions in high-fatigue-performance and corrosion-resistant martensitic stainless steel. Compared with the prior art, it has the following advantages and beneficial effects: the main inclusions Al2O3, CaO-Al2O3, CaS, and TiN in the stainless steel are controlled to be dispersed M The g-Al-RE-O type inclusions are tightly bonded to the steel matrix and are not easily deformed. Their size is less than 2μm, thus eliminating inclusion types such as Al2O3, CaO-Al2O3, CaS, and TiN, which are detrimental to fatigue performance and corrosion resistance. At the same time, it avoids the formation of rare earth oxide sulfide agglomeration. The inclusions deform little during the rolling process and are tightly bonded to the steel matrix, reducing the harm to fatigue performance and corrosion resistance. The product has a good surface finish and high processing precision, meeting the requirements of special industries for martensitic stainless steel in terms of fatigue performance, corrosion resistance, and processing performance. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] This invention aims to solve the problem of inclusion control in martensitic stainless steel with high fatigue performance and corrosion resistance. The overall process flow is as follows: molten iron pretreatment → K-OBM-S → slag removal station → VD → LF → ingot casting → electroslag remelting (ESR). It mainly achieves special control of inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance by detitanium removal and three-stage deoxidation, deoxidation and nitrogen alloying, vacuum treatment and slag system control, micro-alloying inclusion modification treatment, and electroslag remelting under a protective atmosphere, so as to meet the requirements of special industries for martensitic stainless steel in terms of fatigue performance, corrosion resistance and processing performance.

[0030] Specifically, the method for controlling inclusions in high-fatigue-performance and corrosion-resistant martensitic stainless steel according to the present invention includes the following steps:

[0031] S1. First remove S in the molten iron ladle until w(S) < 0.01%, then remove Si after slag removal until w(Si) < 0.005%, then remove P until w(P) < 0.015%, and control the Ti content at w(Ti) < 0.003%;

[0032] In the S2 and K-OBM-S converter blowing process, nitrogen is initially used for bottom blowing. After the oxidation period, the C content is controlled at w(C) = 0.2-0.7%, and the Ti content in the added alloy is controlled at w(Ti) < 0.05%. During the reduction period, bottom blowing with argon is used to control the nitrogen content. 20-28 kg of silicon-aluminum-iron alloy is added per ton of steel for reduction. The slag basicity (CaO / SiO2) is controlled at 2.0-2.2, and the C content of the tapped steel is controlled at w(… C) = 0.2-0.7%, Si content controlled at w(Si) = 0.2-0.3%, Al content controlled at w(Al) = 0.008-0.03%, S content controlled at w(S) < 0.01%, P content controlled at w(P) < 0.02%, N content controlled at w(N) = 0.03-0.05%, Ti content controlled at w(Ti) < 0.005%, and the tapping temperature of molten steel controlled above 1650℃;

[0033] Before S3 and VD enter the station, the top slag of the ladle is removed at the slag removal station, and the amount of slag is controlled to be less than 10 kg per ton of steel. The temperature of VD entering the station is controlled to be greater than 1630℃. Before the VD enters the station and is evacuated, lime is added at 1-6 kg per ton of steel and fluorite is added at 0-3 kg per ton of steel. Then, the first and second stage vacuum pumps are turned on to evacuate the station. During the evacuation, Ar is blown through the bottom through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled to be 6-10 Nl / min per ton of steel. After the vacuum degree stabilizes, the bottom blowing is turned off and maintained for 10-20 minutes.

[0034] S4. Add aluminum shot at 2-5 kg / ton of steel, lime at 5-10 kg / ton of steel, and fluorite at 2-5 kg / ton of steel. Gradually increase the volume until the vacuum pump is used to evacuate the system and maintain the ultimate vacuum level <0.1 mBar. Blow Ar through two bottom blow holes, with the bottom blow flow rate of each bottom blow hole controlled at 6-10 Nl / min / ton of steel. Stir for 10-25 min.

[0035] After S5 and LF enter the station, ferrosilicon is added according to the composition analysis results. Lightly calcined magnesia balls or fluorite are added at 1-2 kg per ton of steel to adjust the slag fluidity. If w(Al) < 0.04% or the slag color is dark green, aluminum powder is added at 10-100 kg per ton of steel to adjust the slag. After the slag is fully slagified by power supply, the uniformity and fluidity of the slag are ensured, and the slag color is white.

[0036] S6 and LF do not undergo calcium treatment. The single heating time should not exceed 10 minutes. After the temperature is properly adjusted, Ar is blown through two bottom blowing holes for intermediate stirring. The intermediate stirring time should be controlled at ≥5 minutes, and the bottom blowing flow rate of each bottom blowing hole should be controlled at 2-3 Nl / min per ton of steel. Then, Ar is blown through two bottom blowing holes for weak stirring. The weak stirring time should be controlled at ≥20 minutes, and the bottom blowing flow rate of each bottom blowing hole should be controlled at 0.5-2 Nl / min per ton of steel. After entering the weak stirring stage, heating and adding other alloy auxiliary materials other than rare earth are prohibited.

[0037] S7. After the weak stirring is completed, add high-purity rare earth aluminum-magnesium-iron alloy at a rate of 0.2-1.5 kg per ton of steel for micro-alloying. Stir by bottom blowing Ar through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 1-2 Nl / min per ton of steel. Stir for 3-15 minutes and then leave the station.

[0038] The calming time from the exit of S8 and LF to the start of casting is controlled to be >25min. Argon sealing protection is used during the ingot casting process to prevent secondary oxidation of molten steel.

[0039] S9. Electroslag remelting under a protective Ar atmosphere, the chemical composition of the protective slag is: w(CaO) = 35-40%, w(SiO2) < 2%, w(Al2O3) = 25-30%, w(MgO) = 5-10%, w(RE2O3) = 3-8%, w(CaF2) = 10-25%, w(moisture) < 0.01%, and the rest are unavoidable impurities.

[0040] The stainless steel product finally prepared by treating it with the inclusion control method of the above-mentioned high fatigue performance and corrosion resistance martensitic stainless steel of the present invention has the following chemical composition: w(C) = 0.2-0.7%, w(Si) = 0.3-0.6%, w(Mn) = 0.4-1.0%, w(Cr) = 12.5-14.0%, w(Ni) < 0.4%, w(Mo) = 0.7-1.2%, w(Al) = 0.05-0.08%, w(RE) = 0.003-0.008%, w(Mg) = 0.0008-0.0020%, w(S) ≤ 0.001%, w(P) < 0.02%, w(Ti)·w(N) < 8×10 -9 , w(TO)<15ppm, w(Ca)<5ppm, w(H)<0.5ppm.

[0041] By implementing the inclusion control method for high fatigue performance and corrosion resistance martensitic stainless steel described above in this invention, through hot metal pretreatment, K-OBM-S smelting, reduction and nitrogen alloying, VD vacuum treatment, deep deoxidation and two slag formations, inclusion microalloying modification treatment, and electroslag remelting using a special slag system under a protective atmosphere, the main inclusions Al2O3, CaO-Al2O3, CaS and TiN in stainless steel are controlled to be dispersed Mg-Al-RE-O type inclusions, which are tightly bonded to the steel matrix and are not easily deformed, with a size of less than 2μm. This eliminates inclusion types such as Al2O3, CaO-Al2O3, CaS and TiN that are harmful to fatigue performance and corrosion resistance, and at the same time avoids the formation of rare earth oxide sulfide agglomerates. Therefore, through the inclusion control method of the present invention for high fatigue performance and corrosion resistance martensitic stainless steel, the Mg-Al-RE-O inclusions after being controlled are less prone to agglomeration, the inclusion deformation during the rolling process is small, and they are tightly bonded to the steel matrix, which reduces the harm to fatigue performance and corrosion resistance. The product has a good surface finish and high processing accuracy.

[0042] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the chemical composition of the silicon-aluminum-iron alloy is as follows: w(Si) = 35-40%, w(Al) = 25-55%, w(Ti) < 0.05%, the total mass percentage content of other impurities such as O, P, and S is less than 0.1%, and the remainder is Fe.

[0043] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the mass percentage content of active CaO in lime is controlled to be greater than 90%, the mass percentage content of CaF2 in fluorite is controlled to be greater than 85%, and the remainder is unavoidable impurities.

[0044] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the MgO mass percentage content in the lightly calcined magnesium balls is controlled to be greater than 85%, with the remainder being unavoidable impurities.

[0045] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the Al mass percentage content in the aluminum powder is controlled to be greater than 98%, and the particle size of the aluminum powder is controlled to be less than 1 mm.

[0046] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the chemical composition of the high-purity rare earth aluminum-magnesium-iron alloy is as follows: w(RE) = 25-32%, w(Al) = 15-25%, w(Mg) = 3-8%, w(O) < 100ppm, w(Ti) < 0.05%, and the total mass percentage content of other impurities such as P and S is less than 0.1%, with the remainder being Fe.

[0047] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, the rare earth element RE in the high-purity rare earth aluminum-magnesium-iron alloy is one or more of La, Ce, and Y.

[0048] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, during the slag conditioning process in step S5, the content of w(SiO2) in the slag is controlled to be less than 3%, CaO / Al2O3 = 1.2-2, and w(MgO) = 8-10%.

[0049] Furthermore, in the above-mentioned method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, after step S9, step S10 is also included: further purification by vacuum arc remelting furnace (VAR).

[0050] The following comparative examples and embodiments of the present invention further illustrate the method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance. The comparative examples and embodiments described below are all for martensitic stainless steel.

[0051] Example 1

[0052] Example 1 includes the following steps:

[0053] S11, after pretreatment, the molten iron contains w(S) = 0.003%, w(Si) = 0.002%, w(P) = 0.012%, and w(Ti) = 0.002%.

[0054] In the S12 and K-OBM-S converter blowing process, nitrogen is first used for bottom blowing. After the oxidation period, the C content is controlled at w(C) = 0.25%, and the Ti content in the added alloy is controlled at w(Ti) < 0.05%. During the reduction period, bottom blowing argon is used to control the nitrogen content. Silicon-aluminum-iron alloy is added at 25 kg per ton of steel for reduction. The slag basicity is controlled at 2.1. The chemical composition of the tapped steel is controlled as follows: w(C) = 0.27%, w(Si) = 0.25%, w(Al) = 0.015%, w(S) = 0.008%, w(P) = 0.015%, w(N) = 0.032%, w(Ti) = 0.002%. The tapped steel temperature is controlled at 1673℃.

[0055] Before S13 and VD enter the station, the top slag of the ladle is removed at the slag removal station, and the slag amount is controlled at 8 kg per ton of steel. The temperature of VD entering the station is controlled at 1635℃. Before the VD enters the station and is evacuated, lime is added at 1 kg per ton of steel and fluorite is added at 1 kg per ton of steel. Then, the first and second stage vacuum pumps are turned on to evacuate the station. During the evacuation, Ar is blown through the bottom through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 6 Nl / min per ton of steel. After the vacuum degree stabilizes, the bottom blowing is turned off and maintained for 10 minutes.

[0056] S14. Add aluminum shot at 2 kg per ton of steel, lime at 5.5 kg per ton of steel, and fluorite at 2 kg per ton of steel. Gradually increase the volume until the vacuum pump is used to evacuate the system. Maintain the ultimate vacuum level <0.1 mBar. Blow Ar through two bottom blow holes. Control the bottom blow flow rate of each bottom blow hole to 6 Nl / min per ton of steel. Stir for 15 min.

[0057] After S15 and LF enter the station, add lightly calcined magnesia balls at 2 kg per ton of steel and aluminum powder at 20 kg per ton of steel to adjust the slag, controlling w(SiO2) = 2%, CaO / Al2O3 = 1.2%, and w(MgO) = 8.2% in the slag;

[0058] S16 and LF are not subjected to calcium treatment. The single heating time is 10 minutes. After the temperature is adjusted appropriately, Ar is blown through two bottom blow holes for intermediate stirring. The intermediate stirring time is controlled at 5 minutes, and the bottom blowing flow rate of each bottom blow hole is controlled at 3 Nl / min per ton of steel. Then, Ar is blown through two bottom blow holes for weak stirring. The weak stirring time is controlled at 20 minutes, and the bottom blowing flow rate of each bottom blow hole is controlled at 0.5 Nl / min per ton of steel. After entering the weak stirring stage, no heating is performed and other alloy auxiliary materials other than rare earth are added.

[0059] S17. After the weak stirring is completed, add high-purity rare earth aluminum-magnesium-iron alloy at 0.25 kg per ton of steel for micro-alloying. Stir by bottom blowing Ar through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 1 Nl / min per ton of steel. Stir for 5 minutes and then leave the station.

[0060] The calming time from the exit of S18 and LF to the start of casting is controlled at 30 minutes. Argon sealing protection is used during the ingot casting process to prevent secondary oxidation of molten steel.

[0061] S19. Electroslag remelting under a protective Ar atmosphere, the chemical composition of the protective slag is: w(CaO) = 35-40%, w(SiO2) < 2%, w(Al2O3) = 25-30%, w(MgO) = 5-10%, w(RE2O3) = 3-8%, w(CaF2) = 10-25%, w(moisture) < 0.01%, and the rest are unavoidable impurities.

[0062] The chemical composition of the stainless steel product finally prepared after treatment with the inclusion control method of high fatigue performance and corrosion resistance martensitic stainless steel in Example 1 is as follows: w(C) = 0.31%, w(Si) = 0.35%, w(Mn) = 0.77%, w(Cr) = 13.2%, w(Ni) = 0.12%, w(Mo) = 1.05%, w(Al) = 0.05%, w(RE) = 0.0033%, w(Mg) = 0.0013%, w(S) = 0.001%, w(P) = 0.015%, w(Ti) = 0.003%, w(N) = 0.008%, w(TO) = 14ppm, w(Ca) = 4ppm, w(H) = 0.3ppm.

[0063] Example 2

[0064] Example 2 includes the following steps:

[0065] S21. After pretreatment, the molten iron contains w(S) = 0.003%, w(Si) = 0.002%, w(P) = 0.010%, and w(Ti) = 0.002%.

[0066] In the S22 and K-OBM-S converter blowing process, nitrogen is first used for bottom blowing. After the oxidation period, the C content is controlled at w(C) = 0.29%. During the reduction period, argon gas is switched to bottom blowing for stirring to control the nitrogen content. Silicon-aluminum-iron alloy is added at 28 kg per ton of steel for reduction. The slag basicity is controlled at 2.2. The chemical composition of the tapped steel is controlled as follows: w(C) = 0.3%, w(Si) = 0.2%, w(Al) = 0.011%, w(S) = 0.003%, w(P) = 0.012%, w(N) = 0.05%, w(Ti) = 0.003%. The tapped steel temperature is controlled at 1690℃.

[0067] Before S23 and VD enter the station, the top slag of the ladle is removed at the slag removal station, and the amount of slag is controlled at 6 kg per ton of steel. The temperature of VD entering the station is controlled at 1650℃. Before the VD enters the station and is evacuated, lime is added at 6 kg per ton of steel and fluorite is added at 3 kg per ton of steel. Then, the first and second stage vacuum pumps are turned on to evacuate the station. During the evacuation, Ar is blown through the bottom through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 10 Nl / min per ton of steel. After the vacuum degree stabilizes, the bottom blowing is turned off and maintained for 15 minutes.

[0068] S24. Add aluminum shot at 3 kg per ton of steel, lime at 8 kg per ton of steel, and fluorite at 5 kg per ton of steel. Gradually increase the volume until the vacuum pump is used to evacuate the system and maintain the ultimate vacuum level <0.1 mBar. Blow Ar through two bottom blow holes, with the bottom blow flow rate of each bottom blow hole controlled at 10 Nl / min per ton of steel. Stir for 15 min.

[0069] After S25 and LF enter the station, ferrosilicon is added. Lightly calcined magnesia balls are added at 1 kg per ton of steel, and aluminum powder is added at 10 kg per ton of steel to adjust the slag. The slag is white. The slag content is controlled as w(SiO2) = 2.3%, CaO / Al2O3 = 2%, and w(MgO) = 8%.

[0070] S26 and LF are not subjected to calcium treatment. The single heating time does not exceed 10 minutes. After the temperature is adjusted appropriately, Ar is blown through two bottom blow holes for intermediate stirring. The intermediate stirring time is controlled at 8 minutes, and the bottom blowing flow rate of each bottom blow hole is controlled at 3 Nl / min per ton of steel. Then, Ar is blown through two bottom blow holes for weak stirring. The weak stirring time is controlled at 25 minutes, and the bottom blowing flow rate of each bottom blow hole is controlled at 2 Nl / min per ton of steel. After entering the weak stirring stage, no heating is required and other alloy auxiliary materials other than rare earth are added.

[0071] S27. After the weak stirring is completed, add high-purity rare earth aluminum-magnesium-iron alloy at a rate of 1.5 kg per ton of steel for micro-alloying. Stir by bottom blowing Ar through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 1-2 Nl / min per ton of steel. Stir for 15 minutes and then leave the station.

[0072] The calming time from the exit of S28 and LF to the start of casting is controlled at 30 minutes. Argon sealing protection is used during the ingot casting process to prevent secondary oxidation of molten steel.

[0073] S29. Electroslag remelting under a protective Ar atmosphere, the chemical composition of the protective slag is: w(CaO) = 35-40%, w(SiO2) < 2%, w(Al2O3) = 25-30%, w(MgO) = 5-10%, w(RE2O3) = 3-8%, w(CaF2) = 10-25%, w(moisture) < 0.01%, and the rest are unavoidable impurities.

[0074] The chemical composition of the stainless steel product finally prepared after treatment with the inclusion control method of high fatigue performance and corrosion resistance martensitic stainless steel in Example 2 is as follows: w(C) = 0.37%, w(Si) = 0.45%, w(Mn) = 0.6%, w(Cr) = 13.8%, w(Ni) = 0.10%, w(Mo) = 0.7-1.2%, w(Al) = 0.06%, w(RE) = 0.0076%, w(Mg) = 0.0015%, w(S) = 0.0008%, w(P) = 0.012%, w(Ti) = 0.004%, w(N) = 0.009%, w(TO) = 13ppm, w(Ca) = 3ppm, w(H) = 0.4ppm.

[0075] Example 3

[0076] Example 3 includes the following steps:

[0077] S31. After pretreatment, the molten iron contains w(S) = 0.002%, w(Si) = 0.003%, w(P) = 0.010%, and w(Ti) = 0.001%.

[0078] In the S32 and K-OBM-S converter blowing process, nitrogen is first used for bottom blowing. After the oxidation period, the C content is controlled at w(C) = 0.29%. During the reduction period, argon gas is switched to bottom blowing for stirring to control the nitrogen content. Silicon-aluminum-iron alloy is added at 26 kg per ton of steel for reduction. The slag basicity is controlled at 2.2. The chemical composition of the tapped steel is controlled as follows: w(C) = 0.3%, w(Si) = 0.22%, w(Al) = 0.01%, w(S) = 0.002%, w(P) = 0.012%, w(N) = 0.04%, w(Ti) = 0.002%. The tapped steel temperature is controlled at 1695℃.

[0079] Before S33 and VD enter the station, the top slag of the ladle is removed at the slag removal station, and the amount of slag is controlled at 5 kg per ton of steel. The temperature of VD entering the station is controlled at 1645℃. Before the VD enters the station and is evacuated, lime is added at 6 kg per ton of steel and fluorite is added at 3 kg per ton of steel. Then, the first and second stage vacuum pumps are turned on to evacuate the station. During the evacuation, Ar is blown through the bottom through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 8 Nl / min per ton of steel. After the vacuum degree stabilizes, the bottom blowing is turned off and maintained for 20 minutes.

[0080] S34. Add aluminum shot at 4.5g per ton of steel, lime at 10kg per ton of steel, and fluorite at 5kg per ton of steel. Gradually increase the volume until the vacuum pump is used to evacuate the system and maintain the ultimate vacuum level <0.1mBar. Blow Ar through two bottom blow holes, with the bottom blow flow rate of each bottom blow hole controlled at 10Nl / min per ton of steel. Stir for 20min.

[0081] After S35 and LF enter the station, ferrosilicon is added. Lightly calcined magnesia balls are added at 2 kg per ton of steel, and aluminum powder is added at 10 kg per ton of steel to adjust the slag. The slag is white. The slag content is controlled as w(SiO2) = 1.3%, CaO / Al2O3 = 1.5%, and w(MgO) = 10%.

[0082] S36 and LF are not subjected to calcium treatment. The single heating time does not exceed 10 minutes. After the temperature is adjusted appropriately, Ar is blown through two bottom blow holes for intermediate stirring. The intermediate stirring time is controlled at 8 minutes, and the bottom blowing flow rate of each bottom blow hole is controlled at 3 Nl / min per ton of steel. Then, Ar is blown through two bottom blow holes for weak stirring. The weak stirring time is controlled at 25 minutes, and the bottom blowing flow rate of each bottom blow hole is controlled at 2 Nl / min per ton of steel. After entering the weak stirring stage, no heating is required and other alloy auxiliary materials other than rare earth are added.

[0083] S37. After the weak stirring is completed, add high-purity rare earth aluminum-magnesium-iron alloy at a rate of 0.5 kg per ton of steel for micro-alloying. Stir by bottom blowing Ar through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 2 Nl / min per ton of steel. Stir for 10 minutes and then leave the station.

[0084] The calming time from the exit of S38 and LF to the start of casting is controlled at 35 minutes. Argon sealing protection is used during the ingot casting process to prevent secondary oxidation of molten steel.

[0085] S39. Electroslag remelting under a protective Ar atmosphere, the chemical composition of the protective slag is: w(CaO) = 35-40%, w(SiO2) < 2%, w(Al2O3) = 25-30%, w(MgO) = 5-10%, w(RE2O3) = 3-8%, w(CaF2) = 10-25%, w(moisture) < 0.01%, and the rest are unavoidable impurities.

[0086] The chemical composition of the stainless steel product finally prepared after treatment with the inclusion control method of high fatigue performance and corrosion resistance martensitic stainless steel in Example 3 is as follows: w(C) = 0.32%, w(Si) = 0.44%, w(Mn) = 0.8%, w(Cr) = 13.8%, w(Ni) = 0.10%, w(Mo) = 1.05%, w(Al) = 0.08%, w(RE) = 0.0054%, w(Mg) = 0.0010%, w(S) = 0.0003%, w(P) = 0.012%, w(Ti) = 0.003%, w(N) = 0.008%, w(TO) = 5ppm, w(Ca) = 3ppm, w(H) = 0.3ppm.

[0087] Comparative Example

[0088] The comparative example's process flow is: molten iron pretreatment → K-OBM-S → VD → LF → ingot casting → electroslag remelting (ESR). The molten iron pretreatment, K-OBM-S, and ingot casting processes are similar to those in the above embodiments of the present invention. The main difference is that the comparative example does not strictly control inclusions. Specifically, in the VD, LF, and ESR processes of the comparative example, the VD process is carried out without slag removal and directly evacuated to 0.1 mbar. After maintaining the ultimate vacuum for 20 minutes, aluminum shot, lime, and fluorite are added to adjust the slag before leaving the station. The LF process involves adjusting the alloy temperature and then performing calcium treatment. The ESR slag system uses a 50% Al2O3-50% CaF2 slag system.

[0089] The chemical composition of the stainless steel product finally prepared after comparative treatment is as follows: w(C) = 0.33%, w(Si) = 0.46%, w(Mn) = 0.6%, w(Cr) = 13.3%, w(Ni) = 0.12%, w(Mo) = 1.1%, w(Al) = 0.03%, w(Mg) = 0.0003%, w(S) = 0.0013%, w(P) = 0.012%, w(Ti) = 0.01%, w(N) = 0.009%, w(TO) = 37ppm, w(Ca) = 15ppm, w(H) = 0.4ppm, and it does not contain rare earth elements.

[0090] As described above, Examples 1-3 of this invention mainly control inclusions through special control, while the comparative examples do not strictly control inclusions. The TO, S, Mg, and rare earth RE contents in the martensitic stainless steel billets prepared in Examples 1-3 and the comparative examples were analyzed using an oxygen-nitrogen analyzer. Fatigue life tests were conducted on 0.2mm thick stainless steel under the same high-load working conditions for each process. Specific test results are shown in the table below:

[0091] Example 1 0.0014 0.0010 0.0013 0.0033 150 Example 2 0.0013 0.0008 0.0015 0.0076 180 Example 3 0.0005 0.0003 0.0010 0.0054 200 Comparative Example 0.0037 0.0013 0.0003 ＜0.001 55

[0092] In summary, the inclusion control method for high fatigue performance and corrosion resistance martensitic stainless steel of the present invention, through hot metal pretreatment, K-OBM-S smelting, reduction and nitrogen alloying, VD vacuum treatment, deep deoxidation and two slag formations, inclusion microalloying modification treatment, and electroslag remelting using a special slag system under a protective atmosphere, achieves special control of inclusions in high fatigue performance and corrosion resistance martensitic stainless steel. Compared with the prior art, it has the following advantages and beneficial effects:

[0093] By implementing the inclusion control method for high fatigue performance and corrosion resistance martensitic stainless steel of the present invention, the main inclusions Al2O3, CaO-Al2O3, CaS, and TiN in stainless steel are controlled to be dispersed Mg-Al-RE-O type inclusions, which are tightly bonded to the steel matrix and not easily deformed, with a size of less than 2μm. This eliminates inclusion types such as Al2O3, CaO-Al2O3, CaS, and TiN that are harmful to fatigue performance and corrosion resistance, and at the same time avoids the formation of rare earth oxide sulfide agglomeration. The inclusion deformation during the rolling process is small, and the tight bond with the steel matrix reduces the harm to fatigue performance and corrosion resistance. The product has a good surface finish and high processing precision, meeting the requirements of special industries for martensitic stainless steel in terms of fatigue performance, corrosion resistance, and processing performance.

[0094] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance, characterized in that, Includes the following steps: S1, first remove sulfur from the molten iron ladle. w (S) < 0.01%, after slag removal, Si is removed to w (Si) < 0.005%, then remove P to w (P) < 0.015%, and the Ti content is controlled within w (Ti) < 0.003%; In the S2 and K-OBM-S converter blowing process, nitrogen is first used for bottom blowing, and the C content is controlled at [value missing] after the oxidation period. w (C) = 0.2~0.7%, and the Ti content in the added alloy is controlled to be... w (Ti) < 0.05%, during the reduction period, switch to bottom-blown argon stirring to control nitrogen content, add 20-28 kg of silicon-aluminum-ferroalloy for reduction per ton of steel, control the slag basicity at 2.0-2.2, and control the C content of the tapped steel at [missing value]. w (C) = 0.2~0.7%, Si content controlled at w (Si) = 0.2~0.3%, Al content controlled at w (Al) = 0.008~0.03%, S content controlled at w (S) < 0.01%, P content controlled at w (P) < 0.02%, N content controlled at w (N) = 0.03~0.05%, Ti content controlled at w (Ti) < 0.005%, the molten steel temperature at tapping should be controlled above 1650℃; Before the S3 and VD are introduced into the station, the top slag of the ladle is removed, and the amount of slag is controlled to be less than 10 kg per ton of steel. The temperature of the VD entering the station is controlled to be greater than 1630℃. Before the VD enters the station and is evacuated, lime is added at 1~6 kg per ton of steel and fluorite is added at 0~3 kg per ton of steel. Then, the first and second stage vacuum pumps are turned on to evacuate the station. During the evacuation, Ar is blown through the bottom through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled to be 6~10 Nl / min per ton of steel. After the vacuum degree is stable, the bottom blowing is turned off and maintained for 10~20 minutes. S4. Add aluminum shot at 2-5 kg ​​per ton of steel, lime at 5-10 kg per ton of steel, and fluorite at 2-5 kg ​​per ton of steel. Gradually increase the volume until the vacuum pump is used to evacuate the system and maintain the ultimate vacuum level <0.1 mBar. Blow Ar through two bottom blow holes, with the bottom blow flow rate of each bottom blow hole controlled at 6-10 Nl / min per ton of steel. Stir for 10-25 min. After S5 and LF enter the station, add lightly calcined magnesia balls at a rate of 1-2 kg per ton of steel and aluminum powder at a rate of 10-100 kg per ton of steel to adjust the slag color, so that the slag is white. S6 and LF do not undergo calcium treatment. The single heating time should not exceed 10 minutes. After the temperature is properly adjusted, Ar is blown through two bottom blow holes for intermediate stirring. The intermediate stirring time should be controlled at ≥5 minutes, and the bottom blowing flow rate of each bottom blow hole should be controlled at 2~3 Nl / min per ton of steel. Then, Ar is blown through two bottom blow holes for weak stirring. The weak stirring time should be controlled at ≥20 minutes, and the bottom blowing flow rate of each bottom blow hole should be controlled at 0.5~2 Nl / min per ton of steel. After entering the weak stirring stage, heating and adding other alloy auxiliary materials other than rare earth are prohibited. S7. After the weak stirring is completed, add high-purity rare earth aluminum-magnesium-iron alloy at a rate of 0.2~1.5 kg per ton of steel for micro-alloying. Stir by bottom blowing Ar through two bottom blowing holes. The bottom blowing flow rate of each bottom blowing hole is controlled at 1~2 Nl / min per ton of steel. Stir for 3~15 minutes and then leave the station. The calming time from the exit of S8 and LF to the start of casting is controlled to be >25min. Argon sealing protection is used during the ingot casting process to prevent secondary oxidation of molten steel. S9. Electroslag remelting under a protective Ar atmosphere, the chemical composition of the protective slag is as follows: w (CaO) = 35~40%, w (SiO2) < 2%, w (Al2O3) = 25~30%, w (MgO) = 5~10%, w (RE2O3) = 3~8%, w (CaF2) = 10~25%, w Moisture content < 0.01%, the rest are unavoidable impurities.

2. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to claim 1, characterized in that, The chemical composition of silicon-aluminum-iron alloys is controlled as follows: w (Si) = 35~40%, w (Al) = 25~55%, w (Ti) < 0.05%, the total mass percentage of O, P, S and other impurities is less than 0.1%, and the remainder is Fe.

3. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to claim 1, characterized in that, The mass percentage content of active CaO in lime is controlled to be greater than 90%, and the mass percentage content of CaF2 in fluorite is controlled to be greater than 85%.

4. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to claim 1, characterized in that, The MgO content in lightly calcined magnesium balls is controlled to be greater than 85% by mass.

5. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to claim 1, characterized in that, The Al content in the aluminum powder is controlled to be greater than 98% by mass, and the particle size of the aluminum powder is controlled to be less than 1 mm.

6. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to claim 1, characterized in that, The chemical composition of high-purity rare earth aluminum-magnesium-iron alloy is controlled as follows: w (RE) = 25~32%, w (Al) = 15~25%, w (Mg) = 3~8%, w (O) < 100 ppm, w (Ti) < 0.05%, the total mass percentage content of P, S and other impurities is less than 0.1%, and the remainder is Fe.

7. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to claim 6, characterized in that, The rare earth element RE in high-purity rare earth aluminum-magnesium-iron alloys is one or more of La, Ce, and Y.

8. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to claim 1, characterized in that, After step S9, step S10 is also included: further purification by vacuum arc remelting furnace (VAR).

9. The method for controlling inclusions in martensitic stainless steel with high fatigue performance and corrosion resistance according to any one of claims 1 to 8, characterized in that, During the slag conditioning process in step S5, the slag is controlled. w (SiO2)<3%, CaO / Al2O3=1.2~2, w (MgO) = 8~10%.