Production process of large ultralow-N stainless steel

Abstract

The invention relates to the technical field of stainless steel metallurgy, in particular to a production process of large ultralow-N stainless steel. The production process of the large ultra-low-N stainless steel is used for preparing and obtaining the large ultra-low-N stainless steel with N smaller than or equal to 0.010 wt%. The production process comprises the steps of internal control component design, electric furnace primary smelting, ladle refining, pouring and electroslag remelting. Wherein in the ladle refining process, multiple alloying treatment and multiple VD vacuum refining treatment are carried out in a ladle refining furnace. Low-N control of the novel 9Cr-3W-3Co stainless steel material is achieved, and by controlling the N content to be 0.010 wt% or below, better toughness and fatigue performance of the novel 9Cr-3W-3Co stainless steel can be achieved; the problem that in the smelting process of a novel 9Cr-3W-3Co stainless steel material, due to the fact that interaction between other elements and the N element is high, N is difficult to remove is solved, and production of the large ultralow-N stainless steel ingot with the N content smaller than 0.008 wt% can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel metallurgy, and in particular to a production process of large-scale ultra-low N stainless steel. Background Art

[0002] The development of high-efficiency coal-fired power generation technology towards high parameters (increasing the steam temperature and steam pressure of the steam turbine unit) can achieve the goal of improving power generation efficiency and reducing emissions. In order to achieve the high-parameter development of steam turbine units, it is also necessary to greatly increase the operating temperature of key components of steam turbine units (such as rotors and other components). However, the traditional 30Cr1Mo1V and Cr12 (COSTE) series steel grades can no longer meet the operating temperature requirements of the high-parameter development of steam turbine units. It is necessary to design new materials that are resistant to higher temperatures to adapt to the use requirements of high-parameter units; in this context, the new 9Cr-3W-3Co stainless steel material [1] This new type of stainless steel material came into being. It has excellent durability and fatigue resistance, and has the characteristics of high strength and high toughness, so it can be used for turbine rotor forgings that serve for a long time at 630°C.

[0003] At present, the B and N elements in the new 9Cr-3W-3Co stainless steel are mainly designed with high B and low N components, which can avoid the formation of large-sized inclusions and improve toughness and fatigue performance. Therefore, the general requirement for the N content of the new 9Cr-3W-3Co stainless steel is 0.006-0.014%. However, as a non-metallic element, the N element has a strong affinity with the Cr, Mn, V, Nb, Al, Ti and other elements in the new 9Cr-3W-3Co stainless steel and forms a relatively stable compound. The introduction of raw materials during the smelting process or the presence of nitrogen in the smelting process environment can easily lead to difficulty in removing N from the molten steel, which makes the N content of the new 9Cr-3W-3Co stainless steel prepared by the traditional smelting method maintained within the general requirement range. The upper limit area (0.010-0.014%) of the range is difficult to obtain, while it is difficult to obtain the lower limit area (0.006-0.010%) where the N content is maintained within the general required range, and it is also difficult to meet the design purpose of low N of the new 9Cr-3W-3Co stainless steel material; reducing the N element brought into the smelting raw materials means that the higher the requirements for the smelting raw materials, the higher the production cost will be, and the traditional vacuum smelting is difficult to overcome the affinity between the N element and other metal elements. Therefore, the new 9Cr-3W-3Co stainless steel material with a N content of less than 0.010wt% is still in the research stage. It is still challenging to improve the production process of the new 9Cr-3W-3Co stainless steel material to solve the problem of further removing N from the new 9Cr-3W-3Co stainless steel material and smelting it in large quantities.

[0004] In the prior art, CN116716545A discloses a martensitic heat-resistant steel and its preparation method and application. The specific implementation method of the specification discloses a preparation method of a martensitic heat-resistant steel ingot containing Cr, Mn, V, Nb, Al, Ti and N content of 0.06-0.014%, which is: determine the raw material ratio according to the mass percentage of each element, and cast it into a 500kg steel ingot after vacuum induction melting and protective atmosphere electroslag remelting, and strictly control the content of impurity elements. This method controls the content of B, Zr, and N elements to avoid the formation of large-sized inclusions and improve toughness and fatigue resistance. However, the N content in the martensitic heat-resistant steel products provided in Examples 1-11 is ≥0.097%, which is still difficult to achieve the design requirement of maintaining the N content in the lower limit area (0.006-0.010%) of the general required range. Summary of the invention

[0005] The invention provides a production method of large ultra-low N stainless steel, which realizes the denitrification control of molten steel and can produce large ultra-low N stainless steel electroslag remelting ingots with a N content of less than 0.010%.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] A production process of large ultra-low N stainless steel, the chemical element composition and content of the large ultra-low N stainless steel are:

[0008] C 0.11~0.15wt%;Mn 0.30~0.60wt%;P≤0.010wt%;S≤0.002wt%;Si≤0.10wt%;Cr 8.5~10.5wt%;Ni≤0.10wt%;N≤0.014wt%;Mo 0.5~1.60wt%;Co 1.00~4.00wt%;W 0.30~4.00wt%;Al≤0.010wt%;O≤15ppm;Ti≤0.010wt%;Nb 0.04~0.06wt%;V 0.15~0.25wt%;B 0.0030~0.030wt%;As≤0.010wt%;Sn≤0.007wt%;Sb≤0.0015wt%;the balance is iron and unavoidable impurities;

[0009] The production process comprises the following steps:

[0010] 1) Internal control component design:

[0011] The chemical element composition and content of the internal control components of large ultra-low N stainless steel are: C 0.11-0.12wt%; Mn 0.30-0.40wt%; P≤0.010wt%; S≤0.002wt%; Si≤0.10wt%; Cr 8.60-9.10wt%; Ni≤0.10wt%; N≤0.010wt%; Mo 1.10-1.40wt%; Co 2.00-3.50wt%; W 1.50-2.50wt%; Al≤0.010wt%; O≤15ppm; Ti≤0.010wt%; Nb 0.04-0.06wt%; V 0.15-0.25wt%; B 0.010-0.018wt%; the balance is iron and unavoidable impurities;

[0012] 2) Electric furnace primary smelting:

[0013] The carbon steel material is used for primary smelting and strong oxygen blowing and carbon injection treatment is performed to obtain molten steel;

[0014] Among them, the ingredient requirements of carbon steel materials are: Ni≤0.08wt%, As≤0.008wt%, Sn≤0.006wt%, Sb≤0.0012wt%;

[0015] The composition control requirements of molten steel: C≤0.04wt%, P≤0.0015wt%, N≤0.050wt%;

[0016] 3) Ladle refining:

[0017] Step 2) the molten steel initially refined in the electric furnace enters the ladle refining furnace for ladle refining, and the N content of the tapped molten steel is adjusted to be less than 0.008 wt%;

[0018] The specific method of ladle refining is:

[0019] 3.1) Slag making:

[0020] Step 2) the molten steel from the primary refining in the electric furnace enters the ladle refining furnace, and slag is made with lime and fluorite to control the thickness of the slag layer and the basicity of the molten steel;

[0021] 3.2) Diffusion deoxidation:

[0022] Step 2) The molten steel from the primary refining in the electric furnace enters the ladle refining furnace, and a diffusion deoxidizer is added to the molten steel every 10 to 30 minutes for diffusion deoxidation;

[0023] 3.3) Alloying treatment:

[0024] When the slag color is gray or off-white after the slag making in step 3.1) is completed and the diffusion deoxidation process in step 3.2) is in progress, the alloy raw materials of the alloy components are added in batches to the ladle refining furnace to perform multiple alloying treatments, provided that the upper limit value or target value of the alloy components in the internal control components is not exceeded and the upper limit value of the restricted residual elements in the internal control components is not exceeded;

[0025] Wherein, the alloy components are C, Cr, Mn, Mo, Co, W, Nb and V;

[0026] The limiting residual elements are Si, P, S, As, Sn, Sb and Cu;

[0027] 3.4) Vacuum refining treatment:

[0028] Step 3.3) During the alloying process, a VD vacuum refining process may be performed before or after each alloying process, and a VD vacuum refining process must be performed after the last alloying process;

[0029] After the last VD vacuum refining treatment, samples were taken to analyze the N content;

[0030] When N≤0.008wt%, step 3.3) alloying treatment and step 3.4) VD vacuum refining treatment are completed;

[0031] When N>0.008wt%, repeat step 3.3) alloying treatment to step 3.4) VD vacuum refining until N≤0.008wt%;

[0032] 3.5) Microalloying treatment:

[0033] According to the component analysis result of the last VD vacuum refining treatment in step 3.4), alloy raw materials are added to the molten steel for micro-alloying treatment to adjust the contents of all components of the molten steel to be between the upper limit and / or lower limit of the internal control components, and the steel is tapped after the temperature of the molten steel meets the tapping requirements;

[0034] 4) Pouring:

[0035] Step 3) The molten steel refined from the ladle is cast in a fully sealed and protected manner to obtain an electrode blank;

[0036] Wherein, the oxygen concentration is controlled to be ≤4400ppm during the fully sealed protection pouring process;

[0037] The nitrogen content of the whole process of fully sealed protection casting is controlled within ≤0~10ppm;

[0038] 5) Electroslag remelting:

[0039] Step 4) The cast electrode blank is electroslag remelted in a protective atmosphere electroslag remelting furnace based on the five-element slag system components to obtain a large ultra-low N stainless steel ingot.

[0040] In the production process of large ultra-low N stainless steel of the present invention, the interaction coefficients of each chemical element of large ultra-low N stainless steel and N are The statistics are shown in Table 1:

[0041] Table 1

[0042] element Al B C Cr Co Cu Action coefficient -0.028 0.094 0.13 -0.047 0.011 0.009 element Mn Mo Ni Nb 0 P Action coefficient -0.021 -0.011 0.01 -0.06 0.05 0.045 element S Si Ti V W Zr Action coefficient 0.007 0.047 -0.53 -0.093 -0.0015 -0.63

[0043] In large ultra-low N stainless steel, the theoretical solubility of N element at 1600°C is calculated using the formula shown in Formula 3:

[0044]

[0045] in, It is expressed as the interaction coefficient between N and other chemical elements of large ultra-low N stainless steel, selected from Table 1; [J%] is expressed as the content of each chemical element in Table 1 in large ultra-low N stainless steel;

[0046] According to the interaction coefficients of each chemical element in Table 1 The content range of each chemical element in the large ultra-low N stainless steel is about 1020-1331 ppm (0.1020-0.1331 wt%) at a smelting temperature of 1600° C. Therefore, based on the prior art, all raw materials for smelting large ultra-low N stainless steel are added into a furnace for vacuum smelting, which is difficult to overcome the interaction between other chemical elements and N element in the molten steel, and it is also difficult to achieve the purpose of lowering the N content (≤0.010 wt%) of the large ultra-low N stainless steel. In view of this, in the production process of the large ultra-low N stainless steel of the present invention, the carbon steel material is firstly smelted in an electric furnace, and at the same time, strong oxygen blowing and carbon spraying are coordinated to remove P, remove C and degas, and the C in the molten steel smelted in the electric furnace is controlled to be ≤0.04 wt%, P ≤0.001 5wt%, N≤0.050wt%; multiple alloying treatments are performed during the ladle refining process in the ladle furnace, so that the solubility of N in the molten steel is gradually increased in batches, and VD vacuum refining is performed before or after each alloying treatment to further reduce the N content in the molten steel, so that the N content in the molten steel can be controlled below 0.0080wt% (ingot≤0.010%); microalloying is performed in the ladle refining furnace, and the pouring process is fully sealed and protected (the increase in N is controlled at ≤0-10ppm), and the electroslag remelting process is fully argon protected (the increase in N is controlled at ≤10ppm). Although the N content in the molten steel is inevitably increased to a certain extent, it is ultimately possible to obtain a large ultra-low N stainless steel ingot with a N content of less than 0.010wt%.

[0047] In a specific embodiment of the present invention, step 2) electric furnace primary smelting, the basicity of the molten steel is controlled to be 3-8 during the primary smelting process.

[0048] In a specific embodiment of the present invention, in step 2) electric furnace primary refining, the specific parameters of the strong oxygen blowing carbon spraying treatment are: oxygen pressure 0.6-1.2MPa, oxygen flow rate 1000-2500m 3 / h; carbon powder dosage 15 ~ 50kg / min; oxygen lance inserted into the slag layer ≥ 30mm, and the angle with the horizontal plane is 20 ~ 50°.

[0049] In a specific embodiment of the present invention, in step 3.1), slag is formed, and the thickness of the slag layer is controlled to be 200-450 mm, and the basicity is controlled to be 3-6.

[0050] In a specific embodiment of the present invention, step 3.2) diffusion deoxidation, the diffusion deoxidizer is made of carbon powder and calcium silicon powder in a mass ratio of 3:2, and the single dosage of the diffusion deoxidizer is 5 to 30 kg.

[0051] In a specific embodiment of the present invention, step 3.3) alloying treatment, the multiple alloying treatments are specifically:

[0052] 3.3.1) Primary alloying: adding Cr alloy for primary alloying, controlling the Cr content in the molten steel to 0-3wt%;

[0053] 3.3.2) Secondary alloying: adding Cr alloy, Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and V alloy for secondary alloying, controlling the Cr content in the molten steel to 5-7wt%, and controlling other alloy components in the molten steel not to exceed the upper limit value or target value of the internal control component;

[0054] 3.3.3) Three-stage alloying: Add Cr alloy, Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and / or V alloy for three-stage alloying to control all alloy components in the molten steel to be between the upper limit and lower limit of the internal control components, or control all alloy components in the molten steel to meet the target value requirements.

[0055] In a specific embodiment of the present invention, step 3.4) vacuum refining treatment, the parameters of the VD vacuum refining treatment include vacuum degree, refining argon blowing, vacuum refining temperature T 精 and vacuum refining time τ;

[0056] The vacuum degree is ≤400Pa;

[0057] The argon flow rate of the refining argon blowing is 50-200 L / min, and the argon pressure is 0.2-1.0 MPa;

[0058] The vacuum refining temperature T 精 It is calculated by the following formula:

[0059] Formula 1: T 精 =T 溶 +Δt+K1τ;

[0060] Among them, T 熔 It is the melting point of the molten steel in the ladle refining furnace, ℃; Δt is the superheat, which is 60-80℃; τ is the vacuum refining time, min; K1 is the heat dissipation coefficient of the ladle, which is 0.7-2.5;

[0061] The vacuum refining time τ is calculated by the following formula 2:

[0062] Formula 2: τ = K2V / S;

[0063] Where K2 is a coefficient with a value of 0.5 to 3.5; V is the volume of the ladle refining furnace, m 3 ; S represents the pumping rate, m 3 / min.

[0064] In a specific embodiment of the present invention, step 3.5) microalloying treatment, argon gas is introduced during the microalloying treatment to control the flow rate of argon gas so as to blow the slag surface with a diameter of ≤400mm; the temperature of the molten steel for tapping is determined by 50 to 90°C above the melting point of the molten steel in the ladle refining furnace.

[0065] In a specific embodiment of the present invention, in step 5) electroslag remelting, the components and contents of the five-component slag system are: CaF2 50-65wt%, Al2O3 15-25wt%, CaO 5-20wt%, SiO2 0-2.0wt%, B2O3 0-3wt%.

[0066] In a specific embodiment of the present invention, in step 5) electroslag remelting, the protective atmosphere is argon with an oxygen concentration of ≤800 ppm.

[0067] The beneficial effects of the present invention are:

[0068] 1. The present invention solves the problem of low N content in 9Cr-3W-3Co new stainless steel. By controlling the N content to below 0.010wt%, it is beneficial to achieve better toughness and fatigue performance of 9Cr-3W-3Co new stainless steel.

[0069] 2. The present invention overcomes the problem that other elements have strong interactions with N elements during the smelting process of the new 9Cr-3W-3Co stainless steel material, resulting in difficulty in removing N. Multiple alloying treatments and vacuum refining are carried out in the ladle refining furnace, which is conducive to removing N. Compared with the prior art, the production of large-scale ultra-low N stainless steel ingots with a N content of ≤0.010wt%, especially the production of large-scale ultra-low N stainless steel ingots with a N content of <0.0080wt%, is achieved. DETAILED DESCRIPTION

[0070] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0071] A production process of large ultra-low N stainless steel, the chemical element composition and content of large ultra-low N stainless steel are:

[0072] C 0.11~0.15wt%; Mn 0.30~0.60wt%; P≤0.010wt%; S≤0.002wt%;

[0073] Si≤0.10wt%;Cr 8.5~10.5wt%;Ni≤0.10wt%;N≤0.014wt%;Mo 0.5~1.60wt%;Co 1.00~4.00wt%;W 0.30~4.00wt%;Al≤0.010wt%;O≤15ppm;Ti≤0.010wt%;Nb 0.04~0.06wt%;V 0.15~0.25wt%;B 0.0030~0.030wt%;As≤0.010wt%;Sn≤0.007wt%;Sb≤0.0015wt%;the balance is iron and unavoidable impurities;

[0074] In order to realize the production of the aforementioned large ultra-low N stainless steel ingot, the production process includes the following steps:

[0075] 1) Internal control component design:

[0076] The chemical element composition and content of the internal control components of large ultra-low N stainless steel are: C 0.11-0.12wt%; Mn 0.30-0.40wt%; P≤0.010wt%; S≤0.002wt%; Si≤0.10wt%; Cr 8.60-9.10wt%; Ni≤0.10wt%; N≤0.010wt%; Mo 1.10-1.40wt%; Co 2.00-3.50wt%; W 1.50-2.50wt%; Al≤0.010wt%; O≤15ppm; Ti≤0.010wt%; Nb 0.04-0.06wt%; V 0.15-0.25wt%; B 0.010-0.018wt%; the balance is iron and unavoidable impurities;

[0077] 2) Electric furnace primary smelting:

[0078] The carbon steel material is used for primary smelting and strong oxygen blowing and carbon injection treatment is performed to obtain molten steel;

[0079] Among them, the ingredient requirements of carbon steel materials are: Ni≤0.08wt%, As≤0.008wt%, Sn≤0.006wt%, Sb≤0.0012wt%;

[0080] The composition control requirements of molten steel: C≤0.04wt%, P≤0.0015wt%, N≤0.050wt%;

[0081] 3) Ladle refining:

[0082] Step 2) the molten steel initially refined in the electric furnace enters the ladle refining furnace for ladle refining, and the N content of the tapped molten steel is adjusted to be less than 0.008 wt%;

[0083] The specific method of ladle refining is:

[0084] 3.1) Slag making:

[0085] Step 2) the molten steel from the primary refining in the electric furnace enters the ladle refining furnace, and slag is made with lime and fluorite to control the thickness of the slag layer and the basicity of the molten steel;

[0086] 3.2) Diffusion deoxidation:

[0087] Step 2) The molten steel from the primary refining in the electric furnace enters the ladle refining furnace, and a diffusion deoxidizer is added to the molten steel every 10 to 30 minutes for diffusion deoxidation;

[0088] 3.3) Alloying treatment:

[0089] When the slag color is gray or off-white after the slag making in step 3.1) is completed and the diffusion deoxidation process in step 3.2) is in progress, the alloy raw materials of the alloy components are added in batches to the ladle refining furnace to perform multiple alloying treatments, provided that the upper limit value or target value of the alloy components in the internal control components is not exceeded and the upper limit value of the restricted residual elements in the internal control components is not exceeded;

[0090] Wherein, the alloy components are Cr, Mn, Mo, Co, W, Nb and V;

[0091] The limiting residual elements Si, P, S, As, Sn, Sb and Cu;

[0092] 3.4) Vacuum refining treatment:

[0093] Step 3.3) During the alloying process, a VD vacuum refining process may be performed before or after each alloying process, and a VD vacuum refining process must be performed after the last alloying process;

[0094] After the last VD vacuum refining treatment, samples were taken to analyze the N content;

[0095] When N≤0.008wt%, step 3.3) alloying treatment and step 3.4) VD vacuum refining treatment are completed;

[0096] When N>0.008wt%, repeat step 3.3) alloying treatment to step 3.4) VD vacuum refining until N≤0.008wt%;

[0097] 3.5) Microalloying treatment:

[0098] According to the component analysis result of the last VD vacuum refining treatment in step 3.4), alloy raw materials are added to the molten steel for micro-alloying treatment to adjust the contents of all components of the molten steel to be between the upper limit and / or lower limit of the internal control components, and the steel is tapped after the temperature of the molten steel meets the tapping requirements;

[0099] 4) Pouring:

[0100] Step 3) The molten steel refined from the ladle is cast in a fully sealed and protected manner to obtain an electrode blank;

[0101] Wherein, the oxygen concentration is controlled to be ≤4000ppm during the fully sealed protective pouring process; the N increase during the entire fully sealed protective pouring process is controlled to be ≤0-10ppm;

[0102] 5) Electroslag remelting:

[0103] Step 4) The cast electrode blank is electroslag remelted in a protective atmosphere electroslag remelting furnace based on the five-element slag system components to obtain a large ultra-low N stainless steel ingot; the N increase in the entire electroslag remelting process is controlled to be ≤10ppm.

[0104] In some examples, step 2) electric furnace primary smelting is performed, and the basicity of the molten steel is controlled to be 3-8 during the primary smelting process.

[0105] In some examples, in step 2) electric furnace primary refining, the specific parameters of the strong oxygen blowing carbon spraying treatment are: oxygen pressure 0.6-1.2MPa, oxygen flow rate 1000-2500m 3 / h; carbon powder dosage 15 ~ 50kg / min; oxygen lance inserted into the slag layer ≥ 30mm, and the angle with the horizontal plane is 20 ~ 50°.

[0106] In some examples, in step 3.1), slag is formed, and the thickness of the slag layer is controlled to be 200-450 mm, and the basicity is controlled to be 3-6.

[0107] In some examples, step 3.2) diffusion deoxidation, the diffusion deoxidizer is made of carbon powder and calcium silicon powder in a mass ratio of 3:2, and the single dosage of the diffusion deoxidizer is 5 to 30 kg.

[0108] In some examples, step 3.3) alloying treatment, the multiple alloying treatments are specifically:

[0109] 3.3.1) Primary alloying: adding Cr alloy for primary alloying, controlling the Cr content in the molten steel to 0-3wt%;

[0110] 3.3.2) Secondary alloying: adding Cr alloy, Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and V alloy for secondary alloying, controlling the Cr content in the molten steel to 5-7wt%, and controlling other alloy components in the molten steel not to exceed the upper limit value or target value of the internal control component;

[0111] 3.3.3) Three-stage alloying: Add Cr alloy, Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and / or V alloy for three-stage alloying to control all alloy components in the molten steel to be between the upper limit and lower limit of the internal control components, or control all alloy components in the molten steel to meet the target value requirements.

[0112] In some examples, step 3.4) vacuum refining treatment, the parameters of the VD vacuum refining treatment include vacuum degree, refining argon blowing, vacuum refining temperature T 精 and vacuum refining time τ;

[0113] The vacuum degree is ≤400Pa;

[0114] The argon flow rate of the refining argon blowing is 50-200 L / min, and the argon pressure is 0.2-1.0 MPa;

[0115] The vacuum refining temperature T 精 It is calculated by the following formula:

[0116] Formula 1: T 精 =T 熔 +Δt+K1τ;

[0117] Among them, T 熔 It is the melting point of the molten steel in the ladle refining furnace, ℃; Δt is the superheat, which is 60-80℃; τ is the vacuum refining time, min; K1 is the heat dissipation coefficient of the ladle, which is 0.7-2.5;

[0118] The vacuum refining time τ is calculated by the following formula 2:

[0119] Formula 2: τ = K2V / S;

[0120] Where K2 is a coefficient with a value of 0.5 to 3.5; V is the volume of the ladle refining furnace, m 3 ; S represents the pumping rate, m 3 / min.

[0121] In some examples, step 3.5) microalloying treatment is performed, wherein argon is introduced during the microalloying treatment to control the flow rate of argon so as to blow through the slag surface with a diameter of ≤400 mm; and the temperature of the molten steel at the tapping is determined by being 50 to 90° C. above the melting point of the molten steel in the ladle refining furnace.

[0122] In some examples, in step 5) electroslag remelting, the components and contents of the five-component slag system are: CaF2 50-65wt%, Al2O3 15-25wt%, CaO 5-20wt%, SiO2 0-2.0wt%, B2O 30-3wt%.

[0123] In some examples, in step 5) electroslag remelting, the protective atmosphere is argon with an oxygen concentration of ≤800 ppm.

[0124] To further demonstrate the effect of the production process of the present invention in nitrogen removal, the following examples are provided:

[0125] Example 1

[0126] This embodiment provides a production process of large-scale ultra-low N stainless steel, comprising the following steps:

[0127] 1. Internal control component design

[0128] The chemical element composition and content of the internal control components of large ultra-low N stainless steel are: C 0.11-0.12wt%; Mn 0.30-0.40wt%; P≤0.010wt%; S≤0.002wt%; Si≤0.10wt%; Cr 8.60-9.10wt%; Ni≤0.10wt%; N≤0.010wt%; Mo 1.10-1.40wt%; Co 2.00-3.50wt%; W 1.50-2.50wt%; Al≤0.010wt%; 0≤15ppm; Ti≤0.010wt%; Nb 0.04-0.06wt%; V 0.15-0.25wt%; B 0.010-0.018wt%; the balance is iron and unavoidable impurities;

[0129] 2. Primary smelting in electric furnace

[0130] In order to produce about 100t large ultra-low N stainless steel ingots, carbon steel material is used as the material, and the requirements of carbon steel material are: Ni≤0.08wt%, As≤0.008wt%, Sn≤0.006wt%, Sb≤0.0012wt%; the carbon steel material is smelted in an electric furnace, the basicity of the slag is controlled at 3-5, and strong oxygen blowing and carbon spraying are carried out; the operating parameters of the strong oxygen blowing and carbon spraying treatment are as follows: oxygen pressure 0.6-0.7MPa, flow rate set to 1000-1200m 3 / h, carbon powder dosage 15 ~ 20kg / min; oxygen lance inserted into the slag layer depth ≥ 30mm, maintain an angle of 20 ~ 50° with the liquid surface, strengthen the stirring of the molten steel in the furnace;

[0131] The output of steel from the electric furnace is 100t, and the composition and content of the steel are shown in Table 2.

[0132] Table 2

[0133] Element C Si Mn P S Cr Content / wt% 0.035 ≤0.01 0.05 0.0015 0.005 ≤2.00 Element Ni Mo V W Co N Content / wt% ≤0.05 ≤1.10 0.01 ≤1.50 ≤2.00 0.02

[0134] 3. Ladle refining

[0135] Ladle refining is carried out in a ladle refining furnace, including slag making - primary alloying - primary VD vacuum refining - secondary alloying - secondary VD vacuum refining - tertiary alloying - tertiary VD vacuum refining - microalloying - steel tapping;

[0136] Slag making: When the molten steel enters the ladle refining furnace, lime and fluorite are used for slag making. The thickness of the slag layer is controlled at 300mm and the basicity is controlled at about 4.5. Carbon powder and calcium silicon powder are mixed in a mass ratio of 3:2 to make a diffusion deoxidizer for diffusion deoxidation. 5 to 30 kg of diffusion deoxidizer is added to the molten steel every 10 to 30 minutes. In the early stage of ladle refining, the amount of diffusion deoxidizer added is 30 kg, and then as the ladle refining proceeds, the single amount of diffusion deoxidizer is reduced according to the slag color and Si content in the composition, until the amount of diffusion deoxidizer is 5 kg in the later stage of ladle refining.

[0137] First alloying: Based on the Cr content of 2wt% in the molten steel, 3.3t of ferrochrome was added into the ladle refining furnace for the first alloying treatment;

[0138] The first VD vacuum refining: the molten steel subjected to the first alloying treatment is subjected to the first VD vacuum refining, with the vacuum degree controlled at ≤400Pa, the temperature at 1650°C, and the time at 30min; after the first VD vacuum refining, the N content in the molten steel is 0.0145wt%.

[0139] Second alloying: According to the requirement that the Cr content in the molten steel is 5wt% and other alloying elements meet the upper limit of the internal control composition, ferrochrome and Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and V alloy totaling 10.5t are added to the molten steel after the first VD vacuum refining for the second alloying treatment; after the second alloying treatment, the composition and content of the molten steel are shown in Table 3:

[0140] Table 3

[0141] Element C Si Mn P S Cr Content / wt% 0.06 0.04 0.25 0.004 0.003 5.01 Element Ni Mo V W Co N Content / wt% 0.07 0.92 0.15 1.80 2.0 0.02

[0142] It can be seen from Table 3 that after the second alloying treatment, the N content in the molten steel has reached 0.02wt%. The N content in the molten steel can be increased during the alloying process.

[0143] Second VD vacuum refining: The molten steel after the second alloying treatment is subjected to second VD vacuum refining, with the vacuum degree controlled at ≤400Pa, the temperature at 1660°C, and the time at 35min; after the second VD vacuum refining, the N content in the molten steel is 0.0098wt%.

[0144] Third alloying: A total of 9.8t of Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and V alloy were added to the molten steel after the second VD vacuum refining for the third alloying treatment, so that all alloy components reached the range of internal control components; after the third alloying treatment, the composition and content of the molten steel are shown in Table 4.

[0145] Table 4

[0146] Element C Si Mn P S Cr Content / wt% 0.08 0.07 0.35 0.006 0.002 8.95 Element Ni Mo V W Co N Content / wt% 0.08 1.20 0.18 1.80 2.60 0.011

[0147] The third VD vacuum refining: the molten steel after the third alloying treatment is subjected to the third VD vacuum refining, with the vacuum degree controlled at ≤400Pa, the temperature at 1670°C, and the time at 35min; after the third VD vacuum refining, the N content in the molten steel is 0.0065wt%.

[0148] Microalloying: Control the argon flow rate to 25L / min or determine the argon flow rate by blowing the slag surface with a diameter of about 400mm. Microalloy the molten steel from the third VD vacuum refining, including: adjusting the B content with B alloy; accurately controlling C with carbonaceous materials; adding a total of 0.09t of alloy to make the content of all elements in the molten steel within the internal control range.

[0149] Steel is tapped when the temperature of the molten steel reaches the melting point of the molten steel + (50-90)°C, and the total amount of molten steel tapped is 124.5t.

[0150] The composition and content of the molten steel after microalloying are shown in Table 5:

[0151] Table 5

[0152] Element C Si Mn P S Cr Content / wt% 0.12 0.07 0.35 0.007 0.002 8.95 Element Ni Mo V W Co N Content / wt% 0.08 1.20 0.18 1.80 2.60 0.0066

[0153] 4. Pouring: Use a sealed center pouring pipe to achieve fully sealed protection pouring of the steel pouring flow; pour the micro-alloyed molten steel, and during the pouring process, control the oxygen concentration to ≤4000ppm; the electrode blank after pouring is finished, about 103t.

[0154] Samples were taken from the electrode blank to test the composition and content. The results are shown in Table 6:

[0155] Table 6

[0156] Element C Si Mn P S Cr Content / wt% 0.12 0.07 0.36 0.007 0.002 8.94 Element Ni Mo V W Co N Content / wt% 0.08 1.21 0.18 1.82 2.61 0.0076

[0157] 5. Electroslag remelting: 103t electrode billet was electroslag remelted, and the five-element slag system composition adopted was: 55.2CaF2-25Al2O3-15CaO-2SiO2-2.8B2O3. The electroslag remelting was carried out under full argon protection with an oxygen concentration of ≤700ppm. The weight of the steel ingot obtained by electroslag remelting was 100t.

[0158] Samples were taken from the steel ingot after electroslag remelting, and the composition and content statistics are shown in Table 7:

[0159] Table 7

[0160] Element C Si Mn P S Cr Content / wt% 0.12 0.06 0.35 0.007 0.002 8.96 Element Ni Mo V W Co N Content / wt% 0.08 1.19 0.17 1.79 2.62 0.0078

[0161] According to the experimental results of this embodiment, it can be seen that multiple alloying and multiple VD vacuum refining are beneficial to the removal of nitrogen from the molten steel, and a large-scale ultra-low N stainless steel electroslag remelting ingot with a N content of less than 0.010wt% can be produced and obtained, which provides a basis for achieving the design purpose of low N in the new 9Cr-3W-3Co stainless steel material. In addition, the obtained large-scale ultra-low N stainless steel ingot is used to manufacture key components of the steam turbine unit, which is beneficial to the high-parameter development of the steam turbine unit.

[0162] Example 2

[0163] This embodiment provides a production process of large-scale ultra-low N stainless steel, comprising the following steps:

[0164] 1. Internal control component design

[0165] The chemical element composition and content of the internal control components of large ultra-low N stainless steel are: C 0.125-0.145wt%; Mn 0.0.35-0.45wt%; P≤0.010wt%; S≤0.002wt%; Si≤0.10wt%; Cr 8.90-9.40wt%; Ni≤0.15wt%; N≤0.010wt%; Mo1.30-1.60wt%; Co 2.50-3.50wt%; W 1.50-2.50wt%; Al≤0.010wt%; 0≤15ppm; Ti≤0.010wt%; Nb0.04-0.06wt%; V 0.15-0.25wt%; B0.008-0.012wt%; the balance is iron and unavoidable impurities;

[0166] 2. Primary smelting in electric furnace

[0167] In order to produce about 50t large ultra-low N stainless steel ingots, carbon steel material is used as the raw material. The requirements of carbon steel material are: Ni≤0.08wt%, As≤0.008wt%, Sn≤0.006wt%, Sb≤0.0012wt%; the carbon steel material is smelted in an electric furnace, the basicity of the slag is controlled at 4-6, and strong oxygen blowing and carbon spraying are carried out; the operating parameters of the strong oxygen blowing and carbon spraying treatment are as follows: oxygen pressure 0.6-0.7MPa, flow rate set to 800-1000m 3 / h, carbon powder dosage 15 ~ 20kg / min; oxygen lance inserted into the slag layer depth ≥ 30mm, maintain an angle of 20 ~ 35° with the liquid surface, strengthen the stirring of the molten steel in the furnace;

[0168] The output of steel from the electric furnace is 47.2t. The composition and content of the steel are shown in Table 8.

[0169] Table 8

[0170] Element C Si Mn P S Cr Content / wt% 0.030 ≤0.01 0.04 0.0015 0.003 0.011 Element Ni Mo V W Co N Content / wt% 0.06 0.07 0.01 0.001 0.001 0.019

[0171] 3. Ladle refining

[0172] Ladle refining is carried out in a ladle refining furnace, including slag making - primary alloying - primary VD vacuum refining - secondary alloying - secondary VD vacuum refining - microalloying - steel tapping;

[0173] Slag making: When the molten steel enters the ladle refining furnace, lime and fluorite are used for slag making. The thickness of the slag layer is controlled at 250mm and the basicity is controlled at about 4.0. Carbon powder and calcium silicon powder are mixed in a mass ratio of 3:2 to make a diffusion deoxidizer for diffusion deoxidation. 5 to 30 kg of diffusion deoxidizer is added to the molten steel every 10 to 30 minutes. In the early stage of ladle refining, the amount of diffusion deoxidizer added is 30 kg, and then as the ladle refining proceeds, the single amount of diffusion deoxidizer is reduced according to the slag color and the Si content in the molten steel, until the amount of diffusion deoxidizer used in the later stage of ladle refining is 5 kg.

[0174] First alloying: Based on the Cr content of 2wt% in the molten steel, 2.1t of ferrochrome was added to the ladle refining furnace for the first alloying treatment; the N content in the molten steel was 0.0215%, and its composition and content are specifically shown in Table 9.

[0175] Table 9

[0176] Element C Si Mn P S Cr Content / wt% 0.05 0.02 0.03 0.002 0.003 2.49 Element Ni Mo V W Co N Content / wt% 0.05 0.06 0.01 0.001 0.002 0.0215

[0177] First VD vacuum refining: The molten steel after the first alloying treatment is subjected to the first VD vacuum refining, with the vacuum degree controlled at ≤400Pa, the temperature at 1650°C, and the time at 30min; after the first VD vacuum refining, the N content in the molten steel is 0.0120wt%.

[0178] Second alloying: According to the requirement that the Cr content in the molten steel is 9.30wt% and other alloying elements meet the internal control composition, ferrochrome and Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and V alloy totaling 13.5t are added to the molten steel for the second alloying treatment; after the second alloying treatment, the composition and content of the molten steel are shown in Table 10:

[0179] Table 10

[0180] Element C Si Mn P S Cr Content / wt% 0.10 0.06 0.40 0.006 0.002 9.30 Element Ni Mo V W <![CDATA[C o ]]> N Content / wt% 0.08 1.50 0.20 2.2 3.2 0.0155

[0181] It can be seen from Table 10 that after the second alloying treatment, the N content in the molten steel has reached 0.0155wt%. The N content in the molten steel can be increased during the alloying process.

[0182] Second VD vacuum refining: The molten steel after the second alloying treatment is subjected to second VD vacuum refining, with the vacuum degree controlled at ≤400Pa, the temperature at 1660°C, and the time at 32min; after the second VD vacuum refining, the N content in the molten steel is 0.0075wt%.

[0183] Microalloying: Control the argon flow rate to 25L / min or determine the argon flow rate by blowing the slag surface with a diameter of about 400mm. Microalloy the molten steel from the second VD vacuum refining, including: adjusting the B content with B alloy; accurately controlling C with carbonaceous materials; adding a total amount of 0.06t of alloy to make the content of all elements in the molten steel within the internal control range.

[0184] Steel is tapped when the temperature of the molten steel reaches the melting point of the molten steel + (50-90)°C. The total amount of alloy added for microalloying is 0.06t; the total amount of molten steel tapped is approximately 62.9t.

[0185] The composition and content of the molten steel after microalloying treatment are shown in Table 11:

[0186] Table 11

[0187] Element C Si Mn P S Cr Content / wt% 0.13 0.07 0.35 0.007 0.002 9.29 Element Ni Mo V W Co N Content / wt% 0.08 1.51 0.19 2.22 3.18 0.0078

[0188] 4. Pouring: Use a sealed center pouring pipe to achieve fully sealed protection pouring of the steel pouring flow; pour the micro-alloyed molten steel, and during the pouring process, control the oxygen concentration to ≤4000ppm; the electrode blank after pouring is finished, about 52t.

[0189] Samples were taken from the electrode blank to test the composition and content. The results are shown in Table 12:

[0190] Table 12

[0191] Element C Si Mn P S Cr Content / wt% 0.13 0.07 0.36 0.006 0.002 9.31 Element Ni Mo V W Co N Content / wt% 0.08 1.50 0.20 2.19 3.20 0.0089

[0192] 5. Electroslag remelting: 52t electrode billet was electroslag remelted, and the five-element slag system composition adopted was: 55.2CaF2-25Al2O3-15CaO-2SiO2-2.8B2O3. The electroslag remelting was carried out under full argon protection with an oxygen concentration of ≤700ppm. The weight of the steel ingot obtained by electroslag remelting was 50t.

[0193] Samples were taken from the steel ingot after electroslag remelting, and the composition and content statistics are shown in Table 13:

[0194] Table 13

[0195] Element C Si Mn P S Cr Content / wt% 0.13 0.06 0.34 0.007 0.001 9.28 Element Ni Mo V W Co N Content / wt% 0.08 1.49 0.19 2.19 3.21 0.0093

[0196] According to the experimental results of this embodiment, it can be seen that multiple alloying and multiple VD vacuum refining are beneficial to the removal of nitrogen from the molten steel, and a large-scale ultra-low N stainless steel electroslag remelting ingot with a N content of less than 0.010wt% can be produced and obtained, which provides a basis for achieving the design purpose of low N in the new 9Cr-3W-3Co stainless steel material. In addition, the obtained large-scale ultra-low N stainless steel ingot is used to manufacture key components of the steam turbine unit, which is beneficial to the high-parameter development of the steam turbine unit.

[0197] Example 3

[0198] This embodiment provides a production process of large-scale ultra-low N stainless steel, comprising the following steps:

[0199] 1. Internal control component design

[0200] The chemical element composition and content of the internal control components of large ultra-low N stainless steel are: C 0.12-0.13wt%; Mn 0.30-0.35wt%; P≤0.010wt%; S≤0.002wt%; Si≤0.10wt%; Cr 8.80-9.20wt%; Ni≤0.10wt%; N≤0.010wt%; Mo 1.10-1.40wt%; Co 2.00-2.90wt%; W 1.80-2.10wt%; Al≤0.010wt%; 0≤15ppm; Ti≤0.010wt%; Nb 0.04-0.06wt%; V 0.15-0.25wt%; B 0.008-0.018wt%; the balance is iron and unavoidable impurities;

[0201] 2. Primary smelting in electric furnace

[0202] In order to produce about 75t large ultra-low N stainless steel ingots, carbon steel material is used as the raw material. The requirements of carbon steel material are: Ni≤0.08wt%, As≤0.008wt%, Sn≤0.006wt%, Sb≤0.0012wt%; the carbon steel material is smelted in an electric furnace, the basicity of the slag is controlled at 4-6, and strong oxygen blowing and carbon spraying are carried out; the operating parameters of the strong oxygen blowing and carbon spraying treatment are as follows: oxygen pressure 0.6-0.7MPa, flow rate set to 1000-1200m 3 / h, carbon powder dosage 15 ~ 20kg / min; oxygen lance inserted into the slag layer depth ≥ 30mm, maintain an angle of 20 ~ 50° with the liquid surface, strengthen the stirring of the molten steel in the furnace;

[0203] The output of primary steelmaking in the electric furnace is 72.5t. The composition and content of the molten steel are shown in Table 14.

[0204] Table 14

[0205] Element C Si Mn P S Cr Content / wt% 0.03 ≤0.01 0.06 0.0015 0.005 0.15 Element Ni <![CDATA[M o ]]> V W Co N Content / wt% 0.05 0.08 0.01 0.001 0.001 0.017

[0206] 3. Ladle refining

[0207] Ladle refining is carried out in a ladle refining furnace, including slag making - primary VD vacuum refining - primary alloying - secondary VD vacuum refining - secondary alloying - tertiary VD vacuum refining - microalloying - steel tapping;

[0208] Slag making: When the molten steel enters the ladle refining furnace, lime and fluorite are used for slag making. The thickness of the slag layer is controlled at 300mm and the basicity is controlled at about 4.5. Carbon powder and calcium silicon powder are mixed in a mass ratio of 3:2 to make a diffusion deoxidizer for diffusion deoxidation. 5 to 30 kg of diffusion deoxidizer is added to the molten steel every 10 to 30 minutes. In the early stage of ladle refining, the amount of diffusion deoxidizer added is 30 kg, and then as the ladle refining proceeds, the single amount of diffusion deoxidizer is reduced according to the slag color and Si content in the composition, until the amount of diffusion deoxidizer is 5 kg in the later stage of ladle refining.

[0209] The first VD vacuum refining: the molten steel after slag making is subjected to the first VD vacuum refining, the vacuum degree is controlled to be ≤400Pa, the temperature is 16450°C, and the vacuum time is 22min; after the first VD vacuum refining, the N content in the molten steel is 0.0092wt%.

[0210] First alloying: alloying is performed according to the requirement that the Cr content in the molten steel is 6wt%, 8t of ferrochrome is added, and the molten steel after the first VD vacuum refining is subjected to the first alloying treatment; after the first alloying treatment, the composition and content of the molten steel are shown in Table 15:

[0211] Table 15

[0212] Element C Si Mn P S Cr Content / wt% 0.08 0.05 0.03 0.005 0.004 6.02 Element Ni Mo V W Co N Content / wt% 0.08 0.07 0.03 0.001 0.002 0.155

[0213] It can be seen from Table 15 that after the first alloying treatment, the N content in the molten steel has reached 0.0155wt%. The N content in the molten steel can be increased during the alloying process.

[0214] Second VD vacuum refining: The molten steel after the first alloying treatment is subjected to a second VD vacuum refining, with the vacuum degree controlled at ≤400 Pa, the temperature at 1660° C., and the time at 28 min. After the second VD vacuum refining, the N content in the molten steel is 0.0088 wt%.

[0215] Second alloying: A total of 13.6t of Cr alloy, Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and V alloy were added to the ladle refining furnace for the second alloying treatment, so that all alloy components were within the internal control range; after the second alloying treatment, the composition and content of the molten steel are shown in Table 16.

[0216] Table 16

[0217] Element C Si Mn P S Cr Content / wt% 0.11 0.07 0.33 0.007 0.002 9.15 Element Ni Mo V W Co N Content / wt% 0.09 1.3 0.20 2.00 2.60 0.0102

[0218] The third VD vacuum refining: the steel liquid subjected to the second alloying treatment is subjected to the third VD vacuum refining, with the vacuum degree controlled to be ≤400Pa, the temperature to be 1670°C, and the time to be 30min; after the third VD vacuum refining, the N content in the steel liquid is 0.0060wt%.

[0219] Microalloying: Control the argon flow rate to 25L / min or determine the argon flow rate by blowing the slag surface with a diameter of about 400mm. Microalloy the molten steel from the third VD vacuum refining, including: adjusting the B content with B alloy; accurately controlling C with carbonaceous materials; adding 0.08t of alloy to adjust the content of all elements in the molten steel to within the internal control range.

[0220] Steel is tapped when the temperature of the molten steel reaches the melting point of the molten steel + (50-90)°C, and the total amount of molten steel is 94.2t.

[0221] The composition and content of the molten steel after microalloying treatment are shown in Table 17:

[0222] Table 17

[0223] Element C Si Mn P S Cr Content / wt% 0.13 0.07 0.35 0.007 0.002 9.14 Element Ni Mo V W Co N Content / wt% 0.08 1.32 0.18 2.01 2.59 0.0056

[0224] 4. Pouring: Use a sealed center pouring pipe to achieve fully sealed protection pouring of the steel pouring flow; pour the micro-alloyed molten steel, and during the pouring process, control the oxygen concentration to ≤4000ppm; the electrode blank after pouring is finished, about 77t.

[0225] Samples were taken from the electrode blank to test the composition and content. The results are shown in Table 18:

[0226] Table 18

[0227]

[0228] 5. Electroslag remelting: 77t electrode billet was electroslag remelted, and the five-element slag system composition adopted was: 55.2CaF2-25Al2O3-15CaO-2SiO2-2.8B2O3. The electroslag remelting was carried out under full argon protection with an oxygen concentration of ≤700ppm. The weight of the steel ingot obtained by electroslag remelting was 75t.

[0229] Samples were taken from the steel ingot after electroslag remelting, and the composition and content statistics are shown in Table 19:

[0230] Table 19

[0231] Element C Si Mn P S Cr Content / wt% 0.13 0.06 0.35 0.007 0.002 9.15 Element Ni Mo V W Co N Content / wt% 0.08 1.29 0.20 1.99 2.62 0.0071

[0232] According to the experimental results of this embodiment, it can be seen that multiple alloying and multiple VD vacuum refining are beneficial to the removal of nitrogen from the molten steel, and a large-scale ultra-low N stainless steel electroslag remelting ingot with a N content of less than 0.010wt% can be produced and obtained, which provides a basis for achieving the design purpose of low N in the new 9Cr-3W-3Co stainless steel material. In addition, the obtained large-scale ultra-low N stainless steel ingot is used to manufacture key components of the steam turbine unit, which is beneficial to the high-parameter development of the steam turbine unit.

[0233] References:

[0234] [1]Qiu Jiajia, He Xikou, Tang Zhengduan, Huo Jie. Study on hot deformation behavior of new martensitic heat-resistant rotor steel C630R[J]. Special Steels, 2024, 45(03): 56-61.DOI: 10.20057 / j.1003-8620.2023-00220.

Claims

1. A production process for large-scale ultra-low N stainless steel, characterized in that: The chemical element composition and content of the large ultra-low N stainless steel are: C 0.11~0.15wt%; Mn 0.30~0.60wt%; P≤0.010wt%; S≤0.002wt%; Si≤0.10wt%; Cr 8.5~10.5wt%; Ni≤0.10wt%; N≤0.014wt%; Mo 0.5~1.60wt%; Co 1.00~4.00wt%; W 0.30~4.00wt%; Al≤0.010wt%; O≤15ppm; Ti≤0.010wt%; Nb0.04~0.06wt%; V 0.15~0.25wt%; B 0.0030~0.030wt%; As≤0.010wt%; Sn≤0.007wt%; Sb≤0.0015wt%; the balance is iron and unavoidable impurities; The production process comprises the following steps: 1) Internal control component design: The chemical element composition and content of the internal control components of large ultra-low N stainless steel are: C 0.11-0.12wt%; Mn 0.30-0.40wt%; P≤0.010wt%; S≤0.002wt%; Si≤0.10wt%; Cr 8.60-9.10wt%; Ni≤0.10wt%; N≤0.010wt%; Mo 1.10-1.40wt%; Co 2.00-3.50wt%; W 1.50-2.50wt%; Al≤0.010wt%; O≤15ppm; Ti≤0.010wt%; Nb 0.04-0.06wt%; V 0.15-0.25wt%; B 0.010-0.018wt%; the balance is iron and unavoidable impurities; 2) Electric furnace primary smelting: The carbon steel material is used for primary refining and then subjected to strong oxygen blowing and carbon spraying treatment to obtain molten steel; Among them, the ingredient requirements of carbon steel materials are: Ni≤0.08wt%, As≤0.008wt%, Sn≤0.006wt%, Sb≤0.0012wt%; The composition control requirements of molten steel: C≤0.04wt%, P≤0.0015wt%, N≤0.050wt%; 3) Ladle refining: Step 2) the molten steel initially refined in the electric furnace enters the ladle refining furnace for ladle refining, and the N content of the tapped molten steel is adjusted to be less than 0.008 wt%; The specific method of ladle refining is: 3.1) Slag making: Step 2) the molten steel from the primary refining in the electric furnace enters the ladle refining furnace, and slag is made with lime and fluorite to control the thickness of the slag layer and the basicity of the molten steel; 3.2) Diffusion deoxidation: Step 2) The molten steel from the primary refining in the electric furnace enters the ladle refining furnace, and a diffusion deoxidizer is added to the molten steel every 10 to 30 minutes for diffusion deoxidation; 3.3) Alloying treatment: When the slag color is gray or off-white after the slag making in step 3.1) is completed and the diffusion deoxidation process in step 3.2) is in progress, the alloy raw materials of the alloy components are added in batches to the ladle refining furnace to perform multiple alloying treatments, provided that the upper limit value or target value of the alloy components in the internal control components is not exceeded and the upper limit value of the restricted residual elements in the internal control components is not exceeded; Wherein, the alloy components are C, Cr, Mn, Mo, Co, W, Nb and V; The limiting residual elements are Si, P, S, As, Sn, Sb and Cu; 3.4) Vacuum refining treatment: Step 3.3) During the alloying process, a VD vacuum refining process may be performed before or after each alloying process, and a VD vacuum refining process must be performed after the last alloying process; After the last VD vacuum refining treatment, samples were taken to analyze the N content; When N≤0.008wt%, step 3.3) alloying treatment and step 3.4) VD vacuum refining treatment are completed; When N>0.008wt%, repeat step 3.3) alloying treatment to step 3.4) VD vacuum refining treatment until N≤0.008wt%; 3.5) Microalloying treatment: According to the component analysis result of the last VD vacuum refining treatment in step 3.4), alloy raw materials are added to the molten steel for micro-alloying treatment to adjust the contents of all components of the molten steel to be between the upper limit and / or lower limit of the internal control components, and the steel is tapped after the temperature of the molten steel meets the tapping requirements; 4) Pouring: Step 3) The molten steel refined from the ladle is cast in a fully sealed and protected manner to obtain an electrode blank; Wherein, the oxygen concentration is controlled to be ≤4000ppm during the fully sealed protection pouring process; 5) Electroslag remelting: Step 4) The cast electrode blank is subjected to electroslag remelting in a protective atmosphere electroslag remelting furnace based on the five-element slag system components to obtain a large ultra-low N stainless steel ingot.

2. The production process according to claim 1, characterized in that: Step 2) primary smelting in an electric furnace, wherein the basicity of the molten steel is controlled to be 3 to 8 during the primary smelting process.

3. The production process according to claim 1, characterized in that: Step 2) Electric furnace primary refining, the specific parameters of the strong oxygen blowing carbon spraying treatment are: oxygen pressure 0.6-1.2MPa, oxygen flow rate 1000-2500m 3 / h; carbon powder dosage 15 ~ 50kg / min; oxygen lance inserted into the slag layer ≥ 30mm, and the angle with the horizontal plane is 20 ~ 50°.

4. The production process according to claim 1, characterized in that: Step 3.1) Slag making, the thickness of the slag layer is controlled to be 200-450 mm, and the basicity is controlled to be 3-6.

5. The production process according to claim 1, characterized in that: Step 3.2) diffusion deoxidation, the diffusion deoxidizer is made of carbon powder and calcium silicon powder in a mass ratio of 3:2, and the single dosage of the diffusion deoxidizer is 5 to 30 kg.

6. The production process according to claim 1, characterized in that: Step 3.3) alloying treatment, the multiple alloying treatments are specifically: 3.3.1) Primary alloying: adding Cr alloy for primary alloying, controlling the Cr content in the molten steel to 0-3wt%; 3.3.2) Secondary alloying: adding Cr alloy, Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and V alloy for secondary alloying, controlling the Cr content in the molten steel to 5-7wt%, and controlling other alloy components in the molten steel not to exceed the upper limit value or target value of the internal control component; 3.3.3) Three-stage alloying: Add Cr alloy, Mn alloy, Mo alloy, Co alloy, W alloy, Nb alloy and / or V alloy for three-stage alloying to control all alloy components in the molten steel to be between the upper limit and lower limit of the internal control components, or control all alloy components in the molten steel to meet the target value requirements.

7. The production process according to claim 1, characterized in that: Step 3.4) Vacuum refining treatment, the parameters of the VD vacuum refining treatment include vacuum degree, refining argon blowing, vacuum refining temperature T 精 and vacuum refining time τ; The vacuum degree is ≤400Pa; The argon flow rate of the refining argon blowing is 50-200 L / min, and the argon pressure is 0.2-1.0 MPa; The vacuum refining temperature T 精 It is calculated by the following formula: Formula 1: T 精 =T 熔 +Δt+K1τ; Among them, T 熔 It is the melting point of the molten steel in the ladle refining furnace, ℃; Δt is the superheat, which is 60-80℃; τ is the vacuum refining time, min; K1 is the heat dissipation coefficient of the ladle, which is 0.7-2.5; The vacuum refining time τ is calculated by the following formula 2: Formula 2: τ = K2V / S; Among them, K2 is a coefficient with a value of 0.5 to 3.5; V is the volume of the ladle refining furnace, m 3 ; S represents the pumping rate, m 3 / min.

8. The production process according to claim 1, characterized in that: Step 3.5) microalloying treatment, during which argon is introduced to control the flow rate of argon so as to blow through the slag surface with a diameter of ≤400 mm; the temperature of the molten steel at the tapping is determined by 50 to 90° C. above the melting point of the molten steel in the ladle refining furnace.

9. The production process according to claim 1, characterized in that: Step 5) electroslag remelting, the components and contents of the five-component slag system are: CaF2 50-65wt%, Al2O3 15-25wt%, CaO 5-20wt%, SiO2 0-2.0wt%, B2O 30-3wt%.

10. The production process according to claim 1, characterized in that: Step 5) electroslag remelting, the protective atmosphere is argon with an oxygen concentration of ≤800ppm.

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