Niobium-containing stainless steel and its preparation method

Abstract

The present invention belongs to the technical field of metal material preparation, and particularly relates to a niobium-containing stainless steel and a preparation method thereof. The preparation method of the niobium-containing stainless steel comprises the following steps: Smelting: Smelting the raw materials of the niobium-containing stainless steel in a vacuum induction melting furnace to obtain molten steel. During the fine adjustment of the steel composition in the smelting process, Nb is added all at once together with ferro-niobium and the alloy finally used for composition adjustment and supplementation; Pouring: When the temperature of the molten steel is 40 - 120 °C higher than the liquidus temperature, tapping and pouring into electrode bars; Vacuum consumable melting: Subjecting the electrode bars to vacuum consumable melting to obtain ingots; Forging: Forging the ingots to obtain finished products. The low-magnification structure of the niobium-containing stainless steel prepared by this preparation method eliminates the irregular local coarse-grained condition, the high-magnification structure is uniform, and at the same time, it has stable impact work.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material preparation, and particularly relates to a niobium-containing stainless steel and a preparation method thereof. Background Art

[0002] Nb is one of the important alloying elements in Cr-based and Cr-Ni-based stainless steels, and its dosage is second only to molybdenum. Its functions are diverse. Especially in heat-resistant stainless steels applied in high-temperature fields, Nb is even more important, and it can partially replace the expensive molybdenum.

[0003] Nb is widely used in stainless steels as an alloying or micro-alloying element.

[0004] Nb is both a strong ferrite-forming element and a strong carbide and nitride-forming element, and it is easy to form metal compounds when heated for a long time. Therefore, the physical metallurgy of niobium in stainless steel is very complex. The role of niobium in stainless steel depends on its existing form. Moreover, the content of free niobium and niobium in carbides and nitrides depends on the solubility products of NbC, NbN, and Nb(CN) as a function of temperature.

[0005] Any existing form of niobium in stainless steel is resource-utilizable and exhibits superior performance compared to any other element. Its role runs through all aspects of the entire process from smelting to the final application of the product.

[0006] Specifically, the physical metallurgy properties of Nb in the steel-making process are as follows:

[0007] (1) Adding a small amount of Nb or applying Nb / Ti in combination in ultra-low carbon stainless steel can fix the residual C in the steel, which is much more economical compared to deep decarburization (such as extending the time required for AOD or VOD).

[0008] (2) During hot working, the precipitates of Nb or the dissolved Nb can be used for thermo-mechanical control processing (TMCP) to obtain excellent refined (including fine structures such as dislocation cell structures, deformed austenite, martensite, and substructures) structures in the hot-worked state, which is of great significance for the production of various stainless steels.

[0009] (3) The purpose of adding Nb to ultra-low carbon martensitic stainless steel is to stabilize carbon by forming niobium carbide, thereby inhibiting the formation of chromium carbide. In addition, the niobium-containing steel has good temper resistance, that is, as the niobium content increases, the decrease in hardness with the decrease in tempering temperature is reduced.

[0010] In the prior art, the low-magnification structure of Nb-containing stainless steel often shows irregular local coarse grains, and the high-magnification observed structure is uneven. Seriously, it will cause a decrease or instability in the impact energy, and cannot meet the use requirements. Summary of the Invention

[0011] In view of the above deficiencies in the prior art, the purpose of the present invention is to provide a niobium-containing stainless steel and a preparation method thereof. The preparation method eliminates the irregular local coarse grain situation in the macrostructure of the niobium-containing stainless steel prepared, the microstructure is uniform, and at the same time, it has stable impact energy.

[0012] To achieve the above purpose, the present invention adopts the following technical solutions:

[0013] In the first aspect, the present invention provides a preparation method of a niobium-containing stainless steel, including the following steps:

[0014] Smelting: Smelt the raw materials of the niobium-containing stainless steel in a vacuum induction melting furnace to obtain molten steel. During the fine adjustment of the steel composition in the smelting process, Nb is added all at once in the form of ferroniobium together with the alloy finally used for composition adjustment and supplementation.

[0015] Pouring: When the temperature of the molten steel is 40 - 120 °C higher than the liquidus (for example, it can be 40 °C, 60 °C, 80 °C, 100 °C or 120 °C, etc.), tap the steel and pour it into an electrode bar.

[0016] Vacuum consumable melting: Perform vacuum consumable melting on the electrode bar to obtain an ingot.

[0017] Forging: Forge the ingot to obtain a finished product.

[0018] By adding all niobium in the form of FeNb simultaneously with the last added ingredients, it is possible to eliminate the irregular local coarse grain situation in the macrostructure of the niobium-containing stainless steel prepared by this method, the microstructure is uniform, and it has stable impact energy.

[0019] In some embodiments, the niobium-containing stainless steel, by mass percentage, includes the following components: C ≤ 0.250%, Si ≤ 1.00%, Mn ≤ 1.50%, P ≤ 0.040%, S ≤ 0.030%, Cr 9.5% - 17.50%, Mo ≤ 2%, Ni ≤ 5.00%, Cu ≤ 5.00%, V ≤ 0.50%, B ≤ 0.030%, N ≤ 0.10%, Nb 0.10% - 1.0%, and the balance is Fe and unavoidable impurities.

[0020] In some embodiments, the niobium-containing stainless steel, by mass percentage, includes the following components: C ≤ 0.250%, Si ≤ 1.00%, Mn ≤ 1.50%, P ≤ 0.040%, S ≤ 0.030%, Cr 9.5% - 17.50%, Ni ≤ 5.00%, Cu ≤ 5.00%, V ≤ 0.50%, Nb 0.10% - 1.0%, and the balance is Fe and unavoidable impurities.

[0021] In some embodiments, the niobium-containing stainless steel comprises the following components by mass percentage: C 0.10% - 0.20%, Si 0.15% - 0.60%, Mn 0.30% - 1.25%, P ≤ 0.040%, S ≤ 0.030%, Cr 9.50% - 11.50%, Ni ≤ 0.50%, V 0.15% - 0.40%, Nb 0.10% - 0.60%, and the balance is Fe and unavoidable impurities.

[0022] In some embodiments, the smelting is vacuum induction smelting, and the vacuum induction smelting sequentially includes the following steps:

[0023] Charging and melting: Adjust the power of the vacuum induction furnace to 700 - 900 KW (for example, it can be 700 KW, 750 KW, 800 KW, 850 KW, or 900 KW, etc.), and continuously and sequentially add all the raw materials in the charge, pure iron and / or scrap steel, and at least one alloy raw material other than ferroniobium (such as nickel (Ni), chromium (Cr), and vanadium (V), etc.) into the vacuum induction furnace for melting of the raw materials. During the melting process, keep the vacuum degree in the furnace ≤ 0.3 Pa; preferably, the addition amount of at least one alloy raw material other than ferroniobium is 25% - 35% of the total mass of the corresponding alloy raw material charged to prevent difficult melting; preferably, during the melting process, when the molten steel boils, reduce the power to 100 - 200 KW until the molten steel does not boil violently;

[0024] Refining: After adjusting the power to 500 - 1000 KW (for example, it can be 500 KW, 600 KW, 700 KW, 800 KW, 900 KW, or 1000 KW, etc.) and maintaining it for 10 - 15 min, carry out stirring with the vacuum degree in the furnace ≤ 0.3 Pa; preferably, the stirring time is 3 - 5 min;

[0025] Composition adjustment: After the end of refining stirring, reduce the power to 250 - 400 KW, conduct the first composition analysis on the refined molten steel, fine-tune the composition according to the results of the first composition analysis, add at least one alloy raw material remaining in the charge other than ferroniobium, then raise the power to 500 - 1000 KW (for example, it can be 500 KW, 600 KW, 700 KW, 800 KW, 900 KW, or 1000 KW, etc.), and carry out melting and stirring; preferably, the stirring time is 3 - 5 min;

[0026] After the first component adjustment is completed, reduce the power to 250 - 400 KW, conduct a second component analysis, add alloys to fine-tune the components according to the results of the second component analysis. While adding the alloys, add all the ferroniobium in the batching at one time, and then raise the power to 500 - 1000 KW (for example, it can be 500 KW, 600 KW, 700 KW, 800 KW, 900 KW or 1000 KW, etc.) to conduct melting and stirring; preferably, the stirring time is 3 - 5 min.

[0027] In some embodiments, before the charging and melting steps of the vacuum induction smelting, it further includes:

[0028] Heating up: In the initial stage of vacuum induction smelting, use low power to heat up the vacuum induction furnace for 1.5 - 2 h, and adjust the vacuum degree in the vacuum induction furnace ≤ 0.3 Pa; preferably, the low power is 250 - 450 KW (for example, it can be 250 KW, 300 KW, 350 KW, 400 KW or 450 KW, etc.).

[0029] In some embodiments, before the smelting step, the preparation method of the niobium-containing stainless steel further includes the following steps:

[0030] Batching: Conduct batching according to the components of the niobium-containing stainless steel; preferably, the raw material pure iron is ultra-low carbon pure iron, and the alloy raw materials include at least one of the raw materials of chromium, nickel, vanadium, manganese, molybdenum, copper and niobium. The raw material of chromium is metal chromium with low S, P (S ≤ 0.010%, P ≤ 0.005%), the raw material of nickel is electrolytic nickel with low S, P (S ≤ 0.001%, P ≤ 0.001%), the raw material of vanadium is ferrovanadium, the raw material of niobium (Nb) is ferroniobium, the raw material of manganese is metallic manganese, the raw material of molybdenum is metallic molybdenum or ferromolybdenum, and the raw material of copper is electrolytic copper.

[0031] In some embodiments, at least one upsetting and drawing process is carried out during the forging process. The one-time upsetting and drawing includes: first upsetting and then drawing. When upsetting, the ingot is upset to 1 / 2 - 1 / 3 of the original ingot height, and then it is drawn to make the diameter of the final forging meet the requirements.

[0032] In some embodiments, the total forging ratio of the forging is greater than or equal to 6.5:1. By limiting the total forging ratio to be greater than or equal to 6.5:1 in this embodiment, it is beneficial to refine the grains. The forging ratio during drawing is the ratio of the cross-sectional area of the ingot before forming to the cross-sectional area of the ingot after forming, the forging ratio during upsetting is the ratio of the height of the ingot before upsetting to the height of the ingot after upsetting, and the total forging ratio is the forging ratio during drawing multiplied by the forging ratio during upsetting.

[0033] In some embodiments, the heat preservation temperature of the forging is 1120 - 1200°C, the starting forging temperature ≥ 1000°C, and the final forging temperature ≥ 800°C.

[0034] In some embodiments, after the forging step, the preparation method further includes:

[0035] Annealing: Anneal the finished material, and then cool it in the furnace to 300 - 500°C (for example, it can be 300°C, 350°C, 400°C, 450°C or 500°C, etc.), and then take it out of the furnace for air cooling or directly take it out of the furnace for air cooling. Among them, the annealing temperature depends on the properties of the steel grade. For example, the annealing temperature can be 800 - 860°C.

[0036] In some embodiments, after the annealing step, the preparation method further includes:

[0037] Quenching: Put the annealed finished material into the furnace at a temperature of 200 - 400°C, heat it to 600 - 800°C (for example, it can be 600°C, 650°C, 700°C, 750°C or 800°C, etc.) at a rate of 50 - 150°C / h (for example, it can be 50°C / h, 100°C / h or 150°C / h, etc.) and hold for 1 - 3h, then heat it to 1000 - 1200°C (for example, it can be 1000°C, 1100°C or 1200°C, etc.) at a rate of 50 - 150°C / h (for example, it can be 50°C / h, 100°C / h or 150°C / h, etc.) and hold. The holding time at 1000 - 1200°C is determined by the diameter of the finished material, calculated as 2 - 4h / 100mm (for example, if the cross-sectional diameter of the finished material is 200mm, then the holding time is 4 - 8h), and then air cool;

[0038] First tempering: Put the quenched finished material into the furnace at a temperature of 50 - 150°C (for example, it can be 50°C, 100°C or 150°C, etc.), heat it to 500 - 700°C (for example, it can be 500°C, 550°C, 600°C, 650°C or 700°C, etc.) at a rate of 30 - 60°C / h (for example, it can be 30°C / h, 40°C / h or 60°C / h, etc.) and hold. The holding time at 500 - 700°C is determined by the diameter of the finished material, calculated as 3 - 6h / 100mm (for example, if the cross-sectional diameter of the finished material is 200mm, then the holding time is 6 - 12h), and then air cool;

[0039] Second tempering: The finished product after the first tempering is put into the furnace at a temperature of 50 - 150°C (such as 50°C, 100°C or 150°C, etc.), heated to 500 - 700°C (such as 500°C, 550°C, 600°C, 650°C or 700°C, etc.) at a rate of 30 - 60°C / h (such as 30°C / h, 40°C / h or 60°C / h, etc.) and held for heat preservation. The heat preservation time at 500 - 700°C is calculated as 3 - 6h / 100mm, and then air-cooled to obtain niobium-containing stainless steel.

[0040] In some embodiments, the crucible ratio of the vacuum consumable melting is 0.6 - 0.9d·D -1 , preferably 0.8d·D -1 ; the melting vacuum degree is 10 -3 ~10 -2 Pa, preferably 0.5×10 -2 Pa; the melting voltage is 25 - 45V (such as 25V, 30V, 35V, 40V or 45V, etc.), preferably 30V; the melting current is 7 - 20KA (such as 7KA, 10KA, 15KA or 20KA, etc.), preferably 10KA; the melting coefficient is 1 - 2kg·(kA·min) -1 , preferably 1.2 - 1.5kg·(kA·min) -1 . Wherein, d is the diameter of the electrode rod and D is the inner diameter of the crucible.

[0041] In some embodiments, the number of times of the vacuum consumable melting is 2 - 3 times.

[0042] In the second aspect, the present invention provides a niobium-containing stainless steel prepared by the preparation method described in the first aspect.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] 1) By adopting the method of the present invention to prepare niobium-containing stainless steel, the high magnification structure of the prepared niobium-containing stainless steel is uniform and the grains are fine.

[0045] 2) The prepared niobium-containing stainless steel has excellent comprehensive properties, the irregular local coarse grain situation of the macrostructure of the material is eliminated, and it has stable impact work. Description of the Drawings

[0046] Figure 1 is a schematic diagram of part of the process flow of the present invention;

[0047] Figure 2 is the macrostructure diagram of the niobium-containing stainless steel prepared in Example 1 of the present invention;

[0048] Figure 3High-magnification microstructure diagram of the niobium-containing stainless steel prepared in Example 1 of the present invention;

[0049] Figure 4 Low-magnification microstructure diagram of the niobium-containing stainless steel prepared in Example 2 of the present invention;

[0050] Figure 5 High-magnification microstructure diagram of the niobium-containing stainless steel prepared in Example 2 of the present invention;

[0051] Figure 6 Low-magnification microstructure diagram of the niobium-containing stainless steel prepared in Example 3 of the present invention;

[0052] Figure 7 High-magnification microstructure diagram of the niobium-containing stainless steel prepared in Example 3 of the present invention;

[0053] Figure 8 Low-magnification microstructure diagram of the niobium-containing stainless steel prepared in Comparative Example 1 of the present invention;

[0054] Figure 9 For the Figure 8 enlarged view at location A in the present invention;

[0055] Figure 10 High-magnification microstructure diagram of the niobium-containing stainless steel prepared in Comparative Example 1 of the present invention. Specific embodiments

[0056] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0057] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the amounts of the experimental reagents used are the amounts of the reagents in conventional experimental operations unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0058] The process route for preparing the niobium-containing stainless steel in the embodiments of the present invention is as follows:

[0059] Batching -> Vacuum induction melting -> Vacuum consumable electrode remelting -> Forging at 220 mm -> Annealing -> Sampling inspection.

[0060] Figure 1 It is a schematic diagram of part of the process flow of the present invention, including the vacuum induction melting (VIM) step and the pouring step, which are the key steps in the preparation method of the niobium-containing stainless steel.

[0061] The specific preparation steps of the method for preparing niobium-containing stainless steel provided by the embodiments of the present invention are as follows:

[0062] 1) Batching: According to the composition requirement range of stainless steel, batching is carried out. Ultra-low carbon pure iron, metal chromium with low S and P, electrolytic nickel, ferrovanadium, ferroniobium, and metal manganese are selected as raw materials. All furnace charges must be clean, dry, free of oil stains and rust, and have accurate compositions. Analyze the C, O, and N contents of all raw materials before smelting to ensure accurate batching. The batching design also needs to consider the influence of element burning loss during the smelting process on the steel composition.

[0063] 2) Vacuum induction melting (VIM):

[0064] Step a) Heating up: In the initial stage of VIM, heat up the vacuum induction furnace at a low power for 1.5 - 2 hours. The low power is between 250 - 450 KW, and adjust the vacuum degree in the vacuum induction furnace ≤ 0.3 Pa;

[0065] Step b) Charging and melting: After heating up in step a), adjust the power to 700 - 900 KW, and continuously add all the raw materials pure iron and / or scrap steel, and part of the alloy raw materials except ferroniobium according to the composition batching for melting the steel materials. During the melting process, keep the vacuum degree in the furnace ≤ 0.3 Pa. During this period, after the molten steel boils, reduce the power to 100 - 200 KW until the molten steel does not boil violently.

[0066] According to the target steel grade composition, select the batching to be added. If the target steel grade composition changes, the required added batching will change accordingly. "All" refers to all the amounts required according to the composition batching requirements, and "part" can refer to 25% - 35% of the amounts required according to the batching requirements. Because the raw materials pure iron, scrap steel, and alloys are all solid, adding them all cannot be melted.

[0067] The main task during the melting period is to smoothly melt the furnace charges.

[0068] Step c) Refining: After melting in step b), measure the temperature of the molten steel. When the temperature reaches or is higher than the liquidus of the target steel grade by 100 - 200 °C, enter the refining period. During the refining period, use a high power of 500 - 1000 KW to maintain for 10 - 15 min and then stir. The stirring time is 3 - 5 min, and the vacuum degree is less than or equal to 0.3 Pa.

[0069] The main task during the refining period is to fully remove oxygen in the steel, remove inclusion elements, and improve the purity of the molten steel.

[0070] Step d) Composition adjustment: After the refining stirring is completed, reduce the power to 250 - 400 KW, conduct the first composition analysis on the refined molten steel, fine-tune the composition according to the results of the first composition analysis, add the remaining alloy raw materials except ferroniobium required by the batching requirements, increase the power to 500 - 1000 KW, melt and stir, and the stirring time is 3 - 5 min.

[0071] For example, the target composition of Cr is 10.50% - 11.5%, and the composition of Cr in the first composition analysis is 9.50%. At this time, when adjusting Cr, 1.00% of Cr should be added to make the Cr composition at least close to the target lower limit.

[0072] After the first composition adjustment is completed, reduce the power to 250 - 400 KW, conduct the second composition analysis, according to the results of the second composition analysis, add alloying elements and at the same time, add all the ferroniobium at one time according to the Nb target content, increase the power to 500 - 1000 KW, melt and stir, and the stirring time is 3 - 5 min. The addition amount is determined according to the composition of the molten pool at this time. The closer to the target composition, the less the addition amount; the farther from the target composition, the more the addition amount. The alloying elements added are at least one of metallic chromium, metallic manganese, metallic molybdenum, metallic vanadium, metallic nickel, and metallic copper.

[0073] 3) Pouring: Conduct the third composition analysis. When the composition is qualified and the temperature of the molten steel is 40 - 120 °C higher than the liquidus temperature, tap the steel and pour it into electrode bars.

[0074] 4) Vacuum consumable melting: Remelt the electrode bars using a 3t vacuum consumable furnace to obtain ingots. The number of times of vacuum consumable melting is 2 - 3 times; the crucible ratio of the vacuum consumable melting is 0.6 - 0.9d·D -1 , preferably 0.8d·D -1 ; The melting vacuum degree is 10 -3 ~10 -2 Pa, preferably 0.5×10 -2 Pa; The melting voltage is 25 - 45 V, preferably 30 V; The melting current is 7 - 20 KA, preferably 10 KA; The melting coefficient is 1 - 2 kg·(kA·min) -1 , preferably 1.2 - 1.5 kg·(kA·min) -1 ; Wherein, d is the diameter of the electrode bar and D is the inner diameter of the crucible.

[0075] 5) Forging: Forge the ingots to obtain finished products. The forging process requires at least one upsetting and drawing, the upsetting height is 1 / 2 - 1 / 3 of the original height, the forging reduction ratio ≥ 6.5:1, the forging holding temperature is 1120 - 1200 °C, the starting forging temperature ≥ 1000 °C, and the final forging temperature ≥ 800 °C.

[0076] 6) Annealing: Anneal the finished product, wherein the annealing temperature depends on the properties of the steel grade. For example, the annealing temperature can be 800 - 860 °C.

[0077] 7) Quenching: Put the annealed finished product into the furnace at a temperature of 200 - 400 °C, heat it to 600 - 800 °C at a rate of 50 - 150 °C / h and hold for 1 - 3 h, then heat it to 1000 - 1200 °C at a rate of 50 - 150 °C / h and hold. The holding time at 1000 - 1200 °C is calculated as 2 - 4 h / 100 mm, and then air-cool.

[0078] 8) First tempering: Put the quenched finished product into the furnace at a temperature of 50 - 150 °C, heat it to 500 - 700 °C at a rate of 30 - 60 °C / h and hold. The holding time at 500 - 700 °C is calculated as 3 - 6 h / 100 mm, and then air-cool.

[0079] 9) Second tempering: Put the finished product after the first tempering into the furnace at a temperature of 50 - 150 °C, heat it to 500 - 700 °C at a rate of 30 - 60 °C / h and hold. The holding time at 500 - 700 °C is calculated as 3 - 6 h / 100 mm, and then air-cool to obtain niobium-containing stainless steel.

[0080] After the preparation is completed, take the end of the niobium-containing stainless steel for inspection.

[0081] The equipment used in the smelting of the example is a 6t vacuum induction smelting furnace, and 2 3-ton ingots are cast. The parameters in the example are all the parameters of 6t vacuum induction smelting.

[0082] In the following examples and comparative examples:

[0083] The tensile strength is inspected according to ASTM A370, and the impact test is inspected according to ASTM E23.

[0084] Example 1

[0085] The composition requirements and batching design of the niobium-containing stainless steel provided in this example are shown in Table 1. This example conducts batching design according to the composition requirement range of the niobium-containing stainless steel.

[0086] Table 1 Composition requirements and batching design of niobium-containing stainless steel in Example 1 (unit: %wt)

[0087]

[0088] The specific preparation steps of the preparation method of the niobium-containing stainless steel provided in the embodiment of the present invention are as follows:

[0089] 1) Ingredients: In this embodiment, batching is carried out according to the range of batching design requirements for stainless steel. Ultra-low carbon pure iron, metal chromium with low S and P, electrolytic nickel, ferrovanadium, ferroniobium, and ferromanganese are selected as raw materials. All furnace charges must be clean, dry, free of oil stains and rust, and have accurate compositions. Analyze the C, O, and N contents of all raw materials before smelting to ensure accurate batching.

[0090] 2) Vacuum Induction Melting (VIM):

[0091] Step a) Heating: In the initial stage of VIM, use a 250KW vacuum induction furnace to heat for 1.5 hours, and adjust the vacuum degree in the vacuum induction furnace to 0.3 Pa;

[0092] Step b) Charging and Melting: After heating in step a), adjust the power to 700KW, and continuously add all the ultra-low carbon pure iron and 25wt% of the required amount of electrolytic nickel, 25wt% of the required amount of metal chromium, and 25wt% of the required amount of ferrovanadium according to the composition batching to melt the steel materials. During the melting process, keep the vacuum degree in the furnace ≤ 0.3 Pa. After the molten steel boils, reduce the power to 100KW until the molten steel does not boil violently.

[0093] Step c) Refining: After melting in step b), measure the temperature of the molten steel. When the temperature is 150℃ higher than the liquidus of the steel grade (the liquidus of this steel grade is about 1490 degrees Celsius), enter the refining period. During the refining period, use a high power of 700KW to maintain for 10 minutes and then stir for 4 minutes, with the vacuum degree ≤ 0.3 Pa.

[0094] Step d) Composition Adjustment: After the refining stirring is completed, reduce the power to 300KW, conduct the first composition analysis on the refined molten steel, fine-tune the composition according to the results of the first composition analysis, and supplement the remaining metal chromium, electrolytic nickel, and ferrovanadium in the required amount of the batching, so that the contents of chromium, nickel, and vanadium meet the batching design. Raise the power to 500KW, melt and stir for 5 minutes.

[0095] After the first composition adjustment is completed, reduce the power to 300KW, conduct the second composition analysis, fine-tune the composition to supplement metal chromium and metal manganese, and at the same time, according to the Nb target content, add all the ferroniobium in the batching at one time. Raise the power to 800KW, melt and stir for 5 minutes. The supplementary amount is determined according to the composition of the molten pool at this time. The closer it is to the target composition, the less the supplementary amount; the farther it is from the target composition, the more the supplementary amount.

[0096] 3) Pouring: Reduce the power to 300KW, conduct the third composition analysis. When the composition is qualified and the temperature of the molten steel is 80℃ higher than the liquidus, tap the steel and pour it into electrode rods.

[0097] 4) Vacuum consumable melting: Remelt the electrode bar using a 3t vacuum consumable furnace to obtain an ingot with a diameter . The number of vacuum consumable melting times is 2 times, and the crucible ratio of the vacuum consumable melting is 0.7d·D -1 (d is the diameter of the electrode bar, D is the inner diameter of the crucible), the melting vacuum degree is 10 -3 Pa, the melting voltage is 25V, the melting current is 7KA, and the melting coefficient is 1kg·(kA·min) -1 , and helium gas is used for cooling.

[0098] 5) Forging: Forge the ingot to obtain the finished product. The holding temperature for forging is 1200°C, the starting forging temperature is 1000°C, and the final forging temperature is 800°C. One upsetting and drawing process is carried out during forging. The one upsetting and drawing process includes: first upsetting and then drawing. When upsetting, the ingot is upset to 1 / 2 of the original ingot height, and then it is elongated by drawing to make the diameter of the final forging meet the requirements. The total forging ratio is 10.3:1, and a finished product with a diameter is obtained.

[0099] 6) Annealing: Anneal the finished product. The annealing temperature is 830°C, hold for 6h, and then cool in the furnace to 400°C and then take out and air-cool.

[0100] 7) Quenching: Put the annealed finished product into the furnace at a temperature of 300°C, heat it to 750°C at a rate of 100°C / h and hold for 2h, then heat it to 1150°C at a rate of 100°C / h and hold for 7h, and air-cool after taking out of the furnace.

[0101] 8) First tempering: Put the finished product after quenching in step 7) into the furnace at a temperature of 100°C, heat it to 570°C at a rate of 50°C / h and hold for 7h, and air-cool after taking out of the furnace.

[0102] 9) Second tempering: Put the finished product after the first tempering in step 8) into the furnace at a temperature of 100°C, heat it to 570°C at a rate of 50°C / h and hold for 7h, and air-cool to room temperature after taking out of the furnace to obtain niobium-containing stainless steel.

[0103] Analyze and detect the chemical elements of the niobium-containing stainless steel prepared in this example, and the detection results are shown in Table 2.

[0104] Table 2 Chemical element detection results of the niobium-containing stainless steel prepared in Example 1 (unit: %wt)

[0105]

[0106] The grain size of the niobium-containing stainless steel prepared in this example is grade 6. Perform macro inspection and micro inspection on the niobium-containing stainless steel prepared in this example, and the results are as Figure 2 andFigure 3 As shown by Figure 2 and Figure 3 (metallographic picture of OLYMPUS microscope at 100x), it can be seen that the grains of the low magnification structure are fine, the situation of irregular local coarse grains is eliminated, and the high magnification structure (magnification is 100) is uniform.

[0107] Using the niobium-containing stainless steel prepared in this example as a sample, its tensile strength is measured to be 1245 Mpa; three stainless steels at different depths at half of the radius of the end section of the niobium-containing stainless steel prepared in this example are intercepted as samples for impact energy testing. The room temperature longitudinal impact energies at different positions are 56 J / 61 J / 68 J. The niobium-containing stainless steel prepared in this example has excellent tensile strength and stable impact energy.

[0108] 20 batches of steel were prepared by the method provided in this example. After sampling and testing, all the impact energies were stable, and the grain sizes could all reach above grade 5.

[0109] Example 2

[0110] The composition requirements and batching design of the niobium-containing stainless steel provided in this example are shown in Table 3. According to the composition requirement range of the niobium-containing stainless steel, batching design is carried out in this example.

[0111] Table 3 Composition requirements and batching design of the niobium-containing stainless steel in Example 1 (unit: %wt)

[0112]

[0113]

[0114] The specific preparation steps of the preparation method of the niobium-containing stainless steel provided by the embodiment of the present invention are as follows:

[0115] 1) Batching: According to the batching design requirement range of the stainless steel, batching is carried out in this example. Ultra-low carbon pure iron, metal chromium with low S and P, electrolytic nickel, electrolytic copper, ferroniobium, and metal manganese are selected as raw materials. All furnace charges must be clean, dry, free of oil and rust, and have accurate compositions. Analyze the C, O, and N contents of all raw materials before smelting to ensure accurate batching.

[0116] 2) Vacuum induction melting (VIM):

[0117] Step a) Heating up: In the initial stage of VIM, use a 400KW vacuum induction furnace to heat up for 1.5 hours, and adjust the vacuum degree in the vacuum induction furnace to 0.3 Pa;

[0118] Step b) Charging and melting: After the temperature is raised in step a), adjust the power to 800 KW. Continuously add all the ultra-low carbon pure iron and 25 wt% of electrolytic nickel, 30 wt% of metallic chromium, and 30 wt% of electrolytic copper required according to the ingredient requirements. Then carry out the melting of the steel materials. During the melting process, keep the vacuum degree in the furnace ≤ 0.3 Pa. During this period, after the molten steel boils, reduce the power to 150 KW until the molten steel does not boil violently.

[0119] Step c) Refining: After melting in step b), measure the temperature of the molten steel. When the temperature is 100 °C higher than the liquidus of the steel grade (the liquidus of this steel grade is about 1465 °C), enter the refining period. During the refining period, use a high power of 900 KW to maintain for 10 min and then carry out stirring. The stirring time is 4 min, and the vacuum degree ≤ 0.3 Pa.

[0120] Step d) Composition adjustment: After the refining stirring is completed, reduce the power to 250 KW. Conduct the first composition analysis on the refined molten steel. Fine-tune the composition according to the results of the first composition analysis, and supplement the remaining metallic chromium, electrolytic nickel, and electrolytic copper required according to the ingredient requirements, so that the contents of chromium, nickel, and copper meet the ingredient design. Raise the power to 700 KW, melt and stir, and the stirring time is 5 min.

[0121] After the first composition adjustment is completed, reduce the power to 400 KW, conduct the second composition analysis. According to the results of the second composition analysis, fine-tune the composition, supplement metallic chromium and metallic manganese, and at the same time, according to the target content of Nb, add all the ferroniobium in the ingredients at one time. Raise the power to 500 KW, melt and stir, and the stirring time is 5 min. The supplementary amount is determined according to the composition of the molten pool at this time. The closer to the target composition, the less the supplementary amount; the farther from the target composition, the more the supplementary amount.

[0122] 3) Pouring: Reduce the power to 300 KW, conduct the third composition analysis. When the composition is qualified and the temperature of the molten steel is 50 °C higher than the liquidus, tap the steel and pour it into an electrode bar.

[0123] 4) Vacuum consumable melting: Remelt the electrode bar using a 3 t vacuum consumable furnace to obtain an ingot with a diameter where the number of times of vacuum consumable melting is 2 times, and the crucible ratio of the vacuum consumable melting is 0.8d·D -1 (d is the diameter of the electrode bar, D is the inner diameter of the crucible), the melting vacuum degree is 10 -2 Pa, the melting voltage is 35 V, the melting current is 10 KA, the melting coefficient is 1 kg·(kA·min) -1 , and helium is used for cooling.

[0124] 5) Forging: The steel ingot is forged to obtain the finished material. The holding temperature for forging is 1200 °C, the starting forging temperature is 1000 °C, and the final forging temperature is 850 °C. One upsetting and drawing process is carried out during forging. The one upsetting and drawing process includes: first upsetting and then drawing. When upsetting, the steel ingot is upset to 1 / 2 of the original height of the steel ingot, and then it is drawn to make the diameter of the final forging meet the requirements. The total forging ratio is 10.3:1, and a finished material with a diameter is obtained.

[0125] 6) Annealing: The finished material is annealed at an annealing temperature of 640 °C for 10 h, and then taken out of the furnace and air-cooled.

[0126] 7) Quenching: The annealed finished material is put into the furnace at a temperature of 300 °C, heated to 750 °C at a rate of 100 °C / h and held for 2 h, then heated to 1150 °C at a rate of 100 °C / h and held for 7 h, and then taken out of the furnace and air-cooled.

[0127] 8) First tempering: The finished material after quenching in step 7) is put into the furnace at a temperature of 100 °C, heated to 570 °C at a rate of 50 °C / h and held for 7 h, and then taken out of the furnace and air-cooled.

[0128] 9) Second tempering: The finished material after the first tempering in step 8) is put into the furnace at a temperature of 100 °C, heated to 570 °C at a rate of 50 °C / h and held for 7 h, and then taken out of the furnace and air-cooled to room temperature to obtain niobium-containing stainless steel.

[0129] The chemical elements of the niobium-containing stainless steel prepared in this example are analyzed and detected, and the detection results are shown in Table 4.

[0130] Table 4 Chemical element detection results of the niobium-containing stainless steel prepared in Example 2 (unit: %wt)

[0131]

[0132] The grain size of the niobium-containing stainless steel prepared in this example is grade 6.5. The macrostructure inspection and microstructure inspection are carried out on the niobium-containing stainless steel prepared in this example, and the results are as Figure 4 and Figure 5 shown. It can be seen from Figure 4 and Figure 5 that the grains of the macrostructure are fine, the situation of irregular local coarse grains is eliminated, and the microstructure is uniform.

[0133] Using the niobium-containing stainless steel prepared in this embodiment as a sample, its tensile strength was measured to be 1383 Mpa; three stainless steels at different depths at half of the radius of the end section of the niobium-containing stainless steel prepared in this embodiment were intercepted as samples for impact energy testing. The longitudinal impact energy at room temperature at different positions was 103 J / 97 J / 99 J. The niobium-containing stainless steel prepared in this embodiment has excellent tensile strength and stable impact energy.

[0134] Twenty batches of steel were prepared by the method provided in this embodiment. After sampling and testing, the impact energy was all stable, and the grain size could reach above grade 6.

[0135] Example 3

[0136] The composition requirements and batching design of the niobium-containing stainless steel provided in this embodiment are shown in Table 5. According to the composition requirement range of the niobium-containing stainless steel, the batching design was carried out in this embodiment.

[0137] Table 5 Composition requirements and batching design of niobium-containing stainless steel in Example 3 (unit: %wt)

[0138]

[0139] The specific preparation steps of the preparation method of the niobium-containing stainless steel provided by the embodiment of the present invention are as follows:

[0140] 1) Batching: According to the batching design requirement range of the stainless steel, batching was carried out in this embodiment. Ultra-low carbon pure iron, metal chromium with low S and P, electrolytic nickel, ferrovanadium, ferroniobium, and metal manganese were selected as raw materials. All furnace charges must be clean, dry, free of oil and grease, rust-free, and the composition must be accurate. Analyze the C, O, and N contents of all raw materials before smelting to ensure accurate batching.

[0141] 2) Vacuum induction melting (VIM):

[0142] Step a) Heating: In the initial stage of VIM, use a 350 KW vacuum induction furnace to heat up for 2 hours, and adjust the vacuum degree in the vacuum induction furnace to 0.2 Pa;

[0143] Step b) Charging and melting: After heating in step a), adjust the power to 800 KW, and continuously add all the ultra-low carbon pure iron and 30 wt% of the electrolytic nickel required by the batching requirements, 30 wt% of the metal chromium required by the batching requirements, and 30 wt% of the ferrovanadium required by the batching requirements according to the composition batching for melting the steel materials. During the melting process, keep the vacuum degree in the furnace ≤ 0.3 Pa. During this period, reduce the power to 200 KW after the steel liquid boils until the steel liquid does not boil violently.

[0144] Step c) Refining: After melting in step b), the temperature of the molten steel is measured. When the temperature is 150 °C higher than the liquidus temperature of the steel grade (the liquidus temperature of this steel grade is approximately 1490 °C), it enters the refining stage. During refining, a high power of 800 KW is used to maintain for 15 min and then stirring is carried out. The stirring time is 4 min, and the vacuum degree ≤ 0.3 Pa.

[0145] Step d) Composition adjustment: After the refining stirring is completed, the power is reduced to 350 KW, and the refined molten steel is subjected to the first composition analysis. According to the results of the first composition analysis, the composition is finely adjusted, and the remaining ferrochromium, electrolytic nickel, and ferroniobium required in the batching requirements are added to make the contents of chromium, nickel, and vanadium meet the batching design. The power is increased to 800 KW, melted and stirred, and the stirring time is 5 min.

[0146] After the first composition adjustment is completed, the power is reduced to 350 KW, and the second composition analysis is carried out. According to the results of the second composition analysis, the composition is finely adjusted, ferrochromium and ferromanganese are added, and at the same time, all the ferroniobium in the batching is added at one time according to the Nb target content. The power is increased to 900 KW, melted and stirred, and the stirring time is 5 min. The addition amount is determined according to the composition of the molten pool at this time. The closer to the target composition, the less the addition amount; the farther from the target composition, the more the addition amount.

[0147] 3) Pouring: The power is reduced to 300 KW, and the third composition analysis is carried out. When the composition is qualified and the temperature of the molten steel is 100 °C higher than the liquidus temperature, tapping and pouring are carried out to form electrode rods.

[0148] 4) Vacuum consumable melting: The electrode rods are remelted using a 3t vacuum consumable furnace to obtain steel ingots with a diameter of . Among them, the number of times of vacuum consumable melting is 2 times, and the crucible ratio of the vacuum consumable melting is 0.7d·D -1 (d is the diameter of the electrode rod, D is the inner diameter of the crucible), the melting vacuum degree is 10 -3 Pa, the melting voltage is 25 V, the melting current is 7 KA, and the melting coefficient is 1 kg·(kA·min) -1 , and helium gas is used for cooling.

[0149] 5) Forging: The steel ingots are forged to obtain finished products. The holding temperature for forging is 1200 °C, the starting forging temperature is 1000 °C, and the final forging temperature is 800 °C. One upsetting and drawing process is carried out during forging. The one upsetting and drawing process includes: first upsetting and then drawing. When upsetting, the steel ingot is upset to 1 / 2 of the original height of the steel ingot, and then it is elongated by drawing to make the diameter of the final forging meet the requirements. The total forging ratio is 10.3:1, and finished products with a diameter of are obtained.

[0150] 6) Annealing: The finished product is annealed at an annealing temperature of 830 °C for 6 h, and then cooled in the furnace to 400 °C and then air-cooled out of the furnace.

[0151] 7) Quenching: The annealed finished product is put into the furnace at a temperature of 300 °C, heated to 750 °C at a rate of 100 °C / h and held for 2 h, then heated to 1150 °C at a rate of 100 °C / h and held for 7 h, and then air-cooled after being taken out of the furnace.

[0152] 8) First tempering: The finished product after quenching in step 7) is put into the furnace at a temperature of 100 °C, heated to 570 °C at a rate of 50 °C / h and held for 7 h, and then air-cooled after being taken out of the furnace.

[0153] 9) Second tempering: The finished product after the first tempering in step 8) is put into the furnace at a temperature of 100 °C, heated to 570 °C at a rate of 50 °C / h and held for 7 h, and then air-cooled to room temperature to obtain niobium-containing stainless steel.

[0154] The chemical elements of the niobium-containing stainless steel prepared in this example are analyzed and detected, and the detection results are shown in Table 6.

[0155] Table 6 Chemical element detection results of the niobium-containing stainless steel prepared in Example 3 (unit: %wt)

[0156]

[0157] The grain size of the niobium-containing stainless steel prepared in this example is 5.5 levels. The macrostructure inspection and microstructure inspection are carried out on the niobium-containing stainless steel prepared in this example, and the results are as Figure 6 and Figure 7 shown. It can be seen from Figure 6 and Figure 7 (metallographic pictures of the OLYMPUS microscope at 100x) that the grains of the macrostructure are fine, the situation of irregular local coarse grains is eliminated, and the microstructure (magnification is 100) is uniform.

[0158] Using the niobium-containing stainless steel prepared in this example as a specimen, its tensile strength is measured to be 1211 Mpa; three stainless steels at different depth positions at half of the radius of the end section of the niobium-containing stainless steel prepared in this example are intercepted as specimens for impact energy testing. The longitudinal impact energy at room temperature at different positions is 54 J / 60 J / 65 J. The niobium-containing stainless steel prepared in this example has excellent tensile strength and stable impact energy.

[0159] 20 batches of steel are prepared by the method provided in this example. After sampling and testing, the impact energy is all stable, and the grain size can reach above level 5.

[0160] Comparative Example 1

[0161] In this comparative example, the composition requirements and batching design of the niobium-containing stainless steel are the same as those in Example 1.

[0162] The preparation method of the niobium-containing stainless steel provided in this comparative example is basically the same as that in Example 1, except for the timing of adding ferroniobium. The specific preparation steps are as follows:

[0163] 1) Batching: In this example, batching is carried out according to the composition requirement range of the stainless steel. Ultra-low carbon pure iron, metal chromium with low S and P, electrolytic nickel, ferrovanadium, ferroniobium, and metal manganese are selected as raw materials. All furnace charges must be clean, dry, free of oil and rust, and have accurate compositions. Analyze the C, O, and N contents of all raw materials before smelting to ensure accurate batching.

[0164] 2) Vacuum induction melting (VIM):

[0165] Step a) Heating: In the initial stage of VIM, use a 250KW to heat the vacuum induction furnace for 1.5 hours, and adjust the vacuum degree in the vacuum induction furnace to 0.3 Pa;

[0166] Step b) Charging and melting: After heating in step a), adjust the power to 700KW, and continuously add all the ultra-low carbon pure iron and 25wt% of the electrolytic nickel, 25wt% of the metal chromium, 25wt% of the ferrovanadium, and 25wt% of the ferroniobium required according to the composition batching to melt the steel materials. During the melting process, keep the vacuum degree in the furnace ≤ 0.3 Pa. During this period, when the molten steel boils, reduce the power to 100KW until the molten steel does not boil violently.

[0167] Step c) Refining: After melting in step b), measure the temperature of the molten steel. When the temperature is 150°C higher than the liquidus of the steel grade (the liquidus of this steel grade is about 1490°C), enter the refining period. During the refining period, use a high power of 700KW to maintain for 10 minutes and then stir for 4 minutes, with the vacuum degree ≤ 0.3 Pa.

[0168] Step d) Composition adjustment: After the refining stirring is completed, reduce the power to 300KW, conduct the first composition analysis on the refined molten steel, fine-tune the composition according to the results of the first composition analysis, and supplement the remaining metal chromium, electrolytic nickel, ferrovanadium, and ferroniobium required in the batching requirements to make the contents of chromium, nickel, vanadium, and niobium meet the batching design. Increase the power to 500KW, melt and stir for 5 minutes.

[0169] After the first component adjustment is completed, reduce the power to 300 KW, conduct the second component analysis. According to the results of the second component analysis, finely adjust the components by adding ferrochrome and ferromanganese. Increase the power to 800 KW, melt and stir. The stirring time is 5 min. The addition amount is determined according to the composition of the molten bath at this time. The closer to the target composition, the less the addition amount; the farther from the target composition, the more the addition amount.

[0170] 3) Pouring: Reduce the power to 300 KW, conduct the third component analysis. When the composition is qualified and the temperature of the molten steel is 80 °C higher than the liquidus temperature, tap the steel and pour it into an electrode bar.

[0171] 4) Vacuum consumable melting: Remelt the electrode bar using a 3t vacuum consumable furnace to obtain an ingot with a diameter . Among them, the number of times of vacuum consumable melting is 2 times. The crucible ratio of the vacuum consumable melting is 0.7d·D -1 (d is the diameter of the electrode bar, D is the inner diameter of the crucible), the melting vacuum degree is 10 -3 Pa, the melting voltage is 25 V, the melting current is 7 KA, and the melting coefficient is 1 kg·(kA·min) -1 , and helium is used for cooling.

[0172] 5) Forging: Forge the ingot to obtain the finished product. The holding temperature for forging is 1200 °C, the starting forging temperature is 1000 °C, and the final forging temperature is 800 °C. One upsetting and drawing process is carried out during forging. The one upsetting and drawing process includes: first upset the ingot and then draw it. When upsetting, the ingot is upset to 1 / 2 of the original ingot height, and then it is elongated by drawing to make the diameter of the final forging meet the requirements. The total forging ratio is 10.3:1, and a finished product with a diameter is obtained.

[0173] 6) Annealing: Anneal the finished product. The annealing temperature is 830 °C, hold for 6 h, and then cool in the furnace to 400 °C and then take out and air-cool.

[0174] 7) Quenching: Put the annealed finished product into the furnace at a temperature of 300 °C, heat it to 750 °C at a rate of 100 °C / h and hold for 2 h, then heat it to 1150 °C at a rate of 100 °C / h and hold for 7 h, and then air-cool after taking out of the furnace.

[0175] 8) First tempering: Put the finished product quenched in step 7) into the furnace at a temperature of 100 °C, heat it to 570 °C at a rate of 50 °C / h and hold for 7 h, and then air-cool after taking out of the furnace.

[0176] 9) Second tempering: Put the finished product after the first tempering in step 8) into the furnace at a temperature of 100 °C, heat it to 570 °C at a rate of 50 °C / h and hold for 7 h, and then air-cool to room temperature to obtain niobium-containing stainless steel.

[0177] The grain size of the niobium-containing stainless steel prepared in this comparative example is Grade 4. The niobium-containing stainless steel prepared in this comparative example is subjected to macro examination and micro examination, and the results are as Figures 8 - 10 shown. It can be seen from Figures 8 - 10 this that there are coarse grains in the local area of the macrostructure, and the microstructure is uneven.

[0178] Using the niobium-containing stainless steel prepared in this comparative example as a specimen, its tensile strength is measured to be 1197 Mpa; three stainless steels at different depth positions at half of the radius of the end cross-section of the niobium-containing stainless steel prepared in this comparative example are intercepted as specimens for impact energy testing. The longitudinal impact energy at room temperature at different positions is 62 J / 29 J / 45 J. The tensile strength of the niobium-containing stainless steel prepared in this comparative example is poor, and the impact energy is unstable.

[0179] Twenty batches of steel are prepared by the method provided in this comparative example, among which 5 batches have unstable impact energy and 4 batches have a grain size not reaching above Grade 5.

Claims

1. A preparation method of niobium-containing stainless steel, the niobium-containing stainless steel comprises the following components by mass percentage: C 0.10% - 0.20%, Si 0.15% - 0.60%, Mn 0.30% - 1.25%, P ≤ 0.040%, S ≤ 0.030%, Cr 9.50% - 11.50%, Ni ≤ 0.50%, V 0.15% - 0.40%, Nb 0.10% - 0.60%, and the balance is Fe and inevitable impurities. Characterized in that, The method comprises the following steps: Smelting: Smelt the raw materials of the niobium-containing stainless steel in a vacuum induction melting furnace to obtain molten steel. During the fine adjustment of the steel composition in the smelting process, Nb is added all at once together with ferro-niobium and the alloys finally used for composition adjustment and supplementation. The smelting is vacuum induction smelting, and the vacuum induction smelting sequentially comprises the following steps: Charging and melting: Adjust the power of the vacuum induction furnace to 700 - 900 KW, and continuously and sequentially add all the raw materials in the charge, namely pure iron or / and scrap steel, and at least one alloy raw material other than ferro-niobium, into the vacuum induction furnace for melting of the raw materials. During the melting process, keep the vacuum degree in the furnace ≤ 0.3 Pa. Refining: After adjusting the power to 500 - 1000 KW and maintaining it for 10 - 15 min, perform stirring, with the vacuum degree in the furnace ≤ 0.3 Pa. Composition adjustment: After the refining stirring is completed, lower the power to 250 - 400 KW, perform the first composition analysis on the refined molten steel, fine-tune the composition according to the results of the first composition analysis, add at least one alloy raw material other than ferro-niobium remaining in the charge, then raise the power to 500 - 1000 KW, perform melting and stirring, and the stirring time is 3 - 5 min. After the first composition adjustment is completed, lower the power to 250 - 400 KW, perform the second composition analysis, supplement alloys to fine-tune the composition according to the results of the second composition analysis. While supplementing the alloys, add all the ferro-niobium in the charge at once, then raise the power to 500 - 1000 KW, perform melting and stirring, and the stirring time is 3 - 5 min. Pouring: When the temperature of the molten steel is 40 - 120 °C higher than the liquidus temperature, tap the steel and pour it into electrode bars. Vacuum consumable melting: Perform vacuum consumable melting on the electrode bars to obtain steel ingots. Forging: Forge the steel ingots to obtain finished products.

2. According to the preparation method of the niobium-containing stainless steel described in claim 1, Characterized in that, In the charging and melting step, the addition amount of at least one alloy raw material other than ferro-niobium is 25% - 35% of the total mass of the corresponding alloy raw materials charged. During the melting process, when the molten steel boils, lower the power to 100 - 200 KW until the molten steel does not boil violently. And / or, in the refining step, the stirring time is 3 - 5 min. And / or, the vacuum induction smelting further comprises before the charging and melting step: Heating: At the initial stage of vacuum induction smelting, the vacuum induction furnace is heated at a low power for 1.5 - 2 h, and the vacuum degree in the vacuum induction furnace is adjusted to ≤ 0.3 Pa. Among them, the low power is 250 - 450 KW.

3. The method for preparing niobium-containing stainless steel according to claim 1, characterized in that, before the smelting step, the method for preparing niobium-containing stainless steel further comprises the following steps: Batching: Batching according to the composition of the niobium-containing stainless steel. The raw material pure iron is ultra-low carbon pure iron, and the alloy raw materials include at least one of the raw materials of chromium, nickel, vanadium, manganese, molybdenum, copper and niobium. The raw material of chromium is low S, P metal chromium, the raw material of nickel is low S, P electrolytic nickel, the raw material of vanadium is ferrovanadium, the raw material of niobium is ferroniobium, the raw material of manganese is metallic manganese, the raw material of molybdenum is metallic molybdenum or molybdenum iron, and the raw material of copper is electrolytic copper.

4. The method for preparing niobium-containing stainless steel according to claim 1, characterized in that, at least one upsetting and drawing is carried out during the forging process. The one upsetting and drawing includes: first upsetting and then drawing. When upsetting, the ingot is upset to 1 / 2 - 1 / 3 of the original ingot height, and then it is drawn to make the diameter of the final forging meet the requirements; and / or, the total forging ratio of the forging is greater than or equal to 6.5:1; and / or, the holding temperature of the forging is 1120 - 1200 °C, the starting forging temperature ≥ 1000 °C, and the finishing forging temperature ≥ 800 °C.

5. The method for preparing niobium-containing stainless steel according to claim 1, characterized in that, after the forging step, the preparation method further includes: Annealing: Annealing the finished product, and then cooling it in the furnace to 300 - 500 °C and then taking it out of the furnace for air cooling or directly taking it out of the furnace for air cooling.

6. The method for preparing niobium-containing stainless steel according to claim 5, characterized in that, after the annealing step, the preparation method further includes: Quenching: The annealed finished product is put into the furnace at a temperature of 200 - 400 °C, heated to 600 - 800 °C at a speed of 50 - 150 °C / h and held for 1 - 3 h, then heated to 1000 - 1200 °C at a speed of 50 - 150 °C / h and held. The holding time at 1000 - 1200 °C is calculated as 2 - 4 h / 100 mm, and then air cooled; First tempering: The quenched finished product is put into the furnace at a temperature of 50 - 150 °C, heated to 500 - 700 °C at a speed of 30 - 60 °C / h and held. The holding time at 500 - 700 °C is calculated as 3 - 6 h / 100 mm, and then air cooled; Second tempering: The finished product after the first tempering is put into the furnace at a temperature of 50 - 150 °C, heated to 500 - 700 °C at a speed of 30 - 60 °C / h and held. The holding time at 500 - 700 °C is calculated as 3 - 6 h / 100 mm, and then air cooled to obtain the niobium-containing stainless steel.

7. The method for preparing niobium-containing stainless steel according to claim 1, characterized in that, The crucible ratio of the vacuum consumable melting is 0.6 to 0.9d·D -1 , the melting vacuum degree is 10 -3 ~10 -2 Pa, the melting voltage is 25 to 45V, the melting current is 7 to 20KA, and the melting coefficient is 1 to 2kg·(kA·min) -1 , where d is the diameter of the electrode rod and D is the inner diameter of the crucible; and / or, the number of times of vacuum consumable melting is 2 - 3 times.

8. A niobium-containing stainless steel, characterized in that, the niobium-containing stainless steel is made by the preparation method according to any one of claims 1 - 7.

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