High-nitrogen stainless steel and preparation method and application thereof

Abstract

The invention provides high-nitrogen stainless steel and a preparation method and application thereof. The preparation method comprises the following steps: putting nickel, molybdenum, niobium, pure iron and chromium into a vacuum induction furnace, and melting a steel material in a low-power stepped manner under a vacuum condition to obtain molten steel with a target content; si is added into the molten steel, and refining deoxidation is carried out; the molten steel is sequentially subjected to first nitrogen adjustment treatment and second nitrogen adjustment treatment, and the first nitrogen adjustment treatment comprises the steps that under the condition that the argon filling pressure ranges from 7000 Pa to 10000 Pa, nitrided ferrochrome and Ce are added into the molten steel, and the nitrogen content in the molten steel is adjusted to range from 1000 ppm to 1500 ppm; in the second nitrogen adjusting treatment, nitrided ferrochrome, Ce and Ca are added under the atmospheric pressure, and the nitrogen content in the molten steel is adjusted to be 3000-4000 ppm; the temperature in the vacuum induction furnace is adjusted to 1500-1580 DEG C, the superheat degree is 80-140 DEG C, tapping is conducted, after tapping is conducted for 60-120 min, demolding is conducted, and the high-nitrogen stainless steel is obtained. The nitrided ferrochrome is added and matched with a proper deoxidation system, so that the material has high nitrogen content and low oxygen content, and has corrosion resistance and low-temperature impact resistance.

Description

Technical Field

[0001] The invention relates to the technical field of new metal materials, in particular to high-nitrogen stainless steel and a preparation method and application thereof. Background Art

[0002] As a clean energy with near-zero emissions, nuclear energy is becoming increasingly prominent in the energy structure, heralding broad development prospects.

[0003] However, traditional nuclear fission technology still has many problems, such as strong radiation hazards, long-term difficult to handle radioactive waste, and serious pollution to the environment. These problems limit the further application and development of nuclear fission technology. In contrast, nuclear fusion, as a clean and sustainable form of energy, has significant advantages such as less radiation and abundant fuel.

[0004] In the research and development and application of nuclear fusion technology, the requirements for materials are extremely strict, especially for protective materials used in fusion test reactors. Such materials need to have high room temperature strength to withstand the influence of extreme environments. Nitrogen has become a key alloying element because it can effectively improve the strength of materials. Traditional smelting processes are difficult to meet the requirements of high nitrogen content and low oxygen content at the same time under low carbon conditions. Especially in the vacuum induction furnace smelting process, due to the low smelting vacuum, the existing technology is difficult to adjust the nitrogen content to more than 3000ppm and the oxygen content to less than 20ppm. Summary of the invention

[0005] 1. Technical issues to be solved

[0006] In view of the deficiencies in the prior art, the present invention provides a high-nitrogen stainless steel and a preparation method and application thereof, and uses a suitable deoxidizer and a nitrogen adjustment process to solve the problems raised in the above-mentioned background technology.

[0007] (II) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] According to a first aspect of the present invention, there is provided a method for preparing high nitrogen stainless steel, comprising the following steps:

[0010] (1) placing metal nickel, metal molybdenum, metal niobium, pure iron and metal chromium in a vacuum induction furnace, and melting the steel material in a low-power step-wise manner under vacuum conditions to obtain molten steel with a target content;

[0011] (2) adding Si to the molten steel for refining and deoxidation;

[0012] (3) subjecting the refined and deoxidized molten steel to a first nitrogen adjustment treatment and a second nitrogen adjustment treatment in sequence, wherein the first nitrogen adjustment treatment comprises: adding ferrochrome nitride and Ce to the molten steel under an argon gas pressure of 7000 to 10000 Pa to adjust the nitrogen content in the molten steel to 1000 to 1500 ppm; and the second nitrogen adjustment treatment comprises: adding ferrochrome nitride, Ce and Ca under atmospheric pressure to adjust the nitrogen content in the molten steel to 3000 to 4000 ppm;

[0013] (4) The temperature in the vacuum induction furnace is adjusted to 1500-1580°C, and the steel is tapped at a superheat of 80-140°C. After 60-120 minutes of tapping, the steel is demolded to obtain high nitrogen stainless steel.

[0014] Preferably, in step (1), the low-power step-by-step method is: under the condition of increasing power ≤ 200 kW per hour, increasing power to 800 kW to melt the steel.

[0015] Preferably, in step (1), the chemical composition and mass fraction of the target content of the molten steel are: ≤0.01% C, ≤0.50% Si, 3.0-6.0% Mn, ≤0.005% S, ≤0.010% P, 20.0-24.0% Cr, 13.0-18.0% Ni, 1.0-3.0% Mo, 0.05-0.30% Nb, 0.2-0.4% N, 0.1-0.5% Cu, ≤0.03% Al, ≤0.05% Co, 0.1-0.5% V and the balance iron.

[0016] Preferably, in step (2), the amount of Si added is 0.1-0.3% of the molten steel.

[0017] Preferably, in step (2), the refining and deoxidation temperature is 1450-1520°C.

[0018] Preferably, in step (3), the first nitrogen adjustment treatment and the second nitrogen adjustment treatment are both performed at 1450-1520°C.

[0019] Preferably, in step (3), during the first nitrogen adjustment treatment, the amount of Ce added is 0.05-0.20% of the molten steel;

[0020] During the second nitrogen adjustment treatment, the added amounts of Ce and Ca are both 0.05-0.30% of the molten steel.

[0021] According to a second aspect of the present invention, there is provided a high nitrogen stainless steel obtained according to the above preparation method, wherein the high nitrogen stainless steel has a nitrogen content of 3000-4000 ppm, a carbon content of ≤0.01%, and an oxygen content of ≤0.002%.

[0022] Preferably, the inclusions ABCD in the high nitrogen stainless steel are ≤1.5 for fine series and ≤1.0 for coarse series.

[0023] According to a third aspect of the present invention, there is provided an application of high-nitrogen stainless steel as a protective material in the field of nuclear fusion.

[0024] (III) Beneficial effects

[0025] The present invention provides a high nitrogen stainless steel and a preparation method and application thereof, which has the following beneficial effects:

[0026] The present invention provides a method for preparing high nitrogen stainless steel. By adding ferrochromium nitride and combining with an appropriate deoxidation system in a vacuum induction furnace, the nitrogen content of the prepared material can reach 3000-4000ppm and the oxygen content is ≤20ppm. The corrosion and low temperature impact properties can be taken into account, and the use requirements as a protective material in the field of nuclear fusion can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The metallographic image of high nitrogen stainless steel prepared in Example 1 of the present invention at 100 times magnification;

[0028] Figure 2 This is a metallographic image of the high nitrogen stainless steel prepared in Example 1 of the present invention at 500 times magnification;

[0029] Figure 3 This is a metallographic image of the high nitrogen stainless steel prepared in Example 2 of the present invention at 100 times magnification;

[0030] Figure 4 This is a metallographic image of the high nitrogen stainless steel prepared in Example 2 of the present invention at 500 times magnification;

[0031] Figure 5 This is a metallographic image of the high nitrogen stainless steel prepared in Example 3 of the present invention at 100 times magnification;

[0032] Figure 6 This is a metallographic image of the high nitrogen stainless steel prepared in Example 3 of the present invention at a magnification of 500 times. DETAILED DESCRIPTION

[0033] In order to better illustrate the content of the present invention, a detailed description is given below in conjunction with specific embodiments.

[0034] A method for preparing high nitrogen stainless steel comprises the following steps:

[0035] Step 1, placing metal nickel, metal molybdenum, metal niobium, pure iron and metal chromium in a high-resolution induction furnace according to the principle of tightening at the bottom and loosening at the top. Specifically, metal nickel is placed at the bottom, metal molybdenum and metal niobium are added in the high-temperature zone to melt them, and then pure iron and metal chromium are added in sequence, the vacuum pump is started to evacuate, and after switching to high vacuum (vacuum degree ≤10Pa), power is supplied, and the power is increased to 800kw at a rate of ≤200kw per hour. Fe, Cr, Mo and Nb are added during the chemical process, and the molten steel is adjusted to meet the following chemical components and mass fractions, as shown in Table 1:

[0036] Table 1

[0037]

[0038] Step 2, adding 0.1-0.3% Si to the molten steel for refining and deoxidation, the refining and deoxidation temperature is controlled at 1450-1520°C, and a medium-low temperature refining process is adopted to reduce the crucible oxygen supply: Al2O3, MgO, and SiO2 in the crucible material are decomposed at high temperature, and O is transferred to the molten steel, causing the molten steel to increase oxygen, and deoxidation is carried out by adding Si to reduce the oxygen concentration in the molten steel;

[0039] Step 3, maintaining the temperature at 1450-1520°C, adding ferrochrome nitride and Ce to the molten steel under the condition of argon gas pressure of 7000-10000Pa, performing the first nitrogen adjustment treatment, adjusting the nitrogen content in the molten steel to 1000-1500ppm; then adding ferrochrome nitride, Ce and Ca under atmospheric pressure, performing the second nitrogen adjustment treatment, adjusting the nitrogen content in the molten steel to 3000-4000ppm; during the first nitrogen adjustment treatment, adding 0.05-0.20% Ce to remove oxygen from the molten steel. During the second nitrogen adjustment treatment, adding 0.05-0.3% Ce and Ca respectively to achieve full deoxidation;

[0040] Step 4, adjusting the temperature in the vacuum induction furnace to 1500-1580° C., tapping the steel at a superheat of 80-140° C., and demolding the steel after 60-120 minutes to obtain high nitrogen stainless steel.

[0041] The high nitrogen stainless steel provided by the present invention and its preparation method and application are described in detail below in conjunction with specific embodiments.

[0042] Example 1

[0043] Adding materials: Place 200kg of nickel with a C content of 0.004% at the bottom of the high-temperature induction furnace, add 110kg of molybdenum and 4.5kg of niobium in the high-temperature zone, and then add 2505kg of pure iron with a C content of 0.015% and 885kg of chromium with a C content of 0.005% in sequence, and place the materials according to the principle of tightening at the bottom and loosening at the top. Start the vacuum pump to evacuate and turn to high vacuum. After the vacuum degree of the smelting chamber is 8.6Pa, power is supplied, and the power is increased to 800kw at a rate of 180kw per hour. During the period of materialization, appropriate Fe, Cr, Mo and Nb are added to obtain molten steel with the target content;

[0044] Refining and deoxidation: add 0.2% Si to the molten steel, control the refining and deoxidation temperature to 1490℃, adopt medium and low temperature refining process, and reduce the oxygen supply in the crucible;

[0045] Nitrogen adjustment and deoxidation: keep the refining temperature at 1490℃, add ferrochrome nitride to the molten steel under the argon filling pressure of 8200Pa, adjust the nitrogen content in the molten steel to 1200ppm at a recovery rate of 45% of the N element, and add 0.1% Ce for deoxidation in the first nitrogen adjustment process; adopt the air-breaking process, add ferrochrome nitride under atmospheric pressure, adjust the nitrogen content in the molten steel to 3300ppm at a recovery rate of 90% of the N element, and add 0.25% Ce and 0.1% Ca for strong deoxidation in the second nitrogen adjustment process to achieve the purpose of sufficient deoxidation;

[0046] Steel tapping: Use a thermocouple to measure the temperature, adjust the temperature in the vacuum induction furnace to 1530°C, and demould 80 minutes after steel tapping to obtain high nitrogen stainless steel.

[0047] The high nitrogen stainless steel in this embodiment is processed by electroslag and forging process, and samples are taken from the forged round steel for testing, and the composition, gas, inclusions and precipitation are detected. Through testing, the C content of the high nitrogen stainless steel is 0.004%, the N content is 3270ppm, and the O content is 0.0017%. Figure 1 and Figure 2 It can be seen that the high nitrogen stainless steel prepared in this embodiment satisfies C≤0.01%, O≤0.0020%, the fine series of inclusions ABCD≤1.5 level, the coarse series≤1.0 level, and no carbides and carbonitrides are precipitated.

[0048] Example 2

[0049] Adding materials: Place 220kg of nickel with a C content of 0.003% at the bottom of the high-temperature induction furnace, add 118kg of molybdenum and 4.9kg of niobium in the high-temperature zone, and then add 2562kg of pure iron with a C content of 0.023% and 894kg of chromium with a C content of 0.032% in sequence, and place the materials according to the principle of tightening at the bottom and loosening at the top. Start the vacuum pump to evacuate and turn to high vacuum. After the vacuum degree of the smelting chamber is 7.8Pa, power is supplied, and the power is increased to 800kw at a rate of 190kw per hour. During the period of materialization, appropriate Fe, Cr, Mo and Nb are added to obtain molten steel with the target content;

[0050] Refining and deoxidation: add 0.25% Si to the molten steel, control the refining and deoxidation temperature to 1486℃, adopt medium and low temperature refining process, and reduce the oxygen supply in the crucible;

[0051] Nitrogen adjustment and deoxidation: keep the refining temperature at 1486℃, under the argon filling pressure of 9100Pa, add chromium nitride to the molten steel, and adjust the nitrogen content in the molten steel to 1350ppm at a recovery rate of 52% of the N element. In the first nitrogen adjustment process, add 0.12% of Ce for deoxidation; adopt the air-breaking process, add chromium nitride under atmospheric pressure, and adjust the nitrogen content in the molten steel to 3800ppm at a recovery rate of 88% of the N element. In the second nitrogen adjustment process, add 0.28% of Ce and 0.12% of Ca for strong deoxidation to achieve the purpose of sufficient deoxidation;

[0052] Steel tapping: Use a thermocouple to measure the temperature, adjust the temperature in the vacuum induction furnace to 1545°C, and demould after 82 minutes of steel tapping to obtain high nitrogen stainless steel.

[0053] The high nitrogen stainless steel in this embodiment is processed by electroslag and forging process, and samples are taken from the forged round steel for testing, and the composition, gas, inclusions and precipitation are detected. Through testing, the C content of the high nitrogen stainless steel is 0.002%, the N content is 3910ppm, and the O content is 0.0018%. Figure 3 and Figure 4 It can be seen that the high nitrogen stainless steel prepared in this embodiment satisfies C≤0.01%, O≤0.0020%, the fine series of inclusions ABCD≤1.5 level, the coarse series≤1.0 level, and no carbides and carbonitrides are precipitated.

[0054] Example 3

[0055] Adding materials: Place 235kg of nickel with a C content of 0.003% at the bottom of the high-temperature induction furnace, add 102kg of molybdenum and 4.0kg of niobium in the high-temperature zone, and then add 2435kg of pure iron with a C content of 0.013% and 876kg of chromium with a C content of 0.004% in sequence, and place the materials according to the principle of tightening at the bottom and loosening at the top. Start the vacuum pump to evacuate and turn to high vacuum. After the vacuum degree of the smelting chamber is 9.7Pa, power is supplied, and the power is increased to 800kw at a rate of 175kw per hour. During the period of materialization, appropriate Fe, Cr, Mo and Nb are added to obtain molten steel with the target content;

[0056] Refining and deoxidation: add 0.18% Si to the molten steel, control the refining and deoxidation temperature to 1504℃, adopt medium and low temperature refining process, and reduce the oxygen supply in the crucible;

[0057] Nitrogen adjustment and deoxidation: keep the refining temperature at 1504℃, under the argon filling pressure of 9500Pa, add chromium nitride to the molten steel, and adjust the nitrogen content in the molten steel to 1280ppm at a recovery rate of 48% of the N element. In the first nitrogen adjustment process, add 0.08% Ce for deoxidation; adopt the air-breaking process, add chromium nitride under atmospheric pressure, and adjust the nitrogen content in the molten steel to 3100ppm at a recovery rate of 86% of the N element. In the second nitrogen adjustment process, add 0.15% Ce and 0.108% Ca for strong deoxidation to achieve the purpose of sufficient deoxidation;

[0058] Steel tapping: Use a thermocouple to measure the temperature, adjust the temperature in the vacuum induction furnace to 1528°C, and demould 90 minutes after steel tapping to obtain high nitrogen stainless steel.

[0059] The high nitrogen stainless steel in this embodiment is processed by electroslag and forging process, and samples are taken from the forged round steel for testing, and the composition, gas, inclusions and precipitation are detected. Through testing, the C content of the high nitrogen stainless steel is 0.006%, the N content is 3120ppm, and the O content is 0.0012%. Figure 5 and Figure 6 It can be seen that the high nitrogen stainless steel prepared in this embodiment satisfies C≤0.01%, O≤0.0020%, the fine series of inclusions ABCD≤1.5 level, the coarse series≤1.0 level, and no carbides and carbonitrides are precipitated.

[0060] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high nitrogen stainless steel, Features: The following steps are involved: (1) placing metal nickel, metal molybdenum, metal niobium, pure iron and metal chromium in a vacuum induction furnace, and melting the steel material in a low-power step-wise manner under vacuum conditions to obtain molten steel with a target content; (2) adding Si to the molten steel for refining and deoxidation; (3) subjecting the refined and deoxidized molten steel to a first nitrogen adjustment treatment and a second nitrogen adjustment treatment in sequence, wherein the first nitrogen adjustment treatment comprises: adding ferrochrome nitride and Ce to the molten steel under an argon gas pressure of 7000 to 10000 Pa to adjust the nitrogen content in the molten steel to 1000 to 1500 ppm; and the second nitrogen adjustment treatment comprises: adding ferrochrome nitride, Ce and Ca under atmospheric pressure to adjust the nitrogen content in the molten steel to 3000 to 4000 ppm; (4) The temperature in the vacuum induction furnace is adjusted to 1500-1580°C, and the steel is tapped at a superheat of 80-140°C. After 60-120 minutes of tapping, the steel is demolded to obtain high nitrogen stainless steel.

2. A method for preparing high nitrogen stainless steel according to claim 1, Features: In step (1), the low-power step-by-step method is: under the condition of increasing power ≤ 200 kW per hour, increasing power to 800 kW to melt the steel.

3. The method for preparing high nitrogen stainless steel according to claim 1, Features: In step (1), the chemical composition and mass fraction of the target content of the molten steel are: ≤0.01% C, ≤0.50% Si, 3.0-6.0% Mn, ≤0.005% S, ≤0.010% P, 20.0-24.0% Cr, 13.0-18.0% Ni, 1.0-3.0% Mo, 0.05-0.30% Nb, 0.2-0.4% N, 0.1-0.5% Cu, ≤0.03% Al, ≤0.05% Co, 0.1-0.5% V and the balance of iron.

4. The method for preparing high nitrogen stainless steel according to claim 1, Features: In step (2), the amount of Si added is 0.1-0.3% of the molten steel.

5. The method for preparing high nitrogen stainless steel according to claim 1, Features: In step (2), the refining and deoxidation temperature is 1450-1520°C.

6. The method for preparing high nitrogen stainless steel according to claim 1, Features: In step (3), the first nitrogen adjustment treatment and the second nitrogen adjustment treatment are both performed at 1450-1520°C.

7. The method for preparing high nitrogen stainless steel according to claim 1, Features: In step (3), during the first nitrogen adjustment treatment, the amount of Ce added is 0.05-0.20% of the molten steel; During the second nitrogen adjustment treatment, the added amounts of Ce and Ca are both 0.05-0.30% of the molten steel.

8. A high nitrogen stainless steel obtained by the preparation method according to any one of claims 1 to 8, Features: The high nitrogen stainless steel has a nitrogen content of 3000-4000 ppm, a carbon content of ≤0.01%, and an oxygen content of ≤0.002%.

9. The high nitrogen stainless steel according to claim 8, Features: The inclusions ABCD in the high nitrogen stainless steel are ≤1.5 for fine series and ≤1.0 for coarse series.

10. Use of the high nitrogen stainless steel according to claim 8 or 9 as a protective material in the field of nuclear fusion.

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