Production process for high-nitrogen austenitic steel

Abstract

Provided in the present invention is a production process for high-nitrogen austenitic steel. The process comprises the steps of forging, a solution treatment, cold rolling, annealing, quenching and tempering, wherein the initial forging temperature is 1120-1160°C, the final forging temperature is 945-1025°C, and the forging ratio is 3-5; the solid solution temperature is 1000-1100°C, and the temperature is maintained for 25-35 minutes; the total rolling deformation is 50-60%; the annealing temperature is 780-820°C, and the temperature is maintained for 2-3 minutes; the steel in the annealing state is heated to 860-920°C, and the temperature is maintained for 40-50 minutes; the temperature is then increased to 1060-1090°C to perform a quenching treatment, and the temperature is maintained for 60-70 minutes; oil quenching is performed; a subzero treatment is then performed at -200°C to -195°C, and the treatment time is 60-70 minutes; and the tempering temperature is 140-150°C, and the tempering time is 2-3 hours. The present invention optimizes the production process for high-nitrogen austenitic stainless steel, and the prepared high-nitrogen austenitic stainless steel has high pitting corrosion resistance and intergranular corrosion resistance, also has great mechanical properties, and can be applied to the fields of energy, chemical engineering, national defense, medical treatment, etc.

Description

A production process for high-nitrogen austenitic steel Technical Field

[0001] This invention relates to the field of alloy preparation technology, and in particular to a production process for high-nitrogen austenitic steel. Background Technology

[0002] In the traditional production process of austenitic stainless steel, nickel and chromium are important alloying elements. However, due to the scarcity and high cost of nickel, it becomes a significant factor determining the cost of austenitic stainless steel. Research shows that nitrogen can replace nickel in austenitic steel for austenite formation; the equivalence between nitrogen and nickel is: 1 kg of nitrogen can replace 6-39 kg of nickel, but the price of nickel is 200 times that of nitrogen. Using inexpensive and widely available nitrogen to replace expensive and scarce nickel in the preparation of austenitic stainless steel can significantly reduce nickel resource consumption and lower the production cost.

[0003] Generally, high-nitrogen austenitic stainless steel is considered to be a high-performance stainless steel with a nitrogen mass fraction higher than 0.4% and a single austenitic microstructure. Compared with traditional austenitic stainless steel, high-nitrogen austenitic stainless steel has superior mechanical properties, corrosion resistance, oxidation resistance, and wear resistance, while also being less expensive, virtually harmless to the human body, and having a wider range of applications. High-nitrogen austenitic stainless steel balances the benefits of improved performance with reduced costs, resulting in significant economic and social benefits.

[0004] High-nitrogen austenitic stainless steel is gaining increasing attention in numerous fields such as energy, chemical industry, defense, and medicine, leading to the development of many new applications. It shows promising development trends in three future material development areas: high-performance steel, resource-saving steel, and bio-friendly steel. While high-nitrogen austenitic stainless steel possesses excellent comprehensive mechanical properties, further strength enhancement is needed to meet the demands of actual industrial production and its application in complex and variable working environments. Rolling is the most common method for increasing material strength. However, while rolling can significantly improve the strength of high-nitrogen austenitic stainless steel, it also drastically deteriorates its plasticity and toughness. Therefore, it is still necessary to explore suitable heat treatment processes to obtain even better comprehensive mechanical properties. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a production process for high-nitrogen austenitic steel, thereby improving the pitting corrosion resistance, intergranular corrosion resistance, and overall mechanical properties of high-nitrogen austenitic steel.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A production process for high-nitrogen austenitic steel, comprising the following steps:

[0008] Step S1: Forging: Place the high-nitrogen austenitic steel ingot into a heating furnace and heat it. The initial forging temperature is 1120-1160℃, the final forging temperature is 945-1025℃, the forging ratio is 3-5, and the forging is followed by water cooling.

[0009] Step S2: Solution treatment: The forged steel billet is subjected to solution treatment at a temperature of 1000-1100℃ for 25-35 minutes; after solution treatment, it is water cooled.

[0010] Step S3: Cold rolling: The solution-treated steel is rolled using a multi-pass cold rolling method, controlling the total rolling deformation to be 50-60%;

[0011] Step S4: Annealing: Annealing temperature 780~820℃, holding time 2~3 minutes;

[0012] Step S5: Quenching: Heat the annealed steel to 860-920℃ and hold for 40-50 minutes. Then raise the temperature to 1060-1090℃ for quenching and hold for 60-70 minutes. Remove and oil quench. Then perform deep cryogenic treatment at -200--195℃ for 60-70 minutes.

[0013] Step S6: Tempering: Tempering temperature 140~150℃, tempering time 2~3 hours.

[0014] Preferably, the chemical composition of the high-nitrogen austenitic steel is as follows (by weight percentage): C: ≤0.12%, Si: 0.55–0.72%, Mn: 15.2–16.35%, Cr: 18.63–19.35%, Mo: 2.88–3.12%, N: 0.86–0.95%, V: 0.56–0.68%, Nb: 0.22–0.30%, Cu: 0.005–0.01%, Al: 0.005–0.01%, P: ≤0.02%, S: ≤0.003%, with the balance being Fe and unavoidable impurities.

[0015] Preferably, the high-nitrogen austenitic steel ingot is prepared by pressurized vacuum induction furnace smelting and protective atmosphere electroslag remelting process.

[0016] Preferably, the solid solution steel has a grain size of 42–48 μm, straight and clear grain boundaries, a single austenitic phase, a microhardness of 280–290 HV, a yield strength of 610–630 MPa, and a tensile strength of 890–910 MPa.

[0017] Preferably, in step S3, a six-pass cold rolling process is adopted, with each pass having a rolling deformation of 10% and a total rolling deformation of 60%.

[0018] Preferably, the yield strength of the annealed steel is 860–890 MPa, and the tensile strength is 1100–1200 MPa.

[0019] Preferably, the yield strength of the tempered steel is 920–980 MPa and the tensile strength is 1250–1380 MPa.

[0020] Preferably, the production process of the high-nitrogen austenitic steel includes the following steps:

[0021] Step S1: Forging: Place the high-nitrogen austenitic steel ingot into a heating furnace and heat it. The initial forging temperature is 1140℃, the final forging temperature is 965℃, the forging ratio is 4, and the forging is followed by water cooling.

[0022] Step S2: Solution treatment: The forged steel billet is subjected to solution treatment at a temperature of 1050℃ for 30 minutes; after solution treatment, it is water cooled.

[0023] Step S3: Cold rolling: The solution-treated steel is rolled using a six-pass cold rolling process, with the total rolling deformation controlled at 60%.

[0024] Step S4: Annealing: Annealing temperature 805℃, holding time 2 minutes;

[0025] Step S5: Quenching: Heat the annealed steel to 870℃ and hold for 50 minutes, then raise the temperature to 1080℃ for quenching and hold for 60 minutes. Remove and oil quench; then perform deep cryogenic treatment at -195.5℃ for 60 minutes.

[0026] Step S6: Tempering: Tempering temperature 150℃, tempering time 3 hours.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention optimizes the production process of high nitrogen austenitic stainless steel, and the prepared high nitrogen austenitic stainless steel has high resistance to pitting corrosion and intergranular corrosion, as well as excellent mechanical properties, and can be applied in many fields such as energy, chemical industry, national defense, and medical treatment. Attached Figure Description

[0028] Figure 1 is a flowchart of the production process of high-nitrogen austenitic steel according to some embodiments of the present invention;

[0029] Figure 2 shows the metallographic structure of steel after annealing according to an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It is understood that, without conflict, some technical means of the various embodiments described herein can be substituted for or combined with each other.

[0031] In the description of this invention, the terms "first," "second," etc., are used only to distinguish the described objects and have no sequential or technical meaning. Therefore, objects specified with "first," "second," etc., may explicitly or implicitly include one or more of those objects. Furthermore, the words "one" or "a" do not indicate a quantity limitation, but rather indicate the presence of at least one, while "multiple" indicates at least two.

[0032] In the description of this invention, references to "one embodiment" or "some embodiments" mean that one or more embodiments of the invention include a particular feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "one embodiment," "some embodiments," "other embodiments," "and other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0033] This invention provides a production process for high-nitrogen austenitic steel, the chemical composition of which, by weight percentage, is: C: ≤0.12%, Si: 0.55~0.72%, Mn: 15.2~16.35%, Cr: 18.63~19.35%, Mo: 2.88~3.12%, N: 0.86~0.95%, V: 0.56~0.68%, Nb: 0.22~0.30%, Cu: 0.005~0.01%, Al: 0.005~0.01%, P: ≤0.02%, S: ≤0.003%, with the balance being Fe and unavoidable impurities.

[0034] In the aforementioned high-nitrogen austenitic steels, carbon (C) is a strong austenite-forming and stabilizing element that expands the austenite region. It significantly improves the strength of austenitic stainless steel through interstitial solid solution strengthening and also enhances its resistance to stress corrosion. Chromium (Cr) is the most important alloying element contributing to the corrosion resistance of stainless steel. In oxidizing media, chromium rapidly forms a chromium oxide passivation film on the alloy surface, improving the corrosion resistance of stainless steel. Nitrogen (N) is an austenite-stabilizing element that inhibits the formation of ferrite and strain-induced martensite in steel. Furthermore, N is highly beneficial for improving the steel's resistance to pitting and stress corrosion. Cr effectively improves the steel's resistance to pitting and crevice corrosion; this effectiveness is greatly enhanced when N is also present in the steel. Si is a strong ferrite-forming element; N in stainless steel can combine with Si to form a small amount of silicon nitride in the passivation layer, contributing to its composition and improving corrosion resistance. Ni is used to improve the toughness and impact resistance of steel, reduce its hardness and strength, and improve its machinability. In addition, Ni can improve the corrosion resistance of steel, especially against some strong acid and alkali solutions. Mn can form a strengthening phase with N, further improving the strength and hardness of steel, and can also improve the heat resistance and corrosion resistance of high-nitrogen austenitic stainless steel. V can refine grains and stabilize the structure, improving the hardness and high-temperature resistance of stainless steel through its properties, making it more suitable for use in high-temperature environments, while also enhancing the wear resistance and corrosion resistance of steel. By adding Nb, the pitting corrosion resistance of austenitic stainless steel can be effectively improved, enhancing its corrosion resistance in specific environments. The addition of Mo can improve the steel's resistance to corrosion in reducing media and its resistance to pitting corrosion and crevice corrosion.

[0035] Referring to Figure 1, the production process of this high-nitrogen austenitic steel includes the following steps:

[0036] Step S1: Forging: Place the high-nitrogen austenitic steel ingot into a heating furnace and heat it. The initial forging temperature is 1120-1160℃, the final forging temperature is 945-1025℃, the forging ratio is 3-5, and the forging is followed by water cooling.

[0037] Step S2: Solution treatment: The forged steel billet is subjected to solution treatment at a temperature of 1000-1100℃ for 25-35 minutes; after solution treatment, it is water cooled.

[0038] Step S3: Cold rolling: The solution-treated steel is rolled using a multi-pass cold rolling method, controlling the total rolling deformation to be 50-60%;

[0039] Step S4: Annealing: Annealing temperature 780~820℃, holding time 2~3 minutes;

[0040] Step S5: Quenching: Heat the annealed steel to 860-920℃ and hold for 40-50 minutes. Then raise the temperature to 1060-1090℃ for quenching and hold for 60-70 minutes. Remove and oil quench. Then perform deep cryogenic treatment at -200--195℃ for 60-70 minutes.

[0041] Step S6: Tempering: Tempering temperature 140~150℃, tempering time 2~3 hours.

[0042] In some preferred embodiments, the high-nitrogen austenitic steel ingot in step S1 is prepared by pressurized vacuum induction furnace smelting and protective atmosphere electroslag remelting process.

[0043] The grain size of the solution-treated steel is 42–48 μm, the grain boundaries are straight and clear, a single austenite phase exists, the microhardness is 280–290 HV, the yield strength is 610–630 MPa, the tensile strength is 890–910 MPa, and the elongation is 55–60%.

[0044] In some preferred embodiments, step S3 employs a six-pass cold rolling process, with each pass having a rolling deformation of 10% and a total rolling deformation of 60%.

[0045] In some preferred embodiments, the yield strength of the annealed steel is 860–890 MPa and the tensile strength is 1100–1200 MPa.

[0046] In some preferred embodiments, the yield strength of the tempered steel is 920–980 MPa and the tensile strength is 1250–1380 MPa.

[0047] In a preferred embodiment, the chemical composition of the high-nitrogen austenitic steel is as follows (weight percentage): C: 0.11%, Si: 0.69%, Mn: 15.62%, Cr: 18.86%, Mo: 3.06%, N: 0.91%, V: 0.63%, Nb: 0.28%, Cu: 0.006%, Al: 0.006%, P: 0.004%, S: 0.0015%, with the balance being Fe and unavoidable impurities. The production process of this high-nitrogen austenitic steel includes the following steps:

[0048] Step S1: Forging: Place the high-nitrogen austenitic steel ingot into a heating furnace and heat it. The initial forging temperature is 1140℃, the final forging temperature is 965℃, the forging ratio is 4, and the forging is followed by water cooling.

[0049] Step S2: Solution treatment: The forged steel billet is subjected to solution treatment at a temperature of 1050℃ for 30 minutes; after solution treatment, it is water cooled.

[0050] Step S3: Cold rolling: The solution-treated steel is rolled using a six-pass cold rolling process, with the total rolling deformation controlled at 60%.

[0051] Step S4: Annealing: Annealing temperature 805℃, holding time 2 minutes;

[0052] Step S5: Quenching: Heat the annealed steel to 870℃ and hold for 50 minutes, then raise the temperature to 1080℃ for quenching and hold for 60 minutes. Remove and oil quench; then perform deep cryogenic treatment at -195.5℃ for 60 minutes.

[0053] Step S6: Tempering: Tempering temperature 150℃, tempering time 3 hours.

[0054] After the annealing treatment in step S4 above, the metallographic structure of the steel is shown in Figure 2. It can be seen that the grains are refined. Testing revealed that the high-nitrogen austenitic steel produced using the above process has a yield strength of 965 MPa, a tensile strength of 1286 MPa, and an elongation of 24%.

[0055] This invention optimizes the production process of high-nitrogen austenitic stainless steel. The prepared high-nitrogen austenitic stainless steel has high resistance to pitting corrosion and intergranular corrosion, as well as excellent mechanical properties, and can be applied in many fields such as energy, chemical industry, national defense, and medical treatment.

[0056] The present invention has been described in the above-described embodiments; however, these embodiments are merely examples for implementing the present invention. It must be noted that the disclosed embodiments do not limit the scope of the present invention. Conversely, any modifications and refinements made without departing from the spirit and scope of the present invention are within the scope of patent protection of the present invention.

Claims

1. A production process for high-nitrogen austenitic steel, characterized in that: The production process of the high-nitrogen austenitic steel includes the following steps: Step S1: Forging: Place the high-nitrogen austenitic steel ingot into a heating furnace and heat it. The initial forging temperature is 1120-1160℃, the final forging temperature is 945-1025℃, the forging ratio is 3-5, and the forging is followed by water cooling. Step S2: Solution treatment: The forged steel billet is subjected to solution treatment at a temperature of 1000-1100℃ for 25-35 minutes; after solution treatment, it is water cooled. Step S3: Cold rolling: The solution-treated steel is rolled using a multi-pass cold rolling method, controlling the total rolling deformation to be 50-60%; Step S4: Annealing: Annealing temperature 780~820℃, holding time 2~3 minutes; Step S5: Quenching: Heat the annealed steel to 860-920℃ and hold for 40-50 minutes. Then raise the temperature to 1060-1090℃ for quenching and hold for 60-70 minutes. Remove and oil quench. Then perform deep cryogenic treatment at -200--195℃ for 60-70 minutes. Step S6: Tempering: Tempering temperature 140~150℃, tempering time 2~3 hours.

2. The production process of high-nitrogen austenitic steel as described in claim 1, characterized in that: The chemical composition of the high-nitrogen austenitic steel by weight percentage is as follows: C: ≤0.12%, Si: 0.55~0.72%, Mn: 15.2~16.35%, Cr: 18.63~19.35%, Mo: 2.88~3.12%, N: 0.86~0.95%, V: 0.56~0.68%, Nb: 0.22~0.30%, Cu: 0.005~0.01%, Al: 0.005~0.01%, P: ≤0.02%, S: ≤0.003%, with the balance being Fe and unavoidable impurities.

3. The production process of high-nitrogen austenitic steel as described in claim 1, characterized in that: The high-nitrogen austenitic steel ingot was prepared by pressurized vacuum induction furnace smelting and protective atmosphere electroslag remelting process.

4. The production process of high-nitrogen austenitic steel as described in claim 1, characterized in that: The solid solution steel has a grain size of 42–48 μm, straight and clear grain boundaries, a single austenitic phase, a microhardness of 280–290 HV, a yield strength of 610–630 MPa, and a tensile strength of 890–910 MPa.

5. The production process of high-nitrogen austenitic steel as described in claim 1, characterized in that: In step S3, a six-pass cold rolling process is adopted, with each pass having a rolling deformation of 10% and a total rolling deformation of 60%.

6. The production process of high-nitrogen austenitic steel as described in claim 1, characterized in that: The yield strength of the annealed steel is 860–890 MPa, and the tensile strength is 1100–1200 MPa.

7. The production process of high-nitrogen austenitic steel as described in claim 1, characterized in that: After tempering, the yield strength of the steel is 920–980 MPa, and the tensile strength is 1250–1380 MPa.

8. The production process of high-nitrogen austenitic steel as described in claim 1, characterized in that: The production process of the high-nitrogen austenitic steel includes the following steps: Step S1: Forging: Place the high-nitrogen austenitic steel ingot into a heating furnace and heat it. The initial forging temperature is 1140℃, the final forging temperature is 965℃, the forging ratio is 4, and the forging is followed by water cooling. Step S2: Solution treatment: The forged steel billet is subjected to solution treatment at a temperature of 1050℃ for 30 minutes; after solution treatment, it is water cooled. Step S3: Cold rolling: The solution-treated steel is rolled using a six-pass cold rolling process, with the total rolling deformation controlled at 60%. Step S4: Annealing: Annealing temperature 805℃, holding time 2 minutes; Step S5: Quenching: Heat the annealed steel to 870℃ and hold for 50 minutes, then raise the temperature to 1080℃ for quenching and hold for 60 minutes. Remove and oil quench; then perform deep cryogenic treatment at -195.5℃ for 60 minutes. Step S6: Tempering: Tempering temperature 150℃, tempering time 3 hours.

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