High-strength austenitic steel and method for producing same

Abstract

The application provides a high-strength austenitic steel and a preparation method thereof, and relates to the technical field of austenitic steel processing. The high-strength austenitic steel is composed of C, N, Mn, Si, Cr, Ni, Al, Nb, V, S, Cu, Mo, P, Fe and inevitable impurities, and the content of Nb+V is 0.14%-0.22%; the content ratio of C / N is greater than or equal to 3; the high-strength austenitic steel is obtained through vacuum refining casting after melting of each raw material, preliminary heat treatment, variable-temperature aging heat treatment and salt water and clean water quenching treatment. The application overcomes the defects of the prior art, effectively improves the strength of the austenitic steel, further guarantees the specific heat capacity, thermal conductivity and other performances of the austenitic steel, and improves the practical application value of the material.

Description

Technical Field

[0001] This invention relates to the field of austenitic steel processing technology, specifically to a high-strength austenitic steel and its preparation method. Background Technology

[0002] Austenitic steel is steel that has an austenitic structure after normalizing. By adding alloying elements such as Ni, Mn, N, and Cr, the normalized metal has a stable austenitic structure. Generally, austenitic steel has characteristics such as low density and excellent comprehensive mechanical properties. As a lightweight steel, it can be widely used in automobiles, metallurgy, chemical industry, and offshore platforms.

[0003] The main alloying elements in austenitic steel include Ni, Mn, N, and Cr. The addition of these elements allows austenitic steel to maintain a stable austenitic structure even at room temperature. Austenitic steel has good oxidation and acid resistance, can work for extended periods at high temperatures, and has a wide range of applications. However, although austenitic steel has high toughness and plasticity, its strength is relatively low. Generally, its strength can only be enhanced through subsequent cold working. To further improve the strength of austenitic steel, adjusting the elemental composition and subsequent annealing and quenching processes is a feasible method. However, while elemental adjustments in existing technologies can enhance the strength of austenitic steel, other properties are correspondingly altered. For example, adjusting the chromium, nickel, and nitrogen content of steel grade QN1804 effectively improves its strength, but the specific heat capacity and thermal conductivity decrease significantly. Therefore, it is crucial to improve the strength of the material while ensuring its existing properties. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-strength austenitic steel and its preparation method, which effectively improves the strength of austenitic steel while further ensuring its specific heat capacity, thermal conductivity and other properties, thereby enhancing the practical application value of the material.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A high-strength austenitic steel, wherein the austenitic steel is composed of the following raw materials in the following mass percentages: C 0.7%-1.2%, N 0.2%-0.3%, Mn 20.0%-24.0%, Si 0.2%-0.4%, Cr 3.2%-4.8%, Ni 1.4%-2.4%, Al 1.2%-3.8%, Nb 0.02%-0.12%, V 0.08%-0.16%, S 0-0.30%, Cu 0.06%-0.08%, Mo 0.02%-0.04%, P 0-0.04%, with the balance being Fe and unavoidable impurities, and the Nb+V content being 0.14%-0.22%; the C / N ratio is ≥3.

[0007] The preparation method of high-strength austenitic steel includes the following steps:

[0008] S1. Weigh out carbon iron, manganese nitride, manganese, ferrosilicon, ferrochrome, nickel, ferroniobium, ferrovanadium, ferromolybdenum, copper and iron ingots, place them in an electric arc furnace under the protection of inert gas, and then heat them up by electric current. Then feed aluminum wire into the furnace to melt and prepare molten steel. Adjust the proportions of each component of the molten steel for later use.

[0009] S2. The molten steel is placed in a vacuum induction furnace for refining, and then cast into an ingot.

[0010] S3. After cooling the above-mentioned ingots to room temperature, heat them to 1050-1100℃ for preliminary heat treatment, then cool them to 900-950℃ and then stack them for cooling to obtain billets for later use.

[0011] S4. The above billets are subjected to aging heat treatment at 450-500℃, 800-850℃ and 600-650℃ respectively for 4-12 hours, and then cooled to obtain heat-treated billets.

[0012] S5. Heat the above heat-treated billet to 1030-1050℃, then quench it in boiling salt water for 20-40 seconds, and then cool it in room temperature water to obtain high-strength austenitic steel.

[0013] Preferably, the inert gas in step S1 is argon.

[0014] Preferably, the vacuum degree of refining in step S2 is 0.5-0.8 mbar, the refining temperature is 1550-1580℃, and the refining time is 20-30 min.

[0015] Preferably, the heating rate of the preliminary heat treatment in step S3 is 40-60℃ / min, and the preliminary heat treatment time is 10-15min.

[0016] Preferably, the heating rate of the preliminary heat treatment in step S3 is 15-20℃ / min, and the treatment time is 10-15min.

[0017] Preferably, the cooling rate in step S3, which cools the temperature to 900-950°C, is 20-30°C / min.

[0018] Preferably, the heating rate and subsequent cooling rate during the aging heat treatment in step S4 are both 20-30℃ / min.

[0019] Preferably, the heating rate in step S5 is 40-50℃ / min, and the brine used is a sodium chloride solution with a mass concentration of 0.8%.

[0020] This invention provides a high-strength austenitic steel and its preparation method, which has the following advantages compared with the prior art:

[0021] This invention improves the strength of austenitic steel by adjusting the proportions of various elements and controlling the total amount of Nb and V and the ratio of C to N, while preventing the reduction of other properties. Subsequent heat treatments and quenching in different media further enhance the strength and mechanical properties of the austenitic steel. Furthermore, the use of boiling brine for initial quenching followed by water quenching effectively prevents surface cracks, facilitating subsequent processing. The water quenching also reduces the corrosion of the steel by the brine, thus comprehensively improving the performance of the austenitic steel. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the 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.

[0023] Example 1:

[0024] Preparation of austenitic steel:

[0025] (1) Carbon iron, manganese nitride, manganese, ferrosilicon, ferrochrome, nickel, ferroniobium, ferrovanadium, ferromolybdenum, copper and iron ingots are placed in an electric arc furnace under the protection of argon and smelted until completely melted. Then aluminum wire is fed into it to melt and prepare molten steel. The proportions of each component of the molten steel are checked and adjusted before use.

[0026] (2) Place the above molten steel in a vacuum induction furnace, adjust the vacuum degree to 0.7 mbar, and the temperature to 1570℃ for refining for 25 minutes, and then cast it into an ingot for later use.

[0027] (3) After cooling the above ingot at room temperature, heat it to 1050°C at a rate of 20°C / min for preliminary heat treatment for 15 min, and then cool it to 950°C at a rate of 25°C / min for stacking cooling to obtain billet for use.

[0028] (4) The above billet is heated to 480°C at a rate of 25°C / min for 8 hours, then heated to 830°C at a rate of 25°C / min for 4 hours, then cooled to 630°C at a rate of 25°C / min for 12 hours, and then cooled to room temperature at a rate of 25°C / min to obtain the heat-treated billet.

[0029] (5) The heat-treated billet is heated to 1040°C at a rate of 45°C / min, and then placed in boiling brine (sodium chloride solution with a mass concentration of 0.8%) for quenching treatment for 30s. Then it is transferred to room temperature water to cool to room temperature to obtain austenitic steel.

[0030] Referring to the above preparation method, the element mass percentages in Table 1 below are used as the adjusted steel composition in step (1) (the balance is Fe and unavoidable impurities, and S and P are impurities introduced by other materials, which can be controlled within a certain range):

[0031] Table 1

[0032]

[0033] Example 2:

[0034] Preparation of austenitic steel:

[0035] (1) Carbon iron, manganese nitride, manganese, ferrosilicon, ferrochrome, nickel, ferroniobium, ferrovanadium, ferromolybdenum, copper and iron ingots are placed in an electric arc furnace under the protection of argon and smelted until completely melted. Then aluminum wire is fed into the furnace to melt and prepare molten steel. The composition ratio of the molten steel is checked and adjusted as follows: C 1%, N 0.2%, Mn 22%, Si 0.3%, Cr 4.3%, Ni 2.0%, Al 2.2%, Nb 0.06%, V 0.16%, S 0.1%, Cu 0.07%, Mo 0.03%, P 0.01%, with the balance being Fe and unavoidable impurities;

[0036] (2) Place the above molten steel in a vacuum induction furnace, adjust the vacuum degree to 0.7 mbar, and the temperature to 1570℃ for refining for 25 minutes, and then cast it into an ingot for later use.

[0037] (3) After cooling the above ingot at room temperature, heat it to 1050°C at a rate of 20°C / min for preliminary heat treatment for 15 min, and then cool it to 950°C at a rate of 25°C / min for stacking cooling to obtain billet for use.

[0038] (4) The above billet is heated to 480°C at a rate of 25°C / min for 8 hours, then heated to 830°C at a rate of 25°C / min for 4 hours, then cooled to 630°C at a rate of 25°C / min for 12 hours, and then cooled to room temperature at a rate of 25°C / min to obtain the heat-treated billet.

[0039] (5) The heat-treated billet is heated to 1040°C at a rate of 45°C / min, and then placed in a brine solution (sodium chloride solution with a mass concentration of 0.8%) at room temperature for 30s. After that, it is cooled to room temperature in clean water to obtain austenitic steel.

[0040] Example 3:

[0041] Preparation of austenitic steel:

[0042] (1) Carbon iron, manganese nitride, manganese, ferrosilicon, ferrochrome, nickel, ferroniobium, ferrovanadium, ferromolybdenum, copper and iron ingots are placed in an electric arc furnace under the protection of argon and smelted until completely melted. Then aluminum wire is fed into the furnace to melt and prepare molten steel. The composition ratio of the molten steel is checked and adjusted as follows: C 1%, N 0.2%, Mn 22%, Si 0.3%, Cr 4.3%, Ni 2.0%, Al 2.2%, Nb 0.06%, V 0.16%, S 0.1%, Cu 0.07%, Mo 0.03%, P 0.01%, with the balance being Fe and unavoidable impurities;

[0043] (2) Place the above molten steel in a vacuum induction furnace, adjust the vacuum degree to 0.7 mbar, and the temperature to 1570℃ for refining for 25 minutes, and then cast it into an ingot for later use.

[0044] (3) After cooling the above ingot at room temperature, heat it to 950°C at a rate of 25°C / min and then stack it to cool it to obtain a billet for later use;

[0045] (4) The above billet is heated to 630°C at a rate of 25°C / min for 24 hours and then cooled to room temperature at a rate of 25°C / min to obtain a heat-treated billet.

[0046] (5) The heat-treated billet is heated to 1040°C at a rate of 45°C / min, and then placed in a brine solution (sodium chloride solution with a mass concentration of 0.8%) at room temperature for 30s. After that, it is cooled to room temperature in clean water to obtain austenitic steel.

[0047] Detection:

[0048] Using QN1804 as the control material, steel plates with a thickness of 0.5 mm were prepared from the austenitic steels of each group in the above examples, and the physical properties of each group of materials were tested. The specific results are shown in Table 2 below:

[0049] Table 2

[0050]

[0051] As shown in the table above, the austenitic steels prepared in groups 1, 2, and 3 have the best performance.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-strength austenitic steel, characterized in that, The austenitic steel is composed of the following raw materials by mass percentage: C 0.7%-1.2%, N 0.2%-0.3%, Mn 20.0%-24.0%, Si 0.2%-0.4%, Cr 3.2%-4.8%, Ni 1.4%-2.4%, Al 1.2%-3.8%, Nb 0.02%-0.12%, V 0.08%-0.16%, S 0-0.30%, Cu 0.06%-0.08%, Mo 0.02%-0.04%, P 0-0.04%, with the balance being Fe and unavoidable impurities, and the Nb+V content being 0.14%-0.22%; the C / N ratio is ≥3; The method for preparing the high-strength austenitic steel includes the following steps: S1. Weigh out carbon iron, manganese nitride, manganese, ferrosilicon, ferrochrome, nickel, ferroniobium, ferrovanadium, ferromolybdenum, copper and iron ingots, place them in an electric arc furnace under the protection of inert gas, and then heat them up by electric current. Then feed aluminum wire into the furnace to melt and prepare molten steel. Adjust the proportions of each component of the molten steel for later use. S2. The molten steel is placed in a vacuum induction furnace for refining, and then cast into an ingot. S3. After cooling the above-mentioned ingots to room temperature, heat them to 1050-1100℃ for preliminary heat treatment, then cool them to 900-950℃ and then stack them for cooling to obtain billets for later use. S4. The above billets are subjected to aging heat treatment at 450-500℃, 800-850℃ and 600-650℃ respectively for 4-12 hours, and then cooled to obtain heat-treated billets. S5. Heat the above heat-treated billet to 1030-1050℃, then quench it in boiling salt water for 20-40 seconds, and then cool it in room temperature water to obtain high-strength austenitic steel.

2. The high-strength austenitic steel according to claim 1, characterized in that: In step S1, the inert gas is argon.

3. The high-strength austenitic steel according to claim 1, characterized in that: In step S2, the vacuum degree of refining is 0.5-0.8 mbar, the refining temperature is 1550-1580℃, and the refining time is 20-30 min.

4. The high-strength austenitic steel according to claim 1, characterized in that: The heating rate of the preliminary heat treatment in step S3 is 40-60℃ / min, and the duration of the preliminary heat treatment is 10-15min.

5. The high-strength austenitic steel according to claim 1, characterized in that: The heating rate of the preliminary heat treatment in step S3 is 15-20℃ / min, and the treatment time is 10-15min.

6. The high-strength austenitic steel according to claim 1, characterized in that: In step S3, the cooling rate to 900-950℃ is 20-30℃ / min.

7. The high-strength austenitic steel according to claim 1, characterized in that: In step S4, the heating rate and subsequent cooling rate during the aging heat treatment are both 20-30℃ / min.

8. The high-strength austenitic steel according to claim 1, characterized in that: In step S5, the heating rate is 40-50℃ / min, and the brine used is a sodium chloride solution with a mass concentration of 0.8%.

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