High-strength austenitic steel and preparation method thereof

Abstract

The invention provides 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 ranges from 0.14% to 0.22%. The C / N content ratio is greater than or equal to 3; the high-strength austenitic steel is obtained by melting all the raw materials, performing vacuum refining and casting, performing primary heat treatment, performing variable-temperature aging heat treatment and performing saline water and clear water quenching treatment. The method overcomes the defects in the prior art, effectively improves the strength of the austenitic steel, further ensures the specific heat capacity, heat conductivity and other properties, and improves the practical application value of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of austenitic steel processing, and in particular to high-strength austenitic steel and a preparation method thereof. Background Art

[0002] Austenitic steel is steel with an austenitic structure after normalizing. By adding alloying elements such as Ni, Mn, N, and Cr, the metal after normalizing has a stable austenitic structure. Generally, austenitic steel has the characteristics of low density and excellent comprehensive mechanical properties. As a lightweight steel, it can be widely used in the automotive, metallurgical, chemical and offshore platform industries.

[0003] The main alloying elements of austenitic steel include Ni, Mn, N, Cr, etc. The addition of these elements enables austenitic steel to maintain a stable austenitic structure even at room temperature. Austenitic steel has good oxidation resistance and acid resistance, can work for a long time at high temperature, and has a wide range of corresponding 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. In order to further improve the strength of austenitic steel, adjusting the elemental composition of austenitic steel and the subsequent annealing and quenching process is also a feasible method. However, although the element adjustment in the existing technology can enhance the strength of austenitic steel in the group, other properties are changed accordingly. For example, the strength of QN1804 steel is effectively improved by adjusting elements such as chromium, nickel, and nitrogen, but the corresponding specific heat capacity and thermal conductivity are greatly reduced. Therefore, it is crucial to improve the strength of the material while ensuring the performance of the existing steel. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a high-strength austenitic steel and a preparation method thereof, which effectively improves the strength of austenitic steel while further ensuring its specific heat capacity, thermal conductivity and other properties, thereby improving the practical application value of the material.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A high-strength austenitic steel is composed of the following raw materials in percentage by mass: 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%, the balance being Fe and unavoidable impurities, wherein the Nb+V content is 0.14%-0.22%; and the C / N ratio is ≥3.

[0006] The method for preparing high-strength austenitic steel comprises the following steps: S1. Weigh 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, apply electricity and heat to smelt them, then feed aluminum wire into the furnace to melt and prepare molten steel, and adjust the proportions of the various components of the molten steel for later use; S2, placing the molten steel in a vacuum induction furnace for refining, and then casting to form an ingot; S3, cooling the ingot at room temperature, heating it to 1050-1100° C. for preliminary heat treatment, and then cooling it to 900-950° C. and stack cooling it to obtain a billet for standby use; S4, performing aging heat treatment on the above blank at 450-500°C, 800-850°C, and 600-650°C for 4-12 hours respectively, and then cooling to obtain a heat-treated blank; S5. The heat-treated blank is heated to 1030-1050° C., then placed in boiling salt water for quenching for 20-40 seconds, and then placed in clean water at room temperature and cooled to room temperature to obtain high-strength austenitic steel.

[0007] Preferably, the inert gas in step S1 is argon.

[0008] Preferably, the vacuum degree of refining in step S2 is 0.5-0.8 mbar, the refining temperature is 1550-1580° C., and the refining time is 20-30 min.

[0009] Preferably, the heating rate of the preliminary heat treatment in step S3 is 40-60° C. / min, and the time of the preliminary heat treatment is 10-15 min.

[0010] Preferably, the heating rate of the preliminary heat treatment in step S3 is 15-20°C / min, and the treatment time is 10-15 min.

[0011] Preferably, the cooling rate to 900-950° C. in step S3 is 20-30° C. / min.

[0012] Preferably, the heating rate and subsequent cooling rate during the aging heat treatment in step S4 are both 20-30°C / min.

[0013] Preferably, the heating rate in step S5 is 40-50° C. / min, and the brine used is a sodium chloride solution with a mass concentration of 0.8%.

[0014] The present invention provides a high-strength austenitic steel and a preparation method thereof, which have the following advantages over the prior art: The present invention adjusts the ratio of various elements in austenitic steel and controls the total amount of Nb and V and the ratio of C to N, thereby comprehensively improving the strength of austenitic steel and preventing the reduction of other properties. Subsequently, multiple heat treatments and quenching with different media are performed to further improve the strength and mechanical properties of the austenitic steel. At the same time, boiling salt water is used for quenching first and then clear water is used for quenching, which effectively prevents cracks from occurring on the steel surface and facilitates subsequent processing. The subsequent clear water quenching also reduces the corrosion of the steel by salt water, thereby comprehensively improving the performance of the austenitic steel. DETAILED DESCRIPTION

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0016] Example 1: Preparation of austenitic steel: (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 gas and heated and smelted until completely melted. Aluminum wire is then fed into the furnace to melt and prepare molten steel. The proportions of the various components of the molten steel are checked and adjusted before use. (2) placing the molten steel in a vacuum induction furnace and adjusting the vacuum to 0.7 mbar and the temperature to 1570°C for refining for 25 minutes, and then casting to form an ingot for standby use; (3) After the ingot is cooled at room temperature, it is heated to 1050°C at a rate of 20°C / min for preliminary heat treatment for 15 minutes, and then cooled to 950°C at a rate of 25°C / min and stacked cooled to obtain a billet for standby use; (4) The above-mentioned blank was 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 finally cooled to room temperature at a rate of 25°C / min to obtain a heat-treated blank; (5) The heat-treated body is heated to 1040°C at a rate of 45°C / min, then placed in boiling brine (sodium chloride solution with a mass concentration of 0.8%) for quenching for 30 seconds, and then transferred to room temperature water and cooled to room temperature to obtain austenitic steel.

[0017] Referring to the above preparation method, the mass percentages of the elements in Table 1 below are used as the adjusted molten 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): Table 1 Example 2: Preparation of austenitic steel: (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 gas and heated and smelted until they are completely melted. Aluminum wire is then fed into the furnace to melt and prepare molten steel. The composition ratio of the molten steel is checked and adjusted to: C 1%, N 0.2%, Mn 22%, Si 0.3%, Cr 4.3%, Ni 2.0%, Al 2.2%, Nb0.06%, V 0.16%, S 0.1%, Cu 0.07%, Mo 0.03%, P 0.01%, and the balance is Fe and unavoidable impurities; (2) placing the molten steel in a vacuum induction furnace and adjusting the vacuum to 0.7 mbar and the temperature to 1570°C for refining for 25 minutes, and then casting to form an ingot for standby use; (3) After the ingot is cooled at room temperature, it is heated to 1050°C at a rate of 20°C / min for preliminary heat treatment for 15 minutes, and then cooled to 950°C at a rate of 25°C / min and stacked cooled to obtain a billet for standby use; (4) The above-mentioned blank was 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 finally cooled to room temperature at a rate of 25°C / min to obtain a heat-treated blank; (5) The heat-treated body is heated to 1040°C at a rate of 45°C / min, and then quenched in normal temperature salt water (sodium chloride solution with a mass concentration of 0.8%) for 30 seconds. It is then transferred to normal temperature clean water and cooled to room temperature to obtain austenitic steel.

[0018] Example 3: Preparation of austenitic steel: (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 gas and heated and smelted until they are completely melted. Aluminum wire is then fed into the furnace to melt and prepare molten steel. The composition ratio of the molten steel is checked and adjusted to: C 1%, N 0.2%, Mn 22%, Si 0.3%, Cr 4.3%, Ni 2.0%, Al 2.2%, Nb0.06%, V 0.16%, S 0.1%, Cu 0.07%, Mo 0.03%, P 0.01%, and the balance is Fe and unavoidable impurities; (2) placing the molten steel in a vacuum induction furnace and adjusting the vacuum to 0.7 mbar and the temperature to 1570°C for refining for 25 minutes, and then casting to form an ingot for standby use; (3) Cooling the ingot at room temperature, heating it to 950°C at a rate of 25°C / min, and then stack cooling it to obtain a billet for standby use; (4) heating the above-mentioned blank to 630°C at a rate of 25°C / min for 24 hours, and then cooling it to room temperature at a rate of 25°C / min to obtain a heat-treated blank; (5) The heat-treated body is heated to 1040°C at a rate of 45°C / min, and then quenched in normal temperature salt water (sodium chloride solution with a mass concentration of 0.8%) for 30 seconds. It is then transferred to normal temperature clean water and cooled to room temperature to obtain austenitic steel.

[0019] Detection: Using QN1804 as a control material, each group of austenitic steel in the above embodiment was prepared into a steel plate with a thickness of 0.5 mm, and the physical properties of each group of materials were tested. The specific results are shown in Table 2 below: Table 2 It can be seen from the above table that the austenitic steels prepared in groups 1, 2 and 3 have the best performance.

[0020] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various 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 in percentage by mass: 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%, the balance being Fe and unavoidable impurities, and the Nb+V content is 0.14%-0.22%; and the C / N ratio is ≥3.

2. A method for preparing high-strength austenitic steel according to claim 1, characterized in that: The preparation method comprises the following steps: S1. Weigh 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, apply electricity and heat to smelt them, then feed aluminum wire into the furnace to melt and prepare molten steel, and adjust the proportions of the various components of the molten steel for later use; S2, placing the molten steel in a vacuum induction furnace for refining, and then casting to form an ingot; S3, cooling the ingot at room temperature, heating it to 1050-1100° C. for preliminary heat treatment, and then cooling it to 900-950° C. and stack cooling it to obtain a billet for standby use; S4, performing aging heat treatment on the above blank at 450-500°C, 800-850°C, and 600-650°C for 4-12 hours respectively, and then cooling to obtain a heat-treated blank; S5. The heat-treated blank is heated to 1030-1050° C., then placed in boiling salt water for quenching for 20-40 seconds, and then placed in clean water at room temperature and cooled to room temperature to obtain high-strength austenitic steel.

3. The preparation method according to claim 2, wherein: In step S1, the inert gas is argon.

4. The preparation method according to claim 2, wherein: The vacuum degree of refining in step S2 is 0.5-0.8 mbar, the refining temperature is 1550-1580° C., and the refining time is 20-30 min.

5. The preparation method according to claim 2, wherein: The heating rate of the preliminary heat treatment in step S3 is 40-60° C. / min, and the time of the preliminary heat treatment is 10-15 min.

6. The preparation method according to claim 2, wherein: The heating rate of the preliminary heat treatment in step S3 is 15-20°C / min, and the treatment time is 10-15 min.

7. The preparation method according to claim 2, characterized in that: The cooling rate to 900-950° C. in step S3 is 20-30° C. / min.

8. The preparation method according to claim 2, wherein: The heating rate and subsequent cooling rate during the aging heat treatment in step S4 are both 20-30°C / min.

9. The preparation method according to claim 2, wherein: The heating rate in step S5 is 40-50° C. / min, and the brine used is a sodium chloride solution with a mass concentration of 0.8%.

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