Method for producing high-alloy steel

Abstract

The application discloses a preparation method of high-alloy steel, and the method comprises the following steps: hot rolling and coiling a high-alloy continuous casting billet to obtain a hot-rolled coil; directly placing the hot-rolled coil in a bell-type furnace for heating; immediately placing the hot-rolled coil in the bell-type furnace for heating after the hot-rolled coil is discharged; and performing heat preservation and cooling on the steel coil according to the CT temperature of the steel grade to obtain a steel coil with uniform performance. The method can improve the uneven performance of high-carbon, high-manganese, high-chromium, boron-containing and other high-hardening high-steel grades caused by uneven cooling of the hot-rolled coil, facilitates subsequent rolling or forming and other processes, improves the material qualification rate, and reduces the processing difficulty.

Description

Technical Field

[0001] This application belongs to the field of high alloy steel preparation technology, specifically relating to a method for preparing high alloy steel. Background Technology

[0002] With the development of the national economy, the demand for steel is becoming increasingly diversified, and the development of materials is moving towards higher strength and higher alloying. In the production of high alloy steel, due to the high hardenability of the material, the hot-rolled steel coil often exhibits uneven performance due to differences in cooling conditions at the head, tail, and edges. The strength at the edges and heads is more than 200 MPa higher than that at the core of the steel coil, which cannot meet the requirements of subsequent rolling and processing.

[0003] To mitigate this issue, related technologies involve cutting off the unevenly distributed sections at the beginning, end, and edges of the steel coil before proceeding to the next processing step. While this method is simple and easy to implement, it results in a low yield. Typically, it requires cutting off over 100mm of material from the beginning and end (approximately 50 meters in length and 100mm in width), leading to a material loss of around 20% and significant waste. Therefore, an improvement is urgently needed. Summary of the Invention

[0004] In view of this, this application provides a method for preparing high alloy steel, which can improve the uneven performance caused by uneven cooling of hot-rolled steel coils due to the high hardenability of high carbon, high manganese, high chromium, boron and other steel grades, and improve a high alloy steel with balanced tensile strength and yield strength at the head and tail.

[0005] In a first aspect, embodiments of this application provide a method for preparing high-alloy steel, the method comprising:

[0006] High-alloy continuous casting billets are hot-rolled and coiled to obtain hot-rolled coils;

[0007] The hot-rolled coil is immediately placed in a bell-type furnace for heating after it comes off the production line. The coil is then kept warm and cooled according to the CT temperature of the steel grade to obtain the high-alloy steel coil.

[0008] According to one embodiment of this application, the heat preservation time is 2-15 hours to ensure that the temperature of each part of the steel coil is uniform before cooling.

[0009] According to one embodiment of this application, the chemical composition of the high-alloy continuous casting billet, by mass percentage, includes the following: C: 0.17%-0.25%, Si: 0.5%-

[0010] 1.5%, Mn: 1.0%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.20%, Cr: 1.5%-2.0%, B: 0.002%-0.004%, balance Fe and unavoidable impurities, and a carbon equivalent Ceq ≥ 0.3% steel grade.

[0011] According to an embodiment of one aspect of this application, the chemical composition of the high-alloy continuous casting billet, by mass percentage, includes the following: C: 0.62%-0.7%, Si: ≤0.5%, Mn: 0.9%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.10%, with the balance being Fe and unavoidable impurities, and a carbon equivalent Ceq ≥ 0.3% steel grade.

[0012] According to one embodiment of this application, the atmosphere in the bell-type furnace is an inert gas.

[0013] According to one embodiment of this application, the cooling rate is 30-200°C / hour.

[0014] According to one embodiment of this application, the steel coil is kept at a temperature of ±20°C based on the CT temperature of the steel grade.

[0015] Secondly, embodiments of this application provide a high-alloy steel, which is obtained by the production method of the first aspect.

[0016] This application has at least the following beneficial effects:

[0017] According to the method in this application embodiment, the hot-rolled coil is directly subjected to bell-type annealing after coming off the production line, and then cooled in the furnace after a period of holding. This allows for precise control of the holding temperature and time of the steel coil, ensuring the conversion rate of ferrite and pearlite phase transformation, making the properties of all parts of the steel coil uniform, and eliminating the performance differences between the head, tail, and edge of the steel coil and the core. At the same time, inert gas can be introduced during the holding and cooling processes to avoid the problem of thickened iron oxide scale in slowly cooled steel coils, which leads to difficulties in pickling. Furthermore, heating and holding are arranged immediately after the hot-rolled coil comes off the production line, saving the energy required for heating.

[0018] The method of this application can improve the uneven performance of high-hardenability steels such as high-carbon, high-manganese, high-chromium, and boron-containing steels caused by uneven cooling of hot-rolled steel coils, making it easier to directly perform rolling or forming processes in the next step, improving the material qualification rate and reducing the processing difficulty. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the implementation regulations of this application, the drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The accompanying high-alloy steel appearance drawing is shown as a comparative example of this application.

[0021] Figure 2 An external view of the high-alloy steel according to an embodiment of this application is shown. Detailed Implementation

[0022] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the implementation details described in this specification are merely for illustrative purposes and are not intended to limit the scope of this application.

[0023] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0024] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0025] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0026] In related technologies, placing hot-rolled high-alloy steel coils in a slow-cooling insulated pit after production is simple and convenient, but it cannot eliminate the performance differences that occur during the natural cooling period on the walking beam. The strength at the edges and ends remains relatively high, making subsequent processing more difficult and requiring increased trimming. Furthermore, because the coils are held at higher temperatures for a longer period, iron oxide scale thickens, making it difficult to remove completely in later processes. Annealing the hot-rolled coils in a bell-type furnace at a cold-rolling plant results in more uniform finished product properties for the high-alloy steel, but the process is lengthy, the temperature drop of the coils is significant, and energy consumption is high.

[0027] Based on this, this application provides a preparation method to solve the performance inconsistencies caused by uneven cooling of hot-rolled steel coils due to the high hardenability of high-carbon, high-manganese, high-chromium, and boron-containing steel grades.

[0028] In a first aspect, embodiments of this application provide a method for preparing high-alloy steel, comprising:

[0029] High-alloy continuous casting billets are hot-rolled and coiled to obtain hot-rolled coils;

[0030] The hot-rolled coil is immediately placed in a bell-type furnace for heating after it comes off the production line. The coil is then kept warm and cooled according to the CT temperature of the steel grade to obtain the high-alloy steel coil.

[0031] In this embodiment, a bell-type furnace is installed in the hot-rolled finished product warehouse to heat and slowly cool hot-rolled steel coils of high alloy steel grades.

[0032] According to the embodiments of this application, the hot-rolled coil is directly subjected to bell-type annealing after it comes off the production line. After holding it at a certain temperature for a period of time, it is cooled in the furnace. This allows for precise control of the holding temperature and time of the steel coil, ensuring the conversion rate of the ferrite and pearlite phase transformation, making the properties of all parts of the steel coil uniform, and eliminating the performance differences between the head, tail, and edge and the core of the steel coil. At the same time, nitrogen can be introduced during the holding and cooling process to avoid the problem of thickened iron oxide scale in slowly cooled steel coils, which leads to difficulty in pickling.

[0033] In addition, loading hot-rolled steel coils into the furnace immediately after they come off the production line can greatly save the energy consumption required for heating the steel coils. Based on an average temperature of 500°C before the steel coils begin annealing and an energy utilization rate of 50% during the heating and annealing process, compared to heat treatment after cooling the steel coils, it can save 460 MJ of energy per ton of steel, which is equivalent to saving 128 kWh of electricity per ton of steel and reducing carbon emissions by 100.4 kg.

[0034] Meanwhile, this method keeps the hot-rolled coils warm before they cool down, which greatly saves the energy required for subsequent heat treatment. In addition, the cooling process is completed under a protective atmosphere, resulting in less oxidation and better consistency on the surface of the strip compared to normal cooling. This is beneficial for subsequent pickling or shot blasting, reduces processing difficulty, and improves surface quality.

[0035] Generally, after the hot rolling process, the steel plate process includes: steel coil unloading → steel coil flattening by a turning machine → steel coil loading into the furnace → nitrogen gas purging into the inner shroud → heating → heat preservation → cooling → unloading from the furnace → turning → warehousing.

[0036] It is understandable that the process of purging nitrogen into the inner casing, heating, heat preservation, and cooling can be understood as different temperature stages of spheroidizing annealing.

[0037] In some alternative embodiments, the heat preservation time is 2-15 hours to ensure that the temperature of the steel coil is uniform throughout before cooling.

[0038] In some optional embodiments, the chemical composition of the high-alloy continuous casting billet, by mass percentage, includes the following: C: 0.17%-0.25%, Si: 0.5%-1.5%, Mn: 1.0%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.20%, Cr:

[0039] 1.5%-2.0%, B: 0.002%-0.004%, balance Fe and unavoidable impurities, carbon equivalent Ceq≥0.3% steel grades.

[0040] In some optional embodiments, the chemical composition of the high-alloy continuous casting billet, by mass percentage, includes the following: C: 0.62%-0.7%, Si: ≤0.5%, Mn: 0.9%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.10%, with the balance being Fe and unavoidable impurities, and a carbon equivalent Ceq ≥ 0.3% steel grade.

[0041] In some optional embodiments, the atmosphere in the bell-type furnace is an inert gas, optionally nitrogen. An inert gas can prevent the thickening of iron oxide scale during heating and holding, and in an oxygen-deficient atmosphere, transforms the difficult-to-pickle Fe2O3 into the easily pickled FeO, improving the strength uniformity of the high-alloy steel.

[0042] In some optional embodiments, the cooling rate is 30–200°C / hour. A cooling rate of ≤200°C / hour is equivalent to ≤0.056°C / second, which is far lower than the critical cooling rate required for the martensitic transformation of ordinary alloy steel, thus avoiding the formation of martensite that would lead to increased material strength.

[0043] In some alternative embodiments, the high-alloy steel comprises 85% to 92% ferrite and 8% to 14% pearlite by volume fraction, with the remainder being bainite.

[0044] In some optional embodiments, the method further includes pickling (pickling speed 50-100 mpm) and cold rolling (reduction rate 40-65%).

[0045] In some alternative embodiments, the steel coil is kept at CT temperature ±20°C of the steel grade.

[0046] In some optional embodiments, the steel coil is kept at the CT temperature of the steel grade, including: the CT temperature of the steel coil is 540 to 600°C, and the heat preservation temperature of the steel coil is 520 to 620°C.

[0047] In some optional embodiments, the average temperature of the hot-rolled steel coil before annealing is 500°C.

[0048] Secondly, embodiments of this application provide a high-alloy steel, which is obtained by the production method of the first aspect.

[0049] According to embodiments of this application, the chemical composition of the high-alloy continuous casting billet, by mass percentage, includes the following: C: 0.17%-0.25%, Si: 0.5%-1.5%, Mn: 1.0%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.20%, Cr: 1.5%-2.0%, B: 0.002%-0.004%, with the balance being Fe and unavoidable impurities, and a carbon equivalent Ceq ≥ 0.3%. The mechanical properties of this steel include: yield strength of 470-520 MPa, tensile strength of 685 to 725 MPa, elongation of 25%-27%, and hardness of 220 to 260 HV.

[0050] The chemical composition of the high-alloy continuous casting billet, by mass percentage, includes the following: C: 0.17%-0.25%, Si: 0.5%-1.5%, Mn: 1.0%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.20%, Cr: 1.5%-2.0%, B: 0.002%-0.004%, with the balance being Fe and unavoidable impurities, and a carbon equivalent Ceq ≥ 0.3%. The mechanical properties of this steel include: yield strength of 480-560 MPa, tensile strength of 750 to 845 MPa, elongation of 15%-20%, and hardness of 220 to 270 HBW.

[0051] Example

[0052] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0053] Example 1

[0054] This application provides a method for preparing high-alloy steel, comprising:

[0055] A 230mm thick continuously cast slab was obtained by converter smelting → refining → continuous casting. The chemical composition of the continuously cast slab is as follows: C: 0.17%-0.25%, Si: 0.5%-1.5%, Mn: 1.0%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.20%, Cr: 1.5%-2.0%, B: 0.002%-0.004%, with the balance being Fe and unavoidable impurities.

[0056] The slabs from the aforementioned heats were rolled into 2.8mm hot coils via hot continuous rolling. After being coiled at a CT temperature of 650℃, the coils were air-cooled in a coil storage area and then heated to 650℃ in a bell-type furnace and held for 10 hours before slow cooling. The bell-type furnace was filled with a nitrogen atmosphere. The average cooling rate was 70℃ / hour.

[0057] Example 2

[0058] The difference between this embodiment and Embodiment 1 is that: after being coiled at a CT temperature of 600℃, the coils are heated to 600℃ in both an air-cooling chamber and a bell-type furnace and held at that temperature for 8 hours before being slowly cooled. The slow cooling rate is 50℃ / hour.

[0059] Example 3

[0060] The difference between this embodiment and Embodiment 1 is that:

[0061] A continuously cast slab with a thickness of 230 mm was obtained by smelting in a converter, refining, and then continuously casting. The chemical composition of the continuously cast slab is as follows: C: 0.62%-0.7%, Si: ≤0.5%, Mn: 0.9%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.10%, with the balance being Fe and unavoidable impurities.

[0062] The slabs from the aforementioned heats were rolled into 3.0mm hot coils via hot continuous rolling. After being coiled at a CT temperature of 620℃, the coils were air-cooled in a coil storage area and then heated to 620℃ in a bell-type furnace and held for 10 hours before slow cooling. The bell-type furnace was filled with a nitrogen atmosphere. The average cooling rate was 70℃ / hour.

[0063] Example 4

[0064] The difference between this embodiment and Embodiment 3 is that after being coiled at 700°C, the coils are air-cooled in a steel coil storage room and then heated to 700°C in a bell-type furnace and held for 15 hours before slow cooling. The bell-type furnace is filled with a nitrogen atmosphere. The average cooling rate of the slow cooling is 50°C / hour.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that the hot rolling process involves coiling at 600°C and then air cooling in the steel coil warehouse.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 3 is that the hot rolling process involves coiling the coil at 650°C and then air-cooling it in a slow cooling pit in the steel coil warehouse.

[0069] Test section

[0070] The steel plates obtained in the examples and comparative examples were tested for yield strength, tensile strength and elongation in accordance with GB / T 228.1-2021 Metallic materials, tensile testing - Part 1: Test method at room temperature.

[0071] The steel plates obtained in the examples and comparative examples were tested for hardness according to GB / T 4340.1-2024 Metallic materials Vickers hardness test - Part 1: Test method and GB / T 231.1-2018 Metallic materials Brinell hardness test - Part 1: Test method.

[0072] Table 1 Hardness of steel coils in the width direction

[0073]

[0074] Table 2 Tensile properties of the steel flange and center section

[0075]

[0076] The performance parameters measured above are taken as average values.

[0077] Furthermore, comparing the surface quality of the normally air-cooled coil of Example 1 and the slowly cooled coil of Example 1 under the protective atmosphere of a bell-type furnace after cold rolling and pickling, it was found that hot-rolled bell-type annealing has a significant effect on improving the uneven performance of high-alloy steel, while making it easier to remove iron oxide scale by pickling, thus improving the surface quality of the finished product. The results are as follows: Figures 1-2As shown. Figure 1 The steel coil in Comparative Example 1 had poor surface quality after cold rolling and pickling. Figure 2 The steel coil in Example 1 showed better surface quality after cold rolling and pickling.

[0078] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any skillful means or substitutions should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing high-alloy steel, characterized in that, include: High-alloy continuous casting billets are hot-rolled and coiled to obtain hot-rolled coils. The chemical composition of the high-alloy continuous casting billet, expressed as a percentage by mass, includes the following: C: 0.17%-0.25%, Si: 0.5%-1.5%, Mn: 1.0%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.20%, Cr: 1.5%-2.0%, B: 0.002%-0.004%, balance being Fe and unavoidable impurities, carbon equivalent Ceq≥0.3%; or, the chemical composition of the high-alloy continuous casting billet, by mass percentage, includes the following: the chemical composition of the continuous casting slab is as follows: C: 0.62%-0.7%, Si: ≤0.5%, Mn: 0.9%-2.0%, P: ≤0.025%, S: ≤0.015%, Al: 0.02%-0.10%, balance being Fe and unavoidable impurities, carbon equivalent Ceq≥0.3%; The hot-rolled coil is immediately placed in a bell-type furnace for heating after it comes off the production line. The coil is then held at and cooled according to the CT temperature of the steel grade to obtain the high-alloy steel coil. The CT temperature of the coil is 540 to 600°C. The holding time is 2 to 15 hours to ensure that the temperature of each part of the coil is uniform before cooling.

2. The preparation method according to claim 1, characterized in that, The atmosphere in the bell-type furnace is an inert gas.

3. The preparation method according to claim 1, characterized in that, The cooling rate is 30~200℃ / hour.

4. A high-alloy steel, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 3.

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