Preparation method of high alloy steel

Abstract

The invention discloses a preparation method of high-alloy steel, which comprises the following steps: carrying out hot rolling and coiling on a high-alloy continuous casting billet to obtain a hot-rolled coil; and the hot-rolled coil is directly placed in a bell-type furnace to be heated, the hot-rolled coil is immediately placed in the bell-type furnace to be heated after being offline, and the steel coil is subjected to heat preservation and cooling according to the CT temperature of the steel grade to obtain the steel coil with the uniform performance. By means of the method, the phenomenon that the performance of high-hardenability steel such as high-carbon steel, high-manganese steel, high-chromium steel and boron-containing steel is uneven due to uneven cooling of hot rolled steel coils can be improved, machining such as rolling or forming can be directly carried out in the next procedure conveniently, the material percent of pass is increased, and the machining difficulty is reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of high alloy steel preparation, and specifically relates to a method for preparing high alloy steel. Background Art

[0002] With the development of the national economy, the demand for steel is becoming increasingly diversified, and the development of materials is moving towards high strengthening and high alloying. When producing high alloy steel, due to the strong hardenability of the material, it is often encountered that the performance of hot rolled steel coils is uneven due to the difference in cooling conditions at the head, tail and edge. The strength of the edge and head and tail is higher than that of the steel coil core by more than 200MPa, which cannot meet the requirements of subsequent rolling and processing.

[0003] In order to alleviate this phenomenon, in the related technology, the uneven performance parts of the head and tail of the steel coil and the edge are cut off before the next process. Although this method is simple and easy to implement, the yield rate is low. It usually needs to cut off the head and tail of 50 meters in length and the edge of more than 100mm in width, and the material loss is about 20%, resulting in a certain amount of waste. Therefore, it is urgently needed to be improved. Summary of the invention

[0004] In view of this, the present 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-containing and other steels, and improve a high alloy steel with balanced tensile strength and yield strength at the head and tail.

[0005] In a first aspect, an embodiment of the present application provides a method for preparing high alloy steel, the method comprising:

[0006] Hot rolling and coiling the high alloy continuous casting billet to obtain a hot rolled coil;

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

[0008] According to an embodiment of one aspect of the present application, the insulation time is 2-15 hours so that the temperature of each part of the steel coil is uniform before cooling.

[0009] According to an embodiment of one aspect of the present application, the chemical composition of the high alloy continuous casting billet includes, by mass percentage, the chemical composition of the continuous casting slab is as follows: 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%, the balance is Fe and unavoidable impurities, carbon equivalent Ceq ≥ 0.3% of steel.

[0011] According to an embodiment of one aspect of the present application, the chemical composition of the high alloy continuous casting billet includes, in mass percentage: 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%, the remainder is Fe and unavoidable impurities, and the carbon equivalent Ceq is ≥0.3% of the steel grade.

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

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

[0014] According to an embodiment of one aspect of the present application, the steel coil is kept warm at a CT temperature of the steel grade ±20°C.

[0015] In a second aspect, an embodiment of the present application provides a high alloy steel produced by the production method of the first aspect.

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

[0017] According to the method of the embodiment of the present application, the hood annealing is directly carried out after the hot coil is off the line, and the steel coil is cooled with the furnace after being kept warm for a period of time. The temperature and time of the steel coil can be accurately controlled to ensure the conversion rate of ferrite and pearlite phase transformation, so that the performance of each part of the steel coil is uniform, and the performance difference between the head, tail, edge and core of the steel coil is eliminated; at the same time, inert gas can be introduced during the heat preservation and cooling process to avoid the problem of thickening of the oxide scale of the slow-cooled steel coil, which makes it difficult to pickle. And heating and heat preservation are arranged immediately after the hot coil is off the line, saving the energy required for heating.

[0018] The method of the present 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, facilitate direct rolling or forming processing in the next step, improve the material qualification rate, and reduce the processing difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the implementation regulations of this application, the following is a brief introduction to the drawings required for use in the embodiments of this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 The appearance of the high alloy steel of the comparative example of the present application is shown.

[0021] Figure 2 The appearance of the high alloy steel of the embodiment of the present application is shown. DETAILED DESCRIPTION

[0022] In order to make the application purpose, technical solution and beneficial technical effect of this application clearer, the application is further described in detail below in conjunction with the embodiments. It should be understood that the implementation regulations described in this specification are only for explaining this application, not for limiting this application.

[0023] For simplicity, the present application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0024] In the description of the present application, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number, and the “multiple” in “one or more” means two or more than two.

[0025] The above application content of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided through a series of embodiments, and these implementation regulations can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0026] In the related art, when the hot-rolled coils of high-alloy steel are placed in an insulation slow cooling pit after they come off the production line, although it is simple and easy, it cannot eliminate the performance differences that occur during the natural cooling period of the coils on the walking beam, and the strength of the edges and heads and tails is still relatively high. The subsequent processing is difficult and the amount of cutting still needs to be increased. In addition, because the coils are kept at a higher temperature for a long time, the iron oxide scale thickens, which is difficult to remove in the subsequent process. When the hot-rolled coils are sent to the hood furnace of the cold-rolled plate plant for annealing, the finished product performance of the high-alloy steel is more uniform, but the process flow is longer, the temperature drop of the coils is larger, and the energy consumption is higher.

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

[0028] In a first aspect, an embodiment of the present application provides a method for preparing high alloy steel, comprising:

[0029] Hot rolling and coiling the high alloy continuous casting billet to obtain a hot rolled coil;

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

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

[0032] According to the embodiments of the present application, hood annealing is performed directly after the hot coil comes off the production line, and the coil is cooled with the furnace after being kept warm for a period of time. The temperature and time of the steel coil insulation can be accurately controlled to ensure the conversion rate of ferrite and pearlite phase transformation, make the performance of each part of the steel coil uniform, and eliminate the performance difference between the head, tail and edge and the core of the steel coil. At the same time, nitrogen can be introduced during the insulation and cooling process to avoid the problem of thickening of the oxide scale of the slow-cooled steel coil, which makes it difficult to pickle.

[0033] In addition, loading the hot-rolled steel coils into the furnace as soon as they come off the line can greatly save the energy consumption required for heating the steel coils. Calculated based on the 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 with heat treatment after the steel coils are cooled, 460MJ of energy can be saved per ton of steel, which is equivalent to saving 128 kWh of electricity per ton of steel and reducing carbon emissions by 100.4kg.

[0034] At the same time, this method keeps the hot coil warm before it cools down, which greatly saves the energy consumption required for subsequent heat treatment heating. In addition, the cooling process is completed under a protective atmosphere, and the surface oxidation of the strip is lighter and more consistent than under normal cooling, which is conducive to pickling or shot blasting removal in subsequent processes, reducing processing difficulty and improving surface quality.

[0035] Generally speaking, after the hot rolling process, the process of steel plate includes: steel coil coming off the line → steel coil is laid flat by steel turning machine → steel coil is loaded into furnace → nitrogen is passed through inner cover → heating → heat preservation → cooling → coming out of furnace → steel turning → storage.

[0036] It can be understood that: nitrogen passing through the inner cover → heating → heat preservation → cooling can be understood as different temperature stages of spheroidizing annealing.

[0037] In some optional embodiments, the insulation time is 2-15 hours, so that the temperature of each part of the steel coil is uniform before cooling.

[0038] In some optional embodiments, the chemical composition of the high alloy continuous casting billet includes, by mass percentage: the chemical composition of the continuous casting 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:

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

[0040] In some optional embodiments, the chemical composition of the high alloy continuous casting billet includes, in mass percentage: 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%, the remainder is Fe and unavoidable impurities, and the carbon equivalent Ceq is ≥0.3% of the steel.

[0041] In some optional embodiments, the atmosphere in the bell-type furnace is an inert gas, which can be nitrogen. The inert gas can prevent the thickening of the iron oxide scale during heating and insulation, and transform the Fe2O3 that is difficult to pickle into FeO that is easy to pickle in an oxygen-deficient atmosphere, thereby improving the strength balance 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 much lower than the critical cooling rate required for martensitic transformation of ordinary alloy steel, and can avoid the formation of martensite and increase the material strength.

[0043] In some optional embodiments, the high alloy steel includes 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 comprises pickling (pickling speed 50-100 mpm) and cold rolling (reduction ratio 40-65%).

[0045] In some optional embodiments, the steel coil is kept warm at a temperature of ±20°C according to the CT temperature of the steel grade.

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

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

[0048] In a second aspect, an embodiment of the present application provides a high alloy steel produced by the production method of the first aspect.

[0049] According to the embodiment of the present application, the chemical composition of the high alloy continuous casting billet includes, by mass percentage: the chemical composition of the continuous casting 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%, the remainder is Fe and unavoidable impurities, and the carbon equivalent Ceq is ≥0.3%. The mechanical properties of this steel include: yield strength of 470-520MPa, tensile strength of 685 to 725MPa, elongation of 25%-27%, and hardness of 220 to 260HV.

[0050] The chemical composition of the high alloy continuous casting billet includes, by mass percentage, the chemical composition of the continuous casting slab 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%, the balance is Fe and unavoidable impurities, and the carbon equivalent Ceq is ≥0.3%. The mechanical properties of this steel include: yield strength of 480-560MPa, tensile strength of 750 to 845MPa, elongation of 15%-20%, and hardness of 220 to 270HBW.

[0051] Example

[0052] The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations may be made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0053] Example 1

[0054] The present application provides a method for preparing high alloy steel, comprising:

[0055] The continuous casting slab with a thickness of 230 mm is obtained by converter smelting → refining → continuous casting. The chemical composition of the continuous casting 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%, and the remainder is Fe and unavoidable impurities.

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

[0057] Example 2

[0058] The difference between this embodiment and embodiment 1 is that after coiling at a CT temperature of 600°C, the steel coil is air-cooled in a steel coil warehouse and heated to 600°C in a bell furnace for 8 hours before being slowly cooled. The cooling rate of the slow cooling is 50°C / hour.

[0059] Example 3

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

[0061] The continuous casting slab with a thickness of 230 mm is obtained by converter smelting → refining → continuous casting. 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%, and the remainder is Fe and unavoidable impurities.

[0062] The slabs from the above heats were rolled into 3.0 mm hot coils by hot continuous rolling, coiled at a CT temperature of 620°C, and then air-cooled in the coil warehouse and heated to 620°C in a bell furnace for 10 hours before slow cooling. The bell furnace was filled with nitrogen atmosphere. The average cooling rate of the slow cooling was 70°C / hour.

[0063] Example 4

[0064] The difference between this embodiment and embodiment 3 is that after coiling at 700°C, the steel coil is air-cooled in the steel coil warehouse and heated to 700°C in a bell furnace for 15 hours before slow cooling. The bell furnace is filled with 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 is carried out at 600° C. and then the steel coils are air-cooled in the steel coil warehouse.

[0067] Comparative Example 2

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

[0069] Test Section

[0070] The steel plates prepared in the embodiments and comparative examples were tested for their yield strength, tensile strength and elongation in accordance with “GB / T 228.1-2021 Tensile test of metallic materials - Part 1: Room temperature test method”.

[0071] The hardness of the steel plates prepared in the examples and comparative examples was tested 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 coil in width direction

[0073]

[0074] Table 2 Tensile properties of the edge and middle of the steel coil

[0075]

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

[0077] In addition, the surface quality of the steel coils of the normal air cooling coils of the comparative example 1 and the steel coils of the embodiment 1 slowly cooled in the bell furnace protective atmosphere after cold rolling and pickling was compared. It was found that the bell annealing of the hot coil had a significant effect on improving the uneven performance of high alloy steel, and at the same time made the iron oxide scale easier to be removed by pickling, thereby improving the surface quality of the finished product. The results are as follows Figure 1-Figure 2shown. Figure 1 The surface quality of the steel coil of Comparative Example 1 after cold rolling and pickling is poor. Figure 2 The steel coil of Example 1 has better surface quality after cold rolling and pickling.

[0078] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto, and any familiarity with the present technology or replacement should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing high alloy steel, characterized in that: include: Hot rolling and coiling the high alloy continuous casting billet to obtain a hot rolled coil; The hot rolled coil is immediately placed in a bell-type furnace for heating after it comes off the production line, and the steel coil is kept warm and cooled according to the CT temperature of the steel grade to obtain the high alloy steel coil.

2. The method according to claim 1, characterized in that The insulation time is 2-15 hours so that the temperature of each part of the steel coil is uniform before cooling.

3. The production method according to claim 1, characterized in that The chemical composition of the high alloy continuous casting billet includes, in percentage by mass: the chemical composition of the continuous casting 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%, the remainder is Fe and unavoidable impurities, and the carbon equivalent Ceq≥0.3%.

4. The production method according to claim 1, characterized in that The chemical composition of the high alloy continuous casting billet includes, in percentage by mass: 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%, the remainder is Fe and unavoidable impurities, and the carbon equivalent Ceq≥0.3%.

5. The production method according to any one of claims 1 to 3, characterized in that: The atmosphere in the bell-type furnace is an inert gas.

6. The production method according to any one of claims 1 to 3, characterized in that: The cooling speed is 30-200°C / hour.

7. The production method according to any one of claims 1 to 3, characterized in that: The steel coil shall be kept warm at CT temperature ±20℃ of the steel grade.

8. A high alloy steel, characterized in that: The method is prepared by the production method according to any one of claims 1 to 7.

Images