A production method for improving hot charging rate of low-carbon aluminum killed steel billet

Abstract

The application discloses a production method for improving hot charging rate of low-carbon aluminum killed steel billets, and belongs to the technical field of metallurgy. The production method comprises the following steps: hot metal desulphurization, converter, LF furnace, RH furnace, continuous casting, cogging and rolling; in the continuous casting process, the surface temperature of the cast billet is less than or equal to 300 DEG C after three times of cooling, and the surface temperature is less than or equal to 600 DEG C after surface temperature recovery before hot charging; in the cogging process, the surface temperature of the steel billet is greater than or equal to 450 DEG C before entering the furnace. In the application, the steel billet is hot charged under the premise of ensuring product quality, and the steel billet does not need to be subjected to stack cooling treatment, so that the purposes of saving energy and reducing consumption and improving yield are achieved, and meanwhile, the product surface quality is good, and surface quality defects such as cracks and scabs are not found.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a production method for improving the hot charging rate of large square blooms of low-carbon aluminum-killed steel billets. Background Art

[0002] Aluminum, currently the most widely used deoxidizer in steelmaking, boasts high deoxidation efficiency and low cost. AlN inclusions are a typical inclusion in aluminum-killed steel. Small AlN inclusions pin austenite grain boundaries and inhibit austenite grain growth. However, as the Al-N concentration product in steel increases, the precipitation temperature rises, leading to the formation of larger AlN inclusions. These inclusions not only fail to pin grain boundaries but also significantly harm the performance and quality of the steel product.

[0003] This type of steel is prone to sporadic surface cracks during production. When the finished product is rolled to smaller specifications (e.g., wire rod specifications φ < 26mm), the compression ratio is high, so despite the presence of surface cracks, it still meets standard requirements. However, when the finished product is rolled to larger specifications (e.g., wire rod specifications φ ≥ 26mm), the compression ratio is low, and sporadic surface defects on the ingot cannot be rolled to within the standard range, resulting in a high percentage of cracking in the product during the cold heading process.

[0004] At present, most of the tertiary cooling devices used by other steel mills are installed before the continuous casting straightening section, close to the secondary cooling device. The purpose is to increase the thickness of the ingot shell and increase its resistance to stress cracks caused by the straightening process in the straightening section. The tertiary cooling device of the present invention is installed after the straightening section. The purpose is to produce a uniform quenching layer with a thickness of ≥15mm, thereby solving the problem of thermal stress cracks easily caused by rapid heating in the subsequent hot charging process.

[0005] For continuous casting processes with large cross-sections and short cooling beds, if improvement measures are not taken, the temperature of the continuous cast billets entering the heating furnace will reach over 700°C. During the billeting process of low-carbon aluminum-killed steel billets, if the grain boundaries on the billet surface have weak crack resistance, thermal stress may cause cracks to form during hot delivery of the billet. If the billet is then subjected to a stack cooling treatment, production efficiency will be seriously affected.

[0006] The product quality of the previous process is the basis for the product quality of the next process. In order to ensure the final product quality and improve production efficiency, it is very necessary to take a series of improvement measures.

[0007] In view of the above problems, it is necessary to provide a production method for improving the hot charging rate of low-carbon aluminum killed steel billets, which can greatly improve the hot charging efficiency and achieve a relatively ideal balance between product quality, increased production capacity and energy saving and consumption reduction. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a production method for improving the hot charging rate of large square low-carbon aluminum killed steel billets. The method realizes hot charging of billets with good surface quality and no surface defects such as cracks and scars.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: a production method for improving the hot charging rate of large square low-carbon aluminum-killed steel billets, the production method including molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, billet opening, and rolling processes; the continuous casting process, after three coolings, always pays attention to the surface temperature of the billet after three coolings, regularly checks the blockage and water volume of the three cooling nozzles, ensures that the surface temperature of the billet after three coolings is ≤300℃, and the temperature after the surface is warmed up before hot charging is ≤600℃; the billet opening process: the surface temperature of the billet before entering the furnace is ≥450℃.

[0010] In the blanking process of the present invention, when the Al-N concentration product is ≤2.4 (the Al content is calculated as mass percentage and the N content is calculated as ppm), the steel blank is hot charged, thereby achieving the purpose of energy saving, consumption reduction and increased production.

[0011] The chemical composition and mass percentage of the low-carbon aluminum-killed steel described in the present invention are as follows: C: 0.05-0.23%, Si≤0.10%, Mn: 0.30-1.00%, P≤0.030%, S≤0.030%, Alt: 0.02-0.04%, N≤0.0060%, and the balance is Fe and unavoidable impurities.

[0012] The converter process of the present invention adopts one-time carbon drawing and steel production; the refining process has a heating frequency of ≤3 times.

[0013] The specifications of the large square bloom selected in the blanking process of the present invention are width*height*length of 325*280*6200mm.

[0014] The continuous casting process of the present invention uses protective pouring throughout the entire process; after three cooling steps, a uniform quenching layer with a thickness of ≥15 mm is formed on the surface of the casting.

[0015] In the continuous casting process of the present invention, the cooling rate of the three cooling steps and the final cooling temperature are respectively: the cooling rate of the three cooling steps is greater than 10°C / second, and the surface temperature of the final cooling billet is less than or equal to 300°C.

[0016] The steel billets obtained by the production method of the present invention do not need to be subjected to stack cooling treatment and can be directly delivered hot.

[0017] The low-carbon aluminum-killed steel finished wire obtained by the production method of the present invention has a specification of φ≥28mm.

[0018] The low-carbon aluminum-killed steel obtained by the production method of the present invention can be 100% hot-loaded, and the surface quality qualification rate of the final product reaches more than 99.7%.

[0019] The design idea of the present application: in view of the problem of short cold bed and high cracking rate of hot charging in the bloom continuous casting process, the present application provides a production method for improving the hot charging rate of low-carbon aluminum killed steel billets, optimizes the chemical composition and continuous casting cooling process, so that the bloom gets a chilled layer with a surface thickness of ≥15 mm and uniform grain size, and the crack resistance of the casting billet is improved. The key process improvement for improving the hot charging rate of low-carbon aluminum killed steel billets in the present application is to add three cooling devices after the billet straightening section, and the composition control is aluminum content (0.02%-0.04%) and nitrogen content (<0.0060%). The temperature of the billet after straightening is >800℃, the surface temperature of the casting billet after three times of cooling is lower than 300℃, and the temperature of the surface after temperature recovery before hot charging is ≤600℃. The above measures can greatly improve the hot charging efficiency, so that the product quality, production capacity and energy saving and consumption reduction achieve a relatively ideal balance.

[0020] The beneficial effects produced by the above technical scheme are: 1. The present application improves the hot charging rate of low-carbon aluminum killed steel billets, under the premise of ensuring product quality, the billets are hot charged, and no longer need to be subjected to stack cooling treatment, achieving the purpose of energy saving and consumption reduction and improving production capacity. 2. The present application realizes 100% hot charging of the product under the premise of ensuring the basic performance of the low-carbon aluminum killed steel finished product, and the qualified rate of the surface quality of the final product reaches more than 99.7%. DETAILED DESCRIPTION

[0021] The present application will be further described in detail below in combination with specific embodiments.

[0022] Example 1

[0023] A production method for improving the hot charging rate of low-carbon aluminum killed steel billets of bloom, including the processes of molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, blooming, and rolling; the specific control processes are as follows:

[0024] Converter process, one-time carbon extraction and tapping are adopted.

[0025] Refining process, the heating frequency is 3 times.

[0026] Continuous casting process, protective pouring is used throughout the process; after three times of cooling, a quenching layer with a surface thickness of 17 mm and uniform grain size is formed on the casting billet, and the crack resistance of the casting billet is improved;

[0027] The surface temperature of the casting billet after three times of cooling is monitored at all times, and the plugging condition and water quantity of the three times of cooling water nozzles are periodically inspected. The cooling speed of the three times of cooling is 11.3℃ / s, the surface temperature of the casting billet after three times of cooling is 183℃, and the temperature of the surface after temperature recovery before hot charging is 550℃.

[0028] Billeting process: The surface temperature of the billet before entering the furnace is 523℃; the Al-N concentration product is 2.4 (the Al content is calculated as mass percentage and the N content is calculated as ppm). The billet is hot charged and the large square billet size is 325*280*6200mm.

[0029] The steel billets obtained from the billet opening process do not need to be pile-cooled and can be directly delivered hot.

[0030] The specifications, chemical composition and mass percentage of the low-carbon aluminum-killed steel obtained in this embodiment are shown in Table 1. The low-carbon aluminum-killed steel was 100% hot-loaded, and the surface quality qualification rate of the final product was 100%, with no surface quality defects such as cracks and scars found.

[0031] Example 2

[0032] A production method for improving the hot charging rate of large square low-carbon aluminum-killed steel billets includes the following steps: molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, billeting, and rolling; the specific control steps are as follows:

[0033] In the converter process, carbon is drawn out in one go to produce steel.

[0034] Refining process, heating times 2 times.

[0035] During the continuous casting process, protective pouring is used throughout. After three cooling steps, the slab forms a quenching layer with a surface thickness of 19mm and uniform grain size, which improves the slab's crack resistance.

[0036] Always pay attention to the surface temperature of the billet after the third cooling, and regularly check the blockage of the third cooling nozzle and the water volume. The third cooling rate is 12.1℃ / second, the surface temperature of the billet after the third cooling is 156℃, and the surface temperature after warming up before hot charging is 600℃.

[0037] Billeting process: The surface temperature of the billet before entering the furnace is 509℃; the Al-N concentration product is 1.84 (the Al content is calculated as mass percentage and the N content is calculated as ppm). The billet is hot charged and the large square billet size is 325*280*6200mm.

[0038] The steel billets obtained from the billet opening process do not need to be pile-cooled and can be directly delivered hot.

[0039] The specifications, chemical composition and mass percentage of the low-carbon aluminum-killed steel obtained in this embodiment are shown in Table 1. The low-carbon aluminum-killed steel was 100% hot-loaded, and the surface quality qualification rate of the final product was 100%, with no surface quality defects such as cracks and scars found.

[0040] Example 3

[0041] A production method for improving the hot charging rate of large square low-carbon aluminum-killed steel billets includes the following steps: molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, billeting, and rolling; the specific control steps are as follows:

[0042] In the converter process, carbon is drawn out in one go to produce steel.

[0043] Refining process, heating times 2 times.

[0044] During the continuous casting process, protective pouring is used throughout. After three cooling steps, the slab forms a quenching layer with a surface thickness of 15mm and uniform grain size, which improves the slab's crack resistance.

[0045] Always pay attention to the surface temperature of the billet after the third cooling, and regularly check the blockage of the third cooling nozzle and the water volume. The third cooling rate is 11.9℃ / second, the surface temperature of the billet after the third cooling is 171℃, and the surface temperature after warming up before hot charging is 544℃.

[0046] Billeting process: The surface temperature of the billet before entering the furnace is 517℃; the Al-N concentration product is 1.48 (the Al content is calculated as mass percentage and the N content is calculated as ppm). The billet is hot charged and the large square billet size is 325*280*6200mm.

[0047] The steel billets obtained from the billet opening process do not need to be pile-cooled and can be directly delivered hot.

[0048] The specifications, chemical composition and mass percentage of the low-carbon aluminum-killed steel obtained in this embodiment are shown in Table 1. The low-carbon aluminum-killed steel was 100% hot-loaded, and the surface quality qualification rate of the final product was 100%, with no surface quality defects such as cracks and scars found.

[0049] Example 4

[0050] A production method for improving the hot charging rate of large square low-carbon aluminum-killed steel billets includes the following steps: molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, billeting, and rolling; the specific control steps are as follows:

[0051] In the converter process, carbon is drawn out in one go to produce steel.

[0052] Refining process, heating times 3 times.

[0053] During the continuous casting process, protective pouring is used throughout. After three cooling steps, the slab forms a quenching layer with a surface thickness of 18mm and uniform grain size, which improves the slab's crack resistance.

[0054] Always pay attention to the surface temperature of the billet after the third cooling, and regularly check the blockage of the third cooling nozzle and the water volume. The third cooling rate is 10.0℃ / second, the surface temperature of the billet after the third cooling is 300℃, and the surface temperature after warming up before hot charging is 553℃.

[0055] Billeting process: The surface temperature of the billet before entering the furnace is 521℃; the Al-N concentration product is 2.01 (the Al content is calculated as mass percentage and the N content is calculated as ppm). The billet is hot charged and the large square billet size is 325*280*6200mm.

[0056] The steel billets obtained from the billet opening process do not need to be pile-cooled and can be directly delivered hot.

[0057] The specifications, chemical composition and mass percentage of the low-carbon aluminum-killed steel obtained in this embodiment are shown in Table 1. The low-carbon aluminum-killed steel was 100% hot-loaded, and the surface quality qualification rate of the final product was 100%, with no surface quality defects such as cracks and scars found.

[0058] Example 5

[0059] A production method for improving the hot charging rate of large square low-carbon aluminum-killed steel billets includes the following steps: molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, billeting, and rolling; the specific control steps are as follows:

[0060] In the converter process, carbon is drawn out in one go to produce steel.

[0061] Refining process, heating times 3 times.

[0062] During the continuous casting process, protective pouring is used throughout. After three cooling steps, the slab forms a quenching layer with a surface thickness of 21mm and uniform grain size, which improves the slab's crack resistance.

[0063] Always pay attention to the surface temperature of the billet after the third cooling, and regularly check the blockage of the third cooling nozzle and the water volume. The third cooling rate is 12.8℃ / second, the surface temperature of the billet after the third cooling is 149℃, and the surface temperature after warming up before hot charging is 534℃.

[0064] Billeting process: The surface temperature of the billet before entering the furnace is 450℃; the Al-N concentration product is 1.65 (the Al content is calculated as mass percentage and the N content is calculated as ppm). The billet is hot charged and the large square billet size is 325*280*6200mm.

[0065] The steel billets obtained from the billet opening process do not need to be pile-cooled and can be directly delivered hot.

[0066] The specifications, chemical composition and mass percentage of the low-carbon aluminum-killed steel obtained in this embodiment are shown in Table 1. The low-carbon aluminum-killed steel was 100% hot-loaded, and the surface quality qualification rate of the final product was 100%, with no surface quality defects such as cracks and scars found.

[0067] Example 6

[0068] A production method for improving the hot charging rate of large square low-carbon aluminum-killed steel billets includes the following steps: molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, billeting, and rolling; the specific control steps are as follows:

[0069] In the converter process, carbon is drawn out in one go to produce steel.

[0070] Refining process, heating times 3 times.

[0071] During the continuous casting process, protective pouring is used throughout. After three cooling steps, the slab forms a quenching layer with a surface thickness of 20mm and uniform grain size, which improves the slab's crack resistance.

[0072] Always pay attention to the surface temperature of the billet after the third cooling, and regularly check the blockage of the third cooling nozzle and the water volume. The third cooling rate is 13.0℃ / second, the surface temperature of the billet after the third cooling is 138℃, and the surface temperature after warming up before hot charging is 526℃.

[0073] Billeting process: The surface temperature of the billet before entering the furnace is 497°C; the Al-N concentration product is 1.50 (the Al content is calculated as mass percentage and the N content is calculated as ppm). The billet is hot charged and the large square billet size is 325*280*6200mm.

[0074] The steel billets obtained from the billet opening process do not need to be pile-cooled and can be directly delivered hot.

[0075] The specifications, chemical composition and mass percentage of the low-carbon aluminum-killed steel obtained in this embodiment are shown in Table 1. The low-carbon aluminum-killed steel was 100% hot-loaded, and the surface quality qualification rate of the final product was 100%, with no surface quality defects such as cracks and scars found.

[0076] Table 1 Specifications and chemical composition of low carbon aluminum killed steel of Examples 1-6 (wt%)

[0077]

[0078] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A production method for improving the hot charging rate of large square low-carbon aluminum killed steel billets, characterized in that: The production method includes the steps of molten iron desulfurization, converter, LF furnace, RH furnace, continuous casting, cogging and rolling; In the continuous casting process, the surface temperature of the ingot after three coolings is ≤300°C, and the surface temperature after returning to temperature before hot charging is ≤600°C; The billet opening process: the surface temperature of the billet before entering the furnace is ≥450°C; The billet opening process: when the Al-N concentration product is ≤2.4, the billet is hot charged; The chemical composition and mass percentage of the low-carbon aluminum-killed steel are as follows: C: 0.05-0.23%, Si≤0.10%, Mn: 0.30-1.00%, P≤0.030%, S≤0.030%, Alt: 0.02-0.04%, N≤0.0060%, and the balance is Fe and unavoidable impurities; In the continuous casting process, the cooling rate and final cooling temperature of the three cooling processes are as follows: the cooling rate of the three cooling processes is ≥10°C / second, and the surface temperature of the final cooling billet is ≤300°C; The steel billets obtained by the production method do not need to be subjected to stack cooling treatment and can be directly delivered hot. The low-carbon aluminum-killed steel obtained by the production method can be 100% hot-loaded, and the surface quality qualification rate of the final product is ≥99.7%.

2. The method for improving the hot charging rate of low-carbon aluminum killed steel billets according to claim 1, characterized in that: The converter process adopts one-time carbon drawing and steel production; and the refining process has a heating number of ≤3 times.

3. A production method for improving the hot charging rate of low-carbon aluminum killed steel billets according to claim 1 or 2, characterized in that: The specifications of the large square billets selected in the blanking process are width*height*length of 325*280*6200mm.

4. A production method for improving the hot charging rate of low-carbon aluminum killed steel billets according to claim 1 or 2, characterized in that: The continuous casting process uses protective pouring throughout the entire process; after three cooling steps, a uniform quenching layer with a thickness of ≥15 mm is formed on the surface of the ingot.

5. A production method for improving the hot charging rate of low-carbon aluminum killed steel billets according to claim 1 or 2, characterized in that: The low-carbon aluminum-killed steel finished wire obtained by the production method has a specification of φ≥28mm.

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