A thin, wide, extremely long and high flatness steel plate and its preparation method

Abstract

The present invention relates to the field of metallurgical technologies, and particularly relates to a thin, wide, extremely long and highly flat steel plate and a preparation method thereof. The thin, wide and extremely long steel plate is prepared by a preparation method including smelting, slab heating, slab descaling and rolling processes. The specifications of the thin, wide and extremely long steel plate are a thickness of 4 - 10 mm, a width of 2000 - 3000 mm and a length of 150 - 200 m; the yield strength of the steel plate is ≤400 MPa, and the flatness is 2 - 4 mm / m. The present invention adopts a medium and low carbon micro-niobium composition design, high cleanliness steel smelting, and a one-stage controlled rolling process, fully considering the temperature uniformity in the length direction of the steel plate and the rolling stability, stably controlling the grain size and uniformity, so that the obtained steel plate has beneficial plasticity and high flatness, and can meet the manufacturing and application requirements of special and high-end structural parts.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a thin, wide, extremely long and high-straightness steel plate and a preparation method thereof. Background Art

[0002] Thin and wide steel plates are widely used in equipment and engineering manufacturing fields such as bridge structural parts welding and pipe welding due to their advantages such as fewer welding points and light weight. 1. Due to uneven heat dissipation, there is a temperature difference in the horizontal direction. As the thickness becomes thinner, the lateral temperature difference becomes larger. The metal flow ability is different during the rolling process at different temperatures, which can easily cause plate shape problems such as edge waves and middle waves; 2. The temperature drop during the rolling process of thin and wide steel plates is large. The thinner the thickness, the greater the temperature difference between the head, middle and tail of the steel plate, and the longer the steel plate, the greater the temperature difference between the head, middle and tail; due to different temperatures in the length direction of the steel plate, different rolling pressures in different parts, and different rolling deformations, huge internal stress is formed inside the steel plate, resulting in poor plate shape of the steel plate. In severe cases, accidents may occur due to poor plate shape and collision with equipment.

[0003] Due to the above two reasons, it is extremely difficult to control the shape of thin and wide steel plates. In addition, due to the rapid cooling during the rolling process and the large temperature difference between the head, middle and tail, the performance of the steel plates is easily unqualified. At present, due to serious shape and performance problems in the production process of thin and wide steel plates, it is impossible to produce or stably produce; and the length of thin and wide ultra-long steel plates increases, making production more difficult; currently, hot continuous rolling is mainly used to produce coils, and then flatten them into steel plates, but this type of flattened steel plates have large internal stress and cannot meet performance requirements.

[0004] CN106544597A discloses an ultra-thin and ultra-wide steel plate for nuclear power pressure equipment and a manufacturing method thereof, wherein the chemical composition is: C: ≤0.20%; Si: ≤0.10%; Mn: 0.50%-1.80%; P: ≤0.008%; S: ≤0.003%; Ni: 0.20%-1.00%; Cr: 0.30%-0.80%; Cu: 0.10%-0.80%; Mo: ≤0.08%; Alt: ≤0.040%; N: ≤0.008%; the steel plate is rolled by a two-fire process and heat-treated by a normalizing process. The precious alloy has a high content of added elements such as Cr, Cu, and Ni, and the two-fire rolling and normalizing heat treatment have many processes, are complicated, and are costly.

[0005] CN113235010A discloses a method for preparing a thin steel plate for nuclear power with uniform performance throughout the plate, which is designed with low carbon, low silicon and a small amount of rare earth alloy components, uses hot rollers, heating of ingots, and cooling water protection of idle rollers to control the plate shape, and uses normalizing and high-temperature stacking and slow cooling to improve the performance and shape of the steel plate, and successfully achieves mass production of 5.5-10.5 mm steel plates. Rare earth alloy components are added, and hot rollers, normalizing, high-temperature stacking and slow cooling are used to ensure the plate shape and performance. The process is complex and the production cycle and cost are high. Summary of the Invention

[0006] Aiming at the problems of complex production process of steel plates in the prior art and difficulty in preparing steel plates with thin, wide, extremely long specifications, the present invention provides a thin, wide, extremely long, high flatness steel plate and a preparation method thereof.

[0007] In the first aspect, the present invention provides a thin, wide, extremely long, high flatness steel plate. The thickness of the steel plate is 4 - 10 mm, the width is 2000 - 3000 mm, and the length is 150 - 200 m. Calculated by weight percentage, the chemical composition of the steel plate is: C: 0.14% - 0.17%, Si: 0.10% - 0.30%, Mn: 1.20% - 1.40%, P ≤ 0.020%, S ≤ 0.005%, Al: 0.015% - 0.045%, Nb: 0.030% - 0.045%, Ti: 0.010% - 0.025%, and the rest is Fe and unavoidable impurities.

[0008] Furthermore, C is the main solid solution strengthening element in steel, which can significantly improve the strength of the steel plate, but is not beneficial to the welding, toughness and plasticity of the steel plate. In order to avoid large tensile deformation, large rolling pressure and increased difficulty in plate shape control during the preparation of steel, the carbon content needs to be controlled. Silicon is one of the effective deoxidizing and exothermic elements in the steelmaking process, and has a certain solid solution strengthening effect. At the same time, too high silicon content will reduce the surface quality, welding performance and low temperature toughness of the steel. Manganese has a strong solid solution strengthening effect, can significantly reduce the phase transformation temperature of the steel, and refine the microstructure of the steel. In order to avoid large tensile deformation, large rolling pressure, increased difficulty in plate shape control, slab segregation, formation of banded structure and reduction of the plasticity of the steel plate, the manganese content is controlled at 1.20% - 1.40%. Aluminum is one of the effective deoxidizing elements in the steelmaking process, which can effectively reduce the inclusion content in the steel and refine the grains. However, if the content is too high, it is easy to cause cracks on the surface of the slab and a large increase in the strength of the fine grains. In the present invention, the aluminum content is controlled at 0.015% - 0.045%. Niobium is one of the important elements for fine grain strengthening, which can increase the austenite recrystallization temperature, prevent austenite recrystallization and inhibit grain growth, and refine austenite grains. Its carbonitride precipitates on dislocations and segregates at the austenite grain boundary, improving strength and toughness. The rolling of thin and wide specification steel plates requires good plasticity and uniform plasticity of the material, and requires a high heating temperature of the slab and good overall uniformity of the slab. In order to prevent the growth or coarsening of austenite during heating, the niobium content is controlled at 0.030% - 0.045%.

[0009] Furthermore, the yield strength of the steel plate is ≤ 400 Mpa, and the flatness is 2 - 4 mm / m.

[0010] In the second aspect, the present invention provides a preparation method for a thin, wide, extremely long, high flatness steel plate, including smelting, slab heating, slab descaling and rolling processes.

[0011] Furthermore, in the smelting process, hot metal pretreatment is carried out to control the S content ≤ 0.004%.

[0012] Furthermore, argon blowing is carried out to produce white slag during the smelting process; the RH vacuum degree reaches 200 Pa, and the vacuum time is not less than 10 min; the molten steel calming time before tapping is not less than 30 min.

[0013] Furthermore, when 4 mm ≤ finished product thickness ≤ 6 mm, the casting blank furnace outlet temperature is 1240 - 1270 °C, and the heat preservation time is 40 - 90 min; when 6 mm < finished product thickness ≤ 10 mm, the casting blank furnace outlet temperature is 1220 - 1250 °C, and the heat preservation time is 30 - 60 min; the thinner the product, the higher the furnace outlet temperature, so as to ensure that the temperature of the rolled piece will not be too low during the rolling process, and further avoid the appearance of large rolling internal stresses; through the heat preservation time, the internal and external temperatures of the casting blank are ensured to be uniform. The thinner the product, the longer the heat preservation time of the casting blank, the better the uniformity of the internal and external temperatures of the casting blank, the smaller the transverse temperature difference of the rolled piece during the rolling process, and the metal flow difference at different transverse positions during the rolling deformation of the rolled piece is greatly reduced, avoiding the appearance of plate shapes such as edge waves and middle waves.

[0014] Furthermore, after the casting blank leaves the furnace and is descaled by high-pressure water, rolling begins. One-stage rolling is adopted; compared with two-stage rolling carried out at a lower temperature, one-stage rolling enables the steel plate to be rolled at a high temperature state, which can improve the flatness of the steel plate.

[0015] Furthermore, the heating temperature of the coiling box is not less than 950 °C.

[0016] Furthermore, when 4 mm ≤ finished product thickness ≤ 6 mm and the blank thickness is 26 - 30 mm, coiling rolling starts, the starting coiling rolling temperature is 1000 - 1050 °C, the coiling rolling passes are controlled within 4 - 6 passes, the reduction ratio of the first two passes of coiling rolling is greater than 30%, and the reduction ratio of the coiling rolling passes gradually decreases, and the final pass rolling temperature is 730 - 800 °C.

[0017] Furthermore, when 6 mm < finished product thickness ≤ 10 mm and the blank thickness is 32 - 40 mm, coiling rolling starts, the starting coiling rolling temperature is 950 - 1000 °C, the coiling rolling passes are controlled within 1 - 4 passes, and the reduction ratio of the passes gradually decreases after starting coiling rolling, and the final pass rolling temperature is 800 - 860 °C; by controlling the temperature of the rolled piece before coiling rolling, the heat preservation temperature of the coiling furnace, the coiling rolling passes, and increasing the reduction ratio of the first few passes of rolling, the temperature difference between the head, middle, and tail of the steel plate is controlled.

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) The preparation method provided by the present invention solves the production problems of thin, wide, and extremely long steel plates in China, and the batch production output is stable;

[0020] (2) The steel composition design of the present invention is simple, the production process is simple, with high stability, short production cycle, low cost, and great prospects for popularization and application;

[0021] (3) The present invention adopts a medium and low carbon micro-niobium composition design, high cleanliness steel smelting, and one-stage controlled rolling process, fully considering the temperature uniformity in the length direction of the steel plate and the stability of rolling, stably controlling the grain size and uniformity, so that the obtained steel plate has beneficial plasticity and high flatness, and can meet the manufacturing and application requirements of special and high-end structural parts;

[0022] (4) The present invention adopts one-stage rolling to complete rolling at high temperature, which ensures the flatness of the steel plate and can meet the performance and shape requirements of the product without heat treatment; the manufacturing process is simple and the cost is low, which is suitable for large-scale industrial stable production;

[0023] (5) The present invention jointly ensures the flatness of the steel plate by controlling the size of the continuous casting billet, the tapping temperature, the holding time, the rolling temperature, the thickness of the rolled piece before coiling, the coiling passes and the reduction rate of the coiling passes, reduces the temperature difference between the head, middle and tail of the rolled piece, and ensures the shape and performance of the extremely thin, wide and long steel plate. Detailed Embodiment

[0024] In order to enable those skilled in the art of the present technology to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0025] Embodiment 1

[0026] An extremely thin, wide and high-toughness steel plate, with chemical composition: C: 0.15%, Si: 0.21%, Mn: 1.25%, P: 0.012%, S: 0.003%, Al: 0.035%, Nb: 0.043%, Ti: 0.017%, and the rest being Fe and inevitable impurities. The thickness of the steel plate is 4 mm, the width is 2920 mm, and the length is 190 m.

[0027] The steel plate is made by the method of smelting and refining the raw materials to obtain molten steel and finally continuous casting into a continuous casting billet, which specifically includes the following steps:

[0028] (1) Smelting: Adopt hot metal pretreatment, with the end S content of 0.0025%; the converter adopts top and bottom combined blowing, fully dephosphorize, with the end P content of 0.004%, argon blowing throughout the process, weak stirring, the slag surface slightly turned over without exposure, and use lime and fluorite to make white slag; the RH vacuum degree is 200 Pa, and the vacuum time is 12 min; the molten steel calming time before tapping is 34 min.

[0029] (2) Slab heating: The slab thickness is 150 mm, the slab furnace outlet temperature is 1277 °C, and the holding time after the slab reaches the furnace outlet temperature is 86 min.

[0030] (3) Slab descaling and rolling: After the slab is taken out of the furnace and descaled by high-pressure water at 31 MPa, it is subjected to the first-stage rolling. The heating temperature of the coiling box is 960 °C. When the billet thickness reaches 27 mm, coiling rolling starts. The starting coiling rolling temperature is 1048 °C. Coiling rolling is carried out for 6 passes. The reduction ratios of the first two passes of coiling rolling are 34% and 32% respectively. The reduction ratio of the coiling rolling passes gradually decreases. The average temperatures of the head, middle, and tail of the 4-mm rolled steel plate in the final pass are 738 °C, 778 °C, and 768 °C respectively. After rolling, the steel plate is subjected to preliminary straightening, sectional shearing, and enters the cooling bed for air cooling.

[0031] The comprehensive properties of the steel plate are shown in Table 1.

[0032] Example 2

[0033] An extremely thin wide-specification high-toughness steel plate, with chemical composition C: 0.16%, Si: 0.20%, Mn: 1.31%, P: 0.013%, S: 0.002%, Al: 0.034%, Nb: 0.032%, Ti: 0.016%, and the rest being Fe and unavoidable impurities. The steel plate thickness is 10 mm, the width is 3000 mm, and the length is 170 m.

[0034] The raw materials are obtained by smelting and refining to obtain molten steel, and finally continuous casting into slabs; the specific steps are as follows:

[0035] (1) Smelting: The end-point S content is controlled at 0.003% by hot metal pretreatment; the converter uses top-bottom combined blowing to fully dephosphorize, and the end-point P content is 0.005%. Argon is blown throughout the process with weak stirring, and the slag surface is slightly turned over without being exposed. Lime and fluorite are used to make white slag; the RH vacuum degree is 200 Pa, and the vacuum time is 13 min; the molten steel calming time before tapping is 35 min.

[0036] (2) Slab heating: The slab thickness is 150 mm, the slab furnace outlet temperature is 1246 °C, and the holding time after the slab reaches the furnace outlet temperature is 43 min.

[0037] (3) Slab descaling and rolling: After the slab is taken out of the furnace and descaled by high-pressure water at 31 MPa, it is subjected to the first-stage rolling. The heating temperature of the coiling box is 1000 °C. When the billet thickness reaches 32 mm, coiling rolling starts. The starting coiling rolling temperature is 989 °C. Coiling rolling is carried out for 2 passes. The reduction ratio of the subsequent passes of coiling rolling gradually decreases. The average temperatures of the head, middle, and tail of the 10-mm rolled steel plate in the final pass are 808 °C, 826 °C, and 817 °C respectively. After rolling, the steel plate is subjected to preliminary straightening, sectional shearing, and enters the cooling bed for air cooling.

[0038] The comprehensive properties of the steel plate are shown in Table 1.

[0039] Table 1 Comprehensive properties of the steel plate in the examples

[0040]

[0041] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all fall within the scope of the present invention. / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention.

Claims

1. A thin, wide, extremely long and high flatness steel plate, characterized in that, The thickness of the steel plate is 4 - 10 mm, the width is 2000 - 3000 mm, the length is 150 - 200 m, the flatness is 2 - 4 mm / m, the yield strength of the steel plate is ≤400 Mpa. By weight percentage, the chemical composition of the steel plate is: C: 0.14% - 0.17%, Si: 0.10% - 0.30%, Mn: 1.20% - 1.40%, P ≤ 0.020%, S ≤ 0.005%, Al: 0.015% - 0.045%, Nb: 0.032% - 0.045%, Ti: 0.010% - 0.025%, and the rest is Fe and unavoidable impurities; The preparation method of the thin, wide, extremely long and high flatness steel plate includes smelting, continuous casting billet heating, descaling of continuous casting billet and rolling processes; after the continuous casting billet is discharged from the furnace and descaled by high-pressure water, rolling starts, and one-stage rolling is adopted; when 4 mm ≤ finished product thickness ≤ 6 mm, coiling rolling starts when the billet thickness is 26 - 30 mm, the starting coiling rolling temperature is 1000 - 1050 °C, the coiling rolling passes are controlled within 4 - 6 passes, the reduction ratio of the first two passes of coiling rolling is greater than 30%, and the reduction ratio of the coiling rolling passes gradually decreases, and the final pass rolling temperature is 730 - 800 °C; when 6 mm < finished product thickness ≤ 10 mm, coiling rolling starts when the billet thickness is 32 - 40 mm, the starting coiling rolling temperature is 950 - 1000 °C, the coiling rolling passes are controlled within 1 - 4 passes, and the reduction ratio of the passes gradually decreases after starting coiling rolling, and the final pass rolling temperature is 800 - 860 °C; when 4 mm ≤ finished product thickness ≤ 6 mm, the continuous casting billet discharge temperature is 1240 - 1270 °C, and the heat preservation time is 40 - 90 min; when 6 mm < finished product thickness ≤ 10 mm, the continuous casting billet discharge temperature is 1220 - 1250 °C, and the heat preservation time is 30 - 60 min; the heating temperature of the coiling box is not less than 950 °C.

2. A preparation method of the thin, wide, extremely long and high flatness steel plate as claimed in claim 1, characterized in that, It includes smelting, continuous casting billet heating, descaling of continuous casting billet and rolling processes; after the continuous casting billet is discharged from the furnace and descaled by high-pressure water, rolling starts, and one-stage rolling is adopted; when 4 mm ≤ finished product thickness ≤ 6 mm, coiling rolling starts when the billet thickness is 26 - 30 mm, the starting coiling rolling temperature is 1000 - 1050 °C, the coiling rolling passes are controlled within 4 - 6 passes, the reduction ratio of the first two passes of coiling rolling is greater than 30%, and the reduction ratio of the coiling rolling passes gradually decreases, and the final pass rolling temperature is 730 - 800 °C; when 6 mm < finished product thickness ≤ 10 mm, coiling rolling starts when the billet thickness is 32 - 40 mm, the starting coiling rolling temperature is 950 - 1000 °C, the coiling rolling passes are controlled within 1 - 4 passes, and the reduction ratio of the passes gradually decreases after starting coiling rolling, and the final pass rolling temperature is 800 - 860 °C.

3. The preparation method of the thin, wide, extremely long and high flatness steel plate as claimed in claim 2, characterized in that, During the hot metal pretreatment in the smelting process, the S content is controlled ≤ 0.004%.

4. The preparation method of the thin, wide, extremely long and high flatness steel plate as claimed in claim 2, characterized in that, During the smelting process, argon blowing is carried out to make white slag; the RH vacuum degree reaches 200 Pa, and the vacuum time is not less than 10 min; the molten steel calming time before tapping is not less than 30 min.

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