High-toughness lightweight hot continuous rolling steel plate and preparation method thereof

Abstract

The invention relates to a high-toughness lightweight hot continuous rolling steel plate and a preparation method thereof, and belongs to the technical field of metallurgy. The steel plate comprises the following chemical components in percentage by mass: 0.60 to 1.00 percent of C, 0.10 to 0.3 percent of Si, 17.00 to 25.00 percent of Mn, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, 7.00 to 10.00 percent of Al, 3.00 to 6.00 percent of Ni, 0.1 to 0.3 percent of Mo, 0.01 to 0.03 percent of V, 0.02 to 0.04 percent of Nb and the balance of Fe and inevitable impurities, and the density of the steel plate is 6.75 to 7.3 g / cm < 3 >. According to the method, the light alloy steel plate with the thickness of 3-12 mm and the thickness of 1400-2200 mm is produced through a hot continuous rolling mill, industrial production of light alloy steel with the thinner thickness and the narrower thickness tolerance is achieved, steel plate shape control is better, and the method has important significance on lightweight development in the fields of special vehicles, weaponry, ships and the like.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy, specifically relating to Fe-Mn-Al-C lightweight thin steel plates and their preparation methods. Background Technology

[0002] With the rise of green manufacturing concepts such as weight reduction, energy conservation, and carbon emission reduction, high-strength, high-toughness, and lightweight advanced steel materials have become an international research hotspot. Fe-Mn-Al-C lightweight steel possesses advantages such as high strength, good ductility and toughness, and corrosion resistance, making it a promising candidate for applications in automobiles, armored vehicles, ships, and aerospace. Therefore, major countries worldwide are paying close attention to the research on the industrial production technology and engineering application technology of this type of steel. In recent years, the applicant has mastered the key technologies for the entire production process of Fe-Mn-Al-C lightweight steel through technological breakthroughs, successfully achieving large-scale industrial production of this type of steel, becoming one of the few companies in China to achieve industrial-scale production of Fe-Mn-Al-C lightweight steel.

[0003] With the increasing demands for lightweight and high mobility in automobiles and special equipment, the demand for Fe-Mn-Al-C lightweight steel sheets is gradually increasing, especially for 4-5mm thick sheets. Currently, the minimum thickness of Fe-Mn-Al-C lightweight steel directly rolled using a hot-roll mill is 6mm, which cannot meet market demand. Moreover, hot-roll mill rolling is a single-sheet rolling method, resulting in low production efficiency. Therefore, this invention innovatively proposes using hot continuous rolling to produce Fe-Mn-Al-C lightweight steel sheets, achieving thinner thicknesses, a wider range of thickness specifications, and higher efficiency for industrial production. Summary of the Invention

[0004] To address the technical challenge of low production efficiency and inability of hot-rolled coil mills to produce Fe-Mn-Al-C lightweight steel plates with a thickness less than 6 mm, this invention provides a high-strength, high-toughness, lightweight hot-rolled steel plate and its preparation method. This invention uses Fe-Mn-Al-C lightweight steel slabs as the raw material for hot rolling, and through slab heating, descaling, rough rolling, hot-rolling mill finishing, laminar flow cooling, coiling, cooling, uncoiling, and inspection processes, produces a Fe-Mn-Al-C lightweight hot-rolled steel plate with high strength, good toughness, thin thickness, high thickness control precision, and high flatness.

[0005] The technical solution adopted in this invention is: a high-strength and tough lightweight hot-rolled steel plate and its preparation method. The chemical composition of the lightweight hot-rolled steel plate by mass percentage is: C: 0.60-1.00%, Si: 0.10-0.30%, Mn: 17.00-25.00%, P: ≤0.010%, S: ≤0.003%, Al: 7.00-10.00%, Ni: 3.00-6.00%, Mo: 0.1-0.3%, V: 0.01-0.03%, Nb: 0.02-0.04%, with the remainder being Fe and unavoidable impurities.

[0006] The specific preparation process steps of the lightweight hot-rolled steel plate of the present invention are as follows: 1. Slab Production: Molten steel is smelted and cast into steel ingots or continuously cast slabs. The steel ingots or continuously cast slabs are rolled into intermediate slabs with a thickness of 150-220mm, a width of 1400-2200mm, and a length of 5300-11000mm, which serve as hot-rolled billets. The surface quality of the intermediate slabs should meet the following basic conditions: ① The end faces of the intermediate slabs are neatly cut and free from visible shrinkage cavities, cracks, cutting steps with a height greater than 15mm, flame cutting nodules with a height greater than 5mm, and other defects that affect rolling quality; ② The surface of the slabs is free from visible cracks, overlaps, flaking, scabs, inclusions, cold splashes, ears, and pores. The surface of the slabs is also free from vibration marks, wrinkles, scratches, indentations, abrasions, pits, bumps, and hairline cracks with a depth or height greater than 2.5mm; ③ Slabs requiring grinding must be ground symmetrically, and the thickness difference between symmetrical parts after grinding should be ≤3mm.

[0007] 2. Heating: The intermediate billet is heated using a walking beam furnace with natural gas as the heating medium. To prevent surface cracking of the intermediate billet, the preheating section temperature is controlled at 400-800℃, and the preheating time is ≥1.5h, ensuring that the temperature difference between the inside and outside of the intermediate billet does not exceed 100℃; the first heating section temperature is controlled at 800-950℃, and the heating time is ≥0.5h, ensuring a heating rate of <20℃ / min; the high-temperature section temperature is controlled at 1200-1250℃, and the heating time is ≥2h, ensuring that the temperature difference between the inside and outside of the intermediate billet does not exceed 30℃.

[0008] 3. Descaling: After exiting the furnace, the intermediate billet is descaled by high-pressure water with a descaling water pressure of >20MPa.

[0009] 4. Rough rolling: The rolling stage adopts high-temperature fast rolling method, with an initial rolling temperature of 1100-1150℃ and a total of 7-11 rolling passes, ensuring a reduction rate of ≥15% in 3 passes and at least 3 passes of on-machine descaling.

[0010] 5. Hot continuous rolling: After rough rolling, the round head is cut online and enters the hot continuous rolling mill. According to the rolling thickness, the reduction of the seven hot continuous rolling mills is allocated. The reduction of the first mill is large and the reduction of the last mill is small and gradually decreases. The final rolling temperature is 900-950℃.

[0011] 6. Laminar flow cooling: After hot continuous rolling, laminar flow cooling is used for controlled cooling to 650-750℃. Optionally, the water volume and water group of the laminar flow cooling section and the speed of the roller conveyor are controlled to make the cooling rate of the steel plate greater than 30℃ / s.

[0012] 7. Underground coiling machine: After the steel plate is water-cooled, it enters the underground coiling machine to form a hot-rolled coil.

[0013] 8. Water cooling of rolled coils: Hot rolled coils are placed in a water cooling tank and cooled to room temperature.

[0014] 9. Uncoiling and straightening: After being uncoiled, the hot-rolled coil enters the straightening machine, where it is segmented and cut to length on both sides online; subsequently, the steel plate is subjected to strong straightening by a (nine-roll) straightening machine to ensure that the flatness of the finished steel plate is ≤3mm / m.

[0015] The lightweight hot-rolled steel sheet prepared by this invention has a density of 6.75-7.3 g / cm³. 3 Thickness specifications: 3-12mm; width: 1400-2200mm; surface unevenness: ≤3mm / m; thickness accuracy: controllable within ±0.15mm. Tensile strength: 1000-1250MPa; yield strength: 900-1160MPa; elongation after fracture: 20-40%; KV2≥20J at -40℃ (sample size: 5*10*55mm); no cracks when bent to 180° (using a bending mandrel with a thickness of 3 times).

[0016] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention uses hot continuous rolling, which has a faster rolling speed than traditional hot rolling mills. As a result, the steel plate has a higher temperature during the rolling deformation process, which is beneficial for controlling the thickness tolerance and shape of the steel plate.

[0017] 2. When the hot continuous rolling process ends, the steel plate can maintain a high temperature and then undergo laminar flow cooling. By controlling the cooling rate, the precipitation of carbides on the grain boundaries during the cooling process can be suppressed, which helps the steel plate to obtain high plasticity and toughness.

[0018] 3. When steel plates are rolled into hot-rolled coils, the relatively slow air-cooling rate deteriorates the steel plate's performance. This invention rapidly places the hot-rolled coils into a water-cooling tank, combined with circulating water agitation, which accelerates the cooling rate of the hot-rolled coils. This allows the steel plate microstructure to quickly pass through the 500-600°C temperature difference, avoiding the deterioration of the steel plate's ductility and toughness caused by excessive precipitation of secondary phases within the grains due to prolonged residence time in the 500-600°C temperature range. At the same time, it ensures that a certain amount of secondary phases precipitate within the grains, giving the steel plate higher strength.

[0019] 4. The lightweight alloy steel with a thickness of 6mm and below to be produced by this invention has high deformation resistance, a large rolling compression ratio, many rolling passes, and rapid temperature drop during the process, making direct rolling extremely difficult and prone to warping. Using a lap rolling process results in a long production cycle, and the lap-rolled welds are prone to cracking during rolling, making it difficult to straighten the sheet shape after separation. This invention uses hot continuous rolling equipment, which offers high rolling speed and high rolling temperature, reducing rolling difficulty and facilitating control of sheet shape and thickness. Laminar flow cooling and hot-rolled coil water cooling after rolling ensure rolling performance. The method of this invention can produce lightweight alloy steel sheets with a thickness of 3-12mm and a width of 1400-2200mm, with thickness tolerance controllable within ±0.15mm and straightness controllable within ≤3mm / m. The production process is stable, efficient, and suitable for industrial-scale mass production. Attached Figure Description

[0020] Figure 1 This is the microstructure of the high-strength, high-toughness, lightweight hot-rolled steel plate with a thickness of 6 mm in Example 2 of the present invention.

[0021] Figure 2 This is the microstructure of the high-strength, high-toughness, lightweight hot-rolled steel plate with a thickness of 4 mm in Example 3 of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0023] Through the production process of steelmaking-continuous casting / in-sink casting-slow cooling-billet cleaning, hot-rolled 150-220mm lightweight steel billets are obtained; then through the process of heating-rough rolling-hot continuous rolling-laminar cooling-coiling-cooling-uncoiling-straightening, high-strength and tough lightweight hot-rolled steel plates with a thickness of 3-12mm are obtained.

[0024] The following examples further illustrate the main aspects of the billet, rolling process, and cooling process.

[0025] Example 1: Producing high-strength, high-toughness, lightweight hot-rolled steel plates with a thickness of 10mm and a width of 2160mm using hot continuous rolling, including the following steps: (1) Production of slabs: Slabs with dimensions of 200*2200*6000mm are produced by rolling steel ingots. The surface and cutting quality of the slabs must meet the specifications of claim 3. The chemical composition of the slabs by mass percentage is: C=0.69%, Si=0.38%, Mn=20.05%, P≤0.01%, S≤0.003%, Al=7.5%, Ni=4.2%, Mo=0.26%, V=0.023%, Nb=0.027%, with the balance being Fe and unavoidable impurity elements.

[0026] (2) Slab heating: The temperature of the preheating section is 559℃ and the heating time of the preheating section is 116min; the temperature of the first heating section is 912℃ and the heating time is 47min; the temperature of the high temperature section is 1230℃ and the high temperature section time is 215min. When the slab is taken out of the furnace, the core temperature is 1190℃, the upper surface temperature is 1188℃ and the lower surface temperature is 1191℃; normal coarse descaling is performed after the slab is taken out of the furnace.

[0027] (3) Rough rolling: The initial rolling temperature is 1170℃, with a total of 9 passes, of which the reduction rate of 3 passes is ≥15%. During the rolling process, descaling is performed on the machine in passes 1, 3, and 5, and the final rolling thickness is 40mm.

[0028] (4) Hot continuous rolling: The starting rolling temperature is 980℃, and it passes through 7 continuous rolling mills to a thickness of 10mm. The final rolling temperature is 917℃.

[0029] (5) Laminar flow cooling: Inlet water temperature 860℃, laminar flow cooling section opening water flow and water group 60 / 120 m 3 / h *10 sets, roller speed is 1.9m / s, average cooling rate is 36.8℃ / s, and outlet water temperature is 740℃.

[0030] (6) Rolling and cooling: The hot continuous rolled coil is cooled to room temperature in a water pool at a water temperature of 16°C for 8.8 hours.

[0031] (7) Straightening: After the steel plate is uncoiled, it is subjected to strong straightening by a 9-roll straightener, and the flatness of the steel plate is 3mm / m.

[0032] The 10mm thick lightweight hot-rolled steel sheet produced using the above process has a tensile strength of 1039MPa, a yield strength of 915MPa, an elongation after fracture of 35.5%, a KV²=65J at -40℃ (sample size 7.5*10*55mm), exhibits no cracking when bent to 180° (bending mandrel diameter 30mm), and a density of 7.03g / cm³. 3 .

[0033] Example 2: Producing high-strength, high-toughness, lightweight hot-rolled steel plates with a thickness of 6mm and a width of 2160mm using hot continuous rolling, including the following steps: (1) Production of slabs: 150*2200*6000mm continuously cast slabs are directly used as hot continuous rolling blanks. The surface and cutting quality of the slabs must meet the specifications of claim 3. The chemical composition of the slabs by mass percentage is: C=0.88%, Si=0.41%, Mn=21.01%, P≤0.01%, S≤0.003%, Al=7.8%, Ni=3.2%, Mo=0.22%, V=0.021%, Nb=0.025%, with the balance being Fe and unavoidable impurity elements.

[0034] (2) Slab heating: The temperature of the preheating section is 600℃ and the heating time of the preheating section is 95min; the temperature of the first heating section is 950℃ and the heating time is 55min; the temperature of the high temperature section is 1237℃ and the high temperature section time is 174min. When the slab is taken out of the furnace, the core temperature is 1198℃, the upper surface temperature is 1209℃, and the lower surface temperature is 1206℃; normal coarse descaling is performed after the slab is taken out of the furnace.

[0035] (3) Rough rolling: The initial rolling temperature is 1150℃, with a total of 7 passes, of which the reduction rate of 3 passes is ≥15%. During the rolling process, descaling is performed on the machine in passes 1, 3, and 5, and the final rolling thickness is 30mm.

[0036] (4) Hot continuous rolling: The starting rolling temperature is 972℃, and it passes through 7 continuous rolling mills to a thickness of 6mm. The final rolling temperature is 910℃.

[0037] (5) Laminar flow cooling: The inlet water temperature is 845℃, and the water flow rate and water group of the laminar flow cooling section are 60 / 120 m³. 3 / h *12 groups, roller speed is 2.0m / s, average cooling rate is 30.9℃ / s, and outlet water temperature is 730℃.

[0038] (6) Coiling and cooling: The hot continuous rolled coil is cooled to room temperature in a water pool at a water temperature of 19°C for 8.5 hours; (7) Straightening: After the steel plate is uncoiled, it is straightened by strong force, and the flatness of the steel plate is 3mm / m.

[0039] Lightweight hot-rolled steel sheet with a thickness of 6mm produced using the above process has a tensile strength of 1150MPa, a yield strength of 1067MPa, an elongation after fracture of 31.5%, a KV²=35J at -40℃ (sample size 5*10*55mm), exhibits no cracking when bent to 180° (bending mandrel diameter 18mm), and a density of 6.96g / cm³. 3 .

[0040] Example 3: Producing high-strength, high-toughness, lightweight hot-rolled steel plates with a thickness of 4mm and a width of 1660mm using hot continuous rolling, including the following steps: (1) Production of slabs: 150*1700*6000mm continuously cast slabs are directly used as hot continuous rolling blanks. The surface and cutting quality of the slabs must meet the specifications of claim 3. The chemical composition of the slabs by mass percentage is: C=0.89%, Si=0.43%, Mn=21.08%, P≤0.01%, S≤0.003%, Al=7.9%, Ni=3.9%, Mo=0.20%, V=0.023%, Nb=0.022%, with the balance being Fe and unavoidable impurity elements.

[0041] (2) Slab heating: The temperature of the preheating section is 600℃ and the heating time of the preheating section is 99min; the temperature of the first heating section is 950℃ and the heating time is 58min; the temperature of the high temperature section is 1237℃ and the high temperature section time is 180min. When the slab is taken out of the furnace, the core temperature is 1197℃, the upper surface temperature is 1210℃ and the lower surface temperature is 1208℃; normal coarse descaling is performed after the slab is taken out of the furnace.

[0042] (3) Rough rolling: The initial rolling temperature is 1150℃, with a total of 7 passes, of which the reduction rate of 3 passes is ≥15%. During the rolling process, descaling is performed on the machine in passes 1, 3, and 5, and the final rolling thickness is 30mm.

[0043] (4) Hot continuous rolling: The starting rolling temperature is 970℃, and the thickness is 4mm after passing through 7 continuous rolling mills. The final rolling temperature is 910℃.

[0044] (5) Laminar flow cooling: The inlet water temperature is 832℃, and the water flow rate and water group of the laminar flow cooling section are 60 / 120m. 3 / h*8 sets, roller speed is 2.0m / s, average cooling rate is 37.5℃ / s, and outlet water temperature is 723℃.

[0045] (6) Coiling and cooling: The hot continuous rolled coil is cooled to room temperature in a water pool at a water temperature of 19°C for 7.2 hours; (7) Straightening: After the steel plate is uncoiled, it is subjected to strong straightening to achieve a flatness of 3mm / m.

[0046] Lightweight hot-rolled steel plates with a thickness of 4mm produced using the above process have a tensile strength of 1230MPa, a yield strength of 1145MPa, an elongation after fracture of 23.5%, a KV²=12J at -40℃ (test size 2.5*10*55mm), show no cracks when bent to 180° (bending mandrel diameter 12mm), and a density of 6.95g / cm³. 3 .

Claims

1. A high-strength, high-toughness, lightweight hot-rolled steel plate, characterized in that: The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.60-1.00%, Si: 0.10-0.45%, Mn: 17.00-25.00%, P: ≤0.010%, S: ≤0.003%, Al: 7.00-10.00%, Ni: 3.00-6.00%, Mo: 0.1-0.3%, V: 0.01-0.03%, Nb: 0.02-0.04%, with the remainder being Fe and unavoidable impurities. The density of the steel plate is 6.75-7.3 g / cm³. 3 .

2. The high-strength, high-toughness, lightweight hot-rolled steel plate according to claim 1, characterized in that: The chemical composition of the steel plate by mass percentage is as follows: C: 0.60-1.00%, Si: 0.10-0.3%, Mn: 17.00-25.00%, P: ≤0.010%, S: ≤0.003%, Al: 7.00-10.00%, Ni: 3.00-6.00%, Mo: 0.1-0.3%, V: 0.01-0.03%, Nb: 0.02-0.04%, with the remainder being Fe and unavoidable impurities.

3. The high-strength, high-toughness, lightweight hot-rolled steel plate according to claim 1, characterized in that: The steel plate has a thickness of 3-12mm, a width of 1400-2200mm, a surface unevenness of ≤3mm / m, and a thickness accuracy that can be controlled within ±0.15mm.

4. The high-strength, high-toughness, lightweight hot-rolled steel plate according to claim 1, characterized in that: The tensile strength of the steel plate is 1000-1250MPa, the yield strength is 900-1160MPa, the elongation after fracture is 20-40%, the KV2 is ≥20J at -40℃, and there is no crack when bent to 180° with a mandrel of 3 times the thickness.

5. A method for preparing the high-strength, high-toughness, lightweight hot-rolled steel plate according to claim 1, characterized in that: include, S1. Slab Production: Steel is smelted according to its chemical composition and cast into steel ingots or continuously cast slabs. The steel ingots or continuously cast slabs are then rolled into intermediate slabs with a thickness of 150-220 mm, a width of 1400-2200 mm, and a length of 5300-11000 mm, which serve as hot-rolled slabs. The surface quality of the intermediate slabs should meet defect requirements. When slabs need to be ground for this purpose, symmetrical grinding must be performed at relatively symmetrical positions, ensuring that the thickness difference between symmetrical parts after grinding is ≤3 mm. S2. Heating: The intermediate billet is heated by a walking beam furnace using natural gas as the heating medium, and a segmented, slow heating method is adopted. S3. Descaling: After exiting the furnace, the intermediate billet is descaled by high-pressure water with a descaling water pressure >20MPa. S4. Rough rolling: The rolling stage adopts high-temperature fast rolling method, with an initial rolling temperature of 1100-1150℃ and a total of 7-11 rolling passes, ensuring a reduction rate of ≥15% in 3 passes and at least 3 passes of on-machine descaling. S5. Hot continuous rolling: After rough rolling, the round head is cut online and enters the hot continuous rolling mill. According to the rolling thickness, the reduction of 7 hot continuous rolling mills is allocated, and the final rolling temperature is 900-950℃. S6. Laminar flow cooling: After hot continuous rolling, laminar flow cooling is used for controlled cooling to 650-750℃. S7. Coiling: After being water-cooled, the steel plate enters an underground coiling machine to form a hot-rolled coil; S8. Water cooling of rolled coils: Hot rolled coils are placed in a water cooling tank and cooled to room temperature; S9. Uncoiling and straightening: After being uncoiled, the hot-rolled coil enters the straightening machine, where it is segmented and cut to length on both sides online. Subsequently, the steel plate undergoes strong straightening to ensure that the flatness of the finished steel plate is ≤3mm / m.

6. The method according to claim 5, characterized in that: In S1, the surface quality of the intermediate billet shall meet the following requirements: ① The end face of the intermediate billet shall be neatly cut and shall not have visible shrinkage cavities, cracks, cutting steps with a height greater than 15mm, flame cutting nodules with a height greater than 5mm, or other defects that affect the rolling quality; ② The surface of the slab shall not have visible cracks, overlaps, peeling, scars, inclusions, cold splashes, ears, or pores, and the surface of the slab shall not have vibration marks, wrinkles, scratches, indentations, abrasions, pits, bumps, or hairline marks with a depth or height greater than 2.5mm.

7. The method according to claim 5, characterized in that: In S2, to avoid surface cracking of the intermediate billet, the preheating section temperature is controlled at 400-800℃, and the preheating time is ≥1.5h to ensure that the temperature difference between the inside and outside of the intermediate billet does not exceed 100℃; the first heating section temperature is controlled at 800-950℃, and the heating time is ≥0.5h to ensure that the heating rate is <20℃ / min; the high temperature section temperature is controlled at 1200-1250℃, and the heating time is ≥2h to ensure that the temperature difference between the inside and outside of the intermediate billet does not exceed 30℃.

8. The method according to claim 5, characterized in that: In S6, the water volume and water group of the laminar flow cooling section and the speed of the roller conveyor are controlled to make the cooling rate of the steel plate greater than 30℃ / s.

Images