A production method of 1180MPa grade quenched and partitioned steel with high strength, high yield ratio and high elongation

Abstract

The application discloses a production method of 1180MPa grade quenched and partitioned steel with high strength, high yield ratio and high elongation, which controls the molten steel composition supplied to the casting machine in the smelting and continuous casting process of the steel plate as follows: C: 0.15-0.17%, Si: 1.80-1.90%, Mn: 1.5-1.8%, P≤0.020%, S≤0.005%, Alt: 0.025-0.060%, Ni: 0.008-0.012%, Ti: 0.035-0.045%, and the rest is Fe and inevitable impurities; and the rolling process, cooling process and continuous annealing process parameters are optimized and controlled, so that the 1180MPa grade quenched and partitioned steel with mechanical properties meeting the following requirements can be obtained: tensile strength≥1280MPa, yield ratio≥0.75, elongation A 50 ≥19.

Description

Technical Field

[0001] This invention belongs to the field of materials metallurgy technology, and specifically relates to a production method of 1180MPa grade quenched steel with high strength, high yield strength ratio and high elongation. Background Technology

[0002] Lightweighting technology has become a current trend in the automotive industry and has received widespread attention. High-strength and high yield strength ratio steels are highly effective in reducing vehicle weight and improving safety, and their application in body manufacturing is increasing. ULSAB vehicles utilize 90% high-strength steel sheets, among which cold-rolled quenched steel, due to its high strength, is suitable for manufacturing stamped parts with complex shapes and high strength requirements. However, the production of 1180MPa grade cold-rolled quenched steel is currently quite difficult, especially the production of 1180MPa grade quenched steel that combines high strength, high yield strength ratio, and high elongation.

[0003] Patent document CN115505840A (hereinafter referred to as Document 1) discloses a method for producing high-strength quenched steel. By optimizing and controlling the mass percentage content of the chemical composition of the quenched steel to: C: 0.20–0.22%, Si: 1.45–1.55%, Mn: 2.0–2.1%, P: ≤0.020%, S≤0.005%, Alt: 0.025–0.060%, Cr: 0.19–0.21%, Ti: 0.010–0.014%, Ce≤0.0025%, with the remainder being Fe and unavoidable impurities, and by optimizing and controlling the production process parameters, a high-strength quenched steel with a tensile strength of over 1200 MPa can be obtained. Its mechanical and technological properties meet GB / T20564.9-2016 and the customer's technical requirements. However, the high-strength quenched steel produced by Document 1 has a yield strength ratio of only 0.72 at most, and its elongation A... 50 At a maximum of only 14%, its impact resistance and formability are not ideal, which is insufficient to significantly improve the safety performance of automobiles and is not conducive to the manufacture of stamped parts with complex shapes. Summary of the Invention

[0004] To address the problems existing in the prior art, one aspect of the present invention provides a method for producing 1180MPa grade quenched steel with high strength, high yield strength ratio, and high elongation, comprising the following process steps: smelting and continuous casting process, heating process, rolling process, cooling process, pickling and cold rolling process, and continuous annealing process, wherein...

[0005] In the smelting and continuous casting process, the composition of the molten steel supplied to the casting machine is controlled as follows: C: 0.15-0.17%, Si: 1.80-1.90%, Mn: 1.5-1.8%, P≤0.020%, S≤0.005%, Alt: 0.025-0.060%, Ni: 0.008-0.012%, Ti: 0.035-0.045%, with the remainder being Fe and unavoidable impurities;

[0006] In the rolling process, the initial rolling temperature of the finishing rolling is controlled at 1100±10℃, and the final rolling temperature is controlled at 820±10℃.

[0007] In the cooling process, the cooling rate is controlled at 15±5℃ / s, and the winding temperature is 520±10℃.

[0008] In the continuous annealing process, the heating and soaking temperature of the annealing step is controlled to be 800-820℃, the rapid cooling start temperature is 680-690℃, the rapid cooling rate is 40-50℃ / s, the temperature is cooled to 280-300℃, and the over-aging temperature is 360-420℃.

[0009] The mechanical properties of the 1180MPa grade quenched steel, which combines high strength, high yield strength ratio, and high elongation, meet the following requirements: tensile strength ≥ 1280MPa, yield strength ratio ≥ 0.75, and elongation A. 50 ≥19.

[0010] In some embodiments, the yield strength of the 1180MPa grade quenched fractional steel, which combines high strength, high yield strength ratio and high elongation, is 980-1100MPa.

[0011] In some embodiments, the composition of the molten steel supplied to the casting machine in the smelting and continuous casting process is controlled as follows: C: 0.15-0.17%, Si: 1.81-1.89%, Mn: 1.52-1.77%, P≤0.020%, S≤0.005%, Alt: 0.025-0.059%, Ni: 0.009-0.012%, Ti: 0.036-0.044%, with the remainder being Fe and unavoidable impurities.

[0012] In some embodiments, the smelting and continuous casting process includes the following steps: hot metal pretreatment—converter—LF refining—RH vacuum treatment—casting machine.

[0013] In some embodiments, the heating process controls the slab time in the furnace to be 200-240 minutes and the exit temperature to be 1230±20℃.

[0014] In some embodiments, the rolling process includes roughing and finishing, wherein the roughing is performed using a 3+3 mode 2-stand mill and the finishing is performed using a 7-stand continuously variable crown (CVC) mill.

[0015] In some implementations, the cooling process employs laminar flow cooling equipment and a front-end cooling mode.

[0016] In some embodiments, the flattening elongation is controlled to be 0.5 to 1.0% in the continuous annealing process.

[0017] In some embodiments, in the continuous annealing process, the soaking time is 170-190 s and the over-aging holding time is 350-450 s.

[0018] In another aspect, the present invention provides a 1180MPa grade quenched fractional steel with high strength, high yield strength ratio and high elongation, which is obtained by the above-described production method.

[0019] In some embodiments, the thickness of the 1180MPa grade quenched steel is 1.2 to 1.8 mm.

[0020] In some embodiments, the microstructure of the 1180MPa grade quenched steel is: ferrite + martensite + a small amount of austenite.

[0021] Based on the above technical solutions, this invention optimizes and controls the chemical composition system of the quenched steel to a C, Si, Mn, Ni, and Ti system, and optimizes and controls the production process parameters, mainly including rolling and cooling process parameters. This enables the production of a 1180MPa grade quenched steel with high strength, high yield strength ratio, and high elongation. Its microstructure consists of ferrite + martensite + a small amount of austenite. The mechanical properties meet the following requirements: yield strength 980–1100MPa, tensile strength ≥1280MPa, yield strength ratio ≥0.75, and elongation A. 50 ≥19, therefore, compared with the high-strength quenched steel produced in the above-mentioned literature 1, it has higher strength, higher yield strength ratio and higher elongation, which can give it better anti-collision performance and formability, significantly improve the safety of automobiles, and facilitate the use of it to manufacture stamped parts with complex shapes, which is suitable for the material needs of car bumpers and other similar products. Attached Figure Description

[0022] Figure 1 Metallographic image of the 1180MPa grade cold-rolled quenched fractional steel produced for Example 1. Detailed Implementation

[0023] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0024] Example 1

[0025] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1640℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1550℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1220℃ for 220 minutes, and the heated slab is then descaled using high-pressure water. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1105℃, and the final rolling temperature is 820℃, resulting in a finished product thickness of 4mm. Laminar flow cooling uses pre-dispersion cooling, reducing the strip temperature to 520℃ before coiling. Hot-rolled strip steel was pickled in a hydrochloric acid bath using MH's newly developed i-BOX technology, which greatly simplifies operation and maintenance, saving energy and labor. After removing surface iron oxide scale, the hot-rolled strip steel was cold-rolled on a 5-stand UCM mill with a cold rolling reduction of 62.5%, rolling to the target thickness of 1.5 mm. Continuous annealing of the cold-rolled coil was carried out in a simulated annealing furnace. The strip running speed was 90 m / min, the soaking temperature was 800℃, the soaking time was 180 s, the rapid cooling start temperature was 680℃, the rapid cooling rate was 45℃ / s, cooling to 290℃, the over-aging temperature was 420℃, the over-aging holding time was 400 s, and the leveling elongation was 0.8%. Finally, product performance testing was performed, as shown in Table 2 below. Figure 1 The metallographic image of the 1180MPa grade cold-rolled quenched fractional steel produced in this embodiment is shown. Its metallographic microstructure consists of ferrite, martensite, and a small amount of retained austenite.

[0026] Example 2

[0027] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1630℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1550℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheat is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1224℃ for 223 minutes, and the heated slab is then descaled using high-pressure water. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1100℃, the finishing temperature is 825℃, and the finished product thickness is 4.0mm. Laminar flow cooling uses pre-dispersion cooling, reducing the strip temperature to 525℃ before coiling. Hot-rolled strip steel was pickled in a hydrochloric acid bath using MH's newly developed i-BOX technology, which greatly simplifies operation and maintenance, saving energy and labor. After removing surface iron oxide scale, the hot-rolled strip steel was cold-rolled on a 5-stand UCM mill with a cold rolling reduction of 62.5%, rolling to the target thickness of 1.2 mm. Continuous annealing of the cold-rolled coil was carried out in a simulated annealing furnace. The strip running speed was 90 m / min, the soaking temperature was 800℃, the soaking time was 180 s, the rapid cooling start temperature was 690℃, the rapid cooling rate was 40℃ / s, cooling to 280℃, the over-aging temperature was 380℃, the over-aging holding time was 400 s, and the flattening elongation was 0.8%. Finally, product performance testing was conducted, and the results are shown in Table 2 below.

[0028] Example 3

[0029] Molten iron undergoes desulfurization pretreatment, followed by decarburization and dephosphorization in a top-and-bottom blown converter to obtain steel. Argon blowing is performed throughout the converter smelting process, with scrap steel added. The converter tapping temperature is 1640℃. The molten steel is then subjected to LF ladle refining at a refining temperature ≥1550℃. Temperature measurement and composition fine-tuning are performed during LF ladle refining. The chemical composition supplied to the casting machine after LF ladle refining is shown in Table 1. The slab superheating is 20℃, followed by slab cleaning, slow cooling, and continuous casting slab quality inspection. The slab heating temperature is 1224℃ for 240 minutes, and the heated slab is then descaled using high-pressure water. Width is determined using a width-fixing press, followed by a 2-stand roughing mill and a 7-stand CVC finishing mill. The finishing mill starting temperature is 1095℃, the finishing temperature is 820℃, and the finished product thickness is 4.0mm. Laminar flow cooling uses pre-dispersion cooling, reducing the strip temperature to 520℃ before coiling. Hot-rolled strip steel was pickled in a hydrochloric acid bath using MH's newly developed i-BOX technology, which greatly simplifies operation and maintenance, saving energy and labor. After removing surface iron oxide scale, the hot-rolled strip steel was cold-rolled on a 5-stand UCM mill with a cold rolling reduction of 62.5%, rolling to the target thickness of 1.5 mm. Continuous annealing of the cold-rolled coil was carried out in a continuous vertical annealing furnace. The strip running speed was 80 m / min, the soaking temperature was 806℃, the soaking time was 180 s, the rapid cooling start temperature was 685℃, the rapid cooling rate was 43℃ / s, cooling to 285℃, the over-aging temperature was 368℃, the over-aging holding time was 400 s, and the leveling elongation was 0.8%. Finally, product performance testing was conducted, and the results are shown in Table 2 below.

[0030] Comparative Example 1

[0031] The operation was carried out according to Example 1, with the only difference being that the initial rolling temperature of the finishing mill was controlled at 1030°C and the final rolling temperature at 885°C, and the coiling temperature was controlled at 580°C in the cooling process. Finally, the product performance was tested, and the results are shown in Table 2 below.

[0032] Comparative Example 2

[0033] The operation was carried out according to Example 1, with the only differences being: in the rolling process, the initial rolling temperature of the finishing mill was controlled at 1030℃ and the final rolling temperature at 885℃; in the cooling process, the coiling temperature was controlled at 580℃; and in the continuous annealing process, the rapid cooling termination temperature was controlled at 270℃. Finally, product performance was tested, and the results are shown in Table 2 below.

[0034] Table 1: Chemical composition (wt%) of Examples 1-3 and Comparative Examples 1-2 of the present invention

[0035] Example C Si Mn P S Alt Ni Ti Example 1 0.15 1.81 1.52 0.018 0.004 0.025 0.009 0.036 Example 2 0.16 1.83 1.67 0.015 0.003 0.041 0.012 0.042 Example 3 0.17 1.89 1.77 0.016 0.002 0.059 0.011 0.044 Comparative Example 1 0.15 1.81 1.52 0.018 0.004 0.025 0.009 0.036 Comparative Example 2 0.15 1.81 1.52 0.018 0.004 0.025 0.009 0.036

[0036] Table 2: Mechanical properties of steel strips from Examples 1-3 and Comparative Examples 1-2 of the present invention

[0037]

[0038] As can be seen from the data in Table 2, the steel plates produced in Examples 1 to 3 of this invention all possess high strength, high yield strength ratio, and high elongation. Their mechanical properties meet the following requirements: yield strength 980–1100 MPa, tensile strength ≥ 1280 MPa, yield strength ratio ≥ 0.75, and elongation A. 50 ≥19, therefore, compared with the high-strength quenched steel produced in the above-mentioned literature 1, it has higher strength, higher yield strength ratio and higher elongation, which can give it better anti-collision performance and formability, significantly improve the safety of automobiles, and facilitate the use of it to manufacture stamped parts with complex shapes, which is suitable for the material needs of car bumpers and other similar products.

[0039] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing 1180MPa grade quenched steel with high strength, high yield strength ratio, and high elongation, comprising the following process steps: smelting and continuous casting, heating, rolling, cooling, pickling and cold rolling, and continuous annealing, characterized in that, In the smelting and continuous casting process, the composition of the molten steel supplied to the casting machine is controlled as follows: C: 0.15~0.17%, Si: 1.80~1.90%, Mn: 1.5~1.8%, P≤0.020%, S≤0.005%, Alt: 0.025~0.060%, Ni: 0.008~0.012%, Ti: 0.035~0.045%, with the remainder being Fe and unavoidable impurities; In the rolling process, the initial rolling temperature of the finishing rolling is controlled at 1100±10℃, and the final rolling temperature is controlled at 820±10℃. In the cooling process, the cooling rate is controlled at 15±5℃ / s, and the winding temperature is 520±10℃. In the continuous annealing process, the heating and soaking temperature of the annealing step is controlled to be 800~820℃, the rapid cooling start temperature is 680~690℃, the rapid cooling rate is 40~50℃ / s, the temperature is cooled to 280~300℃, and the over-aging temperature is 360~420℃. The mechanical properties of the 1180MPa grade quenched steel, which combines high strength, high yield strength ratio, and high elongation, meet the following requirements: tensile strength ≥ 1280 MPa, yield strength ratio ≥ 0.75, and elongation A. 50 ≥19%.

2. The production method according to claim 1, characterized in that, The yield strength of the 1180MPa grade quenched steel, which combines high strength, high yield strength ratio and high elongation, is 980~1100 MPa.

3. The production method according to claim 1 or 2, characterized in that, In the smelting and continuous casting process, the composition of the molten steel supplied to the casting machine is controlled as follows: C: 0.15~0.17%, Si: 1.81~1.89%, Mn: 1.52~1.77%, P≤0.020%, S≤0.005%, Alt: 0.025~0.059%, Ni: 0.009~0.012%, Ti: 0.036~0.044%, with the remainder being Fe and unavoidable impurities.

4. The production method according to claim 1 or 2, characterized in that, The smelting and continuous casting process includes the following steps: molten iron pretreatment—converter—LF refining—RH vacuum treatment—casting machine.

5. The production method according to claim 1 or 2, characterized in that, In the heating process, the slab is controlled to be in the furnace for 200-240 minutes and the furnace exit temperature is 1230±20℃.

6. The production method according to claim 1 or 2, characterized in that, The rolling process includes roughing and finishing, wherein the roughing is performed using a 3+3 mode 2-stand rolling mill, and the finishing is performed using a 7-stand continuous variable crown rolling mill.

7. The production method according to claim 1 or 2, characterized in that, The cooling process employs laminar flow cooling equipment and a front-end cooling mode.

8. The production method according to claim 1 or 2, characterized in that, In the continuous annealing process, the flattening elongation is controlled to be 0.5~1.0%.

9. A 1180MPa grade quenched fractional steel with high strength, high yield strength ratio and high elongation, obtained by the production method of any one of claims 1-8.

10. The 1180MPa grade quenched steel according to claim 8, characterized in that, The thickness of the 1180MPa grade quenched steel is 1.2~1.8 mm.

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