A 1285MPa grade passenger car steel and its production method

Abstract

The present invention belongs to the field of metal materials, and particularly relates to a 1285MPa-grade passenger vehicle steel and its production method. The steel's chemical composition is designed to be C, Si, Mn, Al, Nb, V, Ta, Bi, Sb, W, Cr, Pt, Zr, and Y, with an Al / Si ratio of 1.0-2.0, a Ta+Pt ratio of 0.020%-0.030%, and P ≤ 0.015%, S ≤ 0.005%, and N ≤ 0.006%, with the remainder being Fe and unavoidable impurities. The steel is produced using a hot rolling, EPS, continuous annealing, and skin-passing process, simplifying the production process and preventing environmental pollution.

Description

Technical Field

[0001] The present invention belongs to the field of metal materials, and in particular relates to a 1285MPa grade passenger car steel and a production method thereof. Background Art

[0002] The automotive industry is a major user of steel products, and the research, development, and application of steel products are closely related to the development trends of the automotive industry. In today's society, with the rapid development of my country's automotive industry, automotive steel has begun to develop in the direction of low cost, high strength, green environmental protection, and high safety. In order to reduce the weight of automotive structural components and reduce their weight, thereby saving energy and reducing environmental pollution, the application of high-performance and high-surface quality automotive steel plates has been promoted. Conventional technology for the production of automotive thin plates is obtained by hot rolling + pickling + cold rolling + continuous annealing + skin-passing process, for example:

[0003] Chinese patent application publication number CN113416890A discloses a high-hole expansion and high-plasticity 980MPa grade cold-rolled continuously annealed steel plate and its preparation method. It uses a common C-Mn composition system to design and add a certain amount of Mo, Cu and B to produce hot-rolled + pickling + cold-rolled + continuous annealing + skin-passing steel plates. The yield strength is ≤850MPa, the tensile strength is ≥980MPa, and the hole expansion rate is ≥50%, which does not meet the requirements of ultra-high-strength passenger car parts. In addition, the process system is prepared through hot rolling + pickling + cold rolling + continuous annealing + skin-passing, which has a large process flow and high production costs. In particular, pickling is required. The pickling process has problems such as large acid mist pollution, environmental pollution, and high waste acid treatment costs.

[0004] Chinese patent application publication number CN116377334A discloses an ultra-high-plasticity isotropic 980MPa grade cold-rolled high-strength steel plate and its preparation method. The plate is produced by hot rolling, pickling, cold rolling, continuous annealing and skin-passing by adding a certain amount of Nb and Ti to a conventional C-Mn composition system. The plate has a yield strength of ≤850MPa, a tensile strength of ≥980MPa, and no hole expansion requirement. It does not meet the requirements of ultra-high-strength passenger car parts and does not have certain corrosion resistance and oxidation resistance. In addition, the process system is prepared by hot rolling, pickling, cold rolling, continuous annealing and skin-passing, which has a large process flow and high production costs. In particular, pickling is required. The pickling process has problems such as large acid mist pollution, environmental pollution, and high waste acid treatment costs.

[0005] Chinese patent application publication number CN115652207A discloses a 780MPa-grade short-process economical cold-rolled DH steel plate and its production method. It uses a common C-Mn composition system to design and add a certain amount of Ti, Mg and Ca to produce hot-rolled + pickling + cold-rolled + continuous annealing + skin-passing steel plates. The yield strength is ≥440MPa, the tensile strength is ≥780MPa, the hole expansion rate is ≥30%, and the hole expansion rate is small, which does not meet the requirements of ultra-high-strength passenger car parts and does not have certain corrosion resistance and oxidation resistance. In addition, the process system is prepared through hot rolling + pickling + cold rolling + continuous annealing + skin-passing, which has a large process flow and high production cost. In particular, pickling is required. The pickling process has problems such as large acid mist pollution, environmental pollution, and high waste acid treatment costs. Summary of the Invention

[0006] The purpose of the present invention is to provide a 1285MPa grade passenger car steel and its production method, with a steel plate yield strength ≥1088MPa, a tensile strength ≥1285MPa, a transverse elongation A ≥21%, a hole expansion rate ≥54%, a qualified transverse cold bending 180°D=a, good surface quality, no iron oxide stripes and color defects, and a surface roughness Ra of 1.10~1.60μm. According to GB / T10125-2021 "Artificial Atmosphere Corrosion Test-Salt Spray Test", a neutral salt spray test is performed to simulate the marine atmospheric environment, using a NaCl solution with a concentration of 50±5g / L. Within a 168h test period, the steel plate corrosion rate is ≤0.51g / (m 2 •h). Furthermore, the conventional hot rolling + pickling + cold rolling + continuous annealing + skin-passing process is not required. Instead, the hot rolling + EPS (wet sandblasting descaling process) + continuous annealing + skin-passing process is adopted, which reduces the pickling + cold rolling process, resulting in low production costs and no pollution to the environment.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A 1285MPa grade steel for passenger cars, the chemical composition of the steel by weight percentage is: C: 0.082%-0.173%, Si: 0.25%-0.55%, Mn: 2.15%-2.28%, Al: 0.35%-0.55%, Nb: 0.065%-0.072%, V: 0.120%-0.135%, Ta: 0.015%-0.023%, Bi: 0.005%-0.014%, Sb: 0.015% ~0.050%, W: 0.010%~0.036%, Cr: 0.56%~0.66%, Pt: 0.002%~0.009%, Zr: 0.015%~0.020%, Y: 0.006%~0.010%, and Al / Si: 1.0~2.0, Ta+Pt: 0.020%~0.030%, and limit P≤0.015%, S≤0.005%, N≤0.006%, the balance is Fe and unavoidable impurities.

[0009] The main functions of the composition of the 1285MPa grade passenger car steel in the present invention are:

[0010] C: Carbon is a common strengthening element in steel. The interstitial solid solution atomic carbon causes a certain lattice distortion in the matrix, which plays a role in solid solution strengthening. The role of carbon in the present invention can ensure the bainite content, thereby improving the forming performance and hole expansion performance of the steel plate. If the carbon content is too low, the mechanical properties of the steel plate in the present invention cannot be obtained. If the content is too high, the steel plate will become brittle, and there will be a risk of delayed fracture and hot-rolled edge cracking, which is also detrimental to the welding performance, plasticity and toughness of the steel plate. The carbon requirement in the present invention is generally in the low carbon range, which is beneficial to reducing the risk of delayed fracture and hot-rolled edge cracking, and is also beneficial to the welding performance of the steel plate. Therefore, the optimal range of carbon in the present invention is 0.082% to 0.173%.

[0011] Si: Silicon is one of the important elements of the present invention. Sufficient silicon addition to ferrite can ensure the strength of the ferrite matrix, and silicon addition will increase the A C3 The silicon content in the steel sheet is 0.25% to 0.55%, which is a significant improvement over the conventional annealing process. The addition of silicon to the steel sheet effectively regulates the annealing process window during the continuous annealing phase, ensuring an appropriate ferrite-austenite ratio in the critical zone at industrial continuous annealing temperatures. Furthermore, sufficient silicon addition can reduce inclusions in the steel sheet, inhibiting their formation and preventing the steel sheet from degrading its mechanical properties and hole expansion performance due to inclusion formation. However, if the silicon content is too low, it will not ensure the strength of the ferrite matrix and inhibit inclusion formation. If the silicon content is too high, it will affect the hot-rolled surface quality, resulting in the formation of large amounts of iron oxide scale and poor weldability. Therefore, the silicon content in the present invention is 0.25% to 0.55%.

[0012] Mn: Manganese strengthens the solid solution in steel by inducing lattice distortion through substitutional solid solution. It is also an austenite stabilizing element in steel, expanding the austenite region, reducing the critical quenching rate of steel, and delaying the transformation of austenite to pearlite. However, if the manganese content is too low, the supercooled austenite will be unstable, reducing the plasticity, toughness and hole expansion performance of the steel plate. In addition, the added content of manganese should not exceed the scope of the present invention. The main consideration is the problem of C or Mn segregation caused by excessive manganese content, which deteriorates the uniformity of the steel plate structure during hot rolling and easily causes serious banded structure defects in the structure. In addition, the excessive manganese involved in the steel of the present invention leads to increased hardenability, suppressed bainite formation, and is not conducive to hole expansion performance. In addition, excessive manganese content will lead to poor welding performance of the steel plate. Therefore, based on comprehensive considerations, the present invention selects a manganese content of 2.15% to 2.28%.

[0013] P: Phosphorus is an impurity element in steel and is easily segregated at grain boundaries. When the phosphorus content in steel is high, Fe2P particles are easily formed, which reduces the plasticity, toughness and hole expansion performance of the steel. Therefore, the lower the content, the better. In order to obtain a higher elongation, the upper limit is set at 0.015%.

[0014] S: Sulfur is an impurity element in steel. It easily combines with Mn to form MnS inclusions, which become the starting point of cracks and deteriorate the processing performance, seriously affecting the plasticity, formability and hole expansion performance of the steel plate. Therefore, the lower the content, the better. The upper limit is set at 0.005%.

[0015] Al: Al is a deoxidizer in traditional steelmaking processes. It also combines with nitrogen in steel to form AlN, which refines grains and inhibits the decomposition of retained austenite. Together with Si, it inhibits cementite formation, raising the austenitization temperature, facilitating optimal process window selection and accelerating martensitic transformation. Excessive Al content can cause nozzle blockage during continuous casting, impacting production efficiency and increasing costs. Therefore, in this invention, the Al content is limited to 0.35% to 0.55%, and the Al / Si ratio must be 1.0-2.0.

[0016] Nb: Nb effectively delays the recrystallization of deformed austenite, inhibits austenite grain growth, increases the austenite recrystallization temperature, refines grains, and improves the strength and toughness of the steel. Because free nitrogen atoms in the steel degrade the toughness of the steel plate, Nb combines with impurity nitrogen in the steel to form NbN. This NbN formation acts as a nitrogen fixation agent. Furthermore, Nb combines with carbon and nitrogen to form Nb(C, N), which contributes to grain refinement and precipitation strengthening. It also strengthens ferrite and bainite, resulting in excellent mechanical properties and hole expansion performance. Therefore, the optimal range of Nb content in the present invention is between 0.065% and 0.072%.

[0017] V: Vanadium has significant precipitation strengthening and grain refinement effects. Its effects are primarily achieved by forming precipitates with carbon and nitrogen. In particular, the VN precipitation formed with nitrogen significantly enhances the strength of the steel plate. Furthermore, a large number of V precipitates remain within the steel plate structure, acting as hydrogen traps and reducing the risk of delayed cracking in the Sb-containing steel plate of the present invention during service. The combined addition of V and Nb allows for the retention of a large number of V and Nb composite carbides within the Sb-containing steel plate of the present invention, which act as hydrogen traps and significantly enhance the Sb-containing steel plate's resistance to hydrogen-induced cracking during service, resulting in excellent mechanical properties, hole expansion performance, and resistance to hydrogen-induced cracking. Higher V contents degrade the toughness of the weld heat-affected zone, so the V addition in the present invention is 0.120% to 0.135%.

[0018] Ta: Tantalum has a strong affinity with elements such as carbon and nitrogen in steel, and can form fine and dispersed carbides, nitrides or carbonitrides. These compounds hinder grain growth and refine the grains of the steel, thereby improving the comprehensive mechanical properties of the steel, such as strength, toughness, and plasticity, and the pore expansion rate. In addition, tantalum forms a dense and stable oxide film (Ta2O5) on the surface of the steel. This oxide film can prevent external corrosive media from contacting the steel matrix, thereby improving the corrosion resistance of the steel. Therefore, the optimal range of the Ta content in the present invention is between 0.015% and 0.023%.

[0019] Bi: Bismuth (Bi) is primarily distributed within grain boundaries and grain interiors in steel, increasing steel sheet strength, reducing the diffusion rate of elements like carbon and oxygen at grain boundaries, minimizing decarburization and oxidation, and improving the surface and mechanical properties of the steel sheet. Therefore, the present invention limits the Bi content to 0.005% to 0.014%.

[0020] Sb: Antimony can make the corrosion products dense and inhibit H2O, O2, Cl - and SO4 2- Sb diffuses into the steel matrix and accumulates near the steel matrix in an acidic environment, forming a uniform, dense oxide film (rich in elements such as Sb) on the steel plate surface, resisting further corrosion. However, Sb is a low-melting-point element and tends to accumulate at grain boundaries, causing grain boundary cracks. The risk of steel plate cracking increases rapidly with increasing Sb content, so the present invention limits the Sb content to 0.015% to 0.050%.

[0021] W: Tungsten has the highest melting point of any metal, and the WC it forms is highly hard. Its effect in steel is similar to that of molybdenum, enhancing wear resistance more effectively than molybdenum. It also improves the hardenability of steel and effectively inhibits grain growth. When its content is less than 0.010%, the effect is minimal, while exceeding 0.036% increases brittleness. Therefore, the optimal range for the W content in this invention is between 0.010% and 0.036%.

[0022] Cr: Chromium delays pearlite transformation and improves the hardenability of steel. This facilitates the formation of martensite and refines the structure, resulting in a strengthening effect. Chromium forms a dense oxide film (primarily Cr2O3) on the steel surface. This film prevents further contact between oxygen and water and the steel matrix, improving the steel's corrosion resistance. Therefore, the Cr content is limited to 0.56% to 0.66%.

[0023] Pt: Platinum has excellent chemical stability and corrosion resistance. Platinum can react with oxygen in steel to form a dense oxide protective film. This protective film can isolate the steel from direct contact with the corrosive medium, thereby slowing down the corrosion process, improving the corrosion resistance and oxidation resistance of the steel, and increasing the service life of the steel in highly corrosive environments and high temperatures. Therefore, the present invention limits the Pt content to 0.002% to 0.009%, and satisfies the Ta + Pt: 0.020% to 0.030%.

[0024] Zr: Zirconium is a strong deoxidizer that can react with oxygen to form stable ZrO2, effectively reducing the oxygen content in steel, reducing oxide inclusions, and improving the purity of steel. It can also react with sulfur to form ZrS, reducing the sulfur content in steel. When the steel solidifies, it can act as a heterogeneous core to promote grain nucleation, inhibit grain growth, and refine the cast grains. During hot rolling and continuous annealing, it forms stable carbides, hindering the growth of austenite grains, obtaining a fine and uniform grain structure, and improving the strength, toughness, plasticity and hole expansion performance of the steel. Therefore, the present invention limits the Zr content to 0.015% to 0.020%.

[0025] Y: Yttrium can refine the grains in steel, enhance the strength and plasticity of the grain boundaries, and is beneficial to improving the hole expansion performance. It can also improve the welding performance and oxidation resistance of steel, thereby increasing the service life of steel at high temperatures. Therefore, the present invention limits the Y content to 0.006% to 0.010%.

[0026] N: Regarding the N content in steel, the lower the N content, the better. However, too low a content will lead to production difficulties and increase costs. However, the present invention requires the precipitation of VN formed with V to perform precipitation strengthening and fine grain strengthening to improve the strength and hole expansion performance of the steel plate. Therefore, the N content in the present invention is ≤0.006%.

[0027] After nitric acid corrosion, the microstructure analysis was performed under an optical microscope. The microstructure of the finished steel plate was 8% to 12% by volume of ferrite, 81% to 85% by volume of martensite, and 7% to 11% by volume of retained austenite.

[0028] The steel plate has a yield strength of ≥1088MPa, a tensile strength of ≥1285MPa, a transverse elongation A ≥21%, a hole expansion rate ≥54%, a transverse cold bending 180°D=a that is qualified, and a surface roughness Ra of 1.10~1.60μm.

[0029] The thickness of the steel plate is 1.75~2.88mm; according to GB / T10125-2021 "Artificial atmosphere corrosion test - salt spray test", a neutral salt spray test is performed to simulate the marine atmosphere environment, using a NaCl solution with a concentration of 50±5g / L. Within a 168h test period, the steel plate corrosion rate is ≤0.51g / (m 2 •h).

[0030] A production method for 1285MPa grade passenger car steel includes smelting, hot rolling, wet sandblasting descaling, continuous annealing, and skin-passing steps, as follows:

[0031] (1) Smelting process: RH+LF process is adopted, H and O contents are strictly controlled, H≤0.0002%, O≤0.0015%, calcium treatment is carried out in the refining process, electromagnetic stirring and light reduction technology are used in the continuous casting process, the billet pulling speed is ≤1.5m / min, and the light reduction amount is 1.5~2.5mm, which reduces the center segregation of the continuous casting billet, which is beneficial to reduce the banded structure in the subsequent rolling of hot rolled steel plates.

[0032] (2) Hot rolling process: The continuous casting slab with a thickness of 112 to 200 mm and a width of 1000 to 1450 mm is directly hot-transferred and hot-charged into a walking beam heating furnace for heating at a temperature of 1210 to 1240°C and a holding time of 182 to 210 min. The chemical composition of the present invention contains Sb, which has a low melting point and is easily enriched at the grain boundary to generate cracks. Therefore, the heating temperature should not be too high. The rough rolling adopts a 3+3 rolling process (R1 adopts 3 rolling passes, R2 adopts 3 rolling passes), with a total of 6 rolling passes. The rough rolling outlet temperature is 1050~1095℃, the intermediate billet thickness is 34.0~53.0mm, and the width is 1000~1450mm. The intermediate billet is insulated with a heat preservation cover before entering the hot rolling and finishing mill to reduce the temperature drop of the intermediate billet on the delay roller and the temperature difference between the head, tail and plate width directions. The finishing rolling is a 7-stand continuous rolling. High-pressure water descaling is used before finishing rolling. The finishing rolling inlet temperature is not higher than 1050℃. The final rolling temperature is 900~940℃. After final rolling, the laminar cooling mode is adopted, and the laminar cooling rate is ≥60℃ / s. After cooling to 530~577℃, it is coiled and air-cooled to room temperature. Laminar cooling to 530-577°C is intended to rapidly generate bainite, inhibiting grain growth while ensuring bainite content, thereby refining bainite grains. Finishing mill F1 reductions range from 16-25mm, F2 reductions from 7-12mm, F3 reductions from 4-7mm, F4 reductions from 2.0-3.5mm, F5 reductions from 1.0-2.2mm, F6 reductions from 0.6-1.4mm, and F7 reductions from 0.2-0.5mm. The rolled thickness ranges from 1.75-2.88mm. After rolling, the hot-rolled steel sheet has a ferrite volume percentage of 15-20% and a bainite volume percentage of 80-85%.

[0033] (3) EPS (wet sandblasting descaling process): After cooling the steel coil with a thickness of 1.75-2.88 mm to room temperature, wet sandblasting is performed to remove the iron oxide scale on the steel plate surface. The main processes are uncoiling, straightening, sandblasting descaling, and coiling. The uncoiling tension of the steel plate is ≥60 kN, the straightening elongation is 1.01-1.21%, the travel speed is 20-30 m / min, the steel grit hardness is HRC>75, the sandblasting motor speed is 2600-3000 rpm, and the coiling tension is 90-100 kN.

[0034] (4) Continuous annealing: The steel coils after wet sandblasting descaling are continuously annealed, with the belt speed controlled at 50-75 m / min, the soaking section temperature at 805-865 °C, the soaking time at 8-14 min, the slow cooling outlet temperature at 670-705 °C, the rapid cooling rate at more than 60 °C / s, and the rapid cooling outlet temperature at 308-322 °C. The soaking section temperature is 805-865°C, the purpose of which is to ensure a suitable phase ratio of ferrite and austenite in the critical zone. If the soaking section temperature is greater than 865°C, the ferrite ratio in the organization will be greatly reduced, reducing the plasticity of the steel. If the soaking section temperature is less than 805°C, the austenite content in the critical zone temperature stage is obviously insufficient, affecting the subsequent martensite content, which in turn leads to insufficient strength. The soaking time is 8-14 minutes, the purpose of which is to ensure sufficient recrystallization of the steel plate grains during the heating and holding stages and to avoid excessive time leading to grain growth of the steel plate. If the soaking time is too short, the steel plate will not have enough time for continuous annealing and recrystallization, resulting in a decrease in the elongation of the steel plate. The slow cooling outlet temperature is 670-705°C, the purpose of which is to enable the rapid generation of ferrite, while suppressing grain growth and ensuring the ferrite content, thereby refining the ferrite grains. The fast cooling outlet temperature is 308-322°C, the purpose of which is to enable the rapid generation of martensite, while suppressing grain growth and ensuring the martensite content, thereby refining the martensite grains.

[0035] (5) Skin pass: After rapid cooling, the steel is directly air-cooled and enters the skin pass mill. The skin pass adopts rolling force control, which is controlled at 1800~3500kN and the rolling tension is 1000~2000kN.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. Tantalum has a strong affinity with elements such as carbon and nitrogen in steel, and can form fine and dispersed carbides, nitrides or carbonitrides. These compounds hinder grain growth and refine the grains of steel, thereby improving the comprehensive mechanical properties such as strength, toughness, plasticity and pore expansion rate of steel. Tantalum forms a dense and stable oxide film (Ta2O5) on the surface of steel. This oxide film can prevent external corrosive media from contacting the steel matrix, thereby improving the corrosion resistance of steel.

[0038] 2. Bismuth is mainly distributed in the grain boundaries and inside the grains in steel, which improves the strength of the steel plate, reduces the diffusion rate of elements such as carbon and oxygen on the grain boundaries, reduces decarburization and oxidation, and improves the surface and mechanical properties of the steel plate.

[0039] 3. The addition of Sb can make the corrosion products dense and inhibit the formation of H2O, O2, and Cl - and SO4 2- It diffuses isotropically into the steel matrix and can be enriched near the steel matrix in an acidic environment, prompting the formation of a uniform and dense oxide film (rich in elements such as Sb) on the surface of the steel plate matrix to resist further erosion of the steel matrix.

[0040] 4. The WC formed by W has high hardness, enhances wear resistance, improves the hardenability of steel, and effectively inhibits grain growth.

[0041] 5. Cr can delay pearlite transformation and improve the hardenability of steel. This facilitates the formation of bainite and refines the structure, thus strengthening it. Chromium forms a dense oxide film (primarily Cr2O3) on the steel surface. This film prevents further contact between oxygen and water and the steel matrix, improving the steel's corrosion resistance.

[0042] 6. The addition of Pt in steel can react with oxygen to form a dense oxide protective film. This protective film can isolate the steel from direct contact with the corrosive medium, thereby slowing down the corrosion process, improving the corrosion resistance and oxidation resistance of the steel, and increasing the service life of the steel in strong corrosive environments and high temperatures.

[0043] 7. Zr: Effectively reduces the oxygen content in steel, reduces oxide inclusions, improves the purity of steel, inhibits grain growth, refines cast grains, and forms stable carbides during hot rolling and continuous annealing, hindering the growth of austenite grains, obtaining a fine and uniform grain structure, and improving the strength, toughness, plasticity and hole expansion performance of steel.

[0044] 8. The addition of Y can refine the grains in the steel, enhance the strength and plasticity of the grain boundaries, which is beneficial to the improvement of the hole expansion performance. It can also improve the welding performance and oxidation resistance of the steel, thereby increasing the service life of the steel at high temperatures.

[0045] 9. The present invention does not require the conventional hot rolling + pickling + cold rolling + continuous annealing + skin-passing process, but adopts hot rolling + EPS (wet sandblasting descaling process) + continuous annealing + skin-passing process, which reduces the pickling + cold rolling process, has fewer process flows, low production costs, and does not pollute the environment.

[0046] 10. The microstructure of the steel of the present invention is ferrite, martensite and retained austenite, which can significantly improve the hole expansion performance of the steel plate during the forming process.

[0047] 11. The present invention has excellent mechanical properties, yield strength ≥ 1088MPa, tensile strength ≥ 1285MPa, transverse elongation A ≥ 21%, hole expansion rate ≥ 54%, transverse cold bending 180° D = a qualified, surface roughness Ra is 1.10 ~ 1.60μm, according to GB / T10125-2021 "Artificial atmosphere corrosion test - salt spray test", a neutral salt spray test is used to simulate the marine atmospheric environment, using a NaCl solution with a concentration of 50±5g / L, within a 168h test period, the corrosion rate is ≤ 0.51g / (m 2 •h), the steel plate of the present invention is mainly suitable for manufacturing passenger car structural parts. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with examples. The following examples are used to specifically illustrate the contents of the present invention. These examples are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0049] The embodiments of the invention are as follows:

[0050] The smelting process adopts the RH+LF process, strictly controlling the H and O contents, H≤0.0002%, O≤0.0015%. Calcium treatment is carried out in the refining process. Electromagnetic stirring and soft reduction technology are used in the continuous casting process. The casting speed is ≤1.5m / min, and the soft reduction is 1.5-2.5mm. The continuous casting slabs with a thickness of 112-200mm and a width of 1000-1450mm are directly hot-charged into the walking beam heating furnace for heating at a temperature of 1210-1240℃ and a holding time of 182-210min. The rough rolling adopts a 3+3 mode rolling process (R1 uses 3 rolling passes and R2 uses 3 rolling passes) for a total of 6 rolling passes. The rough rolling outlet temperature is 1050-1095℃, and the intermediate billet thickness is 34.0-53.0mm. The width is 1000~1450mm. The intermediate billet is kept warm by an insulation cover before entering the hot rolling and finishing rolling unit to reduce the temperature drop of the intermediate billet on the delay roller and the temperature difference between the head, tail and plate width directions. The finishing rolling is 7-stand continuous rolling. High-pressure water descaling is used before finishing rolling. The finishing rolling entrance temperature is not higher than 1050℃. The finishing rolling temperature is 900~940℃. After finishing rolling, the laminar cooling mode is adopted, and the laminar cooling rate is ≥60℃ / s. After cooling to 530~577℃, it is coiled and air-cooled to room temperature. The finishing mill F1 has a reduction of 16-25mm, F2 has a reduction of 7-12mm, F3 has a reduction of 4-7mm, F4 has a reduction of 2.0-3.5mm, F5 has a reduction of 1.0-2.2mm, F6 has a reduction of 0.6-1.4mm, and F7 has a reduction of 0.2-0.5mm, with a rolling thickness of 1.75-2.88mm. After the 1.75-2.88mm thick steel coils are cooled to room temperature, they are wet-blasted to remove scale from the steel surface. The main processes include uncoiling, straightening, descaling by blasting, and coiling. The uncoiling tension is ≥60kN, the straightening elongation is 1.01-1.21%, the travel speed is 20-30m / min, the steel grit hardness is HRC>75, the blasting motor speed is 2600-3000rpm, and the coiling tension is 90-100kN. Continuous annealing is performed on wet sandblasted, descaled coils with a thickness of 1.75 to 2.88 mm. The strip speed is controlled at 50 to 75 m / min, the soaking zone temperature is 805 to 865°C, the soaking time is 8 to 14 minutes, the slow cooling outlet temperature is 670 to 705°C, the rapid cooling rate is greater than 60°C / s, and the rapid cooling outlet temperature is 308 to 322°C. After rapid cooling, the coils are directly air-cooled before entering the skin-pass mill. Skin-passing utilizes rolling force control, ranging from 1800 to 3500 kN, and rolling tension is 1000 to 2000 kN. The finished product thickness ranges from 1.75 to 2.88 mm.

[0051] The specific composition, hot rolling process, EPS (wet sandblasting descaling process), continuous annealing process, steel plate properties and microstructure volume percentages of the six embodiments of the present invention are shown in Tables 1-6.

[0052] Table 1 Chemical composition of the present invention (wt, %)

[0053]

[0054] Table 2 Hot rolling process system of the embodiment of the present invention

[0055]

[0056] Table 3 EPS (wet sandblasting descaling process) system of the embodiment of the present invention

[0057]

[0058] Table 4 Continuous annealing process system of the embodiment of the present invention

[0059]

[0060] Table 5 Mechanical properties parameters of the embodiments of the present invention

[0061]

[0062] Table 6 Tissue volume percentage in the examples of the present invention

[0063]

Claims

1. A 1285MPa grade passenger car steel, characterized in that: The chemical composition of the steel is calculated by weight as follows: C: 0.082% ~ 0.173%, Si: 0.25% ~ 0.55%, Mn: 2.15% ~ 2.28%, Al: 0.35% ~ 0.55%, Nb: 0.065% ~ 0.072%, V: 0.120% ~ 0.135%, Ta: 0.015% ~ 0.023%, Bi: 0.005% ~ 0.014%, Sb: 0.015% ~ 0.050%, W: 0.010% ~ 0.036%, Cr: 0.56% ~ 0.66%, Pt: 0.002% ~ 0.009%, Zr: 0.015% ~ 0.020%, Y: 0.006% ~ 0.010%, and Al / Si: 1.0 ~ 2.0, Ta + Pt: 0.020% ~ 0.030%, and limit P ≤ 0.015%, S ≤ 0.005%, N ≤ 0.006%, the balance is Fe and unavoidable impurities; The production method of the 1285MPa grade passenger car steel includes smelting, hot rolling, wet sandblasting descaling, continuous annealing and skin-passing processes, as follows: Hot rolling: heating temperature 1210 ~ 1240 ℃, holding time 182 ~ 210min, rough rolling outlet temperature 1050 ~ 1095 ℃, the intermediate billet is kept warm by a heat preservation cover before entering the hot rolling and finishing mill, the finishing rolling inlet temperature is not higher than 1050 ℃, the finishing temperature is 900 ~ 940 ℃, and the laminar cooling mode is adopted after the final rolling, the laminar cooling rate is ≥ 60 ℃ / s, and the coil is taken up after cooling to 530 ~ 577 ℃ and air-cooled to room temperature; Continuous annealing: The steel coils after wet sandblasting descaling are continuously annealed, with the belt speed controlled at 50-75 m / min, the soaking section temperature at 805-865°C, the soaking time at 8-14 min, the slow cooling outlet temperature at 670-705°C, the rapid cooling rate at more than 60°C / s, and the rapid cooling outlet temperature at 308-322°C.

2. The 1285MPa grade passenger car steel according to claim 1, characterized in that: The microstructure of the finished steel plate is 8% to 12% by volume of ferrite, 81% to 85% by volume of martensite, and 7% to 11% by volume of retained austenite.

3. The 1285MPa grade passenger car steel according to claim 1, characterized in that: The steel plate has a yield strength of ≥1088MPa, a tensile strength of ≥1285MPa, a transverse elongation A ≥21%, a hole expansion rate ≥54%, a transverse cold bending 180°D=a that is qualified, and a surface roughness Ra of 1.10~1.60μm.

4. The 1285MPa grade passenger car steel according to claim 1, characterized in that: The thickness of the steel plate is 1.75~2.88mm; according to GB / T10125-2021 "Artificial atmosphere corrosion test - salt spray test", a neutral salt spray test is performed to simulate the marine atmosphere environment, using a NaCl solution with a concentration of 50±5g / L. Within a 168h test period, the steel plate corrosion rate is ≤0.51g / (m 2 •h).

5. A method for producing 1285 MPa grade passenger car steel according to any one of claims 1 to 4, characterized in that: It includes smelting, hot rolling, wet sandblasting descaling, continuous annealing and skin-passing processes, as follows: Hot rolling: heating temperature 1210 ~ 1240 ℃, holding time 182 ~ 210min, rough rolling outlet temperature 1050 ~ 1095 ℃, the intermediate billet is kept warm by a heat preservation cover before entering the hot rolling and finishing mill, the finishing rolling inlet temperature is not higher than 1050 ℃, the finishing temperature is 900 ~ 940 ℃, and the laminar cooling mode is adopted after the final rolling, the laminar cooling rate is ≥ 60 ℃ / s, and the coil is taken up after cooling to 530 ~ 577 ℃ and air-cooled to room temperature; Continuous annealing: The steel coils after wet sandblasting descaling are continuously annealed, with the belt speed controlled at 50-75 m / min, the soaking section temperature at 805-865°C, the soaking time at 8-14 min, the slow cooling outlet temperature at 670-705°C, the rapid cooling rate at more than 60°C / s, and the rapid cooling outlet temperature at 308-322°C.

6. The method for producing 1285MPa grade passenger car steel according to claim 5, characterized in that: The rough rolling adopts the 3+3 mode rolling process, the intermediate billet thickness is 34.0~53.0mm, and the width is 1000~1450mm; the finishing rolling unit F1 reduction is 16~25mm, F2 reduction is 7~12mm, F3 reduction is 4~7mm, F4 reduction is 2.0~3.5mm, F5 reduction is 1.0~2.2mm, F6 reduction is 0.6~1.4mm, and F7 reduction is 0.2~0.5mm.

7. The method for producing 1285 MPa grade passenger car steel according to claim 5 or 6, characterized in that: The microstructure of the hot rolled steel plate after rolling is as follows: the volume percentage of ferrite is 15% to 20%, and the volume percentage of bainite is 80% to 85%.

8. The method for producing 1285MPa grade passenger car steel according to claim 5, characterized in that: The smelting adopts RH+LF process, the casting billet pulling speed is ≤1.5m / min, the soft pressure reduction is 1.5-2.5mm, and the continuous casting billet specification is 112-200mm thick×1000-1450mm wide.

9. The method for producing 1285MPa grade passenger car steel according to claim 5, characterized in that: The wet sandblasting descaling treatment: the main processes include uncoiling, straightening, sandblasting descaling and coiling, the steel plate uncoiling tension is ≥60kN, the straightening elongation is 1.01%~1.21%, the travel speed is 20~30m / min, the steel sand hardness is HRC>75, the sandblasting motor speed is 2600~3000rpm, and the coiling tension is 90~100kN.

10. The method for producing 1285MPa grade passenger car steel according to claim 5, characterized in that: The skin pass: after rapid cooling, it is directly air-cooled and enters the skin pass mill, the skin pass rolling force is controlled at 1800-3500kN, and the rolling tension is 1000-2000kN.

Images