Alloyed hot-dip galvanizing 1180mpa grade dual-phase steel with high hole expansion performance and method of manufacturing the same

Abstract

This invention discloses a high-hole-expansion performance alloyed hot-dip galvanized 1180MPa grade duplex steel and its preparation method. The method involves strict control of the carbon (C) content to ensure welding and forming performance; the addition of trace amounts of nitrogen (Nb) effectively refines the grain size; the addition of trace amounts of boron (B) significantly improves hardenability; and the addition of titanium (Ti) effectively fixes the formation of the second phase of nitrogen (N), ensuring that B does not combine with N to form BN, thus fully leveraging the role of B in improving hardenability. The dispersed precipitation of the Ti-containing second phase strengthens ferrite and helps reduce the hardness difference between the soft and hard phases. The absence of molybdenum (Mo) and relatively low levels of manganese (Mn) and chromium (Cr) reduce production costs. Alloying the zinc layer in an alloying furnace not only changes the coating properties but also improves the hole-expansion performance, better meeting the requirements of high-hole-expansion flanged parts. Adjusting each process according to the product thickness specifications, through flexible control, results in better stability of the product's microstructure and properties.

Description

Technical Field

[0001] This invention belongs to the field of cold-rolled strip production technology, specifically relating to a high-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel and its preparation method. Background Technology

[0002] The automotive industry is a significant contributor to carbon emissions, and the development trend of the modern automotive industry is to reduce emissions by making vehicles as lightweight as possible while maintaining safety performance. With energy and environmental issues becoming increasingly prominent, energy conservation and environmental protection have become unavoidable topics in the development of the automotive industry. Achieving vehicle weight reduction through high-strength, thinner steel in automobiles is considered the most scientific and effective method to promote the sustainable development of the automotive industry. Currently, the tensile strength levels of galvanized advanced high-strength steel research and application are mostly at 1000MPa and below, with fewer reports on 1200MPa-level galvanized advanced high-strength steel. The highest level currently used in cold-formed automotive parts is 1200MPa, mainly applied to collision safety components such as anti-collision beams, B-pillars, and door sills to prevent cabin deformation and improve collision safety. Simultaneously, the use of 1200MPa-level cold-rolled duplex steel will further meet the demands of automotive lightweighting and energy emission reduction. While reducing the thickness of steel plates by using high-strength steel plates, the automotive industry can improve the corrosion resistance, dent resistance, durability, large deformation impact strength and safety of automobiles. Therefore, automotive steel plates will inevitably develop towards high strength, high toughness, corrosion resistance and easy forming and processing.

[0003] In the prior art, CN110499457A discloses a high-surface-quality 1200MPa grade hot-dip galvanized duplex steel and its production method. This steel contains a high amount of Mn (1-4%), which easily leads to segregation and is detrimental to the uniform control of microstructure and properties. It also contains a high amount of Ti (0.04-0.08%), which easily produces liquid-precipitated TiN particles, which is detrimental to the material's plasticity. Furthermore, its rapid cooling temperature is 380-400℃, far lower than the zinc bath temperature (around 460℃), which is unfavorable for surface quality control. The product produced under the guidance of this patent is unalloyed, and its surface is pure zinc (GI) rather than alloyed (GA). CN115181916A discloses a 1280MPa grade low-carbon low-alloy ultra-high strength hot-dip galvanized duplex steel and a rapid heat treatment hot-dip galvanizing manufacturing method. The patented strip steel has extremely high rates of heating to the annealing temperature (50-500℃ / s), heating to the alloying temperature after galvanizing (30-200℃ / s), and cooling (30-250℃ / s), which cannot be achieved on conventional hot-dip galvanizing production lines, thus hindering the promotion of this technology. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, this technical solution controls the C content to ensure welding and forming performance, adds trace amounts of Nb to effectively refine the grains, adds trace amounts of B to significantly improve hardenability, and has no Mo and relatively low Mn and Cr content, thus reducing production costs. The zinc layer is alloyed in an alloying furnace, which not only changes the properties of the coating but also improves the hole-expanding performance, better meeting the needs of high-expanding-hole-flanging parts. Each process is adjusted according to the product thickness specifications, and flexible control makes the product's microstructure and performance stability better.

[0005] To achieve the above-mentioned objectives, this invention provides a high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa grade duplex steel. The chemical composition of the duplex steel, by mass percentage, is: C: 0.05-0.14%, Si: 0.05-0.35%, Mn: 1.20-2.50%, P≤0.020%, S≤0.010%, Als: 0.015-0.070%, N≤0.0060%, Nb: 0.010-0.040%, Ti: 0.020-0.060%, Cr: 0.40-0.80%, B≤0.005%, with the balance being Fe and unavoidable impurities.

[0006] Furthermore, the preferred chemical composition (by mass percentage) of the high-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel is C: 0.10-0.13%, Si: 0.15-0.30%, Mn: 2.0-2.4%, Nb: 0.015-0.030%, Ti: 0.025-0.050%, Als: 0.03-0.05%, Cr: 0.55-0.70%, P≤0.010%, S≤0.002%, N≤0.003%, B: 0.002-0.003%, with the balance being Fe and unavoidable impurities.

[0007] As one of the most important components of duplex steel, carbon primarily affects the volume fraction of austenite formed during annealing. During austenite formation, the diffusion of carbon within austenite or ferrite effectively controls austenite grain growth. With increasing carbon content or critical heating temperature, the austenite volume fraction increases, leading to an increase in the martensitic phase formed after cooling, thus increasing the material's strength. If the carbon content is too low, the stability of austenite and the hardenability of martensite decrease, resulting in lower strength; in duplex steel, the carbon content is generally not less than 0.02%. If the carbon content is too high, the plasticity and weldability of duplex steel decrease; in duplex steel, the carbon content is generally not higher than 0.15%. Therefore, the carbon content of this invention is 0.05%-0.14%, preferably 0.10-0.13%.

[0008] Si plays a significant role in solid solution strengthening in steel and effectively inhibits carbide precipitation and delays pearlite transformation during phase transformation. However, excessively high Si content significantly increases deformation resistance during thin-gauge rolling, which is detrimental to thin-gauge rolling. Si can increase the activity of carbon and promote carbon segregation in the manganese-rich region. During heat treatment in the two-phase region, it accelerates carbon diffusion into austenite, significantly purifies ferrite, improves the purity of ferrite in dual-phase steel, promotes ferrite formation, and expands the process window for ferrite formation, thereby obtaining a lower yield strength ratio. On the other hand, excessively high silicon content increases the brittleness of martensite, resulting in poor toughness, and the formation of high-melting-point oxides on the steel plate surface affects the surface quality of the steel plate. Therefore, it is necessary to minimize the silicon content in the steel. Therefore, the Si content of this invention is 0.05-0.35%, preferably 0.15-0.30%.

[0009] Manganese (Mn) is an excellent deoxidizer and desulfurizer, and a commonly used solid solution strengthening element in steel, typically comprising no less than 1.20% in duplex steel. Mn can combine with carbon (C) to form various carbides, providing precipitation strengthening, or dissolve in the matrix to enhance solid solution strengthening. Mn readily combines with sulfur (S) to form the high-melting-point compound MnS, thereby eliminating or weakening hot brittleness caused by FeS and improving the hot working properties of steel. Mn can improve austenite stability, shifting the C-curve to the right and significantly reducing the critical cooling rate of martensite. However, excessively high Mn content can lead to surface enrichment during annealing, forming large amounts of manganese compounds, resulting in a decline in the quality of surface galvanization. Therefore, in this invention, the Mn content is 1.20%-2.50%, preferably 2.00-2.40%.

[0010] Cr can replace Mn, increasing the strength of steel and reducing segregation. It can also inhibit pearlite transformation. Furthermore, the addition of a certain amount of Cr in this invention can improve surface quality. After Cr is added, it can react with oxygen and aggregate at the interface between the iron oxide scale and the iron matrix, forming a dense (Fe,Cr)₂O₃ or (Fe,Cr)₃O₄ spinel film. The presence of this Fe-Cr spinel film hinders oxygen diffusion, reducing the formation of iron oxide scale. Therefore, adding Cr can effectively reduce the thickness of the iron oxide scale and the formation of AlN, and improve the adhesion of the iron oxide scale, thereby effectively reducing pitting defects caused by the indentation of iron oxide scale. Therefore, in this invention, the Cr content is 0.40-0.80%, preferably 0.55-0.70%.

[0011] Al is a common deoxidizer in steel and can also form AlN pinning grain boundaries, thereby refining the grains. Furthermore, Al, similar to Si, can inhibit carbide precipitation, thus ensuring sufficient carbon enrichment in austenite. Therefore, the Al content in this invention is 0.015%-0.070%, preferably 0.03-0.05%.

[0012] In dual-phase steel, nitrogen (Nb) mainly exists in the form of NbC, which has a significant effect on grain refinement and dispersion precipitation strengthening. During the hot-dip galvanizing annealing process, undissolved NbC particles can pin ferrite grain boundaries, thereby refining the grains. When the annealing temperature increases to the two-phase region, the dissolution temperature of NbC is relatively low, so it dissolves fully in the matrix, while dissolved carbon atoms accumulate in austenite to improve its stability. During cooling, NbC in ferrite will reprecipitate, resulting in significant precipitation strengthening. Therefore, the Nb content is 0.010-0.040%, preferably 0.015-0.030%.

[0013] Ti plays a solid solution strengthening role in steel. Ti combines with C and N in the steel to form TiC and TiN, which provide precipitation strengthening. Simultaneously, TiN inhibits austenite grain growth during hot rolling, and during finish rolling, the Ti-containing second phase precipitates and pins grain boundaries, refining the grains. Therefore, the Ti content is 0.020-0.060%, preferably 0.025-0.050%.

[0014] Boron (B) improves the hardenability of austenite, effectively promoting the formation of martensite in duplex steel. It combines with nitrogen (N) in the steel to form niobium (BN), resulting in precipitation strengthening. However, excessive B content can decrease the toughness of the steel. Therefore, this patent adds titanium (Ti) to fix nitrogen, allowing Ti to fully utilize its hardenability, while controlling B at an extremely low level to reduce its impact on plasticity. Thus, the B content in this invention is ≤0.005%, preferably 0.002-0.003%.

[0015] Phosphorus (P) is an impurity element in steel that tends to segregate at grain boundaries, weakening intergranular bonding. During rapid solidification, a high P content can easily lead to cracking in the cast billet. Therefore, in this invention, the P content is ≤0.020%, preferably ≤0.010%.

[0016] Sulfur (S) is an impurity element in steel. It tends to segregate at grain boundaries and forms low-melting-point FeS with Fe in the steel, reducing the toughness of the steel. During rapid solidification, it easily leads to the appearance of fine microcracks on the surface of the cast billet. Therefore, the S content in this invention is ≤0.010%, preferably ≤0.002%.

[0017] Nitrogen (N), an impurity element in steel, readily enters the interstitial spaces of iron elements due to its small atomic size, significantly increasing lattice distortion and thus greatly enhancing strength. However, it also noticeably deteriorates the steel's ductility and toughness. Furthermore, N readily combines with Al, B, and Ti in steel to form second-phase compounds such as AlN, BN, and TiN, which, while strengthening the steel, also worsen its ductility and toughness. Especially when the N content is too high, the TiN precipitated from the liquid can reach micrometer-sized particles, failing to provide strengthening and instead causing stress concentration and crack initiation. Therefore, the N content must be strictly controlled. Thus, in this invention, the N content is ≤0.0060%, preferably ≤0.0030%.

[0018] Furthermore, the high-expansion-performance alloyed hot-dip galvanized 1180MPa grade duplex steel has a yield strength of 900-1020MPa, a tensile strength of 1195-1280MPa, and an elongation A. 80 The strength is 6.0-10.0%, the yield strength ratio is 0.72-0.83, and the porosity is 35-53%.

[0019] Furthermore, the microstructure of the high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa grade duplex steel comprises: 20-25% ferrite with an average grain size of 1.5μm, 15-20% martensite, and 55-65% tempered martensite.

[0020] A method for preparing the above-mentioned high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa grade duplex steel, the method comprising the following production steps:

[0021] ① Smelting process: The high-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel is smelted according to its chemical composition and continuously cast into slabs.

[0022] ② Hot rolling process: The slab is heated, descaled, rough rolled, finish rolled, laminar flow cooled and coiled to obtain a hot rolled coil; the starting temperature of the finish rolling is 1050-1130℃, and the finishing temperature is 870-950℃; the laminar flow cooling adopts the front-stage cooling method, with the upper and lower surface cooling rates being 25% and 50% respectively, the coiling temperature being 600-750℃, and the hot rolled thickness being 2.0-3.8mm.

[0023] ③ Pickling and rolling process: After the hot-rolled coil is pickled, it is cold-rolled into thin strip steel with a thickness of 0.9-2.4mm. The cold rolling reduction rate is 30-55%. As the thickness of the material increases, the cold rolling reduction rate gradually decreases. For every 0.3mm increase in the thickness of the cold-rolled thin strip steel, the thickness of the raw material is adjusted accordingly, and the cold rolling reduction rate is reduced by 4-6%.

[0024] ④ Hot-dip galvanizing process: Cold-rolled thin strip steel is first heated in sections to 300℃, 700℃, and 810-860℃ at heating rates of 15-20℃ / s, 4-10℃ / s, and 0.5-3℃ / s, respectively; after being heated to a uniform temperature and held for 50-120s, it is then slowly cooled to 690-740℃ at rates of 1-5℃ / s and rapidly cooled to 450-470℃, respectively. After being held at a uniform temperature for a period of time, it enters the zinc plating process. The strip steel undergoes galvanizing in the bath. After galvanizing, it is first cooled to 410-430℃ by an air knife, followed by alloying treatment at 485-540℃ for 5-45 seconds. The alloyed strip steel is then cooled to room temperature using a fan (cooling rate ≥5℃ / s). The plating bath contains 0.15-0.30% Al, with the remainder being Zn and unavoidable impurities. The zinc layer weight per unit area is 80-120 g / cm³. 2 The unit speed is 50-100 m / min. As the cold-rolled material thickness increases, the unit speed gradually decreases. For every 0.3 mm increase in the thickness of the cold-rolled thin strip steel, the unit speed is adjusted accordingly, decreasing by 10 m / min. The leveling elongation ranges from 0.30-0.55%, decreasing by 0.05% for every 0.3 mm increase in material thickness.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention, through strict control of C content (0.10-0.13%), helps ensure welding and forming performance; the addition of trace amounts of Nb (0.015-0.030%) effectively refines the grains; the addition of trace amounts of B (0.0020-0.0030%) significantly improves hardenability, while the addition of Ti (0.025-0.050%) effectively fixes N to form a second phase, ensuring that B does not combine with N to form BN, thus fully leveraging its role in significantly improving hardenability. The dispersed precipitation of the Ti-containing second phase strengthens ferrite, which helps reduce the hardness difference between soft and hard phases. The absence of Mo and relatively low Mn and Cr content reduces production costs. Alloying the zinc layer in an alloying furnace not only changes the coating properties but also improves the hole-expanding performance, better meeting the needs of high-hole-expanding flanged parts. The development of high-hole-expanding performance alloyed hot-dip galvanized 1180MPa grade duplex steel helps improve market competitiveness, optimizes product structure, and will generate significant economic and social benefits. Attached Figure Description

[0027] Figure 1 Metallographic image of the high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel prepared in Example 1;

[0028] Figure 2Scanning electron microscope image of high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel prepared in Example 1;

[0029] Figure 3 Stress-strain curves of high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel prepared in Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

[0031] Example

[0032] The technical solution of this embodiment is as follows: a high-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel plate is produced by using a hot-dip galvanizing unit. Four sets (Examples 1-4) of specific implementation methods for high-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel plates are provided, and their chemical compositions are shown in Table 1.

[0033] Table 1. Chemical composition (wt%) of high-expansion-performance alloyed hot-dip galvanized 1180MPa grade duplex steel.

[0034] serial number C Si Mn P S Cr Nb Ti B N Als Example 1 0.110 0.28 2.10 0.009 0.003 0.62 0.028 0.043 0.0028 0.0029 0.042 Example 2 0.120 0.25 2.18 0.005 0.003 0.65 0.022 0.040 0.0025 0.0032 0.037 Example 3 0.105 0.30 2.15 0.007 0.003 0.68 0.026 0.048 0.0027 0.0028 0.044 Example 4 0.115 0.33 2.20 0.008 0.002 0.58 0.030 0.039 0.0026 0.0027 0.035

[0035] The preparation method of the above-mentioned high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa grade duplex steel is as follows:

[0036] ① Smelting process: Through smelting process, duplex steel slabs with the chemical composition shown in Table 1 are prepared;

[0037] ② Hot rolling process: The slab is heated, descaled, hot rolled, and then cooled and coiled to obtain a hot-rolled coil. The initial rolling temperature for finishing is 1050-1130℃, and the final rolling temperature is 870-950℃. Laminar cooling adopts a front-stage cooling method, with cooling rates of 25% and 50% for the upper and lower surfaces, respectively. The coiling temperature is 600-750℃. Specific hot rolling process parameters are shown in Table 2.

[0038] Table 2 Main process parameters for hot rolling of high-expansion-performance alloyed hot-dip galvanized duplex steel grade 1180MPa.

[0039] serial number Rolling temperature / ℃ Final rolling temperature / ℃ Winding temperature / ℃ Hot-rolled thickness / mm Example 1 1108 925 708 3.00 Example 2 1098 918 698 3.25 Example 3 1088 911 687 2.75 Example 4 1112 923 745 2.50

[0040] ③ Pickling and rolling process: After pickling the hot-rolled coil, it is cold-rolled into thin strip steel. The thickness of the hot-rolled plate, the thickness of the cold-rolled plate, and the cold rolling reduction rate are shown in Table 3.

[0041] Table 3. Cold-rolled raw materials, finished products, and reduction rates of high-expansion-performance alloyed hot-dip galvanized duplex steel grade 1180MPa.

[0042] serial number Hot-rolled plate thickness / mm Cold-rolled sheet thickness / mm Cold rolling reduction rate / % Example 1 3.00 1.80 40 Example 2 3.25 2.10 35 Example 3 2.75 1.50 45 Example 4 2.40 1.20 50

[0043] ④ Hot-dip galvanizing process: Cold-rolled thin strip steel is first heated in sections to 300℃, 700℃, and 810-860℃ at heating rates of 15-20℃ / s, 4-10℃ / s, and 0.5-3℃ / s, respectively; after being heated to a uniform temperature and held for 50-120s, it is then slowly cooled to 690-740℃ at rates of 1-5℃ / s and rapidly cooled to 450-470℃, respectively. After being held at a uniform temperature for a period of time, it enters the zinc plating process. The strip steel undergoes galvanizing in the bath. After galvanizing, it is first cooled to 410-430℃ by an air knife, followed by alloying treatment at 485-540℃ for 5-45 seconds. The alloyed strip steel is then cooled to room temperature using a fan (cooling rate ≥5℃ / s). The plating bath contains 0.15-0.30% Al, with the remainder being Zn and unavoidable impurities. The zinc layer weight per unit area is 80-120 g / cm³. 2 The unit speed is 50-100 m / min. As the cold-rolled material thickness increases, the unit speed gradually decreases. For every 0.3 mm increase in the thickness of the cold-rolled thin strip steel, the unit speed is adjusted accordingly, decreasing by 10 m / min. The leveling elongation ranges from 0.30-0.55%, decreasing by 0.05% for every 0.3 mm increase in material thickness. Specific hot-dip galvanizing process parameters are shown in Table 4.

[0044] Table 4 Hot-dip galvanizing process parameters for high-expansion-performance alloyed hot-dip galvanized duplex steel of 1180MPa grade

[0045]

[0046] The microstructure of the high-hole-expansion-performance alloyed hot-dip galvanized 1180MPa duplex steel prepared by the above process is as follows: Figures 1 to 2 As shown, the stress-strain curves are... Figure 3 As shown in Table 5, the performance of the above-mentioned reinforced duplex steel for continuous annealing was tested according to GB / T228-2010 "Metallic Materials - Tensile Testing at Room Temperature" and the hole-expanding performance of the above-mentioned high-hole-expanding-performance alloyed hot-dip galvanized 1180MPa grade duplex steel was tested according to GB / T24524-2009 "Metallic Materials - Hole-Expanding Test Method for Thin Plates and Strips". Furthermore, the performance of products from existing patented technologies CN115181916A, CN110499457A, CN109536837A, and CN109504930A was compared, demonstrating the significant effect of this technical solution.

[0047] Table 5 Mechanical Properties of High-Expansion-Performance Alloyed Hot-Dip Galvanized Duplex Steel (1180MPa Grade)

[0048]

[0049] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method of producing a high hole expansion performance alloyed hot dip galvanized 1180 MPa grade dual phase steel, characterized by, The chemical composition of the 1180MPa grade dual-phase steel is as follows: C: 0.105% to 0.13%, Si: 0.25% to 0.33%, Mn: 2.10% to 2.20%, Nb: 0.022% to 0.028%, Ti: 0.043% to 0.060%, Als: 0.035% to 0.044%, Cr: 0.62% to 0.70%, P≤0.009%, S≤0.003%, N≤0.0060%, B: 0.002% to 0.003%, and the balance of Fe and inevitable impurities; The preparation method of the high-hole-expansion-property alloyed hot-dip galvanized 1180MPa grade dual-phase steel comprises the following production steps: ①smelting step: smelting according to the chemical composition of the high-hole-expansion-property alloyed hot-dip galvanized 1180MPa grade dual-phase steel, and becoming a slab through continuous casting; ②hot rolling step: obtaining a hot-rolled coil after the slab is heated, descaled, rough rolled, finish rolled, laminarly cooled and coiled; the finish rolling opening temperature is 1050°C to 1130°C, the finish rolling temperature is 870°C to 950°C; the laminar cooling adopts a front section cooling mode, the upper and lower surface cooling rates are 25% and 50% respectively, the coiling temperature is 600°C to 750°C, and the hot-rolled plate thickness is 2.0 to 3.8mm; ③pickling and cold rolling step: cold rolling the hot-rolled coil after pickling to become a thin strip steel with a thickness of 0.9 to 2.4mm, and the cold rolling reduction rate is 30% to 55%; the cold rolling reduction rate is reduced by 4% to 6% per 0.3mm increase in the thickness of the cold-rolled thin strip steel; ④hot-dip galvanizing step: the cold-rolled thin strip steel is heated to 300°C, 700°C and 810°C to 860°C at heating rates of 15 to 20°C / s, 4 to 10°C / s and 0.5 to 3°C / s respectively in sections; after holding for 50 to 120s, the cold-rolled thin strip steel is cooled to 690°C to 740°C at a rate of 1 to 5°C / s and then to 450°C to 470°C at a rate of 10 to 25°C / s, and then is evenly held and then is subjected to galvanizing treatment; after the galvanizing is completed, the strip steel is cooled to 410°C to 430°C, and then is subjected to alloying treatment at an alloying temperature of 485°C to 540°C for an alloying holding time of 5 to 45s; the strip steel after alloying is cooled to room temperature at a cold speed of≥5°C / s; the unit speed is 50 to 100m / min, and the flattening elongation range is 0.30% to 0.55%; in the hot-dip galvanizing step, the unit speed is reduced by 10m / min per 0.3mm increase in the thickness of the cold-rolled thin strip steel; the flattening elongation is reduced by 0.05% per 0.3mm increase in the thickness of the material; The yield strength of the dual-phase steel is 900-1020 MPa, the tensile strength is 1195-1280 MPa, the elongation A 80 is 7.5%-10.0%, the yield strength ratio is 0.72-0.83, and the hole expansion ratio is 43%-53%. the microstructure of the dual-phase steel comprises: 20% to 25% of ferrite, 15% to 20% of martensite and 55% to 65% of tempered martensite; the average grain size of the ferrite is 1.5μm.

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