A 1.0GPa-grade hydrogen embrittlement-resistant cold-formed automobile steel and a production method thereof

Abstract

The invention provides a 1.0GPa grade hydrogen embrittlement resistant cold-formed automobile steel and a manufacturing method thereof. The steel plate components are C: 0.15%-0.25%, Mn: 1.8%-2.8%, Si: 0.5%-2.0%, Al: 0.6%-6.0%, Ni: 0.05%-0.80%, Cu: 0.05%-0.80%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.005%-0.50%, Nb: 0.01%-0.50%, Ti: 0.01%-0.50%, 5≤Al / Si≤20, 0.3≤Ni+Cu≤1.3, and the balance is Fe and inevitable impurities. The production method of the steel plate includes electric furnace smelting, medium and thin slab continuous casting and rolling, pickling and cold rolling, quenching and partitioning, and skin pass. The steel can be used for multiple purposes due to its special design in composition and process, which can significantly save product manufacturing costs; and its yield strength is ≥650MPa, tensile strength is 980~1100MPa, A80 elongation after fracture is ≥20.0%, hole expansion rate is ≥40%, and density is 6.5~7.5g / cm 3 ; The steel was pre-stressed by 180° U-bending and immersed in 0.5mol / L HCl solution for 14 days without any delayed fracture, which was an excellent performance.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled automobile steel and relates to a 1.0 GPa-level hydrogen embrittlement-resistant cold-formed automobile steel and a production method thereof. Background Art

[0002] Hydrogen embrittlement (hydrogen-induced delayed cracking) means that parts do not crack when they are made, but over time, under the dual effects of stress and corrosive media, stress corrosion cracking occurs, which eventually leads to failure of parts and loss of safety protection. In this process, hydrogen promotes crack initiation and expansion, and the sensitivity of ultra-high strength steel to hydrogen-induced delayed cracking will increase significantly with the increase of strength level. In actual production, it is found that cold-formed quenching and partitioning (QP) ultra-high strength automotive steel above 1.0GPa level has serious hydrogen embrittlement (hydrogen-induced delayed fracture) phenomenon during the service of parts, and the sensitivity of ultra-high strength steel to hydrogen-induced delayed fracture will increase significantly with the increase of strength level. Because this phenomenon seriously affects the normal service of parts, the delayed fracture phenomenon of cold-formed ultra-high strength steel has received great attention from manufacturers and users. At the same time, under the background of "dual carbon", the steel industry is actively promoting energy conservation, environmental protection and green transformation and development, and QP steel products have the characteristics of diversified parts, diversified user needs, multiple product specifications and special needs of small batch orders. Therefore, the development of green and low-carbon QP steel products for automobiles, that is, one steel multi-purpose alloy design and short-process low-cost preparation technology, can not only meet the special needs of the automotive industry with multiple parts, diversified user needs, multiple specifications and small batch orders, but also is an effective measure for steel companies to improve their competitiveness, and has become a research hotspot for major steel suppliers. Based on the above research status, it is urgent to solve the poor forming performance and hydrogen embrittlement problems of ultra-high strength quenching and partitioning steel, and at the same time adapt to the green and low-carbon product design of automotive high-strength steel under the background of dual carbon.

[0003] Patent document CN112048680B discloses an alloyed hot-dip galvanized DH980 steel and a preparation method thereof, wherein the main chemical components are: C: 0.16% to 0.23%, Mn: 1.5% to 2.5%, Si: 0.2% to 0.9%, Al: 0.02% to 0.9%, Cr: 0.02% to 0.70%, P≤0.01%, S≤0.01%, Nb≤0.05%, V≤0.05%, Ti≤0.05%, and the rest are Fe and unavoidable impurities. The invention adopts the production process of cold rolling-alloyed hot-dip galvanizing to produce alloyed hot-dip galvanized DH980 steel, which has excellent fatigue resistance and hole expansion performance, but does not take into account the hydrogen embrittlement problem of ultra-high strength steel.

[0004] Patent document CN113403551A discloses a high yield ratio hydrogen embrittlement resistant cold-rolled DH980 steel plate and its preparation method, the main chemical composition of which is: C: 0.16% to 0.23%, Mn: 1.8% to 2.5%, Si: 0.4% to 1.2%, Al: 0.30% to 0.90%, Cr: 0.10 to 0.50%, Mo: 0.10 to 0.60%, P≤0.01%, S≤0.01%, N≤0.005%, Nb: 0.01% to 0.10%, Ti: 0.01% to 0.10%, the remainder is Fe and other inevitable impurities. The invention adopts a cold rolling-continuous annealing production process to produce a 1.0GPa grade cold-rolled DH steel, which exhibits a high yield ratio and hydrogen embrittlement resistance, but the ductility of the product is relatively poor, and it is difficult to meet the problem of both high plasticity and hydrogen embrittlement resistance.

[0005] The above-mentioned ultra-high strength steels all have a tensile strength of 1.0 GPa, which are used to obtain better service and forming properties or for resistance to hydrogen embrittlement. Their hydrogen-induced delayed cracking properties are not involved or are not relevant to the product. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to prepare a 1.0GPa-level hydrogen embrittlement-resistant cold-formed automobile steel and its production method. The present invention develops a high-strength quenching and partitioning steel for automobiles with a short-process low-cost process path and a multi-purpose alloy design that reduces costs. The product has the performance characteristics of hydrogen embrittlement resistance, high plasticity, low density and high formability, with a yield strength of ≥650MPa, a tensile strength of 980-1100MPa, an A80 elongation of ≥20.0%, a hole expansion rate of ≥40%, and a density of 6.5-7.5g / cm 3 ; The steel sheet was pre-stressed by 180° U-bending and immersed in 0.5mol / L HCl solution for 14 days without any delayed fracture, providing a reliable technical solution for automobile manufacturers and steel companies.

[0007] The object of the invention is achieved in this way:

[0008] A 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel, characterized in that the chemical composition of the steel, measured by mass percentage, contains: C: 0.15%-0.25%, Mn: 1.8%-2.8%, Si: 0.5%-2.0%, Al: 0.6%-6.0%, Ni: 0.05-0.80%, Cu: 0.05-0.80%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.005%-0.50%, Nb: 0.01%-0.50%, Ti: 0.01%-0.50%, and the balance is Fe and unavoidable impurities.

[0009] Furthermore, the composition 5≤Al / Si≤20, 0.3≤Ni+Cu≤1.3.

[0010] Furthermore, the steel plate has a yield strength of ≥650 MPa, a tensile strength of 980-1100 MPa, an A80 elongation after fracture of ≥20.0%, a hole expansion rate of ≥40%, and a density of 6.5-7.5 g / cm 3 ; The steel plates were pre-stressed by 180° U-bending and immersed in 0.5mol / L HCl solution for 14 days without delayed fracture; the thickness of the steel plates was 0.8mm to 2.3mm.

[0011] Furthermore, the steel plate microstructure is, by volume percentage, 20% to 50% ferrite, 40% to 70% martensite, and 5% to 20% residual austenite, the total of which is 100%; the residual austenite is in two forms, blocky and filmy, with a grain size of 0.05 μm to 0.50 μm, the blocky residual austenite is mainly distributed at the martensite / ferrite interface and inside the ferrite, while the filmy residual austenite is mainly distributed between the martensite laths.

[0012] The reasons for the alloy design of the present invention are as follows:

[0013] C: Carbon element ensures the strength requirement of steel through solid solution strengthening. Sufficient carbon element helps to stabilize austenite, thereby improving the formability of steel and facilitating the design of one steel for multiple uses. If the content of C element is too low, the mechanical properties of the steel in the present invention cannot be obtained; if the content is too high, the steel will become brittle and there is a risk of hydrogen-induced delayed fracture. Therefore, in the present invention, the content of C element is controlled to 0.15% to 0.25%.

[0014] Mn: Manganese is an austenite stabilizing element in steel. It can expand the austenite phase area and reduce the critical quenching rate of steel. At the same time, it can also refine the grains, which helps to improve the strength by solid solution strengthening. If the Mn content is too low, the supercooled austenite is not stable enough, which reduces the processing properties such as plasticity and toughness of the steel plate; if the Mn content is too high, the welding performance of the steel plate will deteriorate and the production cost will increase, which is not conducive to industrial production. Therefore, in the present invention, the Mn content is controlled to 1.8% to 2.8%.

[0015] Si: Silicon has a certain solid solution strengthening effect in ferrite, ensuring that the steel has sufficient strength. At the same time, Si can also inhibit the decomposition of residual austenite and the precipitation of carbides, reducing inclusions in the steel. In the present invention, the Si element is used in combination with the Al element, and the design concept of replacing silicon with aluminum can significantly improve the surface quality of the steel. If the Si element content is too low, it will not play a strengthening role; if the Si element content is too high, it will reduce the surface quality and welding performance of the steel plate. Therefore, in the present invention, the content of the Si element is controlled to 0.5% to 2.0%.

[0016] Al: The density of aluminum is much lower than that of Fe. Adding an appropriate amount of Al to steel can significantly reduce the density of steel, which is conducive to the lightweight development of steel. At the same time, Al has an antioxidant effect. Adding it in combination with Si can effectively improve the surface quality of steel, which is conducive to the design of one-steel-multiple-purpose products. In addition, Al can inhibit the decomposition of residual austenite and the precipitation of carbides, and accelerate the transformation of bainite to improve the coordinated deformation ability. Too high Al content will not only increase production costs, but also lead to difficulties in continuous casting production. When the aluminum content is too low, low-density material design cannot be achieved. Therefore, in the present invention, the content of Al is controlled within the range of 0.6% to 6.0%.

[0017] Ni: Nickel is an important element for improving the welding performance of steel. The addition of Ni is beneficial to improving the toughness of the weld, especially the low-temperature impact toughness, and reducing the brittle transition temperature. A reasonable combination with Cu can effectively control the phase transformation process of the weld metal, and obtain a composite structure of martensite and a certain proportion of residual austenite, thereby taking into account both high crack resistance and high strength. The present invention controls the content of Ni element in the range of 0.05% to 0.80%.

[0018] Cu: Cu is a solid solution strengthening element, which can not only improve the hardenability of steel, but also effectively improve the thermodynamic stability of austenite, help to form stable residual austenite at room temperature, and thus improve the plasticity and delayed fracture resistance of the material; it can be reasonably matched with Ni to improve the welding performance and hydrogen embrittlement resistance of high aluminum steel; but considering the high cost of copper, the present invention controls the content of Cu element within the range of 0.05% to 0.80%.

[0019] P: P is a harmful element in steel, which is very easy to segregate to the grain boundary and seriously reduce the plasticity and deformation performance of the steel. The lower its content, the better. Considering the cost, the content of P in the present invention is controlled to P≤0.01%.

[0020] S: S is a harmful element in steel. Sulfur and manganese are easily combined to form MnS inclusions. After rolling and deformation, the transverse properties of the material will be significantly reduced, which seriously affects the formability of the steel. The lower the content, the better. Considering the cost, the content of S in the present invention is controlled to S≤0.01%.

[0021] N: N element easily reacts with Ti to precipitate large TiN particles, which act as crack sources during deformation and are detrimental to the anti-hydrogen embrittlement performance. Therefore, the N element content in the steel must be strictly controlled. The present invention controls the N content to N≤0.005%.

[0022] Mg: Magnesium is a good deoxidizer, desulfurizer and spheroidizer in steel. Mg can reduce the number of inclusions in steel, reduce their size, make their distribution uniform and improve their morphology. A small amount of magnesium can improve the carbide size and distribution of QP steel, promote the fine and uniform carbide particles, and also help to achieve low-density material design. In order to control production costs, the Mg content is controlled at 0.005% to 0.50% in the present invention.

[0023] Nb: The microalloying element Nb forms compounds with carbon and nitrogen, which helps to delay the recrystallization of the material during hot rolling, refines the grain size, and significantly improves the strength, toughness and fatigue failure resistance of the material. In the present invention, the Nb element content is controlled at 0.01% to 0.50%.

[0024] Ti: A small amount of Ti element can refine the grain size, and the precipitates can pin dislocations to delay the expansion of crack sources and significantly improve the strength and toughness of the material. In the present invention, the Ti element content is controlled at 0.01% to 0.50%.

[0025] The second technical solution of the present invention is to provide a production method of 1.0GPa grade hydrogen embrittlement resistant cold-formed automobile steel, which is characterized by comprising the following steps: electric furnace smelting, continuous casting and rolling of medium and thin slabs, pickling and cold rolling, quenching and partitioning continuous annealing or continuous hot-dip galvanizing / galvanized aluminum-magnesium or alloyed hot-dip galvanizing, and skin pass.

[0026] The specific steps of the preparation process are as follows:

[0027] Electric furnace smelting: The present invention uses 30% to 70% scrap steel as raw material, which can greatly save energy consumption and smelting cost. By smelting in an electric furnace, molten steel that meets the following composition requirements by mass percentage is obtained: C: 0.15% to 0.25%, Mn: 1.8% to 2.8%, Si: 0.5% to 2.0%, Al: 0.6% to 6.0%, Ni: 0.05 to 0.80%, Cu: 0.05 to 0.80%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.005% to 0.50%, Nb: 0.01% to 0.50%, Ti: 0.01% to 0.50%, and 5≤Al / Si≤20, 0.3≤Ni+Cu≤1.3; the remainder is Fe and unavoidable impurities. The temperature of the molten steel is between 1600 and 1750°C.

[0028] Continuous casting and rolling of medium-thin slabs: Use special protective slag for high aluminum steel (Li2O content ranges from 0.5% to 10.0%) for casting, the casting temperature is between 1530 and 1600℃, the casting machine pulling speed is 1.0 to 5.5m / min, and the thickness of the continuous casting slab is between 60 and 115mm. The starting rolling temperature is between 1000 and 1150℃, the final rolling temperature is above 900℃, and the coiling temperature is between 600 and 700℃. The thickness specification of hot-rolled coils is 2.0 to 4.5mm, and the hot-rolled microstructure of the product is composed of 30% to 60% (volume ratio) ferrite, 20% to 50% (volume ratio) pearlite, 5% to 20% (volume ratio) bainite, and 1% to 5% cementite; the total is 100%.

[0029] Pickling cold rolling: Before cold rolling, the hot rolled steel coil is acidized to remove the surface iron oxide scale, and the cold rolling reduction rate is 45% to 70%. If the reduction rate is too high, the deformation resistance will be too large, and it will be difficult to roll to the target thickness; if the reduction rate is too low, the elongation of the cold rolled steel plate will decrease. The thickness of the finished product after cold rolling is 0.8mm to 2.3mm.

[0030] Continuous annealing with quenching and partitioning: belt speed is controlled at 60-180m / min, furnace temperature in the soaking section is 760-880℃, soaking time is 10-600s, slow cooling outlet temperature is 700-750℃, rapid cooling rate is greater than 50℃ / s, rapid cooling temperature is between 100-250℃, partitioning temperature is 250-450℃, and partitioning time is 60-1000s. The soaking temperature is 760-880℃. If the soaking temperature is too high, the ductility of the steel will be reduced due to the complete austenitization and insufficient ferrite ratio; if the soaking temperature is too low, the soft phase ferrite ratio of the final material will be too high, which will greatly reduce the strength of the material. The soaking time is 30-300s. If the soaking time is too long, the steel plate will have coarse grains. If the soaking time is too short, the steel plate will not have time to complete the annealing and recrystallization process, resulting in a decrease in the elongation of the steel plate.

[0031] Continuous hot-dip galvanizing / galvanized aluminum-magnesium with quenching and partitioning: belt speed is controlled at 60-180m / min, annealing temperature is between 760-880℃, dew point temperature is controlled between -20--10℃, annealing time is between 30-300s, slow cooling outlet temperature is 680-750℃, rapid cooling rate is greater than 40℃ / s, rapid cooling outlet temperature is 150-250℃, galvanizing temperature is 450-470℃, after galvanizing, the strip is first cooled to 400-420℃ by air knife, then cooled by air, and the top roller temperature of the cooling tower is controlled at 250-300℃. The composition of the galvanizing bath contains 0.16%-0.25% Al, the rest is Zn and unavoidable impurities, and the weight of the zinc layer per unit area is 60-200g / cm 2The zinc-aluminum-magnesium plating solution contains 2.0% to 10.0% Al, 1.0% to 5.0% Mg, 0.001% to 0.1% Si, and the rest is Zn and unavoidable impurities. The weight of the zinc-aluminum-magnesium coating per unit area is 50 to 200 g / cm 2 .

[0032] Quenching and alloying hot-dip galvanizing: the strip speed is controlled at 60-180m / min, the annealing temperature is 770-870℃, the annealing time is between 30 and 300s, the dew point is controlled at -20--10℃, the slow cooling outlet temperature is 680-750℃, the rapid cooling rate is greater than 40℃ / s, the rapid cooling outlet temperature is between 150 and 250℃, the galvanizing temperature is 450-470℃, after galvanizing, the strip is first air-knife cooled to 400-420℃, and then alloying treatment is carried out, the alloying temperature is 470-530℃, and the alloying holding time is 5-60s.

[0033] Finishing: The finishing process adopts elongation closed-loop control, and the finishing elongation is 0.3% to 1.0%.

[0034] The microstructure of the 1.0 GPa-level hydrogen embrittlement-resistant cold-formed automobile steel plate prepared by the present invention is 20% to 50% (volume ratio) ferrite, 40% to 70% (volume ratio) martensite, and 5% to 20% (volume ratio) residual austenite, the total of which is 100%; and the residual austenite in the product of the present invention is in block form, with a grain size between 0.05 μm and 0.50 μm, and the blocky residual austenite is mainly distributed at the martensite / ferrite interface and inside the ferrite.

[0035] The beneficial effects of the present invention are:

[0036] 1. The chemical composition of the steel of the present invention mainly includes C, Mn, Al and Si as the main elements, and the original cost is relatively low; the new short-process and low-cost production process of "large proportion of scrap steel + electric furnace smelting + continuous casting and rolling of medium and thin slabs" is adopted, which can greatly reduce carbon emissions and save energy consumption.

[0037] 2. The 1.0GPa-grade hydrogen embrittlement-resistant cold-formed automobile steel produced by the present invention can achieve low-density high-strength steel by adding a large amount of aluminum elements, meeting the requirements of lightweight automobile design.

[0038] 3. The 1.0GPa-grade hydrogen embrittlement-resistant cold-formed automobile steel produced by the present invention can realize a set of alloy systems to meet the diversified product requirements of 1.0GPa-grade quenching and partitioning steel continuous annealing, continuous hot-dip galvanizing / galvanized aluminum-magnesium and alloyed hot-dip galvanizing, etc. due to the special design of composition and process. That is, one steel can be used for multiple purposes, which can not only greatly shorten the product development cycle and R&D costs, but also realize the conversion between multiple grades of products and significantly improve product production efficiency, meeting the energy-saving, environmental protection and green transformation and development of automobile steel;

[0039] 4. The 1.0GPa grade hydrogen embrittlement resistant cold-formed automobile steel produced by the present invention has a yield strength of ≥650MPa, a tensile strength of 980-1100MPa, an A80 elongation after fracture of ≥20.0%, a hole expansion rate of ≥40%, and a density of 6.5-7.5g / cm 3 ; The steel was pre-stressed by 180° U-bending and immersed in 0.5mol / L HCl solution for 14 days without any delayed fracture, which was an excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the typical microstructure of Example 1-1 of the present invention.

[0041] Figure 2 This is a typical microstructure of Example 1-2 of the present invention.

[0042] Figure 3 It is a typical microstructure of Examples 1-3 of the present invention.

[0043] Figure 4 It is a typical microstructure of Examples 1-4 of the present invention.

[0044] Figure 5 This is a typical engineering stress-strain curve of Example 1-1 of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described below by way of examples.

[0046] According to the component ratio of the technical solution, the embodiment of the present invention proposes a method for manufacturing 1.0GPa-level hydrogen embrittlement-resistant cold-formed automobile steel, which includes electric furnace smelting, medium and thin slab continuous casting and rolling, pickling and cold rolling, quenching and partitioning, and skin pass.

[0047] Continuous casting and rolling of medium and thin slabs

[0048] High aluminum steel special protective slag is used for casting, Li2O content ranges from 0.5% to 10.0%, casting temperature is 1530-1600℃, casting machine pulling speed is 1.0-5.5m / min, continuous casting billet thickness is 60-115mm, starting rolling temperature is 1000-1150℃, final rolling temperature is above 900℃, coiling temperature is 600-700℃, and hot rolled coil thickness is 2.0-4.5mm;

[0049] Pickling cold rolling

[0050] Before cold rolling, the hot rolled steel coil is passed through an acid solution to remove the surface iron oxide scale, and the cold rolling reduction rate is 45% to 70%;

[0051] Quenching distribution

[0052] The quenching and partitioning includes one of quenching and partitioning continuous annealing, quenching and partitioning continuous hot-dip galvanizing or galvanized aluminum-magnesium, and quenching and partitioning alloying hot-dip galvanizing;

[0053] Finishing

[0054] The finishing process adopts elongation closed-loop control, and the finishing elongation is 0.3% to 1.0%.

[0055] Furthermore, the quenching and partitioning process is a quenching and partitioning continuous annealing, the belt speed is controlled at 60-180 m / min, the furnace temperature of the soaking section is 760-880°C, the soaking time is 10-600s, the slow cooling outlet temperature is 700-750°C, the rapid cooling rate is greater than 50°C / s, the rapid cooling temperature is between 100-250°C, the partitioning temperature is 250-450°C, the partitioning time is 60-1000s, the soaking temperature is 760-880°C, and the soaking time is 30-300s.

[0056] Furthermore, the quenching and matching process is quenching and matching continuous hot-dip galvanizing or galvanized aluminum-magnesium, the belt speed is controlled at 60-180 m / min, the annealing temperature is between 760 and 880°C, the dew point temperature is controlled between -20 and -10°C, the annealing time is between 30 and 300s, the slow cooling outlet temperature is 680-750°C, the rapid cooling rate is greater than 40°C / s, the rapid cooling outlet temperature is 150-250°C, the galvanizing temperature is 450-470°C, and after galvanizing, the strip is first air-knife cooled to 400-420°C, and then air-cooled, and the temperature of the cooling tower top roller is controlled at 250-300°C.

[0057] Furthermore, the zinc plating solution contains 0.16% to 0.25% Al by weight, and the rest is Zn and unavoidable impurities, and the weight of the zinc layer per unit area is 60 to 200 g / cm 2 The zinc-aluminum-magnesium plating solution contains 2.0% to 10.0% Al, 1.0% to 5.0% Mg, 0.001% to 0.1% Si, and the rest is Zn and unavoidable impurities. The weight of the zinc-aluminum-magnesium coating per unit area is 50 to 200 g / cm 2 .

[0058] Furthermore, the quenching and partitioning process is quenching and partitioning alloying hot-dip galvanizing, the strip speed is controlled at 60-180 m / min, the annealing temperature is 770-870°C, the annealing time is between 30 and 300 s, the dew point is controlled at -20--10°C, the slow cooling outlet temperature is 680-750°C, the rapid cooling rate is greater than 40°C / s, the rapid cooling outlet temperature is between 150 and 250°C, the galvanizing temperature is 450-470°C, and after galvanizing, the strip is first air-knife cooled to 400-420°C, and then alloying treatment is carried out, the alloying temperature is 470-530°C, and the alloying holding time is 5-60s.

[0059] Furthermore, the hot-rolled microstructure of the product during hot rolling is composed of 30% to 60% ferrite, 20% to 50% pearlite, 5% to 20% bainite, and 1% to 5% cementite by volume percentage; the total is 100%.

[0060] The composition of the steel of the embodiment of the present invention is shown in Table 1. The main process parameters of smelting, continuous casting and rolling and the hot rolling structure of the steel of the embodiment of the present invention are shown in Table 2. The main process parameters of continuous annealing of the steel of the embodiment of the present invention are shown in Table 3. The main process parameters of continuous hot-dip galvanizing of the steel of the embodiment of the present invention are shown in Table 4. The main process parameters of continuous hot-dip galvanizing of aluminum-magnesium of the steel of the embodiment of the present invention are shown in Table 5. The main process parameters of alloying hot-dip galvanizing of the steel of the embodiment of the present invention are shown in Table 6. The properties of the steel of the embodiment of the present invention are shown in Table 7. The microstructure composition of the steel of the embodiment of the present invention is shown in Table 8.

[0061] Figure 1 is a typical microstructure of Examples 1-1, 1-2, 1-3 and 1-4, Figure 2 This is the engineering stress-strain curve of Example 1.

[0062] Table 1 Chemical composition of example steel (wt%)

[0063] Example C Mn Si Al Ni Cu P S N Mg Nb Ti Al / Si Ni+Cu 1 0.17 1.94 0.86 4.83 0.55 0.21 0.002 0.006 0.002 0.012 0.062 0.086 5.62 0.76 2 0.22 2.16 0.57 3.96 0.37 0.45 0.005 0.002 0.003 0.023 0.031 0.12 6.95 0.82 3 0.19 2.47 1.12 5.85 0.41 0.33 0.003 0.003 0.001 0.041 0.097 0.21 5.22 0.74 4 0.18 1.95 0.86 5.52 0.44 0.12 0.003 0.004 0.001 0.121 0.16 0.042 6.42 0.56 5 0.23 2.31 0.64 4.49 0.53 0.64 0.002 0.001 0.004 0.304 0.42 0.18 7.02 1.17 6 0.21 2.24 1.08 5.88 0.61 0.20 0.002 0.005 0.003 0.173 0.37 0.39 5.44 0.81

[0064] Table 2 Smelting and continuous casting and rolling process parameters and hot rolling structure of example steel

[0065]

[0066] Table 3 Continuous annealing process of example steel

[0067]

[0068] Table 4 Main process parameters of continuous hot-dip galvanizing of steel in the embodiment of the present invention

[0069]

[0070] Table 5 Main process parameters of continuous hot-dip galvanizing aluminum-magnesium steel in the embodiment of the present invention

[0071]

[0072] Table 6 Main process parameters of hot-dip galvanizing of steel in the embodiment of the present invention

[0073]

[0074] Table 7 Properties of steel according to the present invention

[0075]

[0076]

[0077] Note: The hydrogen embrittlement resistance (delayed fracture resistance) performance is evaluated by U-bending immersion evaluation. The radius of 180° cold bending is 5mm. Five parallel specimens in each group are immersed in 0.5mol / L HCl solution for 14 days. If no fracture occurs, it is judged that the specimen has no delayed fracture risk and is marked with Ο; if fracture occurs, it is judged that the specimen has delayed fracture risk and is marked with ×.

[0078] Table 8 Microstructure of steel according to the present invention

[0079]

[0080]

[0081] It can be seen from the above embodiments that by adopting the composition design of the present invention, large proportion of scrap steel + electric furnace smelting, continuous casting and rolling, quenching and partitioning continuous annealing or continuous hot-dip galvanizing / galvanized aluminum-magnesium or alloyed hot-dip galvanizing process, a 1.0GPa grade hydrogen embrittlement resistant cold-formed automobile steel with a yield strength of ≥650MPa, a tensile strength of 980-1100MPa, an A80 elongation after fracture of ≥20.0%, a hole expansion rate of ≥40%, and a density of 6.5-7.5g / cm 3 ; The pre-stress was set by 180° U-shaped bending and immersed in 0.5mol / LHCl solution for 14 days, but no delayed fracture occurred; it meets the requirements of automobiles for delayed fracture resistance, high strength and high plasticity, and excellent forming performance.

[0082] In order to describe the present invention, the present invention is appropriately and fully illustrated by the examples in the above. The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made should be included in the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A 1.0GPa grade hydrogen embrittlement resistant cold-formed automobile steel, characterized in that: By weight percentage, it includes the following components: C: 0.15%-0.25%, Mn: 1.8%-2.8%, Si: 0.5%-2.0%, Al: 3.96%-6.0%, Ni: 0.05-0.80%, Cu: 0.05-0.80%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.173%-0.50%, Nb: 0.16%-0.50 %, Ti: 0.18%~0.50%, and the balance is Fe and inevitable impurities; the microstructure of the automobile steel is, by volume percentage, 20%~50% ferrite, 40%~70% martensite, 5%~20% residual austenite, the total of which is 100%; the retained austenite is in blocky form, with a grain size between 0.05μm and 0.50μm, and the blocky residual austenite is mainly distributed at the martensite / ferrite interface and inside the ferrite.

2. The 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to claim 1, characterized in that: The composition is 5.22≤Al / Si≤7.02, 0.3≤Ni+Cu≤1.

3.

3. The 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to claim 1, characterized in that: The automobile steel has a yield strength of ≥650MPa, a tensile strength of 980-1100MPa, an A80 elongation after fracture of ≥20.0%, a hole expansion rate of ≥40%, and a density of 6.5-7.5g / cm 3 ; The steel plate was pre-stressed by 180° U-bending and immersed in 0.5mol / LHCl solution for 14 days without any delayed fracture; the thickness of the steel plate was 0.8mm~2.3mm.

4. A method for manufacturing a 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to any one of claims 1 to 3, comprising smelting, continuous casting and rolling of medium and thin slabs, pickling and cold rolling, quenching and partitioning, and skin-passing, characterized in that: Continuous casting and rolling of medium and thin slabs High aluminum steel special protective slag is used for casting, Li2O content ranges from 0.5% to 10.0%, casting temperature is 1530-1600℃, casting machine pulling speed is 1.0-5.5m / min, continuous casting billet thickness is 60-115mm, starting rolling temperature is 1000-1150℃, final rolling temperature is above 905℃, coiling temperature is 617-700℃, and hot rolled coil thickness is 2.0-4.5mm; Pickling cold rolling Before cold rolling, the hot rolled steel coil is passed through an acid solution to remove the surface iron oxide scale, and the cold rolling reduction rate is 45% to 70%; Quenching distribution The quenching distribution is one of quenching distribution continuous annealing, quenching distribution continuous hot-dip galvanizing or galvanized aluminum-magnesium, and quenching distribution alloying hot-dip galvanizing; Finishing The finishing process adopts elongation closed-loop control, and the finishing elongation is 0.3% to 1.0%.

5. The method for manufacturing a 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to claim 4, characterized in that: The quenching and partitioning process is quenching and partitioning continuous annealing, the belt speed is controlled at 60-180 m / min, the furnace temperature of the soaking section is 760-880°C, the soaking time is 10-600s, the slow cooling outlet temperature is 700-750°C, the rapid cooling rate is greater than 50°C / s, the rapid cooling temperature is between 100-250°C, the partitioning temperature is 250-450°C, and the partitioning time is 60-1000s.

6. The method for manufacturing a 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to claim 4, characterized in that: The quenching and distribution process is quenching and distribution continuous hot-dip galvanizing or galvanized aluminum-magnesium, the belt speed is controlled at 60-180 m / min, the annealing temperature is between 760-880°C, the dew point temperature is controlled between -20 and -10°C, the annealing time is between 30 and 300s, the slow cooling outlet temperature is 680-750°C, the rapid cooling rate is greater than 40°C / s, the rapid cooling outlet temperature is 150-250°C, the galvanizing temperature is 450-470°C, after the galvanizing is completed, the strip is first air-knife cooled to 400-420°C, and then air-cooled, and the temperature of the cooling tower top roller is controlled at 250-300°C.

7. The method for manufacturing a 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to claim 6, characterized in that: In terms of weight percentage, the zinc plating solution contains 0.16% to 0.25% Al, the rest is Zn and unavoidable impurities, and the weight of the zinc layer per unit area is 60 to 200 g / cm 2 The zinc-aluminum-magnesium plating solution contains 2.0% to 10.0% Al, 1.0% to 5.0% Mg, 0.001% to 0.1% Si, and the rest is Zn and unavoidable impurities. The weight of the zinc-aluminum-magnesium coating per unit area is 50 to 200 g / cm 2 .

8. The method for manufacturing a 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to claim 4, characterized in that: The quenching and partitioning process is quenching and partitioning alloying hot-dip galvanizing, the strip speed is controlled at 60-180 m / min, the annealing temperature is 770-870°C, the annealing time is between 30 and 300 s, the dew point is controlled at -20--10°C, the slow cooling outlet temperature is 680-750°C, the rapid cooling rate is greater than 40°C / s, the rapid cooling outlet temperature is between 150 and 250°C, the galvanizing temperature is 450-470°C, after the galvanizing is completed, the strip is first air-knife cooled to 400-420°C, and then alloying treatment is performed, the alloying temperature is 470-530°C, and the alloying holding time is 5-60s.

9. The method for manufacturing a 1.0 GPa grade hydrogen embrittlement resistant cold-formed automobile steel according to claim 4, characterized in that: The hot-rolled coil hot-rolled microstructure is composed of 30% to 60% ferrite, 20% to 50% pearlite, 5% to 20% bainite and 1% to 5% cementite in volume percentage, the total of which is 100%.

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