A hydrogen embrittlement resistant cold-rolled DH980 steel plate and its production method

Abstract

The present invention provides a hydrogen embrittlement resistant cold-rolled DH980 steel plate and a production method thereof. The components of the steel plate are as follows by weight percentage: C: 0.10% to 0.20%, Mn: 1.0% to 2.0%, Si: 0.1% to 1.0%, Al: 0.6% to 6.0%, Cr: 0.02% to 0.80%, Cu: 0.05% to 0.80%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.005% to 0.50%, N b: 0.01%~0.50%, Ti: 0.01%~0.50%, and 5≤Al / Si≤20; the rest are iron and unavoidable impurities; the production method includes electric furnace smelting, continuous casting and rolling of medium and thin slabs, pickling and cold rolling, continuous annealing or hot-dip coating process, and skin finishing; the present invention realizes the low-carbon, green and lightweight design and development of automotive high-strength steel with a short-process low-cost process path and an alloy design with multiple uses of one steel for extreme cost reduction, while taking into account the personalized needs of ultra-high-strength steel for hydrogen embrittlement resistance, high plasticity and high formability.

Description

Technical Field

[0001] The invention belongs to the field of metal materials, and in particular relates to a hydrogen embrittlement resistant cold-rolled DH980 steel plate and a production method thereof. Background Art

[0002] In recent years, as the automotive industry has increasingly higher requirements for material forming performance indicators, traditional dual-phase steel has been unable to meet the high drawability requirements of complex stamping parts, and TRIP steel has limited its widespread use due to the high production cost caused by the high alloy content. DH steel, which came into being, introduced a certain amount of residual austenite into traditional dual-phase steel, and the material exhibited excellent forming performance through the TRIP effect, which can significantly overcome the shortcomings of DP steel and TRIP steel in the above-mentioned application process. DH steel has become one of the current research hotspots in the field of automotive steel development. However, there is a serious hydrogen embrittlement (hydrogen-induced delayed fracture) phenomenon in the service process of ultra-high-strength steel parts, and the hydrogen-induced delayed fracture sensitivity of ultra-high-strength steel will increase significantly with the increase of strength level. Since this phenomenon seriously affects the normal service of parts, the delayed fracture phenomenon of 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 the enhanced formability dual-phase 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 automotive DH steel products, that is, one steel multi-purpose alloy design and short process low-cost preparation process, can not only meet the characteristics of multiple parts, diversified user needs, multiple specifications and small batch orders in the automotive industry, 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 formability and hydrogen embrittlement problems of short-process low-cost automotive high-strength 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] The relevant patents are as follows:

[0004] 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. The product of the invention has excellent fatigue resistance and hole expansion performance, but does not consider the hydrogen embrittlement problem of ultra-high strength steel, and the preparation process fails to consider the electric furnace + scrap steel smelting process.

[0005] Patent document CN113403551A discloses a high yield ratio hydrogen embrittlement resistant cold-rolled DH980 steel plate and a preparation method thereof, wherein the main chemical components are: 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%, and the remainder is Fe and other inevitable impurities. This invention adopts the cold rolling-continuous annealing production process to produce cold-rolled DH steel with a strength level of 1.0GPa. The product exhibits a high yield strength ratio and resistance to hydrogen embrittlement. However, the ductility of the product is relatively poor, making it difficult to meet the requirements of both high plasticity and resistance to hydrogen embrittlement. In addition, the preparation process fails to consider the electric furnace + scrap steel smelting process. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned problems and shortcomings and to provide a hydrogen embrittlement-resistant cold-rolled DH980 steel plate and its production method, which realizes the low-carbon, green and lightweight design and development of automotive high-strength steel with a short-process low-cost process path and an alloy design with one steel for multiple uses to achieve extreme cost reduction, while taking into account the personalized needs of ultra-high-strength steel for hydrogen embrittlement resistance, high plasticity and high formability.

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

[0008] A hydrogen embrittlement resistant cold-rolled DH980 steel plate, the components of which are as follows by weight percentage: C: 0.10%-0.20%, Mn: 1.0%-2.0%, Si: 0.1%-1.0%, Al: 0.6%-6.0%, Cr: 0.02%-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 5≤Al / Si≤20; the rest is iron and unavoidable impurities.

[0009] In the steel plate, 0.2%≤Cr+Cu≤1.2%.

[0010] The microstructure of the steel plate is ferrite, martensite, retained austenite and bainite; wherein the microstructure of each phase is as follows by volume percentage: ferrite 20% to 45%, martensite 40% to 70%, retained austenite 3% to 12%, bainite 3% to 15%, the retained austenite is in two forms, block and film, with a grain size of 0.05 μm to 0.50 μm, the block retained austenite is mainly distributed at the martensite / ferrite interface and inside the ferrite, and the film retained austenite is mainly distributed between the martensite laths.

[0011] The steel plate has a yield strength of ≥550 MPa, a tensile strength of 980-1100 MPa, an A80 elongation after fracture of ≥17.0%, a hole expansion rate of ≥30%, and a density of 6.5-7.5 g / cm 3 ; The steel sheets were pre-stressed by 180° U-bending and immersed in 0.5mol / L HCl solution for 14 days without delayed fracture.

[0012] The reasons for the composition 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 0.10% to 0.20%.

[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 1.0% to 2.0%.

[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 have a strengthening effect; 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 Si element content is controlled to 0.1% to 1.0%, and 5≤Al / Si≤20.

[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 also 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%, and 5≤Al / Si≤20.

[0017] Cr: Chromium can increase the hardenability of steel to ensure the strength of steel, and can stabilize the residual austenite. A reasonable combination with Cu helps to improve the crack resistance and high strength of the product, which is conducive to the design of one steel for multiple uses. Too low Cr content will affect the hardenability of steel, and too high content will increase production costs. Therefore, in the present invention, the content of Cr is controlled within the range of 0.02% to 0.80%, preferably 0.2≤Cr+Cu≤1.2;.

[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; reasonable combination with Cr helps to improve the strength and toughness of the product, which is conducive to the design of one steel for multiple uses. However, considering the high cost of copper, the present invention controls the content of Cu in the range of 0.05% to 0.80%, preferably 0.2%≤Cr+Cu≤1.2%;.

[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 DH 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 hydrogen embrittlement resistant cold-rolled DH980 steel plate, including electric furnace smelting, medium and thin slab continuous casting and rolling, pickling cold rolling, continuous annealing or hot-dip coating process, and skin-passing;

[0026] Electric furnace smelting: The present invention uses 30% to 80% scrap steel as raw material, and the temperature of molten steel is between 1600 and 1750°C;

[0027] Continuous casting and rolling of medium and thin slabs:

[0028] Use special protective slag for high aluminum steel for casting, and select Li 2 The mass percentage of O is 0.5% to 10.0%; the casting temperature is 1530 to 1600°C, the casting speed is 1.0 to 5.5 m / min, and the thickness of the continuous casting billet is between 60 and 115 mm.

[0029] The starting rolling temperature is between 1000 and 1150°C, the final rolling temperature is above 900°C, and the coiling temperature is between 600 and 700°C. The thickness of the hot-rolled coil is 2.0 to 4.5 mm; the microstructure of the hot-rolled steel plate is ferrite, pearlite, bainite, and cementite; by volume percentage, ferrite 30% to 60%, pearlite 20% to 50%, bainite 5% to 20%, and cementite / impurities 1% to 5%.

[0030] 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.

[0031] After cold rolling, the steel plate can be continuously annealed: the belt speed is controlled at 60-200m / min, the annealing temperature is 760-880℃, the soaking time is 10-600s, the slow cooling outlet temperature is 700-760℃, the rapid cooling rate is greater than 25℃ / s, the rapid cooling temperature is between 300-450℃, the aging temperature is 280-440℃, and the aging time is 60-1000s. The annealing temperature is 760-880℃. If the annealing temperature is too high, the ductility of the steel will be reduced due to the complete austenitization and insufficient ferrite ratio; if the annealing temperature is too low, the soft phase ferrite ratio of the final material is too high, which will greatly reduce the strength of the material. The annealing time is 10-600s. If the annealing time is too long, the steel plate will have coarse grains. If the annealing 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.

[0032] After cold rolling, the steel sheet can be subjected to a hot-dip process, wherein the hot-dip process is continuous hot-dip galvanizing or continuous hot-dip galvanizing aluminum-magnesium or alloy hot-dip galvanizing;

[0033] The specific process of continuous hot-dip galvanizing or continuous hot-dip galvanized aluminum-magnesium is as follows: 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 680-760℃, rapid cooling rate is greater than 20℃ / s, and rapid cooling outlet temperature is 450-470℃;

[0034] The plating solution temperature is 450-470°C. After galvanizing, the strip is first air-knife cooled to 400-420°C, and then air-cooled. The temperature of the cooling tower top roller is controlled at 250-300°C.

[0035] In the process of continuous hot-dip galvanizing, the composition of the plating solution is 0.16% to 0.25% Al by mass, and the rest is Zn and unavoidable impurities; the weight of the zinc layer of the steel plate after continuous hot-dip galvanizing is 60 to 200 g / cm 2 .

[0036] In the process of continuous hot-dip galvanizing, the composition of the plating solution is calculated by mass percentage: Al: 2.0% ~ 10.0%, Mg: 1.0% ~ 5.0%, Si: 0.001% ~ 0.1%, and the rest is Zn and unavoidable impurities; the weight of the zinc-aluminum-magnesium coating on the steel plate after continuous hot-dip galvanizing is 50 ~ 200g / cm 2 .

[0037] The specific process of alloyed hot-dip galvanizing is as follows: the strip speed is controlled at 60-180m / min, the annealing temperature is 770-870℃, the annealing time is between 30-300s, the dew point is controlled at -20--10℃, the slow cooling outlet temperature is 680-760℃, the rapid cooling rate is greater than 20℃ / s, the rapid cooling outlet temperature is between 450-470℃, the galvanizing temperature is 450-470℃, after galvanizing, the strip is first air-knife cooled to 400-420℃, and then alloyed. The alloying temperature is 470-530℃, and the alloying holding time is 5-60s.

[0038] Finishing: The elongation closed-loop control is adopted, and the finishing elongation is 0.3% to 1.0%.

[0039] The microstructure of the steel plate is 20% to 45% ferrite, 40% to 70% martensite, 3% to 12% residual austenite, and 3% to 15% bainite; and the residual austenite in the product of the present invention is in two forms, block and film, with a grain size between 0.05 μm and 0.50 μm, the block residual austenite is mainly distributed at the martensite / ferrite interface and inside the ferrite, and the film residual austenite is mainly distributed between the martensite laths.

[0040] The beneficial effects of the present invention are:

[0041] (1) The chemical composition of the steel material of the present invention mainly includes C, Mn, Al and Si as main elements, and the initial cost is relatively low.

[0042] (2) The present invention adopts a new short-process, low-cost production process of "large proportion of scrap steel + electric furnace smelting + medium-thin slab continuous casting and rolling", which can significantly reduce carbon emissions and save energy consumption;

[0043] (3) The hydrogen embrittlement resistant cold-rolled DH980 steel plate produced by the present invention has a certain proportion of retained austenite added to the conventional cold-rolled dual-phase steel, and has the characteristics of high strength, high plasticity and formability under the effect of transformation induced plasticity (TRIP);

[0044] (4) The hydrogen embrittlement resistant cold-rolled DH980 steel plate produced by the present invention can add a large amount of aluminum elements to achieve low density of high-strength steel, meeting the requirements of lightweight design of automobiles;

[0045] (5) The hydrogen embrittlement resistant cold-rolled DH980 steel plate produced by the present invention can realize a set of alloy systems to meet the diversified product requirements such as continuous annealing, continuous hot-dip galvanizing / galvanized aluminum-magnesium and alloyed hot-dip galvanizing 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 cost, but also realize the conversion between multiple grades of products and significantly improve product production efficiency;

[0046] (6) The hydrogen embrittlement resistant cold-rolled DH980 steel plate produced by the present invention can achieve a yield strength ≥550MPa, a tensile strength of 980-1100MPa, an A80 elongation after fracture ≥17.0%, a hole expansion rate ≥30%, and a density of 6.5-7.5g / cm3; it adopts 180° U-shaped bending to pre-stress and is immersed in 0.5mol / LHCl solution for 14 days without delayed fracture, showing excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the metallographic microstructure diagram of Example 1-1 of the present invention.

[0048] Figure 2 This is a metallographic microstructure diagram of Example 1-2 of the present invention.

[0049] Figure 3 This is the stress-strain curve of Example 1 of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be further described below by way of examples.

[0051] According to the component ratio of the technical solution, the embodiment of the present invention carries out electric furnace smelting, continuous casting and rolling of medium and thin slabs, pickling and cold rolling, continuous annealing or hot-dip coating, and skin finishing.

[0052] Electric furnace smelting: The present invention uses 30% to 80% scrap steel as raw material, and the temperature of molten steel is between 1600 and 1750°C;

[0053] Continuous casting and rolling of medium and thin slabs:

[0054] The casting temperature is between 1530 and 1600°C, the casting machine pulling speed is between 1.0 and 5.5 m / min, and the continuous casting billet thickness is between 60 and 115 mm.

[0055] The starting rolling temperature is between 1000 and 1150°C, the final rolling temperature is above 900°C, and the coiling temperature is between 600 and 700°C. The thickness of the hot rolled coil is 2.0 to 4.5 mm.

[0056] 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, and the thickness of the finished product after cold rolling is 0.8mm to 2.3mm;

[0057] After cold rolling, the steel sheet can be subjected to continuous annealing or continuous hot-dip process or alloy hot-dip galvanizing, wherein the continuous hot-dip process is continuous hot-dip galvanizing or continuous hot-dip galvanizing aluminum-magnesium.

[0058] Finishing: The elongation closed-loop control is adopted, and the finishing elongation is 0.3% to 1.0%.

[0059] Further; the continuous annealing process: the belt speed is controlled at 60-200m / min, the annealing temperature is 760-880℃, the annealing time is 10-600s, the slow cooling outlet temperature is 700-760℃, the rapid cooling rate is greater than 25℃ / s, the rapid cooling temperature is between 300-450℃, the aging temperature is 280-440℃, and the aging time is 60-1000s.

[0060] Further; continuous hot-dip galvanizing or continuous hot-dip galvanized aluminum-magnesium process: belt speed is controlled at 60-180m / min, annealing temperature is 760-880℃, dew point temperature is -20--10℃, annealing time is 30-300s, slow cooling outlet temperature is 680-760℃, rapid cooling rate is greater than 20℃ / s, and rapid cooling outlet temperature is 450-470℃;

[0061] The plating solution temperature is 450-470°C. After hot-dip coating, the strip is first air-knife cooled to 400-420°C, and then air-cooled. The temperature of the cooling tower top roller is controlled at 250-300°C.

[0062] Further, in the continuous hot-dip galvanizing process, the composition of the plating solution is Al: 0.16% to 0.25% by mass, and the rest is Zn and unavoidable impurities; the weight of the zinc layer of the steel plate after continuous hot-dip galvanizing is 60 to 200 g / cm 2 .

[0063] Furthermore, in the process of continuous hot-dip galvanizing, the composition of the plating solution is calculated by mass percentage: Al: 2.0% to 10.0%, Mg: 1.0% to 5.0%, Si: 0.001% to 0.1%, and the rest is Zn and unavoidable impurities; the weight of the zinc-aluminum-magnesium coating on the steel plate after continuous hot-dip galvanizing is 50 to 200 g / cm 2 .

[0064] Further; the specific process of alloyed hot-dip galvanizing is: the strip speed is controlled at 60-180m / min, the annealing temperature is 770-870℃, the annealing time is 30-300s, the dew point is controlled at -20--10℃, the slow cooling outlet temperature is 680-760℃, the rapid cooling rate is greater than 20℃ / s, the rapid cooling outlet temperature is 450-470℃, the galvanizing temperature is 450-470℃, after the galvanizing is completed, 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.

[0065] Further; the microstructure of the hot-rolled steel plate is ferrite, pearlite, bainite, and cementite; the volume percentages are as follows: ferrite 30% to 60%, pearlite 20% to 50%, bainite 5% to 20%, and cementite / impurities 1% to 5%.

[0066] 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 of the steel of the embodiment of the present invention is shown in Table 8.

[0067] Table 1 Composition of steel according to the present invention (wt%)

[0068] Example C Mn Si Al Cr Cu P S N Mg Nb Ti Al / Si Cr+Cu 1 0.17 1.87 0.25 4.51 0.32 0.27 0.002 0.004 0.001 0.038 0.074 0.048 18.04 0.59 2 0.19 1.24 0.31 3.28 0.26 0.68 0.004 0.002 0.003 0.085 0.092 0.182 10.58 0.94 3 0.13 1.53 0.54 3.72 0.48 0.35 0.003 0.005 0.002 0.167 0.174 0.253 6.89 0.83 4 0.16 1.74 0.73 5.73 0.17 0.15 0.006 0.003 0.005 0.065 0.367 0.059 7.85 0.32 5 0.12 1.42 0.16 1.86 0.56 0.23 0.003 0.002 0.004 0.261 0.225 0.079 11.63 0.79 6 0.14 1.65 0.49 2.67 0.55 0.54 0.001 0.001 0.002 0.192 0.053 0.327 5.45 1.09

[0069] Table 2 Main process parameters and hot rolling structure of steel smelting, continuous casting and rolling according to the embodiment of the present invention

[0070]

[0071] Table 3 Main process parameters of continuous annealing of steel in the embodiment of the present invention

[0072]

[0073] Table 4 Main process parameters of continuous hot-dip galvanizing of steel in the embodiment of the present invention

[0074]

[0075] Table 5 Main process parameters of continuous hot-dip galvanizing aluminum-magnesium steel in the embodiment of the present invention

[0076]

[0077]

[0078] Table 6 Main process parameters of hot-dip galvanizing of steel in the embodiment of the present invention

[0079]

[0080] Table 7 Properties of steel according to the present invention

[0081]

[0082]

[0083] 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 ×.

[0084] Table 8 Microstructure of steel according to the present invention

[0085]

[0086]

[0087] It can be seen from the above embodiments that the composition design, large proportion of scrap steel + electric furnace smelting, continuous casting and rolling, continuous annealing or continuous hot-dip galvanizing / galvanized aluminum-magnesium or alloyed hot-dip galvanizing process of the present invention are adopted to prepare a hydrogen embrittlement resistant cold-rolled DH980 steel plate with a yield strength of ≥550MPa, a tensile strength of 980-1100MPa, an A80 elongation after fracture of ≥17.0%, and a hole expansion rate of ≥30%; 180° U-shaped bending forming pre-stress is adopted, and it is immersed in a 0.5mol / L HCl solution for 14 days, and no delayed fracture occurs; the requirements of delayed fracture resistance, high strength and high plasticity and excellent forming performance of automobiles are met.

[0088] 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 hydrogen embrittlement resistant cold-rolled DH980 steel plate, characterized in that: The composition of the steel plate is as follows by weight percentage: C: 0.10% to 0.20%, Mn: 1.0% to 2.0%, Si: 0.1% to 1.0%, Al: 1.86% to 6.0%, Cr: 0.02% to 0.80%, Cu: 0.05% to 0.80%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.038% to 0.50%, Nb: 0.053% to 0.50%, Ti: 0.059% to 0.50%, and 5≤Al / Si≤20; the rest is iron and unavoidable impurities; 0.2%≤Cr+Cu≤1.2% in the steel plate; The microstructure of the steel plate is ferrite, martensite, retained austenite and bainite; the microstructure of each phase is as follows by volume percentage: ferrite 20%~45%, martensite 40%~70%, retained austenite 3%~12%, bainite 3%~15%, the retained austenite is in two forms, block and film, with a grain size of 0.05μm~0.50μm, the block retained austenite is distributed at the martensite / ferrite interface and inside the ferrite, and the film retained austenite is distributed between the martensite laths.

2. The hydrogen embrittlement resistant cold-rolled DH980 steel plate according to claim 1, characterized in that: The steel plate has a yield strength of ≥550MPa, a tensile strength of 980-1100MPa, an A80 elongation after fracture of ≥17.0%, a hole expansion rate of ≥30%, and a steel plate density of 6.5-7.5 g / cm 3 .

3. A method for producing a hydrogen embrittlement resistant cold-rolled DH980 steel plate according to claim 1 or 2, characterized in that: Including electric furnace smelting, medium and thin slab continuous casting and rolling, pickling and cold rolling, continuous annealing or hot-dip process or alloy hot-dip galvanizing, skin pass; Electric furnace smelting: 30%~80% scrap steel is used as raw material, and the molten steel temperature is 1600~1750℃; Continuous casting and rolling of medium and thin slabs: The casting temperature is 1530~1600℃, the casting speed is 1.0~5.5m / min, and the continuous casting billet thickness is 60~115mm; The starting rolling temperature is 1000~1150℃, the final rolling temperature is above 900℃, and the coiling temperature is 600~700℃; the hot rolled coil thickness is 2.0~4.5mm; Pickling cold rolling: The cold rolling reduction rate is 45%~70%, and the thickness of the finished product after cold rolling is 0.8mm~2.3mm; After cold rolling, the steel sheet is subjected to continuous annealing or continuous hot-dip process or alloy hot-dip galvanizing, wherein the continuous hot-dip process is continuous hot-dip galvanizing or continuous hot-dip galvanizing aluminum-magnesium; Finishing: The elongation closed-loop control is adopted, and the finishing elongation is 0.3%~1.0%.

4. The method for producing a hydrogen embrittlement resistant cold-rolled DH980 steel plate according to claim 3, characterized in that: The continuous annealing process comprises: a belt speed controlled at 60-200 m / min, an annealing temperature at 760-880° C., an annealing time at 10-600 s, a slow cooling outlet temperature at 700-760° C., a rapid cooling rate greater than 25° C. / s, a rapid cooling temperature at 300-450° C., an aging temperature at 280-440° C., and an aging time at 60-1000 s.

5. The method for producing a hydrogen embrittlement resistant cold-rolled DH980 steel plate according to claim 3, characterized in that: Continuous hot-dip galvanizing or continuous hot-dip galvanized aluminum-magnesium process: belt speed is controlled at 60~180m / min, annealing temperature is 760~880℃, dew point temperature is -20~-10℃, annealing time is 30~300s, slow cooling outlet temperature is 680~760℃, rapid cooling rate is greater than 20℃ / s, and rapid cooling outlet temperature is 450~470℃; The plating solution temperature is 450~470℃. After hot-dip coating, the strip is first air-knife cooled to 400~420℃, and then air-cooled. The temperature of the cooling tower top roller is controlled at 250~300℃.

6. The method for producing a hydrogen embrittlement resistant cold-rolled DH980 steel plate according to claim 5, characterized in that: In the process of continuous hot-dip galvanizing, the composition of the plating solution is Al: 0.16%~0.25% by mass, and the rest is Zn and unavoidable impurities; the weight of the zinc layer of the steel plate after continuous hot-dip galvanizing is 60~200g / cm 2 .

7. The method for producing a hydrogen embrittlement resistant cold-rolled DH980 steel plate according to claim 5, characterized in that: In the process of continuous hot-dip galvanizing, the composition of the plating solution is calculated by mass percentage: Al: 2.0%~10.0%, Mg: 1.0%~5.0%, Si: 0.001%~0.1%, and the rest is Zn and unavoidable impurities; the weight of the zinc-aluminum-magnesium coating on the steel plate after continuous hot-dip galvanizing is 50~200g / cm 2 .

8. The method for producing a hydrogen embrittlement resistant cold-rolled DH980 steel plate according to claim 3, characterized in that: The specific process of alloyed hot-dip galvanizing is: belt speed is controlled at 60~180m / min, annealing temperature is 770~870℃, annealing time is 30~300s, dew point is controlled at -20~-10℃, slow cooling outlet temperature is 680~760℃, rapid cooling rate is greater than 20℃ / s, rapid cooling outlet temperature is 450~470℃, 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.

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