A 1.0 GPa-level hydrogen embrittlement-resistant cold-rolled CH steel and its preparation method

Abstract

The present invention provides a 1.0 GPa - level hydrogen embrittlement - resistant cold - rolled CH steel and a preparation method thereof. The composition of the steel plate is 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%, Mo: 0.02 - 0.80%, Ni: 0.05 - 0.80%, P≤0.01%, S≤0.01%, N≤0.005%, Mg: 0.005% - 0.50%, Nb: 0.01% - 0.50%, V: 0.01% - 0.50%, and 5≤Al / Si≤20; the balance is Fe and unavoidable impurities; the preparation method includes electric furnace smelting, medium - thin slab continuous casting and rolling, pickling and cold rolling, continuous annealing or continuous hot - dip plating process or alloying hot - dip galvanizing. With a short - process and low - cost process route and an alloy design for extreme cost reduction, it realizes the low - carbon, green and lightweight design and development of automotive high - strength steel, while taking into account the personalized requirements of ultra - high - strength steel for hydrogen embrittlement resistance, high plasticity and high formability. The produced steel plate has a yield strength ≥780 MPa, a tensile strength of 980 - 1100 MPa, an elongation after fracture of A80≥15.0%, and an expansion rate≥60%.

Description

Technical Field

[0001] The invention belongs to the field of metal materials, and in particular relates to a 1.0 GPa-level hydrogen embrittlement-resistant cold-rolled CH steel and a preparation method thereof. Background Art

[0002] In recent years, as the automotive industry has increasingly higher requirements for material forming performance indicators, traditional complex phase steels have been unable to meet the requirements of complex stamping parts for high ductility, and TRIP steel has been limited in its widespread use due to the high production cost caused by the high alloy content. CH steel, which came into being, introduced a certain amount of residual austenite into traditional complex dual-phase steel, and the material exhibited excellent forming performance through the TRIP effect, which can significantly overcome the shortcomings of CP steel and TRIP steel in the above-mentioned application process. CH 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.

[0003] The development of green and low-carbon CH steel products for automobiles, that is, a one-steel multi-purpose alloy design and a short-process low-cost preparation process, can not only meet the special needs of the automotive industry for 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 problems of poor formability and hydrogen embrittlement of automotive high-strength steel.

[0004] The relevant patent documents are as follows:

[0005] 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.

[0006] Patent document CN113403551A discloses a cold-rolled DH980 steel plate with high yield ratio and hydrogen embrittlement resistance and its preparation method. Its main chemical components are as follows: C: 0.16% - 0.23%, Mn: 1.8% - 2.5%, Si: 0.4% - 1.2%, Al: 0.30% - 0.90%, Cr: 0.10 - 0.50%, Mo: 0.10 - 0.60%, P ≤ 0.01%, S ≤ 0.01%, N ≤ 0.005%, Nb: 0.01% - 0.10%, Ti: 0.01% - 0.10%, and the balance is Fe and other inevitable impurities. This invention adopts a cold rolling - continuous annealing production process to produce a cold-rolled DH steel with a strength level of 1.0 GPa. This product exhibits a high yield ratio and hydrogen embrittlement resistance. However, the ductility of this product is relatively poor, making it difficult to balance high plasticity and hydrogen embrittlement resistance, and the preparation process does not consider the electric furnace + scrap steel smelting process. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above problems and deficiencies, and provide a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel and its preparation method that realizes the low-carbon, green, and lightweight design and development of automotive high-strength steel through a short-process and low-cost process route and an alloy design with extreme cost reduction, while taking into account the personalized requirements of ultra-high-strength steel for hydrogen embrittlement resistance, high plasticity, and high formability.

[0008] The purpose of the present invention is achieved as follows:

[0009] A 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel plate, the components of the steel plate 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%, Mo: 0.02 - 0.80%, Ni: 0.05 - 0.80%, P ≤ 0.01%, S ≤ 0.01%, N ≤ 0.005%, Mg: 0.005% - 0.50%, Nb: 0.01% - 0.50%, V: 0.01% - 0.50%, and 5 ≤ Al / Si ≤ 20; the balance is Fe and inevitable impurities.

[0010] The microstructure of the steel plate includes ferrite, bainite, retained austenite, and martensite; by volume percentage, they are as follows: ferrite 20% - 45%, bainite 30% - 60%, retained austenite 3% - 12%, martensite 3% - 15%; the retained austenite is in a film-like form, with a grain size between 0.05 μm and 0.20 μm, and the film-like retained austenite is mainly distributed between bainite and martensite laths.

[0011] The yield strength of the CH steel plate is ≥780 MPa, the tensile strength is 980 - 1100 MPa, the elongation after fracture of A80 is ≥15.0%, the hole expansion rate is ≥60%, and the density is 6.5 - 7.5 g / cm3. The pre-stress is formed by 180° U-shaped bending and immersed in 0.5 mol / L HCl solution for 14 days, and no delayed fracture occurs. It meets the requirements of anti-hydrogen embrittlement, high strength and high plasticity, and excellent formability of ultra-high strength automotive steel.

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

[0013] C: The carbon element ensures the strength requirements of the steel through solid solution strengthening. A sufficient amount of carbon element helps to stabilize austenite, thereby improving the formability of the steel. 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 be 0.10% - 0.20%.

[0014] Mn: Manganese element is an austenite stabilizing element in steel, which can expand the austenite phase region, reduce the critical quenching speed of the steel. At the same time, it can also refine the grains and contribute to solid solution strengthening to improve the strength. If the content of Mn element is too low, the supercooled austenite is not stable enough, reducing the processing properties such as plasticity and toughness of the steel plate; if the content of Mn element is too high, it will lead to poor welding performance of the steel plate and an increase in production cost, which is not conducive to industrial production. Therefore, in the present invention, the content of Mn element is controlled to be 1.0% - 2.0%.

[0015] Si: Silicon element has a certain solid solution strengthening effect in ferrite to ensure that the steel has sufficient strength. At the same time, Si can also inhibit the decomposition of retained austenite and the precipitation of carbides, reducing inclusions in the steel. In the present invention, Si element and Al element are used in combination, and the design concept of replacing Si with Al can significantly improve the surface quality of the steel. If the content of Si element is too low, it cannot play a strengthening role; if the content of Si element is too high, it will reduce the surface quality and welding performance of the steel plate. Therefore, in the present invention, the content of Si element is controlled to be 0.1% - 1.0%.

[0016] Al: The density of aluminum element is much lower than that of iron element. Adding an appropriate amount of aluminum element to steel can significantly reduce the density of steel, which is helpful for the lightweight development of steel. At the same time, aluminum element has an antioxidant effect. Adding it in combination with silicon element can effectively improve the surface quality of steel, which is conducive to the design of multi-functional steel products. In addition, aluminum element can also inhibit the decomposition of retained austenite and the precipitation of carbides, and accelerate the bainite transformation to improve the coordinated deformation ability. In addition, aluminum element can inhibit the decomposition of retained austenite and the precipitation of carbides, and accelerate the bainite transformation to improve the coordinated deformation ability. If the content of aluminum element is too high, it will not only increase the production cost, but also cause difficulties in continuous casting production, etc. When the aluminum content is too low, the low-density design of the material cannot be achieved. Therefore, in the present invention, the content range of aluminum element is controlled at 0.6% - 6.0%.

[0017] Cr: Chromium element can increase the hardenability of steel to ensure the strength of steel, and can stabilize retained austenite. If the content of Cr is too low, it will affect the hardenability of steel, and if the content is too high, it will increase the production cost. Therefore, in the present invention, the content range of chromium element is controlled at 0.02% - 0.80%.

[0018] Mo: Molybdenum element is a strengthening element in steel, which is helpful for stabilizing retained austenite. At the same time, it has a significant effect on improving the hardenability of steel. When Mo element is used in combination with Ti, a large number of TiMoC precipitates can be formed, which is beneficial to make the diffusible hydrogen in steel be diffusely distributed and reduce the aggregation of diffusible hydrogen. Therefore, both high strength and hydrogen embrittlement resistance can be taken into account. In the present invention, the content range of Mo element is controlled at 0.02% - 0.80%.

[0019] Ni: Nickel element 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; when reasonably combined with Cr, it can effectively control the phase transformation process of the weld metal and obtain a composite structure of martensite and a certain proportion of retained austenite, so as to take into account high crack resistance and high strength. In the present invention, the content range of Ni element is controlled at 0.05% - 0.80%.

[0020] P: Phosphorus element is a harmful element in steel. It is extremely easy to segregate to the grain boundary and seriously reduce the plasticity and deformation performance of steel. The lower its content, the better. Considering the cost, in the present invention, the content of P element is controlled at P ≤ 0.01%.

[0021] S: Sulfur element is a harmful element in steel. Sulfur is easy to combine with manganese element to form MnS inclusions. After rolling deformation, the transverse performance of the material will be significantly reduced, seriously affecting the formability of steel. The lower its content, the better. Considering the cost, in the present invention, the content of S element is controlled at S ≤ 0.01%.

[0022] 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%.

[0023] 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.

[0024] 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%.

[0025] V: Microalloying element vanadium mainly exists in the form of VC, which improves the strength and fatigue resistance of the material through fine grain strengthening and dispersion strengthening. In the hot-dip galvanizing annealing heating process, undissolved VC particles can pin the ferrite grain boundary, thereby playing a role in refining the grains; when the annealing temperature increases to the two-phase region, the VC dissolution temperature is low, so it is fully dissolved in the matrix, and the solid solution C atoms are enriched in the austenite to improve its stability; during the annealing process, the VC in the ferrite will re-precipitate, thereby producing obvious precipitation strengthening. Therefore, in the present invention, the V element content is controlled at 0.01-0.50%.

[0026] The second technical solution of the present invention is to provide a method for preparing 1.0GPa grade hydrogen embrittlement resistant cold-rolled CH steel, including electric furnace smelting, medium and thin slab continuous casting and rolling, pickling cold rolling, continuous annealing or continuous hot-dip process or alloying hot-dip galvanizing,

[0027] Electric furnace smelting: The present invention uses 30% to 70% scrap steel as raw material, and smelts it in an electric furnace to obtain molten steel that meets the following composition requirements by mass 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%, Mo: 0.02% to 0.80%, Ni: 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%, V: 0.01% to 0.50%, and 5≤Al / Si≤20; the remainder is Fe and unavoidable impurities. The temperature of the molten steel is between 1600 and 1750°C.

[0028] Medium and thin slab continuous casting and rolling: Use a special protective slag for high-aluminum steel, and preferably the mass percentage of Li 2 O in the special protective slag for high-aluminum steel is 0.5% - 10.0%; the casting temperature is 1530 - 1600 °C, the casting machine pulling speed is 1.0 - 5.5 m / min, and the thickness of the continuous casting slab is between 60 and 115 mm. The starting rolling temperature is between 1000 and 1150 °C, the finishing rolling temperature is above 900 °C, and the coiling temperature is between 600 and 700 °C.

[0029] After hot rolling, the thickness specification of the steel plate is 2.0 - 4.5 mm. The microstructure of the hot-rolled steel plate includes ferrite, pearlite, bainite, and a small amount of cementite / impurities; the volume percentages of each microstructure are as follows: ferrite 30% - 60%, pearlite 20% - 50%, bainite 5% - 20%, and cementite / impurities 1% - 5%.

[0030] Pickling and cold rolling: Before cold rolling, the hot-rolled steel coil removes the scale on the surface through acid solution, and the cold rolling reduction rate is 45% - 70%. If the reduction rate is too high, it will lead to too high deformation resistance and it is difficult to roll to the target thickness; if the reduction rate is too low, it will lead to a decrease in the elongation of the cold-rolled steel plate.

[0031] After pickling and cold rolling, the steel plate is subjected to continuous annealing or continuous hot-dip coating process or alloying hot-dip galvanizing. The continuous hot-dip coating process is continuous hot-dip galvanizing or continuous galvanized aluminum-magnesium.

[0032] Among them;

[0033] Continuous annealing: The strip speed is controlled at 60 - 180 m / min, the furnace temperature in the soaking section is 760 - 880 °C, the soaking time is 10 - 600 s, the slow cooling outlet temperature is 700 - 760 °C, the rapid cooling rate is greater than 25 °C / s, the rapid cooling temperature is between 350 and 550 °C, the aging temperature is 350 - 550 °C, and the annealing time is 60 - 1000 s. The annealing temperature is 760 - 880 °C. If the annealing temperature is too high, due to the complete austenitization and insufficient ferrite ratio, the ductility of the steel will be reduced; if the annealing temperature is too low, the high proportion of the soft phase ferrite in the final material will greatly reduce the strength of the material. The annealing time is 60 - 1000 s. If the annealing time is too long, it will cause the grains of the steel plate to be coarse. If the annealing time is too short, the steel plate will not have enough time to complete the annealing and recrystallization process, resulting in a decrease in the elongation of the steel plate.

[0034] The specific processes of continuous hot-dip galvanizing and continuous hot-dip galvanizing-aluminum-magnesium are as follows: the strip speed is controlled at 60 - 180 m / min, the annealing temperature is between 760 - 880 °C, the dew point temperature is controlled between -20 - -10 °C, the annealing time is between 30 - 300 s, the slow cooling outlet temperature is 680 - 760 °C, the rapid cooling rate is greater than 20 °C / s, the fast cooling outlet temperature is 450 - 470 °C, the galvanizing temperature is 450 - 470 °C. After galvanizing, the strip is first cooled by an air knife to 400 - 420 °C, and then air-cooled. The temperature of the top roll of the cooling tower is controlled at 250 - 300 °C.

[0035] During continuous hot-dip galvanizing, the components of the galvanizing bath are calculated by mass percentage as follows: Al: 0.16% - 0.25%, and the rest are Zn and inevitable impurities. The weight of the zinc coating per unit area of the steel plate after continuous hot-dip galvanizing is 60 - 200 g / cm 2 .

[0036] During continuous hot-dip galvanizing-aluminum-magnesium, the components of the galvanizing-aluminum-magnesium bath are calculated by mass percentage as follows: Al: 2.0% - 10.0%, Mg: 1.0% - 5.0%, Si: 0.001% - 0.1%, and the rest are Zn and inevitable impurities. The weight of the zinc-aluminum-magnesium coating per unit area of the steel plate after continuous hot-dip galvanizing-aluminum-magnesium is 50 - 200 g / cm 2 .

[0037] 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 - 300 s, the dew point is controlled between -20 - -10 °C, the slow cooling outlet temperature is 680 - 760 °C, the rapid cooling rate is greater than 20 °C / s, the fast cooling outlet temperature is between 450 - 470 °C, the galvanizing temperature is 450 - 470 °C. After galvanizing, the strip is first cooled by an air knife 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 - 60 s.

[0038] It also includes skin pass: the skin pass process uses rolling force control, and the rolling force is controlled at 1000 - 3500 kN, and the rolling tension is 500 - 2000 kN.

[0039] The microstructure of the steel plate obtained after the above process includes ferrite, bainite, retained austenite and martensite; by volume percentage, they are as follows: ferrite 20% - 45%, bainite 30% - 60%, retained austenite 3% - 12%, martensite 3% - 15%; the retained austenite is in the form of a thin film, the grain size is between 0.05 μm - 0.20 μm, and the thin-film retained austenite is mainly distributed between bainite and martensite laths.

[0040] By the above method, a 1.0GPa hydrogen embrittlement resistant cold-rolled CH steel production method can be obtained, in which the yield strength is ≥780MPa, the tensile strength is 980 - 1100MPa, the elongation after fracture of A80 is ≥15.0%, the hole expansion rate is ≥60%, and the density is 6.5 - 7.5g / cm3; pre-stress is formed by 180° U-shaped bending and immersed in 0.5mol / L HCl solution for 14 days, and no delayed fracture occurs.

[0041] The beneficial effects of the present invention are as follows:

[0042] (1) The chemical composition of the steel in the present invention mainly uses C, Mn, Al, and Si as the main elements, and the original cost is relatively low.

[0043] (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 greatly reduce carbon emissions and save energy consumption;

[0044] (3) The 1.0GPa hydrogen embrittlement resistant cold-rolled CH steel produced by the present invention has a certain proportion of retained austenite added on the basis of traditional cold-rolled dual-phase steel. Under the action of the transformation-induced plasticity (TRIP) effect, its high strength, high plasticity and formability are realized;

[0045] (4) Adding a large amount of aluminum element to the 1.0GPa hydrogen embrittlement resistant cold-rolled CH steel produced by the present invention can realize low density of high-strength steel and meet the requirements of automotive lightweight design;

[0046] (5) The 1.0GPa hydrogen embrittlement resistant cold-rolled CH steel produced by the present invention can meet the diverse product requirements of continuous annealing, continuous hot-dip galvanizing / galvanized aluminum-magnesium and alloyed hot-dip galvanizing with a set of alloy systems due to special designs in composition and process, that is, one steel can be used for multiple purposes. It 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 the product production efficiency;

[0047] (6) The 1.0GPa hydrogen embrittlement resistant cold-rolled CH steel produced by the present invention can achieve a yield strength of ≥780MPa, a tensile strength of 980 - 1100MPa, an elongation after fracture of A80 of ≥15.0%, a hole expansion rate of ≥60%, and a density of 6.5 - 7.5g / cm3; pre-stress is formed by 180° U-shaped bending and immersed in 0.5mol / L HCl solution for 14 days, and it has excellent properties of no delayed fracture. Description of the Drawings

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

[0049] Figure 2 It is the metallographic diagram of the microstructure of Example 1-4 of the present invention.

[0050] Figure 3 This is the stress-strain curve of Example 1-1 of the present invention. Detailed implementation mode

[0051] The present invention will be further described below through examples.

[0052] In the examples of the present invention, according to the component ratios of the technical solutions, electric furnace smelting, medium and thin slab continuous casting and rolling, pickling and cold rolling, continuous annealing or continuous hot-dip coating process or alloyed hot-dip galvanizing are carried out.

[0053] Electric furnace smelting: The present invention selects 30% - 70% scrap steel as raw materials, and the molten steel temperature is between 1600 - 1750 °C.

[0054] Medium and thin slab continuous casting and rolling: Special protective slag for high-aluminum steel is used, the casting temperature is 1530 - 1600 °C, the casting machine drawing speed is 1.0 - 5.5 m / min, and the continuous casting billet thickness is 60 - 115 mm; the starting rolling temperature is 1000 - 1150 °C, the final rolling temperature is above 900 °C, and the coiling temperature is 600 - 700 °C;

[0055] Pickling and cold rolling: The cold rolling reduction rate is 45% - 70%;

[0056] After pickling and cold rolling, the steel plate is subjected to continuous annealing or continuous hot-dip coating process, and the continuous hot-dip coating process is continuous hot-dip galvanizing or continuous zinc-aluminum-magnesium coating or alloyed hot-dip galvanizing process;

[0057] Skin pass: In the skin pass process, rolling force control is adopted, the rolling force is controlled at 1000 - 3500 kN, and the rolling tension is 500 - 2000 kN.

[0058] Furthermore; for the continuous annealing: the strip speed is controlled at 60 - 180 m / min, the furnace temperature in the soaking section is 760 - 880 °C, the soaking time is 10 - 600 s, the slow cooling outlet temperature is 700 - 760 °C, the rapid cooling rate is greater than 25 °C / s, the rapid cooling temperature is between 350 - 550 °C, the aging temperature is 350 - 550 °C, and the annealing time is 60 - 1000 s.

[0059] Furthermore; the specific processes of continuous hot-dip galvanizing and continuous zinc-aluminum-magnesium coating are: the strip speed is controlled at 60 - 180 m / min, the annealing temperature is between 760 - 880 °C, the dew point temperature is controlled between -20 - -10 °C, the annealing time is between 30 - 300 s, the slow cooling outlet temperature is 680 - 760 °C, the rapid cooling rate is greater than 20 °C / s, the rapid cooling outlet temperature is 450 - 470 °C, the galvanizing temperature is 450 - 470 °C, after galvanizing, the strip is first cooled by an air knife to 400 - 420 °C, and then air-cooled, and the temperature of the top roll at the cooling tower is controlled at 250 - 300 °C.

[0060] Furthermore, during the continuous hot-dip galvanizing process, the components of the galvanizing bath are as follows by mass percentage: Al: 0.16% - 0.25%, and the rest are Zn and inevitable impurities. After continuous hot-dip galvanizing, the weight of the zinc coating per unit area of the steel sheet is 60 - 200 g / cm 2 .

[0061] Furthermore, during the continuous hot-dip galvanizing of aluminum-magnesium alloy, the components of the galvanizing bath are as follows by mass percentage: Al: 2.0% - 10.0%, Mg: 1.0% - 5.0%, Si: 0.001% - 0.1%, and the rest are Zn and inevitable impurities. After continuous hot-dip galvanizing of aluminum-magnesium alloy, the weight of the zinc-aluminum-magnesium coating per unit area of the steel sheet is 50 - 200 g / cm 2 .

[0062] Furthermore, for 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 - 300 s, the dew point is controlled at -20 - -10 °C, the slow cooling outlet temperature is 680 - 760 °C, the rapid cooling rate is greater than 20 °C / s, the fast cooling outlet temperature is between 450 - 470 °C, the galvanizing temperature is 450 - 470 °C. After galvanizing, the strip is first cooled by an air knife 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 - 60 s.

[0063] Furthermore, the thickness specification of the steel sheet after hot rolling is 2.0 - 4.5 mm. The microstructure of the hot-rolled steel sheet includes ferrite, pearlite, bainite, and a small amount of cementite / impurities. The volume percentages of each microstructure are as follows: ferrite 30% - 60%, pearlite 20% - 50%, bainite 5% - 20%, and cementite / impurities 1% - 5%.

[0064] The composition of the steel in the embodiments of the present invention is shown in Table 1. The main process parameters of steelmaking, continuous casting, continuous rolling, and the hot-rolled microstructure in the embodiments of the present invention are shown in Table 2. The main process parameters of continuous annealing of the steel in the embodiments of the present invention are shown in Table 3. The main process parameters of continuous hot-dip galvanizing of the steel in the embodiments of the present invention are shown in Table 4. The main process parameters of continuous hot-dip galvanizing of aluminum-magnesium alloy of the steel in the embodiments of the present invention are shown in Table 5. The main process parameters of alloying hot-dip galvanizing of the steel in the embodiments of the present invention are shown in Table 6. The properties of the steel in the embodiments of the present invention are shown in Table 7. The microstructure of the steel in the embodiments of the present invention is shown in Table 8.

[0065] Table 1 Composition of the steel in the embodiments of the present invention (wt%)

[0066]

[0067] Table 2 Main process parameters of steelmaking, continuous casting, continuous rolling, and the hot-rolled microstructure of the steel in the embodiments of the present invention

[0068]

[0069] Table 3 Main process parameters of continuous annealing of steel in the embodiments of the present invention

[0070]

[0071] Table 4 Main process parameters of continuous hot-dip galvanizing of steel in the embodiments of the present invention

[0072]

[0073] Table 5 Main process parameters of continuous hot-dip galvanizing-aluminum-magnesium of steel in the embodiments of the present invention

[0074]

[0075] Table 6 Main process parameters of alloying hot-dip galvanizing of steel in the embodiments of the present invention

[0076]

[0077] Table 7 Properties of steel in the embodiments of the present invention

[0078]

[0079]

[0080] Note: The evaluation of the hydrogen embrittlement resistance (anti-delayed fracture) performance is carried out by U-shaped bending immersion evaluation. The bending radius of 180° cold bending is 5 mm. Each group has 5 parallel specimens, which are immersed in 0.5 mol / L HCl solution for 14 days. If no fracture occurs, it is determined that the specimen has no risk of delayed fracture and is marked as Ο; if fracture occurs, it is determined that the specimen has a risk of delayed fracture and is marked as ×.

[0081] Table 8 Microstructure of steel in the embodiments of the present invention

[0082]

[0083]

[0084] In order to describe the present invention, the present invention has been properly and fully described by way of examples above. The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those of ordinary skill 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 replacements, improvements, etc. should be included within the protection scope of the present invention. The patent protection scope of the present invention shall be defined by the claims.

Claims

1. A 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel, characterized in that, the composition of the steel is as follows by weight percentage: C: 0.10% - 0.20%, Mn: 1.0% - 1.65%, Si: 0.1% - 1.0%, Al: 1.86% - 6.0%, Cr: 0.02% - 0.80%, Mo: 0.02% - 0.80%, Ni: 0.05% - 0.80%, P ≤ 0.01%, S ≤ 0.01%, N ≤ 0.005%, Mg: 0.167% - 0.50%, Nb: 0.01% - 0.50%, V: 0.01% - 0.50%, and 10.58 ≤ Al / Si ≤ 20; the balance is Fe and unavoidable impurities; the microstructure of the steel consists of 30.2% - 45% ferrite, 30% - 60% bainite, 3% - 12% retained austenite, and 3% - 15% martensite; the retained austenite is in a film-like form, with a grain size between 0.05 µm and 0.20 µm, and the film-like retained austenite is mainly distributed between bainite and martensite laths.

2. A 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to claim 1, characterized in that, The yield strength of the CH steel plate is ≥780 MPa, the tensile strength is 980 - 1100 MPa, the elongation after fracture of A80 is ≥15.0%, the hole expansion rate is ≥60%, and the density is 6.5 - 7.5 g / cm 3 .

3. A preparation method of a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to any one of claims 1 - 2, characterized in that: It includes electric furnace smelting, medium and thin slab continuous casting and rolling, pickling cold rolling, continuous annealing or continuous hot-dip coating process or alloyed hot-dip galvanizing; Electric furnace smelting: Adding 30% - 70% proportion of scrap steel as raw materials, and the molten steel temperature is 1600 - 1750 °C; Medium and thin slab continuous casting and rolling: Using a special protective slag for high-aluminum steel, the casting temperature is 1530 - 1600 °C, the casting machine pulling speed is 1.0 - 5.5 m / min, and the continuous casting billet thickness is 60 - 108 mm; the starting rolling temperature is 1000 - 1150 °C, the final rolling temperature is above 900 °C, and the coiling temperature is 600 - 700 °C; Pickling cold rolling: The cold rolling reduction rate is 56% - 70%; After pickling cold rolling, the steel plate is subjected to continuous annealing or continuous hot-dip coating process or alloyed hot-dip galvanizing, and the continuous hot-dip coating process is continuous hot-dip galvanizing or continuous galvanized aluminum-magnesium; Skin pass: The skin pass process uses rolling force control, and the rolling force is controlled at 1000 - 3500 kN, and the rolling tension is 500 - 2000 kN.

4. A preparation method of a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to claim 3, characterized in that: Continuous annealing: The strip speed is controlled at 60 - 180 m / min, the annealing temperature is 760 - 880 °C, the soaking time is 10 - 600 s, the slow cooling outlet temperature is 700 - 760 °C, the rapid cooling rate is greater than 25 °C / s, the rapid cooling temperature is 350 - 550 °C, the aging temperature is 350 - 550 °C, and the aging time is 60 - 1000 s.

5. A preparation method of a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to claim 3, characterized in that: The specific processes of continuous hot-dip galvanizing and continuous hot-dip aluminum-magnesium galvanizing are as follows: annealing temperature is 760 - 880 °C, dew point temperature is -20 - -10 °C, annealing time is 30 - 300 s, slow cooling outlet temperature is 680 - 760 °C, rapid cooling rate is greater than 20 °C / s, fast cooling outlet temperature is 450 - 470 °C, galvanizing temperature is 450 - 470 °C. After galvanizing, the strip is first cooled by an air knife to 400 - 420 °C, and then air-cooled. The temperature of the top roll at the cooling tower is 250 - 300 °C.

6. The preparation method of a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to claim 5, characterized in that: During the continuous hot-dip galvanizing process, the composition of the galvanizing bath is as follows by mass percentage: Al: 0.16% - 0.25%, and the rest is Zn and inevitable impurities. After continuous hot-dip galvanizing, the weight of the zinc layer per unit area of the steel plate is 60 - 200 g / cm 2 .

7. The preparation method of a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to claim 5, characterized in that: During the continuous hot-dip galvanizing-aluminum-magnesium process, the components of the galvanizing-aluminum-magnesium plating solution are calculated by mass percentage as follows: Al: 2.0% - 10.0%, Mg: 1.0% - 5.0%, Si: 0.001% - 0.1%, and the rest are Zn and inevitable impurities. The weight of the zinc-aluminum-magnesium coating per unit area of the steel plate after continuous hot-dip galvanizing-aluminum-magnesium is 50 - 200 g / cm 2 .

8. The preparation method of a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to claim 3, characterized in that: Alloying hot-dip galvanizing: annealing temperature is 770 - 870 °C, annealing time is 30 - 300 s, dew point control is -20 - -10 °C, slow cooling outlet temperature is 680 - 760 °C, rapid cooling rate is greater than 20 °C / s, fast cooling outlet temperature is 450 - 470 °C, galvanizing temperature is 450 - 470 °C. After galvanizing, the strip is first cooled by an air knife 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 - 60 s.

9. The preparation method of a 1.0 GPa grade hydrogen embrittlement resistant cold-rolled CH steel according to claim 3, characterized in that: The thickness of the hot-rolled steel plate after hot rolling is 2.0 - 4.5 mm. The microstructure of the hot-rolled steel plate consists of ferrite, pearlite, bainite, and a small amount of cementite / impurities. The volume percentages of each microstructure are as follows: ferrite 30% - 60%, pearlite 20% - 50%, bainite 5% - 20%, cementite / impurities 1% - 5%.

Images