High-strength dual-phase steel with hydrogen-induced crack resistance and hot-dip galvanized by cold rolling and method for producing the same

Abstract

The present invention provides a hydrogen-induced crack-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel including a substrate and a zinc plating layer plated on the substrate. The substrate contains Fe and inevitable impurity elements, and the substrate also contains the following chemical elements in the following mass percentages: C: 0.1 to 0.18%, Mn: 2.2 to 3.0%, Si: 0.2 to 0.6%, Al: 0.03 to 0.3%, Nb: 0.01 to 0.1%, Ti: 0.01 to 0.1%, Mo: 0.04 to 0.2%, B: 0.0005 to 0.003%. The matrix of the microstructure of the substrate is ferrite + martensite, and the microstructure also contains carbide precipitation phases with a size of less than 100 nm. These carbide particles and the matrix are in an aggregated state or a semi-aggregated state. In addition, the present invention further discloses a manufacturing method of the above steel material including the following steps: (1) smelting and casting, (2) hot rolling, (3) pickling, (4) cold rolling, (5) recrystallization annealing of hot-dip galvanizing, (6) cooling after galvanizing.

Description

Technical Field

[0001] The present invention relates to steel materials and a method for manufacturing the same, and more particularly to an ultra-high strength dual-phase steel and a method for manufacturing the same.

Background Art

[0002] In recent years, with the rapid development of the automobile industry, the steel materials used for automobile white bodies have also been rapidly changing, and the proportion of ultra-high strength steel materials used in the field of automobiles has been increasing very significantly.

[0003] Compared with conventional high-strength steels, when the strength of ultra-high strength steels reaches 980 MPa or more, the risk of hydrogen-induced delayed cracking increases significantly, and the safety of the vehicle body is greatly impaired. In particular, when the tensile strength reaches a level exceeding 1180 MPa, the critical hydrogen content for hydrogen-induced cracking becomes very low, and in order to meet the requirements of corrosion resistance, the surface of the steel sheet is usually plated with a zinc layer. Due to the presence of the zinc layer, the overflow of diffusible hydrogen is suppressed, and when the plated zinc becomes extremely high, the risk of hydrogen-induced cracking increases. Therefore, the development of ultra-high strength steels that can avoid the risk of hydrogen-induced cracking while meeting the user's requirements for corrosion resistance has become the focus of future research and development, but there are few related reports and patents of this kind.

[0004] For example, in a Chinese patent document with a publication number of CN1990894A, a publication date of July 4, 2007, and a title of "Ultra-high strength thin steel sheet with excellent hydrogen embrittlement resistance", an ultra-high strength steel with excellent hydrogen embrittlement resistance and a manufacturing method are disclosed. Its typical composition is (0.1~0.3)C-(1~3.5)Mn-(1~3)Si, and when the tensile strength of the material reaches the 1180 MPa level, it has high resistance to delayed cracking. However, in this technical solution, a higher C and Si design is adopted, which is disadvantageous for the spot welding performance of extremely high zinc plating. At the same time, the annealing temperature used when manufacturing the steel material is higher than the A3 temperature, and higher unit conditions are required for the process path, which does not conform to the low-carbon design concept.

[0005] For example, in a Chinese patent document with a publication number of CN102449180A, a publication date of May 9, 2012, and a title of "High-strength steel sheet with excellent hydrogen embrittlement resistance", a high-strength steel sheet with excellent hydrogen embrittlement resistance is disclosed. Its typical composition is (0.15 - 0.25)C - (1.5 - 3)Mn - (1 - 2.5)Si. Through the quenching - tempering process, high formability can be obtained when the tensile strength of the material reaches the 1180 MPa level. However, in this technical solution, higher C and Si designs are adopted, which are disadvantageous for the spot weldability and manufacturability of hot-dip galvanized steel. At the same time, when manufacturing steel, the required quenching - tempering process passes and high annealing temperatures require high unit conditions and equipment, which do not contribute to the expansion of products.

[0006] Therefore, in order to meet the needs of the market and users, while ensuring the manufacturability, production cost, and excellent weldability of cold-rolled hot-dip galvanized dual-phase steel, it is urgent to develop a new hydrogen cracking-resistant cold-rolled hot-dip galvanized ultra-high-strength dual-phase steel by the conventional dual-phase (DP) process.

Summary of the Invention

Problems to be Solved by the Invention

[0007] One of the objectives of the present invention is to provide a hydrogen cracking-resistant cold-rolled hot-dip galvanized ultra-high-strength dual-phase steel. Through reasonable component matching and process design, this steel can obtain excellent manufacturability, formability, weldability, and hydrogen cracking resistance while ensuring ultra-high strength. Its yield strength ≥ 800 MPa, tensile strength ≥ 1180 MPa, elongation A 50 ≥ 6%, diffusible hydrogen content ≤ 0.2 ppm, and has very good application prospects.

Means for Solving the Problems

[0008] To achieve the above object, the present invention provides a hydrogen-induced crack-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel including a substrate and a zinc plating layer plated on the substrate. The substrate contains Fe and inevitable impurity elements, and the substrate also contains the following chemical elements in the following mass percentages: C: 0.1 to 0.18%, Mn: 2.2 to 3.0%, Si: 0.2 to 0.6%, Al: 0.03 to 0.3%, Nb: 0.01 to 0.1%, Ti: 0.01 to 0.1%, Mo: 0.04 to 0.2%, B: 0.0005 to 0.003%.

[0009] The matrix of the microstructure of the substrate is ferrite + martensite, and the microstructure also contains carbide precipitation phases with a size of less than 100 nm. In the present disclosure, the size of the carbide precipitation phase refers to its particle size.

[0010] In the present invention, the hydrogen-induced crack-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel is simply referred to as cold-rolled hot-dip galvanized dual-phase steel.

[0011] Furthermore, in the hydrogen-induced crack-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the mass percentages of the chemical elements of the substrate are C: 0.1 to 0.18%, Mn: 2.2 to 3.0%, Si: 0.2 to 0.6%, Al: 0.03 to 0.3%, Nb: 0.01 to 0.1%, Ti: 0.01 to 0.1%, Mo: 0.04 to 0.2%, B: 0.0005 to 0.003%, and the balance is Fe and inevitable impurities.

[0012] In one or more embodiments, in the hydrogen-induced crack-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the C element is 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, or within the range of any two of the aforementioned values.

[0013] In one or more embodiments, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the Mn element is 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, or within the range of any two of the aforementioned values.

[0014] In one or more embodiments, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the Si element is 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, or within the range of any two of the aforementioned values.

[0015] In one or more embodiments, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the Al element is 0.03%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or within the range of any two of the aforementioned values.

[0016] In one or more embodiments, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the Nb element is 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, or within the range of any two of the aforementioned values.

[0017] In one or more embodiments, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the Ti element is 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, or within the range of any two of the aforementioned values.

[0018] In one or more embodiments, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the Mo element is 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, or within the range of any two of the aforementioned values.

[0019] In one or more embodiments, in the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of element B is 0.0005%, 0.001%, 0.0015%, 0.002%, 0.0025%, 0.003%, or within the range of any two of the aforementioned values.

[0020] In one or more embodiments, the size of the carbide precipitation phase is 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or within the range of any two of the aforementioned values.

[0021] In the present invention, the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel can further introduce precipitation strengthening phases, namely nano-scale carbide precipitation phases, into the ferrite and martensite structures of the conventional dual-phase steel through reasonable composition matching and process design. These carbide precipitation phases not only improve the strength of the steel, but also function as powerful hydrogen traps to fix diffusible hydrogen, which is beneficial to the improvement of the delayed cracking of the steel.

[0022] In the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the design principle of each chemical element is as follows.

[0023] C: In the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, C is an important component element of the hot-dip galvanized dual-phase steel, which is related to the strength and plasticity of the galvanized sheet. If the content of element C in the steel is too low, the austenite content formed during annealing in the critical region will decrease, and the austenite stability and martensite hardenability will decrease, making it difficult to ensure the strength and plasticity of the steel. On the other hand, the content of element C in the steel should not be too high. If the content of element C in the steel is too high, the plasticity and weldability of the dual-phase steel will decrease. Therefore, considering the influence of the content of element C on the properties of the steel, in the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the mass percentage content of element C is controlled to be 0.1 - 0.18%.

[0024] Mn: In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the Mn element improves the stability of austenite, shifts the C curve to the right, and reduces the critical cooling rate of martensite. The content of the Mn element in the steel must not be too low. If the content of Mn is too low, the hardenability of the steel decreases and the strengthening effect also weakens. At the same time, it is not desirable to add excessive Mn to the steel. If the content of the Mn element in the steel is too high, it will affect the weldability of the substrate and the quality of the surface zinc plating. At the same time, the grain boundaries become weak and the risk of hydrogen-induced cracking of the material increases. Therefore, considering the influence of the content of the Mn element on the properties of the steel, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the mass percentage content of the Mn element is controlled to be 2.2 - 3.0%.

[0025] Si: In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, Si is a ferrite solid-solution strengthening element and can strongly improve the strength of the steel sheet. At the same time, the Si element can also promote the enrichment of C atoms from ferrite to austenite, purify ferrite, suppress the precipitation of cementite and ε-carbide, and improve the stability of austenite. However, the content of the Si element in the steel must not be too high. If the content of the Si element is too high, it will directly affect the plating property and spot weldability of the substrate, so attention is required. Therefore, in order to exert the beneficial effects of the Si element, it is necessary to strictly control the content of the Si element in the steel. In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the mass percentage content of the Si element is controlled to be 0.2 - 0.6%.

[0026] Al: In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the Al element functions in the same way as the Si element, can effectively suppress the precipitation of carbides, and can promote the diffusion of carbon element into austenite. However, the Al element cannot suppress the precipitation of ε-carbide. In the present invention, the Al element can increase the stacking defect energy of austenite, effectively suppress the weakening of grain boundaries caused by stress concentration and hydrogen enrichment, and at the same time, Al can form a dense alumina protective layer on the surface to suppress the intrusion of hydrogen, improving the hydrogen embrittlement resistance of the material. Furthermore, the Al added to the steel can also pin the grain boundaries by forming AlN and refine the crystal grains.

[0027] The content of Al element in the steel should not be too high. If the content of Al is too high, problems such as clogging of nozzles during continuous casting and a significant increase in Ac3 are likely to occur, so attention is required. Therefore, in order to exert the beneficial effects of the Al element, it is necessary to strictly control the content of Al element in the steel. In the present invention, the mass percentage content of Al element is controlled to be 0.03 - 0.3%.

[0028] Nb: In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the Nb element strongly suppresses dynamic recrystallization, combines with C and N to form Nb(C,N), effectively suppresses the coarsening of crystal grains during heat treatment, refines the crystal grains, and can strengthen the boundary strength. Furthermore, the Nb precipitates increase the grain boundary area like the Ti element, have the effect of reducing the diffusible hydrogen content per unit area, and are also beneficial for reducing the risk of delayed cracking of the steel sheet by fixing diffusible hydrogen. However, the content of Nb element in the steel should not be too high. Adding excessive Nb will deteriorate the hot working properties of the steel and the toughness of the steel sheet. Based on this, in order to exert the beneficial effects of the Nb element, the mass percentage of Nb element in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention is controlled to be 0.01 - 0.1%.

[0029] Ti: In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, Ti combines with C and N to form Ti(C,N), TiN, and TiC. As a result, the structure in the as-cast state is refined, the coarsening of crystal grains during heat treatment is prevented, the grain boundaries are strengthened, and at the same time, the crystal grains are refined and the grain boundary area increases, which is beneficial for reducing the diffusible hydrogen content per unit area. Furthermore, the precipitates of Ti fix diffusible hydrogen atoms and are beneficial for avoiding the local accumulation of diffusible hydrogen, which is beneficial for improving the delayed cracking of the steel. However, the content of Ti element in the steel should not be too high. Adding excessive Ti will increase the cost and increase the content and size of the above precipitates, resulting in a decrease in the ductility of the steel sheet, so attention is required. Therefore, in order to exert the beneficial effects of the Ti element, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, it is necessary to control the mass percentage of the Ti element to 0.01 - 0.1%.

[0030] Mo: In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the Mo element can shift the C curves of pearlite and bainite to the right, thereby improving the hardenability of the steel. At the same time, the Mo element can also significantly improve the strength of the steel without affecting the quality of the zinc coating on the surface. Furthermore, due to the grain boundary strengthening effect of the Mo element, the resistance of the steel sheet to hydrogen-induced cracking is further improved, and the finely dispersed precipitation phase of Mo reduces the content of diffusible hydrogen and prevents the accumulation of diffusible hydrogen. Therefore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, considering that the Mo element is expensive, the mass percentage of the Mo element is controlled to 0.04 - 0.2%.

[0031] B: In the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the B element can effectively prevent the recrystallization of the steel during the hot rolling process and is beneficial to the refinement of the microstructure caused by cumulative deformation. However, the content of the B element in the steel should not be too high. If excessive B is added, BC will be generated and the ductility of the steel will decrease, so attention is needed. Therefore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the mass percentage content of the B element is controlled to be 0.0005 - 0.003%.

[0032] Furthermore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the chemical elements of the substrate may optionally or preferably contain at least one of the following elements by mass percentage.

[0033] V: 0.005 - 0.2%, Cr: 0.01 - 0.8%, Cu: 0.003 - 0.5%.

[0034] Furthermore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the mass percentage of each chemical element of the substrate is C: 0.1 - 0.18%, Mn: 2.2 - 3.0%, Si: 0.2 - 0.6%, Al: 0.03 - 0.3%, Nb: 0.01 - 0.1%, Ti: 0.01 - 0.1%, Mo: 0.04 - 0.2%, B: 0.0005 - 0.003%, and optionally or preferably at least one of V: 0.005 - 0.2%, Cr: 0.01 - 0.8% and Cu: 0.003 - 0.5%, the balance being Fe and unavoidable impurities.

[0035] In one or more embodiments, when V is contained, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, the mass percentage content of the V element is 0.005%, 0.01%, 0.02%, 0.05%, 0.07%, 0.1%, 0.2%, or within the range of any two of the aforementioned values.

[0036] In one or more embodiments, when Cr is contained, in the cold-rolled hot-dip galvanized ultra-high strength dual-phase steel resistant to hydrogen-induced cracking, the mass percentage content of the Cr element is 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or within the range of any two of the aforementioned values.

[0037] In one or more embodiments, when Cu is contained, in the cold-rolled hot-dip galvanized ultra-high strength dual-phase steel resistant to hydrogen-induced cracking, the mass percentage content of the Cu element is 0.003%, 0.005%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or within the range of any two of the aforementioned values.

[0038] In order to further optimize the performance of the cold-rolled hot-dip galvanized ultra-high strength dual-phase steel resistant to hydrogen-induced cracking according to the present invention, in some preferred embodiments, the elements V, Cr, and Cu may be further added to the steel material.

[0039] V: In the present invention, V mainly exists in the form of VC in the hot-dip galvanized dual-phase steel, pins the grain boundaries to refine the crystal grains, and improves the strength and toughness of the steel by dispersion precipitation strengthening in ferrite. At the same time, the mechanism of improving the delayed cracking of the carbide of the V element is the same as that of Nb and Ti. However, it should be noted that when V is further added, the alloy cost of the steel increases. Therefore, in the present invention, the mass percentage content of the V element is limited to 0.005 - 0.2%.

[0040] Cr: In the present invention, the Cr element can refine the crystal grain structure and suppress the coarsening of crystal grains during hot working. Also, Cr is an element that forms ferrite, promotes the diffusion of C into austenite, improves the stability of austenite, and can reduce the critical cooling rate during annealing. At the same time, when Cr is added, the carbides in the steel are dispersed and precipitated finely, forming effective hydrogen traps and reducing the risk of delayed cracking. However, the content of the Cr element in the steel should not be too high. If the content of the Cr element is too high, the ductility and surface plating properties of the steel will be impaired, so attention is required. Therefore, in the present invention, the mass percentage content of the Cr element is controlled to be 0.01 - 0.8%.

[0041] Cu: In the present invention, Cu can significantly improve the stability of austenite, shift the C curve of bainite to the right, improve hardenability, and thereby reduce the critical cooling rate of martensite. At the same time, the Cu element can strengthen the matrix by precipitating nano-precipitation phases. Furthermore, Cu also functions as a hydrogen trap, effectively pinning diffusible hydrogen and reducing the risk of delayed cracking of the material. However, the content of the Cu element in the steel should not be too high. If the content of the Cu element is too high, copper embrittlement is likely to occur during hot working, so attention is required. Therefore, in the present invention, the mass percentage content of the Cu element is controlled to be 0.003 - 0.5%.

[0042] Furthermore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high-strength dual-phase steel according to the present invention, the mass percentage contents of Si, Al, Mo, and Cr in the substrate satisfy Si + Al + Cr + Mo ≤ 1.0%.

[0043] In one or more embodiments, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high-strength dual-phase steel according to the present invention, the mass percentage contents of Si, Al, Mo, and Cr in the substrate satisfy that Si + Al + Cr + Mo is within the range of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% or any two of the aforementioned values.

[0044] In the above technical solution of the present invention, while controlling the mass percentage content of a single chemical element, the element ratio in the steel may be further controlled such that the mass percentage contents of Si, Al, Mo, and Cr satisfy Si + Al + Cr + Mo ≤ 1.0%. By setting Si + Al + Cr + Mo ≤ 1.0%, while ensuring good manufacturability of the steel plate, sufficient hydrogen traps can be ensured, and both manufacturability and resistance to delayed cracking can be achieved.

[0045] Furthermore, in the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, among the inevitable impurities in the substrate, P ≤ 0.02%, S ≤ 0.01%, and N ≤ 0.008%.

[0046] In the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the P element, S element, and N element are all impurity elements in the substrate. As long as the technical conditions permit, in order to obtain a steel plate with better performance and quality, it is necessary to reduce the content of impurity elements in the steel plate as much as possible.

[0047] In the present invention, due to the weakening effect of impurity elements on the grain boundaries, the susceptibility to hydrogen embrittlement is increased. Therefore, if the contents of P and S in the steel are too high, grain boundary segregation and grain boundary embrittlement will increase, which does not contribute to the hydrogen embrittlement resistance performance of the material. Therefore, it is necessary to strictly control the mass percentage contents of the impurity elements P, S, and N in the steel so that P ≤ 0.02%, S ≤ 0.01%, and N ≤ 0.008%. The higher the purity of the steel, the better the effect.

[0048] In one or more embodiments, in the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the mass percentage content of the P element is 0.001 - 0.02%, the mass percentage content of the S element is 0.001 - 0.01%, and the content of the N element is 0.001 - 0.008%.

[0049] Of course, in some preferred embodiments, in order to obtain better implementation effects, it is more preferable to control P≤0.01%, S≤0.006%, and N≤0.005%.

[0050] Furthermore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the carbide precipitation phase and the matrix are in an aggregated state or a semi-aggregated state.

[0051] Furthermore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the volume ratio of ferrite in the microstructure of the substrate is 10-40%, for example, 15%, 20%, 25%, 30%, 35%.

[0052] Furthermore, in the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, the thickness of the hot-dip galvanized layer on one side of the substrate is 5-200 μm, for example, 10 μm, 25 μm, 35 μm, 50 μm, 75 μm, 100 μm, 120 μm, 130 μm, 150 μm.

[0053] Furthermore, the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention is characterized in that the yield strength≥800 MPa, the tensile strength≥1180 MPa, the elongation A 50 ≥6%, and the diffusible hydrogen content≤0.2 ppm.

[0054] In one or more embodiments, the yield strength of the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention is 800 MPa, 850 MPa, 900 MPa, 950 MPa, 1000 MPa, or within the range of any two of the aforementioned values.

[0055] In one or more embodiments, the tensile strength of the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention is 1180 MPa, 1190 MPa, 1200 MPa, 1220 MPa, 1240 MPa, 1260 MPa, 1270 MPa, or within the range of any two of the aforementioned values.

[0056] In one or more embodiments, the elongation A of the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention 50 is 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or within the range of any two of the foregoing values.

[0057] In one or more embodiments, the diffusible hydrogen content of the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention is 0.01 ppm, 0.02 ppm, 0.04 ppm, 0.06 ppm, 0.08 ppm, 0.1 ppm, 0.2 ppm, or within the range of any two of the foregoing values.

[0058] Therefore, another object of the present invention is to provide a method for manufacturing the above hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, which can optimize the design of the annealing process, effectively manufacture the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, and ensure the hydrogen-induced cracking resistance of the steel material.

[0059] To achieve the above object, the present invention provides a method for manufacturing a hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel, comprising the following steps: (1) Smelting and casting; (2) Hot rolling; (3) Pickling; (4) Cold rolling; (5) Recrystallization annealing for hot-dip galvanizing: (a) Heating the steel plate to the soaking temperature T1 at a heating rate V1 of 1 to 20 °C / s and holding for 30 to 240 s, where T1 > 760 °C; (b) Cooling the soaked steel plate to the intermediate temperature T2 at a cooling rate V2 of 2 to 20 °C / s, where T2 = 600 to 780 °C; (c) Cooling the steel plate to the galvanizing temperature T3 at a cooling rate V3 of 5 to 60 °C / s and holding for 20 to 300 seconds, where V3 > V2 and the galvanizing temperature is 400 to 500 °C; (d) Sending the steel plate to a zinc pot for hot-dip galvanizing; (6) Cooling after zinc plating: After the zinc plating is completed, it is rapidly cooled to 200 °C or lower at a rate of 10 °C / s or more, held within the temperature range of 100 °C to 300 °C for 15 to 100 s, and then cooled to room temperature at a cooling rate of 5 °C / s or more.

[0060] In the present invention, for the production of the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel according to the present invention, a series of processes including steelmaking and casting (such as continuous casting), hot rolling, pickling, cold rolling, hot-dip galvanized recrystallization annealing process, and cooling after zinc plating are required. By adopting the above-described component design, rolling process, and hot-dip galvanized recrystallization annealing process, the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel can be effectively produced. The matrix of the microstructure of the produced steel sheet is ferrite + martensite, and it also contains carbide precipitation phases with a size of less than 100 nm. These carbide particles and the matrix are in an aggregated state or a semi-aggregated state.

[0061] The present invention controls the relative content of ferrite and martensite, comprehensively utilizes grain refinement strengthening, precipitation strengthening, etc. to obtain good strength and plasticity, increases the grain boundary strength, reduces the diffusible hydrogen content, and adopts various control techniques to avoid local accumulation of diffusible hydrogen, thereby improving the delayed fracture resistance of the high-strength steel.

[0062] In the manufacturing method of the present invention described above, the inventor optimized the hot-dip galvanized recrystallization annealing process of step (5) so that the steel sheet can be annealed flexibly after zinc plating. By this process, not only the overflow of diffusible hydrogen is promoted, but also ε-carbide precipitates and the hydrogen trap increases, resulting in a significant decrease in the diffusion coefficient of hydrogen in martensite and an improvement in the delayed fracture resistance of the steel sheet.

[0063] Furthermore, the present invention utilizes a short-time aging treatment (i.e., a process of holding at a temperature range of 100 to 300 °C for 15 to 100 s during cooling after zinc plating) to promote the overflow of hydrogen, significantly reduce the content of diffusible hydrogen in the steel sheet, and enable the steel material to have ultra-high strength and excellent hydrogen embrittlement resistance.

[0064] The parameters of the hot-dip galvanized annealing process are closely related to the steel composition design, and it should be noted that they determine the relative content of the soft-phase ferrite and the hard-phase martensite in the galvanized sheet and affect the optimal matching of the strength and plasticity of the galvanized steel sheet.

[0065] In the present invention, the present invention heat-treats a cold-rolled steel sheet by a continuous annealing method, and its hot-dip galvanized recrystallization annealing process is as shown in the above steps (a) to (d).

[0066] In step (a), the cold-rolled steel sheet needs to be heated to the soaking temperature T1 at the heating rate V1 and then held for the time t1. Here, specifically, V1 = 1 to 20 °C / s, for example, 2 °C / s, 5 °C / s, 7 °C / s, 8 °C / s, 10 °C / s, 12 °C / s, 15 °C / s, 17 °C / s, 18 °C / s are selected; T1 > 760 °C, for example, 770 °C, 780 °C, 790 °C, 800 °C, 810 °C, 820 °C, 830 °C are selected; the holding time t1 = 30 to 240 s, for example, 40 s, 60 s, 80 s, 100 s, 120 s, 160 s, 180 s, 200 s, 220 s is controlled. In the process of this step, when the soaking temperature T1 is lower than 760 °C and the soaking holding time t1 is shorter than 30 s, the matrix structure of the cold-rolled galvanized sheet corresponding to the designed composition of the present invention is mostly banded structure, and sufficient austenite or carbide in the steel sheet matrix cannot be obtained and cannot be completely dissolved to form austenite particles. Among them, the presence of the banded structure has an adverse effect on the use performance of the steel material such as bending and hole expansion.

[0067] In processes (b) and (c), after the steel plate after homogenization heat treatment is slowly cooled to an intermediate temperature T2 at a cooling rate V2, it is immediately rapidly cooled to a galvanizing temperature T3 at a cooling rate V3, and then held for a time t3.

[0068] Here, the selection of the slow cooling rate V2 and the intermediate temperature T2 mainly considers the following: promoting the transformation of a part of austenite into ferrite, the austenite at the temperature T2 has a certain hardenability, reducing the decomposition at the subsequent galvanizing temperature T3, ensuring a certain amount of martensite and ferrite in the final structure, and enabling the steel plate to obtain a certain degree of strength and plasticity.

[0069] If the intermediate temperature T2 is too high, a large amount of austenite exists, the stability of austenite decreases, and it is likely to transform into bainite at the subsequent galvanizing temperature T3, which will affect the strength and elongation of the steel material. If the intermediate temperature T2 is too low, too much ferrite is generated, the amount of austenite is small, and the amount of martensite finally generated decreases, which may result in insufficient strength. Therefore, based on the chemical element composition designed in the present invention, V2 = 2 - 20 °C / s, for example, 4 °C / s, 6 °C / s, 8 °C / s, 10 °C / s, 12 °C / s, 14 °C / s, 16 °C / s, 18 °C / s are selected; T2 = 600 - 780 °C, for example, 620 °C, 640 °C, 660 °C, 700 °C, 720 °C, 740 °C, 760 °C are selected.

[0070] Therefore, in the composition design of the present invention, V3 = 5 - 60 °C / s, for example, 10 °C / s, 15 °C / s, 20 °C / s, 25 °C / s, 30 °C / s, 35 °C / s, 40 °C / s, 45 °C / s, 50 °C / s, 55 °C / s, and V3 > V2 are selected. To select the rapid cooling rate V3, it is necessary to minimize the decomposition of austenite in the steel plate matrix during the cooling process. When the galvanizing temperature T3 exceeds 500 °C, austenite decomposes to generate a fine structure containing pearlite or carbide, thereby consuming the austenite content and its carbon content, and reducing the strength of the steel plate. When the galvanizing temperature T3 is less than 400 °C, the bainite ferrite content increases, and the strength and plasticity of the galvanized steel plate decrease.

[0071] From the viewpoints of effectiveness and economy, specifically, in order to ensure the ratio of ferrite to martensite for the final galvanized steel sheet to obtain the best strength and plasticity, T3 is limited to 450 - 500 °C, such as 460 °C, 470 °C, 480 °C, 490 °C, and the stabilization time (i.e., the holding time at the galvanizing temperature T3) t3 is selected from 20 - 300 s, such as 30 s, 50 s, 70 s, 90 s, 100 s, 110 s, 120 s, 150 s, 200 s.

[0072] Furthermore, in the manufacturing method of the present invention, in the step (2), the slab is heated at 1180 - 1280 °C (for example, 1200 °C, 1220 °C, 1240 °C, 1260 °C), the holding time is 0.5 - 4 h (for example, 1 h, 2 h, 3 h), the final rolling temperature is controlled to be 850 °C or higher (for example, 870 °C, 880 °C, 890 °C, 900 °C, 920 °C, 930 °C, 950 °C), and the coiling temperature is controlled to be 700 °C or lower (for example, 550 °C, 570 °C, 580 °C, 600 °C, 620 °C, 640 °C, 660 °C, 680 °C).

[0073] Furthermore, in the manufacturing method of the present invention, in the step (4), the cold rolling deformation amount is controlled to be 30 - 70%, such as 35%, 40%, 45%, 50%, 55%, 60%, 65%.

[0074] Furthermore, in the manufacturing method of the present invention, in the step (6), after the galvanizing is completed, the galvanized steel sheet is rapidly cooled at a cooling rate V4 of 10 °C / s or higher (for example, 20 °C / s, 30 °C / s, 40 °C / s, 50 °C / s) to 200 °C or lower (for example, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C), held at a holding temperature T4 of 100 - 300 °C (for example, 150 °C, 180 °C, 200 °C, 220 °C, 250 °C, 280 °C), the holding time t4 is 15 - 100 seconds (for example, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s), and then cooled to room temperature at a cooling rate V5 of 5 °C / s or higher (for example, 10 °C / s, 20 °C / s, 30 °C / s, 40 °C / s, 50 °C / s, 60 °C / s, 70 °C / s, 80 °C / s).

[0075] In the current existing technology, for galvanized ultra-high strength dual-phase steel with a tensile strength exceeding 1180 MPa, delayed cracking is very likely to occur, posing a significant safety risk. Whether to apply 1180 MPa grade ultra-high strength steel to vehicle bodies in the future depends on improving the delayed cracking performance of the steel sheet, which is the key.

[0076] For the hot-dip galvanized ultra-high strength steel at the 1180 MPa level, the present invention adopts a rational application of alloying elements and combines it with a rational manufacturing process to obtain a hot-dip galvanized ultra-high strength dual-phase steel with manufacturability, formability, weldability, and hydrogen-induced cracking resistance.

[0077] Compared with the existing technology, the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel and its manufacturing method according to the present invention have the following advantages and beneficial effects.

[0078] In the present invention, when designing the substrate of the galvanized sheet, the inventors adopt various control techniques such as optimizing alloying elements, controlling grain refinement, and distributing fine and dispersed precipitation phases to increase grain boundary strength, reduce diffusible hydrogen content, and avoid local accumulation of diffusible hydrogen, thereby effectively improving the delayed cracking resistance of ultra-high strength steel. Through reasonable composition matching and process design, the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel can further introduce precipitation strengthening phases, namely nano-scale carbide precipitation phases, into the ferrite and martensite structures of conventional dual-phase steel. These carbide precipitation phases not only improve the strength of the steel but also function as powerful hydrogen traps to fix diffusible hydrogen, which is beneficial for improving delayed cracking.

[0079] Furthermore, the present invention utilizes short aging treatment to promote hydrogen overflow, significantly reducing the diffusible hydrogen content in the steel sheet. As a result, the steel has ultra-high strength and excellent hydrogen embrittlement resistance characteristics.

[0080] (1) The present invention optimizes the chemical composition and manufacturing process design, controls the contents of C and Si in the steel sheet, and ensures a certain ferrite ratio in the microstructure, thereby realizing the characteristics of achieving both formability and weldability of dual-phase steel.

[0081] (2) In the present invention, the dispersion and precipitation of nano-scale carbide particles in the steel can be promoted. These carbide particles can not only improve the strength of the steel, but also function as a powerful hydrogen trap for fixing diffusible hydrogen, which is beneficial to the improvement of the delayed cracking performance of the steel.

[0082] (3) In the present invention, after the steel sheet is zinc-plated, the hot-dip galvanized recrystallization annealing process is optimized so that it can be annealed flexibly. This process not only promotes the overflow of diffusible hydrogen, but also increases the precipitation of ε-carbide and the hydrogen trap, thereby greatly reducing the diffusion coefficient of hydrogen in martensite, and thus improving the hydrogen-induced cracking resistance of the steel sheet.

[0083] From the above, it can be seen that in the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength steel provided by the present invention, by controlling the relative contents of ferrite and martensite and comprehensively utilizing tissue control means such as grain refinement strengthening and precipitation strengthening, very excellent strength and plasticity can be obtained.

[0084] At the same time, this steel not only has excellent hydrogen-induced cracking resistance, but also has certain manufacturability and formability. The production of this hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength steel can utilize the existing production line of ordinary hot-dip galvanized high strength steel sheets as it is, and can be manufactured without significant adjustment, and can be used in the manufacture of vehicle parts such as automobile structural parts and collision prevention parts, and has good prospects for popularization and application.

Brief Description of the Drawings

[0085]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0086] Hereinafter, based on the drawings and specific examples of the specification, the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel and its manufacturing method of the present invention will be further interpreted and explained, but such interpretation and explanation do not unduly limit the technical solution of the present invention.

[0087] Examples 1 - 7 The hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steels of Examples 1 - 7 of the present invention were all manufactured by the following steps.

[0088] (1) Smelting and casting were carried out according to the blending of the mass percentages of the chemical elements shown in Table 1. (2) Hot rolling: The obtained slab was hot rolled. The slab was heated at 1180 - 1280°C, the holding time was controlled to be 0.5 - 4 hours, the final rolling temperature was controlled to be 850°C or higher, and the hot rolled sheet was coiled at a coiling temperature of 700°C or lower.

[0089] (3) Pickling: The hot rolled sheet after hot rolling was pickled. (4) Cold rolling: Cold rolling deformation was applied to the hot rolled sheet after pickling, and the cold rolling deformation amount was controlled to be 30 - 70%.

[0090] (5) Hot-dip galvanizing recrystallization annealing: (a) The steel sheet was heated to the soaking temperature T1 at a heating rate V1 of 1 - 20°C / s and held for 30 - 240 s, where T1 > 760°C; (b) The steel sheet after soaking was cooled to the intermediate temperature T2 at a cooling rate V2 of 2 - 20°C / s, where T2 = 600 - 780°C; (c) The steel sheet was cooled to the galvanizing temperature T3 at a cooling rate V3 of 5 to 60 °C / s, and held for 20 to 300 seconds. Here, V3 > V2, and the galvanizing temperature was set to 400 to 500 °C; (d) The steel sheet was sent to a zinc pot for galvanizing.

[0091] (6) Cooling after galvanizing: After the galvanizing was completed, it was rapidly cooled to 200 °C or lower at a cooling rate of 10 °C / s or more, held in the temperature range of 100 °C to 300 °C for 15 to 100 s, and then cooled to room temperature at a cooling rate of 5 °C / s or more. Finally, the corresponding cold-rolled hot-dip galvanized ultra-high-strength steel resistant to hydrogen-induced cracking was obtained.

[0092] In the present invention, the chemical element compositions and related process designs of the cold-rolled hot-dip galvanized ultra-high-strength dual-phase steels resistant to hydrogen-induced cracking in Examples 1-7 of the present invention all meet the requirements of the design specifications of the present invention.

[0093] Table 1 lists the mass percentages of each chemical element in the cold-rolled hot-dip galvanized ultra-high-strength dual-phase steels resistant to hydrogen-induced cracking in Examples 1-7.

[0094]

Table 1

[0095] Tables 2-1 and 2-2 list the specific process parameters used in the above manufacturing process steps of the cold-rolled hot-dip galvanized ultra-high-strength dual-phase steels resistant to hydrogen-induced cracking in Examples 1-7.

[0096]

Table 2-1

[0097]

Table 2-2

[0098] In addition, in the above manufacturing process, before zinc plating the manufactured substrate, in order to analyze the microstructure of the substrate, samples of the substrates manufactured in each example were collected, and the microstructures of the substrate samples manufactured in Examples 1-7 were observed and analyzed using a metal microscope and a transmission electron microscope (TEM), and the related observation and analysis results are shown in Table 3 below.

[0099] Table 3 lists the results of microstructure observation and analysis of the hydrogen-induced cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel substrates of Examples 1-7.

[0100]

Table 3

[0101] As shown in Table 3 above, in the present invention, the matrix of the microstructure of the substrates manufactured in Examples 1-7 is ferrite + martensite, and the microstructure also contains carbide precipitation phases with a size of 15 to 70 nm. Here, the volume ratio of ferrite in the microstructure of the substrates of Examples 1-7 is 20 to 40%. In the substrates of Examples 1-7 manufactured according to the present invention, it was observed that the carbide precipitation phase and the matrix are in an aggregated state or a semi-aggregated state.

[0102] Therefore, after completing the observation and analysis of the above microstructure, in order to further explain that the hydrogen cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel of Examples 1-7 manufactured according to the present invention has excellent properties, the inventor further collected samples of the hydrogen cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel of the finished products manufactured in Examples 1-7, and various performance tests were carried out on the samples of the hydrogen cracking resistant cold-rolled hot-dip galvanized ultra-high strength dual-phase steel of Examples 1-7, and the related test results are shown in Table 4.

[0103] The related performance test methods are as follows. (1) Tensile test: In accordance with GB228.1-2021, a sheet tensile test specimen with a gauge length of 50 mm was used to measure and obtain the yield strength, tensile strength, and elongation values of the steel materials of each example indoors.

[0104] (2) Hydrogen-induced cracking test: In accordance with ISO3690-2012, the diffusible H content of the steel materials of each example was measured and obtained. Among them, the higher the diffusible H content, the lower the hydrogen-induced cracking resistance of the steel material, and the higher the risk of delayed cracking. The lower the diffusible H content, the higher the hydrogen-induced cracking resistance of the steel material, and the lower the risk of delayed cracking.

[0105] The performance test results of the hydrogen-induced cracking-resistant cold-rolled galvanized ultra-high-strength dual-phase steel of Examples 1-7 are listed in Table 4.

[0106]

Table 4

[0107] Referring to Table 4, it can be seen that the hydrogen-induced cracking-resistant cold-rolled galvanized ultra-high-strength dual-phase steel obtained in Examples 1-7 according to the present invention all have excellent mechanical properties, with a yield strength of 840-940 MPa, a tensile strength of 1190-1260 MPa, and an elongation of 8-11%.

[0108] In addition, the hydrogen-induced cracking-resistant cold-rolled galvanized ultra-high-tensile dual-phase steel of Examples 1-7 designed according to the present invention also has very excellent hydrogen-induced cracking resistance, with a diffusible H content of 0.07-0.15 ppm, and has good prospects for popularization and application.

[0109] Figure 1 schematically shows the control process when the manufacturing method of the hydrogen-induced cracking-resistant cold-rolled galvanized ultra-high-strength steel of the present invention performs a continuous galvanized recrystallization annealing process and cooling after galvanizing in one embodiment.

[0110] As shown in Fig. 1, in the present invention, when performing a continuous hot-dip galvanized recrystallization annealing process, first, the cold-rolled sheet is heated to the soaking temperature T1 at the heating rate V1, then held for the time t1. After that, the steel sheet after soaking treatment is first slowly cooled to the intermediate temperature T2 at the cooling rate V2, then cooled to the galvanizing temperature T3 at the rapid cooling rate V3, and then held for the time t3. After the above steps are completed, the steel sheet is sent to a zinc pot for galvanizing.

[0111] Accordingly, after the completion of galvanizing, it is necessary to cool the steel sheet. The galvanized steel sheet is rapidly cooled to the holding temperature T4 at the cooling rate V4, held at this holding temperature for the time t4, and finally cooled at the cooling rate V5.

[0112] Fig. 2 is a photograph of the microstructure of the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high-strength dual-phase steel of Example 1.

[0113] As shown in Fig. 2, in this example, the volume fraction of the light-colored ferrite of the hydrogen-induced cracking-resistant cold-rolled hot-dip galvanized ultra-high-strength dual-phase steel of Example 1 is about 30%. At the same time, due to the atomization effect of the microalloying elements, the tissue particles become finer.

[0114] It should be noted that the combination method of each technical feature in this application is not limited to the combination method described in the claims of this application or the combination method specifically described in the examples. All the technical features described in this application can be freely combined or combined in any way as long as they do not conflict with each other.

[0115] It should be noted that the examples listed above are only specific examples of the present invention. Of course, the present invention is not limited to the above examples, and similar changes or deformations made based on the examples are directly derivable or easily associable by those skilled in the art from the content disclosed in the present invention and belong to the protection scope of the present invention.

Claims

1. It includes a substrate and a zinc plating layer plated on the substrate, wherein the substrate is a cold-rolled hot-dip galvanized dual-phase steel containing Fe and inevitable impurity elements, and the substrate contains the following chemical elements in the following mass percentages: C: 0.1 - 0.18%, Mn: 2.2 - 3.0%, Si: 0.2 - 0.6%, Al: 0.03 - 0.3%, Nb: 0.01 - 0.1%, Ti: 0.01 - 0.1%, Mo: 0.04 - 0.2%, B: 0.0005 - 0.003%; The substrate is characterized in that the matrix of the microstructure is ferrite + martensite, and the microstructure also contains carbide precipitation phases with a size of less than 100 nm. This is a cold-rolled hot-dip galvanized dual-phase steel.

2. The mass percentages of the chemical elements of the substrate are C: 0.1 - 0.18%, Mn: 2.2 - 3.0%, Si: 0.2 - 0.6%, Al: 0.03 - 0.3%, Nb: 0.01 - 0.1%, Ti: 0.01 - 0.1%, Mo: 0.04 - 0.2%, B: 0.0005 - 0.003%, and the balance is Fe and inevitable impurities. The cold-rolled hot-dip galvanized dual-phase steel according to Claim 1 is characterized by this.

3. The chemical elements of the substrate further contain at least one of the following in the following mass percentages: V: 0.005 - 0.2%, Cr: 0.01 - 0.8%, Cu: 0.003 - 0.5%. The cold-rolled hot-dip galvanized dual-phase steel according to Claim 1 is characterized by this.

4. The mass percentage contents of Si, Al, Mo, and Cr in the substrate satisfy Si + Al + Cr + Mo ≤ 1.0%. The cold-rolled hot-dip galvanized dual-phase steel according to Claim 1 is characterized by this.

5. Among the inevitable impurities in the substrate, the mass percentage contents of P, S, and N satisfy P ≤ 0.02%, S ≤ 0.01%, and N ≤ 0.008%. The cold-rolled hot-dip galvanized dual-phase steel according to Claim 1 is characterized by this.

6. The carbide precipitation phase and the matrix are in an aggregated state or a semi-aggregated state. The cold-rolled hot-dip galvanized dual-phase steel according to Claim 1 is characterized by this.

7. The volume ratio of ferrite in the microstructure of the substrate is 10 - 40%. The cold-rolled hot-dip galvanized dual-phase steel according to Claim 1 is characterized by this.

8. The thickness of the zinc plating layer on one side of the substrate is 5 - 200 μm. The cold-rolled hot-dip galvanized dual-phase steel according to Claim 1 is characterized by this.

9. The cold-rolled hot-dip galvanized dual-phase steel has a yield strength ≧ 800 MPa, a tensile strength ≧ 1180 MPa, an elongation A ５０ ≧ 6%, and a diffusible hydrogen content ≦ 0.2 ppm, and is the cold-rolled hot-dip galvanized dual-phase steel according to claim 1, characterized in that.

10. A method for manufacturing a cold-rolled hot-dip galvanized dual-phase steel according to any one of Claims 1 to 9, comprising the following steps: (1) Smelting and casting; (2) Hot rolling; (3) Pickling; (4) Cold rolling; (5) Recrystallization annealing for hot-dip galvanizing: (a) Heating the steel sheet to a soaking temperature T1 at a heating rate V1 of 1 to 20 °C / s, and holding for 30 to 240 s, where T1 > 760 °C; (b) Cooling the steel sheet after soaking to an intermediate temperature T2 at a cooling rate V2 of 2 to 20 °C / s, where T2 = 600 to 780 °C; (c) Cooling the steel sheet to a galvanizing temperature T3 at a cooling rate V3 of 5 to 60 °C / s, and holding for 20 to 300 seconds, where V3 > V2 and the galvanizing temperature is 400 to 500 °C; (d) Sending the steel sheet to a zinc pot for galvanizing; (6) Cooling after galvanizing: After the galvanizing is completed, rapidly cooling to 200 °C or lower at a cooling rate of 10 °C / s or more, holding for 15 to 100 s within the temperature range of 100 °C to 300 °C, and then cooling to room temperature at a cooling rate of 5 °C / s or more. A method for manufacturing a cold-rolled hot-dip galvanized dual-phase steel, characterized by including the above.

11. In the step (2), the slab is heated at 1180 to 1280 °C, the holding time is 0.5 to 4 h, the final rolling temperature is controlled to be 850 °C or higher, and the coiling temperature is controlled to be 700 °C or lower. The manufacturing method according to Claim 10, characterized by this.

12. In the step (4), the cold rolling reduction is controlled to be 30 to 70%. The manufacturing method according to Claim 10, characterized by this.

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