Galvanized dual-phase steel with different yield strength grades and 780 MPa tensile strength grade and manufacturing method thereof

Abstract

The invention discloses galvanized dual-phase steel with different yield strength levels and 780 MPa tensile strength levels and a manufacturing method of the galvanized dual-phase steel. The method comprises the following steps: providing a continuous casting sheet billet comprising the following components in percentage by mass: 0.06%-0.09% of C, 0.10%-0.25% of Si, 1.9%-2.3% of Mn, 0.40%-0.70% of Als, 0.01%-0.025% of Nb, 0.22%-0.30% of Cr, 0.15%-0.20% of Mo, less than or equal to 0.015% of P, less than or equal to 0.025% of S, less than or equal to 0.005% of N and the balance of Fe; carrying out hot rolling treatment on the continuous casting sheet billet to obtain a hot rolled steel coil; pickling the hot rolled steel coil to obtain a pickled steel coil; performing cold rolling on the pickled steel coil to obtain a cold hard coil; and annealing and galvanizing the cold hard coil to obtain the galvanized steel sheet.

Description

Technical Field

[0001] The present application belongs to the field of metallurgical technology, and in particular relates to a galvanized dual-phase steel with different yield strength levels and 780 MPa tensile strength level and a manufacturing method thereof. Background Art

[0002] Galvanized duplex steel is a material with good cost and performance in automotive structural parts. It has good corrosion resistance, high initial work hardening rate, high collision energy absorption capacity, good welding performance, and good matching of strength and ductility. Its application in automobiles is gradually increasing. At the same time, with the development of lightweight automobiles, users' increasingly high requirements for automobile corrosion protection, and the environmental protection problems faced by the automobile industry, automobile lightweighting has become an important development strategy for the automobile industry. According to relevant research, under the premise of ensuring personnel safety, every 10% weight reduction of the automobile will reduce fuel consumption by about 8% and emissions by about 4%. Therefore, automobile lightweighting is the best means of energy conservation and emission reduction. While reducing the thickness and weight of steel plates, personnel safety must be ensured, which inevitably requires the improvement of the strength of steel plates. At present, the application of galvanized duplex steel with a tensile strength of 780MPa in automobiles is becoming more and more widespread. With the rapid development of new energy vehicles, new energy vehicles have higher requirements for weight reduction than fuel vehicles. Structural parts, reinforcements, battery packs and other parts all use galvanized duplex steel with a tensile strength of 780MPa. Different usage scenarios have different strength requirements for materials. Taking the battery pack of new energy vehicles as an example, this component generally does not require large stamping deformation during use. While ensuring formability, it is necessary to have as high a yield strength and tensile strength as possible to reduce the deformation of the battery pack when it is impacted. Compared with the battery pack, structural parts and reinforcements have a larger stamping deformation. While ensuring strength, they need to have a lower yield strength, higher elongation and hole expansion rate to reduce stamping cracking. Therefore, it is necessary to develop galvanized duplex steel with 780MPa tensile strength level at different yield strength levels according to user needs.

[0003] However, due to the production organization problems of enterprises, it is difficult to meet the requirements of galvanized duplex steel with different yield strength levels and 780MPa tensile strength level to achieve both multi-performance and rapid production. Summary of the invention

[0004] The embodiment of the present application provides a method for manufacturing galvanized dual-phase steels with different yield strength levels and 780 MPa tensile strength level, which can use continuous casting slabs of the same composition system to produce galvanized dual-phase steels with yield strengths of 420 MPa to 550 MPa, 500 MPa to 650 MPa, and tensile strengths of ≥780 MPa.

[0005] In a first aspect, the present application provides a method for manufacturing galvanized dual-phase steel with different yield strength levels and 780 MPa tensile strength level, comprising: providing a continuous casting slab, wherein the continuous casting slab comprises the following components in terms of mass percentage: C: 0.06% to 0.09%, Si: 0.10% to 0.25%, Mn: 1.9% to 2.3%, Als: 0.40% to 0.70%, Nb: 0.01% to 0.025%, Cr: 0.22% to 0.30%, Mo: 0.15% to 0.20%, P≤0.015%, S≤0.025%, N≤0. .005%, and the rest are Fe and unavoidable impurities; the continuous casting slab is hot rolled at 1220℃~1290℃ to obtain hot rolled steel coil; wherein, the finishing rolling temperature in the hot rolling treatment is 850℃~930℃, and the coiling temperature is 520℃~640℃; the hot rolled steel coil is pickled to obtain the pickled steel coil; the pickled steel coil is cold rolled to obtain the chilled coil; wherein, the total reduction rate of the cold rolling is 55%~67%; the chilled coil is annealed and galvanized to obtain the galvanized steel sheet; wherein, the annealing temperature is 755℃~770℃ or 775℃~790℃.

[0006] According to an embodiment of the first aspect of the present application, providing the continuous casting slab includes: obtaining the continuous casting slab by smelting according to the chemical composition of the continuous casting slab.

[0007] According to an embodiment of the first aspect of the present application, the thickness of the continuous casting slab is 220 mm to 260 mm.

[0008] According to an embodiment of the first aspect of the present application, hot rolling the continuously cast slab at 1220°C to 1290°C includes: heating the continuously cast slab to 1220°C to 1290°C; sequentially performing rough rolling and finish rolling on the continuously cast slab heated to 1220°C to 1290°C to obtain hot-rolled steel; and coiling the hot-rolled steel to obtain a hot-rolled steel coil.

[0009] According to an embodiment of the first aspect of the present application, the continuous casting slab is heated at 1220° C. to 1290° C. for a heating time of 150 minutes to 400 minutes.

[0010] According to an embodiment of the first aspect of the present application, the thickness of the hot-rolled steel coil is 2.4 mm to 4.5 mm.

[0011] According to an embodiment of the first aspect of the present application, the temperature of the pickling treatment of the hot-rolled steel coil is ≥75°C, and the concentration of the acid solution is ≥100g / L.

[0012] According to the embodiment of the first aspect of the present application, the manufacturing method of galvanized dual-phase steel with different yield strength levels of 780MPa also includes: performing skin-finishing and tension-correcting treatment on the galvanized steel sheet, wherein the skin-finishing elongation of the galvanized steel sheet subjected to skin-finishing treatment is 0.3% to 0.6%, the skin-finishing rolling force is ≥200T, and the tension-correcting elongation of the galvanized steel sheet subjected to tension-correcting treatment is 0.05% to 0.15%.

[0013] According to an embodiment of the first aspect of the present application, the manufacture of galvanized dual-phase steel with a yield strength of 420MPa to 550MPa and a tensile strength level of 780MPa includes: hot rolling the continuous casting slab at 1220℃ to 1290℃ to obtain a hot-rolled steel coil; wherein the finishing rolling temperature in the hot rolling process is 850℃ to 930℃, and the coiling temperature is 560℃ to 640℃.

[0014] According to an embodiment of the first aspect of the present application, the manufacture of galvanized dual-phase steel with a yield strength of 500MPa to 650MPa and a tensile strength level of 780MPa includes: hot rolling the continuous casting slab at 1220℃ to 1290℃ to obtain a hot-rolled steel coil; wherein the finishing rolling temperature in the hot rolling process is 850℃ to 930℃, and the coiling temperature is 520℃ to 600℃.

[0015] In the second aspect, the present application provides a galvanized duplex steel, which is prepared according to the above-mentioned method for manufacturing galvanized duplex steel with different yield strength levels and 780MPa tensile strength levels. The galvanized duplex steels have a yield strength of 420MPa to 550MPa, a tensile strength of ≥780MPa, and an elongation of ≥17%; and a yield strength of 500MPa to 650MPa, a tensile strength of ≥780MPa, and an elongation of ≥14%.

[0016] According to an embodiment of the second aspect of the present application, the thickness of the galvanized dual-phase steel is 0.8 mm to 2.0 mm.

[0017] The manufacturing method of galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level in the embodiment of the present application can use continuous casting slabs of the same composition system to produce galvanized dual-phase steel with yield strengths of 420MPa-550MPa, 500MPa-650MPa, and tensile strength ≥780MPa, thereby solving the problem that it is difficult to simultaneously take into account the multiple performances and rapid production of galvanized dual-phase steel, meeting the requirements of production organization, reducing the production costs of the enterprise, and ensuring the requirements for multi-level performance of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 It is a flow chart of a method for manufacturing galvanized dual-phase steel with different yield strength levels and 780 MPa tensile strength level provided in an embodiment of the present application.

[0020] Figure 2 This is the metallographic structure diagram of galvanized dual-phase steel with a yield strength of 420 MPa and a tensile strength of 780 MPa provided in Example 3 of the present application.

[0021] Figure 3 This is the metallographic structure diagram of galvanized dual-phase steel with a yield strength of 500 MPa and a tensile strength of 780 MPa provided in Example 7 of the present application. DETAILED DESCRIPTION

[0022] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0023] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0024] The inventors of the present application discovered that galvanized duplex steel can obtain a suitable dual-phase structure of martensite and ferrite to ensure strength through reasonable composition design and controlled rolling and controlled cooling process. By controlling the different martensite contents in the galvanized duplex steel with a tensile strength level of 780MPa, galvanized duplex steel with different yield strength levels can be obtained. Based on this principle, a manufacturing method for galvanized duplex steel with different yield strength levels and 780MPa tensile strength level can be developed.

[0025] In order to solve the problems of the prior art, the present invention provides a galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level and a manufacturing method thereof. The manufacturing method of the galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level provided by the present invention is first introduced below.

[0026] Figure 1 A schematic flow chart of a method for manufacturing galvanized dual-phase steels with different yield strength levels and 780 MPa tensile strength level provided in an embodiment of the present application is shown.

[0027] like Figure 1 As shown, the manufacturing method of galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level includes: providing a continuous casting slab, wherein the continuous casting slab includes the following components in terms of mass percentage: C: 0.06% to 0.09%, Si: 0.10% to 0.25%, Mn: 1.9% to 2.3%, Als: 0.40% to 0.70%, Nb: 0.01% to 0.025%, Cr: 0.22% to 0.30%, Mo: 0.15% to 0.20%, P≤0.015%, S≤0.025%, N≤0.005% , the rest are Fe and unavoidable impurities; hot rolling the continuous casting slab at 1220℃~1290℃ to obtain hot rolled steel coil; wherein the finishing rolling temperature in the hot rolling treatment is 850℃~930℃, and the coiling temperature is 560℃~640℃; pickling the hot rolled steel coil to obtain pickled steel coil; cold rolling the pickled steel coil to obtain chilled coil; wherein the total reduction rate of cold rolling is 55%~67%; annealing and galvanizing the chilled coil to obtain galvanized steel sheet; wherein the annealing temperature is 755℃~770℃ or 775℃~790℃.

[0028] The manufacturing method of galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level in the embodiment of the present application effectively controls the key process parameters of each process to achieve the use of the same component system, and sequentially provides continuous casting slabs, hot rolling, pickling, cold rolling and galvanizing processes through steelmaking to produce galvanized dual-phase steel with two different yield strengths of 420MPa to 550MPa and 500MPa to 650MPa, and the tensile strength is ≥780MPa. The manufacturing method can meet the requirements of production organization, reduce the production cost of the enterprise, and ensure the requirements for multi-level performance of the product.

[0029] The manufacturing method of galvanized duplex steel with different yield strength levels and 780MPa tensile strength levels in the embodiment of the present application, the development of galvanized duplex steel with different yield strength levels and 780MPa tensile strength levels can meet different stamping requirements, solve the production organization problems of enterprises, ensure delivery time, and reduce unnecessary losses. At the same time, since the production of galvanized duplex steel with a tensile strength of 780MPa has high requirements for equipment capacity, technical level, and on-site production stability control, the product has good benefits. Therefore, the use of continuous casting slabs with the same component system to produce galvanized duplex steel with more than two yield strength levels and 780MPa tensile strength levels is not only conducive to the rapid organization of production of steel production enterprises, reducing enterprise production costs, and bringing certain benefits, but also can meet the requirements of the automotive industry for multiple parts, multiple performance, and fast delivery, thereby solving the problem that it is difficult to take into account the multiple performance and rapid production of galvanized duplex steel at the same time.

[0030] The manufacturing method of galvanized dual-phase steels with different yield strength levels and 780MPa tensile strength level in the embodiments of the present application improves the hardenability of austenite during critical zone annealing by reasonably selecting chemical element components and their contents, especially by controlling the reasonable C, Si, Mn, Cr, Al, Mo, and Nb contents in the galvanized dual-phase steel, ensures the martensite content in the galvanized dual-phase steel structure, and controls S and N at extremely low contents, thereby ensuring that the galvanized dual-phase steel has good mechanical properties and formability.

[0031] In the manufacturing method of galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level in the embodiment of the present application, the manufacturing method adopts low-carbon components and adds low-cost alloys such as Si and Mn, and adds suitable Al, Nb, Cr, and Mo alloys to ensure product performance and process feasibility.

[0032] In the embodiments of the present application, the composition of the continuous casting slab obtained by steelmaking, the hot rolling treatment and the coiling temperature after rolling, the pickling treatment, the cold rolling and the galvanizing treatment play an important role in obtaining galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level.

[0033] In some embodiments of the present application, providing the continuous casting slab includes: smelting the continuous casting slab according to the chemical composition of the continuous casting slab. The smelting can be performed according to a smelting method commonly known in the art to obtain the continuous casting slab.

[0034] In some embodiments of the present application, the thickness of the continuous casting slab is 220 mm to 260 mm.

[0035] In some embodiments of the present application, the continuous casting slab is heated at 1220° C. to 1290° C. for a heating time of 150 minutes to 400 minutes.

[0036] In some embodiments of the present application, the thickness of the hot-rolled steel coil is 2.4 mm to 4.5 mm.

[0037] In some embodiments of the present application, the temperature of the pickling treatment for the hot-rolled steel coil is ≥75°C, and the acid concentration is ≥100g / L. Exemplarily, the acid concentration is 110g / L, 120g / L, 125g / L, 140g / L, 150g / L, 160g / L, 170g / L, 180g / L. The present application ensures the pickling effect of the surface of the hot-rolled steel coil and the surface quality after galvanizing by controlling the pickling process.

[0038] In some embodiments of the present application, the manufacturing method of galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level also includes: performing skin-finishing and tension-correcting treatment on the galvanized steel sheet, wherein the skin-finishing elongation of the galvanized steel sheet subjected to skin-finishing treatment is 0.3% to 0.6%, the skin-finishing rolling force is ≥200T, and the tension-correcting elongation of the galvanized steel sheet subjected to tension-correcting treatment is 0.05% to 0.15%.

[0039] In some embodiments of the present application, manufacturing galvanized dual-phase steel with a yield strength of 420MPa~550MPa and a tensile strength level of 780MPa includes: hot rolling the continuous casting slab at 1220℃~1290℃ to obtain a hot-rolled steel coil; wherein the finishing rolling temperature in the hot rolling process is 850℃~930℃, and the coiling temperature is 560℃~640℃.

[0040] In some embodiments of the present application, manufacturing galvanized dual-phase steel with a yield strength of 500MPa~650MPa and a tensile strength level of 780MPa includes: hot rolling the continuous casting slab at 1220℃~1290℃ to obtain a hot-rolled steel coil; wherein the finishing rolling temperature in the hot rolling process is 850℃~930℃, and the coiling temperature is 520℃~600℃.

[0041] The manufacturing method of the present application realizes different yield strength levels of galvanized duplex steel products by adopting different coiling processes, that is, by controlling the grain size and precipitates of the hot-rolled substrate (i.e., continuous casting slab), starting from the performance of the hot-rolled substrate and obtaining different substrate strength indicators. In the present application, the hot rolling treatment and the coiling temperature after rolling play an important role in achieving different yield strength levels of galvanized duplex steel. By controlling different coiling temperatures, controlling the grain size and precipitates of the hot-rolled continuous casting slab to achieve different substrate strength indicators, galvanized duplex steel products with different yield strength levels are obtained.

[0042] In the manufacturing method of the present application, the cold rolling adopts a single-stand rolling process, which plays an important role in achieving different yield strength levels. The single-stand rolling can ensure that the pickled steel coil has a suitable cold rolling reduction rate, further obtain better performance and organization, and ensure that the galvanized steel coil obtains higher strength, stable performance and uniform organization after galvanizing annealing, while solving the problem of difficulty in ultra-high strength acid continuous rolling.

[0043] In the manufacturing method of the present application, the annealing temperature before galvanizing plays an important role in achieving different yield strength levels. By controlling different annealing temperatures, the transformation amount of austenite, the grain size during the heating process, and the transformation mode and transformation amount of austenite during the cooling process are controlled to achieve different strength indicators of galvanized dual-phase steel.

[0044] The present application adopts the above-mentioned manufacturing method to prepare galvanized dual-phase steels with different yield strength levels and 780MPa tensile strength level. The process is simple and easy to control. Galvanized dual-phase steels with two different yield strength levels of 420MPa and 500MPa and tensile strength of 780MPa are prepared. The thickness of each steel is 0.8mm to 2.0mm, which can meet the requirements of the automotive steel plate field.

[0045] The manufacturing method of galvanized dual-phase steel with different yield strengths and 780MPa tensile strength grade in the embodiment of the present application mainly adopts galvanizing continuous annealing, and realizes the production of steel plates with different structures and properties through temperature control. The process is simple, operability is strong, and cost is low.

[0046] In the manufacturing method of the present application, the functions of the key chemical composition ratios and process steps are as follows:

[0047] 1) Ratio and function of key chemical components

[0048] C: Carbon is an indispensable and economical strengthening element in steel, which affects the strength and formability of steel plates. As the carbon content increases, the strength of the steel increases, while the formability decreases. Therefore, the carbon content should not be too high. The C content in the continuous casting slab of this application should be controlled within the range of 0.06% to 0.09%.

[0049] Si: Silicon is a strengthening element that improves the strength of materials. As the silicon content increases, the material strength increases. At the same time, when the silicon content is high, it is easy to generate iron oxide scale that is difficult to pickle, and it will also cause leakage after galvanizing, affecting the surface quality of the steel plate. Therefore, the Si content should be controlled at 0.10% to 0.25%.

[0050] Mn: Manganese is a material strengthening element like silicon. Adding a small amount of manganese to steel is beneficial to improving the strength of steel. At the same time, adding a certain amount of manganese can combine with sulfur to form MnS, avoiding hot brittle quality problems and reducing the possibility of rust perforation caused by MnS inclusions. However, when adding too much zinc plating, it is easy to generate oxides and cause leakage plating, which is also not conducive to stamping processing. Therefore, the Mn content should be controlled at 1.9% to 2.3%.

[0051] Cr: Chromium can significantly delay the transformation of pearlite and bainite, thereby allowing austenite to fully transform into martensite structure. Therefore, chromium is added in the present invention. In this application, Cr should be controlled at 0.22% to 0.30%.

[0052] P: Phosphorus can improve the strength of materials, but it can also cause cold brittleness of materials. Therefore, the P content should be as low as possible and should be controlled at ≤0.015%.

[0053] S: Sulfur can increase material strength and reduce plastic forming properties. At the same time, sulfur can cause hot brittleness and affect the surface quality of steel plates. In addition, sulfur will combine with Mn in steel to produce MnS inclusions, which can easily become the starting point of rust perforation. Therefore, the S content should be as low as possible and should be controlled at ≤0.025%.

[0054] Als: Aluminum is added as a deoxidizer during steelmaking. When the content is less than 0.01%, the inclusions in the steel increase and the stamping performance deteriorates. At the same time, aluminum can refine the grains, fix the N in the steel, and increase the transformation temperature of martensite. Therefore, the Al content in this application should be controlled at 0.40% to 0.70%.

[0055] N: Nitrogen and aluminum combine to form AlN precipitates. Dispersed AlN particles hinder grain growth, refine grains, significantly increase strength, and reduce formability. Therefore, the N content should be controlled at ≤0.005%.

[0056] Nb: Niobium can form carbon and nitrogen compounds with C and N, and precipitate at the phase interface during the transformation from austenite to ferrite, preventing the growth of ferrite grains and playing a role in grain refinement; when Nb is added to a certain value, it can produce precipitation strengthening. In this application, the Nb content should be controlled at 0.01% to 0.025%.

[0057] Mo: Molybdenum can be dissolved in ferrite, austenite and carbide in steel, improving the hardenability of steel and is an element that reduces the austenite phase area. Molybdenum has a solid solution strengthening effect on ferrite and can also improve the stability of carbides, thereby increasing the strength of steel. At the same time, adding molybdenum can greatly improve the stability of the metastable structure of steel and ensure the acquisition of dual-phase structure. The Mo content in this application should be controlled at 0.15% to 0.20%.

[0058] 2) Key process steps and functions

[0059] ① Finishing rolling temperature: The finishing rolling temperature in hot rolling treatment is higher than the austenite zone temperature of Ar3. If the temperature is too high, the scale will be serious and difficult to pickle, affecting the surface quality of the steel plate; if the temperature is too low, mixed crystals will appear when entering the two zones, and snowflake defects will be generated during stamping, affecting the appearance of enamel products. Therefore, the finishing rolling temperature of hot rolling treatment is generally controlled at 850℃~930℃.

[0060] ② Coiling temperature: High coiling temperature is conducive to grain growth, reducing strength and improving formability. However, too high coiling temperature will cause serious iron scale on the surface of the steel plate and make it difficult to pickle, affecting the quality of the steel plate. Therefore, the coiling temperature control range is: the yield strength 420MPa level is controlled at 560℃~640℃, and the yield strength 500MPa level is controlled at 520℃~600℃.

[0061] ③ Pickling process: Hot-rolled steel coils will inevitably generate iron oxide scale. Under the condition that the iron oxide scale is controllable, unreasonable pickling process will lead to unclean pickling of the surface iron oxide scale, resulting in oxide intrusion and over-pickling. Therefore, the pickling process is controlled as follows: pickling temperature ≥ 75℃, acid concentration ≥ 100g / L.

[0062] ③Cold rolling deformation: The pickled steel coil is cold rolled and rolled to obtain a cold hardened coil. A larger cold rolling deformation can reduce the recrystallization temperature and phase transformation temperature, obtain higher strength and ensure the uniformity of strength and structure; but too much deformation will increase the difficulty of rolling. Therefore, the cold rolling deformation should be selected according to the actual situation of the single stand, and the total cold rolling reduction rate is between 55% and 67%.

[0063] ④ Galvanizing annealing temperature: The appropriate heating section temperature can ensure the production of the appropriate amount of austenite in the annealing furnace. Too high or too low temperature will result in too much or too little austenite, and the appropriate martensite and ferrite dual-phase structure cannot be obtained after cooling. Therefore, the annealing temperature of the yield strength of 420MPa is controlled between 755℃ and 770℃, and the annealing temperature of the yield strength of 500MPa is controlled between 775℃ and 790℃.

[0064] ⑤ Leveling elongation: The purpose of leveling is to eliminate the yield platform of the steel plate, avoid the tensile strain mark defects in the stamping process, and improve the plate shape and the surface quality of the galvanized surface. The characteristic of galvanized duplex steel products is that there is no yield platform. The main purpose of galvanized duplex steel skin finishing is to improve the plate shape and surface quality. Therefore, the control range of leveling elongation is more suitable between 0.3% and 0.6%.

[0065] ⑥ Elongation of straightening: The purpose of straightening is to adjust and optimize the plate shape to avoid side waves and middle waves. If the elongation of straightening is too low, the plate shape will be bad. If the elongation of straightening is too high, straightening lines will easily appear. Therefore, it is more appropriate to control the flat elongation in the range of 0.05% to 0.15%.

[0066] The technical solution of the present application is further described in detail below in conjunction with specific embodiments.

[0067] Examples 1-10

[0068] According to the manufacturing method of galvanized dual-phase steel with different yield strength levels and 780 MPa tensile strength level in the present application, according to the steel smelting process, a continuous casting slab meeting the continuous casting slab composition definition shown in Table 1 below is provided:

[0069] Table 1 Chemical composition of the continuous casting slabs of Examples 1-10 and Comparative Examples 1-3

[0070]

[0071] The continuous casting slabs provided in the above-mentioned embodiments 1-10 are heated in a heating furnace, so that the furnace discharge temperature of the continuous casting slabs is 1220°C to 1290°C, the intermediate slabs are subjected to rough rolling for 7 passes, the intermediate slabs have an intermediate thickness of 40 mm, and the intermediate slabs are subjected to finish rolling at a finishing temperature of 850°C to 900°C to obtain hot-rolled steel coils; the coiling temperature of the hot-rolled steel coils of embodiments 1-5 is 560°C to 640°C, and the coiling temperature of the hot-rolled steel coils of embodiments 6-10 is 520°C to 600°C;

[0072] After the hot rolled steel coil is stretched and leveled to break the phosphorus, it is pickled, the temperature of the pickling treatment is ≥75°C, and the concentration of HCl acid in the acid tank is ≥100g / L, to obtain the pickled steel coil;

[0073] The pickled steel coil is cold rolled by a single stand with 6 passes to obtain a cold hardened coil with a thickness of 0.8 mm to 2.0 mm; wherein the total reduction rate of the cold rolling is 55% to 67%;

[0074] The cold hardened coil is galvanized after continuous annealing. The annealing temperature of the galvanized dual-phase steel of Examples 1-5 is controlled at 755°C to 770°C, and the annealing temperature of the galvanized dual-phase steel of Examples 6-10 is controlled at 775°C to 790°C. The skin-pass rolling force is ≥200T, and the tensile elongation is 0.05% to 0.15%. Finally, the import and export coiling and sub-coiling are obtained to obtain hot-dip galvanized steel coils with a thickness of 0.8mm to 2.0mm. The process parameters for preparing the galvanized dual-phase steel of Examples 1-10 and Comparative Examples 1-3 are specifically shown in Table 2.

[0075] Table 2 Rolling process parameters of galvanized dual-phase steel of Examples 1-10 and Comparative Examples 1-3

[0076]

[0077] The galvanized dual-phase steels of Examples 1-10 and Comparative Examples 1-3 were subjected to performance tests according to GB / T 228-2010, and the mechanical property test results of Examples 1-10 and Comparative Examples 1-3 are recorded in the following Table 3:

[0078] Table 3 Mechanical properties test results of galvanized dual-phase steel of Examples 1-10 and Comparative Examples 1-3

[0079] Case Thickness / mm Width / mm Yield strength / MPa Tensile strength / MPa Elongation after break / % Example 1 0.8 1000 475 808 19.5 Example 2 1.0 1250 440 792 20 Example 3 1.2 1250 447 802 19 Example 4 1.5 1200 467 807 20.5 Example 5 2.0 1200 468 793 19 Example 6 0.8 900 541 851 16 Example 7 1.0 1200 565 861 16.5 Example 8 1.2 1150 546 846 16.5 Example 9 1.5 1150 569 865 15 Example 10 2.0 1200 529 856 17.5 Comparative Example 1 1.2 1150 404 768 22 Comparative Example 2 2.0 1200 668 902 10.5 Comparative Example 3 1.2 1150 413 789 19

[0080] As can be seen from Table 2 and Table 3, compared with the galvanized dual-phase steels of Comparative Examples 1-3, they do not meet the limited range of the component content or process parameters of the manufacturing method of the present application, and the galvanized dual-phase steels obtained either have a qualified elongation after fracture, but the yield strength and tensile strength do not meet the standards, or the yield strength and tensile strength meet the standards, but the elongation after fracture does not meet the standards, or the tensile strength and elongation after fracture meet the standards, but the yield strength does not meet the standards.

[0081] According to the manufacturing method of galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level of the present application, Examples 1-5 prepared galvanized dual-phase steel with a yield strength of 440MPa-475MPa and a tensile strength of 780MPa at a coiling temperature of 580℃-618℃, and the elongation after fracture reached more than 19%. Examples 6-10 prepared galvanized dual-phase steel with a yield strength of 529MPa-569MPa and a tensile strength of 780MPa at a coiling temperature of 542℃-577℃, and the elongation after fracture reached more than 15%, meeting the requirements of galvanized dual-phase steel for automobiles. Among them, Figure 2 As shown, the product structure of the galvanized dual-phase steel of Example 3 is ferrite + martensite, where M represents martensite and F represents ferrite. Figure 3 As shown, the product structure of the galvanized dual-phase steel of Example 7 is ferrite+martensite, M represents martensite, and F represents ferrite. Figure 2 and Figure 3The grain sizes of martensite and ferrite in the above embodiment 3 and embodiment 7 are obviously different. The metallographic structure diagrams of the above embodiment 3 and embodiment 7 prove that the manufacturing method of the present application can finally obtain metallographic structures with different grain sizes through different process controls, thereby being able to produce galvanized dual-phase steels with different yield strengths and 780MPa tensile strength levels. Figure 2 and Figure 3 The ferrite and martensite in the Figure 3 The martensite density in the steel is higher and the structure is finer, so its corresponding yield strength and tensile strength are also higher.

[0082] The above is only a specific implementation method of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working process described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. It should be understood that the protection scope of the present application is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application.

Claims

1. A method for manufacturing galvanized dual-phase steel with different yield strength levels and 780MPa tensile strength level, characterized in that: include: A continuous casting slab is provided, wherein the continuous casting slab comprises the following components, measured by mass percentage: C: 0.06% to 0.09%, Si: 0.10% to 0.25%, Mn: 1.9% to 2.3%, Als: 0.40% to 0.70%, Nb: 0.01% to 0.025%, Cr: 0.22% to 0.30%, Mo: 0.15% to 0.20%, P≤0.015%, S≤0.025%, N≤0.005%, and the remainder is Fe and unavoidable impurities; The continuous casting slab is hot rolled at 1220°C to 1290°C to obtain a hot rolled steel coil; wherein the finishing rolling temperature in the hot rolling process is 850°C to 930°C, and the coiling temperature is 520°C to 640°C; Performing pickling treatment on the hot-rolled steel coil to obtain a pickled steel coil; The pickled steel coil is cold rolled to obtain a chilled coil; wherein the total reduction ratio of the cold rolling is 55% to 67%; The chilled coil is annealed and galvanized to obtain a galvanized steel sheet; wherein the annealing temperature is 755°C to 770°C or 775°C to 790°C.

2. The manufacturing method according to claim 1, characterized in that: Also includes: The galvanized steel sheet is subjected to skin-finishing and straightening treatments, wherein the skin-finishing elongation of the galvanized steel sheet subjected to skin-finishing treatment is 0.3% to 0.6%, the skin-finishing rolling force is ≥ 200T, and the straightening elongation of the galvanized steel sheet subjected to straightening treatment is 0.05% to 0.15%.

3. The manufacturing method according to claim 1, characterized in that: The hot rolling treatment of the continuous casting slab at 1220° C. to 1290° C. comprises: Heating the continuous casting slab to 1220° C. to 1290° C.; The continuous casting slab heated to 1220° C. to 1290° C. is subjected to rough rolling and finish rolling in sequence to obtain hot-rolled steel; The hot-rolled steel material is coiled to obtain a hot-rolled steel coil.

4. The manufacturing method according to claim 1, characterized in that: Meet at least one of the following requirements: The thickness of the continuous casting slab is 220 mm to 260 mm; The thickness of the hot-rolled steel coil is 2.4 mm to 4.5 mm.

5. The manufacturing method according to claim 1, characterized in that: The continuous casting slab is heated at 1220° C. to 1290° C. for 150 minutes to 400 minutes.

6. The manufacturing method according to claim 1, characterized in that: The temperature of the pickling treatment for the hot-rolled steel coil is ≥75°C, and the concentration of the acid solution is ≥100g / L.

7. The manufacturing method according to claim 1 or 2, characterized in that: Galvanized duplex steels with yield strengths of 420MPa to 550MPa and tensile strengths of 780MPa include: The continuous casting slab is hot rolled at 1220°C to 1290°C to obtain a hot rolled steel coil; the finishing rolling temperature in the hot rolling process is 850°C to 930°C, and the coiling temperature is 560°C to 640°C.

8. The manufacturing method according to claim 1 or 2, characterized in that: Galvanized duplex steels with yield strengths of 500MPa to 650MPa and tensile strengths of 780MPa are manufactured as follows: The continuous casting slab is hot rolled at 1220°C to 1290°C to obtain a hot rolled steel coil; the finishing rolling temperature in the hot rolling process is 850°C to 930°C, and the coiling temperature is 520°C to 600°C.

9. A galvanized dual-phase steel, characterized in that: The galvanized dual-phase steel having different yield strength levels and 780 MPa tensile strength level is prepared according to the manufacturing method of any one of claims 1 to 7, wherein the galvanized dual-phase steel has a yield strength of 420 MPa to 550 MPa, a tensile strength of ≥780 MPa, and an elongation of ≥17%.

10. A galvanized dual-phase steel, characterized in that: The galvanized dual-phase steel is obtained by the manufacturing method of different yield strength levels and 780MPa tensile strength level according to any one of claims 1-6 and 8, wherein the galvanized dual-phase steel has a yield strength of 500MPa to 650MPa, a tensile strength of ≥780MPa, and an elongation of ≥14%.

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