980MPa-grade galvanized dual-phase steel and preparation method thereof

Abstract

The invention provides 980 MPa-grade galvanized dual-phase steel and a preparation method thereof, and the 980 MPa-grade galvanized dual-phase steel is composed of the following components in percentage by mass: 0.06%-0.09% of C, 0.20%-0.30% of Si, 2.2%-2.8% of Mn, 0.10%-0.22% of Al, 0.015%-0.04% of Nb, 0.25%-0.40% of Cr, 0.070%-0.140% of Mo, less than or equal to 0.015% of P, less than or equal to 0.015% of S, less than or equal to 0.007% of N and the balance of Fe and inevitable impurities. On the basis that low-carbon components are adopted and low-cost alloys such as Si and Mn are added, a small amount of Al, Nb, Cr and Mo alloys are added, and the product performance and the process feasibility are guaranteed. By reasonably selecting chemical element components and contents, especially by controlling the reasonable contents of C, Si, Mn, Cr, Al, Mo and Nb, the hardenability of austenite during annealing in a critical zone is improved, the martensite content in the structure is ensured, S and N are controlled to be extremely low, it is ensured that the galvanized steel plate has good mechanical properties and formability, a component system is adopted, and the production cost is reduced. And the 980MPa-grade galvanized dual-phase steel with different yield strength grades can be produced by one steelmaking component.

Description

Technical Field

[0001] The present application relates to the field of metallurgical technology, and in particular to a 980MPa grade galvanized duplex steel and a preparation method thereof. Background Art

[0002] Galvanized duplex steel has the advantages of 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. It is a material with good comprehensive cost and performance in automobile structural parts.

[0003] Lightweighting of automobiles is the best means of energy conservation and emission reduction. To reduce the thickness and weight of steel plates while ensuring personnel safety, it is necessary to improve the strength of steel plates. Currently, the galvanized duplex steel with a tensile strength of 450-780MPa, which is widely used in automobiles, can no longer fully meet the development of lightweighting in the automobile industry. The application of materials with higher strength levels has become the direction of efforts of major automobile companies. Therefore, the application ratio of galvanized duplex steel with a tensile strength of 980MPa in automobiles will gradually increase.

[0004] Automobile OEMs and supporting factories require different yield strength materials for different stamping parts, so there is a demand for galvanized duplex steel of various yield strength levels. At the same time, it also causes the order volume to be relatively dispersed, which brings difficulties to the company's organized production and also brings uncertainty to the customer's delivery time. Summary of the invention

[0005] The embodiment of the present application provides a 980MPa grade galvanized dual-phase steel and a preparation method thereof, which is conducive to the rapid organization of production by steel enterprises, reduces production costs, and can also meet the needs of the automotive industry for multiple parts, multiple performances, and fast delivery.

[0006] In the first aspect, an embodiment of the present application provides a 980 MPa grade galvanized dual-phase steel, composed of the following components by mass fraction: C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 2.2-2.8%, Al: 0.10-0.22%, Nb: 0.015-0.04, Cr: 0.25-0.40%, Mo: 0.070-0.140%, P≤0.015%, S≤0.015%, N≤0.007%, and the rest are Fe and unavoidable impurities.

[0007] According to the embodiment of the first aspect of the present application, the yield strength is 550-730 MPa, the tensile strength is ≥980 MPa, and the elongation is ≥10%.

[0008] According to the embodiment of the first aspect of the present application, the yield strength is 650-900 MPa, the tensile strength is ≥980 MPa, and the elongation is ≥8%.

[0009] According to the embodiment of the first aspect of the present application, the yield strength is 700-900 MPa, the tensile strength is ≥980 MPa, and the elongation is ≥8%.

[0010] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned 980 MPa grade galvanized dual-phase steel, comprising the following steps:

[0011] Continuously casting to obtain a casting billet, the casting billet consists of the following components by mass fraction: C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 2.2-2.8%, Al: 0.10-0.22%, Nb: 0.015-0.04, Cr: 0.25-0.40%, Mo: 0.070-0.014%, P≤0.015%, S≤0.015%, N≤0.005%, and the rest is Fe and unavoidable impurities;

[0012] The ingot is processed through hot rolling, pickling, cold rolling and galvanizing to obtain 980MPa grade galvanized duplex steel.

[0013] According to an embodiment of the second aspect of the present application, the hot rolling process comprises: heating the continuous casting billet at 1180-1250°C for 200-400 minutes; rough rolling, finish rolling and coiling the heated billet to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900°C and the coiling temperature is 540-620°C;

[0014] The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained;

[0015] The cold rolling process includes: cold rolling the pickled coil on a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction rate is 54-67%;

[0016] The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it to obtain a 980MPa grade galvanized dual-phase steel with a yield strength of 550MPa; wherein the annealing temperature is 745-760°C; the galvanized steel sheet is skin-passed and straightened to obtain a galvanized low-alloy high-strength steel sheet; wherein the skin-pass elongation is 0.3-0.6%, the skin-pass rolling force is above 250t, and the straightening elongation is 0.05-0.15%.

[0017] According to an embodiment of the second aspect of the present application, the hot rolling process comprises: heating the continuous casting slab at 1180-1250°C for 200-400 minutes; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900°C and the coiling temperature is 520-600°C;

[0018] The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained;

[0019] The cold rolling process includes: cold rolling the pickled coil on a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction rate is 54-67%;

[0020] The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it; wherein the annealing temperature is 760-775°C; performing skin pass and straightening on the galvanized steel sheet to obtain a galvanized low alloy high strength steel sheet; wherein the skin pass elongation is 0.3-0.6%, the skin pass rolling force is above 280t, and the straightening elongation is 0.05-0.15%.

[0021] According to an embodiment of the second aspect of the present application, the hot rolling process comprises: heating the continuous casting slab at 1180-1250°C for 200-400min; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900°C and the coiling temperature is 500-580°C;

[0022] The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained;

[0023] The cold rolling process includes: cold rolling the pickled coil on a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction rate is 54-67%;

[0024] The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it; wherein the annealing temperature is 775-790°C; the galvanized steel sheet is skin-passed and straightened to obtain a galvanized low-alloy high-strength steel sheet; wherein the skin-pass elongation is 0.3-0.6%, the skin-pass rolling force is above 300t, and the straightening elongation is 0.05-0.15%.

[0025] Compared with the prior art, this application has at least the following beneficial effects:

[0026] In the technical solution of the present application, a small amount of Al, Nb, Cr, and Mo alloys are added on the basis of low-carbon components and low-cost alloys such as Si and Mn, thereby ensuring product performance and process feasibility. By rationally selecting the chemical element composition and content, especially by controlling the reasonable C, Si, Mn, Cr, Al, Mo, and Nb content, the hardenability of austenite during critical zone annealing is improved, the martensite content in the organization is ensured, and S and N are controlled at extremely low contents, thereby ensuring that the galvanized steel sheet has good mechanical properties and formability, and adopting a component system to achieve a steelmaking component to produce 980MPa-grade galvanized duplex steel with different yield strength levels, thereby reducing the production cost of the enterprise and meeting the use requirements of automobile steel sheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly described below; obviously, the drawings described below only involve some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0028] Figure 1 This is the metallographic structure with a yield strength of 550 MPa in Example 1 of the present application.

[0029] Figure 2 This is the metallographic structure with a yield strength of 650 MPa in Example 5 of the present application.

[0030] Figure 3 This is the metallographic structure with a yield strength of 700 MPa in Example 12 of the present application. DETAILED DESCRIPTION

[0031] The following detailed description and drawings of the embodiments of the present application are used to illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0032] In the description of the present application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inside", "outside", etc., indicating the orientation or positional relationship are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. "Vertical" does not require verticality in the strict sense, but may include allowable errors. "Parallel" does not require parallelism in the strict sense, but may include allowable errors.

[0033] Automobile OEMs and supporting plants require different yield strength materials for different stamping parts, so there is a demand for galvanized duplex steel of various yield strength levels, which also causes the order volume to be scattered. Some steel companies' small converters (about 100 tons) are easier to organize production, but currently large domestic steel companies all use 200-300 ton converters, which brings difficulties to the company's production organization and uncertainties to customer delivery time.

[0034] In view of the above problems, the present application provides a method for producing 980MPa galvanized duplex steel with various yield strength levels using a single component system, which is not only conducive to the rapid organization of production and reduction of production costs for steel enterprises, but also can meet the automotive industry's demands for multiple parts, multiple performances and fast delivery.

[0035] 980MPa grade galvanized duplex steel

[0036] In the first aspect, an embodiment of the present application provides a 980 MPa grade galvanized dual-phase steel, composed of the following components by mass fraction: C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 2.2-2.8%, Al: 0.10-0.22%, Nb: 0.015-0.04, Cr: 0.25-0.40%, Mo: 0.070-0.140%, P≤0.015%, S≤0.015%, N≤0.007%, and the rest are Fe and unavoidable impurities.

[0037] In the technical solution of the present application, a small amount of Al, Nb, Cr, and Mo alloys are added on the basis of low-carbon components and low-cost alloys such as Si and Mn, thereby ensuring product performance and process feasibility. By rationally selecting the chemical element composition and content, especially by controlling the reasonable C, Si, Mn, Cr, Al, Mo, and Nb content to improve the hardenability of austenite during critical zone annealing, ensuring the martensite content in the organization, and controlling S and N at extremely low contents, it is ensured that the galvanized steel sheet has good mechanical properties and formability, and adopts a component system to achieve a steelmaking component to produce 980MPa-grade galvanized dual-phase steel with three yield strength levels of 550MPa, 650MPa, and 700MPa, thereby reducing the production cost of the enterprise and meeting the use requirements of automobile steel sheets.

[0038] In this application, the role of the key chemical composition ratio is as follows:

[0039] 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 increases, while the formability decreases. Therefore, the carbon content should not be too high. In this patent, C should be controlled within the range of 0.06-0.09%.

[0040] 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, Si should be controlled at 0.20-0.30%.

[0041] Mn: Manganese is a material strengthening element like silicon. Adding a small amount of manganese to steel is conducive to improving strength. 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, Mn should be controlled at 2.2-2.8%.

[0042] 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 this application. In this patent, Cr should be controlled at 0.25-0.40%.

[0043] 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%.

[0044] 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 ≤0.015%.

[0045] Al: 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, Al in this patent should be controlled at 0.10-0.22%.

[0046] N: Nitrogen and aluminum combine to form AlN precipitates. Dispersed AlN particles hinder grain growth, refine grains, significantly increase strength, and reduce formability. Therefore, N should be controlled at ≤0.007%.

[0047] 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, precipitation strengthening can be produced. In this patent, Nb should be controlled at 0.015-0.04%.

[0048] Mo: Mo can be dissolved in ferrite, austenite and carbide in steel, improving the hardenability of steel and is an element that reduces the austenite phase. Mo 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. In this patent, Mo should be controlled at 0.070-0.14%.

[0049] According to the embodiment of the first aspect of the present application, the yield strength is 550-730 MPa, the tensile strength is ≥980 MPa, and the elongation is ≥10%.

[0050] According to the embodiment of the first aspect of the present application, the yield strength is 650-900 MPa, the tensile strength is ≥980 MPa, and the elongation is ≥8%.

[0051] According to the embodiment of the first aspect of the present application, the yield strength is 700-900 MPa, the tensile strength is ≥980 MPa, and the elongation is ≥8%.

[0052] The present application adopts a component system that can produce 980MPa-grade galvanized duplex steel with three yield strength levels of 550MPa, 650MPa, and 700MPa using one steelmaking component, thereby reducing the production cost of the enterprise and meeting the use requirements of automobile steel plates.

[0053] Preparation method of 980MPa grade galvanized dual-phase steel

[0054] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned 980 MPa grade galvanized dual-phase steel, comprising the following steps:

[0055] Continuously casting to obtain a casting billet, the casting billet consists of the following components by mass fraction: C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 2.2-2.8%, Al: 0.10-0.22%, Nb: 0.015-0.04, Cr: 0.25-0.40%, Mo: 0.070-0.140%, P≤0.015%, S≤0.015%, N≤0.007%, and the rest is Fe and unavoidable impurities;

[0056] The ingot is processed through hot rolling, pickling, cold rolling and galvanizing to obtain 980MPa grade galvanized duplex steel.

[0057] In the present application, steelmaking composition, hot rolling coiling temperature, pickling process, cold rolling process and galvanizing process play an important role in obtaining 980MPa grade galvanized dual-phase steel with different yield strength levels.

[0058] In this application, the hot rolling coiling temperature plays an important role in achieving different strength levels. By controlling different coiling temperatures, the grain size and precipitates of the hot rolled substrate are controlled to achieve different substrate strength indicators, thereby achieving different yield strength levels of the galvanized finished product.

[0059] In this application, the single-stand rolling process for cold rolling plays an important role in achieving different strength levels. Single-stand rolling can ensure that the cold-hardened substrate has a suitable cold rolling reduction rate, ensure that the galvanized annealing obtains higher strength, stable performance and uniform structure, and solve the problem of difficulty in acid continuous rolling of ultra-high strength steel.

[0060] In this application, the galvanizing annealing temperature plays an important role in achieving different strength levels. By controlling different annealing temperatures, the transformation amount of austenite during heating, the grain size, and the transformation mode and transformation amount of austenite during cooling can be controlled to achieve different strength indicators.

[0061] The present application adopts different coiling processes, controls the grain size and precipitates of the hot-rolled substrate, starts from the performance of the hot-rolled substrate and obtains different substrate strength indicators to achieve different yield strength levels of the galvanized finished product.

[0062] The present application ensures the pickling effect of the steel coil surface and the surface quality after galvanizing by controlling the pickling process.

[0063] The present application adopts a single-stand rolling process to ensure that the steel coil has a suitable reduction rate, and further obtains better performance and organization.

[0064] It mainly adopts galvanizing continuous annealing, and through temperature control, it can realize the production of steel plates with different structures and properties. The process is simple, the operability is strong and the cost is low.

[0065] The present application obtains 980MPa-grade galvanized duplex steel with three yield strength levels of 550MPa, 650MPa and 700MPa under a component system by controlling key process parameters of each process step.

[0066] 1) The 980MPa grade galvanized dual-phase steel with a yield strength of 550MPa is prepared, and the process parameters of each process are:

[0067] The hot rolling process includes: heating the continuous casting slab at 1180-1250°C for 200-400 minutes; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900°C and the coiling temperature is 540-620°C;

[0068] The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained;

[0069] The cold rolling process includes: cold rolling the pickled coil on a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction rate is 54-67%;

[0070] The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it to obtain a 980MPa grade galvanized dual-phase steel with a yield strength of 550MPa; wherein the annealing temperature is 745-760°C; the galvanized steel sheet is skin-passed and straightened to obtain a galvanized low-alloy high-strength steel sheet; wherein the skin-pass elongation is 0.3-0.6%, the skin-pass rolling force is above 250t, and the straightening elongation is 0.05-0.15%.

[0071] 2) The 980MPa grade galvanized dual-phase steel with a yield strength of 650MPa is prepared, and the process parameters of each process are:

[0072] The hot rolling process includes: heating the continuous casting slab at 1180-1250°C for 200-400 minutes; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900°C and the coiling temperature is 520-600°C;

[0073] The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained;

[0074] The cold rolling process includes: cold rolling the pickled coil on a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction rate is 54-67%;

[0075] The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it; wherein the annealing temperature is 760-775°C; performing skin pass and straightening on the galvanized steel sheet to obtain a galvanized low alloy high strength steel sheet; wherein the skin pass elongation is 0.3-0.6%, the skin pass rolling force is above 280t, and the straightening elongation is 0.05-0.15%.

[0076] 3) The process parameters of the 980MPa grade galvanized dual-phase steel with a yield strength of 700MPa are as follows:

[0077] The hot rolling process includes: heating the continuous casting slab at 1180-1250°C for 200-400 minutes; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900°C and the coiling temperature is 500-580°C;

[0078] The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained;

[0079] The cold rolling process includes: cold rolling the pickled coil on a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction rate is 54-67%;

[0080] The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it; wherein the annealing temperature is 775-790°C; the galvanized steel sheet is skin-passed and straightened to obtain a galvanized low-alloy high-strength steel sheet; wherein the skin-pass elongation is 0.3-0.6%, the skin-pass rolling force is above 300t, and the straightening elongation is 0.05-0.15%.

[0081] The key process steps and their functions are as follows:

[0082] ① Final rolling temperature: The final rolling temperature of hot rolling adopts the austenite zone temperature higher than 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 final rolling temperature is generally controlled at 820-900℃.

[0083] ② Coiling temperature: High coiling temperature is conducive to grain growth, reducing strength and improving formability. However, too high annealing 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 550MPa level is controlled at 540℃~620℃, the yield strength 650MPa level is controlled at 520℃~600℃, and the yield strength 700MPa level is controlled at 500℃~580℃.

[0084] ③ Pickling process: Hot rolled 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.

[0085] ③Cold rolling deformation: The pickled steel plate is cold rolled and rolled to obtain a cold hardened coil. A larger cold rolling deformation can reduce the recrystallization temperature and phase change 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 is based on the actual situation of a single stand, and the total cold rolling reduction rate is between 54% and 67%.

[0086] ④ Galvanizing annealing temperature: The appropriate heating section temperature can ensure the production of the appropriate amount of austenite in the annealing furnace. If the temperature is too high or too low, the amount of austenite will be too much or too little, and after cooling, the appropriate martensite and ferrite dual-phase structure cannot be obtained. Therefore, the annealing temperature of the yield strength of 550MPa is controlled between 745-760℃, the annealing temperature of the yield strength of 650MPa is controlled between 760-775℃, and the annealing temperature of the yield strength of 700MPa is controlled between 775-790℃.

[0087] ⑤ Leveling elongation: The purpose of leveling is to eliminate the yield platform of the steel plate, avoid the tensile strain mark defects during the stamping process, improve the plate shape, and improve the surface quality of galvanized. The characteristic of duplex steel products is that there is no yield platform. The main purpose of duplex steel finishing is to improve the plate shape and surface quality. Therefore, the control range of leveling elongation is between 0.3% and 0.6%.

[0088] ⑥ Tensile elongation: The purpose of tensile straightening is to adjust and optimize the plate shape to avoid side waves and middle waves in the material. If the tensile elongation is too low, the plate shape will be bad. If the tensile elongation is too high, tensile straightening lines will easily appear. Therefore, the control range of flattening elongation is between 0.05 and 0.15%.

[0089] The present application adopts the above-mentioned process method, which has a simple process and convenient control, and produces steel plates with three yield strength levels of 550MPa, 650MPa, and 700MPa, with a thickness of 0.8 to 2.0mm, which can meet the requirements of the automotive steel plate field.

[0090] Example

[0091] The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application will be apparent to those skilled in the art. Unless otherwise stated, all ingredients, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0092] Examples 1 to 15

[0093] The present application embodiment provides a method for manufacturing 980MPa grade galvanized dual-phase steel with different yield strength levels, wherein the chemical composition of the steel billet is C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 2.2-2.8%, Al: 0.10-0.22%, Nb: 0.015-0.04, Cr: 0.25-0.40%, Mo: 0.070-0.014%, P≤0.015%, S≤0.015%, N≤0.005%, and the rest is Fe and unavoidable impurities. The specific chemical composition of the ingots of Examples 1-15 is shown in Table 1.

[0094] Table 1: Chemical composition of the ingots of Examples 1-15 (%)

[0095]

[0096]

[0097] The slab is subjected to heating, hot rolling, pickling, cold rolling, continuous annealing, and galvanizing processes to obtain the 980 MPa galvanized dual-phase steel with a thickness of 0.8 to 2.0 mm and different yield strength levels as described in the present application. Examples 1-5 are at a yield strength of 550 MPa, Examples 6-10 are at a yield strength of 650 MPa, and Examples 11-15 are at a yield strength of 700 MPa.

[0098] The cast billet is heated in a heating furnace, and the furnace temperature is controlled at 1200-1250°C. After 7 rough rolling passes, the intermediate billet thickness is 40 mm, the finishing rolling temperature is controlled at 820-900°C, the coiling temperature of Examples 1-5 is controlled at 540-620°C, the coiling temperature of Examples 6-10 is controlled at 520-600°C, and the coiling temperature of Examples 10-15 is controlled at 500-580°C;

[0099] After the hot rolled coil is straightened and phosphorus broken, it is pickled. The pickling temperature is ≥75℃ and the HCL concentration in the acid tank is ≥100g / L.

[0100] After pickling, it is rolled into 0.8-2.0mm thick cold-hardened coils by 6 passes on a single stand, and the total cold rolling reduction rate is 54-67%;

[0101] The cold hard coil is galvanized after continuous annealing. The annealing temperature of Examples 1-5 is controlled at 745-760°C, the annealing temperature of Examples 6-10 is controlled at 760-775°C, and the annealing temperature of Examples 11-15 is controlled at 775-790°C. After zinc pot galvanizing, it enters the skin-passing and straightening section. The skin-passing elongation is controlled at 0.3-0.6%, the skin-passing rolling force is ≥250t, and the straightening elongation is controlled at 0.05-0.15%. Finally, the hot-dip galvanized steel coil with a thickness of 0.8-2.0 mm is obtained by coiling and dividing at the outlet. The specific process parameters of Examples 1-15 are shown in Table 2.

[0102] Table 2: Process parameters of Examples 1-15

[0103]

[0104]

[0105] The mechanical property test results of the steel in each example of the present application are listed in Table 3. The mechanical properties of the products in Examples 1 to 15 of the present application are tested according to the GB / T 228 method.

[0106] It can be seen from Table 3 that mechanical properties with different yield strength levels of 550MPa, 650MPa, and 700MPa can be obtained through different process controls.

[0107] Table 3: Mechanical properties test results of steels in various examples.

[0108] Example Thickness / mm Width / mm Yield strength / MPa Tensile strength / MPa Elongation after break / % 1 1.2 1200 578 1008 17 2 1.4 1150 605 1024 16.5 3 1.5 1250 640 1043 16.5 4 0.8 1200 658 1052 15.5 5 2.0 1200 675 1052 13.5 6 1.8 1250 687 1047 14 7 1.2 1200 701 1069 14.5 8 0.8 1150 697 1050 14.5 9 2.0 1100 679 1054 14 10 1.2 1250 707 1064 13.5 11 1.8 1150 742 1076 11 12 1.0 1100 725 1058 12 13 1.5 1130 718 1060 11.5 14 2.0 1250 743 1076 10.5 15 1.2 1250 734 1080 11

[0109] The product structure of the 980MPa grade galvanized dual-phase steel in this application is ferrite + martensite. Figure 1-Figure 3 shown. Figure 1 This is the metallographic structure with a yield strength of 550 MPa in Example 1 of the present application. Figure 2 This is the metallographic structure with a yield strength of 650 MPa in Example 5 of the present application. Figure 3 This is the metallographic structure with a yield strength of 700 MPa in Example 12 of the present application.

[0110] In summary, the present application obtains 980 MPa-grade galvanized duplex steel with three yield strength levels of 550 MPa, 650 MPa, and 700 MPa under a composition system by controlling the key process parameters of each process.

[0111] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. 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. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A 980MPa grade galvanized duplex steel, characterized in that: It is composed of the following components by mass fraction: C: 0.06~0.09%, Si: 0.20~0.30%, Mn: 2.2~2.8%, Al: 0.10~0.22%, Nb: 0.015~0.04, Cr: 0.25~0.40%, Mo: 0.070~0.140%, P≤0.015%, S≤0.015%, N≤0.007%, and the rest are Fe and unavoidable impurities.

2. The 980MPa grade galvanized dual-phase steel according to claim 1, characterized in that: Yield strength 550~730MPa, tensile strength ≥980MPa, elongation ≥10%.

3. The 980MPa grade galvanized dual-phase steel according to claim 1, characterized in that: Yield strength 650~900MPa, tensile strength ≥980MPa, elongation ≥8%.

4. The 980MPa grade galvanized dual-phase steel according to claim 1, characterized in that: Yield strength 700~900MPa, tensile strength ≥980MPa, elongation ≥8%.

5. A method for preparing 980MPa grade galvanized dual-phase steel, characterized in that: The steps include: Continuously casting to obtain a cast billet, the cast billet is composed of the following components by mass fraction: Composition: C: 0.06-0.09%, Si: 0.20-0.30%, Mn: 2.2-2.8%, Al: 0.10-0.22%, Nb: 0.015-0.04%, Cr: 0.25-0.40%, Mo: 0.070-0.014%, P≤0.015%, S≤0.015%, N≤0.005%, the rest is Fe and unavoidable impurities; The ingot is processed through hot rolling, pickling, cold rolling and galvanizing to obtain 980MPa grade galvanized dual-phase steel.

6. The method for preparing 980MPa grade galvanized dual-phase steel according to claim 5, characterized in that: The hot rolling process comprises: heating the continuous casting slab at 1180-1250° C. for 200-400 min; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900° C. and the coiling temperature is 540-620° C.; The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained; The cold rolling process comprises: cold rolling the pickled coil in a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction is 54-67%; The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it to obtain the 980MPa grade galvanized dual-phase steel with a yield strength level of 550MPa; wherein the annealing temperature is 745-760°C; performing skin pass and straightening on the galvanized steel sheet to obtain a galvanized low-alloy high-strength steel sheet; wherein the skin pass elongation is 0.3-0.6%, the skin pass rolling force is above 250t, and the straightening elongation is 0.05-0.15%.

7. The method for preparing 980MPa grade galvanized dual-phase steel according to claim 5, characterized in that: The hot rolling process comprises: heating the continuous casting slab at 1180-1250° C. for 200-400 min; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900° C. and the coiling temperature is 520-600° C.; The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained; The cold rolling process comprises: cold rolling the pickled coil in a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction is 54-67%; The galvanizing process includes: uncoiling the cold hard coil, annealing it and then galvanizing it; wherein the annealing temperature is 760-775°C; performing skin pass and straightening on the galvanized steel sheet to obtain a galvanized low-alloy high-strength steel sheet; wherein the skin pass elongation is 0.3-0.6%, the skin pass rolling force is above 280t, and the straightening elongation is 0.05-0.15%.

8. The method for preparing 980MPa grade galvanized dual-phase steel according to claim 5, characterized in that: The hot rolling process comprises: heating the continuous casting slab at 1180-1250° C. for 200-400 min; rough rolling, finish rolling and coiling the heated slab to obtain a hot rolled steel coil, wherein the final finish rolling temperature is 820-900° C. and the coiling temperature is 500-580° C.; The pickling process comprises: uncoiling the hot-rolled steel coil and then pickling it; wherein the pickling temperature is ≥75°C, the acid solution concentration is ≥100g / L, and the pickled coil is obtained; The cold rolling process comprises: cold rolling the pickled coil in a single stand and rolling it to obtain a cold hardened coil, wherein the total cold rolling reduction is 54-67%; The galvanizing process comprises: uncoiling the cold hard coil, annealing it and then galvanizing it; wherein the annealing temperature is 775-790°C; performing skin pass and straightening on the galvanized steel sheet to obtain a galvanized low-alloy high-strength steel sheet; wherein the skin pass elongation is 0.3-0.6%, the skin pass rolling force is above 300t, and the straightening elongation is 0.05-0.15%.

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