980mpa grade hot-dip galvanizing multiphase steel and method for manufacturing the same

Abstract

The application provides a 980MPa grade hot-based galvanizing complex-phase steel and a preparation method thereof. The 980MPa grade hot-based galvanizing complex-phase steel comprises the following chemical components in percentage by mass: C: 0.10-0.15%, Si: 0.20-0.50%, Mn: 1.60-2.20%, P: less than or equal to 0.025%, S: less than or equal to 0.010%, Mo: 0.20-0.35%, Nb: 0.025-0.055%, Ti: 0.035-0.080%, Al: 0.015-0.075%, N: less than or equal to 0.0050%, and the rest is Fe and inevitable impurities. The 980MPa grade hot-based galvanizing complex-phase steel prepared by the application has a required thickness specification, required mechanical properties and good surface quality, and can meet the requirements of users.

Description

Technical Field

[0001] The present invention relates to the technical field of cold-rolled strip production, and in particular to a 980MPa grade hot-dip galvanized complex phase steel and a preparation method thereof. Background Art

[0002] As energy and environmental issues become increasingly prominent, energy conservation and environmental protection have become inevitable issues in the development of the automotive industry. Currently, steel is the most widely used metal material in automobiles. Increasing the proportion of high-strength steel used in automobiles and achieving lightweight vehicles can significantly reduce fuel consumption and exhaust emissions. The types of applications, usage proportions, and strength levels of advanced high-strength steels in vehicle bodies are gradually increasing. Among these high-strength steels, complex phase steels are widely used in the manufacture of various parts with high requirements for local forming capabilities, such as seat rails, chassis structural parts, and suspension parts, due to their high strength and plasticity as well as excellent flanging, bending, and hole expansion properties. Hot-dip galvanizing is a process in which hot-rolled strip steel is pickled and then directly produced into galvanized sheets of the same specifications as after cold-dip rolling. It does not require cold rolling and has the characteristics of a short process, environmental protection, and energy saving. The hot-dip galvanizing production method reduces product costs and maintains product quality. 980MPa grade hot-base duplex steel has good hole expansion performance and high strength, which is highly favored by steel companies and automobile manufacturers. Through the search of relevant patents, the patents that are similar to 980MPa grade hot-base duplex steel prepared with the same composition are as follows:

[0003] CN 113249648 A discloses an 800MPa grade hot-base zinc-aluminum-magnesium coated complex phase steel and its preparation method. The steel comprises the following chemical compositions by mass: C: 0.05% to 0.12%, Si: 0.05% to 0.85%, Mn: 1.4% to 2.0%, Al: 0.01% to 0.08%, P: 0 to 0.008%, S: 0 to 0.001%, N: 0 to 0.008%, components A, B, and C, with the remainder being Fe and unavoidable impurities. A comprises at least one of the following: Cr: 0.05% to 0.5%, Mo: 0.005% to 0.3%; B comprises at least one of the following: Cu: 0.01% to 0.05%, Ni: 0.01% to 0.05%; and C comprises at least one of the following: Nb: 0.001% to 0.04%, and Ti: 0.01% to 0.12%. The slab thickness is 220mm-250mm. The pre-rolling heating temperature is 1230°C-1270°C for 210-260 minutes. The rough rolling end temperature is 1040°C-1100°C. The finishing temperature of the finishing rolling is 880°C-940°C. The coiling temperature is 450°C-500°C. The thickness of the hot-rolled coil is 2.0-3.5mm. Post-rolling cooling adopts a front-end water cooling + back-end air cooling mode. The front-end water cooling rate is 30°C / s-60°C / s, the front-end water cooling end temperature is 550°C-600°C, and the back-end air cooling rate is 10°C / s-20°C / s, with the air cooling end temperature being 450°C-500°C. The scale-breaking elongation during uncoiling and pickling is 0.5%-0.7%, and the temper rolling force is 2000N-4000N. The pickled steel is preheated to 210°C–230°C, then heated to 610°C–660°C at a heating rate of 15°C / s–25°C / s, then soaked for 30–50 seconds. After soaking, it is cooled to 420–440°C at a cooling rate of 8°C / s–16°C / s, followed by zinc-aluminum-magnesium coating with a thickness of 7–17 μm. High Si content is detrimental to achieving good surface quality, while high Ti content can easily produce liquid TiN, hindering good ductility. Low soaking temperatures also hinder connection with other strips.

[0004] CN 112251694 A discloses a hot-dip galvanized sheet with a thick zinc layer and a preparation method thereof. The chemical composition by mass percentage is as follows: C: 0.65-0.75%, Cr: 1.10-1.20%, Si: 0.60-1.00%, Mn: 0.90-1.00%, V: 0.05-0.09%, Mo≤0.01%, and the balance is Fe and unavoidable impurities. The annealing process includes non-oxidation heating, radiant tube heating, electric soaking, and spray cooling. The non-oxidation heating temperature is 680-720°C, the radiant tube heating temperature is 670-710°C, the electric soaking temperature is 660-700°C, and the spray cooling temperature is 450-470°C. The line speed during the knife purging process is 42-46 m / min, the air knife distance is 50-56 mm, the air knife pressure is 40-45 mm, and the air knife height is 76-82 mm. Its high C content (0.65-0.75%) is not conducive to achieving good forming and welding properties, while its high Si content (0.60-1.00%) is prone to defects such as plating leakage, seriously affecting the surface quality of the strip. Furthermore, the production of conventional high-strength steel is significantly different from advanced high-strength steels such as complex phase steel, and the slow unit speed is not conducive to improvement.

[0005] CN 109023106 A discloses a cold-rolled hot-dip galvanized complex phase steel and a preparation method thereof. The chemical composition by mass percentage of the cold-rolled hot-dip galvanized complex phase steel is as follows: C: 0.08-0.12%, Si: 0.3-0.6%, Mn: 2.0-2.5%, P≤0.02%, S: 0.015%, Al: 0.1-0.4%, Cr: 0.2-0.5%, Mo: 0.1-0.4%, Nb: 0.03-0.06%, Ti: 0.03-0.06%, B: 0.002-0.003%, and the remainder is Fe and unavoidable impurities. The heating temperature of the steel billet is 1120-1300° C.; the hot rolling finishing temperature is 860-920° C.; the hot rolling coiling temperature is 600-660° C., the cold rolling reduction rate is 55%-75%, and the hard strip is preheated to 220° C.; then heated to 790-820° C. at a rate of 1-3° C. / s and kept warm; the strip after being kept warm is slowly cooled to 690-720° C. at a cooling rate of 10-20° C. / s; the strip after slow cooling is rapidly cooled to a galvanizing temperature of 450-460° C. at a cooling rate of 20-40° C. / s through high hydrogen cooling, and galvanized after aging for 20-50 seconds; after galvanizing, the strip is air-cooled to 410-430° C. and then cooled to room temperature; the skin-pass elongation is 0.3%-0.5%. The high Al content (0.1-0.4%) added will increase the viscosity of the steel, block the water outlet during casting and cause smelting difficulties, and also lead to an increase in Al2O3 inclusions and reduce the surface quality; in addition, the thickness of the cold-based and hot-based galvanized complex phase steel in this patent is quite different from that of the hot-based galvanized complex phase steel, and the process is also significantly different. Summary of the Invention

[0006] In response to the technical problems raised above, a 980MPa grade hot-dip galvanized complex phase steel and its preparation method are provided. The present invention primarily produces a complex phase steel structure during hot rolling, then undergoes stretching and leveling to break scale, and pickling to improve the surface quality of the strip. Finally, a relatively low soaking temperature is employed to maintain the hot-rolled structure as much as possible, utilizing a hot-dip galvanizing production line to produce 980MPa grade hot-dip galvanized complex phase steel with the required thickness specifications, satisfactory mechanical properties, and good surface quality, thereby meeting user requirements.

[0007] The technical means adopted in the present invention are as follows:

[0008] A 980MPa grade hot-dip galvanized complex phase steel, wherein the composition of the 980MPa grade hot-dip galvanized complex phase steel comprises the following chemical components in percentage by mass:

[0009] C: 0.10~0.15%, Si: 0.20~0.50%, Mn: 1.60~2.20%, P≤0.025%, S≤0.010%, Mo: 0.20~0.35%, Nb: 0.025~0.055%, Ti: 0.035~0.080%, Als: 0.015~0.075%, N≤0.0050%, and the remaining elements are Fe and unavoidable impurities.

[0010] Furthermore, the composition of the 980MPa grade hot-dip galvanized complex phase steel includes the following chemical components in mass percentage:

[0011] C: 0.11~0.14%, Si: 0.25~0.40%, Mn: 1.85~2.10%, Mo: 0.20~0.30%, Nb: 0.030~0.050%, Ti: 0.040~0.060, Als: 0.030~0.065%, P≤0.015%, S≤0.005%, N≤0.0045%, the balance is Fe and unavoidable impurities.

[0012] Furthermore, the microstructure of the 980MPa grade hot-dip galvanized composite steel is composed of 20-25% ferrite, 40-45% martensite and 30-40% bainite, and the average ferrite grain size is 0.8-1.0 μm; the yield strength of the 980MPa grade hot-dip galvanized composite steel is 800-860MPa, the tensile strength is 1000-1100MPa, and the elongation A is 0. 80 The value is 13.5~18.0%, and the hole expansion rate is 65~85%.

[0013] The present invention also provides a method for preparing 980MPa grade hot-dip galvanized composite steel, comprising the following steps:

[0014] Step 1: Smelting process: Smelting according to the chemical composition of 980MPa grade hot-dip galvanized complex phase steel, and obtaining slabs by casting;

[0015] Step 2, hot rolling process: the slab is subjected to heating, descaling, rough rolling, finish rolling and laminar cooling to obtain a hot-rolled coil, i.e., hot-rolled strip;

[0016] Step 3, pickling process: After the hot-rolled strip is uncoiled, straightened and scaled, and the plate shape is adjusted, it is subjected to shallow turbulent pickling to obtain pickled strip;

[0017] Step 4: Hot-dip galvanizing process: The pickled strip steel is hot-dip galvanized to obtain 980MPa grade hot-dip galvanized composite steel.

[0018] Furthermore, in the step 2, the heating temperature of the heating process is 1220-1260° C.; the total furnace time is 290-430 min, the finishing rolling start temperature is 1045-1135° C., the final rolling temperature is 870-940° C., and the hot rolling thickness is 2.5-4.5 mm; and the strip head and tail are adjusted using a hot coil box before entering the finishing mill;

[0019] High-pressure water descaling treatment is carried out at the roughing and finishing rolling entrances respectively. The pressure of high-pressure water is 18-22 MPa, and the descaling water volume at the roughing and finishing rolling entrances is 540m3 respectively. 3 / h and 450m 3 / h, the distances between the nozzle and the slab / strip are 120mm and 90mm respectively.

[0020] Furthermore, in the step 2, the laminar cooling adopts a sparse cooling method, the intermediate temperature is 600-680°C, the coiling temperature is 495-545°C, and a "U-type coiling" method is adopted. "U-type coiling" means that the coiling temperature of the first 80m of the strip is 500-570°C and the coiling temperature of the last 100m of the strip is 515-585°C.

[0021] The laminar cooling type is upper and lower tube laminar cooling, and the laminar cooling water pressure is 0.05~0.08Mpa; the strip is subjected to side water spraying and blowing treatment, wherein the side spraying water pressure is 1.2~1.6MPa, and the maximum side spraying water volume is 350m 3 / h, and the side jet pressure is 0.4~0.6MPa.

[0022] Furthermore, in the step three, during the uncoiling process, the uncoiler threading speed is 45-65 m / min, the tail swinging speed is 80-120 m / min, and the rest of the uncoiling speed is maintained at 130-160 m / min; a six-roll straightening machine is used to pull the strip head out of the uncoiler, and the strip head and tail are straightened to make the strip easy to thread, and the six-roll straightening machine is maintained at a speed of 130-160 m / min for scale breaking treatment, the elongation is maintained at 1.5-2.5%, and the tension of the straightening machine is 40-50 tons.

[0023] Furthermore, in the step 3, the pickling process uses an acid solution to remove the oxide scale on the surface of the hot-rolled coil to obtain a pickled plate, which adopts a low acid consumption, high efficiency immersion acid tank, including three-stage pickling and four-stage rinsing, wherein the acid solution temperature of the three-stage pickling process is 75-93°C, the free HCl concentration of the three-stage pickling is 2.5-5.0%, 6-12%, and 9-15% respectively, and the Fe 2+The four-stage rinsing temperatures are 30-50°C, 40-60°C, 50-70°C, and 60-80°C, and the pH values ​​are controlled at 1.0-2.5, 3.0-4.0, 4.0-5.5, and 5.0-6.5, respectively. -1 The concentration is required to be ≤4; the strip steel after rinsing is dried in a dryer, and the air supply temperature of the dryer is 80-140℃.

[0024] Furthermore, in the step 4, the pickled strip is heated to 300°C and 670-720°C at speeds of 3-8°C / s and 0.3-2.1°C / s, respectively, and after being evenly heated and kept warm for 45-105s, it is cooled to 520-560°C at a speed of 0.8-6.5°C / s, and then cooled to 440-480°C at a speed of 5-23°C / s. After being evenly heated and kept warm for 20-50s, it is immersed in a zinc pot for hot-dip galvanizing, and after exiting the zinc pot, it is cooled to room temperature at a speed of 4-10°C / s to obtain 980MPa grade hot-dip galvanized complex phase steel; the unit speed is 60-100m / min, and the unit speed is reduced by 10m / min for every 0.5mm increase in the strip thickness; the skin-pass elongation is 0.6-1.0%, and the skin-pass elongation is reduced by 0.1% for every 0.5mm increase in the strip thickness.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The 980MPa grade hot-dip galvanized complex phase steel and preparation method thereof provided by the present invention prepare a complex phase steel structure by hot rolling, then change the surface quality of the strip by stretching and leveling to break the scale and pickling, and then adopt a relatively low soaking temperature. Under the premise of maintaining the hot-rolled structure as much as possible, a hot-dip galvanized production line is used to prepare 980MPa grade hot-dip galvanized complex phase steel with required thickness specifications, mechanical properties that meet the requirements, and good surface quality to meet user requirements.

[0027] In summary, the application of the technical solution of the present invention can solve the following current problems: (1) high Si content and poor surface quality, (2) Ti content deteriorating plasticity, (3) difficulty in transitioning the soaking temperature, (4) high C content and poor forming and welding performance, (5) high Al content blocking the water outlet and Al2O3 inclusions and poor surface quality, etc., and obtain 980MPa grade hot-dip galvanized complex phase steel with good mechanical properties and good surface quality.

[0028] Based on the above reasons, the present invention can be widely promoted in fields such as cold-rolled strip production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0030] Figure 1 It is a schematic diagram of the process of the present invention.

[0031] Figure 2 This is a scanned photo of the 980MPa grade hot-dip galvanized duplex steel prepared in Example 1 of the present invention.

[0032] Figure 3 for Figure 2 Magnified image of . DETAILED DESCRIPTION

[0033] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0037] As energy and environmental issues become increasingly prominent, energy conservation and environmental protection have become inevitable issues in the development of the automotive industry. Lightweighting of automobiles can simultaneously address energy consumption, emissions, and safety requirements. The types of applications, usage ratios, and strength levels of advanced high-strength steels in vehicle bodies are gradually increasing. Among these high-strength steels, complex phase steels are widely used in the manufacture of various parts with high requirements for local forming capabilities due to their high strength and plasticity as well as excellent flanging, bending, and hole expansion properties. Hot-base galvanizing is the process of directly producing galvanized sheets of the same specifications after cold-base calendering after hot-rolled strip steel has been pickled without the need for cold rolling. It has the characteristics of short process, environmental protection, and energy saving. 980MPa grade hot-base galvanized complex phase steel that meets the specifications, mechanical properties, and surface quality requirements is produced through conventional hot rolling, pickling, and hot-dip galvanizing units to meet user requirements and generate significant economic and social benefits.

[0038] The present invention provides a 980MPa grade hot-dip galvanized complex phase steel and a preparation method thereof, namely a production process of a 980MPa grade hot-dip galvanized complex phase steel and a preparation method thereof, belonging to the technical field of cold-rolled sheet and strip production.

[0039] The present invention prepares a complex phase steel structure during hot rolling, then changes the surface quality of the strip after stretching and leveling to break scale and pickling, and then adopts a relatively low soaking temperature. Under the premise of maintaining the hot rolled structure as much as possible, a hot dip galvanized production line is used to prepare 980MPa grade hot-dip galvanized complex phase steel with required thickness specifications, mechanical properties that meet the requirements, and good surface quality to meet user requirements.

[0040] The invention discloses a 980MPa grade hot-dip galvanized complex phase steel, whose chemical composition ranges as follows: C: 0.10-0.15%, Si: 0.20-0.50%, Mn: 1.60-2.20%, P≤0.025%, S≤0.010%, Mo: 0.20-0.35%, Nb: 0.025-0.055%, Ti: 0.035-0.080%, Als: 0.015-0.075%, N≤0.0050%, and the remaining elements are Fe and unavoidable impurities.

[0041] A preferred 980MPa grade hot-dip galvanized complex phase steel has the following chemical composition, calculated by weight percentage: C: 0.11-0.14%, Si: 0.25-0.40%, Mn: 1.85-2.10%, Mo: 0.20-0.30%, Nb: 0.030-0.050%, Ti: 0.040-0.060%, Als: 0.030-0.065%, P≤0.015%, S≤0.005%, N≤0.0045%, and the balance is Fe and unavoidable impurities.

[0042] Among them, there is a 980MPa grade hot-dip galvanized composite steel, the microstructure of which is composed of 20-25% ferrite (average grain size of 0.8-1.0μm) + 40-45% martensite + 30-40% bainite, with a yield strength of 800-860MPa, a tensile strength of 1000-1100MPa, and an elongation of A 80 The value is 13.5~18.0%, and the hole expansion rate is 65~85%.

[0043] like Figure 1 As shown, the present invention also provides a method for preparing 980MPa grade hot-dip galvanized complex phase steel, the production steps of which include:

[0044] (a) Smelting process: Smelting according to the chemical composition of 980 MPa grade hot-dip galvanized composite steel and forming slabs by casting;

[0045] (b) Hot rolling process: The slab undergoes heating, descaling, rough rolling, finishing rolling, and laminar cooling to obtain hot-rolled coils. The heating temperature is 1220-1260°C. To ensure uniform chemical composition across the strip, the total furnace time is 290-430 minutes. The start temperature of finishing rolling is 1045-1135°C. The final rolling temperature is 870-940°C, and the hot-rolled thickness is 2.5-4.5 mm. To ensure the stability of the longitudinal microstructure and properties of the strip, sparse cooling is used in laminar cooling, with an intermediate temperature of 600-680°C. Before entering the finishing mill, the strip's head and tail are aligned using a hot coil box. The coiling temperature is 495-545°C, using "U-type coiling" (the coiling temperature for the first 80 meters of the strip is 500-570°C, and the coiling temperature for the last 100 meters of the strip is 515-585°C).

[0046] In order to obtain good surface quality, high-pressure water descaling treatment is carried out at the roughing and finishing entrances. The pressure of high-pressure water is 18-22 MPa, and the descaling water volume at the roughing and finishing entrances is 540 m3 respectively. 3 / h and 450m 3 / h, the distances between the nozzle and the slab / strip are 120mm and 90mm respectively.

[0047] The laminar cooling type is upper and lower tube laminar cooling, and the laminar cooling water pressure is 0.05~0.08MPa. In order to prevent water accumulation on the surface of the steel plate, the strip is subjected to side water spraying and blowing treatment, wherein the side spraying water pressure is 1.2~1.6MPa, and the maximum side spraying water volume is 350m 3 / h, and the side jet pressure is 0.4~0.6MPa.

[0048] (c) Pickling Process: After the hot-rolled strip has been uncoiled, straightened, and scaled, and its shape has been adjusted, it is then pickled using i-BOX (shallow turbulent flow pickling). The uncoiler threading speed is 45-65 m / min, the tailing speed is 80-120 m / min, and the remaining uncoiling speed is maintained at 130-160 m / min. The six-roll straightening machine is used to pull the strip head from the uncoiler and straighten the strip head and tail to facilitate threading. The six-roll straightening machine maintains a speed of 130-160 m / min for scale breaking, and an elongation of 1.5-2.5%. The tension of the straightening machine is 40-50 tons. After removing the oxide scale on the surface of the hot-rolled coil using an acid solution, a pickled plate is obtained. The pickling adopts a low-acid-consumption, high-efficiency immersion acid tank (i-Box) pickling, three-stage pickling, and four-stage rinsing. The acid solution temperature of the three-stage pickling process is 75-93°C, and the free HCl concentration of the three-stage pickling is 2.5-5.0%, 6-12%, and 9-15% respectively. The Fe 2+The four rinsing temperatures are 30-50℃, 40-60℃, 50-70℃, and 60-80℃, respectively. The pH values ​​are controlled at 1.0-2.5, 3.0-4.0, 4.0-5.5, and 5.0-6.5, respectively. -1 The concentration is required to be ≤ 4. The strip steel after rinsing is dried in a dryer (the air supply temperature of the dryer is 80-140°C).

[0049] (d) Hot-dip galvanizing process: The pickled strip is hot-dip galvanized to produce 980MPa grade hot-dip galvanized composite steel. The 980MPa grade hot-dip galvanized composite steel is heated to 300°C and 670-720°C at speeds of 3-8°C / s and 0.3-2.1°C / s, respectively. After being uniformly heated and held for 45-105 seconds, it is cooled to 520-560°C at a speed of 0.8-6.5°C / s. It is then cooled to 440-480°C at a speed of 5-23°C / s, held uniformly for 20-50 seconds, and then immersed in a zinc pot for hot-dip galvanizing. After exiting the zinc pot, it is cooled to room temperature at a speed of 4-10°C / s to obtain the 980MPa grade hot-dip galvanized composite steel. The unit speed is 60-100m / min, and the unit speed is reduced by 10m / min for every 0.5mm increase in strip thickness. The skin-pass elongation is 0.6-1.0%, and the skin-pass elongation is reduced by 0.1% for every 0.5mm increase in strip thickness.

[0050] Carbon determines the strength, plasticity, and formability of steel plates. It is an effective and inexpensive strengthening element that directly affects the volume fractions of bainite, martensite, and other components in complex-phase steel after intercritical treatment. However, low carbon contents (<0.06%) make it difficult to obtain a hard phase structure and achieve the required strength level. This requires increasing the content of alloying elements such as Mn and Cr to ensure strength, which increases costs. Excessive carbon content enhances the steel's hardenability, allowing for a large amount of martensite at lower cooling rates, while bainite is not. Excessive carbon content also reduces welding and formability. Therefore, the carbon content of the present invention is 0.10-0.15%, preferably 0.11-0.14%.

[0051] Si can expand the (α+γ) region in the Fe-Fe3C phase diagram, widening the temperature range for critical zone processing and improving the process performance of complex phase steel. It also increases the slope of the A3 line in the phase diagram, thereby increasing the flexibility of the heat treatment process and facilitating the stability of properties such as the strength of complex phase steel. Si can inhibit the formation of cementite in steel and increase the activity of carbon in austenite, hindering the nucleation and growth of cementite. In addition, Si increases the activity of carbon, further enriching the untransformed austenite with carbon, thereby improving its hardenability. In addition, Si can be dissolved in ferrite and austenite to increase the strength of steel. Its effect is second only to C and P, and is stronger than elements such as Mn, Cr, Ti, and Ni. However, when the Si content is too high, the surface oxide scale formed by Si in the heating furnace is difficult to remove, increasing the difficulty of dephosphorization. At the same time, during the annealing process, it is easy to enrich on the surface to form SiO2, resulting in surface defects such as plating leakage. Therefore, the Si content of the present invention is 0.20-0.50%, preferably 0.25-0.40%.

[0052] Manganese is a typical austenite-stabilizing element, significantly improving the hardenability of steel and reducing the critical cooling rate for the formation of bainite and martensite. This effectively reduces the cooling rate during the rapid cooling stage of the annealing process, thereby facilitating the formation of bainite or martensite. Manganese is a good deoxidizer and desulfurizer and a commonly used solid solution strengthening element in steel. Through solid solution strengthening, manganese lowers the γ-α phase transition temperature, promoting grain refinement and altering the microstructure after the phase transition. Furthermore, manganese readily combines with sulfur to form the high-melting-point compound MnS, thereby eliminating or mitigating the hot brittleness caused by FeS and improving the hot workability of the steel. Furthermore, as an element that expands the γ phase, manganese lowers the A3 and A1 critical points. However, high manganese content delays both pearlite and bainite transformations, narrowing the "process window" and shifting the bainite region to the right. This increases the steel's sensitivity to process conditions and hinders stable mass production. Excessively low manganese content can easily induce pearlite transformation, making it difficult to form sufficient bainite in the microstructure. Therefore, the Mn content of the present invention is 1.60-2.20%, preferably 1.85-2.10%.

[0053] Al is a strong deoxidizing element. In order to ensure that the oxygen content in the steel is as low as possible, a certain amount of aluminum needs to be added. At the same time, soluble aluminum is often used as a microalloying element to combine nitrogen in the steel. Very finely dispersed AlN prevents the growth of austenite grains. During the γ-α transformation process, AlN acts as a nucleator, thereby accelerating the austenite transformation. The most important function of AlN is to refine the grains and obtain aging resistance. When the Als content is less than 0.010%, its effect cannot be exerted; but adding a large amount of aluminum easily forms alumina lumps. This leads to an increase in the viscosity of the mold slag, resulting in improper heat transfer and lubrication during casting. Therefore, the Als content of the present invention is 0.015-0.075%, preferably 0.030-0.065%.

[0054] Mo significantly delays the transformation of pearlite and bainite, resulting in a high volume fraction of martensite, ensuring strength. Furthermore, the Gibbs free energy of Mo oxide is comparable to that of Fe oxide, so Mo does not affect the surface galvanizing quality of duplex steel. However, Mo is relatively expensive. Therefore, the Mo content in the present invention is 0.20-0.35%, preferably 0.25-0.30%.

[0055] Nb exists primarily in the form of NbC in complex-phase steels, which significantly refines grains and promotes dispersion-based precipitation strengthening. During hot rolling, the strain-induced precipitation of niobium carbides hinders the recovery and recrystallization of deformed austenite, resulting in fine phase transformation products in the deformed austenite structure after controlled rolling and controlled cooling. Furthermore, during annealing, the precipitation of fine niobium carbonitrides contributes to precipitation strengthening. During the hot-dip galvanizing annealing heating process, undissolved NbC particles can pin ferrite grain boundaries, thereby refining grains. When the annealing temperature increases to the two-phase region, NbC dissolves at a lower temperature, fully dissolving in the matrix. Meanwhile, dissolved carbon atoms accumulate in the austenite, enhancing its stability. During cooling, NbC in the ferrite reprecipitates, resulting in significant precipitation strengthening. Therefore, the Nb content of the present invention is 0.025-0.055%, preferably 0.030-0.050%.

[0056] Ti inhibits austenite coarsening during heating by forming TiN, and forms TiC to pin grain boundaries during cooling, thereby refining the grains and reducing aging and cold brittleness. Too low a Ti content results in insufficient strength and unsatisfactory performance. Too high a Ti content significantly increases strength, affecting performance and, in severe cases, causing cracking in stamped parts. Therefore, the Ti content of the present invention is 0.035-0.080%, preferably 0.040-0.060%.

[0057] like Figure 2-3 Shown is a scanned photo of 980MPa grade hot-dip galvanized complex phase steel, which is composed of 20-25% ferrite (average grain size of 0.8-1.0μm) + 40-45% martensite + 30-40% bainite.

[0058] Example 1

[0059] This embodiment provides two groups of 980 MPa grade hot-dip galvanized composite steels, the chemical compositions of which are shown in Table 1.

[0060] Table 1 Chemical composition (wt.%) of 980 MPa grade hot-dip galvanized composite steel in the embodiment

[0061] serial number C Si Mn P S Mo Nb Ti Als 1 0.105 0.25 2.00 0.008 0.005 0.28 0.043 0.050 0.044 2 0.115 0.23 1.89 0.005 0.003 0.25 0.039 0.048 0.039

[0062] The specific process of the preparation method of the above-mentioned 980MPa grade hot-dip galvanized complex phase steel is as follows:

[0063] A. Smelting process: After the smelting process, a complex phase steel slab with the chemical composition shown in Table 1 is prepared;

[0064] B. Hot rolling process: The slab is heated, dephosphorized, hot rolled and laminar cooled to obtain a hot rolled coil. The specific hot rolling process parameters are shown in Table 2.

[0065] Table 2 Main process parameters for hot rolling of 980MPa grade hot-dip galvanized composite steel in the embodiment

[0066]

[0067] C. Pickling process: The hot-rolled strip is subjected to stretching, descaling and pickling to obtain good surface quality. The specific process is shown in Tables 3 to 5.

[0068] Table 3 Parameters of the tensile straightening process for 980MPa grade hot-dip galvanized duplex steel in the embodiment

[0069]

[0070] Table 4 Parameters of the pickling process for 980MPa grade hot-dip galvanized composite steel in the embodiment

[0071]

[0072] Table 5 980MPa grade hot-dip galvanized composite steel rinsing process parameters in the embodiment

[0073]

[0074] The pickled and rinsed strips are dried to 88°C and 85°C respectively to obtain pickled plates with good surface quality;

[0075] D. Hot-dip galvanizing process: The pickled strip is processed through hot-dip galvanizing to produce the desired product. The strip is first slowly heated to the soaking temperature and kept warm for a period of time. This is different from the usual cold-based galvanized complex phase steel. The soaking temperature is relatively low to maintain the complex phase structure of the hot-rolled strip as much as possible. Under the action of heating, the recovery and dislocation density are reduced, and the strength is slightly reduced. The strip is then slowly cooled, quickly cooled, and kept warm for a period of time before being immersed in a zinc pot for galvanizing. After leaving the zinc pot, it is air-cooled to room temperature and the strip shape is adjusted through a skin pass mill. The specific hot-dip galvanizing process parameters are shown in Table 6:

[0076] Table 6 Main galvanizing process parameters for 980MPa grade hot-dip galvanized composite steel in the embodiment

[0077]

[0078] The microstructure of 980MPa grade hot-dip galvanized composite steel Case 1 prepared by the above process is as follows Figure 2 and Figure 3 As shown, the performance of the above 980MPa grade hot-dip galvanized composite steel was tested in accordance with GB / T228-2010 "Metallic Materials Room Temperature Tensile Test Methods", and its mechanical properties are shown in Table 7 below:

[0079] Table 7 Mechanical properties of 980MPa grade hot-dip galvanized composite steel in the embodiment

[0080] serial number Yield strength / MPa Tensile strength / MPa <![CDATA[Elongation after fracture A 80 %]]> Yield-to-strength ratio Hole expansion rate / % 1 836 1026 10.0 0.815 55 2 814 1014 9.50 0.803 58 CN 113249648A 713 812 16.4 0.878 70 CN 112251694A 550 620 0.887 CN 109023106A 721 1032 8.50 0.699

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 980MPa grade hot-dip galvanized composite steel, characterized in that: The composition of the 980MPa grade hot-dip galvanized complex phase steel includes the following chemical components in mass percentage: C: 0.10~0.15%, Si: 0.20~0.50%, Mn: 1.60~2.20%, P≤0.025%, S≤0.010%, Mo: 0.20~0.35%, Nb: 0.025~0.055%, Ti: 0.035~0.080%, Als: 0.015~0.075%, N≤0.0050%, the remaining elements are Fe and unavoidable impurities; The microstructure of the 980MPa grade hot-dip galvanized composite steel is composed of 20-25vol.% ferrite, 40-45vol.% martensite and 30-40vol.% bainite, and the average grain size of the ferrite is 0.8-1.0μm. The yield strength of the 980MPa grade hot-dip galvanized composite steel is 800-860MPa, the tensile strength is 1000-1100MPa, and the elongation A is 0. 80 The value is 13.5~18.0%, and the hole expansion rate is 65~85%.

2. The 980MPa grade hot-dip galvanized complex phase steel according to claim 1, characterized in that: The composition of the 980MPa grade hot-dip galvanized complex phase steel includes the following chemical components in mass percentage: C: 0.11~0.14%, Si: 0.25~0.40%, Mn: 1.85~2.10%, Mo: 0.20~0.30%, Nb: 0.030~0.050%, Ti: 0.040~0.060, Als: 0.030~0.065%, P≤0.015%, S≤0.005%, N≤0.0045%, the balance is Fe and unavoidable impurities.

3. A method for preparing the 980MPa grade hot-dip galvanized complex phase steel according to any one of claims 1 to 2, characterized in that: The steps include: Step 1: Smelting process: Smelting according to the chemical composition of 980MPa grade hot-dip galvanized complex phase steel, and obtaining slabs by casting; Step 2, hot rolling process: the slab is subjected to heating, descaling, rough rolling, finish rolling and laminar cooling to obtain a hot-rolled coil, i.e., hot-rolled strip; Step 3, pickling process: After the hot-rolled strip is uncoiled, straightened and scaled, and the plate shape is adjusted, it is subjected to shallow turbulent pickling to obtain pickled strip; Step 4: Hot-dip galvanizing process: The pickled strip steel is hot-dip galvanized to obtain 980MPa grade hot-dip galvanized composite steel.

4. The method for preparing 980MPa grade hot-dip galvanized complex phase steel according to claim 3, characterized in that: In the step 2, the heating temperature of the heating process is 1220-1260° C.; the total furnace time is 290-430 min, the finishing rolling start temperature is 1045-1135° C., the final rolling temperature is 870-940° C., and the hot rolling thickness is 2.5-4.5 mm; the strip head and tail are adjusted using a hot coil box before entering the finishing mill; High-pressure water descaling treatment is carried out at the roughing and finishing rolling entrances respectively. The pressure of high-pressure water is 18~22MPa, and the descaling water volume at the roughing and finishing rolling entrances is 540m3 respectively. 3 / h and 450m 3 / h, the distances between the nozzle and the slab / strip are 120mm and 90mm respectively.

5. The method for preparing 980MPa grade hot-dip galvanized complex phase steel according to claim 3 or 4, characterized in that: In the step 2, the laminar cooling adopts a sparse cooling method, the intermediate temperature is 600-680°C, the coiling temperature is 495-545°C, and a "U-type coiling" method is adopted. "U-type coiling" means that the coiling temperature of the first 80m of the strip is 500-570°C and the coiling temperature of the last 100m of the strip is 515-585°C. The laminar cooling type is upper and lower tube laminar cooling, and the laminar cooling water pressure is 0.05~0.08Mpa; the strip is subjected to side water spraying treatment, wherein the side spraying water pressure is 1.2~1.6MPa, and the maximum side spraying water volume is 350m 3 / h, and the side jet pressure is 0.4~0.6MPa.

6. The method for preparing 980MPa grade hot-dip galvanized complex phase steel according to claim 3, characterized in that: In the step three, during the uncoiling process, the uncoiler threading speed is 45-65 m / min, the tail swinging speed is 80-120 m / min, and the rest of the uncoiling speed is maintained at 130-160 m / min; a six-roll straightening machine is used to pull the strip head out of the uncoiler, and the strip head and tail are straightened to make the strip easy to thread, the six-roll straightening machine is maintained at a speed of 130-160 m / min for scale breaking treatment, the elongation is maintained at 1.5-2.5%, and the tension of the straightening machine is 40-50 tons.

7. The method for preparing 980MPa grade hot-dip galvanized complex phase steel according to claim 3 or 6, characterized in that: In the step 3, the pickling process uses an acid solution to remove the oxide scale on the surface of the hot-rolled coil to obtain a pickled plate, which adopts a low acid consumption, high efficiency immersion acid tank, including three-stage pickling and four-stage rinsing, wherein the acid solution temperature of the three pickling processes is 75~93°C, the free HCl concentration of the three pickling processes is 2.5~5.0%, 6~12%, and 9~15% respectively, and the Fe 2+ The pH values ​​are controlled at 1.0~2.5, 3.0~4.0, 4.0~5.5 and 5.0~6.5 respectively; the strip steel after rinsing is dried in a dryer, and the air supply temperature of the dryer is 80~140℃.

8. The method for preparing 980MPa grade hot-dip galvanized complex phase steel according to claim 3, characterized in that: In the step 4, the pickled strip is heated to 300° C. and 670° C. to 720° C. at a rate of 3 to 8° C. / s and 0.3 to 2.1° C. / s, respectively. After being soaked and held for 45 to 105 seconds, it is cooled to 520 to 560° C. at a rate of 0.8 to 6.5° C. / s. It is then cooled to 440 to 480° C. at a rate of 5 to 23° C. / s, held evenly for 20 to 50 seconds, and then immersed in a zinc pot for hot-dip galvanizing. After exiting the zinc pot, it is cooled to room temperature at a rate of 4 to 10° C. / s to obtain 980 MPa grade hot-dip galvanized complex phase steel. The unit speed is 60 to 100 m / min, and the unit speed is reduced by 10 m / min for every 0.5 mm increase in strip thickness. The skin-pass elongation is 0.6 to 1.0%, and the skin-pass elongation is reduced by 0.1% for every 0.5 mm increase in strip thickness.

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