1180mpa grade hot-dip galvanizing dh steel, preparation method and application thereof

Abstract

The application provides a 1180MPa-grade hot-dip galvanizing DH steel, a preparation method and application. The chemical components of the 1180MPa-grade hot-dip galvanizing DH steel, in percentage by mass, comprise: C 0.20-0.22%, Si 0.5-0.6%, Mn 2.5-2.7%, Al 0.75-0.85%, Cr 0.4-0.5%, Nb 0.02-0.03%, Ti 0.02-0.03%, P≤0.02%, S≤0.01%, N≤0.008%, and the balance of Fe and inevitable impurities; wherein the yield strength of the 1180MPa-grade hot-dip galvanizing DH steel is 600-750MPa, and the elongation is ≥12%. The preparation method is simple and convenient to operate, and only through the accurate regulation of the components and the cooperation of the process, the target performance can be realized, and the method is suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and particularly relates to a 1180MPa grade hot-dip galvanized DH steel, its preparation method, and its application. Background Technology

[0002] In the early stages of automotive lightweighting, traditional dual-phase steel (DP steel) enjoyed excellent strength-plasticity matching and moderate production costs, leading to its widespread application in automotive structural components and driving the lightweighting process. However, as automotive body designs have become more complex and integrated, the inherent defects of traditional DP steel have become increasingly apparent. Its poor flanging and bending performance makes it difficult to meet the forming requirements of complex structural components such as door anti-collision beams and B-pillar reinforcement plates, and it cannot satisfy the high standards of material forming precision and structural reliability required by mid-to-high-end automobiles. To address the technical challenge of insufficient formability of traditional DP steel, formability-enhanced dual-phase steel (DH steel) has gradually achieved industrial application. DH steel not only significantly improves the material's plasticity and work hardening index but also significantly enhances its impact energy absorption performance, perfectly matching the comprehensive performance requirements of complex automotive components. It has rapidly become an ideal material for complex structural components in mid-to-high-end automobiles, demonstrating broad application prospects in the high-end field of automotive lightweighting.

[0003] Currently, existing technologies for preparing 1180MPa grade ultra-high strength DH steel mainly rely on high-alloy additives to ensure the material's ultra-high strength and comprehensive mechanical properties. However, while high-alloy additives significantly improve the strength of the substrate itself, they result in poor uniformity and difficulty in achieving stable rolling. Furthermore, high-alloy components promote the formation of a dense oxide layer on the surface of the hot-rolled plate, which not only increases the difficulty and production cost of the pickling process but also easily leads to quality defects such as residual iron oxide scale and pitting on the steel plate surface, failing to meet the stringent surface precision and quality requirements for automotive steel. Therefore, this invention provides an 1180MPa grade hot-dip galvanized DH steel, its preparation method, and its application, to solve the problems of poor surface quality and high production cost of existing 1180MPa grade hot-dip galvanized DH steel. Summary of the Invention

[0004] The main objective of this invention is to provide a 1180MPa grade hot-dip galvanized DH steel, its preparation method, and its application, aiming to solve the technical problems of poor surface quality and high production cost of 1180MPa grade hot-dip galvanized DH steel in the prior art.

[0005] To achieve the above objectives, the present invention provides a 1180MPa grade hot-dip galvanized DH steel. The chemical composition of the 1180MPa grade hot-dip galvanized DH steel, by mass percentage, includes: C 0.20~0.22%, Si 0.5~0.6%, Mn 2.5~2.7%, Al 0.75~0.85%, Cr 0.4~0.5%, Nb 0.02~0.03%, Ti 0.02~0.03%, P≤0.02%, S≤0.01%, N≤0.008%, with the balance being Fe and unavoidable impurities.

[0006] The yield strength of the 1180MPa grade hot-dip galvanized DH steel is 600~750MPa.

[0007] The elongation after fracture of the 1180MPa grade hot-dip galvanized DH steel is ≥12%.

[0008] According to the embodiments of this application, the thickness of the 1180MPa grade hot-dip galvanized DH steel is 0.8~2.0mm.

[0009] The tensile strength of the 1180MPa grade hot-dip galvanized DH steel is 1100~1380MPa.

[0010] The finishing elongation of the 1180MPa grade hot-dip galvanized DH steel is 0.3~0.5%.

[0011] According to the embodiments of this application, the metallographic structure of the 1180MPa grade hot-dip galvanized DH steel, by volume fraction, comprises 30-40% ferrite, 50-60% martensite, and 5-8% retained austenite.

[0012] The present invention also provides a method for preparing the 1180MPa grade hot-dip galvanized DH steel as described above, comprising the following steps: S1: After heating the continuously cast billet, rough rolling, finish rolling and coiling are performed to obtain hot-rolled steel coils.

[0013] S2: Pickling the hot-rolled steel coil to obtain a pickled coil.

[0014] S3: Anneal the pickled coil and then cold roll it to obtain a cold-hardened coil.

[0015] S4: The cold-hardened coil is subjected to continuous annealing and hot-dip galvanizing in sequence, followed by finishing and tension straightening to obtain the 1180MPa grade hot-dip galvanized DH steel.

[0016] According to an embodiment of this application, the thickness of the continuously cast billet is 200~250mm.

[0017] The heating temperature is 1200~1280℃.

[0018] The heating time is 120~380 minutes.

[0019] The finishing rolling temperature is 890~930℃.

[0020] According to an embodiment of this application, the winding process includes a U-shaped low-temperature segmented winding process.

[0021] The winding temperature for the head and tail sections (40-60m each) is 580-630℃, and the winding temperature for the middle section is 520-580℃.

[0022] According to an embodiment of this application, the pickling temperature is ≥75°C.

[0023] The pickling solution includes hydrochloric acid.

[0024] H in hydrochloric acid + Concentration ≥100g / L.

[0025] The pickling rate is 30~60m / min.

[0026] According to an embodiment of this application, the annealing includes shroud annealing.

[0027] The temperature for the bell-type annealing is 600~630℃.

[0028] The duration of the annealing process is 12-15 hours.

[0029] The total reduction rate of the cold rolling is 50-70%.

[0030] According to the embodiments of this application, the continuous annealing sequentially includes a preheating section, a heating section, a slow cooling section, and a rapid cooling section.

[0031] The temperature of the preheating section is 560~670℃.

[0032] The temperature of the heating section is 810~830℃.

[0033] The temperature of the slow cooling section is 660~690℃.

[0034] The temperature of the rapid cooling section is 460~480℃.

[0035] The atmosphere dew point inside the furnace during continuous annealing is -30 to -10°C.

[0036] The cold-rolled coil operates at a speed of ≥60m / min.

[0037] The present invention also provides an application of the above-mentioned 1180MPa grade hot-dip galvanized DH steel or the 1180MPa grade hot-dip galvanized DH steel prepared by the above-mentioned preparation method in the manufacture of automotive structural parts.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows: The aforementioned 1180MPa grade hot-dip galvanized DH steel uses low-cost alloys such as C, Si, Mn, and Al as its basic components, with only trace amounts of Cr, Nb, and Ti added for performance control. It avoids the introduction of expensive alloys such as Mo throughout the process, while strictly limiting the content of harmful impurities such as P, S, and N. This allows the steel to achieve an ultra-high tensile strength of 1180MPa while also maintaining excellent yield strength, significantly reducing production costs for enterprises and precisely matching the stringent requirements of automotive steel sheets. By designing a low to medium C content, the steel's strength is ensured while avoiding increased brittleness due to excessive carbide precipitation. Combined with the solid solution strengthening and hardenability-enhancing effects of Mn and Cr, and the solid solution strengthening and oxidation resistance-improving effects of Si and Al, multi-element synergy achieves highly efficient improvement in solid solution strengthening. Simultaneously, the precise addition of Nb and Ti microalloying elements forms fine carbonitride precipitates, achieving precipitation strengthening and grain refinement, further enhancing the steel's strength while effectively improving its toughness, thus solving the technical problem of easy toughness deterioration after strength enhancement in ultra-high-strength steel. Furthermore, the 1180MPa grade hot-dip galvanized DH steel produced by this invention has a yield strength of 600~750MPa and a tensile strength of 1100~1380MPa. Its "low yield and high elongation" characteristics are more suitable for complex stamping processing requirements, improving its application applicability.

[0039] Moreover, the preparation method of the present invention is simple and easy to operate. The target performance can be achieved by precise control of the composition and synergistic coordination of the process. No precious metal elements need to be added. While ensuring ultra-high strength, excellent surface quality and hot-dip galvanization compatibility, the production cost of 1180MPa grade hot-dip galvanized DH steel is effectively controlled, making it suitable for large-scale industrial production. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0041] Figure 1 The image shows the metallographic structure of the 1180MPa grade hot-dip galvanized DH steel obtained in Example 1 of this invention. Figure 2 Scanning electron microscope image of 1180MPa grade hot-dip galvanized DH steel obtained in Example 1 of this invention; Figure 3 This is a microstructure diagram of the pickled roll of Embodiment 1 of the present invention after bell-type annealing; Figure 4 This is a scanning electron microscope image of the pickled roll of Embodiment 1 of the present invention after bell-type annealing.

[0042] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0045] To achieve the above objectives, the present invention provides a 1180MPa grade hot-dip galvanized DH steel. The chemical composition of the 1180MPa grade hot-dip galvanized DH steel, by mass percentage, includes: C 0.20~0.22%, Si 0.5~0.6%, Mn 2.5~2.7%, Al 0.75~0.85%, Cr 0.4~0.5%, Nb 0.02~0.03%, Ti 0.02~0.03%, P≤0.02%, S≤0.01%, N≤0.008%, with the balance being Fe and unavoidable impurities.

[0046] The yield strength of the 1180MPa grade hot-dip galvanized DH steel is 600~750MPa.

[0047] The elongation after fracture of the 1180MPa grade hot-dip galvanized DH steel is ≥12%.

[0048] In some embodiments, the chemical composition of the 1180MPa grade hot-dip galvanized DH steel, by mass percentage, includes: C 0.20~0.22%, Si 0.5~0.585%, Mn 2.5~2.6%, Al 0.76~0.81%, Cr 0.41~0.44%, Nb 0.02~0.024%, Ti 0.02~0.025%, P≤0.014%, S≤0.004%, N≤0.005%, with the balance being Fe and unavoidable impurities.

[0049] In some embodiments, carbon (C) acts as the core austenite stabilizing element. The C content directly affects all phase transformation processes and determines the final microstructure and mechanical properties. The C content in retained austenite is a key factor influencing its stability, and the content and stability of retained austenite are crucial factors determining the properties of DH steel. Generally, a high C content in retained austenite results in high stability, but excessively high C content in the steel deteriorates its mechanical properties and weldability. Conversely, a low C content leads to insufficient stability of the retained austenite. Therefore, the C content in this invention is strictly controlled to be 0.20%~0.22%.

[0050] Si is a highly efficient solid solution strengthening element for ferrite. It can accelerate the segregation of carbon into austenite to improve hardenability, promote ferrite purification, and expand the temperature range of the ferrite-austenite two-phase region, ensuring the stability and reproducibility of the microstructure and properties of DH steel. However, excessive Si content can easily lead to oxidation of the steel strip surface during annealing, reduce galvanizing wettability and cause incomplete galvanizing, and also deteriorate weldability. Therefore, the Si content is strictly controlled at 0.5%~0.6%.

[0051] Manganese (Mn) is a typical element that expands the austenite region. During the slow cooling stage, it can delay the formation of pearlite and bainite, improve the hardenability of steel, and create conditions for martensite formation during subsequent cooling. However, too low amn content leads to unstable austenite, which easily transforms into bainite during cooling, failing to form the composite structure of "ferrite + martensite + retained austenite" required for DH steel. Too high amn content, on the other hand, excessively stabilizes austenite, inhibiting the effect of Si in promoting ferrite precipitation, reducing the amount of ferrite and the carbon content of retained austenite, thus decreasing hardenability and making it prone to surface oxidation deposition during annealing, deteriorating the quality of galvanizing. Therefore, the mn content should be strictly controlled at 2.5%~2.7%.

[0052] The main role of Al in steel is to refine grains and fix nitrogen in the steel, which can significantly improve the impact toughness of steel and reduce the tendency for cold brittleness and aging. Al plays a similar role to Si in DH steel, affecting the austenite morphology during critical heating. Al can also form AlN precipitation, further refining the grains. Considering the limited Si addition in galvanized DH steel, Al can act as a substitute for Si. However, excessive Al content increases production costs and leads to difficulties in continuous casting. Therefore, the Al content is strictly controlled at 0.75%~0.85% in this invention.

[0053] Cr can significantly delay the transformation of pearlite and bainite, improve the hardenability of austenite formed during critical zone annealing, and obtain a high martensite volume fraction at a lower cooling rate, thereby enabling austenite to fully transform into martensite. Furthermore, Cr has a significant cost advantage over Mo and Nb. In this invention, the Cr content is strictly controlled to be 0.4%~0.5%.

[0054] Nitrogen (Nb) can form carbon and nitrogen compounds with carbon (C) and nitrogen (N), which precipitate at the phase interface during the austenite-ferrite transformation, preventing ferrite grain growth and refining the grain size. When Nb is added to a certain value, precipitation strengthening can occur. In this invention, the Nb content is strictly controlled to be 0.02%~0.03%.

[0055] Ti (Ti) works synergistically with Nb (Ni), forming more stable carbonitridium compounds with C and N in steel. These compounds precipitate uniformly during hot working and annealing, enhancing grain refinement through a multiple pinning effect. Simultaneously, Ti assists Nb in achieving composite precipitation strengthening, further improving the strength and toughness of the steel. Ti's strong fixing effect on C and N also reduces the adverse effects of free C and N on weldability. However, excessive Ti content increases alloy costs and easily forms large inclusions, affecting the quality of the galvanized surface. In this invention, the Nb content is strictly controlled at 0.02%~0.03%, achieving a synergistic optimization effect with Nb.

[0056] In some embodiments, the yield strength of the 1180MPa grade hot-dip galvanized DH steel is 630~750MPa.

[0057] The elongation after fracture of the 1180MPa grade hot-dip galvanized DH steel is 12-20%.

[0058] In some embodiments, the yield strength of the 1180MPa grade hot-dip galvanized DH steel is 630~720MPa.

[0059] The elongation after fracture of the 1180MPa grade hot-dip galvanized DH steel is 14~18%.

[0060] The aforementioned 1180MPa grade hot-dip galvanized DH steel uses low-cost alloys such as C, Si, Mn, and Al as its basic components, with only trace amounts of Cr, Nb, and Ti added for performance control. It avoids the introduction of expensive alloys such as Mo throughout the process, while strictly limiting the content of harmful impurities such as P, S, and N. This allows the steel to achieve an ultra-high tensile strength of 1180MPa while also maintaining excellent yield strength, significantly reducing production costs for enterprises and precisely matching the stringent requirements of automotive steel sheets. By designing a low to medium C content, the steel's strength is ensured while avoiding increased brittleness due to excessive carbide precipitation. Combined with the solid solution strengthening and hardenability-enhancing effects of Mn and Cr, and the solid solution strengthening and oxidation resistance-improving effects of Si and Al, multi-element synergy achieves highly efficient improvement in solid solution strengthening. Simultaneously, the precise addition of Nb and Ti microalloying elements forms fine carbonitride precipitates, achieving precipitation strengthening and grain refinement, further enhancing the steel's strength while effectively improving its toughness, thus solving the technical problem of easy toughness deterioration after strength enhancement in ultra-high-strength steel. Furthermore, the 1180MPa grade hot-dip galvanized DH steel produced by this invention has a yield strength of 600~750MPa and a tensile strength of 1100~1380MPa. Its "low yield and high elongation" characteristics are more suitable for complex stamping processing requirements, improving its application applicability.

[0061] In some embodiments, the thickness of the 1180MPa grade hot-dip galvanized DH steel is 0.8~2.0mm.

[0062] The tensile strength of the 1180MPa grade hot-dip galvanized DH steel is 1100~1380MPa.

[0063] The finishing elongation of the 1180MPa grade hot-dip galvanized DH steel is 0.3~0.5%.

[0064] In some embodiments, the tensile strength of the 1180MPa grade hot-dip galvanized DH steel is 1150~1200MPa.

[0065] The finishing elongation of the 1180MPa grade hot-dip galvanized DH steel is 0.35~0.45%.

[0066] In some embodiments, the metallographic structure of the 1180MPa grade hot-dip galvanized DH steel, by volume fraction, comprises 30-40% ferrite, 50-60% martensite, and 5-8% retained austenite.

[0067] The present invention also provides a method for preparing the 1180MPa grade hot-dip galvanized DH steel as described above, comprising the following steps: S1: After heating the continuously cast billet, rough rolling, finish rolling and coiling are performed to obtain hot-rolled steel coils.

[0068] In some embodiments, the thickness of the continuously cast billet is 200-250 mm.

[0069] In some embodiments, the thickness of the continuously cast billet is 220~240mm.

[0070] In some embodiments, the heating temperature is 1200~1280°C.

[0071] The heating time is 120~380 minutes.

[0072] In some embodiments, the heating temperature is 1240~1280°C.

[0073] The heating time is 150~350 minutes.

[0074] In some embodiments, the heating time is 190-260 minutes.

[0075] In some embodiments, the heated continuously cast billet is rough-rolled, finish-rolled and coiled to obtain a hot-rolled steel coil, wherein the final rolling temperature of the finish rolling is 890~930℃.

[0076] In some embodiments, the finishing rolling temperature is 900~920℃.

[0077] In some embodiments, the final rolling temperature of hot rolling is set at a temperature higher than that of the austenitic region of Ar3. If the temperature is too high, the iron oxide scale becomes severe and difficult to pickle, affecting the surface quality of the steel plate. If the temperature is too low, entering the two-zone rolling process will result in mixed crystals in the material, producing snowflake-like defects during stamping, affecting the surface quality of the galvanized plate. Therefore, the final rolling temperature of finishing rolling is strictly controlled to be 890~930℃.

[0078] In some embodiments, after the heated continuous casting billet is rolled in 5 to 7 passes, the thickness of the intermediate billet is 35 to 45 mm.

[0079] In some embodiments, the winding process includes a U-shaped low-temperature segmented winding process.

[0080] The winding temperature for the head and tail sections (40-60m each) is 580-630℃, and the winding temperature for the middle section is 520-580℃.

[0081] In some embodiments, a high coiling temperature is beneficial for grain growth, reducing strength and improving formability. However, excessively high annealing temperatures can lead to severe iron oxide scale on the steel plate surface, making it difficult to pickle and affecting the quality of the steel plate. In order to ensure the stability of the continuous coiling performance, a U-shaped coiling process is adopted. The coiling temperature for the first 45-55 meters and the last 45-55 meters is 600-620°C, and the coiling temperature for the middle section is 550-560°C.

[0082] S2: Pickling the hot-rolled steel coil to obtain a pickled coil.

[0083] In some embodiments, hot-rolled coils inevitably generate iron oxide scale. When the iron oxide scale is controllable, improper pickling process can lead to incomplete pickling of surface iron oxide scale, resulting in oxide intrusion and over-pickling. Therefore, hot-rolled steel coils are uncoiled and then pickled to obtain pickled coils; wherein, the pickling temperature is ≥75°C.

[0084] The pickling solution includes hydrochloric acid.

[0085] H in hydrochloric acid + Concentration ≥100g / L.

[0086] The pickling rate is 30~60m / min.

[0087] In some embodiments, the pickling temperature is 75~85°C.

[0088] H in hydrochloric acid + The concentration is 100~170g / L.

[0089] The pickling rate is 30~40m / min.

[0090] In some embodiments, the pickling temperature is 80~85°C.

[0091] H in hydrochloric acid + The concentration is 150~170g / L.

[0092] In some embodiments, the hydrochloric acid contains H + The concentration is 220~240g / L.

[0093] S3: Anneal the pickled coil and then cold roll it to obtain a cold-hardened coil.

[0094] In some embodiments, the annealing includes hood annealing.

[0095] The temperature for the bell-type annealing is 600~630℃.

[0096] The duration of the annealing process is 12-15 hours.

[0097] The total reduction rate of the cold rolling is 50-70%.

[0098] In some embodiments, the pickled coil is subjected to bell annealing, and then the pickled steel coil is cold rolled and coiled on a single stand to obtain a cold-hardened coil. The bell annealing process can reduce the strength of the substrate. If the temperature is too high or the time is too long, the substrate strength will be too low and a large amount of alloy will precipitate, resulting in low product performance after galvanizing. If the temperature is too low or the time is too short, the substrate strength will be too high, making rolling difficult during pickling. Therefore, the bell annealing process is controlled as follows: the bell annealing temperature is 615~625℃ and the bell annealing time is 12~14h.

[0099] After the steel sheet is annealed in a bell, it is rolled and coiled in a single stand to obtain a cold-rolled coil. A larger amount of cold rolling deformation can reduce the recrystallization temperature and phase transformation temperature; however, excessive deformation will increase the rolling difficulty, so the total cold rolling reduction rate is controlled at 52~67%.

[0100] S4: The cold-hardened coil is subjected to continuous annealing and hot-dip galvanizing in sequence, followed by finishing and tension straightening to obtain the 1180MPa grade hot-dip galvanized DH steel.

[0101] In some embodiments, the continuous annealing process sequentially includes a preheating section, a heating section, a slow cooling section, and a rapid cooling section.

[0102] In some embodiments, the cold-rolled coil is unwound and then continuously annealed before galvanizing; wherein, the temperature of the preheating section is 560~670℃; the temperature of the heating section is 810~830℃; the temperature of the slow cooling section is 660~690℃; the temperature of the rapid cooling section is 460~480℃; and the dew point of the atmosphere in the furnace during continuous annealing is -30~-10℃.

[0103] In some embodiments, the temperature of the preheating section is 600~665℃; the temperature of the heating section is 815~830℃; the temperature of the slow cooling section is 665~680℃; and the temperature of the rapid cooling section is 460~480℃.

[0104] In some embodiments, by controlling the humidification process, the external oxidation of alloying elements in the strip steel can be transformed into internal oxidation, ensuring the surface quality of galvanized products. If the dew point in the furnace is too low, the alloying elements will undergo external oxidation, resulting in incomplete galvanization of the galvanized products. If the dew point in the furnace is too high, over-oxidation will occur, resulting in defects such as pitting in the galvanized products. Therefore, the atmosphere dew point in the furnace for continuous annealing is controlled to be -25~-10℃.

[0105] In some embodiments, the cold-rolled roll operates at a speed ≥60m / min.

[0106] In some embodiments, the cold-rolled roll operates at a speed of 60-80 m / min.

[0107] The preparation method of this invention is simple and easy to operate. The target performance can be achieved by precise control of the composition and synergistic coordination of the process. No precious metal elements need to be added. While ensuring ultra-high strength, excellent surface quality and compatibility with hot-dip galvanizing, the production cost of 1180MPa grade hot-dip galvanized DH steel is effectively controlled, making it suitable for large-scale industrial production.

[0108] The present invention also provides an application of the above-mentioned 1180MPa grade hot-dip galvanized DH steel or the 1180MPa grade hot-dip galvanized DH steel prepared by the above-mentioned preparation method in the manufacture of automotive structural parts.

[0109] In some embodiments, the 1180MPa grade hot-dip galvanized DH steel of the present invention is applied to the preparation of automotive structural parts. It has ultra-high strength, excellent hot-dip galvanizing process adaptability, good formability and long-term corrosion resistance. It not only meets the core development needs of the automotive industry of "lightweight, high safety and long service life", but also adapts to the requirements of large-scale and automated production of automotive structural parts, achieving multiple breakthroughs in technical performance, production application and product value.

[0110] To further illustrate the present invention, the following examples are provided: Example 1 A 1180MPa grade hot-dip galvanized DH steel, the chemical composition of the 1180MPa grade hot-dip galvanized DH steel in Example 1 is shown in Table 1.

[0111] A method for preparing 1180MPa grade hot-dip galvanized DH steel, comprising the following steps: S1: After heating the continuously cast billet, it is subjected to rough rolling, finish rolling and coiling to obtain hot-rolled steel coils. The thickness of the continuously cast billet is 230mm; the thickness of the intermediate billet after 7 passes of rough rolling is 40mm; the heating temperature is 1245℃; the heating time is 221min; the final rolling temperature of finish rolling is 915℃; the coiling is a U-shaped low-temperature segmented coiling process; the coiling temperature of the first 50m and the last 50m is 613℃, and the coiling temperature of the middle section is 550℃.

[0112] S2: Pickling of hot-rolled steel coils yields pickled coils; the pickling temperature is 83℃; the pickling solution is hydrochloric acid solution; the hydrochloric acid solution contains H... + The concentration was 162 g / L; the pickling rate was 40 m / min.

[0113] S3: The pickled coil is annealed and then cold-rolled to obtain a chilled coil; the annealing is a bell-type annealing. The annealing temperature is 620℃; the annealing time is 13h; the total reduction rate of cold rolling is 67%.

[0114] S4: The cold-rolled coil is continuously annealed and hot-dip galvanized, followed by finishing and tension leveling to obtain 1180MPa grade hot-dip galvanized DH steel. The continuous annealing process consists of a preheating section, a heating section, a slow cooling section, and a rapid cooling section; the temperature of the preheating section is 665℃; the temperature of the heating section is 825℃; the temperature of the slow cooling section is 671℃; the temperature of the rapid cooling section is 475℃; the dew point of the atmosphere in the furnace during continuous annealing is -22℃; and the running speed of the cold-rolled coil is 60m / min.

[0115] Testing revealed that the metallographic structure of the 1180MPa grade hot-dip galvanized DH steel prepared in Example 1, by volume fraction, consisted of 35% ferrite, 60% martensite, and 8% retained austenite. The 1180MPa grade hot-dip galvanized DH steel prepared in Example 1 had a thickness of 0.8 mm, a yield strength of 648 MPa, a tensile strength of 1233 MPa, an elongation after fracture of 15%, and a finishing elongation of 0.4%.

[0116] Example 2 Compared with Example 1, the chemical composition and relevant parameters in the preparation method of 1180MPa grade hot-dip galvanized DH steel were changed. Specific test parameters and performance test results are shown in Tables 1 to 5.

[0117] Example 3 Compared with Example 1, the chemical composition and relevant parameters in the preparation method of 1180MPa grade hot-dip galvanized DH steel were changed. Specific test parameters and performance test results are shown in Tables 1 to 5.

[0118] Example 4 Compared with Example 1, the chemical composition and relevant parameters in the preparation method of 1180MPa grade hot-dip galvanized DH steel were changed. Specific test parameters and performance test results are shown in Tables 1 to 5.

[0119] Example 5 Compared with Example 1, the chemical composition and relevant parameters in the preparation method of 1180MPa grade hot-dip galvanized DH steel were changed. Specific test parameters and performance test results are shown in Tables 1 to 5.

[0120] Example 6 Compared with Example 1, the chemical composition and relevant parameters in the preparation method of 1180MPa grade hot-dip galvanized DH steel were changed. Specific test parameters and performance test results are shown in Tables 1 to 5.

[0121] Comparative Example 1 Compared to Example 1, Comparative Example 1 altered the chemical composition of 1180MPa grade hot-dip galvanized DH steel.

[0122] The chemical composition of the 1180MPa grade hot-dip galvanized DH steel in Comparative Example 1 is as follows: C 0.2198%, Si 0.3564%, Mn 2.5280%, Al 0.6854%, Cr 0.6719%, Nb 0.3212%, Ti 0.2166%, P≤0.02%, S≤0.01%, N≤0.008%, with the balance being Fe and unavoidable impurities. The other steps are the same as in Example 1, and the 1180MPa grade hot-dip galvanized DH steel is obtained.

[0123] The altered chemical composition resulted in a decrease in the content of ferrite and retained austenite, leading to a reduction in elongation after fracture.

[0124] Testing revealed that the microstructure of the 1180MPa grade hot-dip galvanized DH steel prepared in Comparative Example 1, by volume fraction, consisted of 26% ferrite, 71% martensite, and 3% retained austenite. The 1180MPa grade hot-dip galvanized DH steel prepared in Comparative Example 1 had a thickness of 1.2 mm, a yield strength of 812 MPa, a tensile strength of 1225 MPa, and an elongation after fracture of 13%.

[0125] Comparative Example 2 Compared to Example 1, Comparative Example 2 changed the preparation method of 1180MPa grade hot-dip galvanized DH steel.

[0126] In Comparative Example 2, the preparation method did not use the bell-type annealing in step S3 of Example 1, but instead used direct annealing after cold rolling; the other steps were the same as in Example 1, and 1180MPa grade hot-dip galvanized DH steel was obtained.

[0127] The failure to use a bell-type annealing method resulted in difficulties in rolling and a high strength and low elongation after fracture of the finished product.

[0128] Testing revealed that the microstructure of the 1180MPa grade hot-dip galvanized DH steel prepared in Comparative Example 2, by volume fraction, consisted of 28% ferrite, 65% martensite, and 7% retained austenite. The 1180MPa grade hot-dip galvanized DH steel prepared in Comparative Example 2 had a thickness of 1.5 mm, a yield strength of 988 MPa, a tensile strength of 1340 MPa, and an elongation after fracture of 7%.

[0129] Table 1: Chemical composition (%) of 1180MPa grade hot-dip galvanized DH steel in Examples 1-6 Table 2 Hot rolling process parameters for Examples 1-6 Table 3 Cold rolling process parameters for Examples 1-6 Table 4. Galvanizing process parameters for Examples 1-6 Table 5 Mechanical property parameters of 1180MPa grade hot-dip galvanized DH steel obtained in Examples 1-6 The mechanical properties of the steel in this invention were tested according to GB / T 228. As can be seen from Table 5, the head, middle, and tail properties of the 1180MPa grade hot-dip galvanized DH steel prepared by the method of this invention can be stably controlled. See also... Figure 1 The metallographic diagram of the 1180MPa grade hot-dip galvanized DH steel prepared in Example 1 of the present invention is shown. Figure 2 The image shown is a scanning electron microscope (SEM) image of the 1180MPa grade hot-dip galvanized DH steel prepared in Example 1 of the present invention. It can be seen that the microstructure of the 1180MPa grade hot-dip galvanized DH steel prepared in Example 1 consists of ferrite, martensite, and retained austenite. (See also...) Figure 3 The microstructure of the pickled roll of Embodiment 1 of the present invention after bell-type annealing is shown in the figure. Figure 4 The scanning electron microscope image of the pickled coil of Embodiment 1 of the present invention after bell annealing shows that a large amount of carbides precipitate after bell annealing, thereby reducing the strength and rolling difficulty of the 1180MPa grade hot-dip galvanized DH steel.

[0130] The aforementioned 1180MPa grade hot-dip galvanized DH steel uses low-cost alloys such as C, Si, Mn, and Al as its basic components, with only trace amounts of Cr, Nb, and Ti added for performance control. It avoids the introduction of expensive alloys such as Mo throughout the process, while strictly limiting the content of harmful impurities such as P, S, and N. This allows the steel to achieve an ultra-high tensile strength of 1180MPa while also maintaining excellent yield strength, significantly reducing production costs for enterprises and precisely matching the stringent requirements of automotive steel sheets. By designing a low to medium C content, the steel's strength is ensured while avoiding increased brittleness due to excessive carbide precipitation. Combined with the solid solution strengthening and hardenability-enhancing effects of Mn and Cr, and the solid solution strengthening and oxidation resistance-improving effects of Si and Al, multi-element synergy achieves highly efficient improvement in solid solution strengthening. Simultaneously, the precise addition of Nb and Ti microalloying elements forms fine carbonitride precipitates, achieving precipitation strengthening and grain refinement, further enhancing the steel's strength while effectively improving its toughness, thus solving the technical problem of easy toughness deterioration after strength enhancement in ultra-high-strength steel. Furthermore, the 1180MPa grade hot-dip galvanized DH steel produced by this invention has a yield strength of 600~750MPa and a tensile strength of 1100~1380MPa. Its "low yield and high elongation" characteristics are more suitable for complex stamping processing requirements, improving its application applicability.

[0131] Moreover, the preparation method of the present invention is simple and easy to operate. The target performance can be achieved by precise control of the composition and synergistic coordination of the process. No precious metal elements need to be added. While ensuring ultra-high strength, excellent surface quality and hot-dip galvanization compatibility, the production cost of 1180MPa grade hot-dip galvanized DH steel is effectively controlled, making it suitable for large-scale industrial production.

[0132] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A 1180MPa grade hot-dip galvanized DH steel, characterized in that, The chemical composition of the 1180MPa grade hot-dip galvanized DH steel, by mass percentage, includes: C 0.20~0.22%, Si 0.5~0.6%, Mn 2.5~2.7%, Al 0.75~0.85%, Cr 0.4~0.5%, Nb 0.02~0.03%, Ti 0.02~0.03%, P≤0.02%, S≤0.01%, N≤0.008%, with the balance being Fe and unavoidable impurities; The yield strength of the 1180MPa grade hot-dip galvanized DH steel is 600~750MPa. The elongation after fracture of the 1180MPa grade hot-dip galvanized DH steel is ≥12%.

2. The 1180MPa grade hot-dip galvanized DH steel according to claim 1, characterized in that, The thickness of the 1180MPa grade hot-dip galvanized DH steel is 0.8~2.0mm; The tensile strength of the 1180MPa grade hot-dip galvanized DH steel is 1100~1380MPa; The finishing elongation of the 1180MPa grade hot-dip galvanized DH steel is 0.3~0.5%.

3. The 1180MPa grade hot-dip galvanized DH steel according to claim 1, characterized in that, The microstructure of the 1180MPa grade hot-dip galvanized DH steel, by volume fraction, comprises 30-40% ferrite, 50-60% martensite, and 5-8% retained austenite.

4. A method for preparing 1180MPa grade hot-dip galvanized DH steel as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: After heating the continuously cast billet, rough rolling, finish rolling and coiling are performed to obtain hot-rolled steel coils; S2: Pickling the hot-rolled steel coil to obtain a pickled coil; S3: Anneal the pickled coil and then cold roll it to obtain a cold-hardened coil; S4: The cold-hardened coil is subjected to continuous annealing and hot-dip galvanizing in sequence, followed by finishing and tension straightening to obtain the 1180MPa grade hot-dip galvanized DH steel.

5. The method for preparing 1180MPa grade hot-dip galvanized DH steel according to claim 4, characterized in that, The thickness of the continuously cast billet is 200~250mm; The heating temperature is 1200~1280℃; The heating time is 120~380min; The finishing rolling temperature is 890~930℃.

6. The method for preparing 1180MPa grade hot-dip galvanized DH steel according to claim 4, characterized in that, The winding process includes a U-shaped low-temperature segmented winding process; The winding temperature for the head and tail sections (40-60m each) is 580-630℃, and the winding temperature for the middle section is 520-580℃.

7. The method for preparing 1180MPa grade hot-dip galvanized DH steel according to claim 4, characterized in that, The pickling temperature is ≥75℃; The pickling solution includes hydrochloric acid; H in hydrochloric acid + Concentration ≥100g / L; The pickling rate is 30~60m / min.

8. The method for preparing 1180MPa grade hot-dip galvanized DH steel according to claim 4, characterized in that, The annealing includes shroud annealing; The temperature of the bell-type annealing is 600~630℃; The duration of the hood annealing is 12-15 hours; The total reduction rate of the cold rolling is 50-70%.

9. The method for preparing 1180MPa grade hot-dip galvanized DH steel according to claim 4, characterized in that, The continuous annealing process includes a preheating section, a heating section, a slow cooling section, and a rapid cooling section in sequence. The temperature of the preheating section is 560~670℃; The temperature of the heating section is 810~830℃; The temperature of the slow cooling section is 660~690℃; The temperature of the rapid cooling section is 460~480℃; The atmosphere dew point inside the furnace during continuous annealing is -30 to -10°C. The cold-rolled coil operates at a speed of ≥60m / min.

10. The application of 1180MPa grade hot-dip galvanized DH steel according to any one of claims 1 to 3 or 1180MPa grade hot-dip galvanized DH steel prepared by the preparation method according to any one of claims 4 to 9 in the manufacture of automotive structural parts.

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