800mpa grade alloyed galvanized super high hole expansion performance complex phase steel for automobile and preparation method thereof

Abstract

The application belongs to the field of metal materials, and provides an 800MPa-grade alloyed galvanized super high hole expansion performance composite steel for automobiles and a preparation method thereof.The composition of the steel plate is as follows in terms of percentage by weight: C: 0.12%-0.17%, Mn: 1.90%-2.25%, Si: 0.30%-0.65%, Ti: 0.020%-0.040%, P: <=0.030%, N <=0.002%, S <=0.005%, and the balance of Fe and inevitable impurities.The preparation method comprises smelting, hot rolling, pickling, cold rolling, continuous annealing and galvanizing, and finishing.The steel plate produced by the application has a microstructure mainly composed of bainite and tempered martensite, and has super high hole expansion rate and excellent forming performance.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and particularly relates to an 800MPa grade alloyed galvanized ultra-high hole expansion performance multiphase steel for automobiles and its preparation method, which is particularly suitable for complex-shaped automotive parts. Background Technology

[0002] Complex phase steel typically contains bainite and ferrite, along with small amounts of martensite, retained austenite, and pearlite, making it a high-strength steel with a complex microstructure. By adjusting the composition and proportion of each phase in complex phase steel, the steel sheet can achieve excellent mechanical properties, high hole-expanding performance, and wear resistance. It is mainly used in automotive chassis suspension components, B-pillars, bumpers, and seat rails.

[0003] "Lightweighting" has become a development trend in the automotive industry, which has also promoted the development of high-strength steel for automobiles. With the expanding applications of advanced high-strength steel, higher performance requirements are being placed on it. It needs not only high strength but also good formability, such as high elongation, high bending performance, and high hole-expanding performance. However, generally, increasing the strength of steel sheets reduces their elongation; the higher the strength, the higher its edge crack sensitivity and the worse its hole-expanding performance. Currently, cold-formed 800MPa grade multiphase steel with an elongation of 10-14% has a hole-expanding rate of approximately 45%, which can no longer meet the forming requirements of increasingly complex automotive parts.

[0004] The patent document "An 800MPa Grade Cold-Rolled Hot-Dip Galvanized Multiphase Steel and Its Preparation Method" (CN111926247A) discloses the following chemical composition (mass fraction): C: 0.06%–0.12%, Si: 0.1%–0.4%, Mn: 1.8%–2.6%, Cr: 0.2%–0.7%, P: ≤0.010%, S: ≤0.006%, Ti: 0.01%–0.04%, Nb: 0.01%–0.04%, Al: 0.1%–0.4%, B: 0.0001%–0.005%, with the remainder being Fe and unavoidable impurities; Mn+Cr+B > 2.5%. Using the aforementioned chemical composition, the steel is smelted, forged, hot-rolled, coiled, and cold-rolled. The cold-rolling reduction rate is 40%–65%, followed by annealing, hot-dip galvanizing, and finishing to obtain an 800MPa grade cold-rolled hot-dip galvanized multiphase steel with a tensile strength greater than 800MPa and a yield strength ≥660MPa. This steel grade does not involve alloyed galvanizing, and as seen from the disclosed embodiments, the tensile strength of the steel plate meets the strength requirements, while its hole expansion rate is relatively low (≤42%).

[0005] The patent document "A Multiphase Steel and Its Preparation Method" (CN116287993A) discloses a method for preparing multiphase steel that includes: smelting and continuous casting according to chemical composition to obtain a slab; heating the slab; rolling the heated slab to obtain a strip; cooling the rolled strip; and coiling the cooled strip to obtain a hot-rolled multiphase steel coil with high-expansion hole. The cooling process refers to a delayed two-stage water cooling process in the laminar flow cooling zone. Its chemical composition by weight percentage is as follows: C: 0.04%–0.12%, Si: 0.15%–0.50%, Mn: 0.80%–1.60%, P: ≤0.020%, S: ≤0.008%, Als: 0.015%–0.060%, Nb: 0.025%–0.060%, Cr: 0.20%–0.80%, Ca: 0.0005%–0.0050%, with the balance being Fe and unavoidable impurities. The yield strength of this multiphase steel is 500–560 MPa, the tensile strength is 600–680 MPa, the elongation is ≥20%, and the porosity is ≥75%. This invention is a hot-rolled multiphase steel with a high porosity, but it does not involve cold rolling or alloyed galvanizing processes. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems and shortcomings and provide an 800MPa grade alloyed galvanized ultra-high hole expansion performance multiphase steel for automobiles, which simultaneously has good elongation and ultra-high hole expansion rate, and its preparation method.

[0007] The objective of this invention is achieved as follows:

[0008] A composite steel with 800MPa grade alloyed galvanized ultra-high hole expansion performance for automotive applications, the composition of which is as follows by weight percentage: C: 0.12%~0.17%, Mn: 1.90%~2.25%, Si: 0.30%~0.65%, Ti: 0.020%~0.040%, P: ≦0.030%, N≦0.002%, S≦0.005%, with the balance being Fe and unavoidable impurities.

[0009] The alloyed coating of the multiphase steel contains 9.5% to 11.5% Fe by mass.

[0010] The microstructure of the multiphase steel includes critical zone ferrite, oriented epiphytic ferrite, bainite, tempered martensite, retained austenite, and secondary martensite; by volume percentage as follows: critical zone ferrite: 10%–25%, oriented epiphytic ferrite: 5%–15%, bainite: 15%–40%, tempered martensite: 20%–40%, retained austenite: 6%–12%, secondary martensite: 6%–13%, preferably; bainite + tempered martensite ≥ 45%.

[0011] The multiphase steel plate has a tensile strength ≥815MPa, a yield strength of 620~780MPa, an elongation after fracture ≥15%, and a hole expansion rate ≥80%.

[0012] The rationale for the design of the components in this invention is as follows:

[0013] C: C is an essential additive element in steel. C atoms exist in steel as interstitial atoms, which distort the Fe lattice and thus increase strength. At the same time, the addition of C can effectively increase the martensitic transformation temperature of steel and regulate the martensite content in steel plates. It is also an effective stabilizing element for austenite. However, when the amount of C added is too much, it can easily make the stability of the final residual austenite in the steel plate too high, affecting the formability of the steel plate. At the same time, it can make the carbon equivalent of the steel plate too high, affecting the weldability. Therefore, this invention requires the C element content to be 0.12% to 0.17%.

[0014] Mn: Mn is one of the key elements in this invention. It exists in steel through substitutional atom formation, playing a role in solid solution strengthening and ensuring the strength of the steel plate. Simultaneously, this element improves the hardenability of the steel plate, inhibits pearlite transformation, and is also an effective stabilizing element for austenite, playing a crucial role in the content of retained austenite in the final steel plate. However, adding excessive Mn will lead to segregation, ultimately causing inhomogeneity in the microstructure of the high-strength steel, reducing the plasticity of the steel plate and affecting its formability. It also strongly affects the weldability of the steel plate. Therefore, this invention requires an Mn content of 1.90%–2.25%.

[0015] Si: Si is one of the key elements in this invention. It plays a role in solid solution strengthening, ensuring the strength of the steel plate. Simultaneously, by increasing the chemical potential of carbon in ferrite, it inhibits the diffusion of carbon atoms into ferrite, thus helping to increase the C content in the critical region of austenite. This effectively ensures its hardenability and increases the temperature of the martensitic transformation, contributing to the acquisition of martensite and the retention of the final retained austenite. However, excessive Si content can easily affect the surface properties and weldability of the steel plate. Therefore, this invention requires a Si content of 0.30%–0.65%.

[0016] Ti: Ti is one of the key elements in this invention. Ti readily forms carbonitrides with N and C in steel, and the resulting TiN and nitrogen-rich Ti(N,C) exhibit strong high-temperature stability, effectively preventing grain growth during hot rolling. Simultaneously, TiN precipitates promote ferrite nucleation and formation, thus more effectively dividing the original austenite grains and refining the grains. Therefore, the addition of Ti achieves precipitation strengthening and grain refinement, effectively increasing the strength of the steel plate. Grain refinement also effectively improves the uniformity of the microstructure, thereby enhancing the hole-expanding performance of the steel plate. However, excessive Ti addition causes C in the steel to exist as precipitates, which is detrimental to the formation and stability of the final retained austenite. Furthermore, excessive precipitates are detrimental to formability. Therefore, this invention requires a Ti content of 0.020%–0.040%.

[0017] P: P element tends to segregate at grain boundaries, reducing the plasticity of the steel sheet and affecting its formability. Therefore, this invention requires that the P element content be ≤0.030%.

[0018] N: N is an impurity element in steel, and the lower its content, the better. Therefore, this invention requires that the N content be ≤0.002%.

[0019] S: S is an impurity element in steel, which readily reacts with Mn to form MnS, deteriorating the performance of the steel plate. Therefore, its content should be as low as possible. Thus, this invention requires an S content of ≤0.005%.

[0020] The second technical solution of the present invention is to provide a method for preparing 800MPa grade alloyed galvanized ultra-high hole expansion performance multiphase steel for automobiles, including smelting, hot rolling, pickling, cold rolling, continuous annealing galvanizing, and finishing.

[0021] Smelting:

[0022] The alloy composition within the above range is obtained by smelting in a converter and refining in an RH refining furnace, and then cast into a billet.

[0023] Hot-rolled:

[0024] ① The heating temperature should be between 1250 and 1270℃, and the furnace time should be ≥120 minutes. A heating temperature above 1250℃ ensures that Ti in the steel can effectively precipitate carbonitrides, refining the grains. However, temperatures exceeding 1270℃ can cause excessive austenite grain growth, affecting the final strength of the steel plate. A heating time ≥120 minutes ensures uniform distribution of alloying elements.

[0025] ② The rough rolling temperature is between 1100 and 1150℃, and the final rolling temperature is ≥890℃, which ensures that the steel plate is rolled in the single-phase austenite range, which can effectively cause recrystallization and refine the grains.

[0026] ③ Post-rolling cooling is divided into two stages. The first stage cooling temperature is 700-780℃, and the second stage cooling rate is >70℃ / s. The purpose of cooling to 700-780℃ in the first stage after rolling is to ensure that the Ti (C, N) precipitates are fully precipitated and dispersed, which can effectively refine the microstructure and is conducive to the final uniform microstructure. This helps to improve the material's uniform plastic deformation capacity, reduce local stress concentration, and thus improve the hole expansion performance. The subsequent second stage cooling rate of >70℃ / s can not only avoid the growth and aggregation of precipitates, but also inhibit the growth and coarsening of ferrite grains, which is conducive to the uniform refinement of the final microstructure and improves plasticity and hole expansion performance.

[0027] ④ A coiling temperature between 585 and 620°C can refine the ferrite grains of the steel plate, while avoiding bainitic phase transformation at lower temperatures, which would increase the difficulty of cold rolling.

[0028] Pickling: Pickling is used to remove iron oxides present on the surface of steel after hot rolling to ensure the surface quality of cold-rolled sheets.

[0029] Cold rolling: The cold rolling reduction rate is controlled between 45% and 60% to ensure the energy storage during cold rolling deformation, thereby refining the microstructure after annealing and ensuring the strength and hole expansion performance of the steel plate. Excessive rolling reduction rate will increase the load on the cold rolling mill and may not guarantee the achievement of the target thickness.

[0030] Continuous annealing:

[0031] ① The annealing isothermal temperature is 880~915℃, and the annealing time is 30~80s. This annealing temperature and time can ensure that the cold-rolled structure can fully recover and recrystallize. At the same time, this annealing isothermal temperature ensures that the steel plate is in the two-phase region of austenite and ferrite. In addition, the ferrite content is relatively low in the 880~915℃ range, which can reduce the content of soft phase (ferrite) (10%~25%). Combined with the uniform and fine microstructure, it can effectively ensure the expansion performance of the steel plate.

[0032] ② The slow cooling rate is 2-6℃ / s, and the slow cooling temperature is 680-760℃. During the slow cooling stage, some austenite in the steel plate forms oriented epiphytic ferrite. While adjusting the ferrite content, it is beneficial for carbon to accumulate in austenite, thereby stabilizing the austenite and laying the foundation for the formation of residual austenite. At the same time, the substitutional atoms such as Mn in the oriented epiphytic ferrite during the slow cooling stage are not easy to diffuse into the austenite. Therefore, the hardness of the ferrite is relatively large, which ensures the hole expansion performance of the CP steel of this invention.

[0033] ③ After slow cooling, the temperature is reduced to 340-385℃ at a rapid cooling rate of >25℃ / s: The cooling rate and temperature during the rapid cooling stage cause the supercooled austenite in the steel plate to undergo martensitic transformation. At the same time, the relatively low rapid cooling temperature effectively ensures the martensite content generated in this stage, i.e., the tempered martensite content is 30-40%. The hardness of tempered martensite is higher than that of ferrite and not much different from that of bainite. Therefore, this content of tempered martensite is the guarantee for the high porosity of the CP steel of this invention, while ensuring the high tensile strength and elongation of the steel plate.

[0034] ④ Alloying galvanizing: After rapid cooling, the steel plate is heated to 450-480℃ at a heating rate of 10-15℃ / s. The isothermal time before galvanizing is 10-20s. Then, it enters the zinc pot for galvanizing. The zinc liquid temperature is 460-470℃, and the galvanizing time is 1-3s. Subsequently, it enters the alloying furnace for the alloying process. The alloying temperature is 470-490℃, and the alloying time is 5-20s. Finally, the steel plate is cooled to room temperature at a rate of >10℃ / s.

[0035] The mechanism is as follows: a heating rate of 10–15 °C / s induces bainitic transformation in the supercooled austenite, and isothermal treatment at 450–480 °C for 10–20 s allows for further bainitic transformation in the steel plate. Simultaneously, the rapid cooling stage tempers the martensite, reducing its hardness and adjusting the steel plate temperature to prepare for entry into the molten zinc. An alloying temperature of 470–490 °C and an alloying time of 5–15 s allow zinc-iron diffusion between the coating and the substrate, resulting in an average iron content of 9.5%–11% in the final alloyed coating. Furthermore, the alloying stage ensures the full bainitic transformation of the supercooled austenite and the tempering reaction of the martensite. The bainitic transformation and martensitic tempering in this stage allow the carbon element in these two phases to further diffuse into the austenite, further stabilizing the austenite. At the same time, it ensures that the steel plate of the present invention obtains 15% to 40% bainite and 20% to 40% tempered martensite in this stage, with a total volume percentage of ≥50%. Rapid cooling to room temperature at >10℃ / s ensures that some of the supercooled austenite in the steel plate undergoes martensitic transformation to form secondary martensite, which supplements the strength of the steel plate. The final residual austenite gives the steel plate better plasticity.

[0036] ⑤ After alloying and galvanizing, the steel sheet enters the finishing machine for sheet shape adjustment, and the finishing elongation is controlled at 0.2%~1.0%.

[0037] The effective effects of this invention are as follows:

[0038] (1) The final microstructure of the steel plate of the present invention is 10% to 25% critical zone ferrite + 5% to 15% oriented epiphytic ferrite + 15% to 40% bainite + 20% to 40% tempered martensite + 6% to 12% retained austenite + 6% to 13% secondary martensite, and the volume percentage of bainite + tempered martensite is ≥45%. The surface of the steel plate is an alloyed zinc coating with an average iron content of 9.5% to 11%.

[0039] (2) The steel plate of the present invention has a tensile strength of ≥815MPa, a yield strength of 620~780MPa, an elongation after fracture of ≥15%, and a hole expansion rate of ≥80%.

[0040] (3) The steel plate of the present invention adopts a simple C-Mn-Si alloy composition design compared with the traditional high-expansion CP steel, without precious metals such as Cr and Mo, thus having a greater cost advantage.

[0041] (4) While taking into account the requirements of alloying coating process, the present invention cleverly forms CP steel with fine and uniform microstructure mainly composed of bainite and tempered martensite, giving it an ultra-high hole expansion rate.

[0042] (5) The present invention has a higher hole expansion rate than traditional high hole expansion CP steel, while ensuring that the steel plate has better forming performance. Detailed Implementation

[0043] The present invention will be further illustrated below through examples.

[0044] According to the technical solution, the components (by weight percentage: C: 0.12%–0.17%, Mn: 1.90%–2.25%, Si: 0.30%–0.65%, Ti: 0.020%–0.040%, P: ≤0.030%, N ≤0.002%, S ≤0.005%, with the balance being Fe and unavoidable impurities) are smelted, continuously cast, rolled, continuously annealed, and leveled.

[0045] Hot-rolled:

[0046] ① Heating temperature 1250~1270℃, furnace time ≥120min;

[0047] ② Rough rolling temperature 1100~1150℃, final rolling temperature ≥890℃;

[0048] ③ The post-rolling cooling is divided into two stages. The first stage cooling temperature is 700-780℃, and the second stage cooling rate is >70℃ / s.

[0049] ④ Winding temperature: 585~620℃;

[0050] Cold rolling:

[0051] Cold rolling reduction rate: 45%–60%;

[0052] Continuous annealing:

[0053] ① The isothermal annealing temperature is 880~915℃, and the annealing time is 30~80s;

[0054] ② The slow cooling rate is 2-6℃ / s, and the slow cooling temperature is 680-760℃;

[0055] ③ After slow cooling, the temperature is reduced to 340-385℃ at a rapid cooling rate of >25℃ / s;

[0056] ④ Alloying galvanizing: After rapid cooling, the steel plate is heated to 450-480℃ at a heating rate of 10-15℃ / s. The isothermal time before galvanizing is 10-20s. Then, it enters the zinc pot for galvanizing. The zinc liquid temperature is 460-470℃, and the galvanizing time is 1-3s. Subsequently, it enters the alloying furnace for the alloying process. The alloying temperature is 470-490℃, and the alloying time is 5-20s. Finally, the steel plate is cooled to room temperature at a rate of >10℃ / s.

[0057] Furthermore, after alloying and galvanizing, the steel sheet enters the finishing machine for sheet shape adjustment, and the finishing elongation is controlled at 0.2%~1.0%.

[0058] The composition of the steel in this embodiment of the invention is shown in Table 1. The main process parameters for rolling the steel in this embodiment of the invention are shown in Table 2. The main process parameters for annealing the steel in this embodiment of the invention are shown in Table 3. The microstructure (vol%) of the steel in this embodiment of the invention is shown in Table 4. The properties of the steel in this embodiment of the invention are shown in Table 5.

[0059] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0060] No. C Mn Si Ti P N S 1 0.15 2.03 0.45 0.035 0.017 0.0010 0.003 2 0.17 1.95 0.38 0.027 0.013 0.0008 0.001 3 0.12 2.20 0.52 0.038 0.008 0.0012 0.002 4 0.14 2.15 0.49 0.025 0.022 0.0016 0.002 5 0.15 2.06 0.61 0.038 0.012 0.0010 0.003 6 0.12 2.18 0.55 0.031 0.024 0.0009 0.003

[0061] Table 2 Main process parameters for steel rolling in the embodiments of the present invention

[0062] Example Heating temperature / ℃ Rolling temperature / ℃ Final rolling temperature / ℃ First stage cooling temperature / ℃ Second stage cooling rate / ℃ / s Winding temperature / ℃ Hot-rolled plate thickness / mm Cold rolling reduction rate / % 1 1253 1138 898 723 72 618 2.9 52 2 1267 1127 892 765 83 597 2.8 49 3 1258 1143 902 709 82 586 3.1 48 4 1255 1108 897 751 88 593 3.3 53 5 1268 1118 913 748 76 608 2.9 55 6 1259 1149 916 719 73 614 3.2 56

[0063] Table 3 Main heat treatment process parameters for steel annealing in embodiments of the present invention.

[0064] Example Isothermal temperature / ℃ Isothermal time / s Slow cooling rate / ℃ / s Slow cooling temperature / ℃ Rapid cooling rate / ℃ / s Rapid cooling temperature / ℃ Heating rate before galvanizing / ℃ / s Isothermal temperature before galvanizing / °C Isothermal time before galvanizing / s Zinc liquid temperature / ℃ Zinc plating time / s Alloying temperature / °C Alloying time / s rapid cooling rate / s 1 903 59 3 758 32 372 12 473 16 465 2 482 13 12 2 897 78 5 722 28 353 11 454 12 462 1 478 11 10 3 886 71 7 684 34 361 15 461 18 467 1 472 5 13 4 892 52 8 743 29 384 13 476 13 463 2 479 18 15 5 910 34 2 718 31 379 11 453 19 460 3 471 14 12 6 901 63 7 732 26 357 12 467 17 465 2 470 13 11

[0065] Table 4. Microstructure (vol%) of steel in embodiments of the present invention

[0066] Example Critical region ferrite Oriented epiphytic ferrite bainite Tempered Martensite Residual austenite Secondary martensite Bainite + Tempered Martensite 1 19 8 38 23 6 6 61 2 16 6 27 34 8 9 61 3 18 5 25 36 6 10 61 4 24 13 23 22 11 7 45 5 12 7 26 32 12 11 58 6 19 8 32 26 7 8 58

[0067] Table 5 Steel properties of embodiments of the present invention

[0068] Example Rp0.2 / MPa Rm / MPa A50 / % Hole expansion rate / % Iron content in coating / % 1 704 834 19.2 93 11.0 2 689 839 16.3 89 10.9 3 638 827 16.9 91 9.9 4 623 816 19.1 96 10.2 5 768 834 17.5 116 10.3 6 697 826 18.7 94 10.4

[0069] The final microstructure of the steel plate produced using this invention is 10%–25% critical zone ferrite + 5%–15% oriented epiphytic ferrite + 15%–40% bainite + 20%–40% tempered martensite + 6%–12% retained austenite + 6%–13% secondary martensite, with the bainite + tempered martensite content ≥45%. The steel plate surface has an alloyed zinc coating with an average iron content of 9.5%–11%. Through the above innovative composition and process design, the steel plate obtained has a tensile strength ≥815 MPa, a yield strength of 620–780 MPa, an elongation after fracture ≥15%, and a hole expansion rate ≥80%.

[0070] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A multiphase steel with 800MPa grade alloyed galvanized ultra-high hole-expanding performance for automotive applications, characterized in that... The composition of the multiphase steel, by weight percentage, is as follows: C: 0.12%–0.17%, Mn: 1.90%–2.25%, Si: 0.30%–0.65%, Ti: 0.020%–0.040%, P: ≤0.030%, N ≤0.002%, S ≤0.005%, with the balance being Fe and unavoidable impurities; the Fe mass percentage in the alloyed coating of the multiphase steel is 9.5%–11.5%; the microstructure of the multiphase steel includes critical zone ferrite, oriented epiphytic ferrite, and bainite. The steel plate comprises ferrite, tempered martensite, retained austenite, and secondary martensite; by volume percentage as follows: critical zone ferrite: 10%–25%, oriented epiphytic ferrite: 5%–15%, bainite: 15%–40%, tempered martensite: 20%–40%, retained austenite: 6%–12%, secondary martensite: 6%–13%; bainite + tempered martensite ≥ 45%; the tensile strength of the multiphase steel plate is ≥ 815 MPa, the yield strength is 620–780 MPa, the elongation after fracture is ≥ 15%, and the porosity is ≥ 80%. The preparation method of the 800MPa grade alloyed galvanized ultra-high hole expansion performance multiphase steel for automobiles includes smelting, hot rolling, pickling, cold rolling, continuous annealing galvanizing, and finishing. Hot-rolled: ① Heating temperature 1250~1270℃, holding time ≥120min; ② Rough rolling temperature: 1100~1150℃; Final rolling temperature: ≥890℃; ③ The post-rolling cooling is divided into two stages. The first stage cooling temperature is 700-780℃, and the second stage cooling rate is >70℃ / s. ④ Winding temperature: 585~620℃; Cold rolling: Cold rolling reduction rate: 45%–60%; Continuous annealing: ① The isothermal annealing temperature is 880~915℃, and the annealing time is 30~80s; ② The slow cooling rate is 2-6℃ / s, and the slow cooling temperature is 680-760℃; ③ After slow cooling, the temperature is reduced to 340-385℃ at a rapid cooling rate of >25℃ / s; ④ Alloying galvanizing: After rapid cooling, the steel plate is heated to 450-480℃ at a heating rate of 10-15℃ / s. The isothermal time before galvanizing is 10-20s. Then, it enters the zinc pot for galvanizing. The zinc liquid temperature is 460-470℃, and the galvanizing time is 1-3s. Subsequently, it enters the alloying furnace for the alloying process. The alloying temperature is 470-490℃, and the alloying time is 5-20s. Finally, the steel plate is cooled to room temperature at a rate of >10℃ / s.

2. A method for preparing an 800MPa grade alloyed galvanized ultra-high hole-expanding performance multiphase steel for automobiles as described in claim 1, comprising smelting, hot rolling, pickling, cold rolling, continuous annealing galvanizing, and finishing; characterized in that: Hot-rolled: ① Heating temperature 1250~1270℃, holding time ≥120min; ② Rough rolling temperature: 1100~1150℃; Final rolling temperature: ≥890℃; ③ The post-rolling cooling is divided into two stages. The first stage cooling temperature is 700-780℃, and the second stage cooling rate is >70℃ / s. ④ Winding temperature: 585~620℃; Cold rolling: Cold rolling reduction rate: 45%–60%; Continuous annealing: ① The isothermal annealing temperature is 880~915℃, and the annealing time is 30~80s; ② The slow cooling rate is 2-6℃ / s, and the slow cooling temperature is 680-760℃; ③ After slow cooling, the temperature is reduced to 340-385℃ at a rapid cooling rate of >25℃ / s; ④ Alloying galvanizing: After rapid cooling, the steel plate is heated to 450-480℃ at a heating rate of 10-15℃ / s. The isothermal time before galvanizing is 10-20s. Then, it enters the zinc pot for galvanizing. The zinc liquid temperature is 460-470℃, and the galvanizing time is 1-3s. Subsequently, it enters the alloying furnace for the alloying process. The alloying temperature is 470-490℃, and the alloying time is 5-20s. Finally, the steel plate is cooled to room temperature at a rate of >10℃ / s.

3. The method for preparing an 800MPa grade alloyed galvanized ultra-high hole-expanding performance multiphase steel for automobiles according to claim 2, characterized in that: After alloying and galvanizing, the steel sheet enters the finishing machine for shape adjustment, and the finishing elongation is controlled at 0.2%~1.0%.