1.4 GPa-grade high-yield-ratio hot-dip galvanized TRIP steel and manufacturing method thereof

Abstract

The invention relates to the technical field of advanced high-strength steel materials, in particular to 1.4 GPa-grade high-yield-ratio hot-dip galvanized TRIP steel and a manufacturing method thereof, and the manufacturing method comprises the steps of smelting and forging, hot rolling and ultra-fast cooling, warm rolling, acid pickling and cold rolling, continuous annealing, hot galvanizing and finishing. The microstructure of the 1.4 GPa-grade hot-dip galvanized TRIP steel obtained through the manufacturing method is composed of a ferritic structure, a bainite structure and a retained austenite structure. The 1.4 GPa grade high yield ratio type hot-dip galvanized TRIP steel disclosed by the invention has the characteristic of high yield ratio, and the yield ratio is 0.75-0.85; meanwhile, excellent comprehensive performance is achieved, and the tensile strength is gt; the elongation after fracture is gt under the pressure of 1400 MPa; the product of strength and elongation is gt; %, and the hole expansion rate is gt; and 25%.

Description

Technical Field

[0001] The present invention relates to the technical field of advanced high-strength steel materials, and in particular to a 1.4 GPa-grade high-yield ratio hot-dip galvanized TRIP steel and a manufacturing method thereof. Background Art

[0002] Compared with traditional fuel vehicles, new energy vehicles pay more attention to driving range, safety and service life, and due to the increase in battery packs, they are usually heavier than fuel vehicles of the same level. Taking a compact SUV as an example, a fuel vehicle weighs about 1.4 tons, while a new energy electric vehicle weighs >1.7 tons; the weight of the best-selling electric vehicles on the market is mainly concentrated in 2.2~2.4 tons, which is 300~500kg heavier than the fuel vehicles of the same specifications. High-strength steel materials are important materials used in the manufacture of new energy vehicles. As the demand for lightweighting in the new energy vehicle manufacturing industry continues to escalate, the proportion of high-strength grade, thin-gauge high-performance steel in automobile manufacturing materials will further increase.

[0003] TRIP effect (Transformation Induced Plasticity) can achieve high strength and high plasticity at the same time, and has been the focus of research in recent years. Therefore, TRIP steel has a very broad application prospect in new energy vehicles. Common TRIP steels include Q&P steel, DH, CH steel, etc. However, there is still little research on hot-dip galvanized TRIP steel with a tensile strength above 1.4GPa (i.e. 1400MPa), which is mainly restricted by the following factors: (1) The contradiction between strength and plasticity. When the tensile strength increases, the plasticity of the material will deteriorate, especially when the strength increases to above 1.4 GPa, its plasticity index decreases significantly, which cannot meet the demand for higher strength of modern new energy vehicles.

[0004] (2) Poor formability and insufficient ductility. When the strength increases to 1.4 GPa, the formability and ductility of the material drop sharply, making it difficult to meet the high formability and high ductility requirements of ultra-high strength steel for new energy vehicle manufacturers.

[0005] (3) High manufacturing cost and difficulty. The addition of alloying elements such as Ni and V increases the cost and manufacturing difficulty.

[0006] (4) Unable to meet special performance requirements. Many new energy vehicle parts have special requirements such as flanging, and the strength requirements of such parts are also increasing. When the tensile strength is above 1.4GPa (i.e. 1400MPa), the traditional low yield-to-strength ratio duplex steel with good plasticity cannot meet the requirements of flanging, and flanging cracking often occurs. Therefore, it is necessary to optimize the flanging performance of the material for such parts to meet the requirements of automobile manufacturers.

[0007] CN 114574760 B provides a 1500 MPa grade high formability alloyed hot-dip galvanized dual-phase steel and its preparation method. With a high Cr and high Ti design, the prepared hot-dip galvanized dual-phase steel has a low yield ratio, only 0.53 - 0.62, an elongation after fracture ≥ 8.0%, and a low strength-ductility product, only 12.0 - 16.3 GPa·%.

[0008] CN 113416889 B provides a hot-dip galvanized DH1470 steel with good welding performance and its preparation method. In addition to Nb and Ti, this technical solution also adds high Mo: 0.3% - 0.8%, Ni: 0.2% - 0.9%, V: 0.015% - 0.15%, resulting in a high alloy cost. The prepared hot-dip galvanized DH1470 steel has a yield ratio of 0.67 - 0.84. Although the yield ratio has increased, the strength-ductility product < 16 GPa·%, which cannot meet the steel usage requirements in the new energy vehicle field. Summary of the Invention

[0009] Aiming at the technical problems that the yield ratio and strength-ductility product of the existing 1.4 GPa grade hot-dip galvanized TRIP steel are on the low side and cannot well meet the flanging requirements and strength requirements of new energy vehicle parts, the present invention provides a 1.4 GPa grade high yield ratio type hot-dip galvanized TRIP steel and its manufacturing method.

[0010] In the first aspect, the present invention provides a manufacturing method of a 1.4 GPa grade high yield ratio type hot-dip galvanized TRIP steel. By mass percentage, the chemical composition of the 1.4 GPa grade high yield ratio type hot-dip galvanized TRIP steel is: C: 0.26% - 0.29%, Si: 0.7% - 1.1%, Mn: 2.9% - 3.2%, Nb: 0.045% - 0.065%, Ti: 0.035% - 0.055%, Cr: 0.52% - 0.65%, Mo: 0.22% - 0.34%, Alt: 1.0% - 1.3%, P ≤ 0.004%, S ≤ 0.003%, N ≤ 0.003%, O ≤ 0.004%, 1.9% ≤ Alt + Si ≤ 2.2% and 1.0 ≤ Alt / Si ≤ 1.9, 3.55% ≤ Mn + Cr ≤ 3.85% and 0.17 ≤ Cr / Mn ≤ 0.22 and 0.75 < Cr + Mo < 1.00, 0.08% < Nb + Ti < 0.11%, and the balance is Fe and unavoidable impurities; The manufacturing method includes the following steps: (1) Smelting and forging; (2) Hot rolling and ultra-fast cooling: The austenitizing soaking temperature of the hot rolling process is 1210~1240℃, and the holding time of the soaking section is 40~50min; the starting rolling temperature is 1130~1160℃, and the final rolling temperature is 840~870℃; after rolling, the ultra-fast water cooling mode is adopted, and the cooling rate is >100℃ / s to rapidly cool to 310~360℃ to obtain 6~10mm hot-rolled steel plates; (3) Warm rolling: The hot-rolled steel plate is heated to 680±20℃ and kept at this temperature for 40±10min. Then, it is taken out of the furnace for rolling, with a cumulative reduction of 50%~70% and a final rolling temperature of 525~575℃. After rolling, the steel plate is slowly cooled to room temperature to obtain a 2~5mm warm-rolled steel plate. (4) Pickling and cold rolling: The steel plate is pickled with hydrochloric acid to remove surface oxides, and then cold rolled with a cumulative reduction of 50% to 60% to obtain a 1.0 to 2.0 mm cold-hardened strip; (5) Continuous annealing and hot-dip galvanizing: The cold-hardened steel strip is rapidly heated to 860-890°C at a heating rate of 100-150°C / s and kept at that temperature for 30-70s; then rapidly cooled to 325-355°C in the bainite zone at a cooling rate of >60°C / s and kept isothermal for 120-180s; then induction heating is used to rapidly raise the temperature to the galvanizing temperature of 450-475°C at a rate of >30°C / s. After exiting the zinc pot, a mobile bellows is used to cool the galvanized steel strip to ≤155°C.

[0011] Furthermore, step (1) is specifically as follows: smelting a steel billet according to the chemical composition; heating the cooled steel billet to 1210-1230°C and keeping the temperature for 60±20 min; and then forging the steel billet with a start forging temperature of 1150-1190°C and a final forging temperature of 930-990°C to obtain a forged billet.

[0012] Furthermore, the reduction ratio of the last two passes of warm rolling in step (3) is set to 20% to 25%.

[0013] Furthermore, in step (5), the temperature of the zinc solution is controlled to be 465±5°C.

[0014] Furthermore, the method further comprises step (6) skin finishing: the hot-dip galvanized steel coil is skin finished, the skin finishing elongation is controlled within 1.4% to 1.6%, and then the steel coil is coiled.

[0015] In a second aspect, the present invention provides a 1.4 GPa grade high yield ratio hot-dip galvanized TRIP steel produced by the above manufacturing method.

[0016] Furthermore, the yield strength ratio of 1.4GPa grade hot-dip galvanized TRIP steel is 0.75~0.85, the tensile strength is >1400MPa, the elongation after fracture is >12.5%, the strength-ductility product is >19GPa·%, and the hole expansion rate is >25%.

[0017] Furthermore, the microstructure of 1.4 GPa grade high yield ratio hot-dip galvanized TRIP steel consists of ferrite, bainite and retained austenite.

[0018] Furthermore, in terms of volume fraction, the ferrite content of 1.4 GPa grade high yield ratio hot-dip galvanized TRIP steel is 5%~12%, the bainite content is 75%~87%, and the retained austenite content is 8%~15%.

[0019] Furthermore, the grain size of ferrite with a volume fraction of >85% is ≤1.5 μm.

[0020] The beneficial effects of the present invention are: The 1.4 GPa grade hot-dip galvanized TRIP steel obtained by the manufacturing method of the present invention exhibits high yield strength ratio characteristics, with a yield strength ratio of 0.75-0.85, a tensile strength of >1400 MPa, an elongation after fracture of >12.5%, a strength-ductility product of >19 GPa·%, and a hole expansion rate of >25%, which can provide a new material selection scheme for the new energy vehicle manufacturing industry's demand for lightweight, ultra-high strength, thin-gauge high-performance steel.

[0021] (1) The present invention adds 0.22% to 0.34% Mo when designing the chemical composition. First, the Mo element is used in combination with the strong carbide-forming elements Nb and Ti (the present invention adds 0.045% to 0.065% Nb; 0.035% to 0.055% Ti), and its solid solution strengthening effect is more significant, which can take into account both high strength and high toughness, thereby improving the comprehensive performance of the steel of the present invention. Second, under the condition of a high cooling rate, it can promote bainite phase transformation and refine the grains, so that the bainite structure content in the present invention reaches 75% to 87%, which greatly improves the yield strength of the steel, thereby improving the yield strength ratio of the hot-dip galvanized TRIP steel of the present invention, thereby effectively resisting cracking during the flanging process.

[0022] (2) The present invention adopts an ultra-fast water cooling mode after hot rolling, and rapidly cools to 310-360°C at a cooling rate of >100°C / s for coiling, so that the alloy elements in the organizational structure can be fully diffused and distributed, thereby making the material more homogenized, so as to ensure that the organizational properties of the hot-rolled plate are relatively uniform. From the perspective of organizational property inheritance, it can effectively avoid the phenomenon that the final product meets the strength requirements but cracks during the flanging process.

[0023] (3) The present invention cold-rolls the warm-rolled steel sheet and controls the cumulative reduction to 50% to 60%, which can fully break the structure after warm rolling and accumulate more distortion energy such as dislocations. In the subsequent annealing and recrystallization process, the recrystallized grains are finer and more uniform, and a part of the dislocations can be retained in the grains, which is beneficial to improving the yield strength of the material, that is, it is beneficial to improve the yield strength ratio. When microcracks initiate during the flanging process, the fine grains can effectively increase the number of grain boundaries, and the high-density dislocations can increase the difficulty of crack propagation, thereby avoiding cracking during the flanging process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a typical microstructure diagram of the 1.4 GPa grade high yield ratio hot-dip galvanized TRIP steel prepared in Example 1.

[0026] Figure 2 This is a typical engineering stress-strain curve of the 1.4 GPa grade high yield ratio hot-dip galvanized TRIP steel prepared in Example 1. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solutions in the present invention, 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0028] Embodiment 1~6 In terms of mass percentage, the chemical compositions of the steel plates in Embodiments 1 to 6 of the present invention are as follows: C: 0.26% - 0.29%, Si: 0.7% - 1.1%, Mn: 2.9% - 3.2%, Nb: 0.045% - 0.065%, Ti: 0.035% - 0.055%, Cr: 0.52% - 0.65%, Mo: 0.22% - 0.34%, Alt: 1.0% - 1.3%, P ≤ 0.004%, S ≤ 0.003%, N ≤ 0.003%, O ≤ 0.004%, 1.9% ≤ Alt + Si ≤ 2.2% and 1.0 ≤ Alt / Si ≤ 1.9, 3.55% ≤ Mn + Cr ≤ 3.85% and 0.17 ≤ Cr / Mn ≤ 0.22 and 0.75 < Cr + Mo < 1.00, 0.08% < Nb + Ti < 0.11%, and the balance is Fe and unavoidable impurities.

[0029] The chemical compositions of the steel billets in Specific Embodiments 1 to 6 are shown in Table 1.

[0030] Table 1 Actual smelting compositions of the steels in Embodiments 1 to 6 (mass percentage, %)

[0031] The steel plates in Embodiments 1 to 6 are obtained according to the following manufacturing method: (1) Smelting and forging: Smelt the steel billet according to the described chemical composition; heat the slowly cooled steel billet to 1210 - 1230 °C and hold for 60 ± 20 min; then perform forging, with the starting forging temperature being 1150 - 1190 °C and the final forging temperature being 930 - 990 °C to obtain a forged billet; (2) Hot rolling and ultra - fast cooling: The austenitizing soaking temperature in the hot - rolling process is 1210 - 1240 °C, and the soaking time in the soaking section is 40 - 50 min; the starting rolling temperature is 1130 - 1160 °C, and the final rolling temperature is 840 - 870 °C; after rolling, adopt the ultra - fast water - cooling mode and quickly cool to 310 - 360 °C at a cooling rate of > 100 °C / s, and then perform coiling to obtain a 6 - 10 mm hot - rolled steel plate; (3) Warm rolling: Heat the above - mentioned hot - rolled steel plate to 680 ± 20 °C and hold for 40 ± 10 min; then take it out of the furnace for rolling, with the cumulative reduction being 50% - 70%, and the reduction rate in the last two passes being controlled at 20% - 25%, and the final rolling temperature being 525 - 575 °C; after rolling, slowly cool the steel plate to room temperature to obtain a 2 - 5 mm warm - rolled steel plate; (4) Pickling and cold rolling: Remove the surface oxides of the above - mentioned steel plate by pickling with hydrochloric acid, and then perform cold rolling, with the cumulative reduction being 50% - 60% to obtain a 1.0 - 2.0 mm cold - hard strip steel; (5) Continuous annealing and hot-dip galvanizing: The cold-hardened steel strip is rapidly heated to 860-890°C at a heating rate of 100-150°C / s and kept at this temperature for 30-70s; then rapidly cooled to the bainite temperature of 325-355°C at a cooling rate of >60°C / s and kept isothermal for 120-180s; then induction heating is used to rapidly heat the steel strip to the galvanizing temperature of 450-475°C at a rate of >30°C / s, and the temperature of the zinc liquid is controlled to be within the range of 465±5°C. After exiting the zinc pot, a mobile bellows is used to cool the galvanized steel strip to ≤155°C; (6) Skin finishing: The hot-dip galvanized steel coil is skin-finished, and the skin-finishing elongation is controlled at 1.4% to 1.6%. The finished steel coil of the present invention is then obtained by coiling.

[0032] The specific manufacturing process parameters of forging, hot rolling and rapid cooling in specific embodiments 1 to 6 are shown in Table 2; the specific manufacturing process parameters of warm rolling and cold rolling in specific embodiments 1 to 6 are shown in Table 3; the specific manufacturing process parameters of continuous annealing, hot-dip galvanizing and skin pass in specific embodiments 1 to 6 are shown in Table 4.

[0033] Table 2 Specific manufacturing process parameters of forging, hot rolling and rapid cooling in Examples 1 to 6

[0034] Table 3 Specific manufacturing process parameters of warm rolling and cold rolling in Examples 1 to 6

[0035] Table 4 Specific manufacturing process parameters of continuous annealing, hot-dip galvanizing and skin pass in Examples 1 to 6

[0036] Comparative Example 1 A hot-dip galvanized TRIP steel, with chemical composition of C: 0.25%, Si: 1.0%, Mn: 2.9%, Nb: 0.075%, Ti: 0.042%, Cr: 0.64%, Alt: 1.2%, P: 0.004%, S: 0.002%, N: 0.0024%, O: 0.002%, and the balance is Fe and unavoidable impurities.

[0037] The preparation method comprises the following steps: (1) Smelting and forging: Smelting is performed according to the designed chemical composition to obtain a steel billet with the corresponding composition; the steel billet after slow cooling is heated to 1240°C and kept at this temperature for 90 minutes; then forging is performed with the start forging temperature being 1200°C and the final forging temperature being 995°C to obtain a forged billet; (2) Hot rolling and ultra-fast cooling: The forging billet is hot rolled, the austenitizing soaking temperature is 1245°C, and the soaking period is 50 min; the starting rolling temperature is 1155°C, and the final rolling temperature is 855°C; after rolling, the ultra-fast water cooling mode is adopted, and the cooling rate is >100°C / s to quickly cool to <160°C, and a 5.0 mm hot-rolled steel plate is obtained; (3) Warm rolling and pickling: The hot-rolled steel plate was heated to 690°C and kept warm for 55 min. It was then taken out of the furnace for rolling, with a cumulative reduction of 72%, of which the reduction rate of the last two passes was controlled at 15%-20%, and the final rolling temperature was 545°C. After rolling, it was slowly cooled to room temperature and pickled with hydrochloric acid to remove surface oxides to obtain a 1.4 mm strip. (4) Continuous annealing and hot-dip galvanizing: The strip is rapidly heated to 865°C at a heating rate of 90°C / s and kept at this temperature for 50s; then it is rapidly cooled to the bainite region at a cooling rate of >60°C / s, and the temperature after cooling is 370°C, and the temperature is kept isothermal for 160s; then induction heating is used to rapidly increase the temperature at >30°C / s for hot-dip galvanizing, the galvanizing temperature is 465°C, and the zinc liquid temperature is controlled to be within the range of 465±5°C. After leaving the zinc pot, a mobile bellows is used to cool the galvanized steel strip to ≤155°C; (5) Skin finishing and coiling: The galvanized steel strip is skin-finished, and the skin finishing elongation is controlled at 1.2%, and then coiled.

[0038] The hot-dip galvanized TRIP steel samples prepared in each embodiment and comparative example were subjected to mechanical property test and microstructure analysis. The test and analysis results are shown in Table 5. Figure 1~Figure 2 . From the analysis of the mechanical properties test results, it can be seen that the hot-dip galvanized TRIP steel prepared in Examples 1 to 6 of the present invention presents a high yield strength ratio, and its yield strength ratio is 0.75 to 0.85; at the same time, it has excellent comprehensive performance, tensile strength>1400MPa, elongation after fracture>12.5%, strength-ductility product>19GPa·%, and hole expansion rate>25%, which can meet the needs of the new energy vehicle field for high-strength grade, thin-gauge high-performance steel. Observation of the microstructure shows that the hot-dip galvanized TRIP steel prepared in Examples 1 to 6 of the present invention is composed of 5% to 12% ferrite structure, 75% to 87% bainite structure and 8% to 15% retained austenite structure, wherein the ferrite grain size with a volume fraction>85% is ≤1.5μm.

[0039] Although comparative example 1 has a relatively good strength-ductility match and a hole expansion rate of 36%, cracking occurs during the flanging process after hole expansion. This is related to the low yield strength ratio of comparative example 1 on the one hand; on the other hand, the ferrite size of comparative example 1 is ≤1.8μm and the bainite content is low, while the grain size of the volume fraction>85% of the ferrite structure of the present invention is ≤1.5μm, and the bainite content is relatively higher. Therefore, when microcracks are generated during the flanging process, the hot-dip galvanized TRIP steels of embodiments 1 to 6 of the present invention have more fine grains that can be used to increase the number of grain boundaries, and increase the difficulty of crack propagation through high-density dislocations, thereby better avoiding cracking during the flanging process.

[0040] Table 5 Mechanical properties and volume fraction of each phase of hot-dip galvanized TRIP steel of Examples 1 to 6 and Comparative Example 1

[0041] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for manufacturing 1.4GPa grade high yield ratio hot dip galvanized TRIP steel, characterized in that: In terms of mass percentage, the chemical composition of the 1.4 GPa grade high yield ratio hot-dip galvanized TRIP steel is as follows: C: 0.26% - 0.29%, Si: 0.7% - 1.1%, Mn: 2.9% - 3.2%, Nb: 0.045% - 0.065%, Ti: 0.035% - 0.055%, Cr: 0.52% - 0.65%, Mo: 0.22% - 0.34%, Alt: 1.0% - 1.3%, P ≤ 0.004%, S ≤ 0.003%, N ≤ 0.003%, O ≤ 0.004%, 1.9% ≤ Alt + Si ≤ 2.2% and 1.0 ≤ Alt / Si ≤ 1.9, 3.55% ≤ Mn + Cr ≤ 3.85% and 0.17 ≤ Cr / Mn ≤ 0.22 and 0.75 < Cr + Mo < 1.00, 0.08% < Nb + Ti < 0.11%, and the balance is Fe and unavoidable impurities; The manufacturing method includes the following steps: (1) Smelting and forging; (2) Hot rolling and ultra-rapid cooling: The austenitizing soaking temperature in the hot rolling process is 1210 - 1240 °C, and the soaking time in the soaking section is 40 - 50 min; the starting rolling temperature is 1130 - 1160 °C, and the final rolling temperature is 840 - 870 °C; after rolling, an ultra-rapid water cooling mode is adopted, and it is rapidly cooled to 310 - 360 °C at a cooling rate > 100 °C / s to obtain a hot-rolled steel plate with a thickness of 6 - 10 mm; (3) Warm rolling: Heat the hot-rolled steel plate to 680 ± 20 °C and keep it warm for 40 ± 10 min; then take it out of the furnace for rolling, with the cumulative reduction of 50% - 70%, and the final rolling temperature is 525 - 575 °C; after rolling, the steel plate is slowly cooled to room temperature to obtain a warm-rolled steel plate with a thickness of 2 - 5 mm; (4) Pickling and cold rolling: The above steel plate is pickled with hydrochloric acid to remove the surface oxides and then cold-rolled, with the cumulative reduction of 50% - 60%, to obtain a cold-hardened strip steel with a thickness of 1.0 - 2.0 mm; (5) Continuous annealing and hot-dip galvanizing: The above cold-hardened strip steel is rapidly heated to 860 - 890 °C at a heating rate of 100 - 150 °C / s and kept warm for 30 - 70 s; then it is rapidly cooled to the bainite region of 325 - 355 °C at a cooling rate > 60 °C / s and isothermally held for 120 - 180 s; subsequently, induction heating is adopted to rapidly heat to the galvanizing temperature of 450 - 475 °C at a rate > 30 °C / s, and after coming out of the zinc pot, the galvanized steel strip is cooled to ≤ 155 °C by a moving air box.

2. The manufacturing method according to claim 1, characterized in that: Step (1) is specifically as follows: Smelt the steel billet according to the chemical composition; heat the cooled steel billet to 1210 - 1230 °C and keep it warm for 60 ± 20 min; then carry out forging, with the starting forging temperature of 1150 - 1190 °C and the final forging temperature of 930 - 990 °C to obtain a forged billet.

3. The manufacturing method according to claim 1, characterized in that: In step (3), the reduction rate of the last two passes of warm rolling is set to 20% - 25%.

4. The manufacturing method according to claim 1, characterized in that: In step (5), the temperature of the zinc bath is controlled at 465 ± 5 °C.

5. The manufacturing method according to claim 1, characterized in that: It also includes step (6) skin pass rolling: Carry out skin pass rolling on the hot-dip galvanized steel coil, control the skin pass elongation at 1.4% - 1.6%, and then coil it to obtain the product.

6. A 1.4 GPa grade high yield ratio hot-dip galvanized TRIP steel produced by the manufacturing method according to any one of claims 1 to 5.

7. The 1.4 GPa high yield ratio hot dip galvanized TRIP steel according to claim 6, characterized in that: The yield strength ratio of 1.4GPa grade hot-dip galvanized TRIP steel is 0.75~0.85, the tensile strength is >1400MPa, the elongation after fracture is >12.5%, the strength-ductility product is >19GPa·%, and the hole expansion rate is >25%.

8. The 1.4 GPa high yield ratio hot dip galvanized TRIP steel according to claim 6, characterized in that: The microstructure of 1.4GPa grade high yield ratio hot-dip galvanized TRIP steel is composed of ferrite, bainite and retained austenite.

9. The 1.4 GPa grade high yield ratio hot dip galvanized TRIP steel according to claim 8, characterized in that: Measured by volume fraction, the ferrite content of 1.4GPa grade high yield ratio hot-dip galvanized TRIP steel is 5%~12%, the bainite content is 75%~87%, and the retained austenite content is 8%~15%.

10. The 1.4 GPa grade high yield ratio hot dip galvanized TRIP steel according to claim 8, characterized in that: The grain size of ferrite with volume fraction >85% is ≤1.5μm.

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