Hot-dip galvanized DH steel and preparation method thereof and automobile structural part

Abstract

The present invention relates to a hot-dip galvanized DH steel and a preparation method thereof and an automobile structural part, belonging to the technical field of steel preparation. The hot-dip galvanized DH steel comprises a steel matrix and a galvanized layer attached to at least a part of the surface of the steel matrix; the microstructure of the steel matrix comprises: ferrite, martensite, bainite and residual austenite; the martensite comprises: fresh martensite and tempered martensite; in the microstructure of the steel matrix, the volume fraction of the fresh martensite is less than 10%. The hot-dip galvanized DH steel controls the content of fresh martensite and tempered martensite in the microstructure of the steel matrix of the hot-dip galvanized DH steel, transforms most of the fresh martensite in the microstructure of the steel matrix into tempered martensite, and makes the volume fraction of the fresh martensite less than 10%, thereby reducing the hardness difference between ferrite and martensite, and achieving the purpose of improving the local forming performance of the hot-dip galvanized DH steel.

Description

Technical Field

[0001] The present disclosure relates to the technical field of steel preparation, and in particular to a hot-dip galvanized DH steel and a preparation method thereof and an automobile structural part. Background Art

[0002] DH steel (Dual Phase Steels with Improved Formability, referred to as DH steel), the full Chinese name is enhanced formability dual phase steel. Compared with traditional DP steel (Dual-Phase steel, also known as ferrite-martensite dual phase steel), DH steel contains an appropriate amount of residual austenite in its structure. These residual austenites can continuously produce TRIP (Transformation Induced Plasticity) effect during deformation. Therefore, the total elongation of DH steel is greatly improved compared with traditional DP steel of the same strength level. At present, 590~980MPa grade DH steel has been mass-produced in vehicle body structural parts.

[0003] Although the elongation of DH steel has been improved, DH steel produced by conventional galvanizing process generally has the problem of low local formability, and it is difficult to have both excellent overall formability and local formability. Cracking problems often occur when stamping complex structural parts. Summary of the invention

[0004] The present invention discloses a hot-dip galvanized DH steel and a preparation method thereof and an automobile structural part, so as to solve the technical problem that the existing DH steel has poor local forming performance.

[0005] In a first aspect, the present disclosure provides a hot-dip galvanized DH steel, the hot-dip galvanized DH steel comprising a steel substrate and a galvanized layer attached to at least a portion of the surface of the steel substrate;

[0006] The microstructure of the steel matrix includes: ferrite, martensite, bainite and retained austenite;

[0007] The martensite includes: fresh martensite and tempered martensite;

[0008] In the microstructure of the steel matrix, the volume fraction of the fresh martensite is less than 10%.

[0009] Optionally, the hot-dip galvanized DH steel includes: hot-dip galvanized DH steel of any grade between 590MPa and 1000MPa.

[0010] Optionally, the performance parameters of the hot-dip galvanized DH steel include: hole expansion rate ≥ 25%, longitudinal 90-degree V-bend radius < R1.5.

[0011] Optionally, when the hot-dip galvanized DH steel is 980MPa grade hot-dip galvanized DH steel,

[0012] The chemical components of the 980MPa grade hot-dip galvanized DH steel include, by mass fraction, C: 0.17-0.23%; Si: 0.3-0.9%; Mn: 1.9-2.5%; Cr: 0.1-0.6%; Al: 0.6-1.0%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥0.8%; Fe.

[0013] Optionally, the steel matrix microstructure of the 980MPa grade hot-dip galvanized DH steel includes, by volume fraction, 30% to 50% ferrite, 5% to 10% bainite, 3% to 10% retained austenite, 0% to 10% fresh martensite, and 30% to 50% tempered martensite.

[0014] Optionally, in the 980 MPa grade hot-dip galvanized DH steel, the grain size of the ferrite is less than 10 μm, the grain size of the martensite is less than 5 μm, the grain size of the bainite is less than 5 μm, and the grain size of the retained austenite is less than 1 μm.

[0015] Optionally, when the hot-dip galvanized DH steel is 780MPa grade hot-dip galvanized DH steel,

[0016] The chemical components of the 780MPa grade DH steel include, by mass fraction, C: 0.15-0.19%; Si: 0.3-0.8%; Mn: 1.6-2.0%; Cr: 0.1-0.5%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥0.8%; Fe;

[0017] Optionally, the steel matrix microstructure of the 780MPa grade hot-dip galvanized DH steel comprises, by volume fraction, 55% to 70% ferrite, 5% to 10% bainite, 3% to 8% retained austenite, 0% to 5% fresh martensite, and 20% to 35% tempered martensite;

[0018] Optionally, in the 780 MPa grade hot-dip galvanized DH steel, the grain size of the ferrite is less than 10 μm, the grain size of the martensite is less than 5 μm, the grain size of the bainite is less than 5 μm, and the grain size of the retained austenite is less than 1 μm.

[0019] Optionally, when the hot-dip galvanized DH steel is 590MPa grade hot-dip galvanized DH steel,

[0020] The chemical components of the 590MPa grade DH steel include, by mass fraction, C: 0.12-0.16%; Si: 0.2-0.6%; Mn: 1.3-1.7%; Cr: 0-0.3%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥0.8%; Fe;

[0021] Optionally, the microstructure of the 590MPa grade DH steel comprises, by volume fraction, ferrite 70% to 85%, bainite 0% to 5%, retained austenite 3% to 10%, fresh martensite 0% to 5%, and tempered martensite 10% to 20%;

[0022] Optionally, the 590MPa grade hot-dip galvanized DH steel is characterized in that the grain size of the ferrite is less than 10μm, the grain size of the martensite is less than 5μm, the grain size of the bainite is less than 5μm, and the grain size of the residual austenite is less than 1μm.

[0023] In a second aspect, the present disclosure provides a method for preparing hot-dip galvanized DH steel, which is used to prepare the hot-dip galvanized DH steel described in the first aspect, comprising:

[0024] The steel strip obtained after pickling and cold rolling is subjected to uniform heating at a first preset temperature;

[0025] Slowly cooling the heated steel strip to a second preset temperature;

[0026] Flash cooling the slowly cooled steel strip to a third preset temperature;

[0027] The flash-cooled strip steel is aged at a fourth preset temperature and then hot-dip galvanized to obtain the hot-dip galvanized DH steel.

[0028] Optionally, the first preset temperature is not less than 760°C and is not more than 50°C below the Ac3 temperature line of the hot-dip galvanized DH steel;

[0029] The second preset temperature is 660°C to 740°C;

[0030] The third preset temperature is between the Ms temperature of the hot-dip galvanized DH steel -200°C and the Ms temperature of the hot-dip galvanized DH steel -50°C;

[0031] The fourth preset temperature is between the third preset temperature and the third preset temperature+150° C.

[0032] In a third aspect, the present disclosure provides an automobile structural part, at least part of which is made of the hot-dip galvanized DH steel described in the first aspect.

[0033] Optionally, the automobile structural parts include at least one of side beams, cross beams, pillars, fuel tank brackets, anti-collision parts, energy absorption boxes, central channels, front longitudinal beams, door sill beams and automobile panels.

[0034] The above technical solution provided by the embodiment of the present disclosure has the following advantages compared with the prior art:

[0035] The disclosed embodiment provides a hot-dip galvanized DH steel, wherein the content of fresh martensite in the steel matrix microstructure of the hot-dip galvanized DH steel is low. By controlling the content of fresh martensite and tempered martensite in the steel matrix microstructure, most of the fresh martensite in the steel matrix microstructure is transformed into tempered martensite, so that the volume fraction of fresh martensite is less than 10%, thereby reducing the hardness difference between ferrite and martensite, achieving the purpose of improving the local forming performance of the hot-dip galvanized DH steel, thereby obtaining a hot-dip galvanized DH steel with both excellent overall forming performance and local forming performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0037] 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 labor.

[0038] Figure 1 A schematic diagram of an annealing process in a method for preparing hot-dip galvanized DH steel provided in an embodiment of the present disclosure is shown;

[0039] Figure 2 A typical microstructure diagram of a steel matrix of a hot-dip galvanized DH steel provided by an embodiment of the present disclosure is shown;

[0040] Figure 3 A schematic diagram showing the types of automotive structural parts in the present disclosure is shown. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present disclosure.

[0042] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present disclosure can be purchased from the market or prepared by existing methods.

[0043] DH steel (Dual Phase Steels with Improved Formability, referred to as DH steel for short), the full name in Chinese is enhanced formability dual phase steel, based on the microstructure of DP steel (Dual-Phase steel, also known as martensitic dual phase steel), with additional retained austenite. The retained austenite produces TRIP (Transformation Induced Plasticity) effect during the deformation process, which can overcome the disadvantage of insufficient elongation of DP steel, thereby improving the forming ability of the material. However, DH steel produced by conventional galvanizing process has the problem of insufficient local forming performance, and it is difficult to have both excellent overall forming performance and local forming performance. The relevant prior art is as follows:

[0044] The technical solution provided by the embodiments of the present disclosure is to solve the above technical problems, and the overall idea is as follows:

[0045] In a first aspect, the present disclosure provides a hot-dip galvanized DH steel, the hot-dip galvanized DH steel comprising a steel substrate and a galvanized layer attached to at least a portion of the surface of the steel substrate;

[0046] The microstructure of the steel matrix includes: ferrite, martensite, bainite and retained austenite;

[0047] The martensite includes: fresh martensite and tempered martensite;

[0048] In the microstructure of the steel matrix, the volume fraction of the fresh martensite is less than 10%.

[0049] The disclosed embodiment provides a hot-dip galvanized DH steel, wherein the content of fresh martensite in the steel matrix microstructure of the hot-dip galvanized DH steel is low. By controlling the content of fresh martensite and tempered martensite in the steel matrix microstructure, most of the fresh martensite in the steel matrix microstructure is transformed into tempered martensite, and the volume fraction of fresh martensite can be made less than 10%, thereby reducing the hardness difference between ferrite and martensite, achieving the purpose of improving the local forming performance of DH steel (the local forming performance mainly includes bending performance and hole expansion performance), thereby obtaining DH steel with both excellent overall forming performance (the overall forming performance mainly includes elongation) and local forming performance.

[0050] Compared with the prior art, the hot-dip galvanized DH steel provided in the embodiment of the present disclosure pays more attention to improving its local forming performance. By reducing the fresh martensite content in the microstructure of the hot-dip galvanized DH steel, while ensuring excellent overall formability, excellent local forming ability is obtained, meeting the forming requirements of complex parts in fields such as automobile manufacturing.

[0051] In the present disclosure, "in the steel matrix microstructure of the hot-dip galvanized DH steel, the volume fraction of the fresh martensite is less than 10%." should be understood as: in the microstructures of hot-dip galvanized DH steels of all different strength levels, the maximum volume fraction of fresh martensite does not exceed 10%; at the same time, compared with the prior art, for a certain specific DH steel of the same strength level, and / or, hot-dip galvanized DH steel, the volume fraction of fresh martensite in the hot-dip galvanized DH steel microstructure provided by the embodiments of the present disclosure is lower, thereby achieving the purpose of improving the local forming performance of a certain specific DH steel of the same strength level.

[0052] In the present disclosure, fresh martensite specifically refers to martensite formed in the final cooling process and not tempered; tempered martensite specifically refers to martensite formed in the rapid cooling stage and becomes tempered martensite after significant tempering in the aging stage.

[0053] In the present disclosure, there is no specific limitation on the thickness and chemical composition of the galvanized layer in the hot-dip galvanized DH steel, and the galvanized layer can be prepared according to actual use requirements and the technical content of the galvanized layer disclosed in the prior art.

[0054] As an implementation of the embodiment of the present disclosure, the hot-dip galvanized DH steel includes: hot-dip galvanized DH steel of any grade between 590 MPa and 1000 MPa.

[0055] In the present disclosure, in some specific embodiments, the grade of the hot-dip galvanized DH steel can be any one of the following: 590MPa hot-dip galvanized DH steel, 600MPa hot-dip galvanized DH steel, 650MPa hot-dip galvanized DH steel, 700MPa hot-dip galvanized DH steel, 750MPa hot-dip galvanized DH steel, 780MPa hot-dip galvanized DH steel, 800MPa hot-dip galvanized DH steel, 850MPa hot-dip galvanized DH steel, 900MPa hot-dip galvanized DH steel, 980MPa hot-dip galvanized DH steel, etc.

[0056] In the present disclosure, regarding the grade of hot-dip galvanized DH steel, taking "980 MPa grade hot-dip galvanized DH steel" as an example, the "980 MPa grade hot-dip galvanized DH steel" can be specifically understood as the tensile strength of the hot-dip galvanized DH steel being ≥ 980 MPa.

[0057] As an implementation method of the embodiment of the present disclosure, the hot-dip galvanized DH steel is 980MPa grade hot-dip galvanized DH steel;

[0058] Measured by volume fraction, the steel matrix microstructure of the 980MPa grade hot-dip galvanized DH steel includes: 30% to 50% ferrite, 5% to 10% bainite, 3% to 10% residual austenite, 0% to 10% fresh martensite, and 30% to 50% tempered martensite.

[0059] In some other implementations of the disclosed embodiments, the hot-dip galvanized DH steel is 780MPa grade hot-dip galvanized DH steel;

[0060] Measured by volume fraction, the steel matrix microstructure of the 780MPa grade hot-dip galvanized DH steel includes: 55% to 70% ferrite, 5% to 10% bainite, 3% to 8% residual austenite, 0% to 5% fresh martensite, and 20% to 35% tempered martensite.

[0061] In some other implementations of the disclosed embodiments, the hot-dip galvanized DH steel is 590MPa grade hot-dip galvanized DH steel;

[0062] Measured by volume fraction, the steel matrix microstructure of the 590MPa grade hot-dip galvanized DH steel includes: 70% to 85% ferrite, 0% to 5% bainite, 3% to 10% residual austenite, 0% to 5% fresh martensite, and 10% to 20% tempered martensite.

[0063] In the present disclosure, when the strength level of the hot-dip galvanized DH steel is low (such as 590MPa grade hot-dip galvanized DH steel), the fresh martensite in the conventional galvanized structure is generally less, and the local forming performance of the material can still be at a high level. Compared with the prior art, when the DH steel is 590MPa grade hot-dip galvanized DH steel, the 590MPa grade hot-dip galvanized DH steel provided in the embodiment of the present disclosure has less fresh martensite content in the microstructure, and the local forming performance of the provided 590MPa grade DH steel material is better.

[0064] As an implementation manner of the embodiment of the present disclosure, the grain size of the ferrite is less than 10 μm, the grain size of the martensite is less than 5 μm, the grain size of the bainite is less than 5 μm, and the grain size of the retained austenite is less than 1 μm.

[0065] In the present disclosure, by controlling the grain sizes of ferrite, martensite, bainite and retained austenite in the microstructure to the above parameters, the strength of the steel is ensured to be within a reasonable range.

[0066] As an implementation method of the embodiment of the present disclosure, the steel matrix of the hot-dip galvanized DH steel includes the following chemical components: C, Si, Mn, Cr, Al, P, S, Nb, Ti, Fe and unavoidable impurities;

[0067] Wherein, the mass fractions of Si and Al in the chemical composition of the DH steel satisfy the relationship 1: [Si]+[Al]≥0.8%;

[0068] In the above relational formula 1, [Si] represents the mass fraction of Si, and [Al] represents the mass fraction of Al.

[0069] In the present disclosure, the mass fractions of Si and Al in the chemical composition of hot-dip galvanized DH steel are controlled to satisfy the relationship 1: [Si]+[Al]≥0.8%; the effect of this is to ensure that the elongation of the DH steel meets the requirements.

[0070] In addition, compared with the prior art, the chemical composition design of the hot-dip galvanized DH steel in the present disclosure does not require the addition of expensive alloying elements such as Mo, which ensures the excellent performance of the DH steel material while reducing the cost. However, in some specific embodiments, the present disclosure can further improve the performance of the DH steel material by adding expensive alloying elements such as Mo according to the prior art 1 (Chinese patent CN 202010928571.7).

[0071] As an implementation of the embodiment of the present disclosure, the hot-dip galvanized DH steel is 980MPa grade hot-dip galvanized DH steel; in terms of mass fraction, the chemical components of the 980MPa grade hot-dip galvanized DH steel include:

[0072] C: 0.17-0.23%; Si: 0.3-0.9%; Mn: 1.9-2.5%; Cr: 0.1-0.6%; Al: 0.6-1.0%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥0.8%; Fe.

[0073] As a preferred embodiment of the present disclosure, when the hot-dip galvanized DH steel is 980MPa grade hot-dip galvanized DH steel, the chemical composition of the 980MPa grade hot-dip galvanized DH steel includes: C: 0.17-0.23%; Si: 0.3-0.9%; Mn: 1.9-2.5%; Cr: 0.1-0.6%; Al: 0.6-1.0%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; Fe. Compared with the prior art, the chemical composition design of the DH steel in the present disclosure does not need to add expensive alloy elements such as Mo, which ensures the excellent performance of the DH steel material (including strength performance, overall formability and local formability, etc.) while lowering the cost.

[0074] In some other embodiments of the disclosed embodiments, the hot-dip galvanized DH steel is 780MPa grade hot-dip galvanized DH steel; the chemical components of the 780MPa grade hot-dip galvanized DH steel include, by mass fraction: C: 0.15-0.19%; Si: 0.3-0.8%; Mn: 1.6-2.0%; Cr: 0.1-0.5%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥0.8%; Fe.

[0075] As a preferred embodiment of the present disclosure, when the hot-dip galvanized DH steel is 780MPa grade hot-dip galvanized DH steel, the chemical components of the 780MPa grade hot-dip galvanized DH steel include, by mass fraction: C: 0.15-0.19%; Si: 0.3-0.8%; Mn: 1.6-2.0%; Cr: 0.1-0.5%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; Fe. Compared with the prior art, the chemical composition design of the hot-dip galvanized DH steel in the present disclosure does not need to add expensive alloy elements such as Mo, which ensures the excellent performance of the DH steel material (including strength performance, overall formability and local formability, etc.) while lowering the cost.

[0076] In some other implementations of the disclosed embodiments, the hot-dip galvanized DH steel is 590 MPa grade hot-dip galvanized DH steel; in terms of mass fraction, the chemical components of the 590 MPa grade hot-dip galvanized DH steel include:

[0077] C: 0.12-0.16%; Si: 0.2-0.6%; Mn: 1.3-1.7%; Cr: 0-0.3%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥0.8%; Fe.

[0078] As a preferred embodiment of the present disclosure, when the hot-dip galvanized DH steel is 590MPa grade hot-dip galvanized DH steel, the chemical components of the 590MPa grade hot-dip galvanized DH steel include, by mass fraction: C: 0.12-0.16%; Si: 0.2-0.6%; Mn: 1.3-1.7%; Cr: 0-0.3%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; Fe. Compared with the prior art, the steel matrix chemical composition design of the hot-dip galvanized DH steel in the present disclosure does not need to add expensive alloy elements such as Mo, which ensures the excellent performance of the DH steel material (including strength performance, overall formability and local formability, etc.) while lowering the cost.

[0079] In summary, the first aspect of the disclosed embodiment provides a hot-dip galvanized DH steel having both excellent overall formability and local formability. Specifically, the performance parameters of the hot-dip galvanized DH steel include: hole expansion rate ≥ 25%, longitudinal V-bend radius < R1.5. This solves the problem of low local formability of DH steel produced by conventional galvanizing process, and meets the use requirements of stamping complex structural parts. At the same time, expensive alloy elements such as Mo do not need to be added in the design of the chemical composition of the steel matrix, which ensures the excellent performance of the hot-dip galvanized DH steel material (including strength performance, overall formability and local formability, etc.) while lowering the cost.

[0080] In the present disclosure, the performance parameters of the hot-dip galvanized DH steel include: hole expansion rate ≥ 25%, longitudinal V-bend radius < R1.5. Specifically, when the strength grade of the hot-dip galvanized DH steel is low, such as 590MPa hot-dip galvanized DH steel, the hole expansion rate can reach up to 70%, and the longitudinal V-bend radius can be as low as R0.5; when the strength grade of the hot-dip galvanized DH steel is high, such as 980MPa hot-dip galvanized DH steel, the hole expansion rate can reach up to 30%, and the longitudinal V-bend radius can be as low as R0.5.

[0081] In the present disclosure, the hole expansion ratio is an indicator for evaluating the hole expansion performance of high-strength steel, and the specific detection method and standard are GB / T24524-2009.

[0082] In the present disclosure, V-bend radius is an indicator for evaluating the bending performance of high-strength steel, and the detection method and standard are specifically GB / T232-1999.

[0083] In a second aspect, the present disclosure provides a method for preparing hot-dip galvanized DH steel, for preparing the hot-dip galvanized DH steel described in the first aspect, the preparation method comprising: molten steel smelting, continuous casting, hot rolling, pickling, cold rolling, annealing and hot-dip galvanizing;

[0084] The annealing process comprises:

[0085] The steel strip obtained after pickling and cold rolling is subjected to uniform heating at a first preset temperature;

[0086] Slowly cooling the heated steel strip to a second preset temperature;

[0087] Flash cooling the slowly cooled steel strip to a third preset temperature;

[0088] The flash-cooled strip steel is aged at a fourth preset temperature to obtain the steel matrix of the hot-dip galvanized DH steel.

[0089] The embodiment of the present disclosure provides a method for preparing hot-dip galvanized DH steel, which is used to prepare the hot-dip galvanized DH steel described in the first aspect. Compared with the prior art, the core content of the method for preparing hot-dip galvanized DH steel provided in the embodiment of the present disclosure is: by controlling the annealing process, hot-dip galvanized DH steels of different strength levels are subjected to uniform heating, slow cooling, flash cooling and aging at a preset temperature, so as to control the fresh martensite content in the organization, transform most of the fresh martensite in the organization into tempered martensite, thereby reducing the hardness difference between ferrite and martensite, and achieving the purpose of improving local forming performance.

[0090] In the present disclosure, the preparation method includes: molten steel smelting, continuous casting, hot rolling, pickling, cold rolling, annealing and hot-dip galvanizing. Specifically:

[0091] Smelting molten steel containing the same chemical composition as the steel matrix of the hot-dip galvanized DH steel, followed by continuous casting to obtain a cast billet;

[0092] The ingot is sequentially hot-rolled, pickled, cold-rolled and annealed to obtain a steel matrix of the hot-dip galvanized DH steel;

[0093] The steel substrate of the hot-dip galvanized DH steel is placed in a zinc pot for galvanizing, and after the galvanizing is completed, the steel substrate is cooled using an existing process to obtain the hot-dip galvanized DH steel.

[0094] As an implementation manner of the embodiment of the present disclosure, the first preset temperature is not lower than 760° C., and is not higher than 50° C. below the Ac3 temperature line of the DH steel.

[0095] In the present disclosure, the purpose of controlling the first preset temperature to be not less than 760° C. and not more than 50° C. below the Ac3 temperature line of the DH steel is to obtain a desired phase ratio during the soaking process.

[0096] In the present disclosure, the Ac3 line refers to the complete austenitization temperature when the strip is heated; the "50°C below the Ac3 temperature line of DH steel" should be understood as the temperature value corresponding to the Ac3 line of DH steel minus 50.

[0097] As an implementation of the embodiment of the present disclosure, the second preset temperature is 660°C to 740°C.

[0098] In the present disclosure, the second preset temperature is controlled to be 660°C to 740°C to adjust the ferrite content in the structure. In some specific embodiments, the second preset temperature may be 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, etc.

[0099] As an implementation of the embodiment of the present disclosure, the third preset temperature is between (the Ms temperature of the DH steel - 200°C) and (the Ms temperature of the DH steel - 50°C).

[0100] In the present disclosure, the purpose of controlling the third preset temperature between (the Ms temperature of the DH steel - 200°C) and (the Ms temperature of the DH steel - 50°C) is to obtain the desired tempered martensite content and control the proportion of the microstructure phase.

[0101] In the present disclosure, Ms specifically refers to the starting temperature of the transformation from austenite to martensite in the DH steel; the Ms temperature of the DH steel -200°C specifically refers to the temperature value obtained by subtracting 200 from the starting temperature of the transformation from austenite to martensite in the DH steel; the Ms temperature of the DH steel -50°C specifically refers to the temperature value obtained by subtracting 50 from the starting temperature of the transformation from austenite to martensite in the DH steel.

[0102] As an implementation manner of the embodiment of the present disclosure, the fourth preset temperature is between the third preset temperature and (the third preset temperature+150° C.).

[0103] In the present disclosure, the effect of controlling the fourth preset temperature to be between the third preset temperature and (the third preset temperature+150° C.) is to control the tempering degree of martensite.

[0104] In the present disclosure, the third preset temperature+150°C specifically refers to the temperature value obtained by adding 150 to the third preset temperature value.

[0105] As an implementation of the embodiment of the present disclosure, the process parameters of the hot rolling include: the heating temperature of the casting billet is 1150°C-1250°C.

[0106] In the present disclosure, the role of controlling the heating temperature of the casting to 1150° C.-1250° C. is to achieve microstructure homogenization and solid solution of micro-alloying elements.

[0107] As an implementation of the embodiment of the present disclosure, the process parameters of the cold rolling include: a cold rolling reduction rate of 35%-70%.

[0108] In the present disclosure, the role of controlling the cold rolling reduction ratio to be 35%-70% is to cold-roll the heated rolled sheet to a desired thickness.

[0109] To summarize, the second aspect of the embodiment of the present disclosure provides a method for preparing hot-dip galvanized DH steel, which is used to prepare the hot-dip galvanized DH steel described in the first aspect. More specifically, it provides an annealing process for improving the local forming performance of hot-dip galvanized enhanced formability dual-phase steel. The key lies in controlling the fresh martensite content in the structure and transforming most of the fresh martensite in the structure into tempered martensite, thereby reducing the hardness difference between ferrite and martensite, thereby achieving the purpose of improving the local forming performance. It can be applicable to hot-dip galvanized DH steels of different strength levels (including the hot-dip galvanized DH steel described in the first aspect). In some specific embodiments, the annealing process of the obtained hot-dip galvanized DH steel can be carried out on a hot-dip galvanizing process production line after converter smelting, slab continuous casting, hot rolling, pickling and cold rolling processes to perform the annealing process in the preparation process of hot-dip galvanized DH steel. The specific process includes: heating the strip steel obtained after pickling and cold rolling to a two-phase region uniform heating temperature between 760°C and Ac3-50°C; slow cooling temperature between 660°C and 740°C; flash cooling to Ts point after slow cooling, Ts between Ms temperature -200°C and Ms temperature -50°C; rapidly heating to Th for aging after flash cooling, Th between Ts and Ts+150°C, and aging time between 0.5 and 2min; rapidly heating the strip steel to 460°C and galvanizing in a zinc pot after aging, and cooling by normal process after galvanizing.

[0110] In a third aspect, the present disclosure provides an automobile structural part, at least part of which is made of the hot-dip galvanized DH steel described in the first aspect.

[0111] The automobile structural parts provided in the embodiments of the present disclosure are made of the hot-dip galvanized DH steel described in one aspect, and can meet the use standards of automobile structural parts in all aspects.

[0112] As an implementation of the embodiment of the present disclosure, the automobile structural parts include at least one of side beams, cross beams, pillars, fuel tank brackets, anti-collision parts, energy absorption boxes, central channels, front longitudinal beams, door sill beams and automobile panels.

[0113] In the present disclosure, the specific types of the automotive structural parts are as follows: Figure 3 The cross beams include roof cross beams, floor cross beams, etc.; pillars include A pillars, etc.; and automobile panels include door outer panels, etc.

[0114] The present disclosure is further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present disclosure and are not intended to limit the scope of the present disclosure. The experimental methods in the following examples that do not specify specific conditions are usually measured according to national standards. If there is no corresponding national standard, then it is carried out according to the general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0115] The following embodiment provides a method for preparing hot-dip galvanized DH steel, including converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, annealing, and hot-dip galvanizing; wherein the annealing process in the preparation process of DH steel is carried out on a hot-dip galvanizing process production line, such as Figure 1 As shown, the specific process of the annealing process includes: heating the strip steel obtained after pickling and cold rolling to a temperature between 760°C in the two-phase region.

[0116] ~Ac3-50℃; the slow cooling temperature is between 660℃~740℃; after slow cooling, flash cooling to Ts point, Ts is between Ms temperature -200℃ and Ms temperature -50℃ point; after flash cooling, quickly heating to Th for aging, Th is between Ts and Ts+150℃, and the aging time is between 0.5~2min; after the aging is completed, the strip is quickly heated to 460℃ and put into the zinc pot for galvanizing, and after the galvanizing is completed, it is cooled by normal process to obtain hot-dip galvanized DH steel; the grade of the hot-dip galvanized DH steel includes 590~980MPa grade hot-dip galvanized DH steel.

[0117] Embodiment 1-5 (embodiment 1-5 corresponds to number 1-3, 1-4, 1-5, 1-6, 1-7 respectively) and comparative example 1-2 (comparative example 1-2 corresponds to number 1-1 and 1-2 respectively) provide a method for preparing a 590MPa grade hot-dip galvanized enhanced formability dual-phase steel, specifically comprising:

[0118] (1) The molten steel is smelted in a converter and obtained by continuous casting. The actual chemical compositions of the continuous casting billets in Examples 1-5 (Examples 1-5 correspond to numbers 1-3, 1-4, 1-5, 1-6, and 1-7, respectively) and Comparative Example 1-2 (Comparative Example 1-2 corresponds to numbers 1-1 and 1-2, respectively) are shown in Table 1.

[0119] Table 1 Chemical composition of DH590

[0120] C,％ Si, % Mn, % Al,％ P,％ S,％ Nb,% A3,℃ Ms,℃ 0.11 0.6 1.3 0.52 0.011 0.003 0.02 915 427

[0121] (2) The continuous casting slab is hot-charged into a furnace after cleaning. The heating temperature of the continuous casting slab is 1150-1250°C, the hot rolling final rolling temperature is 900°C, and the coiling temperature is 620°C. The hot-rolled sheet is further cold-rolled to obtain a cold-hardened strip, and the cold rolling deformation is 50%.

[0122] The heating temperature of the slab is between 1150-1250℃ for homogenization of the structure and solid solution of micro-alloying elements. The final rolling temperature is set at 900℃ mainly to ensure a good hot rolling structure. If the final rolling temperature is too high, the grains may become coarse, and if the final rolling temperature is too low, mixed crystals may appear. The coiling temperature is set at 620℃ to comprehensively consider the influence of the cold rolling mill load and the surface quality of the cold-rolled finished coil. If the coiling temperature is too low, cold rolling will become difficult, and if the coiling temperature is too high, the surface quality of the finished coil will deteriorate. The cold rolling reduction rate is set to 50% based on two considerations. If the reduction rate is too low, it will not be conducive to obtaining a finer structure, and the yield strength of the material will be low; if the reduction rate is too high, the mill load will be too large, which is not conducive to plate shape control.

[0123] (3) The above-mentioned cold hardened strip is annealed and hot-dip galvanized. The strip is heated to 780-820°C for uniform heating, then slowly cooled to 680-720°C, then flash cooled to below the Ms point to obtain a partial martensitic structure, and then quickly heated to above the Ms point for aging treatment. The specific annealing process, mechanical properties, and local forming properties are shown in Table 2.

[0124] Embodiment 1-1# is a conventional galvanizing process; processes 1-2 to 1-7# use induction heating to heat the strip steel in the aging stage and before entering the zinc pot, respectively, except that the annealing process is different.

[0125] Table 2 Mechanical properties and local forming properties of DH590 under different hot-dip galvanizing processes (annealing processes)

[0126]

[0127] As shown in Table 2, after the conventional galvanizing process of 1-1#, the mechanical properties of the strip are qualified, the hole expansion rate is 43%, and the longitudinal V-bend radius is R1.5. It can be seen that due to the low strength level, the fresh martensite content in DH590 is small, and its influence on the local forming performance is not significant. Under the 1-2# process, the rapid cooling temperature / aging temperature is 410℃ / 450℃ respectively. Since the rapid cooling temperature is higher than the temperature range of [Ms temperature-200, Ms temperature-50], the mechanical properties and local forming performance of the strip are not significantly improved. Under the process 1-3#, the rapid cooling temperature / aging temperature is 250℃ / 410℃ respectively, and a large amount of primary martensite can be obtained after rapid cooling; since the aging temperature is higher than the range of [Ts, Ts+150℃], the primary martensite is fully tempered, resulting in excessive decrease in hardness and strength. Although the local forming performance of the strip is significantly improved, the tensile strength of the strip is too low. The rapid cooling and aging temperatures of process 1-4# are reasonable, not only the mechanical properties of the strip are qualified, but also the local forming properties are significantly improved. Due to the low austenite content after austenosis in process 1-5#, the yield and tensile strength are too low. Due to the low slow cooling temperature in process 1-6#, the proportion of hard phase in the matrix is ​​too small, resulting in too low tensile strength. Due to the long aging time in process 1-7#, the primary martensite tempering is too sufficient, resulting in low yield and tensile strength of the strip.

[0128] Examples 6-10 (Examples 6-10 correspond to numbers 2-3, 2-4, 2-5, 2-6, and 2-7, respectively) and comparative examples 3-4 (Comparative examples 3-4 correspond to numbers 2-1 and 2-2, respectively) provide a method for preparing a 780 MPa grade hot-dip galvanized enhanced formability dual-phase steel, specifically comprising:

[0129] (1) The molten steel is smelted in a converter and obtained by continuous casting. The actual chemical compositions of the continuous casting billets in Examples 6-10 (Examples 6-10 correspond to numbers 2-3, 2-4, 2-5, 2-6, and 2-7, respectively) and Comparative Examples 3-4 (Comparative Examples 3-4 correspond to numbers 2-1 and 2-2, respectively) are shown in Table 3.

[0130] Table 3 Chemical composition of DH780

[0131]

[0132]

[0133] (2) The continuous casting slab is hot-charged into a furnace after cleaning. The heating temperature of the continuous casting slab is 1150-1250°C, the hot rolling final rolling temperature is 900°C, and the coiling temperature is 580°C. The hot-rolled sheet is further cold-rolled to obtain a cold-hardened strip, and the cold rolling deformation is 50%.

[0134] The heating temperature of the slab is between 1150-1250℃ for homogenization of the structure and solid solution of micro-alloying elements. The final rolling temperature is set at 900℃ mainly to ensure a good hot rolling structure. If the final rolling temperature is too high, the grains may become coarse, and if the final rolling temperature is too low, mixed crystals may appear. The coiling temperature is set at 580℃ to comprehensively consider the influence of the cold rolling mill load and the surface quality of the cold-rolled finished coil. If the coiling temperature is too low, cold rolling will become difficult, and if the coiling temperature is too high, the surface quality of the finished coil will deteriorate. The cold rolling reduction rate is set to 50% based on two considerations. If the reduction rate is too low, it will not be conducive to obtaining a finer structure, and the yield strength of the material will be low; if the reduction rate is too high, the mill load will be too large, which is not conducive to plate shape control.

[0135] (4) The above-mentioned cold hardened strip is annealed and hot-dip galvanized. The strip is heated to 800-840°C for uniform heating, then slowly cooled to 680-720°C, then flash cooled to below the Ms point to obtain a partial martensitic structure, and then rapidly heated to above the Ms point for aging treatment. The specific annealing process, mechanical properties, and local forming properties are shown in Table 4.

[0136] Table 4 Mechanical properties and local forming properties of DH780 under different hot-dip galvanizing processes (annealing processes)

[0137]

[0138] As shown in Table 4, the 2-1# comparative example is a conventional galvanizing process; the 2-2# to 2-7# processes use induction heating to heat the strip in the aging stage and before entering the zinc pot, but the annealing process is different.

[0139] After the conventional galvanizing process of 2-1#, the mechanical properties of the strip are qualified, the hole expansion rate is 19%, and the longitudinal V-bend radius is R2. It can be seen that under the conventional galvanizing process, with the increase of strength level, the local forming performance of DH steel decreases. Under the 2-2# process, the rapid cooling / aging temperatures are 380℃ / 450℃ respectively, and the rapid cooling temperature is higher than the temperature range of [Ms temperature-200, Ms temperature-50]. There is no significant improvement in the mechanical properties and local forming properties of the strip. Under process 2-3#, the rapid cooling / aging temperatures are 240℃ / 400℃ respectively, and the aging temperature is higher than the range of [Ts, Ts+150℃]. Although the local forming properties are significantly improved, the tensile strength of the strip is too low. The rapid cooling and aging temperatures of process 2-4# are reasonable, and the rapid cooling / aging temperatures are 240℃ / 320℃ respectively. The measured mechanical properties are qualified; compared with the conventional galvanizing process, in addition to the significant improvement in elongation, the local forming properties are also significantly improved. The yield and tensile strength of the 2-5# process are too low due to the low soaking temperature. The slow cooling temperature of the 2-6# process is too low, which also leads to low tensile strength. The strength of the strip is too low due to the long aging time of the 2-7# process.

[0140] Examples 11-15 (Examples 11-15 correspond to numbers 3-3, 3-4, 3-5, 3-6, and 3-7, respectively) and comparative examples 5-6 (Comparative examples 5-6 correspond to numbers 3-1 and 3-2, respectively) provide a method for preparing a 980 MPa grade hot-dip galvanized enhanced formability dual-phase steel, specifically comprising:

[0141] (1) The molten steel is smelted in a converter and obtained by continuous casting. The actual chemical compositions of the continuous casting billets in Examples 11-15 (Examples 11-15 correspond to numbers 3-3, 3-4, 3-5, 3-6, and 3-7, respectively) and Comparative Examples 5-6 (Comparative Examples 5-6 correspond to numbers 3-1 and 3-2, respectively) are shown in Table 5.

[0142] Table 5 Chemical composition of DH980

[0143] C,％ Si, % Mn, % Al,％ P,％ S,％ Nb,% A3,℃ Ms,℃ 0.19 0.71 2.2 0.75 0.012 0.005 0.02 885 367

[0144] (2) The continuous casting slab is hot-charged into a furnace after cleaning. The heating temperature of the continuous casting slab is 1150-1250°C, the hot rolling final rolling temperature is 900°C, and the coiling temperature is 650°C. The hot-rolled sheet is further cold-rolled to obtain a cold-hardened strip, and the cold rolling deformation is 50%.

[0145] The heating temperature of the slab is between 1150-1250℃ for homogenization of the structure and solid solution of micro-alloying elements. The final rolling temperature is set at 900℃ mainly to ensure a good hot rolling structure. If the final rolling temperature is too high, the grains may become coarse, and if the final rolling temperature is too low, mixed crystals may appear. The coiling temperature is set at 650℃ to comprehensively consider the influence of the cold rolling mill load and the surface quality of the cold-rolled finished coil. If the coiling temperature is too low, cold rolling will become difficult, and if the coiling temperature is too high, the surface quality of the finished coil will deteriorate. The cold rolling reduction rate is set to 50% based on two considerations. If the reduction rate is too low, it will not be conducive to obtaining a finer structure, and the yield strength of the material will be low; if the reduction rate is too high, the mill load will be too large, which is not conducive to plate shape control.

[0146] (5) The above-mentioned cold-hardened strip is annealed and hot-dip galvanized. The strip is heated to 820-860°C for uniform heating, then slowly cooled to 680-740°C, then flash-cooled to below the Ms point to obtain a partial martensitic structure, and then rapidly heated to above the Ms point for aging treatment. The specific annealing process, mechanical properties, and local forming properties are shown in Table 6.

[0147] Table 6 Mechanical properties and local forming properties of DH980 under different hot-dip galvanizing processes (annealing processes)

[0148]

[0149] It can be seen from Table 6 that the 3-1# comparative example is a conventional galvanizing process; the 3-2# ​​to 3-7# processes use induction heating to heat the strip in the aging stage and before entering the zinc pot, but the annealing process is different.

[0150] After the conventional galvanizing process of 3-1#, the mechanical properties of the strip are qualified, the hole expansion rate is 14%, and the longitudinal V-bend radius is R3. It can be seen that after the strength level is increased to 980MPa, the local forming performance of DH steel under the conventional galvanizing process is further deteriorated. Under process 3-2#, the rapid cooling / aging temperature is 350℃ / 450℃ respectively, and the rapid cooling temperature is higher than the temperature range of [Ms temperature-200, Ms temperature-50]. After rapid cooling, no obvious primary martensite is produced, and the mechanical properties and local forming properties of the strip are not significantly improved. Under process 3-3#, the rapid cooling / aging temperature is 220℃ / 380℃ respectively, and the aging temperature is higher than the range of [Ts, Ts+150℃]. The primary martensite tempering is too sufficient. Although the local forming performance is significantly improved, the tensile strength of the strip is lower than the lower limit requirement. The rapid cooling / aging temperatures of process 3-4# are 220℃ / 330℃ respectively, which can produce a large amount of primary martensite and avoid excessive tempering of primary martensite. Compared with the conventional galvanizing process, in addition to the significant improvement in elongation, the local forming performance is also significantly improved. The yield and tensile strength of process 3-5# are too low due to the low soaking temperature. The slow cooling temperature of process 3-6# is too low, which also leads to low yield and tensile strength. Due to the long aging time of process 2-7#, the primary martensite is tempered too fully, and the strip strength is lower than the lower limit.

[0151] The typical microstructure of the 980MPa grade enhanced formability dual-phase steel with excellent overall formability and local formability obtained in the embodiment of the present disclosure is as follows: Figure 2 shown.

[0152] Various embodiments of the present disclosure may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present disclosure; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0153] In the present disclosure, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present disclosure, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0154] The foregoing is merely a specific embodiment of the present disclosure, which enables those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A 980MPa grade hot-dip galvanized DH steel, characterized in that: The chemical composition of the 980MPa grade hot-dip galvanized DH steel is as follows: Composition: C: 0.17-0.23%; Si: 0.3-0.9%; Mn: 1.9-2.5%; Cr: 0.1-0.6%; Al: 0.6-1.0%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥1.46%; the rest is Fe and unavoidable impurities; In terms of volume fraction, the steel matrix microstructure of the 980MPa grade hot-dip galvanized DH steel includes: 30% to 50% ferrite, 5% to 10% bainite, 3% to 10% retained austenite, 0% to 10% fresh martensite, and 30% to 50% tempered martensite; the grain size of the ferrite is less than 10 μm, the grain size of the martensite is less than 5 μm, the grain size of the bainite is less than 5 μm, and the grain size of the retained austenite is less than 1 μm; the performance parameters of the hot-dip galvanized DH steel include: hole expansion rate ≥ 25%, longitudinal 90 degree V-bend radius < R1.5; The preparation process of the 980MPa grade hot-dip galvanized DH steel comprises heating the strip obtained after pickling and cold rolling to a two-phase region uniform heating temperature between 760°C and Ac3-50°C; slow cooling temperature between 660°C and 740°C; flash cooling to Ts point after slow cooling, Ts between Ms temperature -200°C and Ms temperature -50°C; rapidly heating to Th for aging after flash cooling, Th between Ts and Ts+150°C, and aging time between 0.5 and 2min; and rapidly heating the strip to 460°C after aging and galvanizing in a zinc pot.

2. A 780MPa grade hot-dip galvanized DH steel, characterized in that: The chemical composition of the 780MPa grade DH steel is as follows: Composition: C: 0.15-0.19%; Si: 0.3-0.8%; Mn: 1.6-2.0%; Cr: 0.1-0.5%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb: ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥1.27%; the rest is Fe and unavoidable impurities; In terms of volume fraction, the steel matrix microstructure of the 780MPa grade hot-dip galvanized DH steel includes: ferrite 55%-70%, bainite 5%-10%, retained austenite 3%-8%, fresh martensite 0%-5%, and tempered martensite 20%-35%; the grain size of the ferrite is less than 10 μm, the grain size of the martensite is less than 5 μm, the grain size of the bainite is less than 5 μm, and the grain size of the retained austenite is less than 1 μm; the performance parameters of the hot-dip galvanized DH steel include: hole expansion rate ≥25%, longitudinal 90 degree V-bend radius <R1.5; The preparation process of the 780MPa grade hot-dip galvanized DH steel comprises heating the strip obtained after pickling and cold rolling to a two-phase region uniform heating temperature between 760°C and Ac3-50°C; slow cooling temperature between 660°C and 740°C; flash cooling to Ts point after slow cooling, Ts between Ms temperature -200°C and Ms temperature -50°C; rapidly heating to Th for aging after flash cooling, Th between Ts and Ts+150°C, and aging time between 0.5 and 2min; and rapidly heating the strip to 460°C after aging and galvanizing in a zinc pot.

3. A 590MPa grade hot-dip galvanized DH steel, characterized in that: The chemical composition of the 590MPa grade DH steel is as follows: composition: C: 0.12-0.16%; Si: 0.2-0.6%; Mn: 1.3-1.7%; Cr: 0-0.3%; Al: 0.5-0.9%; P≤0.02%; S≤0.01%; Nb : ≤0.04%; Ti: ≤0.04%; [Si]+[Al]≥1.12%; The rest is Fe and unavoidable impurities; In terms of volume fraction, the microstructure of the 590MPa grade DH steel includes: ferrite 70%-85%, bainite 0%-5%, retained austenite 3%-10%, fresh martensite 0%-5%, and tempered martensite 10%-20%; the grain size of the ferrite is less than 10 μm, the grain size of the martensite is less than 5 μm, the grain size of the bainite is less than 5 μm, and the grain size of the retained austenite is less than 1 μm; the performance parameters of the hot-dip galvanized DH steel include: hole expansion rate ≥25%, longitudinal 90 degree V-bend radius <R1.5; The preparation process of the 590MPa grade hot-dip galvanized DH steel comprises heating the strip obtained after pickling and cold rolling to a two-phase region uniform heating temperature between 760°C and Ac3-50°C; slow cooling temperature between 660°C and 740°C; flash cooling to Ts point after slow cooling, Ts between Ms temperature -200°C and Ms temperature -50°C; rapidly heating to Th for aging after flash cooling, Th between Ts and Ts+150°C, and aging time between 0.5 and 2min; and rapidly heating the strip to 460°C after aging and galvanizing in a zinc pot.

4. An automobile structural part, characterized in that: At least part of the automotive structural parts is made of the hot-dip galvanized DH steel according to any one of claims 1 to 3.

5. The automotive structural component according to claim 4, characterized in that: The automobile structural parts include at least one of side beams, cross beams, pillars, fuel tank brackets, anti-collision parts, energy absorption boxes, central channels, front longitudinal beams, door sill beams and automobile panels.

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