A galvanized high-strength steel and a preparation method and application thereof

Abstract

This application relates to a galvanized high-strength steel, its preparation method, and its application, belonging to the field of steel preparation technology. The steel includes: a steel substrate; a nickel layer attached to at least a portion of the surface of the steel substrate; an intermetallic compound layer comprising an intermetallic compound formed from nickel and zinc, attached to at least a portion of the surface of the nickel layer away from the steel substrate; and a zinc layer attached to at least a portion of the surface of the intermetallic compound layer away from the nickel layer. Due to the addition of the nickel layer, an intermetallic compound is formed between it and the zinc layer, which increases the melting point of zinc and zinc alloys, thus inhibiting the melting or penetration of zinc. This alleviates the liquid metal embrittlement effect caused by the melting of the zinc layer.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a galvanized high-strength steel, its preparation method and application. Background Technology

[0002] Currently, due to the demand for lightweighting in the automotive industry, high-strength automotive steel sheets are used as the material for most key parts of the vehicle body. The anodic protection of the zinc plating layer on the surface protects the base material from corrosion and improves the corrosion resistance of high-strength steel.

[0003] Resistance spot welding is the primary connection method during assembly. The temperature at the center of the weld point is excessively high, reaching approximately 1000℃ during welding, gradually decreasing towards the substrate. However, due to the low melting point of zinc and zinc alloys (420-440℃), zinc and zinc alloys melt and penetrate into the grain boundaries under the high temperature of the welding current during resistance spot welding. Simultaneously, capillary adsorption of the liquid phase occurs at the grain boundaries, exacerbating the penetration of the liquid phase into the grain boundaries and weakening the grain boundary bonding, thus forming liquid metal cracks (LME cracks). During spot welding, a complex tensile and compressive stress field exists. Compressive stress occurs at the grain boundaries in the heating region, while tensile stress is experienced at the grain boundaries in the cooling and contraction region. This exacerbates the formation of LME cracks and accelerates their propagation. Summary of the Invention

[0004] This application provides a galvanized high-strength steel, its preparation method, and its application, to solve the problem of liquid metal cracking that occurs during welding of current galvanized steel.

[0005] Firstly, this application provides a galvanized high-strength steel.

[0006] Specifically, the steel includes:

[0007] steel base;

[0008] A nickel layer, said nickel layer being attached to at least a portion of the surface of the steel substrate;

[0009] An intermetallic compound layer, comprising an intermetallic compound formed of nickel and zinc, is attached to at least a portion of the surface of the nickel layer away from the steel substrate; and

[0010] A zinc layer; the zinc layer is attached to at least a portion of the surface of the intermetallic compound layer away from the nickel layer.

[0011] As an optional implementation, the thickness of the nickel layer is 50-550 nm.

[0012] As an optional implementation, the nickel layer has columnar grains.

[0013] As an optional implementation, the chemical composition of the steel matrix, by mass fraction, includes:

[0014] C: 0.05%-0.20%, Si: 0.11%-0.35%, Mn: 1.0%-3.0%, P: ≤0.02%, S: ≤0.007%, Alt: 0.08%-0.30%, Mo: 0.1%-0.4%, Nb: 0.02%-0.05%, Ti: 0.02%-0.05%, N: ≤0.006%, Cr: 0.29%-0.65%, Cu: 0.01%-0.06%, B: 0.001%-0.003%, with the remainder being Fe and unavoidable impurities.

[0015] As an optional implementation, the chemical composition of the steel matrix, by mass fraction, includes:

[0016] C: 0.07%-0.18%, Si: 0.15%-0.30%, Mn: 1.5%-2.5%, P: ≤0.02%, S: ≤0.007%, Alt: 0.10%-0.20%, Mo: 0.2%-0.3%, Nb: 0.03%-0.04%, Ti: 0.03%-0.04%, N: ≤0.006%, Cr: 0.40%-0.50%, Cu: 0.02%-0.05%, B: 0.001%-0.002%, with the remainder being Fe and unavoidable impurities.

[0017] As an optional implementation, the microstructure of the steel matrix includes ferrite, martensite, and retained austenite; and / or

[0018] The tensile strength of the steel matrix is ​​greater than 980 MPa, the yield strength of the steel matrix is ​​greater than 700 MPa, and the elongation of the steel matrix is ​​≥12%.

[0019] Secondly, this application provides a method for preparing galvanized high-strength steel to achieve the preparation of galvanized high-strength steel as described in any embodiment of the first aspect.

[0020] Specifically, the method includes:

[0021] The billet is hot-rolled, pickled, heat-treated, and cold-rolled to obtain a steel plate;

[0022] The steel plate is pre-plated with nickel to obtain a nickel-plated plate;

[0023] The nickel-plated sheet is subjected to hot-dip galvanizing to obtain galvanized high-strength steel.

[0024] As an optional implementation method,

[0025] The hot-dip galvanizing treatment temperature is 450-470℃; and / or

[0026] The heat treatment temperature is 70-460℃; and / or

[0027] The dew point temperature of the heat treatment environment is -55 to -35°C.

[0028] As an optional implementation, the electroplating time for the pre-nickel plating treatment is 15-20 seconds, and the current density for the pre-nickel plating treatment is 3-4 A / dm². 2 .

[0029] Thirdly, this application provides an application of galvanized high-strength steel as described in any embodiment of the first aspect.

[0030] The technical solutions provided in this application have the following advantages compared with the prior art:

[0031] The galvanized high-strength steel provided in this application, due to the addition of a nickel layer, forms an intermetallic compound with the zinc layer, which increases the melting point of zinc and zinc alloys, thus inhibiting the melting or penetration of zinc. This, in turn, alleviates the liquid metal embrittlement effect caused by the melting of the zinc layer. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart illustrating the method provided in the embodiments of this application;

[0035] Figure 2 This is a schematic diagram of the grain size of the nickel layer provided in an embodiment of this application;

[0036] Figure 3 This is a schematic diagram of the dual-pulse resistance spot welding process provided in the embodiments of this application;

[0037] Figure 4 This is an electron microscope image of the galvanized high-strength steel provided in Embodiment 11 of this application after spot welding.

[0038] Figure 5 This is an electron microscope image of the galvanized high-strength steel provided in Comparative Example 1 of this application after spot welding.

[0039] Figure 6 A schematic diagram illustrating the morphology of liquid zinc in resistance spot welding, provided by existing technology. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0042] This application provides a galvanized high-strength steel, which includes: a steel substrate, a nickel layer, an intermetallic compound layer, and a zinc layer.

[0043] In some embodiments, the chemical composition of the steel matrix, by mass fraction, includes:

[0044] C: 0.05%-0.20%, Si: 0.11%-0.35%, Mn: 1.0%-3.0%, P: ≤0.02%, S: ≤0.007%, Alt: 0.08%-0.30%, Mo: 0.1%-0.4%, Nb: 0.02%-0.05%, Ti: 0.02%-0.05%, N: ≤0.006%, Cr: 0.29%-0.65%, Cu: 0.01%-0.06%, B: 0.001%-0.003%, with the remainder being Fe and unavoidable impurities.

[0045] More preferably, the chemical composition of the steel matrix, by mass fraction, includes:

[0046] C: 0.07%-0.18%, Si: 0.15%-0.30%, Mn: 1.5%-2.5%, P: ≤0.02%, S: ≤0.007%, Alt: 0.10%-0.20%, Mo: 0.2%-0.3%, Nb: 0.03%-0.04%, Ti: 0.03%-0.04%, N: ≤0.006%, Cr: 0.40%-0.50%, Cu: 0.02%-0.05%, B: 0.001%-0.002%, with the remainder being Fe and unavoidable impurities.

[0047] Furthermore, the microstructure of the steel matrix includes ferrite, martensite, and retained austenite; the tensile strength of the steel matrix is ​​greater than 980 MPa, the yield strength of the steel matrix is ​​greater than 700 MPa, and the elongation of the steel matrix is ​​≥12% (gauge length 80 mm).

[0048] A nickel layer, said nickel layer being attached to at least a portion of the surface of the steel substrate;

[0049] In some embodiments, the thickness of the nickel layer is 50-550 nm.

[0050] Currently, in laboratory environments, the maximum thickness of a nickel layer can reach 550nm, with a range of 500-550nm. In current industrial environments, the thickness of a nickel layer can reach between 50-150nm.

[0051] The thickness of the nickel layer should be controlled between 50-550 nm. A nickel layer thickness greater than 50 nm is more conducive to blocking the entry of molten zinc, but excessively thick pre-plated nickel will affect zinc plating.

[0052] In some embodiments, the nickel layer has columnar grains.

[0053] An intermetallic compound layer, comprising an intermetallic compound formed of nickel and zinc, wherein the intermetallic compound layer is attached to at least a portion of the surface of the nickel layer away from the steel substrate;

[0054] Intermetallic compounds increase the melting point of zinc and zinc alloys, thus inhibiting the melting or penetration of zinc.

[0055] A zinc layer; the zinc layer is attached to at least a portion of the surface of the intermetallic compound layer away from the nickel layer.

[0056] Based on a general inventive concept, embodiments of this application also provide a method for preparing galvanized high-strength steel.

[0057] The method for preparing galvanized high-strength steel is used to achieve the preparation of the above-mentioned galvanized high-strength steel. The specific limitations of the galvanized high-strength steel can be referred to the above embodiments. Since the method for preparing galvanized high-strength steel adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0058] Specifically, the methods include:

[0059] S1. The billet is hot-rolled, pickled, heat-treated, and cold-rolled to obtain a steel plate. In some embodiments, the heat treatment temperature before cold rolling is 700-460°C, the heat treatment time depends on the belt speed, and the dew point temperature in the heat treatment furnace is -35 to -55°C.

[0060] The heat treatment process can effectively control residual stress. At the same time, by controlling the parameters of the heat treatment, selective oxidation can be achieved.

[0061] S2. The steel plate is pre-plated with nickel to obtain a nickel-plated plate;

[0062] Pre-plating a layer of nickel before pure zinc plating can raise the melting point of the zinc plating to 880°C, reducing the melting range of zinc and thus reducing the tendency of liquid metal to become brittle. In this embodiment, a nickel layer is pre-plated between the steel substrate and the zinc layer using electroplating technology. A relatively low current density and an appropriate time are selected to make the plating layer denser. Specifically, the electroplating time is 15-20 seconds, and the current density is 3-4 A / dm³. 2 This allows the nickel layer to reach a thickness of 500-550 nm.

[0063] S3. The nickel-plated sheet is subjected to hot-dip galvanizing at a temperature of 450-470℃ to obtain galvanized high-strength steel; preferably, the hot-dip galvanizing temperature is 460℃.

[0064] At 460℃, liquid Zn wets the columnar grain boundaries of the Ni interface, forming a Ni-Zn intermetallic compound to increase the melting point of Zn.

[0065] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0066] Examples 1-10

[0067] To screen suitable nickel plating parameters, Examples 1-10 were conducted. All parameters were the same except for the current and plating time. The current and plating time for each example are shown in the table below:

[0068] <![CDATA[Current A / dm 2 > Electroplating time / s Example 1 6 30 Example 2 5 25 Example 3 5 20 Example 4 4 15 Example 5 4 20 Example 6 3 20 Example 7 6 10 Example 8 3 12 Example 9 3 10 Example 10 2 10

[0069] The nickel-plated plates obtained in each embodiment are shown in the table below:

[0070]

[0071]

[0072] As shown in the table above, the current density should be controlled at 3-4 A / dm². 2 The electroplating time should be controlled within 15-20 seconds, which is a better parameter range.

[0073] Example 11

[0074] A method for preparing galvanized high-strength steel, the method comprising:

[0075] S1. The billet is hot-rolled, pickled, heat-treated and cold-rolled to obtain a steel plate;

[0076] In this embodiment, the heat treatment temperature before cold rolling is 700-460℃, the time depends on the belt speed, and the dew point temperature in the heat treatment furnace is -45℃.

[0077] S2. Perform a laboratory pre-nickel plating treatment on the steel plate to obtain a nickel-plated plate;

[0078] In this embodiment, the steel plate surface is treated with 3A / dm. 2 The current density is adjusted, and the electroplating time is controlled at around 20 seconds, resulting in a coating thickness of approximately 500 nm.

[0079] S3. The nickel-plated sheet is hot-dip galvanized at a temperature of 460°C to obtain galvanized high-strength steel;

[0080] Comparative Example 1

[0081] A method for preparing galvanized steel, the method comprising:

[0082] S1. The billet is hot-rolled, pickled, heat-treated, and cold-rolled to obtain a steel plate;

[0083] In this embodiment, the heat treatment temperature before cold rolling is 700-460℃, the time depends on the belt speed, and the dew point temperature in the heat treatment furnace is -45℃.

[0084] S2. The nickel-plated sheet is hot-dip galvanized to obtain galvanized steel;

[0085] Experimental Example

[0086] The galvanized high-strength steel provided in Example 11 and Comparative Example 1 was subjected to double-pulse resistance spot welding. The processing procedure is described in [link to process description]. Figure 3 As shown, the galvanized high-strength steel after spot welding was subjected to scanning electron microscopy to obtain... Figure 4 (Example 11) and Figure 5 (Comparative Example 1) As shown in the figure, the number of cracks in the liquid metal is significantly reduced compared to the sample without pre-plating nickel.

[0087] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0088] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means 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 single 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, and c can be a single or multiple.

[0089] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily 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 this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A galvanized high-strength steel for resistance spot welding, characterized in that, The steel comprises: steel base; A nickel layer, said nickel layer being attached to at least a portion of the surface of the steel substrate; An intermetallic compound layer, comprising an intermetallic compound formed of nickel and zinc, wherein the intermetallic compound layer is attached to at least a portion of the surface of the nickel layer away from the steel substrate; A zinc layer; the zinc layer is attached to at least a portion of the surface of the intermetallic compound layer away from the nickel layer; The thickness of the nickel layer is 500-550 nm; The nickel layer has columnar grains; The chemical composition of the steel matrix, expressed as a mass fraction, includes: C: 0.05%-0.20%, Si: 0.11%-0.35%, Mn: 1.0%-3.0%, P: ≤0.02%, S: ≤0.007%, Alt: 0.08%-0.30%, Mo: 0.1%-0.4%, Nb: 0.02%-0.05%, Ti: 0.02%-0.05%, N: ≤0.006%, Cr: 0.29%-0.65%, Cu: 0.01%-0.06%, B: 0.001%-0.003%, with the remainder being Fe and unavoidable impurities; The microstructure of the steel matrix includes ferrite, martensite, and retained austenite; The tensile strength of the steel matrix is ​​greater than 980 MPa, the yield strength of the steel matrix is ​​greater than 700 MPa, and the elongation of the steel matrix is ​​≥12%.

2. The galvanized high-strength steel according to claim 1, characterized in that, The chemical composition of the steel matrix, expressed as a mass fraction, includes: C: 0.07%-0.18%, Si: 0.15%-0.30%, Mn: 1.5%-2.5%, P: ≤0.02%, S: ≤0.007%, Alt: 0.10%-0.20%, Mo: 0.2%-0.3%, Nb: 0.03%-0.04%, Ti: 0.03%-0.04%, N: ≤0.006%, Cr: 0.40%-0.50%, Cu: 0.02%-0.05%, B: 0.001%-0.002%, with the remainder being Fe and unavoidable impurities.

3. A method for preparing galvanized high-strength steel, characterized in that, The galvanized high-strength steel is the galvanized high-strength steel according to any one of claims 1 to 2, and the method includes: The billet is hot-rolled, pickled, heat-treated, and cold-rolled to obtain a steel plate; The steel plate is pre-plated with nickel to obtain a nickel-plated plate; The nickel-plated sheet is subjected to hot-dip galvanizing to obtain galvanized high-strength steel; The electroplating time for the pre-nickel plating treatment is 15-20 seconds, and the current density for the pre-nickel plating treatment is 3-4 A / dm². 2 .

4. The method for preparing galvanized high-strength steel according to claim 3, characterized in that, The hot-dip galvanizing treatment temperature is 450-470℃; and / or The heat treatment temperature is 70-460℃; and / or The dew point temperature of the heat treatment environment is -55 to -35°C.

5. An application of galvanized high-strength steel, characterized in that, The application includes using the galvanized high-strength steel of any one of claims 1 to 2 as at least a portion of the material in automobiles.

Images