Laser welding wire, Al-Si coated hot-formed steel plate, preparation method thereof, and vehicle

Abstract

The present disclosure relates to a laser tailor-welded wire, an Al-Si coated hot-formed steel plate, a preparation method thereof and a vehicle. Based on the total weight of the laser tailor-welded wire, the laser tailor-welded wire comprises: 0.01-0.30 wt% C, 1.0-2.5 wt% Mn, 0.30-2.0 wt% Si, 0.02 wt% or less P, 0.04 wt% or less S, 0.01-0.20 wt% V, 0.10-0.50 wt% Cr, 3.0-7.0 wt% Ni, 0.3-1.2 wt% Mo, 0.01-0.04 wt% Nb, 0.005-0.06 wt% rare earth elements, and the balance Fe and impurities; the rare earth elements include La and Ce, and the weight ratio of La:Ce is 1:1.4-2.6. The present invention can reduce the softening effect of Al on the weld and the α-ferrite content, enhance the weld strength, and meet the oxidation resistance and strength requirements of the hot stamping formed plate.

Description

Technical Field

[0001] The present disclosure relates to the technical field of metal material processing, and in particular, to a laser tailor-welded welding wire, an Al-Si coated hot-formed steel plate, a preparation method thereof, and a vehicle. Background Art

[0002] The tensile strength of aluminum-silicon coated steel after hot stamping can reach 1500MPa and above, becoming the main force of lightweight materials for car bodies and widely used in the manufacture of structural parts such as A-pillars, B-pillars, and crossbeams of car bodies. In order to avoid oxidation during the hot stamping process, a coating is usually prefabricated on the surface of hot-formed steel. Aluminum-silicon coating has become a common coating for coated steel due to its excellent corrosion resistance and high-temperature oxidation resistance. Due to the presence of aluminum-silicon coating, the welding performance is seriously deteriorated. It is difficult to ensure the welding quality with traditional welding methods. Laser welding also has shortcomings. For example, when laser welding is used, the coating will enter the weld, and more ferrite structure will be produced after hot stamping, causing the weld joint to fail in the weld area, reducing the mechanical properties of the weld joint, and cannot meet production applications. Especially for aluminum-silicon coated hot-formed steel at the level of 1500MPa and above, the tensile strength and elongation of the weld obtained by conventional laser welding are difficult to reach the level of the parent material, which in turn affects the overall performance of the obtained welded plate, such as the weld area is prone to fracture. Summary of the invention

[0003] The purpose of the present disclosure is to provide a laser welding wire, an Al-Si coated hot-formed steel plate, a preparation method thereof and a vehicle, which can reduce the softening effect of Al relative to the weld and the α-ferrite content, enhance the weld strength, and meet the oxidation resistance and strength requirements of the hot stamping formed plate.

[0004] In order to achieve the above-mentioned objectives, the first aspect of the present disclosure provides a laser tailored welding wire. Based on the total weight of the laser tailored welding wire, the laser tailored welding wire includes: 0.01-0.30 wt. % C, 1.0-2.5 wt. % Mn, 0.30-2.0 wt. % Si, 0.02 wt. % or less P, 0.04 wt. % or less S, 0.01-0.20 wt. % V, 0.10-0.50 wt. % Cr, 3.0-7.0 wt. % Ni, 0.3-1.2 wt. % Mo, 0.01-0.04 wt. % Nb, 0.005-0.06 wt. % rare earth elements, and the remainder Fe and impurities; the rare earth elements include La and Ce, and the weight ratio of La:Ce is 1:1.4-2.6.

[0005] Optionally, based on the total weight of the laser welding wire, the laser welding wire includes: 0.18-0.24 wt. % C, 1.6-2.2 wt. % Mn, 1.0-1.8 wt. % Si, less than 0.02 wt. % P, less than 0.03 wt. % S, 0.09-0.15 wt. % V, 0.2-0.4 wt. % Cr, 3.5-5.5 wt. % Ni, 0.6-1.0 wt. % Mo, 0.01-0.027 wt. % Nb, 0.015-0.055 wt. % rare earth elements, and the remainder Fe and impurities.

[0006] Optionally, among the rare earth elements, the weight ratio of La:Ce is 1:1.8-2.3.

[0007] Optionally, the ratio of the total weight of Nb and V to the weight of the rare earth element is 1.7-6.3:1, preferably 2.4-5.9:1.

[0008] A second aspect of the present disclosure provides a method for preparing an Al-Si coated hot-formed steel plate, comprising the following steps:

[0009] S1. Using the laser welding wire described in the first aspect of the present disclosure to laser weld the butt joints of two Al-Si coated steel plates to obtain a welded plate;

[0010] S2. performing hot stamping treatment on the tailor-welded blanks.

[0011] Optionally, in step S1, both sides of the Al-Si coated steel plate include Al-Si coatings; the coating thickness on one side of the Al-Si coated steel plate is 20-30 um; the coating thickness on both sides of the Al-Si coated steel plate is the same;

[0012] Optionally, based on the total weight of the Al-Si coating on one side, the Al-Si coating on one side includes more than 85 wt % of Al, 5-11 wt % of Si, 2-4 wt % of Fe and impurity elements.

[0013] Optionally, in step S1, based on the total weight of the steel plate matrix in the Al-Si coated steel plate, the steel plate matrix includes: 0.20-0.25 wt% C, 0.40 wt% or less Si, 1.0-1.4 wt% Mn, 0.025 wt% or less P, 0.01 wt% or less S, 0.01-0.06 wt% Al, 0.02-0.05 wt% Ti, 0.005 wt% or less B, 0.35 wt% or less Cr, 0.008 wt% or less N, and the remainder Fe and impurities;

[0014] Optionally, the thickness of the steel plate substrate is 1.0-1.8 mm, and the thickness of the steel plate substrates in the two Al-Si coated steel plates to be laser welded are the same or different.

[0015] Optionally, in step S1, the conditions for laser welding include: laser power of 2000-6000 W, welding speed of 2.5-5.5 m / min, wire feeding speed of 1-5.0 m / min, and defocus of 0.01-4 mm; preferably, laser power of 2600-4000 W, welding speed of 2.5-4.0 m / min, wire feeding speed of 2-3.5 m / min, and defocus of 0.01-3 mm.

[0016] Optionally, step S2 includes: heating the tailored welded plate in a heating furnace at a temperature of 880-950°C for a heating time of 3-8 min; transferring the heated tailored welded plate to a flat mold for quenching, with a transfer time of 7-12s and a holding time of 6-12s; when the temperature cools to below 150°C, removing the mold and cooling it to 20-40°C in air at a cooling rate of ≥30°C / s.

[0017] A third aspect of the present disclosure provides an Al-Si coated hot-formed steel plate prepared according to the method described in the second aspect of the present disclosure.

[0018] A fourth aspect of the present disclosure provides a vehicle, comprising the Al-Si coated hot-formed steel plate according to the third aspect of the present disclosure.

[0019] Through the above technical scheme, the present disclosure provides a laser tailored welding wire, an Al-Si coated hot-formed steel plate and a preparation method thereof and a vehicle. The laser tailored welding wire is applied to the tailored welding process containing Al-Si coated steel, which can not only ensure the mechanical properties of the weld, but also obtain good weld formation and consistency, thereby realizing the mass production of aluminum-silicon coated steel components; the use of the laser tailored welding wire disclosed in the present disclosure to prepare Al-Si coated hot-formed steel plates can ensure that there is no obvious segregation of Al phase in the weld area, thereby reducing the softening effect of Al phase on the weld and the α-ferrite content, enhancing the weld strength, and meeting the oxidation resistance and strength requirements of the hot stamping formed plate.

[0020] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0022] Figure 1A flow chart showing a method for hot forming a steel plate with an Al-Si coating provided by the present disclosure is shown;

[0023] Figure 2 A welding flow chart of a laser welding wire applicable to Al-Si coated hot-formed steel plates provided by the present disclosure is shown;

[0024] Figure 3 A schematic diagram showing changes in microstructure content (wt%) during welding of Example 1 (solid line) of the present disclosure and Comparative Example 1 (dashed line) is shown;

[0025] Figure 4 The EDS micro-area chemical composition scan of the weld and the base material obtained in Example 1 of the present disclosure is shown;

[0026] Figure 5 The Vickers hardness test diagram of the weld and the base material obtained in Example 1 of the present disclosure is shown;

[0027] Figure 6 The EPMA distribution diagram of Al element in the weld area of ​​Example 1 of the present disclosure is shown. DETAILED DESCRIPTION

[0028] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0029] A first aspect of the present disclosure provides a laser tailored welding wire. Based on the total weight of the laser tailored welding wire, the laser tailored welding wire includes: 0.01-0.30 wt% C, 1.0-2.5 wt% Mn, 0.30-2.0 wt% Si, 0.02 wt% or less P, 0.04 wt% or less S, 0.01-0.20 wt% V, 0.10-0.50 wt% Cr, 3.0-7.0 wt% Ni, 0.3-1.2 wt% Mo, 0.01-0.04 wt% Nb, 0.005-0.06 wt% rare earth elements, and the remainder Fe and impurities; the rare earth elements include La and Ce, and the weight ratio of La:Ce is 1:1.4-2.6.

[0030] The present disclosure provides a laser tailor-welding wire, which is applied to the tailor-welding process of steel containing Al-Si coating, and can not only ensure the mechanical properties of the weld, but also obtain good weld formation and consistency, thereby realizing the mass production of aluminum-silicon coated steel components; the laser tailor-welding wire of the present disclosure is used to prepare Al-Si coated hot-formed steel plates, so that there is no obvious segregation of Al phase in the weld area, thereby reducing the softening effect of Al phase on the weld and the α-ferrite content, enhancing the weld strength, and meeting the oxidation resistance and strength requirements of hot stamping formed plates.

[0031] In the present disclosure, “1:1.4-2.6” includes but is not limited to 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, and 1:2.6.

[0032] Under ideal conditions, the transformation process of weld microstructure content (weight %) during laser welding of hot-formed steel with equal and differential thickness with Al-Si coating is as follows: Figure 3 As shown, it includes the following stages:

[0033] Stage 1: L (liquid) -> δ (ferrite); Stage 2: L+δ -> γ (austenite); Stage 3: δ -> γ; Stage 4: γ -> M (martensite), Figure 3 The microstructure content in the weld is obtained by theoretical calculation (Jmatpro phase content calculation). However, the presence of Al makes the δ-ferrite content high (in stages 1, 2 and 3), resulting in incomplete austenitization of the weld microstructure. Finally, α-ferrite is formed after hot stamping. The presence of α-ferrite soft phase (low dislocation density) and the destruction of martensite continuity make the weld strength low. Therefore, the weld strength depends on the percentage of ferrite phase contained in the weld, that is, the distribution of Al elements in the weld.

[0034] In the laser welding wire provided by the present disclosure, in addition to C and Mn elements stabilizing the austenite phase, there are also V, Nb, Ni, Cr, Mo and other elements, which can exist in the solid solution to stabilize the new austenite on the one hand, and can react with interstitial atoms to form precipitation phases on the other hand, respectively promoting grain refinement through solute drag and pinning effects. Adding a small amount of La and Ce elements to the welding wire can not only expand the austenitization range and inhibit the formation of high-temperature ferrite, but also increase the solubility of C and Mn elements in austenite, improve the austenite content and stability, and also promote grain refinement, reduce the particle size of sulfide and oxide inclusions, and effectively improve the weld strength.

[0035] According to the present disclosure, the C element is a solid solution strengthening element that can ensure the strength of the weld. Among them, the iron-aluminum alloy is the inevitable product of the heating of the hot-formed steel with aluminum-silicon coating, but since the iron-aluminum alloy has almost no solubility in carbon, the discharged incremental carbon will accumulate in the micron thickness close to the steel surface, making the steel on the surface layer brittle. Therefore, the present disclosure controls the C content to 0.01-0.30% by weight to avoid the adverse effects caused by the excessively high carbon content of the above-mentioned welding wire.

[0036] According to the present disclosure, Si and Mn elements have the effect of improving weld strength and weld deoxidation. Mn can expand the austenite phase region, improve hardenability, increase austenite stability, and facilitate obtaining a full martensite structure after hot stamping. Si can fully deoxidize the weld metal, improve the fluidity of the weld molten pool, reduce Al phase segregation, and make the weld structure uniform. The present disclosure controls the Si content to 0.30-2.0% by weight and the Mn content to 1.0-2.5% by weight, which can ensure that the weld has excellent performance.

[0037] According to the present disclosure, P and S elements are harmful elements. Since the smelting cost of deep P and S removal is high, the present disclosure controls the welding wire to include less than 0.02 wt % P and less than 0.04 wt % S, which can reduce the impact of harmful elements on welding results.

[0038] According to the present disclosure, the V content is 0.01-0.20 wt % and the Nb content is 0.01-0.04 wt %, which can effectively refine the grains, increase the formation of precipitated phases, and improve the weld strength and toughness as well as the resistance to hydrogen-induced cracking sensitivity.

[0039] According to the present disclosure, Ni, Cr, and Mo are important alloying elements in welding wires. Adding 3.0-7.0 wt% of Ni to the welding wire can improve the stability of austenite structure and inhibit the formation of high-temperature ferrite structure. Adding 0.10-0.50 wt% of Cr and 0.3-1.2 wt% of Mo to the welding wire can improve the hardenability of steel, improve the hardness and wear resistance of carbon steel, and enhance the corrosion resistance and oxidation resistance of the weld.

[0040] According to the present disclosure, adding a small amount of rare earth elements (La and Ce elements) to the welding wire at 0.005-0.06 wt % can have the following effects: (1) expanding the austenitization range, inhibiting the formation of high-temperature ferrite, and ensuring full austenitization as much as possible; (2) increasing the solubility of C and Mn elements in austenite, improving the austenite content and stability; (3) promoting grain refinement, reducing the particle size of sulfide and oxide inclusions, and effectively improving the weld strength. In addition, rare earth elements are a solute resistance that can hinder subgrain boundary migration and reduce the occurrence of δ-ferrite swallowing γ-austenite.

[0041] In a preferred embodiment, based on the total weight of the laser tailored welding wire, the laser tailored welding wire comprises: 0.18-0.24 wt% C, 1.6-2.2 wt% Mn, 1.0-1.8 wt% Si, 0.02 wt% or less P, 0.03 wt% or less S, 0.09-0.15 wt% V, 0.2-0.4 wt% Cr, 3.5-5.5 wt% Ni, 0.6-1.0 wt% Mo, 0.01-0.027 wt% Nb, 0.015-0.055 wt% rare earth elements, and the balance Fe and impurities. With the optimized welding wire composition provided by this embodiment, the performance of the obtained weld and the overall performance of the final tailored hot-formed steel plate can be further improved.

[0042] In a preferred embodiment, the weight ratio of La:Ce in the rare earth elements is 1.8-2.3, and more preferably 1:2. Adding rare earth elements to the welding wire according to the weight ratio of La:Ce in this embodiment can further improve the performance of the weld obtained by the welding wire.

[0043] In a preferred embodiment, the ratio of the total weight of Nb and V to the weight of the rare earth element is 1.7-6.3: 1, including but not limited to 1.7: 1, 2: 1, 2.4: 1, 2.8: 1, 3.2: 1, 3.6: 1, 4: 1, 4.4: 1, 4.8: 1, 5.2: 1, 5.6: 1, 5.9: 1, 6: 1, 6.3: 1, preferably 2.4-5.9: 1. The laser welding wire having the ratio of the total weight of Nb and V to the weight of the rare earth element in this embodiment can obtain a weld with better performance.

[0044] In a specific embodiment, the diameter of the laser tailored welding wire is 0.4-2.0 mm, preferably 0.6-1.2 mm. The welding wire with the diameter in this embodiment can adjust the chemical composition of the weld and ensure the fullness of the weld.

[0045] The laser welding wire disclosed in the present invention can be prepared by conventional methods, such as vacuum casting, annealing and forging according to the target composition, hot rolling and pickling of the wire followed by cold drawing and annealing.

[0046] A second aspect of the present disclosure provides a method for preparing an Al-Si coated hot-formed steel plate, such as Figure 1 As shown, the following steps are included:

[0047] S1. Using the laser welding wire described in the first aspect of the present disclosure to laser weld the butt joints of two Al-Si coated steel plates to obtain a welded plate;

[0048] S2. performing hot stamping treatment on the tailor-welded blanks.

[0049] The present invention provides a method for preparing an Al-Si coated hot-formed steel plate, wherein two or more steel plates containing an Al-Si coating are laser welded into a tailor-welded plate by a welding wire, and the surface coating does not need to be removed, and the wire-filling welding is directly performed. By adjusting the laser tailor-welding process, the Al phase is controlled to have no obvious segregation in the weld zone, the Al phase content in the weld zone is extremely low (about 0.001-1.3% by weight), and the size of the soft phase α-ferrite is small (below 80 μm), thereby reducing the softening effect of the Al phase on the weld and the α-ferrite content, enhancing the weld strength, and meeting the oxidation resistance and strength requirements of the hot stamping formed plate; then, the Al-Si coated hot-formed steel plate is obtained by a hot stamping process, and the microstructure structure of the weld joint after hot stamping has a high lath martensite content (up to more than 98%), and no aggregated soft phase α-ferrite appears, and the hardness of the welding area is large (up to more than 460 HV).

[0050] In one embodiment, in step S1, both sides of the Al-Si coated steel plate include Al-Si coatings; the coating thickness of one side of the Al-Si coated steel plate is 20-30 um; the coating thickness of both sides of the Al-Si coated steel plate is the same. The Al-Si coating in the present disclosure can be formed by conventional methods in the art.

[0051] In a specific embodiment, based on the total weight of the Al-Si coating, the Al-Si coating includes more than 85 wt % Al, 5-11 wt % Si, 2-4 wt % Fe and impurity elements.

[0052] In one embodiment, in step S1, based on the total weight of the steel plate matrix in the Al-Si coated steel plate, the steel plate matrix includes: 0.20-0.25 wt% C, 0.40 wt% or less Si, 1.0-1.4 wt% Mn, 0.025 wt% or less P, 0.01 wt% or less S, 0.01-0.06 wt% Al, 0.02-0.05 wt% Ti, 0.005 wt% or less B, 0.35 wt% or less Cr, 0.008 wt% or less N, and the remainder Fe and impurities; the steel plate matrix having the composition provided in this embodiment is more suitable for laser welding using the welding wire provided in the first aspect of the present disclosure, and hot stamping to obtain a hot-formed steel plate with better performance. The Al-Si coated steel plate for laser welding used in the present disclosure can be obtained by commercial purchase or prepared by conventional methods in the art.

[0053] In one embodiment, the thickness of the steel plate substrate is 0.8-2.5 mm, preferably 1.0-1.8 mm. A steel plate substrate with this thickness can achieve better welding effect and hot stamping effect. In the present disclosure, the thickness of the steel plate substrates in the two Al-Si coated steel plates to be laser welded can be the same or different, that is, the welding wire provided in the present disclosure can be used for welding steel plates of equal thickness or steel plates of different thickness.

[0054] In a specific embodiment, the yield strength of the steel plate substrate after quenching in the Al-Si coated steel plate is: tensile strength ≥ 1500MPa, and the fracture position of the tensile specimen after flat quenching must be in the parent material, wherein the yield strength test and tensile fracture test adopt the GB / T 228.1 standard. The steel plate substrate with the above properties is used, which has both high performance and weight reduction effects.

[0055] In one embodiment, in step S1, the laser welding conditions include: laser power of 2000-6000W, welding speed of 2.5-5.5m / min, wire feeding speed of 1-5.0m / min, and defocus of 0.01-4mm; preferably, laser power of 2600-4000W, welding speed of 2.5-4.0m / min, wire feeding speed of 2-3.5m / min, and defocus of 0.01-3mm. According to the process conditions provided by the present disclosure, especially the preferred process conditions, after laser welding wire is used for welding, a better weld zone can be obtained.

[0056] In a specific implementation manner, Figure 2 As shown, the step S1 of using the laser welding wire described in the first aspect of the present disclosure to laser weld the butt joints of two Al-Si coated steel plates to obtain a welded plate includes the following steps:

[0057] S101. Take two pieces of hot-formed steel with equal or different thicknesses and Al-Si coating, perform decontamination treatment on them, place them on a workbench and fix them with a welding fixture;

[0058] S102, reserve a gap between the two steel plates, select the laser, set the process parameters, and fill the welding wire during welding;

[0059] S103, using a laser to irradiate the butt joint of the two hot-formed steel plates, so that the plates are melted, solidified and cooled to form a high-strength weld, thereby joining the two hot-formed steel plates to obtain a welded plate. The equipment used for laser welding, such as a laser, is conventionally used in the art.

[0060] In one embodiment, step S2 includes: heating the tailor-welded blank in a heating furnace at a temperature of 880-950°C for a heating time of 3-8 minutes; transferring the heated tailor-welded blank to a flat mold for quenching, with a transfer time of 7-12 seconds and a holding time of 6-12 seconds; when the temperature cools to below 150°C, removing the mold and cooling to room temperature in air at a cooling rate of greater than or equal to 30°C / s. Using the process conditions provided in this embodiment for hot stamping can improve the uniformity of the welded blank.

[0061] A third aspect of the present disclosure provides an Al-Si coated hot-formed steel plate prepared according to the method described in the second aspect of the present disclosure.

[0062] In a specific embodiment, the Al-Si coated hot-formed steel plate has a tensile strength of 1400-1700 MPa and a hardness of 460-500 HV.

[0063] A fourth aspect of the present disclosure provides a vehicle, comprising the Al-Si coated hot-formed steel plate according to the third aspect of the present disclosure.

[0064] According to the present disclosure, Al-Si coated hot-formed steel plates can be applied to automobile bodies and safety structural parts, including but not limited to: left and right anti-collision bars (beams) of the front and rear doors of the vehicle; front and rear bumpers; A-pillar reinforcement plates; B-pillar reinforcement plates; C-pillar reinforcement plates; center channels; roof reinforcement beams and other safety structures.

[0065] The present disclosure is further described in detail by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0066] The composition of the steel plate substrate in the Al-Si coated steel plate used in the following examples and comparative examples includes: 0.22 wt% C, 0.27 wt% Si, 1.2 wt% Mn, 0.013 wt% P, 0.004 wt% S, 0.04 wt% Al, 0.03 wt% Ti, 0.003 wt% B, 0.26 wt% Cr, 0.005 wt% N, the balance Fe and inevitable impurity elements; the single-sided coating thickness of the Al-Si coated steel plate is 25 um; the coating thickness on both sides of the Al-Si coated steel plate is the same; based on the total weight of the Al-Si coating, the Al-Si coating includes 88 wt% Al, 10 wt% Si, 2 wt% Fe and impurity elements. In the present disclosure, the thickness of the two welded steel plates can be the same or different.

[0067] The diameter of the welding wire used in the following Examples and Comparative Examples was 1.0 mm.

[0068] In the present disclosure, the steel plate substrate and coating composition are tested by using a German SPECTRO direct reading spectrometer and a German Zeiss SEM scanning electron microscope instrument and method.

[0069] EDS micro-area chemical composition scanning test instruments and test methods include: German Zeiss SEM scanning electron microscope.

[0070] The testing instruments and methods for Vickers hardness include: German Zwick Micro Vickers Hardness Tester.

[0071] The testing instrument and testing method of the EPMA distribution diagram of the Al element include: Japan Shimadzu EPMA electron probe microanalyzer.

[0072] Examples 1-10

[0073] The Al-Si coated steel plate was laser welded according to the laser welding wire composition listed in Table 1 below. The laser welding conditions included: laser power of 3600 W, welding speed of 2.7 m / min, wire feeding speed of 2.5 m / min, and defocus of 2.8 mm to obtain a welded plate;

[0074] The tailor-welded plate was heated in a heating furnace at 930°C for 5 min. The heated tailor-welded plate was quickly transferred to a flat mold for quenching. The transfer time was 9s and the holding time was 10s. When the temperature was cooled to below 150°C, the mold was removed and cooled to room temperature (20-40°C) in air at a cooling rate of 30°C / s to obtain an Al-Si coated hot-formed steel plate.

[0075] In the embodiment, the thickness of the two welded steel plates can be the same or different, and the specific thicknesses are listed in Table 2.

[0076] Among them, the EDS micro-area chemical composition scanning diagram of the weld and base material of the hot-formed steel obtained in Example 1 is as follows: Figure 4 As shown by Figure 4 It can be seen that the Al phase content in the heat-affected zone (i.e., part of the base material near the weld zone) is basically within the range of 0.14%, and the Al phase content in the weld zone is as high as 1.26%, indicating that the use of welding wire with this composition to adjust the chemical composition of the weld zone can be done directly without removing the surface coating, and the Al phase content in the weld zone is controlled to be extremely low (about 0.001-1.3 wt%) by adjusting the laser welding process, and the size of the soft phase α-ferrite is small (below 80μm), thereby reducing the softening effect of the Al phase on the weld and the α-ferrite content, enhancing the weld strength, and meeting the oxidation resistance and strength requirements of the hot stamping steel plate. The size of the soft phase α-ferrite is shown in the microscope image (such as Figure 5 The white strip-like structure (soft phase) was measured (as shown).

[0077] The Vickers hardness test diagram of the weld and base material of the hot-formed steel obtained in Example 1 is as follows: Figure 5 As shown by Figure 5 It can be seen that the Vickers hardness test experimental values ​​of the weld area are all above 470HV, which meets the target requirements, and the base material is above 490HV. The hardness difference between the two is small, the weld performance is relatively superior, and can reach a level comparable to that of the base material.

[0078] The EPMA distribution diagram of Al element in the weld area of ​​the hot-formed steel obtained in Example 1 is as follows: Figure 6 As shown by Figure 6 It can be seen that there is no Al segregation inside the weld and the overall distribution is relatively uniform, which reduces the softening effect of Al phase concentration on the weld and enhances the weld strength.

[0079] Embodiment 11

[0080] This embodiment refers to the preparation method in Example 1, and uses the same welding wire as in Example 1. The difference from Example 1 is that laser welding is performed according to the following process conditions:

[0081] The laser power is 1800 W, the welding speed is 2.0 m / min, the wire feeding speed is 6 m / min, the defocus amount is 4 mm, and the rest of the process is the same as in Example 1.

[0082] Example 12

[0083] This embodiment refers to the preparation method in Example 1, and the difference from Example 1 is that: Al-Si coated steel plates are laser welded according to the laser welding wire composition listed in Table 1 below, and the rest of the process is the same as Example 1.

[0084] Comparative Examples 1-7

[0085] Al-Si coated hot-formed steel plates were prepared according to the preparation method in Example 1. The difference from Example 1 is that the Al-Si coated steel plates were laser welded using the laser welding wire composition listed in Table 1 below, and the rest of the process was the same as Example 1.

[0086] Schematic diagram of the change of weld microstructure content during welding process of Example 1 and Comparative Example 1 (calculated according to Jmatpro phase content) Figure 3 As shown, Figure 3 In the figure, curve ac represents the schematic curve of the change of the content of the weld structure in Example 1, and curve a'-c' represents the schematic curve of the change of the content of the weld structure in Comparative Example 1. Figure 3It can be seen that when welding is performed using the welding wire provided in Example 1 of the present disclosure, the structure in the weld can be completely austenitized without the presence of ferrite, and the final hot-formed steel plate obtained also only contains martensite; while when welding is performed using the welding wire in Comparative Example 1, the structure in the weld is not completely austenitized, and the weld contains both austenite and ferrite structures, and the final hot-formed steel plate obtained also contains both martensite and ferrite.

[0087] Table 1

[0088]

[0089] The weight ratio of La:Ce and the ratio of the total weight of Nb and V to the weight of the rare earth element in the laser welding wire compositions used in the above embodiments and comparative examples are listed in Table 2 below.

[0090] Table 2

[0091]

[0092] Test Example 1

[0093] The Al-Si coated hot-formed steel plates obtained in the above embodiments and comparative examples were subjected to a tensile strength test, and the test method and test standard included GB / T 228.1-2021·Metallic materials·Tensile tests·Part 1: Room temperature test methods; and the fracture position was obtained during the mechanical property test, and the fracture position of the steel plate was observed;

[0094] The Al-Si coated hot-formed steel plates obtained in the above examples and comparative examples were subjected to hardness tests, and the test methods and test standards included GB / T 4340.1-2009 Metallic materials·Vickers hardness test·Part 1: Test methods;

[0095] The instruments and methods for testing the types of structures in Al-Si coated hot-formed steel plates include the German Zeiss SEM scanning electron microscope and the Japanese Shimadzu EPMA electron probe microanalyzer. Where M represents martensite and F represents ferrite.

[0096] The test results are listed in Table 3 below.

[0097] Table 3

[0098]

[0099] According to the data in Table 1-3, we can see that:

[0100] Comparing the welded hot-formed steel plates obtained in Example 1-10 with those obtained in Comparative Example 1-7, under the same preparation process, the hot-formed steel plates obtained by welded using the welding wire provided by the present disclosure in Example 1-10 have significantly higher tensile strength and hardness than the hot-formed steel plates obtained in Comparative Example 1-7; and the weld of the welded hot-formed steel plates obtained using the welding wire in Example 1-10 contains only martensite phase, while the weld of the welded hot-formed steel plates obtained in Comparative Example 1-7 contains martensite and ferrite, which reduces the weld performance; the fracture position of the welded hot-formed steel plates obtained in Example 1-10 is located in the parent material, while the fracture positions of the welded hot-formed steel plates obtained in Comparative Example 1-7 are all located in the weld, which further illustrates that the weld performance obtained using the welding wire provided by the present disclosure is more excellent;

[0101] Further, comparing Examples 1 and 8 with Examples 2-7, the welding wire component content in Example 1 is within the preferred range provided in the present disclosure, and the welded hot-formed steel plates obtained by welding using the welding wires of Examples 1 and 8 have higher tensile strength and hardness;

[0102] Comparing Examples 1 and 8 with Examples 9-10, it can be seen that the weight ratio of La to Ce of the welding wires used in Examples 1 and 8 is within the preferred range provided by the present disclosure, and the welded hot-formed steel plates obtained by welding using the welding wires of Examples 1 and 8 have higher tensile strength and hardness;

[0103] Comparing Example 1 with Example 11, it can be seen that the laser welding process conditions used in Example 11 are not within the optimized range provided in the present disclosure. The welded hot-formed steel plate obtained by laser welding according to the optimized conditions provided in the present disclosure in Example 1 has higher tensile strength and hardness.

[0104] Comparing Example 1 with Example 12, the ratio of the total weight of Nb and V to the weight of the rare earth element in Example 12 is not within the optimization range provided in the present disclosure. Compared with the steel plate obtained by using the welding wire of Example 12, the steel plate obtained by using the welding wire in Example 1 only contains martensite, the fracture position is also located in the base material, and the tensile strength and hardness of the steel plate are higher.

[0105] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0106] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0107] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A laser welding wire, characterized in that: Based on the total weight of the laser tailor-welding wire, the laser tailor-welding wire includes: 0.01-0.30 wt% C, 1.0-2.5 wt% Mn, 0.30-2.0 wt% Si, 0.02 wt% or less P, 0.04 wt% or less S, 0.01-0.20 wt% V, 0.10-0.50 wt% Cr, 3.0-7.0 wt% Ni, 0.3-1.2 wt% Mo, 0.01-0.04 wt% Nb, 0.005-0.06 wt% rare earth elements, and the remainder Fe and impurities; the rare earth elements include La and Ce, and the weight ratio of La:Ce is 1:1.4-2.6; the ratio of the total weight of Nb and V to the weight of the rare earth elements is 1.7-6.3:1; the laser tailor-welding wire is used for welding Al-Si coated steel plates.

2. The laser welding wire according to claim 1, characterized in that: Based on the total weight of the laser welding wire, the laser welding wire includes: 0.18-0.24 weight % C, 1.6-2.2 weight % Mn, 1.0-1.8 weight % Si, 0.02 weight % or less P, 0.03 weight % or less S, 0.09-0.15 weight % V, 0.2-0.4 weight % Cr, 3.5-5.5 weight % Ni, 0.6-1.0 weight % Mo, 0.01-0.027 weight % Nb, 0.015-0.055 weight % rare earth elements, and the remainder Fe and impurities.

3. The laser welding wire according to claim 1, characterized in that: Among the rare earth elements, the weight ratio of La:Ce is 1:1.8-2.

3.

4. A method for preparing an Al-Si coated hot-formed steel sheet, characterized in that: The following steps are involved: S1. Using the laser welding wire described in any one of claims 1 to 3 to laser weld the butt joints of two Al-Si coated steel plates to obtain a welded plate; S2. performing hot stamping treatment on the tailor-welded blanks.

5. The method according to claim 4, characterized in that In step S1, both sides of the Al-Si coated steel plate include Al-Si coatings; the coating thickness of one side of the Al-Si coated steel plate is 20-30 um; the coating thickness of both sides of the Al-Si coated steel plate is the same; Based on the total weight of the single-sided Al-Si coating, the single-sided Al-Si coating includes more than 85 wt % of Al, 5-11 wt % of Si, 2-4 wt % of Fe and impurity elements.

6. The method according to claim 4, characterized in that In step S1, based on the total weight of the steel plate matrix in the Al-Si coated steel plate, the steel plate matrix includes: 0.20-0.25 wt% C, 0.40 wt% or less Si, 1.0-1.4 wt% Mn, 0.025 wt% or less P, 0.01 wt% or less S, 0.01-0.06 wt% Al, 0.02-0.05 wt% Ti, 0.005 wt% or less B, 0.35 wt% or less Cr, 0.008 wt% or less N, and the remainder Fe and impurities; The thickness of the steel plate substrate is 1.0-1.8 mm, and the thickness of the steel plate substrates in the two Al-Si coated steel plates to be laser welded are the same or different.

7. The method according to claim 4, characterized in that In step S1, the conditions for laser welding include: laser power of 2000-6000 W, welding speed of 2.5-5.5 m / min, wire feeding speed of 1-5.0 m / min, and defocus of 0.01-4 mm.

8. The method according to claim 4, characterized in that Step S2 includes: heating the tailor-welded plate in a heating furnace at a temperature of 880-950°C for a heating time of 3-8 minutes; transferring the heated tailor-welded plate to a flat mold for quenching, with a transfer time of 7-12 seconds and a holding time of 6-12 seconds; when the temperature cools to below 150°C, removing the mold and cooling it in air to 20-40°C, with a cooling rate of ≥30°C / s.

9. An Al-Si coated hot-formed steel plate prepared according to the method of any one of claims 4 to 8.

10. A vehicle, characterized in that: Comprising the Al-Si coated hot-formed steel plate as claimed in claim 9.

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