Micro-textured-tin-nitride-modified nickel foil and delta-trip steel laser welding method and applications

Abstract

The application discloses a micro-texture-TiN modified nickel foil and a laser welding method and application of delta-TRIP steel, and belongs to the technical field of laser welding of advanced high-strength steel. The method clamps two high-aluminum delta-TRIP steel plates in a manner that the to-be-welded edges are opposite, preposes a TiN composite modified nickel foil intermediate layer between the two to-be-welded end faces, sets up a staggered distribution micro-texture on the two surfaces of the nickel foil, and makes the nickel foil continuously distribute along the length direction of the weld. The butt welding is carried out by using a continuous fiber laser, the nickel foil and the to-be-welded edges of the two steel plates are synchronously melted, and a nickel alloyed weld is formed. The tensile strength of the obtained joint reaches more than 645 MPa, the elongation after fracture reaches about 44%, the tensile fracture position is transferred from the weld to the base material, and the cupping value reaches 5.5 mm. The application does not need additional welding wire or post-welding heat treatment, the process is simple, and is suitable for the manufacturing of high-aluminum delta-TRIP steel laser tailor-welded blanks.

Description

Technical Field

[0001] This invention belongs to the field of advanced high-strength steel connection and laser-welded plate manufacturing technology, and relates to a microtextured TiN composite modified nickel foil and its method and application for improving the strength and plasticity of δ-TRIP steel laser-welded joints. Specifically, it relates to a welding method that improves the strength, plasticity, and formability of laser-welded joints by pre-placing a microtextured TiN composite modified nickel foil intermediate layer at the butt joint interface of high-aluminum δ-TRIP steel and using laser melting to achieve nickel-titanium alloying of the weld. Background Technology

[0002] δ-TRIP steel is a third-generation advanced high-strength steel that combines low density, high strength, and good ductility. This steel typically contains a high aluminum content to stabilize δ-ferrite, reduce material density, and, combined with the transformation-induced plasticity effect of retained austenite, achieve a good combination of strength and ductility. Laser welding offers advantages such as concentrated heat input, high welding speed, narrow heat-affected zone, and ease of automation, making it suitable for manufacturing lightweight components for automotive body-in-white.

[0003] However, during the rapid melting and solidification process of laser welding of high-alumina δ-TRIP steel, aluminum expands the ferrite phase region and stabilizes the high-temperature δ-ferrite, making it easy for coarse columnar δ-ferrite to form after the molten pool solidifies. Simultaneously, high-carbon, aluminum-depleted acicular phases may also appear within the coarse δ-ferrite grains. The coarse grains reduce the grain boundary area per unit volume, weakening the grain boundaries' resistance to dislocation movement and crack propagation. Furthermore, the difference in composition and mechanical properties between the acicular phase and the ferrite matrix easily leads to localized stress concentration. Therefore, direct laser-welded joints are prone to transgranular brittle fracture at the weld center.

[0004] In addition, ordinary smooth nickel foil still has the following problems in the clamping and welding process: First, the foil is thin and smooth, which makes it easy to slip, warp or poor local adhesion, resulting in fluctuations in the butt gap and the actual amount added; Second, ordinary nickel foil only provides alloying elements, and local melting, dilution and molten pool flow are mainly affected by random assembly conditions, and the nickel element in the weld may be locally uneven, resulting in a narrow suitable process window; Third, nickel mainly changes phase stability and lacks controllable heterogeneous nucleation cores, so its promoting effect on the transformation of columnar crystals to equiaxed crystals and grain refinement is limited; Fourth, if independent titanium foil is stacked separately, it will easily increase the clamping difficulty and may form local titanium-rich areas or coarse titanium-containing compounds.

[0005] Therefore, there is a need to develop a new type of modified nickel foil and welding method that can simultaneously improve the positioning stability of the intermediate layer, promote element homogenization, provide fine heterogeneous nucleation cores, and avoid the formation of local titanium-rich areas or coarse titanium-containing compounds, rather than simply increasing the thickness of the nickel foil or adjusting the nickel content of the weld. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a microtextured TiN composite modified nickel foil that can simultaneously improve the positioning stability of the intermediate layer, promote element homogenization and provide fine heterogeneous nucleation cores, and avoid the formation of local titanium-rich regions or coarse titanium-containing compounds.

[0007] Meanwhile, the purpose of this invention is to provide a method for welding a microtextured-TiN composite modified nickel foil interlayer to improve the strength and plasticity of laser-welded joints of δ-TRIP steel. A microtextured-TiN composite modified nickel foil interlayer is continuously pre-placed between the weldable end faces of two high-alumina δ-TRIP steel plates. After butt welding and clamping, continuous fiber laser welding is performed. The laser causes the nickel foil and the weldable edges of the two steel plates to melt synchronously, forming a nickel alloyed weld seam through molten pool flow and element diffusion. This solves the problems of weld embrittlement, significant decrease in plasticity, and insufficient formability caused by coarse columnar δ-ferrite and high-carbon, aluminum-depleted acicular phases in the weld seam during direct laser welding of high-alumina δ-TRIP steel, as well as the problems of unstable positioning, uneven local melting and dilution, and the lack of a stable grain refinement mechanism due to the limited ability to control composition in ordinary smooth nickel foil interlayers.

[0008] Meanwhile, the purpose of this invention is to provide a welded joint for δ-TRIP steel welded plates with a strength of 645 MPa or higher.

[0009] Meanwhile, the purpose of this invention is to provide an application of δ-TRIP steel welded plate welded joints.

[0010] To achieve the above objectives, the present invention provides the following technical solution: A method for improving the strength and ductility of laser-welded joints in δ-TRIP steel using microtextured TiN composite modified nickel foil includes the following steps: (1) Provide two high-alumina δ-TRIP steel plates and clean the weldable end face and adjacent surface of the high-alumina δ-TRIP steel plates; (2) Cut and clean the nickel foil with a thickness of 40-60 μm so that the length of the nickel foil is the same as the length of the joint to be welded and the width is compatible with the thickness of the high-aluminum δ-TRIP steel plate. (3) A nanosecond pulsed fiber laser is used to process microtextures sequentially on the surface of the nickel foil; the wavelength of the pulsed laser of the nanosecond pulsed fiber laser is 1030-1070 nm, the pulse width is 80-200 ns, the repetition frequency is 20-80 kHz, the average power is 8-20 W, the scanning speed is 100-400 mm / s, and the number of scans on a single surface is 2-8 times; by adjusting the laser power, scanning speed and number of scans, the microtextures reach the set depth and width, and the microtextures on the two main surfaces are staggered along the width direction of the nickel foil. Microtextures are processed sequentially on the two surfaces of the nickel foil. The depth of the microtextures is 3-5 μm, the width is 25-35 μm, the center distance between adjacent microtextures is 65-85 μm, and the microtextures on the two surfaces are staggered along the width direction. (4) After completing the microtexturing process, the nickel foil after microtexturing is surface cleaned, and then a TiN film is prepared on the surface of the nickel foil by electrochemical deposition. The nickel foil is degreased, cleaned, and surface activated. Using the microtextured nickel foil as the cathode and the pure nickel plate as the anode, it is placed in a composite plating bath containing 300-400 g / L nickel sulfamate, 30-45 g / L boric acid, 5-15 g / L nickel chloride, and 5-15 g / L TiN particles with a particle size of 20-80 nm. The temperature of the plating bath is controlled at 45-55 ℃ and the pH value is 3.8-4.5. Positive pulse electrochemical co-deposition is carried out under stirring conditions of 200-400 r / min, with an average current density of 2-4 A / dm³. 2 The pulse frequency is 500-1000 Hz and the duty cycle is 20%-40%. The thickness of the TiN film is controlled to be about 0.5-0.8 μm by adjusting the deposition time, thus obtaining microtextured TiN composite modified nickel foil. (5) Place the microtextured-TiN composite modified nickel foil between the two high-aluminum δ-TRIP steel plates to be welded, so that it is continuously distributed along the weld length direction and covers the welded end face in the thickness direction of the steel plate, and clamp the two steel plates together. (6) A continuous fiber laser is used to perform full penetration butt welding along the extension direction of the microtextured TiN composite modified nickel foil, so that the composite modified nickel foil and the high-aluminum δ-TRIP steel plates on both sides melt synchronously and form a Ni-Ti microalloyed weld.

[0011] Preferably, the thickness of the composite modified nickel foil is 50 μm; the area of ​​the microtexture on the surface of the nickel foil accounts for 30%, and the microtextures on the two surfaces are staggered.

[0012] Preferably, the microtexture is a microgroove, a micropit, or a combination of microgroove and micropit, and the microtexture is formed by laser micromachining. Preferably, the depth of the microtexture is 4 μm, the width is 30 μm, and the spacing between adjacent microtextures is 75 μm.

[0013] Preferably, the thickness of the TiN film on the surface of the TiN composite modified nickel foil is 0.6 μm.

[0014] Preferably, the length of the composite modified nickel foil along the weld length direction is the same as the length of the joint to be welded, and the height along the thickness direction of the steel plate is 1.5 mm; before welding, the frictional interlocking effect between the microtexture and the two ends to be welded on both sides prevents the nickel foil from slipping during the welding process.

[0015] Preferably, for a 1.5 mm thick high-aluminum δ-TRIP steel plate, the laser power is 1500 W, the welding speed is 2.4 m / min, the laser spot diameter is 0.6 mm, the defocusing amount is 0 mm, and argon gas with a flow rate of 25 L / min and a purity of not less than 99.99% is used for protection.

[0016] Preferably, the weld has a nickel content of about 13 wt.% and a titanium content of about 5 wt.%, and the microstructure of the weld at room temperature is mainly composed of fine martensite with residual austenite and Ti(C,N) particles.

[0017] The present invention relates to the application of δ-TRIP steel laser welding joints in automotive collision safety components, including A-pillars, B-pillars, anti-collision beams, or door sills.

[0018] In a first aspect, the present invention provides a laser welding apparatus, comprising a laser and a base and fixture for fixing the materials to be welded. The welding fixture fixes two high-alumina δ-TRIP steel welding plates onto a platform.

[0019] Furthermore, the laser is a fiber laser; the position of the laser corresponds vertically to the weld seam of the material to be welded, and the robotic arm drives the laser to act on the welding joint of the welded plate according to the programmed route.

[0020] Secondly, the present invention also provides a laser welding method based on the laser welding apparatus described in the first aspect, comprising: fixing a first substrate and a second substrate to be welded on a base, placing a microtextured TiN composite modified nickel foil between the two substrates; and, under a protective atmosphere, forming a molten pool by using a laser to act on the joint of the first substrate and the second substrate along a set path for welding.

[0021] Furthermore, the welding parameters are as follows: laser power of 1400-1600 W, welding speed of 2.2-2.6 m / min, laser spot diameter of 0.5-0.7 mm, defocusing amount of -0.5-0.5 mm, and the protective atmosphere is argon gas with a purity of not less than 99.99% and a flow rate of 20-30 L / min.

[0022] Thirdly, the present invention also provides a δ-TRIP steel, which is welded by the laser welding method described in the second aspect; Secondly, the thickness of the first substrate and the second substrate are each independently selected from 1.5 mm.

[0023] Furthermore, the chemical composition of the high-aluminum δ-TRIP steel plate, by mass percentage, includes: C 0.10%-0.14%, Si 0.60%-0.80%, Mn 1.30%-1.60%, Al 3.50%-4.50%, P≤0.02%, S≤0.01%, with the balance being Fe and unavoidable impurities. This combination of parameters controls the nickel content of the weld to approximately 13 wt.% and the titanium content to approximately 5 wt.%, thereby essentially eliminating coarse δ-ferrite and obtaining a weld microstructure dominated by fine martensite with a small amount of retained austenite and Ti(C,N).

[0024] Fourthly, the application of a welded joint of δ-TRIP steel welded plates with a strength of 645 MPa or higher in the present invention in lightweight components of automotive body-in-white.

[0025] In the welding process of δ-TRIP steel, Ni and Ti play a role throughout the entire welding process, including the initial formation of the molten pool and the solidification process. Nickel causes the weld joint to form a martensitic structure and a trace amount of austenite, suppressing the problem of aluminum forming coarse δ-ferrite in the weld during the welding process. The microtexture increases the effective contact area of ​​the interface, making the nickel foil melt more uniformly. The TiN film partially dissolves and provides Ti and N to the molten pool. Some fine TiN or the subsequently formed Ti(C,N) melt compound serves as heterogeneous nucleation sites for equiaxed grains, providing a basis for the nucleation and growth of equiaxed grains. This effectively promotes the transformation of weld grains from columnar to equiaxed grains, ultimately achieving grain refinement. Compared with weld joints without nickel foil, the disappearance of δ-ferrite in this invention prevents cracking in the weld joint, greatly improving its strength, plasticity, and toughness.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The intermediate layer of the composite modified nickel foil is alloyed in the laser molten pool, which does not require a wire feeding system or post-weld heat treatment. The process path is simple and easy to implement on the laser welding line. (2) The weld nickel content of about 13 wt.% can significantly reduce the δ-ferrite phase region, expand the austenite phase region, and transform austenite into fine martensite during rapid cooling, while retaining a small amount of austenite, thus avoiding brittle fracture dominated by coarse columnar δ-ferrite. (3) The micro-texture generates frictional engagement on the thin nickel foil, reducing clamping slippage and local wrinkling, preventing gaps between the composite modified nickel foil and the steel plate, solving the problem of insufficient positioning stability of ordinary smooth nickel foil, and making the distribution of nickel and titanium elements in the weld more uniform. (4) TiN film provides fine Ti-containing particles or heterogeneous nucleation cores, which further promotes grain refinement on the basis of Ni suppressing δ-ferrite, and makes up for the lack of stable nucleation mechanism in ordinary nickel foil; (5) Microtexture and TiN film are not simply superimposed: microtexture alone cannot change phase stability, and TiN film alone cannot solve the slippage of smooth foil and uneven element distribution. Composite modified nickel foil can simultaneously achieve intermediate layer stability, uniform composition and solidification structure control.

[0027] This invention discloses a microtextured TiN composite modified nickel foil and its method and application for improving the strength and ductility of laser-welded joints of δ-TRIP steel, belonging to the field of advanced high-strength steel laser welding technology. The method involves clamping two high-alumina δ-TRIP steel plates with their weldable edges facing each other. A TiN composite modified nickel foil intermediate layer is pre-placed between the two weldable end faces. A staggered microtexture is set on both surfaces of the nickel foil, ensuring continuous distribution of the nickel foil along the weld length. Continuous fiber laser welding is used for butt welding, causing the nickel foil and the weldable edges of the two steel plates to melt synchronously and form a nickel alloyed weld. For a 1.5 mm thick δ-TRIP steel plate containing 4.00 wt.% aluminum, a laser power of 1500 W, a laser spot diameter of 0.6 mm, a welding speed of 2.4 m / min, and a defocusing amount of 0 mm were used. 99.99% high-purity argon gas with a flow rate of 25 L / min was used for protection, resulting in a weld with a nickel content of approximately 13 wt.% and a titanium content of approximately 5 wt.%. Nickel inhibits the formation of coarse columnar δ-ferrite and high-carbon, aluminum-poor acicular phases, promoting a weld microstructure dominated by fine martensite with a small amount of retained austenite. The TiN film forms fine Ti-containing particles or provides heterogeneous nucleation sites in the molten pool, thus achieving a synergistic effect of compositional homogenization, phase composition regulation, and grain refinement. The resulting joint exhibited a tensile strength exceeding 645 MPa, an elongation after fracture of approximately 44%, and a tensile fracture location shifting from the weld to the base metal, with a cupping value of 5.5 mm. This invention requires no additional welding wire or post-weld heat treatment, has a simple process, and is suitable for manufacturing laser-welded plates of high-alumina δ-TRIP steel. Attached Figure Description

[0028] Figure 1This is a schematic diagram of the structure and process of laser butt welding of the interlayer of the microtextured TiN composite modified nickel foil of the present invention; Figure 2 A schematic diagram of the microtextured TiN composite modified nickel foil structure; Figure 3 This is a metallographic diagram of the weld seam location of the welded plate obtained in Embodiment 1 of the present invention; Figure 4 The metallographic structure of the weld seam of the welded plate obtained in Comparative Example 1 is shown. Figure 5 Metallographic diagram of the weld seam location of the welded plate obtained in Comparative Example 2; Figure 6 The metallographic structure of the weld seam of the welded plate obtained in Comparative Example 3 is shown in the figure. Figure 7 The image shows the metallographic structure of the weld seam of the welded plate obtained in Comparative Example 4. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are used to illustrate the technical concept of the present invention, and not to unduly limit the scope of protection. Test methods not specifically described can be conventional methods in the art. Since existing experimental data correspond to specific steel plate thickness, composition and laser parameters, when changing the plate thickness, bevel form or heat input, the amount of nickel added should be calibrated accordingly based on the volume of the fusion zone to keep the nickel content of the weld at the target content. Example 1

[0031] This embodiment provides a laser welding method for δ-TRIP steel, utilizing the laser welding apparatus described in Embodiment 1. The method specifically includes the following steps: S1: As Figure 1 As shown, a first substrate and a second substrate of the material to be welded are fixed on a base; wherein, both the first substrate and the second substrate comprise a high-aluminum δ-TRIP steel plate and a nickel foil disposed between the two steel plates; the thickness of both the first substrate and the second substrate is 1.5 mm, as shown. Figure 2 As shown, the thickness of its microtextured TiN composite modified nickel foil is 50 μm.

[0032] The chemical composition of high-aluminum δ-TRIP steel sheet by mass percentage includes: C 0.12%, Si 0.70%, Mn 1.45%, P 0.02%, Al 4.00%, with the balance being Fe and unavoidable impurities.

[0033] A microtextured TiN composite modified nickel foil includes a nickel foil with a thickness of 50 μm, microtextures processed on two main surfaces of the nickel foil, the microtextures having a depth of 4 μm, a width of 30 μm, and a center-to-center distance of 75 μm between adjacent microtextures, and the microtextures on the two main surfaces being staggered from each other along the width direction; a TiN film with a thickness of 0.6 μm is deposited on the surface of the microtextures.

[0034] A method for preparing a microtextured TiN composite modified nickel foil includes the following steps: S01, cut and degrease-clean the 50μm thick nickel foil; S02, a nanosecond pulsed fiber laser is used to sequentially process microtextures on the surface of the nickel foil; the wavelength of the pulsed laser of the nanosecond pulsed fiber laser is 1050 nm, the pulse width is 100 ns, the repetition frequency is 50 kHz, the average power is 15 W, the scanning speed is 250 mm / s, and the number of scans on a single surface is 5. S03, after completing the microtexturing process, the nickel foil after microtexturing is surface cleaned, and then a TiN film is prepared on the surface of the nickel foil using an electrochemical deposition method. Using the microtextured nickel foil as the cathode and a pure nickel plate as the anode, it is placed in a composite plating bath containing 350 g / L nickel sulfamate, 40 g / L boric acid, 10 g / L nickel chloride, and 10 g / L TiN particles with a particle size of approximately 50 nm. The plating bath temperature is controlled at 50 ℃ and the pH value at 4.0. Positive pulse electrochemical co-deposition is performed under stirring conditions of 300 r / min, with an average current density of 3 A / dm³. 2 The pulse frequency was 800 Hz and the duty cycle was 30%. Microtextured TiN composite modified nickel foil was obtained.

[0035] In this embodiment, to facilitate splicing and installation, the length and width of the first substrate and the second substrate are uniformly cut to 100mm×50mm; during welding, a butt joint method is adopted, with a type I joint and a preset gap of 0.1mm; before splicing and welding, the surface of the splicing board is cleaned with acetone and alcohol.

[0036] S2: Under a protective atmosphere, a fiber laser is used to form a molten pool at the joint of the first and second substrates according to a predetermined path for welding. Figure 1 As shown.

[0037] In this embodiment, the parameters during the welding process include: welding power of 1500w, welding speed of 2.4 m / min, laser spot diameter of 0.6mm, laser defocusing amount of 0mm; and the protective atmosphere is argon gas with a purity of not less than 99.99% and a flow rate of 25L / min.

[0038] like Figure 3As shown, no δ-ferrite structure appeared in the welded joint obtained in this embodiment. The room temperature structure was mainly composed of fine lath martensite with a small amount of retained austenite and Ti(C,N).

[0039] This embodiment presents an application of δ-TRIP steel in automotive collision safety components, including A-pillars, B-pillars, anti-collision beams, or door sills.

[0040] This embodiment demonstrates the application of δ-TRIP steel in lightweight components of automotive body-in-white. Comparative Example 1: No nickel foil interlayer is provided

[0041] This comparative example provides a direct laser welding method for δ-TRIP steel, using the same base material, clamping method and laser welding parameters as in Example 1, but without pre-placing nickel foil at the butt joint interface.

[0042] In this comparative example, the parameters during the welding process include: laser power of 1500 W, welding speed of 2.4 m / min, laser spot diameter of 0.6 mm, and the protective atmosphere being argon gas with a purity of not less than 99.99% and a flow rate of 25 L / min.

[0043] This comparative example exhibited stable welding without spatter or significant welding defects during the welding process. The final metallographic structure of the weld seam of the welded plate is as follows: Figure 4 As shown. By Figure 4 It is evident that without a nickel foil interlayer, the weld exhibits large polygonal or columnar grains with clearly defined grain outlines. Numerous acicular or strip-like structures are observed within the grains, resulting in a coarse overall microstructure with poor uniformity. This is because the high Al content in the base metal expands the ferrite phase region and stabilizes high-temperature δ-ferrite, promoting the formation of coarse δ-ferrite during rapid solidification. Coarse grains and intragranular acicular structures easily cause stress concentration, hindering crack propagation. These results indicate that direct laser welding cannot effectively suppress the formation of coarse δ-ferrite and related acicular structures in high-alumina δ-TRIP steel welds. Comparative Example 2: Setting a regular nickel foil interlayer

[0044] This comparative example provides a laser welding method for δ-TRIP steel. Referring to Example 1, except that the intermediate layer used is ordinary nickel foil (without microtextured-TiN composite modification), the other materials, process steps and welding parameters are the same as in Example 1.

[0045] The metallographic structure of the weld seam of the final welded plate obtained in this comparative example is as follows: Figure 5 As shown. By Figure 5As can be seen, the addition of ordinary smooth nickel foil reduced the amount of coarse δ-ferrite in the weld compared to the control group without nickel foil, while increasing the lath-like or acicular transformation structures within the grains. This indicates that Ni can expand the austenite phase region and promote the transformation of the weld microstructure to martensite and retained austenite. However, large original grain outlines can still be observed in the figure, and the microstructure scale varies in different regions. This suggests that ordinary smooth nickel foil mainly plays a role in regulating weld composition and is unlikely to provide a stable heterogeneous nucleation site for molten pool solidification. Furthermore, it may lead to uneven Ni distribution due to foil slippage or poor local adhesion. Therefore, the improvement effect of ordinary nickel foil on weld microstructure remains limited. Comparative Example 3: A double-sided microtextured nickel foil was prepared, but no TiN thin film was deposited.

[0046] This comparative example provides a laser welding method for δ-TRIP steel. Referring to Example 1, except that TiN thin film is not deposited, the other materials, process steps and welding parameters are the same as in Example 1.

[0047] The metallographic structure of the weld seam of the final welded plate obtained in this comparative example is as follows: Figure 6 As shown. By Figure 6 As can be seen, the uniformity of the weld structure is significantly improved compared to ordinary smooth nickel foil after using double-sided microtextured nickel foil, with a reduction in coarse continuous structures and refinement in some areas. This is because the microtexture on the nickel foil surface enhances the frictional engagement and adhesion stability between the nickel foil and the two weldable end faces, reducing nickel foil slippage, warping, and local gap fluctuations during clamping, thus making the addition and distribution of Ni elements in the molten pool more stable. However, large grain outlines and local coarsening areas still exist in the figure, indicating that the microtexture mainly improves the positioning and element distribution of the nickel foil, and cannot provide sufficient Ti-containing heterogeneous nucleation particles alone; its grain refinement effect remains limited. Comparative Example 4: A smooth nickel foil modified with TiN film was used, but no microtexture was applied.

[0048] This comparative example provides a laser welding method for δ-TRIP steel. Referring to Example 1, except that the microtexture is not set, the other materials, process steps and welding parameters are the same as in Example 1.

[0049] The metallographic structure of the weld seam of the final welded plate obtained in this comparative example is as follows: Figure 7 As shown. By Figure 7It is evident that after modifying the smooth nickel foil with TiN film, the microstructure size in the weld is significantly reduced compared to direct laser welding, and the cellular or dendritic solidification structure is finer. This indicates that the TiN particles in the TiN film, as well as the TiN and / or Ti(C,N) particles formed during welding, can act as heterogeneous nucleation nuclei, increasing the solidification nucleation rate of the molten pool and inhibiting grain growth. However, microstructure size differences still exist in local areas, indicating that simply applying the TiN film cannot solve the problems of slippage, warping, and localized unstable adhesion of the smooth nickel foil during clamping. Therefore, the TiN film mainly plays a role in heterogeneous nucleation and grain refinement, while the microtexture mainly plays a role in positioning stability and elemental homogenization. Only by using both in combination can synergistic improvement be achieved.

[0050] The properties of the welded joints in the δ-TRIP steels obtained in Examples 1 and Comparative Examples 1 to 4 were tested. The tensile strength was tested using a DNS-300 testing machine, and the elongation was tested using an extensometer. The results are shown in Table 1.

[0051] Table 1: Comparison of welded joint performance in δ-TRIP steel under different intermediate layer conditions

[0052] As shown in Table 1, the δ-TRIP steel laser-welded joint obtained by using microtextured TiN composite modified nickel foil as the intermediate layer in Example 1 of the present invention has superior comprehensive mechanical properties, with a tensile strength of 650 MPa and an elongation after fracture of 44.4%. Moreover, the tensile fracture location shifts to the base material, indicating that the composite modified nickel foil can effectively improve the weld structure and enhance the joint's strength and plasticity.

[0053] As can be seen from the comparison between Example 1 and Comparative Example 1, when no intermediate layer is added, coarse columnar δ-ferrite and brittle acicular phases are easily formed in the weld, which leads to the expansion of cracks along the weld, resulting in low tensile strength and plasticity of the joint, and the fracture location is located in the weld.

[0054] As can be seen from the comparison between Example 1 and Comparative Example 2, ordinary nickel foil can regulate the phase composition of the weld by Ni element, reduce the formation of coarse δ-ferrite, and transform the weld microstructure into fine martensite and a small amount of retained austenite, thus significantly improving the joint performance. However, the joint performance is still lower than that of the composite modified nickel foil of the present invention.

[0055] As can be seen from the comparison between Example 1 and Comparative Examples 3 and 4, both microtextured nickel foil and TiN-modified nickel foil can improve the weld microstructure. Microtexture is beneficial for improving the uniformity of nickel element distribution, while TiN is beneficial for refining the solidified grains of the weld. However, the improvement effect is limited when either is used alone. This invention achieves a synergistic effect of element homogenization and solidification microstructure regulation through a composite design of microtexture and TiN, resulting in a more uniform and refined microstructure in the weld, thereby further improving the strength and ductility of the welded joint. Example 2

[0056] This embodiment provides a laser welding method for δ-TRIP steel, utilizing the laser welding apparatus described in Embodiment 1. The method specifically includes the following steps: S1: Fix the first substrate and the second substrate of the material to be welded onto the base; wherein, the first substrate and the second substrate both include a high-alumina δ-TRIP steel plate and a microtextured-TiN composite modified nickel foil disposed between the two steel plates; the thickness of the first substrate and the second substrate is 1.3 mm, and the thickness of the microtextured-TiN composite modified nickel foil is 50 μm.

[0057] The chemical composition of high-aluminum δ-TRIP steel sheet by mass percentage includes: C 0.10%, Si 0.60%, Mn 1.30%, P 0.01%, S 0.01%, Al 3.50%, with the balance being Fe and unavoidable impurities.

[0058] A microtextured TiN composite modified nickel foil includes a nickel foil with a thickness of 40 μm, microtextures processed on two main surfaces of the nickel foil, the microtextures having a depth of 3 μm, a width of 25 μm, and a center-to-center distance of 65 μm between adjacent microtextures, and the microtextures on the two main surfaces being staggered from each other along the width direction; a TiN film with a thickness of 0.5 μm is deposited on the surface of the microtextures.

[0059] A method for preparing a microtextured TiN composite modified nickel foil includes the following steps: S01, cut and degrease-clean the 40μm thick nickel foil; S02, a nanosecond pulsed fiber laser is used to sequentially process microtextures on the surface of the nickel foil; the wavelength of the pulsed laser of the nanosecond pulsed fiber laser is 1030 nm, the pulse width is 80 ns, the repetition frequency is 20 kHz, the average power is 8W, the scanning speed is 100 mm / s, and the number of scans on a single surface is 2. S03, after completing the microtexturing process, the nickel foil after microtexturing is surface cleaned, and then a TiN film is prepared on the surface of the nickel foil using an electrochemical deposition method. The microtextured nickel foil is used as the cathode and a pure nickel plate as the anode. It is placed in a composite plating bath containing 300 g / L nickel sulfamate, 30 g / L boric acid, 5 g / L nickel chloride, and 5 g / L TiN particles with a particle size of approximately 20 nm. The plating bath temperature is controlled at 45 ℃ and the pH value at 3.8. Positive pulse electrochemical co-deposition is performed under stirring conditions of 200 r / min, with an average current density of 2 A / dm³. 2 The pulse frequency was 500 Hz and the duty cycle was 20%. Microtextured TiN composite modified nickel foil was obtained.

[0060] In this embodiment, to facilitate splicing and installation, the length and width of the first substrate and the second substrate are uniformly cut to 100mm×50mm; during welding, a butt joint method is adopted, with a type I joint and a preset gap of 0.1mm; before splicing and welding, the surface of the splicing board is cleaned with acetone and alcohol.

[0061] S2: Under a protective atmosphere, a fiber laser is used to act on the joint of the first substrate and the second substrate along a set path to form a molten pool for welding.

[0062] In this embodiment, the parameters during the welding process include: welding power of 1400w, welding speed of 2.2 m / min, laser spot diameter of 0.5mm, laser defocusing amount of -0.5mm; and the protective atmosphere is argon gas with a purity of not less than 99.99% and a flow rate of 20L / min.

[0063] The δ-TRIP steel obtained in this embodiment has a weld tensile strength of 645 MPa, an elongation after fracture of 44%, a tensile fracture location that shifts from the weld to the base material, and a cupping value of 5.7 mm. Example 3

[0064] This embodiment provides a laser welding method for δ-TRIP steel, utilizing the laser welding apparatus described in Embodiment 1. The method specifically includes the following steps: S1: Fix the first substrate and the second substrate of the material to be welded onto the base; wherein, the first substrate and the second substrate both include a high-alumina δ-TRIP steel plate and a microtextured-TiN composite modified nickel foil disposed between the two steel plates; the thickness of the first substrate and the second substrate is 1.7 mm, and the thickness of the microtextured-TiN composite modified nickel foil is 60 μm.

[0065] The chemical composition of high-aluminum δ-TRIP steel sheet by mass percentage includes: C 0.14%, Si 0.80%, Mn 1.60%, P 0.01%, S 0.01%, Al 4.50%, with the balance being Fe and unavoidable impurities.

[0066] A microtextured TiN composite modified nickel foil includes a nickel foil with a thickness of 60 μm, microtextures processed on two main surfaces of the nickel foil, the microtextures having a depth of 5 μm, a width of 35 μm, and a center-to-center distance of 85 μm between adjacent microtextures, and the microtextures on the two main surfaces being staggered along the width direction; a TiN film with a thickness of 0.8 μm is deposited on the surface of the microtextures.

[0067] A method for preparing a microtextured TiN composite modified nickel foil includes the following steps: S01, cut and degrease-clean the 60μm thick nickel foil; S02, a nanosecond pulsed fiber laser is used to sequentially process microtextures on the surface of the nickel foil; the wavelength of the pulsed laser of the nanosecond pulsed fiber laser is 1070 nm, the pulse width is 200 ns, the repetition frequency is 80 kHz, the average power is 20W, the scanning speed is 400 mm / s, and the number of scans on a single surface is 8. S03, after completing the microtexturing process, the nickel foil after microtexturing is surface cleaned, and then a TiN film is prepared on the surface of the nickel foil using an electrochemical deposition method. Using the microtextured nickel foil as the cathode and a pure nickel plate as the anode, it is placed in a composite plating bath containing 400 g / L nickel sulfamate, 45 g / L boric acid, 15 g / L nickel chloride, and 15 g / L TiN particles with a particle size of approximately 80 nm. The plating bath temperature is controlled at 55 ℃ and the pH value at 4.5. Positive pulse electrochemical co-deposition is performed under stirring conditions of 400 r / min, with an average current density of 4 A / dm³. 2 The pulse frequency was 1000 Hz and the duty cycle was 40%. Microtextured TiN composite modified nickel foil was obtained.

[0068] In this embodiment, to facilitate splicing and installation, the length and width of the first substrate and the second substrate are uniformly cut to 100mm×50mm; during welding, a butt joint method is adopted, with a type I joint and a preset gap of 0.1mm; before splicing and welding, the surface of the splicing board is cleaned with acetone and alcohol.

[0069] S2: Under a protective atmosphere, a fiber laser is used to act on the joint of the first substrate and the second substrate along a set path to form a molten pool for welding.

[0070] In this embodiment, the parameters during the welding process include: welding power of 1600w, welding speed of 2.6 m / min, laser spot diameter of 0.7mm, laser defocusing amount of 0.5mm; and the protective atmosphere is argon gas with a purity of not less than 99.99% and a flow rate of 30L / min.

[0071] The δ-TRIP steel obtained in this embodiment has a weld tensile strength of 657 MPa, an elongation after fracture of 44.6%, a tensile fracture location that shifts from the weld to the base material, and a cupping value of 5.6 mm. Example 4

[0072] This embodiment provides a laser welding method for δ-TRIP steel, utilizing the laser welding apparatus described in Embodiment 1. The method specifically includes the following steps: S1: Fix the first substrate and the second substrate of the material to be welded onto the base; wherein, the first substrate and the second substrate both include a high-alumina δ-TRIP steel plate and a microtextured-TiN composite modified nickel foil disposed between the two steel plates; the thickness of the first substrate and the second substrate is 1.6 mm, and the thickness of the microtextured-TiN composite modified nickel foil is 45 μm.

[0073] The chemical composition of high-aluminum δ-TRIP steel sheet by mass percentage includes: C 0.13%, Si 0.75%, Mn 1.55%, P 0.01%, S 0.01%, Al 4.20%, with the balance being Fe and unavoidable impurities.

[0074] A microtextured TiN composite modified nickel foil includes a nickel foil with a thickness of 45 μm, microtextures processed on two main surfaces of the nickel foil, the microtextures having a depth of 4 μm, a width of 30 μm, and a center-to-center distance of 70 μm between adjacent microtextures, and the microtextures on the two main surfaces being staggered from each other along the width direction; a TiN film with a thickness of 0.7 μm is deposited on the surface of the microtextures.

[0075] A method for preparing a microtextured TiN composite modified nickel foil includes the following steps: S01, cut and degrease clean a nickel foil with a thickness of 45μm; S02, a nanosecond pulsed fiber laser is used to sequentially process microtextures on the surface of the nickel foil; the wavelength of the pulsed laser of the nanosecond pulsed fiber laser is 1060 nm, the pulse width is 120 ns, the repetition frequency is 40 kHz, the average power is 12W, the scanning speed is 150 mm / s, and the number of scans on a single surface is 5. S03, after completing the microtexturing process, the nickel foil after microtexturing is surface cleaned, and then a TiN film is prepared on the surface of the nickel foil using an electrochemical deposition method. The microtextured nickel foil is used as the cathode and a pure nickel plate as the anode. It is placed in a composite plating bath containing 370 g / L nickel sulfamate, 36 g / L boric acid, 12 g / L nickel chloride, and 13 g / L TiN particles with a particle size of approximately 60 nm. The plating bath temperature is controlled at 50 ℃ and the pH value at 4.2. Positive pulse electrochemical co-deposition is performed under stirring conditions of 300 r / min, with an average current density of 3 A / dm³. 2 The pulse frequency was 700 Hz and the duty cycle was 30%. Microtextured TiN composite modified nickel foil was obtained.

[0076] In this embodiment, to facilitate splicing and installation, the length and width of the first substrate and the second substrate are uniformly cut to 100mm×50mm; during welding, a butt joint method is adopted, with a type I joint and a preset gap of 0.1mm; before splicing and welding, the surface of the splicing board is cleaned with acetone and alcohol.

[0077] S2: Under a protective atmosphere, a fiber laser is used to act on the joint of the first substrate and the second substrate along a set path to form a molten pool for welding.

[0078] In this embodiment, the parameters during the welding process include: welding power of 1550w, welding speed of 2.5 m / min, laser spot diameter of 0.6mm, laser defocusing amount of 0.1mm; and the protective atmosphere is argon gas with a purity of not less than 99.99% and a flow rate of 28L / min.

[0079] The δ-TRIP steel obtained in this embodiment has a weld tensile strength of 664 MPa, an elongation after fracture of 44.5%, a tensile fracture location that shifts from the weld to the base material, and a cupping value of 5.6 mm.

[0080] In the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this disclosure should not be construed as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, the inventive aspect lies in fewer than all features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0081] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A microtextured TiN composite modified nickel foil, characterized in that, It includes a nickel foil with a thickness of 40-60 μm, on which microtextures are processed on two main surfaces. The microtextures have a depth of 3-5 μm, a width of 25-35 μm, and a center-to-center distance of 65-85 μm between adjacent microtextures. The microtextures on the two main surfaces are staggered along the width direction. A TiN film with a thickness of 0.5-0.8 μm is deposited on the surface of the microtextures.

2. The method for preparing a microtextured TiN composite modified nickel foil according to claim 1, characterized in that, Includes the following steps: S01, cutting and degreasing nickel foil with a thickness of 40-60 μm; S02, a nanosecond pulsed fiber laser is used to sequentially process microtextures on the surface of the nickel foil; the wavelength of the pulsed laser of the nanosecond pulsed fiber laser is 1030-1070 nm, the pulse width is 80-200 ns, the repetition frequency is 20-80 kHz, the average power is 8-20 W, the scanning speed is 100-400 mm / s, and the number of scans on a single surface is 2-8 times; S03, after completing the microtexturing process, the nickel foil after microtexturing is surface cleaned, and then a TiN film is prepared on the surface of the nickel foil by electrochemical deposition to obtain a microtextured-TiN composite modified nickel foil.

3. The preparation method according to claim 2, characterized in that, In SO3, a microtextured nickel foil is used as the cathode and a pure nickel plate as the anode. The foil is placed in a composite plating bath containing 300-400 g / L nickel sulfamate, 30-45 g / L boric acid, 5-15 g / L nickel chloride, and 5-15 g / L TiN particles with a particle size of 20-80 nm. The bath temperature is controlled at 45-55 ℃, the pH at 3.8-4.5, and positive pulse electrochemical co-deposition is performed under stirring conditions of 200-400 r / min, with an average current density of 2-4 A / dm³. 2 The pulse frequency is 500-1000 Hz and the duty cycle is 20%-40%.

4. The method for improving the strength and ductility of laser-welded joints of δ-TRIP steel using microtextured TiN composite modified nickel foil according to claim 1, characterized in that, Includes the following steps: Step 1: Provide two high-aluminum δ-TRIP steel plates and clean the welding end face and adjacent surfaces of the high-aluminum δ-TRIP steel plates; Step 2: Place the microtextured TiN composite modified nickel foil between the weldable end faces of two high-aluminum δ-TRIP steel plates, ensuring that it is continuously distributed along the weld length and covers the weldable end faces along the thickness direction of the high-aluminum δ-TRIP steel plates. Then, clamp the two high-aluminum δ-TRIP steel plates together. Step 3: A continuous fiber laser is used to perform full penetration butt welding along the extension direction of the microtextured-TiN composite modified nickel foil, so that the microtextured-TiN composite modified nickel foil and the high-aluminum δ-TRIP steel plates on both sides melt synchronously and form a Ni-Ti microalloyed weld.

5. The method according to claim 4, characterized in that, In step one, the chemical composition of the high-aluminum δ-TRIP steel plate, by mass percentage, includes: C 0.10%-0.14%, Si 0.60%-0.80%, Mn 1.30%-1.60%, Al 3.50%-4.50%, P≤0.02%, S≤0.01%, with the balance being Fe and unavoidable impurities.

6. The method according to claim 4, characterized in that, In step three, the parameters for full penetration butt welding are as follows: laser power of 1400-1600 W, welding speed of 2.2-2.6 m / min, laser spot diameter of 0.5-0.7 mm, defocusing amount of -0.5-0.5 mm, and protective atmosphere of argon gas with a purity of not less than 99.99% and a flow rate of 20-30 L / min.

7. A δ-TRIP steel obtained by the method according to any one of claims 4-6, characterized in that, The weld has a nickel content of 13 wt.% and a titanium content of 5 wt.%. At room temperature, the weld microstructure is mainly composed of fine martensite with residual austenite and Ti(C,N) particles.

8. A δ-TRIP steel according to claim 7, characterized in that, Its weld tensile strength reaches over 645MPa, elongation after fracture reaches over 44%, the tensile fracture location shifts from the weld to the base metal, and the cupping value reaches over 5.5 mm.

9. The application of δ-TRIP steel in automotive collision safety components according to claim 7, characterized in that, Automotive collision safety components include A-pillars, B-pillars, crash beams, or door sills.

10. The application of δ-TRIP steel according to claim 7 in lightweight components of automotive body-in-white.

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