A laser welding method of ultra-high strength hot-formed steel and soft low carbon steel

Abstract

This invention relates to the field of automotive lightweight material joining technology, specifically a laser welding method for ultra-high strength hot-formed steel and soft low-carbon steel. The method involves offsetting the center of the laser beam spot 0.5-2 mm towards the soft low-carbon steel workpiece and controlling the laser beam to act on the workpiece surface with a positive defocusing amount of +4-+6 mm, performing self-fusion welding at a power of 4-8 kW and a speed of 220-240 cm / min. Through the synergistic effect of "offset towards the high melting point" and "specific positive defocusing," the heat input of the dissimilar materials is balanced, the molten pool is stabilized, and the segregation of Al and Si elements in the hot-formed steel is actively suppressed. This method can significantly reduce brittle intermetallic compounds, increase the joint shear strength recovery rate to approximately 90%, and synergistically optimize the performance of the heat-affected zones on both sides, greatly improving the fatigue life of the joint and meeting the high-quality welding requirements of automotive safety structural components.

Description

Technical Field

[0001] This invention relates to the field of automotive lightweight material joining technology, specifically a laser welding method for ultra-high strength hot-formed steel and soft low-carbon steel. Background Technology

[0002] Under the automotive industry's development trend of "energy conservation, environmental protection, and safety," the synergistic improvement of vehicle body lightweighting and passenger compartment safety has become a core objective. Hot-formed steel, with its ultra-high strength (tensile strength exceeding 1500MPa) and excellent collision energy absorption capacity, is widely used in critical safety structural components such as A-pillars, B-pillars, and anti-collision beams. Meanwhile, soft low-carbon steel, due to its good formability and low cost, is commonly used in body panels and non-load-bearing areas. To achieve optimal material layout and a balance between performance and cost, reliably connecting these two types of steel with vastly different properties has become an essential choice.

[0003] However, laser welding of ultra-high strength hot-formed steel and soft low-carbon steel faces more severe combined challenges than conventional dissimilar steel welding, mainly in the following aspects:

[0004] 1. Severe metallurgical compatibility issues: Al and Si elements added to hot-formed steel (such as PHS1500) to achieve hardenability readily react with iron (Fe) in the high-temperature molten pool of laser welding, forming hard and brittle intermetallic compounds such as Al-Fe-Si or FeAlSi. These brittle phases accumulate at the weld interface or grain boundaries, significantly reducing joint toughness and becoming the source of fatigue crack initiation and propagation.

[0005] 2. Significant mismatch in thermophysical properties: The melting point of low-carbon steel (approximately 1530℃) is significantly higher than that of hot-formed steel (approximately 1400~1450℃), and their thermal conductivity also differs by nearly double (approximately 28 W / m·K for hot-formed steel and approximately 51 W / m·K for low-carbon steel). In traditional center-alignment laser welding, this easily leads to over-melting and burn-through on the hot-formed steel side, while the low-carbon steel side suffers from poor fusion, resulting in asymmetrical weld formation and defects such as undercut and lack of fusion.

[0006] 3. Synergistic and contradictory heat-affected zone (HAZ) deterioration: Under the action of welding thermal cycling, the martensitic structure of the heat-affected zone (HAZ) on the hot-formed steel side undergoes tempering softening, and the strength may decrease by more than 40%; while the HAZ on the low-carbon steel side suffers from abnormal grain coarsening, resulting in a sharp drop in ductility. This reverse deterioration of the HAZ properties on both sides, one soft and one brittle, severely weakens the overall synergistic load-bearing capacity and fatigue life of the joint.

[0007] To address the common problems of joining dissimilar metals, existing technologies have proposed various solutions. For example, Chinese patent document CN102091872A discloses a laser offset welding method applicable to magnesium / steel and magnesium / titanium. This method achieves the connection by deflecting a laser beam towards the high-melting-point steel or titanium side and using heat conduction to melt the low-melting-point magnesium. This method mainly addresses the issues of magnesium alloys' easy vaporization and low energy absorption rate. However, when this technical concept is directly applied to steel / steel systems with opposite melting point relationships (hot-formed steel has a lower melting point) and the presence of metallurgical hazards from matrix alloying elements, it not only fails to solve the problem but may even exacerbate the segregation and embrittlement of aluminum and silicon elements.

[0008] For example, Chinese patent document CN110238525A discloses a method to improve the crack resistance of welds by deflecting a laser beam toward low-carbon steel to control the melting ratio of cast iron. The core of this method is to control the dilution of carbon (C) elements, which is completely different from the physical mechanism and control target of this application, which requires suppressing the metallurgical reaction of aluminum (Al) and silicon (Si) elements.

[0009] For example, Chinese patent document CN117047277A proposes to prevent aluminum in the coating on the surface of aluminized silicon hot-formed steel from intruding into the weld by purging with protective gas at a specific angle. This solution is a physical exclusion method for external aluminum sources (coatings) and cannot solve the problem of controlling the intrinsic metallurgical behavior of alloyed aluminum and silicon elements inside the hot-formed steel matrix during the solidification process of the molten pool.

[0010] Furthermore, methods such as resistance spot welding (e.g., CN102581459B) or friction stir welding are insufficient to meet the high-strength, high-efficiency, and high-quality connection requirements of lightweight automotive structural components, either due to high heat input, severe HAZ softening, or the inability to achieve continuous sealing welds. Summary of the Invention

[0011] To overcome the shortcomings of existing technologies, a laser welding method for ultra-high strength hot-formed steel and soft low-carbon steel is provided. By controlling the beam positioning and thermal field in a coordinated manner, the problem of metallurgical compatibility and performance optimization during the welding of ultra-high strength hot-formed steel and soft low-carbon steel is solved.

[0012] To achieve the above objectives, the present invention employs the following technical solution:

[0013] A laser welding method for ultra-high strength hot-formed steel and soft low-carbon steel, wherein the ultra-high strength hot-formed steel has a tensile strength ≥1500MPa and contains Al and Si alloying elements, and the soft low-carbon steel has a tensile strength <300MPa, the method specifically as follows: The ultra-high strength hot-formed steel workpiece and the soft low-carbon steel workpiece are butt-assembled along the edge to be welded; a laser beam is generated using a fiber laser to perform self-fusion welding on the edge to be welded, wherein the center of the laser beam spot is positioned biased towards the soft low-carbon steel workpiece, with an offset distance of 0.5~2mm; the laser beam is controlled to act on the workpiece surface with a positive defocusing amount of +4~+6mm; wherein the laser welding power is 4~8kW, and the welding speed is 220~240cm / min.

[0014] Furthermore, during the welding process, a protective gas is used to protect the molten pool and the heat-affected zone. The protective gas is argon with a purity of ≥99.97% and a gas flow rate of 20~25L / min.

[0015] Furthermore, the nozzle of the protective gas is 3-5 mm away from the weld surface, the gas blowing pressure is 140-160 mbar, and the gas temperature is controlled at 15-25℃; the protective gas is also used to control the cooling rate of the weld, so that the post-weld cooling rate is maintained at 500-800℃ / s.

[0016] Furthermore, during the welding process, an axial pressure of 100~200N is applied to the edge to be welded using a fixture to promote a tight bond at the interface.

[0017] Furthermore, the chemical composition of the ultra-high strength hot-formed steel, by weight percentage, includes: C: 0.22%~0.26%, Si: 0.1%~0.2%, Mn: 1.1%~1.5%, Al: 0.04%~0.08%, B: 0.001%~0.003%, P≤0.010%, S≤0.010%, Ti≤0.03%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the soft low-carbon steel, by weight percentage, includes: C: 0.01%~0.08%, Si≤0.030%, Mn: 0.15%~0.26%, P: 0.015%~0.026%, S≤0.010%, Als: 0.02%~0.06%, Ti≤0.3000%, with the balance being Fe and unavoidable impurities.

[0019] Furthermore, the wavelength of the fiber laser is 1090±10nm, and the spot diameter of the laser beam is 0.3mm.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. Precise control of the molten pool composition actively suppresses the formation of brittle phases. This invention actively reduces the total amount of Al and Si elements molten into the molten pool from hot-formed steel by deflecting the laser beam towards the soft low-carbon steel side (0.5~2mm). Simultaneously, combined with the wide and gentle thermal field distribution resulting from a +4~+6mm positive defocusing, the driving force for the segregation of Al and Si elements at the edge of the molten pool is significantly reduced. The synergistic effect of these two factors suppresses the formation of hard and brittle Fe-Al-Si intermetallic compounds (>700HV) from both the source and the process, reducing the proportion of brittle phases in the weld center region by more than 60% and significantly improving the joint toughness.

[0022] 2. Synergistic optimization of heat input to heterogeneous materials achieves stable and high-quality weld formation. This invention, through an energy input mode combining "shifting towards the higher melting point side" and "specific positive defocusing," physically compensates for the higher melting demand of the low-carbon steel side while avoiding over-melting of the hot-formed steel side. This results in a symmetrical and stable heterogeneous molten pool shape, completely eliminating weld misalignment, undercut, and lack of fusion defects caused by uneven heat distribution, increasing the first-pass welding qualification rate to over 99.5%. Attached Figure Description

[0023] Figure 1 This is the macroscopic morphology of the weld pool of hot-formed steel and low-carbon steel in Embodiment 1 of the present invention.

[0024] Figure 2 This is the reaction interface morphology of the weld between hot-formed steel and low-carbon steel in Embodiment 1 of the present invention.

[0025] Figure 3 This is the interface morphology of the weld between hot-formed steel and low-carbon steel in Embodiment 1 of the present invention.

[0026] Figure 4 This is the interface morphology of the weld between hot-formed steel and low-carbon steel in Embodiment 1 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to examples. Obviously, the described embodiments are merely one example of the present invention, and those skilled in the art can refer to the content herein to appropriately improve the process parameters. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to realize and apply the technology of the present invention.

[0028] In the embodiments, unless otherwise specified, the equipment and reagents used are all commercially available conventional products.

[0029] General conditions and test methods for Examples 1-3 and Comparative Example 1:

[0030] 1. Base Material: The soft low-carbon steel uses commercially available DX51D steel plate, with the following chemical composition (mass percentage): C: 0.01%~0.08%, Si≤0.030%, Mn: 0.15%~0.26%, P: 0.015%~0.026%, S≤0.010%, Als: 0.02%~0.06%, Ti≤0.3000%, with the balance being Fe and unavoidable impurities. The ultra-high strength hot-formed steel uses commercially available PHS1500 steel plate, with the following chemical composition (mass percentage): C: 0.22%~0.26%, Si: 0.1%~0.2%, Mn: 1.1%~1.5%, Al: 0.04%~0.08%, B: 0.001%~0.003%, P≤0.010%, S≤0.010%, Ti≤0.03%, with the balance being Fe and unavoidable impurities. Both types of steel plates have dimensions of 150mm × 50mm × 1.5mm.

[0031] 2. Equipment: An IPGYLS-8000-S2T ytterbium-doped fiber laser with a rated power of 8kW and a beam product (BPP) of <4mm*mrad is used. The welding process employs a KUKA robot for precise trajectory control. The shielding gas is 99.99% pure argon.

[0032] 3. Joint type and assembly: The DX51D steel plate and the PHS1500 steel plate are butt-jointed with zero clearance along their long sides. A special pneumatic clamp is used to apply uniform pressure on both sides of the weld to ensure a tight fit between the interfaces to be welded.

[0033] 4. Testing and characterization methods:

[0034] (1) Macro / micro morphology: After welding, samples were taken along the cross-section of the weld. After grinding and polishing, the samples were etched with 4% nitric acid alcohol solution. The weld formation, fusion line and microstructure were observed using a ZEISS Sigma Observer 7 optical microscope and a ZEISS Sigma 300 field emission scanning electron microscope (SEM).

[0035] (2) Elemental distribution analysis: The surface distribution (Mapping) and line scan (LineScan) of Al and Si elements were analyzed using an Oxford X-Max N80 energy dispersive spectrometer (EDS) attached to the SEM.

[0036] (3) Mechanical property testing:

[0037] A. Microhardness: The FM-ARS9000 fully automatic microhardness tester was used with a load of 500g and a holding time of 15s. The test was conducted along the center of the weld cross-section, from the DX51D base material through the weld center to the PHS1500 base material, with a point spacing of 0.1mm.

[0038] B. Shear strength: Shear specimens were prepared according to ISO 14273 standard and tested on an Instron 5982 universal testing machine at a loading rate of 2 mm / min. Joint shear strength recovery rate = (Joint shear strength / Shear strength of soft low-carbon steel base material) × 100%.

[0039] C. Fatigue life: According to ISO14324 standard, a tensile fatigue test was conducted under the conditions of 100MPa stress amplitude, stress ratio R=0.1, and frequency of 50Hz, and the number of cycles at which the specimen fractured was recorded.

[0040] Example 1:

[0041] Material composition design: The DX51D uses Fe as the base material, with the addition of C: 0.07%, Si: 0.020%, Mn: 0.19%, P: 0.017%, S: 0.008%, Als: 0.02%, Ti: 0.100% and other alloys to form the base material. The PHS1500 uses Fe as the base material, with the addition of C: 0.24%, Si: 0.2%, Mn: 1.3%, Al: 0.05%, S: 0.008%, P: 0.005%, B: 0.001%, Ti: 0.02% and other alloys to form the base material.

[0042] 1. Welding process:

[0043] Welding was performed using a ruby ​​fiber laser with a welding power of 8kW, a wavelength range of 1093nm, a spot diameter of 0.3mm, a welding speed of 220cm / min, a straight path, and a weld seam offset of 0.7mm towards the DX51D base material with a defocusing amount of +5mm. Argon gas with a purity of 99.99% was used as the welding shielding gas at a flow rate of 24L / min.

[0044] The welding process is secured using custom-made fixtures, and a pressure of 200N is applied to the weld to promote a tight bond at the interface. The post-weld cooling rate is controlled at 700℃ / s, the shielding gas nozzle is 5mm away from the weld surface, the blowing pressure is 150mbar, and the gas temperature is controlled at 25℃.

[0045] 2. Technical Principles and Effects Analysis:

[0046] (1) Regarding the shift towards the low-carbon steel side: The melting point of PHS1500 is approximately 1450℃, while that of DX51D is approximately 1530℃, a difference of about 80℃. Shifting the center of the laser beam 0.7mm towards the high-melting-point DX51D side essentially means directly inputting more energy into the high-melting-point material to compensate for its higher heat of fusion, thereby ensuring that the metals on both sides of the interface can melt synchronously and fully. At the same time, this shifting strategy reduces the direct irradiation energy of the laser on the low-melting-point PHS1500, effectively preventing overheating, overmelting, burn-through, and severe evaporation of Al and Si elements.

[0047] (2) Regarding the use of +4 to +6 mm positive defocus: This embodiment uses a defocus amount of +5 mm. Positive defocus increases the diameter of the laser beam's spot on the workpiece surface, and the energy density distribution changes from a sharp Gaussian distribution to a relatively flat "hat-shaped" distribution. This brings two major benefits: First, it expands the heat source's effective area, making heat transfer at the heterogeneous interface smoother, which is conducive to the formation of a wide and shallow molten pool, enhances the stability of the molten pool, and suppresses convection disturbances caused by differences in the thermal properties of the materials; Second, it reduces the peak temperature at the center of the molten pool, slows down the solidification and cooling process of the molten pool, and provides more favorable thermodynamic conditions for the diffusion homogenization of Al and Si elements, rather than segregation under rapid solidification.

[0048] 3. Weld characterization results:

[0049] like Figure 1-4 As shown, the macroscopic morphology shows that the weld formation is continuous, uniform, and aesthetically pleasing, without defects such as undercut or collapse, achieving single-sided welding with double-sided forming.

[0050] SEM observations revealed that the weld center consisted of a mixed microstructure of fine lath martensite and a small amount of bainite. No continuous or discontinuous banded bright white brittle phases were observed near the fusion line on the PHS1500 side. EDS surface distribution analysis clearly showed that Al and Si elements were diffusely and uniformly distributed in the weld center, without significant local enrichment at grain boundaries or fusion lines.

[0051] Microhardness test results show that the hardness of the weld center is about 380-420 HV, the lowest hardness of the HAZ softening zone on the PHS1500 side is 410 HV (softening rate is about 18%), and the highest hardness of the HAZ on the DX51D side is 165 HV. No abnormal hardening peaks were observed.

[0052] 4. Mechanical property data:

[0053] Shear strength: 15.2kN, the joint shear strength recovery rate reaches 92% of that of the soft low carbon steel base material.

[0054] Fatigue life (100MPa stress amplitude): 2.1×10 6 The loop did not break (run-out).

[0055] Example 2:

[0056] Material composition design: The DX51D uses Fe as the base material, with the addition of C: 0.06%, Si: 0.020%, Mn: 0.18%, P: 0.017%, S: 0.008%, Als: 0.02%, Ti: 0.100% and other alloys to form the base material. The PHS1500 uses Fe as the base material, with the addition of C: 0.26%, Si: 0.1%, Mn: 1.5%, Al: 0.08%, P: 0.006%, S: 0.007%, B: 0.003%, Ti: 0.03% and other alloys to form the base material.

[0057] This embodiment, based on embodiment 1, adjusts the offset and defocus amount to verify the implementation effect within the parameter range.

[0058] 1. Welding Process: A ruby ​​fiber laser is used for welding, with a welding power of 7kW, a wavelength range of 1097nm, a spot diameter of 0.3mm, a welding speed of 230cm / min, a straight path, and the weld seam offset towards the DX51D base material by 0.7mm, with a defocusing amount of +5mm. Argon gas with a purity of 99.99% is used as the welding shielding gas, with a gas flow rate of 22L / min.

[0059] The welding process is secured by a custom-made fixture, and a pressure of 180N is applied to the weld to promote a tight bond at the interface. The cooling rate after welding is controlled at 720℃ / s, the distance between the shielding gas nozzle and the weld surface is 4mm, the blowing pressure is 150mbar, and the gas temperature is controlled at 22℃.

[0060] 2. Effect Analysis:

[0061] Increasing the offset to 1.2mm further strengthens the tendency for energy to be distributed towards the higher melting point side. Combined with a +4.5mm decoking allowance, the molten pool morphology remains stable. The weld formation is excellent.

[0062] The microstructure is similar to that of Example 1, with uniform distribution of Al and Si elements. The lowest hardness of the HAZ on the PHS1500 side is 405 HV (softening rate of approximately 19%).

[0063] 3. Mechanical property data:

[0064] Shear strength: 14.8kN, recovery rate: 90%.

[0065] Fatigue life: 1.9 × 10 6 The loop continues.

[0066] Example 3:

[0067] This embodiment uses the upper limit of the offset for verification.

[0068] 1. Welding process parameters: Laser power: 6.5kW; Welding speed: 235cm / min; Laser offset: 1.8mm towards the DX51D side (close to the upper limit of 2mm); Defocusing amount: +4mm; Shielding gas: Argon flow rate 20L / min; Post-weld cooling rate: approximately 680℃ / s; Fixture pressure: 150N.

[0069] 2. Effect Analysis:

[0070] A significant offset (1.8 mm) would require higher total power or a slower speed to ensure full fusion on the low-carbon steel side. This embodiment achieves full penetration weld by optimizing the power-speed match. The weld pool morphology widens slightly towards the low-carbon steel side, but remains generally stable.

[0071] Due to the large offset, the melting amount of PHS1500 is relatively reduced, resulting in lower absolute contents of Al and Si in the weld and further reducing the tendency to embrittlement. The performance of HAZ is comparable to that of Examples 1 and 2.

[0072] 3. Mechanical property data:

[0073] Shear strength: 14.5kN, recovery rate: 88%.

[0074] Fatigue life: 1.8 × 10 6 The loop continues.

[0075] Comparative Example 1: (Laser beam centering welding)

[0076] This comparative example uses the same laser power (8kW), welding speed (220cm / min) and shielding gas conditions as Example 1, but eliminates beam offset to make the laser beam precisely aligned with the center of the butt joint of the two plates (offset = 0mm), and uses conventional negative defocusing amount (-2mm) to pursue maximum penetration depth.

[0077] 1. Welding process and defects:

[0078] During the welding process, violent fluctuations in the molten pool and severe sparking were observed.

[0079] Subsequent macroscopic inspection revealed that the weld had obvious continuous undercut defects on the PHS1500 side, while the DX51D side showed signs of incomplete fusion.

[0080] 2. Microstructure and elemental analysis:

[0081] SEM observation revealed a large number of network and blocky bright white secondary phases near the fusion line on the PHS150 side and in the center of the weld.

[0082] S-point analysis and surface distribution confirm that these bright white phases are brittle intermetallic compounds rich in Al and Si (such as Fe3Al and FeAlSi). Al and Si elements exhibit severe banded enrichment at the fusion line.

[0083] 3. Mechanical property data:

[0084] The microhardness distribution is extremely uneven, with a hardness peak as high as 650 HV appearing in the brittle phase enrichment area, while the hardness fluctuates greatly in other areas of the weld.

[0085] Shear strength: 8.1kN, recovery rate only 49%.

[0086] In the tensile test, all joints underwent brittle fracture along the brittle phase enrichment zone of the weld.

[0087] Fatigue life (100MPa stress amplitude): average only 1.5×10 5 The second cycle was an order of magnitude lower than that of Example 1.

[0088] Table 1 Comparison of key performance data between Examples 1-3 and Comparative Example 1

[0089]

[0090] Conclusion: A thorough comparison of the examples and comparative examples demonstrates that the specific process combination of offsetting the material towards the soft low-carbon steel side by 0.5-2 mm and employing a positive decoking amount of +4 to +6 mm, as described in this invention, is not a simple parameter adjustment. It is an indispensable key technology for coordinating thermophysical mismatch, actively controlling the metallurgical behavior of harmful elements, and synergistically optimizing the performance of the heterogeneous heat-affected zone when welding ultra-high-strength hot-formed steel and soft low-carbon steel—a pair of special materials. This results in joints that are far superior to conventional center-welding or single-parameter optimization in terms of suppressing brittle phases, ensuring strength, improving toughness, and enhancing fatigue performance.

[0091] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A laser welding method for ultra-high strength hot-formed steel and soft low-carbon steel, wherein the ultra-high strength hot-formed steel has a tensile strength ≥1500MPa and contains Al and Si alloying elements, and the soft low-carbon steel has a tensile strength <300MPa, characterized in that... The method is as follows: The ultra-high strength hot-formed steel workpiece and the soft low-carbon steel workpiece are butt-assembled along the edge to be welded. A fiber laser is used to generate a laser beam to perform auto-fusion welding on the edge to be welded. The center of the laser beam spot is positioned on one side biased towards the soft low-carbon steel workpiece, and the offset distance is 0.5~2mm. The laser beam is controlled to act on the workpiece surface with a positive defocusing amount of +4~+6mm; The power of laser welding is 4~8kW, and the welding speed is 220~240cm / min; During the welding process, a shielding gas is used to protect the molten pool and the heat-affected zone. The shielding gas is argon with a purity of ≥99.97% and a flow rate of 20~25L / min. The shielding gas is also used to control the cooling rate of the weld, so that the post-weld cooling rate is maintained at 500~800℃ / s. During the welding process, an axial pressure of 100~200N is applied to the edge to be welded using a fixture to promote a tight bond at the interface.

2. The method of laser welding an ultra-high strength hot-formed steel and a soft low carbon steel according to claim 1, characterized in that, The nozzle of the protective gas is 3-5 mm away from the weld surface, and the gas blowing pressure is 140-160 mbar.

3. The laser welding method for ultra-high strength hot-formed steel and soft low-carbon steel according to claim 1, characterized in that, The chemical composition of the ultra-high strength hot-formed steel, by weight percentage, includes: C: 0.22%~0.26%, Si: 0.1%~0.2%, Mn: 1.1%~1.5%, Al: 0.04%~0.08%, B: 0.001%~0.003%, P≤0.010%, S≤0.010%, Ti≤0.03%, with the balance being Fe and unavoidable impurities.

4. The method of laser welding an ultra-high strength hot-formed steel and a soft low carbon steel according to claim 1, characterized in that, The chemical composition of the soft low-carbon steel, by weight percentage, includes: C: 0.01%~0.08%, Si≤0.030%, Mn: 0.15%~0.26%, P: 0.015%~0.026%, S≤0.010%, Als: 0.02%~0.06%, Ti≤0.3000%, with the balance being Fe and unavoidable impurities.

5. The laser welding method for ultra-high strength hot-formed steel and soft low-carbon steel according to claim 1, characterized in that, The wavelength of the fiber laser is 1090±10nm, and the spot diameter of the laser beam is 0.3mm.

Images