A synchronous pulse laser tailor-welding method and component of a rare earth high-strength steel

Abstract

The application discloses a synchronous pulse laser tailor-welding method and component of rare earth high-strength steel, and belongs to the technical field of laser composite welding and advanced manufacturing processing technology. The application firstly adopts a continuous laser beam to perform deep penetration tailor-welding to form a main weld; subsequently, in a solid phase zone after the main weld is completely solidified, a high-frequency pulse laser beam is synchronously used to perform thermodynamic impact intervention at a focal point, so that a surface layer coarse rare earth phase which is floated and aggregated is in-situ crushed, so that the surface layer coarse rare earth phase is dispersedly distributed in nanometer level and surface layer grains are refined; finally, the pulse laser is adjusted to a low-energy defocusing state, and in-situ scanning surface heat treatment is performed on the weld. Through the synergistic regulation of "solid phase surface physical modification + in-situ defocusing heat treatment", the welding residual stress and segregation embrittlement are effectively eliminated, and the low-temperature impact toughness and comprehensive mechanical properties of the joint are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of laser composite welding and advanced manufacturing technology, and relates to a synchronous pulsed laser welding method and component for rare earth high-strength steel. Specifically, it relates to a synchronous pulsed surface modification and in-situ heat treatment laser welding method and component for rare earth high-strength steel. Background Technology

[0002] As my country's high-end equipment manufacturing (such as aerospace, deep-sea equipment, and new energy vehicles) advances towards lightweighting, high reliability, and long service life, extremely high demands are being placed on the materials for load-bearing structural components. Rare earth high-strength steel, due to the addition of rare earth elements (such as Ce, La, Y, Nd, etc.) and specific microalloying elements (such as Sb, Nb, Sn, Ti, etc.) during the smelting process, possesses excellent strength-toughness matching and corrosion / weather resistance, making it the preferred material for key load-bearing components. However, the "welding difficulty" of rare earth high-strength steel in practical engineering applications, especially high-energy-density laser deep penetration welding, directly restricts its large-scale promotion.

[0003] Under the extreme thermodynamic conditions of high temperature gradient and rapid cooling in conventional continuous laser deep penetration welding, complex metallurgical evolution occurs within the molten pool of rare earth high-strength steel. First, rare earth elements are highly chemically reactive. Under the strong Marangoni convection in the macroscopic deep penetration pool, they readily react with microalloying elements, oxygen, sulfur, etc., in the matrix, forming micron-sized or even larger rare earth inclusions or coarse carbonitrides. These large precipitates readily float to the surface and agglomerate under fluid drive. These brittle, large agglomerates on the surface not only lose the dispersive strengthening effect that rare earth elements should possess, but also become a source of surface fatigue crack initiation under weld stress. Second, conventional continuous laser deep penetration welding has a large temperature gradient. After rapid cooling, the weld and heat-affected zone generate extremely high residual tensile stress on the surface. This stress, combined with the brittle rare earth phases on the surface, leads to a significant decrease in the joint's low-temperature impact toughness and crack propagation resistance.

[0004] Currently, many researchers are dedicated to improving the microstructure of high-strength steel welds by optimizing the heat source arrangement. For example, the paper "A Welding Method for High-Strength Martensitic Stainless Steel Based on Dual-Laser Coordinated Oscillation Scanning" (CN202511818918.1) and the paper "A Dual-Beam Laser Welding Equipment and Method for Large Curvature Panels" (CN202411055087.2) employ dual-beam high-power continuous laser tandem welding to reduce phase transformation stress by increasing the molten pool volume and extending the cooling time. However, the combination of pure continuous lasers can only change the macroscopic temperature field and cannot effectively break up the coarse rare earth phases that have floated and agglomerated on the weld surface. In addition, existing laser remelting technologies often use kilowatt-level continuous lasers applied to the liquid phase region or perform high-power remelting after welding. This not only carries the risk of excessive heat input leading to severe softening of the heat-affected zone, but may even induce secondary hot cracks. How to break the agglomeration of large rare earth phases on the surface of the weld in situ, refine the surface grains, and simultaneously eliminate welding residual stress under the premise of low heat input has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a synchronous pulsed laser welding method for rare earth high-strength steel. By introducing high-frequency pulsed thermodynamic shock into the fully solidified solid phase region, and coordinating with low-energy defocusing in-situ heat treatment, the agglomeration state of large-size rare earth phases on the weld surface is broken in situ, achieving dual regulation of surface grain refinement and stress relief, and significantly improving the low-temperature toughness and comprehensive mechanical properties of the welded joint.

[0006] Meanwhile, the purpose of this invention is to provide a component prepared by a synchronous pulsed laser welding method using rare earth high-strength steel.

[0007] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a method for synchronous pulsed laser welding of rare earth high-strength steel is provided, comprising the following steps: (1) A continuous laser beam is used as the main heat source to perform deep melting welding on the rare earth high-strength steel base material at the focal point to form the main weld; (2) In the solid phase zone after the main weld has completely solidified, a follow-up high-frequency pulsed laser beam is used to perform local pulse intervention at the focal point. The high-frequency thermodynamic impact generated by the laser beam breaks and crushes the large-sized rare earth phase that floats and agglomerates on the weld surface, so that it is dispersed in the nanoscale on the surface and the surface grains are refined. (3) After the above composite welding process is completed, the high-frequency pulsed laser beam is adjusted to a low-energy defocus state, and the weld is subjected to follow-up in-situ scanning surface heat treatment. The low-energy heat accumulation effect is used to regulate the temperature field distribution of the weld and its heat-affected zone to eliminate welding residual thermal stress.

[0008] In a preferred embodiment of the present invention, the rare earth high-strength steel contains at least one of Ce, La, Y, and Nd rare earth elements, and also contains at least one of the microalloying elements Sb, Nb, Sn, and Ti.

[0009] Specifically, the rare earth high-strength steel of the present invention comprises the following components by mass percentage: C: 0.12-0.16%, Si: 0.15-0.55%, Mn: 1.55-2.05%, P≤0.015%, S≤0.004%, Nb: 0.010-0.025%, Ti: 0.020-0.045%, Cr: 0.20-0.50%, N: 20-50ppm, Ce: 20-55ppm, Sb: 0-25ppm, Y: 0-30ppm, and the balance Fe.

[0010] Preferably, the continuous laser beam and the high-frequency pulsed laser beam are arranged in a series along the welding direction; the center of the high-frequency pulsed laser beam lags behind the center of the continuous laser beam, and the distance between their center points is set to 10-20 mm to ensure that the high-frequency pulsed laser accurately acts on the fully solidified region that has crossed the solidification line.

[0011] Preferably, the continuous laser beam process parameters include: an average power of 1500-3000 W, a scanning speed of 50-200 mm / s, a wavelength of 800-1100 nm, and a spot diameter of 0.2-0.6 mm.

[0012] Preferably, in step (2), the processing parameters of the high-frequency pulsed laser at the focal point include: pulse width of 4-10 ns, pulse repetition frequency of 1-10 MHz, average power of 40-100 W, scanning speed of 10-200 mm / s, and wavelength of 800-1100 nm.

[0013] Preferably, in step (3), the processing parameters of the high-frequency pulsed laser in the defocused state include: defocusing amount of +10-+30 mm or -10--30 mm, pulse width of 20-100 ns, pulse repetition frequency of 1-10 MHz, wavelength of 800-1100 nm, scanning speed of 1-5 mm / s, and average power of 1-5 W.

[0014] Preferably, in order to achieve a deep match and spatiotemporal synergy between surface strengthening and surface heat treatment, the high-frequency pulsed laser process parameters of steps (2) and (3) satisfy the following synergistic relationship: the ratio of the pulse width of step (2) to the pulse width of step (3) is set to 1: (5-10); the ratio of the pulse repetition frequency of step (2) to the pulse repetition frequency of step (3) is set to 1: (0.5-1.33).

[0015] Preferably, after the synchronous pulse intervention in step (2), the average size of the rare earth phase in the weld surface layer depth range of 10-100 μm is reduced to less than 1 μm, and the grains in the surface layer region are significantly refined.

[0016] Preferably, during the welding process, a protective gas is applied to the welding area by side blowing or coaxial blowing. The protective gas is argon or helium, and the gas flow rate is 5-20 L / min.

[0017] According to a second aspect of the present invention, the present invention provides a rare earth high-strength steel laser-welded component prepared by any of the above preferred methods, wherein the surface residual tensile stress in the weld zone of the component is reduced by 40%-70% compared with conventional continuous laser welds; and the Charpy impact absorption energy (impact energy) at -30°C is not less than 50 J, which is 30%-60% higher than that of welds without pulse treatment and heat treatment.

[0018] The component obtained by the synchronous pulsed laser welding method for rare earth high-strength steel according to the present invention has a reduced average size of rare earth phase in the weld surface layer depth range of 10-100 μm to less than 1 μm, and the grains in this surface layer region are significantly refined.

[0019] The residual tensile stress on the weld surface of the component obtained by this invention is significantly reduced to 160-175 MPa, the strength and toughness of the weld are improved, the tensile test specimens all fracture at the base material far away from the weld, and the average Charpy impact absorption energy of the weld joint of the component at -30℃ reaches 53-58 J.

[0020] The components of this invention are used in aerospace, deep-sea equipment, and new energy vehicles.

[0021] Compared with the prior art, the significant advantages of this invention are: (1) This invention utilizes the transient thermodynamic impact of nanosecond-level high-frequency pulses in the solid region to successfully break up the agglomeration of large-sized rare earth phases on the weld surface, achieving a nanoscale dispersed distribution. Addressing the challenge of rare earth compounds easily floating to the surface and crystallizing agglomerating with the molten pool during deep penetration welding, this invention creatively lags the high-frequency pulse spot 10-20 mm behind the main laser, ensuring its precise application to the completely solidified solid region. The high-frequency pulse laser (pulse width 4-10 ns, repetition frequency 1-10 MHz) generates extremely high peak power density and extremely cold and hot transient thermal cycles on the local surface, exciting strong surface photoacoustic / thermodynamic shock waves. This high-frequency physical impact directly shatters the agglomerated large-sized rare earth phases (such as Ce-OS) and microalloyed carbonitrides on the weld surface, forcibly pulverizing them into particles smaller than 1 μm (even nanoscale), resulting in a uniform dispersed distribution within a surface layer depth of 10-100 μm, completely eliminating the source of brittle surface cracks.

[0022] (2) This invention induces a significant fine-grain strengthening effect on the weld surface through pulsed surface modification, achieving gradient microstructure control. Conventional continuous laser deep penetration welds typically exhibit highly directional, easily cleaved coarse columnar crystals (average grain size is usually in the range of 50-150 μm). In this invention, high-frequency pulses generate rapid, extremely shallow thermal cycling on the surface of the solid phase region. The shattered nano-scale rare earth particles serve as a large number of ideal heterogeneous nucleation cores, strongly inhibiting grain boundary growth. After the intervention of step (2) of this invention, the microstructure of the weld surface is completely transformed from coarse columnar crystals to extremely fine equiaxed crystals, and the surface grain size is significantly refined to 2-8 μm. This gradient structure of "internal deep penetration structure + surface ultrafine grain dispersion layer" greatly enhances the surface strength and toughness of the weld.

[0023] (3) This invention innovatively integrates low-energy defocus in-situ scanning heat treatment, achieving effective control of residual stress and a leapfrog improvement in low-temperature toughness. After completing the surface impact modification, step (3) of this invention adjusts the high-frequency pulsed laser to a state of large defocus (+10-+30 mm or -10--30 mm) and low power (1-5 W). This "soft" laser beam with significantly reduced power density acts as an in-situ annealing heat source, utilizing its low-energy heat accumulation effect to slow down the cooling rate of the weld and heat-affected zone, greatly reducing the temperature gradient. Tests show that this in-situ heat treatment reduces the residual tensile stress on the component surface by 40%-70% compared to conventional continuous laser deep penetration welds, effectively preventing stress corrosion and cold cracking.

[0024] (4) Excellent low-temperature impact toughness. Based on the cross-scale synergistic regulation of "surface rare earth phase crushing, surface grain refinement, and overall residual stress elimination," the welded components prepared by this invention exhibit extremely excellent low-temperature mechanical properties. Low-temperature toughness test method and data comparison: According to the national standard GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials," standard V-notch impact specimens containing welds (notch at the center of the weld) were cut and impact tested at a low temperature of -30℃. Comparative example (existing technology): Rare earth high-strength steel specimens welded using pure continuous laser deep melting with the same power exhibit large rare earth agglomerates of approximately 5-15 μm on their surface, and high residual tensile stress. Their average Charpy impact absorption energy (impact work) at -30℃ is only 36 J. In contrast, the specimens prepared using the synchronous pulse intervention and defocusing heat treatment method of this invention have surface grains refined to 2-8 μm, rare earth phases dispersed at the submicron level, and significantly reduced residual stress. Its average Charpy impact absorption energy (impact energy) at -30℃ reached 56 J, which is significantly improved by about 55.6% compared with the comparative example (welds without pulse treatment and heat treatment) (within the range of 30%-60% improvement). The fracture morphology shows ductile fracture with a large number of fine dimples, which solves the engineering problem of low-temperature embrittlement of laser-welded joints of rare earth high-strength steel.

[0025] This invention discloses a synchronous pulsed laser welding method and component for rare-earth high-strength steel, belonging to the field of laser composite welding technology. Addressing the problem of large-size rare-earth phase agglomeration, microalloying element segregation, and high residual tensile stress leading to low-temperature embrittlement of the joint during conventional continuous laser welding of rare-earth high-strength steel, this invention proposes the following: First, a continuous laser beam is used for deep penetration welding to form the main weld; then, in the solidified solid region of the main weld, a follow-up high-frequency pulsed laser beam is used simultaneously to perform thermodynamic impact intervention at the focal point, breaking up the floating agglomerates of coarse rare-earth phases in situ, dispersing them into nanoscale particles and refining the surface grains; finally, the pulsed laser is adjusted to a low-energy defocusing state, and the weld is subjected to in-situ scanning surface heat treatment. This invention, through the synergistic control of "solid-phase surface physical modification + in-situ defocusing heat treatment," effectively eliminates welding residual stress and segregation embrittlement, significantly improving the low-temperature impact toughness and comprehensive mechanical properties of the joint. Attached Figure Description

[0026] Figure 1 The macroscopic morphology of welds from conventional single-beam deep penetration welding and synchronous pulse remelting laser welding is shown. Figure 2 Macroscopic morphology of tensile fracture of rare earth high-strength steel by conventional single-beam deep penetration welding. Figure 3 The metallographic structure of the weld seam in the synchronous pulse remelting laser welding of the present invention; Figure 4 The macroscopic morphology of tensile fracture of rare earth high-strength steel spliced ​​by synchronous pulse remelting laser welding according to the present invention. Figure 5 The fracture microstructure of rare earth high-strength steel subjected to conventional single-beam deep penetration welding. Figure 6 The fracture microstructure of rare earth high-strength steel produced by synchronous pulse remelting laser welding according to the present invention is shown. Detailed Implementation

[0027] 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. Example 1

[0028] This embodiment uses a 1.5 mm thick high-strength steel plate with a tensile strength of 1180 MPa and containing trace amounts of rare earth element Ce, produced by Hebei Iron & Steel Group Handan Iron & Steel Co., Ltd. (batch number HC820 / 1180DP-CF-1), as the research substrate. Its specific composition is shown in Table 1. The study aims to verify the regulatory effect of synchronous pulse surface modification and in-situ defocusing heat treatment on rapid solidification metallurgical defects. In the comparative process (conventional single-beam deep penetration welding), the butt joint surfaces of the substrates were first milled, and then ultrasonically cleaned with anhydrous ethanol to remove oil and mechanically ground to remove the surface oxide film. Subsequently, the two test plates were rigidly butt-jointed without gap on a fixture, and single-pass self-fusion welding was performed using a continuous fiber laser (laser wavelength 1070 nm, defocusing amount 0 mm, average power 2000 W, welding speed 50 mm / s, side-blown 99.99% pure argon gas protection, flow rate 15 L / min).

[0029] In the implementation process of this invention, while maintaining the energy input, clamping conditions, and gas protective environment of the aforementioned continuous main heat source, a high-frequency nanosecond pulse laser (wavelength 1064 nm, average power 50 W, pulse width 5 ns, pulse repetition frequency 5 MHz) is spatially cascaded behind it along the weld centerline. By adjusting the dual-wavelength beam combiner and focusing system, the center of the high-frequency pulse spot lags behind the center of the main continuous laser spot by 15 mm. This spatial lag allows the high-frequency pulse energy to accurately act on the surface region of the main weld that has crossed the solidification line and is completely solidified. Utilizing the extremely high peak power density induced by the nanosecond pulse, a strong high-frequency thermodynamic shock wave and an extremely cold and hot transient thermal cycle are excited on the surface of the solid region. Subsequently, after completing the aforementioned composite welding passes, the high-frequency pulsed laser beam was immediately adjusted to a low-energy defocus state (defocusing amount set to +20mm, average power reduced to 3W, scanning speed set to 2 mm / s, pulse width 30 ns, pulse repetition frequency 4 MHz) (at this time, the ratio of the pulse width of the high-frequency nanosecond pulsed laser to that of the low-energy defocused high-frequency pulsed laser = 5:30 = 1:6; the ratio of the pulse repetition frequency of the high-frequency nanosecond pulsed laser to that of the low-energy defocused high-frequency pulsed laser = 5:4 = 1:0.8), and follow-up in-situ scanning surface heat treatment was performed along the original weld trajectory, using both processes ( Figure 1 The top left image shows the front morphology of a common continuous laser weld, the bottom left image shows the front morphology of the weld in this embodiment, the top right image shows the back morphology of a common continuous laser weld, and the bottom right image shows the back morphology of the weld in this embodiment. The difference between the common continuous laser welding process and this embodiment lies only in that: only continuous laser welding is used, without the use of high-frequency nanosecond pulsed lasers or low-energy defocused high-frequency pulsed lasers. The weld morphology is as follows: Figure 1 As shown, common continuous laser welding processes often result in poor weld formation quality, uneven welds, and localized voids and microcracks in the weld center. In contrast, the weld formation quality in this embodiment is superior, with a continuous and uniform weld, free from defects such as cracks.

[0030] After welding, joint samples from both processes were cut perpendicular to the weld direction. After standard metallographic preparation and weak acid etching, their microstructure and mechanical properties were characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-ray residual stress testing, pendulum impact testing, and universal tensile testing. The results showed that, due to the higher temperature gradient and rapid cooling conditions of the conventional weld in the comparative process, the internal solidification structure of the conventional weld was mainly composed of directionally grown coarse columnar crystals. Furthermore, due to the strong thermocapillary convection of the macroscopic molten pool, highly reactive Ce elements easily floated to the surface and agglomerated, precipitating numerous irregular blocky Ce-OS composite phases or Ce-containing segregated aggregates with sizes ranging from 5-15 μm. Macroscopic mechanical tests indicated that these large and brittle rare-earth aggregates, combined with high surface residual tensile stress (measured peak value reaching 450 MPa), formed extremely strong stress concentration sources and crack initiation sources. This caused the conventional joint to fracture in the central weld zone during tensile testing, with its actual tensile strength decreasing to 870 MPa. In the Charpy impact test at -30℃, its average impact absorption energy was only 36 J, and the fracture surface exhibited obvious cleavage / quasi-cleavage mixed brittle fracture characteristics. The joint's load-bearing capacity was lower than the design requirements of the base material.

[0031] Conversely, the composite welding process in this embodiment utilizes the physical impact generated by high-frequency pulses on the surface of the solid phase region to directly break up the micron-sized Ce-containing compounds that float and agglomerate on the surface. High-magnification SEM observation confirmed that within a surface layer of approximately 50 μm weld depth, there were virtually no coarse inclusions >5 μm. The Ce-containing precipitates were refined into spherical particles <1 μm in size (mainly distributed in the submicron and nanometer scales), exhibiting a uniform and dispersed distribution. Furthermore, these dispersed micro- and nano-sized particles acted as heterogeneous nucleation cores, inducing the microstructure of the weld surface layer to transform from coarse columnar crystals to fine, dense equiaxed crystals (average grain size less than or equal to 3 μm). Simultaneously, after the low-energy defocusing in-situ scanning heat treatment step, the temperature gradient of the weld and heat-affected zone was effectively alleviated, and the residual tensile stress on the surface was significantly reduced to 160 MPa, a reduction of up to 64.4%. The final macroscopic mechanical test results showed that the tensile specimens of conventional single-beam deep penetration welding all fractured at the weld ( Figure 2 The component prepared in this embodiment has a unique gradient structure of "fine-grained dispersion on the surface + low residual stress". Figure 3 The strength and toughness of the core weld zone were effectively improved, and all tensile specimens fractured in the base material away from the weld. Figure 4 The tensile strength remained consistently above the nominal 1180 MPa. More importantly, the average Charpy impact absorption energy of the joint in this embodiment reached 58 J at -30°C, an improvement of approximately 61.1% compared to the comparative process. Conventional single-beam deep penetration welds exhibited obvious cleavage steps and void structures in the fracture surface. Figure 5 In this embodiment, the joint fracture surface exhibits a uniform and dense morphology of fine dimples. Figure 6 The results show that the process in this embodiment effectively solves the problems of high residual stress and low-temperature embrittlement in laser-welded joints of rare-earth high-strength steel, and achieves a comprehensive leap in the overall mechanical properties of the joint.

[0032] The components obtained in this embodiment are used in aerospace, deep-sea equipment, and new energy vehicles. Example 2

[0033] This embodiment uses a 1.6 mm thick high-strength steel plate with a tensile strength of 1200 MPa, containing trace amounts of rare earth element Ce and microalloying element Sb, produced by Hebei Iron & Steel Group Handan Iron & Steel Co., Ltd. (batch number HC820 / 1180DP-CF-2). The specific composition is shown in Table 1. This study aims to verify the effects of synchronous pulse surface modification and in-situ defocusing heat treatment on the microstructure control and toughening of easily segregated elements in complex microalloying systems.

[0034] In the comparative process (conventional single-beam deep penetration welding), the mating surfaces of the substrates were first milled, and then ultrasonically cleaned with anhydrous ethanol to remove oil and mechanically ground to remove the surface oxide film. Subsequently, the two test plates were rigidly butt-welded without gaps on the fixture, and a single-pass self-fusion welding was performed using a continuous fiber laser (laser wavelength 1070 nm, defocusing amount 0 mm, average power 2200 W, welding speed 60 mm / s, side-blown argon gas protection with a purity of 99.99%, flow rate 18 L / min).

[0035] In the implementation process of this invention, while maintaining the energy input, clamping conditions, and gas protective environment of the aforementioned continuous main heat source, a high-frequency nanosecond pulse laser (wavelength 1064 nm, average power 60 W, pulse width 4 ns, pulse repetition frequency 3 MHz) is spatially cascaded along the centerline of the weld seam behind it. By adjusting the dual-wavelength beam combiner and focusing system, the center of the high-frequency pulse spot lags behind the center of the main continuous laser spot by 15 mm. This spatial lag allows the high-frequency pulse energy to accurately act on the surface region of the main weld seam that has crossed the solidification line and is completely solidified. Utilizing the extremely high peak power density induced by the nanosecond pulse, a strong high-frequency thermodynamic shock wave and an extremely cold and hot transient thermal cycle are excited on the surface of the solidification region. Subsequently, after completing the aforementioned composite welding passes, the high-frequency pulsed laser beam was immediately adjusted to a low-energy defocus state (defocusing amount set to +20mm, average power reduced to 5W, scanning speed set to 4 mm / s, pulse width 20 ns, pulse repetition frequency 4 MHz) (at this time, the ratio of the pulse width of the high-frequency nanosecond pulsed laser to that of the low-energy defocused high-frequency pulsed laser = 4:20 = 1:5; the ratio of the pulse repetition frequency of the high-frequency nanosecond pulsed laser to that of the low-energy defocused high-frequency pulsed laser = 3:4 = 1:1.33), and follow-up in-situ scanning surface heat treatment was performed along the original weld trajectory.

[0036] After welding, joint samples from the two processes were cut along the direction perpendicular to the weld seam. After standard metallographic preparation and weak acid etching, the microstructure and mechanical properties were characterized using an optical microscope (OM), scanning electron microscope (SEM), X-ray residual stress tester, pendulum impact tester, and universal tensile testing machine.

[0037] The results showed that in the conventional weld of the comparative process, due to the easy redistribution of Sb in the rapidly solidifying liquid-solid phase zone, a large amount of Sb segregated and accumulated at the original austenite grain boundaries, forming a low-melting-point network segregation band. Simultaneously, highly reactive Ce combined with Sb, O, and other elements, easily floated to the surface and agglomerated on the weld surface under the strong thermocapillary convection of the macroscopic molten pool, precipitating numerous coarse, blocky Ce-Sb compounds with a size of 10-20 μm. Macroscopic mechanical tests indicated that these coarse and brittle surface rare-earth aggregates and internal segregation networks, combined with high residual tensile stress (measured peak value reaching 470 MPa), formed extremely strong stress concentration sources and crack initiation sources. This caused the conventional joint to fracture in the central weld zone during tensile testing, with its actual tensile strength decreasing to 850 MPa. In the Charpy impact test at -30℃, its average impact absorption energy was only 34 J, and the fracture surface exhibited obvious intergranular / cleavage mixed brittle fracture characteristics. The joint's load-bearing capacity was lower than the design requirements of the base material.

[0038] Conversely, the composite welding process of this invention utilizes the physical impact generated by high-frequency pulses on the surface of the solid phase region to directly break up the micron-sized Ce-Sb compounds that float and agglomerate on the surface. High-magnification SEM observation confirms that within a surface layer of approximately 60 μm in weld depth, there are virtually no coarse inclusions >5 μm, and the precipitated phase is refined into spherical particles <1 μm in size (mainly distributed in the 200-500 nm range), exhibiting a uniform and dispersed distribution. Furthermore, this rapid thermal cycling in the extremely shallow surface layer and the pinning effect of the dispersed micro-nano particles effectively suppress the continuous segregation of Sb elements towards the grain boundaries and induce the surface microstructure of the weld to completely transform from coarse columnar crystals to fine, dense equiaxed crystals (average grain size refined to approximately 4 μm). Simultaneously, after low-energy defocusing in-situ scanning heat treatment, the temperature gradient of the weld and heat-affected zone is effectively alleviated, and the residual tensile stress on the surface is significantly reduced to 175 MPa, a reduction of up to 62.8%.

[0039] The final macroscopic mechanical test results showed that the tensile specimens from conventional single-beam deep penetration welding all fractured at the weld seam. However, the component prepared by this invention, due to its unique gradient structure of "fine-grained dispersion on the surface + low residual stress," exhibited significantly improved strength and toughness in the core weld zone. The tensile specimens fractured in the base material far from the weld seam, with the tensile strength consistently maintained above the nominal 1200 MPa. More importantly, the joint of this invention achieved an average Charpy impact absorption energy of 53 J at -30℃, an improvement of approximately 55.9% compared to the comparative process. The fracture surface of the joint of this invention exhibited a uniform and dense morphology of fine dimples. These results demonstrate that the process of this invention effectively solves the problems of high residual stress, elemental segregation, and low-temperature embrittlement in laser-welded joints of complex microalloyed rare-earth high-strength steel, achieving a comprehensive leap in the overall mechanical properties of the joint.

[0040] The components obtained in this embodiment are used in aerospace, deep-sea equipment, and new energy vehicles. Example 3

[0041] This embodiment uses a 1.9 mm thick high-strength steel plate with a tensile strength of 1220 MPa, containing trace amounts of rare earth elements Y and Ce and microalloying element Sb, produced by Hebei Iron & Steel Group Handan Iron & Steel Co., Ltd. (batch number HC820 / 1180DP-CF-3). The specific composition is shown in Table 1. This study aims to verify the regulatory effect of synchronous pulse surface modification and in-situ defocusing heat treatment on the uniformity of joint structure and ultra-low temperature toughness under multi-component rare earth and microalloying systems.

[0042] In the comparative process (conventional single-beam deep penetration welding), the mating surfaces of the substrates were first milled, and then ultrasonically cleaned with anhydrous ethanol to remove oil and mechanically ground to remove the surface oxide film. Subsequently, the two test plates were rigidly butt-welded without gaps on the fixture, and a single-pass self-fusion welding was performed using a continuous fiber laser (laser wavelength 1070 nm, defocusing amount 0 mm, average power 2400 W, welding speed 70 mm / s, side-blown argon gas protection with a purity of 99.99%, flow rate 18 L / min).

[0043] In the implementation process of this invention, while maintaining the energy input, clamping conditions, and gas protective environment of the aforementioned continuous main heat source, a high-frequency nanosecond pulse laser (wavelength 1064 nm, average power 75 W, pulse width 10 ns, pulse repetition frequency 10 MHz) is spatially cascaded along the centerline of the weld seam behind it. By adjusting the dual-wavelength beam combiner and focusing system, the center of the high-frequency pulse spot lags behind the center of the main continuous laser spot by 12 mm. This spatial lag allows the high-frequency pulse energy to accurately act on the surface region of the main weld seam that has crossed the solidification line and is completely solidified. Utilizing the extremely high peak power density induced by the nanosecond pulse, a strong high-frequency thermodynamic shock wave and an extremely cold and hot transient thermal cycle are excited on the surface of the solidification region. Subsequently, after completing the aforementioned composite welding passes, the high-frequency pulsed laser beam was immediately adjusted to a low-energy defocus state (defocusing amount set to +25mm, average power reduced to 1W, scanning speed set to 2 mm / s, pulse width 50 ns, pulse repetition frequency 5 MHz) (at this time, the ratio of the pulse width of the high-frequency nanosecond pulsed laser to that of the low-energy defocused high-frequency pulsed laser = 10:50 = 1:5; the ratio of the pulse repetition frequency of the high-frequency nanosecond pulsed laser to that of the low-energy defocused high-frequency pulsed laser = 10:5 = 1:0.5), and follow-up in-situ scanning surface heat treatment was performed along the original weld seam trajectory.

[0044] After welding, joint samples from the two processes were cut along the direction perpendicular to the weld seam. After standard metallographic preparation and weak acid etching, the microstructure and mechanical properties were characterized using an optical microscope (OM), scanning electron microscope (SEM), X-ray residual stress tester, pendulum impact tester, and universal tensile testing machine.

[0045] The results showed that in the conventional weld of the comparative process, due to the synergistic segregation of multiple elements including Y, Ce, and Sb, the enrichment of Sb at the grain boundaries was further intensified, forming a continuous network of brittle bands. Simultaneously, the highly chemically reactive Y and Ce elements collided, grew, and floated upwards, forming numerous coarse, blocky Y-Ce composite inclusions with a size of 15-25 μm on the weld surface. Macroscopic mechanical tests indicated that these coarse surface aggregates and the severe internal segregation network, combined with extremely high residual tensile stress (measured peak value reaching 490 MPa), caused the conventional joint to fracture rapidly in the central weld zone during tensile testing, with its actual tensile strength decreasing to 830 MPa. In the Charpy impact test at -30℃, the average impact absorbed energy was only 32 J, and the fracture surface exhibited obvious brittle cleavage characteristics, indicating a severe lack of joint toughness.

[0046] Conversely, the composite welding process of this invention utilizes the physical impact intervention generated by high-frequency pulses on the surface of the solid phase region, directly shattering the Y-Ce-containing composite compounds that float and agglomerate on the surface through a strong photoacoustic effect. High-magnification SEM observation confirmed that within the surface layer of approximately 70 μm weld depth, there were virtually no coarse inclusions >5 μm, and the precipitated phase was refined into nanoscale spherical dispersed particles with a size of less than 1 μm (mostly in the 100-400 nm range). Furthermore, these multi-component dispersed particles suppressed grain boundary coarsening through a strong pinning effect and induced the microstructure of the weld surface layer to transform into extremely fine and uniform equiaxed crystals (average grain size refined to approximately 3-5 μm). Simultaneously, after low-energy defocusing in-situ scanning heat treatment, the temperature field distribution in the weld zone was effectively controlled, and the residual tensile stress on the surface was significantly reduced to 165 MPa, a reduction of up to 66.3%.

[0047] The final macroscopic mechanical test results showed that the tensile specimens from conventional single-beam deep penetration welding all fractured at the weld seam. However, the components prepared by this invention, due to their significant fine-grained strengthening and low residual stress distribution on the surface, exhibited a substantial improvement in the strength and toughness of the core weld zone. The tensile specimens from this invention all fractured in the base material far from the weld seam, with the tensile strength consistently maintained above 1220 MPa. More importantly, the joint of this invention achieved an average Charpy impact absorption energy of 55 J at -30℃, an increase of approximately 71.9% compared to the comparative process, and the fracture surface exhibited a dense and uniform dimple morphology. These results demonstrate that the process of this invention, through multi-scale metallurgical control, effectively overcomes the problems of segregation embrittlement and stress concentration in multi-component rare-earth high-strength steel joints, achieving high-performance connections.

[0048] The components obtained in this embodiment are used in aerospace, deep-sea equipment, and new energy vehicles.

[0049] Table 1. Composition (%) of rare earth high-strength steel in each embodiment Comparative Example 1

[0050] This applies to pulse width coordination ratios that exceed the specified range.

[0051] This comparative example uses a 1.5 mm thick high-strength steel plate containing trace rare earth Ce with a tensile strength of 1180 MPa produced by Hebei Iron & Steel Group Handan Iron & Steel Co., Ltd. as the research substrate. The aim is to verify the effect of surface strengthening and in-situ heat treatment depth matching when the pulse width ratio of step (2) and step (3) does not meet the synergistic relationship defined in this application.

[0052] In the implementation process of this comparative example, the parameters of the continuous laser main heat source and the clamping conditions used in step (1) are completely consistent with those in Example 1. In the subsequent step (2), the high-frequency pulse process parameters at the focal point are set as follows: average power 60W, scanning speed 50 mm / s, pulse width 5 ns, and pulse repetition frequency 5 MHz. After completing the composite welding passes, the low-energy defocusing follow-up in-situ scanning surface heat treatment in step (3) is performed, and its parameters are adjusted as follows: defocusing amount +20 mm, average power 3W, scanning speed 2 mm / s, and pulse repetition frequency 5 MHz, but the pulse width is set to 75 ns. At this time, the pulse width ratio of step (2) to step (3) is 5:75, that is, 1:15, which exceeds the synergistic range of 1:5-10 set by the present invention.

[0053] After welding, joint samples were cut perpendicular to the weld direction and characterized for microstructure and mechanical properties after standard metallographic preparation and weak acid etching. The results showed that, due to the pulse width of step (3) being too large compared to step (2), the heat penetration depth of a single pulse far exceeded the depth of the physical modification layer formed in step (2). This severe mismatch in depth caused the excessive heat accumulation generated in step (3) to directly affect the microstructure that had just been refined in step (2). High-magnification SEM and metallographic observation confirmed that the nano-scale rare earth phase and fine equiaxed crystals that had been physically refined in step (2) underwent severe secondary growth and grain coarsening under the excessively deep heat conduction of annealing (the average grain size of the surface layer grew back to more than 25 μm). Macroscopic mechanical tests showed that grain coarsening led to the loss of the fine grain strengthening and dispersion strengthening effects of the surface layer, and the tensile strength decreased to 990 MPa; in the Charpy impact test at -30℃, its average impact absorption energy was only 37 J. Test data shows that if the pulse width ratio exceeds the limit, it will cause secondary thermal damage, completely destroy the tissue modification results of step (2), and fail to achieve deep synergistic matching. Comparative Example 2

[0054] This applies to frequency coordination ratios that exceed the specified range.

[0055] This comparative example uses the same 1.5 mm thick high-strength steel plate containing trace amounts of rare earth Ce as Comparative Example 1 as the research substrate, aiming to verify the effect on the synergistic effect of thermodynamic control and tissue regulation when the ratio of pulse repetition frequency between step (2) and step (3) does not meet the synergistic relationship defined in this application.

[0056] In the implementation process of this comparative example, the deep penetration welding process of the main heat source in step (1) is completely consistent with that in Example 1. The synchronous pulse intervention parameters of the solid phase region surface in step (2) are set as follows: average power 60 W, pulse width 5 ns, and pulse repetition frequency 2 MHz. When performing the low-energy defocusing surface heat treatment in step (3), the parameters are adjusted as follows: defocusing amount +15 mm, average power 3 W, and pulse width 25 ns (at this time, the pulse width ratio is 1:5, which is within a reasonable range), but the pulse repetition frequency is set to 8 MHz. At this time, the ratio of the pulse repetition frequencies of step (2) and step (3) is 2:8, that is, 1:4, which does not fall within the synergistic range of 1:0.5-1.33 set by this invention.

[0057] After welding and heat treatment, the joint specimen was subjected to microstructure and mechanical property tests using the same characterization methods as Comparative Example 1. Microstructure and stress characterization showed that, due to the excessively high pulse repetition frequency in step (3) compared to step (2), a severe mismatch occurred between the surface thermal cycle rhythm of the in-situ heat treatment and the stress relaxation time of the microstructure. The high-frequency laser pulses caused heat to accumulate at an extremely fast rate in the very shallow surface layer, failing to provide sufficient thermal conduction and stress release gaps for the subsurface microstructure, and even inducing slight thermal ablation defects on the local surface. The X-ray residual stress test results showed that, due to the failure of thermal stress to effectively disperse and relax to the deeper layers, the residual tensile stress on the surface of the comparative example joint was still as high as 420 MPa, with a very small reduction. Affected by the combined effects of surface micro-defects and high residual stress, the joint showed increased sensitivity to microcracks during tensile testing, and the tensile strength decreased to 1020 MPa; in the Charpy impact test at -30℃, the average impact absorption energy was 39 J, exhibiting brittle fracture characteristics dominated by residual stress concentration. Test data shows that frequency ratio mismatch disrupts the spatiotemporal coordination of the two-step process, resulting in residual stress that cannot be effectively eliminated and severely weakening the overall mechanical properties of the joint. Comparative Example 3

[0058] For pulse width synergy ratios below a specified range.

[0059] This comparative example uses a 1.5 mm thick high-strength steel plate containing trace amounts of rare earth Ce with a tensile strength of 1180 MPa produced by Hebei Iron & Steel Group Handan Iron & Steel Co., Ltd. as the research substrate. The aim is to verify the effect of surface strengthening and in-situ heat treatment depth matching when the pulse width ratio of step (2) and step (3) does not meet the synergistic relationship defined by the present invention.

[0060] In the implementation process of this comparative example, the parameters of the continuous laser main heat source and the clamping conditions used in step (1) are completely consistent with those in Example 1. In the subsequent step (2), the high-frequency pulse process parameters at the focal point are set as follows: average power 60W, scanning speed 50 mm / s, pulse width 5 ns, and pulse repetition frequency 5 MHz. After completing the composite welding passes, the low-energy defocusing follow-up in-situ scanning surface heat treatment in step (3) is performed, and its parameters are adjusted as follows: defocusing amount +20 mm, average power 3W, scanning speed 2 mm / s, and pulse repetition frequency 5 MHz, but the pulse width is set to 20 ns. At this time, the pulse width ratio of step (2) to step (3) is 5:20, that is, 1:4, which is lower than the synergistic range of 1:5-10 set by the present invention.

[0061] Microscopic morphology and stress characterization show that, due to the reasonable process parameters in step (2), the rare earth phase on the surface of the comparative joint was effectively broken up and the grains were refined. However, because the pulse width in step (3) is too narrow compared to step (2), the heat penetration depth of a single pulse is extremely shallow, significantly lower than the depth of the physical modification layer formed in step (2). This inverted mismatch in depth causes the low-energy heat accumulation generated in step (3) to remain only on the very shallow surface of the material, and cannot be effectively conducted downward to cover the entire fine-grained modification layer and heat-affected zone. Due to the obstruction of deep heat conduction, the cooling temperature gradient inside the material has not been substantially homogenized or alleviated. The X-ray residual stress measurement results confirm that the residual tensile stress on the surface of the comparative joint is still as high as 430 MPa, achieving only a slight stress relaxation, far from achieving the stress relief depth and magnitude expected in this application. Macroscopic mechanical tests show that under the continuous action of high residual stress inside, the joint is highly susceptible to microcrack propagation during low-temperature service, with a tensile strength of 1030 MPa. In the Charpy impact test at -30℃, the average impact absorbed energy is 41 J, and the fracture surface exhibits brittle fracture characteristics influenced by stress concentration. Test data indicate that when the pulse width ratio is below the specified range, the heat conduction depth cannot match the thickness of the modified layer, rendering the in-situ heat treatment ineffective and failing to achieve the technical effect of multi-scale synergistic toughening. Comparative Example 4

[0062] For frequency coordination ratios below a specified range.

[0063] This comparative example uses a 3 mm thick high-strength steel plate containing trace amounts of rare earth Ce with a tensile strength of 1180 MPa produced by Hebei Iron & Steel Group Handan Iron & Steel Co., Ltd. as the research substrate. The aim is to verify the effect on thermal accumulation stability and residual stress elimination effect when the ratio of pulse repetition frequency between step (2) and step (3) is lower than the synergistic relationship defined in this invention.

[0064] In the implementation process of this comparative example, the main heat source deep penetration welding process in step (1) is completely consistent with that in Example 1 (average power 2000 W, welding speed 50 mm / s). The synchronous pulse intervention parameters of the solid phase region surface in step (2) are set as follows: average power 60 W, pulse width 5 ns, pulse repetition frequency 5 MHz. After completing the composite welding passes, the low-energy defocusing follow-up in-situ scanning surface heat treatment in step (3) is performed, and its parameters are adjusted as follows: defocusing amount +20 mm, average power 3 W, pulse width 25 ns (at this time, the pulse width ratio is 1:5, which is within the limited 1:5-10 coordination range), but its pulse repetition frequency is set to 1 MHz. At this time, the pulse repetition frequency ratio of step (2) and step (3) is 5:1, that is, 1:0.2, which is lower than the lower limit of the coordination range of 1:0.5-1.33 set by the present invention.

[0065] After welding and heat treatment, the joint specimens were subjected to microstructure and mechanical property tests using the same characterization methods as the aforementioned comparative example.

[0066] Microscopic morphology and stress characterization show that, due to the relatively low pulse repetition frequency in step (3) compared to step (2), the time interval between two adjacent laser pulses is significantly prolonged. In this state, the low-energy laser beam cannot form a continuous and stable "annealing heat accumulation" effect on the material surface, but instead degenerates into an intermittent local heating and rapid cooling process. This low-frequency heat input causes the surface structure, which has just undergone high-free-energy metastable state after high-frequency impact modification in step (2), to experience repeated microscopic heating and cooling cycles (thermal fatigue impact), which greatly hinders the regular slippage of dislocations at grain boundaries and the gradual release of internal stress. The X-ray residual stress measurement results show that, due to the lack of a stable heat treatment temperature field, the residual tensile stress on the surface of this comparative joint is still as high as 415 MPa. At the same time, the repeated microscopic heating and cooling cycles even induce new microscopic thermal stress concentration points at a few grain boundaries. Macroscopic mechanical tests revealed that the failure to effectively eliminate the high residual stress combined with microscopic defects introduced by intermittent thermal cycling reduced the joint's load-bearing capacity; the tensile strength of the tensile specimen was 1040 MPa, and the average impact absorbed energy in the Charpy impact test at -30℃ was only 40 J. Test data indicate that when the frequency ratio is below the specified range, stable thermal accumulation and stress relaxation rhythm cannot be maintained, leading to failure of the in-situ annealing process and preventing effective improvement of the joint's low-temperature toughness. Example 4

[0067] The only difference between this embodiment and Embodiment 1 is that: A synchronous pulsed laser welding method for rare earth high-strength steel includes the following steps: Step 1: Using a continuous laser beam as the main heat source, deep penetration welding is performed on the rare earth high-strength steel base material at the focal point to form the main weld. The continuous laser beam process parameters include: average power of 1500 W, scanning speed of 200 mm / s, wavelength of 800 nm, and spot diameter of 0.2 mm. Step 2: In the solidified zone after the main weld has completely solidified, a local pulse intervention is performed at the focal point using a follow-up high-frequency pulsed laser beam; the center of the high-frequency pulsed laser beam lags behind the center of the continuous laser beam, and the distance between the centers of the two beams is 10 mm. The processing parameters for high-frequency pulsed laser at the focal point include: pulse width of 4 ns, pulse repetition frequency of 1 MHz, average power of 40 W, scanning speed of 10 mm / s, and wavelength of 800 nm. Step 3: After the above composite welding process is completed, adjust the high-frequency pulsed laser beam to a low-energy defocus state and perform follow-up in-situ scanning surface heat treatment on the weld. The processing parameters for high-frequency pulsed laser in defocused state include: defocusing amount of +10 mm, pulse width of 20 ns, pulse repetition frequency of 1 MHz, wavelength of 800 nm, scanning speed of 1 mm / s, and average power of 2 W.

[0068] The ratio of the pulse width in step 2 to the pulse width in step 3 is 1:5; the ratio of the pulse repetition frequency in step 2 to the pulse repetition frequency in step 3 is 1:1.

[0069] During the welding process, a protective gas is applied to the welding area using side blowing or coaxial blowing. The protective gas is helium, and the gas flow rate is 5 L / min. Example 5

[0070] The only difference between this embodiment and Embodiment 1 is that: A synchronous pulsed laser welding method for rare earth high-strength steel includes the following steps: Step 1: Using a continuous laser beam as the main heat source, deep penetration welding is performed on the rare earth high-strength steel base material at the focal point to form the main weld. The continuous laser beam process parameters include: average power of 3000 W, scanning speed of 100 mm / s, wavelength of 1100 nm, and spot diameter of 0.6 mm. Step 2: In the solidified zone of the main weld after complete solidification, a local pulse intervention is performed at the focal point using a follow-up high-frequency pulsed laser beam; the center of the high-frequency pulsed laser beam lags behind the center of the continuous laser beam, and the distance between the centers of the two beams is 20 mm. The processing parameters for high-frequency pulsed laser at the focal point include: pulse width of 10 ns, pulse repetition frequency of 10 MHz, average power of 100 W, scanning speed of 200 mm / s, and wavelength of 1100 nm. Step 3: After the above composite welding process is completed, adjust the high-frequency pulsed laser beam to a low-energy defocus state and perform follow-up in-situ scanning surface heat treatment on the weld. The processing parameters for high-frequency pulsed laser in defocused state include: defocusing amount of +30 mm, pulse width of 100 ns, pulse repetition frequency of 10 MHz, wavelength of 1100 nm, scanning speed of 5 mm / s, and average power of 3 W.

[0071] The ratio of the pulse width in step 2 to the pulse width in step 3 is 1:10; the ratio of the pulse repetition frequency in step 2 to the pulse repetition frequency in step 3 is 1:1.

[0072] During the welding process, a protective gas is applied to the welding area using side blowing or coaxial blowing. The protective gas is helium, and the gas flow rate is 20 L / min. Example 6

[0073] The only difference between this embodiment and Embodiment 1 is that: In step 3, the defocusing amount is -10 mm. Example 7

[0074] The only difference between this embodiment and Embodiment 1 is that: In step 3, the defocusing amount is -30 mm.

[0075] 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.

[0076] 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.

[0077] 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 method for synchronous pulsed laser welding of rare earth high-strength steel, characterized in that, Includes the following steps: Step 1: Using a continuous laser beam as the main heat source, deep penetration welding is performed on the rare earth high-strength steel base material at the focal point to form the main weld. The continuous laser beam process parameters include: average power of 1500-3000 W, scanning speed of 50-200 mm / s, wavelength of 800-1100 nm, and spot diameter of 0.2-0.6 mm; Step 2, in the solidified region of the main weld after complete solidification, a follow-up high-frequency pulsed laser beam is used to perform local pulse intervention at the focal point; the processing parameters of the high-frequency pulsed laser at the focal point include: pulse width of 4-10 ns, pulse repetition frequency of 1-10 MHz, average power of 40-100 W, scanning speed of 10-200 mm / s, and wavelength of 800-1100 nm; Step 3, after the above composite welding process is completed, the high-frequency pulsed laser beam is adjusted to a low-energy defocus state, and the weld is subjected to follow-up in-situ scanning surface heat treatment; the processing parameters of the high-frequency pulsed laser in the defocus state include: defocusing amount of +10 to +30 mm or -10 to -30 mm, and pulse width of 20-100 nm. The pulse repetition frequency is 1-10 MHz, the wavelength is 800-1100 nm, the scanning speed is 1-5 mm / s, and the average power is 1-5 W; the ratio of the pulse width in step 2 to the pulse width in step 3 is 1:(5-10); the ratio of the pulse repetition frequency in step 2 to the pulse repetition frequency in step 3 is 1:(0.5-1.33).

2. The synchronous pulsed laser welding method for rare earth high-strength steel according to claim 1, characterized in that, Rare earth high-strength steel contains at least one of the rare earth elements Ce, La, Y, and Nd, as well as at least one of the microalloying elements Sb, Nb, Sn, and Ti.

3. The synchronous pulsed laser welding method for rare earth high-strength steel according to claim 1, characterized in that, Rare earth high-strength steel comprises the following components by mass percentage: C: 0.12-0.16%, Si: 0.15-0.55%, Mn: 1.55-2.05%, P≤0.015%, S≤0.004%, Nb: 0.010-0.025%, Ti: 0.020-0.045%, Cr: 0.20-0.50%, N: 20-50ppm, Ce: 20-55ppm, Sb: 0-25ppm, Y: 0-30ppm, and the balance Fe.

4. The synchronous pulsed laser welding method for rare earth high-strength steel according to claim 1, characterized in that, The continuous laser beam in step 1 and the high-frequency pulsed laser beam in step 2 are arranged in a series along the welding direction; the center of the high-frequency pulsed laser beam lags behind the center of the continuous laser beam, and the distance between their center of beams is 10-20 mm, so as to ensure that the high-frequency pulsed laser acts on the fully solidified zone that has crossed the solidification line.

5. The synchronous pulsed laser welding method for rare earth high-strength steel according to claim 1, characterized in that, During the welding process, a protective gas is applied to the welding area by side blowing or coaxial blowing. The protective gas is argon or helium, and the gas flow rate is 5-20 L / min.

6. A component obtained by the synchronous pulsed laser welding method for rare earth high-strength steel according to any one of claims 1-5, characterized in that, The average size of rare earth phases in the weld surface layer of the component, within a depth range of 10-100 μm, is reduced to less than 1 μm, and the grains in this surface region are significantly refined.

7. The component according to claim 6, characterized in that, The residual tensile stress on the weld surface of the component was significantly reduced to 160-175 MPa, the strength and toughness of the weld were improved, and the tensile test specimens all fractured at the base material far away from the weld. The average Charpy impact absorption energy of the weld joint of the component at -30℃ reached 53-58 J.

8. The application of the component according to claim 6 in aerospace, deep-sea equipment, and new energy vehicles.

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