Method for improving low-temperature performance of 430 ferritic stainless steel laser welding seam

Abstract

The invention discloses a method for improving the low-temperature performance of a 430 ferritic stainless steel laser welding seam, and relates to the technical field of stainless steel cold rolling production, the method comprises the following steps: carrying out negative defocusing low-power laser welding: welding by adopting the defocusing amount of-1 to-2mm and the laser power of 8-10kW; hot wire laser welding is conducted, specifically, the front section of the welding wire is preheated in the welding process, and the temperature of the front section of the welding wire is increased to 300-400 DEG C; short-time induction annealing is conducted, specifically, induction heating is conducted on a weld joint after welding, the temperature of the weld joint is increased to 700 + / -5 DEG C within 10-12 seconds, and heat preservation is conducted; induction heating before rolling: heating a welding seam area to 50-65 DEG C by adopting a medium-frequency induction coil before the welded stainless steel is subjected to cold continuous rolling; and coordinated adjustment of rolling parameters: dynamically adjusting five-rack continuous rolling parameters according to the workshop temperature. According to the method, the low-temperature rolling bottleneck of the 430 ferritic stainless steel welding seam can be fundamentally broken through, and the low-temperature performance of the 430 ferritic stainless steel welding seam is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of stainless steel cold rolling production technology, and in particular to a method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel. Background Technology

[0002] In the continuous production of cold-rolled stainless steel strip, 430 ferritic stainless steel has become an important material due to its excellent corrosion resistance and formability. However, in the low-temperature conditions of northern winters (-5℃ to -10℃), 430 stainless steel strips with a thickness ≥4.5mm, after laser welding, frequently experience cracking and even strip breakage in the weld area during subsequent cold rolling. Industry data shows that under traditional production processes, the average monthly weld cracking frequency is as high as 2.6 times, and each failure requires a production stoppage of 3-6 hours, severely restricting the continuous operation of the production line and causing significant economic losses.

[0003] Research has revealed that the root cause of the above problems lies in the systematic performance degradation of welded joints under low-temperature environments, mainly manifested in the following key defects:

[0004] 1. Abnormal coarsening of grains in the heat-affected zone (HAZ): Conventional 12kW laser welding causes the peak temperature of the HAZ to exceed 1100℃ and the grain size to reach more than 200μm, resulting in the ductile-brittle transition temperature (DBTT) dropping below room temperature; in the -10℃ low-temperature impact test, the impact toughness of the weld zone is only 5-10J, which is significantly lower than the 20-30J level of the base material.

[0005] 2. Formation of hard and brittle martensite phase: Due to rapid cooling, a continuous martensitic structure is formed near the weld fusion line, and the microhardness increases sharply to 380-450HV, forming a hardness gradient of up to 200HV with the base material (190-220HV), which becomes a source of stress concentration.

[0006] 3. High residual stress is difficult to release: The welding cooling process generates residual stress with a peak value of 280MPa, while the material elongation decreases to 8% at low temperature. Insufficient plastic deformation capacity leads to the inability to effectively relax the stress.

[0007] 4. Low-temperature performance drops precipitously: The pass rate of the weld cupping test at room temperature is only 10%, far lower than the 90% pass rate under 60℃ hot conditions. Traditional production processes cannot compensate for the performance degradation caused by low temperature.

[0008] In practical applications, traditional production processes struggle to simultaneously achieve grain refinement and residual stress control through welding parameter optimization; they cannot meet the dual objectives of martensite decomposition and grain refinement within the required production line timeframe; the rolling process parameters and welding process lack a dynamic matching mechanism; and corresponding temperature compensation measures are ineffective against -10°C low-temperature shocks.

[0009] Therefore, there is an urgent need to develop a method to improve the low-temperature performance of laser welds in 430 ferritic stainless steel, so as to fundamentally improve the low-temperature performance of 430 ferritic stainless steel welds. Summary of the Invention

[0010] To address some or all of the technical problems existing in the prior art, the present invention provides a method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel.

[0011] The technical solution of the present invention is as follows:

[0012] A method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel is provided, comprising:

[0013] Negative defocus low-power laser welding: Welding is performed using a defocus amount of -1 to -2 mm and a laser power of 8 to 10 kW, with the spot energy density controlled at 200 to 300 W / mm². 2 The welding speed is 2 ± 0.05 m / min;

[0014] Hot wire laser welding: During the welding process, a current of 28-30A is applied to the front section of the welding wire for preheating, so that the temperature of the front section of the welding wire rises to 300-400℃;

[0015] Short-time induction annealing: After welding, the weld is induction heated to raise the temperature to 700±5℃ within 10 to 12 seconds and then held at that temperature.

[0016] Pre-rolling induction heating: Before cold continuous rolling of welded stainless steel, a medium-frequency induction coil is used to heat the weld area to 50-65°C.

[0017] Coordinated adjustment of rolling parameters: The parameters of the five-stand continuous rolling mill are dynamically adjusted according to the workshop temperature. When the workshop temperature is ≥0℃, the reduction rate of the first stand is 15% to 20%, and the reduction rate of subsequent stands is increased compared to the first stand. The tension of the first stand is also increased according to the adjusted reduction rate of the first stand to stabilize the bite. When the workshop temperature is <0℃, the reduction rate of the first stand is 18% to 20%, and the reduction rate of subsequent stands is increased compared to the first stand. The tension of the first stand is also increased according to the adjusted reduction rate of the first stand to stabilize the bite. The rolling speed in the weld area is reduced by 20% to 50% compared to the rolling speed when the workshop temperature is ≥0℃.

[0018] In some alternative implementations, during the hot-wire laser welding step, a current of 28–30 A is applied to a region of 0.1 ± 0.01 m in front of the welding wire for preheating.

[0019] In some alternative implementations, rapid heating with a power of 200±5KW is used in the short-time induction annealing step.

[0020] In some alternative implementations, the induction heating step before rolling is performed using a frequency of 10 kHz and a power density of 5–8 kW / m². 2 The intermediate frequency induction coil heats the weld area of ​​the stainless steel and controls the stainless steel to pass through the intermediate frequency induction coil at a speed of 20±1m / min.

[0021] In some alternative implementations, the intermediate frequency induction coil is positioned in front of the No. 3 tension roll of the cold rolling mill.

[0022] In some alternative implementations, during the pre-rolling induction heating step, if the workshop temperature is <0°C, the weld area is heated to 65°C.

[0023] In some optional implementations, the step of coordinating the adjustment of rolling parameters further includes: adjusting the rolling force of each stand according to the adjusted reduction rate of each stand to avoid overload.

[0024] In some optional implementations, the step of coordinating the adjustment of rolling parameters further includes: adjusting the bending roll value of each stand according to the adjusted reduction rate of each stand, so as to avoid plate shape deviation caused by changes in the reduction rate.

[0025] In some alternative implementations, during the negative defocus low-power laser welding step, the defocusing amount is calculated using the following formula based on the stainless steel thickness:

[0026] d = -0.3 × h + 0.2;

[0027] Where d represents the defocusing amount and h represents the stainless steel thickness.

[0028] The main advantages of the technical solution of this invention are as follows:

[0029] The method of improving the low-temperature performance of laser welds of 430 ferritic stainless steel of the present invention achieves a fundamental breakthrough in the low-temperature rollability bottleneck of 430 ferritic stainless steel welds by synergistically optimizing multiple aspects such as welding process control, heat treatment microstructure optimization, pre-rolling temperature compensation, and rolling parameter adjustment. It significantly improves the low-temperature performance of 430 ferritic stainless steel welds, increases the low-temperature impact toughness of 430 ferritic stainless steel welds to above 22J, and significantly reduces the probability of weld cracking of 430 ferritic stainless steel welds in low-temperature environments. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0031] Figure 1A flowchart illustrating a method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel, provided as an embodiment of the present invention;

[0032] Figure 2 This is a SEM image of the grain size and martensite distribution in the weld heat-affected zone obtained using a conventional process in Embodiment 1 of the present invention.

[0033] Figure 3 This is a SEM image of the grain size and martensite distribution in the weld heat-affected zone obtained using the method of the present invention in Embodiment 1 of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] refer to Figure 1 This invention provides a method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel, the method comprising the following steps:

[0037] Negative defocus low-power laser welding: Welding is performed using a defocus amount of -1 to -2 mm and a laser power of 8 to 10 kW, with the spot energy density controlled at 200 to 300 W / mm². 2 The welding speed is 2 ± 0.05 m / min;

[0038] Hot wire laser welding: During the welding process, a current of 28-30A is applied to the front section of the welding wire for preheating, so that the temperature of the front section of the welding wire rises to 300-400℃;

[0039] Short-time induction annealing: After welding, the weld is induction heated to raise the temperature to 700±5℃ within 10 to 12 seconds and then held at that temperature.

[0040] Pre-rolling induction heating: Before cold continuous rolling of welded stainless steel, a medium-frequency induction coil is used to heat the weld area to 50-65°C.

[0041] Coordinated adjustment of rolling parameters: The parameters of the five-stand continuous rolling mill are dynamically adjusted according to the workshop temperature. When the workshop temperature is ≥0℃, the reduction rate of the first stand is 15% to 20%, and the reduction rate of subsequent stands is increased compared to the first stand. The tension of the first stand is also increased according to the adjusted reduction rate of the first stand to stabilize the bite. When the workshop temperature is <0℃, the reduction rate of the first stand is 18% to 20%, and the reduction rate of subsequent stands is increased compared to the first stand. The tension of the first stand is also increased according to the adjusted reduction rate of the first stand to stabilize the bite. The rolling speed in the weld area is reduced by 20% to 50% compared to the rolling speed when the workshop temperature is ≥0℃.

[0042] The mechanism of a method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel, provided by an embodiment of the present invention, is explained below:

[0043] (1) The adjustment of laser power needs to take into account both welding speed and penetration depth requirements. The adjustment of defocusing amount directly affects the shape of the weld and the stability of the molten pool. By adjusting the defocusing amount to a negative defocusing of -1 to -2 mm, the energy density can be increased to 200 to 300 W / mm. 2 On the one hand, this can increase the penetration depth, and on the other hand, it can compress the width of the weld heat-affected zone (HAZ). Simultaneously, using an 8-10 kW laser power reduces the overall heat input. In this embodiment of the invention, negative defocus low-power laser welding, through energy density control and heat input optimization, can significantly improve the low-temperature crack resistance of 430 stainless steel welds. The specific working principle is as follows:

[0044] Using a negative defocus of -1 to -2mm can increase the spot energy density from 150W / mm 2 Increased to 200-300W / mm 2 While maintaining the melting depth, reducing the laser power to 8-10 kW can reduce heat input by 30%-40%. According to the Rosenthal heat source model, the cooling rate can be reduced from 10 kW to 10 kW. 4 The temperature / s scale decreased to the order of 10. 3 ℃ / s, which prolongs the transformation time window from austenite to ferrite and inhibits the formation of martensite;

[0045] High energy density intensifies the flow of the molten pool, refines the solidification structure, and reduces the grain size of the weld heat-affected zone from over 200 μm to 50–80 μm. The total area of ​​grain boundaries increases by 3–4 times, effectively hindering crack propagation. The hardness of the fusion line decreases from 380–450 HV to 280–320 HV, the gradient distribution becomes gentler, and the local stress concentration factor is reduced.

[0046] Low-power welding reduced the peak temperature from 1100℃ to 950-1000℃, avoiding the austenite stability region. The critical cooling rate was reduced from 15℃ / s to 8℃ / s, and the amount of martensite transformation was reduced by more than 60%. Observation by transmission electron microscopy showed that the size of grain boundary precipitates was refined from 50-80nm to 10-20nm.

[0047] (2) In traditional laser welding processes, the rapid cooling rate during the welding of 430 stainless steel leads to coarse grains, martensitic formation, and significant residual stress in the heat-affected zone. In this embodiment of the invention, by applying an external power source to the front section of the welding wire and preheating it with a current of 28–30 A during welding, the temperature of the front section of the welding wire rises to 300–400°C. This reduces the cooling rate of the weld without significantly increasing the overall heat input, improves the weld's microstructure, and enhances its toughness and crack resistance. The specific working principle is as follows:

[0048] Preheating the welding wire replenishes heat to the molten pool, slows down the weld cooling rate, inhibits the formation of hard and brittle phases such as martensite, promotes ferrite transformation, and improves weld toughness.

[0049] By achieving a uniform temperature distribution in the molten pool, the temperature gradient between the weld and the base material is reduced, thermal stress concentration is alleviated, and the risk of low-temperature cracking is decreased.

[0050] Preheating improves the melting efficiency of the welding wire and the fluidity of the molten pool, promotes gas escape and the floating of inclusions, reduces defects such as porosity and lack of fusion, and improves the density of the weld.

[0051] (3) In this embodiment of the invention, to address the low-temperature cracking problem of 430 stainless steel welds, short-time induction annealing is employed. After welding, the weld is induction heated to 700±10℃ within 10-12 seconds and held at that temperature. Utilizing the critical annealing characteristics of ferritic stainless steel, martensite decomposition and stress release are triggered in a short time, while simultaneously inhibiting grain coarsening and improving the low-temperature toughness of the weld. The specific working principle is as follows:

[0052] At around 700℃, the martensite is activated and decomposed into ferrite and carbides, and the hardness decreases from 380-450HV to 280-320HV.

[0053] Short-term heating (10-12 seconds) forms an "incompletely annealed" structure, retaining some fine carbide reinforcing phases to balance hardness and toughness;

[0054] At around 700℃, the yield strength of the material drops to 120MPa, and the residual stress in the weld (peak value 280MPa) is released by 40% to 50% through plastic deformation, thus reducing the stress concentration factor.

[0055] Synergistic effects with negative defocus low-power laser welding and hot wire laser welding: When used in conjunction with negative defocus low-power laser welding, it can reduce martensite formation through low heat input and further eliminate residual hard phases through annealing; when used in conjunction with hot wire laser welding, it can reduce the cooling rate by preheating the welding wire and then supplement stress release through annealing, forming a "two-stage regulation".

[0056] (4) In this embodiment of the invention, pre-rolling induction heating is used, specifically, before cold continuous rolling of the welded stainless steel, a medium-frequency induction coil is used to heat the weld area to 50-65°C. This can rapidly increase the temperature of the weld area to exceed the ductile-brittle transition temperature (DBTT) of the material, restore its plastic deformation capacity, and at the same time reduce the temperature stress during the rolling process, avoiding low-temperature cracking. The specific working principle is as follows:

[0057] The ductile-brittle transition temperature of 430 stainless steel is approximately -20℃ to 0℃. When heated to above 50℃, the material's plasticity is significantly restored, and the elongation increases from 8% at low temperatures to 15%. Increased temperature reduces dislocation slip resistance, enhances deformation compatibility in the weld area, and reduces stress concentration during rolling.

[0058] Heating allows residual stress in the weld to be released through thermal expansion. Finite element simulations show that heating to 50°C can eliminate about 30% of the residual welding stress, and the stress release rate reaches 60% after adding pre-rolling tension.

[0059] (5) In this embodiment of the invention, by coordinating the rolling parameters of the five-stand continuous rolling mill, the reduction rate of the first stand is first reduced, which can disperse stress and reduce the instantaneous stress borne by the weld area in the initial rolling stage. Especially in low-temperature environments and when the material has poor plasticity, it can effectively reduce the risk of crack initiation. The deformation is transferred to the subsequent stands (such as increasing the reduction rate of the intermediate stands), which allows the weld to gradually adapt to deformation and avoids cracking caused by concentrated stress. Considering that an excessively small reduction rate of the first stand may lead to insufficient front tension, affecting the stability of the strip and even causing defects such as steel piling or narrowing, and may also cause poor strip shape, the tension of the first stand is adjusted on the basis of adjusting the stand reduction rate to ensure stable strip bite and stable tension between stands, and to avoid fracture caused by sudden tension changes when the weld passes through. At the same time, for low-temperature environments (workshop temperature < 0℃), the rolling speed of the weld area is reduced by 20%-50%, which can prolong the residence time of the weld in the rolling mill and reduce dynamic impact stress.

[0060] The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel provided in this invention achieves synergistic optimization and adjustment from multiple aspects, including welding process control, heat treatment microstructure optimization, pre-rolling temperature compensation, and rolling parameter adjustment. This fundamentally breaks through the low-temperature rollability bottleneck of 430 ferritic stainless steel welds, significantly improves their low-temperature performance, and can increase the low-temperature impact toughness of 430 ferritic stainless steel welds to above 22J, significantly reducing the probability of weld cracking in 430 ferritic stainless steel welds under low-temperature conditions.

[0061] Furthermore, in this embodiment of the invention, in the hot wire laser welding step, a current of 28 to 30 A is applied to the area of ​​the front 0.1 ± 0.01 m of the welding wire for preheating.

[0062] In this embodiment of the invention, in the hot-wire laser welding step, the heating area and heating current of the welding wire are specifically calculated and determined based on actual conditions, taking into account factors such as contact resistance, heating power efficiency, convection and radiation losses, and molten pool fusion requirements.

[0063] Furthermore, in this embodiment of the invention, in the short-time induction annealing step, a power of 200±5KW is used for rapid heating.

[0064] In this embodiment of the invention, by using 200±5KW power for rapid heating in the short-time induction annealing step, the growth of austenite grains can be suppressed, the grain size of the weld heat-affected zone can be stabilized at 80-100μm, and the grain boundary area can be increased by 20%.

[0065] Furthermore, in this embodiment of the invention, in the pre-rolling induction heating step, a frequency of 10kHz and a power density of 5-8kW / m are used. 2 The intermediate frequency induction coil heats the weld area of ​​the stainless steel and controls the stainless steel to pass through the intermediate frequency induction coil at a speed of 20±1m / min.

[0066] In this embodiment of the invention, by using the above-mentioned medium-frequency induction coil to heat the weld area of ​​stainless steel and controlling the speed at which the stainless steel passes through the medium-frequency induction coil, it is possible to ensure that the weld area of ​​stainless steel is heated to above 60°C, and to ensure that the weld temperature is not lower than 50°C when the stainless steel enters the rolling mill.

[0067] Specifically, in order to facilitate heating and ensure that the weld temperature is not lower than 50°C when the heated stainless steel enters the rolling mill, the medium frequency induction coil is set in front of the No. 3 tension roll of the cold continuous rolling mill.

[0068] Furthermore, in this embodiment of the invention, in the pre-rolling induction heating step, if the workshop temperature is <0°C, the weld area is heated to 65°C.

[0069] In this embodiment of the invention, when the workshop temperature is <0℃, heating the weld area to 65℃ can ensure that the weld temperature is not lower than 50℃ when the stainless steel enters the rolling mill.

[0070] Furthermore, in this embodiment of the invention, the step of coordinating the adjustment of rolling parameters further includes: adjusting the rolling force of each stand according to the adjusted reduction rate of each stand, so as to avoid overload.

[0071] Furthermore, in this embodiment of the invention, the step of coordinating the adjustment of rolling parameters further includes: adjusting the bending roll value of each stand according to the adjusted reduction rate of each stand, so as to avoid plate shape deviation caused by the change in reduction rate.

[0072] Specifically, in this embodiment of the invention, the rolling force of each stand is calculated and determined according to the actual situation to avoid overload. The bending roll value of each stand is calculated and determined according to the actual situation to avoid sheet shape deviation caused by changes in the reduction rate.

[0073] Furthermore, in this embodiment of the invention, in the step of negative defocus low-power laser welding, the defocusing amount is calculated based on the stainless steel thickness using the following formula:

[0074] d = -0.3 × h + 0.2;

[0075] Where d represents the defocusing amount and h represents the stainless steel thickness.

[0076] Specifically, when the calculated defocus amount is greater than -1, the value is -1; when the calculated defocus amount is less than -2, the value is -2.

[0077] In this embodiment of the invention, by dynamically adjusting the decoking amount according to the thickness of the stainless steel, the problem of precise energy density control under multiple thickness conditions can be solved, and the problems of overheating of thin plates and insufficient melting depth of thick plates can be prevented.

[0078] To make the above technical solutions of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0079] Example 1

[0080] In this embodiment 1, a five-stand continuous rolling mill is used to weld and continuously cold roll 430 ferritic stainless steel with a thickness of 4.5 mm.

[0081] Specifically, in this embodiment 1, the welding process parameters and rolling parameters are set as follows:

[0082]

[0083]

[0084] The remaining rolling parameters are set as follows:

[0085] When the workshop temperature is ≥0℃:

[0086]

[0087] When the workshop temperature is <0℃:

[0088]

[0089] refer to Figure 2-3 , Figure 2 The image shows the SEM (Scanning Electron Microscope) image of grain size and martensite distribution in the weld heat-affected zone obtained using conventional processes in Embodiment 1 of the present invention. Figure 3 This is a SEM image of the grain size and martensite distribution in the weld heat-affected zone obtained using the method of the present invention in Example 1 of this invention. In this Example 1, based on the parameters set above, when welding and continuously cold rolling 4.5mm thick 430 ferritic stainless steel using a five-stand continuous rolling mill, the low-temperature cracking rate of the weld decreased from 2.6 times / month to less than 1 time / month, the overall performance improved by more than 40%, the cupping qualification rate increased from 10% to 95%, the -10℃ low-temperature impact toughness increased from 5-10J to 22J, approaching the level of the base material, the grain size in the weld heat-affected zone was refined from more than 200μm to 50-80μm, the martensite content was significantly reduced, and the fusion line hardness decreased from 380-450HV to 280-320HV, which is closer to the 190-220HV of the base material, and the hardness gradient is gentler.

[0090] Assuming an average coil weight of approximately 15 tons for 430 stainless steel, a marginal contribution of 350 yuan / ton, and a 430 production capacity of 50 tons / hour for the RAP line, the benefit from reduced downtime is 350 * 50 * (13 - 5) = 140,000 yuan. Each downtime results in at least two coils of overheated or over-acidified coils, with a loss of 2,000 yuan / ton, resulting in a loss reduction of (2.6 - 1) * 15 * 2,000 = 48,000 yuan. During downtime, the unit experiences significant waste in gas, electricity, water, and steam, resulting in a loss reduction of at least 300,000 yuan / month. The total monthly loss reduction is at least 488,000 yuan, generating an annual benefit of 5,856,000 yuan.

[0091] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the terms "front," "back," "left," "right," "upper," and "lower" in this document refer to the placement shown in the accompanying drawings.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel, characterized in that, include: Negative defocus low-power laser welding: Welding is performed using a defocus amount of -1 to -2 mm and a laser power of 8 to 10 kW, with the spot energy density controlled at 200 to 300 W / mm². 2 The welding speed is 2 ± 0.05 m / min; Hot wire laser welding: During the welding process, a current of 28-30A is applied to the front section of the welding wire for preheating, so that the temperature of the front section of the welding wire rises to 300-400℃; Short-time induction annealing: After welding, the weld is induction heated to raise the temperature to 700±5℃ within 10 to 12 seconds and then held at that temperature. Pre-rolling induction heating: Before cold continuous rolling of welded stainless steel, a medium-frequency induction coil is used to heat the weld area to 50-65°C. Coordinated adjustment of rolling parameters: The parameters of the five-stand continuous rolling mill are dynamically adjusted according to the workshop temperature. When the workshop temperature is ≥0℃, the reduction rate of the first stand is 15% to 20%, and the reduction rate of subsequent stands is increased compared to the first stand. The tension of the first stand is also increased according to the adjusted reduction rate of the first stand to stabilize the bite. When the workshop temperature is <0℃, the reduction rate of the first stand is 18% to 20%, and the reduction rate of subsequent stands is increased compared to the first stand. The tension of the first stand is also increased according to the adjusted reduction rate of the first stand to stabilize the bite. The rolling speed in the weld area is reduced by 20% to 50% compared to the rolling speed when the workshop temperature is ≥0℃.

2. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 1, characterized in that, In the hot wire laser welding process, a current of 28–30 A is applied to the area of ​​the first 0.1 ± 0.01 m of the welding wire for preheating.

3. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 1, characterized in that, In the short-time induction annealing step, rapid heating is performed using a power of 200±5KW.

4. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 1, characterized in that, In the pre-rolling induction heating step, a frequency of 10kHz and a power density of 5–8kW / m are used. 2 The intermediate frequency induction coil heats the weld area of ​​the stainless steel and controls the stainless steel to pass through the intermediate frequency induction coil at a speed of 20±1m / min.

5. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 4, characterized in that, The medium-frequency induction coil is placed in front of the No. 3 tension roll of the cold rolling mill.

6. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 1 or 5, characterized in that, In the pre-rolling induction heating step, if the workshop temperature is <0℃, the weld area is heated to 65℃.

7. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 1, characterized in that, The step of coordinating the adjustment of rolling parameters also includes: adjusting the rolling force of each stand according to the adjusted reduction rate of each stand in order to avoid overload.

8. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 1, characterized in that, The step of coordinating the adjustment of rolling parameters also includes: adjusting the bending roll value of each stand according to the adjusted reduction rate of each stand, so as to avoid plate shape deviation caused by changes in the reduction rate.

9. The method for improving the low-temperature performance of laser welds in 430 ferritic stainless steel according to claim 1, characterized in that, In the negative defocus low-power laser welding process, the defocusing amount is calculated based on the stainless steel thickness using the following formula: d = -0.3 × h + 0.2; Where d represents the defocusing amount and h represents the stainless steel thickness.

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