High-strength martensitic stainless steel welding method based on dual-laser collaborative oscillation scanning

Abstract

The invention discloses a high-strength martensitic stainless steel welding method based on dual-laser collaborative oscillation scanning, which is used for welding two workpieces to be welded, at least one of the workpieces to be welded is high-strength martensitic stainless steel, and the method comprises the following steps: carrying out heat treatment on the high-strength martensitic stainless steel, the high-strength martensitic stainless steel comprises, by mass, 0.5% < = C < = 1.1%, 11.0% < = Cr < = 18.0%, 0.5% < = Mo < = 1.2%, 0.1% < = V < = 0.35%, 0.35% < = Mn < = 0.5%, 0.35% < = Si < = 0.45% and the balance Fe. Performing oscillation scanning welding on the two to-be-welded workpieces which are butted, mounted and fixed through first oscillation laser; and laser oscillation scanning in-situ heat treatment is carried out on a hardened area in the weld joint heat affected area through second oscillation laser. By means of the method, the defect problem that high-strength martensitic stainless steel is extremely prone to having welding cracks, hardened areas and the like due to high strength can be avoided, meanwhile, the welding process is simplified, the welding efficiency is improved, and the mechanical property is guaranteed.

Description

Technical Field

[0001] This application relates to the field of laser welding technology for high-strength martensitic stainless steel, and in particular to a welding method for high-strength martensitic stainless steel based on dual-laser coordinated oscillation scanning. Background Technology

[0002] The demand for dissimilar metal welded joints is increasing in industries such as aerospace, transportation, shipbuilding, supercritical power plants, and pressure vessels, particularly between low-alloy high-strength steel and stainless steel, as well as between different grades of stainless steel. Currently, gas tungsten inert gas welding (GTAW) is a commonly used process for welding dissimilar stainless steels. However, GTAW suffers from high heat input and low welding efficiency, leading to significant deformation and high residual stress in the weldment. These problems can induce hot cracking, cold cracking, carbon migration, and brittle intermetallic compounds, severely shortening the service life of the welded components. Furthermore, high-strength martensitic stainless steel is typically in a stripped state before welding, followed by stress-relief annealing, quenching, and low-temperature tempering to ensure the mechanical properties of the weld. This process is cumbersome and uncontrollable. If the high-strength martensitic stainless steel is in a quenched state before welding, welding cracks are highly likely to occur during the welding process, or a hardened zone of a certain width may appear near the weld after welding, both of which reduce the service performance of the weld.

[0003] To further improve the reliability of dissimilar stainless steel joints, laser welding has attracted widespread attention due to its inherent advantages. However, the narrow heating area of ​​the laser beam leads to unstable keyhole formation during the welding process, easily resulting in coarse microstructure and porosity. Simultaneously, laser welding demands extremely high assembly precision from the welded components, requiring gaps between parts to be less than 0.2 mm. Therefore, a new technology is urgently needed to shorten the welding process, improve weld performance, and extend the service life of the welded parts while ensuring efficiency. Summary of the Invention

[0004] This application provides a welding method for high-strength martensitic stainless steel based on dual-laser coordinated oscillation scanning, which solves the problem that high-strength martensitic stainless steel is prone to defects such as welding cracks and hardened zones due to its high strength. At the same time, it simplifies the welding process, improves welding efficiency, and ensures mechanical properties.

[0005] The technical solution is as follows: A welding method for high-strength martensitic stainless steel based on dual-laser coordinated oscillation scanning, used for welding two workpieces, at least one of which is high-strength martensitic stainless steel, characterized in that it includes: The high-strength martensitic stainless steel is heat-treated, wherein the mass percentage of the high-strength martensitic stainless steel is: 0.5%≤C≤1.1%, 11.0%≤Cr≤18.0%, 0.5%≤Mo≤1.2%, 0.1%≤V≤0.35%, 0.35%≤Mn≤0.5%, 0.35%≤Si≤0.45%, and the remainder is Fe; The first oscillating laser is used to perform oscillating scanning welding on two workpieces that have been docked, installed and fixed. The hardened zone in the heat-affected zone of the weld is subjected to in-situ heat treatment by laser oscillation scanning using a second oscillating laser.

[0006] Preferably, during the in-situ heat treatment of the hardened zone in the heat-affected zone of the weld by laser oscillation scanning using the second oscillating laser, the surface temperature of the hardened zone is maintained at 500-650℃ for 1-5 minutes.

[0007] Preferably, the specific parameters for the oscillating laser scanning welding are: laser power 2500-4000W, welding speed 25-30mm / s, oscillation frequency 50-100Hz, oscillation amplitude 1-2.5mm, and shielding gas flow rate 20L / min.

[0008] Preferably, the specific parameters of the second oscillating laser are: laser power 1500-2000W, scanning speed 15-20mm / s, oscillation frequency 100-300Hz, oscillation amplitude 2-4mm, and protective gas flow rate 20L / min.

[0009] Preferably, the heat treatment of the high-strength martensitic stainless steel includes quenching followed by low-temperature tempering, specifically: quenching temperature is 1000-1150℃, holding temperature is 5-20 min, and water cooling is performed; tempering temperature is 150-250℃, holding temperature is 2-8 h, and air cooling is performed.

[0010] Preferably, the gap between the two workpieces to be welded that have been connected, installed and fixed is no more than 1 mm.

[0011] Preferably, both the first and second oscillating lasers are performed under inertial protection during the oscillating scanning process.

[0012] Preferably, the first oscillating laser performs oscillating scanning according to one or any two or three of the following modes: transverse oscillation, circular oscillation, or infinite oscillation.

[0013] Preferably, the second oscillating laser performs oscillating scanning according to one or any two or three of the following modes: transverse oscillation, circular oscillation, or infinite oscillation.

[0014] The beneficial effects of the technical solutions provided in some embodiments of this application include at least the following: welding two pre-assembled and fixed workpieces to be welded using a first oscillating laser, wherein at least one workpiece to be welded is high-strength martensitic stainless steel, and the mass percentage of the high-strength martensitic stainless steel is: 0.5%≤C≤1.1%, 11.0%≤Cr≤18.0%, 0.5%≤Mo≤1.2%, 0.1%≤V≤0.35%, 0.35%≤Mn≤0.5%, 0.35%≤Si≤0.45%, with the remainder being Fe; and then performing in-situ heat treatment of the hardened zone in the heat-affected zone of the weld using a second oscillating laser, which can avoid the defects such as welding cracks and hardened zones that are easily caused by the high strength of high-strength martensitic stainless steel, while simplifying the welding process, improving welding efficiency, and ensuring mechanical properties. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the high-strength martensitic stainless steel welding method based on dual-laser coordinated oscillation scanning according to the present invention; Figure 2 This is a schematic diagram of the weld structure shown in this invention; Figure 3 This is a longitudinal section grain morphology diagram of Example 1 of the present invention; Figure 4 This is a schematic diagram of the gradient martensite structure of the present invention; Figure 5 These are cross-sectional microhardness images of Embodiments 1, 2, and Comparative Example 1 of the present invention; Figure 6 This is a microstructure diagram of the weld in Comparative Example 2 of the present invention; Figure 7 Microcracks appeared in the hardened zone in Comparative Example 2 of this invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0018] Example 1 This embodiment provides a high-strength martensitic stainless steel welding method based on dual-laser coordinated oscillation scanning, such as... Figure 1 As shown.

[0019] Pre-welding preparation: Taking a 3 mm thick high-strength martensitic stainless steel as an example, the mass percentage of the high-strength martensitic stainless steel is: C 0.5 wt.%, Cr 11.0 wt.%, Mo 0.5 wt.%, V 0.2 wt.%, Mn 0.4 wt.%, Si 0.4 wt.%, with the remainder being Fe. For example... Figure 2 As shown, in this embodiment, the two workpieces to be welded can be the same type of stainless steel or different types of stainless steel, but at least one of them is a high-strength martensitic stainless steel with the above composition, and stainless steel 2 in this embodiment is also a high-strength martensitic stainless steel. Before welding, the plates to be welded undergo heat treatment. The specific process is as follows: quenching temperature is 1000℃, holding for 5 minutes, followed by water cooling; tempering temperature is 150℃, holding for 2 hours, followed by air cooling. Then, the heat-treated high-strength martensitic stainless steel parts to be welded are ground to remove oxide scale and oil, and the workpieces to be welded are fixed on a fixture to ensure that the gap between the martensitic stainless steel parts to be welded is less than 1mm. Before the first oscillating laser (laser beam 1) oscillates and scans for welding, the high-strength martensitic stainless steel to be welded does not require preheating.

[0020] Laser oscillation scanning welding: A first oscillating laser with a wavelength λ1 of 1064 nm was selected and oscillated along the laser path 1 under inert gas protection for oscillation scanning welding. The laser power was 2500W, the welding speed was 25mm / s, the oscillation frequency was 50Hz, the oscillation amplitude was 1mm, the shielding gas flow rate was 20L / min, and the beam oscillation pattern was circular. The intense stirring effect of the first oscillating laser on the molten pool widened the weld width, increased the solidification rate of the molten pool, reduced the temperature gradient of the molten pool, and simultaneously increased the cooling rate and compositional supercooling, promoting the refinement of columnar crystals and the formation of equiaxed crystals, such as... Figure 3 The image shown is a grain morphology diagram formed after the first oscillating laser scan.

[0021] In-situ oscillating scanning heat treatment: After the first oscillating laser scanning welding is completed, a second oscillating laser (laser beam 2) with a wavelength λ2 of 1064 nm is selected to perform in-situ scanning heat treatment on the hardened zone in the heat-affected zone near the weld under inert gas protection along the oscillating laser path 2. Through the in-situ heat treatment with the second oscillating laser, the hardened zone achieves rapid annealing, reducing its hardness and strength, and avoiding the risk of weld cracking. Figure 4 As shown, Figure 4 The base material to be welded is high-strength martensitic stainless steel. Figure 4 The area on the left side of the middle section represents the hardened zone formed on the inner side of the weld after the first oscillating laser scanning. Figure 4The right side of the image shows the effect of in-situ heat treatment of the hardened zone by oscillating scanning with a second oscillating laser. In-situ heat treatment by oscillating scanning can promote the decomposition and softening of high-strength martensite in the heat-affected zone of the weld, and form a gradient distribution of martensite in the depth direction of the hardened zone of the weldment. By controlling the surface temperature of the hardened zone at 500°C and the in-situ heat treatment time at 1 minute through oscillating scanning with a second oscillating laser, the high-strength martensite in the hardened zone decomposes to different degrees along the depth direction. That is, the gradient distribution of high-strength martensite along the depth direction is tempered sorbite, tempered troostite and tempered martensite in sequence, thereby achieving a gradient distribution of hardness along the depth direction.

[0022] In this embodiment, the temperature and processing time of the hardened area surface can be controlled by controlling the parameters of the second oscillating laser. The specific parameters are: laser power 1500W, welding speed 15mm / s, oscillation frequency 100Hz, oscillation amplitude 2mm, and protective gas flow rate 20L / min.

[0023] In addition, the second oscillating laser oscillation pattern in this embodiment is a horizontal zigzag pattern.

[0024] It should be noted that the wavelength of the first oscillating laser in this embodiment may be the same as or different from that of the second oscillating laser. The oscillating scanning pattern may be the same or different. The first oscillating laser and the second oscillating laser may perform oscillating scanning according to one or any two or three of the following modes: transverse oscillation, circular oscillation, or infinite oscillation.

[0025] Example 2 This embodiment provides a high-strength martensitic stainless steel welding method based on dual-laser coordinated oscillation scanning, which differs from Embodiment 1 in some parameter settings. Specifically: Pre-welding preparation: Taking 3 mm thick high-strength martensitic stainless steel as an example, the mass percentage of the high-strength martensitic stainless steel is: C 0.8 wt.%, Cr 15.0 wt.%, Mo 0.8 wt.%, V 0.2 wt.%, Mn 0.4 wt.%, Si 0.4 wt.%, with the remainder being Fe. Before welding, the plates to be welded are heat-treated. The specific process is as follows: quenching temperature is 1075℃, holding for 10 min, water cooling; tempering temperature is 200℃, holding for 5 h, air cooling. Then, the heat-treated high-strength martensitic stainless steel to be welded is ground to remove oxide scale and oil, and the workpieces to be welded are fixed on a fixture, ensuring that the gap between the high-strength martensitic stainless steel pieces to be welded is less than 1 mm.

[0026] Laser oscillation scanning welding: An oscillating laser with a wavelength λ1 of 1064 nm was selected for oscillation scanning welding. The laser power was 3200W, the welding speed was 28mm / s, the oscillation frequency was 75Hz, the oscillation amplitude was 1.8mm, and the shielding gas flow rate was 20L / min. The beam oscillation pattern was circular.

[0027] In-situ oscillating scanning heat treatment: After the first oscillating laser beam completes the oscillating scanning welding, a second oscillating laser with a wavelength λ2 of 450nm is selected to perform in-situ scanning heat treatment on the hardened zone in the heat-affected zone near the weld. The second oscillating laser is a blue laser. Specific parameters are: laser power 1500W, welding speed 18mm / s, oscillation frequency 200Hz, oscillation amplitude 3mm, and shielding gas flow rate 20L / min. The beam oscillation pattern is a horizontal zigzag pattern.

[0028] By adjusting oscillating laser welding and oscillating laser scanning in-situ heat treatment, and controlling solidification and cooling conditions, a microstructure consisting of fine columnar and equiaxed crystals in the weld was obtained using the first oscillating laser beam. The surface temperature of the hardened zone was controlled at 575℃ using the second oscillating laser beam, with an in-situ heat treatment time of 3 minutes. This induced varying degrees of martensite decomposition along the depth direction in the hardened zone, resulting in a gradient distribution of martensite along the depth direction: tempered sorbite, tempered troostite, and tempered martensite. This achieved a gradient distribution of hardness along the depth direction.

[0029] Example 3 This embodiment provides a high-strength martensitic stainless steel welding method based on dual-laser coordinated oscillation scanning. The difference between this embodiment and Embodiments 1 and 2 lies in some parameter settings. Specifically: Pre-welding preparation: Taking 3 mm thick high-strength martensitic stainless steel as an example, the mass percentage of the high-strength martensitic stainless steel is: C 1.1 wt.%, Cr 18.0 wt.%, Mo 1.2 wt.%, V 0.35 wt.%, Mn 0.4 wt.%, Si 0.4 wt.%, with the remainder being Fe. Before welding, the plates to be welded are heat-treated. The specific process is as follows: quenching temperature is 1150℃, holding for 20 min, water cooling; tempering temperature is 250℃, holding for 8 h, air cooling. Then, the heat-treated high-strength martensitic stainless steel to be welded parts are ground to remove oxide scale and oil, and the workpieces to be welded are fixed on a fixture, ensuring that the gap between the martensitic stainless steel pieces to be welded is less than 1 mm.

[0030] Laser oscillation scanning welding: An oscillating laser with a wavelength λ1 of 1064 nm was selected for oscillation scanning welding. The laser power was 4000W, the welding speed was 30mm / s, the oscillation frequency was 100Hz, the oscillation amplitude was 2.5mm, and the shielding gas flow rate was 20L / min. The beam oscillation pattern was transverse oscillation.

[0031] In-situ oscillating scanning heat treatment: After laser oscillating scanning welding is completed, a second oscillating laser with a wavelength λ2 of 450 nm is selected to perform in-situ scanning heat treatment on the hardened zone in the heat-affected zone near the weld. The second oscillating laser is a blue laser. Specific parameters are: laser power 2000W, welding speed 20mm / s, oscillation frequency 300Hz, oscillation amplitude 4mm, and shielding gas flow rate 20L / min. The beam oscillation pattern is circular.

[0032] By adjusting oscillating laser welding and oscillating laser scanning in-situ heat treatment, and controlling solidification and cooling conditions, the first oscillating laser was used to obtain a weld microstructure composed of fine columnar and equiaxed crystals. A second oscillating laser was then used for in-situ heat treatment, controlling the surface temperature of the hardened zone at 650℃ for 5 minutes. This promoted the decomposition of martensite along the depth direction in the hardened zone, resulting in a gradient distribution of martensite along the depth direction: tempered sorbite, tempered troostite, and tempered martensite. This achieved a gradient distribution of hardness along the depth direction.

[0033] In summary, by vigorously stirring the molten pool, the weld width is widened, the solidification rate of the molten pool is increased, and the temperature gradient of the molten pool is reduced. Simultaneously, the cooling rate and compositional supercooling are improved, promoting the refinement of columnar grains and the formation of equiaxed grains, resulting in a weld with a high proportion of equiaxed grains and finer columnar grains. Subsequently, the hardened zone is immediately subjected to in-situ scanning heat treatment using a second oscillating laser. This modifies the hardened zone in the heat-affected zone into a gradient-distributed martensitic structure, specifically tempered sorbite, tempered troostite, and tempered martensite from the upper to the lower surface of the weldment. The synergistic effect of oscillating laser scanning welding and oscillating laser scanning in-situ heat treatment significantly improves the mechanical properties of the weld and the hardness of the heat-affected zone, effectively solving the problem of cracking in high-strength martensitic welds.

[0034] Meanwhile, based on the relevant process parameters of the second oscillating laser oscillation scanning in-situ heat treatment, the proportion of each tissue in the gradient martensite structure can be adjusted.

[0035] The first oscillating laser scanning welding process eliminates the need for preheating, and the second oscillating laser scanning in-situ heat treatment eliminates the need for further heat treatment. This effectively simplifies the traditional complex welding process, improves manufacturing efficiency, and saves costs and energy. It solves the problems of difficult and costly post-weld heat treatment for high-strength martensitic stainless steel. Simultaneously, the second oscillating laser scanning in-situ heat treatment eliminates the hardened zone in the heat-affected zone, constructs a gradient martensitic structure along the depth direction, and avoids the risk of cracking. It also helps reduce welding thermal stress during the welding process, improves the uniformity of the weldment microstructure, and further ensures the uniformity of hardness and mechanical properties.

[0036] Comparative Example 1 The welding process described in this comparative example differs from that in Example 1 in that, in this comparative example, after the high-strength martensitic stainless steel to be welded is laser oscillation scanning welded, the hardened area is not subjected to in-situ scanning heat treatment by a second oscillating laser.

[0037] After all welding processes are completed, such as Figure 5 As shown, the weld was tested and analyzed. The results showed that the hardened zone near the weld exhibited extremely high hardness, reaching a maximum of 620 HV, which is much higher than the microhardness of the base metal (550 HV).

[0038] Comparative Example 2 The difference between the welding process described in this comparative example and that in Example 1 is that this comparative example does not use oscillating scanning laser welding, but instead uses direct laser welding.

[0039] After all welding processes are completed, the weld seam exhibits a large columnar crystal structure, such as... Figure 6 As shown, the microhardness is relatively low at 400 HV, and microcracks appeared in the hardened area, such as... Figure 7 As shown, the tensile strength of the weld is only 68% of that of the base material.

[0040] Comparative Example 3 The difference between the welding process described in this comparative example and that in Example 1 is that the high-strength martensitic stainless steel to be welded in this comparative example does not undergo any related heat treatment before the first oscillating laser oscillation scanning welding.

[0041] After all welding processes were completed, the weld was tested and analyzed. It was found that the microhardness of the weld reached 620 HV, which is much higher than the 500 HV of the heat-affected zone and the 248 HV of the base material being welded. Tensile tests showed that the tensile strength under this condition was only 65% ​​of that of the weld of the heat-treated sample.

[0042] Comparative Example 4 The difference between the welding process described in this comparative example and that in Example 1 is that a 2000W laser is used for oscillating scanning welding in this comparative example.

[0043] After all welding processes were completed, the weld was tested and analyzed. It was found that the weld joint was not fully penetrated, there was a large gap on the back of the weld, and the tensile strength of the weld joint was only 45.6% of that of the base material.

[0044] Comparative Example 5 The difference between the welding process described in this comparative example and that in Example 1 is that a 5000W laser is used for oscillating scanning welding in this comparative example.

[0045] After all welding processes were completed, the weld was tested and analyzed. It was found that the weld surface had severe depressions and undercut, and there were a lot of spatter particles around the weld, resulting in extremely poor forming effect.

[0046] By comparing the examples and comparative examples, it can be found that the welding method of the present invention can obtain extremely fine columnar and equiaxed crystals, and the oscillating scanning in-situ heat treatment hardened zone can prepare a martensitic structure with a gradient distribution. These properties synergistically improve the strength and plasticity of the weldment. The sample without oscillating laser scanning in-situ heat treatment showed a significant hardened zone, a marked increase in microhardness, and cracks appeared in the hardened zone.

[0047] The above-described specific embodiments are merely illustrative of the principles of the present invention and should not be construed as limiting the scope of protection of the present invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the present invention without any inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for welding two workpieces to be welded by means of a dual laser synergistic oscillation scanning based high strength martensitic stainless steel welding method, wherein at least one of the workpieces to be welded is a high strength martensitic stainless steel, characterized in that, The method comprises: carrying out heat treatment on the high-strength martensitic stainless steel, wherein the high-strength martensitic stainless steel has the following mass percentages: 0.5%≤C≤1.1%, 11.0%≤Cr≤18.0%, 0.5%≤Mo≤1.2%, 0.1%≤V≤0.35%, 0.35%≤Mn≤0.5%, 0.35%≤Si≤0.45%, and the rest is Fe; oscillating and scanning the two workpieces to be welded, which have been abutted, installed and fixed, by a first oscillating laser; carrying out in-situ heat treatment on the hardened zone in the heat affected zone of the weld by oscillating and scanning the hardened zone by a second oscillating laser.

2. The method of claim 1, wherein: During the process of carrying out in-situ heat treatment on the hardened zone in the heat affected zone of the weld by oscillating and scanning the hardened zone by the second oscillating laser, the surface temperature of the hardened zone is maintained at 500-650℃ for 1-5 min.

3. The method according to claim 1 or 2, characterized in that: The specific parameters of the oscillating and scanning welding of the first oscillating laser are as follows: laser power 2500-4000W, welding speed 25-30mm / s, oscillation frequency 50-100Hz, oscillation amplitude 1-2.5mm, and protective gas flow 20L / min.

4. The method of claim 1 or 2, wherein: The specific parameters of the second oscillating laser are as follows: laser power 1500-2000W, scanning speed 15-20mm / s, oscillation frequency 100-300Hz, oscillation amplitude 2-4mm, and protective gas flow 20L / min.

5. The method of claim 1, wherein: The heat treatment on the high-strength martensitic stainless steel comprises quenching and then low-temperature tempering, and the specific process is as follows: quenching temperature 1000-1150℃, holding for 5-20min, and water cooling; tempering temperature 150-250℃, holding for 2-8h, and air cooling.

6. The method of claim 1, wherein, The gap of the two workpieces to be welded, which have been abutted, installed and fixed, is not greater than 1mm.

7. The method of claim 1, wherein: The first oscillating laser and the second oscillating laser are both under inert protection during the oscillating and scanning process.

8. The method of claim 1, wherein, The first oscillating laser oscillates and scans in one or any two or three of the following modes: horizontal oscillation, circular oscillation or infinite oscillation.

9. The method of claim 1, wherein, The second oscillating laser oscillates and scans in one or any two or three of the following modes: horizontal oscillation, circular oscillation or infinite oscillation.

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