A welding wire for thick-gauge ultra-high-strength steel and a welding method thereof

Abstract

The application discloses a kind of anti cold crack welding wire for thick gauge super high strength steel and welding method thereof, belong to welding technical field, construct the low-cost alloy system with Mn as leading, Cr is auxiliary, using Mn reduces Ms point, Cr hardenability promotion, the Ms point of weld metal is regulated to 100~150 ℃ low-temperature phase change interval;In the welding process, by controlling the temperature between tracks is always higher than Ms point, so that each layer of weld in filling process all maintain austenite state, all welds uniform cooling synchronous low-temperature martensite phase change occurs, avoid early phase change of first weld weld and lead to pressure stress relaxation and retain part residual austenite.The application utilizes the characteristics of medium Mn alloy system, effectively avoids the risk of cold crack in thick plate high restraint welding, ensures that weld metal has super high strength while significantly reducing alloy cost, so as to break through the technical bottleneck of thick gauge super high strength steel in low-cost efficient welding application.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a cold-cracking resistant welding wire for thick-gauge ultra-high-strength steel and its welding method. Background Technology

[0002] Ultra-high strength steel (UHSW) is an ideal material for large-scale national defense equipment and critical infrastructure due to its superior impact and penetration resistance, as well as its simple and low-cost production process. However, after welding, UHSW forms highly hardened, hydrogen-sensitive martensite in the heat-affected zone (HAZ) near the fusion zone. This region experiences high tensile stress and localized high hydrogen concentration, leading to an extremely high tendency for cold cracking. Particularly with increasing thickness, the restraint of UHSW joints and the amount of weld filler increase, exacerbating the cold cracking problem. This has become a bottleneck for the widespread application of thick-gauge UHSW.

[0003] Currently, preheating, post-heat treatment, and the use of austenitic welding materials are the main measures to suppress cold cracking in ultra-high strength steel welding. However, most technologies are mainly aimed at levels below 1000MPa, while 1700MPa grade steel has extremely high thermal sensitivity and cold cracking tendency, making existing conventional heat input windows unsuitable and easily leading to cracking failure. For example, invention patent CN116329715B discloses an austenitic welding wire and welding method suitable for high-strength steel structures, aiming to improve the forming quality and toughness of austenitic welding materials through the combination of Ar-He-N2-O2 multi-element protective gas; however, it is aimed at 800MPa grade high-strength steel, forming an extremely low strength match with 1700MPa base material, severely restricting the load-bearing capacity of the joint and failing to leverage the material advantages of ultra-high strength steel.

[0004] In addition, the invention patent with publication number CN119115152A discloses a root welding method for thick high-strength steel under high restraint conditions. It adopts a process route of "preheating at 140~180℃ + post-weld heat treatment" and combines current and voltage control to avoid root cold cracking. Although it is designed for thick ultra-strong steel, it relies excessively on strict preheating and post-weld heat treatment. For large thick plate structures in the field, this not only greatly increases energy consumption and cost, but also seriously slows down the construction progress, resulting in poor engineering practicality.

[0005] Based on the above problems, a cold crack resistant welding wire for 1700MPa grade ultra-high strength steel and its welding method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a cold-cracking resistant welding wire for thick-gauge ultra-high-strength steel and its welding method, so as to solve the problems in the background art.

[0007] To achieve the above objectives, the present invention provides a cold-cracking resistant welding wire for thick-gauge ultra-high-strength steel, comprising the following components by weight percentage: C: 0.05%~0.3%, Mn: 3%~7%, Cr: 3%~10%, Ni: 0~1%, Si: 0~2%, Mo: 0~2%, balance Fe and unavoidable impurities.

[0008] Preferably, the diameter of the welding wire is 1mm to 1.4mm.

[0009] This invention also provides a method for welding thick-gauge ultra-high-strength steel using the aforementioned anti-cold-cracking welding wire, comprising the following steps: S1. Process the bevel on the ultra-high strength steel plate to be welded; S2. Mechanically grind the bevel obtained in S1 and the area within at least 20mm on both sides (e.g., using a grinding wheel or angle grinder) until the metal luster is exposed. Thoroughly remove the scale, rust and primer from the bevel. Then clean with an organic solvent and dry. S3. At room temperature, the gas metal arc welding method is used, and multi-layer and multi-pass welding is performed using anti-cold crack welding wire. No preheating is performed before welding, and no hydrogen removal or stress relief heat treatment is performed after welding. The welding is air-cooled to room temperature.

[0010] Preferably, in S1, the welding tensile strength of the ultra-high strength steel plate is 1700MPa and the thickness is 35mm~80mm.

[0011] Preferably, the thickness of the ultra-high strength steel plate is 40mm~60mm.

[0012] Preferably, in S1, the bevel is a narrow V-shaped bevel with a bevel angle of 40°~50°, a blunt edge of 2~4mm, and a root gap of 0~2mm. This design aims to reduce the amount of filler metal while ensuring root fusion and creating a high restraint stress environment to simulate extreme working conditions. This type of bevel gives the welded joint a high degree of restraint, making thick-gauge ultra-high-strength steel highly susceptible to hydrogen-induced cracking.

[0013] Preferably, in S2, the organic solvent is anhydrous ethanol or acetone.

[0014] Preferably, in step S3, the shielding gas used for welding is a mixture of argon and carbon dioxide, with a gas flow rate of 20 L / min to 25 L / min.

[0015] Preferably, the volume fraction of carbon dioxide is 20%.

[0016] Preferably, in step S3, during the entire multi-layer, multi-pass welding process, the interpass temperature is controlled to always be higher than the martensitic phase transformation initiation temperature of the weld metal deposited by the welding wire, and is maintained at 150℃~320℃.

[0017] Preferably, based on the aforementioned welding wire composition design, the martensitic phase transformation initiation temperature Ms of the weld metal is controlled to a low-temperature phase transformation range of 100~150℃.

[0018] Preferably, the interpass temperature is monitored in real time by an infrared thermometer. If the previous weld cools to close to 150°C, the next weld is immediately performed. This measure ensures that all welds maintain an austenitic state during the welding process and do not undergo martensitic transformation.

[0019] Preferably, in step S3, the welding parameters are: welding current 220A~280A, arc voltage 24V~30V, welding speed 3mm / s~5mm / s, and single-pass welding heat input controlled between 10kJ / cm~20kJ / cm.

[0020] Preferably, by combining the welding wire with the specific composition mentioned above with a specific process, the resulting weld metal exhibits the following characteristics: The Ms point of the weld metal is controlled to 100℃~150℃; when the welding is completed and the weld is uniformly air-cooled to room temperature, all the accumulated weld beads (from the root pass to the cover pass) undergo low-temperature martensitic phase transformation almost simultaneously; this "synchronous phase transformation" will cause the huge volume expansion effect of the entire weld bead, which will transform the originally dispersed "multi-layer and multi-pass" stress evolution into a concentrated expansion similar to "single-pass welding", generating significant residual compressive stress inside the thick plate, effectively offsetting the restraint tensile stress; During the welding process, the weld metal, which remains in the austenitic state, blocks the migration of hydrogen to the heat-affected zone. After cooling to room temperature, the weld forms a multiphase structure of "lamellar martensite + 10%~60% retained austenite". The retained austenite after cooling continues to play a hydrogen trapping role, thereby effectively reducing the risk of hydrogen-induced cracking in the heat-affected zone.

[0021] Therefore, the present invention provides an anti-cold cracking welding wire for thick-gauge ultra-high-strength steel and its welding method, which has the following beneficial effects: (1) The low-cost alloy design strategy of replacing Ni with Mn is adopted. The characteristic of Mn element to effectively reduce Ms point is utilized to significantly reduce alloy cost and reduce hot crack sensitivity. This removes obstacles to the low cost and large-scale industrial application of high-performance thick-gauge ultra-high strength steel welding.

[0022] (2) The interpass temperature (>Ms point) is maintained by continuous welding heat accumulation. The austenitic state of the weld is maintained by the heat accumulation effect of the welding itself, and the low-temperature martensitic phase transformation is forced to occur synchronously in the cooling stage of the entire weld. This mechanism transforms the dispersed phase transformation process into a concentrated volume expansion effect, forming significant residual compressive stress inside the thick plate joint. Combined with the effective suppression of hydrogen enrichment in the heat-affected zone by the residual austenite formed by the weld, the cold cracking risk of thick 1700MPa grade steel is eliminated.

[0023] (3) The welded joint obtained by using the welding wire and method described in this invention can achieve a tensile strength of more than 1100MPa under the premise of ensuring no cracks. It is significantly better than existing austenitic welding materials and achieves an excellent balance between high strength and high crack resistance of ultra-high strength steel welded joints, which has extremely high engineering practical value.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the shape of the welding test plate processed according to Embodiment 1 of the present invention; Figure 2 This is a cross-sectional view of the weld seam of the welding material in Embodiment 1 of the present invention; Figure 3 This is a SEM image of the weld metal in Embodiment 1 of the present invention; Figure 4 This is an electron backscattering diffraction pattern of the weld metal microstructure in Embodiment 1 of the present invention; Figure 5 This is a thermal expansion curve of the weld metal in Embodiment 1 of the present invention; Figure 6 This is a cross-sectional view of the weld seam of the welding material in Embodiment 2 of the present invention; Figure 7 Here is a SEM image of the weld metal in Embodiment 2 of the present invention; Figure 8 This is an electron backscattering diffraction pattern of the weld metal microstructure in Embodiment 2 of the present invention; Figure 9 This is a thermal expansion curve of the weld metal in Embodiment 2 of the present invention; Figure 10 This is a cross-sectional view of the weld seam of the welding material in Embodiment 3 of the present invention; Figure 11 This is a SEM image of the weld metal in Embodiment 3 of the present invention; Figure 12 This is an electron backscattering diffraction pattern of the weld metal microstructure in Embodiment 3 of the present invention; Figure 13 This is a thermal expansion curve of the weld metal in Embodiment 3 of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0028] This invention constructs a low-cost alloy system with Mn (3%~7%) as the main component and Cr as the auxiliary component. It utilizes the high efficiency of Mn in reducing the martensite initiation phase transformation temperature (Ms point) (its effect in reducing the phase transformation temperature is about twice that of Ni), combined with the hardenability enhancement effect of Cr, to control the Ms point of the weld metal to a low-temperature phase transformation range of 100℃~150℃ under low-cost conditions with low or no Ni. During thick plate welding, by controlling the interpass temperature to remain above the Ms point, each weld bead maintains an austenitic state during the filling process. Upon completion of welding and uniform cooling, all weld beads undergo a synchronized low-temperature martensitic transformation, preventing premature phase transformation in earlier weld beads that could lead to stress relaxation and retaining some residual austenite. Furthermore, the weld seam remaining in an austenitic state for an extended period, with the HAZ also in a martensitic state, helps suppress hydrogen accumulation in the heat-affected zone and reduces local hydrogen concentration in the HAZ.

[0029] Specifically, this invention specifies the use of cold-crack resistant welding wire with a diameter of 1mm to 1.4mm, which, by weight percentage, comprises the following components: C: 0.05%~0.3%, provides martensitic matrix strength and stabilizes austenite; Mn: 3%~7%, core element, Mn can significantly reduce the Ms point to below 150℃, while reducing material costs; Cr: 3%~10%, works with Mn to improve hardenability, enhance corrosion resistance and solid solution strengthening effect; Ni: 0~1%, limits the expensive Ni content, retaining only trace amounts to assist toughness, mainly relying on Mn for its role; Si: 0~2%, deoxidizer, and inhibits carbide precipitation; Mo: 0~2%, improves tempering resistance and high-temperature strength; the balance is unavoidable impurities such as Fe, P or S.

[0030] Through composition design, the martensitic phase transformation initiation temperature Ms of the weld wire deposited metal is controlled to a low-temperature phase transformation range of 100~150℃.

[0031] The aforementioned anti-cold-cracking welding wire is used for welding thick-gauge ultra-high-strength steel plates with tensile strengths reaching 1700 MPa and thicknesses of 35 mm to 80 mm (especially 40 mm to 60 mm). These steel plates, due to their large thickness and extremely high strength, have a restraint degree far exceeding that of conventional thin plates and are extremely sensitive to cold cracking. The welding process includes the following steps: S1. Process a narrow V-shaped bevel on the ultra-high strength steel plate to be welded; the bevel angle is 40°~50°, the blunt edge is 2~4mm, and the root gap is 0~2mm. S2. Mechanically grind the bevel obtained in S1 and the area within at least 20mm on both sides (e.g., using a grinding wheel or angle grinder) until the metal luster is exposed. Thoroughly remove the bevel scale, rust and primer. Then, use anhydrous ethanol or acetone to repeatedly wipe and clean the ground area and blow it dry to ensure that the oil and moisture adsorbed on the surface are completely removed. S3. Under room temperature conditions, the gas metal arc welding method is adopted, and multi-layer, multi-pass welding is performed using anti-cold cracking welding wire. No preheating is performed before welding, and the welding process is air-cooled to room temperature. No hydrogen removal or stress relief heat treatment is performed after welding. The shielding gas is a mixture of argon and carbon dioxide, with a carbon dioxide volume fraction of 20% and a gas flow rate of 20~25L / min. The welding parameters are: welding current 220A~280A, arc voltage 24V~30V, welding speed 3mm / s~5mm / s, and single-pass welding heat input controlled between 10kJ / cm~20kJ / cm.

[0032] Throughout the multi-layer, multi-pass welding process in step S3, an infrared thermometer is used for real-time monitoring to strictly control the interpass temperature, ensuring it remains above the Ms point temperature of the weld metal (i.e., 150℃~320℃). If the previous weld cools to near 150℃, the next weld should be performed immediately. This measure ensures that all weld passes maintain an austenitic state during welding, preventing martensitic transformation.

[0033] The following specific examples demonstrate the effectiveness of the above method in suppressing hydrogen-induced cracking in the welding of extremely thick steel plates with a Mn and Cr composition system.

[0034] Example 1 In this embodiment, two ultra-high strength steel plates with dimensions of 400mm × 200mm × 40mm (thickness) were selected as the base material, with a tensile strength grade of 1700MPa. The chemical composition of the solid welding wire with specific composition is shown in Table 1, and the diameter is 1.2mm. Its design features are high Mn and high Cr, and the mechanical properties of its deposited metal are shown in Table 2.

[0035] Table 1: Chemical Composition

[0036] Table 2: Mechanical Properties

[0037] The specific welding steps are as follows: S1. Process a bevel on the ultra-high strength steel plate to be welded, such as... Figure 1 As shown, the test plate was processed into a single-sided bevel angle of about 22.5° using flame cutting, and the bevel surface was ground with an angle grinder to produce a blunt edge of about 2mm and a root gap of 1mm. Finally, the ground test plates were arranged in position to form a butt joint sample (forming a V-shaped bevel with a total angle of about 45° after assembly).

[0038] S2. Clean the surface of the specimen, the bevel obtained in S1, and the area within at least 20mm on both sides using a grinding wheel and sandpaper. Then clean with alcohol and blow dry to ensure that the oxide film, water, oil, etc. near the bevel surface are completely removed. During welding, after each weld is completed, the weld bead needs to be ground and slag-removed before welding the next weld.

[0039] S3. At room temperature, multi-layer, multi-pass gas metal arc welding (GMAW) is used for welding. During the welding process, an infrared thermometer is used for real-time monitoring to strictly control the interpass temperature between 150℃ and 300℃ (always higher than the predicted Ms point). After each weld is completed, the temperature is maintained using residual heat or auxiliary heating if necessary. The slag is immediately cleaned and the next weld is performed until the entire 40mm deep bevel is filled (approximately 30 passes in total). Welding parameters: welding current 260A, arc voltage 28V, welding speed 4mm / s, corresponding linear energy approximately 12.9kJ / cm, wire extension 20mm, shielding gas 80%Ar + 20%CO2, gas flow rate 25L / min.

[0040] After welding, the specimens were air-cooled to room temperature without post-weld heat treatment. The specimens were then left to stand at room temperature for 48 hours to fully induce potential hydrogen-induced delayed cracking. The chemical composition of the formed weld metal was analyzed, and the results are shown in Table 3.

[0041] Table 3: Chemical composition of weld metal

[0042] Crack inspection was then performed on the weld cross-section, such as... Figure 2 As shown, a 40mm thick specimen was cut transversely along the weld. Metallographic observation revealed no microcracks (crack rate 0%) from the root to the cover, interlayer, and heat-affected zone.

[0043] Metallographic samples were taken from the center region of the weld for microscopic analysis. The morphology of the scanned electron micrographs is as follows: Figure 3As shown, the weld metal microstructure consists of lath martensite and irregularly shaped retained austenite distributed within it. The electron backscatter diffraction pattern is as follows: Figure 4 As shown, the retained austenite is uniformly dispersed in the martensitic matrix, and statistics show that the volume fraction of retained austenite is approximately 37.3%.

[0044] Thermal expansion curve as shown Figure 5 As shown, the Ms point of the weld metal was measured to be approximately 105℃. Since the interpass temperature (>150℃) remained consistently higher than the Ms point (105℃), the weld maintained its austenitic state during welding, preventing hydrogen diffusion into the heat-affected zone. During cooling, the volume expansion effect accompanying the low-temperature phase transformation generated some residual compressive stress within the thick plate, which to some extent offset the restraint tensile stress; simultaneously, the 37.3% austenite further mitigated the adverse effects of hydrogen.

[0045] Example 2 The base material used in this embodiment is the same as that in Embodiment 1. The chemical composition of the solid welding wire with specific composition is shown in Table 4. The diameter is 1.2 mm. Its design features are medium Mn and medium Cr, which are intended to improve the strength of the base material and reduce the cost of the alloy. The mechanical properties of its deposited metal are shown in Table 5.

[0046] Table 4: Chemical Composition

[0047] Table 5: Mechanical Properties

[0048] The specific welding steps are the same as in Example 1, except that step S3 is modified as follows: the interpass temperature is controlled between 160℃ and 320℃. Through continuous welding and necessary auxiliary heat preservation, the temperature of any weld bead is ensured not to fall below 160℃ during the filling process, maintaining the austenitic state of all weld beads. This continues until the entire 40mm deep bevel is filled (approximately 30 passes in total). Welding parameters: welding current is 270A, arc voltage is 29V, welding speed is 4.5mm / s, and other parameters are the same as in Example 1.

[0049] After welding, the specimens were air-cooled to room temperature. The chemical composition of the resulting weld metal was analyzed, and the results are shown in Table 6.

[0050] Table 6: Chemical composition of weld metal

[0051] Crack inspection was then performed on the weld cross-section, such as... Figure 6 As shown, a 40mm thick specimen was cut transversely along the weld. Metallographic observation revealed no microcracks (crack rate 0%) from the root to the cover, interlayer, and heat-affected zone.

[0052] Metallographic samples were taken from the center region of the weld for microscopic analysis. The morphology of the scanning electron microscopy images is as follows: Figure 7 As shown, the weld metal microstructure consists of lath martensite and columnar retained austenite distributed between it. The electron backscatter diffraction pattern is as follows: Figure 8 As shown, the retained austenite is uniformly dispersed within the martensite. Statistical analysis indicates that the volume fraction of retained austenite is approximately 21.5%.

[0053] Thermal expansion curve as shown Figure 9 As shown, the Ms point of the weld metal was measured to be approximately 132℃.

[0054] Because the interpass temperature (>160℃) is consistently higher than the Ms point (132℃), the weld remains in an austenitic state during welding, preventing hydrogen diffusion into the heat-affected zone. During cooling, the significant volume expansion effect accompanying the low-temperature phase transformation generates substantial residual compressive stress within the thick plate, offsetting the restraining tensile stress; simultaneously, the 21.5% austenite further mitigates the risk of residual hydrogen.

[0055] Example 2 shows that as the Ms point rises to 132°C, although the austenite content drops to 21.5%, the compressive stress generated by the synchronous phase transformation still completely suppresses the cracking of the 40mm thick plate under high restraint, and the tensile strength of the weld is improved compared with Example 1.

[0056] Example 3 The base material used in this embodiment is the same as that in Embodiment 1. The chemical composition of the solid welding wire with specific composition is shown in Table 7. The diameter is 1.2 mm, and its design features are low Mn, low Cr, and no Ni, aiming to obtain the highest strength and lowest cost. The mechanical properties of its deposited metal are shown in Table 8.

[0057] Table 7: Chemical Composition

[0058] Table 8: Mechanical Properties

[0059] The specific welding steps are the same as in Example 1, except that step S3 is modified to: control the interpass temperature between 180℃ and 320℃, ensuring that the temperature of any weld pass is not lower than 180℃ (an external heat preservation device can be added if necessary) to prevent local phase transformation during welding. Welding parameters: welding current is 280A, arc voltage is 30V, welding speed is 4mm / s, and other parameters are the same as in Example 1.

[0060] After welding, the specimens were air-cooled to room temperature. The chemical composition of the resulting weld metal was analyzed, and the results are shown in Table 9.

[0061] Table 9: Chemical composition of weld metal

[0062] Crack inspection was then performed on the weld cross-section, such as... Figure 10 As shown, a 40mm thick specimen was transversely cut along the weld seam. Metallographic observation revealed no microcracks (crack rate 0%) from the root to the capping layer, interlayer, and heat-affected zone. This indicates that the specimen can effectively suppress hydrogen-induced cracking under preheating conditions for a 40mm thick plate. The method of this invention remains effective even under conditions of extremely low cost and relatively high Ms point.

[0063] Metallographic samples were taken from the center region of the weld for microscopic analysis, and their morphology as shown in the scanning electron microscope images are as follows. Figure 11 As shown, the weld metal microstructure consists of lath martensite and retained austenite distributed within it. The electron backscatter diffraction pattern is as follows: Figure 12 As shown, the retained austenite is uniformly dispersed within the martensitic matrix. Statistical analysis indicates that the volume fraction of retained austenite is approximately 11.7%.

[0064] Expansion curve as shown Figure 13 As shown, the Ms point of the weld metal is approximately 148°C. Given the relatively low austenite content (11.7%) leading to a relatively weakened hydrogen fixation capacity, this embodiment primarily relies on the significant phase transformation volume expansion effect occurring at 148°C. Due to the strict synchronous phase transformation control, the compressive stress generated throughout the weld becomes the main factor in crack resistance.

[0065] In summary, Example 3 verifies that under the extreme conditions of low alloy and high phase transformation temperature, the present invention can overcome the adverse effects of low austenite content and achieve crack-free welding of low-cost welding materials on 40mm thick plates by generating large phase transformation expansion stress through synchronous phase transformation process.

[0066] As can be seen from the above embodiments 1-3, the cold crack resistant welding wire and welding method for 1700MPa grade thick ultra-high strength steel protected by this invention successfully breaks through the dependence of traditional high-strength welding materials on expensive nickel elements, and achieves a highly competitive low-cost welding crack resistant technology. By synergistically adjusting the content of alloying elements such as Mn and Cr and the "synchronous phase transformation" welding process, the strength and toughness of the weld and the manufacturing cost can be flexibly balanced.

[0067] When the focus is on achieving higher toughness and hydrogen capture effect (as in Example 1), higher Mn and Cr contents can be designed to obtain a lower phase transformation temperature and a high proportion of retained austenite. When the focus is on achieving the ultimate joint strength and the lowest alloy cost (as in Example 3), the phase transformation temperature can be increased by appropriately reducing the alloy input, and the phase transformation volume expansion effect can be used to dominate the crack resistance mechanism. However, regardless of the component ratio used, as long as the low-cost alloy system and interpass temperature control (synchronous phase transformation) technical characteristics defined in this invention are followed, efficient, low-cost, and crack-free welding of 1700MPa grade thick ultra-high strength steel can be achieved under thick plate, preheating-free, and high-constraint conditions.

[0068] Therefore, this invention provides an anti-cold cracking welding wire for thick ultra-high strength steel and its welding method. Through the synergistic effect of "low-cost alloy design" and "synchronous phase transformation process control," it effectively overcomes the technical bottleneck of welding 1700MPa-grade thick ultra-high strength steel. In terms of process, it breaks through the limitation of traditional welding requiring interpass cooling. It adopts a continuous multi-layer, multi-pass welding process, utilizing the preheating effect of each layer to ensure that the interpass temperature remains above the Ms point, ensuring that the weld is in an austenitic state during welding, thus constructing a "hydrogen barrier" to prevent hydrogen migration to the heat-affected zone. In terms of microstructure control, it achieves synchronous evolution of the weld microstructure; after welding, the entire weld undergoes a low-temperature martensitic phase transformation synchronously during the cooling stage. The compressive stress generated by the phase transformation expansion offsets the restraining tensile stress, while simultaneously preventing hydrogen diffusion from the weld to the heat-affected zone. Furthermore, the residual austenite further mitigates the adverse effects of hydrogen, reducing the risk of hydrogen-induced cracking in the heat-affected zone. This provides reliable technical support for meeting the special requirements of national defense equipment and key protective facilities for welding thick ultra-high strength steel plates.

[0069] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for welding thick-gauge ultra-high-strength steel using anti-cold-cracking welding wire, characterized in that, Includes the following steps: S1. Process a bevel on the ultra-high strength steel plate with a tensile strength of 1700MPa and a thickness of 35mm~80mm to be welded. S2. Mechanically grind the bevel obtained in S1 and the area within at least 20mm on both sides until a metallic luster is exposed, then clean with an organic solvent and dry. S3. Under room temperature conditions, the gas metal arc welding method is used, and multi-layer, multi-pass welding is performed using anti-cold cracking welding wire. The anti-cold cracking welding wire, by mass percentage, includes the following components: C: 0.05%~0.3%, Mn: 3.52%~7%, Cr: 3%~10%, Ni: 0~1%, Si: 0~2%, Mo: 0~2%, with the balance being Fe. The martensitic transformation initiation temperature of the weld metal is controlled to a low temperature range of 100℃~150℃. No preheating is performed before welding. During the entire process of multi-layer and multi-pass welding, the temperature between passes is controlled to always be higher than the martensitic transformation temperature of the weld metal and maintained at 150℃~320℃. No hydrogen removal or stress relief heat treatment is performed after welding; the material is air-cooled to room temperature.

2. The welding method according to claim 1, characterized in that: The diameter of the welding wire is 1mm to 1.4mm.

3. The welding method according to claim 1, characterized in that: In S1, the bevel is a narrow V-shaped bevel with a blunt edge of 2-4 mm, a bevel angle of 40°-50°, and a root gap of 0-2 mm.

4. The welding method according to claim 1, characterized in that: In S2, the organic solvent is anhydrous ethanol or acetone.

5. The welding method according to claim 1, characterized in that: In step S3, the shielding gas used for welding is a mixture of argon and carbon dioxide, with a gas flow rate of 20 L / min to 25 L / min.

6. The welding method according to claim 1, characterized in that: In S3, the welding parameters are: welding current 220A~280A, arc voltage 24V~30V, welding speed 3mm / s~5mm / s, and single-pass welding heat input controlled between 10kJ / cm~20kJ / cm.

Images