Control method for inhibiting hydrogen-induced cracks in welding of ultrahigh-strength steel without heat treatment

Abstract

The invention discloses a heat-treatment-free control method for inhibiting hydrogen-induced cracks in ultrahigh-strength steel welding, which belongs to the technical field of welding, and enables weld metal to obtain a low-phase-transition-temperature characteristic and a double-phase structure containing retained austenite under a specific dilution rate window by cooperatively regulating and controlling components of a welding material and welding process parameters. Therefore, preheating-free and post-heat-treatment-free efficient welding of the ultrahigh-strength steel is achieved. According to the method, the volume expansion effect generated by low-temperature martensite phase transformation of weld metal is utilized to actively counteract restrained tensile stress formed by welding cooling shrinkage; on the other hand, the effect of the retained austenite serving as an efficient'hydrogen trap 'is fully played, migration and enrichment of hydrogen to crack sensitive areas such as a heat affected zone or a fusion line are effectively blocked, and finally effective inhibition of hydrogen-induced cracks in ultrahigh-strength steel welding is achieved; the obtained welding joint is free of hydrogen-induced cracks and has the mechanical property level well matched with base metal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding, in particular to a control method for inhibiting hydrogen-induced cracking of ultra-high strength steel welding without heat treatment. BACKGROUND

[0002] Hydrogen-induced cracking (commonly known as HIC or welding cold cracking) has always been a major challenge in the welding of ultra-high strength steel. In particular, for steel with a tensile strength of 1300 MPa or more, the welding hydrogen-induced cracking tendency is very large, and it is difficult to control in field welding manufacturing. In the welding of some ultra-high strength steel structures, strict preheating, post-weld heat treatment and the use of low-hydrogen welding processes are required according to the specifications, but these requirements are often time-consuming and costly, and in the field environment or super-large structure, these measures are difficult to implement or ineffective. In addition, in the scene where hydrogen is difficult to completely eliminate and the strength of the weld is maintained through martensitic hardened microstructure, the HIC problem is particularly prominent.

[0003] However, the existing technology is mainly limited to welding of 1000 MPa and below, such as the invention patent with publication number CN119243037A, which discloses a new preheat-free welding high-strength steel HPDB700 and its production method; and the arc welding electrode for 1000 MPa high-strength steel preheat-free welding and its preparation method disclosed in publication number CN116586816A, both of which are limited to 1000 MPa and below, and the first method cannot support the strength and toughness required by ultra-high strength steel due to the depleted alloy system, and the second method is subject to low efficiency of manual welding and hydrogen-induced cracking caused by moisture absorption of the coating.

[0004] Therefore, the existing technology is mainly limited to welding of 1000 MPa and below, and there is currently a lack of a control method that can effectively solve the high cold cracking sensitivity and strength-toughness matching of ultra-high strength steel under the stringent conditions of preheat-free and post-weld heat treatment-free for 1300 MPa and above.

[0005] Therefore, in view of the long-term technical problem of hydrogen-induced cracking (HIC) in the welding process of ultra-high strength steel (tensile strength ≥ 1300 MPa), the traditional method relies on preheating, post-weld heat treatment and low-hydrogen process, resulting in high cost, low efficiency and limited applicability, a control method for inhibiting hydrogen-induced cracking of ultra-high strength steel welding without heat treatment is proposed. SUMMARY

[0006] The purpose of the present application is to provide a control method for inhibiting hydrogen-induced cracking of ultra-high strength steel welding without heat treatment to solve the problems in the background art.

[0007] In order to achieve the above-mentioned purpose, the application provides a control method for inhibiting hydrogen-induced cracking of super-high-strength steel welding without heat treatment, which realizes efficient welding of super-high-strength steel without preheating and post-heat treatment by synergistically regulating the composition of welding material and welding process parameters, so that the weld metal obtains low phase change temperature characteristics and contains dual-phase structure of residual austenite under a specific dilution rate window. S1, selecting welding material, the chemical composition of the welding material is as follows in terms of mass percentage: C: 0.03%-0.3%, providing necessary strength basis and austenite stability; Mn: 0.5%-3%, stabilizing austenite and reducing phase change temperature; Cr: 3%-15%, significantly improving hardenability and cooperating with Ni to adjust Ms point; Ni: 5%-15%, core element, greatly reducing Ms point and stabilizing residual austenite; Si: 0.2%-2%, inhibiting carbide precipitation and promoting carbon enrichment in austenite; Mo: 0%-2%, improving high-temperature strength and tempering stability; Cu+V+Ti: 0%-1.1%, micro-alloying elements, used for grain refinement and precipitation strengthening; the balance is Fe and unavoidable impurities; S2, performing beveling and surface cleaning on the super-high-strength steel plate to be welded; S3, welding at room temperature by adopting gas metal arc welding process to obtain a super-high-strength steel welded joint; no preheating before welding and no stress relief annealing or hydrogen removal heat treatment after welding; during the welding process, the welding line energy is controlled to be between 8kJ / cm and 20kJ / cm, and the dilution rate of the molten pool is controlled to be between 20% and 50%.

[0008] Preferably, in S1, the welding material is any one of solid wire, flux-cored wire or arc welding electrode.

[0009] Preferably, in S2, the welding tensile strength of the super-high-strength steel plate is 1300MPa-1700MPa, and the thickness is 5mm-40mm.

[0010] Preferably, in S2, the bevel angle is 60°, and the reserved width gap at the bottom of the bevel is 1.8mm-2.2mm.

[0011] Preferably, in S2, the surface cleaning includes: removing the oxide scale and rust within a range of at least 20mm on both sides of the bevel surface by mechanical polishing until the metal luster is exposed, then wiping and cleaning the polished area with anhydrous ethanol or acetone and blowing dry to completely remove the oil stains and moisture adsorbed on the surface; avoiding the decomposition of surface pollutants due to heating to produce hydrogen, thereby causing the weld diffusion hydrogen content to exceed the standard.

[0012] Preferably, in S3, the gas metal arc welding process adopts argon-rich mixed gas as the protective gas.

[0013] Preferably, the argon-rich mixed gas is a mixture of 80% argon and 20% carbon dioxide by volume.

[0014] Preferably, in the S3, the flow rate of the shielding gas during welding is 20 L / min to 25 L / min, the wire extension length is 18 to 20 mm, and the operation of advancing the gas by 2 s in advance and stopping the gas by 2 s in lag is performed.

[0015] Preferably, in the S3, the welding current is 240 A to 280 A, the welding voltage is 21 V to 24 V, and the welding speed is 3 mm / s to 5 mm / s.

[0016] Preferably, after the base material is fused with the welding material having the above-mentioned composition, the final weld metal formed exhibits the following characteristics during the cooling process: The martensite start transformation temperature (Ms point) of the weld metal is regulated to below 350℃, preferably to 100 to 300℃; this means that the martensite phase change mainly occurs in the low-temperature stage of welding cooling, and the volume expansion of the phase change produced at this time can maximize the offset of the accumulated thermal shrinkage tensile stress; After cooling to room temperature, the weld structure is not full martensite, but retains 3% to 50% volume fraction of residual austenite; the residual austenite is uniformly distributed in the martensite lath in the form of a film or a block, and the average particle size is 10 nm to 50 μm.

[0017] Preferably, in the S3, the tensile strength of the ultra-high strength steel welded joint can reach more than 85% of the tensile strength of the base material, achieving good matching of the joint strength and the base material strength.

[0018] Therefore, the control method for inhibiting hydrogen-induced cracking of ultra-high strength steel welding by heat treatment-free has the following beneficial effects: (1) By matching the welding material composition and the dilution rate process, the application range of the preheating-free and post-welding heat treatment-free welding technology is expanded to the 1300 MPa to 1700 MPa level of ultra-high strength steel.

[0019] (2) By regulating the weld microstructure, the volume expansion effect produced by the low-temperature phase change of martensite is utilized to relieve the high restraint tensile stress produced by welding cooling shrinkage; at the same time, the capture effect of the residual austenite (3% to 50%) in the weld on diffusible hydrogen is utilized to reduce the enrichment degree of diffusible hydrogen in the crack sensitive area; through the above-mentioned synergistic control of "stress" and "hydrogen", the risk of HIC of the ultra-high strength steel welded joint is effectively reduced.

[0020] (3) The method simplifies the welding process and reduces manufacturing cost; without pre-welding preheating and post-welding stress relief heat treatment, the long period and high energy consumption problems caused by heat treatment in the traditional process are avoided; the method is helpful to simplify the production process, especially in the scene of field operation or welding of large structural parts which is difficult to equip heat treatment equipment, and has good engineering practicability and economic benefits.

[0021] The technical solutions of the present application are described in further detail below by means of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A schematic diagram of the shape of the welding test plate processed by the present application; Figure 2 A weld flaw detection surface graph of the welding material used in Example 1 of the present application; Figure 3 A weld cross-sectional view of the welding material used in Example 1 of the present application; Figure 4 An SEM graph of the weld metal microstructure formed in Example 1 of the present application; Figure 5 An electron backscatter diffraction graph of the weld metal microstructure formed in Example 1 of the present application; Figure 6 A thermal expansion curve graph of the weld metal formed in Example 1 of the present application; Figure 7 A weld flaw detection surface graph of the welding material used in Example 2 of the present application; Figure 8 A weld cross-sectional view of the welding material used in Example 2 of the present application; Figure 9 An SEM graph of the weld metal microstructure formed in Example 2 of the present application; Figure 10 An electron backscatter diffraction graph of the weld metal microstructure formed in Example 2 of the present application; Figure 11 A thermal expansion curve graph of the weld metal formed in Example 2 of the present application; Figure 12 A weld flaw detection surface graph of the welding material used in Example 3 of the present application; Figure 13 A weld cross-sectional view of the welding material used in Example 3 of the present application; Figure 14 An SEM graph of the weld metal microstructure formed in Example 3 of the present application; Figure 15 An electron backscatter diffraction graph of the weld metal microstructure formed in Example 3 of the present application; Figure 16A thermal expansion curve of the weld metal formed for the inventive example 3; Figure 17 A weld flaw surface graph of the welding material used for the inventive comparative example 1; Figure 18 A weld section graph of the welding material used for the inventive comparative example 1; Figure 19 An SEM graph of the weld metal microstructure formed for the inventive comparative example 1; Figure 20 An electron backscatter diffraction graph of the weld metal microstructure formed for the inventive comparative example 1; Figure 21 A thermal expansion curve of the weld metal formed for the inventive comparative example 1. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be further described below through the drawings and examples.

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application.

[0025] The present application provides a heat treatment-free hydrogen-induced crack control method for ultra-high strength steel welding, which realizes efficient welding of the ultra-high strength steel with a preheating-free and post-heat treatment-free tensile strength of 1300 MPa to 1700 MPa and a thickness of 5 mm to 40 mm by synergistically regulating the composition of the welding material and the welding process parameters, so that the weld metal obtains a low phase change temperature characteristic and a dual-phase structure containing residual austenite in a specific dilution rate window. S1, any one of the solid welding wire, the flux-cored welding wire or the electric arc welding rod is selected as the welding material, and the chemical composition of the welding material is as follows in terms of mass percentage: C: 0.03% to 0.3%, Mn: 0.5% to 3%, Cr: 3% to 15%, Ni: 5% to 15%, Si: 0.2% to 2%, Mo: 0% to 2%, Cu+V+Ti: 0% to 1.1% (Cu: 0% to 1%, V: 0 to 0.05%, Ti: 0 to 0.05%), and the balance is Fe and inevitable impurities (such as P, S, etc.).

[0026] S2, the super-high strength steel plate to be welded is bevel processed, the angle is 60°, and the reserved width gap at the bottom of the bevel is 1.8 mm to 2.2 mm.

[0027] Before welding, the test piece and the groove need to be strictly cleaned. The oxide scale and rust within a range of at least 20 mm on both sides of the groove surface are removed by mechanical polishing (such as using a grinding wheel or sandpaper) until the metal luster is exposed. Then, the polished area is cleaned and dried with anhydrous ethanol or acetone to completely remove the oil stains and water adsorbed on the surface.

[0028] S3, in a room temperature environment, using a gas shielded arc welding process, using argon-rich mixed gas (80% Ar + 20% CO2) as the protective gas to obtain stable spray transition or pulse transition, to obtain a super high strength steel welded joint; no preheating before welding, and no stress relief annealing or hydrogen removal heat treatment after welding; during welding, the wire extension length is 18-20 mm, the gas is sent 2 s in advance and stopped 2 s later, the protective gas flow is 20-25 L / min, the welding current is 240-280 A, the welding voltage is 21-24 V, and the welding speed is 3-5 mm / s; the welding line energy is controlled to be between 8-20 kJ / cm, and the matching relationship of the welding current, the arc voltage and the welding speed is adjusted to control the dilution rate of the molten pool to be 20%-50%, so as to avoid too high dilution rate (> 50%) caused by large current deep penetration, which introduces too many impurity elements of the base material, or too low dilution rate (< 20%) caused by small current, which causes poor fusion.

[0029] After the above-mentioned welding material and the base material are fused, the final weld metal formed in the cooling process exhibits the following characteristics: The martensite start temperature (Ms point) of the weld metal is controlled to below 350℃, preferably 100-300℃; this means that the martensite transformation mainly occurs in the low temperature stage of welding cooling, and the volume expansion of the phase change at this time can maximize the offset of the accumulated thermal shrinkage tensile stress.

[0030] After cooling to room temperature, the weld structure is not full martensite, but retains 3%-50% volume fraction of residual austenite; the residual austenite is uniformly distributed in the martensite lath in the form of film or block, and the average particle size is 10 nm-50 μm.

[0031] Based on the above welding method and microstructure control, efficient welding of super high strength steel under non-heat treatment conditions is realized, and the obtained welded joint not only has no hydrogen-induced cracks, but also has good mechanical property level matching with the base material; on the one hand, the volume expansion effect of the low-temperature martensite phase change of the weld metal is used to actively offset the restraint tensile stress formed by the welding cooling shrinkage; on the other hand, the role of residual austenite as an efficient "hydrogen trap" is fully played, which effectively blocks the migration and enrichment of hydrogen to the heat affected zone or the fusion line and other crack sensitive areas, and finally realizes the effective inhibition of hydrogen-induced cracks of super high strength steel welding.

[0032] The effectiveness of the above method in inhibiting hydrogen-induced cracking of ultra-high strength steel welding was verified by the "inclined y-shaped groove welding crack test" method combined with specific examples.

[0033] Example 1 The base material selected in this example is two pieces of ultra-high strength steel plate with a size of 200mm x 75mm x 20mm as the base material, and the tensile strength grade is 1300MPa grade, and the specific steps are as follows: S1, select solid welding wire as welding material, diameter is 1.2mm, specific composition is shown in table 1, mechanical properties are shown in table 2.

[0034] Table 1: Chemical composition

[0035] Table 2: Mechanical properties

[0036] S2, according to GB / T4364-2013 standard, groove processing is carried out on the ultra-high strength steel plate test piece to be welded, as shown in Figure 1 The test weld groove angle is 60°, the length is 80mm, and the root gap is 2mm.

[0037] In order to detect, before the formal test weld is welded, the restraint area at both ends of the test piece is welded (restraint weld) to simulate the high restraint stress state in the actual engineering structure; after the restraint weld is welded, it is cooled to room temperature to ensure that the test weld is in a high tensile restraint state; First, use a grinding wheel and sandpaper to remove the oxide scale and rust within a range of at least 20mm on both sides of the test piece and the groove surface until the metal luster is exposed, then use anhydrous ethanol to wipe and clean the polished area and blow dry to completely remove the oil stains and moisture adsorbed on the surface.

[0038] S3, in a room temperature environment, a test weld is welded in the test groove of the above restraint test piece by using gas metal arc welding; no preheating is carried out on the test piece before welding, and no post heat treatment is carried out after welding. The welding parameters are: welding current is 230A, arc voltage is 25V, welding speed is 4mm / s, corresponding line energy is about 14.4kJ / cm, welding wire dry length is 18mm, protective gas is 80% Ar + 20% CO2, and gas flow is 18L / min.

[0039] Under this welding parameter, the dilution rate of the base material to the weld metal is controlled within 31%, after the welding is completed, the test piece is placed at room temperature for 48h to fully induce potential hydrogen-induced delayed cracking, and after detection, the chemical composition of the finally formed weld metal is shown in table 3.

[0040] Table 3: Chemical composition of weld metal

[0041] Subsequently, hydrogen-induced cracking detection was performed in accordance with GB / T4364-2013 standard. As shown in FIG. 6, no surface open crack was found by using dye penetrant testing technology to detect the surface open crack of the weld. Subsequently, the weld section crack was observed, as shown in FIG. 7, no micro crack was found. It can be seen that the above method can effectively inhibit hydrogen-induced cracking of the test piece under the condition of no preheating. Figure 2 Figure 3

[0042] The metallographic sample was taken from the center area of the weld for microscopic analysis, and the scanning electron micrograph image morphology is shown in FIG. 8. The weld metal structure is composed of lath-shaped martensite and residual austenite distributed therebetween. The electron backscatter diffraction image of the weld metal is shown in FIG. 9. The residual austenite (red area in the figure) is uniformly dispersed in the martensite matrix (green area in the figure). The average grain size of the residual austenite is between 20 µm, and the volume fraction is about 25%, and such complex phase structure is the basis for achieving the balance of strength, toughness and crack resistance. Figure 4 Figure 5

[0043] The thermal expansion curve is shown in FIG. 10. The Ms of the weld metal is about 134℃, although the transformation is not complete when cooled to room temperature, but the volume expansion effect accompanied by such low temperature phase change, to some extent, offsets the thermal shrinkage during welding cooling, reduces the restraint stress. In addition, the higher content of austenite dissolves the adverse effects of hydrogen on the weld. Figure 6 Example 2

[0044] The base material used in this example is the same as that in Example 1, and the composition of the solid wire used is replaced by the composition shown in Table 4. The mechanical properties are shown in Table 5. Compared with Example 1, the tensile strength of the welding material of Example 2 is improved. Table 4: Chemical composition

[0045] Table 5: Mechanical properties

[0046] The welding parameters in step S3 are modified as follows: welding current is 240 A, arc voltage is 26 V, and welding speed is 5 mm / s. The corresponding line energy is about 12.5 kJ / cm.

[0047] Under this welding parameter, the dilution rate of the base material to the weld metal is about 29%. The chemical composition of the finally formed weld metal is shown in Table 6. The tensile strength of the welding material of this example is improved compared with Example 1.

[0048]

[0049] ​​​​​Table 6: Weld metal chemical composition

[0050] Hydrogen-induced cracking detection was performed according to GB / T4364-2013 standard, as shown in FIG. 6, no surface open crack was found by using dye penetrant testing technology to detect the surface open crack of the weld. Subsequently, the weld section crack was observed, as shown in FIG. 7, no micro crack was found; indicating that even in the case of weld strength improvement, the method protected by the present application can still effectively inhibit hydrogen-induced cracking under the condition of no preheating. Figure 7 Figure 8

[0051] The metallographic sample was taken from the center area of the weld for microscopic analysis, the scanning electron micrograph image morphology is shown in FIG. 8, the weld structure is still composed of lath-shaped martensite and residual austenite distributed therebetween, but the average particle size of the austenite is reduced. The electron backscatter diffraction image of the weld is shown in FIG. 9, the residual austenite (red area in the figure) is fine and uniformly dispersed in the martensite matrix (green area in the figure). The statistical results show that the average particle size of the residual austenite is between 10 μm, and the volume fraction is about 13%. Figure 9 Figure 10 The thermal expansion test is shown in FIG. 10, the Ms point of the weld of this composition is about 175℃, although the Ms point is slightly higher than that of Example 1, but it still belongs to the low temperature phase transition interval, and the phase transition after cooling to room temperature is more complete than that of Example 1. Therefore, the volume expansion effect accompanied by phase transition is more significant, effectively offsetting the thermal shrinkage during welding cooling, reducing the restraint stress, in addition, the 13% residual austenite can also resolve the adverse effects of hydrogen.

[0052] The thermal expansion test is shown in FIG. 10, the Ms point of the weld of this composition is about 175℃, although the Ms point is slightly higher than that of Example 1, but it still belongs to the low temperature phase transition interval, and the phase transition after cooling to room temperature is more complete than that of Example 1. Therefore, the volume expansion effect accompanied by phase transition is more significant, effectively offsetting the thermal shrinkage during welding cooling, reducing the restraint stress, in addition, the 13% residual austenite can also resolve the adverse effects of hydrogen. Figure 11 It can be seen that by optimizing the composition to reduce the alloy content, the tensile strength of the welding material is improved in Example 2, although the phase transition temperature is increased and the volume fraction of austenite is reduced, but the obtained weld metal still maintains excellent anti-cracking performance, successfully realizing the ultra-high strength, crack-free connection of 1300MPa grade ultra-high strength steel under the condition of no preheating and high restraint.

[0053] Example 3

[0054] The base material used in this example is the same as that of Example 1, the composition of the solid wire used is replaced by the composition shown in Table 7, the mechanical properties are shown in Table 8, compared with Example 1, the tensile strength of the welding material of Example 2 is improved. Table 7: Chemical composition

[0055] Table 8: Mechanical properties

[0056] ​​​​

[0057] The welding parameters in step S3 are modified as follows: welding current is 220A, arc voltage is 24V, welding speed is 4.5mm / s, and the corresponding line energy is approximately 13.8kJ / cm.

[0058] Under these welding parameters, the base metal dilution rate of the weld metal is approximately 30%. The chemical composition of the final weld metal is shown in Table 9. The tensile strength of the welding material in this embodiment is improved compared to that in Example 1.

[0059] Table 9: Chemical composition of weld metal

[0060] Hydrogen-induced cracking was detected according to GB / T4364-2013 standard. For example... Figure 12 As shown, dye penetrant testing was used to detect surface-opening cracks in the weld, and no surface-opening cracks were found. Subsequently, the cracks in the weld cross-section were observed, as shown... Figure 13 As shown, no microcracks were found, indicating that even when the strength of the welding material is increased to 1321 MPa, this composition system exhibits the best crack resistance stability.

[0061] 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 14 As shown, the weld microstructure is mainly martensite. Due to the small content and size of austenite, it is difficult to distinguish under scanning electron microscopy. The electron backscatter diffraction image of the weld is shown below. Figure 15 As shown, fine retained austenite (red area in the figure) is dispersed between the martensitic matrix (green area in the figure). Statistical results show that the average particle size of retained austenite is between 3 μm. Compared with Examples 1 and 2, the proportion of austenite phase is significantly reduced to about 4%.

[0062] Its thermal expansion test, such as Figure 16 As shown, the Ms point of this weld composition is around 248℃; this high phase transformation temperature means that the martensite almost completely transforms when cooled to room temperature, and the resulting volume expansion effect can largely offset the accumulated thermal shrinkage stress. At the same time, a small amount of retained austenite also mitigates the adverse effects of hydrogen to some extent.

[0063] As can be seen, Example 3 verifies the effectiveness of the present invention under extreme high-strength matching conditions. Although the alloy content was reduced in pursuit of ultra-high strength, resulting in a decrease in the volume fraction of retained austenite to 4%, the method protected by the present invention compensates for the toughness loss caused by the reduction of austenite by relying on the huge volume expansion effect generated by the martensitic phase transformation as the dominant crack-resistant mechanism, thus achieving ultra-high strength crack-free connection under preheating-free and high-constraint conditions.

[0064] Comparative Example 1 The comparative example uses the same base material as Example 3, but the solid welding wire used is replaced with the traditional ultra-high strength steel ER140S-G welding wire. The composition is shown in Table 10, and the mechanical properties are shown in Table 11.

[0065] Table 10: Chemical Composition

[0066] Table 11: Mechanical Properties

[0067] The remaining parameters are the same as in Example 3. Under these welding parameters, the base metal dilution rate of the weld metal is approximately 30%. The chemical composition of the final weld metal is shown in Table 12.

[0068] Table 12: Chemical composition of weld metal

[0069] Subsequently, hydrogen-induced crack detection was performed according to GB / T4364-2013 standard, using dye penetrant testing technology. Figure 17 The weld surface and fusion line show obvious longitudinal through-cracks that extend into the crater. Observation of the weld cross-section reveals... Figure 18 As shown, severe cross-sectional cracking was found, with cracks penetrating the entire weld section. Traditional ER140S-G welding wire was completely unable to suppress the initiation of hydrogen-induced cracks under preheat-free and high-constraint conditions.

[0070] Metallographic samples were taken from the center region of the weld for microscopic analysis. The morphology of the scanning electron microscope images is as follows: Figure 19 As shown, the weld microstructure is a fully martensitic structure. Unlike Examples 1-3, almost no retained austenite is observed in this microstructure. Figure 20 Electron backscatter diffraction (EBSD) analysis further confirmed that the matrix was almost entirely martensite (green area), with extremely rare face-centered cubic residual austenite (red area), accounting for less than 1% of the volume.

[0071] Its thermal expansion test, such as Figure 21 As shown, the Ms point of this comparative welding material is as high as 493℃. Due to the excessively high phase transformation temperature, the martensitic transformation is completed at a relatively high temperature. When the weld continues to cool to room temperature, the weld metal mainly exhibits significant thermal shrinkage behavior. This shrinkage, under the constraint at both ends, is transformed into huge residual tensile stress. At the same time, due to the lack of hydrogen storage capacity of retained austenite in the weld, diffusible hydrogen migrates to the heat-affected zone under stress-induced conditions.

[0072] The residual high tensile stress caused by the high phase transformation temperature, combined with hydrogen enrichment due to the lack of austenite trapping, led to 100% cracking of the specimen in Comparative Example 1 under preheating conditions. The welding materials used in Comparative Example 1, when welding ultra-high strength steel, cannot effectively suppress hydrogen-induced cracking without preheating measures.

[0073] As can be seen from the above Examples 1-3 and Comparative Example 1, the heat treatment-free method for controlling hydrogen-induced cracking described in this invention can flexibly adjust the volume fraction of residual austenite in the weld metal and the strength and toughness matching of the martensitic matrix by synergistically adjusting the alloy content of the welding material and the welding process parameters.

[0074] When pursuing ultimate crack resistance and hydrogen capture capability (as in Example 1), a higher alloy content can be designed to obtain a higher proportion of retained austenite. When focusing on pursuing ultimate joint strength (as in Example 3), a higher-strength martensitic matrix can be obtained by appropriately reducing the alloy content and austenite proportion. However, regardless of the performance orientation, as long as the weld microstructure meets the technical characteristics of "low-temperature phase transformation characteristics and retention of a certain amount of retained austenite" as defined in this invention, the generation of hydrogen-induced cracks can be effectively suppressed under conditions of no preheating, no post-heating, and high restraint, thus achieving reliable welding of ultra-high-strength steel.

[0075] Therefore, the present invention provides a method for controlling hydrogen-induced cracking in ultra-high strength steel welding without heat treatment. By selecting welding materials with specific compositions and coordinating process control, the phase transformation behavior and microstructure of the weld metal are regulated during the welding process. Specifically, a fine and uniformly dispersed residual austenite phase with a volume fraction of 3% to 50% and an average particle size of 10 nm to 50 μm is formed in the weld. This achieves dual synergistic control over the two major influencing factors of high tensile residual stress and diffusible hydrogen accumulation required for HIC generation.

[0076] First, addressing the high tensile residual stress caused by welding cooling shrinkage, this invention utilizes the low-temperature phase transformation characteristics of the weld metal, causing the austenite-to-martensite transformation to occur at a lower temperature range (such as near ambient temperature). The accompanying volume expansion effect of this solid-state phase transformation effectively counteracts the thermal shrinkage during the welding thermal cycle, thereby reducing the residual tensile stress in the weld region and overcoming the difficulty of existing technologies in handling the extremely high stress levels of ultra-high-strength steel exceeding 1300 MPa. Second, the heat-affected zone (HAZ) is typically a region of hydrogen enrichment after welding in ultra-high-strength steel. To address hydrogen diffusion and enrichment, this invention utilizes the high solubility and low diffusion coefficient of hydrogen in retained austenite, effectively dissolving the diffusing hydrogen introduced during welding into the austenite lattice, blocking hydrogen migration to the HAZ, and inhibiting hydrogen accumulation and crack induction in this region. Based on these dual regulatory mechanisms, this invention can effectively suppress HIC without preheating or post-weld heat treatment; while ensuring the weld strength matches the ultra-high-strength steel base material, it significantly reduces the manufacturing cost of welded structural components and broadens their application range in harsh environments such as armor and heavy equipment.

[0077] 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 controlling hydrogen-induced cracking in ultra-high strength steel welding without heat treatment, characterized in that, Includes the following steps: S1. Select welding materials. The chemical composition of the welding materials by mass percentage is as follows: C: 0.03%~0.3%, Mn: 0.5%~3%, Cr: 3%~15%, Ni: 5%~15%, Si: 0.2%~2%, Mo: 0%~2%, Cu+V+Ti: 0%~1.1%, with the balance being Fe; S2. Beveling and surface cleaning of the ultra-high strength steel plate to be welded; S3. At room temperature, use gas metal arc welding (GMAW) process for welding. No preheating is required before welding and no heat treatment is required after welding. During welding, control the welding heat input between 8kJ / cm and 20kJ / cm and control the dilution rate of the molten pool between 20% and 50%.

2. The method for controlling hydrogen-induced cracking in ultra-high-strength steel welding without heat treatment according to claim 1, characterized in that: In S1, the welding material is one of solid welding wire, flux-cored welding wire, or arc welding electrode.

3. The method for controlling hydrogen-induced cracking in ultra-high-strength steel welding without heat treatment according to claim 1, characterized in that: In S2, the weld tensile strength of the ultra-high strength steel plate is 1300MPa~1700MPa, and the thickness is 5mm~40mm.

4. The method for controlling hydrogen-induced cracking in ultra-high-strength steel welding without heat treatment according to claim 1, characterized in that: In S2, the bevel angle is 60°, and the width gap reserved at the bottom of the bevel is 1.8mm~2.2mm.

5. The method for controlling hydrogen-induced cracking in ultra-high-strength steel welding without heat treatment according to claim 1, characterized in that: In S2, surface cleaning includes: using mechanical grinding to remove oxide scale and rust from the bevel surface and at least 20mm on both sides of the bevel until the metal luster is exposed, and then wiping and cleaning the ground area with anhydrous ethanol or acetone and blowing it dry.

6. The method for controlling hydrogen-induced cracking in ultra-high-strength steel welding without heat treatment according to claim 1, characterized in that: In S3, the gas metal arc welding process uses an argon-rich mixed gas as the shielding gas.

7. The method for controlling hydrogen-induced cracking in ultra-high-strength steel welding without heat treatment according to claim 6, characterized in that: The argon-rich mixed gas is a mixture of 80% argon and 20% carbon dioxide by volume.

8. The method for controlling hydrogen-induced cracking in ultra-high strength steel welding without heat treatment according to claim 1, characterized in that: In step S3, the shielding gas flow rate during welding is 20L / min to 25L / min, the welding wire extension length is 18 to 20mm, and the operation of early gas supply and delayed gas stop is performed.

9. The method for controlling hydrogen-induced cracking in ultra-high strength steel welding without heat treatment according to claim 1, characterized in that: In S3, the welding current is 240A~280A, the welding voltage is 21V~24V, and the welding speed is 3mm / s~5mm / s.

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