Ultra-high strength al-si plated hot-formed steel tailor-welding hydrogen embrittlement resistant welding wire and welding method

Abstract

This invention discloses an anti-hydrogen embrittlement welding wire and welding method for hot-formed steel with ultra-high strength aluminum-silicon coating, belonging to the field of metal materials technology. The wire comprises the following components: C ≤ 0.1%; Ni: 5.0%~7.0%; Mo: 0.3%~0.6%; Nb: 0.08%~0.12%; Mo, Nb, and C react to form a Mo2C / NbC nanophase to fix free hydrogen; V: 0.05%~0.1%; reacting to form a VC nanophase to fix free hydrogen; La: 0.5%~0.8%; Ce 0.3%~0.5%; Ti: 0.1%~0.5%; the remainder being iron and unavoidable impurities. This invention can capture hydrogen atoms diffused during welding, significantly reducing the hydrogen content in the weld. The hydrogen-capturing effect of the retained austenite reduces the amount of diffused hydrogen by more than 40%, thereby reducing the susceptibility to hydrogen-induced cracking by 70%.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, and specifically relates to a hydrogen embrittlement resistant welding wire and welding method for welding ultra-high strength aluminum-silicon coated hot-formed steel. Background Technology

[0002] Hot-formed parts are now widely used in automobile bodies. To avoid surface decarburization and oxidation of steel sheets during hot stamping, an aluminum-based or silicon-based coating is often applied to the steel sheet surface. However, during welding, the coating melts into the weld, causing the high Al-Si coating (≥150g / m²) to melt into the weld, exacerbating the formation of δ-ferrite. Carbon dilution in the weld zone results in lower strength than the base material. At the same time, the risk of hydrogen-induced delayed cracking in high-strength steel welds is significant, which is difficult to control using traditional processes.

[0003] To address the welding challenges of hot-formed steel with aluminum-silicon coatings, industry and academia have explored numerous methods. One of the main technologies currently used in industrial production is the pre-removal of the aluminum-silicon coating (CN200780013854.1). However, this method obviously increases manufacturing processes and equipment requirements, while also reducing the manufacturing efficiency of aluminum-silicon coated welded plates.

[0004] Techniques for removing coatings using plasma ablation (CN201810223902.X) and high-energy electron beam (CN201810581119.0) also suffer from the same drawbacks. Secondly, methods to improve the mechanical properties of welds by optimizing welding processes have attracted considerable attention from experts and scholars. Patents such as CN201910949005.1 propose using pulsed laser welding to promote the uniform distribution of coating elements in the molten pool, and CN201180034151.3, CN201611036496.3, and CN201810507547.9 use methods such as oscillating lasers and dual-beam lasers to control the distribution of weld elements. These methods place higher demands on the lasers, and the processes themselves affect welding speed, hindering improvements in production efficiency. Summary of the Invention

[0005] The purpose of this invention is to address the problems and shortcomings described in the background art by providing an anti-hydrogen embrittlement welding wire and welding method for welding ultra-high strength aluminum-silicon coated hot-formed steel.

[0006] The ultra-high strength aluminum-silicon coated hot-formed steel welding wire for hydrogen embrittlement resistance comprises the following components by mass fraction:

[0007] C: ≤0.1%;

[0008] Ni: 5.0%~7.0%;

[0009] Mo: 0.3%~0.6%;

[0010] Nb: 0.08%~0.12%; Mo, Nb and C react to form Mo2C / NbC nanophase to fix free hydrogen;

[0011] V: 0.05%~0.1%; The reaction forms a VC nanophase to fix free hydrogen;

[0012] La: 0.5%~0.8%;

[0013] Ce: 0.3%~0.5%;

[0014] Ti: 0.1%~0.5%;

[0015] The remainder consists of iron and unavoidable impurities.

[0016] A hydrogen embrittlement resistant welding method for hot-formed steel with ultra-high strength aluminum-silicon coating includes the following steps:

[0017] Step 1: After cleaning the hot-formed steel with aluminum-based or silicon-based coating, place them at intervals to create gaps between them.

[0018] Step 2: Fill the gaps with hydrogen embrittlement resistant welding wire for hot-formed steel welding with ultra-high strength aluminum-silicon coating to obtain the hot-formed steel welded plate with aluminum-silicon coating;

[0019] During welding, laser beam welding is used, with a welding speed A of 4m / min-8m / min; the laser beam oscillation frequency is 100Hz-300Hz, the pulse wire feeding speed is 2m / min-10m / min, and the pulse wire feeding frequency is 5~15Hz.

[0020] Preferably, the laser beam oscillation frequency and the welding speed A satisfy the following relationship: Where Fre(L) is the laser beam oscillation frequency; the pulse wire feeding frequency and the welding speed A satisfy... , where Fre(W) is the pulse wire feeding frequency.

[0021] Preferably, the oscillation amplitude is 0.5 mm, the total oscillation width is 1.0 mm, and the pulse wire feeding speed is 2 m / min-10 m / min.

[0022] Preferably, the laser welding power adopts a stepped control strategy: 7.0-8.0kW for 0-2s, 6.0-6.5kW for 2-12s, and 5.5kW for 12-15s.

[0023] Preferably, the process also includes step three: heating the weld area with a rectangular laser spot, with a laser power of 1-6kW and a laser speed of 2-6m / min.

[0024] Preferably, the process also includes step four: after welding, the welding surface is locally and rapidly cooled by liquid nitrogen, while the back side of the welding surface is cooled by water, thereby increasing the cooling rate of the heat-affected zone of the weld joint with the assistance of rapid liquid nitrogen cooling.

[0025] Preferably, the process also includes step five: the hot-formed steel welded plate with aluminum-silicon coating obtained after welding is placed at 20°C for 15 days to allow for natural aging and dehydrogenation.

[0026] Preferably, the real-time relationship between the gap D between two pieces of hot-formed steel with aluminum-based or silicon-based coatings and the laser welding power P satisfies the following equation: Where P0 is the basic fixed power in W; t1 is the thickness of the first sheet material to be welded in mm; and t2 is the thickness of the second sheet material to be welded in mm.

[0027] The beneficial effects of this invention are:

[0028] The laser beam oscillation frequency is between 100Hz and 300Hz. This oscillation frequency forms a periodic vortex in the molten pool through mechanical stirring, breaking the laminar flow state of traditional laser welding and increasing the flow velocity of the molten pool by 2-3 times. The matching of oscillation frequency and amplitude can reduce the temperature gradient on the surface of the molten pool, suppress flow stagnation caused by uneven temperature, and disperse the Al-Si phase after the coating melts.

[0029] High-frequency oscillation, through the periodic opening and closing of the keyhole, causes the gas in the molten pool to escape rapidly, reducing the porosity to 0.1% and increasing the turbulence intensity of the molten pool by 30%.

[0030] Matching the pulse frequency with the wire feeding speed can achieve a stable transition of "one pulse, one drop", reducing the disturbance of the molten droplets to the molten pool;

[0031] The hydrogen diffusion coefficient was reduced by 40% through a V / Nb / Mo multi-path hydrogen trap design. The phase transformation temperature was lowered by using high-Ni welding wire, forming stable retained austenite and reverse-transformed austenite, which act as strong hydrogen traps to capture hydrogen atoms diffusing during welding, significantly reducing the hydrogen content in the weld. The hydrogen trapping effect of the retained austenite reduced the amount of diffused hydrogen by more than 40%, thereby reducing the susceptibility to hydrogen-induced cracking by 70%.

[0032] Ultra-fast cooling can rapidly reduce the temperature of the weld and heat-affected zone (HAZ), shorten the high-temperature dwell time, and inhibit the formation of coarse ferrite and pearlite, instead forming a fine-grained bainite-martensite mixed structure, effectively avoiding HAZ softening or hardening in traditional welding. This phase transformation stress-induced effect can reduce welding thermal stress by 30-50%, and combined with the low phase transformation temperature characteristics of high-Ni welding wire, further reduces the risk of cold cracking.

[0033] The combination of laser beam oscillation and pulsed wire feeding can improve the fluidity of the molten pool and the uniformity of element distribution. The faster the welding speed, the higher the oscillation frequency and the higher the wire feeding pulse frequency are required to achieve sufficient stirring of the molten pool. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the hydrogen trap distribution;

[0035] Figure 2 This is a comparison chart of hydrogen embrittlement tests;

[0036] Figure 3 This is a TEM image of the VC / NbC precipitate phase. Detailed Implementation

[0037] A hydrogen embrittlement resistant welding wire for welding ultra-high strength aluminum-silicon coated hot-formed steel, comprising the following components by mass fraction:

[0038] C: ≤0.1%; Reduce carbon segregation;

[0039] Ni: 5.0%~7.0%; expands the austenite phase region and improves hardenability;

[0040] Mo: 0.3%~0.6%;

[0041] Nb: 0.08%~0.12%; Mo, Nb and C react to form Mo2C / NbC nanophase, which forms pinned grain boundaries, inhibits crack propagation and traps hydrogen;

[0042] V: 0.05%~0.1%; generates VC hydrogen traps, fixing free hydrogen;

[0043] La: 0.5%~0.8%;

[0044] Ce: 0.3%~0.5%; purifies grain boundaries and suppresses brittle phases;

[0045] Ti: 0.1%~0.5%;

[0046] The remainder consists of iron and unavoidable impurities.

[0047] A hydrogen embrittlement resistant welding method for hot-formed steel with ultra-high strength aluminum-silicon coating includes the following steps:

[0048] Step 1: After cleaning the hot-formed steel with aluminum-based or silicon-based coating, place them at intervals to create gaps between them.

[0049] Step 2: Fill the gaps with hydrogen embrittlement resistant welding wire for hot-formed steel welding with ultra-high strength aluminum-silicon coating to obtain the hot-formed steel welded plate with aluminum-silicon coating;

[0050] During welding, a laser beam is used, with a welding speed A of 4m / min-8m / min; the laser beam oscillation frequency is 100Hz-300Hz, the oscillation amplitude is 0.5mm, the total oscillation width is 1.0mm, the pulse wire feeding speed is 2m / min-10m / min, the pulse wire feeding frequency is 5~15Hz, and the welding wire diameter is 1mm.

[0051] Preferably, the laser beam oscillation frequency and the welding speed A satisfy the following relationship: Where Fre(L) is the laser beam oscillation frequency; the pulse wire feeding frequency and the welding speed A satisfy... , where Fre(W) is the pulse wire feeding frequency.

[0052] Preferably, the real-time relationship between the gap D (mm) between two pieces of hot-formed steel with aluminum-based or silicon-based coatings and the laser welding power P (W) needs to satisfy the following formula: Where P0 is the basic fixed power in W; t1 is the thickness of the first sheet material to be welded in mm; and t2 is the thickness of the second sheet material to be welded in mm.

[0053] Preferably, the laser welding power adopts a gradient control strategy: 7.0-8.0kW for 0-2s to achieve penetration of the coating and form a keyhole, with the temperature rising sharply to 2200-2500℃ (peak); 6.0-6.5kW for 2-12s to maintain the dynamic balance of the molten pool, with the temperature stabilizing at 1800-2000℃; and 5.5kW for 12-15s to reduce heat input, promote grain refinement, and reduce the temperature gradient to below 1500℃, with a spot diameter of 0.6mm~0.9mm.

[0054] The functions of dynamically adjusting the pulse wire feeding frequency and dynamically adjusting the laser beam oscillation frequency are as follows:

[0055] Defect elimination: Through dynamically optimized stirring, porosity and spatter are eliminated, and weld density is improved;

[0056] Improved structure and performance: The refined weld grains and uniform chemical composition enable the weld's toughness, strength, and fatigue resistance to match those of the base material, achieving equal strength matching and super strength matching;

[0057] Stable forming: The weld surface is smooth, the excess height is uniform, and there is no undercut; the requirements for workpiece assembly clearance and misalignment are moderately relaxed, reducing production preparation costs and excessive reliance on equipment processing accuracy, and facilitating online quality monitoring and control through sound, light, and electrical signals.

[0058] Preferably, it also includes step three: post-weld treatment (laser heat treatment): using a rectangular laser spot to heat the weld area, with a laser power of 1-6kW and a laser moving speed of 2-6m / min; the rectangular laser spot treatment allows the laser beam to accurately scan the weld area. This heating process will promote the decomposition of unstable martensite and transform it into softer and more resilient tempered sorbite, while helping to reduce the risk of hydrogen-induced cracking, reduce local plastic flow in the weld, and significantly reduce welding residual stress.

[0059] Preferably, the method also includes step four: after welding, the welding surface is locally cooled rapidly by liquid nitrogen cooling (local ≥300℃ / s), and the back side of the welding surface is cooled by water cooling (cooling rate ≥150℃ / s), thereby increasing the cooling rate of the heat-affected zone of the welded joint with the assistance of liquid nitrogen rapid cooling.

[0060] Preferably, the process also includes step five: the hot-formed steel welded plate with aluminum-silicon coating obtained after welding is placed at 20°C for 15 days to allow for natural aging and dehydrogenation.

Claims

1. A hydrogen embrittlement resistant welding wire for welding ultra-high strength aluminum-silicon coated hot-formed steel, characterized in that: By mass fraction, it includes the following components: C：≤0.1%； Ni: 5.0%~7.0%; Mo: 0.3%~0.6%; Nb: 0.08%~0.12%; Mo, Nb and C react to form Mo2C / NbC nanophase to fix free hydrogen; V: 0.05%~0.1%; The reaction forms a VC nanophase to fix free hydrogen; La: 0.5%~0.8%; Ce: 0.3%~0.5%; Ti: 0.1%~0.5%; The remainder consists of iron and unavoidable impurities.

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