Technological Investigation On Laser-MAG Hybrid Welding Of High Strength Steels

Low alloy high strength steel has been widely used in the welded structure because of its excellent performance and remarkable economic benefits. The study on the weld ability of the low alloy high strength steel was attracted people's more and more attention. As the rapid development of hybrid laser welding, the study was focused on the welding technology instead of the welding metallurgy. Compared with the regular MAG welding, this paper studied the welding metallurgy of JFE980S low alloy high strength under the hybrid laser welding.This paper systematically studied the influence of welding parameter to the weld ability of low alloy high strength steel. The result showed that low alloy high strength steel was sensitive to the welding heat input. When heat input increased, the toughness reduced obviously, hybrid laser welding has high speed of welding and cooling, it reduced the heat input and avoided the adverse effects of oversized heat input.The deposited metal experiment indicated that hybrid laser - electric arc welding has metallurgy characteristic of the lower loss alloying element burned, it could obviously enhance the intensity and toughness of the metal. Compared with the regular MAG welding, hybrid welding increased the tensile strength by 9.7%, increased the resilience by 47%. We discovered from the fracture analysis: the stretch fracture appearance of laser hybrid welding and regular MAG welding are basically the same, both were dimple fracture, the break way of the tensile specimen both were the gliding fracture, but dimple of laser hybrid welding was deeper. When attacked the macroscopic fracture, we discovered that the brittle zone of regular MAG welding was relatively broader, the fracture of MAG welding with quasi-cleavage, the fracture mode was brittle fracture. The laser hybrid welding impact test specimen was mixed fracture with main characteristic of dimple fracture and quasi-cleavage. It showed that the performance of tear- resistance and toughness of deposited metal in hybrid laser welding was better than that in regular MAG welding.In the weld joint performance test, the performance of laser hybrid welding also surpassed regular MAG welding, compared with regular MAG welding, the tensile strength was increased by 12.7%, the impact toughness was improved 2-4 times as well as the MAG welding. The tensile fracture dimple of regular weld joint had various depth, small crack source and brittle fracture trace, but hybrid welding had dimple fracture morphology. The MAG welding has even macroscopic fracture, low lateral expansion ratio and broad brittle zone. MAG welding and laser hybrid welding both were quasi-cleavage fracture in microscopic view, the fracture of laser hybrid welding had large fluctuation. Furthermore, they both fractured along the austenite grain boundary, Observing from the break position, the regular welding organization was obviously coarser than laser hybrid welding and it has bad brittleness. So the weld joint performance of laser hybrid welding was better than MAG welding.Based on this, we carried on the systematic study in view of the brittle, soften and cold cracking of low-alloy high strength steel weld joint. The result showed that due to the higher welding speed, shorter time of high temperature resident and narrower heat-affected zone, laser pulse MAG welding could obtain the fine lath martensite structure and tiny crystal grain, it improved anti-brittle and softened ability of weld joint. Regarding the attachment cold cracking aspect, we analyzed separately in diffusible hydrogen and slit type cracking test, the result showed that in resistance cold cracking aspect the weld joint performance of laser hybrid welding was better than MAG welding.In view of some real product, in order to solve low efficiency problem of high strength steel cylinder wall wire filling TIG welding, the experiment proved that: the weld joint's mechanical properties of laser -MAG hybrid welding may achieve performance wire filling TIG welding and increased welding efficiency 6 times, it has provided the experimental study for the practical production.