Effect of beam oscillation on microstructure and properties of laser-TIG hybrid welding of D406A ultra-high strength steel

30Si2MnCrMoVE (referred to as D406A) has not only ultra-high strength but also good toughness, which is the most critical material for solid rocket engine shell. But current methods are low efficient and poor welding quality. In this paper, a laser-TIG hybrid welding with beam oscillation was employed to join 2 mm-thick D406A steel in butt joint. Two beam oscillation modes that are continuous and pulse circular were investigated. It was found that the beam oscillation refined the dendrite structure and was beneficial to the formation of equiaxed grains in the fusion zone, and turned the columnar grains into different orientations and homogenized structures. The continuous circular oscillation had the best stirring effect on the molten pool, and the weld had the finest grain and the most amount of equiaxed grains. As a result, the transverse residual stress obtained using continuous circular oscillating of the weld was the lowest (422 MPa) and the most uniform, 40.6 % lower than the weld without oscillating. Besides, the beam oscillation had little effect on the tensile strength of the weld, but improved the ductility obviously. The strain with continuous circular oscillation was up to 5.9 %, 18 % higher than that of the pure TIG weld.