Microstructure and properties of high-power laser welding of SUS304 to SA553 for cryogenic applications

By matching with the welding speed, the distance between the laser focus and butt seam was adjusted to obtain various fusion ratios of the two base metals. The main phases in weld metal were martensite and retained austenite whose proportions and morphology were measured by XRD and EBSD, respectively. The proportion of retained austenite, both at grain boundary and among martensite laths in core region of grain, increased with the fusion ratio of SUS304. The maximum content of retained austenite at grain boundary and in core region of grain could reach about 22% and 5.8%, respectively. The low-temperature impact toughness of the joint was improved with the increment of retained austenite content. The low-temperature impact energy at −196 °C had displayed a significant raise from 15 J to 44.3 J. The corresponding impact fracture section also transformed from cleavage fracture to entirely ductile fracture.