The effects of fusion ratio on microstructure and cryogenic toughness of dissimilar joint between SA553 and SUS304

Abstract

The fusion ratio of base metal was adjusted by changing the welding conditions for dissimilar joint between SA553 and SUS304. Both the content and the size of retained austenite (RA) both at grain boundary and among martensite laths increased when the fusion ratio of SUS304 increased. The content, distribution and stability of RA were compared by SEM, TEM, XRD and EBSD before and after cryogenic treatment (−196 ℃, 100 h). After cryogenic treatment, the RA in weld metal of all specimens declined. The lower the austenite content, the more the decline ratio after low temperature immersion. The stress resulted from phase transformation played a vital role in the stability of RA according to EBSD analysis. With the decrease of RA content, the room temperature impact energy of weld metal increased, but the low temperature impact energy decreased. The difference between room temperature impact energy and low temperature impact energy is affected by the content of retained austenite. When the austenite content was higher than 30 %, the cryogenic impact toughness of weld metal met the application requirements. It is demonstrated that the dissimilar joint between SA553 and SUS304 made by autogenous laser welding is practical in the field of liquid natural gas (LNG).