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).

通过改变SA553和SUS304之间异种接头的焊接条件，可以调节母材的熔化率。当SUS304的熔融比增加时，晶界和马氏体板条中残余奥氏体（RA）的含量和尺寸均增加。在低温处理（-196℃，100 h）前后，通过SEM，TEM，XRD和EBSD比较了RA的含量，分布和稳定性。低温处理后，所有试样的焊缝金属的RA均下降。奥氏体含量越低，低温浸渍后的下降率越大。根据EBSD分析，相变产生的应力在RA的稳定性中起着至关重要的作用。随着RA含量的降低，焊缝金属的室温冲击能增加，而低温冲击能下降。室温冲击能量和低温冲击能量之间的差异受残余奥氏体含量的影响。当奥氏体含量高于30％时，焊缝金属的低温冲击韧性满足应用要求。结果表明，通过自发激光焊接制成的SA553与SUS304之间的异种接头在液化天然气（LNG）领域中是可行的。