Obviously at high temperature within the sigma phase formation temperature range of austenitic SS -that is 560 to 980 deg C , if the welds are kept in this service temperature range , the sigma phase will form. This is true for welds of all austenitic SS electrodes or fillers all over the world including E/ER 308/308L, 309/309L , 316/316L , 317/317L , 321, 347 etc etc. However there are few Austenitic SS electrodes / fillers made having less than 3 % ferrite in weld to serve special service conditions. Hence I think in our M38 weld also , we are expected to get within 3 -9% ferrite which at high temperature of 700 deg C will convert to sigma phase .