However , the problem of sigma phase embrittlement come at lower temperature below 150 deg C as the weld or base metal becomes harder at this low temperature s and looses impact resistance due to sigma phase retention . Hence if the service condition is such that the weld is subjected to high temperature of 700 deg C for some time - then cooled down to low or room temperature and then after sometime again heated to 700 deg C and then again cooled down to low or room temperature and so on then we have to be little careful.