Stress relief cracking in MnMoNi and MnMoNiCr pressure vessel steels

A constant displacement stress relaxation test at 6150C on notched bars which were given a prior treatment to simulate a heat-affected zone in a welded joint was used to characterize the susceptibility to stress relief cracking (SRC) of various heats of two types of commercial pressure vessel steels, SA 533-B and SA 508-2. The susceptibility of the former steel was quite variable, and that of the latter was uniformly high. It is shown that the SRC susceptibility of these steels can be rationalized in terms of their impurity and chromium concentrations. The susceptibility increases linearly with a composition parameter which contains both impurity elements and chromium. The physical basis for this is discussed. (Auth.)