Impurity effects in stress relief cracking of a Mn–Cr–Mo–Ni steel

Abstract

AbstractIsothermal stress relaxation tests at fixed displacement on coarse-grained laboratory heats of A508-2-type steel, normally highly susceptible to stress relief cracking (SRC), have established that trace impurities are essential for this phenomenon. An undoped heat made from iron containing ~5 ppm sulphur in a high-purity crucible was found to be extremely resistant to SRC. Subsequent chemical analysis showed that this steel contained 2 ppm boron and an inadvertant 66 ppm nitrogen, which presumably scavenged the boron to some extent. Other high-purity heats were doped with boron, sulphur, and phosphorus, singly and in combinations. Boron and sulphur additions were always deleterious; phosphorus sometimes appeared to have beneficial effects. High-resolution scanning Auger spectroscopy confirmed the role of surface-adsorbed sulphur in the cracking mechanism.MST/564