The influence of oxidation on the stress-rupture properties of a nitride-strengthened, austenitic steel

Prior oxidation of thin-walled tubes of a nitride-strengthened, 20%Cr/25%Ni stainless steel impairs the rupture properties in subsequent tube-burst tests. The oxidation process results in the formation of a surface, protective film of chromia with concurrent formation of sub-surface voids affecting up to 125 μm of metal. In severe cases local cracking of the chromia films results in internal oxidation of the underlying chromium-depleted zone. Such structures are the most effective in reducing life but it is shown that in no instance does the metal section effectively lost exceed approximately 75% of the depth affected. (author)