Self-healing Effect of Boron Nitride Precipitation on Creep Cavitation in Austenitic Stainless Steel

In this study, the precipitation of boron nitride (BN) on creep cavity surfaces during creep and its beneficial effect on the creep rupture properties are reported for a type 304 austenitic stainless steel. In the conventional 304 stainless steel, the trace of soluble S segregates strongly on the creep cavity surfaces and promotes its growth during creep. In the modified 304 stainless steel added with B, Ce, and Ti, the trace of soluble S is removed effectively by the formation of Ce and Ti sulfides, and the segregation of S on the creep cavity surface is replaced by the precipitation of the BN compound. As BN is very stable at high temperatures, its precipitation on the cavity surface is expected to suppress the creep cavity growth rate. It is suggested that the precipitation of BN on the creep cavity surface provides austenitic stainless steel with the function of self-healing for creep cavitation with an associated increase in the creep rupture strength and ductility.