Life extension by cavity annihilation heat treatment in AISI 316 stainless steel under creep-fatigue interaction conditions

Abstract

The creep-fatigue life extension of AISI 316 austenitic stainless steel by heat treatment for cavity annihilation was investigated. Different heat treatments were conducted to find better conditions which could enhance the effect of treatments for the life extension. Cavities formed during creep-fatigue tests were found to be annihilated during solution heat treatment, and the cavity annihilation led the materials to have longer creep-fatigue lives. Having different heat treatments, it can also be suggested that the extension of the creep-fatigue life can be maximized by changing the ageing condition, after solution treatment, to have the lower density of grain boundary carbides that serve as nucleation sites for the cavities. The specimen aged at a higher temperature which has the lower value of cavity nucleation factor, P', has a longer extended creep-fatigue life. In this specimen, cavity re-generation during the loading after annihilation of previous cavities is retarded owing to the lower density of the grain boundary carbide.