Creep of Cr-Ni stainless steels due to stress-induced martensitic transformations

Abstract

Commercial Cr-Ni austenitic stainless steels show an anomalous fall of proof yield strength and critical stress of microdeformation at temperatures above M s due to the development of FCC→HCP (γ→e) transformation in elastic range of loading. The e martensite formation under elastic stresses causes low-temperature creeps and elongation of specimens is proportional to the amount of the e phase Low-temperature creep at temperatures below M s e-+γ occurs on reverse transformation of stress-induced e martensite to austenite as well. High-temperature thermomechanical treatment and aging, on the one hand, suppress the low-temperature creep, and on the other hand. intensify the anomalous fall of yield strength at temperatures above M s and move the start of this fall to higher temperatures. Key factors responsible for this effect are the decrease of e martensite formation rate, expansion of elastic region due to strengthening of austenite, and rise of martensitic points as a result of phase precipitation.