Study of strain induced martensite formation in a Ti modified 316 stainless steel bellow by transmission electron microscopy

This paper presents a study of strain induced martensite formed in a Ti modified SS 316 bellow by electron microscopy methods. This bellow is part of a bellows sealed valve used in a sodium testing facility. It is known that Ti is added to austenitic stainless steel to overcome the problem of intergranular corrosion due to sensitization. However, the addition of Ti, a strong ferrite stabilizer can influence the stability of gamma phase especially under strained conditions. Detailed electron microscopy studies showed the presence of strain induced martensite in an austenite matrix. The reasons for its formation and stability at the operating temperature are discussed, since sensitization kinetics is reported to be accelerated by the formation of martensite.