Microstructure in 316LN stainless steel fatigued at low temperature

The internal structure of AISI 316LN austenitic stainless steel cyclically strained at liquid nitrogen temperature has been studied using transmission electron microscopy and electron diffraction. High amplitude cyclic straining promotes the transformation of austenite with face centred cubic (f.c.c.) structure into ε-martensite with hexagonal close packed (h.c.p.) structure and α′-martensite with distorted base centred cubic (b.c.c.) structure. Thin plates containing ε-martensite were identified in all grains. α′-martensite nucleates at the intersection of the plates in grains with two or more systems of plates and can grow in the bands. The orientation of transformed phases follows the Shoji–Nichiyama and Kurdjumov–Sachs relations. Mechanisms of low temperature cyclic straining are discussed.