Extension of high cycle fatigue life by the formation of nano-sized martensite particles at intersections of dislocations in an austenitic stainless steel

A new fatigue strengthening method which is applicable for both the micro-sized materials and ordinary-sized materials have been proposed. Dislocations are pinned at their intersections by the formation of nano-crystals after cold work in this strengthening method. Nano-sized α′-martensite particles, the diameter of which was approximately 5 nm, were formed by a cryogenic treatment at a certain temperature above M _sα ^b (martensite burst starting temperature) in a commercially available 316-type austenitic stainless steel. These nano-particles are considered to be formed at intersections of dislocations. Fatigue life tests using ordinary-sized specimens revealed that high cycle fatigue life of the 316-type austenitic stainless steel was extended by the cryogenic treatment and this is considered to be due to the pinning of dislocations by the formation of nano-sized α′-martensite particles.