Characterization of a Metastable Austenitic Stainless Steel with Severe Plastic Distortions

Abstract

Surface treatment, e.g. shot peening and deep rolling, is popular in aero engine industry, which induces not only high residual stresses but also severe distortions into the subsurface of mechanical parts. In the present work a meta-stable austenitic steel is experimentally investigated by taking into account of martensitic transformations in plastic deformations and fatigue life assessment. The mechanical behavior of the deformed material with phase transformation is described by J2 plasticity combining with the Santacreu model. The plastic strain hardening is decomposed into plastic strain related part and martensitic phase part verified experimentally. It is found that the contribution of the martensitic phase transformation is limited only for large strain beyond 20% in the AISI 304 stainless steel. Experiments confirm, furthermore, that the martensitic phase transformation arises yield strength and improves fatigue limit of the material. However, the severe deformations diminish material's ductility. Further fatigue tests reveal the fatigue life increases significantly, should the applied load not be much higher than the fatigue limit. In this loading region the martensitic phase transformation improve material's fatigue resistance. With the increasing loading amplitude, however, the benefits from the martensitic phase transformation decrease and the plastic deformation may even reduce fatigue life of the material in the LCF region.