Study on the microstructural variation and fatigue performance of microplasma arc welded thin 316L sheet

Abstract

Welding is a venerable and reliable fabricating technique to integrate materials into complex geometry desired for various industrial applications. However, localized heat concentration leading to microstructural variations can deteriorate the fatigue life of welded components. The present study explains tensile and high cycle fatigue performance of microplasma arc welded 316L SS thin sheet (0.5 mm thickness) material. The square butt joint configuration with a single pass weld was achieved for 316L SS similar sheet material. The skeletal and lathy delta-ferrite-austenitic structures were observed in the fusion zone (FZ) due to non-equilibrium solidification, which is attributed to the different thermal cycle behaviour of the FZ. This morphology is explained by the pseudo phase diagram and the Schaeffler diagram of SS material. The tensile test showed that the microplasma arc welding process achieved a joining efficiency of 93%. The high cycle fatigue performance of welded specimens was analysed at different alternating stress amplitude. The presence of a dense delta ferrite phase in the austenitic matrix is responsible for fatigue failure of the welded specimen. However, the development of deformation-induced martensite in the crack initiation site promotes fatigue life. The crack initiation, propagation, and sudden failure site were investigated to explain the fatigue fracture behaviour.