Comparative Assessment of Dislocation Density in Cyclically Deformed Austenitic Stainless Steel Determined by X-Ray Diffraction and Hardness Tests

Abstract

Among all types of steels, austenitic stainless steel, mostly known for its formability and corrosion resistance, has found its utility in diverse field of applications including pipelines, automobile engine and gear parts. ISO/TR 15510 X12CrMnNiN17-7-5 is a special grade of austenitic stainless steel which was developed to conserve Ni. This non-conventional stainless steel is used in automobile parts such as automotive trim, wheel covers, conveyor belts and railway train bodies etc. In most of these applications, components go through cyclic loading resulting in low cycle fatigue failure. In general, any deformation in metallic systems is controlled by its internal sub-structural variations (dislocation density) and so it is essential to study sub-structural changes in austenitic stainless steel under cyclic loading. Further, it is well known that austenite in stainless steel is metastable upon monotonic and cyclic deformation. In this investigation, strain induced transformation of austenite to martensitic using X-Ray diffraction profile analysis has been studied and volume fraction of martensitic and austenitic phases in cyclically deformed specimens under various constant strain amplitudes has been calculated. In order to calculate the dislocation densities and dislocation character in the specimens subjected to cyclic loading under various constant strain amplitudes X-ray diffraction profile analysis using the modified Williamson–Hall equation has been carried out. Estimation of dislocation density has also been done using variation in hardness values of deformed specimens subjected to varying loads incorporating the model of indentation size effect and compared with that of XRD profile analysis. It has been found that dislocation density increases with increase in strain amplitude which implies that non-conventional austenitic stainless steel is cyclically harden able material.