Microstructural Studies in Understanding the Role of Metallurgical Parameters on Creep Behaviour of Austenitic Alloys

Abstract

Studies on creep behaviour of austenitic steels as a function of metallurgical variables like: (a) extent of cold work (b) trace alloying elements (c) choice of joining method indicate the need to understand their role through microstructural studies. As the materials evolve during creep exposure in terms of defect structure and precipitation behaviour, extensive electron microscopy studies were carried out to understand the influence of the above variables. It was observed that cold work shows an increase in creep life as it is varied from 10 to 24 % due to the enhanced prior defect structure providing a complex tangled dislocation structure when the material undergoes creep deformation. The addition of Ti results in enhanced nanoscale precipitation of TiC which was found to influence the creep strength up to 0.23 % of Ti. Employing modified TIG joining over the conventional TIG process it has been found less creep cavitation in the former joint which led to the improvement in creep rupture strength. The paper would discuss in detail of the microchemical variations, microstructural evolution in terms of defect structure and precipitation behaviour on the creep life.