Mechanisms for Producing Ultra Fine Nano Grained Microstructure for Austenitic Stainless Steels

Abstract

In the recent times the need for excellent mechanical properties of engineering materials for specific applications is realized. Austenitic stainless steels are very important as engineering materials. These are a large group of special alloys that have been developed, primarily, to withstand corrosion. Other desirable features may include excellent formability, room-temperature and cryogenic toughness, and good resistance to oxidation and creep at elevated temperatures. But these alloys show relatively low yield strength which is an area of considerable interest. Mechanical properties of steels strongly depend on their microstructure which is controlled by phase transformation, precipitation, recrystallization, and so on. Various methods have been adopted to enhance mechanical properties of these steels. The present work focuses mainly on improving the yield strength of austenitic stainless steels through grain refinement. The grain refining method includes thermo-mechanical treatment, which combines deformation and heat treatment. The method has been very effective for microstructural control and hence for improving the mechanical properties. In addition to thermomechanical treatment, thermal cycling process has also been developed in order to form ultrafine or nano-grained austenitic stainless steel. This helps to achieve a good combination of strength and ductility. Thermal cycling process consists of cold rolling and repetitive annealing to reduce the grain size. The study revealed suitability of thermal cyclic process for the production of ultrafine gained austenitic stainless steel having combination of high strength and good ductility