Production and characterization of high performance super austenitic stainless steels

Abstract

Super austenitic stainless steels (SASS) are widely recognized for use in modern technology due to their versatile range of mechanical properties and corrosion resistance. SASS belongs to the family of high alloy steels with chromium (19-28 wt %) and nickel (17-24 wt %) being the principal alloying elements. They also contain molybdenum (2- 8 wt %) and nitrogen (0.15-0.5 wt %) as the supplementary alloy additions. Though conventional austenitic stainless steels (304, 316 and 317, etc.) are widely used for corrosion resistance applications, they do not have sufficient corrosion resistance and high strength for some critical applications. With the advent of nitrogen and molybdenum alloying, this notion has changed to give rise to SASS and the newly developed SASS has exceptional strength, toughness and corrosion resistance. Some very common applications of SASS involve piping in gas, oil, pulp and paper industry or structures for heat exchanger and seashore applications The main difficulty in the production of SASS is the solubility of nitrogen. Therefore SASS has been processed by several advanced techniques such as AOD, VOD, VIM, ESR, VAR etc. and by a stringent process control. Among the various techniques one common limitation existing is that all these processes have to be processed in controlled atmosphere conditions with specialized equipment, which is highly expensive. Hence, the present research focuses with the production of high performance super austenitic stainless steel in the low cost conventional air induction melting and to bridge the gap between conventional melting technique and advanced melting techniques on the development of SASS. This work involves production and characterization of high Mo cast SASS in both i) solution-annealed and ii) isothermal aged conditions. The methodology adopted in the present work is discussed briefly in the following chapters as given below: Chapter 1 gives introduction to SASS, its advantages over the conventional austenitic stainless steels,