Influence of Mechanical Processing and Heat Treatment on Microstructure Evolution in Nickel Free High Nitrogen Austenitic Stainless Steels.

Abstract

A series of nickel free high nitrogen austenitic stainless steels were processed by various mechanical processing and heat treatment conditions to study the evolution of microstructure at every stage of processing. About eleven steels varying in composition, especially in terms of carbon contents, were processed through forging, rolling, solution annealing, cold rolling and warm rolling etc. The microstructure at every stage of processing was studied. The hot rolled condition, hot rolled and cold rolled condition gave deformation induced fragmented grain structure. The high carbon steels in the hot rolled conditions showed banding and grain boundary carbo-nitride precipitation. There were also intragranular carbide prcipitation in some of the high carbon steels.The solution treated microstructure in all steels showed extensive annealing twins and the lattice parameter increased with carbon and nitrogen contents. Cold rolling followed by solution treatment lead to development of slip lines in the fully austenitic matrix due to strain hardening of the matrix. The 600°C warm rolled condition showed grain boundary carbide precipitation.