Deformation effects on chromium diffusivity and grain boundary chromium depletion development in type 316 stainless steels

This paper reports on austenitic stainless steels (SS) susceptible to the development of grain boundary chromium depletion (GBCD), or sensitization, during thermomechanical (TM) treatment. The depletion is induced by the precipitation of intergranular (IG) chromium-rich M23C6 carbides during the TM processes. The presence of GBCD produces localized breakdown of the chromium-rich passive oxide film that protects the SS. This renders the SS susceptible to IG corrosion and IG stress corrosion cracking (SCC) in certain aqueous environments. The development of GBCD is dependent on the thermodynamics of carbide precipitation and kinetics of chromium diffusion, both of which may be altered by thermal and strain cycles produced during TM treatment. A thermodynamic and kinetic evaluation of temperature and strain effects on GBCD phenomena can, therefore, be used to understand trends in precipitation-depletion processes occurring in SS during TM treatment. This can be extended further to develop a mechanistic understanding of TM effects on microstructure, microchemistry and property development in materials