Some observations on the carburisation of type 316 stainless steel foil in a low carbon activity sodium environment

The carburisation of Type 316 stainless steel in a low carbon activity sodium environment has been studied utilising T.E.M. and S.T.E.M. techniques coupled with energy dispersive X-ray analysis measurements. It has been found that the attainment of an equilibrium carbon level and associated microstructure within the steel is a complex process which cannot be simply described by carbon diffusion into the steel. The equilibrium carbide, when finally established, is given by the formula Cr20Fe3C6 with a derived chemical carbon activity of 3.14 x 10-4 at 6500C. (orig.)