Modelling of composition and stress profiles in low temperature surface engineered stainless steel

Thermochemical surface engineering by nitriding/carburizing of stainless steel causes a wear and corrosion resistant case of expanded austenite.  As a consequence of the thermochemical surface engineering, huge residual stresses are introduced into the case, arising from the volume expansion that accompanies the dissolution of high contents of nitrogen/carbon in austenite.

Modelling of the composition and stress profiles developing during low temperature surface engineering from the processing parameters. A realistic model should take the following into account:

-          concentration dependent diffusion coefficient

-          finite flux of interstitials through the surface

-          trapping of nitrogen/carbon

-          effect of residual stress on diffusive flux

-          effect of residual stress on solubility of interstitials

-          plastic accommodation of stress exceeding the yield strength

The effect of all these contributions on composition and stress profiles will be addressed and the differences between nitriding and carburizing will be discussed.