Effect of a plated Fe-Cr-Ni alloy layer for rapid nitriding of invar

The nitriding rate in a plated invar with an Fe-Ni-Cr alloy (face-centred cubic) layer were compared by optical microscopy with the rate in an unplated invar. In the plated invar rapid nitrogen diffusion was discovered. The plated layer plays a role in enhancing the nitriding rate. The result gives a solution for an abnormal enhancement nitriding rate in austenitic stainless steels. The enhancement is explained from the viewpoint of non-equilibrium thermodynamics.