Martensitic Induction Hardening of Nitrided Layers*

Abstract In this research a combination of nitriding and induction hardening is investigated, as this is expected not only to result in significant savings in process time and energy, but also to produce surface layer properties that cannot be set with one of the individual processes. The focus of the current investigations was on the dissolution of the compound layer during inductive heating and the resulting microstructure formation and the hardness profile. Furthermore, it was investigated how the absence of a compound layer affects the subsequent martensitic transformation. For this purpose, differently nitrided surface layers were martensitically hardened and the microstructure was investigated metallographically and physically. After the martensitic transformation of the nitrided layer porosity and retained austenite were observed due to the decomposition of the nitrides of the compound layer. The retained austenite could be reduced by higher temperatures during surface hardening and compound layer removal. The investigations showed, that the optimum initial condition for induction hardening is nitriding with compound layer and a mechanical removal of the latter prior to induction heat treatment.