Impact of pre-machining on the surface and subsurface characteristics of deep rolled metastable austenitic 18CrNiMo7-6

Abstract

Steels with a certain amount of retained metastable austenite derived from e.g. heat treatment can undergo martensitic transformation induced by mechanical loads. Pre-machining is of high relevance for the following processes. Milling and grinding were chosen here for the pre-machining with subsequent deep rolling of 18CrNiMo 7-6 (AISI 4820) in carburized and carbonitrided states. Deep rolling is used to improve the surface and subsurface strength by inducing compressive residual stresses, strain hardening, and in this case martensitic transformation. The results of this paper show clearly that the pre-machining is sufficient to generate mechanically induced martensite and enhance the surface regarding the resulting hardness. These changes of the surface integrity are affecting the following deep rolling process, which is why a constant pre-machining is necessary for future investigations in order to compare deep rolling processes across each other.