Influence of machining processes on rim zone properties and high temperature oxidation behavior of 42CrMo4

The influence of different machining processes, grinding, electrochemical machining, and electro discharge machining on the surface integrity, described by residual stresses, roughness, and chemical composition, is investigated to explain their effect on the high temperature oxidation behavior of martensitic 42CrMo4 steel in an oxygen atmosphere. The results obtained by thermogravimetric in situ experiments reveal that compressive residual stresses and a smaller reactive surface adjusted by grinding lead to an improved oxidation resistance compared with electrochemical machined surfaces. Surface modification by electro discharge machining appears to be most suitable to achieve oxidation resistance due to decelerated initiation of the oxide layer growth compared with the ground surface. The improved oxidation resistance of electro discharge machined and ground surfaces is linked to the modified chemical composition of the rim zone and the rim zone residual stresses, respectively.