Determination of a hardening behaviour law for a cold forging TiN-coated tool steel

Damage occurrence has been industrially observed in cold forging tooling even though stresses remain lower than the yield point derived from a conventional rigid perfectly plastic law. A hardening stress–strain law has therefore been determined for the TiN-coated AISI M2 tool steel to improve the knowledge of the tool behaviour. The methodology used to establish the hardening law is based on the Brinell indentation test, which is simulated under increasing load. For each increment of the load, the parameters of the behaviour law are adjusted in order to make the numerical diameter and the experimental results of the Brinell test converge. In parallel, scanning electron microscope observations on the Brinell indentations show the presence of cracks at high loads, justifying the slight decay of the behaviour law towards the non-coated specimen behaviour one. Finally, this behaviour law is applied to an industrial process showing plastic deformation on the surface of the tool.