A stress state dependent damage model for the high temperature failure of free-cutting steels

Free-Cutting Steels (FCS), also referred to as Free Machining Steels, are characterised by their excellent chip formation and low cutting force during machining. However, the microstructure features which provide the advantageous machining properties have been linked to poor formability during secondary processing such as those occurring during hot rolling of bar products (Y. Liu et al., On micro-damage in hot metal working Part 1: Experimental investigation, Eng. Trans. 54 (2006) 271287). In this paper physically-based modelling equations are formulated from microstructure and flow stress observations, specifically for the high temperature deformation of FCS. The isotropic, viscoplastic-damage and stress state dependent material model is determined for a typical low-carbon FCS. The model is integrated with the commercial FE code ABAQUS Explicit through user routine VUMAT. Results are validated with the recently introduced conical splay test.