Profilometry-Based Indentation Plastometry Testing for Characterization of Case-Hardened Steels

An attraction of the profilometry-based indentation plastometry (PIP) procedure is that, while it involves interrogation of volumes sufficiently large to ensure that bulk properties are obtained, it still allows stress–strain curves to be inferred for relatively small regions, such that local properties can be mapped where they are changing over short distances. It is employed here to obtain these characteristics as a function of depth in samples that have been case hardened by the diffusional penetration of carbon, to a depth of just over a mm. This has been done for a grade of steel that is commonly treated in this way. The thickness of the layer characterized by the PIP test is around 200 μm. In addition, curvature measurements on strip samples, after incremental removal of thin layers, have been used to evaluate the (compressive) residual stresses in near-surface regions. These range up to around 200 MPa. Such stresses have only a small effect on the PIP measurements. The carburization raises the peak yield stress from the base level of around 1000 MPa to about 1400 MPa, followed by considerable work hardening. The reliability of these PIP-derived stress–strain relationships has been confirmed by comparing experimental outcomes of Vickers hardness tests with FEM predictions based on their use.