Since tempered martensitic steels have a multi phases microstructure and each component has different physical properties, the evaluation of fundamental mechanical properties by nanoindentation technique is essential to understand the property of martensitic microstructure itself. We measured the nanohardness of SCM440 martensitic steel to obtain the load-displacement behavior; it depends on measured position at the specimen surface and/or the size of plastically deformed zone corresponding to the applied peak load. The result clearly represents the inhomogeneity of the multi-phase microstructure, because this dependence came from the difference of mechanical properties and strength of each component. The relationship between microstructural features and the standard deviation with the contacted depth (hc) is also discussed in order to consider the critical condition for the disappearance of inhomogeneity effect on the deformation behavior.
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