Abstract
The influence of residual stresses as well as of loading stresses on microhardness is systematically investigated using a combined application of registered microhardness measurements and stress analysis by X-ray diffraction in order to evaluate the ability of the microhardness testing to estimate residual or loading stresses, respectively. Measurements were carried out on steel samples of type S690QL and SAE1045 using a conventional Vickers indentor as well as a ball indentor. The investigations cover samples subjected to 4-point bending as well as uniaxially loaded samples. The investigations show that loading as well as residual stresses have a marked influence on the results of registered microhardness measurements. This effect overlaps with consequences of strain hardening and influences hardness distributions in case of the 4-point-bending experiments as well as in case of the uniaxially tensile loaded samples in a characteristic way. It becomes visible that the microstructure of the tested steel samples as well as the type of the indentor have a significant influence on the correlation between the applied load and the resulting change in hardness. As a conclusion, it appears to be ambiguous to deduce residual or loading stresses directly only from results of microhardness readings, in particular as it cannot be accounted for the effect of directionality of microstructure and applied loading state on the results of microhardness testing.
