Two approaches for enhancing the accuracy of the Rockwell hardness test

Two approaches have been investigated in our study in order to develop indenter calibration methods with high accuracy. One approach is by establishing a group standard utilizing several indenters, which yields better statistical results than the calibration using only one indenter. The second approach is by correcting the hardness test values using the indenter's area function determined by a highly accurate stylus profilometer. In the stylus profilometer developed in this study, the indenter is scanned in 3D and is detected by a position stationary stylus probe. The 3D geometry of the indenter is thus derived from the displacements of the indenter which are measured by three homodyne laser interferometers, offering direct measurement traceability. In addition, for achieving a better measurement performance a special radial scan function is designed where the indenter is scanned radially over its apex. A data evaluation method has been established for calculating the indenter's area function from its measured 3D geometry. The correction method of hardness values based on the indenter's area function is described. In this paper, a group of three Rockwell indenters has been investigated. The mean deviation of HRC values measured by this group of Rockwell indenters has been reduced from 0.11 HRC to 0.06 HRC by using the proposed correction method.