Non-Destructive Quantification of Residual Austenite in Bearing Steels using Harmonic Analysis of Eddy Current Signals

Abstract Retained austenite is an essential structural component of rolling bearing steels, which significantly influences their mechanical and tribological properties. Although conventional quantification of the retained austenite content using X-ray diffraction provides high accuracy, it is time-consuming and unsuitable for process-integrated applications. Therefore, this study investigates the suitability of a multi-frequency electromagnetic testing method for the non-destructive determination of the retained austenite content in 100Cr6 and 100CrMn-Si6-4. A wide range of retained austenite contents was generated by systematically varying the austenitising and tempering temperatures. Strong correlations (r values of up to 0.97) were obtained between signal components and retained austenite content. Regression models based on these correlations enable reliable prediction of the retained austenite content. The results demonstrate the potential of harmonic analysis of eddy current signals for fast and process-oriented quality control of heat-treated components. However, additional microstructural changes may also influence the electromagnetic response and must be considered in robust quantitative evaluation.