Comparison of Two Procedures for Reliable Measurement of Residual Stress in Carburized Steels by Magnetic Barkhausen Noise Method

Sign, magnitude and distribution of residual stresses are extremely important for service performance and useful life of engineering components. Hence, monitoring their variation (qualitative approach) and measuring their magnitudes (quantitative approach) are critical issues in the manufacturing chain. Various destructive and semi-destructive methods exist to measure residual stresses; however, a rapid and reliable nondestructive method will be more appropriate for industrial applications. Recently the magnetic Barkhausen noise (MBN) method has gained importance for non-destructive determination of residual stresses in ferromagnetic materials. However, this method has some challenges due to mixed influences of residual stress and microstructure that require careful pre-calibration and verification procedures for obtaining reliable quantitative results. This paper presents the comparison of two MBN procedures for measurement of surface residual stresses in the carburized steels. Carburizing is a widely used surface treatment process that creates compressive residual stress state at the surface-near region, and thus, it remarkably improves the wear resistance and fatigue performance of low-C low-alloys steels. In the experiments 19CrNi5H and 21NiCrMo2 samples were carburized for at 900oC for different periods, and then, tempered in the range of 180oC and 600oC. In the first procedure, the MBN parameters were optimized and then MBN-r.m.s. values were correlated with the results of XRD stress measurements. In the second procedure, a pre-calibration technique based on instantaneous MBN measurements on the samples during tension/compression loading was applied. The results of two procedures were compared and discussed by focusing on reliability and applicability of the MBN method for measurement of residual stresses in industry