Mechanical hardness estimation of heat-treated DIN50Cr3 spring steel utilizing laser-induced breakdown spectroscopy (LIBS) inverse calibration

Abstract

In various industrial applications, particularly for suspension systems, a range of mechanical properties are required to meet the designer requirements. In the present work, the semi-nondestructive laser-induced breakdown spectroscopy (LIBS) technique was used for the first time to estimate the hardness (HV units) of the light duty low-carbon spring steel DIN50Cr3 through LIBS calibration curves. For this purpose, three distinct spring steel samples, namely DIN50Cr3 were successfully treated by subjecting to various treatment regimes, namely R1 annealing, R2 quenching and R3 normalizing. The calibration curves were constructed using the ratio of ionic to atomic line intensities of LIBS spectra versus the Vickers mechanical hardness as well as microstructural analyses were performed. The mechanical hardness for spring steel DIN50Cr3 subjected to different tempering heat treatment regimes R4, R5 and R6 is then deduced from the calibration curves, and their values were correlated with those obtained from Vickers test. Microstructural analysis was performed using scanning electron microscopy (SEM) and correlated the variation of the obtained hardness level to the microstructural changes accompanying all heat treatment regimes.