Case depth measurement of steel components by contact ultrasonic backscattering technique

Surface hardening is one of the common methods to improve the surface properties of steel components such as axles and gears. One of the control parameters measured in this process is the case depth, which can be measured by either destructive or nondestructive methods. In this paper, the ultrasonic nondestructive backscattering technique is utilized to measure the case depth of steel shafts. Measurements are carried out on four steel shafts with different case depths by using contact ultrasonic testing method. The ultrasonic signals collected from these shafts are rectified and filtered by smoothing filters. Comparison of the results of the ultrasonic tests with those of the destructive tests confirms the capability and high precision of the ultrasonic backscattering technique in measuring the case depth. The maximum error in ultrasonic backscattering measurements was less than 4%. Due to its nondestructive and portable nature, this technique can be a good choice for quality control induction hardened components with a case depth of 2 mm or more.