Determination of effective thickness of cemented steel layer

The aspects of increasing the strength of heavily loaded steel parts of transmissions of energy-intensive machinery are considered. It is noted that, along with hardness, an important parameter of the hardened cemented steel layer is its effective thickness, which is a distance from the surface of the sample (part) to the zone with a hardness of 50 HRC (529 HV0.5). It is shown that unavoidable banding of metal in the area of hardness measurement and instrumental errors during hardness measurements greatly affect the accuracy of determining the effective thickness. A method for determining the effective thickness of the cemented layer is proposed, which is based on using a second-degree polynomial to interpolate the distribution of experimentally measured values of hardness (HV0.5) in an extended range of distances from the surface of the part to the HV0.5 hardness measurement point. The error of determining the effective thickness of the cemented layer is reduced by expanding the HV0.5 hardness range in the analyzed zone, and by approximating its monotonous variation in this area, followed by solving the resulting quadratic equation. The approximating polynomial provides a statistically correct description of the behavior of cemented steel hardness (HV0.5) in the analyzed area depending on the distance from the part surface to the hardness measurement point. The effectiveness of the method was confirmed by determining the effective thickness of the cemented layer of a steel sample (grade 18KhGT) after carburizing and quenching. The obtained results will be useful when optimizing the carburizing conditions of heavily loaded gear wheels of vehicle and tractor transmissions.