Determination of ef ective thickness of cemented steel layer

Abstract

The problems of increasing the strength of high-loaded steel parts of transmissions of energy-saturated machines are considered. It is noted that, along with hardness, an important parameter of the hardened cemented steel layer is its effective thickness the distance from the surface of the sample (part) to the zone with hardness 50 HRC (529 HV0.5). It is shown that great infl uence on accuracy of its defi nition have unavoidable banding of metal in the area of hardness measurement and an instrumental error of hardness measurement. A method of increasing the accuracy of determining the effective thickness of the cemented layer, based on interpolation by polynomial of the second degree of distribution of experimentally measured hardness values HV0.5 in an extended range of changing distances from the surface of the article to the hardness measurement HV0.5 is offered. Error of defi nition of an effective thickness of the cemented layer is reduced at the expense of expansion of area of change of hardness HV0.5 in an analyzed zone with approximation of its monotonous change in this area and the subsequent solution of the received square equation. Approximating polynomial statistically correctly refl ects the character of hardness change HV0.5 of cemented steel in the analyzed area depending on the distance from the workpiece surface to the hardness measurement place. The effectiveness of the method was confi rmed when determining the effective thickness of the grouted layer of a sample of 18CrNiGt steel after carburizing and hardening. The obtained results will be useful in the development of optimal regimes of carburizing of high-loaded gearwheels of automobile and tractor transmissions.