Microstructural adjustment of carburized steel components towards reducing the quenching-induced distortion

Abstract

It is crucial to control and minimize the geometrical distortions resulted from the application of carburizing and quenching processes. This is particularly of the utmost importance for high quality steel products such as power transmission components which require high performance and dimensional precision in the range of micrometers. Carburized steel components are quenched from hardening temperature to room temperature to acquire a very hard martensitic layer (case). During the quenching process, due to the phase transformation-induced volumetric expansion in case and the interior region (core), unwanted dimensional changes may occur. In the present work, the effects of a modified hardening temperature and different soaking times on the core microstructure, the final dimensional stability and the mechanical properties are systematically investigated. Navy C-ring specimens are employed to quantify and correlate the effect of the developed microstructural constituents, magnitude of distortion, distribution of residual stresses and hardness values (macro, micro and nanohardness). Mini-tensile specimens are additionally fabricated out of the Navy C-rings’ core to evaluate the overall tensile behavior of the developed microstructures. The results show that by application of the modified hardening temperature the quenching-induced distortion can be reduced up to 27% while retaining the hardness properties of the case and core similar to that in the reference specimens which are quenched from a typical hardening temperature. The overall tensile properties of the core microstructures developed by the reference and modified heat treatments also show a nearly similar behavior.