Experimental investigation of the effect of the carburisation process on the magnetic response of a low-carbon steel

Carburising-quenching is a standard thermo-chemical treatment used to harden the surface of mechanical parts. The technique is based on the diffusion of carbon atoms at high temperature, followed by a rapid cooling, which induces a structural transformation of austenite into martensite. Given the differences in magnetic properties between austenite and martensite, as well as the internal stresses caused by the process, a change in the magnetic response of the treated parts is observed. This work aims to characterise the evolution of magnetic parameters after carburising and quenching and to determine their connection with mechanical properties. To this end, microhardness measurements and magnetic characterisations were performed on samples subjected to different thermo-mechanical routes in order to establish a link between the induced microstructure and the magnetic properties. The remanent induction B r and the maximum magnetostriction λ exhibit complex evolutions, and establishing the link to mechanical properties is shown to be challenging. On the other hand, the results show that the coercive field H c , the relative permeability μ r , and hysteresis losses P clearly reflect the processing route and can be used as relevant non-destructive indicators of the material state.