Abstract
In this work we have studied the nitriding effect for the 42CrMo4 steel on the evolution of their thermal and mechanical properties. The thermal properties are determined by the "Photothermal Deflection technique" method. It was shown that the thermal conductivity as well as the thermal diffusivity decreases if the nitrogen fraction in steel increases conversely the microhardness increases with the growth of the nitrogen rate. After, we have correlated the thermal and mechanical properties with an empirical equation that permits to determine the microhardness without its measure.