Investigation of the Tempering Effect during Nitriding*

Abstract

Abstract Nitriding is a widely used treatment to increase the performance of unalloyed and alloyed steels. Because nitriding majorly affects the hardness of the surface region of the material it is common to perform a quenching and tempering treatment before nitriding in order to get a suitable core hardness and microstructure for application. The hardness from pre-heat treatment is nearly not affected by the following nitriding process if the temperature of tempering exceeds the nitriding temperature more than ca. 30 °C. Nevertheless in some cases where a high nitriding depth, i. e. 0.8 mm and more, is necessary, the nitriding parameters temperature and time can affect the material's state, which was achieved by tempering, even though the nitriding temperature is lower than the temperature of the tempering treatment. The current investigations concern the tempering behaviour of typical nitriding and heat treatable steels. In nitriding experiments with different treatment temperature and time the stability of the pre-heat treatment state was investigated and the Hollomon-Jaffe parameter was used to describe the effect of temperature and time on the material's properties. Furthermore it was shown, that the Hollomon-Jaffe parameter is also suitable to predict the tempering effect of a long time nitriding process.