The Joint Effects of Nitriding and Parameters Related to the Destabilisation of Austenite on Wear Resistance in White Cast Iron with 25% Cr

Abstract

In this article, the effects of an ionic nitriding treatment are analysed, together with deliberate variation of different thermal parameters associated with the destabilisation of austenite, on erosive wear resistance of white cast irons with 25% Cr. The methodology followed in this research was an experimental design, where six factors were analyzed by performing eight experiments. The thickness of the nitrided layer is much smaller than in white cast iron with lower percentages in Cr, never reaching 20 microns. The nitriding treatment entails considerable softening of the material underneath the nitriding layer. This softening behaviour becomes partially inhibited when the destabilisation temperature of austenite is 1100 °C and dwell times at such temperature are prolonged. This temperature seems to play a significant role in the solubilization of non-equilibrium eutectic carbides, formed during industrial solidification. The nitriding treatment leads to additional hardening, which, in these cases, favours a second destabilisation of austenite, with additional precipitation of secondary carbides and the transformation of retained austenite into martensite. Despite softening of the material, the nitriding treatment, together with air-cooling after destabilisation of the austenite, allows a noticeable increase in resistance to erosive wear.