Plasma Nitriding and Nitrocarburizing of Austempered S.G. Cast Iron

Abstract

The effects of varying austempering parameters on the response of S.G. cast iron to plasma nitriding and nitrocarburizing was studied. The ideal austempered microstructure of bainite and austenite yielded poor compound layers and the shallowest case depth. A microstructure consisting wholly of bainite obtained by austempering at too high a temperature yielded the best surface-engineered product. Adding carburizing potential to the plasma reduced the thickness of compound layers and case depth. The results were explained by the different distributions of cementite arising when the differently austempered microstructures were tempered on heating to the nitriding temperature. It is concluded that S.G. iron destined to be plasma nitrided should be austempered at higher than normal temperatures, and that nitriding should be preferred to nitrocarburizing.