Thermo-chemical Treatment of Austempered Ductile Iron Castings

Abstract

The article presents some basic and well-known information on the surface modification of austempered ductile iron (ADI) parts and castings. It has been shown that the best way of improving the surface properties of ADI is machining or surface deformation through shot penning or surface rolling. It was mentioned that the conventional thermo-chemical treatment of ADI is very complicated because of destruction of the ausferritic matrix at high temperatures. That is why the author proposes a non-conventional thermo-chemical treatment as a part of ADI heat treatment. In this way it is possible to obtain a favorable change in the properties of ADI surface layer. In the article author presents results of a special thermo-chemical treatment in case of carbonitriding and microstructural, hardness and wear resistance investigations. It has been shown that after carbonitriding during austenitization of ductile iron it is possible to increase hardness of surface layer of ADI and its wear resistance significantly. The microstructure of such layer after carbonitriding is different and depending on parameters of the treatment. The investigation showed great potential such additional processes producing in one cycle different properties of core and surface layer.