Tensile strength and elongation properties of malleable iron are similar to that of low carbon steel. Malleable iron is produced by heat treating the as-cast white iron. The microstructure of white iron is composed of massive carbides and pearlite. Characteristics of carbides are hard and brittle with virtually no ductility and extremely low impact value. Such behaviors make white iron finds little industrial usage but in some wear-resistance application. Also, the very long heat treating time to convert white iron to malleable iron makes it very inefficient and uneconomical for society nowadays. On the other hand, the rise of austempered ductile iron (ADI) to greatly improve strength, toughness, hardness, wear and fatigue resistance has been successfully developed in recent years by subjecting ductile iron to austemtering heat treatment. Since the microstructure of malleable iron is similar to ductile iron, it is the intention of this research to carry out austempering during heat treatment of white iron to produce austempered malleable iron. The experimental results indicated that the higher the austenitizing temperature or the longer the holding time effectively dissolve massive carbides of white iron into matrix. Also addition of copper enhanced carbide dissolution such that ductility and impact properties were increased while hardness was only impaired a little bit. Fractography observation of the fractured surface was found to be of brittle in nature despite the fact that impact toughness was enhanced from that of the as-cast state. Comparing the properties of ADI and malleable iron, the austempered malleable iron was found to possess higher mechanical properties except impact value was a bit lowered.
Malleable iron Austempering White iron Mechanical properties