The ordinary cast iron is hard and brittle. It is, therefore, unsuitable for articles which are thin, light and subjected to shock and vibrations or for small castings used in various machine components.
The malleable cast iron is obtained from white cast iron by a suitable heat treatment process i.e., Annealing. The annealing process separates the combined carbon of the white cast iron into nodles of free graphite. Two methods, (i) White heart process, and (ii) Black heart process, are used for this purpose.
The malleable cast iron is ductile and may be bent without breaking or fracturing the section. Its tensile strength is usually higher than that of grey cast iron and has excellent machine qualities. It is used for making machine parts for which the metal should have a fair degree of accuracy e.g., hubs of wagon wheels, small fittings for railway rolling stock, brake supports, parts of agricultural machinery, pipe fittings, door hinges, and locks etc.