The ordinary cast iron is very hard and brittle. Malleable cast iron is unsuitable for articles which are thin, light and subjected to shock. It can be flattened under pressure by forging and rolling. It is an alloy in which all combined carbon changed to free form by suitable heat treatment. Graphite originally present in iron in the form of flakes which is the source of weakness and brittleness. Carbon in this cast iron is dispersed as tiny specks instead of being flaky or in combined form. The tiny specks have not such weakening effect and casting would not break when dropped. The tensile strength of this cast iron is usually higher than that of grey cast iron. It has excellent machining quality and is used for making machine parts for which the steel forging and in which the metal should have a fair degree of machining accuracy e.g., hubs of wagon, heels small fittings for railway rolling brake supports, parts of agricultural machinery, pipe fittings, hinges, locks etc.
It can be obtained by annealing the castings. The cast iron castings are packed in an oxidizing material such as iron ore or in an inert material such as ground fire clay depends upon the process used either white heart or black heart. The packed casting is put into an oven and is heated around 900°C temperature and is kept at that temperature for about two days and it is then allowed to cool slowly in the furnace itself. Iron ore acting as an oxidizing agent reacts with C and CO2 escape. Thus annealed cast product is free from carbon. If the castings are packed in an inert material then slow cooling will separate out the combined carbon to temper carbon. To produce malleable casting, first casting is produced which has all combined carbon. The produced castings are then heat-treated in a special manner according to white heart method or black heart method.