The main advantage of cast irons is the possibility of obtaining near-shape parts by moulding, without forging after solidification. The term malleable refers to the possibility of conferring more deformability to the cast irons through heat treatment in solid state. Two kinds of ferritic malleable irons will be described in this chapter, white and black heart malleable cast irons. Malleablizing treatment in white heart malleable cast irons is based on the decomposition of the cementite into iron and carbon atoms, diffusing then the carbon towards the periphery where it oxidizes, being modified the chemical composition of the initial white cast iron. In the case of black heart malleable cast irons , the chemical composition of the original white cast iron is not modified, and cementite is decomposed into carbon, which transforms into nodular graphite, and austenite, which allows obtaining either pearlitic or ferritic matrix depending on the cooling conditions after its transformation.