How Does Heat Treatment Affect Microscopic Structure and Properties?
AS-CAST: Ductile iron is the most economical type and the one most commonly used. With proper selection of the chemical composition, most grades of ductile iron can be produced as-cast. ANNEALED: Ductile iron is ferritic with corresponding high impact resistance and relatively low strength. Annealing is necessary for austenitic ductile irons operating at elevated temperatures in order to avoid warpage. NORMALIZING: Promotes a pearlitic structure. Strength and wear resistances are high; ductility is moderate. Bainitic structure can be produced either as cast or through isothermal heat treatment (i.e., quenching in a bath held at a pre-determined temperature). Bainitic ductile iron is normally Ni-Mo alloyed. QUENCHING: Results in a martensitic, hard, brittle and highly wear resistant structure. TEMPERING: Relieves most of the brittleness caused by quenching resulting in a high strength and still highly wear-resistant structure. STRESS RELIEVING: Is a low temperature heat treatment seldom
