EN-GJMB-350 | 5.4101 Ferritic black heart malleable cast iron

Malleable cast iron initially solidifies without graphite as a hard, brittle white cast iron. Long annealing subsequently transforms the microstructure and causes the cementite to decompose, in the case of black heart malleable cast iron into ferrite and flake- or nodule-shaped graphite. This graphite form has a lower notch effect than lamellar graphite, which makes the malleable cast iron tougher than normal cast iron with lamellar graphite. The matrix of black heart malleable cast iron is predominantly ferritic due to slow cooling between 700 and 800 °C.