Abstract The open hearth steel plant at Seraing is equipped with a Leybold installation for vacuum casting of steel. Vacuum casting is carried out in two different ways: —for heavy forging ingots: the degassing takes place directly when pouring steel into the ingot mould; —for small forging ingots: the degassing is obtained when transferring steel from the tapping ladle to another ladle; then steel is air-cast. The hydrogen content of the liquid degassed steel is of the order of 2 to 3 cm 3/100g. The cracks initiated by the oxidized inclusions completely disappear thanks to the vacuum casting technique. Elongation and reduction in area are improved; as well, the impact values recorded from transverse radial test specimens. This technique is therefore particularly beneficial to heavy stressed forgings.