Studies of segregation leading to blowhole formation in steel ingots.

The theoretical model of another author, dealing with gas reactions, producing CO, H2 and N2 within an interdendritic cell during solidification, has been developed to the extent that it can be applied to steels containing up to 0.5% carbon, deoxidised with silicon and manganese. The total gas pressures (= PCO + PH2 + PN2) developed in a number of steels, all onthe borderline betv/een being porous and solid, aiid containing various amounts of CO, and have been computed. It has been shown that the gas pressures in steels of borderline porosity fall within discrete ranges, which can be used to predict other borderline compositions. The model has been applied to the production of ladle balanced steels. Good agreement has been found between plant data and predicted results from the model.An attempt has also been made to account for blowhole nucleation and growth in terms of the computed gas pressures developed during solidification. The model has the advantage over others so far described in the literature in that it deals comprehensively with the effect of hydrogen and nitrogen in promoting blowholes in steel ingots.