LAUSR

The effect of heat treatment on the transformation of inclusions in linepipe steels was investigated experimentally and theoretically. During heat treatment, CaO-Al2O3 type of inclusions in steels before heating transformed into Al2O3-CaS type, and in the form of CaS-Al2O3-MgO eventually with CaS formed on the surface of Al2O3-MgO phase, depending on the heating temperature, heating time, size of inclusions, and components such as T.Ca and T.O in steels. The transformation details were revealed by thermodynamic calculations and kinetics analysis; what is more, the coefficients kinc of each composition in inclusions such as Al2O3, MgO, CaO, and CaS at 1473 K (1200 °C) were calculated, respectively. The theoretical results in this paper are in good agreement with the experimental observations.