Shrinkage of carbon steel by thermal contraction and phase transformation during solidification

Abstract

In high speed continuous casting, optimisation of mould taper is important for intensifying heat transfer and improving the quality of cast products. In order to calculate the shrinkage during cooling, the thermal linear expansion coefficient (TLE) model has been developed and combined with phase transformation relevant to continuous casting of steel. In the present paper, a model to predict the shrinkage and to optimise mould taper for high speed casting is presented by taking into account variations in the TLE of steel and the effect of phase transformation during solidification of steel with varying carbon content. The TLE of steel purely from thermal contraction is nearly independent of carbon content when no δ→γ phase transformation is involved. For example, the TLE of 0·05% carbon steel is calculated to be 21·3 × 10⁻⁶ K⁻¹, while the TLE of 0·60% carbon steel is shown to be 19·88 × 10⁻⁶ K⁻¹. However, phase transformation processes which are greatly dependent upon the carbon content account for large difference in the shrinkage behaviour between the various grades of steel and extremely high apparent TLEs are calculated for low carbon steels; for example the apparent TLE for a 0·05 wt-%C steel is calculated to be 111·81 × 10⁻⁶ K⁻¹.