Dynamic Coarsening of 3.3C–1.9Si Gray Cast Iron

Abstract

The dynamic coarsening of primary austenite has been investigated by means of interrupted solidification in a hypoeutectic gray cast iron at three different cooling rates. The fundamental characteristic of the coarsening phenomenon, which is the reduction of the total interfacial area (i.e., the primary austenite surface) over time, has been investigated along the solidification interval for the first time in gray cast iron. The primary austenite surface is confirmed to decrease with increasing solidification time. The relation between primary austenite surface reduction and the secondary dendrite arm spacing is reported as well as the time dependence of the inverse surface area of the primary phase per unit volume. The primary austenite surface has been determined via a stereological approach. The secondary dendrite arm spacing is observed to increase throughout the whole solidification range. A novel stereological relation, the modulus of primary dendrite, has been implemented on the calculation of the primary austenite surface. The size scale of the interdendritic phase has been determined by the hydraulic diameter of the interdendritic phase. The linear relations between secondary arm spacing and eutectic cells size and between secondary arm spacing and solidification time have been found to exist during solidification independently of cooling rate. The cooling rate dependence of the secondary dendrite arm spacing and the eutectic cells size is confirmed.