Columnar-to-Equiaxed Transition in Cast Irons: An Experimental and Numerical Analysis

This work is focused on the study of the columnar-to-equiaxed transition in free graphite cast irons and the correlation of this phenomena with the temperature gradients during solidification. Samples of lamellar, compacted and spheroidal graphite irons were cast and their solidification macrostructures were revealed by application of the direct austempering after solidification technique. All the samples presented a sharp columnar-to-equiaxed transition and the determination of its location was carried out by visually inspecting each of the macrostructures obtained. In addition, computational simulations of filling and solidification of the castings were carried out to calculate the temperature gradient profiles along the whole volume of the casting samples. The comparison of experimental and numerical results showed that there is a critical temperature gradient value defining the columnar-to-equiaxed transition for all the free graphite cast irons samples analyzed in this work, regardless of their graphite morphology and casting geometry.