Space-Time-Structure Map for As Cast Massive Rolls

Abstract

A thermal gradients’ field was studied for an as cast massive roll. Three ranges within the thermal gradients field were differentiated. The thermal gradient is constant along with the second range of thermal gradients’ field. Thus, columnar into equiaxed structure transition (CET) is to be expected within the second range. This statement is in good qualitative agreement with a similar observation given by Hunt’s theory. The columnar structure formation was significantly slowed down within the second range of thermal gradients field. At beginning of the second range the liquidus isotherm tears away from columnar structure / liquid interface. The columnar structure is still formed within the time adequate to the second range of thermal gradients but its growth vanishes due to lost competition, and at the end of the second range the equiaxed structure growth dominates, exclusively. In fact, the extrapolation of the velocity of the columnar structure / liquid interface to its value equal with zero confirms the appropriate location of the end of the second range within which the CET is observed. The detailed analysis of the solidus isotherm / liquidus isotherm movements allows a development of the Space-Time-Structure Map for a solidifying massive roll. The Map shows the location of the CET in time (solidification time) and in space (along the roll radius). Moreover a proper locations of structural zones are drawn in the Map. The simulation of the thermal gradients’ field is a very useful tool in the industrial practice. The results of simulation can be used to predict the Space-Time-Structure Map (STSM) for a given massive roll or a massive ingot. Additionally, the equation for solute redistribution after back-diffusion was formulated on the basis of the new theory for microsegregation. It allows formulating the so-called macrosegregation index dealing with the whole ingot/roll volume.