Evaluation of the heat of solidification of cast irons from continuous cooling curves

摘要

This article describes an evaluation procedure which uses a thermal analysis technique based upon cooling curves, taken from the geometrical centre of casting sections, in order to evaluate the heat released during a transformation reaction, withspecial emphasis on the study of the solidification of cast irons. The mathematical procedure allows the evaluation of the heat of solidification, as well as the associated error, through the product of V{sub}ρC{sub}p by the area between the firstderivative of the cooling curve of the real section and the first derivative of the cooling curve of a fictitious neutral body, generated according to the Newtonian cooling principle, which assumes that there are no thermal gradients before the beginningof the reaction. The method has been applied to the study of the solidification of some nodular, grey and ledeburitic irons. Different types of test castings have been used: a step casting with a different section thickness, isolated sections with thesame thickness as the different sections of the step casting and, finally, a Tectip cartridge The results obtained enable the conclusiou to be made that the neutral body has to be generated very carefully in order to avoid the influence of the sharptransition that occurs at the end of the solidification on the value calculated for the heat of solidification.