Determination of the structure in cast irons with thermal analysis method

ABSTRACT Ductile irons with their superior mechanical properties are used extensively by the industry. However, melt treatment step of the production to obtain the necessary spherical graphite structure of the ductile iron needs special care in order to achive the required quality castings. Especially the effect of the modulus variation of the casting on the graphite formation is important. Thermal analysis is one of the important tools used to control microstructure and graphite formation in the foundry industry. Previously used single cup thermal analysis systems do not consider the effect of the modulus on the microstructure. In this study thermal analysis with three cups with different modulus is used for Al-Si alloys and for ductile irons. In addition, new zero curves, for the calculation of latent heat that is necessary for the analysis of the cooling curves has been proposed and used. Latent heats obtained from the proposed zero curves found to be coinciding with the data obtained from previous studies and the method of obtaining zero curve was found to be better than some earlier studies. Proposed modulus dependent, multiple cups thermal analysis of the casting microstructures, used in this study, might be a useful tool for the Al-Si alloy castings and ductile iron castings. Keywords: Thermal analysis, modulus, zero curve, microstructure, ductile iron. xiv