STUDIES ON SOLIDIFICATION AND CONTRACTION AND THEIR RELATION TO THE FORMATION OF HOT TEARS IN STEEL CASTINGS.*

Abstract

ABSTRACT.The following studies, resulting from a compilation of data and expressions, consider the relation of solidification and contraction to the formation of hot tears. Casting solidification involving the principle of equal cooling throughout is undesirable. Such conditions should be replaced by the more natural method of directional solidification. Controlled directional solidification is successful only when certain principles of casting design are adopted. These principles stress the importance of feeding smaller sections through heavier ones and by studying mass effect by the use of inscribed circles. Metal contraction and hindered contraction resulting from mold resistance is responsible in the major part for the existence of hot‐tear cracks in steel castings. Other important factors are cavities and the physical properties of the steel. There are two types of hot‐tear cracks, (a) the internal hot tear that develops during the solidification of the casting, and (b) the external hot tear that develops after solidification is complete, but while the temperature is about 1300 degrees C. Intelligent application of certain principles in casting design is one of the most important of seven methods that may be adopted to obviate the danger of hot tears, or at least limit the hot tear formation.1. There are many conflicting opinions on all phases of casting procedure and various remedies for all the numerous problems arising in the industry. These remedies often have been applied by rule of thumb or as experience has dictated their use. It is surprising to note how little experimental data are available on the actual physical processes which occur during the solidification and contraction of steel castings.2. It is not possible to review as large a field as the entire casting process in one article and do justice to all of its phases. The authors have selected, therefore, only one of the important phases, that of solidification, contraction and the formation of hot tears, and have attempted to bring together the best of available data and to supplement them with the results of some experiments.3. In the industry today there are so many definitions for the several terms that in order to clarify the discussion it has been found necessary to define certain of these terms.