Effects of Ingot Weight and Size on Loose Structure and the Reduction of Area in Z-direction of Steel Plate

Abstract

Recent tendency to the enlargement of various structures made of steel plates, such as ships and bridges brings about the need for the production of the large ingots which weigh more than 30 tons. Such large ingots have a loose structure in the center of ingot along axis, which deteriorates not only the homol.eneity of solidification structure, but also mechanical properties of end-products, eapecially reduction of area in tensile test in the thickness direction of plates (Z-tensile test).
Research works on the loose structure and its effects on mechanical properties have been seldom reported before. The present report has proposed a new method using ultrasonic test to measure quantitatively the looseness of the structure of ingots. With this method, the effects of ingot weight and shape on the formation of the loose structure were investigated and clarified. Furthermore, the change of the looseness by rolling was investigated. Investigations have revealed that the reduction of area in Z-tensile test, which is of prime importance on heavy plates, is substantially dependent on the looseness of the plates originating from that of ingots.