抄録
The cast rolls made of special steel containing chromium and molybdenum has been manufactured since the year of 1927 by the Yawata Iron & Steel Works. At present, these products have the life of rolling 70, 000 tons in average in contrast with 38, 000 tons of the past, and on some occasions 120, 000 tons of billets could be passed.
It is widely known that the quality of cast steel is not improved in the course of forging or rolling to the favorable extent of eliminating their coarse structure and internal stress of casting.
But they could be improved by means of such heat treatments as spheroidizing, normalizing and tempering which influenced mainly on the toughness and hardness.
Special cast steel rolls manufactured recently by Yawata Works having the chemical composition of 0.8%C, 1.0%Cr, 0.3%Mo, etc. and Shore hardness number of 40 after such heat treatments as mentioned above, were found to have the longer life in comparison with the others.
However, the chemical composition and hardness were not always regarded as the prime factors having an influence upon the defect of crack.
It was considered therefore this kind of crack was due not only to the methods and techniques of rolling operation but to the segregation of chemical composition at the stage of casting. Accordingly, the anthors investigated the segregation of these rolls under various thermal Conditions.
As the result, they studied quantitatively each characteristics of segregated elements at the longitudinal and transverse sections of some of rolls cast under different conditions and made clear the solidifying and cooling process by means of chemical analysis, microscopic inspection and mechanical test.
