Effects of Rare Earth Elements on Properties of High Quality Ingots

Abstract

To produce high quality high-tensile steels, rare earth metals (REM) were added into molten steel with a sulfur content 0.007% in the mould, and investigation was made on the inner quality of the 30 t big-end down ingots (amount of added REM: 0.032 and 0.052 wt%), and on the properties of the plates from these ingots. Conclusions reached are as follows:
(1) REM treatment to killed steel results in the conversion of MnS to sulphides and oxisulphides of rare earths which are hardly deformable by hot rolling. Thus, sulphide shape control can be successfully made of REM addition.
(2) REM has a stronger deoxidizing ability than Al.
(3) The separation of REM inclusions from sound ingot portions can be sufficiently made by this method as industrial process.
(4) Among inverse V-segregation in REM treated ingot, sulphur shows negative segregation. A proposal is presented to explain the cause of this negative segregation of sulphur.