INFLUENCE OF REM TREATMENT ON TEAR RESISTANCE OF PEARLITIC STEEL CASTINGS.

The tear resistance of pearlitic steel 40KhNML castings can be improved by treatment with a complex additive (KM) containing Ca, Mg and Ce. The tear resistance of steel 40KhNML is critical dependent on the nature of the nonmetallic inclusions it contains. Large silicate inclusions, normally occurring on the grain boundaries and remaining molten down to about 1250 degree C, are responsible for initiating major hot tears which propagate along the affected boundaries. KM treatment redistributes and spheroidizes the inclusions and the grain boundaries remain cleaner. KM treatment is effective for steel 40KhNML first because it lowers the initial shrinkage temperature and secondly because it lowers the nonmetallic inclusion content and spheroidizes the residual particles, and removes them from the primary grain boundaries.