The present work has been made to elucidate the quantitative effects of the amount and shape of inclusions in carbon-manganese steel plates on the tensile and impact ductilities in connection with test directions.

The influence of rolling conditions on ductility can be expressed as a function of the shape parameter of the inclusions in terms of the aspect ratio of elliptical manganese sulflde on the polished surface.

Tensile and impact ductilities in transverse and through-thickness directions were improved by rare earth metal (REM) additions to such an extent that the ductilities of REM-treated steel specimens were nearly the same as those of the REM-free steel specimens, although the inclusion content of the former was as much as two or three times more than that of the latter.

Efforts were made to express ductility in one parameter regardless of the inclusion shape and test directions, and it was found that the ductility was closely related to an inclusion area fraction on the ductile fracture surface.