Effect of sulfide inclusion morphology and pearlite banding on anisotropy of mechanical properties in normalized C-Mn steels

Abstract

The influence of sulfur content, sulfide shape, and pearlite banding on the anisotropy of mechanical properties was evaluated in a series of 0.2 pct carbon, 1.0 pct manganese steels containing either 0.004 or about 0.013 pct sulfur with and without rare-earth additions. Both globular and stringered sulfide inclusions had a detrimental effect on reduction of area and Charpy shelf energy; this effect was particularly evident in the deterioration of through-thickness properties and was much more severe for stringered inclusions than for globular inclusions. The effect of the sulfide inclusions in the different steels on the through-thickness reduction of area and Charpy shelf energy correlated with differences in their mean free distances or nearest-neighbor distances, both of which depended upon the inclusion characteristics of volume fraction, size, and aspect ratio. The projected length of sulfide inclusions per unit area on a plane perpendicular to the transverse direction seemed to reflect the overall effect of the inclusion characteristics on through-thickness reduction of area and Charpy shelf energy and appeared to be a useful parameter for assessment of steel’s susceptibility to fracture. Pearlite banding had no obvious effect on reduction of area or Charpy shelf energy in any of the steels studied. The improvement observed for the steel with stringered sulfide inclusions as a result of the removal of pearlite banding was a consequence of the inclusions coarsening during the short-time high-temperature treatment used to remove banding.