Effect of various sulfide stringer populations on the ductility of hot-rolled CMn steels

Abstract

The effect of sulfide inclusions on anisotropy of axisymmetric and plane-strain fracture strain was investigated in three 0.1% C, 1.0% Mn steels containing 0.004, 0.021, or 0.028% S. The effect of the sulfide inclusions on axisymmetric and plane-strain fracture strain correlated with the projected area of inclusions per unit volume, A r , or the mean local area fraction of inclusions on a plane perpendicular to the tensile direction regardless of tensile direction: transverse or through thickness. The magnitude of A r was orientation dependent and was directly proportional to the volume fraction of inclusions and inversely proportional to the inclusion dimension parallel to the tensile direction. Dirichlet cell tessellation procedures were used to calculate local area fractions of inclusions, nearest-neighbor distances, and near-neighbors distances on longitudinal, transverse, and through-thickness planes. The mean local area fraction of inclusions was orientation dependent and was significantly larger than the total area fraction. The mean nearest-neighbor and near-neighbors distances were also dependent on orientation. The near-neighbors distances were incorporated into a simple anisotropic model of ductile fracture which gave good agreement with the observed fracture strains for both transverse and through-thickness specimens.