Effect of shape of sulfide inclusions on anisotropy of inclusion spacings and on directionality of ductility in hot-roll
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I.
INTRODUCTION
A previous study examined the influence of sulfide inclusions and pearlite on the anisotropy of mechanical properties in a series of hot-rolled 0.1 and 0.2 pct carbon, 1.0 pct manganese steels containing either 0.004 or about 0.013 pet sulfur, with and without rare-earth additions. ~ It was found that both globular and stringered sulfide inclusions had a detrimental effect on fracture strain and Charpy shelf energy, which was particularly evident in deterioration of through-thickness properties and which was more severe for stringered inclusions than for globular inclusions. In another study, it was shown that the effect of the sulfide inclusions in these steels on fracture strain or Charpy shelf energy correlated with a single parameter, the total projected length of inclusions per unit of specimen area on a plane perpendicular to the greatest principal stress direction, regardless of the amount or shape of inclusions or the test direction. 2 The magnitude of this parameter was directly proportional to the volume fraction of inclusions and inversely proportional to the inclusion dimension parallel to the tensile direction. For modeling the effect of inclusions on mechanical properties it is desirable to have a measurement for describing inclusion spacings in addition to the measured values for overall inclusion volume fraction, size, and shape. This study examines the anisotropy of inclusion spacings in the 0.1 and 0.2 pct carbon, 1.0 pct manganese steels used in previous studies.~'2 The anisotropy of inclusion spacings is compared with the anisotropy of fracture strain and Charpy shelf energy observed for these steels. These inclusion spacings are incorporated into a model of ductile fracture, and the predicted fracture strains are compared with those observed previously for these steels. W.A. SPITZIG, formerly with United States Steel Corporation, Research Laboratory, Monroeville, PA 15146, is now at Ames Laboratory, Iowa State University, Ames, IA 50011. Manuscript submitted December 7, 1982.
METALLURGICALTRANSACTIONS A
II. MATERIALS, PROCEDURES, AND EXPERIMENTAL RESULTS Three 0.1 pct carbon, 1.0 pct manganese steels and three 0.2 pct carbon, 1.0 pct manganese steels were prepared as Si-Al-killed 227-kg laboratory vacuum-induction-melted heats. At each carbon level one steel had a low sulfur content (0.004 pct) and the other two steels a higher sulfur content (about 0.013 pct). Rare-earth silicide was added to one heat of the higher sulfur steel at each carbon level. The chemical compositions of the six steels are given in Table I along with the number designation used for reference throughout this paper. The preparation and processing of these steels into Z6-cm-thick plates and the mechanical properties of longitudinal, transverse, and through-thickness tension and Charpy V-notch specimens fabricated from these plates have been described previously. ~The mechanical properties pertinent to the present study are summarized in Table II. The 0.1 pct carbon steels had yield strengths of about 23
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