Effect of volume fraction and shape of sulfide inclusions on through-thickness ductility and impact energy of high-stren
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I.
INTRODUCTION
A L T H O U G H much effort has been devoted to studying the effect of inclusions on the ductility and toughness of highstrength plate steels for testing directions lying in the plane of the plate, t-s little attention has been directed at studying their effects in the through-thickness testing direction. In contrast, a large effort on through-thickness testing of lowstrength plate steels has developed in the last few years because of the concern with lamellar tearing during welding, which has been shown to be related to through-thickness ductility. 9'~~This lack of information is unfortunate because the deleterious effect of inclusions on ductility or toughness in high-strength plate steels is greatly accentuated in this testing direction, and in some cases, for example ballistic fracture of armor plate, the through-thickness ductility may be an important consideration. Much of the work on low-strength plate steels has shown that the through-thickness ductility and impact energy are intimately related to both the volume fraction and shape of the sulfide inclusions, l~ Decreasing the volume fraction of inclusions or changing the shape of the inclusions from elongated sulfide inclusions to more globular inclusions by rare-earth treatment has been shown to result in marked improvements in through-thickness ductility. In the present study, the effect of the volume fraction and shape of sulfide inclusions on the through-thickness ductility and impact enG.R. SPEICH, Research Consultant, and W . A . SPITZIG, Associate Research Consultant, are both with United States Steel Research Laboratory, Mortroeville, PA 15146. Manuscript submitted December 29, 1981.
METALLURGICAL TRANSACTIONS A
ergy of high-strength plate steels has been investigated at various strength levels. In the present work, the axisymmetric and plane-strain tensile ductility, and the impact energy and transition temperature of a series of quenched and tempered, high-strength AISI* 4340 plate steels were measured in both the trans*American Iron and Steel Institute
verse and through-thickness testing directions. The steels had been prepared by electroslag-refining, low-sulfur practice, and by rare-earth treatment to vary systematically the volume fraction and shape of the sulfide inclusions. Four tensile-strength levels of 930, 1210, 1410, and 1960 MPa (135, 175,205, and 285 ksi) were studied.
II.
M A T E R I A L S AND E X P E R I M E N T A L PROCEDURE
The chemical compositions of the eight steels used in this work are given in Table I. All the steels had the standard AISI 4340 steel composition and were prepared by vacuum induction melting of 227-kg (500 pound) melts. The steels were all aluminum-deoxidized and then cast as rectangular 200- by 300- by 460-mm (8 by 12 by 18 inch) ingots. One of the steels was subsequently used as an electrode and electroslag-refined** to achieve a very low sulfur content of **The electroslag-refining was performed at Army Materials and Mechanics Research Center, Watertown, Massachusetts.
0.002 pct. Th
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