Control of Cast Grain Size of Steel Castings; Effect of Grain Refinement on Properties

摘要

Inoculation techniques were developed to refine the as cast structure of high strength steel. Titanium was found to be the most effective inoculant. Large titanium additions (0.6%) form sulfides which embrittle the steel. Small titanium additions (0.1%) together with controlled superheat and mold design may produce significant refinement. Under these conditions the structure of unidirectionally solidified castings was changed from columnar to equizxed and the reduction in area increased by approximately 25% for specimens oriented vertically to the direction of heat flow and increased about 75% for horizontally oriented specimens. A small improvement in reduction in area of keel block castings was obtained by lthis method. Some improvement in toughness was also obtained by this grain refinement. The influence of vacuum melting on the cast structure of the same steel was investigated. A hypothesis explaining the mechanism of refinement by vacuum melting was proposed. (Author)