SEGREGATION IN SMALL STEEL CASTINGS

Carbon segregation in small castings often occurs near riser necks. Systematic studies were continued to determine effect on segregation of such interrelated factors as size and shape of riser and casting, and design of riser contact. Results from numerous specimens show quantitatively that intensity of carbon segregation under neck-down risers varies directly as the neck length and inversely as the neck diameter. The degree of segregation also increases as the section thickness of the casting increases. Segregation beneath knock-off riser contacts is minimized by 1 larger neck diameters, 2 shorter necks, 3 use of exothermic materials for knock-off riser cores, 4 increase in ratio of riser thickness to casting thickness, or 5 any combination of these. Centerline segregation, resembling that in ingots, was found in long, slender castings, but this segregation relates more to centerline shrinkage than to riser contact design. Centerline segregation is reduced by increasing the taper of castings to provide more complete feeding.