Chilling effect and ferrite formation should be avoided in order to obtain thin-wall gray iron castings having high quality. The influences of mold and inoculation on the strength and microstructure of thin-wall gray iron castings were investigated in relation to the cooling rate.
The microstructure of thin-wall castings having composition of high carbon equivalent is composed of fine graphite of eutectic form and ferrite. When the cooling rate increased, the amount of ferrite in the structure decreased and the tensile strength increased. When the cooling rate is kept constant, the thinner the thickness of castings, the more the ferrite ratio is.
Inoculation is effective to prevent chilling effect. The use of combination of 75% ferrosilicon and tin as inoculant is useful to obtain thin-wan castings having high strength. The mechanical properties of round-bar test piece (diameter D) are somewhat better than those of plate test piece (thickness T) under conditions D=2T.
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