Small amounts of the following various elements were added to high purity white cast irons, whose chemical compositions were adjusted to 2.4%C, 1.1%Si, 0.01%P, 0.01%S. Three values of the Mn content were used: 0.04%, 0.15% and 0.3%Mn, (Mn/S ratio; 3∼5, 15∼25 and 25∼35). The elements were: Cu, Ag, Mg, Ca, Zn, Cd, B, Al, Ti, Sn, Pb, V, Nb, Ta, Ce, N, P, As, Sb, Bi, Cr, Mo, W, Co, Ni and Te.
Melting of the specimens was carried out mainly by carbon resistance electric furnace (Kryptol). In the case of nitrogen, a vacuum high frequency induction furnace was used. Alloying elements were added as high purity ferro-alloys, pure metals or nitrogen gas.
The required times for the first- and second-stage graphitization were measured by a dilatometric method, which was carried out at 950°C (first-stage) and about 700°C (second-stage), respectively.
Mn up to 0.5% promotes the first-stage graphitization. Mn up to 0.15% promotes the second-stage graphitization, but Mn beyond 0.3% retards it.
In the case of the first-stage graphitization, B(<0.01%), Ca and Mg are the strongest graphitizers, Ti(Mn/S ratio 4), Zr and Al are strong, and Ti(Mn/S ratio 20, 30), Ni, Co, Cu, Pb, Ag, As, P and Sn are weak graphitizers. Zn, Ta, W, Sb and Cd show almost no effect. Ce(<0.02%), Mo, Bi and Nb are moderate anti-graphitizers, Cr and V are strong and B(>0.01%), N and Te are the strongest anti-graphitizers.
In the case of second-stage graphitization, the effects on the graphitization of cementite are similar to the first-stage graphitization, except for some elements. P(>0.06%), Sb, As and Sn show no effect or rather are weak graphitizer in the first-stage, but in the case of second-stage graphitization, these elements become strong anti-graphitizers.
The graphitization of cementite is a function of the bond of cementite, the carbon activity, the diffusion rate of carbon atoms and the nucleation frequency of graphite. Further, it is necessary to consider the interaction between various elements and N or S, etc.
Effects of various elements on as-cast and annealed structure were also studied.
These results may be of use not only in malleable cast iron production, but also in the gravity diecasting technique of flake and spheroidal graphite cast iron.
抄録全体を表示