抄録
The addition of 0.3∼0.6% Mn to 3.2% C-5.5% Si grid iron melt lowers both the specific electric resistance and the hardness, while it raises the deflection amount and transverse strength at the bending test. The phenomenon can be explained as follows : MnO produced from the addition of manganese acts on suspended particles of 2 FeO2 · Sio2 or other silicates in molten iron, lowers the melting point of such non-metallic inclusions and promotes their growth, resulting easy separation of these inclusions from molten iron and prevention of the appearance of the normal flaky graphite in cast iron. The elimination of such reaction products promotes to make the reaction of FeO+Mn=MnO+Fe proceeding to the right side, resulting good deoxidation by adding small amount of manganese. This fact brings the appearance of the eutectic graphite structure in iron by the aid of the elimination of silicates which cause the growth of the graphite. Excess manganese besides that used for deoxidation and the killing alloys in iron and erases the eutectic graphite. Increase of silicon from 1% to 4% in 3% C-15% Ni-iron enhances the electric resistance and lessens its temperature coefficient, while the hardness is hardly influenced thereby. The reason why the electric resistance is greatly increased by the Si-addition depends mainly on the increase of the amount of the graphite and its large flaky form due to the Si-addition. By 0.5% Mn-addition the high-Ni, high-Si castings become tough and strong, and its electrical resistance is decreased, which is caused by the less amount of the graphite separated from the melt and the suppression of the growth of the graphite. Moreover, the addition of 0.5% Mn makes the amount of martensite maximum in the range of 0∼2% Mn-addition.
