鑄鐵凝固時に於ける黒鉛發生機構並球状黒鉛鑄鐵の研究(I)

抄録

This paper deals with the graphite formation at the freezing range of cast iron, as the form and distribution of graphite is mainly influenced by the time kept at the freezing range.
Quench tests from various higher temperatures were made for normal gray cast irons and for cast irons which were treated with magnesium.
It was shown that both flaky and nodular graphite are formed directly from the melt when the iron is cooled down to the eutectic temperature.
In the case of nodular graphite cast iron, following facts were shown;
The velocity of graphite formation is much smaller as compared to normal gray cast iron.
When the magnesium contents is more than the requisite amount (for example 0.06% for some composition) nodular graphite can be formed only at a slow cooling rate. If the cooling velocity is not slow enough, white cast iron is formed.
Magnesium treated iron which has aquired the ability of nodular graphite formation, does not lose its ability, so far as the magnesium content is more than the requisite amount.
Therefore, if the magnesium treated iron is solidified and remelted under a non-oxidizing atomosphere, the nodular form can be reproduced.
When the remelting temperature reaches as high that magnesium is easily volatilized, the ability of nodular formation is gradually lost, even under the non-oxidizing atomosphere.
The authers have the opinion that magnesium treated iron has a plenty of graphite nuclei in the melt, but the cementite is stable and the graphite is difficulty to grow, and these condition relate to the nodular graphite.