球状黒鉛可鍛鋳鉄の黒鉛析出と溶解

抄録

Experiments were carried out on graphite precipitation and dissolution of carbon in ordinary malleable iron castings and malleable iron castings with spheroidal graphite.
The results obtained are as follows:
(1) Graphite is not present in the as-cast state of the ordinary malleable iron castings, while numerous spheroidal graphite nuclei were observed in the malleable iron castings treated with a spheroidization agent and graphite spheroids precipitate by the same heat treatment as that of the malleable iron castings.
(2) The first stage of graphitization is accelerated by the addition of the spheroidization agent.
(3) Marked deoxidation by the addition on the spheroidization agent was not observed, but there was a slight increase in oxygen content.
(4) Only one white core is usually observed at the center of the graphite spheroid in nodular iron. However, since the white core in this cast iron is due to decomposition of the cementite which has been drawn in during graphitization, one to several white cores are observed in different locations and shapes.
(5) As the contact surface of graphite spheroids with iron is smaller than that of tempered graphite, the diffusion velocity of carbon in the spheroidal malleable iron is faster than in the case of malleable cast iron if the conditions are the same. But it appears that the difference in velocity disappears as the temperature becomes higher.
(6) Dissolution of graphite in the spheroidal malleable iron is faster than in the case of malleable cast iron when held at 1200°C and the surface oxidation is greater.