On the Quality-Change of Molten Iron during Holding under Low Pressure (1st Report)

Abstract

The solidification behaviors of molten cast irons after they were held for various durations under low pressure at 1400° were clarified, and the spherulite formation in cast iron was discussed:—(1) The effect of high temperature melting in air is expected to take place by vacuum melting at lower temperature. Both the dissolved oxygen and, the combined one as non-metallic inclusions, in molten iron are gradually reduced by carbon (2) At the first stage of melting, the fracture of the iron becomes mottled, the black part having spheroidal growth and undercooled graphite. The dendritic austenite is densely separated in the rosette grouping differing from that in the white part. The stage is mainly that of the removal of the dissolved oxygen. (3) At the intermediate stage, the fracture becomes all black having undercooled graphite, the stage being that of the removal of non-metallic inclusions. (4) At the last stage, it becomes white again, the structure consisting of undercooled acicular carbide and supersaturated austenite, in which, if graphitization proceeds, spheroidal or massive graphite appears. (5) It appears to be true that in oxidizing iron, oxygen is attracted to and strongly adsorbed upon graphite surfaces to form flaky one, and in deoxidizing iron, the oxygen is removed causing a change of the graphite form; Mg-treatment of predeoxidized molten iron probably not only removes the remaining oxygen and sulphur but also forms C-Mg atom binding, which accomplishes the spheroidization of graphite.