鋳鉄の研究（第3報）純鉄-炭素系合金の凝固条件による組織の変化

Abstract

In Fe-C alloys, carbon usually appears as Fe3C or graphite. The experiments were carried out to find the condition in which either Fe3C or graphite can be found in these alloys. The specimens were practically, pure Fe3-C alloys, and to reject the influence of atmosphere the experiments were carried out in high vacuum of (2∼3)×10−2 mmHg, using high frequency induction furnace. The maximum melting temperature was 1400° to all the specimens. After reaching the maximum temperature the specimens were cooled at the rate of 10°/min to the temperature 50° above the desired temperature at which furnace current is cut off, then cooled at the rate of 10°/3 min. The specimens were cooled in high vacuum and their surfaces were observed as they solidified, then examined their microstructurs. The results were as follows: Even melting in high vacuum of (2∼3)×10−2 mmHg, the structures of pure Fe-C alloys are not always gray, but they depend much upon the carbon contents. For an example, if the furnace current is cut off at 1240° and specimen, whose carbon content lie between 3.7∼4.0%, is cooled as above mentioned, the microscopic structure indicates entirely eutectic graphite, but if the carbon content of the specimen is more than 4% or less than 3.7%, the structure indicates white pig structure or gray pig structure accompanied by white pig structure.But this range of carbon contents depends upon the temperature at which the furnace current is cut off, and it decreases as the temperature rises, then about 1400° is the critical temperature of this range under these conditions. In short, there is a definite range of carbon content in which the structure of Fe-C alloys becomes perfectly gray pig structure, while, out of this range, white pig structure is always accompanied, and this range depends upon the temperature at which the furnace current is cut off. Furthermore, the authors found that not high but low vacuum nearly 10 mmHg is sufficient to show perfect gray structure in Fe-C alloys of this range. As the conclusion, the authors deduce that the condition in which the carbon in pure Fe-C alloys appears as Fe3C or graphite depends not only upon the gas, super cooling, but also on solidifying practice.