Abstract
The following equations of the carburizing equilibrium have been confirmed by many investigators.
3Fe+2CO Fe3C+CO2[Fe-C-O System]
3Fe+CH4 Fe3C+2H2[Fe-C-H System]
Lately Mr. Madono presented the opinion in which he asserted the carburizing equation should be represented as follows:
(Solid Sol.)+2CO (Solid Sol.)+CO2
(Solid Sol.)+CH4 (Solid Sol.)+2H2
On account of the unstableness of Fe3C, after iron or steel is saturated with carbon the equilibria coincide with 2CO C+CO2 or CH4 C+2H2. He carried out experiments on carburizing of the electrolytic iron sheet for a long time at various temperatures with the solid carburizing mixture, and the result obtained was that C contents absorbed in the iron sheet coincided with the saturated concentration of graphite in austenite. He cosidered that this result proved the truth of his own theory.
The authors also carried out carburizing experiments with the electrolytic iron wire, 0·5mm thick, by pure CO gas, and found that at a temperature below A1 point the formation of Fe3C was surely recognized by means of magnetic and X-ray analyses, and at a temperature above A1 point C was absorbed over the saturation value of that in austenite. In considering this fact, the authors supports the old theory of carburization. In the case of the pack carburizing, however, the carburizing action stops when C% reaches the saturation value at any temperature, but this fact does not suggest the carburizing equilibrium to be 2CO C+CO2 in all cases.
