滲炭平衡及び諸炭酸鹽による滲炭促進作用に關する理論

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概要

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• An accurate consideration is given on the carburizing reaction which has heretofore been wrongly represented thus : 3Fe+2CO=Fe_3C+CO_2. The reaction should be denoted as follows : (Solid sol.)+2CO⇌(Solid sol.)+CO_2. The concentration of carbon dissolved in iron increases as the partial pressure of CO increases until the solid solution becomes saturated with respect to carbon. Since Fe_3C is unstable, it does not separate out even when the solid solution is saturated with carbon. The equilibrium existing over the saturated solid solution is, 2CO⇌C+CO_2 in which carbon is no longer dissolving in iron. The concentration of carbon varies with the ratio CO/CO_2, the relation being shown in Fig. 4. In this case, the concentration of CO_2 has a larger influence on the carbon content than CO. On the other hand, the reaction C+CO_2→2CO, in genearl, does not reach an equilibrium because of the comparatively inert nature of carbon. It is due to this fact that carburization with carbon alone is relatively feeble ; that is, the atomosphere in contact with carbon is apart from the equilibrium 2CO⇌C+CO_2. The influence of alkali or alkali-earth carbonates (except CaCO_3) in promoting the carburizing reaction, which has hitherto been erroneously considered as a catalytic action, may also be explained on the ground that the equilibrium 2CO⇌C+CO_2 is established in the presence of these carbonates. On beeing heated, they easily react with carbon producing CO and oxy-carbonates or solution of oxides and carbonates. The CO evolved immediately dissociates maintaining the equilibrium 2CO⇌C+CO_2. Therefore, the surface of iron in contact with this mixture becomes saturated with carbon, which further promotes the diffusion of carbon into the mass of iron. In the case of CaCO_3, however, the temperature at which the decomposition pressure is equal to 1 atm., is 780° Therefore, in a vessel open to air and above this temperature a complete decomposition of CaCO_3 will take place. Accordingly, CaCO_3 cannot have influence upon the carburizing reaction.

• 社団法人日本鉄鋼協会の論文
• 1939-01-25

著者

• 眞殿 統

  理化學研究所

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