## Decarburizing High-Carbon Ferrochrome in Vacuum

Kunio Saijo1, Sanji Nishimura2 and Yoshio Kondo2

1Student, Department of Metallurgy, Kyoto University, and now, Kasei Naoetsu Co. Ltd., Naoetsu
2Department of Metallurgy, Faculty of Engineering, Kyoto University, Kyoto

#### Abstract:

Decarburizing high-carbon ferrochrome with chromium oxide (Eq. (\ref{eq1})) at 1100° to 1400°C in vacuum was studied.

 (FexCr1-x)23C6 + 2Cr2O3 = (Fe23xCr27-23x) + 6CO. \label{eq1}

The results are summarized as follows:
(1) From thermodynamical investigations, the equilibrium partial pressure of carbon monoxide evolved were calculated as more than several mmHg. It is expected from this investigation that the vacuum below 10-1 mmHg is enough to complete the decarburizing reaction.
(2) The reaction starts at 850° to 950°C. Above these temperatures, the decarburizing rate increases with reaction temperature. In the case of an excessive rapid heating, however, the decarburizing is hindered by an eutectic melt formed at 1260°C. Chromium evaporates above 1200°C.
(3) Decarburization is found to be maximal in the stoichiometric mixture of ferrochrome and chromium oxide according to Eq. (\ref{eq1}). The briquetting pressure of 500 kg/cm2 gives the maximal decarburization.
(4) Among various oxides other than chromium oxide, V2O5 and Co2O3 show a good result. Their standard free energies of formation are rather small.
(5) An addition of catalyzer such as alkaline or alkaline earth fluorides improves the initial reaction rate. CaF2 was found to be the best catalyzer among them.
(6) Low carbon ferrochrome below 0.02%C can be prepared with stoichiometric mixture of high carbon ferrochrome and chromium oxide under the conditions of: \begin{enumerate} \item[(a)] Decarburization at 1200°C for 10 hours. 1% of CaF2 is added as catalyzer, or \item[(b)] Two step decarburization at 1200°C in which 5 hours decarburization is repeated twice. The product is ground, mixed and briquetted between decarburizations. \end{enumerate}