PURPOSE:To accurately control the concn. of carbon in the surface of a material to be treated and to prevent ineffective consumption of gaseous hydrocarbon and ineffective spending of carburization time when the material to be treated is carburized with the gas, by increasing or decreasing the concn. of the gas according to the previously established relation between the concn. of the gas and the carburization concn. of the surface of the material. CONSTITUTION:When gaseous hydrocarbon is fed into an evacuated furnace to carburize a material to be treated, the relation between the concn. of the gas and the carburization concn. of the surface of the material is previously established. A gas analyzer for measuring the concn. of the gas is set in the furnace. The amt. of the gas fed into the furnace is controlled according to the concn. measured by the analyzer so as to attain the required concn. of the hydrocarbon in the furnace.
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