Dowa Mining Co., Ltd.

Toshiyuki Kawamura

Hitoshi Goi

Fumitaka Abukawa

Hirofumi Kamisugi

Atsushi Murayama

In a cementation method of metals in which hydrocarbon gas and oxidization gas are introduced into a heat treatment furnace, a small quantity of hydrocarbon gas of is introduced at a low pressure into the heat treatment furnace. The shift time and the gradient of the carbon potential varying toward a predetermined high or low level are controlled by increasing or decreasing the quantity of cementation gas and oxidization gas to be supplied to the furnace. After the carbon potential is reached to the high or low level, the carbon potential is maintained for a predetermined time period so as to prevent the deposited carbide from being bulked. In order to prevent the gas supply pipe from being choked with the soot of the hydrocarbon, oxidization gas of intermediate pressure is flushed into the gas supply pipe. In order to prevent the components of the atmosphere in the furnace from varying due to the change in furnace pressure when the door is opened or closed, hydrocarbon gas of a low pressure and oxidization gas of an intermediate pressure are added in the conversion pipe in the preheating zone. CO.sub.2 of intermediate pressure is supplied into each gas supply pipe at the same time in order to remove the soot in each of the gas supply pipes and to prevent the lack of CO to be introduced into the furnace.

Cementation method of metals

A treating material W pre-heated to a carburizing temperature of 750.degree.-950.degree. C. is heat-treated in a carburizing atmosphere directly supplied with hydrocarbon and oxidizing gases and heated to 1000.degree.-1100.degree. C. Then, the treating material W is forcibly cooled to a temperature below 600.degree. C., the treating material W is re-heated to 750.degree.-850.degree. C., and then it is hardened. Energy required to the carburization can be saved because drastic reduction of the treating time is possible.

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Hamamatsu, Japan

Toshiyuki Kawamura