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1. (WO2018105693) METHOD FOR VACUUM-CURING METAL WORKPIECE AND METHOD FOR PRODUCING METAL WORKPIECE USING SAME

Pub. No.:    WO/2018/105693    International Application No.:    PCT/JP2017/044001
Publication Date: Fri Jun 15 01:59:59 CEST 2018 International Filing Date: Fri Dec 08 00:59:59 CET 2017
IPC: C23C 8/22
C23C 8/26
Applicants: KUNITOMO NEKKOU CO.,LTD.
國友熱工株式会社
UEJIMA Yasutsugu
上島 康嗣
Inventors: UEJIMA Yasutsugu
上島 康嗣
TSUBOTA Terukazu
坪田 輝一
YAMANE Yusuke
山根 裕介
Title: METHOD FOR VACUUM-CURING METAL WORKPIECE AND METHOD FOR PRODUCING METAL WORKPIECE USING SAME
Abstract:
In the present invention, a hydrocarbon gas is introduced into a treatment furnace in a high-temperature vacuum atmosphere in a treatment step. Carbon separated from the hydrocarbon gas forms a carburized layer on the surface of the metal workpiece. At an early stage of the treatment step, a reference hydrogen concentration corresponding to a reference gas amount that allows carbon to adhere to the metal workpiece without shortage or excess is detected, and a target hydrogen concentration corresponding to the reference hydrogen concentration is set. In a subsequent continuation step, the amount of introduced hydrocarbon gas is controlled so that the hydrogen concentration in the treatment furnace does not exceed the target value. Since hydrogen generated by decomposition from the hydrocarbon gas is immediately removed, it is possible to prevent or significantly suppress penetration of hydrogen into the metal workpiece. Consequently, it is possible to suppress pore formation caused by hydrogen and thereby prevent hydrogen embrittlement of the metal workpiece W using conventional vacuum carburizing equipment. A hydrogen nitride gas may be used instead of the hydrocarbon gas.