| 摘要 |
PURPOSE:To prevent precipitation of the free cementite harmful to a carburization hardening layer in the stage of subjecting a steel material to carburization hardening by using a carburizing gas by controlling adequately the carbon potential of the atmosphere in the carburizing period as well as diffusion period and hardening and heating period during the treating stage. CONSTITUTION:A steel material is put into a treating furnace 1 and an RX gas contg. gaseous CO is supplied into said furnace from a conversion furnace 2. The surface of the steel material is subjected to carburization hardening treatment via a carburizing period, diffusing period and hardening and heating period. The temp. of the atmosphere in the treating furnace and concn. of CO2 therein are measured with respective measuring devices 5, 6 during said treatment. The measured value is inputted to a control device 7 and an enriching gas 3 such as propane, butane or the like is supplied in such a way that the carbon potential of the atmosphere gas attains an eutectic point (0.77%C) or above in the carburizing period. A gas 4 for control such as CO2, N2, Ar, etc. is supplied so as to maintain the carbon potential at about the eutectic point in the diffusing, hardening and heating periods. The carburization hardened layer having excellent quality in which harmful free cementite is not precipitated is formed. |
