| 摘要 |
PURPOSE:To purify the surface of a metal material to be treated as well as to reduce carburization irregularity by stirring effect, in transferring the metal material from a carburization period to a diffusion period, by evacuating an inert gas after said inert gas is introduced into a carburization furnace to relatively dilute H2 gas in an atmosphere in said carburization furnace. CONSTITUTION:The interior of a carburization furnace having a metal material (e.g., a steel product) to be treated is evacuated as shown by a line 13 to adjust the inner pressure thereof to a predetermined vacuum degree, for example, about 100mum Hg. On the other hand, the metal material in the furnace is heated to a predetermined carburization temp. 43, for example, about 1,040 deg.C and this temp. is held until a hereinbelow described diffusion period is finished. In a stage wherein the interior of the furnace is held under a predtermined pressure reduced atmosphere as shown by a line 33 and the metal material is held to the aforementioned temp. 43, a carburizing gas is introduced as shown by a line 55. In this case, a vacuum degree is lowered to, for example, about 100mum Hg in this case but a carburization period 65 is maintained in this state for a predetermined time and an inert gas such as Ar is introduced at the terminal period thereof as shown by a line 91. Succeedingly, the residual gas in the furnace is evacuated as shown by a line 75 and, after the diffusion period 85 is elapsed, for example, oil tempering is applied to complete carburization treatment. |
