Nitrocarburizing was carried out with various $CH_4$ gas composition with 4 torr gas pressure at $570^{circ}C$ for 3 hours and post oxidation was carried out with 100% $O_2$ gas atmosphere with 4 torr at different temperatures for various time. In the case of plasma nitrocarburizing, It is that the ratio of ${varepsilon}-Fe_{2-3}$(N, C) and ${gamma}^{prime}-Fe_4$(C, N), which comprise the compound layer phase, depend on concentrations of $N_2$ gas and $CH_4$ such that when the concentration of $N_2$ and $CH_4$ increased, the ratio of ${gamma}^{prime}-Fe_4$(C, N) decreased, but the ratio of ${varepsilon}-Fe_{2-3}$(N, C) increased. The thickness of compound layer consistently increased as gas concentration increased regardless of $N_2$ and $CH_4$ expect when the concentration of $CH_4$ was 3.5 volume%, it decreased insignificantly. When oxidizing for 15min in the temperature range of $460{sim}570{^circ}C$, the study found small amount of $Fe_3O_4$ at the temperature of $460{^circ}C$ and also found that amounts of $Fe_2O_3$. and $Fe_3O_4$ on the surface and amount of ${gamma}^{prime}-Fe_4$(C, N) in the compound layer increased as the increased over $460^{circ}C$, but the thickness of the compound layer decreased. Corrosion resistance was influenced by oxidation times and temperature.