Hydrogen Entry into Pure Iron Treated by Plasma Nitriding

In order to prevent hydrogen entry into steels, the effect of the plasma nitriding treatment on the hydrogen permeation behavior of pre irons was investigated in this study. The plasma nitriding was performed in a nitrogen-hydrogen atmosphere composed of 75 % N-2-25 % H-2 at 400 degrees C and 600 Pa for 3.6 ks. The nitrogen compound layer was composed of epsilon-Fe2-3N and gamma'-Fe4N phases, and its thickness was ca. 2.8 mu m. The hydrogen permeation tests revealed that the hydrogen absorption efficiency of the nitrided pure iron was one fiftieth that of the untreated one. In addition, the nitrided pure iron had a lower diffusion coefficient than the untreated one. The nitrided layer acts as an effective barrier against the hydrogen entry and diffusion in pure iron.