The diffusion of H in steels was examined by using a high-sensitivity H micro-print technique and an electrochemical H permeation method. The main diffusion path in an extremely-low C-steel was the lattice within grains. The grain boundaries were not accelerated diffusion paths. In the case of a hypo-eutectoid steel, the H diffused through proeutectoid ferrite and ferrite in pearlite under steady-state H diffusion. The diffusion paths were carbide/ferrite interfaces when H charging was interrupted before reaching the steady state. This was attributed to a reversible trapping effect of the interface. The detection efficiency of the high-sensitivity H micro-print technique was 75% for the low-C steel and 40% for the hypo-eutectoid steel.

Visualization of Hydrogen Diffusion in Steels by High-Sensitivity Hydrogen Microprint Technique. K.Ichitani, M.Kanno: Science and Technology of Advanced Materials, 2003, 4[6], 545-51