Visualization of Diffusive Hydrogen in Low Alloy Steel by means of Hydrogen Microprint Technique at Elevated Temperatures

Hydrogen diffusion behavior of low alloy steel was visualized by means of hydrogen microprint technique. Effects of exposure time and temperature on the availability of hydrogen microprint technique were also examined. It was found that silver particles, which representing the emission site of hydrogen atoms, were distributed almost uniformly in the matrix after hydrogen charging, and that were arranged at the periphery of second phase particles such as MnS and Al2O3. Area density of the silver particles was clearly increased when the exposure time after cathodic hydrogen charging increased at room temperature or the exposure temperature was higher than room temperature, which was in agreement with the result obtained from the thermal desorption analysis. From a series of the heating experiments, it was also shown that hydrogen microprint technique would be applicable at temperatures below 120°C. After the long time exposure in the hydrogen-charged specimens, preferential accumulation of silver particles around the Al2O3 and MnS particles was identified. This suggested that hydrogen atoms were diffused not through the inside of the second phase particles but through the interface between the second phase particles and matrix phase.