Microscopic visualization of hydrogen diffusion in UNS S32750 super duplex stainless steel: Roles of crystal structure and grain size

The microscopic hydrogen diffusion in UNS S32750 super duplex stainless steel was analyzed using a polyaniline-nickel-based hydrogen video imaging system. The hydrogen flux in the body-centered-cubic ferrite (alpha) phases was larger than in the face-centered-cubic austenite (gamma) phases, causing hydrogen diffusion from the alpha to gamma phases. The order of the hydrogen flux was as follows: (high) the center of the alpha phases > near the alpha-gamma boundaries in the alpha phases > near the alpha-gamma boundaries in the gamma phases > the center of the gamma phases (low). The grain size of the phases also affected the hydrogen flux distribution. A small grain size of the gamma phase led to a large hydrogen flux around the center of the gamma phase, because the effect of the hydrogen outflux from the alpha phase to gamma phase increased with decreasing distance from the alpha-gamma boundary.