Hydrogen Visualization in Steels Using Ag Decoration Method

The relation between hydrogen distribution and metallographic microstructure was investigated by means of Ag decoration technique for a SUS304 austenitic stainless steel, and martensitic and spheroidized SCM440 steels precharged with hydrogen. Preferential distribution of Ag particles was seen on the slip lines of the deformed and hydrogen-charged SUS304 stainless steel, suggesting that the slip lines act as hydrogen trap sites. The martensitic SCM440 steel showed almost no selective Ag deposition, indicative of apparently homogeneous distribution of hydrogen. This is probably because the distribution of dislocations with relatively high concentration and the fine structure including lath boundaries etc. acting as hydrogen traps is homogeneous. The spheroidized SCM440 steel showed almost no Ag deposition on the coarse cementite particles and the Ag particle distribution on the other areas did not show clear selectivity. This result suggests that the hydrogen does not diffuse through the cementite particles. The smallest Ag particle size observed by means of atomic force microscope was in the order of 10 nm. Though the minimum size of the Ag particle does not necessarily indicate the resolution of the hydrogen visualization, Ag decoration technique is useful to observe the hydrogen distribution.