The hydrogen trapping phenomena at the grain boundaries in iron-sulfur system were investigated by using the thermal analysis technique and electrochemical permeation experiments.
The specimens were heat treated to give a same grain size and then the concentration of sulfur at the grain boundaries was controlled by the isochronal treatment at various temperatures or the isothermal treatment with different time.
From the results of hydrogen thermal analysis experiments, the amount of hydrogen trapped at the grain boundaries decreased with increasing the sulfur content at the grain boundaries. This is attributed to both of the lowing of the binding energy between the grain boundary and hydrogen and the site competition effects between the segregated sulfur and hydrogen.
The apparent hydrogen diffusivity was determined by electrochemical permeation experiments.
When sulfur segregated to the grain boundaries, the apparent hydrogen diffusivity increased. This can be explained by the decrease of the trapping effect due to the decrease of the amount of hydrogen trapped at the grain boundaries.
