Local Dissolution of MnS Inclusion and Microstructural Distribution of Absorbed Hydrogen in Carbon Steel

Microelectrochemical polarization and silver decoration techniques were performed on a small area with and without MnS inclusions in carbon steel. The surfaces of the inclusions were found to have partially dissolved in the potential range from 0.35 to −0.25 V (vs. SHE) in a boric-borate buffer ( p H 8.45) solution with 10 mM NaCl, whereas the entire surface of the inclusions was slightly dissolved below and above this potential range. Silver deposition occurred only on and around MnS inclusions below 0.0 V, which generally corresponded to the stable region of hydrogen sulfide ions. When the inclusion surfaces were partially dissolved, silver deposition was observed only in the dissolved area. The dissolution species from MnS inclusions appeared to have promoted the hydrogen absorption reaction.