The Influences of Hydrogen on Microscopic Plastic Deformation Behavior of SUS304 and SUS316L Stainless Steels

The influences of hydrogen on nano-indentation of stainless steels JIS-SUS304 and JIS-SUS316L with electrochemically-polished surfaces before and after hydrogen exposure were investigated. The “pop-in” behavior, which was presumed to correspond to the onset of catastrophic initial dislocation emissions, was obtained in the nano-indentation force-depth curves of both SUS304 and SUS316L. The force at pop-in was lower in the hydrogen-charged specimens than in the uncharged specimens of both SUS304 and SUS316L. In SUS304, the maximum penetration depth in the hydrogen-charged specimens was shallower than that in the uncharged specimens as a given maximum force, although the Vickers hardness was not changed before and after hydrogen-charging. In the hydrogen-charged SUS304, slip bands were less and pile-up on the specimen surface around the indentation was lower compared with the uncharged SUS304. This implies that slip localization by hydrogen leads to the decrease in the penetration depth. In the SUS316L, there was no pronounced difference in the maximum penetration depth and slip bands morphology between in the hydrogen-charged specimen and in the uncharged specimen. These results suggest that hydrogen facilitates dislocation motions and promotes planar slip, and that the slip planarity is more sensitive to hydrogen in SUS304 with lower austenitic stability than in SUS316L with relatively higher one.