  Slow strain rates tests (SSRT) were conducted on hydrogen-containing
specimens of PH13-8Mo maraging stainless steel. Hydrogen-assisted subcritical
quasi-cleavage cracking was shown to take place during SSRT, thus accelerating
material failure. Fractographic analysis showed that quasi-cleavage is composed
of flat brittle areas and rougher areas. Using cross-sectional electron
backscatter diffraction (EBSD) analysis of a secondary subcritically grown
crack, we observed brittle cracks propagated across martensite blocks ahead the
main crack tip. These cracks were stopped at high-angle boundaries. The crack
direction was consistent with propagation along {100} type planes.
High-resolution EBSD showed significant crystal lattice rotation, hence
consequential plastic deformation, concentrated between the main crack tip and
the cracks located ahead it. It is concluded that quasi-cleavage in the
material investigated here consists of {100} cleavage cracks connected by
ductile ridges. A discontinuous mechanism, involving re-initiation of new
cleavage cracks ahead the main crack tip is suggested.
