Characteristics and formation mechanism of serrated markings on the hydrogen-related quasi-cleavage fracture in as quenched low-carbon martensitic steel

The present paper investigated the characteristics of serrated markings on the hydrogen-related quasi-cleavage fracture in an as quenched low-carbon martensitic steel. The serrated markings corresponded to the ridges between {011} micro-facets. The ridges were formed along lath/block/packet boundaries or nearly parallel to 〈211〉 or 〈011〉 directions within the lath. In addition, the angle between {011} micro-facet and tensile axis was the largest of the six crystallographically equivalent {011} planes in each variant, demonstrating that the resolved normal stress imposed on the {011} plane plays a key role on the quasi-cleavage fracture. The above characteristics are common to martensitic steels and ferritic steels. We propose that the coalescence of vacancies/voids induced by hydrogen-enhanced screw dislocation motion needs to be considered to understand the fundamental mechanism of the hydrogen-related quasi-cleavage fracture along {011} planes in BCC steels.