Influence of hydrogen on mechanical properties and fracture of tempered 13 wt% Cr martensitic stainless steel

Slow strain rate tensile (SSRT) tests were performed on tempered 13 wt% Cr martensitic stainless steel (MSS) with hydrogen charging during straining and also separately on hydrogen pre-charged tensile specimens. Microstructural characterization of tempered MSS showed lath martensitic structure with sub-micron sized M23C6 type carbides at lath interfaces and high angle grain boundaries. There was no change in the yield strength but loss in ductility was observed with increase of absorbed hydrogen quantity/pre-charging duration. Fracture surface examination showed increased brittle (intergranular) zone with increase of absorbed hydrogen. Compared to hydrogen pre-charging, effect of hydrogen charging during straining was more pronounced on the mechanical properties as both ductility and yield strength decreased. A change in the fracture mode form ductile dimples to mixed and intergranular fracture was observed with the increase of cathodic current density. Hydrogen enhanced decohesion embrittlement (HEDE) is the dominant mechanism for hydrogen pre-charged and also with hydrogen charging during straining conditions.