Effects of dislocations and hydrogen concentration on hydrogen embrittlement of austenitic 316 stainless steels

Highlights: • High concentration of hydrogen induces martensitic transformation. • Defects induced by hydrogen-charged may be dislocations. • Hydrogen desorption peaks shift to higher temperature for annealing specimen. • Positron annihilation technique studies the evolution of hydrogen and defects. -- Abstract: The effects of dislocations and hydrogen concentration on the hydrogen embrittlement (HE) in 316 austenitic stainless steels (316SS) were systematically investigated in the present study. The results revealed a decrease in tensile strength and ductility of 316SS after hydrogen charging. Furthermore, the severity of HE was dependent on the hydrogen concentration. The results of x-ray diffraction revealed the presence of martensite in the hydrogen-charged (50 mA /cm²) specimen annealed at 1000 ℃. This was attributed to the internal stress originating from hydrogen-induced lattice expansion. The analysis of the fracture surface of all the specimens revealed an increase in the brittleness with the absorption of hydrogen. An increase in the hydrogen concentration induced a transformation of the fracture mode i.e., from ductile dimple fracture to cleavage and intergranular fractures. The evolution of hydrogen in 316SS was associated with the defects induced by deformation. The shift in the major desorption peaks of the annealed specimen to the high-temperature region indicated the formation of effective hydrogen-trapping sites during hydrogen-charging. The specimens were subjected to positron lifetime spectroscopy and thermal desorption spectroscopy. The results for the raw specimen, charged at 20 mA /cm², revealed the gradual escape of hydrogen atoms and recovery of vacancy defects with an increase in the annealing temperature. In addition, the hydrogen-induced and cold rolling-induced dislocations was preserved.