The susceptibility to the hydrogen embrittlement of commercial heat of TRIP 780 steel of the type C-Mn-Si was studied on previously hydrogenated samples by a slow strain rate tensile tests (SSRT) in the initial state and in the state after 5% deformation in the longitudinal and transverse directions relative to the rolling direction. Samples were hydrogenated in 0.1N sulfuric acid solution with the addition of KSCN. Due to the transformation of retained austenite to deformation-induced martensite after 5% deformation, an increase of yield strength of 230 MPa, a tensile strength of 30 MPa and elongation at fracture decrease by 6.5 % occurred in contrast with the initial state without hydrogen. The presence of hydrogen in the steel in the initial state caused a decrease of steel strength from 900 MPa to 753 MPa, and a significant reduction in elongation at fracture from 34 % to 6 %. Hydrogen present in the samples after the 5% deformation had an effect on an increase of the yield strength by 60 MPa, a decrease in the tensile strength by 100 MPa, while the elongation at fracture reached only 2.5 %. There were no differences found in the mechanical properties of the samples taken in the longitudinal and transverse direction relative to the rolling direction. Fracture surfaces of the tensile test bars were subjected to fractographic analysis. For hydrogenated samples, the proportion of brittle fracture and quasi-cleavage fracture increased.Keywords: Hydrogen embrittlement, TRIP steel, slow strain rate test (SSRT), retained austenite
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