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In order to investigate the hydrogen embrittlement sensitivity of the low-grade pipeline steel in medium-pressure hydrogen environment，the hydrogen embrittlement sensitivity of L245 steel in air environment and 4 MPa hydrogen environment was studied by smooth and notched slow tensile tests，combined with macroscopic and microscopic fracture characterization and analysis.Results showed that the loss rates of tensile strength，area reduction，and elongation of the L245 steel smooth samples under slow stretching in 4 MPa hydrogen were 5.2%，4.8%，and -0.1%，respectively.However，the loss rates of tensile strength，area reduction and tensile displacement of the notched samples under slow stretching in 4 MPa hydrogen were 19.1%，45.6%and 15.4%，respectively，indicating the occurrence of hydrogen embrittlement.The slow tensile fracture mode of the L245 steel smooth sample in air was ductile fracture.After the notch was opened，the crack source of the smooth samples started at a certain position of the notch and expanded inward in the way of quasi-cleavage fracture，accelerating the fracture process of the sample，but the overall fracture method was still ductile fracture.In contrast，the crack source generated at the necking position when the L245 steel smooth sample was exposed to 4 MPa hydrogen.After the notch was opened，a significant increase in the quasi-cleavage fracture area generated from the notch position towards the interior，which rapidly accelerated the fracture process，and the hydrogen-induced ductile fracture occurred in the center.The fracture mode of L245 steel after notch opening in 4 MPa hydrogen gas was a combination of quasicleavage fracture and hydrogen induced ductile fracture.