Effect of Temperature and H₂ Pressure on Fracture Behavior of X80 Steel in Pure Hydrogen Environment

slow strain rate tensile tests in pure hydrogen environment under different H₂ pressures (2.5, 6.0, 10.0 MPa) and temperatures (−2, 23, 48 ℃) were carried on X80 steel. The effect of H₂ pressure and temperature on the tensile properties and hydrogen embrittlement fracture of the steel was studied. The influencing mechanism was analyzed by fracture morphology observation. The results show that with the increase of H₂ pressure, the tensile strength and percentage elongation after fracture of X80 steel decreased, and the hydrogen embrittlement sensitivity increased. With the increase of temperature, the tensile strength and percentage elongation after fracture decreased first and then increased, and the hydrogen embrittlement sensitivity increased first and then decreased. Increasing hydrogen pressure would promote hydrogen atoms to penetrate into the steel and concentrate at the junctions of crystal boundaries or internal inherent defects, accelerating the initiation and expansion of micro-cracks, thereby leading to fracture. Increasing the temperature would accelerate hydrogen diffusion and reduce the segregation of hydrogen at grain boundaries, and the tensile fracture changed from brittle fracture to ductile fracture.