Effect of hydrogen charging on the mechanical properties of advanced high strength steels

• The effect of hydrogen charging on four high strength steels is evaluated by tensile tests.
• TRIP lost 60% of its ductility, DP 54% and FB 37% at a deformation speed of 5 mm/min.
• HSLA steel did not suffer from hydrogen embrittlement at a deformation speed of 5 mm/min.
• The fracture surface of the H-charged samples showed brittle transgranular cleavage failure.
• Decreasing the deformation speed to 0.05 mm/min increased the hydrogen embrittlement.

The present work investigates the influence of hydrogen on the mechanical properties of four multiphase high strength steels by means of tensile tests on notched samples. This was done by performing mechanical tests on both hydrogen charged and uncharged specimens at a cross-head displacement speed of 5 mm/min. A considerable hydrogen influence was observed, as the ductility dropped by 8–60%. In order to demonstrate the influence of diffusible hydrogen, some parameters in the experimental set-up were varied. After tensile tests, fractography was performed. It was found that hydrogen charging caused a change from ductile to transgranular cleavage failure near the notch with a transition zone to a fracture surface with ductile features near the centre.