The Fracture Behavior of Hydrogen-Charged A508III Low Alloy Steel in the Process of Natural Hydrogen-Escaping

The effects of hydrogen charging as well as natural hydrogen escaping on fracture behavior of A508III steel at room temperature were investigated. The presence of hydrogen caused a slightly increase in yield strength and a distinct decrease in the elongation and reduction in area, but no or hardly any influence on the ultimate tensile strength (UTS). Non-charged specimen exhibited a ductile mode of failure with micro-void coalescence, while the H-charged specimens showed typical brittle fracture with “fish eye” appearance. The presence of hydrogen gave an increase in the dislocation density after tensile deformation. Nucleation of defects occurred primarily from the inclusions which contain complex oxides of Al, Mg and Ca, and (Ca, Mn)S, as well as MnS only to a small extent. The parameters of non-metallic inclusions, such as type, shape, size and content play the decisive role at the defect formation. In the process of natural H-escaping, the fracture surface characteristics of H-charged steels gradually transferred from brittle fracture mode to ductile fracture mode. At the same H-charged time, the H-escaping time required for the brittle-ductile transition was related to the H-charged current density.