Effect of the Electro-Chemical Hydrogen Charging Time on Hydrogen Embrittllement of X70 Steel Using for Gas Pipeline

摘要

This study investigated the effect of the hydrogen charging time under the elect ro-chemical hydrogen charging condition on hydrogen embrittlement of hot-rolled :ind then air-cooled AIM X70 steel. Tensile and V-notch Charpy impact test specimens were held for 0 h. 2h ,4h,and 10h in the electrolyte pot during electro-chemical hydrogen charging processes and then both of tensile and impact tests wrer completed at room temperature. The microstructure consisted of fine acicular ferrite ,coarse polygonal ferrite and pearlite. The yield and tensile strength decreased slightly and elongation decreasedrapidly up to 2 h holding time and then decreased slowly with the holding time.The V-notch Charpy impact value decreased continuously up to 4 h holding time and then increased slightly up ti 10th.the morphology of the fracture surface changed from a ductile type to a brittle type with the hydrogen charging time Secondary cracks were observed in the hydrogen charged specimens. No external cracks were formed at the specimen surface of the tensile tested with 0 h holding time, but many external cracks were observeed at the surface of the hydrogen charged specimens. Cracks were observed in the- nominal and parallel directions to the tensile direction at the longitudinal cross-section region near the tensile fractured surface with the 2 h held specimen.