Effect of Strength and Precipitation on the Mechanisms of Hydrogen Embrittlement in 2 1/4CR1MO Steel

摘要

The effect of material strength on the propensity to embrittlement by hydrogen of 2 1/4 CrlMo steel was investigated. Tensile test pieces were quenched and tempered at 550C for up to 500 hours, after which, specimens were tested in the uncharged and electrolytically hydrogen charged condition. It was found that tensile strength remained virtually unaffected by the presence of hydrogen, although the reduction of area and strain to failure were severely affected. Examination of fracture surfaces revealed that specimens in the uncharged condition exhibited microvoid coalescence and shear modes, while hydrogen charged material exhibited brittle intergranular and cleavage modes at high strengths. Tempering to a lower strength level resulted in the complete disappearance of brittle modes and the appearance of a quasi-cleavage fracture mode which involved a significant degree of plastic deformation. This transition from brittle to ductile modes of hydrogen embrittlement was found to be coincident with the onset of M2C carbide precipitation.