Characterization of inclusions of X80 pipeline steel and its correlation with hydrogen-induced cracking

By Xue, H.B. & Cheng, Y.F.
Published in Corrosion Science NULL 2011

Abstract

In this work, the microstructures of an X80 pipeline steel were characterized, and their susceptibilities to hydrogen-induced cracking (HIC) were investigated by hydrogen-charging, electrochemical hydrogen permeation and surface characterization. It is found that the microstructure of X80 pipeline steel consists of a polygonal ferrite and bainitic ferrite matrix, with martensite/austenite (M/A) constituents distributing along grain boundaries. The inclusions existing in the steel include those enriched with Si, Al oxide, Si–ferric carbide and Al–Mg–Ca–O mixture, respectively. The majority of inclusions are Si-enriched. Upon hydrogen-charging, cracks could be initiated in the steel in the absence of external stress. The cracks are primarily associated with the Si- and Al oxide-enriched inclusions. The diffusivity of hydrogen in X80 steel at room temperature is 2.0 X 10-11 m2/s, and the estimated hydrogen trapping density in the steel is as high as 3.33 X 1027 m-3.

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