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

HB Xue, YF Cheng - Corrosion science, 2011 - Elsevier
Corrosion science, 2011Elsevier
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 …
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 2.0×10−11m2/s, and the estimated hydrogen trapping density in the steel is as high as 3.33×1027m−3.
Elsevier