Abstract
The hydrogen effect on a X65 carbon steel was investigated using in-situ electrochemical nanoindentation approach. The alterations in elastic behavior, pop-in load, and hardness under hydrogen-free and hydrogen-charged conditions in both ferrite and bainite were compared and discussed. The results demonstrated a non-affected elastic behavior by hydrogen in both microconstituents. The homogeneous and heterogeneous dislocation nucleation are proposed as the dominant mechanisms for pop-in behavior in ferrite and bainite, respectively. In addition, the reduction of pop-in load by hydrogen in both microconstituents indicates a hydrogen-enhanced dislocation nucleation in both homogenous and heterogeneous manners. Moreover, a hydrogen-induced hardness increment was detected in both microconstituents, which is related to the hydrogen-enhanced lattice friction on dislocations. Also, the more prominent hardness increment in bainite was caused by its significantly more trapping sites.
Highlights
Carbon steels have been widely used for decades as efficient means for long distance transportation in oil and gas industries due to its low cost, simple manufacture, and remarkable mechanical properties [1]
It shows that the local misorientation in the bainite area is higher than the ferrite matrix, indicating a stronger distortion in the bainite microstructure, which is in consistent with the higher dislocation den sity in bainite than that in ferrite from electron channeling contrast imaging (ECCI) results (Fig. 2c and d)
The hydrogen effect on nanomechanical properties of a ferrite-bainite X65 carbon steel was examined by using the in-situ electrochemical hydrogen charging (ECNI) test
Summary
Carbon steels have been widely used for decades as efficient means for long distance transportation in oil and gas industries due to its low cost, simple manufacture, and remarkable mechanical properties [1]. A combination of different mechanisms is often applied to explain some complicated hydrogen degradation behavior [6,27] This is because hydrogen embrittlement is a complex phenomenon that depends heavily on the intrinsic properties of mate rials, the testing approaches, as well as the applied hydrogen environ ment. The macroscopic testing methods cannot reveal the hydrogen effect on individual phases, which is very important for the pipeline industries to develop advanced carbon steels by adjusting the volume fraction of each phase to obtain proper mechanical properties as well as a high hydrogen embrittlement resistance. The in-situ ECNI test was carried out to investigate the hydrogen effect on the nanomechanical response of different microconstituents in the studied carbon steel and providing a better fundamental understanding of the associated material degradation mechanisms
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