Abstract
Abstract The hydrogen uptake by steels naturally corroding in an acidic H2S solution, varied significantly with microstructure and chemical composition. It changed in very close association with the secondary precipitation hardening process; i.e., hydrogen entry was enhanced by the precipitation of Mo2C and (Fe,Cr)7C3 carbides, and such enhancement diminished as the overaging process took place. The precipitation of fine carbide particles provides sites of hydrogen trap at the carbide interface and increases the amount of hydrogen absorbed. (Fe,Cr)7C3 carbide appears to have a larger binding energy with hydrogen than Mo2C carbide because Cr-containing steels absorbed hydrogen to a significantly greater extent. Cementite of Cr steels played a peculiar role in hydrogen uptake; i.e., it had only a minimal effect in tempered martensite structure, but absorbed large amounts of hydrogen in upper bainite structure. Because of the effect of (Fe,Cr)7C3, hydrogen uptake increased with Cr content of steel up to 17% ...
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