Crystallographic texture helps reduce HIC cracking in pipeline steels

The resistance of sour-service steels to hydrogen-induced cracking (HIC) has been traditionally improved through reduction in sulphur content, control of inclusion morphology, and use of low segregated, uniform microstructures. Other approaches are currently investigated; among them, the control of crystallographic texture as a mean to further reduce the susceptibility of pipeline steels to HIC. In this study, low-carbon steel samples, all within API specifications, were produce using different rolling/recrystallization schemes. These samples showed similar microstructure, but differed in their crystallographic textures. After cathodic hydrogen charging, HIC was detected in the cold- and hot-rolled/recrystallized steels, whereas the warm-rolled/recrystallized steels proved resistant to this damage. These results can be related to the differences in texture and grain boundary distribution observed in these groups of samples. It is concluded that it is feasible to improve the HIC resistance of pipeline steels through crystallography texture control and grain boundary engineering. The use of warm rolling schedules has been proven an effective solution in achieving this goal as they lead to crystallographic texture dominated by the {111}ND-fiber texture, and to a high proportion of low-angle grain boundaries. These two characteristics are necessary to further reduce, beyond traditional methods, the susceptibility of pipeline steels to HIC.