13th International Conference on Fracture June 16–21, 2013, Beijing, China 4. Discussion In the group of samples where HIC was observed, the absence of a strong {111}ND texture fiber and the proximity of the texture to that of the random polycrystal is critical to the results of the HIC tests. In this group, HRB is the only sample whose texture significantly differs from that of the random polycrystal. The sharpness of the texture of this sample can be unambiguously related to the observed dominant proportion of {001}ND-oriented grains. The observed susceptibility of these samples to HIC can be associated with their grain mesotexture, which results from the texture that they develop during deformation and recrystallization. The relatively large proportion of high-angle GBs observed in samples HRA and CRA provide plentiful of low-resistance paths for the propagation of intergranular HIC. Sample HRB shows a significantly increased fraction of low-angle GBs, but between grains with orientatio l se t {0 1}ND ( ig. the pipe’s r nce paths to n that it is feasible to improve the HIC resistance of pipeline steels using ns c o o 0 F 5 m e HRB d es the resistanc ). The large number of {001}ND grains observed in sa pl re uc e of this sample to HIC as it facilitates intragranular crack propagation along {001} cleavage planes oriented parallel olling plane. In addition, LABs shared by {001}ND also provide low-resista to intergranular, cleavage-like propagation of HIC in the same plane [5,6,12]. In a remarkable contrast, the warm-rolled, HIC-free samples show a crystallographic texture dominated by well-developed, strong {111}ND or {112}ND texture fibers. In reference [7] it was shown that, at a grain scale, these orientations impede transgranular HIC propagation on the rolling plane. One can also point out that, for a mode I loading, shear stress is null ahead of crack tips [13]; therefore, propagation of HIC in the rolling plane by shear/slip-related fracture along grains with orientation within these fibers can be predicted to be very unlikely. Another characteristic of grains with {111}ND orientations is that they can accumulate large plastic deformation when cracks are close enough to induce interaction and coalescence. This improves the resistance of the steel to HIC by reducing the driving force for growth of interacting cracks, with the consequent reduction in the probability of coalescence of closely-spaced, non-coplanar cracks [13,14]. In addition to the foregoing, the warm-rolled group of samples is particularly prone to have improved HIC resistance because it exhibits an increased number of LABs between {111}ND-oriented grains. It has been reported [7] that LABs with <111> disorientation axis have lower energies than LABs with <100> axis. As a result, a steel with a strong {111}ND texture is expected to show a reduced susceptibility to HIC due to the increased presence of low-angle boundaries with the lowest possible energy. 5. Conclusions It has been show crystallography texture control and grain-boundary engineering. At a macroscopic scale, this can be achieved through controlled warm (ferritic) rolling schedules. These thermomechanical processes lead to a crystallographic texture dominated by the {111}ND-fiber texture and to a mesotexture with a high proportion of low-angle, low-energy grain boundaries. These two characteristics are critical to reduce, beyond traditional practices, the susceptibility of these steels to hydrogen-induced cracking. Acknowledgments The comments and suggestions made by the reviewers are greatly appreciated. References [1] Review of Published Literature on Wet H2S cracking of Steels Through 1989, 2003 Edition, NACE International Publication 8X294, Houston TX, 2003. [2] C.R.F. Azevedo, Failure analysis of a crude oil pipeline. Eng. Failure Anal. 14 (2007) 978–994. -6-
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