Investigation of hydrogen-induced embrittlement in pearlitic steels for the use in tensile armor of risers.

• Assessment of hydrogen-induced crack propagation along the grain boundaries orientated to {0 0 1} planes. • Influence of hydrogen on loading at low strain rate test. • Evaluation of the chemical composition of two different pearlitic steels related to hydrogen embrittlement. Understanding hydrogen embrittlement (HE) in pearlitic steels is crucial for manufacturing tensile reinforcements used in pipes for the oil and gas industry. This study aimed to elucidate the susceptibility of pearlitic steels to HE, focusing on microstructural influences. Two types of steel (Fe-0.3 %C and Fe-0.7 %C wt.) used in the tensile armor of flexible ducts, differing in chemical compositions and thermomechanical treatments, were analyzed, both exhibiting HE in a hydrogen-rich environment. Samples were investigated using microstructural examination, mechanical testing at low strain rates, and crystallographic texture analysis via Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), and X-ray Diffraction (XRD). Slow strain rate tests (SSRT) at 1.0 × 10–⁶ s–1 were conducted in air and in a 3.5 % NaCl solution with cathodic protection. Sample A showed a decrease in yield strength from 810 MPa in air to 687 MPa after hydrogen charging, with total elongation reduced from 11.15 % to 7.38 %. Sample B, with higher carbon content, showed the highest YS and UTS overall, with YS slightly increased from 1216 MPa in air to 1246 MPa after hydrogen charging. UTS increased from 1311 MPa in air to 1336 MPa after hydrogen charging, while elongation significantly dropped from 8.52 % in air to 2.82 % after hydrogen charging. Fracture surfaces were analyzed by SEM, revealing that cracks propagated through ferrite-cementite interfaces and preferential intergranular pathways. The Hollomon model illustrated reduced plasticity due to hydrogen interaction, highlighting embrittlement risks. EBSD analysis revealed that cracks caused by HE propagates more easily along the {0 0 1} planes due to their lower planar atomic density. Taylor factor analysis indicated that {1 1 1} grains harden under load, preventing crack propagation and causing the crack to change direction at {1 1 0} and {1 1 1} grain interfaces. The kernel misorientation map showed that regions of high plastic deformation deflect the crack path, emphasizing the influence of crystallographic orientation on crack propagation dynamics. [ABSTRACT FROM AUTHOR]