Hydrogen-enhanced fatigue crack growth behaviors in a ferritic Fe-3wt%Si steel studied by fractography and dislocation structure analysis

Abstract

The effect of hydrogen (H) on the fatigue behavior is of significant importance for metallic structures. In this study, the hydrogen-enhanced fatigue crack growth rate (FCGR) tests on in-situ electrochemically H-charged ferritic Fe-3wt%Si steel with coarse grain size were conducted. Results showed strong difference between the H-charged and the non-charged conditions (reference test in laboratory air) and were in good agreement with the results from literature. With H-charging, the fracture morphology changed from transgranular (TG) type to "quasi-cleavage" ("QC"), with a different fraction depending on the loading frequency. With the help of electron channeling contrast imaging (ECCI) inside a scanning electron microscope (SEM), a relatively large area in the failed bulk specimen could be easily observed with high-resolution down to dislocation level. In this work, the dislocation sub-structure immediately under the fracture surfaces were investigated by ECCI to depict the difference in the plasticity evolution during fatigue crack growth (FCG). Based on the analysis, the H-enhanced FCG mechanisms were discussed.

Effect of hydrogen on the embrittlement susceptibility of Fe–22Mn-0.6C TWIP steel revealed by in-situ tensile tests

“…Recently, the effect of hydrogen on strength has also been studied by fatigue crack growth testing showing a hydrogen-restricted plasticity evolution [42], nanoindentation testing showing a hydrogenenhanced lattice friction [11] and micro-pillar compression test showing a hydrogen-increased stress level [43]. These studies as well as the current work show a similar hardening effect of hydrogen on different metallic materials.…”

Influence of hot-dip galvanization on the fatigue performance of high-strength bolted connections

“…As a matter of fact, typical evidences of hydrogen-assisted fatigue crack growth can be identified as IG-and QC-type fracture features, e.g., as observed in pure Fe [59][60], Fe-3wt%Si [61][62], medium-Mn steels [63] and X70 pipeline steels [64]. Such features are quite similar to the ones observed in tested galvanized samples shown in Figures 9-10.…”

“…A working distance of ≈30 mm was adopted in order to get secondary electron images from the fracture surface. A peculiar attention was paid to detecting possible traces of hydrogen embrittlement (HE), which has been deemed to play a role in fracture of galvanized details by several researchers [57][58][59][60][61][62][63][64][65]. Figure 8 shows the crack initiation sites as derived from the fractographic investigations of specimens.…”

Hydrogen-assisted Crack Propagation in Pre-strained Twinning-induced Plasticity Steel: from Initiation at a Small Defect to Failure

“…The effect of plastic pre-strains is an important factor in failure of austenitic steels even without hydrogen. 9,10) In particular, the formation and growth of cracks and voids can result from the accumulation of lattice defects, such as vacancies, 11,12) dislocations, 13,14) and twins, 15,16) which reduces the stress accommodation capability and creates a microstructural crack growth path. In addition, plasticity-induced damage can act together with hydrogen effects.…”