The Positive Role of Nanometric Molybdenum–Vanadium Carbides in Mitigating Hydrogen Embrittlement in Structural Steels

Abstract

The influence of hydrogen on the fracture toughness and fatigue crack propagation rate of two structural steel grades, with and without vanadium, was evaluated by means of tests performed on thermally precharged samples in a hydrogen reactor at 195 bar and 450 °C for 21 h. The degradation of the mechanical properties was directly correlated with the interaction between hydrogen atoms and the steel microstructure. A LECO DH603 hydrogen analyzer was used to study the activation energies of the different microstructural trapping sites, and also to study the hydrogen eggresion kinetics at room temperature. The electrochemical hydrogen permeation technique was employed to estimate the apparent hydrogen diffusion coefficient. Under the mentioned hydrogen precharging conditions, a very high hydrogen concentration was introduced within the V-added steel (4.3 ppm). The V-added grade had stronger trapping sites and much lower apparent diffusion coefficient. Hydrogen embrittlement susceptibility increased significantly due to the presence of internal hydrogen in the V-free steel in comparison with tests carried out in the uncharged condition. However, the V-added steel grade (+0.31%V) was less sensitive to hydrogen embrittlement. This fact was ascribed to the positive effect of the precipitated nanometric (Mo,V)C to alleviate hydrogen embrittlement. Mixed nanometric (Mo,V)C might be considered to be nondiffusible hydrogen-trapping sites, in view of their strong hydrogen-trapping capability (~35 kJ/mol). Hence, mechanical behavior of the V-added grade in the presence of internal hydrogen was notably improved.

Hydrogen Embrittlement as a Conspicuous Material Challenge─Comprehensive Review and Future Directions

“…The high HE susceptibility of the cast variant was attributed to the platelet structure of pearlite and H trapping at carbides, leading to increased H concentration. This observation seemingly contrasts with other research indicating a protective role of carbides as strong traps mitigating HE, as suggested by other authors. , …”

“…This observation seemingly contrasts with other research indicating a protective role of carbides as strong traps mitigating HE, as suggested by other authors. 570,571 The 17−4 precipitation-hardened stainless steel fabricated via L-PBF exhibits a microstructural divergence from its conventionally produced counterpart, too. Typically, wrought 17−4 precipitation-hardened stainless steel has a martensitic microstructure.…”

Hydrogen Interactions with Defects in Materials

“…The mean value can be even higher than that of the interstitial sites. Adding deep traps such as interfaces between carbides and the metal can bind internal hydrogen and protect the metal from hydrogen embrittlement [34][35][36][37] -as long as there is no external hydrogen source.…”

Influence of the Hydrogen Doping Method on the Atomic Structure, Mechanical Properties and Relaxation Behaviors of Metallic Glasses

“…Hydrogen is generally considered a kind of point defect in metals and alloys, which can interact with other defects and significantly reduce the ductility of materials even when the H content is quite low. This phenomenon is known as hydrogen embrittlement (HE) [ 1 , 2 , 3 , 4 ]. The detrimental effect of H is a long-standing problem for structural materials.…”