Hydrogen Desorption Spectra from Excess Vacancy-Type Defects Enhanced by Hydrogen in Tempered Martensitic Steel Showing
- PDF / 1,488,678 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 26 Downloads / 192 Views
I.
INTRODUCTION
HIGH-STRENGTH steels are required for making lightweight automobile parts and structural products. Degradation of the mechanical properties of highstrength steels due to hydrogen embrittlement (HE) is a crucial challenge for maintaining the safety of automobile parts and structural products. Since susceptibility of HE increases with increasing strength of steels, clarification of the HE mechanism is necessary for expanding the application of high-strength steels. Many studies have been conducted for that purpose and some promising mechanisms have been proposed concerning the direct or indirect effects of hydrogen on the degradation of metals.[1–8] Hydrogen directly reduces the cohesive energy of lattice bonding, which
KEI SAITO is with the Graduate School of Science and Technology, Sophia University, Tokyo 102-8554, Japan and also with Nissan Motor Co., Ltd., Kanagawa 243-0192, Japan. TETSUYA HIRADE is with the Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Ibaraki 319-1195, Japan. KENICHI TAKAI is with the Department of Engineering and Applied Sciences, Faculty of Science and Technology, Sophia University, Tokyo 102-8554, Japan. Contact e-mail: [email protected] Manuscript submitted March 22, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
has been called the hydrogen-enhanced decohesion model (HEDE).[1,2] One of the models of indirect hydrogen effects is hydrogen-enhanced localized plasticity (HELP), in which hydrogen weakens the interaction between two dislocations and promotes dislocation motion, resulting in mature fracture.[3–5] In addition, hydrogen stabilizes strain-induced vacancies and enhances the formation of lattice defects (vacancies) in metal, which results in mature fracture. This is referred to as the hydrogen-enhanced strain-induced vacancy (HESIV) model.[6–8] Intergranular,[9,10] quasi-cleavage[11–13] and shallow dimple[7,14] fracture modes have been reported as typical fracture surfaces related to HE. Intergranular and quasi-cleavage fracture modes have often been observed in high-strength martensitic steel.[9–12] Close observation beneath the quasi-cleavage fracture surface revealed that local plastic deformation is related to this type of fracture.[12] However, the relationship between the final fracture mode and the embrittlement process occurring at the atomic order level is not clearly understood. Thermal desorption spectroscopy (TDS) has been applied to determine the kinds and quantities of lattice defects using hydrogen as a probe, i.e., tracer hydrogen.[6,11,15] This method uses the property that hydrogen is trapped at lattice defects in metal. When tracer hydrogen is charged into metals under identical charging
conditions, it is trapped at various lattice defects depending on their densities and binding energies. Thus, the amount of tracer hydrogen and tracer hydrogen desorption temperatures measured using TDS correlate with the quantity of trapping sites such as lattice defects and the binding energies between hydrogen and trapping sites, resp
Data Loading...
