Quantitative analysis on hydrogen trapping of TiC particles in steel

Abstract

The change in the hydrogen-trapping behavior of a TiC particle accompanying its coherent to incoherent interfacial-character transition in a 0.05C-0.20Ti-2.0Ni steel that was quenched and tempered in a partially protective argon atmosphere and in ultrahigh vacuum (UHV) has been studied by thermal desorption spectrometry (TDS). The results indicated that (semi)coherent TiC precipitates demonstrate distinctly different hydrogen-trapping features from that of incoherent TiC particles with respect to hydrogen capacity, interaction energy with hydrogen, locations available for hydrogen occupation, and the capability of hydrogen absorption from the environment. The broad (semi)coherent interface of the disc-shaped (semi)coherent TiC precipitate does not trap hydrogen during tempering in a partially protected argon atmosphere, but traps hydrogen during cathodic charging at room temperature. The semicoherent interface traps 1.3 atoms/nm 2 of hydrogen at the core of the misfit dislocation with short-time charging (1 hour), which is characterized by a desorption activation energy of 55.8 kJ/mol. The side interface of the (semi)coherent TiC precipitate acts like the broad interface when the precipitate is small. As the precipitate grows, the side interface gradually loses its coherency and results in a simultaneous increase in the trapping activation energy and the binding energy. An increase in the trapping activation energy, i.e., the energy barrier for trapping, makes hydrogen trapping more difficult in cathodic charging at room temperature, while an increase in the binding energy enhances the capability of hydrogen absorption from the atmosphere during heat treatment. An incoherent TiC particle is not able to trap hydrogen during cathodic charging at room temperature due to its high energy barrier for trapping, but absorbs hydrogen during heat treatment at high temperatures. The amount of hydrogen that is trapped by incoherent TiC particles depends on their volume, which strongly indicates that incoherent TiC particles trap hydrogen within them rather than at the particle/matrix interface. Octahedral carbon vacancies are supposedly the hydrogen trap sites in incoherent TiC particles.

Evaluation of Delayed Fracture Property of High Strength Bolt Steels

“…Wurushihara et al conducted SSRT of round smooth bar specimen of high strength steels containing hydrogen traps related to the additive V 29,53) and/or Ti [54][55][56] after CCT or immersion in an acidic aqueous solution, and evaluated the reduction of elongation.…”

“…To avoid hydrogen release from the steels which do not contain hydrogen traps such as carbides of V 29,53) and Ti, [54][55][56] the environment surrounding the specimen was kept wet during those tensile tests.…”

Further Assessment of the Kissinger Formula in Simulation of Thermal Desorption Spectrum of Hydrogen

“…Then, the temperature was raised successively by φΔt, where Δt is the real time step. The fraction of released hydrogen at the (i+1)-th time step Xi+1 was calculated from the equation, .... (16) where Ti=iφΔt is the temperature at the i-th time step.…”

Rolling Direction Dependent Diffusion Coefficients of Hydrogen in Ferritic Steel by SDCM Charging and SKP Probing

“…Numerous techniques have been developed in order to study hydrogen diffusion in metals and enabling determination of the hydrogen diffusion coefficient, amount of diffusible hydrogen as well as trapping effects. Thermal desorption spectroscopy [1][2][3][4] and electrochemical methods 1,[5][6][7][8] constitute a large part of these techniques. However, the number of techniques capable of visualizing diffusible hydrogen and its distribution in a metal sample is very limited.…”