Modeling Thermal Desorption Analysis of Hydrogen in Steel

Abstract

A computer model was developed to simulate the thermal desorption flux of hydrogen from steel specimens by an explicit finite difference method, which is convergent and stable for all time increment. The influences of experimental parameters, e.g. ramp rate, specimen size and duration of exposure at ambient temperature etc., on the desorption spectrum, concentration profile of hydrogen in the lattice and fractional occupancy at the trapping sites, were studied assuming that the major trapping sites were dislocations. The increase in ramp rate caused a marked shift in the desorption peak to a higher temperature, whilst the increase in the specimen size shifted the peak to higher temperatures to a moderate extent. The duration of exposure may have a considerable influence on the thermal desorption spectra when the desorption peak is associated with a lower binding energy trap site.

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

“…The primary trap sites in these steels are considered to be dislocations, lath boundaries, martensite packet and prior austenite grain boundaries. 13,15) As expected, the simulated spectra fit very well at a small specimen size (a=10 -3 m) while a significant amount of deviation, increasing in the order of sphere, cylinder and plate, is observed at a large specimen (a=5×10 -3 m). Detrappingcontrolled desorption has to meet two requirements.…”

Numerical Analysis of Influence of Hydrogen Charging Method on Thermal Desorption Spectra for Pre-strained High-Strength Steel

“…In the paper, 21) the binding energy of 27 kJ/mol is adopted for simulations by considering that the peak in the spectrum of the unstrained SCM435 specimen results from the elastic field of dislocation. In the recent paper, 26) it is supposed that the same peak is caused by the core of edge dislocations whose binding energy is reduced from 42 kJ/mol due to repulsive interaction between hydrogen atoms and carbon atoms segregating at the dislocation core.…”

“…2(a). Since the numerical simulation of thermal desorption spectra of unstrained SCM435 steels is reported in the paper, 21) we adopted the binding energy and the concentration of trap sites of the paper. As for the diffusion coefficient, we employed Q = 3.9 kJ/mol and D0 = 4.2×10 /s.…”

“…Since thermal desorption spectra depend on many factors such as binding energy and concentration of trap sites which characterize the hydrogen trap state, the heating rate, and the specimen size, the numerical simulation is also employed for examining sensitivity of desorption spectra to these factors. [19][20][21][22] …”

Influence of Specimen Thickness on Thermal Desorption Spectrum of Hydrogen in High Strength SCM435 Steel

“…trap energy and detrapping coefficient, were determined by fitting with the spectra of cylindrical specimens of 2.5 mm in radius by trial and error. From the value of the detrapping coefficient p 0 = 25-30 s − 1 , 2) it was thought that hydrogen desorption seemed to occur almost in the detrapping-controlled condition because the interval of detrapping events, i.e. inverse of p 0 , was calculated to be greater than the diffusion time to the surface of the specimen.…”