Precise determination of the activation energy for desorption of hydrogen in two Ti-added steels by a single thermal-desorption spectrum

Critical assessment of the existing models for the desorption rate of hydrogen trapped in steel indicated that the desorption rate can be described by the kinetic formula dX/dt = A(l - X) exp (-E-d/RT). Good fit of the formula has been found to the hydrogen released during thermal-desorption spectrometry (TDS) analysis from the coherent and incoherent TiC particles in 0.05C-0.22Ti-2.0Ni and 0.42C-0.30Ti steels. The activation energy (E-d) and the constant parameter A can be determined uniquely with high accuracy by a single spectrum simulation. The activation energy for hydrogen desorption from the incoherent TiC particle in the well-tempered 0.05C-0.22Ti-2.0Ni steel is 85.7 kJ/mol. In the 0.42C-0.30Ti steel, a higher activation energy of 116 kJ/mol was obtained for the coarse incoherent TiC when tempered at 650 degreesC and 700 degreesC. The activation energy decreased from 116 kJ/mol at 650 degreesC to 68 kJ/mol at 500 degreesC. The nanosized TiC coherent precipitates in the 0.42C-0.30Ti steel were found to have an activation energy ranging from 46 to 59 kJ/mol, depending on the tempering temperature. A low value of much less than 10(4) s(-1) was obtained for the constant parameter A for most cases, which suggested that the retrapping of the released hydrogen is not important in the thermal-desorption analysis.