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

Abstract

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 ϭ A(1 Ϫ X) exp (ϪE 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 °C and 700 °C. The activation energy decreased from 116 kJ/mol at 650 °C to 68 kJ/mol at 500°C. 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 Ϫ1 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.

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.…”

Effect of Ti on Evolution of Microstructure and Hardness of Martensitic Fe–C–Mn Steel during Tempering

“…The heating up time to the tempering temperature is 138 s. The tempering temperature of 300°C is chosen to assure that all Ti atoms remain in solid solution and the tempering level of 550°C is chosen to assure that TiC nucleation and growth takes place during tempering. 8,9) All specimens are prepared by grinding and polishing to 1 μm diamond dispersion, followed by 5% nital etching or electro-polishing conducted in a solution of 8% perchloric, 10% butylcellosolve, 60% ethanol and 22% water. Electron probe micros-analysis (EPMA) is performed to verify that the specimens are indeed homogeneous in composition after the homogenization treatment, as determined with a spatial resolution of 1 μm.…”

“…This is estimated by comparing the Tifree and the Ti-containing steel during annealing at 300°C and by knowing that no TiC-precipitates were present after quenching and that no TiC-precipitates nucleate at 300°C. 8,9) The influence of TiC precipitates on the macroscopic hardness of martensite can be observed first after 30-60 minutes of annealing at 550°C, see Fig. 5(a).…”

“…The single-dislocation-assisted growth of spherical precipitates is given by: 46) .................... (9) where is expressed via Eqs. (3)- (8).…”

“…7) Martensitic steel with medium carbon content and a small addition of Ti (around 0,04 wt%) is therefore an interesting candidate steel for making steels for fasteners that are stronger at higher temperatures. Furthermore are TiC-precipitates known to act as hydrogen traps [8][9][10] and improve the resistance to hydrogen-induced damage, a very desirable feature when creating a highstrength steel for the automotive industry.…”