Effect of Heating Rate and Sample Size on Thermal Desorption of Hydrogen in X80 Steel

The hydrogen concentration as well as the desorption energy of reversible and irreversible traps in steel can be effectively analyzed through thermal desorption spectroscopy (TDS) method. However, the thermal desorption curves are affected by sample size and heating rate. Whether the hydrogen amount and the desorption energy are affected by the heating rate and sample size are unknown. First, standard hydrogen-filled samples provided by LECO corporation were tested to ensure the stability and accuracy of the test instrument. Then, hydrogen was introduced into X80 pipeline steel cylinder samples of different sizes at 300 °C, 20 MPa gaseous hydrogen environment for 48 hours. Finally, thermal desorption tests were carried out to analyze the effect of heating rate and sample size on the desorption results of hydrogen. The results show that the sample size and heating speed have little influence on the hydrogen concentration test results, but have significant influence on the thermal desorption curve. As the specific surface area of the sample increases from 0.48 mm−1 to 0.86 mm−1, the peak temperature decreases approximately linearly. There are two obvious desorption peaks (Peak1 and Peak2) of X80 pipeline steel after hydrogen charging, and the trap desorption energy obtained from samples of different sizes is similar. The desorption energy of Peak1 trap is 13 ± 1.46 kJ/mol, which may correspond to the hydrogen traps of interstitial lattice sites, dislocations and low angle grain boundaries (LAGB). Peak2 consists of two overlapping desorption peaks (Peak2-1 and Peak2-2). the desorption energy Peak2-1 trap is 48.3 ± 14.78 kJ/mol, which may correspond to martensite/austenite (M/A) interface and dislocation nucleus. The desorption energy of Peak2-2 trap is 80.43 ± 9.98 kJ/mol, which may correspond to high angle grain boundaries (HAGB). The reversible, irreversible and total hydrogen concentration in X80 steel are 0.05 ± 0.006ppm, 0.54 ± 0.04ppm and 0.59 ± 0.04ppm, respectively. When conducting thermal desorption analysis, samples of the same size should be kept, and the heating rate should not be too fast, otherwise the overlap of different desorption peaks will cause non-negligible decoupling errors.