Issue 36

F. Z. Liu et alii, Frattura ed Integrità Strutturale, 36 (2016) 139-150; DOI: 10.3221/IGF-ESIS.36.14 148 Quenching state 100 °C tempering state 200 °C tempering state 400 °C tempering state Activation energy of diffusible hydrogen, KJ/mol 15.3 12.9 14.3 16.2 Activation energy of non-diffusible hydrogen, KJ/mol 63.9 118.9 119.6 79.5 Table 6 : Hydrogen trap activation energy of experimental materials. Diffusion of hydrogen in experimental materials It was found that, hydrogen-induced crack was closely correlated to the local concentration of hydrogen [24]. As for diffusible hydrogen, local concentration is determined by average content and diffusion process. Therefore, it is important to study the diffusion process of diffusible hydrogen in samples. Fig. 9 shows the vibration of the content of diffusible hydrogen in steels along with the changes of time. It can be seen that, the content of diffusible hydrogen in experimental materials decreased with the increase of storage time; when the storage time exceeds 72 h, the concentration of diffusible hydrogen in experimental steels was around 0. 15 × 10 -6 . Figure 9 : Effects of storage time after hydrogen charging on the concentration of diffusible hydrogen of experimental materials in different states. Carnerio Filho et al. [25] once studied the diffusion of hydrogen in steels based on the rules of decline of hydrogen content of hydrogen-filled round bar samples which were stored for different periods of time. The equation of diffusion of hydrogen in steels is: 2 0 0.72( )exp( 22.2 / ) t C C C C Dt d       (3) In the formula, C t refers to the concentration of diffusible hydrogen in steels at time point t; C ∞ refers to the concentration of diffusible hydrogen of experimental materials when t is equal to ∞; C 0 refers to the concentration of diffusible hydrogen when t = 0; d refers to the diameter of sample; D stands for diffusion coefficient of hydrogen in experimental materials. The experimental results of experimental materials in different states were substituted into formula (3); regression analysis results are shown in Fig. 9. It can be seen that, the diffusion coefficients of hydrogen in materials processed by quenching, 100 °C tempering, 200 °C tempering and 400 °C tempering were D 1 = 3.71 × 10 -7 , D 2 = 2.98 ×