Hydrogen solubility, diffusivity, and trapping in quenched and tempered Ni-containing steels

Abstract Hydrogen permeation experiments were performed in quenched and tempered (Q&T) low alloy steels with varying Ni contents exposed to 1 bar H2 at 30, 50 and 70 °C. From the analysis of build-up and decay transients, it is concluded that the permeation coefficient, the apparent diffusion coefficient ( D a p p ) and the concentration of hydrogen in interstitial sites on the charging surface ( C 0 ) decreases as the Ni concentration increases from 0 to 5 wt.%. The total concentration of hydrogen on the charging surface ( C 0 , r ), which includes interstitial and reversibly trapped hydrogen, is about an order of magnitude larger than C 0 . The hydrogen binding energy ( E b ) and trap density ( N r ) were calculated from the D a p p vs. temperature dependence, under the hypothesis of low trap occupancy. C 0 , r , E b and N r do not show a clear correlation with Ni content, indicating that trapping is controlled by a microstructural feature other than Ni atoms in solid solution.