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 (Dapp) and the concentration of hydrogen in interstitial sites on the charging surface (C0) decreases as the Ni concentration increases from 0 to 5 wt.%. The total concentration of hydrogen on the charging surface (C0,r), which includes interstitial and reversibly trapped hydrogen, is about an order of magnitude larger than C0. The hydrogen binding energy (Eb) and trap density (Nr) were calculated from the Dapp vs. temperature dependence, under the hypothesis of low trap occupancy. C0,r, Eb and Nr 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.