Abstract: In order to improve strength and simultaneously reduce hydrogen embrittlement sensitivity, a low-alloy high-strength steel with 0.11wt%Nb and 0.55wt%V was developed. The effect of three different tempering temperatures (560, 600, 640 ℃) on the microstructure, hydrogen diffusion behavior and hydrogen embrittlement sensitivity of the tested steel was characterized and studied by using optical microscope (OM), X-ray diffraction (XRD), transmission electron microscope (TEM), hydrogen permeation technique of double electrolytic cells and slow strain rate tensile test. The results show that with the increase of tempering temperature, the ferrite grain size increases while the dislocation density reduces, and the carbides precipitated become coarse, hence the tensile strength decreases and the elongation increases. Meanwhile, with the increase of tempering temperature, the density of hydrogen reversible traps reduces and the activation energy of hydrogen diffusion decreases, as well as the hydrogen diffusion coefficient increases, hence the hydrogen embrittlement sensitivity becomes lower.

Key words: low-alloy high-strength steel, tempering temperature, dislocation density, hydrogen diffusion, hydrogen embrittlement