Study of the nickel concentration effect on toughness and hydrogen embrittlement resistance of pipeline steel

Experimental tests and molecular dynamics simulations were employed to investigate the effect of Ni concentration on the toughness and hydrogen embrittlement resistance of pipeline steel. A slow strain rate test (SSRT) was conducted under both air and electrochemical hydrogen charging conditions. The results indicate that the tensile toughness, impact toughness, and hydrogen embrittlement resistance of steel increase when Ni concentration is less than 1 %, followed by a decrease when Ni concentration exceeds 1 %. Additionally, an increase in Ni concentration leads to a reduction in both the free surface energy and stacking fault energy of Fe-Ni alloys. Since Ni has a greater influence on the stacking fault energy, dislocation emission is facilitated, which aids in releasing strain energy. However, when the Ni concentration surpasses 1 %, the formation of carbides, which are sensitive to hydrogen embrittlement, occurs. Consequently, when the Ni concentration is higher than 1 %, the toughness and hydrogen embrittlement resistance of steel decrease.