Low hydrogen pressure effect over microhardness and impact toughness of an experimental X-120 microalloyed steel

In the present work, the susceptibility to hydrogen embrittlement under hydrogen pressure was evaluated for an experimental X-120 microalloyed steel with four quenching treatments to determine the effect of hydrogen on the hardness and toughness behaviour, for its use in gas and oil transport. The steel was reheated at 820 degrees and 900 degrees C and then quenched in four different cooling media. The microstructure obtained by quenching in spray water showed a martensite-bainite type microstructure, and the pressurized air condition showed a micro-structure composed of bainite and acicular ferrite. In contrast, a microstructure composed mainly of finer lath martensite-bainite and acicular ferrite was obtained in the water-oil emulsion. In the oil quenching condition, a microstructure consisting of banded martensite, polygonal ferrite, and acicular ferrite was obtained. Suscepti-bility to hydrogen embrittlement was determined by hydrogen gas pressure testing at 1, 4, and 7 MPa. The results showed a clear trend where the steel decreases its impact toughness due to the effect of hydrogen pressure, with a maximum decrease of 29%, 24%, and 39%, respectively, for each hydrogen pressure condition (1, 4, 7 MPa).