Hydrogen gaseous embrittlement effect over mechanical properties of an experimental X-120 microalloyed steel subjected to heat treatments and different cooling rates

This research work aimed to determine the hydrogen gas pressure effect on the mechanical properties of an experimental X-120 microalloyed steel, subjected to heat treatments and quenched in different mediums. The steel in its as-received condition was reheated at 900 °C and quenched in spray water (900QSW), pressurized air (900QPA), and emulsion of water-oil medium (900QWO) which produces complex microstructures formed by martensite–bainite–acicular ferrite; otherwise, reheated at 820 °C and quenched in oil media (820QO) which produces a banded martensite-polygonal ferrite microstructure. To determine the hydrogen embrittlement susceptibility, in-situ tension tests were developed at 1, 4, and 7 MPa of hydrogen gas pressure. The results showed that as hydrogen gas pressure increases, the mechanical properties reduce in all quenched conditions, being the most susceptible condition the 820QO sample which presented the higher embrittlement index; on the contrary, the less susceptible condition was the 900QPA sample.