Mohammad Ali Mohtadi Bonab

In this research, the efficacy of specific heat treatment procedures in mitigating hydrogen embrittlement in X100 pipeline steels is discussed. The studied steels underwent a one-step austenitization process at temperatures of 780 °C (HT1), 830 °(HT2), and 880 °C (HT3) for 90 min, followed by oil quenching, tempering at 600 °C, and air cooling. The susceptibility of both the heat-treated and as-received (REF) specimens to HIC was assessed using an electrochemical hydrogen charging, tensile testing, micro-hardness testing, and electron backscatter diffraction (EBSD) techniques. The results showed that an increase in annealing temperature from 780°C to 880° considerably decreases hydrogen embrittlement susceptibility. The hardness value at the centerline of the as-received (REF) specimen was found to be higher than that of the heat-treated specimens. Additionally, calculations of the hydrogen embrittlement (HE) index for all specimens were conducted. The results show that the REF specimen, which demonstrated the highest hardness and HE index values, has greater susceptibility to HIC. Conversely, the HT3 specimen, which was annealed at 880°C and displayed the lowest hardness and HE index values, showed commendable resistance to HIC. The EBSD analysis revealed a decrease in Kernel average misorientation (KAM) values in heat-treated specimens, with the lowest values found in HT3. Dominant textures in all studied steels, {011} and {111}, were considered HIC-resistant and recrystallization mapping indicated a peak area of recrystallized grains in the REF specimen.