Comparative Study of Hydrogen Embrittlement of Tempered Martensitic Steels Containing Ti, Nb and V

Tempered martensitic steels have potential for use in high-pressure gaseous hydrogen storage and transport required to meet the increasing demand for hydrogen fuel. However, hydrogen embrittlement remains a challenge, particularly in high-strength steels. One key solution involves introducing hydrogen traps into the steel microstructure. In this study, the effects of adding Ti, Nb, and V into steels on hydrogen embrittlement resistance were examined by focusing on trap site properties such as susceptibility, trap density, and binding energy. Thermodynamic calculations were performed by using the Thermo-Calc software to determine the volume fractions of TiC, NbC, and VC in the Fe–0.38C alloy system. Microstructural analysis revealed the formation of MC carbides and finer grains because of the addition of the micro-alloys. Mechanical tests, including ex-situ and in-situ slow strain-rate tests, were conducted to evaluate the tensile properties and hydrogen embrittlement resistance. The results indicated that all the microalloyed steels exhibited higher strength and improved hydrogen embrittlement resistance than the base steel. Ti and Nb additions provided the highest resistance owing to the high binding energies of TiC and NbC, whereas V addition significantly increased the strength and hydrogen content at the reversible trap sites. Thermal desorption analysis confirmed the trapping behavior of the MC carbides and showed that different hydrogen desorption temperatures correlated with the binding energy. Thus, MC carbides were found to be crucial for enhancing the hydrogen embrittlement resistance because they acted as effective hydrogen trap sites, with Ti and Nb being more beneficial than V.