The role of the microstructure on the influence of hydrogen on some advanced high-strength steels

The role of microstructure was studied for dual-phase (DP), quenched and partitioned (Q&P), and twinning induced plasticity (TWIP) steels. The hydrogen influence changed the fracture mode at the ultimate tensile strength, there being no subcritical crack growth at a lower stress. The fractures initiated (i) in the hard martensite and/or at the interfaces of ferrite and martensite for DP steels, (ii) in the martensite and/or at the interfaces of retained austenite and martensite for Q&P steels, and (iii) at mechanical twins for TWIP steels. Tempering may improve the resistance to hydrogen of DP and Q&P steels.