Enhancement of hydrogen embrittlement resistance in a Fe-18Mn-0.6C twinning induced plasticity steel by copper alloying

The effect of Cu alloying on hydrogen embrittlement (HE) in TWIP steel was studied using the low-speed linearly increasing stress test (LIST) with simultaneous cathodic hydrogen charging. Cu alloying influenced HE resistance by the following mechanism. (i) Cu alloying increased the stacking fault energy, which canceled out the embrittling effect of hydrogen on promoting local plasticity and mechanical twins/dislocations concentration. (ii) Cu alloying refined the austenite grains, especially after low-temperature (700 °C) annealing and thus delayed mechanical twinning that causes an increased hydrogen concentration. (iii) Cu alloying caused the formation of a Cu-rich surface which reduced the diffusible hydrogen content, particularly for the steel annealed at 900 °C. (iv) Cu alloying dispersed mechanical twins by Cu precipitate/Cu-rich clusters, which homogenized the diffusible hydrogen and decreased the local hydrogen concentration at the HE vulnerable interfaces. Mechanism (iv) in the 700 °C annealed Cu-alloyed TWIP steel produced the greatest increase in HE resistance.