Improving the hydrogen embrittlement resistance of a 18Cr ferrite-austenite-martensite triplex stainless steel by copper alloying

This study investigates the influence of copper (Cu) alloying on the hydrogen-induced cracking behavior of a ferrite-austenite-martensite triplex stainless steel (TSS) containing 18 wt.% Cr, by means of the slow strain rate tensile testing with the extensometer, scanning electron microscopy, electron backscatter diffraction, thermal desorption spectroscopy, and finite element simulations. TSS samples with Cu contents of 0.02 and 1.94 wt.% were tested in air, both with and without electrochemically pre-charged hydrogen. The results show that the addition of ca. 2 wt.% Cu reduces the elongation loss by approximately 10% in the hydrogen pre-charged condition. Under uniaxial tensile testing, the pre-charged Cu-alloyed steel maintains a comparable work hardening rate before failure. This improvement is attributed to the increased austenite and martensite fractions in the matrix due to Cu addition: (i) increased austenite fraction helps hinder hydrogen ingress during pre-charging and contributes to work-hardening during tensile testing, and (ii) increased martensite fraction helps provide more high angle grain boundaries that disperse hydrogen, and (iii) the synergistic effect reduces the depth of the hydrogen-induced brittle layer near the surface, and thereby mitigating macroscopic mechanical inhomogeneity during tensile loading.