Studies on the degree of sensitization of hyper-duplex stainless steel 2707 at 900℃ using a modified DL-EPR test

Highlights: • The optimal DL-EPR test procedure is in 2 M H₂SO₄ + 1.25 M HCl + 0.001 M KSCN. • DOS is initially increases and then decreases, peaking at 10 h. • The sigma phase occurs at α/γ grain boundaries and inside the α phase. • The Cr₂N forms at α/γ grain boundaries and inside the γ phase. • The DL-EPR tests are consistent with the etching pattern and LSC morphology. The effects of thermal aging of hyper-duplex stainless steel (HDSS) 2707 at 900℃ for various aging times up to 26 h on the localized, selective corrosion were investigated by electrochemical methods. The results demonstrate that the optimum test condition is 2 M H₂SO₄ + 1.25 M HCl + 0 0.001 M KSCN with the scan rate of 1.5 mV·s⁻¹ at 30℃. The degree of sensitization (DOS) of HDSS 2707 initially increases rapidly, because of particle precipitation (σ phase/Cr₂N), and then decreases as a result of self-healing by back diffusion of Cr and Mo into the depleted areas, peaking at 10h.