Hydrogen embrittlement of 22-5 duplex stainless steel

Abstract

The influence of hydrogen on 22Cr-5Ni duplex stainless steel with an austenitic-ferritic microstructure was investigated. Notched test specimens were cathodically charged in 1N H₂SO₄ containing NaAsO₂ at a current density of 0·4 mA cm⁻² while undergoing tensile strain over a wide range of crosshead speeds (833, 83, and 8·3 μm S^−l and 833, 83, and 9·8 nm S^·1) at room temperature of 22 ± 2°C and at 70 ± 2°C. For comparison, the same number of specimens was tested in air. The degree of embrittlement was evaluated by calculating the elongation and stress to fracture in air and solution. Then the elongation to fracture ratio E_sol/E_air and stress to fracture ratio σ_sol/σ_air were calculated at each applied crosshead speed. A marked reduction in the mechanical properties, particularly the E_sol/E_air ratio, was exhibited by the duplex stainless steel test specimens when the embrittlement test was carried out at room temperature using slow crosshead speeds of 83 and 9·8 nm S⁻¹. However, when the embrittlement test was carried out at 70°C at the same crosshead speeds, less reduction in the E_sol/E_air ratio was observed. A transgranular cleavage fracture mode was observed in both the ferritic and austenitic phases of duplex stainless steel specimens when tested at room temperature with slow crosshead speeds. Large faceted cleavage fracture was predominant in the ferritic phase, while cleavage associated with slight plastic deformation was exhibited by the austenitic phase. In keeping with the results concerning mechanical properties, less change in fracture morphology was exhibited by the duplex stainless steel specimens when the test was carried out at 70°C. In this case, cleavage fracture was predominant only in the ferritic phase, while the austenitic phase exhibited quasicleavage fracture associated with the extensive plastic deformation.