Hydrogen embrittlement of duplex stainless steel Z2CND2205 hydrogen charged at 200 deg C

Ageing the duplex stainless steel below 500 deg. C, the main and usually phenomenon is the unmixing of the δ-FeCr solid solution by spinodal decomposition (or precipitation of α-Cr at higher temperatures). Various intermetallics are detected such as fine disperses (Ni, Si, Mo-rich)G-phase. At higher ageing temperatures (between 600 deg. C and 1050 deg. C), a variety of secondary phases may form, such as γ2, σ, R, χ and Π. The precipitation of carbides M23C6, M7C2 and Cr2N are also detected.This paper is devoted to study the interactions between hydrogen atoms and these phases in a 2205 duplex steel. Hydrogenation had been achieved at 200 deg. C and 1050 deg. C in a molten salts bath, during 3 hours (tempering time also) with an applied cathodic potential equal to - 1.5 V/Ag/AgCl. After hydrogen charging, samples have been out-gassed under vacuum at 600 deg. C to measure the quantity of hydrogen QH. The ageing temperature was varied between 200 deg. C. The hydrogen embrittlement factor was determined by performing 10-6 S-1 tensile tests at room temperature. The results show that the variation of U.T.S. is sensitive to the microstructure change in absence and in presence of hydrogen. The relationship between λ(U.T.S.Hyd/U.T.S.Air) and QH is linear; λ is low (i.e. high embrittlement) in presence of σ phase with low QH level, while, in presence of the other phases, even with high QH, σ is relatively high (low embrittlement). (author). 7 refs., 4 figs