Hydrogen‐enhanced cracking of 2205 duplex stainless steel

Abstract

A B S T R A C T Tensile and fatigue crack growth tests of 2205 duplex stainless steel (DSS) were performed in laboratory air, gaseous hydrogen at 0.2 MPa and saturated H 2 S solution. The longitudinal specimen showed a lesser degradation of tensile properties than the transverse ones in saturated H 2 S solution. The orientation of specimens with respect to rolling direction had little influence on the fatigue crack growth rate (FCGR) of the alloy in air. Furthermore, 2205 duplex stainless steel was susceptible to hydrogen-enhanced fatigue crack growth. Transmission electron micrographs, in addition to X-ray diffraction, revealed that the strain-induced austenite to martensite transformation occurred near the crack surface within a rather narrow depth. Fatigue fractography of the specimens tested in air showed mainly transgranular fatigue fracture with a small amount of flat facet fracture. Furthermore, extensive quasi-cleavage fracture of 2205 duplex stainless steel was associated with the hydrogen-enhanced crack growth.Keywords: duplex stainless steel; fatigue crack growth rate; hydrogen-enhanced crack growth; quasi-cleavage; strain-induced martensite. I N T R O D U C T I O NDuplex stainless steels (DSSs), consisting of approximately equal proportion of austenite (γ ) and ferrite (α) in the microstructure, are known to have better resistance to stress corrosion cracking (SCC) than traditional austenitic stainless steels, especially in chloride containing solutions. Moreover, the high Cr, and Mo content together with N in DSSs, markedly improves the pitting resistance of the alloy compared with austenitic stainless steels. 1,2 Therefore, DSSs have been used extensively in petrochemical and power generation industries, in which H 2 S, CO 2 , and chloride are present. On the other hand, inferior corrosive and mechanical properties of the DSS relative to austenitic stainless steels are reported. The presence of elongated γ embedded in the α matrix, owing to the partition of the alloy element in the hot-rolled plate, leads to the marked anisotropy of mechanical properties. 3 Meanwhile, the banded microstructure in the DSS results in a directional selective corrosion attack. 4 Although powder metallurgy or homogenization treatment at high temperature can reduce the anisotropy, 4 the difference in mechanical and electrochemical properCorrespondence: L. W. Tsay. ties between γ and α phases still has a complicated influence on the environment-assisted crack initiation and propagation. The susceptibility to SCC of the DSS is affected by alloy additions, 2,4 microstructures 4-7 and environments. 8,9 Environment-enhanced cracking of 2205 DSS in acidic 26 wt% NaCl solution at room temperature was strongly dependent on the applied potential. 9 At a high anodic polarization condition, pitting corrosion assists the initiation of SCC in chloride solution. On the other hand, selective dissolution of the ferrite phase is involved in the crack propagation. 10 Under deep cathodic polarization, the pick-up of hydrogen promotes hydrog...

Delayed cracking of low‐nickel austenitic stainless steel studied with constant load tensile testing

“…In both specimens, the microstructure in the immediate vicinity of the fracture surface consists completely of α′‐martensite, so cracking seems to propagate along α′‐phase. Similar observations of high local content of α′‐martensite in the fracture surfaces have been reported in hydrogen embrittlement studies of stainless steels and also in investigations on the effect of hydrogen on fatigue crack growth in austenitic stainless steels . The intense plastic straining at the crack tip area results in localised martensitic transformation and high dislocation density, which enhances hydrogen entry and trapping in the region .…”

“…Similar observations of high local content of α′-martensite in the fracture surfaces have been reported in hydrogen embrittlement studies of stainless steels 38,39 and also in investigations on the effect of hydrogen on fatigue crack growth in austenitic stainless steels. 13,40 The intense plastic straining at the crack tip area results in localised martensitic transformation and high dislocation density, which enhances hydrogen entry and trapping in the region. 41 Increase in the amount of dissolved hydrogen decreases the stacking fault energy of austenite and in turn, increases the volume fraction of strain-induced α′-martensite.…”

The effect of short time post-weld heat treatment on the fatigue crack growth of 2205 duplex stainless steel welds

“…DSSs are highly anisotropic because of the elongated c phases embedded in the a matrix [3]. As shown in the previous work [4], the anisotropy had little influence on the fatigue crack growth rate (FCGR) of 2205 DSS in air.…”

Understanding Corrosion Morphology of Duplex Stainless Steel Wire in Chloride Electrolyte

“…Hence, the EBSD data points towards the formation of strain-induced martensite, with the martensite being indexed as ferrite. The austenite phase is metastable and transforms when high strains above the yield point are formed [61,62]. The necessary stress to deform austenite grains in the lacy cover can only be explained by hydrogen absorption, resulting in heavy local elastic and elasticplastic deformation [63][64][65].…”