Role of Sigma Phase on Hydrogen Embrittlement of Super Duplex Stainless Steels

Ikeuchi Kenji

doi:10.18910/11360

The role of sigma phase on corrosion and hydrogen embrittlement of super duplex stainless steels was investigated by using corrosion tests, transmission electron microscopy (TEM) and fractography. The materials used were type 329J1, SAF2205 and SAF2507 duplex stainless steels. The specimens were heated at 923K to 1223K in order to investigate the precipitation of sigma phase (Fe-Cr-Mo compound). The evaluation of corrosion was made using a 10% oxalic acid test (ASTM A262A) and Strauss test (ASTM A262E). Hydrogenation of the specimens was achieved by cathodic charging in a 5%H₂SO₄ solution and the hydrogen embrittlement was evaluated using slow strain rate testing (SSRT). The duplex stainless steels consist of ferrite and austenite microstructure. The secondary austenite was preferentially corroded but the sigma phase was hardly corroded by using ASTM A-262A and A262E tests. The sigma phase enhanced hydrogen embrittlement. The fracture morphology showed that the fracture facet size was related to the sigma phase precipitated around austenite. The crack due to hydrogen embrittlement occurred and propagated at the sigma-ferrite interface on the basis of the 3-D reconstruction system of fractography.

Role of Sigma Phase on Hydrogen Embrittlement of Super Duplex Stainless Steels

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