二相ステンレス鋼の高温高圧水中の応力腐食割れ

概要

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Relation between microstructure and stress corrosion cracking in high temperature water for duplex stainless steel was investigated using transmission electron microscopy and fractography. The samples were solution-treated at various temperatures and then sensitized at 923 K for 72 ks. The slow strain rate testing (SSRT) was carried out at 562K in water with 8 ppm dissolved oxygen under 8 MPa pressure at a strain rate of 4.17 × 10^<-6>s^<-1>. The volume fraction of α phase and Cr_2N in the α phase increased with increasing the solution treatment temperature. For the sensitized sample, M_<23>C_6 precipitated at α/γ interface, the bowing area of secondary austenite, namely γ^* phase occurred, and σ phase precipitated at the γ^*/α interface. They increased with decreasing solution treatment temperature and with decreasing the volume fraction of α phase. The stress corrosion cracking in high temperature water hardly occurred for the solution-treated samples. The reduction of area of the sensitized sample was much lower than that of the solution-treated samples and decreased with decreasing solution treatment temperature, because the γ^* phases near the M_<23>C_6 and the σ phase were predominantly corroded and resolved during the test.
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1995-02-05