Role of Secondary Austenite on Corrosion and Stress Corrosion Cracking of Sensitized Duplex Stainless Steel Weldments(Materials, Metallurgy & Weldability)

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The role of secondary austenite on corrosion and stress corrosion cracking in high temperature water for sensitized duplex stainless steel weldment was investigated using transmission electron microscopy and fractography. Pitting potential measurements, 10% oxalic acid tests (ASTM A262A), Strauss tests (ASTM A262E) and Huey tests (ASTM A262C) were carried out for the corrosion assessment. For stress corrosion cracking, the slow strain rate testing (SSRT) was carried out at 562K with 8ppm dissolved oxygen under 8MPa at a strain rate of 4.17x10^<-6>s^<-1>. Volume fraction of γphase decreased with increasing peak temperature and the grain size of the γphase increased with increasing peak temperature. The amount of precipitation of Cr_2N at the grain boundary and in the grain increased with increasing peak temperature. The region around Cr_2N showed intergranular corrosion. For the sensitization at 923K for 72ks, σphase precipitated and secondary γphases (named γ^*phase) appeared between primary γphase and σphase. The γ^*phases were predominantly corroded and the pitting potentials were low. Stress corrosion cracking in high temperature water hardly occurred for the solution-treated specimen. The reduction in area of the specimen sensitized at 923K for 72ks was much lower than that of the solutiontreated specimens and decreased with decreasing peak temperature, because the γ^*phases near the M_<23>C_6 and σphase were predominantly corroded and dissolved.
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Role of Secondary Austenite on Corrosion and Stress Corrosion Cracking of Sensitized Duplex Stainless Steel Weldments(Materials, Metallurgy & Weldability)

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