Anomalous Intergranular Corrosion of Austenitic Stainless Steel Exposed to Higher Temperature and Pressure Hydrogen

Abstract

The sensitivity of intergranular corrosion of austenitic stainless steel, which was sensitized and then exposed to hydrogen, was investigated in Strauss solution (CuSO₄-H₂SO₄) in contact with copper chips. Results obtained are summarized as follows: 1) Anomalous increase of intergranular corrosion is observed in 304, 304L and 316 stainless steel which have been sensitized and exposed to hydrogen, but not in stabilized 321 and 20Cr-30Ni-Nb steel. 2) Anomalous intergranular corrosion depends on hydrogen content. 3) This anomalous corrosion is recovered completely with the short time heating at 650-700°C. 4) In 1N H₂SO₄ solution at 73°C, anodic polarization curves of 304 steels containing hydrogen exhibit an increase of i_crit and a secondary anodic peak. 5) The clustering of tangled dislocations is observed to punch out at grain boundaries or Cr carbide interfaces in 304 steel exposed to hydrogen. It is suggested from these results that the anomalous intergranular corrosion is caused by the formation of internal micro defects due to hydrogen trapped at the interfaces of grain boundary carbides.