1988 Volume 52 Issue 12 Pages 1276-1284
Intergranular corrosion behavior of 13Cr and 17Cr martensitic stainless steels was studied by electrochemical and immersing corrosion tests. Effects of the metallurgical and environmental conditions on the intergranular corrosion of various tempered steels were examined by the following tests and discussed.
(a) Anodic polarization measurement and electrolytical etching test in 0.5 kmol/m3 H2SO4 solution at 293 K.
(b) Immersion corrosion test in 0.88 kmol/m3 HNO3 solution at 293 K.
(c) Long-time immersion test for specimens with a crevice in a high purity water at 473 K∼561 K.
It was found from the anodic polarization curves in 0.5 kmol/m3 H2SO4 solution at 293 K that the steels tempered at 773∼873 K had susceptibility to intergranular corrosion in the potential region indicating a second current maximum (around −0.1 V. vs. SCE). But the steel became passive in the more noble potential region than the second current peak potential, while in the less noble potential region general corrosion occurred independent of its microstructure. The intergranular corrosion occurred due to the localized dissolution along the pre-austenitic grain boundary and the martensitic lath boundary. It could be explained by the same dissolution model of the chromium depleted zone as proposed for the intergranular corrosion of austenitic and ferritic stainless steels. The intergranular corrosion occurred entirely at the free surface in 0.88 kmol/m3 HNO3 solution, while in the high temperature and high purity water only the entrance of the crevice corroded. It was also suggested that this intergranular corrosion might serve as the initiation site for stress corrosion cracking of the martensitic stainless steel.
