Hideo Sugawara1 and Tetuo Hanami2
1Department of Metals Engineering, Muroran Institute of Technology, Muroran
The susceptibility of high purity Fe-Cr alloys containing 18%Cr, 0.003 to 0.05%C and 0 to 5%Ni was determined by an electrochemical method after subjecting the alloys to various heat treatments. Some data on the occurrence of the second anodic current maximum (SACM) observed on the anodic polarization curves of the alloys are presented and applied to the interpretation of the mechanism of intergranular corrosion in ferritic stainless steels. SACM is sensitive to heat treatment (degree of senstization). Air cooling from 1050°C causes an increase in SACM which is very high in 18%Cr steel with more than 0.004%C. The sensitization which develops in such alloys upon air cooling from 1050°C develops at temperatures below 800°C. Addition of 1∼2%Ni causes a remarkable decrease in SACM of 18%Cr steels air cooled from 1050°C, but there is a rather sharp change in SACM for these alloys furnace cooled from 1050°C. The tendency of 18%Cr steel to become sensitized to intergranular corrosion is closely related to the amount of C in α and γ phases and the area fraction of each phase. This investigation lends support to Cr depletion theory for sensitization.
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