Hideo Sugawara1 and Kenji Konishi2
1Department of Metals Engineering, Muroran Institute of Technology, Muroran
Measurements of anodic polarization in 1N-H2SO4 and pitting corrosion in 0.1M-NaCl solution were performed on the samples of 13∼52%Cr-Fe alloys which were aged for 0∼5000 hr at 475°C. The most marked change is a separation of critical passivation potential Ep, which separated into Ep-1 and Ep-2 with 1000 hr or longer aging. Both the critical current for passivation icrit-1 at Ep-1 and current in the transpassive region decreased with increasing aging time, while icrit-2 at Ep-2 and the current in the passive region increased with aging time. The critical pitting potential of Fe-Cr alloys was shifted to an active value with increasing aging time and approached that of unaged 13%Cr alloy. In 13∼31%Cr-Fe alloys the sensitization was observed after 300∼500 hr aging at 475°C. The degree of sensitization is severe in the 13%Cr alloy and decreases with increasing Cr level. Microscopic examination as revealed by potentiostatic etching method shows that intergranular attack and pitting corrosion occur around the grain boundary. All of the property changes studied can be interpreted by assuming the formation of Cr-rich ferrite.
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