2011 Volume 60 Issue 10 Pages 449-456
As reported before, conventional group of flat heald, heald C, has used to serve for about two years, while a new group of flat heald, heald X, suffered significant localized corrosion earlier in one or two months. In this study, steel C’ of chemical composition similar to heald C is heat-treated to reproduce the heald C in terms of metallurgical characteristics (hardness Hv ; amount of insoluble carbide [MC]; prior austenite grain size dγ). The characteristics of heald C (484 Hv ; 1.2% ; 12 μm) is found to be reproduced by a solution-treatment at 1040°C for 180 s, WQ followed by tempering at 450°C for 20 s, AC. Those of heald X (474 Hv ; 2.0% ; 12 μm), lower in hardness and more in insoluble carbide than C, could be reproduced by solution-treatment at 1040°C for around 100 s, shorter time than heald C. The heat treatment condition determined as above is confirmed to corrode the steel C’ in 6.8 vol% HNO3 solution similarly in surface appearance to healds C and X. Their corrosion rates in the same solution vs. soluble Cr content, [Cr]relationship are nearly equal to the corrosion rates vs. [Cr] relationship for relevant solution-treated steels. The repassivation potential for crevice corrosion, ER.CREV, in 0.85, 2.8 or 28 mM NaCl solution depends also on [Cr], nearly constant between [Cr] range of 11.5 and 12.8%, and above which becomes more noble with increasing [Cr] up to 13.4%. Then, [Cr] values of 11.5% (heald X) and 12.5% (heald C) make no difference in ER.CREV. Real crevice corrosion for heald X was attributed to more noble spontaneous electrode potential, ESP, of heald X than ER.CREV under increased residual chlorine, as reported before.
