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Effects of Alloy Additions and Annealing Parameters on Microstructure in Cold-Rolled Ultra Low Carbon Steels  

Jeong, Woo Chang (School of Mechanical and Automotive Engineering, Catholic University of Daegu)
Publication Information
Journal of the Korean Society for Heat Treatment / v.17, no.2, 2004 , pp. 78-86 More about this Journal
Abstract
Effects of the annealing parameters on the formation of ferrites transformed at low temperatures were studied in cold-rolled ultra low carbon steels with niobium and/or chromium. Niobium and chromium were found to be effective in the formation of the low temperature transformation ferrites. The low temperature transformation ferrites more easily formed when both higher annealing temperature and longer annealing time, allowing substitutional alloying elements to distribute between phases, are in combination with faster cooling rate. It was found from EBSD study that the additions of niobium or chromium resulted in the increase in the numbers of high angle grain boundaries and the decrease in those of the low angle grain boundaries in the microstructures. Both granular bainitic ferrite and bainitic ferrite were characterized by the not clearly etched grain boundaries in light microscopy because of the low angle grain boundaries.
Keywords
Ultra-low carbon steel; IF(Interstitial Free) steel; Cold-rolled sheet steel; Low temperature transformation ferrites; Polygonal ferrite; Quasi-polygonal ferrite; Granular bainitic ferrite; Bainitic ferrite; EBSD;
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