Selective Oxidation of a C-2Mn-1.3Si (Wt Pct) Advanced High-Strength Steel During Continuous Galvanizing Heat Treatments
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The influence of oxygen partial pressure and annealing time on the selective oxidation of a Fe-0.1C-2Mn-1.3Si (wt pct) advanced high-strength steel during intercritical annealing was investigated. The steel was intercritically annealed at 1093 K (820 °C) for annealing times in the range of 60 to 600 seconds in a N2-5 vol pct H2 gas atmosphere with dew points ranging from 223 K to 278 K (− 50 °C to + 5 °C). The morphology, thickness, and chemistry of the oxides were determined as a function of process atmosphere oxygen partial pressure and annealing time by means of SEM, XPS, and TEM. It was found that for the 223 K (− 50 °C) dew point atmosphere, a compact, film-like external oxide comprising MnSiO3, Mn2SiO4, and SiO2 and nodule-like MnO oxides covered the surface. On the other hand, for the 278 K (+ 5 °C) dew point atmosphere, MnSiO3, Mn2SiO4, and MnO nodule/plate-like external oxides were formed, while Si was oxidized internally. Longer annealing times resulted in increasing either the thickness of the external oxide layer or the depth of internal oxidation. A comparison between the predictions of the Wagner internal-to-external transition model found good agreement between the experimental results for Mn and Si in ferrite.
The authors would like to thank Stelco Inc. and the Natural Sciences and Engineering Research Council of Canada (NSERC) for their financial support of this work through the NSERC/Stelco Industrial Research Chair in Advanced Coated Steels. The authors also thank John Thomson and Ray Fullerton from the McMaster Steel Research Centre for assistance with the galvanizing simulations, Travis Casagrande and Andreas Korinek from the Canadian Centre for Electron Microscopy for assistance with sample analysis, and Li Sun (ArcelorMittal Dofasco) for assistance with XPS.
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