ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Surface Treatment and Corrosion
Effects of Surface Microstructure on Selective Oxidation Morphology and Kinetics in N2 + 5%H2 Atmosphere with Variable Dew Point Temperature
Mary E. StoryBryan A. Webler
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2019 Volume 59 Issue 5 Pages 918-926

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Abstract

Starting surface microstructure has been shown to influence selective oxidation morphology and kinetics on cold-rolled grades of CMnSi advanced high strength steels (AHSSs). The research presented below examined this phenomenon after 120 and 1800 s and under N2 + 5%H2 with 0°C and −30°C dewpoint temperatures (DPTs). Starting microstructures were altered by pre-annealing, which led to decarburization and grain growth. All samples were oxidized in a high temperature confocal scanning laser microscope (CSLM) at 850°C. External oxides were subsequently examined using secondary electron scanning electron microscopy (SE SEM) and energy-dispersive spectroscopy (EDS). Cross-sections were produced and examined in a focused ion beam scanning electron microscope (FIB-SEM). Oxidizing atmosphere, surface microstructure, and time all influenced selective oxidation behavior. High and low DPT atmospheres had expected effects. Variation between microstructures was only apparent in 1800 s samples oxidized in a high DPT atmosphere. Decarburized samples oxidized at higher DPTs exhibited surfaces covered with discrete iron nodules which may facilitate reactive zinc wetting.

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© 2019 by The Iron and Steel Institute of Japan
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