Effect of Annealing Atmosphere and Steel Alloy Composition on Oxide Formation and Radiative Properties of Advanced High-Strength Steel Strip

This study elucidates the effect of alloy composition, annealing atmosphere, and pre-annealed surface state on the radiative properties of dual-phase (DP) steels. Twelve samples of varying alloy composition and pre-annealed surface roughness were heated in a 95 pct/5 pct (vol) N 2 /H 2 process atmosphere under dew points of + 10 °C and − 30 °C. The surface profile and surface topography were characterized using scanning electron microscopy and optical profilometry, while radiative properties were measured using a UV–Vis–NIR spectrophotometer and a Fourier transform infrared spectrometer. The surface oxide speciation and thickness were determined using X-ray photoelectron spectroscopy and focused ion beam milling, respectively. The results showed that smooth oxidized surfaces with lower Si/Mn mass ratios give rise to prominent interference effects observed in the measured reflectance. The thin-film interference model accurately predicts measured radiative properties. These findings can be used to improve the industrial pyrometry measurements in the continuous galvanizing line, and, potentially, to evaluate the oxide formation of DP steels during annealing via in-situ optical measurements.