Study of steel emissivity characteristics and application of multispectral radiation thermometry (MRT)

Experiments were first conducted to measure the emissivity values of a variety of steel samples at 700, 800, and 900 K. The effects of wavelength, temperature, alloy composition, and heating time on emissivity were investigated. Multispectral radiation thermometry (MRT) with linear emissivity models (LEMs) and log-linear emissivity models (LLEs) were then applied to predict surface temperature. Parametric influences of the number of wavelengths and order of emissivity models were examined. Results show that the spectral emissivity decreases with increasing wavelength and increases with increasing temperature. Steel with higher chromium content has lower emissivity value because of the chromium oxide protection layer. The spectral emissivity reaches steady state after the third hour heating due to the surface oxidation becoming fully developed. Increasing the order of polynomial and increasing the number of wavelengths cannot improve temperature measurement accuracy. Overall, the first-order LEM and the first-order LLE showed the best accuracy for different alloys, the number of wavelengths, and temperatures.