Optical Constants and Emissivities of Iron and Steel in the Ferrite and Austenite Phases at High Temperatures

Infrared emissivities of iron, mild steel and hard steel are measured at temperatures from 850 to 1350 K including the A1, A2, and A3 transformation points and at wavelengths from 0.95 to 12.0 μm. The radiative properties are found to be continuous at the three transformation points, and the experimental results can be explained well by a two-electrons-type dispersion model of optical constants. Electronic constants of the equation are given and formulated in order to correlate the macroscopic properties of the radiative heat transfer at temperatures of 800 - 1600 K and at wavelengths longer than 0.7 μm. Spectral and total emissivities are calculated for the three metals as the functions of temperature and phase of crystals.