The emissivities of different new steel grades for reactor use were determined. Numerical models for optimizing of the radiation heat transfer need total emissivities. For idealized bright metals the calculation of emissivities is possible, but not for different thermally treated surfaces. The emissivity of technical surfaces depends on numerous factors and cannot be calculated exactly based on theoretical relations. Therefore the emissivities of different pretreated steel samples have to be determined experimentally. The emissivity properties of two new steel qualities with and without
different pre-treatments were investigated in the wavelength range between approx. 1.5 μm and 24 μm and the temperature range 200°C and 700°C. The results will be shown as spectral emissivities. Differences in the emissivities caused by pre-treatments will be discussed. The University of Duisburg-Essen has a measuring device for spectral emissivities. With these values temperature dependent total- and band-emissivities for use in heat transfer calculations and non-contact temperature measurements can be determined.