The laser treatment processes are specified due to the laser-matter interaction instabilities. Modern additive manufacturing technologies such as selective laser melting provide layer-by-layer part growth with continuous operation for hours and days but without adequate controlling systems at present. In this paper, a method for determining a temperature in the laser action zone during the process based on a study of microscopic structure, phase and element analyses of the processed material is proposed. A fixed point corresponding to melting temperature was acquired, and the corresponding emissivity coefficient was calculated with the assumption of its wavelength and temperature independence. The experimental data were corroborated with good agreement with mathematical calculations. The obtained results reveal an impact of scanning speed and of laser emission power on temperature in molten zone, which presents interest for optimization of laser-processing technologies and more specifically selective laser melting process parameters.