Mössbauer study of thermal behavior of CL20ES and CL50WS steel powders used in selective laser melting

The phase and structural changes of steel powders CL20ES and CL50WS used in additive manufacturing were studied by Mössbauer spectroscopy and X-ray diffraction. Investigated powders were annealed in the temperature range 500 °C–1100 °C in oxidizing and inert atmosphere. Annealing in an oxidizing atmosphere resulted in the formation of different iron oxides in both steel powders depending on the annealing temperature. In addition, a phase change of ferrite to austenite was identified when annealing CL50WS steel powder in an oxidizing atmosphere. This phase change was confirmed by annealing given CL50WS steel powder in an inert nitrogen atmosphere. The transformation of austenite to ferrite phase was observed only, when annealing CL20ES steel powder in an inert atmosphere at 1100 °C. Morphological changes on the surface of the spherical powders were observed by scanning electron microscopy.