Magnesium alloys due to their low density and high strength-to-weight ratio are promising material for the automotive and aerospace industries. Many elements made from magnesium alloys are produced by means of sand casting. It is essential to investigate impact of the applied mould components on the microstructure and the quality of the castings. For the research, six identical, 100x50x20mm plates has been sand cast from the Elektron 21 magnesium casting alloy. Each casting was fed and cooled in a different way: one, surrounded by mould sand, two with cast iron chills 20mm and 40mm thick applied, another two with the same chills as well as feeders applied and one with only the feeder applied. Solid solution grain size and eutectics volume fraction were evaluated quantitatively in Met-Ilo program, casting defects were observed on the scanning electron microscope Hitachi S3400N. The finest solid solution grain was observed in the castings with only the chills applied. Non metallic inclusions were observed in each plate. The smallest shrinkage porosity was observed in the castings with the feeders applied.

Non-metallic inclusions found in steel can affect its performance characteristics. Their impact depends not only on their quality, but also,

among others, on their size and distribution in the steel volume. The literature mainly describes the results of tests on hard steels,

particularly bearing steels. The amount of non-metallic inclusions found in steel with a medium carbon content melted under industrial

conditions is rarely presented in the literature. The tested steel was melted in an electric arc furnace and then desulfurized and argonrefined.

Seven typical industrial melts were analyzed, in which ca. 75% secondary raw materials were used. The amount of non-metallic

inclusions was determined by optical and extraction methods. The test results are presented using stereometric indices. Inclusions are

characterized by measuring ranges. The chemical composition of steel and contents of inclusions in every melts are presented. The results

are shown in graphical form. The presented analysis of the tests results on the amount and size of non-metallic inclusions can be used to

assess them operational strength and durability of steel melted and refined in the desulfurization and argon refining processes.