Non-metallic inclusions in micropores of massive steel castings

The study of the cast structure of castings makes it possible to optimize the technological parameters of the casting process and improve the quality of cast billets. Electron microscopic studies of nonmetallic inclusions and X -ray spectral analysis of their micro-volumes in metal plates cut from defective sections of a massive casting were carried out. The “fresh” fractures of impact samples with a sharp V -shaped incision destroyed at –60 °C were investigated. It was found that there are practically no oxide films and non-metallic inclusions at the boundaries and in the body of the casting grains. The latter occur on the inner surface of micropores or near them at the edge, and aluminum carbonitrides are present at the grain boundaries or in their body. Determination of chemical composition of non-metallic inclusions in micro-volumes of the order of 1 µm 3 allowed us to establish their nature and possible causes of their appearance, as well as formulate practical recommendations for the prevention of visually observable defects in a massive casting. To improve the quality and reduce the number of micropores occurring in the casting, it is necessary to use a cleaner charge that does not contain zinc. Zinc has a low boiling point (907 °C [10]), and, when casting the mold, its vapors, along with other gases, rise to a casting head, under which, as a result of crystallization, they settle in pure form or in the form of ZnO-type compounds on the walls of the resulting micropores, shrinkage porosities, cavities. In addition, it is necessary to remove the slag more carefully so that it does not participate in pores formation, and its particles do not precipitate in or near the pores in the form of magnesia spinel, calcium and manganese sulfides, iron, aluminum, calcium oxides, etc. It is also required to limit the residual aluminum content in steel after its deoxidation to 0.03 %, as is customary in metallurgical production, and to minimize the resin content in the mold material.