Deoxidation and modification of steels with reduced silicon content

Abstract

The object of research is the processes that affect the mechanical characteristics of steels after the treatment of melts with silicon-free complex master alloys according to existing technologies. One of the most problematic places is the negative effect of silicon on the weldability of low-alloy steel, sharply increasing the heterogeneity of welds in sulfur and phosphorus and increasing their susceptibility to hot cracks. The cyclic strength of welded joints decreases markedly with an increase in the silicon concentration of steel. Also in this case, there is a threat of the formation of silicon monoxide, which significantly increases the fragility of the finished steel products. Also, steels processed with alloys containing silicon are prone to decarburization, the formation of surface defects during hot working and graphite formation, which reduces their endurance limit. In the research it was possible to prove that the use of silicon-free complex ligatures (SFCL) in smelting made it possible to obtain an increase (2–3 times) in the entire complex of mechanical and operational properties, especially ductility, impact strength at normal and negative test temperatures (cold resistance) , fatigue strength. In some cases, the level of properties of cast metal reaches the deformed version of its manufacture, for example, rolled products and even metal obtained by electroslag remelting. Processing of the melt of various BKL steels when tapping from the furnace into a pouring ladle instead of aluminum master alloys, silicocalcium and ferrocerium (according to the current technology) provided the required level and high stability of the mechanical properties of 20GML steel. Also, thanks to the use of BCL, it was possible to reduce the consumption of ligatures and deoxidizers by 4.2 kg per ton of liquid metal and increase the yield of rejection of casting defects by 6–10 %. It has been established in the work that BCL treatment leads to stabilization of the chemical composition, refinement of the grain structure of steels, as well as an increase in its dispersion and the level of mechanical characteristics.