The binary phase diagram of silicon and iron is shown in Figure 1. Silicon and iron constitute Fe3Si, Fe5Si3, FeSi, FeSi2 and other compounds. The melting temperature range of 75 FeSi75 is 1300 ~ 1330℃, and that of 45 FeSi45 is 1250 ~ 1360℃. Ferrosilicon density decreases with increasing silicon content (see Figure 2). Figure 2 can be used to quickly determine the silicon content of ferrosilicon. In the slow cooling process of liquid ferrosilicon, the dense silicon-rich parts float up, while the dense ferrosilicon sinks, resulting in segregation of ferrosilicon components. In order to reduce segregation of ferrosilicon ingots, it is necessary to reduce the casting temperature, control the thickness of ingots, or layer casting and accelerate the cooling rate of ingots. Visible in the silicon phase diagram, when the silicon content between 53.5% ~ 56.5%, ferrosilicon zeta in phase. In the cooling process, as the zeta FeSi2 violent transformation, the volume of a solid silicon ingot of significant change, make the iron ingot internal cracks, cause ferrosilicon powder. Metallographic studies have shown that impurities in ferrosilicon mostly concentrate in the form of phosphates and arsenide at grain boundaries. When the moisture in the air penetrates into the cracks in the iron ingot, it reacts with phosphates and arsenides that accumulate in the grain boundary to form toxic PH3 and AsH3 gases, which completely destroy the grain boundary and is also another factor in silication of ferrosilicon. The content of hydrogen and oxygen in industrial ferrosilicon depends on its original content. The relationship between hydrogen and oxygen content and silicon content in ferrosilicon after solidification is shown in Figure 3.
