Silicon in Steels

Silicon in Steels  Silicon (Si) (atomic number 14 and atomic weight 28.09) has density of 2.34 gm/cc. Melting point of Si is 1412 deg C and boiling point is 2355 deg C. The phase diagram of the Fe-Si binary system is at Fig 1. Fig 1 Fe-Si phase diagram  Si is present in all the types of steels either as an intentional addition or as a residual from the ore, scrap or deoxidizing agents. Available forms  There are many Si containing addition agents which are used in steel making. Ferrosilicon (Fe-Si) and silico manganese (Si- Mn) are by far the most common addition agents. Fe-Si is a ferroalloy of iron (Fe) and Si. Fe – Si contains 65 % to 90 % of Si and minor amounts of Fe, aluminum (Al) and carbon (C).  Fe – Si is usually produced in four grades. These are standard grade, low Al grade, low C grade, and high purity grade having low content of titanium (Ti). The standard grade of Fe- Si contains Al up to 2 % while the low Al grade has Al content of 0.5 % maximum. It is produced by reduction of quartzite (SiO2) with coke in presence of iron ore.  Fe- Si is made in the submerged arc furnace. Si – Mn is a ferroalloy with high content of Mn and Si. It is produced by heating a mixture of oxides of MnO2, SiO2 and Fe2O3 with C in a furnace. These oxides undergo a thermal decomposition reaction. The standard grade contains Mn in the range of 62 % to 68 %, Si in the range of 12 % to 18 % and C in the range of around 2.0 %.  The low C grade of Si – Mn has a C...