Ferrosilicon is a commonly used inoculant. Among them, the content of aluminum and calcium played an important role in the inoculation effect. Ferrosilicon, which is free of aluminum and calcium, has been reported to have little or no effect on the inoculation of gray cast iron. It is generally believed that molten iron, aluminum and calcium will react with oxygen and nitrogen to form high melting point compounds, which will become the core of stone crystallization. Moreover, after adding the inoculant, local silicon-rich micro-regions can be formed in the molten iron, which is beneficial to the precipitation of graphite. When purchasing ferrosilicon for inoculation, the content of aluminum and calcium should be considered. For 75 ferrosilicon used as an inoculant, the upper limit of aluminum content is 0.5%, 1.0%, and 1.5%, respectively, and the upper limit of calcium content is 1.0%. However, the aluminum content in molten iron should not be too high. The addition of 0.01% aluminum may cause subcutaneous porosity in castings.
Silicon barium alloy inoculant can significantly reduce the whitening tendency of cast iron and can prolong the maintenance time of the inoculation effect to about 30 minutes, especially suitable for large castings.
Calcium Silicon Inoculants
Although siliconcalcium alloy has a strong inoculant effect, it is not suitable to use granular alloy as an inoculant for cast iron except for the application of cored wire. Its main disadvantage is:
Density is much lower than molten iron, easy to float, affecting the relationship with molten iron
Inoculation effectiveness declines rapidly
Rare earth mixed metal and rare earth ferrosilicon orother inoculants containing rare earths, when properly added, have a strong inoculation effect, and its effect is several times that of 75 ferrosilicon, which can effectively eliminate whitening and slow down the whitening rate. However, if the amount of rare earth inoculant is too much, supercooling and cementite structure may appear when the cast iron crystallizes, so the amount of addition must be strictly controlled during use.