The selection of inoculants should be based on the purpose of inoculation and the production conditions of gray cast iron castings. Generally, when the carbon equivalent of gray cast iron is low, the eutectic undercooling increases, and gray cast iron castings are easy to produce white cast iron. In this case, strong inoculants should be selected, such as carbon silicon calcium alloy containing strontium and barium or strontium silicon iron, and the amount of inoculants should be increased appropriately.
When selecting inoculant, attention should be paid to the wall thickness of gray cast iron castings. For thinner gray cast iron castings, in order to prevent white cast iron, the compound inoculant composed of strontium ferrosilicon or strontium ferrosilicon and stabilized alloy is the most effective. Graphitized inoculants containing rare earth elements are suitable for thin-walled gray cast iron castings with high sulfur content. If gray cast iron castings are very thick and have long cooling and solidification time, long-term inoculants, such as barium ferrosilicon or stabilized inoculants containing barium, need to be used in order to avoid inoculation recession. If the strength of gray cast iron castings after inoculation treatment is required to be high, it is best to use nitrogen-containing stabilizing inoculant or rare earth calcium barium silicon alloy. At present, the most widely used inoculant in domestic factories is 75 inoculated ferrosilicon containing aluminum and calcium. If there are no special requirements for inoculation treatment, the inoculation recession will not occur before pouring. It is appropriate to choose this inoculant. When selecting inoculant.
After selecting the appropriate inoculant, an appropriate amount should be added. Too little inoculant will lead to deterioration of processing performance, uneven matrix structure and reduction of mechanical properties. However, too much inoculant will lead to excessive slag, reduction of molten iron temperature and shrinkage cavity. If the inoculant block is too small, it is easy to oxidize and cause slag and inoculation recession, but if the block is too large, it can not inoculate the molten iron evenly. The amount of inoculant added to thin-walled gray cast iron castings should be increased due to the white cast iron problem. When the pouring time of inoculated molten iron is long, the inoculant added should be increased accordingly due to the decay of inoculation. The inoculation dose of nodular cast iron is generally higher than that of gray cast iron.