The purpose of inoculation treatment is to eliminate white mouth, improve processing performance, refine eutectic clusters, promote A-type graphite, make the graphite coarser and shorter, the end becomes blunt, the shape deformation and bending, the graphite distribution is uniform, improve the body structure, improve mechanical properties, reduce section sensitivity, and so on. For ductile iron, it is to refine the graphite ball while refining the eutectic mass, the number of balls increases, the diameter of the ball becomes smaller, the roundness is improved, the spheroidization level is improved, the body organization is improved, and the comprehensive performance of ductile iron is improved.
All kinds of different inoculation elements are C, Si, Ca, Ba, Sr, Al, Zr, RE, Mn, etc., and their behavior in the inoculation process is not the same, they show their own characteristics in eliminating the white gap, refining the eutectic group to improve the matrix structure and the rate of inoculation decay, and the side effects and effects on the quality of castings are also significantly different. Therefore, it is necessary to develop a variety of inoculants, and choose a more suitable inoculant according to the different requirements of the different production process conditions for the casting material.
The inoculation effect of the compound inoculant composed of several inoculant elements is not equal to the simple superposition of the inoculation effect of the inoculant elements separately. The combination of some inoculation elements can greatly enhance the inoculation effect, such as Si and Ca,Si and Ba,Si and Ca, Ba, Mn,Si and RE,Si and Al,Si and Sr, and so on. The combination of some breeding elements weakens the breeding effect, such as Sr and Al, Ca, Sr and RE, Ti and RE, and so on. Therefore, when developing a new compound inoculant and determining its structure and ratio, it is necessary to take into account the possibility that the compound may greatly increase the inoculation effect or weaken the inoculation effect.
In general, the stronger the gestation effect of the gestation agent, the faster the rate of decline. For most inoculants, more than half of the inoculation effect has disappeared within 5 minutes after inoculation, so it is required to pour the hot metal as soon as possible after inoculation. The decline of inoculation is manifested as the rise of white hole tendency, the coarsening of eutectic clusters, the thickening of graphite sheets, and the appearance of supercooled graphite (D and E type graphite), which reduces the quality of castings. The decay rate of the incubation effect of the same inoculant may be very different, such as the inoculant containing RE for the inoculation of ductile iron, showing a very prominent anti-decay ability, and for the inoculation of ordinary gray cast iron, the anti-decay ability is not very obvious.
The sulfur content of gray iron molten iron plays a very important role in inoculation, and the appropriate amount of S in gray iron (S≥0.06%, ≤0.12%) can improve the mechanical properties of gray iron and improve the machining performance. It is the result that S in hot metal improves and enhances the inoculation effect, improves the morphology of graphite and refines the eutectic clusters. With the increase of S amount, the graphite becomes shorter, the end becomes blunt, and the shape becomes curved, so the performance of gray iron can be improved. If S≤0.025%, for most inoculants, the inoculation effect is very poor, and the inoculation effect is maintained for a short time and soon disappears. The cast iron melted by electric furnace contains about 0.03% S, in order to improve the inoculation effect, it is best to add FeS to the charge and increase the sulfur content of hot metal to 0.06-0.12%. The inoculant containing RE, Ca and Ba can obtain better inoculant effect on cupola hot metal with high S content and electric hot metal with low S content.
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