Inoculant is a necessary additive in casting production. In the production of cast iron, inoculant can refine grains, reduce white edges, promote graphitization and improve the strength of gray cast iron.In addition, inoculant can also increase the content of the cast element and increase the elongation of ductile iron.
The rare earth inoculant combined with the melting process and the casting temperature adjustment can partially or completely eliminate the porosity defects in gray cast iron.
At present, there are about 200 kinds of inoculants, and there are more than 30 varieties of commonly used inoculants, and suitable inoculants should be selected for different castings.
There are many types of inoculants:
First, according to the composition classification: divided into silicon inoculant, carbon inoculant, rare earth inoculant, etc.;
Second, according to the function of inoculant classification: divided into stabilization inoculant, compound inoculant, etc.;
Three, according to the scope of use classification: gray cast iron inoculant, ductile cast iron inoculant, cast ductile iron inoculant, wear-resistant cast iron inoculant.
There are several commonly used inoculants:
75 Ferro silicon is the most commonly used inoculant, and the content of aluminum and calcium plays an important role in the inoculation effect. In general, in liquid iron, aluminum and calcium will react with oxygen and nitrogen to form high-melting compounds that become the core of graphite crystallization. Moreover, after the inoculant is added, a local Si-rich micro-region can be formed in the iron liquid, which is conducive to the precipitation of graphite. Therefore, when purchasing ferric silicon for inoculation, the content of aluminum and calcium should be considered. For 75 ferro silicon as inoculant, the relevant standards stipulate that the aluminum content is 0.75-1.75% and the calcium content is 0.5-1.5%. However, the aluminum content in the liquid iron cannot be too high, and adding 0.01% aluminum may lead to subcutaneous pores in the casting. This should be considered when selecting the inoculant varieties and determining the inoculant dosage.
The ability of strontium-containing ferro silicon to eliminate white holes is very strong, especially conducive to improving the form and distribution of graphite in thin-wall castings, so that the difference in the structure of different thickens is smaller, and the supercooled structure is only on the surface of the casting.
At present, ferro silicon containing strontium supplies two kinds of content, respectively, with strontium content of 0.6-1.0% and 1.0-2.0%. Generally, varieties with strontium content of 0.6-1.0% can be selected, and if the strontium content is too high, it can not give full play to its role. The addition of strontium-containing ferro silicon is about half of that of 75 ferro silicon.
Barium-containing ferro silicon also has a strong ability to promote graphitization, which can improve the form and distribution of graphite in thin-wall castings, and has the effect of slowing down the gestation decline, and the amount of treatment is less than 75 ferro silicon
Zirconium has A deoxidation effect, which is conducive to improving the fluidity of liquid iron, reducing the white tendency of cast iron, and promoting uniform and fine A-type graphite. It also has the effect of slowing the incubation decline.
Using silicon-barium alloy containing 20-30% barium as inoculant can significantly reduce the white tendency of cast iron, and can increase the incubation time to about 30min, especially for large castings. During treatment, the amount of alloy added is about 0.1%.
Although the silica-calcium alloy has a strong inoculation effect, in addition to the application of coated wire, the granulated alloy is not suitable for the inoculant of cast iron, because its density is lower than the liquid iron, it is easy to float and affect its effect with the liquid iron, and the inoculation effect is fast.
The inoculant containing rare earth metals such as rare earth mixed metals and rare earth ferro silicon, when the amount is appropriate, the inoculation effect is very strong, and the effect can be several times that of 75 ferro silicon, which can effectively eliminate the white gate and slow down the decline of the inoculation effect. If the amount of addition is too high, it may cause the cast iron crystallization to produce supercooling, cementite structure. The dosage must be strictly controlled when used.
Carbonaceous inoculants are mainly used for pre-treatment of liquid iron inoculation, and are generally crystallized carbonaceous materials. There are research reports that: for gray cast iron, the metallurgical silicon carbide of 85-90% is the best effect, and crystalline graphite is also effective. The amount of addition during pretreatment is generally 0.75%-1.0%, and the optimal value should be obtained according to the experimental results.
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