The choice of charge

(1) Scrap Steel

Scrap used in the production of ductile iron should be carbon scrap. It should not contain elements that hinder graphitization, such as chromium. It should not contain anti-spheroidizing alloying elements. The lumps of scrap steel should be about 30% in the form of thick flakes, which can be laid flat in the furnace.

(2) Recarburizer

(3) Cast Iron

It is mainly used to adjust the carbon content of molten iron. Hope to use high-carbon low-sulfur pig iron with wC>4%. The silicon content in the pig iron is appropriately higher, and the production of nodular cast iron can be less ferrosilicon.

(4) Spheroidizing

Spheroidizing agent and inoculant are used according to traditional techniques, and are determined in accordance with the actual conditions of each factory.

Smelt

Smelting process: Coke block + scrap steel → electrode block → temperature increase → pull out coke block and electrode block → sample and analyze carbon content → pig iron → return material → sample and analyze Si, Mn → temperature increase → ferromanganese + ferrosilicon → discharge →Inoculation + spheroidization → pouring.

The precautions during the smelting process are as follows:

Composition adjustment calculation

As we all know, the mechanical properties of ductile iron mainly depend on the chemical composition, cooling rate (as-cast ductile iron) and heat treatment process. The chemical composition is the internal cause, the root, and the variable, almost every furnace is different. Therefore, it is necessary to strengthen the detection of chemical components and make careful adjustments, and it is not appropriate to adopt "fixed ratio production". In the chemical composition, carbon equivalent is particularly important. In particular, nodular cast iron produced by using scrap steel as the main charge, because the efficiency of carbon increase is difficult to control, and the carbon equivalent fluctuates greatly, so special attention should be paid to adjusting the carbon equivalent.

This is because nodular cast iron is melted in the induction furnace, and the elements are not burnt much, and the iron is also burned to a certain extent. If you encounter special circumstances, you should pay attention to burning.

Composition adjustment application example:

4. Concluding remarks

In the production of induction electric furnace, we use scrap steel to produce QT800-2, the strength is 800～1000MPa, and the elongation is more than 4%.

At present, there is a lot of scrap steel in the market, pig iron is expensive, and high-quality pig iron is even more scarce. Therefore, we suggest that manufacturers with nodular cast iron production tasks can refer to the above-mentioned assumption and "substituting steel for iron" to produce nodular cast iron.