I. Selection of pig iron,scrap steel,and recycled iron
The selection of pig iron must first ensure that the composition is uniform,and then select the appropriate pig iron according to the grade of ductile iron. Of course,some foundries do not use pig iron,and the method of adding carburizer and scrap steel is also relatively common. The selection of scrap steel is generally based on carbon steel,as far as possible to control alloy elements. The furnace iron should be strictly distinguished,and try to use the same material to ensure the accuracy of the ingredients.
2. Selection of nodularizer and inoculant
Spheroidizing agent is a necessary condition for spheroidizing. Without it,spheroidizing is impossible. Spheroidizing agent is divided into heavy rare earth and light rare earth,generally less than 500kg,castings with wall thickness less than 100mm use light rare earth spheroidizing agent; and castings with wall thickness greater than 120mm and weight greater than 3 tons use heavy rare earth spheroidizing agent.
Inoculation in ductile iron production is also indispensable. Inoculants and their inoculation treatment are important guarantees for the success of spheroidization. The nodular graphite spheres can only be obtained after nodularizing the molten iron after spheroidization,and the mechanical properties of the tissue can be guaranteed. Common inoculants are 75SiFe,Si-Ba-Ca,Si-Re-Mn-Cr,and so on. When producing major castings,multi-element compound inoculants must be used,such as Si-Ba-Ca,Si-Re-Mn-Cr,etc.,in order to achieve a good inoculation effect.
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