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2022
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What are the characteristics of ductile iron?
In ductile iron, graphite is embedded in the basic structure of steel. Spheroidal graphite can only cause small fractures in the material, so ductile iron has high strength and good elongation at break. Among various cast irons, the properties of ductile iron are close to those of steel. The elongation at break of this cast iron can be improved by annealing, and the strength can be improved by quenching and tempering. Spheroidal graphite cast iron can also be surface carburized. Spheroidal graphite cast iron contains spheroidal graphite and has high strength and toughness.
In ductile iron, graphite is embedded in the basic structure of steel. Spheroidal graphite can only cause small fractures in the material, so spheroidal graphite iron has high strength and good elongation at break. Among various cast irons, the properties of ductile iron are close to those of steel. The elongation at break of this cast iron can be improved by annealing, and the strength can be improved by quenching and tempering. Spheroidal graphite cast iron can also be surface carburized. Spheroidal graphite cast iron contains spheroidal graphite and has high strength and toughness.
The original material of malleable cast iron contains about Iron water containing carbon, silicon, and manganese. It is cast into thin-walled castings (malleable castings). The billet must undergo long-term continuous heat treatment. According to the annealing process or the appearance of the generated structure, we divide malleable cast iron into decarburized annealed malleable cast iron. Decarburized malleable cast iron billets are annealed in an oxidizing furnace for several days, and the decarburized surface fracture shows a bright metallic luster. This cast iron has the same properties as steel. However, the decarburization depth of the workpiece can only reach about 5 mm, and in deeper sections, the iron carbide inside the workpiece can be seen to decompose into amorphous carbon.
Anneal the non-decarburized annealed malleable cast iron billet in a neutral furnace environment for a few days. During the annealing process, the cementite decomposes into ferrite and flocculent amorphous carbon. The black granular fracture structure is independent of the wall thickness. Both malleable cast irons have better toughness than flake graphite cast iron and have good casting properties. Special malleable cast iron EN-GJMW-360-12 is also weldable. The microstructure of decarburized annealed malleable cast iron surface contains less carbon, while the carbon in non-decarburized annealed malleable cast iron is flocculent.
Ductile iron has high strength and toughness, and it has developed rapidly at home and abroad. Its output has exceeded that of cast steel and malleable cast iron, becoming a casting alloy material second only to gray cast iron. The reason why graphite in ductile iron is spherical is that a spheroidizing agent that can make graphite spherical is added to the molten iron. The products produced by ductile iron casting technology have the advantages of high strength, high toughness, and low price, which meet the requirements of automobile production. Therefore, ductile iron casting technology has been widely used in automobile production. As-cast pearlitic ductile iron crankshafts and as-cast ferritic ductile iron automobile chassis parts have been used in China Automobile factory of the enterprise Put into use, which also marks that China's ductile iron production has reached a higher level. The application of ductile iron in the automotive industry shows its superiority. With the continuous improvement of technical level, it is believed that ductile iron will be applied in various fields in the future.
In ductile iron, because the graphite is spherical, after the graphite ball precipitates, it begins to adsorb the surrounding graphite, and the surrounding liquid becomes solid austenite due to The w(C) content decreases and surrounds the graphite ball; because the graphite ball is surrounded by austenite, the carbon that can only be absorbed from the austenite is limited, and the carbon in the liquid slowly diffuses into the graphite ball through the solid, and is surrounded by austenite to limit its growth. Therefore, even if the carbon equivalent of ductile iron is much higher than that of gray cast iron, the graphitization of ductile iron is difficult, so there is not enough graphitization expansion to offset the solidification shrinkage. Therefore, ductile iron is prone to shrinkage cavities.
Cast iron
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