Ductile Iron Casting and its Development

Ductile iron castings are spherical graphite through spheroidizing treatment, which are of relatively high mechanical properties, plasticity and toughness, therefore ductile iron is better than carbon steel in strength.

Chemical composition of ductile iron

carbon content is 3.5~4.0%, silicon content is 2.1~3.1%, the contents of manganese, phosphorus and sulfur are not more than 1.7%, and proper amount of rare earth and magnesium.

There are many classifications of ductile iron castings, according to molding

1. Ordinary sand casting includes green sand mold, dry sand mold and chemically solidifying sand mold. Ductile iron castings require relatively high hardness as bearings, thus the castings after quenching and tempering in low temperature are of high hardness and toughness, retained lubrication performance of the graphite, and improved wear resistance.

2. Special casting according to molding materials can be divided into the natural mineral sand and gravel as the main form of special casting material (such as investment casting, cement casting, foundry shell casting, vacuum casting, solid casting, ceramic casting, etc.) and metal as the main cast of special casting material (such as metal casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.).

Production research and development of ductile iron casting

1. Pearlite ductile iron cast crankshaft and ferrite ductile iron car base indicate that China’s ductile iron production reaches a high level. Meanwhile the applications of outsourcing desulfurization, double melting method, instantaneous birth, audio analysis and fast thermal analysis narrow the gap between Chinese automotive castings technology and international advanced technology.

2. The process of forced cooling, solidification and delayed birth can prevent graphite distortion in the center of ductile iron and porosity.

3. In the early of 1970s, austenitic-bainitic ductile iron has been used, and the tensile strength of this material can be reach 1000MPa, thus it is widely used in gear and structural parts, and has higher economic and social benefits.

4. The ductile iron pipe foundry whose annual production gets to 90 tons gives to birth and the casting production line of ductile iron pass inspections by the state inspection center.

5. According to the mechanical properties researches of rare earth magnesium ductile iron, it is of high stress-strain properties, shock resistance and fracture toughness, therefore it is widely put into production.

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