Ductile and Malleable

Some buyers are confused about the ductile and malleable cast iron. Actually, I was confused about these concepts for long time. I just knew that our Dandong Foundry could produce the ductile iron, but can not produce malleable iron. As for what is malleable cast iron, I never made it clear, but herein, I will talk about these two definitions.

Ductile is meaning the cast iron has ductility, which means the ductile iron can be pulled longer than normal cast iron, such as grey cast iron. It is called higher elongation. Malleable is also meaning good ductility, so what are the differences of these two cast irons? We could distinguish their differences from two aspects, the microstructure and casting process.

As for the microstructure of ductile iron, the graphite is existed as many small balls, but in the malleable cast iron, the graphite is existed as cottony, which means the graphite looks like cotton. Therefore, both ductile iron and malleable iron have better strength, ductility and impact resistance.

As for the casting process, the production for ductile iron is made similar with the normal casting iron, just has a inoculation process. Inoculation means we will add the spheroidizing agents during melting and pouring process to make the graphite into balls. The production of malleable iron includes a special heat treatment process, which can make the graphite into cottony.

Because of the special heat treatment of malleable cast iron, its production difficulty is higher and production period is longer. So, in China, the most of malleable iron products have been replaced by ductile cast iron. It is difficult to find a good iron foundry who could produce malleable iron castings in China.

According to our experience, as for the buyers and designers, you should consider to use ductile iron. The most important issues for the users are the physical properties. As long as the ductile iron can meet your required physical properties, such as tensile strength and elongation, the ductile iron will be the better choice.

By the way, you may find some articles on internet say the malleable iron is cheaper than ductile iron, this article was correct in the past, but wrong for now. In the past, the ductile iron castings were difficult to produce, the spheroidizing agents were expensive, in the past, the malleable iron was cheaper than ductile iron, but after years development, for now, the ductile iron is cheaper, and the production process is more mature.

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