What is ductile iron?

Ductile iron (cast iron in which graphite exists in a spherical form) is a high-strength material developed in the 1950s, with low price and comprehensive performance close to steel. It is based on its excellent cost performance, and has been successfully used to cast some parts with complex stress, high strength, toughness, and wear resistance requirements.

Ductile iron (cast iron in which graphite exists in a spherical form) is a high-strength material developed in the 1950s, which is inexpensive and has comprehensive properties close to steel. It is based on its excellent cost performance and has been successfully used to cast some parts with complex stress and high requirements for strength, toughness, and wear resistance.

Ductile iron improves its mechanical properties effectively by spheroidizing the carbon in pig iron, especially improving plasticity and toughness, thereby obtaining higher strength than carbon steel. It has rapidly developed into a new casting material second only to gray iron. The so-called 'replacing steel with iron' mainly refers to this material.

In 1947, pig iron with spherical graphite in the as-cast state was discovered. The following year, ductile iron was produced by adding an appropriate proportion of Ce to high-carbon, low-sulfur, and low-phosphorus gray iron. Almost simultaneously, another American company obtained the same cast pig iron by adding an appropriate amount of manganese to gray iron.

Pig iron is an iron-carbon alloy with a carbon content greater than 2.11%. The carbon in it will precipitate in the form of graphite. If the precipitated graphite is spherical, it is called ductile iron. The general chemical composition is: carbon content 3.0～4.0%, silicon content 1.8～3.2%, total manganese, phosphorus, and sulfur content not exceeding 3.0%, and appropriate amounts of rare earth, magnesium, and other spheroidizing elements.

Ductile iron has been applied in almost all major industrial sectors, which require better mechanical properties, resistance to wear, severe thermal and mechanical shock, high or low temperatures, corrosion, and dimensional stability. To meet these usage needs, ductile iron has derived many grades, which can cover a wide range of mechanical and physical property distributions.

Ductile iron is often used to produce parts with complex stress and high requirements for various performance indicators, such as crankshafts, camshafts, and medium-pressure valves for general machinery. It can also be used as storage and transportation containers for highly radioactive objects.

In the early 1970s, China, the United States, and Finland almost simultaneously announced the successful research and development of high-strength, high-toughness austempered ductile iron. The tensile limit of this material reaches 1000MPa, so it is widely used in gears and various structural parts. Compared with alloy steel, austempered ductile iron has significant economic and social benefits.

With the concept of green environmental protection deeply rooted in people's hearts, many original products are facing redesign and manufacturing. The high strength-to-weight characteristics of ductile iron are increasingly attracting the attention of designers and can effectively reduce production costs. Currently, ductile iron castings are expanding their application places at a very alarming rate, but the end of the application is still not visible. This is worth considering for manufacturers who are not currently engaged in ductile iron casting.

Therefore, it is expected that as ductile iron castings replace the original pig iron castings and some steel castings, we will also witness the continuous increase in the content of ductile iron from the content position. With the development of science and technology, it is estimated that more ductile iron castings will be introduced in the future.