Ductile iron (also known as ductile iron or ductile iron) is actually a group of irons that exhibit high strength, flexibility, durability and resiliency due to their unique microstructure. Ductile iron typically contains more than 3% carbon; it can bend, twist or deform without breaking. Its mechanical properties are similar to steel and far exceed standard cast iron.
Ductile iron castings are solid metal objects produced by injecting molten ductile iron into voids in a mold. The ductile iron then cools and solidifies into the shape of the void it occupies.
Invented in 1943, ductile iron is the modern iteration of cast iron. Cast iron and ductile iron have contrasting physical properties due to differences in their microstructure.
Graphite and carbon contained in cast iron exist as flakes; cast iron exhibits positive compressive load capacity, but tensile loads above its natural tensile strength can cause cracks to form and rapidly propagate from stress points within the flake graphite microstructure . As a result, cast iron has almost no elongation. It is a brittle material, so its use in tensile and shock loading applications is limited.
The graphite in ductile iron is spherical, so it is sometimes called spheroidal graphite. Likewise, the term ductile iron stems from the fact that the carbon contained in ductile iron exists in the form of spherulites. This unique microstructure allows ductile iron to withstand bending and shock loads better than conventional cast iron.
What is ductile iron made of?
Pig iron is used in the production of ductile iron
While ductile iron can be produced from steel or scrap iron, pig iron is the main source of input for most modern ductile iron foundries. Pig iron refers to primary iron production in blast furnaces containing more than 90% iron.
The term "pig iron" comes from the old-fashioned method of casting blast furnace iron into molds in a sand bed so they can be fed from a common runner. Since the die set resembles a litter of suckling pigs, the individual iron blocks are called "pigs" and the runners are called sows. Modern pigs are produced by pig continuous casters.
Pig iron is used as the main source of pure iron in ductile iron production. It offers many unique advantages: pig iron contains low residual or harmful elements, has a consistent chemical composition, promotes optimal slag conditions, and improves process control by providing consistent charging characteristics. Demand for pig iron has increased in recent years as ductile iron plants take advantage of their advantages over alternative iron sources such as scrap iron or melting scrap and adding carbon.
Advantages of ductile iron
Ductile iron offers designers several advantages:
Ductile iron can be easily cast and machined.
It has an excellent strength-to-weight ratio.
Ductile iron is much less expensive to manufacture than steel.
It has superior castability and machinability.
Ductile iron offers designers an excellent combination of toughness, low-cost manufacturing and reliability.
Characteristics of ductile iron
To manufacture different grades of ductile iron, the matrix structure around the graphite must be controlled during the casting process or by subsequent heat treatment. There are small compositional differences between the different grades of ductile iron to create the desired matrix (microstructure).
Ductile iron can be thought of as steel with graphite spheres interspersed in its matrix. The quality of the metal matrix in which the graphite spheres are suspended has a significant effect on the properties of ductile iron, but the graphite spheres themselves do not.