Ductile cast iron has been widely used across various industrial sectors. Due to its many excellent properties and economic advantages, it has replaced — and continues to replace — other materials. Since its discovery, ductile cast iron has primarily competed with forged steel, stamped steel parts, and welded components. For example, in the United States, 40% of ductile iron castings are used as substitutes for forged steel, stamped steel, and welded parts, while 25% replace malleable cast iron parts, 20% replace gray cast iron parts, and 15% replace steel castings.
In the production of ductile iron, ferritic-based ductile iron accounts for 60% by mass, pearlitic-based for 15%, ferrite–pearlite mixed matrix for 20%, and other types for 5%. In other words, ductile iron with ferritic and pearlitic matrices accounts for 95% of the total production by mass.
The excellent performance of ductile iron is mainly reflected in its outstanding mechanical properties. Ductile iron does not exhibit a distinct yield point; its stress-strain curve beyond the proportional limit is smooth and continuous. This is because once the stress exceeds the elastic limit, the graphite spheroids no longer deform. Although they appear to be part of the matrix, under tensile stress, they form voids in the longitudinal direction, causing an increase in volume. This volumetric expansion cannot be compensated by lateral compression.
According to the national standards comparing the properties of gray iron and malleable cast iron, ductile iron has clear advantages in terms of strength and ductility:
1. The mechanical property of gray iron is defined only by its tensile strength, and even its highest grade only reaches 350 MPa.
2. Malleable cast iron — whether black-heart, pearlitic, or white-heart — may have ductility indices, but their overall mechanical performance is inferior to ductile iron.
3. Cast steel and structural steel may have higher elongation after fracture and impact toughness, but their yield strength is lower than that of ductile iron.
Ductile iron not only surpasses gray iron and malleable iron in performance, but also compares favorably with cast steel and structural steel in terms of strength. Additionally, because of its excellent casting performance and low production cost, ductile iron has already replaced — or is expected to replace — a variety of materials, including gray cast iron, malleable cast iron, cast steel, ordinary structural steel, and alloy forged steels. As a result, the global annual output of ductile iron continues to grow at a rate of 4% to 8% per year.
With the development of the automotive industry, the application of ductile iron in the automotive sector has also expanded rapidly. According to statistics, three sectors account for the majority of ductile iron consumption in the United States: automobiles (40% by mass), pipes and fittings (26% by mass), and agricultural machinery (5% by mass).
Post time: Jul-17-2025