How is ductile iron formed? What are its advantages?

Ductile iron boasts advantages such as high strength, lightweight design, excellent toughness, and resistance to impact as well as extreme temperatures, making it widely used in critical mechanical components like crankshafts, valves, and pipelines. However, like all other materials, ductile iron also has certain drawbacks, among which Relatively It's important that casting requirements are stringent, as they can easily lead to product defects. For instance, when the content of a certain element is too high, the internal structure of the cast ductile iron may change, resulting in defects such as porosity, sink marks, and rough surfaces.

How is ductile iron formed? The casting process for ductile iron is known as spheroidal graphite casting. Like steel, ductile iron can undergo heat treatment and other processes to enhance its performance characteristics. During the formation of ductile iron, the graphite in the molten iron is transformed into spherical shapes—this very spheroidization of graphite gives ductile cast iron its numerous advantages. The process of forming spherical graphite actually involves two distinct stages. 1 The stage is graphite nucleation. ， During the process of molten iron turning into a liquid, many non-metallic elements and some impurities collide with each other as they float around, eventually coming together to form graphite spheres. After graphite nucleation begins, numerous carbon atoms start clustering onto the graphite nucleus. As more and more carbon atoms accumulate, Then It will become spherical—this is the spherical graphite's first 2 The secondary growth process. Therefore, to obtain spheroidal graphite during casting, controlling the graphite growth process is crucial.

Precautions in ductile iron production: (1) The sulfur content and other trace elements in molten iron must not be too high. If the levels of sulfur and other trace elements in the molten iron exceed the acceptable range, more spheroidizing agents—or spheroidizing agents with higher rare-earth content—will be required. This, however, increases the cost of the spheroidizing agents. Moreover, an excessive amount of spheroidizer can lead to increased slag inclusion, which negatively impacts the stability of casting quality. On the other hand, if the rare-earth content is too high, it may easily cause brittle graphite formation in large-section castings. (2) The stability of the spheroidizing process. Spheroidizing is a critical step in the production of ductile iron. Only when the spheroidizing process remains stable can the quality of the castings be consistently reliable. (3) Avoid long wait times. After ball inoculation treatment, pouring should be done immediately. Over time, residual magnesium will burn off, leading to a decline in the nurturing effect. (4) Avoid excessive residual magnesium content. High levels of residual magnesium can increase the tendency for shrinkage in castings. For general ductile iron, the residual magnesium content should be kept within a controlled range. 0.035% to 0.045% For high-nickel ductile iron, the residual magnesium content should be controlled below 0.06% to 0.07% 。 (5) Use higher-quality inoculants for castings with stringent requirements. For wind power components and high-speed rail components that demand precision, it’s best to choose flow-inoculants with strong inoculation effects. These inoculants are characterized by their ability to Very large Increase the number of graphite spheres, and ensure the graphite spheres are round in shape.

Ductile iron, as a material with numerous advantages, has now advanced to its… 2 Compared to conventional ductile iron, this new type incorporates a higher silicon content—so much so that silicon actually exceeds carbon in proportion. As a result, the new material boasts superior tensile strength and significantly reduced weight, marking a substantial departure from earlier grades of ductile iron, where increased strength often came at the expense of ductility. As China, a global leader in casting technology, continues to pursue lightweight designs while simultaneously enhancing material strength, this approach is set to become the future direction of materials development. By continually refining the composition and performance of ductile iron, this versatile material is poised for even broader applications across an expanding range of industries in the years ahead.