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Introduction
Ductile iron (also known as spheroidal graphite iron, abbreviated SG Iron or SG) is a type of cast iron. It has a nodular graphite shape in a matrix formed by ferrite, pearlite, and sometimes ferrite-pearlite. It is stronger, more ductile, and more fatigue resistant than traditional cast iron. Ductile iron also offers a wider range of choice for the mechanical properties required for a given application, as well as better castability and improved impact strength.
Hardness of Ductile Iron
The hardness of ductile iron is typically measured according to the Rockwell scale. There are a number of different grades of ductile iron, which vary in hardness, ranging from 65 HRC (Rockwell C) to 73 HRC (Rockwell C). Generally, grades with higher hardness are better suited for applications involving wear and impact resistance.
Microstructure of Ductile Iron
Ductile iron is composed of a ferrite-pearlite matrix, with the proportion depending on the type of alloy. Usually, there is a higher concentration of pearlite near the surface of the casting, which gives the metal excellent surface hardness and wear resistance. At greater depths, where the pearlite content tends to decrease, the metal is softer and more ductile, which makes it more resistant to fatigue and makes it easier to machine.
In terms of crystalline structure, ductile iron typically forms nodular graphite. A nodular graphite structure is composed of small, individual graphite particles dispersed throughout the metal matrix. The graphite cores are generally spherical or ellipsoidal in shape, surrounded by metal in a matrix of ferrite and pearlite.
Conclusion
In conclusion, ductile iron is a type of cast iron with a nodular graphite structure, which provides a range of benefits. It is stronger, more ductile and fatigue-resistant than traditional cast iron, offering a range of choice for the mechanical properties and better castability and impact strength. The hardness of ductile iron is typically measured according to the Rockwell scale, ranging from 65 HRC (Rockwell C) to 73 HRC (Rockwell C). Ductile iron is composed of a ferrite-pearlite matrix, with the proportion depending on the type of alloy, and its crystalline structure forms nodular graphite, composed of small, individual graphite particles distributed throughout the metal matrix.
