Introduction
One of the most widely used metals in industry worldwide is cast iron. It is preferred due to its strong mechanical properties, low cost and its capacity for manufacturing complex shapes. Of the various forms which cast iron can take, grey cast iron and ductile cast iron are the most commonly used. Grey cast iron is a traditional form of cast iron and is found in most modern engine blocks and other mechanical parts; ductile cast iron is a newer form of cast iron which has superior properties and is used for applications which require superior durability and strength [1]. This paper will focus on the mechanical properties of Austenitic Special Purpose Cast Iron, a type of ductile cast iron produced to British Standards.
Types of Cast Iron
Cast iron is a group of iron-carbon alloys which contains more than 2% carbon, 1-3% silicon and traces of other metals. All of these alloys have a graphitic form of carbon which forms in layers, producing a strong collision barrier between iron particles. This gives cast iron strong mechanical properties, such as high compressive strength, high wear resistance and low fatigue strength [2].
Grey cast iron is the traditional form of cast iron and is the weaker of the two types. It is formed by melting iron, carbon and silicon into a single alloy and then cooling it in the mould. Grey cast iron is produced in large quantities for industrial and domestic applications, such as engine blocks and other mechanical parts. It is also used in the construction of infrastructure, due to its low cost and good abrasion resistance [3].
Ductile cast iron is a newer form of cast iron which has superior properties to grey cast iron. It is produced by adding certain elements such as magnesium and/or cerium to the molten metal and then cooling it in the mould. Ductile cast iron has superior mechanical properties such as higher tensile strength, fatigue and impact resistance compared to that of grey cast iron [4]. It is used in the production of heavy machinery, agricultural machinery and other heavy-duty machinery.
Mechanical Properties of Austenitic Special Purpose Cast Iron
Austenitic Special Purpose Cast Iron (ASPCI) is a type of ductile cast iron produced to British Standards. It is produced by a process of quenching and tempering which gives it superior mechanical properties compared to other forms of cast iron, such as grey cast iron.
ASPCI has a strong tensile strength of between 600-900 MPa and a modulus of elasticity (E) of between 210 and 240 GPa, meaning it can withstand high stresses and is suitable for applications requiring high wear resistance and impact strength. Its compressive strength is between 530 and 780 MPa, making it suitable for applications requiring compressive strength such as housing, bridges and other structural components. Its fatigue strength is between 130 and 170 MPa and its impact strength is between 4 and 6 J/cm2.
ASPCI also has excellent corrosion resistance due to its high chromium and molybdenum content. Its corrosion resistance is further enhanced by its surface finish, which typically consists of chromium nitride, molybdenum nitride and titanium nitride layers which act as a protective barrier against corrosion [5].
Conclusion
Austenitic Special Purpose Cast Iron (ASPCI) is a type of ductile cast iron produced to British Standards. It has superior mechanical properties compared to other forms of cast iron and is suitable for applications requiring high wear resistance and impact strength, compressive strength, fatigue strength and corrosion resistance.
References
[1] ASTM A536 (2018). Standard Specification for Ductile Iron Castings. ASTM International, doi 10.1520/A0536-18
[2] Grandbois, A., Roy, R., & Côté, S. (2019). Microstructure and mechanical properties of grey cast irons. Metallogr. 3 (2), 422–434.
[3] Abousaleh, H. N. (2006). Grey cast iron: Mechanical properties and uses. Int. j. ironmaking m. 5 (3), 11–18.
[4] Lee, H., Kim, H., Joo, Y., Han, K., & Kim, S. (2014). Study on properties of ductile iron with different Mg and La content by inoculation. J. Korea Powder Metall Institute 21 (4), 413–420.
[5] Hofman, D., & Ohadi, M. (2003). Austenitic Special Purpose Cast Irons for Wear and Corrosion Resistant Metal Components. In Wear of Materials (pp. 397–404). CRC Press, doi 10.1201/9781420035173.ch41
