Gray Cast Iron, also known as gray iron, is a popular type of iron used in castings. The composition of gray cast iron is 2.5%–4% carbon, 1%–3% silicon, and some additions of manganese ranging from 0.1% to 1.2%. Gray iron contains graphitic microstructures, giving the iron it’s gray color. This iron is easily cast but it cannot be forged or worked mechanically, either hot or cold. While the tensile strength and impact resistance of gray iron is weaker than most other metals, the compressive strength is equivalent to low-carbon and medium-carbon steel. For most applications, gray cast iron typically has acceptable ductility, tensile strength, yield strength, and impact resistance.
Hardness (Vickers): 161-321
Tensile Strength: 7 tons per square inch on average
Tensile Strength, Ultimate: 16700-102000 psi (115-700 MPa)
Tensile Strength, Yield: 9500-60900 psi (65.5-420 MPa)
Compressive Yield Strength: 83000-200000 psi (572-1380 MPa)
Melting Point: 1140-1200 degrees Celsius
There are many unique benefits of using gray cast iron. One of the most notable is gray iron’s enhanced lubrication. The graphite flakes in gray iron allow for better lubrication creating less wear on the cast iron. This makes gray cast iron a great choice for parts like brake rotors. Gray cast iron also has the ability to dampen vibrations making it an excellent choice for housing applications or industrial applications such as machinery bases. Additionally, gray iron has high thermal conductivity allowing it to move heat more easily through the metal.
Gray cast iron can withstand thermal cycling, meaning the iron can go through high and low temperature changes without strain. Thermal cycling can create stress and premature failure in other forms of metal casting, however gray cast iron has continuously proved its ability to withstand thermal cycling. Gray iron is very resistant when it comes to oxidation. Gray cast iron iron develops a protective film or scale on the surface, making it more resistant to corrosion than wrought iron or mild steel.
One of gray cast iron’s biggest pros is also its biggest con. The graphite flakes that give gray iron its added lubrication and resistance to wear, also allows areas of weakness in the metal where fractures can begin. These fractures can cause splits and breakage. Fracturing is why gray iron has low tensile and impact strength.
Gray cast iron has many applications and is often used across every industry such as automotive, construction, and manufacturing.
Examples of gray cast iron applications: