Gray Cast Iron properties
Gray cast iron is the most common cast iron, named for the gray fracture surface caused by graphite flakes. It is inexpensive, easy to cast, machines well, and damps vibration, but it is brittle with little ductility. Values are for Class 30.
Mechanical properties
| Property | Value |
|---|---|
| Tensile strength | 30 ksi (207 MPa) |
| Yield strength | no distinct yield (brittle) |
| Elongation | under 1% (brittle) |
| Hardness | about 190 HB (Brinell) |
| Modulus of elasticity | 14,000 ksi (97 GPa) |
Physical properties
| Property | Value |
|---|---|
| Density | 0.260 lb/in³ (7200 kg/m³) |
| Melting point | about 1175 to 1290 °C |
Thermal properties
| Property | Value |
|---|---|
| Thermal conductivity | 53 W/m·K |
| Thermal expansion | 11.8 µm/m·°C |
| Specific heat | 490 J/kg·K |
Values are typical for the grade and condition shown. Actual properties vary with temper, heat treatment, and product form, so use these for comparison and preliminary design and confirm against material certificates for final work.
Compare with other materials
See the Material Properties Comparison, Yield Strength, and Density charts.
Typical uses
Gray cast iron is used for engine blocks, machine bases, pump and valve housings, cookware, and pipe. Its excellent castability, machinability, vibration damping, and low cost make it the default material for large, complex cast shapes under compression.
How it compares
Gray iron is cheap and easy to cast but brittle, strong in compression yet weak and unforgiving in tension, unlike ductile steel. Ductile (nodular) iron, with rounded graphite, is far tougher; gray iron is chosen where damping and castability matter and loads are compressive.
FAQ
Why is gray cast iron brittle?
Its graphite flakes act as internal stress raisers, so it fractures with almost no stretching. It is strong in compression but weak and brittle in tension.
What is gray cast iron used for?
Engine blocks, machine bases, housings, and cookware: large cast parts where castability, machinability, vibration damping, and low cost matter.
Why does cast iron damp vibration?
The graphite flakes absorb and dissipate vibration energy, which is why machine tool bases are often made of gray iron for stability.