COEFFICIENT OF LINEAR THERMAL EXPANSION OF IRON AND IRON ALLOYS
The linear thermal expansion coefficient (α) relates temperature change
to dimensional change via ΔL = α · L₀ · ΔT.
The values below apply specifically to pure iron, cast irons,
and selected iron–based alloys such as Invar.
For a general comparison of thermal expansion coefficients across metals,
see the main reference:
Thermal Expansion Coefficient of Metals
.
This page focuses on iron and cast iron materials.
For carbon steels, alloy steels, and stainless steels,
use the dedicated page:
Thermal Expansion Coefficient of Steel
.
|
Linear Thermal Expansion Coefficient Values of Iron and Iron Alloys
|
| Material |
Temp. |
Coefficient of Thermal Expansion (CTE) |
| 10−6/°C |
10−6/°F |
| Pure iron |
20 °C / 68 °F |
11.7 |
6.5 |
| Fe–C alloys |
| 0.06% C | 20–100 °C / 68–212 °F | 11.7 | 6.5 |
| 0.22% C | 20–100 °C / 68–212 °F | 11.7 | 6.5 |
| 0.40% C | 20–100 °C / 68–212 °F | 11.3 | 6.3 |
| 0.56% C | 20–100 °C / 68–212 °F | 11.0 | 6.1 |
| 1.08% C | 20–100 °C / 68–212 °F | 10.8 | 6.0 |
| 1.45% C | 20–100 °C / 68–212 °F | 10.1 | 5.6 |
| Invar (36% Ni) | 20 °C / 68 °F | 2.0 | 1.1 |
| 13Mn – 1.2C | 20 °C / 68 °F | 18.0 | 10.0 |
| 13Cr – 0.35C | 20–100 °C / 68–212 °F | 10.0 | 5.6 |
| 17.7Cr – 9.6Ni – 0.06C | 20–100 °C / 68–212 °F | 16.5 | 9.2 |
| 18W – 4Cr – 1V | 0–100 °C / 32–212 °F | 11.2 | 6.2 |
| Gray cast iron | 0–100 °C / 32–212 °F | 10.5 | 5.8 |
| Malleable iron (pearlitic) | 20–400 °C / 68–752 °F | 12.0 | 6.7 |
Notes: Values are typical / representative for the ranges shown. Use applicable material standards or design allowables when required.
Why cast iron expands differently from steel
Cast irons typically exhibit slightly lower thermal expansion than many steels
because of their high carbon content and the presence of graphite.
In gray cast iron, graphite flakes interrupt the iron matrix,
reducing overall thermal strain.
As a result, gray cast iron commonly shows CTE values around
10–11 × 10⁻⁶/°C,
making it suitable for machine tool bases, engine blocks,
and structures requiring dimensional stability.
How to use the coefficient (quick refresher)
To estimate length change with temperature: ΔL = α · L₀ · ΔT.
For example, a 1.2 m Invar bar (α ≈ 2×10⁻⁶/°C) heated by 30 °C changes length by ΔL ≈ 2×10⁻⁶ × 1.2 × 30 = 72 µm.
Related
Reference
- Davis, J.R. Metals Handbook Desk Edition. ASM, 1998.