What is the linear thermal expansion coefficient of steel?

At room temperature, steel typically has a linear thermal expansion coefficient of 10–17×10⁻⁶/°C (5.5–9.5×10⁻⁶/°F), depending on the grade and alloy composition.

Does the expansion coefficient vary by steel grade?

Yes. Austenitic stainless steels like 304 and 316 expand more (~16–17×10⁻⁶/°C), while carbon and tool steels expand less (~10–12×10⁻⁶/°C).

How do I convert the thermal expansion coefficient between °C⁻¹ and °F⁻¹?

Multiply α in °C⁻¹ by 1.8 to obtain α in °F⁻¹, or divide by 1.8 to convert the other way.

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Linear Thermal Expansion Coefficient of Steel (α)

Typical range: 10–17 × 10⁻⁶/°C (5.5–9.5 × 10⁻⁶/°F), depending on grade and temperature.

The tables below show the linear coefficient of thermal expansion (CTE) specifically for steel and steel alloys, including carbon steels, alloy steels, stainless steels, and tool steels.

For a general comparison of thermal expansion coefficients across metals, see the main reference: Thermal Expansion Coefficient of Metals .

Note: The CTE is usually measured between 20–100°C (68–212°F). Austenitic stainless steels expand more than ferritic and martensitic steels.

Plain Carbon and Low-Alloy Steels

Room temperature CTE for carbon and low-alloy steels
Material	Temperature Range	α (×10⁻⁶/°C)	α (×10⁻⁶/°F)
AISI 1010 (annealed)	0–100°C / 32–212°F	12.2	6.8
AISI 1020 (annealed)	0–100°C / 32–212°F	11.7	6.5
AISI 1025 (annealed)	0–100°C / 32–212°F	12.0	6.7
AISI 1040 (annealed)	0–100°C / 32–212°F	11.2	6.2
AISI 1045 (annealed)	0–100°C / 32–212°F	11.6	6.4

Alloy Steels

CTE values for common alloy steels
Material	Temperature Range	α (×10⁻⁶/°C)	α (×10⁻⁶/°F)
AISI 4140 (oil hardened, tempered)	0–100°C / 32–212°F	12.3	6.8
AISI 4340 (tempered at 600°C)	20–100°C / 68–212°F	12.3	6.8

Stainless Steels

CTE for austenitic, ferritic, and martensitic stainless steels
Material	Temperature Range	α (×10⁻⁶/°C)	α (×10⁻⁶/°F)
304 (annealed)	0–100°C / 32–212°F	17.2	9.6
316 (annealed)	0–100°C / 32–212°F	15.9	8.8
405	0–100°C / 32–212°F	10.8	6.0
440C	0–100°C / 32–212°F	10.1	5.6
PH 15-7 Mo (annealed)	21–93°C / 70–200°F	14.4	8.0
17-4 PH (annealed)	20°C / 68°F	10.8	6.0
17-7 PH (annealed)	21–93°C / 70–200°F	15.3	8.5

Tool Steels

CTE values for tool steels at room temperature
Material	Temperature Range	α (×10⁻⁶/°C)	α (×10⁻⁶/°F)
D2 (annealed)	20–100°C / 68–212°F	10.5	5.8
T1	20–200°C / 68–390°F	9.7	5.4
M2	20–100°C / 68–212°F	10.1	5.6
W1	20–100°C / 68–212°F	10.4	5.8
O6 (annealed)	25–450°C / 77–842°F	13.6	7.6

Why thermal expansion differs between steel grades

The thermal expansion coefficient of steel varies mainly with crystal structure and alloying elements. Austenitic stainless steels (such as 304 and 316) have a face-centered cubic (FCC) structure and therefore expand more, typically 16–17 × 10⁻⁶/°C.

Ferritic and martensitic steels have a body-centered cubic (BCC) structure, resulting in lower expansion values, usually 10–12 × 10⁻⁶/°C. This difference is important when designing assemblies that combine carbon steel with stainless or aluminum components.

Reference

Cverna, F. (2002). ASM Ready Reference: Thermal Properties of Metals. ASM International, Materials Park, Ohio.