Invar 36 Vs Invar 42: A Comparison Of Properties And Applications Of Two Low-Expansion Alloys

Sep 04, 2026

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As aerospace, precision instrumentation, electronic packaging, and advanced manufacturing technologies continue to advance, the dimensional stability of materials under temperature fluctuations has become a critical factor affecting product precision and reliability. Invar 36 and Invar 42 are both typical iron-nickel low-expansion alloys; however, they differ in nickel content and thermal expansion characteristics, leading to distinct roles in practical applications.

What is the difference between Invar 36 and Invar 42?

Invar 36 focuses more on "its own dimensional stability", while Invar 42 focuses more on "expansion matching with other materials".

Invar 36 typically contains about 36% nickel and is a classic ultra-low-expansion alloy; its primary advantage is an extremely low coefficient of thermal expansion. Because the material maintains excellent dimensional stability in environments with significant temperature fluctuations, it is predominantly used for structural components and precision equipment that require strict control over thermal deformation.

Invar 42 has a nickel content of approximately 42%; while its coefficient of thermal expansion is higher than that of Invar 36, it aligns more closely with the thermal expansion characteristics of glass, ceramics, and certain electronic packaging materials. Consequently, the advantage of Invar 42 lies not merely in "low expansion," but in its ability to minimize thermal stress between dissimilar materials through matched thermal expansion.

LNG storage and transportation equipment

Chemical composition

Element	Invar 36	Invar 42
Ni	35.0 - 37.0%	41.5 - 42.5%
Fe	rest	rest
C	max 0.05%	max 0.05%
Mn	0.20 - 0.60%	max 0.80%
Si	max 0.30%	max 0.30%
P	max 0.02%	max 0.02%
S	max 0.02%	max 0.02%
Co	max 0.50%	max 1.0%

The primary difference between the two materials lies in their nickel content. As the nickel content increases from approximately 36% to about 42%, the thermal expansion behavior of the alloy changes; consequently, although both Invar 36 and Invar 42 are classified as low-expansion alloys, their design objectives differ.

Physical and Mechanical Properties (Typical Values)

1. Physical properties

	Invar 36	Invar 42
Density	8.1 g/cm³	8.12 g/cm³
Curie temperature	230°C (low-expansion characteristics are lost above this temperature)	360°C (low-expansion characteristics are lost above this temperature)
Young's modulus	145 GPa	145 GPa

2. Coefficient of thermal expansion

	Invar 36	Invar 42
20–100°C range	≤ 1.2 × 10⁻⁶ /K	4.2–4.8 × 10⁻⁶ /°C
-250°C to +200°C range	Maintains an extremely low coefficient of expansion	4.8–5.4 × 10⁻⁶ /°C

3. Mechanical properties(Room-temperature annealed state)

	Invar 36	Invar 42
Tensile strength	450–490 MPa	450–550 MPa
Yield strength (0.2%)	240–274 MPa	180–250 MPa
Elongation	≥ 30–42%	≥ 30%

Why do differences in nickel content lead to variations in performance?

The low-expansion characteristics of Invar-series alloys are linked to the unique microstructure and magnetic properties of iron-nickel alloys. Their thermal expansion behavior is not simply determined by the rule that "lower nickel content results in lower expansion"; rather, it arises from the interplay of nickel content, crystal structure, and magnetic state.

Invar 36 falls within the compositional range where the "Invar effect" is most pronounced, enabling it to achieve exceptionally low thermal expansion. This characteristic makes it particularly suitable for precision structures where temperature fluctuations could otherwise lead to dimensional errors.

As the nickel content increases to approximately 42%, the alloy's thermal expansion behavior changes. While Invar 42 still exhibits low-expansion properties, its primary value lies in matching the thermal expansion of other low-expansion materials, rather than in simply achieving the lowest possible coefficient of thermal expansion.

application

Invar 36

Suitable for high-precision dimensional control

Precision measuring instruments
Optical equipment
Aerospace structural components
Precision mechanical assemblies
High-precision tooling
Composite manufacturing molds
Temperature-sensitive structural components

Invar 42

Suitable for glass and ceramic packaging.

Electronic packaging
Glass-to-metal seal
electron tube
ceramic package
Electrical components
Precision electronic components
Some aerospace electronic equipment

Which is better, Invar 36 or Invar 42?

In reality, there is no simple hierarchy of superiority or inferiority between the two materials.

If the design requirement is for the material itself to undergo minimal dimensional change, Invar 36 is generally the more suitable choice.

If the design requirement calls for thermal expansion behavior closely matching that of materials such as glass or ceramics, Invar 42 typically offers a distinct advantage.

Therefore, material selection should not be based solely on the coefficient of thermal expansion; instead, factors such as operating temperature, structural design, mating materials, and precision requirements must be considered to fully leverage the performance advantages of low-expansion alloys.

Lork Group Supply Capability

With fifteen years of expertise in specialty alloy supply chain management, Lork Group has incorporated Invar 36 and Invar 42 into its core product portfolio, offering a comprehensive range of forms including plates, bars, tubes, strips, wires, forgings, and rings. It supports custom-length cutting and small-batch orders.

Standards:

Invar 36: ASTM B753 / F1684, GB/T 15018, UNS K93600

Invar 42: ASTM F30, YB/T 5235, UNS K94100

In addition to the Invar alloy mentioned in the article, Lork offers more series of precision alloys; we welcome your inquiries and orders.