Invar 36 · UNS K93600 · W. Nr. 1.3912 · GB 4J36 · Ni36 · Fe-Ni36
Invar 36 / 4J36 (K93600): composition, properties, fittings and flanges
Invar 36 (UNS K93600, W. Nr. 1.3912, Chinese 4J36) is a 36 % nickel iron-nickel alloy famous for its near-zero coefficient of thermal expansion: typically about 1.2 x 10⁻⁶ per °C between 20 °C and 100 °C, roughly one tenth that of carbon steel. The low expansion arises from the magnetostrictive balance of the face-centred cubic…
- UNS
- K93600
- W. Nr.
- 1.3912
- Density
- 8.11 g/cm³ (0.293 lb/in³)
- Key strength
- 490 MPa / 71 ksi
Identification and standards
| Short form | Invar 36 · UNS K93600 · W. Nr. 1.3912 · GB 4J36 · Ni36 · Fe-Ni36 |
|---|---|
| Classification | Controlled low thermal expansion nickel-iron alloy |
| UNS | K93600 |
| Werkstoff number | 1.3912 |
| Material family | Precision Alloys |
Chemical composition
| Element | Composition (wt %) | Why it is there |
|---|---|---|
| Nickel (Ni) | 35.0 - 37.0 | Sets the Invar near-zero expansion composition |
| Iron (Fe) | Balance | Matrix |
| Manganese (Mn) | 0.60 max | - |
| Silicon (Si) | 0.40 max | - |
| Cobalt (Co) | 0.50 max | Slightly raises expansion if increased |
| Carbon (C) | 0.10 max | - |
| Phosphorus (P) | 0.020 max | - |
| Sulphur (S) | 0.020 max | - |
| Chromium (Cr) | 0.25 max | - |
| Copper (Cu) | 0.50 max | - |
Note Single figures are maximum limits unless shown as a range. Always confirm against the heat-specific EN 10204 3.1 certificate supplied with your order.
Mechanical properties
| Tensile strength, min (annealed) | 490 MPa / 71 ksi |
|---|---|
| 0.2 % yield strength, min | 240 MPa / 35 ksi |
| Elongation in 2 in, min | 30 % |
| Typical hardness, annealed | 130 - 180 HB |
| Curie temperature | About 230 °C |
| Modulus of elasticity | 141 GPa (20.5 x 10⁶ psi) |
Warning Values depend on product form, section thickness and heat treatment. Larger sections generally achieve lower strength than thin product; always design against the applicable code allowable stress rather than these figures.
Physical properties
| Density | 8.11 g/cm³ (0.293 lb/in³) |
|---|---|
| Melting range | 1425 - 1460 °C (2600 - 2660 °F) |
| Thermal conductivity at 20 °C | 10.5 W/m·K |
| Mean CTE, 20-100 °C | 1.2 x 10⁻⁶ /°C |
| Mean CTE, 20-300 °C | About 5.0 x 10⁻⁶ /°C |
| Electrical resistivity at 20 °C | 0.80 µΩ·m |
Specifications by product form
| Bar / rod | ASTM F1684, ASTM B753 where applicable |
|---|---|
| Plate / sheet / strip | ASTM F1684, GB/T 15018 where applicable |
| Seamless tube | Supplied to drawing or customer specification |
| Forgings | To drawing, EN 10204 3.1 certified |
| Welding consumables | Matching Invar filler or high-nickel filler depending on joint duty |
| UNS / EN / China | UNS K93600 · EN Ni36 · W. Nr. 1.3912 · GB 4J36 |
Product forms available
Hangbo supplies this grade in the following forms. Sizes outside the listed range can often be produced to order.
- Wire and rod for electronic components
- Forged blocks and rings for tooling
- Machined components to drawing
- Composite lay-up tooling and fixture plates
Typical applications
- LNG carrier membrane tanks, cryogenic piping supports and transfer line components
- Aerospace composite bonding and lay-up tooling where expansion must match carbon fibre
- Precision instruments, optical benches, lasers and metrology frames
- Electronic components, lead frames, shadow masks and resonator cavities
- Thermostat bimetal strip and temperature compensation devices
- Clock pendulums, seismic devices and scientific apparatus
Welding, forming and machining
- Heat treatment
- Anneal at 830-870 °C then air cool to stabilise dimensions, followed by a low temperature artificial age around 315 °C for 1 hour and slow cool. This stabilisation is essential for maximum dimensional stability.
- Welding
- Weld by GTAW with matching Invar filler metal and low heat input. Excessive heat input or dilution with high expansion alloys destroys the Invar effect locally.
- Machining
- Invar is gummy and work hardens; use sharp tools with positive rake, moderate speeds and generous cutting fluid to avoid surface tearing.
- Design limit
- Do not rely on the low expansion behaviour above about 230 °C, the Curie point, because the magnetic balance that causes the Invar effect no longer applies.
Buy Invar 36 / 4J36 from Hangbo
Material is supplied with full heat-number traceability, solution annealing or ageing performed under calibrated furnace control, and an EN 10204 3.1 certificate covering chemical analysis, mechanical properties, heat treatment records and the agreed NDT scope. Positive material identification and third party inspection and test reports from SGS are available for critical service.