Invar 36
INVAR 36 is a nickel-iron, low expansion alloy containing 36% nickel. It maintains nearly constant Dimensions Over the range of normal atmospheric temperatures, and has a low coefficient of expansion from cryogenic temperatures to about 500° F. The alloy also retains good strength and toughness at cryogenic temperatures.
INVAR 36 can be hot and cold formed and machined using processes similar to austenitic stainless steels. INVAR 36 is weldable using Filler Metal CF36 which is available in bare wire for both the GTAW and GMAW process.
Chemical composition
| composition | % | Fe | Ni | Mn | C | P | S | Si |
|---|---|---|---|---|---|---|---|---|
| content | min | Bal | 35.0 | 0.2 | - | - | - | - |
| content | max | Bal | 37.0 | 0.6 | 0.05 | 0.02 | 0.02 | 0.3 |
Physical properties
| Property Name | Value |
|---|---|
| Density (g/cm3) | 8.1 |
| Electrical resistivity at 20ºC(mm2/m) | 0.78 |
| Temperature factor of resistivity(20ºC~200ºC)X10-6/ºC | 3.7~3.9 |
| Thermal conductivity, λ/ W/(m*ºC) | 11 |
| Curie point Tc/ ºC | 230 |
| Elastic Modulus, E/ Gpa | 144 |
| Melting point ºC | 1430 |
INVAR (Invar), also known generically as FeNi36 (64FeNi in the US), is a nickel-iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α).
The name Invar comes from the word invariable, referring to its relative lack of expansion or contraction with temperature changes.
It was invented in 1896 by Swiss physicist Charles Édouard Guillaume. He received the Nobel Prize in Physics in 1920 for this discovery, which enabled improvements in scientific instruments.
Invar 36 is used where high dimensional stability is required, such as precision instruments, clocks, seismic creep gauges, television shadow-mask frames, valves in motors, and antimagnetic watches. In land surveying, when first-order (high-precision) elevation leveling is to be performed, the Level staff (leveling rod) used is made of Invar, instead of wood, fiberglass, or other metals. Invar struts were used in some pistons to limit their thermal expansion inside their cylinders.
Coefficient of expansion
| θ/ºC | α1/10-6ºC-1 | θ/ºC | α1/10-6ºC-1 |
|---|---|---|---|
| 20~-60 | 1.8 | 20~250 | 3.6 |
| 20~-40 | 1.8 | 20~300 | 5.2 |
| 20~-20 | 1.6 | 20~350 | 6.5 |
| 20~-0 | 1.6 | 20~400 | 7.8 |
| 20~50 | 1.1 | 20~450 | 8.9 |
| 20~100 | 1.4 | 20~500 | 9.7 |
| 20~150 | 1.9 | 20~550 | 10.4 |
| 20~200 | 2.5 | 20~600 | 11.0 |
Typical Mechanical properties
| Tensile Strength | Elongation |
|---|---|
| Mpa | % |
| 641 | 14 |
| 689 | 9 |
| 731 | 8 |
Temperature factor of resistivity
| Temperature range, ºC | 20~50 | 20~100 | 20~200 | 20~300 | 20~400 |
|---|---|---|---|---|---|
| aR/ 103 *ºC | 1.8 | 1.7 | 1.4 | 1.2 | 1.0 |
The heat treatment process
| Annealing for stress relief | Annealing | The stabilization process | Precautions |
|---|---|---|---|
| Heated to 530~550ºC and hold 1~2 h. Cold down | In order to eliminate hardening, which be bring out in cold-rolled, cold drawing process. Annealing needs heated to 830~880ºC in vacuum,hold 30 min. | In protective media and heated to 830 ºC, hold 20min. ~ 1h, quench Due to the stress generated by quenching, heated to 315ºC,hold 1~4h. | Can not be hardened by heat treatment. Surface treatment can be sandblasting, polishing or pickling. Alloy can be used 25% hydrochloric acid pickling solution at 70 ºC to clear oxidized surface. |
Style of supply
| Alloys Name | Type | Dimension |
|---|---|---|
| INVAR 36 | Wire | D= 0.05~8mm |
INVAR 36 | Strip | W= 3~300mm, T= 0.1mm INVAR 36 | Foil | W= 10~100mm, T= 0.01~0.1 INVAR 36 | Bar | Dia= 8~100mm, L= 50~1000