INVAR
commonly known as INVAR 36
FORMS -------------- SIZES ------------------ CONDITIONS
| Per Mil-I-23011C
Class 7 |
| FORMS |
STANDARD GAUGES |
WIDTH & LENGTH |
CONDITIONS |
| Coil/Strip |
.001"-.040" |
Up to 3" Coil |
Annealed |
| Chem Mill |
.005" |
16" x Coil |
1/2 Hard |
| Sheet |
.015" - .125" |
12"/27" x 72" |
Annealed |
| Plate |
.125"-1.500" |
15"/30" x 72" |
Annealed |
| Rod |
.062"-4.00" |
72"-144" R/L |
As Drawn |
| Per Mil-S-16598
(Free Machining) |
| FORMS |
STANDARD GAUGES |
WIDTH & LENGTH |
CONDITIONS |
| Bar/Rod |
.1875"-4.00 dia. |
144" R/L |
As Drawn |
APPLICABLE SPECIFICATIONS
- Mil-I-23011C Class 7
- Mil-S-16598 Chemistry only
- ASTM F-1684 (96)
NOMINAL CHEMICAL COMPOSITION:
- 36% Nickel, Balance Iron.
EXPANSION:
(Typical for material to Mil-I-23011C Class 7):
cm/cm/°C x 10^-6
25°C to 100°C 1.18
25°C to 200°C 1.72
25°C to 300°C 4.92
25°C to 350°C 6.60
25°C to 400°C 7.82
25°C to 450°C 8.82
25°C to 500°C 9.72
25°C to 600°C 11.35
25°C to 700°C 12.70
25°C to 800°C 13.45
25°C to 900°C 13.85
PHYSICAL PROPERTIES:
- Density
- .291 lbs/in³
- Specific Gravity
- 8.05
- Curie Temperature
- 535°F/279°C
- Melting Point
- 2600°F/1427°C
- Heat of Fusion
- .515 kJ/kg/K
- Thermal Conductivity
- 72.6 BTU-in/ft²/hour/°F
- Electrical Resistivity
- 495 ohms/cir. mil ft
- 820 micro ohm/mm
- Temperature Coefficient of Resistance
- .001 per degree
- 20°C to 100°C
- .0006 per degree
- 70°F to 212°F
- Specific Heat
- .123 BTU/lb-°F
MECHANICAL PROPERTIES:
(typically annealed material):
- Hardness
- 70 HRB
- Tensile
- 65,000 psi
- Yield
- 40,000 psi
- Elongation
- 35% in 20
- Modulus of Elasticity
- 20.5 x 10-6;
WORKING AND FORMING
Invar may be worked using any conventional metal working method. Annealed
material, that is material with an RB hardness of less than Rockwell B 70,
is desirable for material involving deep drawing, hydro-forming, or spinning.
For blanking, material between 1/4 and 3/4 hard will usually present a cleaner
cut. Invar may be chemically etched. For operations where there is a large
quantity of machining, Free Cutting Invar is available in round rod.
Heat Treatment for Invar
Invar can be heat treated using one of the following methods. Heating and
cooling rates shall be controlled to prevent damage to the parts (cracking,
warpage, etc.).
Annealing Method 1
Heat parts to 1525°F ±25°F and hold at temperature one-half
hour per inch of thickness, then furnace cool at a rate not to exceed 200°F
per hour to 600°F. No additional machining should be performed on these
parts.
Annealing Method 2 - Annealing plus stabilization
- Rough machine.
- Heat parts to 1525°F ±25°F and hold at temperature
one-half hour per inch of thickness, then furnace cool at a rate not to
exceed 200°F per hour to 600°F. Still air cool is acceptable below
600°F.
- Semi finish machine.
- Heat parts for one hour at 600°F ±20°F followed by
air cooling.
- Heat parts for 48 hours at 205°F followed by air cooling.
- Finish machine.
Annealing Method 3 - Annealing plus water quench and stabilization method.
- Rough machine.
- Heat parts at 1525°F ±25°F and hold at temperature
for one-half hour per inch of thickness, then water quench.
- Semi finish machine.
- Heat parts for one hour at 600°F ±20°F followed by
air cooling.
- Heat parts for 48 hours at 205°F followed by air cooling.
- Finish machine.
WELDING
Conventional welding methods can be used with Invar. Invar filler rod is
recommended for those welds requiring filler rod.
BRAZING
First anneal the material as above. Avoid over stressing joints during brazing.
Use silver and zinc free brazes for brazing Invar.
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