Invar® – Commonly known as Invar® 36

Technical Data

Nominal Chemical Composition: 36 % Nickel, Balance Iron

Expansion: (cm/cm/°C x 10-6)
25° C to 100° C1.18
25° C to 200° C1.72
25° C to 300° C4.92
25° C to 350° C6.60
25° C to 400° C7.82
25° C to 450° C8.82
25° C to 500° C9.72
25° C to 600° C11.35
25° C to 700° C12.70
25° C to 800° C13.45
25° C to 900° C13.85
Physical Properties:
Density291 lbs / ln
Specific Gravity8.05
Curle Temp.535°F / 279°C
Melting Point2600°F / 1427°C
Heat of Fusion.515 kj / kg / k
Thermal Conductivity2.6 BTU / IN / ft / hour / °F
Electrical Resistivity820 microohm / mm495 ohms / clr.mil ft
Temperature coefficient of Resistance.001 per degree20° to 100° C

.0006 per degree70°C to 212°F
Specific Heat.123 BTU/lb °F
Mechanical Properties
Hardness70 HRB
Yield30,000 PSI
Modulus of Elasticity20.5 x 10°
Tensile65,000 PSI
Elongation35% in 2″
Glass Matches
Corning7052 or 7050, 7055, 7056, 7062 & others
KimbleEN-1 (Owens-Corning) K650, K704
Physical Properties
Density.302 lb / in
Specific Gravity8.36
Curie Temp815°F / 435°C
Melting Point2640°F / 1450°C
Specific Heat.105 cal / gm / degree °C @ 0°C.155 @ 430°C
Heat of Fusion64 cal / gram
Thermal Conductivity120 BTU-IN / ft / hour / °F @77°F17l3 w/meter xk
Electrical Resistivity294 ohm / clr.mil ft490 microohm / mm
Mechanical Properties
Shear Module7.5 x 10
Modulus of Elasticity20 x 10
Ultimate Strength75, 000 psi
Yield Strength50,000 psi
Kink Point806°F / 430°C
Polsson’s Ratio317
Elongation30%
Velocity of Sound16,300 ft/sec

Working and Forming

Invar® may be worked using any conventional 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 operation 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
1. Rough Machine
2. 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
4. Heat Parts for one hour at 600″F +- 20°F followed by air cooling
5. Heat parts for 48 hours at 205°F followed by air cooling
6. Finish Machine.

Annealing Method 3 – Annealing plus water quench and stabilization method
1. Rough Machine
2. Heat parts to 1525°F +- 25°F and hold at temperature one-half hour per inch of thickness, then water quench
3. Semi finish machine
4. Heat Parts for one hour at 600″F +- 20°F followed by air cooling
5. Heat parts for 48 hours at 205°F followed by air cooling
6. 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®.

Heat Treatment – Because of its affect on the actual structure of the material, there is a distinction made between heat treating the material to facilitate fabrication and heat treating the material to insure optimum conditions for glass sealing, plating, or brazing.

Stress Relief Annealing – To relieve stress and work hardening of parts at intermediate stages o fabrication. It is intended particularly for drawing, forming and spinning operations.
1. Wash and degrease parts
2. Anneal in atmosphere controlled furnace. Atmosphere may be wet or dry hydrogen, dissociated ammonia, cracked gas or similar neutral atmosphere.
3. Annealing temperature is not critical; however, high temperatures (greater than 900°C) or extended time periods (longer than 60 minutes) should be avoided because such treatments promote grain growth.
Typical cycle – 850°C for 30 minutes.
4. Parts should be held at temperature for the indicated time and then furnace cooled to less than 175°C to avoid oxidation and/or thermal shock (which may cause distortion)

Heat Treatment for Oxidation
1. Make sure that proper methods are used to clean, degrease and bright dip parts
2. Oxidation – Heat treat in an electric air furnace to 850°C to 900°C until parts are cherry red (dull red heat). The length of heat cycle is approximately 3 minutes, but due to differences n humidity and furnaces, the proper cycle has to be varied. Then reduce heat approximately 10°C per minute. When parts are cooled, oxide will be formed. The oxide may appear from light gray to black in color. Black is normally considered to be over-oxidation and is not necessarily desirable for a good glass to metal seal

Alloy 48: (Nominal Data Sheet)
Nickel (Ni)48.0
Chromium (Cr)0.10
Manganese (Mn)0.80
Silicon (Si)0.30
Carbon (C)0.05
Aluminum (Al)0.10
Magnesium (Mg)0.50
Zirconium (Zr)0.00
Titanium (Ti)0.00
Phosphorus (P)0.025
Sulfur (S)0.025
IronBalance
Typical Linear Coefficient of Thermal Expansion ( cm per cm. c x 10 -6 )
30 to 1009.4
30 to 2009.4
30 to 3008.8
30 to 3509.0
30 to 4008.7
30 to 4258.9
30 to 4509.0
30 to 5009.4
30 to 550 & 30 to 60010.4
30 to 70011.3
30 to 80012.1
30 to 90013.0
30 to 100013.9

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Invar® & Super Invar® are registered trademarks of CRS Holding, a subsidiary of Carpenter Technologies – Contact Eagle Alloys, your premier Invar® 36 suppliers, today!