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 folowing 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.
Coefficient of Thermal Expansion
29% Nickel 17% Cobolt 53% Iron
Coefficient of Thermal Expansion
| 30°-200°C |
5.5 |
30°-600°C |
7.9 |
| 30°-300°C |
5.1 |
30°-700°C |
9.3 |
| 30°-400°C |
4.9 |
30°-800°C |
10.4 |
| 30°-450°C |
5.3 |
30°-900°C |
11.5 |
| 30°-500°C |
6.2 |
|
|
Glass Matches
| Corning |
7052 or 7050, 7055, 7056, 7062 & others |
| Kimble |
EN-1 (Owens-Corning) K650, K704 |
Physical Properties
| Density |
.302 lb/in |
| Specific Gravity |
8.36 |
| Curie Temp |
815°F/435°C |
| Melting Point |
2640°F/1450°C |
| Specific Heat |
.105 cal/gm/degree °C @ 0°C
.155 @ 430°C |
| Heat of Fusion |
64 cal/gram |
| Thermal Conductivity |
120 BTU-IN/ft/hour/°F @77°F
17l3 w/meter xk |
| Electrical Resistivity |
294 ohm/clr.mil ft
490 microohm/mm |
Mechanical Properties
| Shear Module |
7.5 x 10 |
| Modulus of Elasticity |
20 x 10 |
| Ultimate Strength |
75, 000 psi |
| Yield Strength |
50,000 psi |
| Kink Point |
806°F/430°C |
| Polsson's Ratio |
317 |
| Elongation |
30% |
| Velocity of Sound |
16,300 ft/sec |
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
Typical Nominal Chemistry
| 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 |
| Iron |
Balance |
Typical Linear Coefficient of Thermal Expansion ( cm per cm. c x 10 -6 )
| 30 to 100 |
9.4 |
| 30 to 200 |
9.4 |
| 30 to 300 |
8.8 |
| 30 to 350 |
9.0 |
| 30 to 400 |
8.7 |
| 30 to 425 |
8.9 |
| 30 to 450 |
9.0 |
| 30 to 500 |
9.4 |
| 30 to 550 |
10.2 |
| 30 to 600 |
10.4 |
| 30 to 700 |
11.3 |
| 30 to 800 |
12.1 |
| 30 to 900 |
13.0 |
| 30 to 1000 |
13.9 | |
