Type Analysis | Description | Applications | Physical Properties
Heat Treatment | Workability | Applicable Specifications

Type Analysis

Description

Invar 36 is a 36% nickel-iron alloy possessing a rate of thermal expansion approximately one-tenth that of carbon steel at temperatures up to 400°F(204°C)

Applications

This alloy has been used for applications where dimensional changes due to temperature variation must be minimized such as in radio and electronic devices, aircraft controls, optical and laser system, etc.
Invar 36 alloy has also been used in conjunction with high expansion alloys in applications where a motion is desired when the temperature changes, such as in bimetallic thermostats and in rod and tube assemblies for temperature regulators.

Physical Properties

Mean coefficient of thermal expansion

Curie temperature
  °F ............................................................................................. 535
  °C ............................................................................................. 279
Melt point
  °F ........................................................................................... 2600
  °C ........................................................................................... 1427
Specific Heat
  Btu/lb þ°F ............................................................................. 0.123
  kJ/kg þK ................................................................................ 0.515
Modulus of elasticity
               Cold Rolled Strip    Annealed Bar and Strip
psi x 10(6)........... 21.5........................... 20.5
MPa x 10(3) ....... 148 .......................... 141

Heat Treatment<

Proper heat treatment is critical to ensure that Invar 36 remains in a low internal stress condition both throughout fabrication and during the service life of the tool.
Recommended heat treatment parameters are shown in table below

Note:

A. For plate thickness over 1.00", modify the heat treatment time at temperature.
Add one hour per additional inch of thickness. Example: 5 hrs at 600°F require to stress relieve anneal 4.00"
thick plate.

B. Invar 36 will develop oxidation scale that increases as both heat treatment time and temperature increase. For applications where sand blasting is not an available process, a controlled atmospheric heat treatment oven will be required.

C. Invar 36 must be free of surface contaminants and cleaned before heat treatment.

D. Thermally inducted tool distortion can be minimized by controlling heat up and cool down during full anneal heat treatment. During heat up, first stabilize the tool at 500°F and then increase by 50°F per hour to full anneal temperature. During cool down, decrease the temperature by 50°F per hour until temperature of the tool is below 600°F. For tools exceeding 8 feet in length, weights may be added to the ends and/or center of the tool as required to further assist in maintaining contour.

Workability

Forging
The principal precaution to observe in forging is to heat quickly and avoid soaking in the furnace. Long soaking may result in a checked surface due to absorption of sulfur from the furnace atmosphere and/or oxide penetration. A forging temperature of 2000/2150°F is preferred.

Coolant
It is important to control heat build up, the major cause of warpage. A suggested coolant would be Cool Tool. Cool Tool contains fatty esters to reduce friction in the cutting zone and a refrigerant to remove the heat generated by friction between the cutting tool and work place.

Tooling
T-15 Alloy, such as Vasco Supreme-manufactured by Vanadium Alloys Company. M-3 Type 2, such as Van Cut Type 2-manufactured by Vanadium Alloys Company. Congo manufactured by Braeburn.
For machining with carbide tools, a K-6 manufactured by Kennemetal, Firthie HA manufactured by Firth Sterling, or #370 Carboloy could be used, or a K2S manufactured by Kennemetal, or Firthie T-04 manufactured by Firth Sterling would be satisfactory. One thing of prime importance is that all feathered or wire edges should be removed from the tools. They should be kept in excellent condition by repeated inspection.

Turning
If steel cutting tools are used, try a feed of approximately .010" to .012" per revolution and a speed as high as 35/FPM could probably be attained. Some of the angels on the cutting tools would be as follows:

• End cutting edge angle -Approximately 7°

• Nose radius -Approximately .005"

• Side cutting edge angle -Approximately 15°

• Back rake -Approximately 8°

• Side rake -Approximately 8°

When cutting off high speed tools are better than carbide tools, and a feed of approximately .001" per revolution should be used. The cutting tools should have a front clearance of about 7° and a fairly big tip--larger than 25° would be helpful.

Welding
Invar 36 can be welded by the convetional methods. Caution must be taken so as not to overheat the molten metal. This will avoid spattering of the molten metal and pits in the welded area. When filler rod is required , Invarod has been used.

Drilling
When drilling a 3/16" diameter hole, a speed of about 40/FPM could possibly be used, and the feed should be about .002" to .0025" per revolution, for a 1/2" hole, approximately the same speed could be used with a feed of about .004" to .005" per revolution. The drills should be as short as possible, and it is desirable to make a thin web at the point by conventional methods. By conventional methods, we mean do not notch or make a crank shaft grinding. It is suggested that heavy web type drills with nitrided or electrolyzed surfaces be used. The hole, of course, should be cleaned frequently in order to remove the chips, which will gall, and also for cooling. The drill should be ground to an included point angle of 118° to 120°

Reaming
Reaming speeds should be haft the drill speed, but the feed should be about three times the drill speed. It is suggested that the margin on the land should be about .005" to .010", and that the chamfer should be .005" to .010" and the chamfer angle about 30°. The tools should be as short as possible, and have a slight face rake of about 5° to 8°.

Tapping
In tapping, a tap drill slightly larger than the standard drill recommended for conventional threads should be used, because the metal will probably flow into the cut. It is suggested that on automatic machines, a two or three fluted tapping tool should be used. For taps below 3/16", the two fluted would be best. Grind the face hook angle to 8° to 10°, and the tap should have a .003" to .005" chamfered edge. If possible, if binding occurs in the hole in tapping, the width of the land may be too great, and it is suggested that the width of the heel be ground down. Again, it is suggested that nitrided or electrolyzed tools be used. Speed should be about 20/FPM.

• *When using carbide tools, surface speed feet/minute (SFM) can be increased between 2 and 3 times over the high speed suggestions. Feeds can be increased between 50 and 100%.

• Note: Figures used for all metal removal operations covered are average. On certain work, the nature of the part may require adjustment of speeds and feeds. Each job has to be developed for best production results with optimum tool life. Speeds or feeds should be increased or decreased in small steps.

• The information and data presented herein are typical or average values and are not a guarantee of maximum or minimum values. Applications specifically suggested for material described herein are made solely for the purpose of illustration to enable the reader to make his own evaluation and are not intended as warranties, either express or implied, of fitness for these or other purposes.

Applicable Specifications

Invar 36 alloy meets the requirement of specification Boeing D-33028.

Invar 36 - Current Inventory Stock