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Super Alloy Inconel(r) Alloy 718

Related Metals:

Specifications:

Chemistry Data

Aluminum

0.2 - 0.8

Boron

0.006 max

Carbon

0.08 max

Chromium

17 - 21

Cobalt

1 max

Copper

0.3 max

Iron

Balance

Manganese

0.35 max

Molybdenum

2.8 - 3.3

Nickel

50 - 55

Niobium

4.75 - 5.5

Phosphorus

0.015 max

Silicon

0.35 max

Sulphur

0.015 max

Titanium

0.65 - 1.15

General Information

Principal Design Features

This is a high-strength, high-temperature resistant and corrosion resistant nickel-chromium alloy. It is suitable for use at cryogenic temperatures and also for use in air up to 1300 F. The alloy is readily worked and can be age-hardened.

Applications

Applications include gas turbine hot section components and cryogenic storage tanks.

Machinability

Conventional machining techniques used for iron based alloys may be used. This alloy does work-harden during machining and has higher strength and "gumminess" not typical of steels. Heavy duty machining equipment and tooling should be used to minimize c

Forming

This alloy has good ductility and may be readily formed by all conventional methods. Because the alloy is stronger than regular steel it requires more powerful equipment to accomplish forming. Heavy-duty lubricants should be used during cold forming. I

Corrosion Resistance

This alloy is resistant to corrosion from organic acids and also resists attack by many acids. It is especially resistant to chloride stress-corrosion cracking.

Welding

The commonly used welding methods work well with this alloy. Matching alloy filler metal should be used. If matching alloy is not available then the nearest alloy richer in the essential chemistry (Ni, Co, Cr, Mo) should be used. All weld beads should

Heat Treatment

The alloy is age-hardenable (see under "Aging") and can be annealed at 1900 F followed by air cooling.

Forging

Forging is done in the range of 2050 F to 1700 F. Final reductions of 20% for open die work and 10% for closed die are desired to maintain proper grain structure and finishing temperatures should be in the 1750 F - 1700 F range.

Hot Working

Hot working may be done in the temperature range of 2050 F to 1650 F. It is important to reheat the alloy if hot working temperatures fall below 1650 F.

Cold Working

Cold forming may be done using standard tooling although plain carbon tool steels are not recommended for forming as they tend to produce galling. Soft die materials (bronze, zinc alloys, etc.) minimize galling and produce good finishes, but die life is

Annealing

Annealing may be done at 1900 F followed by rapid air cooling.

Aging

Two slightly different aging heat treatments are available. 1. 1800 F anneal and age at 1325 F for 8 hours, then furnace cool to 1150 F and hold at that temperature for 10 hours, then air cool. This is the optimum treatment for the highest room temp

Hardening

Cold work will cause an increase in both hardness and strength. The alloy may also be age-hardened -- see "Heat Treat".

Other Mechanical Props

Impact strength values for Charpy V-Notch: At room temperatures: 20.5 ft. lbs. At minus 320 F: 19 ft. lbs.

Physical Data

Density (lb / cu. in.)

0.29

Specific Gravity

7.98

Specific Heat (Btu/lb/Deg F - [32-212 Deg F])

0.104

Electrical Resistivity (microhm-cm (at 68 Deg F))

753

Melting Point (Deg F)

2420

Poissons Ratio

0.284

Thermal Conductivity

77

Mean Coeff Thermal Expansion

7.3

Magnetic Permeability

1.001

Modulus of Elasticity Tension

29

Mechanical Data