INCONEL 718: Nickel-Chromium-Molybdenum Superalloy

Inconel 718 is a nickel-chromium-molybdenum alloy that has been built to resist many severely corrosive environments, pitting and crevice corrosion. This alloy shows significantly high tensile, yield and creep-rupture characteristics at high temperatures. This nickel alloy is employed from cryogenic temperatures as much as long-term service at 1200° F.

A unique feature of Inconel 718’s composition is the fact that nobium is put into allow age hardening that allows welding and annealing without spontaneous hardening during cooling and heating. Adding nobium acts with molybdenum to stiffen the alloy’s matrix and offer high strength with out a strengthening heat treatment.

Other famous nickel-chromium alloys are age hardened with the addition of titanium and aluminium. This nickel steel alloy is fabricated readily and may even be welded either in the precipitation or annealed age-hardened condition. This super alloy is utilized in a selection of industries including chemical processing, aerospace, pollution-control equipment, marine engineering and nuclear reactors.

Chemical Composition, %

The chemical composition of Inconel 718 is:

Ni	Fe	Cr	Cu	Mo	Nb	C	Mn	P	S	Si	Ti	Al	Co	B
50.00-55.00	Remainder	17.00-21.00	.30 max	2.80-3.30	4.75-5.50	.08 max	.35 max	.015 max	.015 max	.35 max	.65-1.15	.20-.80	1.00 max	.006 max

Forms of Inconel 718

Inconel is available as sheet, plate, wire and bar.

Properties

The properties of Inconel 718 are:

• Excellent mechanical properties – tensile, fatigue and creep-rupture.
• Yield tensile strength, creep, and rupture strength properties are considerably high.
• Highly resistant to chloride and sulfide stress corrosion cracking.
• Resistant to aqueous corrosion and chloride ion stress corrosion cracking.
• High temperature resistant.
• Age-hardenable with a unique property of slow aging response that permits heating and cooling during annealing without the danger of cracking.
• Excellent welding characteristics, resistant to post-weld age cracking.

Mechanical Properties (Typical room temperature properties, 1800°F annealed condition)

The mechanical properties of Inconel 718 are:

Ultimate Tensile Strength, psi	0.2% Yield Strength psi	Elongation %	Hardness Rockwell B
135,000	70,000	45	100

ASTM Specifications

The ASTM specifications of Inconel 718 are:

Sheet/Plate	Bar	Wire
B670	B637	-

Applications of Inconel 718

The applications of Inconel 718 are:

• Pollution-control equipment
• Nuclear reactors
• Inconel 718 properties flanges
  
• Valves, fasteners, springs, pipes, tubing hangers
• Chemical processing
• Aerospace
• Fittings
• Liquid fuel rocket motor components
• Well head completion equipment and blow out preventers (BOP’s)
• Gas turbine engine parts.

This information has been sourced, reviewed and adapted from materials provided by yaang.com .

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