UNS N07718 (Alloy 718) is often seen as the workhorse of the nickel-chromium alloy range, with many applications in Aerospace, General Engineering and the Oil & Gas industry. The grade is one of a type that is precipitation-hardenable, and which, with its addition of niobium, molybdenum, aluminium and titanium, provides a metal that is relatively high strength, and has excellent creep-stress rupture strength and good corrosion resistance. It is easy to weld and durable at high temperatures, although has a spread of operating temperatures of between -200°C and +550°C.

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Alloy 718 is well suited for use in fasteners, pump and valves, turbine parts, motor components, springs, cryogenic tanks, and down-hole applications and tools. However, as with most grades, there are different variations rather than just one “Alloy 718”.

This article is one of a series that will explain each variant and pin-point differences:

This first article detailed the “Oil & Gas” API 6A CRA properties. The second article contrasted AMS5662 with API 6A CRA 718 properties. This third will address AMS5663 properties, and finally the fourth will discuss the general engineering ASTM B637 standard requirements.

I will compare and contrast API 6A 718 and AMS 5662 and AMS 5663 below. However, be aware that many end users of Alloy 718 may write their own specifications, usually extending certain requirements of the standards detailed below, and such specifications must always be checked to ensure material conforms with the requirements.

Our AMS5663 stock range is between 22 mm and 177 mm in diameter.

Alloy 718 To AMS5663

For bars, forgings, flash welded rings up to 10” (254 m) in least cross=sectional dimension and stock for any size for forging or flash welded ring. Typically used for parts requiring high resistance to creep and stress rupture up to 704o C and oxidation resistance up to 902o C. I will compare AMS5662 and AMS5663 together as parts are typically formed or machined from material meeting AMS5662, then precipitation heat treated to develop their required properties of AMS5663. AMS5662 material therefore comes with “capability” test results, where the test piece has been aged at the required times and temperatures, then tested to show what results would be achieved as AMS5663 with that ageing treatment.

Standard properties:

Alloy 718 to AMS 5662/5663Alloy 718 to API 6A CRA
Material Designation:
While AMS5662 has a 120K designation (Yield strength 120 ksi minimum), AMS5663 does not include a material designation.
C-0.080 - 0.045 max
P-0.0150 – 0.010 max
S-0.0150 – 0.010 max
Nb4.755.50Reported with Ta
Range: 4.87 – 5.20
Ti0.651.150.80 – 1.15
Al0.200.800.40 – 0.60
Cu-0.300 – 0.23
Pb-0.00050 – 0.0010
Bi-0.000030 – 0.00005
SeNot required0 – 0.0005
CaNot requiredReported if intentionally added.
Range 0 – 0.0030
MgNot requiredReported if intentionally added.
Range 0 – 0.0060
Melt Practice:
Multiple melted using consumable electrode practice in the remelt cycle or shall be induction melted under vacuum.Dual melted – usually VIM (Vacuum Induction Melted) & VAR (Vacuum Arc Remelted) or ESR (ElectroSlag Remelted).
Forge & Hot Working Ratio:
Not formally requiredGreater than 4.0:1
Heat Treatment
Equipment control:
Equipment and controls used are to be qualified as per API 6A or to a similar standard such as AMS 2750.Same
Temperature Monitoring:
Temperatures are only monitored by either a contact surface thermocouple or heat sink. Heat treatment monitoring charts are provided.Same
Heat Treatment:
Solution Anneal - 941o C to 1010o C for time commensurate with cross-sectional thickness and cool in air or faster (liquid).Solution Anneal - 1021o C to 1052o C for 1 hour to 2.5 hours and usually cool in liquid
AMS5662 Age Hardening only required for capability tests. AMS5663 – Precipitation Heat Treatment:
718o C to 760o C, hold at temp (+/-8o C) for 8 hours,
cool at 48o C to 64o C per hour to 621o C to 649o C,
hold at temp (+/-8o C) for 8 hours and air cool.
Alternatively, instead of the cooling at 48o C to 64o C per hour, the material may be furnace cooled providing the time at 621o C to 649o C is for a total precipitation heat treatment of time of 18 hours.
Age Hardening - 774o C to 802o C for 6 hours to 8 hours and air cool.
Material Testing Requirements:
Macroetch examination:
Not formally requiredOn full transverse cross-sectional slices representative of the top and bottom of the final remelt ingot or product thereof, and the acceptance criteria is no worse than severity A on all 4 classes of ASTM A604.
Microstructural Analysis
Grain size:
Bars under 9 in2 in cross-sectional area – ASTM 5 or finer (up to 20% may be ASTM 3-5)
Bars 9 in2 to 78 in2 cross-sectional area – ASTM 4 or finer (up to 20% may be ASTM 2-4)
ASTM 2 or finer
No topological duplex grain size allowed
Deleterious phases:

Free from laves phases
Deleterious phases (at 100x and 500x magnification) (free from acicular phases except for individual and isolated grains, free from continuous networks of secondary phases along grain boundaries, and no laves phases).
Tensile Properties:
AMS5663 Tensile Properties
RoomRoomAt 649o CAt 649o CAt 649o CAt 649o C
≤254 mm
≤127 mm
127-254 mm
≤127 mm
127-254 mm
≤127 mm
127-254 mm
Tensile ksi>185>180>180>145>145>140>140
0.2% Yield Strength ksi>150>150>145>125>122>125
Elongation in 4D %>12>6
Reduction of Area %
*transverse tensile properties only apply where test specimen of not less than 2.5” (63 m) can be taken
API 6A CRA Tensile Properties
Size≤ 3” (76 mm) Ø3” (76 mm) -10” (254 mm) Ø> 10” (254 mm) Ø
Tensile ksi
0.2% Yield Strength ksi
120 – 145120 – 145120 – 145
Elongation in 4D %
Reduction of Area %
Stress Rupture:
≤254 mm
Not Required
TemperatureAt 649o C
Load100 ksi
689 MPa
Time to Rupture
>23 hours
Elongation in 4D

Impact Toughness:
Not formally requiredSee 718 API 6A CRA paper
Hardness Test Requirements:
<277 HB
<21 HRC
<331 HB
<36 HRC
32 – 40 HRC
Non-destructive Examination:
AMS5662 / AMS5663
Not formally required100% ultrasonic tests shall be carried out in accordance with API 6A PSL 3 or PSL 4 (with Operator qualified to minimum SNT level 2.)

The next paper in the series will consider ASTM B637 alongside AMS5663 properties.

Please contact Broder Metals Group Limited, either through the webform section of the website or by any of the other contact methods list on the website if you have any questions.

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