Inconel 751 Alloy
General Characteristics of Inconel 751 Alloy
This is a high-strength nickel-base high-temperature alloy whose excellent properties may be obtained through age hardening. The alloy resists both chemical corrosion and oxidation, and has good creep strength under high stresses in the temperature range 1200/1500ºF (650/820ºC.) It has good rupture properties to 1600ºF (870ºC.)
| Chemical Analysis | |
|---|---|
| C | Carbon 0.08 max |
| Mn | Manganese 0.50 max |
| S | Sulfur 0.005 max |
| Si | Silicon 0.50 max |
| Ni + Co | Nickel + Cobalt 70.0 min |
| Cr | Chromium 14.0/17.0 |
| Fe | Iron 5.0/9.0 |
| Cu | Copper 0.50 max |
| Al | Aluminium 1.00/1.50 |
| Ti | Titanium 2.10/2.70 |
| Cb + Ta | Columbium + Tantalum 0.70/1.20 |
Applications
The alloy is used for engine valves.
Forging
Alloy 751 should be forged in the temperature range 2100/1800ºF (1150/980ºC.) Care must be taken not to exceed the maximum and minimum temperatures since hot or cold shortness may occur.
Forge furnace atmospheres should be low in sulfur, to prevent excessive oxidation.
Forgings may be cooled in air or by fan. Water quenching should be used with caution as cracking may occur.
Heat treatment
In certain cases valves are used as-forged. They may be aged at 1300ºF (700ºC) after forging.
Solution annealing is carried out at 2100ºF (1150ºC), with soaking for 4 hrs and air cooling.
Aging is carried out at 1550ºF (840ºC), with soaking for 24 hrs, cooling to 1300ºF (700ºC), holding for 20 hrs then air cooling.
A finer grain size may be obtained, for improved tensile properties – albeit at the expense of some creep-rupture strength – by using a lower solution annealing temperature in the range 1800/1950ºF (980/1070°C) followed by the normal aging cycle.
Machinability
This alloy machines somewhat like a high-speed tool steel. It is machinable in all conditions, but a double-aging heat treatment will result in improved machinability.
Such a treatment would involve 1525/1575ºF plus 1275/1325ºF (830/860 plus 690/720ºC).
Weldability
The alloy may be joined by the flash butt welding procedures employed in valve manufacture.
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