Heat Resistant Alloys
NAS 660 (UNS S66286) - A-286 Alloy
A precipitation hardening stainless steel, NAS 660 (SUH 660, UNS S66286) maintains superior strength at high temperatures up to 700℃, surpassing austenitic stainless steels. With a higher nickel content than SUS 304, NAS 660 also includes such elements as titanium and aluminum for hardening. Aging treatment is used to precipitate the face-centered cubic phase—technically referred to as the γ’ or gamma prime phase [Ni3(Al, Ti)]—making this an extraordinarily strong metal at high temperatures. Nippon Yakin supplies this product in plate, sheet and strip forms.
Coil
Sheet
Plate
Chemical Composition
JIS G4312 / SUH 660
| C | Si | Mn | P | S | Ni | Cr | Mo | Al | Ti | B | V | Co | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | ― | ― | ― | ― | ― | 24.00 | 13.50 | 1.00 | ― | 1.90 | 0.001 | 0.10 | ― |
| Max | 0.08 | 1.00 | 2.00 | 0.040 | 0.030 | 27.00 | 16.00 | 1.50 | 0.35 | 2.35 | 0.010 | 0.50 | ― |
AMS 5525 / UNS S66286
| C | Si | Mn | P | S | Ni | Cr | Mo | Al | Ti | B | V | Co | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | ― | ― | ― | ― | ― | 24.00 | 13.50 | 1.00 | ― | 1.90 | 0.003 | 0.10 | ― |
| Max | 0.08 | 1.00 | 2.00 | 0.025 | 0.025 | 27.00 | 16.00 | 1.50 | 0.35 | 2.35 | 0.010 | 0.50 | 1.00 |
Physical Properties
| Specific heat (J/kg･K) | 460 | |
| Specific resistivity (μΩ･cm) | 91 | |
| Thermal conductivity (W/m･K) | 150℃ | 15.0 |
| Coefficient of thermal expansion (10-6/℃) | 20–100℃ | 16.8 |
| 20–500℃ | 17.7 | |
| 20–650℃ | 17.4 | |
| 20–750℃ | 18.5 | |
| 20–950℃ | 19.4 | |
| Young's modulus (MPa) | 20.1 x 104 | |
| Ferromagnetism | None | |
| Melting point (℃) | 1371-1427 | |
Mechanical Properties
Solution treatment
JIS G4312 / SUH 660
| 0.2% Yield strength (N/mm2) |
Tensile strength (N/mm2) |
Elongation (%) |
Hardness (HRB) |
Special notes |
|---|---|---|---|---|
| ― | ≤ 730 | ≥ 25 | ≤ 91 |
AMS 5525 / UNS S66286
| 0.2% Yield strength (N/mm2) |
Tensile strength (N/mm2) |
Elongation (%) |
Hardness (HRB) |
Special notes |
|---|---|---|---|---|
| ― | ≤ 724 | ≥ 25 | ≤ 90 | At least 1-mm thick |
Examples
| 0.2% Yield strength (N/mm2) |
ensile strength (N/mm2) |
Elongation (%) |
Hardness (HRB) |
Special notes | |
|---|---|---|---|---|---|
| Cold-rolled sheet | 344 | 665 | 40 | 86 | 0.2% Yield strength for reference |
Solution treatment and aging
JIS G4312 / SUH 660
| 0.2% Yield strength (N/mm2) |
ensile strength (N/mm2) |
Elongation (%) |
Hardness (HRC) |
Special notes |
|---|---|---|---|---|
| ≥ 590 | ≥ 900 | ≥ 15 | ≥ 24 | ― |
AMS 5525 / UNS S66286
| 0.2% Yield strength (N/mm2) |
ensile strength (N/mm2) |
Elongation (%) |
Hardness (HRC) |
Special notes |
|---|---|---|---|---|
| ≥ 655 | ≥ 965 | ≥ 15 | 24–35 | At least 1-mm thick |
Examples
| 0.2% Yield strength (N/mm2) |
ensile strength (N/mm2) |
Elongation (%) |
Hardness (HRC) |
Special notes | |
|---|---|---|---|---|---|
| Cold-rolled sheet | 774 | 1099 | 25 | 32 | ― |
Work Hardening Properties
The work hardening of NAS 660 is no different from S310S, and cold working is possible on the same level.
Age Hardening Behavior
NAS 660 was held at various temperatures for 16 hours to investigate its age hardening behavior. Solution-treated NAS 660 reaches its maximum hardness at 16 hours of heat treatment around 700℃, though this temperature can be lowered if the NAS 660 is cold rolled.
High-Temperature Strength
High-Temperature, Brief Pull
Creep Strength
An example of test values for solution-treated NAS 660 that is aged for 16 hours at 720℃
| Testing temp. (℃) | Rupture strength (N/mm2) | Elongation (%) | Creep strength (N/mm2) | ||
|---|---|---|---|---|---|
| 0.5% total strain | 1.0% total strain | ||||
| a) 100 hr Strength properties | 538 | 689 | 3 | 559 | 634 |
| 593 | 562 | 3 | 525 | 551 | |
| 649 | 434 | 5 | 365 | 414 | |
| 704 | 304 | 12 | 207 | 244 | |
| 732 | 241 | 28 | ― | ― | |
| 816 | 90 | 55 | ― | ― | |
| b) 1000 hr Strength properties | 538 | 599 | 3 | 537 | 585 |
| 593 | 490 | 3 | 469 | 482 | |
| 649 | 317 | 9 | 241 | 282 | |
| 704 | 207 | 24 | ― | 155 | |
| 732 | 148 | 35 | ― | ― | |
| 816 | 58 | ― | ― | ― | |
Corrosion Resistance
NAS 660 provides superior corrosion resistance beyond the standard austenitic stainless steel SUS 304, and this does not vary even with thermal aging.
Evaluation of Pitting Corrosion Resistance
| Material | Treatment | Pitting potential |
|---|---|---|
| NAS 660 | Solution | 0.37V |
| Thermal aging | 0.38V | |
| SUS 304 | Solution | 0.28V |
Test conditions: 5% NaCl at 30℃
Heat Treatment
NAS 660 is a precipitation hardening alloy. Its strength is increased and its properties emerge through aging after solution treatment. Two stages of heat treatment are generally carried out, as follows:
- Solution treatment at 980℃ followed by oil or water cooling
- Age hardening at 720℃ for 16 hours, followed by air cooling
For solution treatment cooling, either oil or water cooling is required, though air cooling is better for thinner metal. Note that it is important to use a suitable temperature and holding time for aging to obtain the target strength.
Typically, NAS 660 is delivered with solution treatment already applied.
Weldability
Spot, TIG, MIG and shield metal arc welding can be used on thin NAS 660 sheets under similar conditions to austenitic stainless steels.
