Corrosion Resistant Alloys
NAS 74N (UNS S32750) - Super Duplex Stainless Steel
A super duplex stainless steel with a pitting resistance equivalent (PRE) of at least 40, NAS 74N provides excellent corrosion resistance and strength properties. Compared to UNS S32205, SUS 329J3L and SUS 329J4L (NAS 64), NAS 74N offers superior localized corrosion resistance and is therefore suitable for use in chemical plants, desalination plants and other such harsh environments. Nippon Yakin supplies this product in plate, sheet and strip forms.
Coil
Sheet
Plate
Designation / Standard
| Nippon Yakin Grade | ASTM A240 | EN 10088-2 / 10028-7 | JIS |
|---|---|---|---|
| NAS 74N | UNS S32750 | 1.4410 | ― |
Chemical Composition
UNS S32750
| C | Si | Mn | P | S | Ni | Cr | Mo | N | Cu | |
|---|---|---|---|---|---|---|---|---|---|---|
| Min | ― | ― | ― | ― | ― | 6.0 | 24.0 | 3.0 | 0.24 | ― |
| Max | 0.030 | 0.80 | 1.20 | 0.035 | 0.020 | 8.0 | 26.0 | 5.0 | 0.32 | 0.50 |
EN 1.4410 *
| C | Si | Mn | P | S | Ni | Cr | Mo | N | Cu | |
|---|---|---|---|---|---|---|---|---|---|---|
| Min | ― | ― | ― | ― | ― | 6.0 | 24.0 | 3.0 | 0.24 | ― |
| Max | 0.030 | 1.00 | 2.00 | 0.035 | 0.015 | 8.0 | 26.0 | 4.5 | 0.35 | ― |
* EN 10088-2
Physical Properties
| Specific heat (J/kg･K) | 453 | |
| Specific resistivity (μΩ･cm) | 83.0 | |
| Thermal conductivity (W/m･K) | 12.3 | |
| Coefficient of thermal expansion (10-6/℃) | 30–100℃ | 13.4 |
| 30–200℃ | 13.7 | |
| 30–300℃ | 13.8 | |
| 30–400℃ | 14.0 | |
| Young's modulus (MPa) | 19.7 x 104 | |
| Ferromagnetism | Yes | |
| Melting point (℃) | 1390-1455 | |
Mechanical Properties
Mechanical Properties at Room Temperature
UNS S32750
| 0.2% proof stress (N/mm2) | Tensile strength (N/mm2) | Elongation (%) | Hardness (HB) | Impact Value R.T/Vnotch/Fullsize (J) |
|
|---|---|---|---|---|---|
| ≥ 550 | ≥ 795 | ≥ 15 | ≤ 310 | ― | ― |
EN 1.4410 *
| 0.2% proof stress (N/mm2) | Tensile strength (N/mm2) | Elongation (%) | Hardness (HB) | Impact Value R.T/Vnotch/Fullsize (J) |
|
|---|---|---|---|---|---|
| ≥ 530 | 730-930 | ≥ 20 | ― | ≥ 100 (long) | ≥ 60 (tr) |
* EN 10088-2 hot rolled plate
Examples
| 0.2% proof stress (N/mm2) | Tensile strength (N/mm2) | Elongation (%) | Hardness (HB) | Impact Value R.T/Vnotch/Fullsize (J) |
||
|---|---|---|---|---|---|---|
| Hot-rolled plate sheet, 20-mm thick |
588 | 849 | 38 | 235 | 298 | 298 |
| Hot-rolled plate sheet, 8-mm thick |
655 | 880 | 37 | 255 | ― | ― |
High-Temperature Strength
| Temperature (℃) | 0.2% proof stress (N/mm2) | Tensile strength (N/mm2) | Elongation (%) |
|---|---|---|---|
| 100 | 530 | 789 | 33 |
| 150 | 509 | 774 | 31 |
| 200 | 470 | 751 | 31 |
| 250 | 465 | 761 | 29 |
| 300 | 457 | 775 | 27 |
| 350 | 458 | 775 | 26 |
| 400 | 440 | 758 | 29 |
Impact Value
Corrosion Resistance
NAS 74N has excellent localized resistance against pitting and crevice corrosion as well as superior acid resistance in comparison with general austenitic stainless steels such as SUS 304 and SUS 316L and such duplex stainless steels as NAS 329J3L (UNS S32205) and NAS 64.
Pitting and Crevice Corrosion Resistance
Acid Resistance
Corrosion resistance in various acids (test duration: 24 hr)
| Concentration | Temperature | Critical pitting corrosion temperature (CPT) | ||||
|---|---|---|---|---|---|---|
| NAS 74N | NAS 64 | NAS 329J3L | SUS 316L | |||
| H2SO4 | 10% | boiling | 2.25 | 3.64 | 3.70 | 19.70 |
| HCl | 1% | boiling | 0.02 | 0.03 | 5.41 | 6.94 |
| HNO3 | 60% | boiling | 0.06 | 0.08 | 0.11 | 0.17 |
| H3PO4 | 80% | boiling | 2.83 | 4.99 | 5.52 | 25.00 |
| CH3COOH | 80% | boiling | < 0.01 | < 0.01 | < 0.01 | < 0.01 |
Isocorrosion curve in sulfuric acid (corrosion rate < 0.1 mm/y)
Workability
Care should also be taken when cold working as NAS 74N has a higher yield strength and a lower elongation than SUS 304.
Weldability
In welding, the interpass temperature should be no more than 100℃ to prevent intermetallic compounds from forming. No preheating is required. UNS S32750 welding consumables should be used.
Heat Treatment
Rapid cooling is required after heating the solution treatment to between 1080 and 1120℃. The cooling should be carried out as rapidly as possible to to prevent 475℃ embrittlement and sigma-phase embrittlement.
