Corrosion Resistant Alloys
NAS 64 (UNS S32506) - Duplex Stainless Steel
An austenitic-ferritic duplex stainless steel, NAS 64 (SUS 329J4L, UNS S32506, ASME Code Case 2543) was developed by Nippon Yakin to provide superior resistance to corrosive substances. NAS 64 is particularly resistant to phosphoric acid, acetic acid and various types of sulfur compounds. Owing to its exceptionally low carbon and high molybdenum composition, it provides a level of local corrosion resistance markedly improved over SUS 329J1. Nippon Yakin supplies this product in plate, sheet and strip forms.
Coil
Sheet
Plate
Designation / Standard
| Nippon Yakin Grade | ASTM A240 | EN | JIS G4304 / 4305 |
|---|---|---|---|
| NAS 64 | UNS S32506 | ― | SUS 329J4L |
Chemical Composition
SUS 329J4L
| C | Si | Mn | P | S | Ni | Cr | Mo | N | W | |
|---|---|---|---|---|---|---|---|---|---|---|
| Min | ― | ― | ― | ― | ― | 5.50 | 24.00 | 2.50 | 0.08 | ― |
| Max | 0.030 | 1.00 | 1.50 | 0.040 | 0.030 | 7.50 | 26.00 | 3.50 | 0.30 | ― |
UNS S32506
| C | Si | Mn | P | S | Ni | Cr | Mo | N | W | |
|---|---|---|---|---|---|---|---|---|---|---|
| Min | ― | ― | ― | ― | ― | 5.5 | 24.0 | 3.0 | 0.08 | 0.05 |
| Max | 0.030 | 0.90 | 1.00 | 0.040 | 0.015 | 7.2 | 26.0 | 3.5 | 0.20 | 0.30 |
Physical Properties
| Specific heat (J/kg･K) | 25℃ | 460 |
| Specific resistivity (μΩ･cm) | 88.7 | |
| Thermal conductivity (W/m･K) | 25℃ | 12.6 |
| Coefficient of thermal expansion (10-6/℃) | 30–200℃ | 10.5 |
| 30–300℃ | 11.4 | |
| 30–400℃ | 12.2 | |
| Young's modulus (MPa) | 19.6 x 104 | |
| Ferromagnetism | Yes | |
| Melting point (℃) | 1420-1462 | |
Mechanical Properties
Mechanical Properties at Room Temperature
SUS 329J4L
| 0.2% proof stress (N/mm2) |
Tensile strength (N/mm2) |
Elongation (%) |
Hardness | |
|---|---|---|---|---|
| (Hv) | (HB) | |||
| ≥ 450 | ≥ 620 | ≥ 18 | ≤ 320 | ≤ 302 |
UNS S32506
| 0.2% proof stress (N/mm2) |
Tensile strength (N/mm2) |
Elongation (%) |
Hardness | |
|---|---|---|---|---|
| (Hv) | (HB) | |||
| ≥ 450 | ≥ 620 | ≥ 18 | ― | ≤ 302 |
Examples
| 0.2% proof stress (N/mm2) |
Tensile strength (N/mm2) |
Elongation (%) |
Hardness | ||
|---|---|---|---|---|---|
| (Hv) | (HB) | ||||
| Cold-rolled sheet, 1.6-mm thick |
732 | 853 | 23 | 258 | 248 |
| Hot-rolled plate, 10-mm thick |
657 | 800 | 26 | ― | 252 |
Corrosion Resistance
NAS 64 has excellent local corrosion resistance, including resistance against pitting corrosion and stress corrosion cracking, and can be used in environments that SUS 316L cannot withstand. NAS 64 boasts a pitting resistance more than twice that of SUS 329J1, and its crevice corrosion resistance is far superior as well.
Pitting Corrosion Resistance
Pitting corrosion resistance of beads and the heat-affected zone after TIG welding
| Test | Pitting corrosion resistance | |
|---|---|---|
| Designation | V'c10 70℃ 3.5% NaCl (V'c10 vs SCE) |
10%FeCl3 . 6H2O 40℃ 4hr (g/m²/h) |
| NAS 64 Welding material/base material | 0.39 / 0.68 | < 0.1 |
| SUS 329J1 Welding material/base material | 0.14 / 0.26 | 1.0-5.0 |
Stress Corrosion Cracking Resistance
| Test conditions | 20% NaCl+ (107℃) | 1130 ppm Cl-250℃ | |||
|---|---|---|---|---|---|
| Designation | ― | 1% NaO2 | 1/4% CrCl3 | 1% Na2Cr2O7•2H2O | |
| SUS 304 | ×× (2/2) |
× (2/3) |
×× (3/3) |
×× (3/3) |
×× (2/2) |
| SUS 316 | ○ (0/2) |
× (1/3) |
× (1/3) |
×× (3/3) |
― ― |
| NAS 64 | ○ (2/2) |
○ (2/3) |
○ (3/3) |
○ (3/3) |
○ (2/2) |
| SUS 329J1 | ○ (0/2) |
○ (0/2) |
○ (0/2) |
○ (0/3) |
― ― |
U-bending test, test duration: 240-300 hr for SUS, 336 hr for NAS 64
××: All pieces cracked
×: Some pieces cracked
○: No cracks
Numbers in parentheses indicate the number of cracked pieces to the total number of test pieces.
Acid Resistance
| Shape | Test conditions | ||
|---|---|---|---|
| 5% sulfur acid, boiling, 6hr | 1% HCl, boiling, 6hr | 49%P2O5, 0.5%F- 5%H2SO4, 0.05%Cl- 1.0%e3+, 80℃ | |
| NAS 64 Cold-rolled sheet (2.0mm) | 0.36 | < 0.1 | < 0.1 |
| NAS 64 Hot-rolled plate sheet (10.0mm) | 0.53 | < 0.1 | ― |
| SUS 316L | 4.50 | 46.7 | 95.8 |
| SUS 329J1 Cold-rolled sheet (2.0mm) | 1.26 | < 0.1 | ― |
Workability
Between 950 and 1150℃, the hot working strength is comparable to SUS 430. This strength rapidly increases below 900℃, so care is required. After hot working, solution treatment is needed. Care should also be taken when cold working as NAS 64 has a higher yield strength and a lower elongation than SUS 304.
Weldability
Such welding techniques as TIG, MIG and shield metal arc welding can be used for NAS 64 as with standard austenitic stainless steels. 329J4L welding consumables should be used, though pre-heating and post-heating are not required.
Heat Treatment
Heat treatment does not harden NAS 64. Rapid cooling is required after heating the solution treatment to between 1050 and 1080℃. The cooling should be carried out as rapidly as possible to prevent 475℃ embrittlement and sigma-phase embrittlement.
Pickling
A mixture of nitric and hydrofluoric acids is used in pickling. To the extent that NAS 64 is more resistant to corrosion than SUS 304, descaling is more difficult. Alkaline immersion for a short time before pickling and shot blasting if possible are effective at descaling.
Applications
NAS 64 is suitable for use in a wide range of chemical equipment used in environments that SUS 316 cannot withstand. Applications including anti-pollution equipment and devices that handle such substances as petrochemicals, fiber, pulp and seawater. Due to its high strength, NAS 64 can also be used in harsh environments requiring both mechanical strength and corrosion resistance such as sluice gates, OCTG (oil country tubular goods) and geothermal power generation plants.
