Nippon Yakin Kogyo Co., Ltd
Nippon Yakin Kogyo NAS325N Corrosion Resistant Alloys
Manufacturer: Nippon Yakin Kogyo Co., Ltd
Model: NAS325N
NAS325N (UNS N08031)
High Corrosion Resistance Stainless Steel
The stainless steel NAS325N (UNS N08031) offers extremely superior corrosion resistance and is suitable for use in many severe corrosion environments. The stainless steel NAS325N (UNS N08031) offers extremely superior corrosion resistance and serves in many severe corrosion environments.. In addition to local corrosion resistance approaching that of nickel-base corrosion-resistant alloys, it also provides excellent acid resistance. Nippon Yakin supplies this product in plate, sheet, and strip form.
| Chemical Composition | 27Cr-31Ni-6.5Mo-1.2Cu-0.2N | ||
| Product Shape |  Coil |  Sheet |  Plate |
| Workability | Cold and hot workability similar to standard austenitic stainless steels; care needed due to high strength in cold and hot conditions. | ||
| Weldability | TIG, MIG, and shielded metal arc welding are applicable; Alloy 276 consumable recommended. | ||
| Machinability | Machining is difficult compared to standard austenitic stainless steels but easier than Ni-based alloys; superhard tools and slow feed speed advised. | ||
| Heat Treatment | Solution annealing at 1150 to 1180°C, followed by quenching or rapid cooling in water. | ||
| Pickling | Nitric acid and hydrofluoric acid mixture used for pickling; alkaline solution immersion advised; shot blasting effective. | ||
| Applications | Chemical plants, Environment-related equipment, Oil and gas extraction, Heat exchangers. | ||
Steel Grade/Standard
| Nippon Yakin Grade | JIS | ASTM B625 | EN |
|---|---|---|---|
| NAS325N | — | UNS N08031 | — |
Chemical Composition
| Specification | C | Si | Mn | P | S | Ni | Cr | Mo | Cu | N |
|---|---|---|---|---|---|---|---|---|---|---|
| ASTM B625 | ≦0.015 | ≦0.3 | ≦2.0 | ≦0.020 | ≦0.010 | 30.0 – 32.0 | 26.0 – 28.0 | 6.0 – 7.0 | 1.0 – 1.4 | 0.15 – 0.25 |
Physical Properties
| Density [g/cm³] | 8.07 |
|---|---|
| Specific heat [J/kg·K] | 448 |
| Electrical resistivity [µΩ·cm] | 105 |
| Thermal conductivity [W/m·K] | 10.7 |
| Average coefficient of thermal expansion [10⁻⁶/°C] | 30 – 100°C: 15.0 30 – 200°C: 14.8 30 – 300°C: 15.0 30 – 400°C: 15.4 |
| Young’s modulus [MPa] | 19.2 × 10⁴ |
| Magnetism | None |
| Melting range [°C] | 1330 – 1397 |
Mechanical Properties
Mechanical Properties at Room Temperature
| Specification | 0.2% proof stress [MPa] | Tensile strength [MPa] | Elongation [%] | Hardness [HRBW] |
|---|---|---|---|---|
| Specification (ASTM B625) | ≥276 | ≥650 | ≥40 | — |
| Example: Cold-rolled sheet 2.0mm | 396 | 785 | 50 | 182 |
| Example: Hot-rolled plate 25mm | 358 | 731 | 63 | 174 |
Corrosion Resistance
NAS325N has excellent pitting corrosion resistance due to its high contents of chromium and molybdenum. It also has excellent acid resistance to sulfuric acid, etc.
Pitting Corrosion Resistance
| Alloy | ASTM G48 Method A | ASTM G48 Method C | |
| 22°C | 50°C | Critical pitting corrosion temperature CPT (°C) | |
| NAS255 | ○ | × | 50 |
| NAS329J3L | ○ | × | 50 |
| NAS64 | ○ | ○ | 55 |
| NAS185N | ○ | ○ | 70 |
| NAS325N | ○ | ○ | 100 |
ASTM G48 Method A (○: No pitting corrosion, ×: Pitting corrosion)
Test solution: 6%FeCl3
Test temperature: 22°C, 50°C (Recommended temperature in this test)
Test time: 72h
Crevice Corrosion Resistance
| Alloy | ASTM G48 Method D |
| Critical crevice corrosion temperature CCT (°C) | |
| NAS255 | 10 |
| NAS329J3L | 25 |
| NAS64 | 30 |
| NAS185N | 40 |
| NAS325N | 50 |
Test conditions: ASTM G48 Method D
Test solution: 6%FeCl3 + 1%HCl
Test time: 72h
Stress Corrosion Cracking Resistance
| Alloy | MgCl₂ concentration (boiling point °C are in brackets) | |||||||
| 45% (155°C) | 42% (143°C) | 40% (138°C) | 38% (134°C) | 35% (126°C) | 30% (115°C) | 25% (110°C) | 20% (108°C) | |
| NAS255 | × | × | × | × | ○ | ○ | ○ | ○ |
| NAS329J3L | × | × | × | × | × | ○ | ○ | ○ |
| NAS64 | × | × | ○ | ○ | ○ | ○ | ○ | |
| NAS185N | × | × | ○ | ○ | ○ | ○ | ○ | |
| NAS325N | × | × | × | × | ○ | ○ | ○ | ○ |
Test conditions: Immersion in boiling MgCl₂ solution
They use a U-bend test specimen.
○: No stress corrosion cracking ×: Stress corrosion cracking
Acid Resistance
Corrosion rate in sulfuric acid at 80°C (mm/y)
| Alloy | 5% | 10% | 20% | 40% | 60% | 80% |
|---|---|---|---|---|---|---|
| NAS255 | <0.01 | <0.01 | 0.78 | 2.95 | 0.48 | 5.01 |
| NAS329J3L | 0.01 | 0.17 | 4.65 | 365.9 | 1456 | 106.4 |
| NAS64 | <0.01 | 0.02 | 1.07 | 191.9 | 1054 | 60.72 |
| NAS185N | 0.02 | 0.04 | 1.02 | 2.11 | 2.16 | 7.76 |
| NAS325N | — | <0.01 | 0.02 | 0.03 | — | 3.54 |
Test time: 24h
Corrosion rate in hydrochloric acid at 80°C (mm/y)
| Alloy | 0.1% | 1% | 2% | 3% |
|---|---|---|---|---|
| NAS255 | <0.01 | 0.01 | 2.70 | 3.72 |
| NAS329J3L | 0.02 | 0.03 | 31.10 | 60.62 |
| NAS64 | 0.01 | 0.12 | 12.94 | 30.51 |
| NAS185N | 0.01 | 0.02 | 0.01 | 9.14 |
| NAS325N | <0.01 | <0.01 | 3.22 | 5.66 |
Test time: 24h
Reference
| Alloy | JIS | UNS No. | Chemical composition |
| NAS255 | SUS890L | N08904 | 20Cr-24Ni-4.3Mo-1.5Cu |
| NAS329J3L | SUS329J3L | S32205 | |
Workability
NAS325N has cold and hot workability similar to that of standard austenitic stainless steels. However, the high strength of this material must be considered in both cold working and hot working.
Weldability
Welding can be performed by TIG, MIG, and shielded metal arc welding in much the same manner as with standard austenitic stainless steels. Alloy 276 welding consumable should be used.
Machinability
As a feature of high Ni stainless steels, machining of NAS325N is difficult in comparison with standard austenitic stainless steels, but it is easier than with nickel-based alloys. A ultrahard tool should be used in machining if at all possible. It is also advisable to use a slower feed rate and deeper cutting depth.
Heat Treatment
Solution annealing of NAS325N is normally performed at the temperature range from 1150 to 1180°C followed by being quenched in water or rapidly cooled by other means.
Pickling
A mixture of nitric acid and hydrofluoric acid is used in pickling. However, due to the high corrosion resistance of NAS325N, scale is somewhat difficult to remove in comparison with Type 304. Therefore, the material should be immersed in an alkaline solution before pickling, or if possible, shot blasting is extremely effective.
Applications
Chemical plants, Environment-related equipment, Oil and gas extraction, Heat exchangers.
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