Nippon Yakin Kogyo Co., Ltd
Nippon Yakin Kogyo NAS255NM Corrosion Resistant Alloys
Manufacturer: Nippon Yakin Kogyo Co., Ltd
Model: NAS255NM
NAS255NM (UNS N08926)
High Corrosion Resistant Super Stainless Steel
NAS255NM (UNS N08926 equivalent) is a high corrosion resistant stainless steel with high contents of chromium and molybdenum, and provides excellent corrosion resistance under severe environments such as high temperature seawater and flue gas desulfurization plants. Depending on the environment, it is a highly economical stainless steel with corrosion resistance comparable to that of Nickel alloy and pure titanium. Nippon Yakin supplies this product in plate, sheet, and strip form.
| Chemical Composition | 20Cr-25Ni-6Mo-1Cu-0.2N | ||
| Product Shape |
|
 Sheet |
|
| Workability | Cold and hot workability similar to Type 304 and 316; care needed due to high strength in cold and hot conditions. | ||
| Weldability | Shielded metal arc welding, TIG welding, and plasma welding are applicable; use Alloy 276 as consumables; no preheating/post-welding heat needed. | ||
| Machinability | Machining is easier than with Ni-based alloys; use of superhard tools, slow feed speed, and large cut depth recommended. | ||
| Heat Treatment | Solution annealing at 1100°C, followed by quenching or rapid cooling in water, ASTM A480/A480M conditions. | ||
| Pickling | Nitric acid and hydrofluoric acid mixture used for pickling; alkaline solution immersion before pickling is advised; shot blasting effective. | ||
| Applications | Chemical plants, Flue gas desulfurization plants, Heat exchangers. | ||
Coil
PlateSteel Grade/Standard
| Nippon Yakin Grade | JIS | ASTM A240/B625 | EN |
|---|---|---|---|
| NAS255NM | — | UNS N08926 | 1.4529 |
Chemical Composition
| Specification (UNS N08926) | C | Si | Mn | P | S | Ni | Cr | Mo | Cu | N |
|---|---|---|---|---|---|---|---|---|---|---|
| *ASTM A240 | ≤0.020 | ≤0.50 | ≤2.00 | ≤0.030 | ≤0.010 | 24.0 – 26.0 | 19.0 – 21.0 | 6.0 – 7.0 | 0.5 – 1.5 | 0.15 – 0.25 |
Physical Properties
| Density [g/cm³] | 8.06 |
|---|---|
| Specific heat [J/kg·K] | 466 |
| Electrical resistivity [µΩ·cm] | 94.7 |
| Thermal conductivity [W/m·K] | 11.8 |
| Average coefficient of thermal expansion [10⁻⁶/°C] | 20-100°C: 15.0 20-200°C: 15.4 20-300°C: 15.8 20-400°C: 16.1 |
| Young’s modulus [MPa] | 21.1 × 10⁴ |
| Magnetism | None |
| Melting range [°C] | 1320 – 1390 |
Mechanical Properties
Mechanical Properties at Room Temperature
| Specification | 0.2% proof stress [MPa] | Tensile strength [MPa] | Elongation [%] | Hardness [HRBW] |
|---|---|---|---|---|
| Specification (UNS N08926) | ≥295 | ≥650 | ≥35 | — |
| Example: Cold-rolled sheet 3mm | 356 | 731 | 48 | 84 |
Corrosion Resistance
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 |
| NAS255NM | ○ | ○ | 75 |
* 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 |
| NAS255NM | 40 |
* 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 | × | × | ○ | ○ | ○ | ○ | ○ | ○ |
| NAS255NM | ○ | ○ | ○ | ○ | ○ | ○ | ○ | ○ |
* Test conditions: Immersion in boiling MgCl₂ solution
* Test time: 300h
* U-bend test specimen is used.
○: No stress corrosion cracking ×: Stress corrosion cracking
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 |
| NAS255NM | <0.01 | 0.02 | 0.05 | 1.07 | 0.34 | 3.81 |
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 |
| NAS255NM | <0.01 | <0.01 | 3.22 | 5.66 |
Test time: 24h
| Alloy | JIS | UNS No. | Chemical composition |
|---|---|---|---|
| NAS255 | SUS890L | N08904 | 20Cr-24Ni-4.3Mo-1.5Cu |
| NAS329J3L | SUS329J3L | S32205 | 22Cr-5.3Ni-3.0Mo-0.16N |
| NAS64 | SUS329J4L | S32506 | 25Cr-6.5Ni-3.3Mo-0.17N |
| NAS255NM | — | N08926 | 20Cr-25Ni-6Mo-1Cu-0.2N |
Workability
Cold and hot workability are approximately equal to those of Type 304, 316, and other standard austenitic stainless steels. However, care is necessary for both cold and hot worked materials because they have high strength.
Weldability
Possible welding methods include shielded metal arc welding, TIG welding, and plasma welding, in the same manner as with standard austenitic stainless steels. As welding consumables, Alloy 276 should be used. Preheating and post-welding heat treatment are not necessary.
Machinability
As a distinctive feature of high Ni stainless steels, machinability is difficult in comparison with the austenitic stainless steels, but is easier than with Ni-based alloys. Use of a superhard tool whenever possible, together with a slow feed speed and large cut depth, is advised.
Heat Treatment
Solution annealing of NAS255NM should be performed at 1100°C and higher followed by being quenched in water or rapidly cooled by other means. (Conditions provided in ASTM A480/A480M)
Pickling
A mixture of nitric acid and hydrofluoric acid is used in pickling. However, due to the high corrosion resistance of NAS255NM, 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, Flue gas desulfurization plants, Heat exchangers.
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