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 Composition27Cr-31Ni-6.5Mo-1.2Cu-0.2N
Product Shape

Coil

SheetPlate
WorkabilityCold and hot workability similar to standard austenitic stainless steels; care needed due to high strength in cold and hot conditions.
WeldabilityTIG, MIG, and shielded metal arc welding are applicable; Alloy 276 consumable recommended.
MachinabilityMachining is difficult compared to standard austenitic stainless steels but easier than Ni-based alloys; superhard tools and slow feed speed advised.
Heat TreatmentSolution annealing at 1150 to 1180°C, followed by quenching or rapid cooling in water.
PicklingNitric acid and hydrofluoric acid mixture used for pickling; alkaline solution immersion advised; shot blasting effective.
ApplicationsChemical plants, Environment-related equipment, Oil and gas extraction, Heat exchangers.

Steel Grade/Standard

Nippon Yakin GradeJISASTM B625EN
NAS325NUNS N08031

Chemical Composition

SpecificationCSiMnPSNiCrMoCuN
ASTM B625≦0.015≦0.3≦2.0≦0.020≦0.01030.0 – 32.026.0 – 28.06.0 – 7.01.0 – 1.40.15 – 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
MagnetismNone
Melting range [°C]1330 – 1397

Mechanical Properties

Mechanical Properties at Room Temperature

Specification0.2% proof stress [MPa]Tensile strength [MPa]Elongation [%]Hardness [HRBW]
Specification (ASTM B625)≥276≥650≥40
Example: Cold-rolled sheet 2.0mm39678550182
Example: Hot-rolled plate 25mm35873163174

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

AlloyASTM G48 Method AASTM G48 Method C
22°C50°CCritical pitting corrosion temperature CPT (°C)
NAS255×50
NAS329J3L×50
NAS6455
NAS185N70
NAS325N100

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

AlloyASTM G48 Method D
Critical crevice corrosion temperature CCT (°C)
NAS25510
NAS329J3L25
NAS6430
NAS185N40
NAS325N50

Test conditions: ASTM G48 Method D
Test solution: 6%FeCl3 + 1%HCl
Test time: 72h

Stress Corrosion Cracking Resistance

AlloyMgCl₂ 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)

Alloy5%10%20%40%60%80%
NAS255<0.01<0.010.782.950.485.01
NAS329J3L0.010.174.65365.91456106.4
NAS64<0.010.021.07191.9105460.72
NAS185N0.020.041.022.112.167.76
NAS325N<0.010.020.033.54

Test time: 24h

Corrosion rate in hydrochloric acid at 80°C (mm/y)

Alloy0.1%1%2%3%
NAS255<0.010.012.703.72
NAS329J3L0.020.0331.1060.62
NAS640.010.1212.9430.51
NAS185N0.010.020.019.14
NAS325N<0.01<0.013.225.66

Test time: 24h

Reference

AlloyJISUNS No.Chemical composition
NAS255SUS890LN0890420Cr-24Ni-4.3Mo-1.5Cu
NAS329J3LSUS329J3LS32205

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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