Corrosion Resistant Alloys

NAS 325N (UNS N08031)

Providing an extremely high degree of corrosion resistance, NAS 325N (UNS N08031) is a stainless steel that may be used in many harsh corrosive environments. In addition to local corrosion resistance similar to nickel-base corrosion resistant alloys, NAS 325N (UNS N08031) also provides superior resistance to acid. Nippon Yakin supplies this product in sheet and strip forms.


  • Coil

  • Sheet

  • Plate

Designation / Standard

Nippon Yakin Grade ASTM B625 EN JIS
NAS 325N UNS N08031

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Chemical Composition

ASTM B625

[wt %]

  C Si Mn P S Ni Cr Mo Cu N
Specification ≦ 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

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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
Coefficient of thermal expansion (10-6/℃) 30–200℃ 14.8
30–300℃ 15.0
30–400℃ 15.4
Young's modulus (MPa) 19.2 x 104
Ferromagnetism None
Melting point (℃) 1330-1397

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Mechanical Properties

Mechanical Properties at Room Temperature

ASTM B625

0.2% proof stress
(MPa)
Tensile strength
(MPa)
Elongation
(%)
Hardness
(HB)
≧ 276 ≧ 650 ≧ 40

Examples

  0.2% proof stress
(MPa)
Tensile strength
(MPa)
Elongation
(%)
Hardness
(HB)
Cold-rolled sheet,
2.0-mm thick
396 785 50 182(Hv)
Hot-rolled plate sheet,
25-mm thick
358 731 63 174

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Corrosion Resistance

Because of the high chromium and molybdenum content, NAS 325N (UNS N08031) has outstanding pitting corrosion resistance. It also provides exceptional resistance to sulfuric and other acids.

Pitting Corrosion Resistance

Image: Pitting Corrosion Resistance

Acid Resistance

Results of immersion test in 80° C sulfuric acid

Concentration of sulfuric acid 5% 10% 20% 40% 60% 80%
NAS 325N 0.01 mm/y 0.02 mm/y 0.03 mm/y 0.03 mm/y 0.03 mm/y 3.27 mm/y
NAS 185N 0.01 mm/y 0.03 mm/y 0.03 mm/y 2.06 mm/y 3.02 mm/y 4.98 mm/y
SUS 316L 1.67 mm/y 4.69 mm/y 71.97 mm/y 764.93 mm/y 704.46 mm/y 33.74 mm/y

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Workability

The cold and hot workability are nearly equivalent to standard austenitic stainless steels, and it is worthy of note that NAS 325N (UNS N08031) has a high level of strength for both cold and hot working. Meaning not very clear.

Weldability

Such welding techniques as TIG, MIG and shield metal arc welding can be used for NAS 825 as with standard austenitic stainless steels. We recommend Alloy276 for consumables.

Machinability

As with any stainless steel endowed with a high nickel content, machining NAS 325N is more challenging than standard austenitic stainless steels, though NAS 325N is more easily handled than other nickel-based alloys. We recommend the use of an cemented carbide tool, and suggest combining a slower feed rate with a greater cutting depth.

Heat Treatment

For solution treatment, quenching is performed between 1150 and 1180°C.

Pickling

A mixture of nitric and hydrofluoric acids is used in pickling. To the extent that NAS 325N is more resistant to corrosion than SUS 304, descaling is more difficult. Alkaline immersion for a short time before acid pickling and shot blasting if possible are effective at descaling.

Applications

Chemical plants, flue gas desulfurization system, paper mills, seawater heat exchangers, marine structures

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