Corrosion Resistant Alloys

NAS 185N (UNS S31254) - Super Austenitic Stainless Steel

A stainless steel with high chromium and high molybdenum content, NAS 185N (SUS 312L, UNS S31254) provides superior corrosion resistance in environments that are exceptionally corrosive such as high temperature seawater. Among the corrosion-resistant stainless steel alloys on the market, NAS 185N is an economic choice with corrosion resistance comparable to Hastelloy® alloys and pure titanium. Nippon Yakin supplies this product in plate, sheet and strip forms.

  • Image: Coil
    Coil
  • Image: Sheet
    Sheet
  • Image: Plate
    Plate

Designation / Standard

Nippon Yakin Grade ASTM A240 EN 10088-2 / 10028-7 JIS G4304 / 4305
NAS 185N UNS S31254 1.4547 SUS 312L

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Chemical Composition

SUS 312L

  C Si Mn P S Ni Cr Mo Cu N
Min ― ― ― ― ― 17.50 19.00 6.00 0.50 0.16
Max 0.020 0.80 1.00 0.030 0.015 19.50 21.00 7.00 1.00 0.25

UNS S31254

  C Si Mn P S Ni Cr Mo Cu N
Min ― ― ― ― ― 17.5 19.5 6.00 0.50 0.18
Max 0.020 0.80 1.00 0.030 0.010 18.5 20.5 6.5 1.00 0.22

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Physical Properties

Specific heat (J/kg･K) 20℃ 464
Specific resistivity (μΩ･cm) 88.2
Thermal conductivity (W/m･K) 12.3
Coefficient of thermal expansion (10-6/℃) 20–200℃ 15.6
20–300℃ 16.1
20–400℃ 16.8
Young's modulus (MPa) 16.7 x 104
Ferromagnetism None
Melting point (℃) 1360-1405

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Mechanical Properties

Mechanical Properties at Room Temperature

SUS 312L

0.2% proof stress
(N/mm2)		 Tensile strength
(N/mm2)		 Elongation
(%)		 Hardness
(Hv) (HB)
≥ 300 ≥ 650 ≥ 35 ≤ 230 ≤ 223

UNS S31254

  0.2% proof stress
(N/mm2)		 Tensile strength
(N/mm2)		 Elongation
(%)		 Hardness
(Hv) (HB)
Sheet and strip ≥ 310 ≥ 690 ≥ 35 ― ≤ 223
Plate ≥ 310 ≥ 655 ≥ 35 ― ≤ 223

Examples

  0.2% proof stress
(N/mm2)		 Tensile strength
(N/mm2)		 Elongation
(%)		 Hardness
(Hv) (HB)
Cold-rolled sheet,
1.5-mm thick		 379 744 41 182 ―

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Corrosion Resistance

NAS 185N is high in both chromium and molybdenum content, which endow this stainless steel with excellent pitting corrosion and crevice corrosion resistance in high-chlorine environments. Its high nickel content also provides exceptional stress corrosion cracking resistance.

Pitting Corrosion Resistance

Image: Pitting Corrosion Resistance

Crevice Corrosion Resistance

Image: Crevice Corrosion Resistance

Stress Corrosion Cracking Resistance

Alloy
Main chemical composition (wt%)		 45%
(154℃)		 42%
(142℃)		 40%
(138℃)		 38%
(134℃)		 35%
(126℃)		 30%
(115℃)		 25%
(110℃)		 20%
(108℃)
SUS 304
18Cr-8Ni		 × × × × × × × ×
SUS 316L
17Cr-12Ni-2Mo		 × × × × × × × ○
NAS 64
25Cr-6Ni-3.3Mo-0.16N		 × × × × × × ○ ○
NAS 155N
18Cr-15Ni-4Mo-3Cu-0.15N		 × × × × × ○ ○ ○
NAS 185N
20Cr-18Ni-6Mo-0.8Cu-0.2N		 × × × × ○ ○ ○ ○

Test conditions:
U-bend test piece in boiling MgCl2 aqueous solution for 300 hr
○: No cracks
×: Cracks present

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Workability

Although NAS 185N can be hot- and cold-worked much like standard austenitic stainless steels such as SUS 304 and SUS 316, the high strength of the alloy must be kept in mind when doing so.

Weldability

Our NAS 185N alloy can be shield metal arc welded, TIG welded and plasma welded much as any standard austenitic stainless steel. We recommend using Hastelloy® C-type welding consumables with this product. Preheating and post-heating are not required.

Machinability

As with any stainless steel endowed with a high nickel content, machining NAS 185N is more challenging than standard austenitic stainless steels, though NAS 185N 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

As NAS 185N is an austenitic stainless steel, the same sort of heat treatment may be used. In general, we suggest that NAS 185N be water cooled with a solution treatment between 1125 and 1175 ℃.

Pickling

A mixture of nitric and hydrofluoric acids is used in pickling. To the extent that NAS 185 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

  • Seawater environments: desalination systems, seawater heat exchangers, condenser tubes
  • High-chlorine environments: pulp and paper mills, bleaching equipment
  • Environments containing concentrated sodium chloride: plastic manufacturing equipment, chemical reactor vessels and tubing

* Hastelloy is a registered trademark of Haynes International, Inc.

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