Manufacturer: Nippon Yakin Kogyo Co., Ltd
Model: NAS185N

NAS185N (UNS S31254)
High Corrosion Resistant Super Stainless Steel

NAS185N (SUS312L, UNS S31254) is a high corrosion resistant austenitic stainless steel with a high nickel, high chromium, high molybdenum alloy design, and provides excellent corrosion resistance in severe corrosion environments such as seawater. Depending on the environment, this stainless steel offers high economy combined 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 18Ni 6Mo 0.8Cu 0.2N
Product shape	Coil	Sheet	Plate
Workability	Hot and cold workability similar to standard austenitic stainless steels like Type 304, 316; requires care due to high strength
Weldability	Various methods applicable; shielded metal arc welding, TIG welding, and plasma welding suitable. Alloy 276 consumables recommended.
Machinability	Machining is difficult but easier than with Ni-based alloys; use of ultra-hard tool and slow feed rate recommended
Heat Treatment	Solution annealing at 1150°C, quenching in water or rapid cooling
Pickling	Mixture of nitric acid and hydrofluoric acid; material should be immersed in alkaline solution before pickling, shot blasting effective
Applications	Chemical plants, Marine structures, Heat exchangers, Bleaching equipment
Certification	Manufacturable as UNS S31254, up to 40mm thickness, NORSOK M 650, NORSOK M 630 MDS R15

Steel Grade/Standard

Nippon Yakin Grade	JIS G 4304/4305	ASTM A240	EN 10088-2/10028-7
NAS185N	SUS312L	UNS S31254	1.4547

Chemical Composition

Specification	C	Si	Mn	P	S	Ni	Cr	Mo	Cu	N
SUS312L	≤0.020	≤0.80	≤1.00	≤0.030	≤0.015	17.50 – 19.50	19.00 – 21.00	6.00 – 7.00	0.50 – 1.00	0.16 – 0.25
UNS S31254	≤0.020	≤0.80	≤1.00	≤0.030	≤0.010	17.50 – 18.50	19.50 – 20.50	6.00 – 7.00	0.50 – 1.00	0.18 – 0.25
EN 1.4547	≤0.020	≤0.70	≤1.00	≤0.030	≤0.010	17.50 – 18.50	19.50 – 20.50	6.00 – 7.00	0.50 – 1.00	0.18 – 0.25

Physical Properties

Property	Value
Density [g/cm³]	8.02
Specific heat [J/kg·K] 20°C	464
Electrical resistivity [µΩ·cm]	89.4
Thermal conductivity [W/m·K]	12.3
Average coefficient of thermal expansion [10⁻⁶/°C]	20-100°C: 15.3 20-200°C: 15.7 20-300°C: 16.1 20-400°C: 16.4
Young’s modulus [MPa]	19.7 × 10⁴
Magnetism	None
Melting range [°C]	1360 – 1405

Mechanical Properties

Mechanical Properties at Room Temperature

Specification	0.2% proof stress [MPa]	Tensile strength [MPa]	Elongation [%]	Hardness [HV]	Hardness [HBW]	Hardness [HRBW]
SUS312L (sheet and strip)	≥300	≥650	≥35	≤230	≤223	≤96
SUS312L (plate)	≥310	≥690	≥35	≤223	≤96
Example: Hot-rolled plate 8mm	361	707	53	187	—
Cold-rolled sheet 1.5mm	379	744	41	182	—

Corrosion Resistance

NAS185N is a high Cr, high Mo stainless steel which provides excellent pitting corrosion resistance and crevice corrosion resistance in high Cl environments.As a high Ni steel, moreover, it provides exceptional resistance to stress corrosion cracking, positioning it as an optimal solution** for use in highly corrosive environments.

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

 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

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% (145°C)	42% (143°C)	40% (142°C)	38% (138°C)	35% (136°C)	20% (108°C)
NAS255	×	×	×	×	○	○
NAS329J3L	×	×	×	×	×	○
NAS64	○	○	○	○	○	○
NAS185N	○	○	○	○	○	○

Test conditions: Immersion in boiling MgCl₂ solution
Test time: 300h
U-bend test specimen is used.
○: 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	0.76	2.95	4.85	5.01
NAS329J3L	0.01	0.17	4.65	36.5	40.6	60.74
NAS64	<0.01	0.07	1.07	191.9	198.5	206.72
NAS185N	0.02	0.04	1.32	2.89	3.4	4.78

Test time: 24h

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

Alloy	0.1%	1%	3%	5%
NAS255	0.01	0.03	0.19	0.37
NAS329J3L	0.01	0.07	0.94	2.37
NAS64	0.01	0.12	12.94	30.51
NAS185N	0.01	0.2	4.20	7.21

Test time: 24h

Reference

Alloy	JIS	UNS No.	Chemical composition
NAS255	SUS890L	N08904	20Cr-24Ni-4.3Mo-1.5Cu
NAS329J3L	SUS329J3L	S32205	22Cr-5.3Ni-3.0Mo-0.17N
NAS64	—	N08904	25Cr-6.3Ni-3.6Mo-0.16N
NAS185N	SUS312L	S31254	20Cr-18Ni-6Mo-0.8Cu-0.2N