Properties
Alloy 825 (UNS N08825) is a titanium-stabilised fully austenitic Ni-Fe-Cr alloy with additions of copper and molybdenum.
These alloys are characterised by:
- Good resistance to stress-corrosion cracking
- Satisfactory resistance to pitting and crevice corrosion
- Good resistance to oxidising and non-oxidising hot acids
- Good mechanical properties at both room and elevated temperatures, up to approximately 550°C (1020°F)
- Permission for pressure-vessel use at wall temperatures up to 425°C (800°F)
Designation and Standards
| Country National Standards |
Material Designation |
Specification | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Chem. Compo- sition |
Tube & Pipe | Sheet & Plate |
Rod & Bar |
Strip | Wire | Forgings | |||
| Seamless | Welded | ||||||||
| France AFNOR |
NC21FeDU | ||||||||
| Germany DIN VdTÜV |
W.-Nr . 2.4858 NiCr21Mo |
17744 432 |
17751 432/2 |
17750 432/1 |
17460 412/434 |
17750 432/1 |
17460 412/434 |
||
| United Kingdom BS |
NA 16 | 3074 | 3072 | 3076 | 3073 | ||||
| USA ASTM ASME AMS |
UNS N08825 | B423 SB423 |
B163 B704/705 SB163 |
B424 SB424 |
B425 SB425 |
B424 SB424 |
B564 SB564 |
||
| ISO | NiFe30Cr21Mo3 | ||||||||
Chemical Composition (%)
| Alloy 825 | Ni | Cr | Fe | C | Mn | Si | Cu | Mo | Al | Ti | P | S |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | 38.0 | 19.5 | bal. | 1.5 | 2.5 | 0.6 | ||||||
| Max | 46.0 | 23.5 | 0.05 | 1.0 | 0.5 | 3.0 | 0.403.5 | 0.2 | 1.2 | 0.020 | 0.010 |
Mechanical Properties
The following properties are applicable to alloy 825 in the soft-annealed (stabilising annealed) condition and indicated size ranges.
Specified properties of material outside these size ranges are subject to special enquiry.
| Form | Dimensions | Tensile Strength |
0.2% Yield Strength |
0.2% Yield Strength |
Elong A5 % |
Brinell Hardness HB |
||||
|---|---|---|---|---|---|---|---|---|---|---|
| mm | in | N/mm2 | Ksi | N/mm2 | Ksi | N/mm2 | Ksi | |||
| Sheet,Strip cr Plate hr |
0.5-6.4 | 0.018-0.25 | 585 | 85 | 240 | 35 | 265 | 38 | 30 | ≤ 200 |
| 5-100 | 3/16 -4 | 585 | 85 | 240 | 35 | 265 | 38 | 30 | 135-165 | |
| Rod, Bar cf hf |
1.6-64 | 1/16-2.1/2 | 585 | 85 | 240 | 35 | 265 | 38 | 30 | - |
| 25-100 | 1-4 | 585 | 85 | 240 | 35 | 265 | 38 | 30 | - | |
| > 100-240 | >4-9.1/2 | 550 | 80 | 220 | 32 | 250 | 36 | 35 | - | |
| Tube, Pipe hf cf |
64-240 | 2.1/2-9.1/2 | 530 | 75 | 180 | 25 | - | - | 30 | - |
| 5-100 | 3/16 -4 | 585 | 85 | 240 | 35 | 265 | 38 | 30 | - | |
| Condenser and heat exch. tube |
16 -76 | 5/8 -3 | 585 | 85 | 240 | 35 | 265 | 38 | 30 | - |
Minimum mechanical properties at room temperature (ASTM) Please Note: The figures quoted are intended for guidance only. For further information, please refer to the standards listed or contact our sales or QA department.
Conditional Stress Values
The higher conditional stress values of up to 90% of the yield strength at temperature may be used for applications in which slightly greater deformation is acceptable. These stresses may result in dimensional changes due to permanent strain and are not recommended for flanges of gasketed joints.
Metallurgical Structure
Alloy 825 has a stable face-centred cubic structure. The chemical composition and optimised annealing treatment ensure that corrosion resistance is not impaired by sensitisation.
Corrosion Resistance
Alloy 825 is a versatile general engineering alloy with resistance to corrosion in acids and alkalis under both oxidising and reducing conditions.
High nickel content gives the alloy virtual immunity to stress corrosion cracking.
Corrosion resistance is good in media as diverse as sulphuric, sulphurous, phosphoric, nitric and organic acids, alkalis such as sodium or potassium hydroxide, and aqueous chloride solutions.
The versatility of alloy 825 is illustrated by its use in nuclear fuel element dissolvers where a variety of corrosive media, e.g. sulphuric and nitric acids and sodium hydroxide, are handled in the same equipment.
Applications
Alloy 825 is used in a wide variety of applications up to a temperature of approximately 550°C (1020°F)
Typical applications include
- Components such as heating coils, tanks, crates, baskets and chains in sulphuric acid pickling plants
- Fuel element dissolvers
- Sea-water-cooled heat exchangers; offshore product piping systems; tubes and components in sour gas service
- Heat exchangers, evaporators, scrubbers, dip pipes etc. in phosphoric acid production
- Air-cooled heat exchangers in petroleum refineries
- Food processing and chemical plant
