General Properties
Alloy 825 (UNS N08825) is an austenitic nickel-iron-chromium alloy with additions of molybdenum, copper and titanium. It was developed to provide exceptional resistance to numerous corrosive environments, both oxidizing and reducing.
The nickel content of Alloy 825 makes it resistant to chloride stress-corrosion cracking, and combined with molybdenum and copper, provides substantially improved corrosion resistance in reducing environments when compared to conventional austenitic stainless steels. The chromium and molybdenum content of Alloy 825 provides resistance to chloride pitting, as well as resistance to a variety of oxidizing atmospheres. The addition of titanium stabilizes the alloy against sensitization in the as-welded condition. This stabilization makes Alloy 825 resistant to intergranular attack after exposure in the temperature range which would typically sensitize un-stabilized stainless steels.
Alloy 825 is resistant to corrosion in a wide variety of process environments including sulfuric, sulfurous, phosphoric, nitric, hydrofluoric and organic acids and alkalis such as sodium or potassium hydroxide, and acidic chloride solutions.
Chemical Analysis
Typical Values (Weight %)
| Nickel | 38.0 min.–46.0 max. | Iron | 22.0 min. |
| Chromium | 19.5 min.–23.5 max. | Molybdenum | 2.5 min.–3.5 max. |
| Molybdenum | 8.0 min.-10.0 max. | Copper | 1.5 min.–3.0 max. |
| Titanium | 0.6 min.–1.2 max. | Carbon | 0.05 max. |
| Niobium (plus Tantalum) | 3.15 min.-4.15 max. | Titanium | 0.40 |
| Carbon | 0.10 | Manganese | 1.00 max. |
| Sulfur | 0.03 max. | Silicon | 0.5 max. |
| Aluminium | 0.2 max. |
Physical Properties
Density
0.294 lbs/in3
8.14 g/cm3
Specific Heat
0.105 BTU/lb-°F
440 J/kg-°K
Modulus of Elasticity
28.3 psi x 106 (100°F)
196 MPa (38°C)
Magnetic Permeability
1.005 Oersted (μ at 200H)
Thermal Conductivity
76.8 BTU/hr/ft2/ft-°F (78°F)
11.3 W/m-°K (26°C)
Melting Range
2500 – 2550°F
1370 – 1400°C
Electrical Resistivity
678 Ohm circ mil/ft (78°F)
1.13 μ cm (26°C)
Linear Coefficient of Thermal Expansion
7.8 x 10-6 in / in°F (200°F)
4 m / m°C (93°F)
Mechanical Properties
Typical Room Temperature Mechanical Properties, Mill Annealed
| Yield Strength 0.2% Offset | Ultimate Tensile Strength | Elongation in 2 in. | Hardness | ||
|---|---|---|---|---|---|
| psi (min.) | (MPa) | psi (min.) | (MPa) | % (min.) | Rockwell B |
| 49,000 | 338 | 96,000 | 662 | 45 | 135-165 |
Alloy 825 has good mechanical properties from cryogenic to moderately high temperatures. Exposure to temperatures above 1000°F (540°C) can result in changes to the microstructure that will significantly lower ductility and impact strength. For that reason, Alloy 825 should not be utilized at temperatures where creep-rupture properties are design factors. The alloy can be strengthened substantially by cold work. Alloy 825 has good impact strength at room temperature, and retains it’s strength at cryogenic temperatures.
Table 6 - Charpy Keyhole Impact Strength of Plate
| Temperature | Orientation | Impact Strength* | ||
|---|---|---|---|---|
| °F | °C | ft-lb | J | |
| Room | Room | Longitudinal | 79.0 | 107 |
| Room | Room | Transverse | 83.0 | 113 |
| -110 | -43 | Longitudinal | 78.0 | 106 |
| -110 | -43 | Transverse | 78.5 | 106 |
| -320 | -196 | Longitudinal | 67.0 | 91 |
| -320 | -196 | Transverse | 71.5 | 97 |
| -423 | -253 | Longitudinal | 68.0 | 92 |
| -423 | -253 | Transverse | 68.0 | 92 |
Corrosion Resistance
The most outstanding attribute of Alloy 825 is its excellent corrosion resistance. In both oxidizing and reducing environments, the alloy resists general corrosion, pitting, crevice corrosion, intergranular corrosion and chloride stress-corrosion cracking.
Resistance to Laboratory Sulfuric Acid Solutions
| Alloy | Corrosion Rate in Boiling Laboratory Sulfuric Acid Solution Mils/Year (mm/a) | ||
|---|---|---|---|
| 10% | 40% | 50% | |
| 316 | 636 (16.2) | >1000 (>25) | >1000 (>25) |
| 825 | 20 (0.5) | 11 (0.28) | 20 (0.5) |
| 625 | 20 (0.5) | Not Tested | 17 (0.4) |
