Incoloy 825
I. Implementation standards
The core technical specifications of Incoloy 825 cover American standards, European standards and national standards, targeting different product forms (pipes, plates, bars, etc.):
- American standards (ASTM/ASME):
- Seamless pipes: ASTM B163 / ASME SB163 (high – temperature corrosion – resistant pipes);
- Plates/strips: ASTM B423 / ASME SB423;
- Bars/forgings: ASTM B424 / ASME SB424, ASTM B705 / ASME SB705;
- Welded pipes: ASTM B366 / ASME SB366.
- International standards:
- European standards (EN): W.Nr. 2.4858 (Germany), NC21FeDu (France), NA16 (UK);
- Chinese national standard: GB/T 15007 corresponds to NS142 (corrosion – resistant alloy grade);
- Unified number: UNS N08825 (American unified numbering system, core identifier).
II. Name and code standard
- General name: Incoloy 825;
- Authoritative grades:
- American standard: UNS N08825;
- European standard: W.Nr. 2.4858 (Germany), NiCr21Mo3Cu (component abbreviation);
- National standard: NS142 (Chinese corrosion – resistant alloy system).
III. Chemical composition (mass fraction,%, typical value of ASTM standard)
Incoloy 825 is a nickel – chromium – iron – based alloy, with Mo, Cu, and Ti added to optimize corrosion resistance and stability:
| Element | Content Range | Core Function |
|---|---|---|
| Nickel (Ni) | 38.0 – 46.0 | Matrix, resists stress corrosion cracking |
| Chromium (Cr) | 19.5 – 23.5 | Resists oxidation, pitting corrosion and crevice corrosion |
| Iron (Fe) | Balance (≈22 – 26) | Reduces cost and assists in strengthening |
| Molybdenum (Mo) | 2.5 – 3.5 | Resists reducing media (such as sulfuric acid, phosphoric acid) |
| Copper (Cu) | 1.5 – 3.0 | Resists sulfuric acid and organic acid corrosion |
| Titanium (Ti) | 0.6 – 1.2 | Stabilizes carbon (TiC) and prevents intergranular corrosion |
| Carbon (C) | ≤0.025 | Avoids carbide precipitation and embrittlement |
| Manganese (Mn) | ≤1.0 | Improves hot working fluidity |
| Silicon (Si) | ≤0.5 | Optimizes casting/forging structure |
| Cobalt (Co) | ≤1.0 | Impurity control (usually residual elements) |
IV. Mechanical properties (solid solution treatment state, typical value)
After solution treatment (water quenching at 900 – 950°C), Incoloy 825 combines medium – high strength and high plasticity, and can maintain performance for a long time at ≤550°C:
| Performance Indicator | Typical Value (Solution State) | Remarks |
|---|---|---|
| Tensile Strength | ≥690 MPa | Can be further improved by cold working |
| Yield Strength (0.2%) | ≥275 MPa | |
| Elongation (%) | ≥30 | Excellent formability, easy for rolling/welding |
| Hardness (HB) | ~190 – 220 | Aging treatment has no obvious strengthening (different from precipitation hardening alloys) |
V. Heat Treatment Requirements
- Core Process: Solution Treatment
- Temperature: 900 – 950°C (925°C is commonly used), hold for 1 – 2 hours;
- Cooling: Water quenching (rapid cooling to uniformly dissolve elements such as Ti and Mo and ensure corrosion resistance).
- Stabilization Treatment (Optional, for Sensitization Risk)
- Scenario: If exposed to 649 – 760°C (sensitization temperature range) for a long time, intergranular corrosion needs to be prevented;
- Process: Hold at 870°C ± 10°C for 2 – 4 hours, then air cool (to promote TiC precipitation, stabilize carbon elements, and inhibit Cr₂₃C₆ precipitation).
- Processing Precautions:
- Hot working temperature: 980 – 1180°C (avoid lower than 900°C to prevent hot brittleness);
- Cold working: Easy to form in the solution state, and the hardness change after aging is small (because there is no significant precipitation strengthening phase).
VI. Main application fields
Incoloy 825, due to its “resistance to multi – element corrosion (oxidation + reduction) + wide – temperature strength”, focuses on strong corrosion + medium – high temperature environments:
- Chemical Metallurgy:
- Sulfuric acid pickling equipment: (heating pipes, tanks, chains), phosphoric acid production: (evaporators, heat exchangers);
- Resistant to dilute sulfuric acid, phosphoric acid, organic acid and strong alkali corrosion, especially resistant to sulfuric acid concentration ≤40% (boiling state).
- Marine Engineering:
- Seawater cooling heat exchangers, offshore platform pipelines: (resistant to seawater/salt spray corrosion, resistant to chloride ion pitting/crevice corrosion).
- Oil and Natural Gas:
- Acid gas field pipelines: (containing H₂S/CO₂), crude oil distillation towers: (resistant to high – temperature corrosion).
- Nuclear Energy:
- Nuclear waste treatment systems: (resistant to strong corrosive media), steam generator components: (≤550°C service).
- Special Fields:
- Food industry: (resistant to organic acids and high – temperature sterilization), pharmaceutical equipment: (resistant to chemical cleaning agents), flame – retardant alloys: (oxygen – free environments).
Supplementary Characteristics
- Corrosion resistance limitation: Not resistant to strong oxidizing acids (concentrated nitric acid, chromic acid) and strong corrosive environments containing fluoride ions;
- Weldability: Compatible with TIG, MIG, and manual arc welding, ERNiCrMo – 3 welding wire is recommended (matches corrosion resistance);
- Magnetism: Non – magnetic (austenitic matrix, no ferromagnetism in solution/stabilized state).
Incoloy 825 is a “general engineering alloy resistant to multi – element corrosion”. Its core advantage is resisting both oxidation and reduction media at the same time. When selecting materials, it is necessary to match heat treatment and processing states based on medium type, temperature, and stress level.