EXHAUSTIVE METALLURGICAL ANALYSIS AND SPECIFICATION OF INCOLOY 825 (UNS N08825) FASTENERS
Incoloy 825 (designated as UNS N08825) is a titanium-stabilized, austenitic nickel-iron-chromium superalloy enhanced with deliberate additions of molybdenum and copper. Originally engineered to provide exceptional resistance to both oxidizing and reducing environments, it serves as a high-performance evolution of the Incoloy 800 series, specifically optimized for superior aqueous corrosion resistance.
The alloy is particularly renowned for its resilience against sulfuric and phosphoric acids, as well as its virtual immunity to chloride-induced stress-corrosion cracking. In the form of industrial fasteners—bolts, nuts, studs, and washers—Incoloy 825 provides critical structural integrity in environments where standard stainless steels would succumb to localized pitting or intergranular attack.
■ Product Overview
| Material Designation | Incoloy Alloy 825 |
|---|---|
| UNS Number | N08825 |
| Microstructural Phase | Austenitic (Face-Centered Cubic) |
| Density | 8.14 g/cm³ |
| Melting Point Range | 1370°C - 1400°C (2500°F - 2550°F) |
| Magnetic Permeability | 1.005 (at 200 oersted) |
| Maximum Operating Temp | ~540°C (1000°F) for structural applications |
| Pitting Resistance (PREN) | Typically ≥ 35 |
■ Proprietary Datasheet Download
For principal engineers requiring granular empirical data—including high-temperature yield curves, stress-relaxation models, and detailed Larson-Miller parameter charts—please access our secure portal.
Incoloy 825 / UNS N08825 — Complete Technical Datasheet
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⬇ DOWNLOAD DATASHEET■ Chemical Composition
The chemical architecture of Incoloy 825 is a carefully balanced thermodynamic system. The high nickel content ensures resistance to stress-corrosion cracking, while the addition of titanium (typically 0.6% to 1.2%) prevents chromium carbide precipitation at grain boundaries, effectively stabilizing the alloy against sensitization.
| Ni | Fe | Cr | Mo | Cu | Ti | Mn | C | Si | Al | S |
|---|---|---|---|---|---|---|---|---|---|---|
| 38.0 - 46.0 | Bal. | 19.5 - 23.5 | 2.5 - 3.5 | 1.5 - 3.0 | 0.6 - 1.2 | 1.00 max | 0.05 max | 0.50 max | 0.20 max | 0.03 max |
Values are weight percentages as per UNS N08825 and ASTM B425.
■ Mechanical Properties
Incoloy 825 fasteners exhibit robust mechanical strength and high ductility. While it maintains its oxidation resistance at higher temperatures, exposure above 540°C (1000°F) may lead to microstructural changes that reduce impact strength.
| Mechanical Parameter | Metric Value (Annealed) | Imperial Equivalent |
|---|---|---|
| Ultimate Tensile Strength | 550 - 690 MPa | 80,000 - 100,000 psi |
| 0.2% Offset Yield Strength | 220 - 338 MPa | 32,000 - 49,000 psi |
| Elongation at Break | 30% - 45% | 30% - 45% |
| Hardness (Rockwell B) | 83 - 85 HRB | 83 - 85 HRB |
| Modulus of Elasticity | 196 GPa | 28,400 ksi |
■ International Equivalent Grades
| Standard / System | Grade Designation |
|---|---|
| UNS (USA) | N08825 |
| Werkstoff / EN | 2.4858 (NiCr21Mo) |
| JIS (Japan) | NCF 825 |
| United Kingdom (BS) | NA 16 |
| France (AFNOR) | NC 21 Fe DU |
| Common Trade Name | Alloy 825, Nicrofer 4221 |
■ Key Characteristics & Industrial Applications
The specific chemical defensiveness of Incoloy 825 fasteners makes them indispensable in industries handling highly aggressive acids and chlorides.
- Chemical Processing: Equipment handling sulfuric (H₂SO₄), phosphoric (H₃PO₄), and nitric acids; used in heating coils and scrubber units.
- Oil & Gas Production: Sour gas well piping systems and offshore seawater heat exchangers where H₂S and CO₂ resistance is critical.
- Pollution Control: Flue-gas desulfurization (FGD) systems and wet scrubbers handling sulfur-containing gases.
- Nuclear & Power Generation: Nuclear fuel reprocessing systems and sheathing for electrical heating elements.
- Acid Pickling: Fasteners for heating coils, baskets, and chains exposed to aggressive acid baths.
■ Complete Range of Incoloy 825 Fasteners
| Bolts & Screws | Nuts & Washers | Studs & Rods |
|---|---|---|
| Hex Bolts / Heavy Hex Bolts | Standard Hex / Square Nuts | Fully Threaded Studs |
| Socket Head Cap Screws | Lock Nuts / Nylock Nuts | Double-End Studs |
| U-Bolts / Eye Bolts | Coupling / Wing Nuts | Threaded Rods (M2 to M160) |
| Countersunk / J-Bolts | Plain / Star Washers | Precision Dowel Pins |
■ Standards & Specifications
| Material Specs | ASTM B425 / ASME SB 425 (Rod/Bar), ASTM B564 (Forgings) |
|---|---|
| Sour Service Compliance | NACE MR0175 / ISO 15156 |
| Bolt Dimensions | ANSI/ASME B18.2.1, DIN 931, DIN 933 |
| Nut Dimensions | ANSI/ASME B18.2.2, DIN 934, ISO 4032 |
■ Mill Test Certificate (MTC)
All Incoloy 825 fasteners are supplied with an integrated EN 10204 3.1 Mill Test Certificate (MTC), providing:
- Chemical Spectrography: Verified results proving Ni, Cr, Mo, and Ti content.
- Mechanical Verification: Actual lab results for tensile, yield, elongation, and hardness.
- Complete Traceability: Linking each fastener to its unique heat number and melt origin.
- Compliance: Confirmation of NACE MR0175 and PED 2014/68/EU standards.
■ Why Choose Ananka
Ananka Fasteners is a premier manufacturer and global exporter based in Mumbai, India, specializing in high-performance fasteners for critical infrastructure.
- PED Certification: Legally qualified for high-pressure systems in the EU and global oil & gas sectors.
- Advanced Manufacturing: Utilizing modern hot forging and precision CNC centers for sizes M2 to M160.
- ISO Standards: Operating under integrated ISO 9001:2015, ISO 14001:2015, and ISO 45001:2018 systems.
- Rigorous Testing: 6-step quality checks including PMI, IGC testing, and destructive testing.
■ Frequently Asked Questions
Q1: What is the fundamental difference between Incoloy 800 and Incoloy 825?
Incoloy 825 is an evolution of the 800 series designed for superior aqueous corrosion resistance. It adds molybdenum and copper, making it significantly more resistant to pitting and crevice corrosion in acidic and chloride environments.
Q2: Is Incoloy 825 immune to stress-corrosion cracking?
Thanks to its high nickel content (min 38%), Incoloy 825 is highly resistant to chloride-ion stress-corrosion cracking, performing exceptionally well in standard industrial and marine chloride environments.
Q3: Why is titanium added to Incoloy 825 fasteners?
Titanium acts as a stabilizer. It reacts with carbon to form titanium carbides, preventing the carbon from depleting chromium at the grain boundaries, which avoids intergranular corrosion (sensitization).
Q4: What is the maximum temperature limit for Incoloy 825 fasteners?
For structural load-bearing applications, the limit is approximately 540°C (1000°F). Above this, microstructural phases can form that reduce ductility and impact toughness.
■ Secure Your Infrastructure Against Acid and Saline Corrosion
The reliability of your offshore platforms and chemical tanks depends on the uncompromising integrity of your structural fasteners. Partner with Ananka Fasteners for globally certified, precision-engineered Incoloy 825 components. Contact our technical engineering team today to submit custom CAD drawings or request a technical quote.
