Incoloy 825 at a glance: key takeaways
Incoloy 825 is the common trade name for UNS N08825 / Werkstoff 2.4858. "Inconel 825," which shows up often on inquiries, is a misnomer for the same material.
It belongs to the nickel-iron-chromium (Ni-Fe-Cr) family. This is an iron-bearing corrosion-resistant alloy (CRA), and on the corrosion ladder it sits above super-austenitic stainless.
- Chemistry: ~38–46% Ni, 19.5–23.5% Cr, 2.5–3.5% Mo, 1.5–3% Cu, titanium-stabilized, balance iron (≥22%).
- Resistance: handles sour service (H2S) to NACE MR0175 / ISO 15156, resists reducing and oxidizing acids alike, and pushes the chloride-SCC threshold well past what austenitic stainless can take.
- Supply spec: flat product conforms to ASTM B424 / ASME SB-424. Welds use ERNiFeCr-1 (FM 65) filler. It comes as sheet and plate; coil availability is limited.
"Inconel 825" vs "Incoloy 825": clearing up the name
There's no real "Inconel 825." That name is just a common mix-up for Incoloy 825 (UNS N08825). The two trademarks describe different metallurgies: Incoloy covers nickel-iron-chromium alloys that keep substantial iron on purpose, whereas Inconel covers nickel-chromium(-molybdenum) alloys, such as Inconel 625, with no iron added intentionally. Since 825 carries iron and is stabilized with titanium, its correct name is Incoloy 825, not Inconel 825. Special Metals Corporation owns the Incoloy trademark.
In our own order desk experience, buyers routinely ask for "Inconel 825," and we clarify and supply the correct N08825. Getting the designation right on the purchase order and mill test certificate is what keeps receiving-inspection disputes from happening in the first place.
| Trademark line | Base chemistry | Typical grades |
|---|---|---|
| Incoloy | Nickel-iron-chromium (iron-bearing) | 825, 800, iron retained by design |
| Inconel | Nickel-chromium(-molybdenum) | 625, 600, no deliberate iron |
| Conclusion: 825 is iron-bearing and titanium-stabilized → it is an Incoloy, not an Inconel. | ||
What is Incoloy 825? Family & identity
Incoloy 825 is a nickel-iron-chromium alloy, UNS N08825 / W.-Nr. 2.4858. On the corrosion-resistant-alloy ladder, it sits one step above super-austenitic stainless: 316L → 904L → Incoloy 825 → Inconel 625 / Hastelloy C276. People reach for it once chlorides and reducing acids have worn out a 904L super-austenitic stainless steel, but a full solid-nickel 625 would cost too much and do more than the job needs. For the wider alloy context, see nickel alloys explained and the Incoloy 825 grade hub.
Chemical composition: and why each element is there
Incoloy 825 to ASTM B424 (N08825), weight percent:
| Element | Content (wt%) |
|---|---|
| Nickel (Ni) | 38.0–46.0 |
| Iron (Fe) | ≥22 (balance) |
| Chromium (Cr) | 19.5–23.5 |
| Molybdenum (Mo) | 2.5–3.5 |
| Copper (Cu) | 1.5–3.0 |
| Titanium (Ti) | 0.6–1.2 |
| Carbon (C) | ≤0.05 |
| Manganese (Mn) | ≤1.0 |
| Silicon (Si) | ≤0.5 |
| Sulfur (S) | ≤0.03 |
| Aluminum (Al) | ≤0.2 |
The job of each element: Ni, Mo, Cu, Cr, Ti
Every element in N08825 earns its place: this is a balanced alloy, not four separate trade-offs. For the wider principle, see the role of alloying elements.
| Element | What it does in Incoloy 825 |
|---|---|
| Nickel (Ni) | The high ~38–46% content lifts resistance to chloride stress-corrosion cracking far above austenitic stainless. |
| Molybdenum + Copper (Mo + Cu) | Together they give resistance to reducing acids, notably sulfuric and phosphoric acid. |
| Chromium (Cr) | Provides passivity and resistance to oxidizing acids such as nitric. |
| Titanium (Ti) | Stabilizes the alloy against sensitization and intergranular corrosion by tying up carbon, the same route used in 321/347 stainless. |
How Incoloy 825 resists corrosion: the mechanism
One balanced chemistry drives 825. That's the whole reason it exists: it covers four attack modes at once.
Sour service & NACE MR0175 / ISO 15156
With its high nickel and stable austenitic structure, Incoloy 825 resists cracking in wet H2S environments and is widely used in qualified condition for sour service (H2S). For sour duty, cite NACE MR0175 / ISO 15156 on the order so the heat is supplied and documented in the qualified metallurgical condition.
Reducing & oxidizing acids: sulfuric & phosphoric
The molybdenum-and-copper pairing resists reducing acids, which gives Incoloy 825 real sulfuric-acid resistance across a wide concentration and temperature range. Chromium, meanwhile, takes care of oxidizing acids. It's that dual resistance to both reducing and oxidizing acids that leads engineers to pick 825 over 316L or 904L in mixed-acid and fertilizer or phosphoric-acid service.
Chloride stress-corrosion cracking resistance
Austenitic stainless steels crack under tensile stress when hot chlorides are in the picture. N08825's roughly 38–46% nickel content pushes the chloride stress-corrosion cracking threshold well past anything 304 or 316 can manage. That gap is the single most common reason specifiers move up from stainless to alloy 825.
Intergranular corrosion & titanium stabilization
Incoloy 825 is titanium-stabilized. Titanium ties up carbon preferentially, so chromium carbides don't precipitate at grain boundaries during welding or service in the sensitizing range, roughly 425–815 °C. That stabilization guards against intergranular corrosion & sensitization, and it does so without needing an ultra-low-carbon grade.
PREN & pitting
Incoloy 825 has a PREN (pitting resistance equivalent) of roughly 31–40. That puts it just behind 904L when it comes to pitting and crevice resistance. Lined up by rank: 304 (~18) < 316 (~24) < 904L (~34) < Incoloy 825 (~31–40). Duplex 2205 (~35) and Super-Duplex 2507 (~43) sit alongside that group.
Mechanical & physical properties
Typical solution-annealed properties to ASTM B424 (non-magnetic, austenitic):
| Property | Value (annealed) |
|---|---|
| Tensile strength | ≥85 ksi (586 MPa) |
| Yield strength (0.2% offset) | ≥35 ksi (241 MPa) |
| Elongation | ≥30% |
| Hardness | ~75–90 HRB |
| Density | 8.14 g/cm³ |
| Melting range | ~1370–1400 °C |
| Mean CTE (20–100 °C) | ~14 µm/m·°C |
| Thermal conductivity | ~11 W/m·K |
| Elastic modulus | ~196 GPa |
| Magnetic response | Non-magnetic (austenitic) |
Equivalent grades & designations
| System | Designation |
|---|---|
| UNS | N08825 |
| Werkstoff (W.-Nr.) | 2.4858 |
| DIN | NiCr21Mo |
| EN | NiCr21Mo |
| BS | NA16 |
| JIS | NCF 825 |
| Common trade name | Incoloy 825 (misnomer: "Inconel 825") |
Full cross-walks are on the UNS / Werkstoff / JIS cross-reference.
Incoloy 825 vs the alternatives: where it sits on the CRA ladder
vs 316L & 904L (the austenitic limit)
Alloy 825 outperforms both 316L stainless and 904L once austenitic stainless hits its limit: hot chlorides that drive stress corrosion cracking, and reducing acids that move past what 904L's copper-bearing chemistry can handle. Under those thresholds, though, 904L is the smarter economic choice. There's no need to over-specify 825 when 904L's iso-corrosion limits already cover the acid concentration and temperature in question.
vs Inconel 625
Inconel 625 is a solid-nickel Ni-Cr-Mo alloy with broader resistance but higher cost. Where 825's iron-bearing chemistry already meets the sour/acid duty, specifying 625 is paying for margin you may not need. See the full Incoloy 825 vs Inconel 625 comparison.
vs Alloy 20 (acid selection)
| Grade | Family | Pick it when… |
|---|---|---|
| 316L | Austenitic SS | Moderate chlorides, no reducing-acid or SCC risk. |
| 904L | Super-austenitic SS | Sulfuric-acid and high-chloride duty within its iso-corrosion limits. |
| Incoloy 825 | Ni-Fe-Cr alloy | Mixed reducing + oxidizing acids, chloride SCC, and sour (H2S) service. |
| Alloy 20 | Ni-Fe-Cr-Cu alloy | Dedicated hot/concentrated sulfuric-acid service. |
| Inconel 625 | Ni-Cr-Mo alloy | Severe service beyond 825's envelope; higher budget. |
Standards & specifications
Incoloy 825 flat product conforms to ASTM B424 / ASME SB-424 (sheet, strip and plate for N08825). For sour applications it is specified to NACE MR0175 / ISO 15156. These are the two spec lines a buyer must put on the order.
Testing & MTC: EN 10204 3.1/3.2, PMI, IGC
An EN 10204 3.1 mill test certificate is provided with every order, a 3.1 or 3.2 certificate documents the heat chemistry and mechanical results against B424. We can furnish positive material identification (PMI) confirming N08825, and intergranular-corrosion testing per ASTM A262 on request. For how these fit together, see PMI, MTC & NDT testing.
Where Incoloy 825 is used: applications
- Oil & gas (sour service): downhole tubulars, wellhead components and gas-gathering lines, where wet H2S and chlorides show up together.
- Chemical / acid processing: heat exchangers, pickling lines and vessels that handle sulfuric and phosphoric acids, along with pollution-control and FGD duty.
- Fertilizer / phosphoric-acid service: evaporators and reactors used in phosphoric-acid plants and acid-regeneration units.
Forms, fabrication & welding
Incoloy 825 comes as sheet and plate, with coil offered only in limited form for this grade. Welding calls for an over-alloyed Ni-base filler, ERNiFeCr-1 (FM 65), which keeps the weld chemistry at least as corrosion-resistant as the base metal. Our step-by-step how to weld Incoloy 825 guide walks through the filler choice and procedure.
Need to specify or source the grade? Head to Incoloy 825 sheet, Incoloy 825 plate, or Incoloy 825 coil (limited). The grade selector and weight calculator will help you confirm the grade and work out section weight.
FAQ
Is "Inconel 825" the same as Incoloy 825?
Is Incoloy 825 a stainless steel or a nickel alloy?
Is Incoloy 825 suitable for sour service?
What is the PREN of Incoloy 825?
What is the maximum temperature for Incoloy 825?
Where can I buy Incoloy 825 sheet and plate?
Source genuine Incoloy 825: RFQ
Nandini Steel has been operating as an ISO 9001:2015-certified stockist and supplier since 2003, supplying genuine, mill-traceable Incoloy 825 (UNS N08825) sourced from reputable producers. The material is held ex-stock as sheet and plate, ready for immediate dispatch. Every order ships with an EN 10204 3.1/3.2 mill test certificate carrying full heat and cast traceability. PMI and IGC testing can be arranged on request, and live pricing is quoted on inquiry.
Send your spec, grade, form, thickness, quantity and any NACE MR0175 requirement, to our team for a quote: Incoloy 825 sheet, Incoloy 825 plate, or the Incoloy 825 grade hub. Reach us by email at reachus@nandinisteel.com. You can also call +91 22 43404600 or drop a message on WhatsApp at +91 99202 09184.