Inconel 625 vs Hastelloy C-276: Which Nickel Alloy for Severe Corrosion?

Specifying a nickel-based corrosion-resistant alloy (CRA) for chemical-process or offshore service almost always comes down to a binary choice: Inconel® 625 (UNS N06625) or Hastelloy® C-276 (UNS N10276). They occupy adjacent tiers in the corrosion-resistance ladder, both cost an order of magnitude more than 316L, and a wrong choice — either over-engineering or under-spec'ing — will haunt the project for its 20-30 year service life.

This guide compares the two alloys across every dimension that matters during material selection: chemistry, corrosion performance in real media, mechanical properties, weldability, cost, and a 5-step decision flowchart. All data is sourced from manufacturer datasheets and ASTM/NACE standards (see the references). Skip to the quick verdict if you only need the bottom line.

Quick verdict — which one wins?

There is no universally better alloy. The right choice depends on what is in the process stream and how hot it is. The table below summarises where each alloy is the better default.

Chemical composition compared

Both alloys are nickel-chromium-molybdenum solid solutions, but the deltas in chromium, molybdenum, tungsten and niobium are what drive every downstream property difference.

Why the chemistry matters

• Mo + W (the "reducing-acid duo"): C-276's combined Mo+W of 18-21% is the highest of any commercial Ni-Cr-Mo alloy. This is the single biggest reason it outperforms 625 in HCl, dilute H₂SO₄ and other reducing media.
• Cr (the "oxidising-acid hero"): 625's higher Cr content stabilises the protective Cr₂O₃ passive film in oxidising service (HNO₃, mixed acid). It is also the reason 625 oxidises less in dry air at high temperature.
• Nb (precipitation strengthening): 625 forms γ″ (gamma double prime) precipitates upon long thermal exposure, which raises strength but can embrittle the alloy after thousands of hours at 650-750 °C — a trade-off for high-temperature service.
• Low C and Si in C-276: minimises carbide and intermetallic-phase precipitation in welds, which is why C-276 is so weld-friendly.

Corrosion performance head-to-head

Generic PREN (Pitting Resistance Equivalent Number) is a useful first-pass screen but oversimplifies for high-Mo nickel alloys. We list it here for reference and then break out media-specific data.

Acid-by-acid behaviour

The pattern is consistent: C-276 wins reducing media; 625 holds parity or wins oxidising media. The classic test is to put a sample of each in 50% H₂SO₄ at 80 °C for 168 hours — 625 corrodes visibly while C-276 looks like it never entered the bath. Reverse the test to 65% HNO₃ at 80 °C and 625 stays bright while C-276 develops a faint scale.

Mechanical & high-temperature properties

Inconel 625 is the clear winner on strength, both at room temperature and elevated temperature. The niobium-driven γ″ precipitates carry load up to about 700 °C, which is why 625 dominates aerospace exhaust components, gas-turbine seal rings, and long-life flare-tip applications. C-276's strength advantage is in thermal-shock resistance — it tolerates rapid temperature cycling (e.g. quench- regenerator service) better than 625 because it does not age-harden.

Weldability and fabrication

Both alloys are routinely TIG, MIG, plasma-arc and submerged-arc welded with matching filler. The key fabrication notes that come up in shop QA reviews:

• Matching filler: ERNiCrMo-3 for Inconel 625; ERNiCrMo-4 for Hastelloy C-276.
• Heat input: keep below 1.5 kJ/mm to limit grain coarsening and intermetallic-phase precipitation in the HAZ.
• Inter-pass temperature: ≤ 150 °C is the standard rule; some specs go down to 100 °C for thick sections.
• Post-weld heat treatment (PWHT): not normally required for either alloy; both stay non-sensitised through normal weld thermal cycles thanks to low C content.
• Solution annealing: 625 typical 1095-1150 °C, water quench. C-276 typical 1175-1230 °C, water quench.
• Cold-forming: both formable up to ~30% reduction without intermediate anneal; beyond that, anneal between passes.

Cost, lead time and availability

The exact quote varies week-to-week with LME nickel and molybdenum, region and order quantity. For a 10 mm × 1500 mm × 6000 mm hot-rolled, solution-annealed, pickled plate FOB China, current ranges (Q2 2026):

Stock availability is comparable: both alloys are stocked in plate, sheet, bar and seamless pipe in common sizes. Custom widths or thicker than 60 mm typically pull from a 12-16 week mill rolling. For Inconel and Hastelloy items in stock, see Tisco Steel's catalogue.

5-step selection flowchart

Use this decision tree as a starting point. It does not replace a full corrosion analysis but covers ~80% of routine selections.

Typical applications side-by-side

Worked example: FGD scrubber spray header

A coal-fired power plant operating a wet-limestone FGD scrubber asked us to spec the spray header. Service: 50 °C, pH 4-6 (slurry recycle), 5,000 ppm Cl⁻, 8,000 ppm SO₄²⁻, occasional acid spikes to pH 2 during shutdown. Our recommendation: Hastelloy C-276 plate per ASTM B575. Inconel 625 was considered and would have saved ~22% on material, but the chloride/H₂SO₄ combination at the upper end of the operating window puts it inside its corrosion-rate plateau, whereas C-276 stays comfortably within its low-corrosion zone for 25-year design life.

For more on the parent alloy families, see our Inconel range (which also covers 600, 601, 718) and the Hastelloy series (C-22, B-3, X). For a full materials-science primer on the ranking, see Special Metals' Inconel 625 datasheet↗ and Haynes International's C-276 brochure↗.