Inconel 625 vs Hastelloy C276: A Complete Alloy Comparison

Inconel 625 (UNS N06625) and Hastelloy C276 (UNS N10276) are two of the most widely specified nickel-based alloys in the world. Both belong to the Ni-Cr-Mo family, both offer exceptional corrosion resistance, and both are used in some of the harshest environments on Earth.

This guide provides the composition, corrosion, mechanical, welding, cost, and application data.

For a broader overview of Inconel 625 properties, applications, and product forms, see our comprehensive Inconel 625 guide hub page. This article is part of that series, focusing specifically on the head-to-head comparison with Hastelloy C-276.

What Are Inconel 625 and Hastelloy C-276?

Inconel 625 is a nickel-chromium-molybdenum-niobium alloy engineered for high strength and oxidation resistance at elevated temperatures. Hastelloy C-276 is a nickel-molybdenum-chromium-tungsten alloy engineered for maximum corrosion resistance in aggressive chemical environments.

Inconel 625 (UNS N06625 / W.Nr. 2.4856)

Developed in the 1960s by Inco (now Special Metals), Inconel 625 was originally created for steam-line piping in ultra-supercritical power plants. Its key innovation was the addition of niobium (3.15–4.15%) alongside molybdenum (8–10%), which provides solid-solution strengthening without requiring precipitation hardening. The result is an alloy with outstanding strength from cryogenic temperatures up to 980°C, excellent fatigue resistance, and superior weldability.

Today, Inconel 625 is used across aerospace, oil and gas, marine, nuclear, and chemical processing.

Hastelloy C-276 (UNS N10276 / W.Nr. 2.4819)

Developed by Haynes International, Hastelloy C276 evolved from the earlier Hastelloy C (which suffered from sensitization during welding). The breakthrough was reducing carbon to ultra-low levels (≤0.010%), which eliminated the grain-boundary chromium carbide precipitation that caused intergranular corrosion in the heat-affected zone after welding.

Combined with very high molybdenum (15–17%) and tungsten (3–4.5%), C-276 delivers what many consider the best all-around corrosion resistance of any commercial alloy.

Hastelloy C276 is the workhorse of chemical processing, pollution control, pulp and paper bleach plants, pharmaceutical equipment, and waste treatment incinerators. It excels in environments where reducing acids, chlorides, and mixed chemicals make other materials fail.

How Do Their Chemical Compositions Differ?

The three compositional differences that drive most performance divergence are: molybdenum (9% in 625 vs 16% in C-276 — controls reducing-acid resistance), niobium (3.15–4.15% in 625 vs zero in C-276 — controls high-temperature strength), and tungsten (zero in 625 vs 3–4.5% in C-276 — synergizes with Mo for crevice corrosion resistance). Carbon content also differs significantly: 0.10% max in 625 vs 0.010% max in C-276.

Which Alloy Has Better Corrosion Resistance?

Hastelloy C276 has significantly better corrosion resistance in reducing acids, chloride-rich environments, and mixed chemical media. Inconel 625 is superior only in oxidizing environments (nitric acid, high-temperature air) where its higher chromium content provides an advantage.

The Pitting Resistance Equivalent Number (PREN) is: C-276 ≈ 68, Inconel 625 ≈ 51.

PREN Higher is better.

Corrosion Resistance by Environment

Critical Pitting and Crevice Temperatures

ASTM G150 and ASTM G48 tests measure the temperature at which pitting or crevice corrosion initiates in a standardized chloride solution. Higher is better.

 

The practical implication: in seawater cooled heat exchangers where crevice corrosion is the primary failure mode, C-276 provides a 30–40°C temperature margin over 625. In ambient seawater below 60°C, both alloys perform well and the lower-cost 625 is often sufficient.

Which Alloy Is Stronger?

Inconel 625 is significantly stronger than Hastelloy C-276 at all temperatures.

At room temperature, 625 has 46% higher yield strength and 20% higher tensile strength. The strength advantage increases at elevated temperatures, where 625's niobium strengthening maintains its integrity while C276 softens.

How Do They Compare in High-Temperature Service?

Inconel 625 is superior for high-temperature service above 500°C, with a maximum service temperature of approximately 980°C for oxidation resistance and 815°C for structural/creep-limited applications.

Hastelloy C276 is not recommended for sustained service above 600°C because it loses mechanical strength and can form detrimental intermetallic phases at elevated temperatures.

Practical takeaway: if your service temperature exceeds 500°C, Inconel 625 is almost always the correct choice. If your environment is highly corrosive but at ambient or moderate temperature (below 200°C), C276's superior corrosion resistance makes it the better option.

Which Alloy Is Easier to Weld?

Both alloys have excellent weldability using all standard processes (GTAW, GMAW, SMAW, FCAW).

Hastelloy C276 has a slight edge in as-welded corrosion resistance because its ultra-low carbon eliminates sensitization without needing a stabilizer. Inconel 625 also resists sensitization thanks to niobium, but may require solution annealing after welding for critical corrosion service. C276 generally does not require post-weld heat treatment.

How Much Does Each Alloy Cost?

Hastelloy C276 is consistently 30–35% more expensive than Inconel 625 due to its higher molybdenum and tungsten content. Molybdenum and tungsten are both costly alloying elements, and C276's nearly double molybdenum content is the primary cost driver. On a large project, specifying 625 where C276 is not needed can save hundreds of thousands of dollars.

Note: Prices fluctuate with nickel, molybdenum, and tungsten commodity markets. The 30–35% premium for C-276 is relatively stable but can widen during molybdenum supply shortages. Always request current quotes for project budgeting.

Never substitute 625 for C-276 to save money if the service environment requires C-276's corrosion resistance. Conversely, never overspecify C-276 when 625 is technically sufficient — the 35% premium buys corrosion performance you may not need.

Which Industries Use Which Alloy?

Inconel 625 dominates in aerospace, oil and gas downhole, nuclear, and marine applications where high-temperature strength and mechanical integrity are primary. Hastelloy C276 dominates in chemical processing, pollution control (FGD), pulp and paper, pharmaceutical, and waste treatment where severe corrosion is the primary challenge.

Common Misconceptions

The most dangerous misconception is that C-276 is universally superior because it costs more. It is not. C-276 is a corrosion specialist that is weaker and less temperature-stable than 625. The second misconception is that 625 can replace C-276 in any environment — it cannot survive concentrated HCl or high-temperature wet chlorine service.

Misconception 1: “C-276 is always better because it is more expensive.”

False. C-276 costs more because it contains nearly double the molybdenum and significant tungsten — expensive elements. But this chemistry is optimized for corrosion, not strength. In high-temperature structural service above 500°C, C-276 will underperform 625 and may form embrittling intermetallic phases. In oxidizing environments like nitric acid, 625's higher chromium actually gives it better corrosion resistance than C-276.

Misconception 2: “Inconel 625 can handle any chemical environment.”

False. While 625 has excellent general corrosion resistance, it cannot match C-276 in concentrated hydrochloric acid, hot sulfuric acid above 40%, wet chlorine, or mixed acid environments. Specifying 625 in these environments will result in premature failure. Always verify the specific chemical medium, concentration, and temperature against published corrosion data before selecting.

Misconception 3: “Both alloys are non-magnetic.”

True for both in the annealed condition. Both Inconel 625 and Hastelloy C-276 are fully austenitic with face-centered cubic (FCC) crystal structures. They are non-magnetic at room temperature, with relative magnetic permeability approximately 1.001. However, heavy cold working can introduce slight magnetism in 625 due to strain-induced martensite formation.

Misconception 4: “You can weld them with the same filler metal.”

False and dangerous. Inconel 625 uses ERNiCrMo-3 filler; Hastelloy C-276 uses ERNiCrMo-4. While 625 filler is sometimes used for welding C-276 in dissimilar joints (because it is more widely available), using the wrong matching filler for same-metal welding can result in weld metal with inadequate corrosion resistance for the service environment. Always use the matching filler specified by the alloy manufacturer.

Frequently Asked Questions

Is Hastelloy C-276 more corrosion-resistant than Inconel 625?

Yes, in most chemical environments. C-276's PREN of ~68 (vs 625's ~51) means significantly better resistance to pitting and crevice corrosion. C-276 also dramatically outperforms 625 in reducing acids (HCl, H₂SO₄), wet chlorine, and mixed acid environments. However, 625 is superior in oxidizing environments (nitric acid) and high-temperature air, where its higher chromium content provides better oxidation resistance.

Which alloy is cheaper, Inconel 625 or Hastelloy C-276?

Inconel 625 is consistently 30–35% cheaper than Hastelloy C-276. The price difference is driven by C-276's higher molybdenum content (15–17% vs 8–10%) and tungsten addition (3–4.5%), both of which are expensive alloying elements. The premium can widen during molybdenum supply shortages.

Can Inconel 625 be used instead of Hastelloy C-276?

It depends entirely on the service environment. In seawater below 60°C, oxidizing acids, and high-temperature applications, 625 is an excellent and more economical choice. In concentrated hydrochloric acid, hot sulfuric acid above 40%, wet chlorine service, or FGD scrubber environments, 625 is NOT a suitable substitute and will fail prematurely. Always verify against corrosion data for your specific medium, concentration, and temperature.

Can both alloys be used above 900°C?

Inconel 625 can be used up to approximately 980°C for oxidation-limited service and 815°C for structural/creep-limited applications. Hastelloy C-276 is not recommended for sustained service above 600°C because its high molybdenum and tungsten content promotes formation of embrittling intermetallic phases (mu phase, eta phase) at elevated temperatures.

What filler metal should I use for welding each alloy?

Use ERNiCrMo-3 (Alloy 625 filler, AWS A5.14) for welding Inconel 625. Use ERNiCrMo-4 (Alloy C-276 filler, AWS A5.14) for welding Hastelloy C-276. Never substitute one for the other in same-metal welding. For dissimilar metal joints between the two alloys, ERNiCrMo-4 is generally preferred because it provides the corrosion resistance of the more demanding environment.

Are both alloys non-magnetic?

Yes, both are fully austenitic and non-magnetic in the annealed condition. Inconel 625 has a relative permeability of approximately 1.001; Hastelloy C-276 is similarly non-magnetic. Neither will attract a permanent magnet at room temperature.

Which alloy is better for seawater service?

For ambient seawater below 60°C, both alloys perform excellently and Inconel 625 is the more economical choice. For seawater at elevated temperatures (>60°C) or in crevice-prone geometries (tube-to-tubesheet joints, flange faces), Hastelloy C-276 is preferred due to its higher critical crevice temperature (CCT).

What is the PREN difference between Inconel 625 and Hastelloy C-276?

Inconel 625 has a PREN of approximately 51 (21.5% Cr + 3.3 × 9% Mo). Hastelloy C-276 has a PREN of approximately 68 (15.5% Cr + 3.3 × 16% Mo). The 17-point difference means C-276 provides significantly higher resistance to pitting and crevice corrosion in chloride-containing environments.