C-276 in reducing media — hydrochloric acid, wet chlorine. 625 where high temperature adds to corrosion, or where hot mechanical strength is required. Both are expensive; the choice turns on the medium, not the price.

Why does the PREN exceed 50?

Because 20 to 23% chromium combines with 8 to 10% molybdenum. That said, at this level PREN stops discriminating: the mechanisms that limit the alloy are no longer pitting.

Can it be welded without heat treatment?

Yes, its niobium stabilisation allows it, which is one of its practical advantages on complex assemblies. The filler metal must be of equivalent composition.

GRADE PROFILE

Alloy 625 — 2.4856 / NiCr22Mo9Nb

Alloy 625 carries at least 58% nickel, 20 to 23% chromium, 8 to 10% molybdenum and niobium. Its PREN exceeds 50. It is one of the most versatile alloys in the catalogue — and one of the most expensive, at cost index 900.

Nickel alloy
PREN 50–54
Cost index 900
Welded · Seamless · Heat exchanger
Ø 10 to 219 mm

When to choose it

In severe acidic chlorinated media, offshore, flue gas treatment, aerospace. Alloy 625 earns its place where several constraints stack — acidity, chlorides, temperature — and no cheaper grade covers them all. Niobium stabilises it, allowing welding without post-weld heat treatment.

It is also the fallback where a repair has to be made once and for all on equipment whose downtime costs more than the material.

When not to choose it

By default, on cost grounds. In an ordinary chlorinated medium, a 2507 or a 254 SMO covers the requirement for three to four times less. Alloy 625 is justified by stacked constraints, not by excess caution.

On a tight-schedule project without anticipation. Lead times are long and common sizes limited; discovering that at order stage means delaying the site.

Composition

Chemical composition (% by mass)
Element	%
C	≤ 0.1
Cr	20–23
Ni	≥ 58
Mo	8–10
Nb	3.15–4.15
Fe	≤ 5

Mechanical properties

We only publish mechanical properties tied to a specific standard and product form — welded tube, seamless tube and bar do not share the same values, and the gap routinely exceeds 30%. The figures that apply to your specification appear on the material certificate; ask us at enquiry stage.

Designations and standards

Equivalent normative designations
Reference	Designation
EN (numeric)	2.4856
EN (symbolic)	NiCr22Mo9Nb
ASTM / AISI	Alloy 625
UNS	N06625
JIS	—
AFNOR	—

Tube product standards :

ASTM B444
ASTM B704
EN 10216-5

Availability

Welded, seamless and heat exchanger tube, Ø 10 to 219 mm, to ASTM B444, B704 and EN 10216-5. Partner stock or mill depending on the size and quantity. EN 10204 3.1 material certificates supplied with the goods. ⚠️ Allow for lead times from enquiry stage.

Related grades

C-276 (N10276) — the grade for reducing acids and wet chlorine, with tungsten.
254 SMO (1.4547) — the step below in saline media, far cheaper.
Alloy 825 (N08825) — the nickel-iron-chromium route for sulphuric and phosphoric acid.

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Frequently asked questions

625 or C-276?: C-276 in reducing media — hydrochloric acid, wet chlorine. 625 where high temperature adds to corrosion, or where hot mechanical strength is required. Both are expensive; the choice turns on the medium, not the price.
Why does the PREN exceed 50?: Because 20 to 23% chromium combines with 8 to 10% molybdenum. That said, at this level PREN stops discriminating: the mechanisms that limit the alloy are no longer pitting.
Can it be welded without heat treatment?: Yes, its niobium stabilisation allows it, which is one of its practical advantages on complex assemblies. The filler metal must be of equivalent composition.