Nickel alloy · Werkstoff 2.4618 · UNS N06007

2.4618 Forgings: UNS N06007 / NiCr22Mo6Cu / Alloy G Rolled Rings, Flanges, Shafts and Discs

Published 10 September 2020. Last updated 8 August 2026. Reviewed by the metallurgical engineering team at Jiangyin Jiangnan Metal Co., Ltd. Data referenced to ASTM B581, ASTM B582, DIN 17744 and published nickel-alloy handbooks (see references).

UNS

N06007

Werkstoff

2.4618

Nickel

~44wt %, bal.

Chromium

21–23.5wt %

Molybdenum

5.5–7.5wt %

Density

8.3g/cm³

UTS typ.

690MPa (100 ksi)

Melting

1260–1340°C

PREN ≈

43Cr+3.3Mo

Six 2.4618 engineering tools

All six run in your browser. Nothing is uploaded and nothing is stored. They are built around the UNS N06007 chemistry and the way this grade behaves in acid service, rather than around generic stainless-steel assumptions.

What is 2.4618 / UNS N06007?

2.4618 (UNS N06007, NiCr22Mo6Cu, Alloy G) contains nominally 22 % chromium, 20 % iron, 6.5 % molybdenum, 2 % copper and 2 % niobium plus tantalum, with nickel making up the balance. It belongs to the nickel-chromium-iron-molybdenum-copper family covered by ASTM B581 and ASTM B582. The alloy exists for corrosion resistance rather than strength. Chromium handles oxidising conditions, molybdenum handles reducing conditions, and the copper addition improves behaviour specifically in sulfuric and phosphoric acid. That is why the grade turns up in phosphate fertiliser plants, sulfuric acid plants, pickling lines and flue-gas desulfurisation systems.

The niobium and tantalum addition is the second thing that defines this alloy. At 1.75 to 2.50 %, Nb+Ta ties up carbon as stable niobium carbides instead of chromium carbides, which cuts sensitisation and intergranular attack in the weld heat-affected zone. That was the original selling point in the 1960s. Cleaner melting practice later made it possible to take the carbon out altogether, and that is the route Alloy G-3 (UNS N06985 / 2.4619) took.

Where 2.4618 sits between the stainless steels and the C-type alloys

Corrosion alloys form a cost and performance ladder. Type 316L is the bottom rung. 904L and Alloy 20 add nickel, molybdenum and copper for sulfuric acid duty. Alloy 825 adds nickel again, mainly for chloride stress-corrosion resistance. 2.4618 is the next step up, at roughly 44 % nickel with 6.5 % molybdenum, which gives a PREN near 43 and real hot-acid capability. Above it sit Alloy 625 and Alloy C-276. Both cost considerably more, and they are usually only worth the money when chlorides or hydrochloric acid are in the process.

2.4618 equivalent designations and standards

Engineers meet this alloy under at least six names, depending on which standards body wrote the drawing. They all describe the same chemistry. We accept purchase orders under any of them and will list the equivalents on the material test certificate if you ask.

No ASTM forging-specific specification lists N06007 by name, so forgings are normally ordered to the chemistry of ASTM B581, ASTM B582 or DIN 17744, with mechanical properties, heat treatment and NDT agreed on the purchase order. State the intended standard on your enquiry and we will confirm what can be certified.

Chemical composition of 2.4618 / UNS N06007

The composition below is per ASTM B581, ASTM B582 and DIN 17744. Percentages are by weight. A single value marked "max" is an upper limit only.

Mechanical properties of 2.4618

2.4618 is not a strength alloy. Solution-annealed UNS N06007 has roughly the strength of an austenitic stainless steel with far better acid resistance, and it work-hardens noticeably during forming and machining. The values below are typical room-temperature properties for solution-annealed wrought product.

Physical properties of 2.4618

Corrosion resistance: what 2.4618 is actually for

Alloy G exists because of one problem, which is sulfuric acid at temperature with contaminants in it. Plain austenitic stainless steels fail there. The C-type nickel-molybdenum-chromium alloys will handle it, but they cost more than the job needs unless chlorides or hydrochloric acid are involved. 2.4618 occupies the middle ground.

Intergranular attack and why Nb+Ta matters

Chromium carbides that precipitate at grain boundaries between roughly 600 and 900 °C strip chromium from the metal next to them and open up a corrosion path. In 2.4618 the niobium and tantalum take the carbon first, so the alloy tolerates welding and slow cooling better than an unstabilised grade at the same carbon level. It is not immune, though. A proper solution anneal and water quench after forging is still essential, and ASTM G28 Method A (boiling ferric sulfate in 50 % sulfuric acid) is the accepted acceptance test. Put it on the purchase order if your service is severe, because no supplier runs it automatically.

2.4618 compared with G-3, 825, 904L, 625 and C-276

The question we get most often on this grade is whether to stay with 2.4618 or move to a neighbour. Here is the short version.

PREN calculated as Cr + 3.3 Mo at nominal chemistry, for ranking only. Relative cost is an order-of-magnitude indication of raw material with 316L as 1×, and it moves with the nickel and molybdenum markets.

2.4618 (Alloy G) or 2.4619 (Alloy G-3)?

If the part will be welded into a fabrication, G-3 is usually the better specification. If the drawing calls out 2.4618 or N06007, supply 2.4618. G-3 caps carbon near 0.015 % instead of 0.05 % and drops Nb+Ta to around 0.5 % max, which gives better heat-affected-zone behaviour without relying on stabilisation. G-3 has largely taken over for new construction, while 2.4618 keeps being ordered for replacement parts, legacy plant and drawings written before the change. Both forge the same way, and we supply Alloy G-3 / UNS N06985 from the same shop.

Forging and heat treatment of 2.4618

Nickel alloys punish sloppy thermal practice far more than carbon steel does. 2.4618 has roughly a quarter of the thermal conductivity of steel, so it heats and cools slowly through section. The hot-working window is narrow. And it picks up sulfur readily from fuel-fired furnaces. Here is how we run UNS N06007.

2.4618 forged product forms we supply

We forge 2.4618 / UNS N06007 to drawing in the forms below. Open-die forging covers shafts, blocks and heavy sections. Radial-axial ring rolling covers seamless rings and ring-derived flanges. Upsetting covers short large-diameter discs and hubs.

2.4618 production capability

Ring OD

200–3000mm

Disc / tube sheet Ø

to 1800mm

Shaft Ø

50–600mm

Shaft length

to 6000mm

Single piece

to 5000kg

Min order

1piece

Those figures are for nickel alloys. The shop envelope across all grades is larger, at 80 mm to 6,000 mm diameter, 10 kg to 15,000 kg and up to 12,000 mm long, but we run nickel alloys well inside it because of the narrow hot-working window and the press loads involved. Confirm the envelope for your part at enquiry.

Testing, NDT and certification for 2.4618 forgings

Welding and machining 2.4618

Welding

2.4618 is welded by GTAW, GMAW, SMAW and plasma processes. The matching filler family is ERNiCrMo-1 (AWS A5.14 bare wire) and ENiCrMo-1 (AWS A5.11 covered electrode). ERNiCrMo-3 gets substituted where availability is a problem, but check that with the corrosion engineer first. No preheat is needed. Keep interpass temperature below about 150 °C and keep heat input modest, because nickel-alloy weld pools are sluggish and heavy heat input coarsens the structure. Clean the joint to bright metal and degrease it: sulfur, lead, zinc and phosphorus from grease, marker pen or galvanised fixtures all cause grain-boundary cracking. Because of the Nb+Ta stabilisation, post-weld solution annealing is not always mandatory, but for severe acid service a full re-solution and quench after welding is the safe route.

Machining

Machinability runs around 15 to 20 % of free-machining carbon steel. Treat it like a superalloy, not like stainless. The alloy work-hardens fast, so use a rigid setup, sharp positive-rake carbide tooling and low surface speed, and never let the tool dwell or rub. Too light a feed glazes the surface and the next pass is cutting a hardened layer. Use flood coolant generously. Take deeper cuts at lower speed rather than the other way round, and change inserts on a schedule instead of waiting for the finish to go off. A starting point for turning with coated carbide is 15 to 25 m/min surface speed, 0.20 to 0.35 mm/rev feed and 2 to 4 mm depth of cut.

Where 2.4618 forgings are used

How to specify a 2.4618 forging order

Seven lines on a purchase order remove nearly every ambiguity that later turns into a dispute. Copy this structure into your enquiry.

MATERIAL:   UNS N06007 / W.Nr. 2.4618 / NiCr22Mo6Cu
            Chemistry per ASTM B581 / DIN 17744
CONDITION:  Solution annealed approx. 1150 C, water quenched
            NOT age hardenable. No ageing cycle permitted
NDT:        UT per EN 10228-4 (or ASTM E2375), class as agreed
            PT per ASTM E165. MT not applicable (non-magnetic)
CORROSION:  ASTM G28 Method A, max rate as agreed  [severe service only]
CERT:       EN 10204 3.1  (3.2 witnessed by ______ if required)
MARKING:    Heat number, grade, drawing no. Low-sulfur marking only

Eight specification mistakes on 2.4618 orders

1. Writing "solution treated and aged". 2.4618 is solid-solution strengthened. An ageing cycle does not raise strength, and it does push the part through the carbide-precipitation range. Fix: specify "solution annealed and water quenched".
2. Specifying magnetic particle testing. The alloy is non-magnetic, so MT finds nothing and the inspection report means nothing. Fix: specify liquid penetrant testing to ASTM E165 or EN ISO 3452.
3. Calling out EN 10228-3 for ultrasonic testing. That part of the standard covers ferritic and martensitic steel forgings. Fix: use EN 10228-4 for non-ferritic forgings, or ASTM E2375.
4. Ordering by trademark. A purchase order that says "Hastelloy G" can strictly only be filled by the trademark holder. Fix: order "UNS N06007 / 2.4618" and note the trade name for reference only.
5. Confusing 2.4618 with 2.4619. Those are Alloy G and Alloy G-3, with different carbon and niobium levels and different HAZ behaviour. Fix: confirm which the drawing means before you buy, especially on replacement parts for old plant.
6. Leaving out the intergranular corrosion test. Chemistry and tensile testing will not detect a badly quenched forging. Fix: add ASTM G28 Method A with an acceptance rate for acid service.
7. Assuming steel machining data applies. Quoting a machining budget from stainless-steel rates leads to blown lead times. Fix: budget for roughly 15 to 20 % of free-machining steel productivity and let the forger leave less stock.
8. Silence on cobalt. N06007 permits up to 2.5 % cobalt, which some nuclear and radiation-service specifications prohibit. Fix: state the required cobalt maximum explicitly on the enquiry.

Glossary

Frequently asked questions about 2.4618 / UNS N06007

References

Page facts and how to cite this page

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