What Is 2.4617 (NiMo28) Alloy?
A Complete Material Guide for Engineers

What Is 2.4617 (NiMo28)?

2.4617 — known as NiMo28 in European industrial practice — is a binary nickel-molybdenum alloy designed for one primary mission: surviving strongly reducing chemical environments that destroy virtually every other practical engineering alloy available today.

Most corrosion-resistant alloys — Hastelloy C-grades, Inconel, duplex stainless steels — rely on a chromium-oxide passive film for protection. NiMo28 takes a fundamentally different approach. It contains almost no chromium (≤1.0%) and instead exploits the thermodynamic stability of the Ni–Mo matrix itself to resist dissolution in hydrochloric acid (HCl), hydrobromic acid (HBr), and hydrogen-rich reducing media at all concentrations.

The quantitative difference is striking: in 10% HCl at 60°C, NiMo28 shows a corrosion rate below 0.05 mm/year (ASTM G31). The same test yields greater than 10 mm/year for 316L stainless steel — a resistance advantage exceeding 200:1. No chromium-bearing alloy achieves comparable performance in concentrated reducing acids. Engineers sourcing this alloy can review available product forms, size ranges, and test certificate options on the 2.4617 NiMo28 forging parts product page.

Global Designation Equivalents

The same alloy chemistry appears under different codes depending on the standards system used. All of the following refer to the same nickel-molybdenum composition family:

Chemical Composition — Why Every Element Matters

NiMo28's performance is defined as much by what it excludes as by what it contains. Understanding each element's role lets engineers specify the right incoming inspection tests and catch non-conforming material before it enters service.

★ Fe ≤2.0%, Cr ≤1.0%, and C ≤0.020% are the three most critical incoming-inspection checkpoints. Material failing any of these limits may look identical to 2.4617 but will not perform as specified in reducing acid service.

Mechanical Properties

In the solution-annealed and water-quenched condition, 2.4617 forgings combine high tensile strength with exceptional ductility — a combination rare among corrosion-resistant nickel alloys. This mechanical profile makes the alloy well suited for heavy-wall pressure vessels, rotating pump shafts, and downhole drilling components subject to cyclic loading.

Elevated-Temperature Strength Retention

Corrosion Resistance: Where NiMo28 Leads the Field

The chart below compares measured corrosion rates (mm/year) in 10% hydrochloric acid at 60°C — the single most discriminating benchmark for alloy selection in chemical processing. All data compiled from ASTM G31 static immersion testing on production-grade alloys.

10% HCl at 60°C corrosion rate comparison (mm/year) — lower is better:

Multi-Media Corrosion Data (ASTM G31 Immersion)

Critical Limitations — Where NOT to Use 2.4617

NiMo28's extraordinary reducing-environment performance coexists with hard limits that have caused real-world catastrophic equipment failures when overlooked by engineers unfamiliar with the alloy.

Absolute Exclusions

• Nitric acid (HNO₃) at any concentration: Corrosion exceeds 5 mm/year at room temperature. No safe operating regime exists for this alloy in HNO₃.
• Oxidising salt solutions — FeCl₃, CuCl₂: Dissolved oxidising metal ions depolarise the alloy surface and trigger immediate dissolution. Even trace contamination can initiate failure.
• Oxidising atmosphere above 450°C (air or steam): No chromium means no protective oxide. MoO₃ above 795°C is volatile — mass loss can exceed several millimetres per week.
• Mixed HCl + oxidising acid streams: Even trace HNO₃ or H₂O₂ in an HCl stream switches the surface chemistry from resistance to rapid attack. Mixed streams require alloy re-selection.

Process Conditions Requiring Special Attention

• Sensitisation range 400–700°C: Holding 2.4617 in this range nucleates Mo₂C carbides at grain boundaries, locally depleting molybdenum. Always follow with solution anneal at 1,060–1,080°C plus rapid water quench.
• Hardness above 241 HB in H₂S service: Exceeding the NACE MR0175 / ISO 15156 ceiling creates susceptibility to hydrogen-assisted stress corrosion cracking. Specify and verify per individual piece, not per heat.
• Cold working without re-annealing: Residual stresses from cold forming accelerate SCC in aggressive environments. Never size, straighten, or cold-form forgings after final heat treatment without a full solution anneal and quench.

Industrial Applications by Sector

NiMo28's combination of reducing acid resistance, high tensile strength, and exceptional ductility makes it the standard material specification across six major sectors wherever reducing chemical environments are present.

For full details on available product forms — open-die forgings, seamless rolled rings, forged bars, and hollow components — in 2.4617 NiMo28, see the 2.4617 NiMo28 forged parts product page, which covers custom size ranges from 30 kg to 30,000 kg, available product forms, and how to request a quote.

Why Forging Is the Preferred Process Form for 2.4617

2.4617 can be supplied as plate, bar, casting, or forging. For high-pressure, cyclic-loaded components in aggressive chemical service, forging is the engineering standard, for four distinct structural and metallurgical reasons.

How to Specify 2.4617 Correctly: A Procurement Checklist

Based on two decades of failure analysis, the specification errors below account for the vast majority of 2.4617 field failures sourced from non-specialist suppliers. Address every item explicitly on the purchase order before placing any order for NiMo28 forgings.

On the Purchase Order — Required Clauses

• Cite both EN and UNS designations: "2.4617 per EN 10095 / UNS N10001 per ASTM B335." Never use trade names alone — they are not enforceable composition standards under any major procurement code.
• Specify heat treatment precisely: "Solution annealed at 1,060–1,080°C, water quenched." Never accept "annealed" alone — furnace annealing in the 400–700°C sensitisation range is the single leading cause of NiMo28 field failures worldwide.
• Specify melt practice: "VIM+ESR+VAR triple melt" for oil & gas or nuclear service. "VIM+VAR" is the minimum acceptable melt practice for standard chemical processing applications.
• Add hardness limit for sour service: "Maximum 241 HB (22 HRC) per NACE MR0175 / ISO 15156, measured at surface, mid-radius, and center of each individual forging piece" — not just per heat.
• Specify certificate level: EN 10204 3.1 for standard industrial. EN 10204 3.2 where required — customers may nominate their own third-party inspection authority.
• Include NDE requirements: 100% UT per ASTM A388 or EN 10228-3 for forgings above Ø100mm; MT or PT on all machined surfaces as a minimum.

At Incoming Inspection — Critical Verification Points

• Verify Mo ≥26.0% and Fe ≤2.0% by OES or XRF on every heat received. These are the two most critical chemistry checkpoints — failure of either means the material is non-conformant 2.4617.
• Perform portable Brinell hardness checks on each individual piece at minimum 3 locations per piece, regardless of MTC-reported hardness values.
• Check end-face colour coding: 2.4617 / NiMo28 is marked orange–orange–blue per DIN EN convention. Unmarked or incorrectly coded material is a non-conformance warranting quarantine.
• Request full heat traceability: each piece must carry a heat number traceable to the original VIM melt chemistry certificate and the solution anneal furnace chart with actual soak temperature and quench time.
• Review UT reports and confirm 100% volumetric scan coverage — not end-face spot checks, which are a common shortcut that leaves large internal volumes uninspected.

Frequently Asked Questions About 2.4617 (NiMo28)

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