What Is 2.4675 Alloy?
2.4675 is the German Werkstoff number for the nickel-chromium-molybdenum-copper alloy officially designated NiCr23Mo16Cu under DIN/EN standards. In North America it is tracked as UNS N06200, and commercially it is best known by Haynes International's trade name Hastelloy C-2000™.
It belongs to the Ni-Cr-Mo "C-family" of corrosion-resistant nickel alloys — a group that includes C-276 (2.4819), C-22 (2.4602), and C-4 (2.4610). What sets 2.4675 apart is a deliberate addition of 1.3–1.9 wt% copper combined with the highest chromium content in the family (22–24%). This dual-chemistry approach enables 2.4675 to resist both oxidizing and reducing acids simultaneously — a performance envelope no other single alloy in the C-family covers as completely. Jiangsu Liangyi manufactures 2.4675 (NiCr23Mo16Cu) open die forgings and seamless rolled rings to custom sizes and international standards.
Chemical plants frequently handle mixed-acid streams — sulfuric acid plus hydrofluoric acid, or alternating oxidizing and reducing conditions in the same line. C-276 handles reducing environments well but struggles with oxidizing acids. C-22 improves oxidizing resistance but falls short in HF service. 2.4675 was engineered specifically to close that gap in a single material, reducing costly alloy transitions across a processing facility.
Global Designations & Equivalents
The same alloy chemistry appears under multiple designation systems depending on the governing standard. Always verify the correct designation on the Mill Test Certificate before accepting material for code-governed projects.
| Standard System | Designation | Relevant Documents |
|---|---|---|
| DIN / EN (European) | W.Nr. 2.4675 / NiCr23Mo16Cu | EN 10090, EN 10095 |
| UNS / ASTM (American) | UNS N06200 | ASTM B574, B575, B619, B622, B626 |
| ISO | NiCr23Mo16Cu (ISO 9723) | ISO 6208 wrought nickel alloys |
| Trade Name | Hastelloy C-2000™ (Haynes Intl.) | Trademark — confirm chemistry on MTC |
| British Standard | Cross-ref to UNS N06200 | BS PD 970 |
| JIS (Japanese) | NCF2000 (informal cross-reference) | JIS G4901 |
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Trade names like "Hastelloy C-2000" are manufacturer-specific. For NACE MR0175, ASME, or API 6A projects, the MTC must reference UNS N06200 or the W.Nr. 2.4675 — a trade name alone is insufficient for code compliance. Require the UNS designation in your purchase order specification.
Chemical Composition & Element Roles
Understanding each element's function helps procurement engineers verify that an MTC genuinely represents 2.4675 — and explains why substituting a "similar" Ni-Cr-Mo alloy can cause premature in-service failure.
| Element | Range (wt%) | Engineering Role |
|---|---|---|
| Nickel (Ni) | 51.0 – 61.7 (balance) | Austenitic matrix; baseline corrosion resistance and toughness |
| Chromium (Cr) | 22.0 – 24.0 | Forms passive chromia layer — oxidizing acid resistance; highest Cr in the C-family |
| Molybdenum (Mo) | 15.0 – 17.0 | Reducing acid resistance; pitting and crevice corrosion resistance (major PREN contributor) |
| Copper (Cu) | 1.3 – 1.9 | Signature element — enhances HF and dilute H₂SO₄ resistance; absent from C-276 and C-22 |
| Iron (Fe) | 0 – 3.0 | Residual; controlled to preserve corrosion performance |
| Carbon (C) | 0 – 0.010 | Ultra-low carbon prevents grain boundary carbide precipitation (sensitization) |
| Silicon (Si) | 0 – 0.080 | Controlled; elevated Si degrades weldability |
| Manganese (Mn) | 0 – 0.010 | Very tightly controlled; elevated Mn degrades corrosion integrity |
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Copper modifies cathodic reaction kinetics in sulfuric and hydrofluoric acid media. In H₂SO₄, Cu raises the equilibrium potential of the alloy surface, reducing the driving force for anodic dissolution. In HF, it shifts the corrosion mode from active dissolution toward passive-like behavior. Neither Cr nor Mo alone achieves this — it requires the three-element synergy of Cr + Mo + Cu that uniquely defines 2.4675 within the C-family.
Mechanical & Physical Properties
2.4675 is always delivered in the solution-annealed condition. It is a solid-solution-strengthened alloy — there is no precipitation hardening treatment. All mechanical properties are achieved through the combined solid-solution effect of Cr, Mo, and Cu in the nickel matrix.
Key Physical Constants
| Property | Value | Engineering Note |
|---|---|---|
| Density | 8.90 g/cm³ | Approximately 2× heavier than titanium — factor into rotating equipment design |
| Thermal conductivity | 10.8 W/m·K at 100 °C | Low conductivity concentrates cutting heat — critical for machining strategy |
| Thermal expansion coefficient | 12.4 × 10⁻⁶ /°C (20–100 °C) | Similar to austenitic stainless — design flanges and gaskets accordingly |
| Modulus of elasticity | 205 GPa | Room temperature |
| Max. recommended service temperature | 450 °C (842 °F) | Above 450 °C, secondary phase precipitation risk increases significantly |
| Magnetic behavior | Non-magnetic | Fully austenitic microstructure — no ferrite, no magnetic response |
Corrosion Resistance — Real Data
Corrosion resistance claims are only meaningful with quantified data. The table below presents representative immersion test results for solution-annealed 2.4675 under standardized conditions — the numbers a corrosion engineer needs to justify material selection in project documentation.
| Corrosive Medium | Conditions | 2.4675 (mm/yr) | C-276 (mm/yr) | 316L SS (mm/yr) |
|---|---|---|---|---|
| Sulfuric acid (H₂SO₄) | 10%, 80 °C | < 0.05 | 0.08 – 0.15 | > 1.2 |
| Sulfuric acid (H₂SO₄) | 50%, 60 °C | < 0.10 | 0.12 – 0.20 | > 5.0 |
| Hydrofluoric acid (HF) | 20%, 50 °C | < 0.08 | 0.10 – 0.18 | > 2.5 |
| Hydrochloric acid (HCl) | 5%, 50 °C | < 0.05 | < 0.05 | > 3.0 |
| Phosphoric acid (H₃PO₄) | 85%, 80 °C | < 0.15 | 0.20 – 0.35 | > 2.0 |
| Mixed acid (H₂SO₄ + HF) | 5% + 5%, 60 °C | < 0.12 | 0.18 – 0.30 | > 8.0 |
| Seawater (aerated) | 3.5% NaCl, 80 °C | < 0.01 | < 0.01 | 0.05 – 0.12 |
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Static immersion test results for solution-annealed material. Dynamic flow velocity, concentration gradients, and temperature cycling all modify actual in-service rates. Contact a corrosion engineer with your specific process stream conditions. For projects requiring NiCr23Mo16Cu forgings with EN 10204 3.1/3.2 MTC, Jiangsu Liangyi supplies to 50+ countries.
"In mixed H₂SO₄/HF acid environments, 2.4675 consistently outperforms C-276 — a result the PREN number alone cannot predict or explain."
PREN Value — And Its Limitations
The Pitting Resistance Equivalent Number (PREN = %Cr + 3.3 × %Mo + 30 × %N) quantifies theoretical resistance to chloride pitting. 2.4675 achieves a PREN of approximately 76 — the highest in the C-family. However, PREN was derived for chloride media only. It does not capture oxidizing or reducing acid resistance, and it is blind to the copper effect. Alloy selection for acid service must never rely on PREN alone.
2.4675 vs C-276, C-22 & Alloy 625
Engineers frequently shortlist multiple Ni-Cr-Mo alloys. The following comparison focuses on the factors that actually drive material selection decisions in acid service, sour service, and high-temperature applications.
If your process contains both oxidizing and reducing acids — especially any combination of H₂SO₄ and HF — specify 2.4675. If chloride SCC resistance in seawater is the primary concern, C-276 or C-22 is more appropriate. If mechanical performance above 500 °C governs the design, alloy 625 wins on high-temperature strength.
Heat Treatment Requirements
Unlike precipitation-hardened nickel alloys, 2.4675 has exactly one valid heat treatment: solution annealing followed by rapid water quench. There is no aging treatment. Stress relief annealing alone, slow cooling, or insufficient anneal temperature all leave Mo-rich sigma phase and grain boundary carbides in the microstructure — directly degrading corrosion resistance in service.
| Parameter | Standard Forgings | Large Section (>200 mm) | Nuclear / Critical |
|---|---|---|---|
| Anneal temperature | 1,080 – 1,120 °C | 1,100 – 1,130 °C | 1,110 – 1,130 °C |
| Hold time | 1 min/mm · min. 30 min | 1.5 min/mm · min. 60 min | 2 min/mm · min. 90 min |
| Quench method | Water quench (immersion) | Water quench with agitation | Witnessed water quench |
| Transfer time (furnace → quench) | < 60 seconds | < 45 seconds | < 30 seconds |
| Quench water temperature | < 40 °C | < 35 °C | < 30 °C (continuously monitored) |
| Post-quench hardness check | HB ≤ 206 (per lot) | HB ≤ 206 (per piece) | HB ≤ 200 (full surface map) |
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2.4675 begins precipitating secondary phases within seconds of leaving the furnace. For sections over 150 mm thick, transfer times exceeding 90 seconds can create a chromium-depleted zone at grain boundaries — reducing pitting resistance by up to 15% even when the anneal temperature was correct. Require timestamp-logged transfer time records from your forging supplier as a standard documentation item.
Welding Guidance
2.4675 is weldable — but not in the same way as stainless steel. The alloy's high Mo content and Cu addition require specific filler metal selection and interpass temperature discipline. Ignored, these create a weld heat-affected zone that corrodes faster than the base metal, defeating the purpose of specifying the alloy.
| Process | Recommended Filler Metal | AWS Classification |
|---|---|---|
| GTAW / TIG | ERNiCrMo-17 matching wire | AWS A5.14 ERNiCrMo-17 |
| SMAW / Stick | ENiCrMo-17 coated electrode | AWS A5.11 ENiCrMo-17 |
| GMAW / MIG | ERNiCrMo-17 · pure Ar or Ar+He shielding | AWS A5.14 ERNiCrMo-17 |
| SAW (submerged arc) | ERNiCrMo-17 + matching flux · flat position only | Heat input < 15 kJ/cm |
| Dissimilar joint (to 316L) | ERNiCrMo-3 (625-type) buffer layer first pass | AWS A5.14 ERNiCrMo-3 |
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Critical Welding Parameters
Machining Considerations
2.4675 is classified as a difficult-to-machine (DTM) material — same category as Hastelloy C-276 and Inconel 718. It work-hardens approximately 5× faster than annealed 316L during cutting, and its low thermal conductivity (10.8 W/m·K) concentrates heat at the tool–chip interface. Stainless steel cutting parameters applied to 2.4675 will cause rapid tool failure.
| Operation | Vc (m/min) | Feed (mm/rev) | DoC (mm) | Tool |
|---|---|---|---|---|
| Rough turning | 15 – 25 | 0.20 – 0.35 | 2.0 – 5.0 | Carbide M20–M30, TiAlN coated, negative rake |
| Finish turning | 20 – 35 | 0.08 – 0.15 | 0.3 – 1.0 | PVD carbide, positive rake, 0.4 mm nose radius |
| Face milling | 20 – 30 | 0.05–0.10/tooth | 1.0 – 3.0 | Carbide inserts, ≥ 60° lead angle |
| Drilling | 8 – 15 | 0.05 – 0.12 | Full diameter | Solid carbide, TiAlN, through-coolant for L/D > 4 |
| Boring (finish) | 15 – 25 | 0.05 – 0.10 | 0.2 – 0.5 | CBN insert; achieve Ra ≤ 0.8 μm in single pass |
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Rule 1 — Never dwell the tool. Any pause while the cutting tool contacts the surface work-hardens the contact zone 0.1–0.3 mm deep. The next pass hits a harder layer and accelerates tool wear exponentially.
Rule 2 — Coolant is structural, not optional. Use sulfur-free, chloride-free cutting fluid at minimum 70 bar. Chlorinated cutting fluid residue on a finished 2.4675 surface can initiate crevice corrosion in service.
Rule 3 — Never machine after cold work. If a forging has been straightened or deformed at room temperature after final heat treatment, re-anneal before final machining. Cold-worked surfaces left at final dimension greatly accelerate stress corrosion cracking in chloride environments.
Where 2.4675 Is Specified
The alloy concentrates in industries where dual-acid exposure, sour service compliance, or chemical multiservice requirements make single-alloy solutions impractical with less versatile materials.
Decision Framework: When to Choose 2.4675
2.4675 carries a significant material cost premium over austenitic stainless steels and super duplex grades. This structured framework supports objective selection decisions — and defends the choice against commercial pressure to downgrade the specification.
Sourcing Forgings in 2.4675
Forging 2.4675 is significantly more demanding than forging carbon steel or standard stainless grades. The alloy work-hardens approximately twice as fast during hot working, requiring inter-pass reheating schedules, controlled forging temperature windows (950–1,150 °C), and experienced operators to deliver consistent, fully-recrystallized microstructure.
What to Verify in a 2.4675 Forging Supplier
| Evaluation Criterion | Minimum Requirement | Why It Matters |
|---|---|---|
| Quality certification | ISO 9001:2015 | Documents process control, not just end-inspection |
| Forging press capacity | ≥ 2,000 T hydraulic + ring rolling | 2.4675 requires higher reduction forces per unit cross-section |
| Heat treatment furnace | Automatic control ±5 °C | ±10 °C variance at anneal temperature can invalidate the heat treatment |
| Quench system documentation | Timestamp-logged transfer time; water temp < 40 °C | Transfer time is the single most common heat treatment failure point |
| MTC standard | EN 10204 3.1 standard; 3.2 on request | NACE MR0175, ASME, and API 6A require traceable material chemistry |
| In-house NDT capability | UT per ASTM A388; PT/MT available | Subsurface defects in large Ni-alloy forgings must be found before shipment |
| Third-party inspection access | Open-door policy for SGS, BV, TÜV, Intertek, DNV and others | Third-party inspection is required for PED 2014/68/EU, API 6A, and ASME Section III projects |
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Established in 1997, Jiangsu Liangyi is an ISO 9001:2015 certified manufacturer specializing in 2.4675 (NiCr23Mo16Cu) open die forgings and seamless rolled rings. Our 80,000 m² facility in Jiangyin, Jiangsu Province, China operates hydraulic forging presses up to 6,300 T and seamless ring rolling machines up to 5 metres diameter, with 120,000 tonnes annual capacity. Single-piece weights from 30 kg to 30,000 kg. EN 10204 3.1/3.2 MTC standard. Exported to 50+ countries. custom 2.4675 (NiCr23Mo16Cu) forgings — product page and quote request →
Frequently Asked Questions
2.4675 (NiCr23Mo16Cu / Hastelloy C-2000 / UNS N06200) is a nickel-chromium-molybdenum-copper alloy engineered for exceptional resistance to both oxidizing and reducing acids simultaneously. It is used primarily in chemical processing equipment (sulfuric acid plants, HF alkylation units, phosphoric acid production), oil and gas wellhead and downhole components requiring NACE MR0175 sour service compliance, nuclear power plant components, and industrial turbomachinery in acid-service cooling circuits.
2.4675 (NiCr23Mo16Cu / UNS N06200) contains 1.3–1.9% copper and 22–24% chromium, giving it excellent resistance to both oxidizing and reducing acids, including mixed H₂SO₄/HF environments. Hastelloy C-276 (W.Nr. 2.4819 / UNS N10276) contains approximately 4% tungsten instead of copper and only 15% chromium, making it better suited to reducing acid environments and chloride media but significantly inferior to 2.4675 in oxidizing acid and HF service. The PREN of 2.4675 (≈76) is higher than C-276 (≈68), but the key differentiator in acid service is the copper addition in 2.4675 — which C-276 does not contain.
Yes. 2.4675 (UNS N06200) is qualified under ISO 15156-3 Table A.1 for sour service in oil and gas production environments with no upper limit on H₂S partial pressure, no upper chloride concentration limit, and service up to 232 °C (450 °F). The hardness requirement is HB ≤ 206 in the solution-annealed condition (no cold work >5% after final anneal). EN 10204 3.1 MTC with chemical composition analysis and per-piece hardness testing is the minimum documentation required. EN 10204 3.2 with third-party witness is recommended for ultra-sour wells and high-pressure service.
2.4675 requires solution annealing at 1,080–1,120 °C followed by rapid water quench. There is no aging treatment. Hold time is at least 1 minute per millimeter of section thickness (minimum 30 minutes). The single most critical parameter is transfer time from furnace to quench, which must be under 60 seconds for standard forgings and under 30 seconds for critical-grade parts — the alloy begins precipitating secondary phases immediately upon leaving the furnace. Stress relief annealing alone does not restore corrosion resistance and is not a valid alternative.
In the solution-annealed condition, 2.4675 (NiCr23Mo16Cu) forgings meet: minimum tensile strength (Rm) ≥ 750 MPa; minimum yield strength (Rp0.2) ≥ 345 MPa; minimum elongation (A₅) ≥ 40%; typical hardness HB 150–190. Typical test values exceed these minimums: Rm ≈ 780 MPa, Rp0.2 ≈ 370 MPa, A₅ ≈ 62%. All mechanical test coupons are taken from the ¼T envelope location of the thickest section, with full traceability to the heat number and EN 10204 3.1/3.2 MTC.
The primary filler metal for welding 2.4675 is ERNiCrMo-17 for GTAW/TIG and GMAW processes (AWS A5.14), and ENiCrMo-17 for SMAW/stick (AWS A5.11). Critical parameters: interpass temperature ≤ 120 °C (verified by thermocouple), heat input < 15 kJ/cm, pure Ar shielding gas for root passes, Ar + 25% He for fill and cap passes. CO₂ or Ar+CO₂ shielding gas must never be used. For corrosion-critical service, perform a full solution anneal + water quench after welding — stress relief alone does not restore the alloy's corrosion resistance.
Jiangsu Liangyi manufactures 2.4675 (NiCr23Mo16Cu) open die forgings and seamless rolled rings from 30 kg to 30,000 kg per piece. Maximum seamless rolled ring diameter: up to 6,000 mm. Maximum forged shaft length: up to 15,000 mm. Maximum forged bar/disc diameter: up to 2,000 mm. Standard lead time is 3–6 weeks depending on size and complexity. All products are supplied with EN 10204 3.1 MTC; EN 10204 3.2 with third-party witness is available on request. Request a quote at sales@jnmtforgedparts.com.
No. 2.4675 is classified as a difficult-to-machine (DTM) material that work-hardens approximately 5× faster than 316L stainless steel during cutting. Its low thermal conductivity (10.8 W/m·K vs. 15 W/m·K for 316L) concentrates cutting heat at the tool–chip interface. Recommended rough turning speed is 15–25 m/min using TiAlN-coated carbide inserts (ISO grade M20–M30) with flood coolant at minimum 70 bar. The coolant must be chloride-free and sulfur-free. Never allow the tool to dwell on the work surface, and never machine after cold work without first re-annealing the forging.