Alloy Overview & Designation System
When procurement engineers, metallurgists, and equipment designers across the world need a nickel alloy for high-temperature oxidizing service, one designation appears on specification sheets in almost every language: 2.4851. Behind that number sits one of the most widely used heat-resistant nickel-chromium-iron superalloys ever developed — a material with a continuous service ceiling above 1,200 °C and a set of corrosion credentials that almost no iron-based alloy can match.
The alloy has accumulated multiple designations as it spread across global standards bodies, which creates genuine confusion in procurement. Here is what each label means:
| Designation | Standard / Country | Full Form | Context |
|---|---|---|---|
| 2.4851 | EN 10095 / DIN | Werkstoff number | Most common in EU, China procurement |
| NiCr23Fe | DIN / EN | Compositional shorthand | Tells you Ni base, ~23% Cr, Fe addition |
| UNS N06601 | ASTM / SAE | Unified Numbering System | Required in US ASTM standards (B564, B168) |
| Inconel® 601 | Trade name | Special Metals / PCC | Common in OEM specs & repair manuals |
| NCF 601 | JIS H 4551 | Japanese Industrial Standard | Japan / Southeast Asia procurement |
| NC23FeA | AFNOR | French national standard | French-language engineering documents |
| NA 49 | BS 3076 | British Standard | UK specifications and legacy documentation |
2.4851, NiCr23Fe, UNS N06601, and Inconel 601 are four names for the same alloy. When requesting quotes from manufacturers, you may use any designation — a reputable forging supplier will recognize all four instantly. On this page, we use 2.4851 as the primary reference, consistent with EN standards.
A Brief History of the Alloy
The alloy now designated 2.4851 was developed in the early 1960s by the International Nickel Company (INCO) as a direct response to industrial demand for a material that could survive the increasingly severe thermal environments inside petrochemical furnaces, heat treatment equipment, and power generation turbines. The addition of approximately 1.4% aluminum — a minor but decisive change from earlier NiCr alloys — fundamentally transformed its oxidation behavior by enabling a dual-layer protective oxide scale consisting of both chromia (Cr₂O₃) and alumina (Al₂O₃). That innovation remains the alloy's defining metallurgical feature over six decades later.
Today, Jiangsu Liangyi Co., Limited manufactures a full range of open die forgings and seamless rolled rings in 2.4851 alloy for customers in more than 50 countries. Based in Jiangyin, Jiangsu Province, the company has produced custom 2.4851 components for over 25 years, supplying end-users in oil & gas, nuclear power, thermal processing, and industrial furnace sectors globally.
Chemical Composition & Key Elements
The composition of 2.4851 is tightly controlled across ASTM B168 (sheet/plate/strip), ASTM B564 (forgings), and EN 10095. The following table shows the ranges permitted under each major standard:
| Element | ASTM B564 (wt%) | EN 10095 (wt%) | Typical / Aim |
|---|---|---|---|
| Nickel (Ni) | 58.0 min | 58.0–63.0 | ~60% |
| Chromium (Cr) | 21.0–25.0 | 21.0–25.0 | ~23% |
| Iron (Fe) | Balance | Balance (~14%) | ~14% |
| Aluminum (Al) | 1.0–1.7 | 1.0–1.7 | ~1.4% |
| Carbon (C) | 0.10 max | 0.05–0.10 | 0.05% |
| Manganese (Mn) | 1.0 max | 1.0 max | 0.5% |
| Silicon (Si) | 0.5 max | 0.5 max | 0.2% |
| Sulfur (S) | 0.015 max | 0.015 max | <0.005% |
| Copper (Cu) | 1.0 max | 1.0 max | 0.1% |
Role of Each Major Element
Nickel (~60%) — the structural backbone. The high nickel base gives the alloy austenitic face-centered-cubic (FCC) crystal structure stability across the entire use temperature range. Nickel resists chloride stress corrosion cracking, maintains ductility at cryogenic temperatures, and provides the fundamental solid-solution matrix in which all other alloying effects operate.
Chromium (~23%) — the oxidation and corrosion workhorse. At 21–25 wt%, chromium forms the primary protective chromia (Cr₂O₃) layer that shields the alloy from oxidizing gases, hot combustion products, and many acids. The 23% target places 2.4851 significantly higher in chromium than Inconel 600 (2.4816, NiCr15Fe) at ~15% Cr, which directly explains its superior high-temperature oxidation resistance.
Aluminum (~1.4%) — the secret differentiator. This seemingly small addition is the most important feature distinguishing 2.4851 from most other Ni-Cr alloys. Aluminum reacts preferentially with oxygen to form alumina (Al₂O₃), co-existing with the chromia layer to create a dense, dual-scale oxide. The alumina component dramatically reduces the oxide growth rate — making the alloy significantly more resistant to scale spallation during thermal cycling.
"The aluminum addition in 2.4851 doesn't just improve oxidation resistance — it fundamentally changes the oxide scale architecture from a single Cr₂O₃ layer to a multi-barrier Cr₂O₃ / Al₂O₃ system. That is why it can sustain 1,200 °C cycling that would destroy most competing alloys."
Iron (~14%) — the economic and microstructural moderator. The significant iron content lowers raw material cost versus purely nickel-base alloys. The Ni-Cr-Fe ternary system achieves full austenite stability at room temperature without additional stabilizers. Iron also increases the alloy's thermal expansion coefficient relative to nickel-only alloys, which must be accounted for in joint design and flange specifications.
Mechanical Properties at Temperature
One of 2.4851's most valued engineering attributes is its retention of meaningful mechanical strength at temperatures where carbon steel and most stainless grades have ceased to carry structural load. The tables below present properties for annealed condition material — the standard delivery condition for forgings:
| Temperature | UTS (MPa) | 0.2% Proof Stress (MPa) | Elongation (%) |
|---|---|---|---|
| 20 °C (RT) | 650–750 | 240–310 | ≥ 30 |
| 200 °C | 600–680 | 180–240 | ≥ 28 |
| 400 °C | 560–640 | 165–215 | ≥ 25 |
| 600 °C | 500–580 | 150–200 | ≥ 25 |
| 800 °C | 320–400 | 120–170 | ≥ 30 |
| 1,000 °C | 100–150 | 60–90 | ≥ 40 |
| 1,100 °C | 50–80 | 30–55 | ≥ 45 |
Strength Retention at High Temperature
The bars below show what percentage of room-temperature UTS is retained as temperature rises. The shift from navy to orange indicates the transition from "structural" to "limited load-bearing" service.
| Physical Property | Value | Condition |
|---|---|---|
| Density | 8.06 g/cm³ | Room temperature |
| Melting Range | 1,320–1,368 °C | — |
| Thermal Conductivity | 13.8 W/m·K | 25 °C |
| Thermal Conductivity | 24.5 W/m·K | 800 °C |
| Mean CTE (20–1,000 °C) | 15.3 μm/m·°C | Average over range |
| Specific Heat Capacity | 448 J/kg·°C | Room temperature |
| Hardness (annealed) | 150–200 HB | Annealed delivery condition |
With thermal conductivity of only ~13.8 W/m·K at room temperature (compared to ~50 W/m·K for carbon steel), heat dissipates slowly during forging. This requires experienced die design and careful cooling rate management to avoid thermal gradients in large cross-sections. Jiangsu Liangyi's process engineers account for these thermal effects in every 2.4851 forging program.
Oxidation & Corrosion Resistance
The primary reason 2.4851 is specified over competing alloys in industrial thermal environments is its extraordinary resistance to high-temperature oxidation. Understanding the mechanism — and its limits — is essential for correct material selection.
The Dual-Layer Oxide Scale
When 2.4851 is exposed to oxidizing atmospheres above approximately 600 °C, two competing oxide-forming reactions occur simultaneously on the metal surface:
- Chromia formation: 2Cr + 3/2 O₂ → Cr₂O₃ — The primary barrier layer.
- Alumina formation: 2Al + 3/2 O₂ → Al₂O₃ — A sub-layer that forms at the oxide-metal interface.
The resulting composite oxide — a "Cr₂O₃ outer / Al₂O₃ inner" architecture — is far more resistant to spallation during thermal cycling than a pure chromia scale. Alumina grows at a rate roughly 10× slower than chromia, so the combined scale is self-limiting: even when the outer chromia layer cracks during a rapid temperature change, the alumina sub-layer provides a second line of defense that dramatically slows oxygen diffusion to the base metal.
Corrosion Performance by Environment
| Environment | Performance Rating | Notes |
|---|---|---|
| Oxidizing atmosphere (>600 °C) | Excellent | Core strength — dual Cr₂O₃/Al₂O₃ scale |
| Cyclic oxidation (thermal cycling) | Excellent | Best-in-class vs commercial Ni-Cr-Fe alloys |
| Carburizing atmospheres | Very Good | Al₂O₃ barrier limits carbon ingress significantly |
| Nitriding atmospheres | Very Good | Similar barrier effect as carburizing service |
| Steam at high temperature | Very Good | Well established in reformer furnace tubes >900 °C |
| Oxidizing acids (HNO₃) | Good | High Cr content provides adequate passivation |
| Alkaline solutions (NaOH) | Good | High Ni base resists stress corrosion cracking |
| Reducing acids (HCl, H₂SO₄) | Limited | Low Mo; consider 2.4819 or 2.4602 instead |
| Sulfur-containing gases (H₂S) | Moderate | Better than SS; worse than 2.4665 (Mo-bearing) |
Why Forging Outperforms Casting for 2.4851 Components
2.4851 is supplied in many product forms — sheet, tube, bar, casting, and forging — but for structural, load-bearing components operating at elevated temperatures, open die forgings and seamless rolled rings are the preferred manufacturing route for well-understood metallurgical reasons.
The forging process subjects the 2.4851 billet to controlled compressive deformation at temperatures of approximately 900–1,150 °C. This thermomechanical working breaks up the as-cast dendritic structure, closes solidification porosity, refines grain size, and aligns the alloy's grain flow in the direction of principal stress for the intended component shape. The result is a material with measurably superior tensile strength, impact toughness, fatigue resistance, and creep performance compared to its cast equivalent.
For critical components — valve bodies, flanges, pump casings, rings for pressure vessels — the improved mechanical properties and zero-porosity microstructure achieved through forging translate directly into longer service life and lower total lifecycle cost. Jiangsu Liangyi supplies certified 2.4851 Inconel 601 forgings in a wide range of shapes, sizes, and weight classes to meet your exact project requirements.
Manufacturing Process: From Melt to Finished Forging
Understanding how a 2.4851 forging is made helps buyers evaluate supplier capability and set appropriate expectations for lead time, testing, and documentation. Jiangsu Liangyi's full-service process covers every step in-house:
Alloy Melting — VIM / VIM+ESR / Triple Melt
High-purity nickel, chromium, iron, and aluminum are vacuum induction melted (VIM) to achieve precise composition control. For critical applications requiring ultra-low inclusion content, electroslag remelting (ESR) or the full VIM+ESR+VAR triple-melt route is available. The melt path is selected to match the cleanliness requirement of the end application.
Billet Preparation & Controlled Heating
Ingots or billets are cut to weight and heated in controlled furnaces to the forging temperature window (900–1,150 °C for 2.4851). The alloy's low thermal conductivity requires multi-stage heating and careful soak times to ensure the center temperature matches the surface before forging begins.
Open Die Forging / Seamless Ring Rolling
Using hydraulic presses from 800 T to 8,000 T, the heated billet is shaped through sequential die passes. For ring-shaped components, a punched blank is placed on a ring rolling mill where simultaneous radial and axial rolling produces seamless rings in diameters from 200 mm to 5,000 mm and weights from 10 kg to 30,000 kg.
Solution Annealing Heat Treatment
All 2.4851 forgings are solution annealed at 1,100–1,200 °C followed by rapid water quench or air cool (depending on section size). Annealing dissolves carbide precipitates, relieves forging stresses, recrystallizes the worked microstructure, and establishes the correct grain size — the standard delivery condition per ASTM B564 and EN 10095.
CNC Machining to Drawing
As-forged parts are rough-machined to remove surface oxidation, then finish-machined to the customer's 2D or 3D drawing tolerances. Jiangsu Liangyi's CNC machining department handles turning, milling, drilling, boring, and tapping in-house — no subcontracting required.
Non-Destructive Testing (NDT) & Dimensional Inspection
Standard NDT includes Ultrasonic Testing (UT) per ASTM A388 or EN 10228-3, Liquid Penetrant Testing (LPT) for surface defects, and full dimensional inspection against drawing tolerances. Phased array UT, radiography, and eddy current testing are available on request.
Certification, Packaging & Global Shipment
Each delivery includes EN 10204 3.1 Material Test Certificates (MTC) covering chemical analysis, mechanical test results, heat treatment records, and NDT reports. Packaging is engineered to prevent damage during sea or air freight. Jiangsu Liangyi ships to 50+ countries directly from Jiangyin, Jiangsu, China.
Industry Applications
2.4851 (NiCr23Fe) occupies a well-defined application space: environments where temperatures exceed 800 °C, where oxidation or carburization is the principal degradation mechanism, and where structural integrity must be maintained over multi-year service intervals without replacement.
Industrial Furnace & Thermal Processing
This is historically the largest application sector for 2.4851. Radiant tubes, muffles, retorts, furnace rolls, hearth rails, baskets, fixtures, fans, and burner nozzles are all commonly manufactured from this alloy. The combination of cyclic oxidation resistance, carburization resistance, and sustained structural strength at 900–1,100 °C makes it the default choice for continuous and batch furnace internals in the heat treatment, steel processing, and ceramics industries.
Petrochemical & Reformer Furnaces
In hydrogen reforming furnaces and ethylene cracker heaters — where process gas temperatures routinely exceed 900 °C and tube inner walls are exposed to strongly reducing, carburizing conditions — the alumina sub-layer in 2.4851 provides a critical barrier against carbon ingress (metal dusting), significantly extending tube and component life versus standard austenitic stainless grades.
Valve, Pump & Pressure Vessel Components
For isolation valves, control valves, and pumps handling high-temperature process fluids above 600 °C, forged 2.4851 valve bodies, bonnets, stems, seat rings, and pump casings provide the combination of high-temperature strength, oxidation resistance, and weldability required by API 6A, ASME, and NACE standards.
Waste-to-Energy & Incineration
Municipal and industrial waste incinerators expose structural components to among the most aggressive high-temperature corrosion environments in industry — a simultaneous mix of oxidizing, chlorinating, and sulfidating conditions above 800 °C. 2.4851's proven combination of chlorine resistance (via dense chromia) and oxidation resistance (via alumina sub-layer) has made it widely specified for grate bars, hanging tubes, after-burner parts, and flue gas heat exchanger elements.
2.4851 vs Competing Alloys
No single alloy is correct for every application. The table below positions 2.4851 against its most common direct competitors so you can make cost-effective material selections:
| Alloy | DIN/EN No. | Key Difference vs 2.4851 | Choose Instead When… |
|---|---|---|---|
| Inconel 600 | 2.4816 (NiCr15Fe) | Lower Cr (~15%), no Al; cheaper but weaker oxidation resistance | Cost priority; operating temps <900 °C; no Al₂O₃ barrier needed |
| 310S Stainless | 1.4845 | Fe-based; much lower cost; acceptable to ~1,050 °C in light service | Budget-driven; non-cyclic oxidizing service below 1,000 °C |
| Inconel 625 | 2.4856 (NiCr22Mo9Nb) | High Mo and Nb; far superior corrosion in aqueous/reducing service | Seawater, reducing acids, chloride-containing process fluids |
| Hastelloy X | 2.4665 (NiCr21Fe18Mo9) | Mo addition; better sulfidation & reducing atmosphere performance | Sulfur-containing reducing environments; gas turbine combustors |
| Alloy 602 CA | 2.4633 (NiCr25FeAlY) | Higher Al (~2.3%) & Y addition; superior cyclic oxidation to 1,250 °C+ | Extremely demanding cyclic oxidation; thermal cycling >1,150 °C |
| Inconel 718 | 2.4668 (NiCr19Fe19Nb5Mo3) | Age-hardenable; 3–5× higher strength via γ″ precipitation | High mechanical load at 400–700 °C; aerospace & oil & gas fasteners |
If your operating temperature is continuously above 900 °C in an oxidizing or carburizing atmosphere, and your alloy budget falls between stainless steel and premium superalloys, 2.4851 is almost always the correct starting point. If reducing acids, high chloride, or extreme sulfur conditions dominate — start with 2.4856 or 2.4819 instead.
How to Specify Your 2.4851 Forgings
Getting an accurate quote and correct forging from any manufacturer starts with a clear specification package. Here is what to include when you contact Jiangsu Liangyi:
Send your drawings, specifications, and quantity to sales@jnmtforgedparts.com. Jiangsu Liangyi's technical team reviews every RFQ and responds with pricing, lead time, and technical confirmation within one business day. You can also view available product forms, standard dimensions, and technical specifications on the dedicated product page.