2.4975 (NiFeCr12Mo), also called Alloy 902 or UNS N09902, is a precipitation-hardening nickel–iron–chromium–molybdenum super alloy for continuous service up to 600 °C. It delivers tensile strength ≥ 1180 MPa, proof strength ≥ 835 MPa, and creep resistance retaining ~71–74% of room-temperature strength at peak temperature — making it the optimal alloy for gas turbines, steam turbines and nuclear power plant components in the 450–600 °C window.
Introduction: Why 2.4975 (NiFeCr12Mo) Matters
If you have received a drawing marked 2.4975, a specification calling for NiFeCr12Mo, or a purchase order referencing Alloy 902, Pyromet 860 or Nicrofer 4722 Mo — you are dealing with the same material. These designations all refer to a single alloy, and naming confusion is one of the most common practical problems facing procurement teams and engineers sourcing forgings for power generation and nuclear applications.
This guide resolves that confusion comprehensively. It covers the alloy's full international naming map, explains its metallurgical behaviour in plain terms, presents key mechanical and physical properties with real design data, describes the three-stage heat treatment process, and explains where and why it is specified over competing super alloys. Written for practising engineers and procurement professionals, not academic audiences.
International Designations & Trade Names
2.4975 is a DIN/EN material number. The same alloy chemistry is registered under at least five distinct cross-reference systems globally — the source of most material-identification errors in international procurement.
Procurement tip: Always confirm via UNS number N09902 when cross-referencing documents across national standards. Pyromet® 860 is a registered trademark of Carpenter Technology Corporation. Nicrofer® 4722 Mo is a registered trademark of VDM Metals GmbH. Inconel® is a registered trademark of Special Metals Corporation. Waspaloy® is a registered trademark of United Technologies Corporation. These names are cited solely for material cross-identification purposes. Jiangsu Liangyi Co., Limited has no affiliation with, and is not authorised by, any of these trademark holders.
Chemical Composition of 2.4975 (NiFeCr12Mo)
The composition of 2.4975 is precisely balanced to create a stable population of gamma-prime (γ′) precipitates within a nickel–iron matrix that resists softening under sustained stress at elevated temperatures. Every major alloying element contributes a defined metallurgical function.
| Element | Content Range (%) | Metallurgical Function |
|---|---|---|
| Nickel (Ni) | 40.0 – 45.0 | Forms the austenitic γ matrix; enables γ′ precipitation with Ti and Al |
| Iron (Fe) | Balance (~33–38%) | Reduces cost vs pure Ni alloys; widens the forging window; improves machinability |
| Chromium (Cr) | 11.0 – 14.0 | Forms protective Cr₂O₃ scale; oxidation and corrosion resistance to 600 °C |
| Molybdenum (Mo) | 5.0 – 7.0 | Solid-solution strengthening of the γ matrix; pitting corrosion resistance in Cl⁻ environments |
| Titanium (Ti) | 2.35 – 3.10 | Primary γ′ [Ni₃(Ti,Al)] former — the key strengthening mechanism; controls precipitate stability |
| Aluminium (Al) | ≤ 0.35 | Secondary γ′ former; contributes to oxidation resistance |
| Cobalt (Co) | ≤ 1.00 | Residual element; no significant effect at this level |
| Carbon (C) | ≤ 0.10 | Controlled low to minimise grain boundary carbide precipitation |
| Manganese (Mn) | ≤ 2.00 | Deoxidiser; limits hot shortness during forging |
| Silicon (Si) | ≤ 0.60 | Deoxidiser; controlled low to avoid embrittlement |
| Sulfur (S) | ≤ 0.010 | Impurity; minimised to prevent hot cracking during forging |
| Phosphorus (P) | ≤ 0.020 | Impurity; minimised for grain boundary integrity |
Why High Iron Content Is Commercially Critical
The iron content of approximately one-third of the alloy is 2.4975's most commercially decisive feature. It widens the forging temperature window substantially, allowing large 2.4975 open die forgings and seamless rolled rings to be produced on standard hydraulic press equipment without the tight thermal management that Inconel 718 demands — directly reducing conversion costs per kilogram.
Heat Treatment: The Three-Stage Precipitation Process
2.4975 achieves its properties through a three-stage heat treatment. Each stage targets a specific metallurgical outcome. Departures from specified temperatures, hold times or quench rates produce measurable property degradation — this is a material specification requirement, not a processing guideline.
Dissolves all prior precipitates. Water quench locks the supersaturated single-phase structure, preventing γ′ reformation during cooling.
Nucleates a fine, dense population of γ′ (Ni₃Ti,Al) precipitates. Initial strength increment forms in first 2–3 hours. Air cool preserves precipitate distribution.
Extended hold coarsens precipitates to optimal size for maximum coherency strengthening — determining final creep and stress-rupture properties.
Critical note: Slow cooling through 650–800 °C during either ageing step promotes deleterious Ni₃Mo-type grain boundary phases. This reduces ductility without contributing to creep strength. All Jiangsu Liangyi heat treatment furnaces use programmable cooling rate control to enforce compliance with the air-cool requirement.
Mechanical Properties — Room & Elevated Temperature
Minimum guaranteed room-temperature properties of fully heat-treated 2.4975 per DIN 17754 (longitudinal test direction, forged bars):
| Property | Symbol | Min. Guaranteed | Typical Range |
|---|---|---|---|
| Tensile Strength | Rm | 1180 MPa | 1210 – 1260 MPa |
| 0.2% Proof Strength | Rp0.2 | 835 MPa | 870 – 920 MPa |
| Elongation at Fracture | A | 15% | 18 – 22% |
| Reduction of Area | Z | — | 20 – 30% |
| Brinell Hardness | HB | — | 330 – 375 HB |
Strength Retention at Elevated Temperature
The defining engineering advantage of 2.4975 is its ability to retain a predictable fraction of room-temperature strength as service temperature increases — the characteristic that separates it from conventional Cr-Mo steels above 450 °C:
Typical reference ranges per DIN 17754 data and Jiangsu Liangyi production experience. Certified minimums per EN 10204 3.1 MTC supplied with each shipment.At 600 °C, 2.4975 retains approximately 71–74% of room-temperature tensile strength — a gradual, predictable decline driven by the stable γ′ precipitate structure that remains coherent throughout this range.
Creep & Stress-Rupture: The 100,000-Hour Design Criterion
For turbine rotors, valve spindles and nuclear structural components, designers specify creep allowables — maximum sustained stress causing no more than 1% total strain in 100,000 hours (~11.4 years continuous). At 600 °C, 2.4975 sustains approximately 400–450 MPa under this criterion per DIN 17754 — directly qualifying it for European and Asian power plant procurement specifications that state the 100,000-hour creep condition as a formal requirement.
Physical Properties
| Property | Value | Condition / Note |
|---|---|---|
| Density | 8.05–8.10 g/cm³ | Room temperature, fully heat-treated |
| Thermal Expansion (20–100 °C) | 12.8 µm/(m·K) | Mean CTE; critical for turbine clearance calculations |
| Thermal Expansion (20–500 °C) | 14.3 µm/(m·K) | At typical operating temperature range |
| Thermal Expansion (20–600 °C) | 14.9 µm/(m·K) | At maximum service temperature |
| Thermal Conductivity (20 °C) | 12.5 W/(m·K) | Increases moderately with temperature |
| Thermal Conductivity (500 °C) | 16.8 W/(m·K) | For transient thermal gradient analysis |
| Elastic Modulus (20 °C) | 203–207 GPa | Young's modulus for structural calculations |
| Elastic Modulus (600 °C) | 175–180 GPa | ~14% reduction at maximum service temperature |
| Electrical Resistivity (20 °C) | 1.18–1.22 µΩ·m | Reference for eddy-current NDE calibration |
| Melting Range | 1315–1365 °C | Solidus / liquidus; informs weld procedure |
| Specific Heat Capacity (20 °C) | 460–490 J/(kg·K) | Increases to ~530 J/(kg·K) at 500 °C |
| Magnetic Properties | Low ferromagnetic | Weakly magnetic; responds to MPI inspection |
How 2.4975 Compares to Competing Super Alloys
Inconel 718, A-286 and Waspaloy are the alloys most frequently cited as alternatives in European, Indian and Southeast Asian power plant tender documents. The comparison reflects production experience across all four materials.
Selection guidance: For power-plant and nuclear specifications at 450–600 °C, 2.4975 is the most cost-effective and forging-friendly choice. Inconel 718 earns its premium above 620 °C. A-286 is preferred for fastener assemblies. Waspaloy is for aerospace hot sections where cost is secondary.
Industrial Applications of 2.4975 (Alloy 902) Forgings
2.4975 is specified only where its combination of precipitation-hardened strength, creep resistance to 600 °C, chromia-scale oxidation protection and Mo-enhanced pitting resistance are all simultaneously required.
⚡ Gas & Steam Turbines
- Turbine discs, impellers and blisks
- Valve spindles, stems and seats (MSV/GV/CV/CRV)
- Guide rings, seal rings and labyrinth rings
- Steam turbine control and reheat valve discs
- LPT turbine casings and diaphragm nozzles
- Double-headed studs and fasteners per EN 10269
- Bearing housings and stator end caps
⚛️ Nuclear Power Plants
- Flow limiters and Venturi forgings for steam generators
- Forged tubes for pressuriser surge lines
- Reactor nozzles and primary pump flywheels
- Latch housings and rod travel housings
- End rings and rotor stack plate forgings
- RPV upper shells and HSG shells
- Containment closure heads and waste flasks
🔩 High-Temperature Fasteners
- Turbine flange bolts and studs per EN 10269
- Casing joint bolting for steam and gas turbines
- Pressure vessel closure bolting to 580 °C
- High-load dowel pins and alignment rods
🏭 Industrial Process Equipment
- Geothermal turbine components in H₂S-bearing steam
- Petrochemical reactor internals at 500–580 °C
- Compressor impellers in corrosive gas service
- Heat exchanger tube sheets for high-pressure steam
For full dimensional capabilities, turbine part lists, nuclear component references and seamless rolled ring data, see the 2.4975 / NiFeCr12Mo forging capabilities and dimensions.
Corrosion & Oxidation Resistance
Chromium (11–14%): High-Temperature Oxidation Barrier
The chromium content forms a continuous Cr₂O₃ scale in air or steam to 600 °C. In clean steam environments, oxidation rate is typically below 0.05 mm/year at 550 °C — supporting 100,000-hour design lifetimes without meaningful section loss.
Molybdenum (5–7%): Pitting Corrosion Resistance
The substantial Mo addition stabilises the passive film against localised pitting in chloride or sulphur-bearing environments. In geothermal steam and industrial gas turbines burning sulphur-bearing fuels, 2.4975 demonstrates measurably superior pitting resistance over lower-Mo alloys in the same temperature band.
Limitation: Hot Corrosion Above 650 °C
Like all chromia-forming alloys, 2.4975 is susceptible to Type II hot corrosion (sulphate-induced attack) at 650–750 °C. This exceeds the normal service envelope but should be addressed where excursion temperatures occur during start-up or shutdown in gas turbines burning contaminated fuels.
Aqueous corrosion (room temperature): Excellent resistance to fresh water, demineralised water, steam condensate at pressures up to 200 bar, and dilute HCl/H₂SO₄ below 5%. Alkali resistance excellent to 30% NaOH. Suitable for water-cooled nuclear component applications.
Weldability & Machinability
Welding 2.4975 (NiFeCr12Mo)
2.4975 is weldable by GTAW/TIG (preferred), GMAW/MIG (short circuit), and SMAW (ENiCrFe electrodes). High iron content moderates hot-cracking risk versus pure nickel-base alloys.
| Parameter | Requirement |
|---|---|
| Preheat — sections > 25 mm | 150–200 °C |
| Maximum interpass temperature | 200 °C (mandatory — not advisory) |
| Shielding gas | Argon or Ar-He blend; CO₂-rich mixes not permitted |
| Full post-weld heat treatment | Three-stage cycle: 1090 °C solution + double ageing |
| Stress relief only (minor repairs) | 720 °C / 8 h / air cool |
| Nuclear application welds | WPS/PQR qualification per ASME, RCC-M or PNAE |
Machining 2.4975
Machinability index approximately 40% vs free-cutting steel baseline — significantly better than Inconel 718 (~20%) or Waspaloy (~12%). Key rules: use fresh sharp tooling; flood coolant mandatory; prefer climb milling; final grinding achieves Ra < 0.8 µm more reliably than turning for critical surfaces.
Sourcing & Procurement Guide
Jiangsu Liangyi Co., Limited has manufactured 2.4975 (NiFeCr12Mo) open die forgings and seamless rolled rings since 1997, from its 80,000 m² facility in Jiangyin, Jiangsu Province, China, using 2,000–6,300 ton hydraulic presses and 1–5 metre seamless rolling machines.
| Parameter | Capability / Commitment |
|---|---|
| Single-piece weight range | 30 kg to 30,000 kg (30 tonnes) |
| Rings — maximum OD | Up to 6,000 mm (6 metres) |
| Bars — maximum diameter | Up to 2,000 mm (2 metres) |
| Standard lead time (bars & rings) | 8–12 weeks from order confirmation |
| Complex shapes / large forgings | 12–20 weeks incl. heat treatment and NDT |
| Nuclear-grade with 3rd-party witness | Add 2–4 weeks for TPI scheduling |
| Standard mill test certificate | EN 10204 3.1 with every shipment |
| Mill test certificate | EN 10204 3.1 supplied as standard with every shipment |
| Quotation turnaround | Within 24 hours of receiving drawings and specs |
| Quality management | ISO 9001:2015 certified |
| Countries served | 50+ countries worldwide |
Frequently Asked Questions About 2.4975 (NiFeCr12Mo)
Summary: Is 2.4975 (Alloy 902) Right for Your Application?
2.4975 (NiFeCr12Mo / Alloy 902 / UNS N09902) is optimised for sustained service from 450 °C to 600 °C, where creep resistance, tensile strength retention, oxidation protection and long-term reliability are simultaneously required — and where procurement cost matters as much as peak performance.
It delivers the optimal combination: better forgeability than Inconel 718, higher strength than A-286, and a fraction of the cost of Waspaloy — all within the well-documented DIN 17754 / EN 10269 European standards framework that power generation and nuclear procurement engineers work with directly.
For custom 2.4975 open die forgings, seamless rolled rings, turbine discs, valve spindles and nuclear-grade components with EN 10204 3.1 and ISO 9001:2015, visit the product page to request a custom quotation for 2.4975 (NiFeCr12Mo) forgings.
† Trademark notice: Inconel® is a registered trademark of Special Metals Corporation. Waspaloy® is a registered trademark of United Technologies Corporation. Pyromet® 860 is a registered trademark of Carpenter Technology Corporation. Nicrofer® 4722 Mo is a registered trademark of VDM Metals GmbH. These trademarks are referenced in this article solely for technical identification and material cross-referencing purposes. Jiangsu Liangyi Co., Limited is not affiliated with, endorsed by, or authorised by any of the above trademark holders.