What Is Refractaloy 26?
Refractaloy 26 is a precipitation-hardening nickel–chromium–cobalt–iron (Ni-Cr-Co-Fe) superalloy specifically engineered for components that must sustain high mechanical loads and resist creep deformation at continuous operating temperatures up to 760 °C (1,400 °F) — a temperature regime where most stainless steels and solution-strengthened nickel alloys rapidly lose structural integrity.
Originally developed in the mid-twentieth century for gas and steam turbine applications, Refractaloy 26 remains one of the few commercially available superalloys offering the precise combination of creep resistance, sustained tensile strength, and long-term ductility demanded by large rotating machinery in the 550–760 °C range.
Its balanced chemistry — built around a nickel–cobalt base with chromium, titanium, and molybdenum — produces a two-phase microstructure: a continuous FCC gamma (γ) matrix strengthened by finely dispersed gamma prime (γ') precipitates of ordered Ni₃Ti intermetallics. These coherent particles obstruct dislocation motion at high temperature, maintaining load-bearing capacity far beyond what solid-solution alloys can achieve.
Unlike alloys that become brittle after prolonged thermal exposure, Refractaloy 26 retains measurable ductility even after thousands of hours at service temperature — a characteristic critical in steam turbine valve stems, gas turbine blades, and petrochemical valve bodies where unexpected brittle fracture carries catastrophic consequences.
Designations & International Standards
Refractaloy 26 has been produced across multiple industrial regions for decades, resulting in several concurrent designation systems. Always cross-reference by UNS number (N07026) to eliminate ambiguity.
Chemical Composition of Refractaloy 26
The performance of Refractaloy 26 stems directly from the tightly controlled balance of its alloying elements. The table below shows the nominal composition per AMS 5760 / AISI 690. Iron is the balance element — used deliberately as a cost-effective structural diluent.
| Element | Symbol | Min % | Max % | Metallurgical Role |
|---|---|---|---|---|
| Nickel | Ni | 35.00 | 39.00 | Austenitic FCC matrix; base for corrosion resistance and phase stability |
| Cobalt | Co | 18.00 | 22.00 | Reduces stacking fault energy; solid-solution strengthening; raises solidus temperature |
| Chromium | Cr | 16.00 | 20.00 | Forms Cr₂O₃ passivation layer; oxidation and hot corrosion resistance |
| Titanium | Ti | 2.50 | 3.00 | Primary γ' precipitate former (Ni₃Ti); core creep strengthener |
| Molybdenum | Mo | 2.50 | 3.50 | Solid-solution strengthening; pitting and crevice corrosion resistance |
| Silicon | Si | — | 1.50 max | Deoxidizer; minor oxidation resistance benefit |
| Manganese | Mn | — | 1.00 max | Deoxidizer; sulfur scavenger to improve hot workability |
| Aluminum | Al | — | 0.25 max | Minor γ' contributor; controlled to prevent excess η-phase |
| Carbon | C | — | 0.08 max | Grain boundary carbides; tightly controlled for toughness balance |
| Sulfur | S | — | 0.030 max | Impurity; high levels reduce hot ductility |
| Phosphorus | P | — | 0.030 max | Impurity; controlled to maintain grain boundary toughness |
| Iron | Fe | Balance | Structural diluent; reduces raw material cost vs. pure Ni-Co alloys | |
Source: AMS 5760 / AISI 690 specification. Verify the heat analysis on the mill test certificate (MTC) for each individual lot. Key elements: Ti (2.50–3.00%) and Mo (2.50–3.50%) most directly determine creep and corrosion performance.
The Role of Each Key Alloying Element
Understanding why each element is present — and at precisely what level — enables engineers to predict service behaviour, assess material substitutions, and identify which mill certificate values matter most for a given application.
Stabilizes the FCC austenitic matrix that gives Refractaloy 26 its toughness and fabricability. Nickel prevents formation of brittle BCC phases at elevated temperatures and enables the γ and γ' phases to coexist stably over tens of thousands of service hours.
Reduces the stacking fault energy of the γ matrix, making dislocation cross-slip more difficult and directly increasing creep resistance. Cobalt also raises the solidus temperature, extending the safe operating range — a key advantage over Inconel 718 in the 650–760 °C band.
Forms a dense, adherent Cr₂O₃ oxide layer that prevents further oxidation and hot corrosion at service temperature. The 16–20% range balances maximum oxidation protection with phase stability — excessive Cr above ~22% risks σ-phase embrittlement during prolonged high-temperature exposure.
The primary precipitation hardener. During aging, titanium combines with nickel to form ordered Ni₃Ti intermetallic precipitates (γ') coherent with the FCC matrix. These fine, widely dispersed particles obstruct dislocation movement at high temperature — the core mechanism behind Refractaloy 26's creep strength.
Dissolves in the γ matrix and increases lattice friction stress through solid-solution strengthening. Molybdenum also provides resistance to pitting and crevice corrosion in chloride-containing environments common in petrochemical and offshore applications.
Acts as a cost-effective structural diluent. At the moderate concentrations present, iron does not significantly degrade high-temperature properties while substantially reducing raw material cost compared to alloys based entirely on nickel, cobalt, and molybdenum.
Mechanical & Physical Properties of Refractaloy 26
The following properties represent typical values for Refractaloy 26 in the fully heat-treated condition (solution treated + aged per AMS 5760). Actual lot values depend on section thickness, forging reduction ratio, and heat treatment parameters. Always verify against the mill test certificate (MTC) for each shipment.
| Property | Test Condition | Typical Value | Unit |
|---|---|---|---|
| Ultimate Tensile Strength (UTS) | Room temperature (20 °C) | ≥ 1,000 | MPa |
| 0.2% Proof Strength (Yield) | Room temperature (20 °C) | ≥ 750 | MPa |
| Elongation at Break | Room temperature (20 °C) | ≥ 20% | — |
| Reduction in Area | Room temperature (20 °C) | ≥ 20% | — |
| Hardness (Rockwell C) | As heat-treated | 28–36 HRC | — |
| Creep Rupture Life (100 MPa) | 760 °C | > 1,000 | hours |
| Max Continuous Service Temp. | In air / steam | 760 °C / 1,400 °F | — |
| Density | Room temperature | 8.05 | g/cm³ |
| Thermal Expansion Coefficient | Mean, 20–760 °C | ~14.5 | µm/m·°C |
| Thermal Conductivity | Room temperature | ~12 | W/m·K |
| Elastic Modulus (E) | Room temperature | ~200 | GPa |
| Melting Range | — | 1,300–1,380 | °C |
Precipitation-Hardening Heat Treatment Process
The exceptional mechanical properties of Refractaloy 26 are not inherent to the as-forged state — they are developed entirely through a precisely controlled two-stage precipitation-hardening heat treatment.
The forging is heated to the solution treatment temperature, dissolving all secondary phases into the austenitic γ matrix. This produces a uniform, single-phase microstructure as the controlled starting point for aging. The part is then quenched rapidly to suppress uncontrolled precipitation during cooling and lock in the supersaturated solid solution.
🌡 1,025 °C ± 15 °C · Air cool or rapid quenchThe solutionized forging is reheated to the aging range and held for a precisely specified time. Titanium and nickel atoms diffuse and co-cluster into ordered Ni₃Ti intermetallic particles — the gamma prime (γ') phase — nucleating coherently on the γ matrix. The size, number density, and volume fraction of these precipitates, controlled by aging time and temperature, determine the final hardness, tensile strength, and creep behaviour. Under-aging leaves insufficient precipitate volume; over-aging causes precipitate coarsening (Ostwald ripening) and property loss.
🌡 720 °C ± 10 °C · Hold 8–16 hours · Air coolMandatory acceptance testing confirms that the target microstructure and mechanical properties have been achieved. Metallographic examination verifies γ' distribution and grain size (ASTM 4–7 target). Testing also checks for absence of η-phase (hexagonal Ni₃Ti), which forms when aging is performed at excessively high temperatures and degrades toughness.
✓ ASTM Grain Size 4–7 · Tensile + Hardness + MetallographyAt Jiangsu Liangyi Co., Limited, all heat treatment is performed in calibrated furnaces with continuous data logging. Furnace time-temperature charts for both solution treatment and aging are retained and supplied as part of the documentation package with every order.
Industry Applications of Refractaloy 26
Refractaloy 26 has accumulated more than five decades of documented field service in safety-critical applications. Its combination of sustained high-temperature strength, oxidation resistance, and maintained ductility makes it irreplaceable in the following industries.
Turbine disks, compressor disks, blades, vanes, rotor spacer rings, and high-pressure valve bodies for industrial gas turbines and combined-cycle power plants. Continuous blade path temperatures above 600 °C demand γ' creep resistance.
Main steam valves (MSV), governor valves, control valves (CV), and combined reheat valves: spindles, stems, seats, and casing bonnets for steam circuits up to 650 °C and 160 bar. R26 resists both creep relaxation and steam-side erosion-corrosion.
Aircraft engine turbine section components produced to the AMS 5760 material specification, with ultrasonic inspection and full MTC documentation. Jiangsu Liangyi Co., Limited has supplied Refractaloy 26 forged parts to European aerospace customers.
High-temperature valve bodies, seats, plugs, stems, and piping components for hydrocarbon cracking and reforming units at 500–700 °C. The Mo content also provides pitting corrosion resistance in chloride environments.
Reactor vessel closure components, heat exchanger flanges, and pump impellers for high-temperature chemical processes where both mechanical integrity and corrosion resistance must be maintained simultaneously.
Flanged joint studs and nuts for high-pressure steam and gas circuits where conventional austenitic stainless steel bolts lose clamp load through creep relaxation. R26 bolting maintains preload and joint integrity throughout the design life.
Selected Project References
- Thailand — Canta Ratchaburi Power Plant: Refractaloy 26 forged bars for steam turbine valve assemblies; 650 °C, 160 bar service.
- China — Multiple thermal power plants (Jiangsu / Zhejiang / Guangdong): Forged turbine disks, blades, and valve components for combined-cycle power generation.
- Singapore — Petrochemical complex: R26 forged valve bodies and seats for high-temperature hydrocarbon processing.
- Germany — Power generation: Seamless rolled R26 rings for gas turbine casings and rotor components.
- UAE — 2,000 MW combined-cycle plant: Refractaloy 26 turbine blades and valve components with full MTC documentation.
- European aerospace customers: R26 forged parts for aircraft engine turbine systems with customer-specific quality plans.
Refractaloy 26 vs. Inconel 718 vs. Waspaloy — Comparison
Engineers specifying alloys for the 550–760 °C range routinely evaluate Refractaloy 26 against Inconel 718 (UNS N07718) and Waspaloy (UNS N07001). Each has distinct strengths; the right choice depends on operating temperature, stress level, and cost constraints.
| Criterion | Inconel 718 | Refractaloy 26 ★ | Waspaloy |
|---|---|---|---|
| Max Continuous Service Temp. | ~650 °C | 760 °C | 870 °C |
| Creep Resistance (650–760 °C) | Moderate | Excellent | Excellent |
| Room-Temp Tensile Strength | Very high (>1,240 MPa) | High (≥1,000 MPa) | High (~1,100 MPa) |
| Long-Term Ductility | Moderate (δ-phase risk) | Good | Moderate |
| Oxidation Resistance (to 760 °C) | Good | Very Good | Excellent |
| Relative Material Cost | Lower | Medium | Higher |
| Forgeability | Good | Good | More demanding |
| Primary Hardening Phase | γ'' (Ni₃Nb) + γ' | γ' (Ni₃Ti) | γ' (Ni₃Al/Ti) |
| Governing Material Standard | AMS 5663 / 5664 | AMS 5760 | AMS 5544 / 5706 |
| Best Application Zone | <650 °C, high static load | 550–760 °C turbine & valve | 700–870 °C high-performance turbine |
★ Refractaloy 26 highlighted in blue. "Inconel" and "Waspaloy" are registered trademarks of their respective owners. Used here for technical comparison purposes only.
Bottom line: For turbine and valve applications in the 600–760 °C band, Refractaloy 26 outperforms Inconel 718 on sustained creep life and matches Waspaloy on creep — while offering significantly better forgeability and lower cost than Waspaloy.
Why Open Die Forging for Refractaloy 26 Components?
Refractaloy 26 components are almost exclusively produced by open die forging or seamless ring rolling — not casting. This is driven by the alloy's microstructure physics and the safety requirements of the applications it serves.
1. Grain Flow Alignment
Open die forging mechanically deforms the ingot and directs the metal's internal grain flow to follow the geometry of the finished part. Grain boundaries are oriented to resist the principal stress directions in service — reducing the risk of intergranular crack initiation compared to a cast part where grain orientation is random.
2. Elimination of Casting Porosity and Segregation
Superalloy castings are susceptible to micro-shrinkage porosity, interdendritic segregation, and inclusion entrapment. Forging eliminates porosity through hydrostatic compression and produces a homogeneous internal structure verifiable by ultrasonic testing. For safety-critical rotating components, this is not optional.
3. Controlled Grain Size
The combination of forging thermomechanical processing and heat treatment produces a fine, uniform grain size (ASTM 4–7) that optimises the balance between tensile strength and creep resistance — something casting cannot reproducibly achieve.
4. 100% Ultrasonic Testability
The homogeneous microstructure of a forged Refractaloy 26 part allows reliable 100% volumetric ultrasonic inspection to tight acceptance criteria. Cast parts with dendritic structure can scatter ultrasound, limiting flaw detectability.
Jiangsu Liangyi Co., Limited produces Refractaloy 26 forgings on hydraulic presses from 2,000 to 6,000 tonnes and electro-hydraulic hammers up to 9 tonnes, enabling single-piece production from 30 kg to 30,000 kg. All forgings undergo ultrasonic testing before dispatch. View our full range of custom Refractaloy 26 open die forgings and seamless rolled rings — including dimensions, available shapes, and project references.
How to Source Certified Refractaloy 26 Forged Parts
Procurement of Refractaloy 26 forgings requires more rigour than standard carbon steel purchasing. The following checklist covers the key quality and documentation requirements experienced buyers specify for critical applications.
- Confirm the supplier holds a current ISO 9001:2015 certificate with scope covering forging, heat treatment, and non-destructive testing of nickel alloys. Request a copy and verify it is within its validity period.
- Specify Mill Test Certificates (MTC) in EN 10204 3.1 format as the minimum. For aerospace, power generation OEM supply, or projects with third-party inspection requirements, upgrade to EN 10204 3.2 — requiring a qualified independent inspector to witness testing and co-sign the certificate.
- Verify chemical composition on the MTC against AMS 5760 spec limits. Pay particular attention to Titanium (2.50–3.00%) and Molybdenum (2.50–3.50%) — the primary property-determining elements.
- Require a full heat treatment record with actual furnace charts (time-temperature data logging) for both solution treatment and aging cycles — not just a written statement of nominal parameters.
- Specify ultrasonic testing (UT) per ASTM A388 or equivalent, with written UT report and calibration certificate. State UT acceptance criteria explicitly in the purchase order.
- For rings, discs, and large cross-section bars, request metallographic grain size verification (ASTM E112) to confirm ASTM grain size 4–7 has been achieved after heat treatment.
- Require complete material traceability linking the ingot heat number to every production step through to the final dispatched piece.
- If your quality plan requires witnessing, confirm the supplier can accommodate source inspection by your nominated third-party agency before dispatch.
Jiangsu Liangyi Co., Limited is ISO 9001:2015 certified and issues MTC documentation in EN 10204 3.1 format as standard with every order. EN 10204 3.2 documents, requiring co-signature by an independent third-party inspector, can be arranged upon customer request. Source inspection by customer-nominated agencies is supported. To request a quote or review available shapes, dimensions, and project case studies, visit our Refractaloy 26 forged parts product page.
Frequently Asked Questions About Refractaloy 26
- Round bars, square bars, flat bars, hollow bars
- Seamless rolled rings (up to Ø6,000 mm)
- Discs and disks
- Valve bodies, bonnets, stems, seats, and spindles
- Turbine blades and turbine discs
- Flanges, hubs, sleeves, and bushings
- Custom near-net-shape forgings per customer 2D/3D drawings
Request a Quote for Refractaloy 26 Forged Parts
ISO 9001:2015 certified manufacturer · EN 10204 3.1 MTC standard · 3.2 available on request · 30 kg to 30,000 kg per piece · Custom shapes per drawing · 50+ countries served since 1997
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