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Material Designation: Inconel X-750
UNS Number: N07750
Werkstoff Number: 2.4669
Material Classification: Wrought Nickel-Based Superalloy, γ′ Precipitation-Hardened
Density: Approximately 8.28–8.30 g/cm³
Typical High-Temperature Capability: High-strength applications up to approximately 704°C; oxidation resistance up to approximately 982°C, depending on service conditions
Inconel X-750 is a precipitation-hardenable nickel-based superalloy developed for components that require high mechanical strength, oxidation resistance, and reliable load retention under elevated-temperature conditions. Its principal strengthening mechanism is the formation of γ′ precipitates during controlled aging treatment.
The alloy contains a high proportion of nickel and chromium, together with controlled additions of titanium, aluminum, and niobium. This composition combines the corrosion and oxidation resistance associated with nickel-chromium alloys with the enhanced mechanical properties achieved through precipitation hardening.
Inconel X-750 is widely used in aerospace propulsion systems, gas turbines, high-temperature springs, retaining rings, fasteners, and other components that must maintain mechanical performance during thermal exposure. Its resistance to stress relaxation is particularly valuable in applications where spring force, bolt preload, or dimensional stability must be retained over extended service periods.
However, the alloy's allowable operating temperature depends on the required mechanical properties, applied stress, exposure duration, atmosphere, product form, and heat-treatment condition. Its oxidation resistance at approximately 982°C should not be interpreted as a guarantee of sustained high-load structural performance at that temperature.
This comprehensive guide covers Inconel X-750 chemical composition, physical properties, mechanical performance, precipitation hardening, heat treatment, processing considerations, comparable alloys, applications, and procurement requirements.
Inconel X-750 is a wrought nickel-based superalloy classified as a γ′ precipitation-hardened alloy. It was developed from the nickel-chromium alloy family represented by Inconel 600, with additional aluminum, titanium, and niobium to improve age-hardening capability.
Unlike Inconel 600, which relies primarily on solid-solution strengthening, X-750 develops substantially higher strength through a controlled precipitation-hardening treatment. Its microstructure contains a nickel-rich γ matrix and strengthening γ′ precipitates, commonly described as Ni₃(Al,Ti), with the detailed phase chemistry depending on alloy composition and metallurgical condition.
The principal design concept is to combine:
● A nickel-chromium matrix for corrosion and oxidation resistance.
● γ′ precipitation strengthening for improved mechanical strength.
● Controlled grain-boundary chemistry and carbide formation for specific metallurgical requirements.
● A range of product forms and heat-treatment conditions for springs, fasteners, rings, and other engineered components.
Inconel X-750 offers several properties that support its use in demanding mechanical and thermal environments:
● Precipitation-hardened strength: Controlled aging increases strength relative to the solution-treated condition.
● Stress-relaxation resistance: Useful for springs and fasteners that must retain force or preload during elevated-temperature exposure.
● Oxidation resistance: Chromium-containing chemistry supports protective oxide formation in suitable environments.
● Corrosion resistance: Suitable for a range of applications where nickel-chromium alloy chemistry is advantageous.
● Creep and stress-rupture performance: Can be used in appropriately qualified applications requiring resistance to time-dependent deformation.
● Manufacturing flexibility: Available in multiple product forms, with processing routes selected according to the final component requirements.
These characteristics do not establish a single universal operating-temperature limit. Engineering selection must consider the interaction between temperature, stress, exposure time, atmosphere, and heat-treatment condition.
Inconel X-750 is commonly identified by the following designations:
Designation system | Identification |
Commercial alloy name | Inconel X-750 |
UNS | N07750 |
Werkstoff Number | 2.4669 |
These designations identify the alloy family but do not, by themselves, define the product specification, delivery condition, or mechanical acceptance criteria.
When purchasing or qualifying substitute materials, verify the chemical composition, product form, applicable standard, heat treatment, and required mechanical properties.
The chemical composition of Inconel X-750 is designed to combine a nickel-rich matrix with chromium-based environmental resistance and precipitation-strengthening additions.
The following table summarizes commonly specified composition limits for UNS N07750. Limits can vary by product specification and product form; the applicable standard and material test certificate take precedence.
Element | Symbol | Commonly specified content (wt.%) | Principal function |
Nickel | Ni | ≥ 70.0 | Matrix element; contributes to high-temperature stability and corrosion resistance |
Chromium | Cr | 14.0–17.0 | Supports oxidation resistance and corrosion resistance |
Iron | Fe | 5.0–9.0 | Matrix constituent and composition balance |
Titanium | Ti | 2.25–2.75 | Principal γ′-forming element |
Aluminum | Al | 0.4–1.0 | γ′ formation and contribution to oxidation resistance |
Niobium + tantalum | Nb + Ta | 0.7–1.2 | Alloying additions that influence strengthening and microstructure |
Carbon | C | ≤ 0.08 | Influences carbide formation and grain-boundary behavior |
Manganese | Mn | ≤ 1.0 | Controlled composition constituent |
Silicon | Si | ≤ 0.50 | Controlled composition constituent |
Copper | Cu | ≤ 0.50 | Controlled residual element |
Sulfur | S | ≤ 0.01 | Controlled impurity limit in commonly specified product conditions |
Composition note: The table is a general reference summary rather than a substitute for the governing specification. Additional elements and limits may apply, depending on the product form and applicable standard.
Nickel forms the principal matrix of Inconel X-750, supporting its high-temperature metallurgical stability and resistance to a range of corrosive environments.
Chromium contributes to oxidation resistance by supporting the formation of a protective chromium-rich oxide scale under suitable conditions. This characteristic is important for components exposed to hot gases and oxidizing atmospheres.
The effectiveness of this protection depends on temperature, gas chemistry, exposure time, thermal cycling, and surface condition. Oxidation resistance should therefore be evaluated separately from load-bearing strength.
Titanium and aluminum are central to the precipitation-hardening design of X-750. During appropriate aging treatment, these elements contribute to the formation of γ′ precipitates within the nickel-rich matrix.
Niobium is also an important alloying addition, but the strengthening behavior of X-750 should not be described as identical to that of Inconel 718. Inconel 718 relies primarily on γ″ strengthening, with a contribution from γ′, whereas X-750 is principally associated with γ′ precipitation strengthening.
The resulting properties depend not only on the nominal composition but also on the solution treatment, aging schedule, prior deformation, grain structure, and product geometry.
The following values are useful for preliminary engineering calculations. Final design work should use the property data applicable to the specified product and condition.
Property | Reference value | Engineering note |
Density | Approximately 8.28–8.30 g/cm³ | Confirm against the applicable product data |
Melting range | Approximately 1,395–1,425°C | Reference range; not a service-temperature rating |
Electrical resistivity at 50°C | Approximately 1.22 × 10⁻⁶ Ω·m | Verify the reference condition and source |
Mean coefficient of thermal expansion, 20–200°C | Approximately 13.1 × 10⁻⁶/°C | Reference value |
Mean coefficient of thermal expansion, 20–800°C | Approximately 16.2 × 10⁻⁶/°C | Reference value; confirm the test method |
Physical-property values can vary slightly among technical publications because of differences in test methods, product condition, and reporting conventions.
Temperature capability is one of the most frequently misunderstood aspects of Inconel X-750 selection.
Three different performance considerations should be distinguished:
● High-strength applications: Manufacturer data commonly describe high-strength capability up to approximately 704°C, subject to the applicable condition and design requirements.
● Creep and stress-rupture applications: Appropriately heat-treated material can be considered for selected applications at higher temperatures, including conditions approaching approximately 816°C, when supported by applicable test data.
● Oxidation resistance: Resistance to oxidation may extend to approximately 982°C under suitable environmental conditions, but this does not establish an allowable sustained mechanical load at that temperature.
The melting range is not a suitable basis for setting an operating-temperature limit. Component design must instead use relevant tensile, creep, stress-rupture, oxidation, and fatigue data.
Mechanical properties depend strongly on product form and heat-treatment condition. Solution-treated sheet, aged sheet, cold-worked strip, bar, and forgings should not be assumed to have identical properties.
The table below presents representative minimum values published for selected product forms and specified conditions. It is not a universal property table for all X-750 products.
Product form | Reference condition or specification context | Tensile strength | Yield strength | Elongation |
Plate | Precipitation heat-treated condition under a specified plate or sheet specification | ≥ 1,103 MPa | ≥ 724 MPa | ≥ 18% |
Sheet | Precipitation heat-treated condition under a specified sheet specification | ≥ 1,172 MPa | ≥ 793 MPa | ≥ 18% |
Strip | Precipitation heat-treated condition | Depends on the applicable specification | Depends on the applicable specification | May be specified at ≥ 12% |
Bar or billet | Specified condition under the applicable bar specification | Product- and condition-dependent | Product- and condition-dependent | Product- and condition-dependent |
The values above are illustrative specification-dependent reference points. They must not be combined into a single set of guaranteed properties or used to certify material supplied under a different specification.
For procurement, identify the applicable product standard, heat-treatment condition, thickness or diameter, specimen orientation, and required test method.
Solution treatment and precipitation aging serve different purposes.
Solution-treated condition: Provides a specified starting metallurgical condition for subsequent processing or aging. Strength may be lower than that achieved after precipitation hardening.
Aged condition: Controlled heat treatment promotes the formation of strengthening γ′ precipitates, generally increasing tensile and yield strength relative to the appropriate solution-treated condition.
The magnitude of the increase depends on the product form, initial condition, heat-treatment schedule, and applicable acceptance requirements. A universal strength increase of a fixed number of megapascals should not be assumed.
When X-750 is required for a high-strength spring, fastener, or retaining ring, the purchase order should explicitly state the required delivery condition and whether subsequent aging is to be performed by the supplier or purchaser.
Creep is the time-dependent deformation of a material subjected to sustained stress, particularly at elevated temperatures. Stress-rupture testing measures the time required for failure under specified temperature and stress conditions.
Inconel X-750 is used in selected applications requiring high-temperature stress-rupture resistance. However, stress-rupture results are meaningful only when temperature, stress, product form, heat-treatment condition, and test requirements are clearly specified.
The often-cited condition of approximately 730°C at 362 MPa with a minimum rupture life of 23 hours should be treated as a specification-specific reference, not as a universal guarantee for all X-750 bars, forgings, or finished components. Confirm the requirement against the applicable material specification and test certificate before using it for design or procurement.
Stress relaxation is the gradual reduction in stress under a sustained strain, such as the loss of force in a compressed spring or the reduction of preload in a bolted joint.
Inconel X-750 is widely used for elevated-temperature spring and fastener applications because its precipitation-hardened microstructure can provide useful resistance to stress relaxation under appropriate conditions.
Important factors include:
● Initial stress or spring deflection.
● Operating temperature and exposure duration.
● Aging treatment and prior cold work.
● Component geometry and local stress concentration.
● Thermal cycling and the surrounding environment.
For critical assemblies, stress-relaxation testing or validated design data should be used to establish allowable preload loss and service-life expectations.
Heat treatment is fundamental to the performance of Inconel X-750. The required schedule depends on product form, manufacturing route, applicable specification, and target properties.
The primary strengthening mechanism in X-750 is associated with γ′ precipitates formed during aging. These ordered precipitates interact with dislocations and increase resistance to plastic deformation.
The final microstructure depends on the alloy chemistry, solution treatment, aging temperature, holding time, cooling procedure, and previous processing history.
It is therefore misleading to define a single precipitation-start temperature, peak-strength temperature, or complete-dissolution temperature as universally applicable to all X-750 products. Phase evolution is condition-dependent and should be interpreted using appropriate metallurgical data.
Inconel X-750 can be supplied or processed under different heat-treatment schedules depending on the intended application and governing specification.
A commonly cited two-stage aging approach for certain applications is:
1. Heat to approximately 730°C and hold for the specified duration.
2. Furnace-cool under controlled conditions to approximately 620°C.
3. Hold at the second temperature for the specified duration.
4. Air-cool as prescribed by the applicable procedure.
The original article's schedule of approximately 730°C for 8 hours, followed by furnace cooling to approximately 620°C and a further 8-hour hold, should be used only when it is confirmed as appropriate for the specified product and required condition.
It must not be presented as the universal heat treatment for all X-750 sheets, strips, bars, forgings, and springs. Different product specifications and application requirements may prescribe different solution, stabilization, and precipitation-hardening schedules.
Before heat treatment, confirm:
● The governing product specification and revision.
● The material's original delivery condition.
● The required solution or stabilization treatment, if applicable.
● The precipitation-hardening temperature, holding time, and cooling method.
● Furnace uniformity and temperature-recording requirements.
● Required mechanical testing and final acceptance criteria.
The final properties should be verified against the specified acceptance requirements. A heat-treatment label alone is insufficient evidence that the finished material meets the required strength, ductility, or stress-rupture performance.
Inconel X-750 is available in several forms used for spring and precision component manufacturing, including strip, wire, bar, and other forms where supported by the applicable product specification.
Cold work and heat treatment can be used in combination to achieve specified mechanical properties. The appropriate manufacturing route depends on the required spring force, dimensional tolerances, surface condition, and final heat-treatment state.
Spring manufacturers should verify the properties of the supplied material and finished component rather than relying solely on the alloy designation.
Welding of X-750 requires consideration of the product condition, component thickness, joint geometry, welding process, and required final properties.
The following practices should be considered:
● Qualify the welding procedure for the actual material and joint configuration.
● Select filler material based on metallurgical compatibility and service requirements.
● Control heat input, distortion, and local thermal exposure.
● Evaluate cracking susceptibility and the effects of welding on the precipitation-hardened condition.
● Determine whether post-weld heat treatment is required by the component specification.
Thin sections and small components may be easier to weld than large, highly restrained sections, but this should not be treated as a universal rule. Post-weld stress relief or aging must be specified only after confirming its suitability for the particular material condition and application.
Extended exposure to elevated temperatures can change the microstructure and mechanical properties of precipitation-hardened alloys. The magnitude and direction of these changes depend on temperature, duration, prior heat treatment, and stress.
The original article identifies repeated thermal cycling between approximately 650°C and 870°C as a potential embrittlement concern. This temperature interval should not be treated as a universal prohibited operating range without alloy-specific supporting evidence.
For critical components, assess the applicable long-term aging data, thermal-cycle requirements, stress-rupture performance, and inspection criteria. Avoid uncontrolled heating and cooling where they could introduce thermal stress or impair the specified properties.
Inconel X-750, Inconel 718, Inconel 600, Inconel 625, and cast superalloys such as Inconel 713C serve different engineering requirements. Their performance should be compared using the same product form, temperature, loading condition, and design objective.
Alloy | Principal strengthening approach | Key selection considerations | Representative applications |
Inconel X-750 | Primarily γ′ precipitation strengthening | Spring force retention, fastener preload, elevated-temperature strength | Springs, retaining rings, fasteners |
Inconel 718 | Primarily γ″ precipitation strengthening, with a γ′ contribution | High strength, fatigue performance, suitability for specified structural components | Rotating components, shafts, fasteners |
Inconel 600 | Primarily solid-solution strengthening | Corrosion and oxidation resistance in suitable environments | Furnace equipment, chemical processing |
Inconel 625 | Solid-solution strengthening, including contributions from molybdenum and niobium | Corrosion resistance and broad environmental applicability | Marine, chemical, and energy equipment |
Inconel 713C | Cast, precipitation-strengthened nickel-based superalloy | Casting-specific high-temperature performance and component geometry | Selected turbine and turbocharger components |
The temperature figures often quoted for these alloys should not be treated as directly comparable maximum service temperatures. Allowable temperatures depend on product form, stress, exposure time, environment, and the governing design criteria.
X-750 is worth evaluating when a component must maintain spring force, preload, or dimensional stability during elevated-temperature service and when the required properties can be achieved through an appropriate manufacturing and heat-treatment route.
Inconel 718 may be appropriate when the design prioritizes a different combination of strength, fatigue resistance, fabrication requirements, and operating temperature. Selection should be based on verified design allowables and the specific product condition.
These alloys may be considered when corrosion resistance, environmental compatibility, or solid-solution-strengthened behavior is more important than the particular precipitation-hardened strength and spring performance associated with X-750.
No alloy should be selected solely because its nominal maximum temperature is higher. The correct choice is the alloy whose verified properties satisfy the complete service requirement.
Inconel X-750 is used in aerospace, energy, and industrial equipment where mechanical properties must be retained during elevated-temperature exposure.
Representative applications include:
● Engine retaining rings.
● Sealing rings and related components.
● Selected structural rings.
● High-temperature bolts and fasteners.
● Gas-turbine structural components.
● Components in jet-engine afterburner systems, where the design conditions are suitable.
Fasteners and retaining components can be particularly demanding because loss of preload or spring force may affect joint integrity, sealing performance, or mechanical stability.
X-750 is a well-established material for selected spring applications requiring elevated-temperature strength and stress-relaxation resistance.
Common component types include:
● Helical springs.
● Flat springs.
● Wave springs.
● Spring clips.
● Retaining springs.
● Spring-loaded sealing components.
For these applications, the required performance depends on the spring design, initial stress, working deflection, operating temperature, exposure duration, and final material condition.
Selected gas-turbine and industrial components may use X-750 where its mechanical and environmental properties are appropriate. Potential applications include retaining components, high-temperature fasteners, and structural parts operating within the qualified temperature and stress envelope.
The alloy should not be assumed suitable for every turbine blade, rotating disk, or hot-section component. More demanding applications may require materials with different creep, fatigue, oxidation, or casting characteristics.
X-750 wire and strip can be manufactured and processed to achieve specified dimensional and mechanical characteristics. Depending on the product and delivery condition, cold drawing and subsequent heat treatment can be used to tailor the properties required for precision spring production.
Buyers should confirm wire diameter, dimensional tolerance, surface quality, mechanical properties, delivery condition, and any special requirements for spring manufacture.
Identify the required form, such as sheet, plate, strip, wire, bar, forging, or tube where available. Include dimensions, tolerances, quantity, delivery condition, and the governing specification.
Specify whether the material is required in the solution-treated, aged, cold-worked, or other condition defined by the applicable standard.
For high-strength springs and fasteners, confirm whether the material is to be supplied in its final condition or undergo further processing after delivery.
Review the material test certificate against the actual purchasing specification. Confirm the required chemical elements, tensile properties, hardness, elongation, and any stress-rupture or other testing requirements.
Do not assume that a chemical-composition certificate alone establishes compliance with the mechanical requirements.
For critical applications, define requirements for heat or lot traceability, dimensional inspection, surface quality, chemical analysis, mechanical testing, nondestructive examination, and material documentation.
Acceptance criteria should be established before production or shipment.
Bozhong Alloy presents Inconel X-750 supply options for aerospace, energy, and industrial applications. The product range and service capabilities should be confirmed against current inventory, mill documentation, and the specific purchase requirements.
Subject to availability and the applicable manufacturing specification, supply options may include:
● Inconel X-750 plate and sheet.
● Inconel X-750 bar and rod.
● Inconel X-750 strip.
● Inconel X-750 wire.
● Inconel X-750 forgings.
● Tubes, where the required product form and specification can be supported.
Supply arrangements may include qualified domestic manufacturers and imported material channels, depending on the product, specification, and order requirements.
Inventory locations, delivery lead times, and shipment commitments should be confirmed at the time of quotation. Any claim of shipment within 24–72 hours should apply only to verified in-stock products that have completed the required inspection and documentation process.
Depending on the agreed supply scope, documentation and services may include:
● Material Test Certificate (MTC).
● Chemical composition and mechanical property results.
● Material traceability documentation.
● Optical emission spectroscopy (OES) re-inspection, where available.
● Cutting-to-size services.
● Small-batch supply and customized dimensions, subject to manufacturing capability.
For critical applications, the purchase order should specify the required certificate type, inspection scope, testing methods, and acceptance criteria.
Inconel X-750 is a wrought nickel-based superalloy strengthened primarily through γ′ precipitation hardening. It is used in selected applications requiring elevated-temperature strength, oxidation resistance, and stress-relaxation resistance.
The UNS designation is N07750, and its commonly listed Werkstoff Number is 2.4669.
A commonly reported density is approximately 8.28–8.30 g/cm³. Use the applicable product documentation when accurate mass calculations are required.
There is no single maximum service temperature applicable to every condition. Manufacturer data commonly describe high-strength capability up to approximately 704°C and oxidation resistance up to approximately 982°C. Creep and stress-rupture applications require separate evaluation using the relevant temperature, stress, exposure time, and heat-treatment data.
Aging promotes the formation of γ′ strengthening precipitates in the nickel-rich matrix. The resulting microstructure increases resistance to plastic deformation. The final strength depends on the product form, starting condition, aging schedule, and applicable specification.
X-750 is widely used in selected elevated-temperature spring applications because it can provide useful strength retention and resistance to stress relaxation. The final material condition and spring design must be matched to the working temperature, stress, and required service life.
X-750 can be welded using suitable procedures, but weldability and the resulting properties depend on the product condition, section thickness, joint configuration, and welding process. Procedure qualification and evaluation of any required post-weld heat treatment are important.
The applicable standard depends on the product form. ASTM B637 covers specified precipitation-hardenable and cold-worked nickel-alloy rod, bar, forgings, and forging stock for moderate- or high-temperature service. Plate, sheet, and strip products may require different ASTM or AMS specifications.
Always verify the exact standard designation, edition, product form, and required condition in the purchase order.
No. Although both are precipitation-hardened nickel-based superalloys, their strengthening behavior, composition, processing requirements, and application characteristics differ. Substitution requires a technical assessment against the actual design requirements.
Inconel X-750 is a well-established nickel-based precipitation-hardened superalloy for selected high-temperature springs, fasteners, retaining rings, and aerospace or industrial structural components. Its principal advantages include γ′ precipitation strengthening, useful oxidation resistance, and the ability to retain mechanical force under appropriate elevated-temperature conditions.
Successful material selection depends on more than the alloy designation. Product form, chemical composition, heat treatment, mechanical acceptance criteria, operating temperature, applied stress, and service duration must all be considered together.
For reliable procurement and engineering qualification, confirm the governing product specification and verify the supplied material certificate against the purchase requirements. This approach helps ensure that Inconel X-750 is selected and processed for the actual operating conditions rather than on the basis of generalized temperature ratings alone.
