If you need a superalloy that delivers exceptionalrésistance au fluage, résistance à la fatigue, and corrosion resistance—all enhanced by heat aging—NOUS N07750 (communément appelé Inconel X-750) est le choix idéal. Utilisé dans l'aérospatiale, nucléaire, et industries de l'énergie, cet alliage résout le problème critique du maintien de la résistance à 650+ °C là où d'autres matériaux se ramollissent. Dans ce guide, nous allons décomposer ses propriétés clés, utilisations réelles, étapes de fabrication, and how it compares to alternatives—so you can build components that perform reliably in long-term high-temperature service.
1. Material Properties of UNS N07750 (Inconel X-750) Superalliage
UNS N07750’s superalloy status comes from its unique aging mechanism: titanium-aluminum-niobium precipitates (γ’ and γ”) that form during heat treatment, boosting strength without sacrificing corrosion resistance. Let’s explore its properties in detail:
1.1 Composition chimique
Every element in UNS N07750 is engineered to enable age hardening while preserving corrosion performance. Below is its standard composition (per ASTM B637):
| Élément | Gamme de contenu (%) | Key Role |
|---|---|---|
| Nickel (Dans) | 70.0 – 75.0 | The base element—providesstabilité à haute température and resistance to chloride stress cracking. |
| Chrome (Cr) | 14.0 – 17.0 | Forms a protective Cr₂O₃ layer—resists oxidation and general corrosion (par ex., carburéacteur, seawater). |
| Fer (Fe) | 5.0 – 9.0 | Enhances workability and balances cost without reducing aging performance. |
| Titane (De) | 2.25 – 2.75 | The “aging core”—forms γ’ (Ni₃Ti) precipitates, the primary source of high-temperature strength. |
| Aluminium (Al) | 0.40 – 1.00 | Aids γ’ precipitate formation; improves oxidation resistance at extreme heat. |
| Niobium (Nb) | 0.70 – 1.20 | Forms γ” (Ni₃Nb) precipitates—boosts strength and creep resistance; prevents over-aging. |
| Molybdène (Mo) | ≤ 0.50 | A minor additive that enhances corrosion resistance to pitting. |
| Carbone (C) | 0.04 – 0.10 | Low enough to avoid carbide brittleness; high enough to aid grain boundary strength. |
| Manganèse (Mn) | ≤ 1.00 | Enhances weldability; minimizes hot cracking during manufacturing. |
| Soufre (S) | ≤ 0.015 | Ultra-low to prevent welding defects and corrosion susceptibility. |
1.2 Propriétés physiques
These properties reflect UNS N07750’s ability to withstand long-term high temperatures—critical for aerospace and nuclear applications. All values are measured at room temperature unless noted:
- Densité: 8.28 g/cm³ (higher than steel, due to nickel, titane, and niobium content).
- Point de fusion: 1390 – 1450 °C (high enough to resist softening in gas turbine engines and nuclear reactors).
- Conductivité thermique: 11.7 Avec(m·K) (à 100 °C); 19.3 Avec(m·K) (à 600 °C)—low heat transfer, ideal for components needing structural integrity at high temperatures.
- Coefficient de dilatation thermique: 12.8 × 10⁻⁶/°C (20–100 °C); 17.0 × 10⁻⁶/°C (20–600 °C)—stable expansion for precision parts like jet engine fasteners.
- Specific Heat Capacity: 440 J/(kg·K) (à 25 °C)—efficient at absorbing heat without rapid temperature changes, reducing thermal stress during aging.
- Conductivité électrique: 7.5 × 10⁶ S/m (à 20 °C)—lower than copper, but suitable for electrical components in high-heat environments (par ex., nuclear reactor sensors).
1.3 Propriétés mécaniques
UNS N07750’s mechanical properties shine after age hardening—its strength peaks at 650 °C, making it ideal for long-term high-temperature service. Below are typical values (age-hardened condition, per ASTM B637):
| Propriété | Valeur typique (Age-Hardened) | Test Standard | Why It Matters |
|---|---|---|---|
| Dureté (CRH) | 35 – 40 | ASTM E18 | Balanced hardness—strong enough for high stress, tough enough to avoid brittle failure. |
| Résistance à la traction | ≥ 1100 MPa | ASTM E8 | Handles extreme pressure (par ex., jet engine combustion chambers, nuclear reactor vessels). |
| Limite d'élasticité (0.2% offset) | ≥ 790 MPa | ASTM E8 | Resists permanent deformation at 650 °C—critical for long-term creep resistance. |
| Élongation (dans 50 mm) | ≥ 15% | ASTM E8 | Moderate ductility—allows forming into complex shapes (par ex., pales de turbine) sans craquer. |
| Résistance aux chocs (Charpy V-notch) | ≥ 60 J. (à 20 °C) | ASTM E23 | Good toughness—prevents failure from sudden stress (par ex., engine startup/shutdown). |
| Résistance au fluage | 172 MPa at 650 °C (10⁵ hours) | ASTM E139 | Maintains strength under long-term high-temperature stress—outperforms many superalloys. |
| Fatigue Strength | ~480 MPa (10⁷ cycles) | ASTM E466 | Resists failure from repeated thermal/mechanical stress (par ex., turbine rotation, reactor cycling). |
1.4 Autres propriétés
- Résistance à la corrosion: Very Good. Résiste:
- Oxidation up to 870 °C (thanks to chromium and aluminum).
- Seawater corrosion and pitting (due to molybdenum and nickel).
- Mild acids and alkalis (suitable for chemical processing and marine applications).
- Oxidation Resistance: Excellent. Forms a dense oxide layer that prevents further oxidation at 800–870 °C—ideal for gas turbine components.
- Weldability: Bien (with post-weld aging). Requires preheating (200–300 °C) and post-weld solution annealing + age hardening to restore strength; use ERNiFeCr-3 filler metal.
- Usinabilité: Équitable. Work hardens rapidly—requires sharp carbide tools, slow cutting speeds (6–10 m/min for turning), and high-pressure cutting fluids to reduce friction.
- Formabilité: Modéré. Can be hot-formed (at 980–1150 °C) into complex shapes; cold forming is possible but requires intermediate annealing to reduce work hardening.
2. Applications of UNS N07750 (Inconel X-750) Superalliage
UNS N07750 is used in applications where long-term high-temperature strength is non-negotiable—industries where component failure risks safety or costly downtime. Voici ses utilisations les plus courantes, avec des exemples réels:
2.1 Aerospace and Jet Engines
- Exemples: Jet engine turbine blades, combustion chamber liners, attaches pour avions (for high-temperature zones), and rocket motor casings.
- Why it works: Age-hardened strength resists creep at 650+ °C, while corrosion resistance handles jet fuel and atmospheric pollutants. Un États-Unis. aerospace manufacturer used UNS N07750 for turbine blades—blade life increased by 450% contre. Inconel 625.
2.2 Nuclear Reactors
- Exemples: Reactor pressure vessel components, control rod guide tubes, and fuel assembly brackets.
- Why it works: Resists radiation-induced embrittlement and corrosion from reactor coolants (par ex., eau, liquid sodium). A French nuclear operator used UNS N07750 for control rod tubes—no maintenance issues in 20 années.
2.3 Gas Turbines (Energy Industry)
- Exemples: Gas turbine stator vanes, rotor components, and exhaust liners for power generation (natural gas plants).
- Why it works: Creep resistance handles long-term operation at 1000+ °C, while oxidation resistance resists exhaust gases. A German energy firm used UNS N07750 for stator vanes—vane life extended to 18 années (contre. 10 years for Inconel 718).
2.4 Oil and Gas Industry
- Exemples: Outils de fond (for high-temperature, high-pressure reservoirs) and subsea wellhead components (exposed to seawater).
- Why it works: Resists sulfide stress cracking and creep at 200+ °C. A Saudi Arabian oil company used UNS N07750 downhole tools—tools operated for 11 years without failure (contre. 3 years for stainless steel).
2.5 High-Temperature Fasteners
- Exemples: Boulons, noix, and washers for furnace components, structures aérospatiales, et réacteurs nucléaires.
- Why it works: Age-hardened strength maintains clamp load at high temperatures, preventing fastener loosening. A Japanese heat treatment shop used UNS N07750 bolts for furnace doors—bolt replacement frequency dropped by 80%.
3. Manufacturing Techniques for UNS N07750 (Inconel X-750) Superalliage
UNS N07750’s manufacturing is centered on precise age hardening—this step is critical to unlock its full strength. Its work-hardening nature also demands careful machining. Voici une ventilation étape par étape:
- Fusion:
- Matières premières (high-purity nickel, chrome, titane, aluminium) are melted in a vacuum induction furnace (VIF) followed by vacuum arc remelting (VAR). This dual melting ensures ultra-low impurities and uniform composition (critical for consistent precipitate formation).
- Casting/Forging:
- Molten alloy is cast into ingots (jusqu'à 4 tons for turbine components) or investment-cast into near-net-shape parts (par ex., pales de turbine).
- Ingots are hot-forged at 980–1150 °C—forging aligns grain structure to maximize creep resistance; complex shapes use precision forging.
- Rolling/Forming:
- Hot rolling (at 950–1100 °C) produces plates, barres, or tubes; cold rolling is limited to thin sheets and requires intermediate annealing (at 900–1000 °C).
- Traitement thermique (Critical for Aging Strength):
- Solution Annealing: Heat to 980–1065 °C, hold 1–2 hours, water quench. Dissolves excess precipitates and carbides, preparing the alloy for aging.
- Intermediate Aging (Facultatif): Heat to 700–760 °C, hold 2–4 hours, air cool. Forms small γ’ precipitates to boost preliminary strength.
- Final Aging: Heat to 620–650 °C, hold 16–24 hours, air cool. Forms large γ’ and γ” precipitates—the main source of UNS N07750’s ultra-high high-temperature strength.
- Usinage:
- Use carbide tools with negative rake angles and sharp cutting edges to minimize work hardening.
- Cutting speeds: 6–9 m/min (tournant), 4–6 m/min (fraisage); taux d'avance: 0.06–0.10 mm/rev.
- Use high-pressure (100–140 bar) fluides de coupe (water-soluble with EP additives) to cool the tool and flush chips—prevents re-cutting work-hardened material.
- Soudage:
- Preheat to 200–300 °C to reduce thermal stress.
- Use TIG welding with ERNiFeCr-3 filler metal (matches composition).
- Post-weld heat treatment: Solution anneal (1020 °C) + full age hardening to restore strength (critical for load-bearing joints).
- Traitement de surface (Facultatif):
- Aluminizing (applying an aluminum coating) enhances oxidation resistance for components operating above 870 °C (par ex., pales de turbine).
- Shot peening (cold working the surface) improves fatigue strength by creating compressive stress—used for fasteners and turbine components.
4. Étude de cas: UNS N07750 in Nuclear Reactor Control Rod Tubes
Un États-Unis. nuclear power plant faced a problem: their Inconel 600 control rod tubes failed after 12 years due to creep deformation and radiation embrittlement. They switched to UNS N07750, and here’s what happened:
- Processus: UNS N07750 tubes (25 mm diamètre, 2 mm wall) were vacuum-melted, hot-rolled, solution annealed (1040 °C), age-hardened (630 °C pour 20 heures), and shot-peened to improve fatigue strength.
- Résultats:
- Tube life extended to 20 années (67% amélioration)—no creep deformation or embrittlement even after 85,000 hours of reactor operation.
- Reactor safety margins increased—tube dimensional stability ensured control rods operated smoothly.
- Maintenance costs fell by $600,000/year (fewer tube replacements, no unplanned shutdowns).
- Why it works: γ’ and γ” precipitates in UNS N07750 prevented creep at high temperatures, while nickel’s radiation resistance avoided embrittlement—solving the plant’s core reliability issue.
5. NOUS N07750 (Inconel X-750) contre. Other Superalloys
How does UNS N07750 compare to alternatives for long-term high-temperature applications? Let’s evaluate key properties:
| Matériel | Résistance au fluage (MPa at 650 °C, 10⁵h) | High-Temp Stability (Max °C) | Résistance à la traction (MPa) | Coût (contre. NOUS N07750) | Idéal pour |
|---|---|---|---|---|---|
| NOUS N07750 (Inconel X-750) | 172 | 870 | ≥ 1100 | 100% | Long-term high temp (nucléaire, fixations aérospatiales) |
| NOUS N07718 (Inconel 718) | 207 | 700 | ≥ 1240 | 90% | High stress (pales de turbine) |
| NOUS N06625 (Inconel 625) | 138 | 1095 | ≥ 827 | 80% | High heat (less creep resistance) |
| Hastelloy C276 | 90 | 1010 | ≥ 690 | 150% | Extreme corrosion (faible fluage) |
| 316 Acier inoxydable | 10 | 870 | ≥ 515 | 20% | Mild heat (no long-term creep) |
Key takeaway: UNS N07750 is the top choice for long-term high-temperature applications (10+ années) like nuclear reactors and aerospace fasteners. It balances creep resistance, corrosion performance, and cost better than Inconel 718 (which has higher stress strength but lower temperature stability) and Hastelloy C276 (which excels at corrosion but not creep).
Yigu Technology’s View on UNS N07750 (Inconel X-750) Superalliage
Chez Yigu Technologie, UNS N07750 is our go-to for clients needing long-term high-temperature reliability—like nuclear operators and aerospace manufacturers. Its unique aging mechanism solves the biggest challenge: maintaining strength over decades of high-heat service. We specialize in precise age hardening (controlling time/temperature to optimize precipitates) et usinage, often shot-peening critical components to boost fatigue life.