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- 2025-2-8
- handaseal
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INCONEL® X-750 is a precipitation-hardenable nickel-chromium alloy engineered for high strength, low creep and excellent oxidation resistance at elevated temperature. It is commonly used for spring-energized seals (including canted coil springs and helical energizers) where preload retention and low relaxation at temperature are required.
Contents
Introduction & quick summary
INCONEL® X-750 (UNS N07750) is a nickel-chromium alloy strengthened by precipitation (Al/Ti/Nb additions). It is prized for its ability to retain preload and resist stress-relaxation at elevated temperatures, plus good oxidation/scale resistance. Typical uses include springs and clips in aerospace, turbine, power generation and other high-temperature sealing applications. For corrosive seawater or sour H₂S applications, consider alternatives such as Inconel 625, Elgiloy or MP35N.
Need X-750 springs or application guidance? Request a quote — include operating temperature profile and gland geometry.
Core characteristics
Typical chemical composition
Typical ranges — confirm exact lot values on supplier mill certificate:
| Element | Typical (wt.%) |
|---|---|
| Nickel (Ni) | Balance (majority) |
| Chromium (Cr) | ~14–17% |
| Iron (Fe) | ~6–10% |
| Niobium / Columbium (Nb / Cb) | ~1.0–2.5% |
| Aluminium (Al) | ~0.4–1.0% |
| Titanium (Ti) | ~0.4–1.0% |
| Carbon (C) | ≤ 0.08% |
Key physical data (typical)
Typical physical & thermal properties — always verify with supplier datasheet for selected product form & temper:
| Property | INCONEL® X-750 (typical) |
|---|---|
| Density | ≈ 8.30 g/cm³ (≈ 0.300 lb/in³) |
| Modulus of Elasticity (E) | ≈ 28–30 ×10⁶ psi (≈ 190–207 GPa) (RT) |
| Modulus of Rigidity (G) | ≈ 11–12 ×10⁶ psi (≈ 76–83 GPa) |
| Coefficient of thermal expansion | Use supplier tables (temperature dependent) |
| Typical tensile strength (precipitation-hardened) | High — depends on aging schedule; typical psi/MPa data provided in supplier temper charts |
| Service temperature guidance | Short-term / intermittent: some properties retained to ≈ 1800°F (≈ 982°C). Recommended long-term continuous: conservative engineering guidance commonly ≤ ≈ 1300°F (≈ 704°C) to maintain precipitation-strengthened properties and minimise over-aging; for springs consult supplier stress-relaxation & creep curves for chosen diameter & temper. |
| Form availability | Wire, strip and bar (confirm available diameters & tempers with supplier) |
X-750 — Core capabilities
- High-temperature preload retention: excellent resistance to stress-relaxation and creep when correctly solution-treated and aged.
- Precipitation strength control: aging schedule (solution + age) allows tuning strength vs ductility vs relaxation behaviour.
- Good oxidation resistance: suitable for hot oxidizing atmospheres common in turbine/aerospace service.
- Dimensional stability: when processed per supplier guidance it offers repeatable spring performance critical for precision energizers.
- Formability for springs: available as spring wire; final aging must be matched to coil/geometry to control relaxation and fatigue.
- Limitations: precipitation hardening effectiveness reduces if exposed long-term above recommended long-term temperatures; not the top choice for extreme sour/H₂S corrosion resistance (use Elgiloy/MP35N where SSC is primary risk).
Typical applications
- High-temperature spring energizers in aerospace and turbine systems.
- Actuator and valve springs requiring low relaxation at temperature.
- Helical and canted coil springs where preload retention in hot gas environments is critical.
- Clips, fasteners and retaining rings exposed to elevated temperatures.
Forming into springs & spring types
Reminder: spring energizers are formed from wire (round or profiled) or strip. X-750 is produced as spring wire and strip — confirm temper, aging schedule and diameter availability with your supplier before ordering. Common forms include:
Forming notes
- Coiling may be done in solution-treated or pre-aged condition; many producers perform final aging after forming to achieve target relaxation and UTS.
- Control tooling finish; electropolishing or careful mechanical finishing improves fatigue and corrosion performance.
- Qualification testing (force-deflection, fatigue, stress-relaxation at operating temperature) is recommended for critical parts.
Alternatives & comparison
Quick comparison of commonly considered alternatives for spring energizers (temperature guidance shown as short-term max vs recommended long-term continuous):
| Material | Corrosion / behavior summary | Strength (typical) | Short-term max temp | Recommended long-term continuous temp |
|---|---|---|---|---|
| INCONEL X-750 | Good oxidation; designed for low relaxation at high T | High (precipitation-hardened) | ≈ 1800°F (≈ 982°C) | ≈ 1300°F (≈ 704°C) — conservative guidance for prolonged service |
| INCONEL 718 | Good corrosion; very high strength after ageing | Very high (age-hardened) | ≈ 1400°F (≈ 760°C) | ≈ 1000–1100°F (≈ 538–593°C) depending on temper |
| INCONEL 625 | Excellent corrosion & chloride resistance; good ductility | Moderate to high (solid-solution + cold work) | ≈ 1800°F (≈ 982°C) | ≈ 1100°F (≈ 593°C) conservative for long-term |
| Hastelloy C-276 | Outstanding chemical resistance (acids/chlorides) | Moderate | ≈ 1000°F (≈ 538°C) | ≈ 700°F (≈ 371°C) (application dependent) |
| Elgiloy® | Excellent SSC resistance; excellent elastic recovery | Very high (cold-worked tempers) | ≈ 850°F (≈ 454°C) | ≈ 850°F (≈ 454°C) per supplier guidance |
| MP35N® | Excellent SSC, chloride & hydrogen resistance | Very high (work-hardened) | ≈ 750°F (≈ 399°C) | ≈ 750°F (≈ 399°C) |
| 17-7 PH / 316L | Good general corrosion; 17-7 PH has excellent spring properties | Moderate to high (depends on temper) | Varies | Typically much lower than nickel superalloys — consult supplier |
Notes: table values are indicative and consolidated from supplier datasheets. For spring/energizer design always use supplier diameter-by-temper tables, mill certificates and stress-relaxation curves.
Selection guidance
Below are concise, direct choice rules to help pick the best alloy for a specific dominant constraint. If multiple constraints apply, rank them and follow the checklist at the end.
- Dominant: High continuous operating temperature / preload retention — choose INCONEL X-750 (or, in some designs, INCONEL 718 if higher static strength and toughness are required).
- Dominant: Highest tensile/Yield strength & formability — choose INCONEL 718 (better balanced strength/toughness and often preferred when tight formability + age hardening are needed).
- Dominant: Corrosion (chlorides / seawater / chemical exposure) — choose INCONEL 625 or Hastelloy C-276 for the most aggressive chemical environments.
- Dominant: Sulfide stress cracking (sour H₂S) / SSC risk — prioritise Elgiloy or MP35N and require NACE MR0175 / ISO 15156 qualification and hardness limits.
- Dominant: Elastic recovery & miniature high-cycle fatigue — choose Elgiloy (cobalt-nickel) or MP35N for highest fatigue life and elastic limit in small diameters.
- Cost-sensitive / moderate conditions — consider stainless steels (17-7 PH, 316L) when extreme temperature or SSC are not the primary constraints.
Quick validation checklist (must-do before final selection)
- Obtain supplier mill certificate and diameter-by-temper mechanical tables (UTS/YS/hardness).
- Request stress-relaxation / creep curves at the intended operating temperature for the chosen wire diameter & temper.
- Specify representative fatigue + corrosion test coupons (same finish, join and assembly geometry) for qualification if component is critical.
FAQ
Q1: Is X-750 suitable for canted coil springs that operate continuously at 600 °C?
A1: Yes — X-750 is designed for elevated-temperature preload retention. For continuous 600 °C service confirm supplier stress-relaxation data for the chosen diameter and temper.
Q2: Between X-750 and 718 which is better for fatigue-critical springs?
A2: If fatigue at moderate-to-high temperature is dominant and formability matters, INCONEL 718 often offers the best balance. If long-term preload at very high temperature dominates, X-750 is preferred.
Q3: Can X-750 be used in sour H₂S service?
A3: X-750 is not the preferred alloy for severe sour H₂S. For SSC-prone service prefer Elgiloy or MP35N and require project-specific NACE/ISO qualification.
Q4: What are the typical heat treatments for spring wire?
A4: Typical sequence: solution anneal (per supplier recommendation) followed by controlled aging to develop the required precipitation-strengthened temper. Final aging schedules depend on wire diameter and part geometry.