Inconel 718

Introduction & quick summary

INCONEL® 718 (UNS N07718) is a versatile precipitation-hardenable nickel-chromium alloy, engineered for combinations of high strength, fatigue resistance and weldability across a broad temperature range (from cryogenic to several hundred °C). It is widely specified for springs, fasteners and components that require stable mechanical performance after age-hardening. When corrosion resistance dominates, compare with Inconel 625 or Hastelloy C-276; when sour/SCC risk dominates compare with Elgiloy or MP35N.

Need 718 spring energizers or help choosing a material? Request a quote — include operating temperature profile and gland geometry.

Core characteristics

Typical chemical composition (limiting ranges, wt.%)

Typical limiting composition ranges for INCONEL 718 — verify exact lot values on the mill certificate:

(Source: supplier technical bulletins — use mill certificate for procurement acceptance.)

Key physical data (typical)

Typical physical & thermal properties — always confirm with your wire/strip supplier for the selected product form & temper:

718 — core capabilities (why choose 718)

• High strength across a broad temperature range: age-hardening produces excellent tensile/creep strength and good fatigue life.
• Good weldability and toughness: slower age response allows anneal/weld without spontaneous hardening during heating and cooling, providing excellent weldability when compared to other PH alloys.
• Cryogenic to elevated-temperature use: retains ductility at low temperatures and strength at elevated temperatures (use supplier data to set limits).
• Reliable spring / fastener performance: commonly used where high static/dynamic loads and post-weld mechanical integrity are required.
• Limitations: localized corrosion (pitting) resistance is lower than 625; for aggressive chloride/pitting environments consider 625 instead.

Typical applications

• High-strength springs and energizers requiring age-hardened performance and fatigue resistance.
• Actuator springs, valve springs and fasteners in aerospace and power generation.
• Parts requiring both good weldability and high strength (e.g., welded assemblies with post-process age hardening).
• Applications from cryogenic service up to moderate elevated temperatures where strength is critical.

Forming into springs & spring types

Reminder: spring energizers are formed from wire (round or profiled) or strip. INCONEL 718 is available as spring wire; always confirm available diameters, degree of cold work and recommended aging schedules with the wire supplier before production.

• Canted Coil Springs
• Helical Springs
• Cantilever V / U Springs
• Full Contact Springs

Forming & finishing notes

• Coiling is often performed in the annealed or pre-aged condition with a final controlled aging cycle tailored to component geometry to achieve target stress-relaxation and UTS.
• Cold work (drawing/coiling) and aging interact strongly — supplier diameter-by-temper tables and stress-relaxation charts are required design inputs.
• Surface finish, shot peening and post-forming processes improve fatigue/corrosion performance for springs used in dynamic sealing applications.

Alternatives & comparison

Quick comparison of common alternatives — Min/Max temperatures and recommended continuous temperature are shown to aid selection. Values are engineering guidance compiled from supplier datasheets; verify with your supplier and mill certificate.

Note: table values are indicative consolidated guidance. For spring design always rely on supplier diameter-by-temper data, mill certificates and stress-relaxation curves for the chosen wire diameter and temper.

Selection guidance

Direct, practical rules to choose between INCONEL 718 and nearby alternatives for spring-energized seals:

• Dominant: Highest age-hardened strength & fatigue at moderate-to-high temperature — choose INCONEL 718.
• Dominant: Long-term creep / preload retention at very high temperature — choose INCONEL X-750.
• Dominant: Pitting / chloride corrosion — choose INCONEL 625.
• Dominant: Sulfide stress cracking / sour gas — prioritise Elgiloy or MP35N and require NACE MR0175 / ISO 15156 qualification.
• Dominant: Cryogenic performance — 718 offers excellent low-temperature toughness (verify specific temp/geometry with supplier).

Quick validation checklist (must-do before final selection)

• Obtain supplier mill certificate and diameter-by-temper mechanical tables.
• Request stress-relaxation / creep curves at the intended operating temperature for the selected wire diameter/temper.
• Specify representative fatigue + corrosion test coupons for qualification of critical parts.

FAQ

Q1: What makes INCONEL 718 different from INCONEL 625?

A1: INCONEL 718 is age-hardenable with very high tensile/fatigue strength after precipitation; 625 is a solid-solution strengthened alloy with superior pitting/crevice corrosion resistance. Choose 718 where strength/fatigue is primary; choose 625 where corrosion resistance is primary.

Q2: Can 718 be used for springs that must operate at 600 °C continuously?

A2: 718 retains useful strength up to elevated temperatures, but for continuous long-term service near 600 °C you must consult supplier stress-relaxation and creep data for the specific wire diameter and temper before final selection.

Q3: What standards/specifications apply to INCONEL 718 spring wire / bar?

A3: Common specifications include SAE/AMS conditions (e.g., AMS 5662 / AMS 5663 for bar/forgings), ASTM/ASME product specs (e.g., ASTM B637 for precipitation-hardenable rod/bar), and project-specific NACE MR0175 / ISO 15156 guidance for sour service. Always specify the required AMS/ASTM/NACE references on purchase orders.

Q4: What heat treatments are typical for 718 springs?

A4: Typical treatments include solution annealing followed by age hardening (various schedules used depending on diameter and required properties). Supplier datasheets and AMS/industry specs define precise schedules.

References

1. Special Metals — INCONEL® alloy 718 technical bulletin (composition, physical properties and temperature guidance).
2. Carpenter Technology — Alloy 718 product & datasheet (age hardening, mechanical properties).
3. MatWeb / ASM — INCONEL 718 material data & typical properties.
4. ASTM B637 — Standard Specification for Precipitation-Hardening Nickel Alloy Rod, Bar, Forgings and Forging Stock (relevant for precipitation-hardening nickel alloys).
5. NACE MR0175 / ISO 15156 — Materials for use in H₂S-containing environments in oil and gas production (sour service guidance and qualification).