Haynes 282 vs Inconel 718

For mid-range high-temperature structural parts where excellent long-term creep resistance, thermal stability above ~650°C (1200°F), and robust weldability are critical, Haynes 282 is frequently the better choice. For applications that demand very high room-temperature and moderate-temperature yield/tensile strength, broad availability in many wrought/forged forms, and a long track record across oil & gas and aerospace, Inconel 718 remains the default. In practice the right alloy depends on operating temperature, required creep life, fabrication route (weld-intensive vs forged), and cost/supply constraints.

What these alloys are and industrial context

Both Haynes® 282® (UNS N07208) and Inconel® 718 (UNS N07718) are nickel-base superalloys developed for elevated-temperature service, but they were engineered with different tradeoffs in mind.

• Haynes 282 is a gamma-prime (γ′) strengthened wrought superalloy designed to combine high creep resistance at elevated temperatures with good weldability and fabricability. It targets hot-gas-path components, advanced steam and s-CO₂ power cycles and other situations where long creep life above 650°C is required.

• Inconel 718 is a precipitation-hardenable Ni-Cr-Fe alloy (main hardener: γ″ Ni₃Nb) with extremely good strength from cryogenic up to roughly 650°C. It is widely used across aerospace, oil & gas, and tooling because of its combination of fabricability, high yield/UTS in the aged condition, and a mature supply chain.

Chemical composition (typical nominal values)

Below is a compact composition comparison. These are typical nominal ranges used for engineering selection — always verify the exact lot/specification from your material cert.

(Exact composition limits are available in vendor data sheets; Haynes 282 composition shown in the Haynes brochure. Inconel 718 composition is shown in Special Metals technical bulletin.)

Implication: 282 contains substantial cobalt and molybdenum and is formulated for γ′ strengthening and thermal stability; 718 relies on niobium-driven γ″ precipitation and iron content, producing a different strength vs temperature profile.

Strengthening mechanisms and microstructure

Understanding why they behave differently starts with microstructure:

• Inconel 718: principal hardening phase is the metastable γ″ (Ni₃Nb) plus γ′ to a lesser extent; γ″ produces very high yield and tensile strengths at room and moderate temperatures but is sensitive to coarsening at higher temperatures (>650°C) over long exposures. Controlled solution anneal + aging produces fine γ″ precipitates for peak strength.

• Haynes 282: a γ′ strengthened Ni-Cr-Co-Mo-Al-Ti alloy engineered to precipitate a stable γ′ phase slowly (sluggish precipitation kinetics). That slower precipitation gives excellent resistance to strain-age cracking and good retention of strength at higher temperatures for long durations. The alloy was deliberately tuned to balance creep resistance and weldability.

Net result: 718 often has higher short-term yield/UTS in the aged condition at room and moderate temperatures; 282 retains better long-term creep/rupture life and thermal stability at the higher end of the temperature window.

Mechanical performance summary

Representative tensile/yield figures (age-hardened condition; typical ranges)

Creep / rupture and usable temperature window

• Haynes 282: designed for excellent creep strength from ~1200–1700°F (≈650–925°C) with long rupture lives; retains creep resistance and low cycle fatigue life at these temperatures. Haynes publishes detailed creep tables showing superior 1% creep stress and rupture life in the 650–925°C window versus many γ′ alloys.

• Inconel 718: excellent creep-rupture properties up to around 650°C (≈1300°F) — widely used up to ~700°C for some formats — but its γ″ hardening phase coarsens at higher temperatures and long exposures, reducing creep strength relative to alloys like 282. Special Metals states 718 is effective up to roughly 1300°F (≈700°C) for many applications.

Interpretation for design: If your duty requires very long lives under sustained stress at >650°C, 282 is the safer technical choice; if operation is ≤650°C and high short-term strength is needed, 718 may offer the higher margin for static strength and is easier to source.

Heat treatment, welding and fabrication notes

• Heat treatments:

  • Inconel 718 uses solution anneal (≈1700–1850°F or higher for some forms) followed by double-step aging cycles (e.g., 1325°F/8h, furnace cool to 1150°F hold, total aging ≈18h) or alternate cycles for thicker forgings. These treatments maximize γ″ precipitation and yield/UTS.

  • Haynes 282 is typically solution annealed (≈2050–2100°F for sheet) then a two-step age (Haynes standard example: 1850°F/2h AC + 1450°F/8h AC) — the alloy was also qualified with single-step options for ASME boiler applications.

• Weldability & strain-age cracking:

  • 282 was engineered to be weld-friendly: slow γ′ precipitation kinetics and good resistance to strain-age cracking mean components can be welded in solution-annealed condition and then aged to strength with fewer weld-related failures. Haynes publishes GTAW/GMAW weld data showing robust weld metal performance.

  • 718 is weldable and commonly welded in industry, but the HAZ and aging behavior must be accounted for (some HAZ softening can occur depending on the condition). Proper filler selection and post-weld heat treatments are typical to regain properties.

Fabrication practice: buy material in the soft (solution-annealed) condition for heavy fabrication; perform final aging after all welds/finish machining where possible.

Corrosion and oxidation behaviour

Both alloys form protective oxide scales due to chromium and nickel content, giving good oxidation resistance in many environments.

• Haynes 282 shows good high-temperature oxidation resistance and is targeted for hot-gas-path usage in turbines and advanced boilers. Its chemistry (Cr + Co + Mo) contributes to stable scale formation and sulfidation resistance in some aggressive environments.

• Inconel 718 has excellent corrosion resistance in many aqueous and high-temperature oxidizing environments similar to other Ni-Cr alloys; its performance is well characterized in oil & gas (NACE MR0175) and aerospace contexts.

For aggressive oxidizing/halogenated environments, perform coupon testing under expected service conditions; alloy selection should also consider coatings or protective barriers.

Machinability, forming and additive manufacturing (AM)

• Machining & forming: Both alloys are tougher to machine than stainless steels; 718 is widely machined in industry with well-known tooling and speed recommendations. 282’s machinability is similar to other high-temperature Ni alloys; rough machining before aging is commonly recommended.

• Additive manufacturing: Recent AM work compares 282 and 718. Additive forms of 282 can achieve excellent high-temperature performance and show promise for complex hot-section components because of 282’s designed fabricability and slow γ′ kinetics. However, AM microstructure and properties depend strongly on process and post-processing; some AM experiments show variations from wrought behavior and require tailored thermal treatments. Published comparative studies (including NASA/ICAM reports) show that both alloys have successful AM histories but need process-specific qualification.

Typical applications & selection rules of thumb

• Choose Haynes 282 if: you need long creep life and thermal stability at 650–925°C, expect extensive welding/fabrication, require resistance to strain-age cracking, or are designing next-generation power cycle components (turbine combustors, transition pieces, A-USC boilers, supercritical CO₂ systems).

• Choose Inconel 718 if: your service temperature stays ≲650°C, you need the highest possible aged yield/UTS at moderate temperatures, require a widely available alloy in many product forms (bars, forgings, plate), or you need extensive cold-working plus aging to achieve very high strength. 718 also remains preferred for many fasteners, shafts and cryogenic to moderate-temperature structural parts.

Cost, availability and procurement notes

• Availability: Inconel 718 is produced by many mills and has mature supply chains; 718 is often easier to source quickly in many formats. Haynes 282 is produced under license from Haynes International and is increasingly available but may have longer lead times for some large forgings or special forms.

• Cost: Market prices fluctuate with Ni, Co and Mo commodity prices. Haynes 282 contains higher Co and Mo content, which can increase raw-material cost relative to 718 (which has higher Nb). Always get live quotes and consider total lifecycle cost (material + fabrication + inspection + downtime risk).

Standards, testing and qualification

• Inconel 718 is specified under many product standards (UNS N07718; ASTM/ASME product specs; AMS specifications such as AMS 5662/5663/5596 etc. for bars/forgings/sheets). Special Metals technical bulletin and AMS/ASTM documentation give the recommended heat treatments and property tables.

• Haynes 282 has vendor technical data, ASME Code Cases for specific boiler/steam applications (e.g., ASME Code Case for single-step age), and is being adopted into industrial practice with published creep/rupture data. For critical use, follow Haynes published heat treatment and fabrication recommendations and secure material test reports (MTRs) and creep certificates as required.

Practical designer recommendations

1. Define operating envelope first (temperature, sustained stress, creep life requirement). If you need >100,000 hours at ~760°C under sizable stress, bias toward 282.

2. Specify material condition at delivery (solution annealed vs annealed+aged) and plan final aging after fabrication whenever possible.

3. Include welding and post-weld heat treatment clauses in procurement specs; require weld procedure qualifications for your chosen alloy/condition.

4. Ask suppliers for creep/rupture data for the lot when long creep life is required — accept only certified test data that matches the intended heat treatment.

5. If using AM, require process-specific qualification coupons and heat-treat recipes; do not assume wrought properties.

Frequently asked questions (FAQs)

1. Which alloy is stronger at room temperature, 282 or 718?
   In the peak aged and cold-worked conditions, Inconel 718 generally achieves higher room-temperature yield and UTS numbers than Haynes 282. However, 282 in the age-hardened condition still has substantial strength while offering better high-temperature stability.

2. Which alloy resists creep better at 750°C (1382°F)?
   Haynes 282 was designed for superior creep strength in the 650–925°C range and typically outperforms 718 for long-term creep at 750°C.

3. Is Haynes 282 weldable?
   Yes — 282’s chemistry and slow γ′ precipitation kinetics give it unusually good weldability for a γ′-strengthened superalloy. Vendors publish GTAW/GMAW welding data and post-weld aging procedures.

4. Can I substitute 718 for 282 to save money?
   Not without understanding service conditions. Substituting 718 may be acceptable for lower temperatures (<650°C) but risks premature creep/rupture for sustained high-temperature duties. Evaluate life prediction, stress, and temperature before substituting.

5. Which alloy is better for additive manufacturing?
   Both are used in AM, but process windows differ. 282’s fabricability and slower γ′ kinetics are attractive for AM, yet AM parts require process and heat-treat qualification regardless of alloy. Consult AM vendors and published AM studies.

6. Are there service limitations for 718 in oil & gas?
   718 is used in oil & gas and can meet NACE/MR0175 requirements in appropriate heat treatments. However, for extremely hot service or long creep exposures, consider higher-temperature alloys.

7. Which has higher corrosion resistance?
   Both have excellent corrosion/oxidation resistance for many applications. Specific environments (chloride-bearing, sulfidizing, molten salts) need case-by-case testing.

8. What heat treatment should I specify for 282?
   A: Typical Haynes guidance: solution anneal followed by age-hardening (example: 1850°F/2h AC + 1450°F/8h AC). ASME Code Case variations exist for certain steam applications — follow vendor instructions.

9. How does cost compare?
   Cost depends on current commodity prices for Ni, Co, Mo, and Nb and on product form. 282’s higher Co/Mo content can make it more expensive per kg than 718, but life-cycle cost and fabrication savings can offset purchase price. Get up-to-date quotes.

10. How should I qualify a supplier for critical parts?
    Require MTRs, process/heat-treatment records, creep/rupture certificates if applicable, welding procedure qualification records (PQR/WPQ), and dimensional & NDT acceptance criteria. For AM parts, require process control plan and coupons.

Closing practical checklist for procurement & design

• Specify alloy UNS and exact product spec/AMS/ASTM.

• Require delivery condition and post-fabrication aging sequence in the purchase order.

• Ask for creep/rupture test data for design stress/temperature combos.

• Include weld procedure qualifications and NDT acceptance.

• For AM parts, insist on process qualification, stress-relief & aging recipe and coupon testing.

Authoritative references

• • HAYNES® 282® alloy — Technical Brochure (Haynes International)
  • INCONEL® Alloy 718 — Technical Bulletin (Special Metals Corporation)
  • Comparative tensile/temperature study — NASA / ICAM (Inconel 718 vs Haynes 282)