What is Haynes 188 Alloy? UNS R30188, Equivalent Grades (GH5188, 2.4683) & Typical Applications

Haynes 188 (UNS R30188 / W.Nr. 2.4683 / China GH5188) is a solid-solution strengthened cobalt-chromium-nickel-tungsten superalloy​ with a deliberate addition of 0.04–0.08 % lanthanum (La)—a rare-earth element that significantly improves the adherence of the protective chromium-oxide scale during cyclic high-temperature oxidation. Developed in the 1960s by Haynes International (formerly Union Carbide Stellite Division), it is the premier cobalt-base sheet alloy for 870–1095°C (1600–2000°F) oxidizing / slightly sulfidizing environments, especially where thermal cycling, vibration, or complex thin-walled forming (bellows, combustion liner, nozzle extension) is required.

Unlike precipitation-hardenable Ni-base alloys (Inconel 718, René 41), Haynes 188 relies solely on solid-solution and carbide precipitation for strength—it cannot be age-hardened—but offers no ductile-to-brittle transition (DBTT)​ down to –196°C, excellent weldability, and superior resistance to oxide-scale spallation compared to its predecessor Haynes 25 (L-605 / UNS R30605), which lacks rare-earth modification.

1. UNS, Trade Name & International Equivalents

⚠️ GH5188 is nota direct copy of Haynes 25/L-605 (GH5605). The La addition and higher Ni (20–24 % vs 9–11 %) are the differentiating features.

2. Nominal Chemical Composition (ASTM / AMS 5608 Requirement)

3. Key Physical Properties (Annealed, 20°C Unless Noted)

4. Typical Mechanical Properties (Solution-Annealed Condition)

Minimum Requirements — AMS 5608 (Sheet/Strip, annealed):

Representative Elevated-Temperature Tensile — Typical Annealed Sheet:

• No DBTT:​ Retains ≥ 30 % elongation at –196°C → suitable for cryogenic bellows / LNG expansion joints exposed to high-temp excursions.

• Creep:​ Usable for moderate stress to ~870°C (e.g. 70–105 MPa for hundreds–thousands of hours depending on design code). Not a disk alloy (Inconel 718 / René 41 preferred for high creep).

• Long-term exposure 650–870°C:​ Minor M₂₃C₆ / M₆C at grain boundaries; does not impair oxidation resistance or room-temp impact.

5. Oxidation & Corrosion Behavior (Core Advantage)

• Continuous Air Oxidation:​ Protective Cr₂O₃ scale to 1095°C (2000°F). La dopant suppresses scale cracking/spallation during thermal cycling—this is the principal advantage over Haynes 25 (L-605) and over many Ni-base alloys in cyclicservice.

• Cyclic / Thermal Shock Oxidation:​ 870–980°C ↔ ambient repeated cycles → minimal scale loss; L-605 shows measurable spallation → base metal re-oxidizes → higher consumption.

• Sulfidizing / Mixed Combustion Gases:​ More resistant than Ni-base alloys to sulfur-bearing combustion products (no low-melting Ni–S eutectic).

• Carburizing / Nitriding:​ Moderate resistance; for severe carburizing select Inconel 601 / Alloy 800HT (higher Cr, Fe).

• Chloride / Seawater:​ Not a primary candidate (PREN ≈ 22–25 via Cr only); 316L/625/825 cheaper/better for ambient seawater.

6. Fabrication, Welding & Heat Treatment

• Hot Working:​ 1095–1200°C; finish > 980°C; air cool or faster. Avoid prolonged holds 650–870°C (carbide precipitation zone—does not cause sensitization but may affect forming consistency).

• Cold Working:​ Work-hardens similarly to 300-series SS; intermediate anneals at 1175–1230°C → rapid quench restore ductility.

• Solution Anneal:​ 1175–1230°C × (time per section) → water quench or high-velocity air blast (thin sections)​ → single-phase γ + dissolved carbides. Critical for optimum oxidation-scale formation.

• Welding:​ GTAW / GMAW / EBW / LBW all suitable.

  • Recommended filler: ERNiCoCrMo-1 (AWS A5.14 Class, nominal match to R30188 chemistry)​ or same-alloy wire.

  • No PWHT required for corrosion/oxidation; stress-relief ≤ 400°C permissible for dimensional stability.

• Machining:​ Similar to Ni-base superalloys—work-hardens; rigid setup, low SFM, high feed, coolant, carbide inserts.

7. Typical Applications by Industry

Summary

Haynes 188 (UNS R30188 / GH5188 / 2.4683) is a lanthanum-modified, solid-solution Co–Cr–Ni–W superalloy​ optimized for:

• Continuous oxidation resistance to 1095°C (2000°F)

• Exceptional resistance to oxide-scale spallation under thermal cycling​ (rare-earth effect)

• Good strength to 870°C, full ductility to –196°C (no DBTT)

• Excellent thin-sheet formability & weldability

It is the industry reference material for aircraft engine afterburner liners, variable nozzle components, spacecraft extensible nozzles, and high-temperature bellows​ where cyclic oxidation is the life-limiting factor.