Inconel 601 vs Inconel 600: Key Differences in Composition & High Temp Performance

When specifying nickel-chromium alloys for thermal processing, engineers often weigh Inconel 600 (UNS N06600)​ against Inconel 601 (UNS N06601 / W.Nr. 2.4851). While both are solid-solution strengthened, non-precipitation-hardenable alloys with similar Ni-Cr-Fe bases, Inconel 601 was developed as an improved version of Alloy 600—specifically to address high-temperature oxidation, scaling (spalling), and carburization resistance​ in air or mildly sulfurous atmospheres. Shanghai COCESS Special Alloys Co., Ltd​ supplies both Inconel 600 and Inconel 601 in plate, sheet, bar, tube, and forged forms per ASTM B168/B166/B167, with full EN 10204 3.1 certification and custom processing support. This article outlines the metallurgical and performance differences to guide correct selection.

1. Chemical Composition Comparison — The Critical Variables

The single most important difference is Chromium content increased from ~15–17% to ~23% AND the addition of 1.0–1.7% Aluminum (Al)​ in Alloy 601.

Takeaway:​ Inconel 601 = Inconel 600 + ↑Cr (~23%) + intentional Al (~1.4%). The Al addition is the metallurgical game-changer for high-temp exposure.

2. High-Temperature Oxidation & Scaling Resistance

• Inconel 600:​ Forms Cr₂O₃ (chromia) scale in oxidizing atmospheres. At 650–980°C this is protective, but above ~1000°C Cr₂O₃ volatilizes slightly and is prone to thermal-cycle spalling​ (flake-off on cooling), exposing fresh metal.

• Inconel 601:​ Al oxidizes selectively to form a continuous α-Al₂O₃ (alumina) layer, often with (Cr,Al)₃O₄ spinel at the interface. Al₂O₃ has:

  • Lower oxygen diffusivity → slower growth rate

  • Better adherence → resists spalling during heating/cooling cycles

  • Higher stability to ~1200°C in air

• Practical Result:​ Alloy 601 is rated for continuous oxidation service to 1150–1200°C (2100–2190°F); Alloy 600 is typically limited to ~1095°C (2000°F) and less tolerant of thermal cycling. For furnace muffles, radiant tubes, and hearth rolls, 601 is strongly preferred.

3. Carburization & Sulfidation Resistance

• Carburization (e.g., in endothermic RX gas, methanol dissociated atmospheres for case hardening):

  • Alloy 601's dense Al₂O₃/Cr₂O₃ scale impedes inward carbon diffusion better than Alloy 600's Cr₂O₃ alone.

  • In carburizing furnace components (muffles, retorts, radiant tubes), 601 typically outlasts 600 by a factor of 2–3×.

• Sulfidation:

  • In low-oxygen, high-H₂S​ environments, neither alloy forms a stable protective film; both can suffer accelerated attack.

  • In flue gases containing SO₂ + O₂, both are acceptable, with 601 having a slight edge due to the more stable mixed oxide.

4. Mechanical Properties & Allowable Stress

Both are solid-solution alloys supplied in the solution-annealed condition. Strength levels are similar but not identical:

• High-Temp Strength:​ Slightly lower for 601 above 800°C due to lower Ni, but difference is usually negligible for furnace fixture / low-stress applications.

• Creep Rupture:​ Both are moderate; neither matches precipitation-hardened alloys (Inconel 718/X-750). For high stress at > 650°C, consider Nimonic or Inconel 718.

5. Corrosion in Aqueous / Process Environments

• Chloride SCC:​ Both resist chloride-induced SCC better than 300-series stainless steels. Alloy 601 (Cr≈23%) shows marginally better resistance than Alloy 600 (Cr≈15–17%).

• Acid / Reducing Media:​ Neither is a substitute for Alloy 625 (Mo-added) or Hastelloy C-276. Both handle dilute nitric acid and caustic (NaOH/KOH) reasonably well.

• Seawater / Pitting:​ PREN ≈ 23–24 (similar to 316L), so pitting resistance is modest. For marine / sour-gas severe corrosion, Alloy 625 or duplex SS is preferred.

6. Weldability & Fabrication

• Both are readily weldable using GTAW/GMAW.

• Filler Metal:

  • Alloy 600 → ERNiCr-3 (AWS A5.14)

  • Alloy 601 → ERNiCrFe-11 (AWS A5.14)​ or sometimes ERNiCr-3 if code permits (check WPS)

• Post-weld heat treatment (stress relief) is optional for corrosion resistance (both are non-sensitizing when low C), but may be done to reduce residual stress in critical geometries.

7. Selection Guideline — When to Use Which?

Supply & Support – Shanghai COCESS Special Alloys Co., Ltd

We stock and process both alloys in:

• Plate / Sheet:​ ASTM B168 — Thk 0.5–50 mm

• Bar / Forging Stock:​ ASTM B166 — Dia 6–300 mm

• Seamless & Welded Tube / Pipe:​ ASTM B167 / B516 / B517

• Custom Cutting, Beveling, Pickling, UT/ET Inspection

Each shipment includes EN 10204 3.1 MTR. Third-party inspection (SGS/TÜV/DNV) and seaworthy export packaging available.

For Inconel 600 or Inconel 601 inquiries—including comparative quotations, mill test report samples, or assistance selecting the correct grade for your furnace or process—please contact Shanghai COCESS Special Alloys Co., Ltd. Our technical team can review your operating temperature, atmosphere (oxidizing/carburizing/sulfidizing), and stress level to confirm the most cost-effective alloy choice.