Inconel 601 vs Inconel 718 vs Incoloy 925: Which Nickel Alloy Fits Your Application?
At FULLERKREG, we regularly assist engineers and procurement teams in distinguishing between nickel alloys that serve very different purposes despite sharing a common base. Inconel 601 (N06601) is a high-temperature oxidation-resistant alloy; Inconel 718 (N07718) is a precipitation-hardened superalloy delivering exceptional strength up to 700°C; and Incoloy 925 (N09925) is an age-hardenable alloy engineered specifically for oil & gas sour service environments.
This guide provides a direct technical comparison of all three grades per their respective ASTM standards, covering chemical composition and mechanical properties to support your material selection decision.
Alloy Overview
- Inconel 601 (N06601) — A nickel-chromium alloy with aluminum addition for outstanding oxidation resistance at temperatures up to 1175°C. Excellent resistance to carburization and nitriding. Governed by ASTM B166.
- Inconel 718 (N07718) — A precipitation-hardenable nickel-chromium alloy with niobium, molybdenum, and titanium additions. The most widely used superalloy in aerospace and industrial gas turbine applications, offering very high strength from cryogenic temperatures to 700°C. Governed by ASTM B637.
- Incoloy 925 (N09925) — An age-hardenable nickel-iron-chromium alloy with molybdenum, copper, titanium, and niobium. Designed for high-strength sour gas service (H₂S environments) per NACE MR0175 / ISO 15156. Governed by ASTM B637.
Chemical Composition Comparison
All values are weight percent (%). Min = minimum required; Max = maximum allowed per respective ASTM standard.
Inconel 601 — N06601 (ASTM B166)
| C | Mn | S | Si | Cr | Ni | Cu | Fe | Al | |
|---|---|---|---|---|---|---|---|---|---|
| Min | — | — | — | — | 21.0 | 58.0 | — | Rem. | 1.0 |
| Max | 0.10 | 1.0 | 0.015 | 0.5 | 25.0 | 63.0 | 1.0 | — | 1.7 |
Inconel 718 — N07718 (ASTM B637)
| C | Mn | P | S | Si | Cr | Ni | Mo | Al | Cu | Ti | Nb+Ta | Co | B | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | — | — | — | — | — | — | 50 | 2.8 | 0.2 | — | 0.65 | 4.75 | — | — |
| Max | 0.08 | 0.35 | 0.015 | 0.015 | 0.35 | 21 | 55 | 3.3 | 0.8 | 0.3 | 1.15 | 5.5 | 1.0 | 0.006 |
Incoloy 925 — N09925 (ASTM B637)
| C | Mn | P | S | Si | Cr | Ni | Mo | Ti | Cu | Fe | Nb | Al | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min | — | — | — | — | — | 19.5 | 42.0 | 2.5 | 1.9 | 1.50 | 22 | — | 0.1 |
| Max | 0.03 | 1.0 | 0.03 | 0.03 | 0.5 | 22.5 | 46.0 | 3.5 | 2.4 | 3.00 | — | 0.5 | 0.5 |
Mechanical Properties Comparison
| Grade | UNS | Condition | Tensile Strength Rm (N/mm²) min | Yield Strength Rp0.2 (N/mm²) min | Elongation A (%) min | Reduction of Area (%) min | Hardness HB max |
|---|---|---|---|---|---|---|---|
| Inconel 601 | N06601 | Annealed | ≥552 | ≥205 | ≥30 | — | — |
| Inconel 718 | N07718 | Age hardened | ≥1275 | ≥1034 | ≥12 | ≥15 | ≤331 |
| Incoloy 925 | N09925 | Age hardened | ≥965 | ≥758 | ≥18 | ≥25 | ≤38 |
Key Differences at a Glance
| Parameter | Inconel 601 (N06601) | Inconel 718 (N07718) | Incoloy 925 (N09925) |
|---|---|---|---|
| Ni content (%) | 58.0–63.0 | 50–55 | 42.0–46.0 |
| Cr content (%) | 21.0–25.0 | ≤21 | 19.5–22.5 |
| Mo content (%) | — | 2.8–3.3 | 2.5–3.5 |
| Key alloying additions | Al (oxidation resistance) | Nb+Ta, Ti, B (precipitation hardening) | Cu, Ti, Nb (age hardening + sour service) |
| Strengthening mechanism | Solid solution | Precipitation hardening (γ″ + γ’) | Precipitation hardening (γ’) |
| Tensile Strength min (N/mm²) | 552 | 1275 | 965 |
| Yield Strength min (N/mm²) | 205 | 1034 | 758 |
| Elongation min (%) | 30 | 12 | 18 |
| Max service temperature | ~1175°C (oxidizing) | ~700°C (high strength) | ~260°C (sour service per NACE) |
| Sour service (H₂S) rating | Not rated | Limited (per NACE MR0175) | Yes — designed for NACE MR0175 / ISO 15156 |
| Governing ASTM standard | B166 | B637 | B637 |
Application Selection Guide
Choose Inconel 601 (N06601) when:
- High-temperature oxidation resistance is the primary requirement (up to 1175°C)
- Resistance to carburization, nitriding, and sulfidation in furnace atmospheres is needed
- Mechanical strength at room temperature is secondary to thermal stability
- Typical applications: radiant tubes, furnace muffles, heat treating baskets, combustion chambers, industrial heating elements
Choose Inconel 718 (N07718) when:
- Maximum mechanical strength is required at temperatures up to 700°C
- Fatigue resistance, creep strength, and weldability must all be maintained simultaneously
- Aerospace, defense, or industrial gas turbine specifications call for a precipitation-hardened superalloy
- Typical applications: aerospace fasteners, turbine discs and blades, rocket motor components, cryogenic tankage, nuclear reactor components, high-strength bolting
Choose Incoloy 925 (N09925) when:
- High strength is required in sour gas (H₂S-containing) environments per NACE MR0175 / ISO 15156
- Resistance to stress corrosion cracking, pitting, and crevice corrosion in chloride-bearing brines is critical
- Oil & gas downhole or surface equipment specifications require an age-hardenable alloy with controlled hardness (≤38 HRC)
- Typical applications: downhole tubing hangers, wellhead components, subsea fasteners, valve stems, pump shafts in sour service
FULLERKREG Supply Capabilities
FULLERKREG supplies precision fasteners and engineered components in Inconel 601, Inconel 718, and Incoloy 925:
- Material Test Certificates (MTC) — EN 10204 3.1 / 3.2 available on request
- ASTM B166 / B637 compliance — rod and bar forms for fastener and structural applications
- NACE MR0175 / ISO 15156 compliance documentation — for sour service applications (925)
- Custom fastener dimensions — non-standard thread forms, head styles, and lengths
- Bulk wholesale pricing — OEM and MRO procurement with competitive lead times
- Global shipping — from our manufacturing base in China to customers worldwide
Need a quote or technical consultation for Inconel 601, Inconel 718, or Incoloy 925 fasteners? Contact FULLERKREG with your specification and our engineering team will respond promptly.
FULLERKREG — Precision Fasteners. Global Standards. Reliable Supply.