⚡ Quick Specs: Inconel 718M
What Is Inconel 718M?
Inconel 718M is a marine-optimized variant of Inconel 718 (UNS N07718 / W.Nr. 2.4668), the world's most widely used precipitation-hardening nickel superalloy. While standard Inconel 718 was originally developed for aerospace gas turbines, the 718M designation refers to material specifically processed, tested, and qualified for subsea and marine oil & gas applications — including deepwater wellheads, subsea connectors, high-strength fasteners, and structural components exposed to seawater and production fluids.
Inconel 718M retains the same chemical composition and gamma-double-prime (γ″) precipitation hardening mechanism as aerospace-grade Inconel 718, but adds supplementary NACE MR0175/ISO 15156 sour-service qualification, tighter chemistry controls for consistent properties in heavy sections, and specific heat treatment windows validated for subsea pressure-containing parts. As an Inconel 718M manufacturer and supplier, Hangbo Alloy Group delivers the grade in forged bars, rings, fasteners, and machined components with full traceability.
Chemical Composition
Nominal composition of Inconel 718M per UNS N07718. All values in weight percent (wt%).
| Element | Min (wt%) | Max (wt%) |
|---|---|---|
| Nickel (Ni) | 50.0 | 55.0 |
| Chromium (Cr) | 17.0 | 21.0 |
| Iron (Fe) | Balance | Balance |
| Niobium (Nb) | 4.75 | 5.50 |
| Molybdenum (Mo) | 2.80 | 3.30 |
| Titanium (Ti) | 0.65 | 1.15 |
| Aluminum (Al) | 0.20 | 0.80 |
| Carbon (C) | — | 0.08 |
| Manganese (Mn) | — | 0.35 |
| Silicon (Si) | — | 0.35 |
| Phosphorus (P) | — | 0.015 |
| Sulfur (S) | — | 0.015 |
| Boron (B) | — | 0.006 |
| Cobalt (Co) | — | 1.0 |
Physical Properties
| Property | Value | Unit |
|---|---|---|
| Density | 8.19 | g/cm³ |
| Melting Range | 1260 – 1336 | °C |
| Specific Heat (21 °C) | 435 | J/kg·K |
| Thermal Conductivity (21 °C) | 11.4 | W/m·K |
| Electrical Resistivity (21 °C) | 1.25 | μΩ·m |
| Young's Modulus (21 °C) | 200 | GPa |
| Mean CTE (20–100 °C) | 13.0 | μm/m·°C |
Mechanical Properties
| Property | Typical Value |
|---|---|
| Tensile Strength (Rm, aged) | ≥ 1240 MPa (≥ 180 ksi) |
| Yield Strength (Rp0.2, aged) | ≥ 1035 MPa (≥ 150 ksi) |
| Elongation (A%, aged) | ≥ 12% |
| Reduction of Area (aged) | ≥ 15% |
| Hardness (aged) | ≤ 40 HRC (NACE max) |
| Charpy V-Notch Impact (−46 °C) | ≥ 27 J (avg) |
High-Temperature Performance
- Subsea temperature stability: Maintains full mechanical properties at subsea and wellhead operating temperatures up to 150 °C; short-term excursions to 200 °C are acceptable.
- High-pressure hydrogen: Low susceptibility to hydrogen embrittlement under cathodic protection conditions common in subsea installations up to −1100 mV (Ag/AgCl).
- Thermal aging resistance: Retains strength and toughness after prolonged exposure to subsea service temperatures without embrittlement.
- Low-temperature toughness: Excellent Charpy impact values at −46 °C and below, meeting requirements for Arctic and deepwater applications.
Corrosion Resistance
- Seawater corrosion: Good general corrosion resistance in seawater with pitting resistance equivalent (PRE) of approximately 30. Requires cathodic protection for long-term subsea immersion.
- Sour service (H₂S): Qualified per NACE MR0175/ISO 15156-3 up to Level VI (≤150 °C) when hardness is controlled to ≤40 HRC, making it suitable for wellhead and Christmas tree components in sour fields.
- Chloride stress corrosion cracking: High nickel content provides excellent resistance to chloride-induced SCC in marine atmospheres and seawater environments.
- Crevice corrosion: Good resistance to crevice corrosion in subsea bolted connections and flange joints, though tight crevices under deposits require appropriate design and CP monitoring.
Applications
| Application Area | Typical Components & Notes |
|---|---|
| Subsea Wellheads | Valve bodies, bonnets, stems, seats, and pressure-containing blocks in subsea Christmas trees and wellhead assemblies |
| Subsea Connectors | Collet connectors, clamp hubs, and flange connectors for deepwater flowline and riser connections |
| High-Strength Fasteners | API 6A and API 17D bolting, studs, nuts, and washers for subsea pressure-containing equipment |
| Marine Risers | Drilling and production riser components including tension rings, flange adapters, and stress joints |
| Subsea Manifolds | Block forgings, valve blocks, and piping components in subsea production manifolds |
| Downhole Tools | High-strength mandrels, subs, and crossover components for deepwater completion and intervention |
Available Product Forms
| Product Form | Typical Dimensions & Specifications |
|---|---|
| Forged Bar & Billet (API 6A) | φ 25 – φ 600 mm, triple-melt (VIM+ESR+VAR), solution treated and aged per API 6A |
| Forgings & Rings | Custom wellhead blocks, flanges, connectors, and valve bodies up to 2500 mm OD |
| Fasteners (API 20E) | Studs, bolts, nuts per API 6A/17D, full traceability with heat code marking |
| Machined Components | Finish-machined valve internals, stems, seats, and seal rings to customer drawing |
| Welding Wire (AWS A5.14 ERNiFeCr-2) | φ 0.8 – φ 3.2 mm for repair and fabrication of Inconel 718M components |
Heat Treatment
| Step | Temperature | Cooling | Purpose |
|---|---|---|---|
| Solution Treatment | 940 – 1010 °C (1725 – 1850 °F) | Air cool / water quench | Dissolve delta and Laves phases; prepare for aging |
| First Aging Step | 718 – 760 °C (1325 – 1400 °F) | Hold 8 hours, furnace cool to 621 °C | Nucleate and coarsen gamma-double-prime (γ″) precipitates |
| Second Aging Step | 621 – 649 °C (1150 – 1200 °F) | Hold 8 hours, air cool | Develop peak strength while controlling hardness ≤40 HRC |
Related Standards & Specifications
| Standard | Product Scope / Notes |
|---|---|
| UNS | N07718 |
| DIN / W.Nr. | 2.4668 |
| API 6A | Wellhead and Christmas tree equipment (718M qualified) |
| API 17D | Subsea wellhead and tree equipment |
| NACE MR0175 / ISO 15156-3 | Sour service qualification up to Level VI |
| API 20E | Alloy and carbon steel bolting for petroleum and natural gas industries |
| ASTM B637 | Precipitation-hardening nickel alloy bars, forgings, and rings |
Frequently Asked Questions (FAQ)
1. What is Inconel 718M?
Inconel 718M is a marine-optimized variant of Inconel 718 (UNS N07718) specifically processed and qualified for subsea oil and gas applications. It offers the same precipitation-hardening characteristics as aerospace Inconel 718 but includes supplementary NACE MR0175 sour-service qualification, tighter chemistry and heat treatment controls, and mechanical property validation for thick-section forgings used in subsea wellheads, connectors, and fasteners.
2. What is the chemical composition of Inconel 718M?
Inconel 718M shares the same nominal chemistry as standard Inconel 718: Ni 50.0–55.0%, Cr 17.0–21.0%, Fe balance, Nb 4.75–5.50%, Mo 2.80–3.30%, Ti 0.65–1.15%, Al 0.20–0.80%, C ≤0.08%. Marine-grade 718M typically imposes supplementary limits on trace elements (S, P, Bi, Pb, Se) and tighter Nb control for consistent precipitation response in heavy sections.
3. What is the density and melting range of Inconel 718M?
Inconel 718M has a density of 8.19 g/cm³ (0.296 lb/in³) and a melting range of 1260–1336 °C (2300–2437 °F), identical to standard Inconel 718.
4. What are the minimum mechanical properties of Inconel 718M?
After full solution treatment and two-step aging: minimum tensile strength 1240 MPa (180 ksi), minimum 0.2% yield strength 1035 MPa (150 ksi), minimum elongation 12%, minimum reduction of area 15%, hardness ≤40 HRC (NACE maximum). Charpy V-notch impact at −46 °C must average ≥27 J for subsea bolting.
5. How does Inconel 718M differ from standard Inconel 718?
The core chemistry and precipitation mechanism are identical. The 718M designation indicates: (1) NACE MR0175/ISO 15156-3 sour-service qualification; (2) supplementary processing controls for subsea pressure-containing forgings; (3) validated properties in heavy sections (up to 600 mm diameter); (4) full documentation per API 6A/17D including heat code traceability, NDE, and hardness mapping.
6. What is the maximum service temperature of Inconel 718M?
For subsea and wellhead service, Inconel 718M is qualified up to about 150 °C (302 °F) under NACE MR0175. For non-sour applications, the alloy retains useful strength up to 650 °C (1200 °F), though long-term exposure above 540 °C may produce gradual over-aging and hardness changes.
7. Is Inconel 718M resistant to seawater corrosion?
Inconel 718M offers good general corrosion resistance in seawater and marine atmospheres due to its high nickel and chromium content. However, like most high-strength nickel alloys, it is cathodic to steel and requires cathodic protection or coating for long-term subsea immersion. The alloy's pitting resistance equivalent (PRE ≈30) provides useful protection against localized attack.
8. Can Inconel 718M be welded?
Yes, Inconel 718M can be welded using GTAW, GMAW, and SMAW processes with matching ERNiFeCr-2 filler. However, subsea pressure-containing weldments typically require post-weld solution treatment and full aging to restore properties and meet NACE hardness limits. Welding on finished components is generally avoided in favor of monolithic forgings for critical subsea parts.
9. What is the heat treatment for Inconel 718M?
Standard subsea heat treatment: solution anneal at 940–1010 °C (1725–1850 °F), air cool or water quench; first age at 718–760 °C (1325–1400 °F) for 8 hours, furnace cool to 621 °C; second age at 621–649 °C (1150–1200 °F) for 8 hours, air cool. This produces peak strength while keeping hardness ≤40 HRC for NACE compliance.
10. What standards apply to Inconel 718M?
Key standards: API 6A (wellhead equipment), API 17D (subsea trees), NACE MR0175/ISO 15156-3 (sour service), API 20E (bolting), ASTM B637 (bars/forgings). Material is supplied with EN 10204 3.1 certification including chemical analysis, tensile tests, hardness, Charpy impact, and NDE reports.
11. What are typical applications of Inconel 718M?
Primary applications: subsea wellhead and Christmas tree valve bodies, bonnets, and stems; subsea collet and clamp connectors; high-strength API 6A/17D bolting and fasteners; drilling and production riser components; subsea manifold block forgings; and deepwater completion tool mandrels and crossovers.
12. How much does Inconel 718M cost?
Inconel 718M is a premium alloy with pricing typically above standard Inconel 718 bars due to triple-melt (VIM+ESR+VAR) processing, extended NDE, NACE qualification testing, and comprehensive documentation. For forged subsea components, pricing depends heavily on geometry, weight, and certification requirements. Contact Hangbo Alloy at hangbo@nickel-alloy.com for a project-specific quotation.
Need Inconel 718M for Subsea Wellheads, Connectors, or Fasteners?
Hangbo Alloy Group is a trusted global manufacturer and supplier of Inconel 718M (UNS N07718 / 2.4668) in forged bar, ring, fastener, and machined component forms. API 6A / NACE MR0175 compliant, full traceability, and competitive pricing.