Inconel 718 and Inconel X-750 are nickel-chromium-based superalloys known for their exceptional strength and resistance to extreme environments. These alloys are commonly used in high-temperature applications, especially in the aerospace, chemical processing, and power generation industries. Despite their similarities, they have distinct properties and applications. This document will provide a detailed comparison of these two alloys across various parameters.
Chemical Composition
The primary difference between Inconel 718 and Inconel X-750 lies in their chemical composition, which affects their mechanical properties and resistance to environmental degradation.
Table 1: Chemical Composition
| Element | Inconel 718 | Inconel X-750 |
|---|---|---|
| Nickel (Ni) | 50-55% | 70% min |
| Chromium (Cr) | 17-21% | 14-17% |
| Iron (Fe) | Balance | Balance |
| Molybdenum (Mo) | 2.8-3.3% | 2.5-3.0% |
| Niobium (Nb) | 4.75-5.5% | 0.5-1.0% |
| Titanium (Ti) | 0.65-1.15% | None |
| Aluminum (Al) | 0.20-0.80% | 0.2-0.6% |
| Carbon (C) | ≤0.08% | ≤0.05% |
Mechanical Properties
The mechanical properties of Inconel 718 and Inconel X-750 significantly impact their applications in various industries.
Table 2: Mechanical Properties
| Property | Inconel 718 | Inconel X-750 |
|---|---|---|
| Yield Strength (MPa) | 970 – 1,380 | 600 – 1,100 |
| Ultimate Tensile Strength (MPa) | 1,270 – 1,380 | 700 – 1,100 |
| Elongation (%) | 15% (min) | 30% (min) |
| Hardness (Rockwell B) | 40-44 | 35-42 |
High-Temperature Strength
Both alloys exhibit excellent strength at high temperatures, but their performance may vary depending on the specific operating conditions.
Table 3: High-Temperature Strength
| Feature | Inconel 718 | Inconel X-750 |
|---|---|---|
| Service Temperature | Up to 1,300°F (700°C) | Up to 1,400°F (760°C) |
| Oxidation Resistance | Good | Excellent |
| Creep Resistance | Very good | Excellent with additional stability |
Corrosion Resistance
Both Inconel 718 and Inconel X-750 have excellent resistance to oxidation and corrosion, but they perform differently in various environments.
Table 4: Corrosion Resistance
| Corrosion Type | Inconel 718 | Inconel X-750 |
|---|---|---|
| General Corrosion | Excellent | Excellent |
| Pitting Corrosion | Very good | Excellent |
| Stress Corrosion Cracking | Moderate | Good |
| Acid Resistance | Good (in moderate concentrations) | Very good in acidic environments |
Weldability
Both Inconel alloys are weldable, but there are notable differences in their weldability and post-weld treatments.
Table 5: Weldability Comparison
| Feature | Inconel 718 | Inconel X-750 |
|---|---|---|
| General Weldability | Good but requires preheating | Good; usually does not require preheating |
| Post-Weld Heat Treatment | Required to relieve stresses | Not usually required |
| Filler Material | ERNiFeCr-3 (for welding) | ERNiCr-3 |
Applications
Understanding the applications of each alloy helps in selecting the right material for specific environments and engineering needs.
Table 6: Typical Applications
| Application Area | Inconel 718 | Inconel X-750 |
|---|---|---|
| Aerospace Industry | Turbine engines, structural components | Gas turbines, combustion chambers |
| Power Generation | Gas turbine components | Heat exchangers, combustors |
| Chemical Processing | High-temperature reactors | Process equipment in petrochemical |
| Oil and Gas | Downhole tubing and valves | Gas and oil extraction equipment |
| Nuclear Engineering | Reactor cores, control rods | Reactor components |
Summary of Differences
| Feature | Inconel 718 | Inconel X-750 |
|---|---|---|
| Nickel Content | 50-55% | 70% min |
| Chromium Content | 17-21% | 14-17% |
| Strength | Higher yield and tensile strength | Lower but good strength |
| High-Temperature Use | Up to 1,300°F (700°C) | Up to 1,400°F (760°C) |
| Weldability | Good, requires preheating | Good, generally no preheating |
| Applications | Aerospace, power generation | Turbines, nuclear applications |
Conclusion
Inconel 718 and Inconel X-750 are both exceptional superalloys that provide excellent performance in high-temperature and corrosive environments. The choice between these two alloys largely depends on the specific application requirements.
- Inconel 718 is more suitable for aerospace applications due to its higher strength and excellent mechanical properties at elevated temperatures. It is often preferred in applications involving extreme conditions and where structural integrity is vital.
- Inconel X-750 is commonly used in power generation and chemical processing industries due to its high oxidation resistance and good resistance to thermal fatigue. It is ideal for components where stress-corrosion resistance is critical.
Understanding these differences will guide engineers and decision-makers in selecting the most appropriate material for their specific needs and operational requirements. If you have any questions or need further assistance, feel free to ask!