Inconel 718 vs. Inconel X-750: A Comprehensive Comparison

Shanghai Lion Metal Co., Ltd. Nickel-based Alloy Division

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

ElementInconel 718Inconel X-750
Nickel (Ni)50-55%70% min
Chromium (Cr)17-21%14-17%
Iron (Fe)BalanceBalance
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

PropertyInconel 718Inconel X-750
Yield Strength (MPa)970 – 1,380600 – 1,100
Ultimate Tensile Strength (MPa)1,270 – 1,380700 – 1,100
Elongation (%)15% (min)30% (min)
Hardness (Rockwell B)40-4435-42

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

FeatureInconel 718Inconel X-750
Service TemperatureUp to 1,300°F (700°C)Up to 1,400°F (760°C)
Oxidation ResistanceGoodExcellent
Creep ResistanceVery goodExcellent 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 TypeInconel 718Inconel X-750
General CorrosionExcellentExcellent
Pitting CorrosionVery goodExcellent
Stress Corrosion CrackingModerateGood
Acid ResistanceGood (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

FeatureInconel 718Inconel X-750
General WeldabilityGood but requires preheatingGood; usually does not require preheating
Post-Weld Heat TreatmentRequired to relieve stressesNot usually required
Filler MaterialERNiFeCr-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 AreaInconel 718Inconel X-750
Aerospace IndustryTurbine engines, structural componentsGas turbines, combustion chambers
Power GenerationGas turbine componentsHeat exchangers, combustors
Chemical ProcessingHigh-temperature reactorsProcess equipment in petrochemical
Oil and GasDownhole tubing and valvesGas and oil extraction equipment
Nuclear EngineeringReactor cores, control rodsReactor components

Summary of Differences

FeatureInconel 718Inconel X-750
Nickel Content50-55%70% min
Chromium Content17-21%14-17%
StrengthHigher yield and tensile strengthLower but good strength
High-Temperature UseUp to 1,300°F (700°C)Up to 1,400°F (760°C)
WeldabilityGood, requires preheatingGood, generally no preheating
ApplicationsAerospace, power generationTurbines, 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!