Inconel X-750 vs. Inconel 625 vs. Inconel 718: A Comprehensive Comparison

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

Inconel X-750, Inconel 625, and Inconel 718 are all nickel-chromium-based superalloys recognized for their remarkable strength, corrosion resistance, and ability to withstand extreme environments. While they share similarities, each alloy has unique properties and applications that make it suitable for specific uses, especially in aerospace, chemical processing, and power generation industries. Below is a detailed comparison of these three superalloys.


Chemical Composition

The chemical composition of each alloy influences its structural properties, corrosion resistance, and performance under high-temperature conditions.

Table 1: Chemical Composition

ElementInconel X-750Inconel 625Inconel 718
Nickel (Ni)70% min58-63%50-55%
Chromium (Cr)14-17%20-23%17-21%
Iron (Fe)BalanceBalanceBalance
Molybdenum (Mo)2.5-3.0%8-10%2.8-3.3%
Niobium (Nb)0.5-1.0%3.0-4.0%4.75-5.5%
Titanium (Ti)None0.4-0.7%0.65-1.15%
Carbon (C)≤0.05%≤0.10%≤0.08%

Mechanical Properties

The mechanical properties vary significantly among these alloys, impacting their performance in various applications.

Table 2: Mechanical Properties

PropertyInconel X-750Inconel 625Inconel 718
Yield Strength (MPa)600 – 1,100380 – 830970 – 1,380
Ultimate Tensile Strength (MPa)700 – 1,100700 – 1,2001,270 – 1,380
Elongation (%)30% (min)30% (min)15% (min)
Hardness (Rockwell B)35-4240-5040-44

High-Temperature Performance

All three alloys are designed to perform well at high temperatures, but with varying limits and properties.

Table 3: High-Temperature Performance

FeatureInconel X-750Inconel 625Inconel 718
Service TemperatureUp to 1,400°F (760°C)Up to 1,800°F (982°C)Up to 1,300°F (700°C)
Oxidation ResistanceExcellentExcellentGood
Creep ResistanceExcellent with additional stabilityVery goodVery good

Corrosion Resistance

Corrosion resistance is critical for all three alloys, especially in acidic or high-salinity environments.

Table 4: Corrosion Resistance

Corrosion TypeInconel X-750Inconel 625Inconel 718
General CorrosionExcellentExcellentVery good
Pitting CorrosionExcellentExcellentVery good
Stress Corrosion CrackingGoodExcellentModerate
Acid ResistanceVery goodExcellentGood (in moderate concentrations)

Weldability

Weldability is an essential consideration for these alloys, particularly in construction and manufacturing.

Table 5: Weldability Comparison

FeatureInconel X-750Inconel 625Inconel 718
General WeldabilityGood; usually does not require preheatingGood; may require preheatingGood, but requires preheating
Post-Weld Heat TreatmentNot usually requiredGenerally not requiredRequired to relieve stresses
Filler MaterialERNiCr-3ERNi625ERNiFeCr-3

Applications

Understanding the application suitability for each alloy helps in selecting the right material for specific environments and engineering needs.

Table 6: Typical Applications

Application AreaInconel X-750Inconel 625Inconel 718
Aerospace IndustryGas turbines, combustion chambersAerospace components under high thermal stressTurbine engines, structural components
Chemical ProcessingHeat exchangers, aerospace valvesChemical processing equipmentHigh-temperature reactors
Oil and GasDownhole tubing and valvesComponents for oil and gas extractionOil and gas processing equipment
Power GenerationBoiler tubes, componentsTurbines and heat exchangersGas and steam turbine components
Marine ApplicationsComponents in aggressive environmentsMarine applications due to excellent corrosion resistanceLess common but used when required

Summary of Differences

FeatureInconel X-750Inconel 625Inconel 718
Nickel Content70% min58-63%50-55%
Chromium Content14-17%20-23%17-21%
Molybdenum Content2.5-3.0%8-10%2.8-3.3%
Temperature ResistanceUp to 1,400°F (760°C)Up to 1,800°F (982°C)Up to 1,300°F (700°C)
ApplicationsVersatile in oil, gas, and aerospaceExcellent for marine and chemical applicationsPreferred in aerospace and high-stress scenarios

Conclusion

Inconel X-750, Inconel 625, and Inconel 718 each offer unique properties that cater to different applications.

  • Inconel X-750 is well-suited for high-temperature and high-stress environments, particularly in power generation and oil and gas applications.
  • Inconel 625 provides excellent corrosion resistance and high-temperature strength, making it ideal for marine and chemical processing applications.
  • Inconel 718 is characterized by its exceptional mechanical properties and is favored in aerospace applications for turbine components and structures.

Selecting the appropriate alloy is critical for optimizing performance and ensuring the longevity of components in demanding environments. If you have any questions or need further assistance, feel free to ask!