In the world of high-performance nickel-based alloys, three names stand out for their remarkable strength, heat resistance, and corrosion protection — Nickel Alloy 716, Inconel 718, and Alloy 625. Each of these materials is engineered to perform under extreme stress, high temperature, and corrosive environments, yet they differ in their mechanical properties, heat treatment behavior, and optimal applications.
As industries such as aerospace, energy, marine, and oil & gas continue to push materials to their limits, understanding the differences between these alloys is essential for engineers and procurement specialists.
This article provides a detailed comparison of Nickel Alloy 716 Round Bar, Inconel 718, and Alloy 625, focusing on their chemical composition, mechanical performance, corrosion resistance, and industrial applications — and highlights how SASAALLOY supplies premium-quality materials designed for superior reliability and consistency.
Overview of the Three Alloys
| Alloy | Type | Key Features | Typical Applications |
|---|---|---|---|
| Nickel Alloy 716 | Precipitation-hardened nickel-chromium-iron alloy | High strength, superior oxidation resistance, excellent creep performance up to 700°C | Aerospace, turbines, oil & gas, marine |
| Inconel 718 | Precipitation-hardened nickel-based superalloy | Excellent strength up to 650°C, good weldability and fatigue resistance | Jet engines, gas turbines, power generation |
| Alloy 625 | Solid-solution strengthened nickel-chromium-molybdenum alloy | Outstanding corrosion resistance, ductility, and toughness | Chemical plants, seawater systems, marine and offshore use |
All three alloys share a nickel-based matrix, but their strengthening mechanisms and service capabilities vary depending on the balance of elements such as niobium, molybdenum, and chromium.
Chemical Composition Comparison
| Element | Nickel Alloy 716 (%) | Inconel 718 (%) | Alloy 625 (%) |
|---|---|---|---|
| Nickel (Ni) | 50.0 – 55.0 | 50.0 – 55.0 | ≥ 58.0 |
| Chromium (Cr) | 17.0 – 21.0 | 17.0 – 21.0 | 20.0 – 23.0 |
| Iron (Fe) | Balance | Balance | ≤ 5.0 |
| Molybdenum (Mo) | 2.8 – 3.3 | 2.8 – 3.3 | 8.0 – 10.0 |
| Niobium (Nb) + Tantalum (Ta) | 4.8 – 5.5 | 4.75 – 5.50 | 3.15 – 4.15 |
| Titanium (Ti) | 0.6 – 1.15 | 0.65 – 1.15 | ≤ 0.4 |
| Aluminum (Al) | 0.2 – 0.8 | 0.2 – 0.8 | ≤ 0.4 |
| Cobalt (Co) | ≤ 1.0 | ≤ 1.0 | ≤ 1.0 |
| Carbon (C) | ≤ 0.08 | ≤ 0.08 | ≤ 0.10 |
Key Takeaways:
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Nickel Alloy 716 and Inconel 718 have nearly identical base compositions, both utilizing precipitation hardening for strength, while Alloy 625 relies primarily on solid-solution strengthening.
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Alloy 625 contains significantly more molybdenum, making it more resistant to pitting, crevice corrosion, and chloride attack, but with lower overall strength.
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Nickel Alloy 716 is optimized for higher service temperatures (up to 700°C), offering better creep resistance than Inconel 718.
Strengthening Mechanisms
Nickel Alloy 716
Strengthened by the controlled precipitation of γ′ (Ni₃(Al,Ti)) and γ″ (Ni₃Nb) phases during aging. These phases create obstacles to dislocation motion, resulting in exceptional strength and creep resistance at elevated temperatures.
Inconel 718
Also hardened through γ′ and γ″ precipitation, but with slightly less phase stability above 650°C. It provides excellent fatigue resistance and weldability, making it ideal for aerospace fasteners and jet engine components.
Alloy 625
Relies on solid-solution strengthening from molybdenum and niobium within the nickel matrix. While it offers superior corrosion resistance and ductility, it does not achieve the same high-temperature strength as 716 or 718.
Mechanical Properties Comparison
| Property | Nickel Alloy 716 | Inconel 718 | Alloy 625 |
|---|---|---|---|
| Tensile Strength (MPa) | 1250 – 1500 | 1200 – 1350 | 830 – 950 |
| Yield Strength (MPa) | 900 – 1100 | 850 – 1000 | 450 – 620 |
| Elongation (%) | 12 – 20 | 15 – 25 | 30 – 40 |
| Hardness (HB) | 330 – 380 | 320 – 360 | 200 – 240 |
| Density (g/cm³) | 8.19 | 8.19 | 8.44 |
| Operating Temperature (°C) | Up to 700 | Up to 650 | Up to 600 |
Summary of Mechanical Strength:
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Nickel Alloy 716 Round Bar demonstrates the highest tensile and yield strength, especially above 650°C, making it ideal for continuous high-heat applications.
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Inconel 718 provides excellent strength at slightly lower temperatures and superior weldability, making it suitable for complex structural assemblies.
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Alloy 625 offers the best ductility and fabricability, but is not designed for extreme mechanical loading at high temperatures.
Heat Treatment Comparison
Nickel Alloy 716 and Inconel 718
Both alloys undergo a two-step heat treatment process to achieve maximum mechanical strength:
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Solution Annealing:
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Temperature: 980–1010°C (1800–1850°F)
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Purpose: Dissolves precipitates and homogenizes the structure.
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Aging (Precipitation Hardening):
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Temperature: 720–760°C (1325–1400°F)
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Duration: 8–10 hours
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Purpose: Promotes formation of γ′ and γ″ phases for strength.
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Nickel Alloy 716, however, exhibits better phase stability during aging, allowing it to retain its properties at slightly higher temperatures compared to 718.
Alloy 625
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Does not require precipitation hardening.
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Strength depends on solid-solution strengthening, so it only undergoes annealing (870–980°C) followed by rapid cooling.
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Simplifies fabrication and welding but limits high-temperature strength.
Corrosion and Oxidation Resistance
| Type of Resistance | Nickel Alloy 716 | Inconel 718 | Alloy 625 |
|---|---|---|---|
| General Corrosion | Excellent | Excellent | Outstanding |
| Pitting and Crevice Corrosion | Very Good | Good | Excellent |
| Oxidation Resistance (up to 700°C) | Excellent | Very Good | Good |
| Sulfidation Resistance | Excellent | Very Good | Very Good |
| Stress Corrosion Cracking (SCC) | Excellent | Excellent | Excellent |
Performance in High-Temperature Environments
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Nickel Alloy 716 maintains high strength and oxidation resistance up to 700°C, making it ideal for continuous high-heat service such as turbine blades, fasteners, and exhaust systems.
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Inconel 718 performs well up to 650°C, suitable for aircraft engines and gas turbines where fatigue strength and weldability are crucial.
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Alloy 625 is typically limited to 600°C for mechanical applications but excels in chemical plants and offshore systems due to its corrosion protection.
Applications by Industry
| Industry | Nickel Alloy 716 | Inconel 718 | Alloy 625 |
|---|---|---|---|
| Aerospace | Turbine shafts, compressor discs, bolts | Engine casings, turbine wheels | Ducts and bellows |
| Oil & Gas | Subsea valves, completion tools | Drilling tools, wellhead equipment | Seawater piping, risers |
| Power Generation | Steam turbines, nuclear components | Gas turbine parts | Heat exchangers, condensers |
| Chemical Processing | High-pressure reactors | Acid-resistant components | Reactors, distillation columns |
| Marine Engineering | Offshore connectors | Turbine housings | Pumps, fittings, flanges |
Nickel Alloy 716 Round Bar bridges the gap between the high strength of Inconel 718 and the corrosion protection of Alloy 625, making it a versatile choice for hybrid applications that demand both mechanical endurance and chemical resistance.
Cost and Fabrication Considerations
| Factor | Nickel Alloy 716 | Inconel 718 | Alloy 625 |
|---|---|---|---|
| Cost | Moderate | Moderate | High |
| Machinability | Good after annealing | Excellent | Good |
| Weldability | Good | Excellent | Excellent |
| Availability | Moderate | Very High | High |
While Inconel 718 remains the most commonly available due to its long-standing aerospace usage, Nickel Alloy 716 is gaining popularity for its superior high-temperature strength and oxidation resistance at a comparable cost. Alloy 625, though more expensive, is chosen when extreme corrosion protection outweighs strength requirements.
Advantages of Nickel Alloy 716 Round Bar
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Higher Temperature Capability: Performs reliably at temperatures up to 700°C, beyond the safe range of 718.
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Superior Oxidation and Sulfidation Resistance: Ideal for turbine and combustion applications.
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Excellent Corrosion Resistance: Performs well in acidic, chloride, and high-pressure environments.
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Good Machinability and Weldability: Suitable for complex forged or machined parts.
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Long-Term Stability: Maintains mechanical integrity under prolonged heat exposure.
Why Choose SASAALLOY for Nickel Alloy 716 Round Bar
At SASAALLOY, we specialize in producing premium-grade Nickel Alloy 716 Round Bars that meet or exceed international standards for mechanical performance, chemical purity, and corrosion resistance. Our materials are processed using advanced vacuum induction melting (VIM) and electro-slag remelting (ESR) technology to ensure uniform microstructure and superior cleanliness.
Every product undergoes strict mechanical testing, ultrasonic inspection, and heat treatment verification to ensure it performs flawlessly in demanding environments such as aerospace engines, marine equipment, and energy systems.
By choosing SASAALLOY, you gain access to a partner that combines metallurgical expertise with a commitment to quality, providing materials engineered for precision, reliability, and longevity.
Conclusion
When comparing Nickel Alloy 716, Inconel 718, and Alloy 625, it becomes clear that each has its strengths:
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Nickel Alloy 716 Round Bar offers the best high-temperature strength and oxidation resistance.
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Inconel 718 provides excellent weldability and fatigue strength for structural aerospace applications.
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Alloy 625 delivers outstanding corrosion resistance and fabricability for chemical and marine environments.
For industries requiring a combination of high mechanical strength, thermal endurance, and corrosion stability, Nickel Alloy 716 Round Bar stands out as the superior choice.
At SASAALLOY, we are proud to supply Nickel Alloy 716 Round Bars that meet the highest international standards — delivering unmatched performance and reliability in the most extreme operational conditions. Choose SASAALLOY for proven quality and engineering excellence in every forged and machined alloy product.
Post time: Oct-31-2025