Inconel 625 and 718 bolts: Which one is better suited for your application?
Inconel 625 and 718 bolts: Which one is better suited for your application?
Choosing Inconel 625 bolts provides excellent corrosion resistance (to seawater, acids, and chemicals) and better weldability, making them ideal for marine and chemical industries; choosing Inconel 718 bolts offers maximum strength and high-temperature creep resistance, best suited for aerospace, gas turbine, and high-stress oil and gas applications where extreme mechanical loads are present, as the 718 alloy is precipitation-hardened and can withstand extreme conditions.
What is the strength of Inconel 718 bolts?
185-220 ksi
Inconel 718 is twice as strong as its sister alloy, Inconel 625, and is renowned for its extremely high strength after age hardening, with a tensile strength of up to 185-220 ksi. Inconel 718 bolts maintain their strength even under pressure and at high temperatures up to 1300°F (700°C).
Inconel 625 bolts are high-performance fasteners made from Inconel 625 alloy. Their core advantage lies in the comprehensive and superior corrosion resistance of the alloy, effectively resisting pitting corrosion, crevice corrosion, chloride stress corrosion cracking, and oxidation and reduction in acidic media. They also possess excellent high-temperature strength (up to approximately 980°C) and creep resistance. They are specifically designed to provide durable fastening solutions for applications in extreme corrosive and high-temperature environments, such as marine engineering, demanding chemical processing, flue gas desulfurization systems, and aerospace, making them a superior connector with broader and more robust performance than ordinary stainless steel bolts.
Inconel 718 bolts are high-strength fasteners made from a precipitation-hardened nickel-chromium-based high-temperature alloy (Inconel 718). Their core characteristic is precipitation strengthening achieved through elements such as niobium, maintaining ultra-high strength, excellent creep resistance, and fatigue resistance at temperatures up to approximately 700°C, while also possessing good corrosion resistance. They are specifically designed for critical applications requiring fasteners to maintain reliable locking force under extreme stress, high temperatures, and severe vibration, such as in aircraft engines, aerospace structures, oil and gas industries, and high-performance racing cars, making them a top-tier bolt choice for the most demanding mechanical connection challenges.
Chemical Composition: Inconel 625 vs Inconel 718 bolts
| Element | Inconel 625 (UNS N06625) Content (%) | Inconel 718 (UNS N07718) Content (%) |
|---|---|---|
| Nickel (Ni) | ~58 min | 50 – 55 |
| Chromium (Cr) | 20 – 23 | 17 – 21 |
| Molybdenum (Mo) | 8 – 10 | 2.8 – 3.3 |
| Niobium (Nb) | 3 – 4 | 4.75 – 5.5 |
| Iron (Fe) | ≤ 5.0 | ~17 (Balance) |
| Manganese (Mn) | ≤ 0.50 | ≤ 0.35 |
| Silicon (Si) | ≤ 0.50 | ≤ 0.35 |
| Aluminum (Al) | ≤ 0.40 | 0.20 – 0.80 |
| Titanium (Ti) | ≤ 0.40 | 0.65 – 1.15 |
| Carbon (C) | ≤ 0.10 | ≤ 0.08 |
| Phosphorus (P) | ≤ 0.015 | ≤ 0.015 |
| Sulfur (S) | ≤ 0.015 | ≤ 0.015 |
| Copper (Cu) | ≤ 0.07 | ≤ 0.30 |
| Cobalt (Co) | ≤ 1.0 | ≤ 1.00 |
| Boron (B) | – | ≤ 0.006 |
| Tantalum (Ta) | – | ≤ 0.05 |
Inconel 625 vs. 718 Bolts: Which is Best for Your Application?
Inconel fasteners are commonly used in extreme environments and are available in several "grades" depending on the application requirements. This article will briefly compare two of the most common grades, Inconel 625 and Inconel 718, to help you choose the best material.
Key Differences 625 vs. 718
Inconel 625
• Better overall corrosion resistance
• Long-term high-temperature stability
Inconel 718
• Precipitation hardened
• Twice the strength of Inconel 625
Inconel 625
Inconel 625 screws contain high amounts of nickel, chromium, and molybdenum, making them not only strong at high temperatures but also resistant to corrosion, oxidation, and carburization. One of its most notable characteristics is its resistance to stress corrosion cracking, pitting, and crevice corrosion, even when exposed to chloride ions.
Advantages
• Excellent resistance to pitting and crevice corrosion
• Almost 100% resistance to chloride-induced stress corrosion cracking
• High oxidation resistance at high temperatures up to 1050°C
• Good corrosion resistance to acids such as nitric acid, phosphoric acid, sulfuric acid, and hydrochloric acid, as well as alkalis
• Easily welded using standard workshop manufacturing processes
• Longer service life at high temperatures than Inconel 718
Example Applications
Oil and gas production where hydrogen sulfide and elemental sulfur are present, marine applications including propeller blades, submarine propulsion systems, and other naval applications
Inconel 718
Similar to its sister product 625, Inconel 718 is a precipitation-hardened version of the 625 alloy. Age hardening (or precipitation hardening) creates precipitates in the molecular structure, locking the metal grains in place. As a result, the material is typically significantly strengthened. In the case of Inconel, 718 has superior strength, with a yield strength approximately twice that of 625!
Advantages
• Ultra-high strength: Minimum ultimate tensile strength of 185 ksi, minimum yield strength of 150 ksi
• Good corrosion resistance to sour gas, hydrochloric acid, and sulfuric acid
• Excellent weldability
Example Applications
Gas turbines and jet engines, cryogenic storage tanks, downhole oil and gas extraction, and nuclear engineering applications.
Calculating Bolt Breaking or Yield Strength
Question: How do I calculate the actual breaking or yield strength of a specific size bolt?
Answer: For materials like Hastelloy C276, the ultimate tensile strength is independent of the bolt size, as it is based on the cross-sectional area of the bolt, typically 105 ksi (at room temperature).
However, if you are concerned about the bolt's performance in a specific application, you should focus on the yield strength. This is the truly important indicator, and for Hastelloy C276, the yield strength is approximately 49 ksi (at room temperature).
Now, to calculate the actual breaking or yield force of a given size bolt, simply multiply the ultimate tensile strength or yield strength by the cross-sectional area of the bolt. This will give you the actual failure force.
Why Choose Gnee as Your Nickel-Based Alloy Supplier
✅ Over 18 years of export experience, products sold to more than 80 countries
✅ Certified by ISO, SGS, and BV
✅ Global inventory of Inconel, Hastelloy, Incoloy, and Monel alloy tubing, plates, and bars
✅ Custom processing services available – including cutting, polishing, CNC machining, and packaging
✅ Fast delivery within 7-15 days, supported by global logistics partners
📦 Packaging and Shipping
All stainless steel products are packaged using the following methods:
Wooden pallets or crates
Moisture-proof packaging
Labels with furnace number, standard, and size labels
Shipped worldwide by sea, air, or express
About Gnee Steel
Gnee Steel is a professional manufacturer of nickel-based alloys, including Nickel 201, Nickel 202, Hastelloy C-276, Hastelloy C-22, Hastelloy B, Hastelloy C-4, Inconel 600, Inconel 625, Inconel 718, Inconel X-750, Incoloy 800, Incoloy 800H/HT, Incoloy 825, Monel 400, Monel K500, and other high-temperature alloy materials. We specialize in the production and sales of alloy materials. Gnee Steel's products are widely used in aerospace, chemical, power generation, automotive, nuclear energy, and other fields, and we can provide customized alloy material solutions according to customer needs. For inquiries about alloy material prices or customized alloy material solutions, please feel free to contact us via email at ss@gneemetal.com for a quote.
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