In high-risk engineering, Inconel 625 and Inconel 718 are two giants, but their applications are drastically different. For purchasing managers and system designers, one of the most costly mistakes is material failure due to environmental incompatibility.
Problem: Choosing Inconel 625 as the material for a high-speed rotating turbine disk simply because it's "the well-known Inconel"-only to find it sags and deforms under load.
Risk: Choosing Inconel 718 for a seawater-cooled flare tower resulted in catastrophic pitting corrosion within months due to its inferior chemical stability compared to Inconel 625.
The key to choosing between Inconel 625 (UNS N06625) and Inconel 718 (UNS N07718) lies in balancing the relationship between water corrosion and mechanical load.
Click here for an Inconel 625 product quote
Comparison of Inconel 625 and Inconel 718: Corrosion Resistance and High Temperature Performance
Gnee Alloy
Comparison of Inconel 625 and Inconel 718: Corrosion Resistance and High Temperature Performance
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Gnee Alloy
What effect does temperature have on Inconel 625 alloy?
However, the plasticity of Inconel 625 alloy prepared using the laser powder bed melting (LPBF) process decreases sharply with increasing temperature, especially above 700°C. This is due to the fracture mode changing from transgranular ductile fracture to intergranular fracture.
1. Key differences between Inconel 625 and Inconel 718
| Feature | Inconel 625 (UNS N06625) | Inconel 718 (UNS N07718) |
| Primary Attribute | Exceptional Corrosion Resistance | Exceptional Yield & Tensile Strength |
| Hardening Method | Solid Solution Strengthening | Precipitation (Age) Hardening |
| Weldability | Excellent; rarely requires PWHT | Good; requires careful heat control |
| Max Service Temp | Up to 1800°F (982°C) | Up to 1300°F (704°C) |
| Common Forms | Inconel 625 Round Bars | Inconel 718 Round Bars |
2. Chemical Composition Comparison of Inconel 625 vs 718 Alloy
| Element | Inconel 625 (%) | Inconel 718 (%) |
| Nickel (Ni) | 58.0 min | 50.0 – 55.0 |
| Chromium (Cr) | 20.0 – 23.0 | 17.0 – 21.0 |
| Iron (Fe) | 5.0 max | Balance |
| Molybdenum (Mo) | 8.0 – 10.0 | 2.8 – 3.3 |
| Niobium (Nb) | 3.15 – 4.15 | 4.75 – 5.5 |
| Titanium (Ti) | 0.40 max | 0.65 – 1.15 |
| Aluminum (Al) | 0.40 max | 0.2 – 0.8 |
3. Mechanical Properties Comparison of Inconel 625 vs 718 Alloy
| Property | Inconel 625 | Inconel 718 (Aged) |
| Tensile Strength | 120–150 ksi (827–1034 MPa) | 180–210 ksi (1241–1448 MPa) |
| Yield Strength (0.2%) | 60–90 ksi (414–620 MPa) | 150–175 ksi (1034–1206 MPa) |
| Elongation (%) | 30–50% | 12–25% |
| Hardness (Rockwell) | B90 – C35 | C36 – C44 |
Click here to download the Inconel 625 alloy PDF file
4. Applications of Inconel 625 and Inconel 718 features
Inconel 625 (UNS N06625)
Inconel 625 is a solid solution strengthened alloy. It requires no complex heat treatment processes, and its strength derives from the high content of molybdenum (9%) and niobium (3.5%) in a nickel-chromium matrix.
Excellent corrosion resistance: virtually unaffected by chloride stress corrosion cracking and pitting.
Optimal applications: seawater systems, chemical reactors, flare towers, and offshore manifolds.
Commercial advantages: the most cost-effective solution for long-term stable operation in acidic and marine environments.
Inconel 718 (UNS N07718)
Inconel 718 is a precipitation-hardening superalloy. Its strength is achieved through a complex double-aging process that precipitates the γ′′ phase.
Extreme mechanical strength: maintains excellent tensile strength and creep rupture strength at temperatures up to 700°C (1292°F).
Best applications: turbine disks, engine shafts, rocket engines, and high-strength fasteners.
Business value: This is a necessary investment for components where structural integrity under load is paramount.
5. Comparison of high-temperature mechanical properties of Inconel 625 and Inconel 718 Alloy
| Temp (°C) | Property | Inconel 625 | Inconel 718 |
|---|---|---|---|
| 500 | Tensile (MPa) | ~680 | ~1150 |
| Yield (MPa) | ~360 | ~950 | |
| 600 | Tensile (MPa) | ~600 | ~1100 |
| Yield (MPa) | ~330 | ~900 | |
| 650 | Tensile (MPa) | ~550 | ~1000 |
| Yield (MPa) | ~300 | ~850 | |
| 700 | Tensile (MPa) | ~500 | ~850 |
| Yield (MPa) | ~270 | ~750 | |
| 800 | Tensile (MPa) | ~400 | ~500 |
| Yield (MPa) | ~220 | ~450 |
6. Comparison of corrosion resistance between Inconel 625 and Inconel 718 Alloy
| Environment | Inconel 625 | Inconel 718 | Advantage |
|---|---|---|---|
| Oxidizing Acids (HNO₃) | Excellent | Good | 625 |
| Reducing Acids (H₂SO₄, HCl) | Excellent | Poor | 625 |
| Chloride Pitting | Excellent | Moderate | 625 |
| Crevice Corrosion | Excellent | Moderate | 625 |
| Chloride SCC | Excellent | Good | 625 |
| Seawater | Excellent | Limited | 625 |
| Sour Gas (H₂S/CO₂) | Excellent | Good (with proper HT) | 625 |
| High-Temperature Oxidation | Excellent to 980°C | Good to 980°C | Similar |
7. When to Choose Inconel 625 and Inconel 718 Alloys?
Conditions for Choosing Inconel 625:
Your primary concern is corrosion (seawater, acids, acidic gases).
You need excellent weldability without the need for complex post-weld heat treatment.
The application involves high-temperature oxidation but low mechanical loads.
You are sourcing Inconel 625 tubing.
Conditions for Choosing Inconel 718:
You require the highest possible yield strength and tensile strength.
The component must be able to withstand high temperatures and stresses up to 1300°F (700°C).
You are manufacturing bolts, fasteners, or rotating shafts.
You are looking for seamless Inconel 718 tubing for high-pressure environments.
Contact us to customize Inconel 625 products to fit your project dimensions
Why Choose Gnee as Your Nickel-Based Alloy Supplier
✅️VIM + VAR Melting: Ensuring ultra-pure chemistry to maximize fatigue life and ensure Zero-Defect Quality.
✅️Wholesale Pricing: Benefit from Direct Factory Price on bulk orders for large-scale energy and aerospace programs.
✅️Massive Bulk Inventory: Seamless pipes, round bars, and sheets In Stock for immediate global dispatch.
✅️Full Traceability: Every shipment is delivered with an EN 10204 3.1 Mill Test Certificate (MTC) documenting exact PREN and mechanical data.
Gnee Alloy inconel 625 Certificate
📦 Packaging and Shipping
All Nickel Based Alloy 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
Gnee Alloy 625 Alloy Product Packing
Contact us for the latest export price quote for inconel 625 Alloy
FAQ
Q1: Can I use Inconel 625 for high-pressure fuel lines at 650°C?
A: Only if the mechanical load is low. For safety-critical turbine fuel lines with extreme vibration, Inconel 718 is preferred due to its superior vibration fatigue resistance and yield strength.
Q2: Which alloy is more cost-effective for large-diameter exhaust systems?
A: Inconel 625 is typically more cost-effective. It offers excellent oxidation resistance and weldability without the need for post-weld aging heat treatments, significantly reducing fabrication time and costs.
Q3: Is Inconel 718 interchangeable with Inconel 625?
A: Generally, No. They serve different primary engineering functions. Replacing 718 with 625 leads to sagging/deformation; replacing 625 with 718 leads to premature corrosion/leaking. Always consult an expert for a Material Selection Audit.
Q4: Do you support small batch orders for R&D?
A: Yes. As a Reliable Supplier, we support innovation. We offer Flexible MOQs on our in-stock inventory of bars, sheets, and tubes.
