Inconel 625 vs. Inconel 718: Material Performance Comparison

Date:2025-02-25 11:24:36View:1988Tags:Nickel Alloy Supplier

Both Inconel 625 and Inconel 718 are high-performance nickel-based superalloys used in demanding industries. While they share many similarities, their exact chemical compositions, mechanical properties, and performance characteristics differ, making each more suitable for specific applications.

1. Chemical Composition Comparison

Here is a detailed breakdown of the chemical composition for each alloy:

Element	Inconel 625	Inconel 718
Nickel (Ni)	58-72%	50-55%
Chromium (Cr)	20-23%	17-21%
Molybdenum (Mo)	8-10%	2.8-3.3%
Niobium (Nb)	3.15-4.15%	4.75-5.5%
Iron (Fe)	5% max	18-21%
Titanium (Ti)	0.4-1%	0.9-1.3%
Aluminum (Al)	-	0.2-0.8%
Cobalt (Co)	-	1% max

Key Points:

Inconel 625 contains higher levels of nickel and molybdenum compared to Inconel 718, giving it superior corrosion resistance.
Inconel 718 has a higher amount of iron and aluminum, contributing to its high-temperature strength and creep resistance.

2. Mechanical Properties Comparison

Below is a comparison of the mechanical properties of Inconel 625 and Inconel 718:

Property	Inconel 625	Inconel 718
Tensile Strength (MPa)	760 MPa (at room temperature)	1,270 MPa (at room temperature)
Yield Strength (MPa)	310 MPa (at room temperature)	1,030 MPa (at room temperature)
Elongation (%)	35% (at room temperature)	15-25% (at room temperature)
Hardness (Rockwell B)	90-95 HRB	35-45 HRC (heat treated)
Creep Strength (MPa)	160 MPa at 650°C	1,000 MPa at 650°C
Density (g/cm³)	8.44 g/cm³	8.19 g/cm³
Thermal Conductivity (W/m·K)	10.4 W/m·K (at 100°C)	11.4 W/m·K (at 100°C)

Key Points:

Inconel 625 is more ductile with a higher elongation at room temperature, making it suitable for applications where flexibility and toughness are crucial.
Inconel 718 exhibits significantly higher tensile and yield strength, particularly at high temperatures, which is ideal for high-stress, high-temperature environments like gas turbines and aerospace applications.

3. Corrosion Resistance Comparison

Property	Inconel 625	Inconel 718
Corrosion Resistance	Excellent in seawater, acidic environments, and high-temperature corrosive conditions	Good resistance to oxidation and corrosion in high-temperature and sulfur-containing environments, but not as resistant as Inconel 625
Oxidation Resistance	Very high resistance in temperatures up to 1,000°C	High oxidation resistance up to 700°C
Sulfur Resistance	Excellent in sulfur-containing environments	Moderate resistance to sulfur environments

Key Points:

Inconel 625 has superior resistance to aggressive corrosive environments, including seawater and acidic conditions.
Inconel 718 is still highly resistant but more focused on high-temperature environments rather than extreme corrosion resistance.

4. Heat Treatment and Fabrication

Property	Inconel 625	Inconel 718
Heat Treatment	No complex heat treatment; can be welded without significant loss of properties	Requires heat treatment to optimize mechanical properties, especially creep strength
Weldability	Excellent weldability without significant performance degradation	Good weldability, though careful heat treatment is required after welding
Machinability	Moderate machinability, especially in heat-treated forms	Good machinability in annealed condition, but can be challenging in the aged state

Key Points:

Inconel 625 is easier to fabricate and weld without much loss in strength or corrosion resistance, making it suitable for applications requiring complex shapes or frequent welding.
Inconel 718 requires more careful processing, particularly heat treatment, to achieve optimal mechanical properties.

Summary

Both Inconel 625 and Inconel 718 are exceptional materials, but they excel in different areas:

Inconel 625 is the best choice when corrosion resistance, especially in marine and chemical environments, is the primary concern. It is also more ductile and easier to work with.
Inconel 718 is superior in high-temperature applications where mechanical strength, creep resistance, and high tensile strength are needed. It is commonly used in aerospace and turbine components.

Choosing the right material depends on the specific operational conditions, including temperature, mechanical load, and environmental exposure.