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Alloy 400 v Alloy 625

Alloy 400 v Alloy 625

16 May 2024

When selecting materials for industrial applications, it’s crucial to understand the specific characteristics and suitability of different alloys. Alloy 400 and Alloy 625 are two nickel-based alloys that often come up in discussions due to their unique properties and widespread use across various industries. Here, we compare these two alloys to help you make an informed decision.

Understanding the Basics


Alloy 400, part of the Monel family, is a nickel-copper alloy known for its excellent mechanical properties and resistance to various corrosive environments. On the other hand, Alloy 625, from the Inconel family, is a nickel-chromium-molybdenum-niobium alloy noted for its high strength and exceptional resistance to oxidation and corrosion, even at elevated temperatures.

Chemical Composition and Mechanical Properties


The chemical compositions of these alloys dictate their performance characteristics. Alloy 400 primarily comprises nickel (63-70%) and copper (28-34%), with small amounts of iron and manganese. Alloy 625 has a more complex composition, including nickel (58% minimum), chromium (20-23%), molybdenum (8-10%), and niobium (3.15-4.15%).

  Ni Cu Cr Mo Nb Fe Mn C Si S Co Others
Alloy 400
63-70
28-34
2.5
2.0
0.3
0.5
0.024
2.0
Alloy K500
58 min
20-23
8-10
3.15-4.15
5
0.5
0.1
0.5
0.015
1
0.865

These compositions result in notable differences in mechanical properties:

Alloy 400 has a tensile strength of about 600 MPa and good ductility, making it tougher and more impact-resistant at room temperature.
Alloy 625 boasts higher tensile strength (830-1034 MPa) and proof strength, thanks to its niobium and molybdenum content, which also enhance its resistance to deformation under stress.

 
Alloy 400
Alloy 625
<55mm
>55mm
<100mm
0.2% Proof Strength (MPa)
415
170
415
Tensile Strength (MPa)
600
480
830-1034
Elongation (%)
20
35
30
Hardness
186-287HB
35 HRC max

Machinability and Formability


Machinability and formability are key considerations in material selection:

Alloy 400 is easier to machine due to its ductility and tensile strength, and it offers a broader range of hot working temperatures (650°C to 1175°C).
Alloy 625 is more challenging to machine but offers superior mechanical properties and can withstand higher temperatures during hot working (980°C to 1175°C).

Corrosion Resistance


Both alloys are renowned for their corrosion resistance, but they excel in different environments:

Alloy 400 derives its corrosion resistance from its high copper content, making it ideal for marine applications and other environments where exposure to seawater is common.
Alloy 625 leverages its chromium and molybdenum content to provide exceptional resistance to oxidizing and corrosive environments, especially at elevated temperatures. This makes it suitable for high-temperature applications, such as in the chemical processing and power generation industries.

Applications


Given their properties, Alloy 400 and Alloy 625 are used in a variety of applications:

Alloy 400 is typically used in marine fixtures, pump and valve components, propeller shafts, and electronic equipment.
Alloy 625 finds use in more demanding environments like petroleum processing, power generation, pollution control, and waste management, where high strength and corrosion resistance at elevated temperatures are required.

Cost Considerations


While Alloy 625 offers enhanced properties, it also comes with a higher cost due to its complex composition and stringent manufacturing requirements. In contrast, Alloy 400 is more cost-effective for applications where its specific properties are sufficient.

Conclusion


Choosing between Alloy 400 and Alloy 625 depends on the specific requirements of your application. Alloy 400 is an excellent choice for general corrosion resistance and toughness at a more economical price. Alloy 625, however, should be your go-to for applications demanding higher strength and superior resistance to oxidation and high-temperature corrosion. Understanding these nuances ensures you select the right material, balancing performance and cost effectively.

Click here to download a Monel 400 / Alloy 400 datasheet

Click here to download an Alloy 625 datasheet

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