Knowledge
Comparison Between Alloy 400 Castings and Alloy K500 Castings
Among the Monel nickel-copper alloy family, there are two alloys that look very similar in appearance, namely Alloy 400 and Alloy K500. A closer inspection reveals some differences between the two. A further explanation of these differences may be helpful in material selection issues. In this article, we will explore these two alloys and compare and contrast their metallurgical properties.
Both Alloy 400 and Alloy K500 are nickel-copper alloys, containing approximately 65% nickel and 30% copper. However, the chemical composition of Alloy K500 also includes 3% aluminum and 0.5% titanium.
Chemical composition
|
|
Ni |
Cu |
Al |
Fe |
Mn |
Ti |
|
Alloy 400 |
≥63 |
28-34 |
– |
≤2.5 |
≤2.0 |
– |
|
Alloy K500 |
≥63 |
27-33 |
2.30-3.15 |
≤2.0 |
≤1.5 |
0.35-0.85 |
The strengthening methods of these two alloys are also different. Alloy 400 is solid solution strengthened, while K500 is precipitation strengthened. It is precisely these different strengthening mechanisms that lead to the mechanical property differences between Alloy 400 and K500. The solid solution strengthening of Alloy 400 results in its tensile strength being lower than that of K500, but it is tougher than K500.
Mechanical properties (specification minimum values)
|
|
Alloy 400 |
Alloy K500 |
|
Tensile Strength (MPa) |
600 |
1000 |
|
0.2% Yield Strength (MPa) |
415 |
760 |
|
Elongation (%) |
20 |
14 |
The addition of different alloys will affect the cost of each material. The additional alloying elements in K500 have a corresponding impact on the alloy's price. Alloy 400 has a lower price point at a given size while still offering high tensile strength and maintaining K500's excellent corrosion resistance.
The corrosion resistance of Alloy 400 and Alloy K500 often makes them highly sought after in the chemical processing industry. Both alloys offer excellent corrosion resistance, although Alloy K500 may be susceptible to stress corrosion cracking in certain environments (for instance, in hot hydrofluoric acid vapor close to the alloy's yield strength). This is not an issue for Alloy 400, making it an ideal choice for equipment that comes into contact with fluorine, hydrofluoric acid, and hydrogen fluoride or their compounds.
Typical physical properties
|
|
Alloy 400 |
Alloy K500 PH |
|
Density (g/cm3) |
8.80 |
8.44 |
|
Melting Range (oC) |
1300-1350 |
1315-1350 |
|
Young's Modulus (GPa) |
180 |
179 |
|
Thermal Conductivity (W/moC) |
22 |
17.5 |
|
Coefficient of Thermal Expansion (μm/moK) |
13.9 x 10-6 |
13.4 x 10-6 |
|
Electrical Conductivity (IACS) |
34 |
28 |
The choice between these two alloys ultimately depends on the following key factors:
Cost - The lower content of alloying elements in Alloy 400 provides a cheaper alloy by volume.
Mechanical properties - If higher toughness is the top priority, then Alloy 400 will be the preferred choice. Where higher tensile strength is required, K500 alloy will be more favored.
Corrosion resistance - Although both perform well, Alloy 400 has an edge in environments containing fluorine or hydrofluoric acid.
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