Overview
Hastelloy is a very common superalloy. It is characterized by its excellent resistance to high temperatures and corrosion. Depending on the chemical composition, Hastelloy is classified into various grades. You may have questions:
What do all Hastelloy alloys have in common?
What is the difference between Hastelloy and other superalloys?
Why are Hastelloy alloys classified into so many grades?
In this article, we will introduce the properties and characteristics of Hastelloy in detail from various aspects. We believe it can solve your questions.
What is Hastelloy?
Hastelloy is the collective name for a range of nickel-chromium-molybdenum or nickel-molybdenum alloys. As you can see, nickel and molybdenum are the key elements in Hastelloy alloys.
Nickel is the most important element needed in all superalloys. It stabilizes the crystal structure of the alloy at high temperatures. You can say that nickel is the source of high temperature resistance of all superalloys. At the same time, nickel also has some corrosion resistance.
Molybdenum is a corrosion-resistant solid solution strengthening element. It brings significant resistance to reducing corrosion to the alloy. In addition, molybdenum also has a very large solid solution strengthening effect. It significantly enhances the base strength of the alloy.
Thus, in summary, Hastelloy is a superalloy with good resistance to reducing corrosion. It tends to be stronger than other solid solution alloys.
Depending on the composition characteristics, Hastelloy can be divided into the three most common families B, C and G. Of course, there are also some relatively rare Hastelloy alloys such as Hastelloy N / S / W / X. The following chart shows most of the Hastelloy alloys grades:
Among them, the Hastelloy B series is a nickel-molybdenum alloy. The Hastelloy C series reduces the molybdenum and adds more chromium to the B series, which gives the alloy good resistance to oxidation. Hastelloy G series continues to reduce the molybdenum and add chromium to the C series, which gives the alloy more resistance to oxidative corrosion.
B-3
Mn
Al
Ti
Co
V
W
Fe
Mo
Cr
Ni
C-276
Mn
Co
V
W
Fe
Mo
Cr
Ni
G-35
Si
Al
Co
V
W
Fe
Mo
Cr
Ni
Below, we present the properties of Hastelloy in terms of its chemical composition, mechanical properties and physical properties.
Chemical Composition of Hastelloy
Nickel, Chromium and Molybdenum
Nickel, chromium and molybdenum are three inseparable elements in superalloys. The ratio of these three elements determines the different properties of superalloys. In Hastelloy alloys, the proportion of nickel, chromium and molybdenum varies from grade to grade.
The nickel element mainly affects the high temperature resistance of Hastelloy alloys. Generally speaking, the higher the nickel content, the better the high temperature resistance of the alloy.
Chromium and molybdenum both affect the corrosion resistance of the alloy. The difference is that chromium acts as an anti-oxidant while molybdenum acts as an anti-reduction agent. Therefore, the ratio of chromium to molybdenum determines whether the alloy is more focused on oxidative or reductive corrosion. Among the Hastelloy alloys, the Hastelloy B series has the highest molybdenum content and the lowest chromium content. The Hastelloy C series has a relatively balanced content of molybdenum and chromium. It has a comprehensive corrosion resistance. The chromium content of the Hastelloy G series is greater than the molybdenum content of the alloy. These alloys are more important for oxidation resistance.
Tungsten
Tungsten is a typical component of Hastelloy alloys. Its role is mainly to increase the solid solution strengthening effect of the alloy. The higher the tungsten content in the alloy, the higher the strength of the alloy. In addition, tungsten increases the alloy's resistance to pitting.
Copper
The element copper is a good corrosion resistant metal element. Among the Hastelloy alloys, Hastelloy C-2000 is a typical copper-containing alloy. Copper brings excellent resistance to sulfuric acid to this alloy.
Cobalt
Cobalt is an effective solid solution strengthening element. The Hastelloy X alloy contains 0.5% to 2.5% cobalt. This is the basis for its excellent high temperature properties.
Mechanical Properties of Hastelloy
Superalloys can be divided into solid solution strengthened alloys and precipitation strengthened alloys depending on the crystal phase structure. Among them, the precipitation strengthened alloys have higher strength, while the solid solution strengthened alloys have better plasticity.
Unlike Monel, Inconel, and Incoloy alloys, most Hastelloy alloys are solid solution strengthened alloys. Their strengths are hardly as high as those of the precipitation strengthened alloys. However, among the solid solution strengthened alloys, Hastelloy has a relatively high strength. This is mainly due to the presence of more molybdenum and tungsten elements in Hastelloy.
The atomic radii of molybdenum and tungsten are much larger than those of nickel. When they are alloyed with nickel, they increase the interatomic bonding forces and thus the strength of the alloy. Therefore, for Hastelloy alloys, the more molybdenum and tungsten are present, the stronger they are. A typical alloy is Hastelloy B. The molybdenum content of around 30% gives it a much higher hardness and strength than the usual solution strengthened alloys.
However, there is a special alloy in the Hastelloy family: Hastelloy C-22HS, which is the only precipitation strengthened alloy in the Hastelloy family. It can be greatly strengthened by aging treatment. A comparison of the mechanical properties of Hastelloy C-22 and Hastelloy C-22HS is shown in the following table:
| Alloy | Tensile Strength | Yield Strength | Elongation |
|---|---|---|---|
| MPa | MPa | % | |
| Hastelloy C-22 | 690 | 310 | 45 |
| Hastelloy C-22HS | 1227 | 1103 | 15 |
Physical Properties of Hastelloy
In superalloys, the two most important physical properties are melting point and density.
Hastelloy needs to work at high temperatures, which requires it to have a high melting point. This is also due to its high molybdenum content. Molybdenum is a refractory metal and its presence in the alloy raises the melting point of the alloy.
In addition, molybdenum has a much higher density than nickel. As a result, Hastelloy alloys also have the higher density of all superalloys.
You can use the following tools to quickly calculate the weight of different Hastelloy alloys:
FAQ
Besides Hastelloy B, C and G series, what other Hastelloy alloys are available?
In addition to Hastelloy B, C and G series, the four Hastelloy alloys that exist in the market today are Hastelloy N / S / W / X.
Hastelloy N is a high nickel content alloy. It has the highest nickel content of all Hastelloy alloys. As a result, it has excellent high temperature resistance.
Hastelloy S is a strong all-round alloy. It has a greatly reduced iron content, with almost all of its components allocated to nickel, chromium and molybdenum. These three elements give Hastelloy S the ultimate in high temperature corrosion resistance.
Hastelloy W has a composition ratio between the Hastelloy B series and the C series. Its high molybdenum content gives it good resistance to reduction, while it has more chromium than the B series. This gives it a more balanced performance.
Hastelloy X is a high temperature focused alloy, which comes from its cobalt content. In addition, Hastelloy X has a lot of iron added to reduce costs.
What is the price of Hastelloy alloys?
Due to the high molybdenum content, the raw material price of Hastelloy alloy is higher than many nickel-based superalloys. Also, due to their high strength, Hastelloy alloys are more difficult to process, which further increases their price.
What is the difference between Hastelloy alloys and other superalloys?
As stated in the main text, the most important feature of Hastelloy alloy is that it contains molybdenum. This is the biggest difference between it and other superalloys. Although there are other superalloys that contain molybdenum, their molybdenum content is generally lower than that of Hastelloy, so in terms of properties, Hastelloy exhibits better overall corrosion resistance and higher solid solution strength than other superalloys.
Further Reading
Conclusion
Hastelloy is a generic term for a range of superalloys. They all belong to nickel alloys. What Hastelloy alloys have in common is that they all contain molybdenum. Depending on the ratio of chromium to molybdenum, Hastelloy alloys can be classified into B, C, G and other series. In addition, Hastelloy alloys are basically solid solution strengthened alloys. However, their strength is among the higher of the solid solution strengthened alloys.
We produce high quality Hastelloy alloys. If you have any purchasing needs, please contact us via email.
