As distributors of the best superalloys available, we know that each element in an alloy’s compositional makeup is key to its success as a product. The high-end INCONEL range is based on a solid combination of nickel and chromium, with significant additions of other elements, including molybdenum. This killer combination gives INCONEL products their outstanding corrosion resistance, as well as excellent strength capability in both low- and high-temperature environments.
Similarly, the INCOLOY range of alloys is a combination of nickel and chromium, but with iron replacing some of the nickel content to make a more economical product. However, it still offers both good strength and corrosion resistance.
These advantageous properties are in no small part thanks to the important inclusion of chromium in the alloy’s composition. The steel-grey element is hard and brittle, but has a high melting point. It offers excellent resistance against all kinds of corrosion and is valued for its natural hardness. Nickel alloys benefit from an increase in strength when chromium is added.
Chromium is commercially extracted from chromite, which is an oxide of iron, magnesium, aluminium and chromium, and the only ore of chromium. It has been around for many hundreds of years, and has lent itself to a number of different uses including, in the early days, as a component in paints and for electroplating. Nowadays, the majority of chromium produced is for metal alloys (around 85%), and the rest for chemical, refractory and foundry uses.
Use in alloys
Chromium is a key component of the INCONEL and INCOLOY alloy ranges. For example, INCONEL alloy 601 has a particularly high chromium content of 21-25%, and has a broad spectrum of uses across the thermal-processing, chemical-processing, pollution control, aerospace and power-generation industries. The alloy offers outstanding resistance to high-temperature oxidation, as well as other corrosive media, attributed to the substantial chromium content and its nickel base. INCONEL alloy 601 is one of the most widely used materials for thermowell sheathing and oxygen injection tubes in the metal- and glass-making industries.
INCONEL alloy 625, one of the standout superalloys in the INCONEL range, is well known for its combination of high strength, excellent fabricability and corrosion resistance in a wide range of environments. In the most severe corrosive situations, the balanced combination of nickel and chromium here provides resistance to highly oxidising environments. Its versatility means it is used across most key industries, but is particularly accepted in the chemical-processing field.
Another product with a high chromium level is INCOLOY alloy 27-7MO, which we recently looked at in more detail on the blog. This alloy is a viable and lower-cost alternative to more expensive alloys in some industries, which helps to keep costs down without sacrificing quality. With a typical 22% chromium content, the alloy can offer good resistance to oxidising acids, and it has uses power plant, pulp and paper mill, oil extraction, chemical processing and marine environments.