Stellite® is a non-magnetic alloy which contains a variety of different metal components with the main elements being cobalt and chromium. The material itself has been around since the 1900s and was originally seen as a substitute for traditional metal cutlery which suffered from general wear and tear and was also prone to staining. Invented by Elwood Haynes the trademark has changed hands on various occasions and now resides with the Kennametal Stellite Company. Like so many of the groundbreaking alloys we see today Stellite is available in a variety of different compositions and used in so many areas of everyday life it is impossible to list them all.
This is a material that many of us have never heard of but due to its distinctive characteristics it is a vital element of the engineering sector.
What is Stellite?
In simple terms a Stellite alloy is designed to cope with extreme wear and tear and by introducing a variety of other components can be specifically moulded for a particular requirement. The different varieties of Stellite alloy can take in an array of different elements such as nickel, iron, carbon, magnesium, sulphur, silicon and titanium. By introducing other elements to the alloy, specific levels of wear resistance, corrosion resistance and heat resistant materials can be created. The material is commonly used in environments where temperatures range from 600 up to 1112°F (315 to 600°C). It is the ability to maintain the core strength and resistance to wear and tear which is central to the benefits of Stellite.
Main benefits of Stellite
As we touched on above, the main benefits of Stellite are the wear resistance, strength of the material as well as the ability to work under extreme temperatures. Particular characteristics required for a Stellite alloy can be finely tuned by adding a mix of different alloys – something which has been perfected over the years.
It will be no surprise to learn this is a relatively expensive alloy for the simple fact that it is so durable it is almost impossible to machine manipulate. Therefore castings for Stellite based products have to be as perfect as possible so there is minimal corrective action required. Indeed rather than your traditional machine cutting action to “finish off” a rough edged product the only way to manipulate Stellite is by grinding. So, on one hand the toughness and strength of Stellite are perfect for many different applications but on the other the toughness and strength reduce the amount of possible manipulation.
Common uses of Stellite
Those in the engineering industry will have heard of Stellite 100 which is a specific alloy used in cutting tools. This particular mix of elements allows manufacturers to create a cutting-edge which is very hard, able to operate at high temperatures and has a long life. You only need to take a look at a metal saw to see the rigid cutting teeth, the durability and cutting power this material offers. However, there is more to this product than just cutting tools!
There are many different areas of manufacturing where heat resistant and extremely tough materials are required. It will therefore come as no surprise to learn that Stellite has contributed to improvements in areas of manufacturing such as car engines, poppet valves, valve seats, machine gun barrels and rifles. There have also been experimental programs which used Stellite alloy in replacement hips and the first prostatic heart valve back in 1960 utilised the material in the cage design. Where there is erosion, corrosion, resistance and extreme heat, Stellite in its many forms has proven to be a game changer.
With the nuclear industry crying out for extremely tough, temperature resistant and corrosion resistant materials you would have thought that Stellite alloys would have been perfect. Unfortunately the material is not suitable for nuclear power station central reactor piping because of the risk that tiny particles of Stellite may enter the process fluid. If this was the case the cobalt element within the alloy would be converted to cobalt-60 by the neutron flux in the reactor itself.
Cobalt-60 is a radioisotope which releases “energetic” gamma rays and has a 5 ½ year life. While not a danger to the general public, many nuclear power plant workers have been exposed to the material in confined conditions which is certainly detrimental to their health.