High speed steel is a valuable type of steel that is designed to withstand the temperatures and stresses of high-speed applications such as saw blades and drill bits. Some HSS alloys are cobalt steels that have some helpful characteristics from using 5% to 8% cobalt. High speed cobalt tends to have superior hardness and heat resistance compared to other HSS.
What Is Cobalt Steel?
As the name suggests, these alloys include cobalt as a significant addition. For example, M42 is similar to molybdenum high speed steel (another common type) but with an additional 8% cobalt. For many applications, high speed cobalt is a direct upgrade on other high speed steels.
High speed steel alloys with cobalt are more modern alloys than molybdenum alloys. These improved alloys (especially M42) add to the characteristics that users love about HSS and simply make them better.
What Are the Benefits of High Speed Cobalt?
There are many great reasons to consider using a cobalt steel alloy. These are some of the key characteristics of these alloys:
- Superior Red Hardness: The addition of cobalt can bring the Rockwell hardness up to 70 Min. Notably, these alloys perform especially well at high heats, maintaining their hardness and usability in production environments.
- Heat and Abrasion Resistance: Similarly, high speed cobalt tends to perform very well in terms of heat and abrasion resistance. These characteristics are the main reasons why people choose high speed steel. With the improvements of cobalt steel, the advantages are only compounded.
- Shorter Cycles: The above characteristics add up to one very important practical benefit: shorter cycle times. Tools made with these alloys can be run longer with less maintenance. That means cost savings for industrial applications.
What Is M42 Cobalt Steel?
M42 is a specific HSS alloy including 8% cobalt. Otherwise, it is very similar to other molybdenum-series high speed steels. It has become a go-to material for machining applications thanks to its extremely impressive performance. It is one of Griggs Steel’s most popular alloys.
It can take on higher cutting speeds than many other steels. Additionally, it can be used for longer without tool changes. It also costs less compared to tools made with carbide while being less likely to chip when used for interrupted cuts.
What Are M42’s Specifications?
M42 has a density of 0.282 pounds per cubic inch. Its specific gravity is 7.81. The modulus of elasticity is 30 x 106 psi. Finally, the machineability is 35% to 40% that of carbon steel. The following are the amounts of each key element in its chemical composition:
- Carbon – 1.1%
- Chromium – 3.9%
- Tungsten – 1.6%
- Molybdenum – 9.5%
- Vanadium – 1.2%
- Cobalt – 8.25%
The wear resistance is greater than that of M2, M3, M7 and PM23. Its red hardness is superior to M2, M3, M4, M7, PM M4, PM T15 and PM23. However, the ease of grinding of M42 cobalt steel is lower than most alloys due to its hardness. Therefore, it is not a good choice for applications that may involve grinding.
What Are Common Applications for M42 Cobalt Steel?
M42 is a common choice for many typical HSS applications. As mentioned above, it does many of the same things as standard molybdenum HSS only better.
Some applications include end mills, blades, broaches, form tools, taps, reamers, punches, thread roll dies, header tooling and milling cutters. It can be used in cutting, drilling, punching and other production uses.
The cost of M42 combined with its ability to be used with shorter cycle times and fewer interruptions make it a financially attractive option in many cases. However, some users prefer more conventional high speed steels for applications that don’t have high demands for the tooling.