(Following information is from the enco website)
High Speed Steel (HSS)
Provides good wear resistance and costs less than cobalt or carbide end mills. HSS is used for general purpose milling of both ferrous and non-ferrous materials.
Cobalt (M-42: 8% Cobalt)
Provides better wear resistance, higher hot hardness and toughness than high speed steel. There is very little chipping or microchipping under severe cutting conditions allowing the tool to run 10% faster than HSS, resulting in excellent metal removal rates as well as good finishes. This material, combined with the proper geometry has proven the most cost-effective for machining cast iron, heat treated steels and titanium alloys.
Powdered Metal (PM) Cobalt
A cost effective alternative to solid carbide, powdered metal is tougher and less prone to breakage. Tools perform well in materials <30RC. PM is used in high-shock and high-stock applications such as roughing.
Primarily used in finishing applications, carbide provides several advantages over HSS or cobalt materials. Carbide can run much faster because of the material’s extreme hardness. This allows the cutter to withstand high cutting temperatures and provides excellent wear resistance. Carbide also provides better rigidity than HSS, which enables the end mill to provide a higher degree of dimensional accuracy and superior surface finishes. Carbide provides the user with the ability to run faster with less tool wear. However, the user should be aware that carbide’s hardness comes at the expense of its toughness. Carbide is brittle and tends to chip when conditions are not ideal, rather than wear. Heavy feed rates are more suitable for HSS and cobalt tools. Carbide end mills, which can be run 2-3X faster than HSS, are best for maximizing speed and tool life.
Offering some of the advantages of solid carbide tooling, carbide is brazed to the cutting edges of steel tool bodies. This is particularly a cost-effective option for larger diameter tools.