High speed steels are a group of high-performance steel alloys used to produce tool bits and machine parts used in demanding, high-speed machining applications. There are several grades of high speed steel (HSS), all of which include carbon as a common alloying element in addition to various other components such as tungsten, cobalt, and vanadium. Unlike plain tool steel, the alloy compositions of high speed steels allow them to withstand very high operational temperatures without losing their hardness. This characteristic makes them ideal for the manufacture of drill bits, milling bits, and reamers. Lathe tool bits, gear cutters, and saw blades are also commonly produced from HSS.
In the past, the high speed tool bits used in drills and lathes were traditionally made from conventional tungsten tool steel. Although effective, they did not hold their hardness very well at elevated operational speeds. Advancements in metallurgical science, such as the replacement of tungsten with molybdenum, made other alloying options possible and high speed steel was born. These steels have a carbon content ranging from 0.65 percent to 1.1 percent, and also include other alloying components such as tungsten, vanadium, and cobalt. They are generally very hard, with average values exceeding HRC60 and are capable of holding their temper, or hardness, even at high operational temperatures.
Several other treatments for HSS products have seen many new uses come to light. These include coating the bits with substances such as titanium nitride and titanium carbide, which not only enhances the tool's surface hardness, but also lubricates it. This prevents the cut material from galling, or sticking, to the bit due to friction-induced high operating temperatures. The coatings also serve to reduce the temperatures generated during cutting, ensuring cleaner cuts and better tool-bit life.
This characteristic makes high speed steel ideal for the manufacture of tools and tool bits used in demanding, high-friction applications where deep, long cuts are made at speeds not previously possible with the older tool steels. These applications include the tool bits used in turning, shaping, and milling operations. High speed drill bits are also typically made from HSS. Even though they generally do not operate at extremely high speeds, reamers, gear cutters, and saw blades are also made from high speed steel due to the high temperatures generated during their use. For reference, when purchasing these high speed steel products, they are generally marked with a “HSS” or “HS” stamp for easy identification.