High Speed Steel

When tool steels contain a combination of more than 7% tungsten, molybdenum and vanadium, along with more than 0.60% carbon, they are referred to as high speed steel (HSS).  This term describes the ability to cut metal at high speed. 

The T-1 type with 18% W has not changed its composition since 1910 and was the main type used until 1940, when substitution by molybdenum took place.  Nowadays, only 5-10% of the HSS in Europe is of this type and only 2% in the USA.  The addition of about 10% of tungsten and molybdenum in total maximises efficiently the hardness and toughness of high speed steel and maintains these properties at the high temperatures generated when cutting metals.

The main use of high speed steel continues to be in the manufacture of various cutting tools: drills, taps, milling cutters, gear cutters, saw blades, etc, although usage for punches and dies is increasing.

Tool steel, in particular HSS, can be surface treated by nitriding, laser or plasma overlays of hard coatings (eg stellites) as well as by chemical or physical vapour deposition of hard carbides and nitrides.  Coatings, such as TiN, TiAlN or CrAlN significantly increase tool lives but increase tool costs.  Nevertheless, most tools in the higher end applications are coated today as the higher cost is well balanced by the higher productivity during machining.

Global HSS production in 2007 was estimated at 260,000t.