High speed steels (often abbreviated HSS) are ferrous based alloys of the Fe-C-X multicomponent
system where X represents a group of alloying elements comprising mainly Cr, W or Mo, V, and Co.
These steels are mainly used for cutting tools, since they are characterized by their capacity to retain
a high level of hardness while cutting metals at high speed. Generally, the X component is present in
excess of 7%, along with more than 0.60% carbon.

Historically, the first high speed steels were the tungsten base type developed by Robert Mushet in the
UK and F.W.Taylor in the USA toward the end of the XIX century. In 1904 the addition of vanadium was
patented by the Crucible steel company, leading finally to today's best known grade,
18/4/1 (18%W, 4%Cr, 1% V) The first record of the use of cobalt in high speed steels was in Germany 1912.
Later, around 1930, molybdenum-bearing alloys were being introduced in the USA.

High-speed steels are divided into three groups: