High-speed steel

High speed steel (HSS) is a material usually used in the manufacture of machine tool bits and cutters. It is often used in power saw blades and drill bits. It is superior to the older high carbon steel tools in that it can withstand higher temperatures without loseing its temper (hardness). Because of this, high speed steel can cut metal at a higher rate of speed than its predecessor high carbon steel, hence the name high speed steel. It is about as hard as high carbon steel at room temperature. Only at elevated temperatures does it become advantageous.

High carbon steel remains a good choice for low speed applications where a very keen (sharp) edge is required, such as files, chisels and hand plane blades.

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 steels (HSS).

This term is descriptive of their ability to cut metals at the "high speeds" in use through the 1940’s.

The T-1 type with 18% W has not changed its composition since 1910 and was the main type used up to 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 steels and maintains these properties at the high temperatures generated when cutting metals.

The main use of high speed steels 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.

Table 1. Percentage Additions of Alloying Elements to High Speed Steel Grades.

Grade

          C    Cr    Mo    W    V    Co

   T-1   0.75   -    -   18.0  1.1    -

   M-2   0.95  4.2  5.0   6.0  2.0    -

   M-7   1.00  3.8  8.7   1.6  2.0    -

   M-42  1.10  3.8  9.5   1.5  1.2   8.0