A hard steel used for metal cutting tools as it remains hard even at dull red temperatures. It normally contains: Tungsten 12 to 18%, Chromium up to 5% and Carbon 0.4 to 0.7%. Search for machine tool books on Amazon.co.uk
tool steel able to cut at twice the speed of carbon steel. Most commonly used in lathe bits, drills, and end mills. Note that, as a general rule, the harder the tool steel the higher the cutting speed that can be obtained.
(HSS): Hardened steel used in cutters, blades, bits and knives.