Noun
alloy steel that is suitable for making tools; is hard and tough and can retain a cutting edge
Source: WordNetApplication in metal finishing Tool steel toughening Nitrogen or other ions can be implanted into a tool steel target (drill bits, for example). Source: Internet
The purpose of a tool steel face on an anvil is to provide what some call "Rebound" as well as being hard and not denting easily from misplaced hammer blows. Source: Internet