Definition
A family of high-carbon alloy steels formulated to be hardened and tempered to a high degree of hardness, strength, and wear resistance. Tool steels typically contain carbon along with alloying elements such as tungsten, chromium, vanadium, or molybdenum, and are used to make cutting tools, dies, punches, and other parts that must hold a sharp edge or resist deformation under heavy use.
Plain English
A specially made, very hard steel used for things that have to cut, shape, or wear against other metals without dulling or bending.
Context Anchor
Seen in aircraft maintenance and repair discussions when describing the material used for cutting tools, forming tools, punches, dies, and other shop tools.
Derivation
Named directly for its purpose -- steel made for tools. The term has been in use since the industrial era to distinguish these harder, alloyed steels from ordinary structural or mild steels.
Why Pilots Care
Using the wrong material for a tool can lead to dulling, bending, cracking, or damage to the aircraft part being worked on. Tool steel is chosen when the tool itself must be harder and more wear-resistant than the material it is working against.
Intuition Check
Tool steel does not mean any steel tool. It means a specific type of steel made to perform as a hard, wear-resistant tool material.
Example Sentence 1
The mechanic used a tool steel reamer to bring the bushing to its final size.
Example Sentence 2
Mechanics prefer tool steel sockets for high-torque propeller bolt work because they resist rounding under load.