Machining
Machining is the cutting of materials: turning, milling, drilling, broaching. The cutting edge of the tool must be harder than the workpiece and maintain its hardness even when heated – that's exactly what high-speed steels (HSS) are for.
What Machining Is
Machining is removing material with a cutting edge – turning, milling, drilling, broaching, sawing. The tool edge cuts through the workpiece and must be harder and more wear-resistant than the workpiece.
Why the Edge Gets Hot
Machining generates friction heat; the edge can get several hundred degrees hot. A regular tool steel would temper and lose hardness – the edge dulls immediately.
The Material for That: HSS
High-speed steels (HSS) keep their hardness even at red heat because they go through secondary hardening during tempering. That's exactly why they are the classic material for machining tools – from drills to hobs.