Tool and hardened steels
The material arrives already hard, or hardens along the way. That changes the manufacturing question: not what the cutting conditions are, but what can still be machined after hardening and what has to be finished before it.
How it behaves at the cutting edge
Above roughly 55 HRC, cutting with carbide inserts stops being economical: the tool wears faster than the part advances. The shape is therefore produced before heat treatment, with an allowance, and the final dimensions afterwards - by grinding and wire EDM, where hardness no longer matters. On such parts the sequence of operations decides the result more than the speed of any single one, and distortion from quenching is absorbed by the allowance left behind rather than corrected later.
Machined by grinding and wire EDM after heat treatment.
What to state on the drawing
The required hardness and the zone in which it is required are marked on the drawing. A through-hardened part and one hardened only on the working surface are two routings, two prices and two different distortion risks. Dimensions that must hold after hardening are marked as such: they decide whether the part goes to grinding or to wire EDM.
What it means for the routing
After hardening, turning is no longer an option for tight dimensions. What remains is grinding - for surfaces and journals - and wire EDM for contours no cutter can follow any more. Wire EDM does not feel hardness: it cuts a 62 HRC steel the same as a soft one, because it does not cut mechanically. That is why complex contours in hardened parts are left to it, rather than forced into milling before treatment.
Where it is used
- Dies and die components
- Guides and cams
- Wear bushings
- Complex contours in hardened parts
- Parts working in friction
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