This page covers A2 air-hardening cold-work tool steel in a condition that's already been through heat treatment — quenched and tempered to a working hardness in the high-50s to low-60s HRC range, rather than the soft annealed state most bar stock ships in. A2's alloy recipe (roughly 1% carbon, 5% chromium, plus molybdenum and vanadium) was designed specifically around air hardening: the part can cool in still air after austenitizing and still reach full hardness, which keeps distortion and cracking risk far lower than an oil- or water-quenched grade would see on the same geometry. That dimensional stability through hardening is the entire reason A2 gets specified in the first place.

Once hardened, the same chromium-molybdenum-vanadium carbides that made A2 easy to machine in the annealed state now do the opposite — they're what gives the steel its wear resistance and edge-holding ability in service, and they're exactly what a cutting edge has to fight through when the part needs additional machining, grinding, or finishing operations after heat treatment. Typical uses for A2 in this hardened condition include finished blanking and forming punches, trim dies, gauge blocks, and other precision tooling where the part is brought close to final size before hardening and then only light stock removal, hard turning, or grinding is performed afterward.

Machining A2 after it has already been hardened is a completely different job from machining it in the annealed condition, and it's not something a general carbide turning or milling grade is built for. At 57-62 HRC, the chromium-molybdenum-vanadium carbides that make A2 wear-resistant in service are just as abrasive to a cutting edge, and the surrounding matrix no longer deforms or shears the way soft steel does — it behaves closer to a brittle, high-strength material under the tool. Cutting forces concentrate in a very thin zone right at the edge, and heat has almost nowhere to go except into the tool.

Because of this, hardened A2 is normally worked with CBN (cubic boron nitride) or extremely wear-resistant PVD-coated carbide grades rather than standard turning or milling inserts, and only in light, controlled cuts — small depths of cut, moderate feeds, and speeds well below what the same steel would tolerate annealed. Insert geometry leans negative rather than positive: a negative land and larger honing radius support the edge against the high compressive loads of hard machining instead of trying to shear the material cleanly. Rigidity of the machine, toolholder, and workpiece clamping matters enormously at this hardness, since any vibration accelerates edge chipping rather than gradual wear. Where the tolerance and finish allow it, many shops still prefer grinding over hard turning for A2 at the upper end of its hardness range — hard turning is best suited to profiles or interrupted features that are awkward to grind.