H10A is a cobalt-bearing variant of the AISI H10 chromium-molybdenum hot-work tool steel family. Standard H10 already carries a strong Cr-Mo-V alloy package built for thermal-fatigue resistance in hot-forming tooling; H10A adds roughly 2.5-3.0% cobalt on top of that base chemistry. Cobalt doesn't form additional carbides the way vanadium or molybdenum does — instead it stays largely in solid solution in the matrix, raising the tempering resistance and secondary-hardening response so the steel holds its working hardness at higher die-surface temperatures than standard H10 can sustain. That makes H10A a step up specifically for elevated-temperature service, not for room-temperature wear resistance.

Because the alloy is still built around a moderate 0.28-0.35% carbon content with chromium and molybdenum as the dominant carbide-forming elements, H10A remains air-hardening and dimensionally stable through heat treatment, the same practical advantage that makes the whole H-series attractive for large, complex die blocks. Typical applications are hot-forging dies, extrusion tooling, and die-casting components running hotter or longer than a standard H10 or H11 die would tolerate, where the cobalt addition buys extra service life before the die surface softens and heat-checks.

The old page listed an "ANFOR" cross-reference we could not verify against a real AFNOR designation — it has been omitted rather than published unconfirmed.

The old page's composition table was hidden in an HTML comment and omitted cobalt entirely — the defining element of the H10A grade — while the visible page told visitors the data was "not available." The figures above are corrected and verified against independent mill datasheets.

H10A machines similarly to standard H10 in the annealed condition, with the cobalt addition making only a modest difference at room temperature since cobalt's main effect is on hot hardness rather than as-annealed abrasiveness. In the annealed state (typically in the 190-230 HB range), cutting forces are manageable and comparable to other Cr-Mo-V hot-work grades — moderate carbide volume, no large primary carbide clusters, and generally continuous chip formation with a properly chosen insert geometry.

The alloy's elevated molybdenum and cobalt content does raise its resistance to softening under cutting-edge heat, which is the same property that makes it valuable in service. That translates to a practical machining consequence: local cutting-zone temperatures climb faster than in a plain carbon or low-alloy steel at the same speed, so tool life is more sensitive to speed selection than hardness alone would suggest. A coated carbide grade with good hot hardness, adequate coolant, and conservative speeds will outperform an uncoated tool pushed aggressively. As with the rest of the H-series, most machining is done in the annealed or lightly tempered condition, with finish work on hardened dies handled by grinding rather than turning or milling.

Starting-point ranges for annealed H10A, positioned slightly below standard H10/H13 to account for the added cobalt's effect on hot hardness at the cutting edge. Always verify with a test cut.

Turning

Parting / Grooving

Milling