We want to be upfront about this one: "A100" does not correspond to any ASTM, AISI/SAE, DIN, or JIS steel designation we could verify. There is an ASTM standard numbered A100, but it covers ferrosilicon — a foundry additive used in steelmaking, not a machinable steel product — so it isn't a match. The data behind the previous version of this page didn't resolve the question either; its composition figures were never independently checked, and the hardness value quoted alongside them wasn't metallurgically consistent with that same composition, which told us the older data shouldn't be carried forward as fact.

What we can say with confidence is that FM Carbide's own catalog places this material in its "H – Hardened Steel" group, meaning it's referenced here as a pre-hardened tool or die steel rather than a soft, machinable-from-annealed grade. Rather than invent a specific alloy identity to fill in the gaps, this page presents A100 as a general hard-machining reference point within that catalog group — the kind of entry a shop would consult when working a hardened tool steel in roughly the mid-50s to mid-60s HRC range, without a fully documented chemistry to pin the recommendations to. If you have mill certification or a hardness test for your specific material, treat those figures as authoritative over anything general presented below.

Without a confirmed alloy or hardness figure, the most useful guidance for a material in FM Carbide's "H – Hardened Steel" group is general hard-machining practice rather than alloy-specific advice. Steels in this catalog group are typically encountered already heat-treated to a working hardness well above what standard turning or milling inserts are designed for, which changes the cutting mechanics substantially: the material no longer shears cleanly the way annealed steel does, cutting forces concentrate in a very thin zone at the edge, and heat has nowhere to escape except into the tool and the chip.

That combination calls for wear-resistant, chip-resistant tooling run at conservative parameters rather than a general-purpose grade pushed to its limits. Light, controlled depths of cut and moderate feeds reduce edge stress; negative rake geometries and a more substantial edge hone support the cutting edge against high compressive loads instead of trying to shear the material the way a positive, sharp edge would on soft steel. Machine and workholding rigidity matter more here than on almost any other material class — vibration at this hardness accelerates chipping far faster than it accelerates gradual wear.

Where practical, many shops still prefer grinding over hard turning or milling once a part reaches the upper end of this hardness range, reserving hard machining for profiles, contours, or interrupted features that are impractical to grind. Confirming actual hardness before committing to a cutting strategy is the single most useful step you can take on a material with this little documented history.