Carbide grades, explained.

The letter-and-number system

The international system, ISO 513, codes every grade with a letter and a number. The letter names the workpiece material the grade is designed for: P for steel, M for stainless steel, K for cast iron, N for non-ferrous metals, S for superalloys, and H for hardened steel. The number, running from 05 to 45, describes the application range — the tradeoff between wear resistance and toughness. A low number like 05 or 10 means a harder, more wear-resistant grade built for favorable, continuous cutting conditions at high speed. A high number like 30 or 40 means a tougher grade built to survive interrupted cuts and rough conditions. So a P20 and a P40 are both steel-cutting grades, but the P20 is the harder finisher and the P40 the tougher rougher. Manufacturers also use color codes tied to these letters: blue for P (steel), yellow for M (stainless), and red for K (cast iron and non-ferrous). Those colors show up on insert packaging and sometimes on the inserts themselves, and they are a useful first clue when sorting — but laser-etched codes are the real authority.

The ANSI C-grade system

American shops also use the ANSI C-grade classification, and you will see C-codes stamped on tooling constantly. C1 through C4 are straight tungsten carbide bonded with cobalt — no titanium or tantalum additives — intended for cast iron, non-ferrous, and non-metallic work, running from roughing (C1) through general purpose (C2) and finishing (C3) to precision (C4). C5 through C8 are the steel-cutting grades, alloyed with titanium carbide and tantalum carbide to resist the cratering and deformation that steel cutting causes, again ordered from roughing to precision. Beyond cutting tools, C9 through C14 cover wear and impact grades, and C15 through C19 cover specialties: rock bits, cold-header dies, high-temperature wear parts, and even radiation shielding and counterbalances. Coated versions get a CC prefix, as in CC-5 or CC-6. Within any family the pattern holds: a higher number means more toughness and less hardness; a lower number means more wear resistance at higher cutting speeds. Rough cross-mappings exist between the systems — P20 lands near C6, K20 near C2 — but treat those as approximations, not identities.

Three dials, hundreds of grades

Every grade is a point on three dials. First, binder content: more cobalt means more toughness and shock resistance; less cobalt means more hardness and wear resistance. Second, tungsten carbide grain size: fine micrograin gives a sharper, harder edge for precision work; coarse grain gives impact resistance for drilling and mining. Third, alloying additives: titanium carbide, tantalum carbide, and niobium carbide tune how the grade handles specific workpiece materials — the steel-cutting C5–C8 family relies on them, while the straight WC-Co C1–C4 family has none. Coatings are a fourth, thinner layer of the story: gold TiN or dark TiAlN and AlTiN coatings are only microns thick. They improve cutting performance but do not change what is underneath, and they do not add scrap value beyond the carbide itself — nor do they hurt it. One honest complication: real commercial grades often span multiple ISO letters. A single modern grade may be marked P, M, K, N, S, and H with a C2–C3 or C5–C6 range, because the ISO/C designation describes an application range, not a chemical formula.

Grades and recycling value

From a recycler's point of view, grades sort into two buckets. The straight grades — ANSI C1–C4, ISO K, the red-coded cast-iron and non-ferrous family — are the cleanest and most tungsten-rich, with no titanium or tantalum additives complicating the chemistry. They recycle most cleanly through the direct zinc process and sit at the top of the value picture. The alloyed steel-cutting grades — C5–C8, ISO P, blue-coded — contain TiC and TaC additives that change the recycling chemistry and need different handling. This is why sorting inserts by grade family pays: a bucket of separated K-grade inserts is straightforward, high-recovery material, while the same inserts mixed blind with P-grades become a blended lot evaluated as a blend. You do not need to memorize the chart to sell well — but keeping the red-coded and blue-coded families apart is one of the highest-value sorting moves a shop can make.

Carbide questions, answered.