M35 is a cobalt-bearing molybdenum high-speed steel from the AISI M-series, essentially M2 with roughly 5% cobalt added to the alloy package. Like the rest of the M-series, M35 is made into cutting tools — drills, taps, and other tooling — rather than dies. The tungsten, molybdenum, chromium, and vanadium content stay close to M2 levels, so M35 builds a similar carbide population, but cobalt works differently from the other alloying elements: rather than forming its own carbides, cobalt stays largely dissolved in the steel's matrix, where it raises the matrix's own hot strength and boosts the secondary-hardening response during tempering.

That's why M35, often marketed as HSSE or HSS-E (high-speed steel, extra), holds a useful hardness at higher service temperatures than plain M2 and reaches slightly higher as-hardened hardness (typically 64-67 HRC). Tools made from M35 are the standard step-up choice when M2 doesn't hold an edge long enough — drilling and tapping stainless steels, high-temperature alloys, and other gummy or work-hardening materials where cutting-edge temperatures run higher than in general steel machining.

M35's machinability challenge comes from a different source than M3's. Because M35's tungsten, molybdenum, chromium, and vanadium levels closely track M2, its raw carbide volume — and therefore its abrasiveness from hard carbide particles — is similar to M2's. What changes the cutting behavior is cobalt: since it stays in solid solution rather than forming carbides, cobalt raises the strength of the surrounding matrix itself, which means the material resists deformation at the cutting edge more than M2 does, even in the annealed condition (typically 248-269 HB, somewhat harder than M2's typical annealed range).

In practice this shows up as elevated cutting forces and higher temperatures at the tool-chip interface rather than a dramatic change in chip shape or abrasive wear pattern — chips still form short and segmented, similar to M2. Because the heat generated at the edge climbs faster than the abrasive wear does, coated grades with strong hot hardness and good thermal-shock resistance matter as much as raw abrasion resistance on this grade. As with other HSS grades, M35 tooling is machined and profiled in the annealed condition before hardening and finish grinding.

Conservative speeds, good coolant application, and rigid setups all help manage the heat load that cobalt's matrix-strengthening effect creates. Treating M35 as running slightly hotter than M2 at the same parameters, rather than assuming identical behavior, gives more predictable tool life.