M3 is a molybdenum-type high-speed steel from the AISI M-series, positioned as a step up from M2 in wear resistance and edge retention. Like all M-series grades, M3 is made into cutting tools rather than dies — drills, reamers, taps, milling cutters, and punches that need to hold a sharp, wear-resistant edge at elevated cutting temperatures. M3 shares M2's basic tungsten-molybdenum-chromium framework but carries meaningfully more carbon and vanadium, which builds a larger volume of hard vanadium carbide into the microstructure. That extra vanadium carbide is what gives M3 its improved abrasion resistance and edge-holding ability compared with M2, at some cost to grindability during tool manufacture. AISI M3 is produced in two closely related compositions, Class 1 and Class 2, distinguished mainly by carbon and vanadium content; the Class 1 chemistry (UNS T11313) is presented here as the more commonly stocked variant.

M3 reaches roughly 63-66 HRC after heat treatment and holds hardness well at elevated temperature, similar to other molybdenum HSS grades. It's a common choice where M2 doesn't quite hold an edge long enough in abrasive materials, but the extreme vanadium content of a grade like M4 isn't needed or would make finish-grinding the tool too slow and costly.

M3 is one of the more abrasive HSS grades to machine, and the reason is straightforward: its vanadium content — 2.25-2.75%, versus M2's 1.75-2.20% — pushes considerably more hard vanadium carbide into the microstructure. Vanadium carbide is harder than tungsten or molybdenum carbide and harder than most aluminum-oxide abrasives, so even a modest percentage increase translates into a real, measurable jump in tool wear compared with M2 at the same hardness. In the annealed condition (typically around 235-262 HB) M3 still machines with standard carbide tooling, but expect shorter tool life than M2 under otherwise identical cutting parameters.

Chip formation and cutting forces follow the same general pattern as other molybdenum HSS grades — short, segmented chips and elevated forces relative to alloy tool steels — but the higher carbide loading means flank wear progresses faster and is less forgiving of aggressive feeds or speeds. Because M3 tooling is almost always finish-ground rather than turned or milled once hardened, the cutting operations covered here apply to rough and semi-finish machining of annealed bar stock and blanks before heat treatment.

Coated carbide with strong abrasion resistance, conservative speeds, and rigid, well-supported setups give the most consistent results. Treating M3 as noticeably more demanding than M2 — rather than assuming similar parameters will work — avoids most premature tool failures on this grade.