T1 is one of the original tungsten high-speed steels, first developed in the early 1900s and still the reference point the entire T-series is built around. Unlike hot-work or cold-work tool steels, T1 is a true HSS grade — it's made into the cutting tools themselves (drills, taps, reamers, milling cutters, lathe bits, broaches) rather than into dies. Its alloy package centers on roughly 18% tungsten with 4% chromium and just over 1% vanadium, with no significant molybdenum in the mix. That heavy tungsten load builds a dense network of hard tungsten carbides through the matrix, and secondary hardening during tempering precipitates more of them directly, giving T1 the red hardness that defines high-speed steel: the ability to keep cutting at temperatures that would soften a carbon or low-alloy tool steel almost immediately.

T1 hardens to roughly 63-65 HRC and holds useful hardness well above 500°C, which made it the dominant cutting-tool steel for decades before molybdenum-type grades like M2 largely displaced it on cost grounds (tungsten is considerably more expensive and less available than molybdenum). It remains in use today for specific tooling where its particular combination of red hardness and grindability is preferred. This page covers T1 in its pre-hardened, machinable form — round bar and tool blanks that get turned, milled, drilled, and profiled into rough tool shapes before hardening and grinding finish the cutting edges.

T1 is harder to machine than any cold-work or hot-work tool steel of comparable hardness, for the same reason M2 is: high-speed steels carry a large volume fraction of hard carbides even in the annealed state. T1's carbide population is almost entirely tungsten-based rather than the mixed tungsten-molybdenum-vanadium carbides found in M2, but the practical effect on machining is similar — in the annealed condition (typically 223-255 HB), those carbides behave like densely packed abrasive particles that resist the cutting edge on every pass, and the roughly 1% vanadium content adds a smaller population of extremely hard, fine vanadium carbide that disproportionately affects tool wear.

Cutting forces run well above what a Cr-Mo tool steel of similar hardness would require, and flank wear accumulates steadily through the cut. Chip formation tends to be short and segmented. Because T1 is almost always machined in the annealed state before hardening — with grinding handling the hardened cutting edges — shops need coated carbide grades with strong abrasion resistance, conservative feeds, and rigid setups to get acceptable tool life. This is not a forgiving material for aggressive parameters.