AISI/SAE S1 is a chromium-tungsten shock-resisting tool steel, built around roughly 0.40–0.55% carbon with tungsten (1.50–3.00%) and chromium (1.00–1.80%) as the main alloying additions, plus a small vanadium contribution for grain refinement. Like the rest of the S-series, S1 is formulated to strike a balance between hardness and toughness rather than chasing maximum wear resistance — the tungsten and chromium carbides provide a useful edge-holding capability while the moderate carbon content keeps the matrix tough enough to absorb repeated impact without cracking.

That toughness-first balance is what makes S1 a natural fit for pneumatic tooling, chisels, punches, and other tools that see repeated shock loading rather than continuous abrasive wear. It hardens deeply and holds up well under sustained impact, which is exactly the failure mode that a purely wear-resistant tool steel would struggle with. S1 is typically supplied annealed for machining and then hardened and tempered to its working hardness afterward, similar to other tool steels in this class.

In its annealed condition, S1 machines like a moderately alloyed tool steel: the carbon level around 0.5% combined with chromium and tungsten carbides gives it noticeably more cutting resistance than a low-carbon mold steel, but far less than a high-speed steel like M-series grades. Cutting forces and tool wear sit in a middle ground — manageable with the right grade, but not something to treat casually with general-purpose tooling.

The tungsten and chromium carbides in the microstructure are the main driver of tool wear, acting as small abrasive particles that gradually wear down the cutting edge, particularly on flank surfaces. Chip formation is generally reasonable in the annealed state, with chips that respond well to standard chipbreaker geometries at moderate feeds, though heat buildup at the tool-chip interface climbs faster than on plain carbon steels because of the alloy content.

Rigid setups and a grade with good hot hardness pay off here, since S1 tools are often finish-machined close to final dimensions before hardening, and any chatter or edge degradation during that pass shows up directly in the finished tool. A coated carbide grade suited to the P10–P30 ISO range handles S1 well in its typical supply condition; harder heat-treated stock will need reduced speeds accordingly.