S7 is a chromium-molybdenum air-hardening tool steel built around one job: surviving repeated impact without cracking. Where many tool steels trade toughness for maximum hardness, S7 sits deliberately on the tough end of the spectrum — roughly 0.45–0.55% carbon keeps the matrix from becoming brittle, while about 3.00–3.50% chromium and 1.30–1.80% molybdenum supply the hardenability needed to through-harden in air on moderate cross-sections without the distortion risk of a water- or oil-quench grade. A small vanadium addition (around 0.20–0.30%) helps refine grain structure and control carbide size, which is part of why S7 resists chipping and cracking under shock loading better than higher-carbon cold-work grades.

That combination of properties is exactly why S7 shows up in punches, header dies, chisels, pneumatic tool bits, shear blades, and other tooling that takes repeated hammer-like blows rather than steady abrasive wear. It's typically supplied annealed for machining and rough shaping, then hardened and tempered afterward, so most shops encounter it in a softer, more machinable condition than many other tool steel grades — though it still cuts noticeably differently than plain carbon or low-alloy engineering steels because of its alloy carbide content.

In the annealed condition S7 typically runs around 200 HB, which puts it in a machinable range comparable to many medium-alloy engineering steels — but the chromium and molybdenum carbides distributed through the matrix are harder and more abrasive than what you'd find in a plain carbon steel at the same bulk hardness. That abrasiveness, not raw hardness, is the main driver of tool wear on S7: expect steady flank wear on uncoated or under-coated tooling rather than sudden edge failure, provided the setup stays rigid and cuts stay consistent.

Chip control is generally cooperative in the annealed state, with S7 forming manageable chips when insert geometry includes a proper chipbreaker matched to the feed rate in use. Because the alloy was designed for toughness rather than free-machining characteristics, there's no sulfur or lead addition to help chips fracture, so relying on geometry and feed selection — rather than the material itself — is what keeps chips short and clears them from the cut zone.

Heat management matters more on S7 than on unalloyed steels of similar hardness, since the carbide content raises cutting temperatures at the tool-chip interface. Coated carbide grades with good hot hardness hold up better than uncoated tooling across a full tool life, and steady, adequately loaded feeds help avoid the rubbing action that accelerates edge rounding and work hardens the surface on the next pass.