A6 is a genuine AISI A-series air-hardening, cold-work tool steel, and its alloy recipe is unusual among the A-series grades: instead of leaning on chromium and molybdenum alone the way A2 does, A6 carries a notably higher manganese content (roughly 1.8–2.5%) alongside moderate chromium and molybdenum. That extra manganese boosts hardenability enough for the steel to through-harden fully in still air even in fairly heavy sections, which is the whole point of the air-hardening A-series — it lets tool and die makers heat-treat complex or asymmetric shapes with minimal size change and minimal risk of the quench cracking that oil- or water-hardening steels can suffer.

That dimensional stability is why A6 shows up in tooling where holding a tight tolerance through hardening matters more than reaching maximum wear resistance: blanking and trim dies, forming dies, gauges, bushings, and punches, particularly for larger or more intricate tool sections where a water- or oil-hardening steel would be too risky to distort or crack. A6 typically hardens into the high-50s to low-60s HRC range and offers a reasonable balance of toughness and wear resistance for general cold-work die service, sitting alongside A2 as one of the more commonly specified air-hardening tool steels for this kind of tooling.

A6's high manganese content is a double-edged sword at the machine tool. It's exactly what gives the steel its air-hardening capability, but manganese also tends to work-harden readily under cutting forces, which means a light cut, a dull edge, or excessive dwell time can burnish the surface and make the next pass noticeably harder to start cleanly. In the annealed condition (typically in the low-to-mid 200s HB) A6 machines reasonably, but shops that treat it exactly like a plain carbon or chromium tool steel often see faster-than-expected edge wear until they account for this work-hardening tendency.

Chip formation is generally manageable, producing segmented chips that break with a properly matched chipbreaker, though the alloy carbides from chromium and molybdenum do add a meaningful abrasive component compared with unalloyed tool steels like W1. Because most A6 tooling is rough-machined close to final shape before air-hardening and then finished lightly (or ground) afterward, the bulk of the material removal happens in the more forgiving annealed condition — hard-state machining on this alloy is comparatively rare and calls for very conservative parameters.

The practical keys to good tool life on A6 are keeping feeds high enough that the edge is always cutting rather than rubbing (to avoid triggering work hardening), maintaining rigid setups to prevent chatter that accelerates edge chipping, and selecting a coated grade with enough toughness to handle the abrasive carbide content without failing at the edge.