AISI A2 is an air-hardening tool steel containing 5 pct chromium. It replaces O1 when safer hardening, better dimensional stability, and increased wear-resistance are required. Use for dies, punches, and similar forming and blanking tools as recommended for Type O1, but where less distortion in heat-treatment or better wear-resistance is required. More on AISI A2.
A6 is an air hardening, cold work die steel which exhibits less distortion during heat treatment than water or oil hardening steels and most high alloy, air hardening die steels. It is a fully air hardening steel, a 6 inch cube hardening to Rockwell C 60 in still air. In addition, A6 has the advantage of a low hardening temperature range, 1500'-1600F, usually available only in oil hardening steels. More on AISI A6