Availability and Classes

• The A series family of tool steels contains multiple variations designated by a number after the A. A-2 tools steel is the most widely available and is often available in bar form or drill rod. Air hardening tool steels also include A-4, A-6, A-7, A-8, A-9, A-10, A-11 and A-18. There are also modified versions of some steels such as A-7 modified.
  
  

General Chemistry

• Nearly all the steels in the A family contain carbon, manganese, chromium, molybdenum and vanadium with trace impurities such as phosphorous and sulfur. The carbon content carries from .45 percent in A-9 to 2.85 percent in A-7. The variation in carbon determines the eventual hardness of the steel. Other elements vary as widely but to qualify as an air-hardening steel the elemental combination must allow the steel to harden in the air.
  
  

Thermal Properties

• Since the A series of steel hardens at room temperature, heat treating is fairly easy. The steel's temperature must be raised above the critical or non-magnetic temperature and then allowed to cool. Annealing such an easily-hardened steel is more difficult.
  
  

Uses and Precautions

• The A series of tool steels are used almost exclusively in the manufacturing of tools and in general machining. Precaution must be made when machining air-hardening steels since excessive heat during machining can cause the steel to harden.