1.5. Tool Steels

Tool steels are carbon, alloy, or high-speed steels, capable of being hardened and tempered. They are used to make tools for cutting, forming, and shaping of work materials. Tool steels are also used as the work materials where resistance to wear, strength, toughness, and other properties are selected for optimum performance.

According to the American Iron and Steel Institute (AISI) classification, tool steels are divided into seven major groups, each group identified by letter-numeric symbols. Within the various groups there are subdivisions (Ref 8, p.431, Ref 14, p.6):

1. Water-hardening tool steels, W

2. Shock-resisting tool steels, S

3. Cold-work tool steels:

   • Oil-hardening types, O

   • Air-hardening, medium alloy types, A

   • High-carbon, high-chromium types, D

1. Mold steels, P

2. Low alloy special-purpose tool steels, L

3. Hot-work tool steels:

   • Chromium-base types, H10 H19

   • Tungsten-base types, H21 H26

   • Molybdenum-base types, H41 H43

1. High-speed tool steels:

   • Tungsten-base types, T

   • Molybdenum-base types, M

The UNS designation of tool steels consists of the letter T (assigned to tool steel), followed by five digits. Water-hardening types are T723xx; shock-resisting types are T419xx; oil-hardening types are T315xx; air-hardening types are T301xx; high-chromium types are T304xx; low-alloy, special purpose types are T612xx; mold steels are T516xx; hot work types are T208xx; high-speed, tungsten-base types are T120xx; and high-speed, molybdenum-base types are T113xx.

The author studied the relationship between the tensile strength ( ?) and Brinell hardness (HB) of those tool steel grades, for which a sufficient number of data points were available, so the linear...