The tool steels are categorized as shown in Figure 1. Steels are categorized by quench and application. Those categorized by quench are shown as follows:

• W1 to W5 = Low-temperature hardening with water quench
• O1 to O7 = Low-temperature hardening with oil quench
• A2 to A9 = Higher-temperature, high-alloy air hardening

The steels that are categorized by application are:

1.  Shock-resisting steels:

•   S1 to S7 = Shock-resisting tool steels

2.  Hot-work tool steels:

• H (Chromium) H10 to H19 = Hot-work die steel with high operating temperature as well as high hardening temperatures with complex quenching
• H (Tungsten) H21 to H26 = Hot-work tool steels with higher operating temperatures and high hardening temperatures plus complex quenching
• H (Molybdenum) up to H42 = same as H21 to H26

 3.  Dimensionally stable tool steels:

• D2 to D7 = High-carbon, high-chromium cold-work tool steels with a high austenitizing temperature and complex quenching

 4.  High-speed cutting tool steels:

• HSS (tungsten) = T1 to T15 complex steels designed for high-speed cutting
• HSS (molybdenum) = M1 to M36 complex steels designed for high-speed cutting
• HSS (ultra-hard) = M41 to M47 complex steels designed for high-speed cutting

5.  Special Purpose (low-alloy) steels:

• L2 to L6 = Low-alloy, special-purpose tool steels

6.  Mold steels:

• Mold steels = P2 to P21 usually low-carbon and used often for cold hobbing of the impression on coining dies, then carburized or sometimes nitrided

The next part in this series will begin to focus in on the different tool steels and their heat treatments.