Tool steels are wear-resistant, ferrous alloys based on iron and carbon with high levels of alloying (hardenability and property modifying) elements such as chromium, molybdenum, tungsten, and vanadium.

Grades of Tool Steels

There are a number of different grades of tool steel that differ based on the areas for which they are designed. Choice of grade depends on whether a sharp cutting edge, impact resistance, or heat resistance is most important, and also on what machining and hardening processes are being utilized.

• Air hardening (A grade) steels are characterized by low distortion during heat treatment due to high chromium content. They also harden in air because they contain fewer alloys than other grades. They have a balance of wear resistance and toughness and have good machinability.
• Cold work (die and mold) tool steels require minimal distortion during hardening. More alloying elements are used in these steels to increase hardenability than in water-hardening grades.
• Hot work or heat resistant (H grade) tool steels are designed for strength and hardness during prolonged exposure to elevated temperatures.
• Oil hardening (O grade) tool steels are oil hardened and exhibit moderate wear resistance and good machinability.
• Shock resistant or impact resistant (S grade) steels are designed to resist shock at low and high temperatures. Their low carbon content provides the necessary toughness, and carbide forming alloys are responsible for the relatively high hardness and low abrasive resistance.
• Water hardening (W grade) tool steels are those that are water quenched to increase hardness. They are the most commonly used because of their low cost compared to other tool steels. These steels can attain high hardness and are rather brittle.
• High speed or wear resistant (M/T grades) tool steels are used for cutting tools that require retention of hardness and strength properties at high temperatures (up to or exceeding 760°C).

Specifications

Selecting metal alloys requires an analysis of the desired specifications. Dimensions to consider include:

• Outer diameter (OD)
• Inner diameter (ID)
• Overall length
• Overall thickness

Other specifications of importance (based on application) include product shape, tensile strength, yield strength, melting point, conductivity, corrosion resistance, ductility, and malleability. These properties differ based on the metal or alloy composition.

Applications

Tool steels are designed specifically for use as machine and tool blades and components such as knives, dies, rolls, stamps, drill bits, and screws.

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