Tool Steels Guide: Properties, Heat Treatment, and Selection

Introduction to Tool Steels

As the designation implies, Tool Steels serve primarily for making tools used in manufacturing and in the trades for the working and forming of metals, wood, plastics, and other industrial materials.

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Tools must withstand high specific loads, often concentrated at exposed areas. They may have to operate at elevated or rapidly changing temperatures and in continual contact with abrasive types of work materials. Furthermore, they are often subjected to shocks or other varieties of adverse conditions.

Figure 1: Tool steels must maintain their cutting edge even under extreme heat and friction.

Nevertheless, when employed under circumstances that are regarded as normal operating conditions, the tool should not suffer major damage, untimely wear resulting in the dulling of the edges, or be susceptible to detrimental metallurgical changes.

Tools for less demanding uses, such as ordinary handtools (hammers, chisels, files, mining bits, etc.), are often made of standard AISI steels that are not considered as belonging to any of the tool steel categories.

Heat Treatment and Composition

The steel for most types of tools must be used in a heat-treated state, generally hardened and tempered, to provide the properties needed for the particular application. The adaptability to heat treatment with a minimum of harmful effects—which dependably results in the intended beneficial changes in material properties—is a critical requirement that tool steels must satisfy.

To meet such varied requirements, steel types of different chemical composition, often produced by special metallurgical processes, have been developed. Due to the large number of tool steel types produced by the steel mills (often with proprietary designations), it can be difficult for the user to select the most suitable type without specific manufacturer recommendations.

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The Properties of Tool Steels

Tool steels must possess certain properties to a higher than ordinary degree. This makes them adaptable for uses that require the ability to sustain heavy loads and perform dependably even under adverse conditions.

The primary trade-off in selecting a tool steel is usually between Hardness (wear resistance) and Toughness (shock resistance).

Figure 2: Design tips to reduce stress concentrations and prevent breakage during heat treatment.

The extent and types of loads, the characteristics of the operating conditions, and the expected performance (duration and consistency) are the principal considerations. These must be balanced with cost to govern the selection of tool steels for specific applications.

Although it is not possible to define and apply exact parameters for measuring significant tool steel characteristics, certain properties can be determined that greatly assist in appraising suitability. For detailed data, refer to the Machinery's Handbook.