Tool steels are specialty steels, produced in relatively low volumes, optimized for applications requiring precise combinations of wear resistance, toughness, and hot hardness. This chapter describes the AISI classification system by which tool steels are defined. It discusses primary types, including high-speed and shock-resisting steels, and their associated subtype groups (W, L, S, O, A, D, H, M, and T series). It also discusses the types of carbides found in tool steels and their influence on mechanical properties. The chapter concludes with a discussion on heat treatment effects unique to tool steels, including two-phase effects, austenite stabilization, and the conditioning of retained austenite.

This chapter discusses the history of hardness testing and defines the term hardness. It describes the interrelationship between material structure and hardness and the relationships between hardness and other mechanical material properties. In addition, information on the hardness unit and traceability of the hardness measurement are provided.

The unique advantages of the nitriding process were recognized by German researchers in the early 1920s. It was used to treat steels for applications that required: high torque, high wear resistance; abrasive wear resistance; corrosion resistance; and high surface compressive strength. This chapter focuses on key process considerations and factors that helped nitriding gain acceptance. These factors include a low-temperature process, no quench requirement, minimal distortion, high hardness values, and resistance to oxidation.

This article provides an overview of tool steels, discussing their composition, properties, and behaviors. It covers all types and classes of wrought and powder metal tool steels, including high-speed steels, hot and cold-work steels, shock-resisting steels, and mold steels. It explains how the properties of these steels are determined by alloying elements, such as tungsten, molybdenum, vanadium, manganese, and chromium, and the presence of alloy carbides. It describes the types of carbides that form and how they contribute to wear resistance, toughness, high-temperature strength, and other properties.

Durability is a generic term used to describe the performance of a material or a component made from that material in a given application. In order to be durable, a material must resist failure by wear, corrosion, fracture, fatigue, deformation, and exposure to a range of service temperatures. This chapter covers several types of component and material failure associated with wear, temperature effects, and crack growth. It examines temperature-induced, brittle, ductile, and fatigue failures as well as failures due to abrasive, erosive, adhesive, and fretting wear and cavitation fatigue. It also discusses preventative measures.

Tool steels are a special class of alloys designed for tool and die applications. High-speed steels are a subset of tool steels designed to operate at high speeds. This chapter describes the composition, properties, heat treatment, and use of wrought and alloyed tool steels, high-speed steels, and their counterparts made by powder metallurgy. It includes information on the chemical composition and application range of many commercial tool steels and explains how to apply coatings that reduce friction, thermal conductivity, and wear.

Steels for hot-work applications, designated as group H steels in the AISI classification system, have the capacity to resist softening during long or repeated exposures to high temperatures needed to hot work or die cast other materials. These steels are subdivided into three classes according to the alloying approach: chromium hot-work steels, tungsten hot-work steels, and molybdenum hot-work steels. This chapter discusses the composition, characteristics, applications, advantages, and disadvantages of each of these steels.

This chapter provides the definitions of fundamental wear mechanisms. The chapter describes the properties and applications of materials used for wear resistance. It discusses the processes involved in screening tests for wear resistance. In addition, the practical application of wear-resistant principles is covered.

This chapter discusses the general principles of measuring hardness and hardenability of steel. The discussion begins by defining hardness and exploring the history of hardness testing. This is followed by a discussion on the principles, applications, advantages, and disadvantages of commonly used hardness testing systems: the Brinell, Rockwell, Vickers, Scleroscope, and various microhardness testers that employ Vickers or Knoop indenters. The effect of carbon content on annealed steels and hardened steels is then discussed. A brief discussion on the concept of the ideal critical diameter and austenitic grain size of steels is also provided to understand how one can calculate and quantify hardenability. The processes involved in various methods for evaluating hardenability are reviewed, discussing the effect of alloying elements on hardenability.