2. Hardened Steels

Metals, specifically steels, have transformed from their limited use by early blacksmiths to the current state of industrial mass production. The gradual progression of steelmaking processes has led to advancements in manufacturing processes, the quality and performance of products, as well as improving economies. The current chapter covers the machining of hardened steels, which is also known as hard machining. Hard machining refers to the process whereof a cutting tool removes the material from the surface of a workpiece with hardness value over 45 HRC and it can reach even up to 70 HRC. Hard machining can be achieved by almost all of the conventionally used machining operations such as hard turning, hard milling, hard boring, and hard broaching. The main objective of this chapter is to present important information about hardened steels. It briefly provides general information about hardened steels, their history of evolution, and a description of their unique mechanical and metallurgical characteristics. More importantly, it discusses the problems associated with manufacturing hardened steel parts and possible ways to overcome their machining difficulties. In this chapter, the machining operations that can be utilized for machining hard materials are investigated with a main focus on the application of hard turning and hard milling. The main challenges in the machining of hard materials, particularly hardened steels, applicable tool materials, required machine tool specifications, and attainable surface integrity will also be reviewed.