Page 121 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Metal Alloys: Their

Structure and

Strengthening by

Heat Treatment

4.| Introduction |00
4.2 Structure of Alloys IOI ° This chapter examines the structures of alloys, including solid solutions, inter-
4.3 Phase Diagrams |03 metallic compounds, and two-phase systems.
4.4 The Iron-Carbon ° Phase diagrams show graphically the various phases that develop as a function
System |07
4.5 The Iron-Iron-carbide of alloy composition and temperature.
Phase Diagram and ° The important system of iron and carbon and the phases that can be developed
the Development of
are described in detail.
Microstructures in
Steels |08 ° Heat treatment is a common strategy to improve a material’s mechanical prop-
4.6 Cast lrons I I0 erties; it involves establishing a desired phase at elevated temperatures, followed
4.7 Heat Treatment of Ferrous by controlled cooling of the material before the microstructure can transform
Alloys I I I into a different phase. This procedure can profoundly affect the behavior of
4.8 Hardenability of Ferrous steel and produce special forms, including pearlite, martensite, spheroidite, and
Alloys I I5
4.9 Heat Treatment of bainite, each with its own unique characteristics.
Nonferrous Alloys and ° Some materials can be heat treated only by precipitation hardening or aging.
Stainless Steels I I7
4.I0 Case Hardening I I9 ' Often, improving the ductility of a material is at the expense of properties such
4.I I Annealing l2| as strength or hardness. Exposure of a metal to elevated temperatures for a
4.l2 Heat-treating Furnaces certain period of time is often practiced to achieve desired properties.
and Equipment |23
4.I3 Design Considerations for ° The chapter ends with a discussion of the characteristics of heat-treating
Heat Treating |25 equipment.

4.l Introduction

The properties and behavior of metals and alloys during manufacturing and their
performance during their service life depend on their composition, structure, and
processing history as well as on the heat treatment to which they have been subjected.
Important properties such as strength, hardness, ductility, toughness, and resistance
to Wear are greatly influenced by alloying elements and heat-treatment processes. The
properties of non-heat-treatable alloys are improved by mechanical Working opera-
tions, such as rolling, forging, and extrusion (Part III).
The most common example of a process that improves properties is heat treat-
ment (Sections 4.7-4.10), which modifies microstructures and thereby produces a
variety of mechanical properties that are important in manufacturing, such as im-
proved formability and machinability or increased strength and hardness for tools

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