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Heat treatment of ferrous alloys

This unit addresses aspects of the following syllabus outcomes:

Outcomes:

H1.2 differentiates between properties of materials and justifies the selection of materials, components and processing in engineering.

H2.1 determines suitable properties, uses and applications of materials in engineering

Extract from Stage 6 Engineering Studies Syllabus. © Board of Studies, NSW, 1999.

This unit covers the process of heat treatment of ferrous metals and the related property and structure relationships.

Introduction

Heat treatment is a general term referring to a cycle of heating, soaking and cooling that alters the internal structure of a metal and thereby alters its properties. The primary purpose of heat treatment is to give a metal alloy a combination of hardness, strength, toughness, or ductility, that it will need for a specific purpose.

Activity 1

Visit the Efunda web site to answer the following questions in relation to heat treatment.

Note that different heat treatment processes are listed on the left of the web page. Click on a particular process to obtain more detail.

1. Describe the general process of heat treatment and the basic effects on metal alloys.
2. Outline the purposes of heat treatment.

Answer

Activity 2

Heat treatment may be undertaken to either increase the hardness of materials or soften them.

From the links on the Efunda site answer the following questions.

1. Outline why softening processes may be undertaken.
2. Outline why hardening processes may be undertaken.

Answer

There are a number of heat treatment processes that are undertaken to either change the ductility or hardness of materials. These processes include hardening and tempering which produce an increase in the original hardness and toughness of steel and reduced ductility. Alternately annealing and normalising are associated with an overall reduction in hardness and increased ductility.

Activity 3

In order to research answers for the following questions in relation to annealing and normalising, visit the Efunda web site

1. Name the two heat treatment processes that are associated with the softening of steel.
2. Describe how the process of annealing is undertaken.
3. Describe how the process of normalising is undertaken and indicate a reason why this process is more commonly used in industry than full annealing.
4. Compare the properties of materials that are fully annealed to those that are normalised.
5. Sketch the microstrucure of an annealed 0.8%C steel.

Answer

Activity 4

In order to research answers for the following questions in relation to hardening, visit the Efunda web site and click on direct hardening.

1. Describe the structural change that is required within a steel to effectively harden it and indicate how such a change is effected.
2. Name and sketch the microstructure that is associated with hardened steel and identify its mechanical properties.

Answer

Activity 5

In order to research answers for the following questions in relation to tempering, visit the Efunda web site and click on tempering.

1. Name the process that may be used to reduce the effects of hardening.
2. Identify the stages that are undertaken in the tempering process for steel and describe the effects of this process on properties.

Answer