4Thermal processing of metal - Chapter 11 Thermal...

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Chapter 11 - 1 Chapter 11: Thermal Processing of Metals ISSUES TO ADDRESS... What heat treatment procedures are used to improve the mechanical properties of both ferrous and nonferrous alloys?
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Chapter 11 - 2 Based on discussion in Section 11.7, Callister & Rethwisch 8e . Thermal Processing of Metals There is a number of phenomena that occur in  metals and alloys at elevated temperatures e.g.,  Crystallization and decomposition of austenite. These are effective in altering the mechanical  properties characteristic  when appropriate heat  treatments or thermal processes are employed. In fact the use of heat treatment on commercial  alloys us an exceeding common practice
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Chapter 11 - INTRODUCTION A processes of controlled heating and cooling operation applied to metals and alloys in solid state so as to obtain the desired properties In the fabrication process of engineering components, the heat treatment process makes them structurally and physically better suited for some specific applications HEAT TREATMENT KULLIYYAH OF ENGINEERING INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
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Chapter 11 - OBJECTIVES OF HEAT TREATMENT Homogenize microstructure by diffusion Introduces softness in material Improve machinability Harden the material Increase toughness Increase wear resistance Relieve stress Refine grain structures KULLIYYAH OF ENGINEERING INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
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Chapter 11 - HEAT TREATMENT APPLICATION
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Chapter 11 - HEAT TREATMENT PROCESS Annealing Process A heat treatment in which a material is exposed to an elevated temperature for an extended time period and then slowly cooled Normalising A heat treatment in which a material is exposed to an elevated temperature for an extended time period and then cooled in still air Quenching In this heat treatment faster cooling rate is introduced. Quenching media normally-water, oil and air Tempering Heating of quenched specimens to temperature above 200 C and 400 C holding it for a while and then moderately cooling it.
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Chapter 11 - ANEALING PROCESS Annealing is carried out to (1) relieve stresses (2) increase softness, ductility and toughness and or (3) produce specific microstructure 3 stages, (1)heating to a desired temperature (2) holding or soaking at that temperature (3)cooling usually to room temperature. Time is an important parameter in these procedure.
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Chapter 11 - ANEALING PROCESS (CON’T) During heating and cooling, temperature gradient exist between outside and interior portion of the piece; their magnitude depends on the size and geometry of the piece . If the rate of temperature change is too great, temperature gradient and internal stresses may be induced that may be lead to warping and even cracking.
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