session 11 heat treatments

7/23/2019 Session 11 Heat Treatments

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Heat Treatment

for steels


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Growth and structure of pearlite


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TTT diagram - The time-temperature-transformation diagramdescribes the time required at any temperature for a phase

transformation to begin and end. Isothermal transformation - When the amount of a

transformation at a particular temperature depends on the timepermitted for the transformation.

Controlling the Eutectoid Reaction

2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is atrademark used herein under license.


4/13


5/13

2003 Brooks/Co le, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

The effect of the austenite transformation temperature on theinterlamellar spacing of pearlite.


6/13

2003 Brooks/Co le, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

The time-temperature-transformation (TTT) diagram for an eutectoid steel.


7/13

Excellent combinations of hardness, strength, and toughness

are obtained from bainite. One heat treatment facilityaustenitized an eutectoid steel at 750oC, quenched and heldthe steel at 250oC for 15 min, and finally permitted the steelto cool to room temperature. Was the required bainiticstructure produced?

Example


8/13

Martensite - A metastable phase formed in steel and

other materials by a diffusionless, athermaltransformation.

Tempering - A low-temperature heat treatment used toreduce the hardness of martensite by permitting themartensite to begin to decompose to the equilibriumphases.

The Martensitic Reaction and Tempering


9/13

2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

(a) The unit cell of BCT martensite is related to the FCC austenite unit cell.


10/13

Process Annealing Eliminating Cold Work: A low-temperature heat treatment used to eliminate all or partof the effect of cold working in steels.

Annealing and Normalizing Dispersion Strengthening:Annealing - A heat treatment used to produce a soft,

coarse pearlite in steel by austenitizing, then furnacecooling.

Normalizing - A simple heat treatment obtained byaustenitizing and air cooling to produce a fine pearliticstructure.

Spheroidizing Improving Machinability: Spheroidite - Amicroconstituent containing coarse spheroidal cementiteparticles in a matrix of ferrite, permitting excellentmachining characteristics in high-carbon steels.

Simple Heat Treatments


11/13

2003 Brooks/Cole, a division of Thomson Learning, Inc. T homson Learning

is a trademark used herein under license.

Simple heat treatments


12/13

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The effect of carbon and heat treatment on the properties of plain-carbonsteels.


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Determination of Heat Treating Temperatures

session 11 heat treatments

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