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Sheet 2 - TTT Diagram

The document discusses time-temperature transformation (TTT) diagrams for an iron-carbon alloy of eutectoid composition. It provides several time-temperature heat treatment processes and asks to determine the resulting microstructures. It also asks to sketch time-temperature paths on the TTT diagram that would produce specific microstructures and determine the time required for partial and full pearlite transformation at 550°C.

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299 views4 pages

Sheet 2 - TTT Diagram

The document discusses time-temperature transformation (TTT) diagrams for an iron-carbon alloy of eutectoid composition. It provides several time-temperature heat treatment processes and asks to determine the resulting microstructures. It also asks to sketch time-temperature paths on the TTT diagram that would produce specific microstructures and determine the time required for partial and full pearlite transformation at 550°C.

Uploaded by

saxadi4814
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Alexandria University Second Semester (2019/2020)

Faculty of Engineering Basic Manufacturing Methods


Production Engineering Department PEDx19

Sheet 2 : TTT Diagram


1- Using the isothermal transformation diagram for an iron–carbon alloy of eutectoid
composition, specify the nature of the final microstructure (in terms of
microconstituents present and approximate percentages of each) of a small specimen
that has been subjected to the following time–temperature treatments. In each case
assume that the specimen begins at 760oC (1400oF) and that it has been held at this
temperature long enough to have achieved a complete and homogeneous austenitic
structure.

(a) Cool rapidly to 3500oC (660oF), hold for 103s, then quench to room temperature.

(b) Rapidly cool to 625oC (1160oF), hold for 10 s, then quench to room temperature.

(c) Rapidly cool to 600oC (1100oF), hold for 4 s, rapidly cool to 450oC (840oF), hold
for 10 s, then quench to room temperature.

(d) Reheat the specimen in part (c) to 700oC (1290oF)for 20 h.

(e) Rapidly cool to 300oC (570oF), hold for 20 s, then quench to room temperature in
water. Reheat to 425oC (800oF)for 103s and slowly cool to room temperature.

(f ) Cool rapidly to 665oC (1230oF), hold for 103s, then quench to room temperature.

(g) Rapidly cool to 575oC (1065oF), hold for 20 s, rapidly cool to 350oC (660oF), hold
for 100 s, then quench to room temperature.

(h) Rapidly cool to 350oC (660oF), hold for 150 s, then quench to room temperature.
2- Make a copy of the isothermal transformation diagram for an iron–carbon alloy of
eutectoid composition and then sketch and label time–temperature paths on this
diagram to produce the following microstructures:

(a) 100% coarse pearlite

(b) 50% martensite and 50% austenite

(c) 50% coarse pearlite, 25% bainite, and 25% martensite


3- Suppose that a steel of eutectoid composition. is cooled to 550°C from 760°C in less than
0.5 s and held this temperature. III

i- How long will it take for the austenite to pearlite reaction to go to 50 completion?

ii- How long will it take for 100 completion?

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