Question

12. (14pt) Using the TTT diagram for an iron-carbon alloy of eutectoid composition (Figure 1), describe the isothermal heat treatments to provide 50% pearlite, 25% bainite, and 25% martensite. Sketch the time-temperature paths of your treatment on the diagram, and for each step in your treatment, described the microstructures in terms of present microconstituents. Assume that the specimen begins at 760°C (1400°F) and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenite (?) structure. Temperature (°C) 800 A Eutectoid temperature 1400 700 A 1200 600 P S 1000 500 B 800 400 A 600 300 M(start) 200 50% M + A 400 M(50%) M(90%) 100 0 10^-1 1 10 10^2 10^3 10^4 10^5 Time (s) 200 Temperature (°F) Figure 1. TTT (isothermal transformation) diagram for an iron-carbon alloy of eutectoid composition. Step 0 Process initial condition Resulting Microstructure 100% austenite

          12. (14pt) Using the TTT diagram for an iron-carbon alloy of eutectoid composition (Figure 1),
describe the isothermal heat treatments to provide 50% pearlite, 25% bainite, and 25% martensite.
Sketch the time-temperature paths of your treatment on the diagram, and for each step in your treatment,
described the microstructures in terms of present microconstituents. Assume that the specimen begins
at 760°C (1400°F) and that it has been held at this temperature long enough to have achieved a
complete and homogeneous austenite (?) structure.
Temperature (°C)
800
A
Eutectoid temperature
1400
700
A
1200
600
P
S
1000
500
B
800
400
A
600
300
M(start)
200
50%
M + A
400
M(50%)
M(90%)
100
0
10^-1
1
10
10^2
10^3
10^4
10^5
Time (s)
200
Temperature (°F)
Figure 1. TTT (isothermal transformation) diagram for an iron-carbon alloy of eutectoid composition.
Step
0
Process
initial condition
Resulting Microstructure
100% austenite

12. (14pt) Using the TTT diagram for an iron-carbon alloy of eutectoid composition (Figure 1),
describe the isothermal heat treatments to provide 50% pearlite, 25% bainite, and 25% martensite.
Sketch the time-temperature paths of your treatment on the diagram, and for each step in your treatment,
described the microstructures in terms of present microconstituents. Assume that the specimen begins
at 760°C (1400°F) and that it has been held at this temperature long enough to have achieved a
complete and homogeneous austenite (?) structure.
Temperature (°C)
800
A
Eutectoid temperature
1400
700
A
1200
600
P
S
1000
500
B
800
400
A
600
300
M(start)
200
50%
M + A
400
M(50%)
M(90%)
100
0
10^-1
1
10
10^2
10^3
10^4
10^5
Time (s)
200
Temperature (°F)
Figure 1. TTT (isothermal transformation) diagram for an iron-carbon alloy of eutectoid composition.
Step
0
Process
initial condition
Resulting Microstructure
100% austenite

Added by Alexandra C.

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