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14 Apr 2022
Using the T-T-T diagram for an iron-carbon alloy of eutectoid composition shown in figure below, specify the nature of the final micro structure (in terms of micro- constituents 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 760 degree C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. Also use fine or coarse for pearlite wherever applicable. (a) Cool rapidly to 375 degree C, hold for 2000 s, then quench to room temperature. (b) Rapidly cool to 580 degree C, hold for hold till reaching the blue dashed line, then quench to room temperature. (c) Rapidly cool to 620 degree C. hold till reaching the blue dashed line, rapidly cool to 450 degree C. hold for 10 s (use the time reset just as done in example in the class), then quench to room temperature. (d) Cool rapidly to 675 degree C, hold for 10^4 s, then quench to room temperature. (e) Rapidly cool to 600 degree C. hold for 15 s, rapidly cool to 360 degree C. hold for 100 s, quench to room temperature. (f) Rapidly cool to 350 degree C. hold for 150 s, then quench to room temperature.
Using the T-T-T diagram for an iron-carbon alloy of eutectoid composition shown in figure below, specify the nature of the final micro structure (in terms of micro- constituents 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 760 degree C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. Also use fine or coarse for pearlite wherever applicable. (a) Cool rapidly to 375 degree C, hold for 2000 s, then quench to room temperature. (b) Rapidly cool to 580 degree C, hold for hold till reaching the blue dashed line, then quench to room temperature. (c) Rapidly cool to 620 degree C. hold till reaching the blue dashed line, rapidly cool to 450 degree C. hold for 10 s (use the time reset just as done in example in the class), then quench to room temperature. (d) Cool rapidly to 675 degree C, hold for 10^4 s, then quench to room temperature. (e) Rapidly cool to 600 degree C. hold for 15 s, rapidly cool to 360 degree C. hold for 100 s, quench to room temperature. (f) Rapidly cool to 350 degree C. hold for 150 s, then quench to room temperature.
15 Apr 2022
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