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Unformatted text preview: MSE 230 HW7 (due 03/04, 03/05) Spring 2010 1. (a) Using the recrystallization kinetics data for pure copper in Fig. 10.11, what is the “recrystallization temperature,” defined as the temperature for which recrystallization is 95% complete in 1 h. (b) Briefly explain how and why the recrystallization temperature is affected by the following: i) solid solution impurities and ii) %CW. 2. Using the isothermal transformation diagram (Fig. 10.22) for eutectoid (1080) steel, determine the microstructure constituent(s) - Austenite (A), Pearlite (P), Bainite (B), Martensite (M) - and their approximate proportion(s) at the end of each of the following treatments. In each case the starting condition is Austentite at 800°C. Assume all quenching is instantaneous. Assume any Martensite formed by quenching to room temperature contains 5% retained Austenite. (a) Quench to 600°C and hold for 20 s, quench to room temperature. (b) Quench to 600°C and hold for 7 s, quench to room temperature. (c) Quench to 175°C and hold indefinitely. (d) Quench to 250°C and hold for 1 min, quench to room temperature. (e) Quench to 250°C and hold for 5 h, slow cool to room temperature. 3. Callister Problem 10.24: Figure 10.40 (below) shows the continuous cooling transformation diagram for a 0.35 wt.% C iron-carbon alloy. Sketch and label on the diagram continuous cooling curves to yield the following microstructures: (a) Fine pearlite and proeutectoid ferrite (b) Martensite (c) Martensite and proeutectoid ferrite (d) Coarse pearlite and proeutectoid ferrite (e) Marensite, fine pearlite and proeutectoid ferrite. 3. Rank order the structures (a)-(e) in Problem 3 from highest to lowest hardness and briefly justify your ranking by explaining the microstructural origins of the hardness differences. 4. Using Fig. 10.31 and the tempering data in Fig. 10.35, specify a tempering heat treatment (i.e., temperature and time) that when applied to the transformation product in problem 2(d) would result in the same hardness as transformation product in problem 2(e). 5. Sketch or trace the Al-rich end of the Al-Cu phase diagram in Fig. 11.24 out to about 10 wt.% Cu and to the right of it, using the same temperature axis scaling, make a quantitative temperature - time plot analogous to the schematic plot in Fig. 11.22, showing a precipitation hardening heat treatment sequence for an alloy containing 4.4 wt% Cu aged to peak (maximum) hardness at 204°C. Justify your choice of the solution treatment temperature and use a solution treatment time of 1 h. Use the aging kinetics plot in Fig. 11.27. What would be the advantage of conducting the aging treatment at 150°C? What would be the disadvantage? ...
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