8. TTT and CCT diagrams of a eutectoid steel (0.76 C) are provided below. Use the...
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8. TTT and CCT diagrams of a eutectoid steel (0.76 C) are provided below. Use the diagrams to answer the following questions. Temperature (°C) Temperature (°C) 800 700 600 500 400 300 200 100 800 700 600 500 400 300 200 100 0 10-1 0 10-1 A A A M(start) M(50%) M(90%) 1 1 M(start) Austenite M(50%) M(90%) 10 10 M+A Eutectoid temperature P B 10² 10³ 104 Time (s) Pearlite 50% Eutectoid temperature 10² Time (s) Continuous cooling transformation 10³ 104 T 1400 1200 1000 800 600 400 200 105 1400 1200 1000 800 600 400 200 105 Temperature (°F) Temperature (°F) (a) Estimate the minimum cooling rate (approx.) required to obtain 100% martensite at room temperature? Assume continuous cooling from eutectoid temperature (727°C). (b) Describe the microstructure formed by austenizing at 7600C then rapidly cooling to 625°C, holding at that temperature for 4 s and rapidly cooling to 450°C, holding there for 100 s, then rapidly cooling to room temperature. (c) Describe the microstructure formed by austenizing at 760°C then rapidly cooling to 350°C, holding at that temperature for 100 s and rapidly cooling to room temperature. (d) For (a), (b) and (c) estimate the approximate the hardness of the final product using the diagrams shown. 0 15 65 600 60 500 50 400 45 Tempered martensite 40 (tempered at 371°C) 300 30 200 20 100 0 200 700 600 500 400 300 200 100 0 0 3 Percent Fe3C 0.2 6 9 Martensite 12 Fine pearlite 0.4 0.6 Composition (wt% C) 0.8 1.0 300 Bainite Pearlite- 400 Transformation temperature (°C) 500 600 700 800 8. TTT and CCT diagrams of a eutectoid steel (0.76 C) are provided below. Use the diagrams to answer the following questions. Temperature (°C) Temperature (°C) 800 700 600 500 400 300 200 100 800 700 600 500 400 300 200 100 0 10-1 0 10-1 A A A M(start) M(50%) M(90%) 1 1 M(start) Austenite M(50%) M(90%) 10 10 M+A Eutectoid temperature P B 10² 10³ 104 Time (s) Pearlite 50% Eutectoid temperature 10² Time (s) Continuous cooling transformation 10³ 104 T 1400 1200 1000 800 600 400 200 105 1400 1200 1000 800 600 400 200 105 Temperature (°F) Temperature (°F) (a) Estimate the minimum cooling rate (approx.) required to obtain 100% martensite at room temperature? Assume continuous cooling from eutectoid temperature (727°C). (b) Describe the microstructure formed by austenizing at 7600C then rapidly cooling to 625°C, holding at that temperature for 4 s and rapidly cooling to 450°C, holding there for 100 s, then rapidly cooling to room temperature. (c) Describe the microstructure formed by austenizing at 760°C then rapidly cooling to 350°C, holding at that temperature for 100 s and rapidly cooling to room temperature. (d) For (a), (b) and (c) estimate the approximate the hardness of the final product using the diagrams shown. 0 15 65 600 60 500 50 400 45 Tempered martensite 40 (tempered at 371°C) 300 30 200 20 100 0 200 700 600 500 400 300 200 100 0 0 3 Percent Fe3C 0.2 6 9 Martensite 12 Fine pearlite 0.4 0.6 Composition (wt% C) 0.8 1.0 300 Bainite Pearlite- 400 Transformation temperature (°C) 500 600 700 800
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