6. Uaing the kothermal transfomation dagram for a 0.45w C steealloy (Figure 1239
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6. Uaing the kothermal transfomation dagram for a 0.45w C steealloy (Figure 1239) derermine the fnal microsnucture (n emsof jut the microscture present) of a smail specimen hat ha been subjected so the followire imetemperature treatment Ineach cae assume thar the specimen beans at 850°C 1123K) and that it has been held at tristementure long enough to have ??neved a complete and homogenous ustenmc structure. (Total 1S marks) M90%) G. F. VanderWoort, Ednor, 1991. Reprinted by pamissnofASM munational, Mate as Park, CH lal Rapidly cool to 250"C 152 3Kl. hold for 10, then quench to room temperature. (2 marks) b) Rapidly cool to 0C 1973KI, hold for 30s, then quench to room tempereture. 2 marks) (cl Rapidly cool to 398"C (671K), hold 1ar scos, the? quench to room temperature. (2 marks) (a) Rapidly cooll to 700hold tor 10's, then quench to room temperature. (2 marks) (e) Rapidly cool to 650-(923K), hold 1ar 3s, rapidly coolo 398.?671K. hold for 10, then quench to room temperature. (2 maric) Rapidly cool to 448 (721), hold tor i0s, then quench to room temperature. (2 marks) l Rapidly cool to 625C (k), hold for 1s, then quench to room temperature. I2 marks 0) Rapldly cool to 625*C (B93), hoid at this temperature for 10s, rapidy cool to 39BC(BTLK) hold at the temperature for s, then quench to room temperature. 2 merks)Explanation / Answer
A. When rapidly cooled to 250°C , and held there for 10sec., Martensitic microstructure will be formed as the cooling process is very rapid.
B. In this case , Austenite and pearlite composition will be formed , as at 700°C , from transformation curve , we can deduce that it lies in the curved region.
C. At the given condition of cooling, a composition of pearlite and bainite will be formed from the Isothermal curve.
D. At rapid quenching to 700°C , and holding there for 10^5 sec, it will transform completely into coarse pearlite due to less time available for mixing.
E. A composition of pearlite, and Austenite will be formed at such cooling condition.
F. A composition of fine pearlite with Bainite will be formed and pearlite will be around 50% of the microstructure.
G. Transformation to Pearlite just begins at this stage, and hence most of the constituents will be Austenite in microstructure.
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