Question

(1s) The TTT d austenitized. Determine the final amount (approximate percentages) of each microstructure, and show basic path (draw on charts). 6. agram for an iron-carbon alloy w, h 0.76%C steel is given. Assume that the specimen gans above 800°C for each case and that it has been held at this temperature long enough to be fully microstructure (such as bauxite, magnetite, bainite, pearlite, um, martensite, spheroidite, cementite). Must specify microstructure name (not a letter). 800 a) Sample 1- Decrease temperature to Eutectoid temperature 1400 300°C (in less than I second), hold for 10,000 seconds, then quenchto room temperature. to1 700 60% bainite 1200 600 b) Sample 2 - Cool rapidly to 600°C, hold for 100 s,then quench to room temperature. 1000 100% eeaylfte 500 Reheat Sample 2 to 700°C for 20 h. c) 800 400 d) How much carbon does this sample contain? Determine the hardness (HRc) for the final microstructure (Sample 1) in part (a). 600 300 M(start) M( 50%) Ml 90%) 400 200 e) Determine the hardness (HRc) for the final microstructure (Sample 2) in part (c). 100- 200 He 1o10 10 1010 10 Time (s)

Answer 1

800 a) Sample1 -Decrease temperature to 300°C (in less than 1 second), hold for 10,000 seconds, then quench to room temperature. (6 1400 Eutectoid temperature 100% Bainite 100% Pearlite 700 b) e) d) 00% bainte 100% Spherodite 100% Bainite contains 0.76%C and hardeness ofabout 36 HRC 10096 Spherodite contains 0,76%C and hardeness of about $7 HRB or 14 HRC. 600 b) Sample 2-Cool rapidly to 600°C, hold for 100 s then quench to room temperature. 1000 500 Reheat Sample 2 to 700°C for 20 h. 400 600 d) How much carbon does this sample 300 contain? Determine the hardness (HRc) for the final microstructure (Sample 1) in part (a) Mstart 200 -M(50%) M190%) 400 M+ 200 e) Determine the hardness (HRc) for the 100 final microstructure (Sample 2) in part (c) 10 10 1010 10 Time (s)