Question

LOO Etter 700 A certain steel of eutectoid composition transforms according to the isothermal transformation curve shown below. a. Describe a thermal treatment that would result in a structure having 50% pearlite and 25% bainite, and 25% martensite. 1200 1000 Tenger! 500 TO 300 200 00 MASON MO 100 b. Assuming I hold for 105 seconds, what approximate temperature do I need to quench to and hold to get 100% i. Coarse pearlite 200 10 ii. Martensite iii. Bainite

Answer 1

a.

Shown in graph

Heat steel upto 750°C, Due to this steel gets converted to Austenite phase

then sudden cool to 600°C and hold for 6 sec, 50% of austenite gets converted to Pearlite.

Now sudden cool to 400°C and hold for around 50sec half of remaining (25% of total) gets converted to bainite

Now sudden cool to room temperature, remaining austenite (25%) gets converted to Martensite.

B.

i. 600°C to 640°C

ii. Less than 100°C

iii. 400°C to 550°C

800 А Eutectoid temperature 1400 700 t 1200 600 P 1000 500 B Temperature (°C) 800 Temperature (°F) 400 А 300 600 M(start) 200 50% M+A 400 M50%) M(90%) 100 200 0 10-1 1 10 103 101 105 102 Time (s)