Question

3. Consider the isothermal transformation diagram for a eutectoid steel (Fig. 11.23 in text.) Determine the

microstructures present as a result of the following heat treatments. In all cases, the steel samples were

heated to 800 Deg C and held 1 hour to form all austenite. “RC” indicates a rapid (instantaneous) cooling to

the indicated temperature. Your answers should indicated microstructure present and a rough estimate of

the amount.

a) RC to 400C, hold 100s, Water quench to room temperature (WQ).

b) RC to 400C, hold 200s, re-heat to 700C, hold 24 hours, air cool.

c) RC to 600C, hold 100s, WQ.

d) RC to 640C, hold 10s, WQ.

e) RC to 640C, hold 10s, RC to 300C, hold 10s, WQ

f) RC to 250C, hold 1000s, WQ

Answer 1

d) at 640 degree Celsius holding for 10 s, it's still austenite. So on WQ it is transformed completely to martensite with body centred tetragonal shape

e) here the first stage is identical to previous question. It is then brought down to 300 C for 10s, it us still austenite. On rapid quenching to room temperature give 100%martensite