Illustration .3 Heat treatments as mentioned underneath are specified to thin steel strips for that TTT diagram is as represented in figure of Cooling Scheme. What will be the resulting structure of steel in every case?

Treatments

 i.            Water quench to room temperature.

 ii.            Hot quench in molten salt to 690^oC hold for 2 hours and water quench.

iii.            Hot quench to 610^oC and hold 3 minutes, water quench.

 iv.            Hot quench to 580^oC, hold for 25 minutes, water quenches.

v.            Hot quench to 450^oC, hold for 1 hour, water quenches.

vi.            Hot quench to 300^oC, hole for 30 minutes, water quench.

vii.            Hot quench to 300oC, hold for 5 hours, water quenches.

                                          Figure: Cooling Scheme of illustration .3

 Solution:

From above figure the final structures of steel can be calculated:

(a) Martensite

(b) Coarse pearlite

(c) Fine pearlite

(d) 50% suitable pearlite and 50% martensite

(e) Bainite

(f) 50% suitable bainite and 50% martensite

(g) Suitable bainite.