Resulting structure of steel:

Heat treatments as mentioned below are given to thin steel strips for which TTT diagram is as shown in Figure 19. What will be the resulting structure of steel in each case.

Treatments

1.      Water quench to room temperature.

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

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

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

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

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

7.      Hot quench to 300^oC, hold for 5 hours, water quench

Solution

From Figure 19 the final structures of steel can be determined

1.      Martensite

2.      Coarse pearlite

3.      Fine pearlite

4.      50% fine pearlite and 50% martensite

5.      Bainite

6.      50% fine bainite and 50% martensite

7.      Fine bainite

Figure: Cooling Scheme of Example