For the isothermal TTT diagram of an ironcarbon alley provid

For the isothermal TTT diagram of an iron-carbon alley provided below indicate the structures present at the points 1, 2, 3, 4 and 5. The cooling cycle of the iron-carbon alloy is as follows:

Solution

At point 1 as indicated by TTT diagram structure will be austenite only. Then through point 1 to 2 is isothermal cooling and as the end point 2 lies in Austenite+Pearlite region with 50% Pearlite, the structure at point 2 will be Austenite + Pearlite both being 50%.

Now from point 2 to 3 the cooling is very rapid hence there will be no change in structure and it will be same as at point 2.

Then there is isothermal cooling at temp 400 degrees which is above the martensite formation region, and the end point 4 lies in banite region hence the 50% austenite present will totally convert into Banite, As a result structure at point 4 will be 50% Pearlite+ 50% Banite.

Structure at point 5 will also be Pearlite+Banite both 50% as 4 to 5 is rapid quenching.