Dear Avanish, the growth depends on different aspects of your microstruture like initial size, internal stresses and the degree of deviation from thermodynamic equilibrium. But if I wanted to make an approximation in your case I would consider these aspects:

1) Deviation from equilibrium: the larger the deviation from alpha/gamma ratio in your composition, the higher the driving force for growth (This only applies to the evolution of ferrite and austenite against each other). You can roughly estimate it linear: dR_i/dt (V_i - V_i(eq)).

2) Initial grain size: the simplest driving force for growth is interface curvature that we know is roughly dR/dt ~ 2 D sigma/R, where sigma is interface energy. So as you see if the initial grains are small, they are more probable to grow in a given period of time.

3) The diffusion at the given temperature: the rate of growth (as you see above) is usually linearly proportional to the diffusion of atoms across the interface (D). Note that the slower diffusion coeff is the responsible one (bottleneck).

You might need to add these contributions linearly to make an approximation. Cheers, Reza

Since you have treated at 1050C ( much higher than Ac3?), the PAG size should not increase further within short time like hours at the intermediate temperature. The austenite grains change becomes insignificant with time at the lower end of AC1 to AC3.

My dear Avanish Chandan;

I believe you know ac1 and ac3 of your steel .It is clear that PAG size will not increase if you heat sample in between ac1 and ac3 for nominal soaking of about 1 hour/25 mm of sample thickness and cool as per your requirement (air ccol/oil cool/water cool).But if you hold sample at temperature near ac3 for suffeciently long PAG will show some inrease in size.In case of nominal intercritical heat treatment you will get some grain refining