After heating at 950°C and holding the temperature for 3 hours there is a soaking time that is provided for 12 hours. What is the soaking time being referred to here? A detailed reply to this will be very welcome.
At that high temperature , there are some things like carbides and intermetallics going into solid solution. Also some chemical homogenization ( which is similar to the solution). To a small degree the temperature is becoming more uniform ; although the surface has reached temperature the core of a thick component takes longer to reach temperature ; Usually addressed by typical ASME requirement by " one hour per inch of thickness". For a lower temperature like 500 C ,it would be time for stress relieving to develop , as in PWHT. That high temperature sounds like a solution anneal for a ferrous superalloy, followed by a fast cool. However 3 + 12 hours is exceptionally long in my experience.