Do you have access to a microscope and etchants? I would start at half of the melting point and go from there for annealing temperature. For forging you would want to be at least red hot I would think. I cant give exact temperatures as you would have to examine the microstructure to truly know. How accurate do you need to be?
For pure metals, the recrystallization temperature is close to 0,3 Tm , but for commercial alloys it may be as high as 0,7 Tm . Tm is the absolute melting temperature.