This is beyond the scope of materials found in AWS D1.1.
I looked at my ASM book, by it only listed isothermal curves. They are helpful, but they don't provide all the information we welders would like to have at our finger tips.
Basically, once the part is slow cooled below the Mf temperature, the cooling rate can be fairly rapid provided there isn't a danger of differential cooling rates between thick and thin portions of the weldment that can result in distortion damage.
Best regards - Al