White heat? Uhhhh, nope, that's re-melting it. CI melts at 2200F.
For most gray irons, a ferritizing annealing temperature between 700 and 760°C (1300 and 1400°F) is recommended. If you're going by color that's dark red (see below).
You also don't have to keep it in a ramped powered furnace for cool down. just bury the piece in a bucket of wood ashes to cool slowly. In fact you can also do the heating to annealing temps in a wood fire in the brightly glowing embers with a little draft.
Color Temperature [°C] Temperature [°F]
From To From To
Black red 426 593 799 1100
Very dark red 594 704 1100 1299
Dark red 705 814 1300 1497
Cherry red 815 870 1498 1598
Light cherry red 871 981 1599 1798
Orange 982 1092 1799 1998
Yellow 1093 1258 1999 2296
Yellow white 1259 1314 2297 2397
White 1315+ 2397+