For straightening wood...dry heat for dry wood...wet heat for wet wood!
For heat treating wood use dry heat. You are drying out the belly cells and the resin,etc to increase compression strength. Wet heat would defeat the purpose.
Green wood is easier(less effort) to straighten and manipulate than dry wood. If you use steam in the process, the heat from the steam will force out some of the moisture that is in the stave aiding the drying process. Pat