This winter a group of us guys are building and restoring some canoes. In this video, we are bending the "stems" of the canoe. The stems are the structural bones in the bow and stern which create the shape of the ends. To bend these pieces of ash, we first soaked them in water for a week or so. Then we baked them in a "steam box" for a while. The purpose of the steam is simply to conduct heat to the wood, there is no magic in getting the wood moist through using steam. Nor, according to experiments that have been done, is there any point to pressurizing the chamber. We were using a wall paper steamer to generate the steam, and it wasn't quite enough. The rig worked, but barely, so we are going to add some more steam generation when we steam the ribs.
Anyway, so you get the ash pieces hot and then you quickly bend them to shape on the form and clamp the whole thing in place for several weeks. Eventually the ash will maintain it's now shape. This is an ancient technique used by boat builders for centuries.