CAn you steam a board bow?

[BHTGdogs]

To put a little bend in it tn make like a hybrid longbow.

[ChristopherO]

Yes.
If the bend will be at a strong degree then put the back to a form with a metal strap on the belly to keep it from splintering.  A mild bend without a form, even over a padded knee, works well, though.  Oak bends pretty easily, hickory takes a good bend with steam but if it is thick leave in over the steam a long while.  Bend quickly as the wood will cool fast.