duck, dry wood, dry heat! Wet wood, wet heat! Osage bends easily with dry heat and a heat gun works well to heat the wood. You can use any heat source like cook stove(gas or electric) or open fire but the heat gun is more convenient.
When straightening or bending osage I usually oil the wood first. I use olive oil but any veg or animal oil(fat) will work. This prevents the wood from scorching. If you use steam, you introduce moisture into dry wood and as it re-dries it can easily check(crack along the grain). If you decide to use steam, seal the wood with shellac to prevent the wood from taking on moisture. The shellac can take the heat and moisture from the steam. Shellac is easily removed later be lightly scraping or by wiping it off with an alcohol soaked towel.