YES YOU DO!
IF, if , if, if, it is going to be your contention that it WAS steel then You will HAVE to show some TECHNICAL reasoningto bolster than contention.
Is that cross made of two steel truss sections or two aluminum portions of exterior cladding? Did molten aluminum flow along them and form a bond between them that consists of an alloy of steel and aluminum? (no, I do not know if such an alloy is possible)
Besides that though, I can get two pieces of steel coat hanger to bond loosly together in an open air wood bonfire. Clamp them together in a vise and heat the whole works in the fire and allow it to cool. The larger carbon content vise will be less likly to bond to the coat hanger but the two identical metals will. (wrecks the vise though)