Ah, the joys of poor quality wrought iron!
One strategy is to further refine the bar before you begin your project. Draw it out at welding temperature then fold it back on itself and re-weld. If the splitting is just the result of limited refining at the mill, this will often improve your chances of working without excessive splitting.
An extreme application of this would be to criss-cross the grain like plywood as you draw and weld. I did this to make sheet stock for a shovel in my younger days. The finished sheet rang like a bell when tapped and had almost no splits along any edge forging from about 1/2 inch thick to about 1/16 think.
When drawing out plane irons with welded/laminated blades, I also learned to keep the end of the the bar thick to help hold most of it together. Then, just thin the end with one last blazing, dripping heat.
If, on the other hand, the splitting is because of impurities like sulphur in the iron it will crack cross-grain and not much you can do will help.