Those discs are called "Colters", and are found on field plows and other tillage equipment. It might be possible to stack a number of them, but you won't get the same results as using a solid piece of steel due to the microscopic air gaps between the discs, not to mention the effect of the paint. That is, the magnetic flux will always tend to be stuffed along the disc just behind the magnet. Saturation would be likely in that first disc.