GoJo Hand Cleaner with Pumice... Clean your hands first, then scrub the plates with your hands and GoJo. Rinse off the plates really good under tap water. Do a final rinse with deionized water or Distilled water. Let them dry in the sun. Wash your hands in GoJo again prior to touching the dry metal plates or before assembly.
That will definitely solve your problem IF YOU ARE USING THE RIGHT KIND OF STEEL TO START WITH. Use no less than 316L stainless. The Magnetism is not your problem, it is just a symptom. It's just a clue that there is more Iron in the steel and less of the good corrosion proof metals.