The most efficient and nonabrasive method to harden surfaces is ball burnishing.
A mass of steel balls is placed in a vibrating bowl, a rotating sextagon, or an octagonal drum filled with a lubricant of soapy water; the part(s) is set amongst the steel balls. When the containers vibrate or rotate, the steel balls hammer the components being processed, hardening the surfaces on all sides simultaneously.
Ball burnishing is a perfect process for plated or polished components.
If you are unsure what equipment and media you require to achieve your desired surface finish, then send us your part, and we will evaluate it free-of-charge and provide you with a metrology report.