I have a part that gets induction heat treated in one small area to Rc 53-59. Material is 4340. The length of the area to be heat treated is specified on the print. The print also specifies a depth. My question is this, is there any non-destuctive method to test the hardness of this area to the specified depth. The area is approx 2.000 wide by .500 long by .200 deep. Right now I test the hardeness at the surface, and I have sectioned a few samples to test the hardness at the specified depth. I need a method to test every part without cutting it open. Any suggestions? Thanks in advance!