main parts service products       corrugators       box machines       corrolls contact us	corrolls -> hardening Mitsubishi Supplied Corrugating Rolls are inductively hardened, rather than the surface hardening approach used by most competitors. These results in a roll that has the entire flutes and a good deal of below the valleys hardened. Here’s a picture of an acid etched cross section of a Mitsubishi Supplied Corrugating Roll: The dark area is uniformly at a Rockwell hardness of 56.