Molten metal rotor with hardened top

A rotor for use in molten metal, the rotor comprising:

• a graphite body, a top surface, and a plurality of blades, wherein each blade of the plurality of blades includes (i) a leading face, (ii) a trailing face, (iii) a recess on the trailing face of each blade of the plurality of blades, wherein each recess is configured to enlarge an opening between two blades of the plurality of blades so as to allow more molten metal to pass through the opening, and wherein the graphite body has a portion of the trailing face and the recess extends at an angle from the top surface at a position forward of the trailing face and terminates at the trailing face beneath the top surface, and (iv) a hardened material at least twice as hard as the graphite body, wherein the hardened material forms:
• the top surface, less than all of the leading face, less than all of the trailing face, and at least part of the recess.