Induction processing with the aid of a conductive shield

A method for induction heating a workpiece made of an alloy characterized by an austenitizing or solution temperature and a fusion or melt temperature, the workpiece having at least one current concentrating surface, the method comprising the steps of:

• placing a non-magnetic conductive shield in proximity to the current concentrating surface of the workpiece to provide a shielded portion of the workpiece and an unshielded portion of the workpiece;
• exposing the workpiece with the shield in place to a time varying magnetic field having a frequency sufficient to induce eddy currents in a skin depth of a surface of the shield and the workpiece;
• and
• quenching the workpiece;
• wherein at least part of the unshielded portion of the workpiece is heated above the austenitizing or solution temperature and the covered portion is heated to a temperature below the fusion or melt temperature.

A method for heat treating a gear, the gear comprising a plurality of teeth extending radially from a root region and made of a ferrous alloy characterized by an austenitizing temperature and a fusion temperature less than 400° F. higher than the austenitizing temperature, the method comprising the steps of:

• providing a magnetic coil;
• placing a non-magnetic conductive shield in proximity to the root region of the gear;
• positioning the gear with the conductive shield in place within the magnetic coil;
• exposing the gear to a magnetic field varying at a frequency greater than 3000 Hz;
• and
• quenching the gear,
• wherein the teeth of the gear are heated to a temperature higher than the austenitizing temperature and the root of the gear is heated to a temperature less than the fusion temperature.