Heating coil, heat treatment apparatus, and heat treatment method for elongated workpiece

A heat treatment apparatus comprising:

• a heating coil configured to inductively heat an elongated workpiece, the workpiece having a first lateral surface and a second lateral surface adjoining each other along a corner portion. wherein the first lateral surface has a recess at a location spaced away from the corner portion, and the first lateral surface, the second lateral surface and the recess extend continuously in a longitudinal direction of the workpiece;
• and
• a cooling section configured to cool the workpiece,
• wherein the heating coil comprises:
• a base conductor configured to face the first lateral surface;
• and
• a projected conductor configured to face the recess,
• wherein a width of the projected conductor is narrower than a width of the base conductor,
• the projected conductor is arranged to project toward the recess from a position of the base conductor,
• the base conductor and the projected conductor are arranged to extend in the longitudinal direction,
• the heating coil is arranged to inductively heat the workpiece that is being relatively moved in the longitudinal direction,
• the cooling section is arranged downstream of the heating coil in the longitudinal direction, and
• at least a portion of the projected conductor is arranged upstream of the base conductor in the longitudinal direction.

A heat treatment method comprising:

• providing an elongated workpiece having a first lateral surface and a second lateral surface adjoining each other along a corner portion, wherein the first lateral surface has a recess at a location spaced away from the corner portion, and the first lateral surface, the second lateral surface and the recess extend continuously in a longitudinal direction of the workpiece,
• inductively heating the workpiece by moving the workpiece in the longitudinal direction relative to a heating coil;
• and
• cooling the workpiece at a location downstream of the heating coil in the longitudinal direction,
• wherein the heating coil comprises:
• a base conductor configured to face the first lateral surface and
• a projected conductor configured to face the recess,
• wherein a width of the projected conductor is narrower than a width of the base conductor,
• the projected conductor is arranged to project toward the recess from a position of the base conductor,
• the base conductor and the projected conductor are arranged to extend in the longitudinal direction, and
• the projected conductor inductively heats the workpiece at a location upstream of the base conductor in the longitudinal direction.