Abstract: Disclosed herein is a cutter for a rock bit that has an interior bearing race area carburized by pack carburization methods to achieve a high carbon content for extreme hardness. The exterior of the cutter is carburized also, but to a lesser degree, to avoid brittleness in the tooth area. The differential carburizing is accomplished by gas carburizing the exterior while simultaneously pack carburizing the interior. Conventional heat treatment for hardening follows. This results in a cutter having a bearing area much harder than the exterior, giving a long bearing life and reducing tooth breakage.