Friction stir processing tool

Disclosed is an inexpensive tool for friction stir working, which is used for workpiece such as iron or iron alloys requiring high working temperatures and can realize friction stir working without significant abrasion and with high efficiency and high productivity. Also disclosed is a friction stir working method. The tool for friction stir working is formed of a Ni-base double multiphase intermetallic compound alloy. The tool for friction stir working comprises a Ni-base double multiphase intermetallic compound alloy as a base metal. The surface of the base metal has been subjected to hardening treatment by at least one of nitriding or carburizing. The friction stir working method comprises pressing the front end of a tool being rotated at a high speed against a workpiece and plasticizing the workpiece by generated frictional heat for stirring to work the workpiece. In the friction stir working method, the tool for friction stir working is used.