Abstract: In the present invention, after a nitriding process is performed on a steel, a passivating process in which the steel is heated under an atmosphere containing oxygen is performed. The heating condition of the passivating process is within a range surrounded by (100° C., 120 min), (100° C., 10 min), (125° C., 5 min), (190° C., 5 min), (200° C., 10 min), (200° C., 20 min), (190° C., 30 min), (190° C., 40 min), (180° C., 60 min), and (180° C., 120 min) on coordinate axes of temperature and time. In the process for production of the nitrided steel, uniform passivated layer can be easily formed, and fatigue strength is improved as pitting corrosion resistance is improved.

Abstract: A hoop for a CVT belt including foreign matter existing in a nitrided hardened layer and surface of the hoop, the foreign matter comprises at least one of an oxide-type foreign matter, a nitride-type foreign matter, and a carbide-type foreign matter. The oxide-type foreign matter has a particle size of 25 ?m or less, the nitride-type foreign matter and/or the carbide-type foreign matter have particle sizes of 17 ?m or less.

Abstract: A fatigue test device for thin plates can reliably perform tests. The fatigue test device has a rod having ends in a longitudinal direction thereof; a vibration source for excitating a longitudinal end of the rod in the longitudinal direction thereof so as to form a standing wave having node portions and antinode portions formed therebetween and a mounting means for mounting a test piece having a longitudinal direction at one of the antinode portions, the test piece being positioned such that the longitudinal direction thereof is perpendicular to the longitudinal direction of the rod.

Abstract: In the present invention, after a nitriding process is performed on a steel, a passivating process in which the steel is heated under an atmosphere containing oxygen is performed. The heating condition of the passivating process is within a range surrounded by (100° C., 120 min), (100° C., 10 min), (125° C., 5 min), (190° C., 5 min), (200° C., 10 min), (200° C., 20 min), (190° C., 30 min), (190° C., 40 min), (180° C., 60 min), and (180° C., 120 min) on coordinate axes of temperature and time. In the process for production of the nitrided steel, uniform passivated layer can be easily formed, and fatigue strength is improved as pitting corrosion resistance is improved.

Abstract: A fatigue test device for thin plates can reliably perform tests. The fatigue test device has a rod having ends in a longitudinal direction thereof; a vibration source for excitating a longitudinal end of the rod in the longitudinal direction thereof so as to form a standing wave having node portions and antinode portions formed therebetween and a mounting means for mounting a test piece having a longitudinal direction at one of the antinode portions, the test piece being positioned such that the longitudinal direction thereof is perpendicular to the longitudinal direction of the rod.

Abstract: A hoop for a CVT belt including foreign matter existing in a nitrided hardened layer and surface of the hoop, the foreign matter comprises at least one of an oxide-type foreign matter, a nitride-type foreign matter, and a carbide-type foreign matter. The oxide-type foreign matter has a particle size of 25 &mgr;m or less, the nitride-type foreign matter and/or the carbide-type foreign matter have particle sizes of 17 &mgr;m or less.