US Patent 7326306 Method for producing nitriding steel

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.