Abstract: The present invention provides case-hardening steel superior in tooth surface fatigue strength and a gear using the same used for parts of automobiles, construction machines, industrial machines, etc., that is case-hardening steel superior in tooth surface fatigue strength containing, by wt %, C: 0.1 to 0.3%, Si: 1.0 to 2.0%, Mn: 0.3 to 2.0%, S: 0.005 to 0.05%, Cr: 1.0 to 2.6%, Mo: 0.8 to 4.0%, V: 0.1 to 0.3%, Al: 0.001 to 0.2%, and N: 0.003 to 0.03%, limiting P to 0.03% or less, and having as a balance iron and unavoidable impurities, and satisfies the following expression, 31Si (%)+15Mn (%)+23Cr (%)+26Mo (%)+100V (%) is 100 or more, and a gear comprised of case-hardening steel and having an X-ray diffraction half width at a depth of 50 mm from the surface of the gear of 6.4 degrees or more.

Abstract: This invention aims to provide a carburized component realizing a larger strength for power transmission components such as gears, and a method of manufacturing the same. The carburized component of this invention, aimed at realizing the object, consists essentially of, in % by mass and both ends inclusive, C: 0.1-0.30%, Si: 0.80-1.50%, Mn: 0.30-1.20%, Cr: 2.0-5.5%, and the balance of Fe and inevitable impurities; has a mean C concentration over the range from the surface of the steel to a depth of 0.2 mm after vacuum carburization of 1.2% or more and 3.0% or less, and has a ratio of a carbide area over the range from the surface to a depth of 50 ?m of 15% or more and 60% or less, has the carbide precipitated in a finely dispersed manner so that the carbide having a grain size of 10 ?m or less accounts for 90% or more of the entire portion, and has a depth of a grain boundary oxide layer below the surface of 1 ?m or less.