STEEL-MADE COMPONENT

PROBLEM TO BE SOLVED: To provide a bearing part having excellent rolling fatigue life and further excellent in machinability.SOLUTION: There is provided a steel-made component containing specific amounts of C, Si, Mn, P, S, Cr, Al, Ca, Mg and the balance Fe with inevitable impurities, having predictive maximum inclusion diameter √AREAmax calculated by an extreme value statistic treatment of √AREA, a ratio of a composite inclusion of oxide and sulfide, average composition of oxide and content of MnS and CaS in whole inclusion included in specific areas in the inclusion which is breaking origin of an ultrasonic fatigue test, a ratio between retained austenite volume percentage at a depth position at 20 μm from a surface and maximum austenite volume percentage in a range of 200 μm depth from the surface of 0.6 or less and having plastic flow structure with thickness of 1 to 15 μm on the surface.SELECTED DRAWING: Figure 2 【課題】優れた転動疲労寿命を有し、しかも被削性にも優れた軸受部品を提供する。【解決手段】特定量のＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ａｌ、Ｃａ、Ｍｇを含有し、残部はＦｅおよび不可避的不純物からなり、超音波疲労試験の破壊起点である介在物において、√ＡＲＥＡを極値統計処理して求めた予測最大介在物径√ＡＲＥＡｍａｘ、酸化物と硫化物の複合介在物の比率、酸化物の平均組成および、介在物全体に占めるＭｎＳとＣａＳの含有量がいずれも特定の範囲内に含まれ、表面から２０μｍの深さ位置での残留オーステナイト体積率と表面から２００μｍ深さの範囲での最大オーステナイト体積率との比が０．６以下となり、表面に厚さ１〜１５μｍの塑性流動組織を有する、鋼製部品。【選択図】図２