抄録
Recently, ultra high cycle fatigue researches of high strength steel and surface modified steel are studied actively. Because fatigue strength in these materials had decreased again at about (10)^7 cycles in each S-N curves. So, we used SNCM439 steel by radical nitriding and studied about its fatigue strength. As a result, Fracture of radical nitrided one started from surface in short life region and inside in long life region. Fracture pattern on fisheye failure in radical nitrided one was different from quenched and tempered one.
