Application of controlled Cu nano-precipitation for improvement in fatigue properties of steels

In order to improve fatigue properties of steels, it is essential to inhibit crack initiation and crack propagation. Crack propagation mainly depends on the micro-order structure, for example, the grain boundary and the texture. To the contrary, crack initiation depends on the nano-order structure, for example, precipitation, slip and dislocation motion. By the way, it is reported that Cu in steel exhibit high resistance to fatigue crack initiation, but the mechanisms causing Cu to have this effect have not yet been clarified in detail. Thus, in order to clarify the mechanisms that make Cu in steel improve fatigue properties of steel, dislocation structure and precipitates of Cu added steels under different precipitation conditions have been observed and analyzed with electron microscopy. Consequently, it is clarified that reduction of the cross-slip frequency by Cu solid solution or Cu cluster in steel retards fatigue crack initiation.