Circular metallurgy is one of the most widely discussed aspects to achieve eco-friendly and sustainable metallurgy. In addition to the main approaches of enhancing steel recyclability and reducing carbon dioxide emissions, increasing the product lifetime stands out as a promising approach toward sustainability. The product life in functional parts under cyclic loads is determined by their defect tolerance and ability to encounter crack initiation and propagation. In addition to their ability in enhancing the ductility, strength, and ductility strength balance, copper precipitates show a noricable tendency of enhancing the fatigue life in a high cyclic fatigue regime. Although fatigue enhancement is correlated to improved defect tolerance and crack initiation and propagation resistance, the mechanism of how the copper precipitates cause such enhancement has not been investigated. Nonetheless, the effect of copper precipitates on the fatigue life under a very high cyclic fatigue (VHCF) regime and at different loading ratios has not been studied. In our work, we aim at evaluating the effect of different copper precipitation states and different loading ratios on the fatigue behavior in the very high cyclic fatigue (VHCF) regime. Investigations of the fatigue crack initiation and propagation velocity da/dN as a function of the stress intensity factor “K” (Paris law) and the engineering threshold value Kth are to be carried out in the VHCF regime using notched 4-point bend specimens (SENB) in a Rumul CrackTronic resonance testing machine. To investigate the precipitation behavior, the microstructure, the fracture surface, and the dislocation-precipitates interaction, the raw specimen and fractured specimen will be investigated according to a multi-scale investigation protocol that includes atom probe tomography (APT), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A comparative study between the different precipitates state at different loading ratios in the VHCF will enable us to understand how the precipitates nanostructure, the elemental partitioning, and the dislocation-precipitates interaction lead to an enhanced defect tolerance and enhanced crack initiation and propagation resistance. Thus, this study enables the steel society to come one step forward toward better utilization of the copper precipitates in the fatigue application, one step forward toward longer fatigue lifetime, accordingly, one step ahead towards sustainability.