Effects of static load on microstructural and mechanical performance of AISI 1050 medium carbon steel subjected to ultrasonic nanocrystal surface modification

In this study, the effects of mild (M1, M2, M3), moderate (O1,O2), and severe (S1, S2, S3) static loads of ultrasonic nanocrystal surface modification (UNSM) on AISI 1050 steel were investigated. The layer affected by severe plastic deformation at moderate and severe static loadings became much thicker and the nanocrystalline layer became dominant around the surface region. The layer thickness influenced by the UNSM reached approximately 350 mu m. UNSM had a positive effect on the surface roughness and morphology via reducing the Ra between 0,3 mu m and 0,8 mu m excluding the highest static loads. Oxidation formation was observed on the surface at severe static load conditions. The microhardness showed a significant improvement independently of static loads, and the hardness depth reached up to approximately 250 mu m after the UNSM. Remarkable alteration in surface hardness was observed by increasing static load. Higher static loads ensured both deposition the compressive residual stress to the surface and propagation towards interior. The compressive stress of-700 MPa and a stress depth of over 1 mm were obtained by severe static loading. The processes implemented by moderate and severe static loads showed better performance over both low and high-cycle fatigue behavior.