High carbon steel wires are used in many different industries. The length of wires are usually very high in their application. Precise and controlled welding process for the connection of these wires in order to provide basic requirements of their service is very important. Due to considerable influence of welding process on the fatigue behavior of these wires, fatigue design and evaluation for welded wires is vital. To the author’s knowledge, there is no published data about welding process and fatigue design of these wires in the standards and relevant articles, until now and only basic requirements of welded wires are mentioned in some references. Selection of suitable welding process for the connection of these steel wires in order to provide required tensile strength is very challenging and this is due to high carbon percent of base material and formation of brittle martensitic structures in welded areas and very small dimensions of cross-section. The main objective of this thesis is selection of suitable welding process for these wires and optimization of welding parameters in order to provide required tensile strength and the investigation of fatigue strength of welded wires under cyclic loading. Thus, theoretical and practical results are presented. Due to very small dimensions of cross-section and high carbon percent of the material, while considering practical limitations of welding process, three welding processes of Tungsten Inert Gas, Laser Beam Welding and Flash Welding are focused among others. Tensile axial tests are performed on the welded specimens and weld qualities are compared in different states. It was observed that welding process of Tungsten Inert Gas provides the required strength. In order to assure optimum welding conditions, radiographic non destructive tests are performed on the welded specimens. Axial fatigue tests on TIG welded specimens are performed in four stress levels and relevant S-N curves are extracted and compared with the conventional steel fatigue design methods. Fractographic tests are used to determine the cause of failure and fracture type of welded specimens. Cleavage structures are mainly observed in the cross section of failed specimens under cyclic loading which is a sign of brittle fracture for the investigated high carbon steel. Keywords: High carbon steel wires, Welding processes, Tungsten Inert Gas, Design and fatigue analysis based on S-N curves.
