Effect of “additional shear strain layer” on tensile strength and microstructure of fine drawn wire

Fine wires of the order of 0.1 mm in diameter have become popular for mechanical and electrical applications. In the drawing process, a large shear deformation zone with a hardened layer, referred to as the “additional shear strain layer”, is generated beneath the surface layer of the wire. This study clarified that the depth of this additional shear strain layer was about 0.04 mm for various diameter fine wires. As the diameter decreases, the area ratio of additional shear layer increases. Hence, the additional shear strain layer is a factor for the improvement in high strength and ductility of the wires. In order to discuss the cause of the increase in the surface layerʹs tensile strength, the crystal orientation was measured via the electron back-scatter diffraction (EBSD) method. It was ascertained that the crystal of surface layer was subdivided more easily than the center layer, and therefore the tensile strength of surface layer increased.