Drawing a high-carbon steel wire increases the strength of the wire but significantly reduces its ductility. In addition, leading to the delamination, which is characteristic of a high-carbon steel wire and occurs in wires with reduced ductility, appears, and this is the biggest factor in the inhibition of high-strength wire. We investigated the possibility of suppressing delamination by using the alternating wire drawing process, which suppresses additional shear strain during drawing and increases ductility. First, we conducted tension tests on alternately and conventionally drawn wire to investigate changes in mechanical properties, with alternately drawn wire at a breaking strain of 1.9% and conventionally drawn wire at a breaking strain of 1.5%. Next, we conducted a torsion test, as stipulated in the Japanese Industrial Standards, and confirmed that the alternate wire drawing process suppressed the delamination. We also examined whether the alternate wire drawing process suppressed axial tensile residual stress on the wire surface by using the slit method and Finite element method analysis.

Laser peening is a surface treatment designed to improve fatigue life by introducing compressive residual stress via laser-induced shock waves. However, there is currently no simple method of evaluating the depth of a compressive residual stress layer in a production factory. The author attempted to propose a simple evaluation method using a sheet-forming process called laser peen forming, which is based on the same principle as laser peening. In this study, pure titanium sheets were bent by nanosecond green laser peen forming performed in a water pool. The bending angle decreased with the increase in the amount of floating debris generated by laser ablation. Various water injection systems were employed to wash away the debris. The bending angles and their reproducibility were improved by injecting water coaxially with the laser beam. These results demonstrated that the improvement of residual stress distribution could be visualized through bending deformations, and suggested a potential evaluation method. However, further clarification of the process is required.