Wire Drawing Behaviors with Die Angle and Strain Hardening Rate of a Metal

This study investigated the influences of the die angle (α) and strain hardening rate of a metal on the microstructure, hardness, strain, temperature, and drawing force in twinning-induced plasticity (TWIP) and ferritic steels during wire drawing. The microstructure, texture, effective strain, and hardness at the surface region of the drawn specimen are strongly dependent on α, whereas those at the central region are almost constant with α. The inhomogeneity in microstructure and mechanical properties of the drawn wire increases with α owing to the redundant work during the process, and the inhomogeneities of the drawn wire show a linear relation with the shape factor (∆), indicating that the inhomogeneities can be estimated by calculating ∆ during wire drawing. The optimum die angle (α^opt) depends on the strain hardening rate or exponent (n) of a material. α^opt decreases with n value of a material because the influence of redundant stress becomes stronger with increasing n value. For example, α^opt in TWIP steel is approximately 6°, whereas that in ferritic steel is approximately 7°. Therefore, the influence of the strain hardening rate of a metal needs to be considered to determine the optimum drawing conditions. From a materials science perspective, engineers in wire drawing plants should choose a α lower than α^opt derived from the drawing force to improve the wire quality because the microstructural homogeneity of the drawn wire is improved with decreasing α.