TORSION BAR AND METHOD OF FORMING THE SAME

摘要

A method of forming a torsion bar wherein steel, preferably an alloy steel of medium carbon content, is formed in the desired size and shape and is through hardened for providing a desired core hardness. The case of the bar is then hardened for transforming austenite in the case into martensite causing the case to expand thereby inducing high compressive stresses near the surface with the compressive stress decreasing radially inward of the surface. The core of the bar is retained below lower transformation temperature for resisting expansion of the case thereby inducing hoop and axial compressive stresses and radial tensile stressed in the case. The hardened bar is then cold worked by twisting and releasing the bar at least twice for applying a torsional stress in the angular direction of the bar loading which presets the bar by twisting it beyond its initial yield strength for redistributing the stresses and inducing a residual torsional stress therein in a direction opposite to the preset direction. A torsion bar formed by the method of the present invention is also disclosed. -1a-