Residual stresses at the surface of automotive suspension springs

This study concentrates on the origins of unfavourable stresses at the surface of silicon-manganese automotive suspension springs. The residual stresses have been investigated at the various stages of the spring manufacturing-quenching, tempering and shot peening. Residual stresses from quenching depend in a complex fashion on the microstructural state of the surface and on the variation of the thermal gradient into the quenched spring wire. Contrary to expectations, oil-quenching of decarburised spring wire results in tensile residual stresses at the surface, while water quenching results in compressive residual stresses. The residual stresses do not disappear after tempering. Moreover the shot peening after quenching and tempering, if not conducted properly, may result in small compressive or even tensile residual stresses at the surface, which severely diminishes the fatigue resistance of the suspension springs. (C) 2000 Kluwer Academic Publishers.