Evaluation of Fatigue Behavior of SAE 9254 Steel Suspension Springs Manufactured by Two Different Processes: Hot and Cold Winding

Abstract

The fatigue resistance is a property that exerts a strong influence on the suspension spring performance in vehicles. The choice of SAE 9254 steel was due to its wide use in the manufacture of these springs and their fatigue properties and toughness. The manufacture of SAE 9254 steel springs has been made by the hot winding process and the heat treatment by conventional quenching and tempering or by cold winding process and induction hardening and tempering. The shot peening induced a compressive residual stress which increased the fatigue life of the SAE 9254 steel. The residual stress profile from the surface of springs showed a peak in the values of the compressive stress for both manufacturing processes. The maximum residual stress in the cold processed spring was higher than the hot processed spring and maintained much higher values along the thickness of the spring from the surface, resulting from manufacturing processes. The fatigue cracking of the springs, without shot peening, started by torsional fatigue process, with typical macroscopic propagation. The fracture surface showed stretch marks with high plastic deformation.