EFFECT OF CYCLIC PLASTIC DEFORMATION ON THE MECHANICAL PROPERTIES OF SPRING STEEL DIN 50Cr3

In this study the effect of cyclic plastic deformation on the mechanical properties of alight duty grade of spring steel DIN 50Cr3, commonly used in leaf spring wasinvestigated. This steel has a chemical composition of 0.25% C, 0.8% Cr, 0.79% Mn,and 0.2% Si. Primarily, standard tensile specimens of this steel were cut andsubjected to a quenching and tempering heat treatments. Austenitization was carriedout at 870oC for 1h followed by quenching in oil and then tempering was applied at450oC for 1h. Subsequently, Different pre-plastic deformation strains of 1%, 2%, and2.5% were applied followed by various number of tensile stress cycles from zero to amaximum stress of 9%, 12.5%, and 16.5% over the offset yield stress of thequenched and tempering specimens. These plastic strains and stress cycles cansimulate the possible over loading of the vehicle. By increasing the number of cyclesunder a constant amplitude for a given fixed pre-plastic strains, the ultimate andoffset yield strength of the spring material were sensibly increased while ductility wasdrastically decreased.