Study of Bauschinger effect in various spring steels

grantor: University of TorontoIt is recognized that the effective life of automotive suspension springs could be ended by yielding rather than fracture. The industry describes this problem as load loss or sag. Recent trends to design and manufacture light-weight automobiles result in higher working stress in springs requiring a further improved sag resistance of spring steels. The present study is conducted to characterize the sag behavior of the SAE 5160H, 9259V, and Duraspring steels by using Bauschinger effect test. Results of this systematic study showed that 9259V demonstrated a stronger Bauschinger effect compared to 5160H and Duraspring steels. Consequently, 9259V should have a better sag resistance over all. The effects of hardness level on Bauschinger effect were also established. The magnitude of Bauschinger effect reached a peak value when 9259V was hardened to HRc 50 and tested with 1% of pre-plastic strain. However, for 5160H and Duraspring steels, only a continuous reduction in Bauschinger effect with increasing in hardness has been observed. Silicon was realized to be the major alloy element influencing Bauschinger effect. The greater the silicon content in the steel, the larger the Bauschinger effect, and therefore, the better the sag resistance of the spring. In addition to silicon, carbon content also plays a role to affect Bauschinger effect. The results from present study can provide the basis for both the design of new spring steels and the modification of the existing spring steels.M.A.Sc