Abstract
It was considered to improve the corrosion fatigue strength of leaf springs by
improving the corrosion resistance of the spring steel, for the purpose of improvement in
reliability of leaf springs of heavy duty and medium duty trucks.
The steels with addition of Ni, Cu and Cr for the improvement of corrosion resistance were
used in this study. We carried out the combined cyclic corrosion test, and investigated the
influence of alloying elements on the corrosion resistance. Based on the result, we selected
the steel which had an excellent corrosion resistance, and then carried out the corrosion
fatigue test. The result is as follows.
The addition of Ni and Cu was effective in reduction of the corrosion pit depth, whereas,
increasing in the content of Cr was effective in reduction of corrosion loss.
The rust layer of Ni, Cu and Cr added steel contained much Ni, Cu and Cr in the inner side
layer, and it was considered as the barrier effect over Cl.
The developed steel with addition of Ni, Cu and Cr, 'AUP21' had a life of about 3 times of the
conventional steel 'SAE51B60' in the corrosion fatigue test.
The corrosion pit depth of AUP21 was shallower than 51B60, and the corrosion loss was also
lesser, in addition the compressive residual stress remained on the surface of AUP21 after the
corrosion test was 1.3 times of 51B60.
According to these effects, it was thought that corrosion fatigue strength of AUP21 was
improved remarkably.
AUP21 was excellent in corrosion fatigue strength with the evaluation by the leaf spring
assemblies and actual road tests by trucks.
AUP21 is excellent in corrosion resistance and corrosion fatigue strength, and it contributes to
the improvement in reliability of leaf springs greatly.
Therefore, it is adopted as leaf springs for heavy duty and medium duty trucks.
Keywords - leaf spring, spring steel, reliability, corrosion resistance, corrosion fatigue