Abstract
Hereunder is given a report of investigation made of the effect of cast skin and shot peening on the plane bending fatigue strength of annealed and normalized spheroidal graphite cast iron produced by addition of Si. The results obtained are as follows.
(1) The fatigue strength reduction factor due to the cast skin, in the case of annealed iron, is 118. This reduction is attributed mainly to the surface roughness (Hmax=50S) and the decrease of solute Si content in α-Fe of cast skin.
(2) The fatigue limit in normalized iron with cast skin drops to 74% as high as the iron without cast skin. The main factors for this decrease are decaburization, small pits, and the decrease of solute Si content in α-Fe of cast skin. The fatigue strength reduction factor due to the above mentioned two last causes is about 1.17.
(3) Graphite of irregular form is seen near the bottom surface, but the irregularity does not affect the fatigue strength.
(4) The cast skin is strengthened so much by shot peening that subsurface failure occurs in every shot peened specimen.
