Studies on fatigue behavior of some structural steels

Wohler type of reversed bending fatigue tests were carried out on five grades of structural steels in order to study the effect of carbon content and heat treatment on the fatigue limit/ultimate tensile stress (f/U) ratio. Four of the steels were plain carbon steels with varying carbon contents from .13 to .45% while the fifth was a low alloy chromium-manganese-copper high tensile steel. Results of the tests showed that fatigue limit/ultimate tensile stress ratio of all the steels tested varied from 0.56 for low carbon steel to 0.41 for steels of higher carbon range in as rolled, normalized as well as annealed condition. Steels in the higher tensile strength range showed decreased value for the fatigue ratio. Normalizing treatment was noticed not to affect the fatigue ratio to any appreciable extent for steels in the lower U.T.S. range; but steel in higher tensile strength range up to 45 tons normalizing treatment though improved the value of U.T.S., fatigue ratio was definitely decreased. Annealing, however, seemed not to affect the fatigue ratio to any appreciable extent.