Gigacycle Fatigue Properties of Double-Melted SCM440 Steel and Size Effects

Abstract

Ultrasonic fatigue tests up to gigacycle regimes were conducted for double-melted SCM440 low-alloy steel using enlarged and conventional specimens, comparing the results with those of single-melted steel. Although both types of specimens of the double-melted steel showed internal fracture, the difference between the enlarged and conventional specimens was very small in spite of large difference in case of the single-melted steel. The inclusion sizes of an internal fracture origin also showed negligible difference between the two types of the specimens. Namely, size effects were small in case of the double-melted steel, unlike the case of the single-melted steel. These results meant that the double-melted steel showed superior gigacycle fatigue properties to the single-melted steel when the enlarged specimens were used in the fatigue tests, while the superiority was invisible when conventional specimens were used. Moreover, when the inclusion sizes were evaluated by the enlarged specimens, the double-melted steel showed much smaller inclusion sizes than the single-melted. Hence, using the enlarged specimens was highly advisable in evaluating the gigacycle fatigue properties and the inclusion size, particularly in case of high-cleanliness steels.