FCP Report No. 111

Effects of Fatigue in the Elastic Regime on the Impact Properties of Low Carbon Steels and Its Relation to Fracture Toughness

by

Robert William Canty
James F. Stubbins
Nuclear Engineering Program

Abstract

Four low-carbon steels, one ferritic (SAE 1018) and three bainitic (A533B C1 I, C1 I HT, and C1 II) all with similar compositions, were fatigued in the elastic regime at a stress amplitude of ± 207 MPa (± 30 ksi) to 104 cycles. These fatigue conditions were in the elastic regime, well below the endurance limits for these steels. The SAE 1018 was fatigued at room temperature and 100oC and the A533B steels were fatigued at -100°C and room temperature. Following fatigue, instrumented impact tests were performed to determine changes in impact properties of each steel. The data obtained indicates that elastic fatigue causes an increase in ductility for SAE 1018, A533B C1 I, and A533 C1 I HT steels. Similar changes in the ductility were found regardless of the material temperature during fatiguing. The A533B C1 II steel retained its original impact qualities. Several correlations between Charpy V-Notch impact energy and fracture toughness were examined to make a qualitative assessment of these effects upon fracture toughness. The increase in ductility predicts a similar increase in fracture toughness.

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