On the Change in the Internal Friction of Stainless Steels in the Fatigue Process

Abstract

The internal friction has been measured on the specimens of repeat-bend fatigue test with constant strain amplitude using austenitic SUS316, ferritic 11Cr-0.4Ti and semi-austenitic SUS631 steels. A discussion was then made on plastic deformation, initiation and propagation of cracks, and martensitic transformation of these steels during fatigue test.
It was considered that in 11Cr-0.4Ti and SUS316 steels the internal friction increased owing for the most part to an increase of dislocation density by the plastic deformation during fatigue test. In SUS631 steel, the internal friction increased markedly due to martensitic transformation rather in the earlier stage of fatigue. The internal friction increased more strongly owing to the initiation and propagation of cracks in these steels. The initiation and propagation of cracks in these steels was also examined by means of both optical and scanning electron microscopy.