Abstract
This study discussed surface crack and microstructure of Mod. 9Cr-1Mo steel fatigued under multiaxial loadings. Strain controlled multiaxial low cycle fatigue tests were carried out using a hollow cylinder specimen including interruption tests. Strain paths employed were a push-pull straining and circle straining. The latter is the non-proportional loading test where axial and shear strains have 90 degree phase difference and principal directions of stress and strain are changed in a cycle. Surface cracks and microstructures fatigued specimens were observed by a digital microscope and a transmission electron microscope (TEM) in order to investigate mechanisms of cyclic deformation, failure and reduction in life due to non-proportional loading.
