EFFECT OF SMALL DEFECTS ON THE FATIGUE PROPERTIES OF MEDIUMSTRENGTH CAST STEEL

Small defects, such as microshrinkage cavities or pores, act as stress raisers and may initiate fatigue fracture. The effect of defect size on the gatigue strength was investigated in cast steels of 800, 880, and 1040 MN/sq m tensile strength, respectively. This was compared with corresponding results for mild steels, evaluated from earlier investigations. It was shown that fatigue-strength reduction increases with increasing tensile strength. Microshrinkage cavities at the specimen surface caused a larger strength reduction thanhose located in the interior. Pores were found to have a more severe effect than microshrinkage cavities of the same size.