Effect of Rare-Earth Elements on Fatigue Properties of Spring Steel

The morphology and composition of inclusions in spring steel and rare-earth spring steel were analyzed using scanning electron microscopy and energy-dispersive spectroscopy. To examine the impact of rare earths on the fatigue properties of spring steel, particularly on the crack initiation and expansion behavior triggered by inclusions, axial tension and compression load fatigue tests were conducted on spring steel and rare-earth spring steel using a GPS-100 high-frequency fatigue tester. The introduction of rare earths causes modifications in the inclusions present in the spring steel, leading to an augmentation in its fatigue life. The inclusion of rare earths increased the fatigue life of spring steel from 10^7 cycles to more than 10^8 cycles. Three types of inclusions were identified in the fatigue fracture of the spring steel. Conversely, the fatigue fracture of rare-earth spring steel primarily comprises rare-earth inclusions and composite inclusions. The fatigue properties of spring steel are more profoundly affected by surface inclusions than by internal ones. The stress intensity factor of inclusions markedly impacts the fatigue lifespan of spring steel.