HIGH CYCLE FATIGUE STRENGTH OF DISSIMILAR WELDED ROTOR STEELS AT MODERATE TEMPERATURE

摘要

High cycle fatigue (HCF) strength of dissimilar welded rotor steels was investigated under axial loading for lifetime of 5×10~7 cycles in air at 25 °C and 370 °C. Scanning Electronic Microscopy (SEM) was utilized to characterize fractured surface. Results show that the largest fatigue strength occurs in upper side SAW at 25 °C while TIG has the lowest fatigue strength at 370 °C. Subsurface crack initiation with fish-eyes were observed on all fractured surfaces but without fine granular area (FGA). The changing of fatigue strength was rationalized by temperature influence and different crack initiation mechanisms in SAW and TIG, where cracks initiated from internal inclusions and porosities, respectively. Welding pores are more detrimental to fatigue life.