Effect of Testing Atmosphere on Low Cycle Fatigue of Hot Work Tool Steel at Elevated Temperature

抄録

Effects of atmosphere and strain amplitude on low cycle fatigue behavior of AlSl H11 hot work tool steel were investigated. The fatigue life in vacuum was twice as long as that in air. From the result of the fatigue test in vacuum, it became clear that slip bands on the specimen surface were formed during fatigue and they grew up with increasing number of cycles. The initial fatigue cracks were generated at the intersection of slip bands and were vertical to loading direction. The fatigue cracks mainly initiated at internal inclusions when tested in vacuum, whereas superficial cracks were observed on the same fracture surface when applied higher strain amplitude. In contrast, nucleation sites of fatigue cracks when tested in air were specimen surface irrespective of the magnitude of strain amplitude. The extension of low cycle fatigue life in vacuum was mainly due to the decreasing of growth rate of superficial and internal cracks to the critical crack length.