熱間工具鋼の衝撃破面観察

抄録

In order to clarify the difference of impact fracture behavior of hot work tool steel SKD6 over a range from 300K to 873K, the Charpy impact test and the observation of the fracture surfaces were carried out using V notch specimens and without/with prefatigue crack specimens. The energy require to initiate a crack at room temperature is greater than the energy for the crack propagation, while at elevated temperature the tendency becomes reversed. Macroscopic fracture at room temperature occurred in a brittle manner. On the other hand, at 873K the wider ductile shear zone near V notch root and the shear lips appeared. But the specimens with prefatigue crack fractured without the ductile shear zone even at elevated temperature. In the crack propagate region the ripple pattern that consist of the dimple pattern and the slipped flat one was found. And the rate of slipped pattern increased with rising test temperature.