タフトライド処理鋼の疲労き裂と下部組織
1972 年 21 巻 231 号 p. 1136-1141
詳細
1972 年 21 巻 231 号 p. 1136-1141
It has been pointed out by many researchers that substructure affects crack propagation in case of fatigue of metallic materials. However, the materials used in the past investigations were mostly homogeneous, and the microscopic behaviour of surface hardened materials such as tufftrided steel is only little known.
In the present study, some investigations were made to obtain the relation between the crack propagation and substructure of tufftrided steel specimens with notch root through the observations of the crack propagation and the change in substructure in the vicinity of notch root and crack during the fatigue process by using the back reflection X-ray microbeam diffraction technique.
The results obtained are summarized as follows;
(1) The life to fracture or the period preceeding crack initiation of a tufftrided steel specimen increases remarkably as compared with that of a non-tufftrided steel specimen under the same stress amplitude.
(2) The crack initiates at a comparatively early stage in the life to fracture and grows rapidly. However, when the crack tip passes through the position 1∼2mm away from the notch root, the crack propagation rate gradually decreases.
(3) The substructure had already formed at the places with high content of soluted nitrogen after tufftriding, and the same substructure can be observed in the vicinity of crack tips irrespective of crack length.
(4) It is evident from the observations by microbeam X-rays and by a scanning electron microscope that the plastically deformed area in the vicinity of crack in the tufftrided steel is very small and the magnitude of deformation of each crystal is also small as compared with that in the non-tufftrided steel.
