抄録
Hereunder is presented the report of low-cycle fatigue test made of steel Fe-25% Ni-0.17%C, both quenched and tempered, i. e.
quenched and then sub-zero treated (18-100% retained austenite)
tempered (18% retained austenite)
at room temperature 20°C, in respect rather of the total constant bending strain values within their range than of their mean value. Both thinfilm electron microscopy and optical microscopy were applied, not to mention other techniques, to the study of the process of fatigue, through observation of its X-ray diffraction, in respect of changes in the amount of retained austenite, in the half-value breadth and in its martensite. The results obtained are summarized as follows.
(1) The changes in the half-value breadth and in the dislocation structure on the austenite or retained austenite phases during the low-cycle fatigue test will respectively be best accounted for by comparing the above mentioned changes in the annealed materials and those in the cold-worked materials.
(2) As to which part of steel is foremost exposed to the low-cycle fatigue to crack it differs somewhat from martensitic steel to austenitic steel. In martensitic steel early fatigue cracks occur mainly along the edges of the martensite leaves or in the prior austenite grain boundaries, while in austenitic steel, which is apt to be martensitized in the course of cycling strain, they occur mainly in the twin boundaries or in the austenite grain boundaries. In austenitic steel that has been martensitized during fatigue, the edges of the martensite leaves are nearly clean of cracks.
