抄録
The low-cycle fatigue properties of quenched and tempered Fe-21%Ni-0.17%C steel containing 18 and 27 volume percent retained austenite were tested mainly by the X-ray diffraction technique, The fatigue tests were carried out at 20°C under constant total bending strain range of 0.9 1.3 and 1.6% without regard to the mean strain. The results obtained are as follows:
(1) The carbon steel that contains retained austenite presents its characteristic features regarding its changes in half-value breadth, particle size and microstrain estimated upon its martensite phase value, during its fatigue process under the low cycle fatigue testing. These features are similar to those which are revealed by the carbon steel that does not contain retained austenite.
(2) The values of steel in half-value breadth, particle size and microstrain, as they are estimated upon its martensite phase, are various, dependent on various factors, such as the stage of crack initiation and failure, the strain range applied and the tempering conditions, so that their mean value determined on the values estimated in the wide diffraction region where cracks have been abundantly initiated, is at the present time far from being adequate to be taken for the constant estimation of the fatigue damage in martensitic steel.
(3) The amount of martensite in the retained austenisite induced in the course of the fatigue is various, dependent on the tempering conditions preceding the fatigue test, even within one strain field, and the mode of stabilization of the retained austenisite in this case is similar to that of the thermal stabilization.
(4) Earlier fatigue cracks are recognized as having occurred not only in nonmetallic inclusions and in prior austenisite grain boundaries, but along the edges of martensite leaves.
