抄録
For the purpose of developing a structural steel having a good combination of cold forgeability and machinability, cold upsetting and drilling tests have been carried out for a series of the hypo-eutectoid graphitic steels composed of ferrite matrices and graphite nodules.
The upsetting limit of cylindrical specimens with longitudinal notch decreased with increasing amount of graphite up to the volume fraction of 1.4×10−2, and then became almost insensitive to the amount of graphite.
The drillability was improved remarkably with increasing amount of graphite, and no difference in drillability was found before and after the cold upsetting.
In the steels with less amounts of graphite, the good cold forgeability corresponded to the poor machinability as is usually observed. On the other hand, in the steels with a volume fraction of graphite greater than 1.4×10−2, the machinability could be improved without any deterioration of the cold forgeability.
