Abstract
In order to investigate the cause of the defects of the rimmed steel tubes during the piercing process by the Mannesmann type roll, hot w6rking properties of rimmed steels were studied.
When the cross section.of the billets was macro-etched with the ammonium copper chloride solution, many dark grey spots and black spots were detected in the core of billets.
The results of the rotary hammering tests, impact bending tests and piercing tests showed that the dark grey spots were not so injurious, while the black spots acted as defect point for the hot working.
