A study of the mechanism of crack initiation on a mandrel bar for mandrel mill rolling in a seamless tube

An investigation was carried out on the mechanism of crack initiation on a mandrel bar used for the mandrel mill operation in seamless tube manufacturing. Close observations of the mandrel bar surface suggested that crack initiation may be induced by a thermal shock. In order to check the validity of this hypothesis, laboratory tests mainly based on cyclic temperature treatment were then carried out in a laboratory and a method was proposed to improve the mandrel bar life. After the estimation of the temperature on the mandrel bar surface both by numerical analysis during rolling and stripping and by an experimental approach during the stripping operation, an acceleration test using a corrugated mandrel bar was carried out on the mandrel mill to verify the validity of the proposed method (to improve the mandrel bar life).