engleski

The influence of niobium precipitates in the cold drawing pipe

The paper presents the results of the investigation of the influence of the microalloying element niobium at the beginning of the plastic material flow in the cold drawing of the tubes. Studies were conducted on low carbon steel and steel of the same base composition that was micro-alloyed with 0, 046% niobium. The steel strip of 370x3, 00 mm is made of both steel. Longitudinally welded tubes of 57 mm diameter and 3 mm wall thickness were made from the strip. Tubes were cold drawn to a diameter of 42 mm and wall thickness 2 mm. The tubes of both steel are cold drawing by the same parameters. The resulting results show different material behavior at the beginning of cold drawing. In the case of steel containing niobium at the beginning of cold deformation, Lüders bands appear. This phenomenon has not been noted for niobium-containing steel. Detailed structural tests have confirmed the appearance of Lüders bands in micro-alloyed steels. It has been found that niobium-containing steel occurs after non-homogeneous deformation after reaching the proportionality limit. Methods of thermography and digital image choleraeum confirmed that in the area of non- homogeneous deformations the appearance and propagation of Luders lines occurs. Only when it completes the propagation of the Lüders bands through the zone of deformation begins and the plastic deformation takes place. These changes have not been noted for niobium-containing steel.

niobium microalloyed steel, cold drawing tube, Lüders band, thermography, digital image cholera

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