Home > Knowledge > Content
Defect types of continuous casting round tube billet
- Jul 03, 2018 -

The defects of continuous casting tube billet have great influence on the machining performance, mechanical properties and quality of steel tube. 

Common low-level tissue defects are: under the surface bubble, loose, shrinkage, skin crack, center crack, tissue segregation and so on. The subcutaneous bubble of the tube billet: The adjacent surface of the continuous casting billet, the shape is oval. It is generally considered that the deoxidation of molten steel is the main cause of the formation of the skin bubbles of the tube billet. Generally need to the protection slag, Ferroalloy, ladle, tundish for baking, injection flow using protection pouring. For higher steel grades, it is also required to use the outside refining method to remove gas from the molten steel. 


There is a continuous cast round tube billet with subcutaneous bubbles, the inner surface of the bubble will be oxidized when the heating furnace is heated, and the surface defects of the steel pipe will be formed after the rolling is not welded. The skin crack of tube billet: It exists in the columnar region of continuous casting circular tube and the transition of fine grain region. 3~10 mm from the surface of tube billet. As long as the crack does not penetrate to the outer surface, it will not be oxidized and will be welded under the action of rolling pressure. 

Generally do not produce serious surface quality. Intermediate crack and central crack: in columnar grain region of continuous casting round billet, the direction of middle crack and columnar direction are generally the same. The results show that the middle crack and center crack of continuous casting tube are the main cause of the inner folding of seamless steel tubes. During perforation, the Tube billet is subjected to repeated tensile and compressive stress in the oval hole type of the roll and Guide tool, in which the crack or the center crack is expanded or oxidized, and the steel pipe folds are produced. 


The inner fold of the steel tube formed after the center crack or the middle crack expansion of the continuous casting billet is usually deep, which often results in the scrap of steel pipe. Porosity and shrinkage of tube billet: In the equiaxed Crystal region of the central part of the Tube billet. The porosity of the billet is due to the grain effect of the casting billet in the solidification process, the liquid metal movement is hindered by cooling to the solidification direction, or the grain which is sunk by the liquid part of the billet hinders the shrinkage of the billet. When the loose reaches a certain degree, the casting billet will appear shrinkage. The distribution state is discontinuous in the Tube billet. The center porosity of continuous casting tube billet with uniform distribution density and high dispersion is not only harmful to the process of oblique rolling perforation, but is advantageous. Professor University Zhu Jingqing has proved the point through experiments. 


Also, there is a metal band of 5 mm at the front end of the head nose, which separates the center of the cracked tube from the head, thus avoiding the defects of the inner fold and crack. Segregation of tube billet: including microstructure segregation, component segregation and crystallization area segregation. The continuous casting tube billet with crystal is to be scrapped, and the rolling pipe is not allowed to be put in absolutely.