infolding of hot rolled seamless steel pipes
Infolding is the main quality defect in the production of hot rolled seamless steel pipe, which is produced in the perforation process and cannot be eliminated. Infolding is the folding on the inner surface of the seamless steel pipe. The appearance is characterized by a scaly layering, similar to a closed curve, and there are also folds with irregular shapes. Folding is produced in the rolling process due to the poor quality of metal, when there is excessive segregation of non-metallic inclusions, there will be pores concentrated around the metal inclusions, in the perforation process split to form inside folding, after the extrusion of sizing machine it appears in scales or other shapes.
In short, the unqualified round billet quality of rolled seamless steel pipe is mainly caused by the high degree of metal contamination caused by non-metallic inclusions and harmful substances. In addition, strip segregation has a very important effect on the quality of billet during casting. The band segregation depends largely on the chemical composition, holding state and cooling rate of the steel. The increase of the content of harmful elements in steel leads to the increase of their concentration in the segregation zone, thus forming segregation. The increase in carbon content will also increase the segregation of impurities, especially manganese.
The following factors also affect the infolding of seamless steel pipes during the perforation process
1. Influence of perforation deformation parameters on infolding of hot rolled seamless steel pipe
The folding of seamless steel pipe also has a certain relationship with the perforation process. The parameter setting and tool design of the perforation process have a certain influence on the folding. The rupture of the central area of the pipe billet is not only related to the total amount of pressure down in the roll and the total amount of pressure down before the top, but also related to the local amount of pressure down when the pipe billet turns to half a circle.
3. Ensure the heating temperature of the blank before perforation, reduce the amount of pressing down before the top, and improve the quality of the hot tool.