Analysis on the Defects of Hot Rolled SMLS Pipe

Hot-rolled smls pipe is defined in the steel pipe on the inner surface of the spiral, semi-spiral or irregular distribution of jagged folding, and some appear as straight-shaped alice skin. Some of the inner fold in the head of the steel pipe, and some exist in the entire steel pipe; or regular, or irregular. There are broken within the defective steel pipe can be used after grinding, heavy down the use or scrapped. The internal defect has always been one of the main reasons for affecting the yield of steel pipe and the yield index. There are two main reasons for the occurrence of internal defects: continuous casting billet quality (internal) and perforation process system (external factors).

Analysis of internal fold causes
Steel pipe in the inclined rolling piercing, the continuous casting of the core of the tube by the tensile stress, it is prone to metal center rupture phenomenon, the formation of holes. The metal surface of the cavity is rough and will be rapidly oxidized by the head of cooling water and air, forming a fold attached to the inner surface of the pipe during subsequent rolling. Therefore, to eliminate the internal defect, we must avoid the formation of holes.

Relationship between quality of continuous casting billet and defects in steel pipe
In the case of continuous casting billet rolling pipe, if you can get without folding, no internal and external surface cracks and delamination and other defects in the capillary, in general, can produce a qualified finished product tube. Therefore, the smelting process is the key to the production of qualified steel pipe. In recent years, experts and scholars through experimental analysis, the generation of defects and the emergence of the center of the loose, the core shrinkage and columnar crystal in the continuous casting of the depth of the tube.

The relationship between the perforation process system and the internal defect
The deformation of the oblique rolling piercing includes basic deformation and additional deformation. Base deformation refers to the solid continuous casting pipe blanks into the capillary when the rolling geometry and size changes, it is intuitive deformation, and deformation of the geometric size, shape, and the material has nothing to do with the rolling. Additional deformation is due to uneven deformation in the metal produced within the body, which mainly includes torsional deformation, longitudinal shear deformation and tangential shear deformation. This deformation will reduce the quality of the product and increase the energy consumption, so in production should minimize this harmful deformation. Any factor that reduces the metal plasticity and brittle fracture strength or increases the transverse tensile force at the time of piercing of the continuous casting tube will cause the inner fold defect to form, and the inner fold defect is mainly produced in the perforation process, but the specific reason is varied.