Why is Thick-walled Seamless Steel Pipe Cracked?

Rolling situation of thick-walled seamless steel pipe:

1, The hot-rolled rolling position of thick-walled seamless steel tube is 38, 118m away from the strip head, mainly located in the middle of the strip.
2, It is presumed from the shape of the large hole of the rolling, that the crack starts in the middle of the width of the strip. The reason is that the rolling force and the shearing force cause the crack to stretch and form a macroscopic macroscopic hole.
3, The seamless steel pipe has a smooth fracture surface in the cold rolling production process, and no obvious surface defects are observed before and after the fracture.
4, Observing the micro-morphology of the fracture, the typical dimple-like ductile fracture morphology is observed, and the fracture is layered, the central dimple is larger, the dimple is reduced at the near surface, and the crack exhibits divergence and expansion dominated by the central fracture. The fracture morphology is deep, and the depth of the fracture at the center is deep. It is speculated that the layered morphology of the fault zone is closely related to the central segregation.
 

Analysis of the reasons for thick-walled seamless steel tubes:

1, Under the scanning electron microscope, the defects of the hot-rolled rolling cracks of the seamless steel tube were observed, and obvious cracks were observed in the middle of the fracture.
2, For the hot-rolled cracking crack of thick-walled seamless steel tube and its end, it is found that there are obvious oxidized particles near the crack, and there are cracks along the crystal at the crack end, and the complete polygonal ferrite morphology appears near the crack.
3, The characteristics of oxidized particles within 30um near the crack are closely related to the original defects of the continuous casting billet. The long-term heating of the continuous casting billet in the heating furnace causes the elements near the crack to be oxidized, forming a thick oxidized point layer, which ultimately inherits the defect. To the last hot roll.
4, Analysis found that there are obvious cracks and oxidized zones at the center of the thickness and 1/4, and there are also oxidized dots near the crack.

There are different degrees of internal cracks in the whole roll of the fracture. The crack mainly exists near the middle of the coil, showing a continuous through shape and a high risk of rolling.