Casing is prone to external folding defects in production, which affect the improvement of product quality and need to be controlled.


Several outer folding edge oxide particles cause elemental segregation, including folding, intermediate folding, excessive Al, Mg, Ca, S, P, Mn, Si outer folding elements, especially brittle inclusions SiO 2 and silicate with 20 um at grain boundaries, intergranular fracture occurs, and the brittle inclusions are the main reasons for the formation of outer folding.


Smelting process:
1) Ensure that after clicking on carbon pull, the end point of carbon blowing control is avoided > 0.10%;
2) Increase the effect of converter slag and slag under strict control. When slag is used, ladle slag will leave after its thickness is less than 50 mm.
3) Double slag operation to control phosphorus content in molten steel.


Refining process:
1) The refining time of LF is more than 20 minutes.
2) Strengthen the deoxygenation mixing effect. It is required that the basicity of refining slag be more than 2.5, the slag be less than 1%, and the residue time of white slag be more than 15 minutes.
3) Argon refining is finished after bottom blowing, ensuring that soft blowing time is more than 10 minutes, which is convenient for removing inclusions in molten steel.


Casting process:
1) Use ladle and tundish to protect casting and sealed argon, no oxidation to protect casting;
2) Casting temperature: the superheat of tundish is lower than 20 C;
3) Adopting braking control at die level and electromagnetic stirring;
4) Use special flux to ensure the surface quality of slab.


The collation process:
In order to reduce the white spot caused by hydrogen-induced cracking, slow cooling process was used to treat billet and bar.