In casting, the seamless steel billet central portion of carbon, phosphorus, sulfur and manganese content than the phenomenon known as the center of the slab edge segregation. Center segregation will affect the quality and process ability of the final product, is a typical internal defects in the slab, we need to analyze the mechanism and control.

1. Mechanism
1) "Small ingot" theory
Slab during solidification, due to seamless steel slab cooling heat and instability, leading to instability of columnar grain growth, rapid growth of columnar crystals in the billet center meet to form a "bridge", and In the billet center was intermittent distribution, liquid cavity of molten steel was off distribution "bridge" split open, not added when the upper part of the liquid crystal steel bridge below the liquid steel solidification contraction, they form a loose or shrinkage, and accompanied by central segregation.
2) Core slab suction hole theory
Since the end of the slab solidification shrinkage of the liquid to the solid phase volume will have some holes, therefore, solidification enrichment of solute elements is sucked into the hole, causing central segregation; bulging occurs if the re-solidification process, casting Blank Center will produce a hole, the hole has these same suction that solute elements enriched liquid steel billet center inhaled form center segregation.
3) Precipitation of solute elements and enrichment theory
Strand solidification process to the center, because the selected sub-crystallization effect, some of the solute elements (such as carbon, manganese, sulfur, etc.) in the solidification front moving equilibrium occurs solute redistribution. As the solidification process, solute elements increasingly pushed to the central portion of the billet, the central segregation eventually formed.

2, The control center segregation measures
1) Low superheat casting
Seamless steel solidification primarily through crystal nucleation and crystal growth in two stages. Among them, the superheat nucleation rate and the crystal growth rate and liquid metal temperature gradient are closely linked: low superheat, the nucleation rate, the more likely the formation of equiaxed beneficial in reducing the central segregation.
2) Control the cooling intensity
For the secondary cooling water, the use of weak cooling intensity, controlling the growth of columnar crystals, will increase the proportion of equiaxed, get a good slab quality; with a strong cooling intensity in the precipitation of solute elements have not had time to solidify. Therefore, take appropriate secondary cooling intensity can reduce carbon deflection degree.
3) Pull speed
At the same seamless steel casting superheat and electromagnetic stirring, reduce casting speed also makes solidified reduce heat loss, solidified shell thickening, reduce carbon level increased segregation.