Heavy skin defects are common surface quality problems in the continuous casting process of steel. They are manifested as abnormally thickened and irregular skin layers on the surface of the ingot, often accompanied by defects such as inclusions and cracks, which seriously affect the quality and performance of the final product. In today’s increasingly competitive steel industry, effective control of heavy skin defects is crucial to improving the yield rate and reducing production costs.
Typical characteristics of heavy skin defects
Macroscopic manifestations
Abnormal surface roughness: The defective area is obviously rougher than the normal ingot surface
Uneven thickness: The thickness of the skin layer in the defective area can reach 2-3 times that of the normal area
Irregular distribution: It is mostly irregularly distributed in strips or sheets
Accompanying defects: It often coexists with defects such as slag inclusions and cracks
Microstructure
Metallographic analysis shows that the heavy skin defect area has the following characteristics:
Coarse and disorderly grains
Concentrated distribution of oxide inclusions
Obvious component segregation
Weak bonding between the surface and the matrix
Mechanism of formation of heavy skin defects
Analysis of main causes
1. Crystallizer factors (key influencing factors)
Improper vibration parameters: The vibration frequency does not match the negative slip time
Poor performance of protective slag: The melting characteristics do not meet the requirements of the steel grade
Copper plate wear: The change in taper leads to the formation of air gaps
Uneven cooling: Abnormal local heat flux density
2. Influence of process parameters
Drawing speed fluctuation: Typical value exceeds the safety range of ±0.2m/min
Superheat control: The best control should be in the range of 15-25℃
Secondary cooling water distribution: The specific water volume deviation exceeds ±0.1L/kg
3. Molten steel quality factors
[T.O] content exceeds the standard: The risk increases significantly when >30ppm
[S], [P] and other harmful elements are high
Deoxidation products do not float fully
Detailed explanation of the formation process
The formation of heavy skin defects goes through three stages:
Initial solidification abnormality: Uneven solidification shell at the meniscus
Shell tearing: Thermal stress causes local shell rupture
Metal penetration: Molten steel penetrates into the crack to form a “sandwich”
