Products and casting defects
Presently killed steels are cast continuously into slab for flat products and bloom and billet for structural products.
Defects in continuous casting originate from several factors like mould oscillation, mould flux, segregation coefficient of solute elements; phase transformation etc. In the following, a brief presentation is given on defect formation.
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Rhomboidity |
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Longitudinal depression ovality |
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- Center segregation and porosity
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Cracks are originated in the cast product due to mechanical and thermal stresses. Material factors are also responsible
Mechanical stresses are created due to
- Friction.
- Ferro static pressure.
- Bending and straightening operation.
- Roll pressure.
Mechanical stresses can be reduced by improving mold practices like
- Controlling powder feed rate
- Resonance in mold
- More accurate strand guidance
- Casting powder
Thermal stresses are due to non-uniform cooling in the secondary zone. Controlling water flux impinging the surface of the strand and minimizing reheating of strand can alleviate thermal stresses. Also air +water mist spray provides more uniform cooling.
Material factors are related to  transformation. High S and low  ratio cause mid face longitudinal cracks. Control of inclusion is also important.
Readers may go through the references given in this lecture.
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