**5.4. Verification of simulation results**

To verify the obtained simulation results, the slab broadening cast on the #2 caster in Maanshan Iron and Steel Co. Ltd was measured. The online measuring system was designed to measure the width of the slab. The digital camera was fixed above the exit of the caster. Q235 steel was used for the experiments. The parameters of the continuous caster and measured results are listed in Table 6.

Numerical Simulation of Slab Broadening in Continuous Casting of Steel 573

broadening during the process. It is thus concluded that slab broadening is independent of

Soft reduction may strengthen slab broadening and even cause side bulging. For SPHC and Q235 steels, the slabs were broadened in the process of continuous casting with soft reduction set to 0.5~2.5 mm. The broadening width ranges are 2~19 mm and 2~8 mm for SPHC and Q235 steels, respectively. The ratios of broadening are 0.1%~1.46% and 0.15%~0.62% for SPHC and Q235 steels, respectively. Therefore, soft reduction contributes to

For the continuous caster #2 in Maanshan Iron and Steel Co. Ltd, the ultimate thickness of a produced slab is 230 mm, and the bottom thickness of the mold is 237.5 mm. With a casting speed of 1.1 m/min, the molten steel completely solidifies at the start of the 11th sector where the thickness of the slab is 234.3 mm and the roll gap contraction is 3.2 mm. In this zone, the linear shrinkage ratio is 0.5%~0.7% (1.2~1.7 mm) due to the drop of temperature. Without the contribution of the temperature drop, the roll gap contraction is 1.5~2.0 mm. This amount of shrinkage equals soft reduction of medium or light scale. The roll gap contraction is uniformly distributed. The roll gap contraction acts on the slab and affects the fluctuation of the liquid level of molten steel. However, the slab broadening is far less than that induced by soft reduction. So roll gap contraction is not the main cause

The static pressure of the molten steel core and the force of the driving rollers may be the

When there is no support on the narrow face of a slab, the slab deforms in the width direction under the static pressure of molten steel. The high-temperature mechanical properties of the slab are worse than those under normal temperature(Lei H et al,2007; Chen J,1990; S. Kobayashi et al,1988). The slab has good ductility under high temperature and is unable to resist the static pressure of molten steel in the width direction. Therefore, the slab greatly deforms at the edges, and thus the width is broadened. Previous studies found that the hardness of the solidified shell and the ability to resist the static pressure of molten steel are determined by the thickness of the shell and the formation of ferriteaustenite with a dual phase.( Mizukami H et al,1977; Uehara M et al, 1986; Ramacciotti

The shell of the slab is clamped under the pressure of the driving roll cylinders so that it moves forward with the rotation of the driving rollers. The solidifying and soft slab is extended and broadens under the pressure of the driving rollers when passing through

exceptions of equipment or operating parameters.

slab broadening, but is not the main cause.

**6.4. Contraction of roll gap** 

of broadening.

**6.5. Summary** 

A,1988)

main cause of slab broadening.

**6.3. Soft reduction** 

The online measured RUB values are greater than the simulation results for all the experimental slabs. This is because the preset width of a cold slab in the experiments was the upper width of the mold. The upper width is always greater than the defined width. For the slab with a preset width of 2050 mm, the upper width of the mold is 2081.3 mm (a broadening of 1.56%). With this difference taken into account, the experimental results well agree with those of the simulation.


Note: the measured broadening of the slab is the difference between the measured width of the slab and the upper width of the mold, and the calculated broadening of the slab is that between the calculated width and the defined width.

**Table 6.** Measured and calculated widths of slabs
