Investigation on Carbonizing From Mold Flux into Ultra-low-Carbon Steel During Continuous Casting

Carbonizing phenomena from carbon-containing mold flux into ultra-low-carbon liquid steel have always been one of the important factors affecting the surface quality of continuous casting billets. An experimental method has been adopted in this investigation to study the carbonizing behavior of mold flux into liquid steel during continuous casting of ultra-low-carbon liquid steel, and the locations where carbonizing occurs during the continuous casting process were predicted by ANSYS Fluent numerical simulations. The results indicate that the low-carbon mold flux with carbon concentration 2.19 pct would form the thickness of steel carbonizing about 1500 μm, and the high-carbon mold flux with carbon concentration 3.64 pct would form the thickness of steel carbonizing over 4000 μm when liquid steel–mold flux contact for 20 seconds at high temperature. And the metallographic structure of primitive ferrite firstly precipitates the chain pearlite ferritic at the ferrite grain boundary and then grows up to form flake pearlite. Furthermore, the numerical simulation results show that the carbonizing phenomenon is likely to occur at a quarter of the width in the thin slab where there are the violent steel liquid free surface fluctuations during the continuous casting process, which is consistent with the locations of carbonizing found in actual production sampling.