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Causes of Argon bubble scar on the surface of continuous casting billet in MF melting furnace

The surface quality of continuous casting billet in medium frequency electric furnace is an important factor affecting the qualified rate and production cost. Ensuring good surface quality of continuous casting billet is the prerequisite for hot delivery and direct rolling of billet.

The surface defects of billet are different in shape, and the cause is complex. In addition to common cracks, slag inclusion and so on, there may also be surface argon bubble scar.

     When producing wide slab of 45 excellent carbon steel and other steels, argon bubble scar defects often appear on the surface of the billet. The causes of argon bubble scar on the surface of billet are as follows: argon is blown into the nozzle in production, positive pressure is formed inside the nozzle to prevent air from getting involved.

Argon bubbles are fully mixed with molten steel in the nozzle. When the argon blowing into the nozzle flows out from the outlet of the immersion nozzle together with the molten steel, the upper and lower cyclotron regions will be formed after touching the narrow surface of the mold. The bubbles in the upper cyclotron region are easy to discharge with the flow of molten steel, while the bubbles in the lower cyclotron region are not easy to discharge. If the bubbles are captured by the solidification front in the mold, the bubble scar defects will be formed on the billet. And these bubbles are unevenly distributed on the billet.