The tundish is a refractory container used in steelmaking continuous casting. It first receives molten steel poured from the ladle, and then distributes it to various crystallizers through the tundish nozzle.
What are the roles of the tundish in the steelmaking process?
(1) Reduce the static pressure of the molten steel, maintain a stable molten steel level in the tundish, and smoothly pour the molten steel into the crystallizer;
(2) Promote the further floating of inclusions in the molten steel to purify it;
(3) Distribute the molten steel. For multi-strand continuous casting machines, the tundish distributes the molten steel to each crystallizer;
(4) Store the molten steel. The casting speed is not reduced when changing ladles during multi-heat continuous casting, creating conditions for multi-heat continuous casting. Therefore, the main functions of the tundish are pressure reduction, flow stabilization, inclusion removal, storage, and distribution of molten steel.
What are the metallurgical functions of intermediate tundish?
I. Purification Function: To produce high-purity steel, measures such as using baffles, argon blowing, and ceramic filters in the tundish can significantly reduce the content of non-metallic inclusions in the steel.
II. Temperature Regulation Function: To ensure that the temperature change of molten steel in the tundish during the early, middle, and late stages of casting is less than 5°C, and to ensure casting is close to the liquidus temperature, thereby expanding the equiaxed grain zone of the billet and reducing center segregation, measures such as adding small pieces of scrap steel to the tundish and injecting iron powder can be used to regulate the steel temperature.
III. Composition Fine-tuning: Aluminum, titanium, and boron cored wires are fed into the crystallizer through the center hole of the tundish plug rod to achieve fine-tuning of the microalloying composition in the steel. This improves the recovery rate of easily oxidized elements and avoids nozzle blockage.
IV. Refining Function: Adding a double layer of slag to the surface of the molten steel in the tundish absorbs inclusions that float to the surface, or feeding calcium wire into the tundish to change the morphology of Al₂O₃ inclusions, can prevent nozzle blockage.
V. Heating Function Induction heating and plasma heating are employed in the tundish to accurately control the pouring temperature of the molten steel. The longer the molten steel remains in the tundish, the more time inclusions have to float to the surface, resulting in cleaner molten steel. An effective way to increase the residence time of the molten steel is to use a large-capacity tundish with a deep molten pool.
Refractory materials for tundish
The temperature of molten steel in the tundish is approximately 1470–1560℃. Because a certain thickness of excess steel is left in the tundish after casting, and the stopper rod and excess steel are frozen inside the tundish when it is removed from the line, the tundish is removed along with the working lining after cooling. Since the working lining is a one-time service item, its requirements are not as high as those for the ladle.
1. Permanent Lining Castable
The permanent lining of the tundish typically uses aluminosilicate castables. Depending on the tundish’s operating conditions, this castable should possess good strength, volume stability, and thermal shock resistance. The tundish castables produced by Kerui Refractories have a service life of approximately 700–800 heats.
2. Working Liner Dry Material
The basic dry material for the tundish consists of sintered magnesia, magnesia-calcium sand or fused magnesia, magnesia-calcium sand, medium- and high-temperature sintering agents, and a small amount of low-temperature binder. Magnesium dry working lining has advantages such as simple construction, high baking thermal efficiency, easy separation of steel slag from permanent lining, fast tundish turnover, improved steel quality, and long service life.
