Technical measures for smelting clean steel
Smelting clean steel should be based on the variety and application requirements. The operations of hot metal pretreatment-steelmaking-refining-continuous casting should be under strict control. The main technical countermeasures are as follows:
(1) Hot metal pretreatment. The sulfur content of molten iron in the molten iron desulfurization or triple desulfurization process should be less than 0.005% or even less than 0.002%.
(2) End-point control of converter compound blowing and steelmaking. Improve dephosphorization conditions, increase the final hit rate of the end point composition and temperature, reduce the dissolved oxygen content of the steel grade, and reduce the number of non-metallic inclusions in the steel.
(3) Slag blocking and tapping. The slag blocking is adopted for tapping, and the thickness of the slag layer in the ladle is controlled below 50mm. Can avoid phosphorus back and improve the yield of the alloy, reduce oxide inclusions.
(4) Ladle slag modification. In the tapping process, slag modifier is added to the steel stream. Reduce iron oxide and adjust ladle slag composition.
(5) Refining outside the furnace. According to the quality requirements of steel grades, one or more refining combinations are selected to complete the refining task of molten steel, to achieve dehydrogenation, extremely low carbonation, extremely low sulfidation, denitrification, reduce inclusions and form control of inclusions, etc.
(6) Protection pouring. The use of protective pouring technology in the pouring process is particularly important for the production of clean steel. The ladle-tundish-crystallizer adopts long nozzle argon seal protection pouring, the tundish adopts double-layer protective slag, and the crystallizer adopts protective slag. It has the function of adsorbing inclusions and reducing secondary oxidation.
(7) Tundish metallurgy. Organize reasonable molten steel flow and reasonable molten steel residence time in the tundish to promote the floating of inclusions.
(8) Crystallizer operation technology. Choose protective slag with proper performance; immersion nozzle centering and proper insertion depth; pulling speed and liquid level stability; applying crystallizer electromagnetic stirring technology; controlling the flow of molten steel, which is beneficial to the upward discharge of gas and inclusions and improves the quality of the slab .
(9) Internal quality control of the slab. Use electromagnetic stirring and light pressure technology to reduce center looseness, center segregation and shrinkage. Increase the density of the slab.
(10) Use straight crystallizer arc continuous casting machine and vertical curved continuous casting machine to facilitate the floating of inclusions.