Technical measures for smelting clean steel

The smelting of clean steel should be based on the variety and application requirements, and the operations of hot metal pretreatment-steelmaking-refining-continuous casting should be under strict control. The main control technical countermeasures are as follows:

(1) Hot metal pretreatment. For hot metal desulfurization or three desulfurization process, the sulfur content of molten iron should be less than 0.005% or even less than 0.002%.

(2) Converter compound blowing and steelmaking end point control. Improve dephosphorization conditions, increase the end-point composition and temperature one-time hit rate, reduce the dissolved oxygen content of steel grades, and reduce the number of non-metallic inclusions in steel.

(3) Block slag and tap steel. The slag blocking method is used to tap the steel, and the thickness of the slag layer in the ladle is controlled below 50mm. It can avoid phosphorus reversion, increase the yield of alloy, and reduce oxide inclusions.

(4) Ladle slag modification. During the tapping process, a slag modifier is added to the steel stream. Reduce iron oxide and adjust ladle slag composition.

(5) Refining outside the furnace. According to the steel quality requirements, select one or more refining combinations to complete the task of molten steel refining, to achieve dehydrogenation, extremely low carbonization, extremely low vulcanization, denitrification, reduction of inclusions and inclusion shape control, etc.

(6) Protection pouring. The use of protective pouring techniques during pouring is particularly important for the production of clean steel. The ladle-tundish-crystallizer is poured with shroud argon seal protection, the tundish uses double-layer mold slag, and the crystallizer uses mold slag, etc. It has the functions of adsorbing inclusions and reducing secondary oxidation.

(7) Tundish metallurgy. Organize reasonable molten steel flow in the tundish, reasonable residence time of molten steel, and promote the floating of inclusions, etc.

(8) Crystallizer operation technology. Select the casting mold powder with suitable performance; The submerged nozzle is centered and the insertion depth is suitable; the casting speed and the liquid level are stable; The electromagnetic stirring technology of the crystallizer is used; The flow of molten steel is controlled to facilitate the floating and discharge of gas and inclusions, and improve the quality of the slab .

(9) Internal quality control of billets. Use electromagnetic stirring and light pressure technology to reduce center porosity, center segregation and shrinkage cavity. Increase the density of the slab.

(10) Straight crystallizer arc continuous casting machine and vertical curved continuous casting machine are used to facilitate the floating of inclusions.

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