Views: 0 Author: Site Editor Publish Time: 2022-04-25 Origin: Site
After more than 30 years of efforts, continuous cast steel has gradually replaced ingot mold casting. Continuous casting slabs with thickness of 150 ~ 250mm are widely used in various countries to produce plates. In the 1980s, continuous casting technology has made a breakthrough. At present, the continuous casting technology that can pour thinner slabs and higher pouring speed to make the production capacity have economic scale is developed, and even the continuous casting technology that can directly cast molten steel into thin strips and directly serve as finished products or semi-finished products is developed.
In order to improve the productivity of continuous caster, increasing the casting speed is the key. The main technologies to realize high-efficiency continuous casting are: mold lubrication technology; Stable molten steel injection technology and liquid level control technology; Prevent foreign inclusions and protective slag from being involved, as well as the technology to prevent internal crack. By taking these technical measures, the blank drawing speed can reach 3.0m/min on the large-scale casting machine and 5.0m/min on the testing machine. In order to realize high-efficiency continuous casting, the selection of refractory is also one of the important conditions.
The newly developed thin slab caster can produce thin slabs with thickness of 20 ~ 60mm and width of 500 ~ 1200mm, which can be directly supplied to the finishing mill of the hot rolling plant as billets. The thin slab casting rolling process (ISP) developed by Mannesmann Demark company in Germany has the following technical characteristics:
(1) Vertical bending crystallizer. The upper part of the mold is vertical, the lower part is arc structure, and the side plate is adjustable. The billet is vertically pulled to the middle of the mold in the upper area of the mold and tangent to the arc radius of the caster. The crystallizer has a good space suitable for submerged nozzle.
(2) Thin wall submerged nozzle, due to the small space of the mold, puts forward special requirements for the submerged nozzle, so a thin wall submerged nozzle with special shape is developed.
The total thickness of the lower opening of the nozzle is only 30 ~ 35mm. The reinforced nozzle wall is 10mm thick and 250mm wide. The thickness of the nozzle channel is 10 ~ 15mm and the flow rate is 2 ~ 3t / min. the submerged nozzle is made of high alumina carbon containing boron nitride (BN) and zirconia (ZrO2). Its service life is 4H.
The shape of the nozzle is flat, so the internal contact surface with molten steel is 2.5 times larger than that of the circular and oval conventional submerged nozzle, so as to prevent Al2O3 from depositing and blocking on the nozzle wall. In addition, the distance between the submerged nozzle wall and the mold wall is 10 ~ 15mm, so it is necessary to prevent steel bridging. Therefore, it is necessary to bake at high temperature before use. At the same time, in order to prevent blocking and nodulation, it is required to use oxidation-free pouring for molten steel refining.
(3) Protective slag. Due to the shape of the mold and the high pouring speed of pouring thin slab, it is difficult to stabilize and control the protective slag film at the beginning, which will lead to longitudinal cracks in pouring sensitive steel grades. The solution is as follows:
1) Low melting point slag;
2) Low viscosity slag;
3) Granular slag replaces powder slag.