Background technology:
Continuous casting steel billet is opened when watering, and when the molten steel in mold liquid level rises and floods the molten steel discharge opening of submersed nozzle, adds continuous casting covering slag.Prior continuous casting protective slag is usually to contain CaO, SiO
2, Al
2O
3Basic slag Deng composition is formed, and adds Na again
2O, performances such as the fusing point of fluxs such as F adjustment covering slag, viscosity.Common covering slag joins on the molten steel in mold liquid level, and the heat of high-temperature molten steel makes it form a molten slag layer, and molten slag layer can play following effect: (1) secluding air prevents molten steel oxidation, reduces molten steel face heat loss; (2) dissolve the non-metallic inclusion that floats to the molten steel face; (3) slag flows into and forms slag film lubricate between crystallizer and the strand; (4) thus the capacity of heat transmission control strand of the performance change slag film by changing covering slag to the heat transfer of crystallizer.Covering slag is and the closely-related important auxiliary material of cc billet surface quality.Open when watering at continuous casting, wish that covering slag can form molten slag layer rapidly on crystallizer molten steel face, prevent molten steel oxidation, effects such as lubricated strand to play.But can not satisfy the requirement of opening quick slagging when watering according to " body " of the design of normal poring rate with covering slag, and because to open when watering liquid steel temperature low, reasons such as covering slag fusing heat absorption easily on the crystallizer molten steel surface are tied cold steel.Continuous casting is opened and is adopted the covering slag that self can generate heat when watering usually for this reason, and quick slagging is called as the fever type pouring slag on crystallizer molten steel surface.
For the medium carbon steel of phosphorus content 0.08~0.20%, particularly one of major defect of the inferior peritectic steel of phosphorus content 0.08~0.15% is the strand lobe, and to water on the first block casting base occurrence frequency the highest opening equally for this defective.Existing technology is to open at medium carbon steel to adopt the fever type covering slag when watering; the disclosed fever type pouring slag of for example Japanese special fair 1-210157; purpose is that the covering slag self-heating can reduce molten steel temperature drop, and quick slagging, and covering slag can evenly be flowed between strand and the crystallizer wall.Secondly but its shortcoming is quick slagging only considers this measure of generating heat, and does not give consideration for the uniformity of the main body protection slag performance of the performance of the slag of pouring slag and follow-up use.Calculate it and will influence one, two block casting bases because press the unit consumption of pouring slag, and pouring slag with to influence one heat steel after the main body protection slag mixes.
Summary of the invention:
Purpose of the present invention overcomes two shortcomings that exist in the above-mentioned prior art at the pre-fused exothermal pouring slag that provides a kind of continuous casting medium carbon steel slab to use, and prevents medium carbon steel strand lobe.
The special significant difference of pre-fused exothermal pouring slag provided by the invention and prior art is that the basic slag charge in the covering slag adopts fritting to handle.Concrete technical scheme is: pre-fused exothermal pouring slag of the present invention, by weight percentage, chemical analysis is CaO 30~50%, SiO
223~43%, Al
2O
32~8%, Na
2O 6~13%, F4~11%, Fe
2O
35~10%; Control CaO/SiO
2Be 1.0~1.3; Reach above-listed chemical analysis by following two class raw material proportionings: (1) basic slag charge is 75~85% by weight percentage, it is made up of wollastonite 30~50%, fluorite 15~25%, sodium carbonate 10~20% mineral powders, (2) raw materials by weight that participates in exothermic reaction counts 20~25%, and it is made up of silicon calcium powder 8~15%, brown iron oxide 5~10%, sodium nitrate 2~6%.After the raw material of basic slag charge mix, melt, shrend, abrasive dust, become amorphous glass dust of fritting; Then this glass dust and the raw material that participates in exothermic reaction are mixed pre-fused exothermal pouring slag.The amorphous glass powder of fritting in this pre-fused exothermal pouring slag, it is even to have a composition, when melting again heat absorption few, the fireballing characteristics of slagging.If not with the fritting of basic slag charge raw material, in the slag charge as soda ash (Na
2CO
3) waiting can the decomposition reaction of generation heat absorption in the fusion process in crystallizer.So pre-fused exothermal pouring slag is steady at the crystallizer internal reaction, flare is little, flue gas is few, slagging is fast.
The physicochemical property of pre-fused exothermal pouring slag of the present invention is more approaching with the physicochemical property of covering slag with general medium carbon steel, so be the special-purpose pouring slag of medium carbon steel.The basicity CaO/SiO of pre-fused exothermal pouring slag of the present invention
2Than the basicity height of fever type pouring slag of the prior art, this be because: in sheet billet continuous casting, phosphorus content is the steel grade that 0.08~0.15% inferior peritectic steel is the easiest generation lobe.The formation of crack of lobe often just forms at the early solidification of strand, and in order to prevent the lobe of strand, strand needs slow cooling in crystallizer.Adopting slow cooling type covering slag is the major measure that solves strand lobe defective.The characteristics of slow cooling type covering slag are to have higher crystallization temperature, and in the slag film that this covering slag forms between strand and crystallizer wall, solid-phase layer is thicker; the liquid phase layer is thinner; exist air gap between slag film and copper plate of crystallizer, therefore have bigger thermal resistance, thereby played the effect of slow cooling.And the effective measures that improve the crystallization temperature of covering slag are the basicity (CaO/SiO that improve covering slag
2), thereby medium carbon steel is with the normally high basicity covering slag of continuous casting covering slag, basicity is between 1.2~1.5.The pouring slag of prior art is in order to adapt to all steel grades, all is low basicity, and as what point out in the special fair 1-210157 bulletin of Japan, the heating pouring slag is used for medium carbon steel, and to solve the strand lobe obviously be favourable.But the basicity (CaO/SiO) of the present invention exploitation is more approaching at Slag Properties and the main body protection slag of 1.0~1.3 the special-purpose pouring slag of high basicity medium carbon steel, and is more favourable to solution strand lobe.The present invention considers liquid steel temperature, pulling rate of opening when watering and the factors of then using such as main body protection slag; the Slag Properties of medium carbon steel with pouring slag is decided to be: fusion temperature is 1000~1100 ℃; viscosity is (after the fusing, 1300 ℃) 0.20~0.30Pa.s, basicity CaO/SiO
21.0~1.3.
The present invention compared with prior art, have following outstanding feature and remarkable advantage: because the present invention is the spontaneous heating pouring slag of pre-fusibleness, the fusing in advance of the raw material of its basic slag charge, shrend, abrasive dust become the amorphous glass powder, then can avoid in the slag charge as soda ash (Na
2CO
3) wait in crystallizer the decomposition reaction that heat absorption takes place in the fusion process, thus steady at the crystallizer internal reaction, flare is little, flue gas is few, slagging is fast; Basicity (the CaO/SiO of this fritting heat pyrexia pouring slag
2) than the fever type pouring slag basicity height of prior art; the basicity of existing fever type pouring slag is generally about 0.8; and the basicity of this fritting heat pyrexia pouring slag is 1.0~1.3; thereby the physicochemical property that makes its covering slag then can effectively solve medium carbon steel strand lobe problem near the physicochemical property (basicity of general medium carbon steel covering slag is 1.2~1.5) of general medium carbon steel with covering slag.With medium carbon steel of the present invention pre-fused exothermal pouring slag (embodiment 1) and universal heating pouring slag of the prior art (comparative example) service test on medium carbon steel.Use embodiment 1 and comparative example respectively on two streams of a conticaster, test altogether 6 times, embodiment slagging speed is fast, and flare is little, and two kinds of strands that slag waters are not all found the lobe defective, but other defective embodiment is obviously few.Carry out (embodiment 2) expanding test subsequently on medium carbon steel, tested number is above 50 streams, and strand lobe index is 0.7, is 4.0 and use preceding 50 inferior strand lobe indexes of stream of comparative example.Illustrate that thus pre-melted type heating covering slag of the present invention has minimizing really and opens the effect of watering stove strand lobe.