Summary of the invention
Invent problem to be solved
But the molten steel surface heat preserving agent that with MgO is main component is mainly solid phase, thereby can not covers molten steel surface equably because fusing point is higher under serviceability temperature, because of the reaction of outside air and molten steel surface generates Al
2O
3It is field trash.
The object of the present invention is to provide a kind of molten steel surface heat preserving agent; It can address the above problem, and under the effect of the composition that derives from the molten steel surface heat preserving agent, can in molten steel, not generate the alumina series field trash; And, can cover molten steel surface equably in the fusion rapid speed of molten steel surface.
Be used to solve the means of problem
For solving above-mentioned problem, the present invention adopts following formation and method.
(1) the 1st mode of the present invention relates to a kind of molten steel surface heat preserving agent; It is configured in the molten steel surface of the molten steel surface temperature with regulation; Wherein, Said molten steel surface heat preserving agent contains the fusing point high-melting-point raw material higher than said molten steel surface temperature more than 2 kinds, contains the CaO of 10~70 quality %, the Al of 10~60 quality % with the amount that adds up to more than the 70 quality %
2O
3, the MgO of 5~30 quality % and the SiO of 0~10 quality %
2, said CaO and said Al
2O
3Ratio CaO/Al
2O
3Be 0.5~2.0; The fusing point of said molten steel surface heat preserving agent is lower than said molten steel surface temperature, and is that particle diameter is the powder of 30~100 μ m more than the 70 quality %.
(2) the 2nd mode of the present invention relates to a kind of molten steel surface heat preserving method, and wherein, the mode that is the scope of 5~30mm with average melting layer thickness with above-mentioned (1) described molten steel surface heat preserving agent is configured in said molten steel surface.
The effect of invention
According to above-mentioned (1) described formation; Under the effect of the composition of molten steel surface heat preserving agent; Can in molten steel, not generate the alumina series field trash; Molten steel surface heat preserving agent fusion promptly and cover molten steel surface equably, thus the generation of the alumina series field trash that invar water causes with contacting of atmosphere can be suppressed.
According to above-mentioned (2) described method; Evenly and effectively cover molten steel surface owing to the fusion promptly of molten steel surface heat preserving agent; The generation of hanging (hanging) can be prevented, thereby the generation of the alumina series field trash that invar water causes with contacting of atmosphere can be suppressed.
The specific embodiment
The inventor has studied the fusion method of velocity that is used to quicken the molten steel surface heat preserving agent in order to cover molten steel surface equably with the molten steel surface heat preserving agent.The result finds: for through mix fusing point is higher than molten steel surface temperature more than 2 kinds high-melting-point raw material manufacturing and fusing point (mixed fusing point) the molten steel surface heat preserving agent lower than molten steel surface temperature; And the powder that the particle diameter that uses 30~100 μ m accounts for more than the 70 quality % is under the situation of molten steel surface insulation material; Owing to promoted the solid diffusion between the different high-melting-point raw materials, thereby made the rapid fusion of the molten steel surface heat preserving agent that contacts with molten steel surface become possibility.Therefore, the molten steel surface heat preserving agent of dissolving covers molten steel surface equably, thereby can prevent the invar water surface from contacting with outside air and the Al that causes
2O
3It is the generation of field trash.Below just carry out detailed explanation based on the molten steel surface heat preserving agent of the embodiment of the present invention of above-mentioned discovery.In addition, the fusing point of so-called molten steel surface insulation material is meant the temperature that when the temperature that makes material rises, begins fusion, under the situation of polynary system material, is meant the fusing point of the average composition that is equivalent to solidus temperature.In addition, the molten steel surface temperature in continuous casting use tundish and the casting ladle etc. is 1550 ℃~1650 ℃.
The molten steel surface heat preserving agent of this embodiment is characterised in that: be that particle diameter is the powder of 30~100 μ m more than its 70 quality %.The particle diameter here is the size of the mesh of sieve, is the size of the sieve of mesh size that can be through afore mentioned rules.If be the powder of particle diameter more than the 70 quality % of molten steel surface heat preserving agent greater than 100 μ m, then because the molten steel surface heat preserving agent can promptly not melt, thereby molten steel surface contacts with outside air, thus generation Al
2O
3It is field trash.On the other hand, be the powder below the 30 μ m if set particle diameter more than the 70 quality % of molten steel surface heat preserving agent for, then the cost of refinement raw material becomes huge.More preferably being that particle diameter is the powder of 40~90 μ m more than the 70 quality % of molten steel surface heat preserving agent, further preferably is that particle diameter is the powder of 50~80 μ m more than the 70 quality % of molten steel surface heat preserving agent.In addition; At particle diameter is under the situation of the powder of 30~100 μ m ratio that only accounts for the 70 quality % that are less than the molten steel surface heat preserving agent; The molten steel surface heat preserving agent is also less faster owing to dissolution velocity, thereby can not promptly cover molten steel surface with solution, thereby molten steel surface contacts with outside air.
The molten steel surface heat preserving agent can be put in the sack by mixed uniformly state with different high-melting-point raw materials.Can the molten steel surface heat preserving agent that be in the state that is placed in this sack be dropped into molten steel surface together with sack.At the particle diameter of raw material greatly under the condition of different; For example the high-melting-point raw material of 30~100 μ m of the molten steel surface heat preserving agent that mixes this embodiment be lower than 30 μ m, or surpass under the situation of different types of high-melting-point raw material of 100 μ m; Because raw material is distributed in the bag unevenly; Different raw materials is difficult to contact and makes reaction slack-off, thereby can promptly not generate at molten steel surface and to melt liquid, so that molten steel surface contacts with outside air.
Under the fusing point (the average fusing point of forming) of the molten steel surface heat preserving agent situation higher than molten steel surface temperature, the molten steel surface heat preserving agent can not reach molten condition completely, and in the spreadability deterioration of molten steel surface, thereby molten steel surface contacts with outside air.For this reason, the fusing point of the molten steel surface heat preserving agent of this embodiment is set at lower than molten steel surface temperature.
Under the situation of the molten steel surface heat preserving agent that uses full-fusing, the molten damage of refractory materials such as casting ladle and tundish becomes problem.So, in the molten steel surface heat preserving agent of this embodiment, contain the raw material of the magnesia (MgO) that in the coating material of casting ladle and tundish, adopts through use, prevented the molten damage of tundish.Be less than under the situation of 5 quality % in the magnesian amount that contains, the molten damage of the coating material of casting ladle and tundish speeds up, and brings obstacle thereby give in the operation.On the other hand, be higher than under the situation of 30 quality %,, thereby become and evenly to cover molten steel because fusing point rises in the magnesian amount that contains.So, in the molten steel surface heat preserving agent of this embodiment, magnesian containing ratio is defined as 5~30 quality %.If magnesian containing ratio is 7~25 quality %, then be more preferred.
In the molten steel surface heat preserving agent of this embodiment; Mix the back form (the average composition) with 10~70 quality %, be preferably 15~65 quality %, the CaO of 20~60 quality % more preferably, 10~60 quality %, preferred 15~55 quality %, the more preferably Al of 20~50 quality %
2O
3, the MgO of 5~30 quality %, the SiO of 0~10 quality %
2As main component.Wherein, set CaO/Al
2O
3=0.5~2.0.This is because at CaO/Al
2O
3In=0.5~2.0 the scope, the fusing point of molten steel surface heat preserving agent (the average fusing point of forming) reaches minimum.In addition, SiO
2If shared quality surpasses 10 quality % in the molten steel surface heat preserving agent, then through with molten steel in the reaction of Al generate Al
2O
3Be field trash, thereby surface defects of products increase.About the content of MgO, then as above-mentioned.In addition, so-called " as main component " is meant that corresponding composition accounts for the above situation of 70 whole quality %.In the molten steel surface heat preserving agent of this embodiment, the total of above-mentioned composition also can be 80 whole quality % or more than the 90 quality %.
As above-mentioned high-melting-point raw material, can use sintering magnesite and MgO, electric smelting goods MgO or the CaO, the Al that make
2O
3, SiO
2, SrO, ZrO
2, Al
2O
3-MgO, CaO-MgO.
As the molten steel surface heat preserving method, the mode that is the scope of 5~30mm with the molten steel surface heat preserving agent of above-mentioned explanation with average fusion thickness preferably is configured in the surface of molten steel.This is because be lower than under the situation of 5mm at average fusion thickness, becomes insufficient with the isolated of outside air of molten steel surface.In addition; Also because surpass under the situation of 30mm at average fusion thickness; Through making the upper strata cooling that is in away from as the molten steel surface heat preserving agent of the position of the molten steel of thermal source; The molten steel surface heat preserving agent solidify and attached to temperature than the lower casting ladle of molten steel and the refractory surface of tundish, thereby between molten steel and molten steel surface heat preserving agent, form the gap.This is called hanging.If the generation hanging, then owing between molten steel and molten steel surface heat preserving agent, form the gap, thereby molten steel surface contacts with outside air.Also can the mode that the molten steel surface heat preserving agent is the scope of 7~25mm or 9~20mm with average fusion thickness be configured in molten steel surface.
Embodiment
Describe with regard to the present invention based on embodiment below, but the condition of embodiment is a condition example that adopts in order to confirm operational feasibility of the present invention and effect that the present invention is not limited to these condition examples.
The present invention only otherwise break away from aim of the present invention can realize the object of the invention, just can adopt the combination of various conditions and even condition.
The molten steel that is 280t to 1 loadings carries out the preliminary treatment of iron liquid, converter is taken off charcoal, adopted the vacuum outgas of RH to handle, with the melting ultra-low carbon steel.Use the tundish of capacity, it is made strand through continuous casting process as 60t.Molten steel to 15 loadings casts continuously.The molten steel surface temperature is set at 1560~1580 ℃.The molten steel surface heat preserving agent of the present invention or comparative example begins just to be used for the insulation of the molten steel in the tundish from the casting initial stage.The molten steel surface heat preserving agent all is to add 500kg together with sack with respect to tundish under the situation of embodiment, comparative example.The thickness of one block casting base is that 250mm, length are that 7000mm, width are 1500mm.Strand becomes the cold-rolled steel sheet of thickness 0.7mm, width 1500mm through normally used hot rolling, cold rolling process.In addition, the data of in table 1~table 4, having represented embodiment and comparative example.For the convenience of layout, be divided into 4 tables, but table 2 is continuous tables of table 1, table 3 is continuous tables of table 2, table 4 is continuous tables of table 3.
* 1 in the table 1 is at CaO-Al
2O
3In, CaO is 50 quality %, Al
2O
3Be 50 quality %.
* 2 in the table 1 is at CaO-SiO
2In, CaO is 55 quality %, CaO-SiO
2Be 45 quality %.
* 3 in the table 1 is at SrO-SiO
2In, SrO is 50 quality %, SiO
2Be 50 quality %.
* 4 in the table 1 is at Al
2O
3Among-the CaO-MgO, Al
2O
3Be 50 quality %, CaO is 45 quality %, and MgO is 5 quality %.
* 5 in the table 1 is at Al
2O
3-CaO-SiO
2In, Al
2O
3Be 50 quality %, CaO is 45 quality %, SiO
2Be 5 quality %.
* 6 in the table 1 is at Al
2O
3-CaO-ZrO
2In, Al
2O
3Be 50 quality %, CaO is 45 quality %, ZrO
2Be 5 quality %.
* 7 in the table 1 is at Al
2O
3-MgO-SiO
2In, Al
2O
3Be 25 quality %, MgO is 25 quality %, SiO
2Be 50 quality %.
* 8 in the table 2 is at Al
2O
3Among-the MgO, Al
2O
3Be 75 quality %, MgO is 25 quality %.
* 9 in the table 2 is in CaO-MgO, and CaO is 70 quality %, and MgOs is 30 quality %.
* 10 melting layer thickness in the table 4 are that iron staff impregnated in the molten steel, are melting layer thickness with the thickness of the molten steel surface heat preserving agent that adheres to.
* 11 Δ T.O in the table 4 are the total oxygen demand in the tundish molten steel of continuous 1~2 casting ladle of continuous casting is handled the total oxygen demand in the molten steel of back (back is handled in vacuum outgas) with respect to RH variable quantities.
* 12 defective generation numbers in the table 4 are mean number of the blemish that caused by the oxide based field trash that in per 1 volume cold-rolled steel sheet coiled material, exists, and wherein the cold-rolled steel sheet coiled material obtains from the steel billet by 1~2 casting ladle made of continuous continuous casting.
As shown in Figure 1, in an embodiment, the total oxygen demand that the total oxygen demand in the tundish molten steel of continuous 1~2 casting ladle of continuous casting is handled with respect to RH in the molten steel of back (back is handled in vacuum outgas) reduces.This be because: molten steel surface heat preserving agent fusion promptly and cover tundish surface equably; Thereby can suppress the generation that contacts caused alumina series field trash of invar water and atmosphere; Alumina series inclusion floating in the while molten steel, thus can from molten steel, remove.
In addition; As shown in Figure 2; In an embodiment; The mean number of the blemish that is caused by the oxide based field trash that in per 1 volume cold-rolled steel sheet coiled material, exists is compared with comparative example in the past significantly and is reduced, and wherein the cold-rolled steel sheet coiled material obtains from the steel billet by 1~2 casting ladle made of continuous continuous casting.This also is to cover tundish surface equably because of the fusion promptly of molten steel surface heat preserving agent, thereby can suppress the generation that contacts caused alumina series field trash of invar water and atmosphere.
Utilizability on the industry
According to the present invention, a kind of molten steel surface heat preserving agent can be provided, it can not generate the alumina series field trash in molten steel under the effect of the composition that derives from the molten steel surface heat preserving agent, and fast in the fusion speed of molten steel surface, can cover molten steel surface equably.