JPS6186055A - Method for adding flux to tundish for continuous casting - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the quality of a continuous casting product in the first use of a tundish and to improve the yield thereof by pouring a limited amt. of a molten flux which consists of a limited compsn. and is overheated into the tundish just prior to first pouring of a molten steel into the tundish. CONSTITUTION:The molten flux of which the essential compsn. consists, by weight, of 20%<=CaO<=40%, 20%<=SiO2<=60%, 5%<=AlO3<=40%, 5%<=CaF2<=20% is perliminarily overheated to <=1700 deg.C. Such molten flux is poured into the tundish at >=2 kg and <=10 kg for each 1 ton of the molten steel stagnating in the stationary state in the tundish just prior to the first pouring of the molten metal into the tundish to be used in continuous casting by which the production of a clean ingot is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (711 Kawabu de 1 of 1) Unpublished IJI relates to continuous casting technology, fJLv#Tandish book flutter flux method.

[Conventional technology]

When manufacturing slabs, blooms, etc. using continuous H construction,
An intermediate steel container called a tandish is used between the ladle and the mold. Tanditshu is convenient for branching and pouring molten steel into multiple #Ii molds from one ladle, and also allows for delicate control over pouring when pouring from a ladle to [rg, welded molds]. It is used for the purpose of preventing undesirable effects on quality due to fluctuations in the level of molten metal within the mold.

However, Tanditshu not only has the advantages mentioned above, but also has four disadvantages as described below.
I was doing 1. Although the tandish has been preheated to 1 fj by heating the slag, it cannot be heated to 5 to near the molten steel temperature. Therefore, when the first molten steel is poured into the tandish, the molten steel is deprived of heat and cannot be used for metallurgical operations. The temperature unsteadily drops to an undesirable level. In this case, non-metallic inclusions such as brick chips mixed into the molten steel in the tundish cannot be floated and separated in the tundish, and the molten steel with increased viscosity is mixed with the molten steel.
It is brought into Jl'l and deteriorates the cleanliness of the slab.

Therefore, with conventional technology, slabs with a width of 10 to 20 tons corresponding to such non-constant thickness areas have to be downgraded, which causes a low grade 1 yield. Ta.

In addition, during normal operation, 11! A solid oxide is applied as a surface coating. This also removes heat from the molten steel at the initial stage of injection, lowers the molten steel temperature, and is metallurgically unfavorable.Furthermore, since it is a solid oxide, it floats and is difficult to separate when it gets caught up in the UFI steel. This is harmful as it impairs the cleanliness of the slab. A part of the surface coating agent melts due to the heat of the molten steel, but it takes time for it to melt, and the refining effect due to this melting cannot be expected in the relatively early stage after injection into the tundish, which is important. .

[Problems to be solved by Part II] The present invention has been made to solve the above problems, and when pouring molten steel into a tundish, it is possible to remove non-metallic inclusions, etc. in the molten steel. The purpose of the present invention is to obtain molten steel that is HL-clean, and to provide a method of adding tag tundish flux that does not have such an effect.

[Step F for solving problems]

In order to achieve the above objective 1j, the cheap hotel of I41+ has an E composition of 20%≦CaO≦40% by weight.

20%≦SiO2≦60%.

5%≦A203≦40%.

The molten flux with 5%≦CaF2≦20% is heated to 1700°C or higher, and the molten steel is first poured into the tundish used in continuous casting. -10 kg or more +ii
m1J characterized in that a clean slab is manufactured by injecting the molten flux described in i into the tundish.
This is a method of adding tandates, tsuyu, and flux.

In the present invention, no solid surface coating agent is added to the tandish. Instead, the tandish flux is melted and held separately using an air furnace or the like. Ii!, 2
0%≦CaO≦40%, 20%≦SiO2≦60%, 5
%≦A203≦40%, and 5%≦CaF2≦20%. This tundish flux is heated to 1,700℃ or above in an electric furnace to form a molten flux, and at the same time or just before pouring the first molten steel from the pot into the tundish, pour this molten flux into the tundish through a gutter, etc. inject. The injection location may or may not be the drop point of the molten steel.

The molten steel in the initial stage of pouring is in contact with the bottom of the ladle for a long time, so its temperature is lower than the average temperature of the entire molten steel, and there is a great risk that it may contain non-metallic inclusions such as brick chips. It is covered with brick waste. Under such circumstances, the molten steel at the initial stage of injection is usually relatively dyed with metal inclusions. The metallurgical operation in the tundish is effective in such a transient unsteady state fE.The present invention responds to this need for IF, and the injected molten flux (tundish)
flux) immediately acts as a cleaning agent for frflll, ensuring the cleanability of the molten steel in the unsteady area. For this reason, it is preferable to have a composition that not only has a low melting point but also easily absorbs nonmetallic inclusions.For this purpose, the components of the tundish flux according to the present invention must satisfy the following conditions.

If the CaO content exceeds 40% or is less than 20%, the melting point becomes -H and the ability to absorb nonmetallic inclusions decreases.
However, if it exceeds 60%, not only will the melting point rise, but also the oxygen content of the slag will increase, and in cases such as A9 quilt ≦ 11, the AU in the molten steel will exceed the 5i02 of the slag. This has the opposite effect, such as lowering the An content in the molten steel. CaF2 must be added as a cosolvent in an amount of 5% or more, but if it exceeds 20%, it is unsuitable because it causes melting loss of refractories and generation of fumes. Au203 is also a stable oxide that lowers the melting point of the slag along with CaO and Si02, and also lowers the acid and mopotential of the plug, so it is a very desirable constituent to add at least 5% or more of 1. However, adding more than 40% of the content is limited because it will increase the melting point by 1- and also reduce the absorption capacity of A-mono 203, which is one of the main components of nonmetallic inclusions.

? In kmM operation, the amount of molten steel held in the tundish is usually kept constant in a steady state. If the amount of flux is less than 2 kg or more per molten steel, the refining effect and the heat retention effect of the molten steel will be insufficient. −
Even if the flux is increased by more than 10 kg per molten steel, the refining effect will be saturated.Therefore, it is necessary to add more than 2 kg of flux per R steel, which is maintained at 7 days after adding flux, and adding more than 10 kg. do not have to.

[Effect]

The temperature of the continuously cast tundish flux according to the present invention is heated to 1700''C in order to maintain the heat of the molten steel and the refining effect of the flux. Temperature ill!SM
The objective is to reduce the temperature by at least 10°C. For this reason, during molten steel! ! ! The floating properties of turbid nonmetallic inclusions are less likely to be impaired.

In addition, the continuously cast tundish blacks according to the present invention have a large refining effect, effectively capturing floating nonmetallic inclusions and absorbing them into the flux. There is little chance of getting caught in the molten steel.

〔Example〕

The following is a detailed explanation of the uninvented effects based on Examples. Low carbon A for cold rolled coils made in converter-RHg air treatment equipment
250 tons of Q-killed molten steel was made into a slab using a 2-slice, 1-curved slab machine. Slab/1° method: I'l/mi 220 mm,) II l 500mm
Met. The temperature of molten steel in the ladle is +1! Direct casting...-1 for i
The temperature was 585°C. The large-sized tanditshu was MgO-based, and this tanditshu was preheated with carbon residue for 2 hours before use.

Immediately before filling the tandish with molten steel, 200 kg of molten steel melted in a Niru electric furnace at 11,750°C was injected into the tundish through the gutter. Ta7
Holding molten steel in Dinonyu; 11 is 40t in 'lL' state
It is.

The component composition of this flux is 35%CaO-37%
5i02-15% A sentence 203-1-3% CaF2.

In this way, the X-headed slab of Chugetsu (commonly known as non-determined '7?
When we investigated the quality of cold-rolled steel sheets ('+slabs), we found that
%Failure due to sliver generation in tensile test month -1j is J
] 19. It is 0.6% for the slab and 0.5% for the steady slab, which is how much inferior in quality to the slab in the 'tQ regular section. It was confirmed that the effect was large.

- On the other hand, the steel type, casting conditions, etc. are the same as those of the embodiment of the present invention, and the composition is 1.1%T, C-38.8%5i02-7.7%jM1 as a conventional tundish flux.
203-36.7%Ca O-3,9%F e203-
50 kg of a commercially available hot water surface coating agent of 4.4% Na2O was
The failure rate due to the occurrence of sleeper in a 15% tensile test piece of a cold-rolled steel plate for deep drawing manufactured from a conventional leading slab cast with the addition of .
It was 7%. As described above, the conventional leading slab has about three times as much nonmetallic inclusions as the steady slab and is inferior in quality, and the method of the present invention completely improves this.

When we investigated the relationship between the addition of molten flux and the failure rate in the 15% tensile test of cold-rolled steel sheets manufactured from unsteady slabs, including the aforementioned examples, we obtained the results shown in Figure 1, including variations. It was done.

From this, 2 kg/or more is effective! It is clear that the total refining effect of /f'l is saturated and that it is not economical even if the amount of refining exceeds 10111r/L.

[Juvenile fruit with starting point 1] Since the k complete + 5HJj method is structured as below 1,
In the evening, fJ at the beginning of using Nodinotsuyu! People are the ones who are responsible for preventing the low price of R products and improving the yield of non-defective products.

414th page's theory II 1st N is a graph that shows the relationship between the acceleration of the molten flux, A, and the failure of #4 elm manufactured from a steady slab (l).

Claims (1)

[Claims] 1. A molten flux whose main composition is 20%≦CaO≦40%, 20%≦SiO_2≦60%, 5%≦Al_2O_3≦40%, 5%≦CaF_2≦20% by weight is 1700%. ℃ or higher, and immediately before pouring the molten steel for the first time into a tundish used in continuous casting, injecting into the tundish 2 kg or more and 10 kg or less of the molten flux per 1 t of molten steel that remains in the tundish in a steady state. A continuous casting tundish/flux addition method characterized by producing cleaner slabs.