JPH04127948A - Method for continuously casting steel - Google Patents

Abstract

PURPOSE:To prevent the development of trouble, such as breakout, in high velocity continuous casting for steel by prescribing consumption of powder added to a mold with the specific equation formulated with a casting velocity, m.p. and viscosity of the powder. CONSTITUTION:At the time of using Vc(m/sec) for the casting velocity of steel, Tm( deg.C) for the m.p. of powder and eta1300 (poise) for the viscosity of powder, the powder is added into the mold according to the casting velocity so that the powder consumption Q obtd. with the equation Q= K.Vc<-1.38>.(eta1300)<-0.58>.Tm<-1.58> (wherein, K: the fixed value decided with condition of oscillation of the mold) becomes >=0.3. Then, it is desirable that component composition of the powder is about 0.4-1.1 basicity and about 20-50wt.% SiO2 and about 10-40wt.% CaO as the essential component, and Tm is <= about 1200 deg.C and eta1300 is >= about 0.05 poise. By this method, in the high velocity of >=3m/min casting velocity, a sound cast slab having no surface defect can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for continuous casting of steel, particularly for example
The present invention relates to a continuous casting method for performing casting without problems such as breakout even in high-speed continuous casting such as m/sin or higher.

(Prior Art) In order to improve the productivity of continuous steel casting, high-speed casting in which slabs are drawn at high speed is being sought. Particularly in recent years, continuous casting of so-called near-net shave slabs (I-slabs), which are close to the final product, has been considered in order to reduce the load on the subsequent rolling process, but thin slabs are cast at conventional speeds. This reduces the amount of casting per hour and reduces production efficiency. To compensate for this, even higher speeds of continuous casting are required, but with current technology, the speed of continuous casting is 2g+/5h.
It is difficult to stably perform continuous casting at speeds exceeding .

Usually, in continuous casting of sea bream, powder is added to the surface of the molten steel in the mold and melted. The function of this powder is
By coating the surface of molten steel, the purpose is to suppress oxidation and temperature drop of molten steel and to trap floating inclusions.

In addition, it flows between the mold and the slab and acts as a lubricant for drawing the slab, preventing breakouts and surface defects on the slab. Molten slag flows into the gap between the slab and the slab, promoting cooling of the slab. In this way, the role of powder is extremely important in stabilizing casting operations.

There are various factors that hinder the speeding up of continuous casting, but one of the biggest is the problem of powder supply. In other words, as the casting speed increases as described above, the consumption of powder supplied to the gap between the mold and the slab per unit surface area of the slab (
kg/m'') decreases, resulting in poor lubrication between the mold and the slab, and powder consumption in particular decreases by 0.3 kg/m''.
It is known that when the temperature is below, the slab tends to seize into the mold and breakouts occur more frequently. Therefore, various proposals have been made to prevent breakout or surface defects in slabs caused by the reduction in powder consumption associated with high-speed casting.

For example, Japanese Patent Laid-Open No. 60-33861 proposes lowering the softening point and viscosity of powder in order to increase powder consumption.

However, a clear relationship between powder consumption and powder viscosity has not been shown, and the casting speed is 2.0 m/w.
Only an example below 1 is shown, and it is not possible to estimate the case where the speed is further increased.

In addition, in Japanese Patent Application Laid-open No. 177866/1986, 1300
A method using powder whose viscosity at °C is adjusted to an appropriate range depending on the casting speed is disclosed. However, like the method in JP-A No. 60-33861, this method only discloses an example in which the slab drawing speed is 2.0 m/win or less, but it cannot be used for high-speed casting of 2.0 i/sin or more. Furthermore, considering the temperature dependence of the viscosity of molten powder, it is necessary to indicate the viscosity characteristics of the powder as an index value, along with the viscosity at a specific temperature, as well as the melting point or softening point of the powder. There is no description regarding the melting point or softening point of

On the other hand, for the purpose of promoting the formation of a solidified shell in the mold, in order to prevent bulging or breakout of the slab due to thinning of the solidified shell when the casting speed is increased,
Although measures such as adopting a long mold and optimizing the mold taper have been taken, design values that can be applied to high-speed casting of, for example, 3.0 m/win or higher have not yet been proposed.

(Issue I!I to be Solved by the Invention) The present invention has been made with the object of developing a continuous casting method that can stably produce good slabs regardless of the casting speed. In particular, an object of the present invention is to provide a method for producing sound slabs without surface defects by preventing poor lubrication and breakout of slabs caused by reduced powder consumption due to faster casting. It is about providing.

(Means for Solving the Problem) The present inventor believes that maintaining an appropriate amount of powder consumption during casting is most important for increasing the speed of continuous casting, and has investigated the characteristics and behavior of powder in detail. As a result of the investigation, the following facts were confirmed.

(a) The viscosity characteristics of the molten powder during operation are determined by the melting point of the powder (hereinafter abbreviated as T-) and 1300°C.
When expressed in terms of viscosity (hereinafter abbreviated as η10°), a certain relationship is established between the characteristic value, casting speed, and powder consumption.

(b) Based on the above relationship, the melting point and 1300°C
If you use a powder whose viscosity is properly adjusted,
It is possible to avoid the reduction in powder consumption associated with high-speed casting, and prevent the occurrence of slab breakouts and surface cracks.

The present invention was made based on the above findings,
The gist is that [when continuously casting sea bream, the powder consumption amount Q (kg/m'') calculated using the following formula 0 is selected according to the casting speed νc (s/sec) so that it is 0.3 or more. , melting point Ts (°C) and viscosity η at 1300°C (
"Continuous casting method for steel, characterized in that a powder having pores) is added to the mold."

Q = ni-Vc-58-(771306)-58・Te
1-58-■ However, ■Equation 〇 is a constant determined by the oscillation conditions.

The above continuous casting method of the present invention is a method that can be applied regardless of the casting speed, but it is particularly advantageous in that it enables high-speed casting of 3 m/sin or more, which was previously impossible in actual operation. This is noteworthy.

The component composition of the powder used for carrying out the method of the present invention is not particularly limited, and the basicity is 0.4 to 1.1, S
ing 20-50% by weight, CaO 10-40% by weight as main components, Al toy, Na 10, Fo, Mg
By blending appropriate amounts of O1BaO2LitO and carbon, etc., T
It is sufficient to use one in which m and η1300 are adjusted to values determined by the above-mentioned formula 0.

The Tm and η1300 of the powder in the method of the present invention are selected using the above-mentioned formula, and in particular, 3 m/s+
During high-speed casting such as in or above, T- is 1200°C or less and η1300 so that the molten powder flows uniformly into the gap between the mold and the slab and provides sufficient lubrication during drawing of the slab. is preferably 0.05 poise or more.

The proportionality constant in the equation 0 regarding the powder consumption of the present invention is a constant determined by the frequency of the sine curve oscillation of the mold. Casting speed is 3 m/wi
In high-speed casting such as n or more, the number of oscillation cycles is in the range of 150 to 300 c/in.
The value at this time is 180-130.

In addition, the powder Ts+ is 2 built into the bridge circuit.
This is the value measured by an automatic melting point measuring device that detects temperature imbalance due to melting when a microsample is placed on one of two thermistors and the temperature is increased, and η1□. is a value measured using a rotational viscometer that measures the viscous resistance experienced by a rotating body.

(Function) As mentioned above, as the casting speed increases, the amount of powder consumed decreases, so high-speed casting poses a problem of breakout of the slab or the occurrence of vertical cracks on the surface of the slab.

In order to solve this problem, the method of the present invention selects the powder physical properties and changes the speed at which the molten powder flows into the gap between the mold and the slab, thereby achieving appropriate powder consumption according to the casting speed. The goal is to secure the quantity.

The present inventor conducted continuous casting tests using powders having various physical properties at casting speeds of up to 5.4 mm/inch, and investigated the amount of powder consumed and the occurrence of breakout in slabs.

FIG. 1 shows an example of test results when continuous casting was carried out using powder having the physical properties shown in Table 1 below.

As shown in Figure 1, the consumption of all powders decreases as the casting speed increases, and powder consumption reaches 0.
．． If the weight falls below 3 kg's, breakout may occur in the slab, or a breakout warning will be issued during casting, resulting in a situation where the casting speed must be reduced.This breakout limit powder consumption The casting speed to reach the quantity is T-=828°C177+5oo
=0.20 poise powder A is 4.8 m/win
Whereas, Tm=1120°c177 +5oo
=0.70 poise powder E is 2.1 m/s+in. In this way, the powder's T- and η3. . . By selecting , the powder consumption can be set to 0.3 kg/sin2 or more, which is the limit value for breakout occurrence, depending on the casting speed, and it is possible to cast even at high speeds of 3 m/sin or more, which have not been done in the past. It has become clear that stable casting can be performed without the occurrence of piece breakout.

As a means of selecting the Tm and η1300 of the powder, in the method of the present invention, the relationship between powder consumption and casting speed illustrated in FIG. The above-mentioned formula (1) is used, which is an experimental formula obtained by investigating a large number of powders having (1).

In addition, K in formula 0 indicates that the frequency of the sine curve mold oscillation is 150 cycles/sin and 300 cycles/sin.
cycles/sin were 180 and 130, respectively.

FIG. 2 shows the interrelationship between Tm and η1300 of the powder that can ensure powder consumption of 0.3 kg/a'', which is the limit value for occurrence of plaquaud, according to the increase or decrease of the casting speed, determined from the above equation 0.

As shown in the figure, for example, when the casting speed is 3 mo/sin,
η5. . . For powder with 0.4 poise, T-100
When the temperature is 0° C. or lower, the amount of powder consumed can be made equal to or higher than the limit consumption amount for breakout occurrence. Also, T- is 80
If it is powder at 0°C, η. . Furthermore, in the case of high-speed casting of 4.8 s/sin, for powder with η1300 of 0.2 poise, set Ts to 775°C or less to ensure powder consumption above the limit value. be able to. Further, for powder with T- of 1000°C, the same effect can be obtained by setting η1300 to 0.10 poise or less.

Hereinafter, the effects of the present invention will be specifically explained using Examples.

(Example) Using a one-point straightening type continuous casting machine with a bending radius of 10 m, a slab of size 2001 thickness
■ High-speed casting was performed at a casting speed of 1.5 in. The mold oncillation is a sine curve method, and the vibration frequency is 300 cycles/
It was a win.

Example 1 shows that Tm and η3. selected by the method of the present invention.
. . Using powder A shown in Table 1 above having
Continuous casting was carried out with Nα1 strands, and in Comparative Example 1, Nα2 strands were cast using Powder E shown in Table 1, which is predicted to have powder consumption below the breakout generation limit at casting speeds of about 2 m/sin or higher. Continuous casting was performed.

FIG. 3(a) shows the transition of the drawing force and casting speed, which indicate the frictional force between the mold and the slab during slab drawing in Example 1, and
Figure (b) shows the case of Comparative Example 1.

According to the present invention, in Example 1 using powder with physical properties satisfying the above-mentioned formula 0, there was little change in frictional force, and high-speed casting of 4.0+w/win could be stably performed. Further, the powder consumption was 0.40 kg/m'', which was sufficiently higher than the breakout occurrence limit of 0.30 kg/m''. As a result of investigating the surface defects of the slab, it was found that the slab was in good condition with no surface flaws.

On the other hand, in Comparative Example 1, the frictional force frequently increased, and each time,
Although casting was continued by lowering the casting speed to 2 m/sin or less, breakout finally occurred during casting at a casting speed of 2.4 s/sin. The powder consumption in Comparative Example 1 was approximately 0.10 and 0.25 kg/m'' at casting speeds of 4.0 and 2.4 s/sin, respectively, and in both cases, the amount of powder consumed in the gap between the mold and the slab was It is thought that the inflow of molten powder was insufficient and the frictional force increased.

Also, casting speed 4. Vertical cracks occurred on a part of the slab surface up to a casting length of 40 m.

As Comparative Example 2, using Powder A of Example 1, in which stable casting could be performed at a casting speed of 4.0 s/sin, casting was attempted at an increased casting speed of 5.4 m/sin. In this case, as shown in Figure 1 above, the powder consumption amount is 0.26 kg/■2, which is below the breakout occurrence limit value, so as in Comparative Example 1, an increase in frictional force is observed, and breakout occurs. The danger of this increased and stable casting became impossible. However, the casting speed is 4.13s/si.
When it was lowered to n, the drawing force of the slab became constant and the casting became stable.

(Effects of the Invention) According to the method of the present invention, powder consumption can be constantly reduced to 0.3 kg/kg, which is the limit value for breakout occurrence, depending on the casting speed.
m" or more. As a result, even during high-speed casting, it is possible to prevent slab breakouts and the occurrence of vertical cracks on the slab surface, and it is possible to stably produce slabs with a sound surface condition. Particularly in recent near-net-shape continuous casting, productivity can be greatly improved by high-speed casting of 3 s/sin or higher, which has not been practiced in the past.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between casting speed, powder consumption, and slab breakout occurrence when powders with different physical properties are added to the mold. Figure 2 is a diagram showing the correlation between the melting point of the powder and the viscosity at 1300°C, which can ensure powder consumption of 0.3 kg/-2, which is the limit value for breakout occurrence, as the casting speed increases or decreases. be. FIG. 3(a) is a diagram showing the transition of casting speed and slab pulling force in an example of the present invention, and FIG. 3(b) is a diagram similar to FIG. 3(a) in a comparative example. It is.

Claims (2)

[Claims] (1) Powder consumption Q(
Casting speed Vc so that kg/m^2) is 0.3 or more
(m/sec), melting point Tm (°C) and 1
A method for continuous casting of steel, characterized in that a powder having a viscosity of η_1_3_0_0 (poise) at 300° C. is added to a mold. Q=K・V_c＾−＾1＾. ^3^8・(η_1_3_
0_0) ^-^0^. ^5^8・Tm^-^1^. ^5
^8...[1]...1 However, K is a constant determined by the oscillation conditions of the template. (2) Claim (1) that the casting speed is 3 m/min or more
Continuous casting method of steel as described.