JPS5987962A - Continuous casting method - Google Patents

Abstract

PURPOSE:To obtain a high temp. billet which holds always a specified temp. even if the condition for cooling is changed in a curved type continuous casting machine by specifying the solidification rate at the point where spraying of water on the ingot ends. CONSTITUTION:The average temp. at the section of an ingot when it solidifies thoroughly varies with the condition for cooling the billet in a water spraying area if the solidification rate in the stage of ending the water spraying is >=60%. If, however, the solidification rate in the stage of ending the water spraying is <=60%, the average temp. at the section of the billet when it solidifies thoroughly is not affected at all by the condition for cooling the billet in the water spraying area and the billet holding always a suitable high temp. is obtd. The reason for limiting the solidification rate lies in that, if the solidification rate is <=60%, the enthalpy in the unsolidified part is substantially larger with respect to the enthalpy on the shell side and that the influence of the enthalpy on the shell side determined by the cooling condition in the water spraying area on the enthalpy over the entire part of the billet section is lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method suitable for a process in which a continuous casting machine is directly connected without passing through a heating process.

In recent years, continuous casting machines (hereinafter referred to as continuous casting machines) have been used in the steel industry.
Although the continuous casting ratio and the types of steel that can be continuously cast have shown remarkable progress, the requirements for continuous casting machines are also extremely high. Among these, there is a remarkable demand for energy conservation due to the recent rise in energy prices. Particularly in the continuous casting-rolling process, there is a particularly strong need for energy saving by directly connecting the continuous casting machine and rolling equipment.

In the steel industry, conventional continuous casting to rolling processes can be roughly divided into 370 processes shown in FIGS. 1(a), (b), and (c). Note that the steps in parentheses in FIG. 1 are not normally performed except for special needs. The process shown in Figure 1(a) has been widely practiced in the steel industry for some time.

Further, the hot charging process shown in FIG. 1(h) has been gradually put into practical use in the steel industry in recent years due to its remarkable energy saving properties. However, the development of the directly rolled Zorrocess shown in Figure 1(c) is strongly desired since the heating process is omitted except for special needs and no energy is required at that time. There is.

In the direct rolling process shown in Fig. 1(c), the continuous casting machine is required to have high productivity (high-speed casting), and the slabs cast by the continuous machine are defect-free. The essential conditions are that the temperature is high and stable.

As an effective means for obtaining this high-temperature slab, there is known an unsolidified reheating method, in which water injection is stopped until solidification is completed, and water injection is ended in an unsolidified state to perform recuperation. For example, special public service in 1973
In order to obtain defect-free high-temperature slabs, Japanese Patent No. 6974 proposes an unsolidified reheat casting method in which the solidification rate is set at 85 to 95% at the point where water injection is completed.

On the other hand, in the case of a curved continuous casting machine, which is the most popular type of continuous casting machine, the slab that has been primarily cooled in the mold is cooled for the second time by injecting water directly below the mold, which prevents surface flaws, internal cracks, etc., and ensures defect-free casting. In order to obtain a piece, water is poured from just below the mold to the end point of straightening, and the steel type and @
It is necessary to appropriately select the cooling conditions depending on the casting speed, slab size, etc.
It is also known to select cooling conditions suitable for the steel type, casting speed, and slab size within a range of about 30 degrees centigrade.

Furthermore, the relationship between the solidified embankment K (m/min2), the seal thickness d [++++nl] and the time t (mln) is as follows:
There is a relationship of 1/T with d-.

However, as mentioned above, in order to obtain defect-free slabs, the cooling conditions are set in the range of weak cooling to strong cooling (for example, solidification coefficient K = 25 to 30) depending on the steel type, casting speed, and slab size. Select a solidification rate of 85 to 95% at the point where water injection is completed.
When the unsolidified heat is recuperated, the temperature at the solidification completion point is 47. The average temperature of one cross section is affected, making it impossible to stably obtain high-temperature slabs.

That is, for example, the currently widely used 10.5 shown in FIG.
The solidification rate was 85- at high speed casting (1.7tj+/m1n) in a curved continuous slab casting machine with a standard arc radius of mH.
When performing unsolidified heat recuperation in section 95 (water injection length 3077Z - 70 inches for the total length of the aircraft, the water injection completion point is at the horizontal part 14 nz position), the cooling conditions of the injection area are -25 and 23.
The relationship between the distance from the meniscus and the average cross-sectional temperature of the slab shell in the case of 0 is shown in FIG. Further, the relationship between the cooling conditions and the average temperature of the slab cross section at the solidification completion point (approximately equal to the average temperature of the slab cross section at the machine end) is as shown in FIG. Furthermore, Fig. 3 also shows the change in solidification rate and (water injection length/captain length).

As shown in Figures 3 and 4, the average temperature of the slab cross section at the solidification completion point is greatly influenced by the cooling conditions, and in order to obtain defect-free slabs, the cooling conditions are from weak cooling (K=about 25) to strong cooling (K=about 30),
The water injection ratio is 0.7//! If selected within the range of 7 to 1.57/kli', the average temperature N of the slab cross section at the solidification completion point,
] The temperature varies from 240°C to 1160°C, making it impossible to stably obtain slabs with a high and uniform temperature.

Therefore, in order to obtain defect-free slabs, the present inventors determined the steel type,
We conducted various studies to establish a casting method that stably obtains high-temperature slabs regardless of the cooling conditions in the injection area, which are determined according to the casting speed and slab size. Focusing on the cooling rate, we performed heat transfer calculations and analyzed the solidification rate of the slab at the point where water injection is completed under each cooling condition during casting, and the average temperature of the slab cross section at the time of complete solidification. By setting the solidification rate at the solidification recuperation start point to 60 coefficients or less, the average temperature of the slab cross section at the solidification completion point is not affected by the cooling conditions in the injection area, and the recovery from the water injection completion point to the solidification completion point is It was found that the temperature depended only on the thermal conditions.

The present invention has been made based on the new findings described in ``-'', and the present invention is to recuperate unsolidified heat by reducing the solidification rate of continuously cast slabs to 60 degrees or less at one point when water injection is completed in a curved continuous casting machine. The feature lies in the continuous casting method.

Note that the recuperation conditions from the water injection completion point to the quasi-solidification completion point are different from the cooling conditions for the water injection area, and the above-mentioned steel types! 'd construction speed,
Regardless of the slab size, etc., the recuperation conditions can be kept almost constant, and the recuperation conditions are as follows.
For example, air cooling, external cooling with a heat insulating roll, etc. can be used as appropriate. Furthermore, the solidification rate in the present invention is expressed as (dX, +
d, ')/D.

The present invention will be explained in detail below.

Figure 5 shows a concrete example of the heat transfer calculation results of the slab solidification rate at the point of completion of water injection and the average cross-sectional temperature of the slab at the time of complete solidification under various cooling conditions during casting. The solidification rate at the time of completion is 60 inches or more, that is, the solidification rate at the completion point of conventional water injection is 85
In the unsolidified reheating casting method with ~95% solidification, the average temperature of the slab cross section at the time of complete solidification varies depending on the cooling conditions of the slab in the injection area, but if the solidification rate at the time of water injection is completed is 60% or less, it will not be completely solidified. The average cross-sectional temperature of the slab is not affected by the cooling conditions of the slab in the injection area, and is always ideally constant at the disease temperature (1280°C). In addition, Fig. 5 shows a slab thickness of 250 mm,
Cooling conditions: strong cooling (K = 30), weak cooling (K = 25), solidification rate at the completion of water injection O ~ 100%, recuperation conditions: Heat transfer meter results under various conditions of radiation cooling and recuperation be.

In addition, when changing the slab thickness, in the 200 system, the solidification rate at the end of water injection is constant at 60 cm or less and becomes higher than 1280 °C,
Similarly, at 300 mm, the temperature is constant at 1280°C below 60 inches.
It shows a tendency to become lower.

In addition, when changing the reheating conditions, in the case of heat retention, the coagulation rate tends to be constant at 60% or less and higher than 1280 °C, and in the case of external roll cooling, it tends to be constant at 60 coefficient or less and lower than 1280 °C. show.

By setting the solidification rate at the water injection completion point to 60% or less, even if the cooling conditions of the water injection area change, the average temperature of the slab cross section at the solidification completion point does not change and remains at a constant high temperature depending on the recuperation conditions. The reason may be as follows.

There is a small relationship between the enthalpy of the solidified shell side and the enthalpy of the unsolidified part at a specific solidification rate.When the solidification rate is 60 degrees or less, the enthalpy of the unsolidified part becomes sufficiently larger than the enthalpy of the shell side. It is thought that this is because the influence of the enthalpy on the solidified shell side, which is determined by the cooling conditions of the side enclaves, that is, the injection area, on the enthalpy of the entire slab cross section is reduced.

As detailed above, when the solidification rate at the water injection completion point is set to 60% or less, the section temperature at the end of the machine is not affected by the cooling conditions in the injection area, and in order to ensure defect-free slabs, the steel type size speed Even if the cooling conditions are changed and selected depending on the water injection 1jiQ, 3 pieces of high humidity can always be obtained stably.

In a curved continuous casting machine with single point correction of 10.5mR1, the above correction point is located at a distance of 165m from the meniscus, and for example, when the slab thickness is 250+mn1. Casting speed 1.
7 m/m + n, cooling condition range, -2 to solidification coefficient
5 to 30, and if the strong cooling condition, for example -30, is selected, the position of the unsolidified slab with a solidification rate of 60% will be 10.6 m from the meniscus, and the If it is solidified and heated, a constant high temperature slab can be obtained even if it is cast within the above cooling condition range.

However, since the unsolidified reheating starting point is a curved part before the straightening point and the molten steel static pressure is also large, the slab from the above-mentioned starting point to the straightening point is, for example, If bulging etc. are not reduced, there is a strong possibility that defects such as internal cracks will occur.

Therefore, even if the continuous casting method of the present invention is cast under the above-mentioned casting conditions, the solidification rate 60° position will be a horizontal part after the smoking point, and the static pressure of molten steel will be small, and the continuous casting method does not require a top support rock structure, which is known in itself. It is appropriate to use a curved continuous casting machine with a small arc radius of 6 to 3 mR.Next, the present invention will be described in detail.

Example 1 Standard arc radius 3mR, 4-point correction, continuous curved slab T1
In a casting machine, a slab with a thickness of 250 mm is cast at a speed of 1.7 m/
Even if the cooling conditions for the 211 slabs in the injection area are selected in the range of -25 to 30 depending on the steel type, the solidification rate of the slab at the point of completion of water injection will be lower than 60. In order to make it F, for example, set the water injection length to 7 from the solidification rate of 42 at -30.
1, the horizontal g1 of the water injection completion point of the water injection length of 77?1 above.
The 7 m water injection length is 16φ with respect to the aircraft length determined by -25.

Figure 6 shows the relationship between the distance from the meniscus and the average melt temperature of the slab shell cross section when casting the F4 slab in the above injection area under weak cooling (K = 25) and strong cooling (K = 30). ing.

Figure 6 also shows the changes in solidification rate and (water injection length/captain length). Also, -” Two words? , IE water J certain slab cooling conditions (from weak cooling -25 to strong cooling K = 3 +1, water injection ratio 0.
71Ag~1.57/! ? ) and the average temperature of the four-piece tilt surface at the completion of 7Q solidification is shown in Figure 7. Nahu-'
r: +", as is clear from Figure 6, 4E71 at -25 (the solidification rate at the completion point is 34% below 60 cm)
It becomes.

Example 2゜Reference arc radius 6mR, 4-point curved 4fi 17 slab 1!1 A cast slab with a thickness of 250++ m was cast using a casting machine. ? / When casting with ITI f n, the steel type V is 7 + water.

Even if the cooling conditions for the slab are selected in the range of 25 to 30 with a solidification coefficient of 73, in order to keep the 6-1 ratio of the slab at the point where water injection is completed to 60 or less, it is necessary to set the solidification coefficient to -30, for example. The water injection length was set to 10.5 m based on the coagulation rate of 60.

The water injection completion point for the water injection length of 105 m above is at the 1 m horizontal part of the continuous casting machine, which is 10.57 m. ? Water injection length is K
= 25% of the total captain determined by 25.

Figure 8 shows the relationship between the distance from the meniscus and the average cross-sectional temperature of the slab shell when casting under weak cooling (K = 25) and strong cooling (K = 30) in the above injection area. It shows.

Figure 8 also shows the changes in solidification rate and (water injection length/captain length). In addition, the slab cooling conditions of the above injection area (weak cooling from -25 to strong cooling = 30, water injection ratio 0.7 n / 9 to t, s7
/kg) and the average temperature of the slab cross section at the completion of solidification.
As shown in the figure. As is clear from FIG. 8, the solidification rate at the point where the water injection is completed at -25 is 46, which is less than 60%.

As is clear from FIGS. 6 to 9 above, according to the continuous casting method of the present invention, the average temperature of the slab cross section at the time of complete solidification is approximately 1.2 .8 (1℃
It becomes constant.

This average cross-sectional temperature of the slab is 1280'Ct. In an extreme case, if the cooling in the injection area is done only by letting it cool (K = about 22.5), the average temperature of the slab cross-section at the time of complete solidification is This agrees with the calculated value of , which is the ideal and extreme temperature.

As detailed above, according to the continuous casting method of the present invention, in order to obtain defect-free slabs, the cooling conditions in the injection area, which are selected according to the steel type, casting speed, and slab size, are affected. Therefore, it is possible to stably obtain a constant, ideal, extremely high temperature slab, and the direct rolling process can be easily realized.

[Brief explanation of drawings]

Figure 1 (a), (b), and (c) are conventional continuous casting ~
A diagram showing the rolling process. Figures 2, 3, and 4 are explanatory diagrams of the shortcomings of the conventional continuous casting method. Figure 5 is a diagram showing the casting process at the completion point of water injection using the slab cooling conditions in the injection area as a parameter. Figures 6, 7, 8, and 9 are explanatory diagrams of the relationship between the piece solidification rate and the -j piece cross-sectional average temperature at the time of completion of solidification, and are explanatory diagrams of the implementation results of the continuous casting method of the present invention. be. (、Mu Q Tomo) Life J Funansho & S Arubi's Hainumuka Zenno 3 Eno to Kabutocho Nichiji Temple's 2nd day L Toriken (%) (tsu.)'J1g<Regi 11r 4 (%) )K times [z:','y, 7 Tomata 1 Figure 9 weak 1;'F leaving PB*y K("=z-Ai'
%)=J! ;+('). )WWrIBfi'l/T,/
:(%) Zaiko Rokugo 33

Claims (1)

[Claims] A continuous casting method characterized by reducing the solidification rate of continuously cast slabs to 60% or less at the point of completion of water injection in a curved continuous casting machine.