JPH0413455A - Method for continuously casting steel - Google Patents

Abstract

PURPOSE:To prevent breakout, to uniformize thickness of solidified shell in a cast slab and to improve surface quality by detecting developing abnormality of the solidified shell with a third thermometer group set at a third position and executing control for decelerating casting velocity of forcing mold cooling, etc. CONSTITUTION:Based on detected signal from a first thermometer group 41, 42, starting point of solidification in molten steel in the mold 52 is obtd. with a computer 7 and further, based on detected signal from a second thermometer group 43, the thickness of solidified shell 12 in the cast slab 1 at the time of passing through a second position P2 is obtd. Based on the calculated values obtd. in such way, the thickness of solidified shell in the cast slab passed through a fourth position P4, is predicted with the computer 7. Based on this predicted thickness of solidified shell, cooling intense in a cooling unit 6 is controlled. Based on the detected signal from the third thermometer group 4, the developing abnormality of solidified shell in the cast slab is detected and a control signal is transferred to a casting velocity control unit 8 from the computer 7 to control the casting velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for continuous casting of steel using a method for predicting the solidified shell thickness of slabs.

(b) Prior Art Continuous casting molds usually have a length of 600 to 120 On+n, and the inner wall of the mold is made of a material with high thermal conductivity, such as copper or copper alloy.

When casting is performed using such a mold, the molten steel is indirectly cooled by a cooling medium (e.g. water) supplied inside the mold wall, and solidification progresses gradually from the part in contact with the mold wall, forming a solidified shell. As the thickness of the solidified steel grows to the extent that it can withstand the hydrostatic pressure of the internal molten steel, the solidified shell will contract, creating voids between the mold wall solidified shells.

In particular, in a mold with a rectangular cross section, the solidified slab shell in contact with the center of the broad wall of the mold tends to bulge outward due to the internal temperature control pressure, and is likely to come into relatively good contact with the mold wall surface.
At the end of the wide side of the mold and at the bottom of the narrow side of the mold, voids tend to be noticeable.

This generation of voids significantly reduces the heat conduction efficiency from the slab to the mold wall, greatly inhibits the growth of the solidified shell of the slab, and causes quality defects such as surface cracking due to uneven thickness of the solidified shell. This is often a major cause of breakout due to damage to the solidified shell. This is a major fundamental problem with the current continuous casting equipment, and is the biggest obstacle to achieving high-speed casting.

Therefore, the applicant has improved the above problem and added indirect and
In order to have a direct cooling function and only use indirect cooling in the event of abnormal solidified shell formation to achieve stable continuous casting, a first water channel is provided in the mold copper plate facing the slab to indirectly cool the slab. , a second waterway for directly cooling the slab is provided in the copper plate separately from the first waterway, a water supply cutoff valve is provided in the second waterway, and a thermometer detects the surface temperature of the slab. is arranged at a predetermined position in the copper plate, and a plurality of vertical grooves for steam release are formed on the surface of the casting side of the copper plate, and using the mold, the above-mentioned detecting abnormalities in the formation of solidified slab shells with a thermometer;
We have proposed a method for continuous casting of steel, which comprises cutting off the water supply to the second waterway and lowering the casting speed to a predetermined speed when a production abnormality is detected (Japanese Patent Application No. 25722/1999).

In this continuous casting method, a thermometer 4 shown in FIG. 10 is used to detect abnormal formation of the solidified slab shell, thereby preventing breakouts, steam explosions, etc. However, while this temperature measurement is effective for preventing operational troubles, it is also useful for controlling cooling to improve surface quality, i.e. to uniformize shell growth when initially solidified shells are formed unevenly. It was insufficient.

(c) Problems to be solved by the invention The problem to be solved by the present invention is not only to prevent breakouts and steam explosions in continuous casting of steel, but also to prevent the meniscus of the steel at a temperature inside the mold. The purpose of this method is to predict the formation status of a solidified shell between reference positions on the downward side in the casting direction, and to control cooling of the slab below from the reference position based on this predicted value, thereby obtaining a slab with a sound surface quality.

(d) Means for Solving the Problems The continuous steel casting method of the present invention provides a first position in the vicinity of the top and bottom outside the molten steel meniscus fluctuation area in a mold for continuous steel casting, and a downstream side of the first position in the direction of slab movement. A first and second thermometer group for detecting the mold-like copper plate temperature is provided at a second position, respectively, and a third thermometer group is provided at a third position at a predetermined location other than the above-mentioned two positions.
Thermometer groups are provided, and a cooling unit for controlling the solidified slab thickness is provided at a fourth position further downstream than the third position. Determine the solidified shell thickness of the slab when passing the second position,
A slab that passes through the fourth position based on the detection signal from the third thermometer group to detect an abnormality in solidified shell formation in the slab, and based on calculated values obtained by the first and second thermometer groups. predicting the solidified shell thickness of the cooling unit, and controlling the cooling intensity of the cooling unit based on the predicted solidified shell thickness;
The above-mentioned problem is solved by controlling the casting speed based on the solidified shell formation abnormality detected from the third thermometer group.6 The first and second thermometer groups are arranged in the direction of heat flow in the mold. It is preferable that the thermometers each include a pair of thermometers whose detection ends are shifted from each other.

(E) Function In the continuous steel casting method of the present invention, in order to predict the solidified shell thickness of a slab, the position above the highest value and the lowest value during the fluctuation of the melt level during pouring in the mold are used to predict the solidified shell thickness of the slab. 1st in the lower position
A position is taken and a first group of thermometers is installed there. moreover,
Two second thermometer groups are placed at a second position below this, each extending at a predetermined distance in the heat flow direction within the water-cooled copper plate.

By maintaining the meniscus position between the first thermometer positions, the thickness of the solidified shell formed between the first thermometer position below the meniscus can be calculated using the hot water level value. Next, the thickness of the solidified shell formed between the first and second thermometer placement positions 1 can be calculated in the same manner. Here, by arranging the first thermometer at the upper and lower positions outside the meniscus, it becomes possible to accurately predict the heat flux of the meniscus. Furthermore, by arranging two thermometers shifted in the heat flow direction, the heat flux at this position can be directly determined. Since the calculation time required to calculate the solidified shell thickness can be significantly reduced, control using a general-purpose personal computer is possible.

The thermometer group provided at the second reference position is essential for calculating the solidified shell thickness between the first and second thermometer positions 1. If the interval between the first and second temperature measurement positions is longer than 1, or if there is a hot water supply flow line from the immersion nozzle within this section,
In order to improve the accuracy of calculating the solidified shell thickness within this section, it is effective to add more temperature measurement positions.

When determining the reference point position (second position), it is necessary to consider conditions such as the heat transfer characteristics of the mold used, casting speed, solidified shell thickness calculation speed, and cooling control response speed. A reference position is provided.

The present invention is effective in a continuous casting method in which the cooling conditions can be arbitrarily controlled at the fourth position below the reference position based on the solidified shell thickness information. It is effective not only for the above-mentioned continuous casting mold, but also for ordinary continuous casting methods where similar control is possible in the secondary cooling zone near the mold outlet. It is sufficient if any part of the slab can be controlled to be strongly cooled, weakly cooled, etc. Further, the number of cooling condition control parts can be arbitrarily set so as to obtain an effect depending on casting conditions, steel type, etc. A third thermometer group provided at the third position detects an abnormality in solidified shell formation, and performs controls such as slowing down the casting speed or strengthening mold cooling.

(f) Example Before explaining the continuous casting method of steel of the present invention, the continuous casting method disclosed in the above-mentioned patent application filed by the present applicant, on which the present invention is based, will be explained.

As shown in FIG. 10, the continuous casting mold is provided with a first water #121 that indirectly cools the slab 1 in the mold copper plate 2 facing the slab 1, and is separate from the first water 1121. A second water channel 22 is provided in the copper plate 2 to directly cool the slab 1. A water supply cutoff valve 3 is provided in the second waterway 22. A thermometer 4 for detecting the surface temperature of the slab 1 is placed at a predetermined position within the copper plate 2. A plurality of strips 24 for releasing water vapor are formed on the casting side surface 23 of the copper plate 2.

The copper plate 2 is fixed to the back plate 5 with bolts. The output of thermometer 4, which consists of a conventional thermocouple, is calculated by W&
7 is input. The water supply cut-off valve 3 is actuated by a conventional hydraulic cylinder 31. The control signal from computer 7 is
It is sent to the casting speed control device 8 and the cylinder 31.

The detection signal from thermometer 4 is sent to calculation 817, and slab 1
The production abnormality of the solidified shell 12 is determined.

When the solidified shell generation is abnormal, a control signal is sent to the fluid pressure cylinder 31 to close the water supply cutoff valve 3. At the same time, the calculation 617 sends a speed control signal to the casting speed controller 8 to stop or slow down the casting.

Next, an embodiment of the continuous steel casting method of the present invention will be described with reference to FIGS. 1 to 9.

As best shown in FIG. 1, the continuous steel casting method of the present invention includes a first position P1 in the vicinity of the top and bottom outside the fluctuation range of the molten steel meniscus 11 in the continuous steel casting mold 52, and Second position P on the downstream side in the traveling direction of the slab 1
2 and a first thermometer group 41, 42 that detects the temperature of the copper plate 2.
and a second thermometer group 43 are provided.

A third thermometer group 4 is provided at a third position P3 at a predetermined location other than the first position P1 and the second position ffP2.

Even lower than that third position P3? Fourth position P4 on the L side
A cooling unit 6 for controlling the solidified slab layer is installed in the cooling unit 6.

The first thermometer group 41, 42 and the second thermometer group 43, for example, with respect to the thermometer group 41, as shown in FIG. Provided. The same applies to the thermometer groups 42 and 43. In plan view, as shown in FIG. 3(A), the mold 52
For example, as shown in FIG. 4, they are placed at a plurality of locations along the side wall of the mold 52 at predetermined intervals along the copper plate 2 .

The third thermometer group 4 is provided individually at predetermined intervals, as shown in FIG. 3(B). The surroundings of the side walls of the mold are also arranged as shown in FIG.

As shown in FIG. 6, the cooling knit 6 includes a combination of a water-cooled molded copper plate and direct cooling (A), a water-cooled molded copper plate only (B),
Direct cooling water injection only<C) may be used.

In the case of direct cooling water injection, it is preferable to provide a cooling water injection nozzle 61 and arrange it around the slab 1, as shown in FIG. In this case, each of the nozzles 61 can independently adjust the amount of water, and can increase or decrease the amount of water in response to a flow rate control command. These spray bands, which can be individually controlled in flow rate, are arranged in five stages in the casting direction, and the spray bands below this have no nozzles on the short sides, and the long sides can also be controlled with a fixed amount of water for each side. That's how it is.

In the method of the present invention, the solidification start point of molten steel in the mold 52 is determined by the computer 7 based on the detection signals from the first thermometer group 41 and 42, and the solidification start point of the molten steel in the mold 52 is determined based on the detection signals from the second thermometer group 43. Based on this, the thickness of the solidified shell 12 of the slab 1 when passing through the second position P2 is determined. The cooling intensity of the cooling unit 6 is controlled based on the predicted solidified shell thickness in which the solidified shell thickness of the slab passing through the fourth position P4 is predicted by calculation 87 based on the calculated value thus obtained.

For example, as shown in FIG. 8, when the thickness of the predicted solidified shell 12 is uneven, the cooling intensity is adjusted.
A substantially uniform solidified shell 12 is obtained (B).

Based on the detection signals from the third thermometer group, an abnormality in solidified shell formation of the slab is detected, and a control signal is sent from the computer 7 to the casting speed control device 8 to control the casting speed.

Next, specific examples of the method of the present invention will be described.

FIG. 2 shows the position of the thermometer for predicting the solidified shell thickness according to the present invention. Thermometer group 41.4 for predicting solidified shell thickness
2.43 is attached at a position 56 degrees in from the surface of the casting side of the water-cooled copper plate 2, and the other is attached at a position 15 degrees in from the surface of the cast side of the water-cooled copper plate 2. Therefore, the displacement interval e of the detection ends is set to 10 degrees.6 The arrangement position of the slab 1 in the casting direction is as shown in Fig. 5, with the first upper position P1 being 100 mm from the upper end of the mold. Set fP1 to 150 degrees and set the second position P2 to 500 degrees.

In the circumferential direction of the mold, as shown in FIG. 4, it is attached at the center of the width of the long and short sides, and at a position 401+ltl from the short side of the long side. Note that the thermometer 4 in the figure is for detecting an abnormality in the formation of a solidified shell, and is mounted at a position 5 degrees below the surface.

All the signals of thermometers 4.41.42.43 are taken into calculation a7. The computer 7 mainly generates two secondary leg commands, one of which is a casting speed reduction command when an abnormality in solidified shell production is detected, and the other is a command to reduce the casting speed when an abnormality in solidified shell production is detected, and the other is a command to reduce the casting speed according to the predicted solidified shell thickness according to the present invention. This is a command to increase or decrease the amount of water in the water cooling unit 6.

In this embodiment, the water supply system including the water supply cutoff valve 3 of the prior art described above is used as the water cooling unit 6.

Using a vertical test continuous casting machine, slab size 80 rn+
A 400 rm mini-slab was cast at a casting speed of 2.5 n/min.
Do not cast using low viscosity powder. Table 1 shows the composition of the sample steel. The test results are shown in No. 9 []. Immediately after reaching the target casting speed, pouring is performed by intentionally varying the level of the molten metal to generate a solidified shell non-uniformly, and then changing the operating method as described below. In FIG. 9, the signal (A> is the result of casting without controlling the spray water flow rate under normal conditions, based on temperature information for detecting solidified shell generation abnormalities, and the signal (B) was cast by controlling the spray water flow rate based on the predicted solidified shell thickness.

Table 1 Molten Steel Composition In the case of the above operation method (A), as shown in Fig. 9 (A), although good results were obtained in terms of ensuring operational stability, there were variations in surface quality. This made it impossible to obtain high-quality slabs.

CB>, by applying the mold shell thickness prediction method shown in the present invention, the shell thickness, which was uneven within the mold, can be made uniform by controlling the amount of spray water, and a healthy, high-quality slab can be produced. Benefits: (g) Effects According to the method of the present invention, it is possible not only to prevent breakout, which has been a conventional operational trouble, but also to make the thickness of the solidified shell of the piece uniform and to improve the surface quality. You can try to improve.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the continuous steel casting method of the present invention. Second
The figure is a side view showing an example of a thermometer used in the method of the present invention. FIG. 3 is a plan view of an example of the arrangement of thermometers. FIG. 4 is an explanatory diagram of an example of thermometer installation around the mold. FIG. 5 is an explanatory diagram of an embodiment of the method of the present invention. FIG. 6 is a plan view showing a cooling unit for slabs used in the method of the present invention. Figure 7 is the 6th
The side view of figure (C) and FIG. 8 are explanatory views of the cooling mode. FIG. 9 is a graph showing the effects of the present invention, and FIG. 10 is an explanatory diagram of the prior art continuous casting method. 1: @ Piece 2; Copper plate 3: Water supply cutoff valve 4: Thermometer 5: Back plate 6: Water cooling unit 11: Meniscus 12: Solidified shell 21: First water channel
22: Second power waterway 31: Fluid pressure cylinder 41. 42. 43: Thermometer 1 Figure 3 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a mold for continuous casting of steel, the surface temperature of a slab is detected at a first position near the top and bottom outside the molten steel meniscus fluctuation area and at a second position downstream from the first position in the direction of slab movement. First thing to do
and a second thermometer group, and a third thermometer group is provided at a third position at a predetermined location other than the two positions, and the third thermometer group
A cooling unit for controlling the solidification thickness of the slab is provided at a fourth position further downstream from the position, and the cooling unit controls the solidification of the slab when it passes through the second position based on the detection signals from the first and second thermometer groups. The shell thickness is determined, an abnormal solidified shell formation of the slab is detected based on the detection signal from the third thermometer group, and the fourth position is determined based on the calculated value obtained by the first and second thermometer groups. predicting the solidified shell thickness of the slab passing through, controlling the cooling intensity of the cooling unit based on the predicted solidified shell thickness, and controlling the casting speed based on the solidified shell formation abnormality detected from the third thermometer group. A continuous steel casting method characterized by control. 2. The method according to claim 1, wherein the first and second thermometer groups each include a pair of thermometers whose detection ends are shifted in the direction of heat flow within the mold.