JP2016034651A - Continuously cast slab surface cracking determination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuously cast slab surface cracking determination method capable of appropriately determining the probability of the generation of surface cracking in continuously cast slabs from a downstream malfunction of a flow regulating valve for secondary cooling water.SOLUTION: A downstream water pressure and a downstream quantity of water of a flow regulating valve at a time of continuous casting at which no surface cracking occurs to continuously cast slabs S are detected per secondary cooling zone to set a water pressure-water quantity reference line L representing a relation between the downstream water pressure and the downstream quantity of water of the flow regulating valve, and a water pressure-water quantity reference area A is set by adding or subtracting a double value σ of a standard deviation σ of a pressure difference for the water pressure-water quantity reference line L downstream of the flow regulating valve to or from the water pressure-water quantity reference line L. If the downstream water pressure and the downstream quantity of water of the flow regulating valve detected at the time of the continuous casting deviate from the water pressure-water quantity reference area A, it is pointed out that surface cracking may occur to the continuously cast slabs S at the time of the continuous casting. If the surface cracking does not occur to the continuously cast slabs to which it is pointed out that the surface cracking may occur, the water pressure-water quantity reference area A is updated and set.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for determining the possibility of surface cracks occurring in a continuous cast piece produced by continuous casting, and in particular, surface cracks may occur in the continuous cast piece during continuous casting or immediately after continuous casting. It is suitable for determining sex.

  In continuous casting of steel, the molten steel in the ladle is poured into the mold from the tundish, the poured molten steel is cooled in the mold to form a solidified shell, and water is sprayed with a spray nozzle while gradually drawing out the solidified part with a roll. The solidified shell is gradually thickened by spraying and cut from the solidified part to obtain a continuous cast piece (also called a steel piece). The mold is cooled with water, and the cooling of the molten steel by the mold is called primary cooling, and the spraying of water by the spray nozzle is called secondary cooling. Generally, the secondary cooling is divided into a plurality of zones in the casting direction, and a flow rate adjusting valve for adjusting the flow rate of water to the spray nozzle is provided for each zone. When the flow rate of the secondary cooling water is insufficient, cracks occur on the surface of the continuous cast piece. Therefore, in Patent Document 1 below, clogging in the nozzle tip, header, and piping of the spray nozzle is detected by measuring the valve opening and flow rate of the flow rate adjustment valve of the secondary cooling water. Further, in Patent Document 2 below, the pressure (back pressure) and flow rate of the secondary cooling water are measured, and the spray nozzle such as clogging of the spray nozzle or dropping of the nozzle tip is determined based on the combination of the differences from the respective reference values. Abnormalities are detected by type.

JP 2006-175465 A JP 2013-35027 A

  However, in Patent Document 1, when the water pressure on the upstream side of the flow rate adjustment valve changes, the valve opening relative to the reference flow rate changes according to the change even if the spray nozzle is normal. Abnormalities cannot be accurately determined. Moreover, in patent document 2, when the pressure and flow volume of secondary cooling water exceed a reference line, it is considered that the spray nozzle is abnormal. Although this reference line is considered to be important for determining the quality of the continuous cast piece, since the specific setting method is not described, it is impossible to accurately determine the abnormality of the spray nozzle. . That is, none of the spray nozzle determination methods can accurately determine the abnormality of the spray nozzle, and thus cannot properly determine the possibility of surface cracking in the continuous cast piece.

  The present invention has been made paying attention to the above-mentioned problems, and appropriately determines the possibility of surface cracks occurring in the continuous cast piece from the trouble on the downstream side of the flow rate adjustment valve of the secondary cooling water. An object of the present invention is to provide a method for determining the surface crack of a continuous cast piece.

  In order to solve the above problems, according to one aspect of the present invention, the secondary cooling after the primary cooling by the mold is divided into a plurality of zones, and the flow rate of water to the spray nozzle is set for each of the secondary cooling zones. A method of determining the possibility of surface cracks occurring in a continuous cast piece when a flow rate adjusting valve to be adjusted is provided, wherein the flow rate during continuous casting does not cause surface cracks in the continuous cast piece A water pressure-water quantity reference line representing the relationship between the downstream water pressure and the downstream water volume of the flow regulating valve is set for each secondary cooling zone by detecting the downstream water pressure and downstream water volume of the regulating valve for each secondary cooling zone. Calculating a standard deviation of the pressure difference of the water pressure downstream of the flow rate adjustment valve with respect to the water pressure-water amount reference line for each secondary cooling zone, and the water pressure-water amount reference line is twice the pressure difference standard deviation Water pressure-water volume standard by adjusting the value A step of setting a zone for each secondary cooling zone, and the flow rate adjusting valve downstream water pressure and downstream water amount for each secondary cooling zone detected during continuous casting are set for each secondary cooling zone A method for determining the surface crack of a continuous cast piece, comprising the step of indicating that a surface crack may have occurred in the continuous cast piece during the continuous casting when the water pressure-water amount reference region is deviated. The

  According to the method for determining surface cracks of a continuous cast piece of the present invention, it is possible to accurately detect a failure on the downstream side of the flow rate adjustment valve of the secondary cooling water, and based on this, surface cracks may occur in the continuous cast piece. Sex can be determined appropriately.

It is a schematic block diagram which shows one Embodiment of the continuous casting installation to which the surface crack determination method of the continuous cast piece of this invention was applied. It is explanatory drawing which shows 1 zone of the secondary cooling provided in the continuous casting installation of FIG. It is a flowchart which shows the arithmetic processing of the continuous cast piece surface crack determination method performed by the computer of FIG. It is explanatory drawing of the water pressure-water quantity reference | standard area | region obtained by the arithmetic processing of FIG. It is explanatory drawing of the water pressure-water quantity reference | standard area | region obtained by the arithmetic processing of FIG.

  Next, an embodiment of the method for determining surface cracks of a continuous cast piece of the present invention will be described with reference to the drawings. FIG. 1 shows a part of a continuous casting facility to which the surface crack determination method is applied, and a mold 1 is arranged at the top of FIG. A tundish and ladle (not shown) are arranged above the mold 1, and molten steel in the ladle is poured into the mold 1 from the tundish. The mold 1 is water-cooled, and of the molten steel in the mold 1, the outer shell portion in contact with the mold 1 is solidified to form a solidified shell. When the solidified shell is formed in the molten steel in the mold 1, the solidified shell portion is lowered while vibrating the mold 1, and is gradually pulled out by the roll 2. In that case, secondary cooling is performed by spraying water from the spray nozzle 3 arranged around the casting line. In the secondary cooling, the solidified shell becomes thicker and the molten steel eventually solidifies. The continuous cast piece S that has been solidified is cut and sent to a process such as rolling.

  Secondary cooling is performed by spraying water from a spray nozzle 3 disposed between the continuous casting piece drawing rolls 2. And this secondary cooling is divided | segmented into the some zone along the casting line, and is connected to the cooling water supply piping 4 for every zone. A flow rate adjusting valve 5 for adjusting the flow rate of water sprayed from the spray nozzle 3 is provided at the most upstream portion on the cooling water supply pipe side in the secondary cooling zone. An air pipe 7 is connected to the upstream side of the spray nozzle 3 through a mixing unit 6. Air supplied from the air pipe 7 is mixed in the mixing unit 6, and atomized water is supplied from the spray nozzle 3. Be injected. Further, on the downstream side of the flow rate adjustment valve 5, a pressure gauge 8 and a flow meter 9 are used to detect the downstream pressure (water pressure) and the downstream flow rate (water amount) of the flow rate adjustment valve of water supplied from the flow rate adjustment valve 5. Is arranged. In addition, the flow rate adjusting valve downstream water pressure and the downstream water amount are stored at regular intervals, for example, every second by a computer described later.

  The continuous casting equipment including the secondary cooling equipment is controlled by the computer 10. As is well known, the computer 10 is a computer having an advanced arithmetic processing function, and is capable of controlling not only the calculation but also the operating state of the equipment and the driving state of the actuator. In this embodiment, in addition to the state control of the apparatus, the computer 10 performs the arithmetic processing shown in the flowchart of FIG. 3 in order to determine the possibility of surface cracks occurring in the continuous cast piece. This calculation process is executed based on the operation input of the operator after a continuous cast piece is obtained by continuous casting. First, in step S1, the water pressure-water amount for each secondary cooling zone (hereinafter also simply referred to as a zone). It is determined whether or not the reference area A has been set. If the water pressure-water quantity reference area A for each zone has been set, the process proceeds to step S6. If not, the process proceeds to step S2.

  In step S2, among the stored flow control valve downstream water pressure and downstream water amount, the flow control valve downstream water pressure and downstream water amount in each zone at the time of continuous casting where surface cracks were not detected in the continuous cast piece were determined. The process proceeds to step S3 after reading in order from the oldest specified value (for example, 10 points) set in advance. Here, the downstream flow pressure adjustment valve downstream water pressure and downstream water volume data to be read are, for example, retroactive to the time when one of the cut continuous cast pieces was in a specific secondary cooling zone. The statistical processing (for example, the average processing) is performed on a plurality of data stored by the computer at regular intervals between the time when the leading edge of the steel plate reaches the inlet of the zone and the time when the trailing edge of the continuous cast piece passes through the outlet of the zone. ) To give one point.

In step S3, a water pressure-water volume reference line L representing the relationship between the downstream pressure and downstream water volume read in step S2 is set for each zone by, for example, the least square method, and then the process proceeds to step S4. Transition.
In step S4, the pressure difference of the water pressure downstream of the flow rate adjustment valve read in step S2 is obtained with respect to the water pressure-water amount reference line L set in step S3, and the pressure difference standard deviation σ is calculated for each zone from the pressure difference. Then, the process proceeds to step S5.
In step S5, the water pressure-water volume reference line L of each zone set in step S3 is adjusted to a double value 2σ of the pressure difference standard deviation σ of each zone calculated in step S4 to adjust the water pressure-water volume reference area A ( = L ± 2σ) is set for each zone, and then the process proceeds to step S6.

In step S6, the downstream side water pressure and the downstream water amount in each zone at the time of the current continuous casting are read.
Next, the process proceeds to step S7, and whether or not the downstream side water pressure and the downstream water amount in each zone at the time of the current continuous casting read in step S6 are out of the water pressure-water amount reference region A of each zone. If the flow rate adjustment valve downstream water pressure and downstream water amount are out of the water pressure-water amount reference region A, the process proceeds to step S8, and otherwise returns.
In step S8, an inspection of the corresponding continuous cast piece is instructed on the assumption that there is a possibility of surface cracks occurring in the continuous cast piece during the current continuous casting.

Next, the process proceeds to step S9, where it is determined whether or not the inspected continuous cast piece has surface cracks. If the inspected continuous cast piece has no surface cracks, the process proceeds to step S10. Will return.
In step S10, the water pressure-water quantity reference line L representing the relationship between all the flow regulating valves downstream water pressure and downstream water quantity including the downstream regulating water pressure and downstream water quantity at the time of this continuous casting is set to, for example, a minimum of two. Update setting for each zone by multiplication method.
Next, the process proceeds to step S11, and the pressure difference standard deviation σ is calculated for each zone from the pressure differences of all the flow rate adjusting valve downstream water pressures with respect to the water pressure-water amount reference line L updated and set in step S10.
Next, the process proceeds to step S12, and the double pressure value 2σ of the pressure difference standard deviation σ calculated in step S11 is adjusted to the water pressure-water amount reference line L of each zone updated and set in step S10. -The water amount reference area A (= L ± 2σ) is updated for each zone and then returned.

  In this calculation process, when the water pressure-water amount reference area A is not set, out of the stored flow rate adjusting valve downstream side water pressure and downstream side water amount, the surface crack in the continuous casting piece was not detected during continuous casting. The downstream pressure and downstream water pressure of the flow rate adjustment valve in each zone are read in ascending order of the predetermined value set in advance, and the water pressure-water amount reference line L representing the relationship between the downstream pressure and downstream water amount of these flow rate adjustment valves is set to the minimum two. Set for each secondary cooling zone by multiplication. When the water pressure-water amount reference line L is set, the pressure difference of the water pressure downstream of the flow rate adjustment valve with respect to the water pressure-water amount reference line L is obtained, and the pressure difference standard deviation σ is calculated for each secondary cooling zone. Then, the water pressure-water amount reference line L is adjusted by a value 2σ which is twice the standard difference σ of the pressure difference to set a water pressure-water amount reference region A (= L ± 2σ) for each secondary cooling zone. As is well known, most of the referenced data is included in a reference area obtained by adding or subtracting twice the standard deviation of data from a reference line obtained from a plurality of data by the least square method.

  Therefore, in this calculation process, the flow rate adjustment valve at the time of the present continuous casting from the water pressure-water amount reference area A of each zone set by adding or subtracting the double value 2σ of the pressure difference standard deviation σ to the water pressure-water amount reference line L. When the downstream water pressure and the downstream water amount are out of the range, the inspection is instructed that there is a possibility of surface cracks occurring in the continuous cast piece. As a result of the inspection, if a surface crack has occurred in the continuous cast piece at the time of the current continuous casting, the arithmetic processing is terminated and the process returns. On the other hand, as a result of the inspection, if there is no surface cracking in the continuous cast piece during the current continuous casting, the number of sampled data is insufficient, All the flow rate adjustment valves downstream side water pressure to which the side water amount has been added and the water pressure-water amount reference line L representing the downstream water amount are updated and set. Once the water pressure-water volume reference line L is updated and set, the pressure difference standard deviation σ of all the flow control valve downstream water pressures with respect to the water pressure-water volume reference line L is obtained, and further, the pressure difference standard deviation on the water pressure-water volume reference line L The water pressure-water quantity reference region A is updated and set by adjusting the double value 2σ of σ.

  Next, as an example of the method for determining the surface crack of the continuous cast piece of the present invention, [C] = 0.07 wt% to 0.20 wt%, [Si] = 0.00 wt% to 0.40 wt%, [Mn] = 0.30 wt% to 2.00 wt%, [P] = 0.000 wt% to 0.030 wt%, [S] = 0.000 wt% to 0.010 wt%, [Al] = 0.010 wt% to. Continuous casting pieces of 050 wt%, [N] = 0 ppm to 60 ppm were continuously cast using a continuous casting facility having a heat size of 300 ton / heat. The type of continuous casting equipment is vertical bending die, vertical part 3m, curved part radius 10m, machine length 45m, continuous casting piece thickness is 220mm ~ 370mm, continuous casting piece width range is 900mm ~ 2500mm, continuous casting speed is 3 m / min or less. The secondary cooling is atomized jet by air mixing, and the number of secondary cooling zones is 20 zones / strand including the reference surface and the anti-reference surface.

  Among the secondary cooling zones, in the third zone on the side opposite to the reference surface (1.5 m to 3.0 m from the meniscus to the casting direction), the hydraulic pressure-water amount reference set in step S3 of the arithmetic processing in FIG. An example of the line L and the water pressure-water quantity reference area A set in step S5 is shown in FIG. As can be seen from the figure, the initially set water pressure-water amount reference area A is narrow. Further, in the same third zone, after the calculation process of FIG. 3 is repeated many times from the state of FIG. 4, the water pressure-water quantity reference line L set in step S10 and the water pressure-water quantity reference region set in step S12. An example of A is shown in FIG. As is clear from the figure, the sufficient water pressure-water amount reference region A after continuous casting is wide and does not include surface crack defects in the middle, so that it is continuous in the sufficient water pressure-water amount reference region A after continuous casting. It becomes possible to detect the surface crack of a cast piece appropriately.

  In this embodiment, the surface crack inspection instruction rate of the continuous cast piece when the 100 heat continuous casting is carried out with the water pressure-water amount reference area A set in step S5 of the arithmetic processing of FIG. (Continuous cast piece) The number of occurrences of surface cracks in the continuous cast piece was 5.17% with the number of denominators as the denominator, and the occurrence rate was 0.31% with the total number of slabs of 100 heat as the denominator ( It will be judged as an example 1. Next, in step S12 of the calculation process of FIG. 3, when 100-heat continuous casting is performed separately from the determination example 1 while updating and setting the water pressure-water amount reference area A obtained with the same number of data as the determination example 1. The surface crack inspection instruction rate of the continuous cast piece was 1.72%, and the rate of occurrence of surface cracks in the continuous cast piece was 0.30% (judgment example 2). By updating and setting the water pressure-water amount reference region A, the surface crack inspection instruction rate can be reduced, and the efficiency of continuous casting can be improved accordingly.

  As described above, in the surface crack determination method of the continuous cast piece of this embodiment, the secondary cooling is divided into a plurality of zones, and the flow rate of water to the spray nozzle 3 is adjusted for each secondary cooling zone. When the flow control valve 5 is provided, the possibility of surface cracks occurring in the continuous cast piece S is determined. At that time, the flow rate regulating valve downstream water pressure and downstream water amount during continuous casting in which surface cracks do not occur in the continuous casting piece S are detected for each secondary cooling zone, and the flow regulating valve downstream water pressure and downstream water amount are detected. A water pressure-water quantity reference line L representing the relationship is set for each secondary cooling zone. In addition, the standard deviation σ of the pressure difference with respect to the water pressure-water amount reference line L of the water pressure downstream of the flow control valve is calculated for each secondary cooling zone, and the double value 2σ of the pressure difference standard deviation σ is set to the water pressure-water amount reference line L. The water pressure-water volume reference area A is set for each secondary cooling zone. And, when the flow rate adjusting valve downstream water pressure and downstream water amount for each secondary cooling zone detected during continuous casting are out of the water pressure-water amount reference area A set for each secondary cooling zone, during the continuous casting It is pointed out that surface cracks may occur in the continuous cast piece. Thereby, the possibility that the surface crack has generate | occur | produced in the continuous casting piece can be determined appropriately.

  In addition, if there is no surface crack in the continuous cast piece pointed out that the surface crack may have occurred, the flow rate adjusting valve downstream for each secondary cooling zone detected during continuous casting of the continuous cast piece A new water pressure-water amount reference line L representing the relationship between the downstream water pressure and the downstream water amount of all the flow rate adjusting valves to which the side water pressure and the downstream water amount are added is updated for each secondary cooling zone. And all the flow control that added the downstream water pressure of the flow control valve for each secondary cooling zone detected when the surface crack did not occur in the continuous cast piece pointed out that the surface crack might have occurred The standard deviation σ of the pressure difference with respect to the water pressure-water amount reference line L that is updated and set for the water pressure downstream of the valve is newly calculated for each secondary cooling zone, and is newly calculated for the water pressure-water amount reference line L that is updated and set. A new water pressure-water amount reference region A is updated and set for each secondary cooling zone by adding or subtracting the double value 2σ of the pressure difference standard deviation σ. Thereby, the surface crack inspection instruction rate can be appropriately reduced, and the efficiency of continuous casting can be improved by that amount.

DESCRIPTION OF SYMBOLS 1 Mold 2 Roll 3 Spray nozzle 4 Cooling water supply piping 5 Flow rate adjustment valve 6 Mixing part 7 Air piping 8 Pressure gauge 9 Flow meter 10 Computer S Continuous casting piece

Claims (2)

When the secondary cooling after the primary cooling by the mold is divided into a plurality of zones, and each of the secondary cooling zones is provided with a flow rate adjustment valve that adjusts the flow rate of water to the spray nozzle, the surface of the continuous cast piece A method for determining the possibility of cracking,
The downstream water pressure and the downstream water volume of the flow rate adjusting valve during continuous casting where surface cracks are not generated in the continuous casting piece are detected for each secondary cooling zone, and the downstream pressure and downstream water volume of the flow rate adjusting valve are detected. Setting a water pressure-water volume reference line representing the relationship for each secondary cooling zone;
The standard deviation of the pressure difference between the water pressure downstream of the flow rate adjustment valve and the water pressure-water quantity reference line is calculated for each secondary cooling zone, and the double value of the pressure difference standard deviation is added to the water pressure-water quantity reference line. Setting a water pressure-water amount reference region for each secondary cooling zone;
The continuous casting when the downstream side water pressure and the downstream water amount for each secondary cooling zone detected at the time of continuous casting are out of the water pressure-water amount reference region set for each secondary cooling zone. And a step of pointing out that there is a possibility that surface cracks are occurring in the continuous cast piece at the time. When there is no surface crack in the continuous cast piece pointed out that the surface crack may have occurred, the flow control valve for each secondary cooling zone detected during continuous casting of the continuous cast piece Adding a downstream water pressure and a downstream water amount to update and set a new water pressure-water amount reference line for each secondary cooling zone, which represents the relationship between the flow regulating valve downstream water pressure and the downstream water amount;
When there is no surface crack in the continuous cast piece pointed out that the surface crack may have occurred, the flow control valve for each secondary cooling zone detected during continuous casting of the continuous cast piece A standard deviation of a pressure difference with respect to the updated water pressure-water amount reference line of the downstream pressure of the flow rate adjusting valve by adding downstream water pressure is newly calculated for each secondary cooling zone, and the updated water pressure-water amount is set. And a step of renewing and setting a new water pressure-water amount reference region for each of the secondary cooling zones by adding or subtracting a double value of the newly calculated pressure difference standard deviation to a reference line. Item 8. A method for determining surface cracks in a continuous cast piece according to Item 1.

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