KR101400036B1 - Separatimg method for slab of high clean steel - Google Patents

Abstract

The present invention relates to a method for selecting a high-clean steel casting which is capable of selecting only high-clean steel casting with high purity of cast steel. In the continuous casting for producing a cast steel having a preset shape, Comparing the deviation of the short side temperature measured with the reference temperature with the set reference temperature, and if the short side temperature deviation exceeds the set temperature, Calculating a length of an abnormal region by using a time at which the abnormal region determined as described above and a preset casting speed are used; calculating an ideal ratio, which is a ratio of the length of the ideal region calculated in the above- Comparing the set reference ratios, and, if the compared ratio exceeds the set ratio, switching the steel grade of the cast steel The method comprising the steps of:

Description

[0001] SEPARATIMG METHOD FOR SLAB OF HIGH CLEAN STEEL [0002]

The present invention relates to a method for sorting high-clean steel castings, and more particularly, to a method for sorting high-clean steel castings capable of selecting only high-clean steel casts having high clearance.

In general, a continuous casting machine is a machine which is produced in a steel making furnace, receives molten steel transferred to a ladle by a tundish, and supplies it to a mold for a continuous casting machine to produce a cast steel having a predetermined size. The continuous casting machine includes a ladle for storing molten steel, a casting mold for forming a tundish and a molten steel that is guided in the tundish first to form a cast slab having a predetermined shape, and a casting member connected to the mold, A plurality of pinch rolls.

In other words, molten steel introduced from the ladle and the tundish is formed into a cast slab having a predetermined width, thickness and shape in the mold and is transported through the pinch roll, and the slab transferred through the pinch roll is cut by a cutter A slab having a predetermined shape or a cast such as a bloom or a billet.

The molten steel supplied to the mold from the tundish is supplied through the immersion nozzle. At this time, the purity of the molten steel may be lowered due to clogging of the immersion nozzle, and the quality of the cast produced from such molten steel may be low.

A related prior art is Korean Patent No. 0470654 (registered on Jan. 28, 2005, entitled "Method for preventing clogging of immersion nozzle").

The present invention is intended to provide a method of selecting a high clean steel casting which can selectively control cast slabs having a low cleanliness and high cleanliness cast slabs produced in a performance process.

The technical objects to be achieved by the present invention are not limited to the above-mentioned technical problems.

In order to attain the above object, the present invention provides a method for selecting a high-clean steel casting, comprising the steps of: measuring temperatures of a pair of short sides constituting a mold during continuous casting for producing a cast steel having a predetermined shape; Comparing the deviation of the short side temperature with the set reference temperature; and if the short side temperature deviation exceeds the set temperature, judging an abnormality which is an anomaly in the ladle cleanliness, Calculating a length of an ideal zone by using a time and a casting speed set in advance; comparing an ideal zone ratio, which is a ratio of the length of the ideal zone calculated in the above process, to a set reference ratio; And selecting the steel grade to switch the steel grade of the steel grade when the compared reverse ratio exceeds the set ratio.

Specifically, the set reference temperature may be 10 to 20 ° C.

In the comparison with the set reference temperature, the set reference temperature is determined by analyzing the inclusion inclusion area in accordance with the difference in temperature between the left and right mold short sides in the continuous casting process. When the inclusion inclusion in the cast inclusion does not exceed the permissible range, Can be calculated by calculating the temperature difference between the short sides.

The inclusion area in the cast steel can be calculated by irradiating ultrasonic wave to the sample rolled thinly and rolling the cast steel sample, and the area where the inclusions are distributed due to the difference in light and shade between the inclusion part and the non-inclusion part.

The step of calculating the length of the abnormal region can be calculated by the following relational expression.

Relation

(Main Speed: Continuous Casting Speed, Temperature Deviation Occurrence Time: Time at which the temperature deviation between the short side portions is maintained above the set temperature)

The set reference ratio may be 5 to 10%.

In the sorting step, the cast steel having the abnormal reverse ratio exceeding the reference ratio set can be sorted and separated separately by converting the steel grade from high-clean steel to ordinary steel.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, slabs having low cleanliness and high-cleanliness slabs can be selected from among the slabs produced in the performance process, so that the quality of the produced slab can be maintained constant. Further, the use of the cast steel can be switched according to the degree of cleanliness, and the produced cast steel can be used suitably for the intended use.

1 is a side view showing a continuous casting machine according to an embodiment of the present invention.
Fig. 2 is a conceptual diagram for explaining the continuous casting machine of Fig. 1 centered on the flow of molten steel M. Fig.
FIG. 3 is a flowchart illustrating a method for sorting high-clean steel castings according to an embodiment of the present invention in order.
FIG. 4 is a view for explaining the temperature difference of the mold short side due to clogging of the immersion nozzle related to the present invention. FIG.
FIG. 5 is a graph showing the result of numerical model experiment of changes in the molten steel flow rate due to clogging of the immersion nozzle related to the present invention.
6 is a graph showing the temperature difference between the short side of the mold due to clogging of the immersion nozzle and the thermocouple measured according to the present invention.
FIG. 7 is a graph showing a correlation between a mold short side temperature deviation and an inclusion area ratio index according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols whenever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a side view showing a continuous casting machine according to an embodiment of the present invention.

Continuous casting is a casting process in which a molten metal is continuously cast into a bottomless mold while continuously drawing a steel ingot or steel ingot. Continuous casting is used to manufacture slabs, blooms and billets, which are mainly rolled products, and long products of simple cross-section, such as square, rectangular and circular.

The shape of a continuous casting machine is classified into a vertical type and a vertical bending type. In Figs. 1 and 2, a vertical bending-like shape is illustrated.

1, the continuous casting machine may include a ladle 10 and a tundish 20, a mold 30, a secondary cooling stand 60 and 65, a pinch roll 70, and a cutter 90 have.

A tundish 20 is a container for receiving molten metal from a ladle 10 and supplying molten metal to a mold 30. The ladles 10 are provided in pairs to alternately receive molten steel and supply the molten steel to the tundish 20. In the tundish 20, the supply rate of the molten metal flowing into the mold 30 is controlled, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the nonmetallic inclusions are separated.

Mold 30 is typically made of water-cooled copper and allows the molten steel taken to be first cooled. The mold 30 has a pair of structurally opposed faces open to form a hollow portion for receiving molten steel. In the case of producing the cast steel, the mold 30 is composed of a pair of long sides and a pair of short sides connecting the long sides. Here, the short side has a smaller width than the long side. The walls, mainly short sides, of the mold 30 may be rotated to be away from or close to each other to have a certain level of taper. This taper is set to compensate for the shrinkage due to the solidification of the molten steel M in the mold 30. The degree of solidification of the molten steel (M) varies depending on the carbon content according to the steel type, the kind of the powder (strong cold type Vs and cold type), the casting speed and the like.

The mold 30 is formed such that a solidified shell or a solidified shell 81 is formed so as to maintain the shape of the casting pluck pulled out from the mold 30 and to prevent the molten metal from being hardly outflowed from flowing out. . The water-cooling structure includes a method using a copper tube, a method of water-cooling the copper block, and a method of assembling a copper tube having a water-cooling groove.

The mold 30 is oscillated by the oscillator 40 to prevent the molten steel from sticking to the wall surface of the mold. A lubricant is used to reduce the friction between the mold 30 and the solidification shell 81 during oscillation and to prevent burning. As the lubricant, there is oil to be sprayed and powder added to the molten metal surface in the mold 30. The powder is added to the molten metal in the mold 30 to become slag so that not only the lubrication of the mold 30 and the solidification shell 81 but also the prevention and oxidation of the molten metal in the mold 30, It also functions to absorb the emerging nonmetallic inclusions. A powder feeder 50 is installed to feed the powder into the mold 30. The portion of the powder feeder 50 for discharging the powder is directed to the inlet of the mold 30.

The secondary cooling bands 60 and 65 further cool the molten steel that has been primarily cooled in the mold 30. The primary cooled molten steel is directly cooled by the spraying means 65 for spraying water while being maintained by the support roll 60 so that the coagulation angle is not deformed. Most of the solidification of the cast steel is accomplished by the secondary cooling.

The pulling device employs a multi-drive type or the like in which a plurality of pinch rolls (70) are used so as to pull out the casting slides without slipping. The pinch roll 70 pulls the solidified leading end portion of the molten steel in the casting direction so that molten steel passing through the mold 30 can be continuously moved in the casting direction.

The cutter 90 is formed so as to cut a continuously produced musical instrument into a predetermined size. As the cutter 90, a gas torch or an oil pressure shearing machine may be employed.

Fig. 2 is a conceptual diagram for explaining the continuous casting machine of Fig. 1 centered on the flow of molten steel M. Fig.

Referring to this figure, the molten steel M flows into the tundish 20 while being accommodated in the ladle 10. For this flow, the ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends into the molten steel in the tundish 20 so that the molten steel M is not exposed to the air to be oxidized and nitrided. The case where the molten steel M is exposed to air due to breakage of the shroud nozzle 15 or the like is referred to as open casting.

The molten steel M in the tundish 20 is caused to flow into the mold 30 by the submerged entry nozzle 25 extending into the mold 30. The immersion nozzle 25 is disposed at the center of the mold 30 so that the flow of the molten steel M discharged from both the discharge ports of the immersion nozzle 25 can be made symmetrical. The start, discharge speed and interruption of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 provided on the tundish 20 in correspondence with the immersion nozzle 25. [ Specifically, the stopper 21 can be vertically moved along the same line as that of the immersion nozzle 25 so as to open and close the inlet of the immersion nozzle 25. The control of the flow of the molten steel M through the immersion nozzle 25 may be performed by a slide gate method different from the stopper method. The slide gate controls the discharge flow rate of the molten steel (M) through the immersion nozzle (25) while the plate material slides horizontally in the tundish (20).

Molten steel (M) in the mold (30) starts to solidify from a portion in contact with the wall surface of the mold (30). This is because the periphery of the molten steel M is liable to lose heat by the water-cooled mold 30. The rear portion along the casting direction of the cast slab 80 is formed into a shape in which the non-solidified molten steel 82 is wrapped in the solidifying shell 81 by the method in which the peripheral portion first coagulates.

The non-solidified molten steel 82 moves together with the solidifying shell 81 in the casting direction as the pinch roll 70 (Fig. 1) pulls the tip end portion 83 of the fully-solidified cast slab 80. The non-solidified molten steel (82) is cooled by the spraying means (65) for spraying the cooling water in the up-shifting process. This causes the thickness of the non-solidified molten steel (82) to gradually decrease in the cast steel (80). When the cast steel 80 reaches one point 85, the cast steel 80 is filled with the solidified shell 81 as a whole. The solidification casting 80, which has been solidified, is cut to a predetermined size at the cutting point 91 to become a slab P such as a slab, a bloom, a billet, or the like.

1, the apparatus including the support roll 60, the spraying means 65 and the pinch roll 70 is also referred to as a strand.

FIG. 3 is a flowchart illustrating a method for sorting high-clean steel castings according to an embodiment of the present invention in order.

The present invention will now be described in detail with reference to the drawings. First, in the continuous casting process, data on the shape of a cast steel to be manufactured is determined in advance in terms of its length and width. In the continuous casting process, when molten steel is supplied from the tundish 20 to the mold 30, the molten steel starts to solidify from the mold 30, and the solidified cast steel is produced through the process leading to the strand. And cut into a slab form.

At this time, as described above, the mold 30 is formed in a rectangular shape, and a pair of long sides and a pair of short sides make a rectangular shape of the mold 30. When the molten steel flows into the mold 30, the temperature is measured at each of the short sides of the mold 30 using the thermocouple (S10).

The reason for measuring the temperature of the short side of the mold is to predict the clogging of the immersion nozzle 25 in the mold 30. In detail, the immersion nozzle 25, which is a passage for supplying molten steel into the mold 30, is provided with a pair of discharge ports through which molten steel is uniformly supplied to the left and right sides of the mold 30.

However, as shown in Fig. 4, when clogging of the immersion nozzle occurs, the supply of molten steel to either the left side or the right side is reduced as compared with the other side. If the supply of molten steel is not uniform between the right and left sides, the molten steel flow rates on the right and left sides are different from each other. For example, when the discharge port on the left side of the immersion nozzle 25 is partially blocked as shown in FIG. 4, the amount of molten steel supplied to the left side decreases and the molten steel discharged to the right side relatively increases, It will slow down.

If the molten steel discharge amount in the mold 30 is unbalanced on the left and right sides due to the clogging of the immersion nozzle 25, as shown in the numerical model of FIG. 5, the flow rate of the portion where the nozzle is not clogged becomes relatively larger The amount of molten steel flowing to the wall surface of the mold 30 is relatively increased. When the flow velocity of the molten steel in the mold 30 is unbalanced, the upper surface of the mold 30 swings. The mold slag sprayed on the upper end of the molten steel in the mold 30 is mixed into the molten steel by the squeaking of the molten steel bath surface, and the cleanliness of the molten steel is lowered as an extrinsic inclusion. Such incorporation of the mold slag may occur more seriously at the portion where the molten steel flow rate is accelerated.

If the molten steel flow rate in the mold 30 is not uniform right and left and the flow rate of the molten steel in one portion is slowed down, the inclusions present in the molten steel flow into the molten steel portion As shown in FIG. Therefore, the density of the inclusions is relatively higher in the portion where the molten steel flow velocity is slowed by the clogging of the immersion nozzle 25, and the cleanliness of the molten steel is lowered.

6 is a graph showing the results of estimating whether or not the immersion nozzle 25 is clogged by measuring the temperature of each of the short sides formed on the left and right sides of the mold 30 when one of the immersion nozzles 25 is clogged as shown in FIG. As shown in the figure, the temperature of the short side of the mold 30 is almost the same when the process is normally performed, but the temperature measured at the short side of the left mold 30 is suddenly dropped compared to the right side when the discharge port of the left immersion nozzle 25 is closed Able to know. This is because the amount of molten steel flowing out through the left discharge port is relatively smaller than that of the right side, so that the temperature of the short side of the left side of the mold 30 is lower than that of the right side.

The difference in temperature between the short sides of the mold 30 measured as described above is calculated, and the short side temperature deviation of the mold 30 thus obtained is compared with a preset reference temperature (S20). The reference temperature set in advance is a temperature within a range in which it is determined that the temperature deviation between the short side right and left sides of the mold 30 does not affect the cleanliness of the molten steel during the continuous casting process. Preferably, the set reference temperature is 10 to 20 占 폚.

The basis for calculating the set reference temperature is based on the left and right side short side temperature difference and the inclusion area ratio index on the casting shown in FIG. The inclusion area ratio index is a constant expressed in terms of the area of inclusions in a casting. When the inclusion area ratio index is high, the inclusion area is wide. When the inclusion area ratio index is low, the inclusion area in the casting is considered to be narrow. The reason why the inclusion area of the cast steel is wide is that the inclusion of the inclusions in the produced cast steel is considered to be included in the mold 30 because continuous casting is performed in a state where the clearance of molten steel is decreased.

7, when the temperature difference between the left and right mold short sides measured by the experiment is 10 to 20 占 폚, the inclusion area ratio index is less than 200 and the inclusion area ratio index is increased to 200 or more when the temperature difference is 20 占 폚 or more The inclusion area ratio index was measured from 400 to 1000 or more at a temperature difference of about 35 캜.

Based on these experimental results, in the present invention, the permissible range of the inclusion index of the inclusion area is set to 200. Accordingly, when the temperature deviation of the mold side short side is 10 to 20 ° C in the continuous casting process, Respectively.

The method of measuring the inclusion area ratio index is as follows. First, a sample of the cast steel is obtained, cut in the width direction, and rolled to a suitable size to reduce the thickness of the cast steel of 250 mm to 5 mm. The thinly rolled cast sample was ultrasonically inspected. Ultrasonic inspection was performed by ultrasonic irradiation on a thin cast slab, and when there was a difference in the contrast between the part where the inclusions existed and the part where the inclusions exist, the area where the inclusions were present was calculated and the area thereof was calculated. Generally, it can be predicted that a portion having an inclusion in the sample will have a contrast higher than a certain level. In this way, it can be calculated by calculating the area where the contrast is high (dark) compared with the entire sample. The inclusion area calculated through the ultrasonic inspection is visually shown in FIG. 7 by the MIDAS (Mannesmann Inclusion Detection by Analyzing Surfboards) method.

If the measured temperature difference between the short sides of the mold is compared with the set reference temperature, if the temperature difference between the short sides is higher than the set reference temperature, it can be determined that the abnormality occurs in the molten steel clearance (S30). In the present invention, it is preferable that the temperature difference between the left and right sides of the mold exceeds 10 to 20 ° C.

The reason for this is as follows. When the temperature deviation between the left and right sides of the mold is 10 to 20 ° C, the inclusion area falls within the allowable range in the casting through the inclusion area ratio index, but when the temperature exceeds 20 ° C, the area of the inclusions increases sharply It is possible to reduce the cleanliness of the cast steel produced.

When the section determined to be in the opposite direction as described above is started, the length of the abnormal section is calculated (S40). In order to calculate the length of the anomaly, it is possible to introduce the time at which the preset casting speed and the temperature deviation between the left and right sides of the mold exceed the set reference temperature, that is, the time at which the anomaly occurs. In the continuous casting process, the casting speed is continuously measured and set so that the casting speed can be known. Then, since it is possible to measure how long the anomaly occurs and the duration of the anomaly, the length of the anomaly can be calculated as shown in Equation 1 below.

Relationship 1

(Where the temperature deviation occurrence time is the time at which the temperature deviation between the short sides is maintained above the set temperature, and the time at which the abnormal state occurred)

When the length of the anomaly is calculated as described above, the anomaly ratio, which is the ratio of the length of the anomaly in the length of the entire cast steel, is calculated and compared with the established reference ratio (S50). At this time, the abnormal reverse ratio can be expressed by the length of the abnormal range relative to the total length of the pre-set main axis. This is expressed by the following equation (2).

Relation 2

The reason why the abnormal ratio R thus calculated is compared with the set reference ratio is to judge that there is a problem with the cleanliness of the main part when the ratio of the abnormal part exceeds the allowable set ratio. That is, the reference ratio set in the present invention is an allowable rate that can be used as a high-clean steel even if an anomaly appears in the length of the entire cast steel.

At this time, it is preferable that the set reference ratio is 5 to 10%. That is, there may be a slight difference depending on the type of steel, but even if an abnormal range of about 5 to 10% appears, the cast steel produced by this cast steel can be judged to have a good cleanliness. In the performance process, as described above, since the length and the width of the cast steel to be produced are inputted and production is performed, the length of the cast steel to be produced in the process in which the section judged to be the anomaly is generated can be known.

If the abnormal ratio exceeds the set reference ratio, the steel grade is selected so as to switch the steel grade (S60). Specifically, when the abnormal reverse ratio exceeds 5 to 10% of the entire length of the slab, it is judged that the produced slab has fallen to cleanliness, and the slab is separately sorted so as to be used as a general steel.

As described above, in the case where an abnormality occurs in the molten steel purity due to the clogging of the immersion nozzle during the production of the slab through the continuous casting, if the section in which the abnormality occurs exceeds the set reference ratio, the produced slab can not be used as a high- Therefore, it can be sorted and separated to be used as a general steel by converting the steel grade.

The method of sorting the high-clean steel casting as described above is not limited to the configuration and the operating method of the embodiments described above. The embodiments may be configured so that all or some of the embodiments may be selectively combined so that various modifications may be made.

10: Ladle 15: Shroud nozzle
20: tundish 25: immersion nozzle
30: Mold 40: Mold oscillator
50: Powder feeder 60: Support roll
65: spray 70: pinch roll
80: Casting Casting 81: Solidification Shell
82: non-solidified molten steel 83:
85: Solidification completion point 90: Cutter
91: Cutting point

Claims (7)

Measuring a temperature of a pair of short sides constituting the mold during continuous casting for producing a cast product of a predetermined shape;
Comparing the measured deviation of the short side temperature with the set reference temperature;
Determining an abnormality in a range in which the temperature difference between the short sides exceeds the set temperature, which is an abnormality in the steel pipe cleanliness;
Calculating a length of an abnormal region by using a time at which the abnormal region is determined and a preset casting speed;
Comparing the anomaly ratio, which is the ratio of the length of the anomaly calculated in the above step to the total bobbin, and the set reference ratio; And
And selecting a steel grade to switch the steel grade if the compared reverse ratio exceeds the set ratio,
In the comparison with the set reference temperature,
The set reference temperature is calculated by analyzing the inclusion area of the cast steel according to the difference in temperature between the left and right molds in the continuous casting process and calculating the mold short side temperature difference when the occurrence of inclusions in the cast does not exceed the permissible range,
The inclusion area in the cast steel is determined by a method of screening a high-clean steel casting which is obtained by thinly rolling a cast slab and irradiating the rolled sample with ultrasonic waves to calculate an area where inclusions are distributed due to difference in light and shade between the inclusion- .
The method according to claim 1,
Wherein the set reference temperature is 10 to 20 占 폚.
delete delete The method according to claim 1,
Wherein the step of calculating the length of the abnormal region is calculated by the following relational expression.
Relation

(Where the temperature deviation occurrence time is the time at which the temperature deviation between the short sides is maintained above the set temperature, and the time at which the abnormal state occurred)
The method according to claim 1,
Wherein the predetermined reference ratio is 5 to 10%.
The method according to claim 1,
In the selecting step,
A casting method in which a cast steel having a ratio exceeding the reference ratio set as above is converted into a steel from a high-clean steel to separate steel segregation separately.

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