KR20160115319A - Method for manufacturing boron steel - Google Patents

Abstract

Embodiments of the present invention relate to a method for manufacturing boron steel including a step of controlling a cooling rate of a peripheral edge of a cast slab to 1.5C/sec or less in a first high stress zone during a continuous casting of boron steel containing boron at 10 ppm or more, wherein the first high stress zone is a zone from a point where a cabinet angle of a vertical axis and the cast slab is 10 to 35. Accordingly, the embodiments of the present invention can effectively reduce cracks in boron steel and improve the quality and productivity of the boron steel.

Description

[0001] METHOD FOR MANUFACTURING BORON STEEL [0002]

The present invention relates to a method for producing boron steel.

The manufacturing method of the boron steel includes a performance process. The casting process is a process of producing a cast steel having a constant size by supplying molten steel to a mold for continuous casting in a steelmaking furnace. Thus, the molten steel introduced from the steelmaking furnace is formed into a cast steel having a predetermined width, thickness, and shape in the mold and is conveyed through the pinch roll. The cast steel conveyed through the pinch roll is cut by a cutter, (Slab) or a semi-finished product such as Bloom or Billet.

A related prior art is Korean Patent Publication No. 2003-0054425.

An embodiment of the present invention can provide a method of manufacturing a boron steel capable of reducing a crack generated in a performance process.

An embodiment of the present invention can provide a method of manufacturing a boron steel capable of improving the quality of boron steel.

An embodiment of the present invention can provide a method of manufacturing a boron steel capable of manufacturing high quality boron steel at a low production cost.

One embodiment of the present invention includes a step of controlling a cooling rate of a peripheral edge portion of a bobbin in a first high stress zone to 1.5 DEG C / sec or less during continuous casting of boron steel containing boron at 10 ppm or more, Section is a section from the point where the vertical axis and the cabinet angle of the casting mill are 10 DEG to 35 DEG.

The boron steel may be used in an amount of 0.001 to 0.0025% by weight, based on the total weight of the steel; 1.0 wt% or more of manganese; 0.01% to 0.06% by weight of the sum of titanium or niobium; And the remainder of the iron.

The manufacturing method may further include maintaining the edge temperature of the cast steel at 870 캜 to 980 캜.

The manufacturing method may further include maintaining the center temperature of the cast steel at 950 캜 to 1100 캜.

The method of controlling the cooling rate in the first high stress section may be at least one of changing the injection amount of the cooling water, changing the position of the cooling water nozzle, and changing the peripheral speed in the section of the performance casting.

The circumferential speed in the section of the performance casting may be 1.6 m / min or less.

The manufacturing method may further include adjusting a cooling rate of the edge portion of the bobbin to 0.5 deg. C / sec or less in a second high stress zone, wherein the second high- Lt; RTI ID = 0.0 > 10. ≪ / RTI >

The peripheral speed in the first high stress section may be 1.3 m / min or less, and the peripheral speed in the second high stress section may be 1.6 m / min or less.

The boron steel manufacturing method according to the embodiments of the present invention effectively reduces the cracks generated in the cast steel during continuous casting and improves the quality and productivity of the finally produced boron steel.

Figure 1 shows a continuous casting machine in accordance with one embodiment of the present invention.
2 is a schematic view of a continuous casting method according to an embodiment of the present invention.
Fig. 3 is a graph showing the temperature measurement results of the marginal portions of the cast slab of Example 1 and Comparative Example 1. Fig.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

One embodiment of the invention relates to a method of making boron steel. More specifically, the present invention relates to a production method for reducing cracks occurring in a cast slab by controlling a continuous casting process of boron steel containing boron at 10 ppm or more.

1 is a conceptual view showing a continuous casting machine according to an embodiment of the present invention, focusing on the flow of molten steel. In the continuous casting fixation, the molten steel introduced from the steelmaking furnace is processed into a cast slab through the continuous casting machine, and is then made into semi-finished alloy steel such as slab, bloom, or billet.

Specifically, continuous casting is a casting method in which molten metal is continuously cast while casting in a mold having no bottom and cast steel (hereinafter referred to as cast steel) or steel ingot. This makes it possible to produce slabs, blooms or billets, for example, mainly for long products of simple cross-sectional shapes, such as squares, rectangles or circles, and mainly for rolling.

The continuous casting machine may include a ladle 10 and a tundish 20, a mold 30, secondary cooling bands 60 and 65, and a pinch roll (not shown), as shown in Fig.

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 molten metal flowing into the mold 30 is controlled, molten metal is distributed to each mold 30, molten metal is stored, and slag and 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 manufacturing the slab, the mold 30 includes a pair of barriers and a pair of end walls connecting the barriers. Here, the end wall has a smaller area than the barrier. The walls, mainly the walls, of the mold 30 can be rotated to be away from or close to each other to have a certain level of taper.

The mold 30 plays a role to form a solidified shell or a solidified shell 81 so that the casting slip pulled out from the mold keeps a constant shape and a molten metal having less solidification still does not flow 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 to prevent the molten steel from adhering to the wall surface of the mold, and in order to prevent friction between the mold 30 and the solidification shell 81 during oscillation, A lubricant such as a powder may be used. The powder is added to the molten metal in the mold to become slag and functions not only to lubricate the mold 30 and the solidifying shell but also to prevent oxidation and nitriding of the molten metal in the mold and to maintain the temperature and to absorb nonmetallic inclusions floating on the surface of the molten metal do.

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 which uses several pairs of pinch rolls (not shown) so as to pull out the casting slip without slipping. The pinch roll (not shown) pulls the solidified tip portion of the molten steel in the casting direction, thereby allowing molten steel passing through the mold 30 to continuously move in the casting direction.

The continuously produced musical piece is cut to a predetermined size by a predetermined cutter (not shown).

The ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends so as to be submerged in the molten steel in the tundish 20 so that the molten steel M is not exposed to the air and oxidized and nitrided. Thereby, the molten steel M flows into the tundish 20 while being accommodated in the ladle 10.

The molten steel M in the tundish 20 is caused to flow into the mold by the submerged entry nozzle 25 extending into the mold. 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 in 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.

Molten steel (M) in the mold starts to solidify from the portion contacting 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 in such a form that the non-solidified molten steel 82 is wrapped in the solidifying shell 81 by the method in which the peripheral portion is first solidified.

The non-solidified molten steel 82 moves together with the solidifying shell 81 in the casting direction as the pinch roll (not shown) 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 having been solidified is cut to a predetermined size at the cutting point 91 and is divided into a slab P such as a slab or the like.

The method of manufacturing a boron steel of one embodiment can continuously cast a boron steel containing boron in an amount of 10 ppm or more by the above-described exemplary method.

FIG. 2 is a simplified view of a method of manufacturing a boron steel according to an embodiment of the present invention, specifically showing a continuous casting method of an embodiment. Referring to this, the cast slab 80 of the boron steel drawn in the gravity direction (hereinafter referred to as the vertical axis) in the mold 30 is switched to the casting direction (hereinafter referred to as the horizontal axis). Due to this change of direction, the bending portion is generated in the cast steel. That is, the bent portion means from the portion where the directional change of the musical accompaniment piece is started to the portion where the directional change is completely completed. In such a bent portion, stress is generated in the cast steel by the external force generated during the change of direction, and cracks are generated on the surface of the cast steel due to such stress.

In this specification, the stress generation period means from the point where the direction change of the music piece is started to the point where the direction change is completed in the continuous casting. That is, in this specification, the stress generating section refers to a section from a point where the internal angle formed by the vertical axis (gravity direction) and the surface of the casting casting reaches 0 ° to 90 °.

More specifically, the stress-generating section includes high-stress sections 100a and 100b where stresses are particularly higher. For example, the bending stress caused by the bending of the main spindle at the point where the inner angle formed by the surface of the casting spindle with the vertical axis (direction of gravity) occurs at a point exceeding 0 DEG and becomes 45 DEG, The stress may vary in magnitude at each point. On the other hand, at the point of 90 ° from the point of 45 °, the straightening stress that occurs when the bent part spreads again is larger, and the correcting stress may also vary in magnitude at each point. In addition, the bending stress and the correction stress may be opposite to each other in operation, and may be canceled out as the external force acting on them changes.

The method of manufacturing a boron steel according to an embodiment of the present invention includes the step of controlling the cooling rate of the peripheral edge of the bobbin to 1.5 deg. C / sec or less in the first high stress section 100a where high stress occurs in the stress generating section . In this manufacturing method, since the stress is controlled in a short section by separately setting the high stress section, higher productivity can be realized without requiring a large cost in the control process.

Specifically, the first high-stress zone 100a is set from a point at which the internal angle formed by the vertical axis (direction of gravity) and the surface of the casting circumference is 10 ° to a point at 35 °. When the cooling rate is controlled within the above range, the production efficiency can be further improved, and the effect of crack reduction relative to the length of the control section can be excellent. As a result, the productivity of the entire performance process can be improved.

For example, the first high stress section 100a may be defined as a point 30 ° from the point where the internal angle is 15 ° or a point 30 ° from the point 20 °. Within the above range, the generated stress is higher, so that the crack reducing effect can be more excellent when controlling the cooling rate. In addition, a better crack reduction effect can be obtained while narrowing the control period, and the production efficiency can be improved.

In one embodiment, the control of the cooling rate is performed with respect to the marginal portion of the casting cast. In this case, not only the stress is generated but also the crack generated due to the cooling speed difference between the center portion and the edge portion of the cast steel cast can be reduced together.

Concretely, the cooling rate can be controlled with respect to the edge portion determined based on the width of the casting casting, more specifically, from 25% to 30% of the width from the end of the widthwise width. In this case, the reliability of the measured cooling rate can be more excellent.

In one embodiment, in the case of producing a slab having a width of 2 m, the cooling rate can be controlled at a portion located at 500 mm to 600 mm from both ends of the width of the cast slab. In this case, the reliability of the cooling rate is further improved, and the precision of the process can be further improved. Therefore, even when the control period is set to be narrow, a superior crack reduction effect can be obtained and the production efficiency can be improved.

In one embodiment, the cooling rate of the edge portion is controlled to 1.5 deg. C / sec or less. This makes it possible to effectively reduce cracks in the casting cast. When the cooling rate of the edge portion exceeds 1.5 DEG C / sec, the occurrence rate of cracking can be further increased in the case of alloy steels, particularly alloy steels containing boron (boron steel).

Concretely, the cooling rate of the edge portion is in the range of 0.5 占 폚 / sec to 1.5 占 폚 / sec, more specifically, 0.5 占 폚 / sec to 1.5 占 sec, such as 0.6 占 폚 / sec to 1.4 占 sec, 1.3 ° C / sec, 0.8 ° C / sec to 1.2 ° C / sec, or 0.9 ° C / sec to 1.2 ° C / sec. Within the above range, the effect of reducing the crack of the cast steel can be further improved.

The boron steel of one embodiment comprises 0.15 to 0.27% by weight of carbon, 1.20 to 1.50% by weight of manganese, 0.10 to 0.30% by weight of silicon, up to 0.02% by weight of phosphorus, up to 0.005% 0.008% by weight and the balance iron. In this case, it is possible not only to increase the precision of the cooling rate control, but also to further reduce the ductility change of the boron steel.

The boron steel of one embodiment comprises 0.15 to 0.27% by weight of carbon, 1.20 to 1.50% by weight of manganese, 0.10 to 0.30% by weight of silicon, up to 0.02% by weight of phosphorus, up to 0.005% 0.0025% by weight; 0.01% to 0.06% by weight of the total of titanium and niobium; And the balance iron. In this case, it is possible not only to increase the precision of the cooling rate control, but also to further reduce the ductility change of the boron steel. In addition, the effect of stress can be lowered to reduce the occurrence of cracks, and to increase the hardenability and strength.

Specifically, the total content of titanium or niobium may be 0.01 wt% to 0.06 wt%. As a result, even when the cooling rate is reduced as in the embodiments of the present invention, the degree of grain refinement can be maintained. In this case, it is possible to improve the strength while reducing the cracks of the boron steel.

The boron steel of one embodiment may further include aluminum, calcium, etc. in addition to the above-mentioned components. The iron contained in the remainder may contain some unavoidable impurities besides these alloying elements.

In one embodiment, the boron steel comprises from 0.15% to 0.27% by weight of carbon, from 1.20% to 1.50% by weight of manganese, from 0.10% to 0.30% by weight of silicon, up to 0.02% From 0% to 0.03% by weight calcium, from 0% to 0.0025% by weight calcium, from 0.001% to 0.0025% by weight boron, from 0.01% to 0.03% by weight titanium and from 0.01% to 0.03% by weight niobium. In other embodiments, some of the components may be altered.

In the case of boron-added boron steel, ductility can be drastically lowered during the secondary cooling process in the performance process. As a result, the boron - added steel has a significantly higher rate of cracking at the corner of the steel produced during the casting process than the ordinary carbon steel.

The boron steel manufacturing method according to the embodiments of the present invention can reduce the occurrence of such cracks (cracks) through the alloy composition and the boron steel manufacturing method.

In one embodiment, the method of controlling the cooling rate in the high stress section may be at least one of changing the injection amount of the cooling water, changing the position of the cooling water nozzle, and changing the peripheral speed in the section of the performance casting .

For example, if it is detected that the cooling rate of the edge portion exceeds the upper limit of the predetermined range (for example, 1.5 DEG C / sec or less), the cooling water jetted amount is decreased to lower the cooling rate, Is less than a lower limit of a range (for example, 0.5 ° C / sec to 1.5 ° C / sec), the cooling rate may be increased by increasing the amount of cooling water.

The position of the cooling water nozzle can be changed, for example, when it is detected that the cooling rate of the edge portion exceeds the upper limit of the set range (for example, 1.5 DEG C / sec or less) The cooling rate is lowered. If the cooling rate is lower than the lower limit of the set range (for example, 0.5 ° C / sec to 1.5 ° C / sec), the cooling rate may be increased by moving the cooling rate in a direction close to the edge portion.

For example, if it is detected that the cooling rate of the edge portion exceeds the upper limit of the set range (for example, 1.5 DEG C / sec or less), the peripheral speed of the music piece is lowered in the corresponding section If the cooling rate is lowered and is lower than the lower limit of the set range (for example, 0.5 ° C / sec to 1.5 ° C / sec), the cooling rate may be increased by raising the peripheral speed of the casting circumference.

Specifically, a method of controlling the cooling rate may use one or more of the above methods in combination. In one embodiment, it may be difficult to control the cooling rate only by reducing the amount of cooling water. For example, there may be a case where the minimum injection amount of the cooling water is larger than that required for controlling the cooling rate in units of 占 폚 / sec as in the present invention. In this case, the precision of the cooling rate control can be further improved by changing the position of the nozzle or by decelerating the peripheral speed of the casting circumference in the target section.

The method of measuring the temperature of the cooling rate can be directly measured; Or the temperature, the moving time in the section of the performance casting, the moving speed, and the like.

In one embodiment, the method of controlling the cooling rate may be determined after simulation through simulation through cooling rate control simulation. When using these simulations, it is possible to minimize time and material loss by minimizing trial and error in the actual field.

In one embodiment, the circumferential velocity in the measuring zone of the casting circumference may be less than 1.6 m / min. In this case, the precision of the cooling rate control can be further enhanced, and cracking of the cast steel cast can be further reduced.

In one embodiment, the method of manufacturing the boron steel may further include adjusting the cooling rate of the peripheral edge of the bobbin to 0.5 deg. C / sec or less in the second high-stress zone 100b. That is, it is possible to adjust the cooling rate of the edge portion of the bobbin in the first high stress section to 1.5 占 폚 / sec and adjust the cooling rate of the edge portion of the bobbin in the second high stress section to 0.5 占 폚 / sec.

The second high stress section 100b may be defined as a section from the horizontal axis to the point where the internal angle of the casting cast iron is 35 ° to 10 °. When the cooling rate is controlled within the above range, the production efficiency can be further improved, and the effect of crack reduction relative to the length of the control section can be excellent. As a result, the productivity of the entire performance process can be improved.

For example, the second high stress section 100b can be set from a point at which the internal angle is 30 ° to a point at 15 ° or from a point at 30 ° to a point 20 °. Within the above range, the generated stress is higher, so that the crack reducing effect can be more excellent when controlling the cooling rate. In addition, a better crack reduction effect can be obtained while narrowing the control period, and the production efficiency can be improved.

In one embodiment, the first high stress section 100a and the second high stress section 100b may be set to the same degree or different degrees. In one embodiment, the lengths of the first high stress section and the second high stress section may be set to the same degree, but the lengths of the respective sections may be different from each other. This is because the difference in the section length can be formed in a form different from the arc in which the stress generation period in the actual playing casting machine is exactly symmetrical. In this case, although the first high stress section and the second high stress section have the same angle symmetrically, the magnitude of the stress at each corresponding point, the length of the section, and the like may be different from each other. In this case, the cooling rate can be controlled more precisely by changing the peripheral speed in the first high stress section and the peripheral speed in the second high stress section.

For example, the method of making the peripheral velocity in the first high stress section different from the peripheral velocity in the second high stress section may be a method of controlling the thicknesses of T1 and T2 in Fig. 2 differently. In the continuous casting machine, the method of setting the thickness of T2 to be smaller than T1 may be, but not limited to, micro-pressing. For another example, the method of making the peripheral velocity in the first high stress section different from the peripheral velocity in the second high stress section may be a method of setting the length of the first high stress section and the length of the second high stress section differently have. In this case, the angular ranges of the first high stress section and the second high stress section may be different from each other.

In one embodiment, the peripheral speed in the first high stress section and the peripheral speed in the second high stress section can be controlled to be equal to 1.6 m / min or less.

In another embodiment, the peripheral speed in the first high stress section is 1.3 m / min or less, and the peripheral speed in the second high stress section is 1.6 m / min or less. In this case, the stress to be generated is higher, and therefore, the crack reducing effect can be more excellent when controlling the cooling rate. In addition, a better crack reduction effect can be obtained while narrowing the control period, and the production efficiency can be improved.

In one embodiment, the length of the stress generating section is not particularly limited, but may be, for example, a section of 0 m to 21 m from the bath surface, or a section of 0.5 m to 20 m. The length of the section is not limited to the above example, but is determined by the definition of the above-mentioned stress generating section (the relationship between the performance cast and the vertical axis).

In other embodiments, the length of the first high stress section is not particularly limited, but may be, for example, a section of 1.5 m to 3 m from the bath surface or a section of 2.0 m to 2.5 m. The length of the section is not limited to the above example, but is determined by the definition of the first high stress section (the relationship between the performance cast and the vertical axis).

In another embodiment, the length of the second high stress section is not particularly limited, but may be, for example, a section of 1.5 m to 6 m from the bath surface or a section of 2.0 m to 4.0 m. The length of the section is not limited to the above example, but is determined by the definition of the second high stress section (the relationship between the cast piece and the horizontal axis).

The method of manufacturing a boron steel of one embodiment may further include maintaining the edge temperature of the cast steel at 870 캜 to 980 캜.

Specifically, the temperature of the edge portion can be adjusted so as not to exceed the temperature range of 870 캜 to 980 캜. In this case, the temperature change value in the high-stress region is further lowered, so that the control of the cooling rate is more advantageous, and the occurrence of cracks can be further reduced. Further, within the above temperature range, the ductility of the boron steel can be further reduced. Therefore, when the cooling rate is controlled to 1.5 deg. C / sec or less in the above temperature range, the ductility change of the cast steel can be further reduced, and the generation of cracks can be further reduced.

In addition, the method of manufacturing a boron steel of one embodiment may further include maintaining the center temperature of the cast steel at 950 캜 to 1100 캜.

Specifically, the temperature of the edge portion can be adjusted so as not to exceed the temperature range of 950 캜 to 1100 캜. In this case, the temperature change value in the high-stress region is further lowered, so that the control of the cooling rate is more advantageous, and the occurrence of cracks can be further reduced.

The boron steel producing method of one embodiment can achieve a good crack reducing effect by controlling the cooling rate of the edge portion of the cast steel in a high stress region but it is also possible to further control the temperature of at least one of the temperature of the edge portion and the temperature of the center portion , The precision of the process control can be further improved.

For example, in the case of further controlling the temperature of the casting casting, it is possible to further improve the accuracy by controlling the temperature of the edge portion rather than controlling the temperature of the casting portion at the same process cost. However, if the two are controlled together, the accuracy can be further improved.

The temperature of the casting casting may be measured using a noncontact type temperature measuring device, but is not particularly limited.

In one embodiment, it is possible to limit misalignment of a plurality of rolls formed in a stress generating section to prevent cracking of the casting casting. For example, referring to FIG. 1, a plurality of support rolls 60 positioned above and below the casting slab 80 to continuously apply stress to the cast slab 80 discharged through the mold 30 during the continuous casting process, Are arranged at predetermined positions to produce a cast steel having a predetermined thickness. When the support rolls 60 deviate from the predetermined position when stresses are applied to the casting slab 80 in the stress generating section, an unnecessary stress can be applied to the casting slab 80. In one embodiment, by controlling the misalignment of these rolls, it is possible to reduce a crack that may be caused by unnecessary stress applied to the cast slab 80. More specifically, the support rolls 60 can be maintained to have a predetermined position, i.e., a misalignment of less than 1.0 mm in the right position. Within the above range, it is possible to further reduce the crack by preventing the local stress additionally applied.

In one embodiment, the conditions according to the above-described embodiments of the present invention are input to the simulation to calculate the cooling rate, and then the cooling rate is decreased, the position of the injection nozzle is changed, The cooling rate is calculated, and the process conditions can be readjusted as a result of repeating this process, and then reflected in the actual operation. Boron steel casting process is big and can cause big loss even with small errors. In the case of using the above simulation, such an error can be reduced, which helps to improve the productivity, and it is possible to plan the change of the process condition in advance, which is also helpful for improving the process precision.

Example

Manufacturing example

For application to Examples and Comparative Examples, boron steel containing boron at 10 ppm or more was prepared. The main components of the boron steel and the proportions thereof are shown in Table 1 below.

ingredient C Mn Si P S Al Ti Ca B content
(weight%) 0.27 1.5 0.3 0.02 0.05 0.03 0.03 0.0025 0.0025

Examples 1 to 2 and Comparative Example 1

The boron steel prepared in the above Production Example was continuously casted under the conditions shown in Table 2 below to prepare a boron steel specimen. In Examples 1 and 2 and Comparative Example 1, the same boron steel was used and only continuous casting conditions were different.

Example 1 Example 2 Comparative Example 1 The first high stress section Cooling rate 1.3 ° C / sec 1.0 [deg.] C / sec 3.0 DEG C / sec Section Length 2.3 m 2.3 m 2.3 m Section transit time 86 sec 106 sec 86 sec In-segment speed 1.6 m / min 1.3 m / min 1.6 m / min Temperature change maximum value 110 ° C 110 ° C 260 ℃ Control temperature range within the range 980 ~ 870 ℃ 980 ~ 870 ℃ 980 ~ 720 ℃ The second high stress section Cooling rate 0.1 ° C / sec 0.1 ° C / sec 0.1 ° C / sec Section Length 3.2 m 3.2 m 3.2 m Section transit time 120 sec 120 sec 120 sec In-segment speed 1.6m / min 1.6m / min 1.6m / min Temperature change maximum value 10 ℃ 10 ℃ 10 ℃ Control temperature range within the range 955 ~ 945 ℃ 955 ~ 945 ℃ 955 ~ 945 ℃

≪ Evaluation of physical properties &

The boron steel specimens produced by the methods of Examples 1 and 2 and Comparative Example 1 were visually measured for the number and depth of cracks and are shown in Table 3.

Very good: no cracks

Excellent: the number of cracks is 1 to 3, and the total sum of crack length is 10 mm or less

Bad: The number of cracks is 4 or more, or the total sum of crack length is 10mm or more.

Example 1 Example 2 Comparative Example 1 Evaluation results Great Very good Bad

As described above, in the continuous casting of boron steel, the embodiments of the present invention can effectively reduce the cracks that may occur in the cast slab and improve the quality of the slab. In addition, boron-added boron steel products can be produced at an efficient cost without adding expensive equipment.

10: Ladle 20: Tundish
30: Mold 51: Powder layer
60: Support roll 65: Spray
70: pinch roll 80: performance cast
81: Solidification shell 82: Non-solidified molten steel
83: tip portion 85: solidified point
90: Cutter 91: Cutting point

Claims (8)

And controlling the cooling rate of the edge portion of the bobbin to 1.5 deg. C / sec or less in the first high stress section during continuous casting of the boron steel containing boron at 10 ppm or more,
Wherein the first high stress section is a section from a vertical axis to a point where the internal angle of the casting cast is 10 ° to 35 °.
The method according to claim 1,
Wherein the boron steel comprises 0.15 wt.% To 0.27 wt.% Carbon, 1.20 wt.% To 1.50 wt.% Manganese, 0.10 wt.% To 0.30 wt.% Silicon, 0.02 wt.% Or less, 0.005 wt.% Or less sulfur, 0.001 wt.% To 0.0025 wt. %; 0.01% to 0.06% by weight of the total of titanium and niobium; And the remainder of the iron.
The method according to claim 1,
Wherein the manufacturing method further comprises maintaining the edge temperature of the cast steel at 870 캜 to 980 캜.
The method according to claim 1,
Wherein the manufacturing method further comprises maintaining the center temperature of the cast steel at 950 캜 to 1100 캜.
The method according to claim 1,
The method for controlling the cooling rate in the first high stress section may include a step of changing the injection amount of the cooling water, a step of changing the position of the cooling water nozzle, and a step of changing the peripheral velocity in the casting section .
The method according to claim 1,
Wherein the peripheral velocity in the section of the cast steel is 1.6 m / min or less.
The method according to claim 1,
The manufacturing method further includes adjusting a cooling rate of the edge portion of the bobbin to 0.5 deg. C / sec or less in a second high stress zone,
Wherein the second high stress section is a section between a horizontal axis and a point where the internal angle of the casting cast is 35 ° to a point of 10 °.
8. The method of claim 7,
Wherein the peripheral velocity in the first high stress section is 1.3 m / min or less and the peripheral velocity in the second high stress section is 1.6 m / min or less.

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