KR102664187B1 - Beam Blank and Continuous Casting Method of Beam Blank - Google Patents

Abstract

The continuous casting method of the beam blank according to the present invention is carbon (C) 0.10 to 0.13 wt%, silicon (Si) 0.15 to 0.20 wt%, manganese (Mn) 1.30 to 1.50 wt%, aluminum (Al) 0.020 to 0.050 wt. %, vanadium (V) 0.060~0.100wt%, titanium (Ti) 0.010~0.020wt%, and the remaining iron (Fe) and other alloy elements as a continuous casting method of a shell steel beam blank, injecting molten steel into a mold and , Step (a) of performing a primary cooling process by contact with the mold in the process of passing the molten steel through the mold, and performing primary hardening of the molten steel while passing through the mold. Step (b) of performing a secondary cooling process by spraying air mist in the foot zone, and transferring the cast steel that entered the segment area after secondary hardening in the foot zone through a plurality of support rolls and spraying air mist. It includes step (c) of performing a tertiary cooling process, and by controlling the cooling rate in the secondary cooling process and tertiary cooling process performed in steps (b) and (c), the particle size of the surface of the cast steel is reduced. Suppresses the occurrence of defects.

Description

{Beam Blank and Continuous Casting Method of Beam Blank}

The present invention relates to a continuous casting method for Bimblanck.

Beam blank is a material used in the production of H-beam steel products, and peritectic steel is widely applied.

This type of peritoneal steel is a steel with a carbon mass percentage of 0.09 to 0.14%. During the process of solidification from the molten state through the continuous casting process, δ-Ferrite undergoes a phase transformation into γ-Austenite due to the influence of the carbon composition. A volume reduction of approximately 0.38% appears.

In this way, non-uniform solidification occurs between the mold and the solidification layer due to phase transformation and volume reduction that occur during solidification in the continuous casting process, and this non-uniform solidification causes surface defects such as intergranular flaws and longitudinal cracks on the surface of the beam blank. .

To minimize these surface defects, a method commonly used in existing continuous casting processes is to minimize primary cooling while lowering the peripheral speed. However, delaying solidification by minimizing primary cooling in this way has the effect of securing the initial solidification layer more stably, but it is difficult to fundamentally resolve surface defects, and in the case of high alloy steel, problems occurring during the continuous casting process are very difficult. The effect of improving grain boundary defects is minimal.

Intergranular flaws are cracks that occur in a network shape on the surface of the beam blank. The size of the crack varies from a few mm to the total length of the material. In many cases, the depth of the crack is difficult to check with the naked eye, so it must be removed from the material. If not, it will also affect surface defects of the product.

Figure 1 shows the surface texture and normal texture of a material with grain boundary defects, respectively.

As shown in Figure 1, when examining the surface texture of a material with intergranular defects, it can be seen that the surface layer texture appears coarse, unlike the existing normal material.

In the case of such a coarsened structure, a coarse ferrite film is formed at the grain boundary, and this ferrite film acts as a starting point for the generation of defects vulnerable to stress concentration.

Therefore, in order to reduce the occurrence of grain boundary defects as mentioned above, it is necessary to minimize the grain boundary coarsening phenomenon.

Korean Patent Publication No. 10-2000-0013111 Korean Patent Publication No. 10-2002-0086900

The present invention is an invention made to solve the problems of the prior art described above, and has the purpose of providing a continuous casting method for improving the surface quality of shell steel beam blanks to which a large amount of alloy elements are added.

The problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

The continuous casting method of the beam blank of the present invention to achieve the above purpose includes 0.10 to 0.13 wt% of carbon (C), 0.15 to 0.20 wt% of silicon (Si), 1.30 to 1.50 wt% of manganese (Mn), and aluminum ( Molten steel containing 0.020~0.050wt% of Al), 0.060~0.100wt% of vanadium (V), 0.010~0.020wt% of titanium (Ti), and the remaining iron (Fe) and other alloy elements are injected into the mold, and the molten steel is Step (a) of performing a primary cooling process by contact with the mold in the process of passing through the mold, a foot zone directly below the mold for the cast steel produced by primary hardening while passing through the mold. Step (b) of performing a secondary cooling process by spraying air mist in the foot zone, and transferring the cast steel that entered the segment area after secondary hardening in the foot zone through a plurality of support rolls and spraying air mist to perform a tertiary cooling process. It includes step (c) of performing a cooling process, and the occurrence of grain boundary flaws on the surface of the cast steel is prevented by controlling the cooling rate in the secondary cooling process and the tertiary cooling process performed in steps (b) and (c). Suppress.

At this time, the tertiary cooling process in step (c) may be divided into a first cooling zone, a second cooling zone, and a third cooling zone according to the process flow.

In addition, steps (b) and (c) may increase the specific water quantity up to the first cooling zone of the secondary cooling process and the tertiary cooling process to be higher than the preset standard specific water quantity.

In particular, steps (b) and (c) may increase the specific water quantity of the secondary cooling process and the tertiary cooling process to 60% or more than the preset standard specific water quantity.

In addition, steps (b) and (c) are the initial water ratio of the specific water quantity of the secondary cooling process and the tertiary cooling process compared to the specific water quantity of the entire secondary cooling process and the tertiary cooling process. The distribution fee can be increased higher than the preset standard initial distribution fee.

At this time, steps (b) and (c) can increase the initial distribution ratio to 80% or more.

In more detail, steps (b) and (c) are the ratio of the specific water quantity of the first cooling zone of the tertiary cooling process to the specific water quantity of the entire secondary cooling process and the tertiary cooling process. The post-distribution ratio can be increased higher than the pre-distribution ratio, which is the ratio of the specific water quantity of the secondary cooling process to the specific water quantity of the entire secondary cooling process and the tertiary cooling process.

In particular, step (b) increases the pre-distribution ratio to 30% or more, and step (c) can increase the post-distribution ratio to 50% or more.

Meanwhile, in step (b), the secondary cooling process can be controlled so that the temperature of the cast steel at the time of entering the tertiary cooling process is 855°C or lower.

The beam blank of the present invention to achieve the above object includes 0.10 to 0.13 wt% of carbon (C), 0.15 to 0.20 wt% of silicon (Si), 1.30 to 1.50 wt% of manganese (Mn), and 0.020 to 0.050 of aluminum (Al). wt%, vanadium (V) 0.060~0.100wt%, titanium (Ti) 0.010~0.020wt%, the remaining iron (Fe) and other alloy elements are included, molten steel is injected into the mold, and the molten steel passes through the mold. In step (a) of performing a primary cooling process by contact with the mold, air mist is applied to the cast steel produced by primary hardening as the molten steel passes through the mold in the foot zone directly below the mold. Step (b) of performing a secondary cooling process by spraying and transferring the cast steel that entered the segment area after secondary hardening in the foot zone through a plurality of support rolls and performing a tertiary cooling process by spraying air mist. A continuous casting method that includes step (c) and suppresses the occurrence of intergranular flaws on the surface of the cast steel by controlling the cooling rate in the secondary cooling process and the tertiary cooling process performed in steps (b) and (c). It is manufactured with

In addition, after step (c), the average value of the grain size of the surface layer of the beam blank may be 350 ㎛ or less.

The continuous casting method of the beam blank of the present invention to solve the above problems controls the cooling rate of the cast steel by increasing at least one of the specific water quantity and distribution ratio in the secondary cooling process and the third cooling process, thereby reducing the surface of the cast steel. By ensuring that fine ferrite and fine precipitates are evenly distributed within the austenite grains, grain boundary flaws caused by surface coarsening and surface defects caused by precipitates generated during rolling can be minimized.

In addition, through this, the present invention has the advantage of significantly increasing the recovery rate of H-beam steel by reducing the scarfing operation due to the occurrence of cracks, and reducing the overall production cost through the effect of reducing scarfing costs.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

Figure 1 is a view showing the surface texture and normal texture of a material with grain boundary defects, respectively;
Figure 2 is a diagram schematically showing a continuous casting device for performing the continuous casting method of a beam blank according to an embodiment of the present invention;
Figure 3 is a diagram showing each process of the continuous casting method of beam blank according to an embodiment of the present invention;
Figure 4 is a graph showing the temperature change of the surface of the cast slab as the process progresses in the process of performing the continuous casting method of the beam blank according to an embodiment of the present invention; and
Figure 5 is a diagram showing the surface texture of a product manufactured by a conventional continuous casting process and a product manufactured by the Bimblanck continuous casting method according to an embodiment of the present invention, respectively.

In this specification, when a component (or region, layer, portion, etc.) is referred to as being “on,” “connected to,” or “coupled to” another component, it is directly placed/on the other component. This means that they can be connected/combined or a third component can be placed between them.

Like reference numerals refer to like elements. Additionally, in the drawings, the thickness, proportions, and dimensions of components are exaggerated for effective explanation of technical content.

“And/or” includes all combinations of one or more that the associated configurations may define.

Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, a first component may be named a second component, and similarly, the second component may also be named a first component without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

Additionally, terms such as “below,” “on the lower side,” “above,” and “on the upper side” are used to describe the relationship between the components shown in the drawings. The above terms are relative concepts and are explained based on the direction indicated in the drawings.

Unless otherwise defined, all terms (including technical terms and scientific terms) used in this specification have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Additionally, terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and unless interpreted in an idealized or overly formal sense, are explicitly defined herein. do.

Terms such as “include” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but do not include one or more other features, numbers, or steps. , it should be understood that it does not exclude in advance the possibility of the existence or addition of operations, components, parts, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The present invention relates to a continuous casting method. In particular, in the case of this embodiment, carbon (C) 0.10 to 0.13 wt%, silicon (Si) 0.15 to 0.20 wt%, manganese (Mn) 1.30 to 1.50 wt%, and aluminum (Al) 0.020 wt%. Continuous targeting of shell steel beam blanks made of molten steel containing ~0.050wt%, vanadium (V) 0.060~0.100wt%, titanium (Ti) 0.010~0.020wt%, and the remainder iron (Fe) and other alloying elements. An example of the casting method is provided.

Steels with this composition have the risk of uneven solidification due to peritoneal steel, as well as the risk of precipitates such as V(C,N) and Ti(C,N) generated by alloying elements such as vanadium (V) and titanium (Ti) during solidification. There is a high risk of grain boundary defects occurring due to .

However, this is a shell steel beam blank with a composition presented as an example, and the composition ratio of the shell steel beam blank to which the present invention can be applied is not limited to this example.

Figure 2 is a diagram schematically showing a continuous casting device for performing a continuous casting method of a shell steel beam blank according to an embodiment of the present invention.

As shown in FIG. 2, the continuous casting device of this embodiment includes a mold 10 into which molten steel falls and forms the shape of a product, and a cast slab 5 that gradually solidifies after passing through the mold 10. It includes a plurality of support rolls 20 that are continuously transported.

At this time, the continuous casting device of this embodiment is composed of the Mold Zone, which is the primary cooling section, the Foot Zone, which is the secondary cooling section, and the Segment Zone, which is the third cooling section.

The mold zone, which is the primary cooling section where the primary cooling process is performed, is an area corresponding to the mold 10 and is a section where molten steel is cooled by contact with the water-cooled mold 10.

And the foot zone (F), which is a secondary cooling section where the secondary cooling process is performed, is located directly below the mold 10 and is a section where coolant is sprayed as air mist directly onto the surface of the cast steel 5. In this secondary cooling section, solidification gradually progresses from the inside of the material due to the cooling water.

The 3rd cooling section in which the 3rd cooling process is performed is a section in which the cast steel passes through a plurality of segments including a plurality of unit support zones 20 from the point where it passes the foot zone (F) and is cooled. And this tertiary cooling section may include a first cooling zone (S1), a second cooling zone (S2), and a third cooling zone (S3) corresponding to each segment in detail.

Performing appropriate cooling control in such primary to tertiary cooling sections is a very important factor in producing high-quality materials.

In the case of the present invention, a method is provided to suppress the occurrence of grain boundary flaws on the surface of the cast steel 5 by controlling the cooling rate in the secondary cooling section and the tertiary cooling section.

Figure 3 is a diagram showing each process of the continuous casting method of beam blank according to an embodiment of the present invention.

As shown in Figure 3, the continuous casting method of a shell steel beam blank according to this embodiment includes steps (a) to (c).

Step (a) is a process of injecting molten steel into the mold 10 and performing a primary cooling process by contact with the mold 10 while the molten steel passes through the mold 10.

That is, step (a) refers to a cooling process performed in the primary cooling section where the molten steel is cooled by contact with the mold 10 in the mold zone.

Step (b) is a process of performing a secondary cooling process by spraying air mist from the foot zone (F) directly below the mold 10 on the cast piece 5 that has passed through the mold 10 and been primary hardened.

This step (b) refers to a cooling process performed in the secondary cooling section where the primary hardened cast slab 5 is cooled by cooling water in the foot zone (F).

And in step (c), the cast steel 5, which has entered the segment area after secondary hardening in the foot zone (F), is transferred through a plurality of support rolls 10 and air mist is sprayed to perform a tertiary cooling process. am.

That is, step (c) refers to a cooling process performed in the tertiary cooling section in which the secondary hardened cast slab 5 is cooled by coolant in the segment zone. In addition, as described above, the 3rd cooling section where the 3rd cooling process in step (c) is performed is divided into the first cooling zone (S1), the second cooling zone (S2), and the third cooling zone (S3) depending on the process flow. ) can be divided into

Among these steps, the present invention suppresses the occurrence of grain boundary flaws on the surface of the cast steel by controlling the cooling rate in the secondary cooling process and the tertiary cooling process performed in steps (b) and (c).

In addition, the size of the cast slab 5 applied in this embodiment is based on the cast slab 5 having a width of 500 mm or more and 700 mm or less, but the size of the target cast slab 5 is not limited to this.

In particular, in step (b), the secondary cooling process can be controlled so that the temperature of the cast steel 5 at the time of entering the third cooling process is below 855°C, which is the preset target cooling temperature. Specifically, step (b) in this embodiment provides a method of rapidly cooling the surface of the cast steel at a temperature of 1300°C or higher to a temperature of 855°C or lower.

In order to control the cooling rate in the secondary cooling process and the tertiary cooling process, the present embodiment can control at least one of the specific water quantity and the distribution ratio for each section of the coolant sprayed in the air mist method.

And the control method can be implemented as follows.

First, in steps (b) and (c), the specific water quantity of the secondary cooling process and the tertiary cooling process can be increased higher than the preset standard specific water quantity.

More specifically, steps (b) and (c) can increase the specific water quantity of the secondary cooling process and the tertiary cooling process to 60% or more than the preset standard specific water quantity.

Here, in the case of this embodiment, the standard specific water quantity was set to 0.25 ℓ/kg, and therefore, the specific water quantity up to the first cooling zone (S1) of the secondary cooling process and the tertiary cooling process may be 0.4 ℓ/kg.

The reason for setting this is because the conventional cooling method uses a specific water quantity of 0.25 ℓ/kg and gradually increases the cooling water quantity to minimize reheating on the surface of the cast steel until the end of continuous casting. However, in the conventional cooling method, reheating does not occur in the cast steel, but because the surface of the cast steel becomes coarsened, the number of cracks on the surface of the cast steel increases.

In addition, steps (b) and (c) are the specific water quantity up to the first cooling zone (S1) of the secondary cooling process and the tertiary cooling process compared to the specific water quantity of the entire secondary cooling process and the tertiary cooling process. The initial distribution ratio, which is a ratio, can be increased higher than the preset standard initial distribution ratio.

More specifically, steps (b) and (c) can increase the initial distribution ratio to 80% or more. In other words, the specific water volume up to the first cooling zone (S1) of the secondary cooling process and the tertiary cooling process may be more than 4 times the specific water volume of the second cooling zone (S2) and the third cooling zone of the tertiary cooling process. .

And these steps (b) and (c) are the post-distribution ratio, which is the ratio of the specific water quantity of the first cooling zone (S1) of the 3rd cooling process to the specific water quantity of the entire secondary cooling process and 3rd cooling process. It can be increased higher than the pre-distribution ratio, which is the ratio of the specific water quantity of the secondary cooling process to the specific water quantity of the entire secondary cooling process and the tertiary cooling process.

In other words, by dividing the initial distribution ratio in more detail compared to the specific water quantity of the entire secondary cooling process and the 3rd cooling process, the specific water quantity of the first cooling zone (S1) of the 3rd cooling process is greater than the specific water quantity of the secondary cooling process. A further increasing method may be applied.

Specifically, step (b) increases the pre-distribution fee to 30% or more, and step (c) increases the post-distribution fee to 50% or more.

If the above matters are summarized, they can be organized as shown in Table 1 below.

division
non-quantity
(l/kg) Secondary cooling process 3rd cooling process Crack occurrence
jisoo Distribution fee (%) Footzone 1st cooling zone 2nd cooling zone 3rd cooling zone conventional 0.25 20 35 40 5 15.4 Comparative example 0.40 20 35 40 5 10.6 Example 0.40 30 50 15 5 5.8

As shown in Table 1, in the conventional case, a specific water quantity of 0.25 ℓ/kg is used, and a method of gradually increasing the amount of cooling water is used to minimize reheating on the surface of the cast steel until the end of continuous casting.

However, as mentioned above, since the conventional cooling method causes tissue coarsening on the surface of the cast steel, the crack occurrence index was calculated based on the number of cracks on the surface of the cast steel, and cracks at the level of 15.4 were observed. Here, the crack occurrence index can be defined as Equation 1 below.

<Equation 1>

Crack occurrence index = (0.2 x number of cracks) + (0.9 x crack depth per observation area)

And in the case of the comparative example, the cooling effect was improved by simply increasing the specific water volume while maintaining the same distribution ratio as before. In the comparative example, the surface temperature of the cast steel was lowered by about 100°C at the end of continuous casting compared to the conventional cooling method, and the surface defects were somewhat reduced due to the effect of hard cooling compared to the conventional cooling method, so the surface defect occurrence index was reduced by about 30%. effect was achieved.

However, even when simply increasing the amount of coolant, grinding work is required after actual product production, which is judged to be insufficient to obtain a sufficient surface defect suppression effect.

In the case of this embodiment, the distribution cost is increased along with the method of increasing the specific quantity by 60% compared to the previous one, increasing the initial distribution cost to more than 80%, and even within this initial distribution cost, the pre-distribution cost is increased to more than 30%, and the post-distribution cost is increased to 50% or more. A method of increasing it by more than % was applied.

In this example, as a result of calculating the crack occurrence index based on the cracks generated on the surface of the cast steel, it was confirmed that crack occurrence was reduced by 62% compared to the conventional cooling method.

In other words, it can be confirmed that the continuous casting method according to the present invention achieves the best results in cast surface quality.

Figure 4 is a graph showing the temperature change of the surface of the cast steel as the process progresses in the process of performing the continuous casting method of a shell steel beam blank according to an embodiment of the present invention.

As shown in Figure 4, in the case of the conventional continuous casting process, the temperature change on the surface of the cast steel appears to gradually decrease from the beginning to the end of the process, whereas the continuous casting method of the shell steel beam blank according to this embodiment It can be seen that the temperature of the cast steel at the time of entering the third cooling process fell below the preset target cooling temperature of 855°C.

That is, when the cast steel is cooled to a temperature below the target cooling temperature by initially increasing the specific water quantity and distribution ratio as in this embodiment, fine ferrite and fine precipitates are evenly distributed within the austenite grains on the surface of the cast steel, which is consistent with the conventional constant cooling. Due to the speed method, there is a clear difference from the distribution of ferrite and precipitates along the austenite grain boundaries.

In this way, when ferrite and precipitates are finely distributed within the austenite grains, even if recuperation is achieved above the target cooling temperature, there is a limit to the growth of ferrite and precipitates compared to the conventional cooling method. Therefore, fine ferrite and precipitates remain in the cast steel. It has the effect of refining the grain boundary size of the surface, which leads to the effect of suppressing surface defects such as grain boundary flaws.

Figure 5 is a diagram showing the surface texture of a product manufactured by a conventional continuous casting process and the surface texture of a product manufactured by the continuous casting method of a shell steel beam blank according to an embodiment of the present invention.

Based on the tissue photo of FIG. 5 derived using an optical microscope, the grain size of each cast piece was measured using Clemex Vision Pe S/W.

As a result, in the case of cast steel to which the conventional continuous casting process was applied, the grain size of the surface layer was measured to be 1830㎛ on average, and in the case of cast steel to which the continuous casting method according to the present invention was applied, it was observed to have an average grain size of 350㎛.

In other words, in the present invention, forming fine ferrite and fine precipitates through a quenching process directly under the mold has the effect of refining the grains on the surface of the cast steel, and this grain refinement effect ultimately leads to the effect of suppressing the occurrence of intergranular flaws on the surface of the cast steel. It can be proven that it does.

As described above, preferred embodiments according to the present invention have been examined, and the fact that the present invention can be embodied in other specific forms in addition to the embodiments described above without departing from the spirit or scope thereof is recognized by those skilled in the art. It is self-evident to them. Therefore, the above-described embodiments are to be regarded as illustrative and not restrictive, and thus the present invention is not limited to the above description but may be modified within the scope of the appended claims and their equivalents.

5: Cast iron
10: mold
20: Support roll
F: Foot zone
S1: First cooling zone
S2: Second cooling zone
S3: Third cooling zone

Claims (11)

Carbon (C) 0.10~0.13wt%, Silicon (Si) 0.15~0.20wt%, Manganese (Mn) 1.30~1.50wt%, Aluminum (Al) 0.020~0.050wt%, Vanadium (V) 0.060~0.100wt%, Molten steel containing 0.010~0.020wt% of titanium (Ti), the remaining iron (Fe), and other alloy elements is injected into the mold, and a primary cooling process is performed by contact with the mold as the molten steel passes through the mold. Step (a) of doing;
Step (b) of performing a secondary cooling process on the cast steel produced by primary hardening of the molten steel while passing through the mold by spraying air mist from a foot zone directly below the mold; and
Step (c) of performing a tertiary cooling process by transferring the cast steel that entered the segment area after secondary hardening in the foot zone through a plurality of support rolls and spraying air mist;
Including,
The tertiary cooling process in step (c) is divided into a first cooling zone, a second cooling zone, and a third cooling zone according to the process flow,
Step (b) and step (c) are,
The initial distribution ratio, which is the ratio of the specific water quantity up to the first cooling zone of the secondary cooling process and the tertiary cooling process to the specific water quantity of the entire secondary cooling process and the tertiary cooling process, is higher than 55%,
By controlling the cooling rate in the secondary cooling process and the tertiary cooling process performed in steps (b) and (c), the occurrence of intergranular flaws on the surface of the cast steel is suppressed.
Wimblank’s continuous casting method. delete According to paragraph 1,
Step (b) and step (c) are,
Setting the specific water quantity of the secondary cooling process and the tertiary cooling process to be higher than 0.25 L/kg,
Wimblank’s continuous casting method. According to paragraph 3,
Step (b) and step (c) are,
Increasing the specific water quantity of the secondary cooling process and the tertiary cooling process from 0.25 L/kg to 60% or more,
Wimblank’s continuous casting method. delete According to paragraph 1,
Step (b) and step (c) are,
Increasing the initial distribution ratio to 80% or more,
Wimblank’s continuous casting method. According to paragraph 1,
Step (b) and step (c) are,
The post-distribution ratio, which is the ratio of the specific water quantity of the first cooling zone of the tertiary cooling process to the specific water quantity of the entire secondary cooling process and the tertiary cooling process, is the total of the secondary cooling process and the tertiary cooling process. Increased higher than the pre-distribution ratio, which is the ratio of the specific water quantity of the secondary cooling process to the specific water quantity of
Wimblank’s continuous casting method. In clause 7,
In step (b),
Increase the pre-distribution ratio to more than 30%,
In step (c),
Increasing the post-distribution ratio to 50% or more,
Wimblank’s continuous casting method. According to paragraph 1,
In step (b),
Controlling the secondary cooling process so that the temperature of the cast steel at the time of entering the tertiary cooling process is below 855°C,
Wimblank’s continuous casting method.
Carbon (C) 0.10~0.13wt%, Silicon (Si) 0.15~0.20wt%, Manganese (Mn) 1.30~1.50wt%, Aluminum (Al) 0.020~0.050wt%, Vanadium (V) 0.060~0.100wt%, Contains 0.010~0.020wt% of titanium (Ti), the remaining iron (Fe) and other alloy elements,
Step (a) of injecting molten steel into a mold and performing a primary cooling process by contact with the mold while the molten steel passes through the mold;
Step (b) of performing a secondary cooling process on the cast steel produced by primary hardening of the molten steel while passing through the mold by spraying air mist from a foot zone directly below the mold; and
It includes step (c) of transferring the cast steel that entered the segment area after secondary hardening in the foot zone through a plurality of support rolls and performing a tertiary cooling process by spraying air mist,
The tertiary cooling process in step (c) is divided into a first cooling zone, a second cooling zone, and a third cooling zone according to the process flow,
Step (b) and step (c) are,
The initial distribution ratio, which is the ratio of the specific water quantity up to the first cooling zone of the secondary cooling process and the tertiary cooling process to the specific water quantity of the entire secondary cooling process and the tertiary cooling process, is higher than 55%,
A beam blank manufactured by a continuous casting method that suppresses the occurrence of grain boundary flaws on the surface of the cast steel by controlling the cooling rate in the secondary cooling process and the tertiary cooling process performed in steps (b) and (c). According to clause 10,
After step (c) above,
Wimblank, where the average value of the grain size of the surface layer is 350㎛ or less.