Method for producing high-chromium (Cr) molten steel, method for producing a cast slab, and method for producing a rolling mill roll

Abstract

A method for producing high chromium (Cr) molten steel is provided that can produce high chromium (Cr) molten steel without polluting the converter when producing high chromium (Cr) molten steel using a converter. [Solution] The present invention relates to a method for producing high chromium (Cr) molten steel having a chromium (Cr) content of 4.5 wt% to 5.5 wt%, and includes the steps of charging molten steel into a converter used in a stainless steelmaking process, and charging a chromium ferroalloy containing chromium (Cr) into the converter so that the chromium (Cr) content in the molten steel is 4.5 wt% to 5.5 wt%, the oxygen blowing process of blowing oxygen into the converter into which chromium alloy ferroalloy is charged to remove carbon (C) from the molten steel, the process of adding a deoxidizer to the converter to remove oxygen (O) from the molten steel, and the process of adding a reducing agent to the converter to reduce chromium oxide contained in slag floating on the surface of the molten steel to chromium (Cr), and the steelmaking process further comprises the steps of tapping the molten steel from the converter into a ladle, and a temperature control process of heating the molten steel received in the ladle using a ladle refining furnace (LF), which is a heating device used in a carbon steelmaking process, and a degassing process of removing hydrogen (H2) and nitrogen (N2) from the molten steel received in the ladle using a reflux vacuum degassing (RH) device, which is a vacuum drawing device used in a steelmaking process of carbon steel, The degassing process is performed after the temperature adjustment process is completed.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing high-chromium (Cr) molten steel, a method for manufacturing a slab, and a method for manufacturing a rolling roll. More specifically, the present invention relates to a method for manufacturing high-chromium (Cr) molten steel that can efficiently manufacture high-chromium (Cr) molten steel, and can suppress or prevent the occurrence of segregation simply and at low cost, a method for manufacturing a slab, and a method for manufacturing a rolling roll.

Background Art

[0002] A rolling roll is a steel type containing a high content of chromium (Cr), and is manufactured through a process of solidifying molten steel to produce an ingot and forging the ingot. More specifically, first, molten steel containing a high content of chromium (Cr) is manufactured and solidified to produce an ingot. Then, the ingot is forged and shaped to manufacture a rolling roll. However, when forging the ingot as it is, there are problems such as non-uniform structure of the rolling roll due to segregation inside the ingot, cracking, and low hardness. Therefore, before forging the ingot, segregation contained in the ingot is removed by the electro-slag remelting (ESR) method. Regarding the ESR method, first, an electrode rod is manufactured using the produced ingot. Then, an arc is generated with the produced electrode rod to remelt the electrode rod. At this time, the molten steel formed by remelting the electrode rod is solidified while being dropped in the shape of water droplets to produce an ingot again. At this time, by dropping the molten steel formed by remelting in the shape of water droplets, an ingot with less segregation can be manufactured.

[0003] However, the ESR method requires the following steps: the production of electrode rods from the ingots manufactured as described above, the remelting of the electrode rods, and the dripping and re-solidification of the remelted molten steel. In other words, it must go through multiple stages. As a result, there is a problem in that the time and cost required for the process to suppress segregation are enormous. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Korean Registered Patent Publication No. 10-1346636 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide a method for producing high-chromium (Cr) molten steel using a converter, which allows for the production of high-chromium (Cr) molten steel without contaminating the converter.

[0006] The present invention provides a method for manufacturing cast slabs and rolling rolls that can simplify the process of suppressing or preventing segregation and reduce costs.

[0007] The present invention provides a method for manufacturing a cast slab and a rolling roll that can suppress or prevent the occurrence of cracks, achieve a uniform structure, and have high hardness. [Means for solving the problem]

[0008] The present invention relates to a method for producing high-chromium (Cr) molten steel, comprising the steps of: charging molten steel into a converter used in the stainless steelmaking process; and introducing chromium (Cr)-containing ferroalloys into the converter so that the chromium (Cr) content in the molten steel becomes 4.5 wt% to 5.5 wt%.

[0009] The present invention's method for producing high-chromium (Cr) molten steel may include an oxygen blowing step in which oxygen is blown into the converter into which chromium ferroalloy is introduced to remove carbon (C) from the molten steel; a step in which a deoxidizing agent is introduced into the converter to remove oxygen (O) from the molten steel; and a step in which a reducing agent is introduced into the converter to reduce chromium oxides contained in the slag floating on the surface of the molten steel to chromium (Cr).

[0010] The present invention's method for producing high-chromium (Cr) molten steel may include a step of tapping the molten steel from the converter into a ladle, and a temperature control step of heating the molten steel received in the ladle using a ladle refining furnace (LF), which is a heating device used in the carbon steelmaking process.

[0011] In the aforementioned temperature control process, it is preferable to adjust the temperature of the molten steel to 1560°C to 1600°C.

[0012] The present invention relates to a method for producing high-chromium (Cr) molten steel, which includes a degassing process in which hydrogen (H2) and nitrogen (N2) are removed from the molten steel being received in the ladle using a reflux vacuum degassing (RH: Rheinstaal Huttenwerke und Heraus) apparatus, which is a vacuum device used in the steelmaking process of carbon steel. The degassing process may be carried out after the temperature control process has been completed.

[0013] When tapping the molten steel from the converter into a ladle, it is preferable to tap it into a ladle used in the carbon steelmaking process.

[0014] The present invention provides a method for manufacturing a cast slab, comprising: a step of preparing molten steel containing 4.5 wt% to 5.5 wt% chromium (Cr); a casting step of supplying the molten steel to a mold of a casting apparatus and allowing the molten steel to solidify inside the mold to produce a cast slab containing unsolidified molten steel; a step of withdrawing the cast slab produced in the casting step to the lower side of the mold; and a solidification step of applying a magnetic field to the cast slab withdrawn to the lower side of the mold to allow the unsolidified molten steel contained in the cast slab to flow and solidify to produce a cast slab.

[0015] The solidification process may include a process of heating the end portion of the cast slab that has been withdrawn to the lower side of the mold.

[0016] The casting process may include a step of applying a magnetic field to the mold to cause the molten steel inside the mold to flow.

[0017] When withdrawing the cast slab to the lower side of the mold, it is preferable to withdraw it at a speed of 0.04 m / min or less.

[0018] The solidification process includes a step of spraying cooling water onto the cast slab that has been withdrawn from the mold, and it is preferable to spray the cooling water onto the cast slab so that the surface temperature of the cast slab reaches 800°C to 900°C.

[0019] In the drawing process, it is preferable to draw the cast slab from the mold so that it is perpendicular to the ground, and in the solidification process, it is preferable to allow the cast slab to solidify in a position perpendicular to the ground.

[0020] The present invention provides a method for manufacturing a rolling roll, comprising the steps of: heating a cast slab; forging the heated cast slab to form the shape of a rolling roll; and heating the rolling roll manufactured in the forming step to remove hydrogen (H2) from the rolling roll, wherein the step of heating the cast slab includes a step of heating the cast slab to a target temperature in multiple stages.

[0021] The process of heating the ingot to the target temperature may include a process of heating the ingot to a first temperature of 250°C to 350°C, a process of heating the ingot to a second temperature of 450°C to 550°C, a process of heating the ingot to a third temperature of 650°C to 750°C, and a process of heating the ingot to the target temperature of 1100°C to 1250°C.

[0022] When heating the ingot to the first to third temperatures and the target temperature, the ingot may be held at the first temperature for 3 to 5 hours, held at the second temperature for 5 to 7 hours, held at the third temperature for 3 to 5 hours, and held at the target temperature for 14 to 18 hours.

[0023] When forging the ingot, the ingot heated to a temperature of 1100°C to 1250°C is pressed and forged, and each time the ingot is pressed using a pressing device, the ingot may be pressed so that the thickness of the ingot decreases by 250 mm to 350 mm.

[0024] When removing hydrogen (H2) from the rolling roll, it may include a process of heating the rolling roll to a temperature of 200°C to 400°C.

[0025] When heating the rolling roll to the temperature of 200°C to 400°C, it is preferably heated for 48 hours or more.

Advantages of the Invention

[0026] According to the present invention, while utilizing a converter used for steelmaking of other steel grades, high-chromium (Cr) molten steel can be produced without contaminating the converter used for steelmaking of other steel grades. Further, when raising the temperature of the high-chromium (Cr) molten steel or performing degassing to exhaust gas, the temperature of the molten steel can be effectively raised, and the degassing efficiency can be increased.

[0027] Furthermore, it is possible to suppress or prevent segregation within the cast slab more easily and at a lower cost than conventional methods. In addition, when forging the cast slab to manufacture rolling rolls, crack formation is suppressed or prevented, resulting in the manufacture of rolling rolls with a uniform structure and high hardness. [Brief explanation of the drawing]

[0028] [Figure 1] This is a step diagram showing a method for manufacturing the rolling rolls of the present invention. [Figure 2] This is a step procedure diagram showing the molten steel preparation process (a) to (g) of the present invention in order. [Figure 3] This diagram shows the operation of the casting apparatus of the present invention in order from (a) to (d). [Figure 4] This diagram shows, in order, a process procedure for manufacturing a rolling mill roll using a cast slab produced by a method according to an embodiment of the present invention (a) to (c). [Figure 5] (a) and (b) show the results of cutting the cross-section of the rolling roll and etching the cross-section to check for the presence or absence of coarse segregation. [Modes for carrying out the invention]

[0029] The present invention will be described in more detail below with reference to the attached drawings. However, the present invention is not limited in any way and can be embodied in various different forms, which are provided merely to complete the disclosure of the present invention and to fully inform those in the ordinary skill of the scope of the invention. The drawings may be exaggerated in order to illustrate the present invention, and in the drawings, the same reference numerals refer to the same components.

[0030] Figure 1 is a step diagram showing a method for manufacturing the rolling roll of the present invention.

[0031] As shown in Figure 1, the method for manufacturing rolling rolls includes the steps of preparing molten steel (S100), solidifying the molten steel to produce a cast slab (S200), heating the cast slab (S300), forging the heated cast slab to manufacture rolling rolls (S400), and heating the rolling rolls (S500).

[0032] The rolling mill rolls are made of ferroalloy with a high chromium (Cr) content. More specifically, the rolling mill rolls are made of high-chromium (Cr) ferroalloy, with a chromium (Cr) content of 4.5 wt% to 5.5 wt% throughout the entire material. To explain in more detail, the rolling mill rolls are an alloy ferroalloy consisting of 4.5 wt% to 5.5 wt% chromium (Cr), 0.75 wt% to 0.95 wt% carbon (C), 0.2 wt% to 0.5 wt% silicon (Si), 0.2 wt% to 0.5 wt% manganese (Mn), 0.4 wt% to 0.65 wt% molybdenum (Mo), 0.5 wt% or less (0 wt% or more) nickel (Ni), 0.2 wt% or less (0 wt% or more) copper (Cu), 0.0025 wt% or less (0 wt% or more) phosphorus (P), and 0.015 wt% or less (0 wt% or more) sulfur (S), with the remainder being iron (Fe) (91.16 wt% to 93.15 wt%).

[0033] Adjusting the chromium (Cr) content of the rolling mill roll to 4.5 wt% to 5.5 wt% and the carbon (C) content to 0.75 wt% to 0.95 wt% is done to ensure hardness and workability. For example, if the chromium (Cr) content in the rolling mill roll is less than 4.5 wt% or the carbon (C) content is less than 0.75 wt%, there is a risk of the rolling mill roll having low hardness. Conversely, if the chromium (Cr) content in the rolling mill roll exceeds 5.5 wt% or the carbon (C) content exceeds 0.95 wt%, the rolling mill roll will have poor workability, which may make it difficult to process the manufactured rolling mill roll as needed.

[0034] Furthermore, adjusting the phosphorus (P) content in the rolling rolls to 0.025 wt% or less and the sulfur (S) content to 0.015 wt% or less is done to make the structure of the rolling rolls uniform and to suppress or prevent the occurrence of cracks. In other words, if the phosphorus (P) content in the rolling rolls exceeds 0.025 wt% or the sulfur (S) content exceeds 0.015 wt%, there is a risk that the structure will become non-uniform due to segregation inside the rolling rolls. As a result, when the object to be rolled is pressed using the rolling rolls, there is a risk that cracks will occur in the rolling rolls. Therefore, the phosphorus (P) content in the rolling rolls is adjusted to 0.025 wt% or less, and the sulfur (S) content is adjusted to 0.015 wt% or less.

[0035] The rolling rolls to be manufactured in this invention may be rolls used in a rolling apparatus that applies force to an object to be rolled, such as a cast slab or a steel plate, for rolling.

[0036] In the process of preparing molten steel (S100), molten steel for manufacturing rolling rolls is prepared. That is, in the process of preparing molten steel (S100), molten steel having the content of the components that rolling rolls should have is prepared. In other words, high-chromium (Cr) molten steel is prepared, in which the chromium (Cr) content in the molten steel is 4.5 wt% to 5.5 wt%. More specifically, when preparing molten steel, the molten steel is made up of 4.5 wt% to 5.5 wt% chromium (Cr), 0.75 wt% to 0.95 wt% carbon (C), 0.2 wt% to 0.5 wt% silicon (Si), 0.2 wt% to 0.5 wt% manganese (Mn), 0.4 wt% to 0.65 wt% molybdenum (Mo), 0.5 wt% or less (0 wt% or more) nickel (Ni), 0.2 wt% or less (0 wt% or more) copper (Cu), 0.0025 wt% or less (0 wt% or more) phosphorus (P), and 0.015 wt% or less (0 wt% or more) sulfur (S), with the remainder being iron (Fe) (91.16 wt% to 93.15 wt%). This can be achieved by sequentially carrying out each stage of the molten steel preparation process, which will be described later.

[0037] Figures 2(a) to (g) are step-by-step process diagrams showing the molten steel preparation process of the present invention.

[0038] As shown in Figure 2, the process of preparing molten steel M (S100) may include a process of processing the molten steel M using a converter 11 (hereinafter referred to as the converter processing process (S110)), a process of tapping the molten steel M from inside the converter 11 into a ladle 20 (S120), a temperature control process (S130) in which the temperature of the molten steel M tapped into the ladle 20 is adjusted using a temperature control device 30, and a degassing process (S140) in which gas is removed from the molten steel M using a vacuum device 40.

[0039] The converter treatment process (S110) is a process of adjusting the composition of molten steel M while it is charged into the converter 11. The converter 11 used in the converter treatment process (S110) is a converter used in the steelmaking process (hereinafter referred to as the stainless steel steelmaking process) that prepares molten steel for the manufacture of stainless steel (hereinafter referred to as molten steel for the manufacture of stainless steel). In other words, when preparing the molten steel according to the embodiment, the converter 11 used in the stainless steel steelmaking process is utilized.

[0040] For a more detailed explanation, we will briefly describe the stainless steelmaking process using a converter. The stainless steelmaking process includes the process of charging molten steel into the converter, the process of adding ferroalloys containing chromium (Cr) and ferroalloys containing nickel (Ni) into the converter, and the oxygen blowing process, in which oxygen is injected into the converter using a lance to remove carbon (C) and phosphorus (P), etc. When adding chromium (Cr) ferroalloys into the converter, the amount is increased so that the chromium (Cr) content in the molten steel is 10.5 wt% to 11 wt%. Therefore, the molten steel prepared in the stainless steelmaking process using a converter contains 10.5 wt% to 11 wt% chromium.

[0041] For comparison, a brief explanation will be given of the steelmaking process using a converter in the process of preparing molten steel for the production of carbon steel (hereinafter referred to as the carbon steel production process). The carbon steel production process includes the process of charging molten steel into the converter and the oxygen blowing process, in which oxygen is injected into the converter using a lance to remove carbon (C) and phosphorus (P), etc. Carbon steel is a steel with a low chromium (Cr) content. Therefore, in the carbon steel production process, chromium (Cr) is not added to the converter, and the chromium (Cr) content in the molten steel is adjusted to be low, between 0.1 wt% and 1.0 wt%.

[0042] As mentioned above, in the converters used in the stainless steelmaking process, molten steel with a high chromium (Cr) content of 10.5 wt% to 11 wt% is prepared. In other words, molten steel with a high chromium (Cr) content of 10.5 wt% to 11 wt% is placed inside the converters used in the stainless steelmaking process. However, in the converters used in the carbon steelmaking process, molten steel with a low chromium (Cr) content of 0.1 wt% to 1.0 wt% is placed inside.

[0043] Therefore, when preparing molten steel for the manufacture of rolling mill rolls with a high chromium (Cr) content of 4.5 wt% to 5.5 wt%, if a converter used in the carbon steel manufacturing process is used, there is a risk that the carbon steel manufacturing converter will become contaminated. In other words, if molten steel with a high chromium (Cr) content of 4.5 wt% to 5.5 wt% is put into a carbon steel manufacturing converter, there is a risk that a large amount of chromium (Cr) will remain inside the carbon steel manufacturing converter even after the molten steel has been tapped. For example, there is a risk that a large amount of chromium (Cr) will adhere to or solidify on the inner wall of the carbon steel manufacturing converter. As a result, the carbon steel manufacturing converter becomes contaminated with chromium (Cr). When a carbon steel manufacturing converter with a large amount of residual chromium (Cr) is used in the carbon steel manufacturing process, a large amount of chromium (Cr) will be included in the molten steel, and as a result, the chromium (Cr) will act as an impurity that degrades the quality of the carbon steel.

[0044] However, when preparing high-chromium (Cr) molten steel with a high chromium (Cr) content of 4.5 wt% to 5.5 wt%, if a converter used in the stainless steel manufacturing process is used, the converter for stainless steel production will not become contaminated. That is, even if molten steel with a high chromium (Cr) content of 4.5 wt% to 5.5 wt% is placed into the converter 11 for stainless steel production and then tapped, leaving a large amount of chromium (Cr) inside the converter, the chromium remaining inside the converter will not act as an impurity. This is because the converter for stainless steel production is a means of handling molten steel with a high chromium content of 10.5 wt% to 11 wt%. Furthermore, the chromium (Cr) content of the molten steel placed into the converter for stainless steel production is even higher than that of the molten steel intended to be produced in this embodiment. Therefore, even if molten steel for the production of rolling rolls is placed into the converter for stainless steel production, the converter for stainless steel production will not become contaminated. Therefore, when using a converter for stainless steel production that contains molten steel according to the embodiment to produce molten steel for stainless steel production again, problems caused by chromium (Cr) from the previously contained molten steel do not occur.

[0045] Therefore, in this embodiment, when processing molten steel using the converter 11 (S110), the converter 11 used in the stainless steelmaking process described above is used. This allows the converter to be used without causing contamination of the converter 11 with chromium (Cr). Furthermore, the converter used to prepare the molten steel according to the embodiment containing 4.5 wt% to 5.5 wt% of chromium (Cr) can be used to prepare molten steel for stainless steel production. In other words, the converter for stainless steel production can be interchanged between the operation to prepare molten steel for stainless steel production and the operation to prepare molten steel according to the embodiment containing 4.5 wt% to 5.5 wt% of chromium (Cr).

[0046] As the temperature control device 30 used in the temperature control process and the vacuum device 40 used in the degassing process, a ladle refining furnace (LF) and reflux vacuum degassing (RH) apparatus used in the steelmaking process (hereinafter referred to as the carbon steel steelmaking process) for preparing molten steel for the production of carbon steel (hereinafter referred to as molten steel for the production of carbon steel) are used. The reason for using a ladle refining furnace and RH apparatus in the carbon steel steelmaking process will be explained later.

[0047] The molten steel preparation process of the present invention will be explained in more detail below, based on Figure 2.

[0048] As explained above, the molten steel preparation process (S100) includes the process of processing the molten steel M using the converter 11 (S110), the process of tapping the molten steel M from inside the converter 11 into a ladle (S120), the process of adjusting the temperature of the molten steel M using the temperature control device 30 (S130), and the degassing process (S140) of removing gas from the molten steel M using the vacuum device 40.

[0049] As shown in Figures 2(a) to 2(d), the process of processing molten steel M using the converter 11 (S110) may include the process of introducing chromium (Cr)-containing ferroalloy (hereinafter referred to as chromium (Cr) ferroalloy) into the converter 11 (S111) (Figure 2(a)), the oxygen blowing process of injecting oxygen into the molten steel inside the converter 11 (S112) (Figure 2(b)), the deoxidation process of removing oxygen (O) contained in the molten steel M (S113) (Figure 2(c)), and the process of reducing chromium oxide contained in the slag floating on the surface of the molten steel M to chromium (Cr) (S114) (Figure 2(d)).

[0050] Although not shown in the diagram, the molten steel preparation process may also include a preliminary refining process to remove sulfur (S), phosphorus (P), and silicon (Si) contained in the molten steel before charging it into the converter. First, the preliminary refining process will be briefly explained. The preliminary refining process may include a first preliminary refining process to remove sulfur (S) from the molten steel, and a second preliminary refining process to remove phosphorus (P) and silicon (Si) from the molten steel. In the first preliminary refining process, the sulfur (S) content in the molten steel is adjusted to 0.04 wt% or less. Then, in the second preliminary refining process, the silicon (Si) content in the molten steel is adjusted to 0.05 wt% or more, and the phosphorus (P) content is adjusted to 0.03 wt% or less. In carrying out these first and second preliminary refining processes, quicklime (CaO) and fluorite (CaF2) are added to the ladle containing the molten steel to remove sulfur (S), silicon (Si), and phosphorus (P) from the molten steel. Furthermore, the first and second preliminary refining processes can be carried out in a Hot Metal Pretreatment Station (HMPS).

[0051] Once the first and second preliminary refining processes are completed, the molten steel M is charged into the converter 11. Here, the converter 11 into which the molten steel M is charged is the same converter 11 used in the stainless steelmaking process, as described above.

[0052] Once molten steel M is charged into the converter 11, chromium (Cr) alloy ferrolithium is added to the inside of the converter 11, as shown in Figure 2(a). As a result, the chromium (Cr) alloy ferrolithium added to the converter 11 is melted by the heat of the molten steel M. At this time, the amount of chromium (Cr) alloy ferrolithium added is adjusted so that the total chromium (Cr) content of the molten steel M is between 4.5 wt% and 5.5 wt%. Therefore, molten steel M with a high chromium (Cr) content of 4.5 wt% to 5.5 wt% is produced.

[0053] Next, as shown in Figure 2(b), oxygen blowing is performed by blowing or spraying oxygen into the molten steel M inside the converter 11. That is, after inserting a part of the lance into the converter 11, oxygen (O) is supplied into the lance 12. As a result, oxygen (O) is blown in or sprayed out from the lance 12. The oxygen (O) blown into the converter 11 using the lance 12 reacts with the carbon (O) contained in the molten steel M (C + O- → CO(gas)). At this time, the carbon (O) in the molten steel M reacts with the oxygen (O) to become carbon monoxide (CO) gas, and the generated carbon monoxide (CO) gas is exhausted to the outside of the converter 11. As a result, the carbon (C) content contained in the molten steel M decreases. In other words, decarburization occurs, in which the carbon (C) content of the molten steel M decreases. At this time, at least one of the oxygen injection flow rate and time is adjusted so that the carbon (C) content in the molten steel M is between 0.75 wt% and 0.95 wt%.

[0054] In this way, when oxygen is blown into the converter 11 to promote decarburization, reaction byproducts consisting of metal oxides are produced in addition to carbon monoxide (CO) gas. These reaction byproducts then rise to the upper surface of the molten steel M, that is, to the molten surface side of the molten steel M, and float above the surface of the molten steel M. These reaction byproducts floating above the surface of the molten steel are called slag (SL).

[0055] When the carbon (C) content in the molten steel M reaches 0.75 wt% to 0.95 wt% and decarburization is complete, or when the carbon (C) content in the molten steel M decreases and approaches 0.95 wt% in the final stages of decarburization, a dephosphorizing agent is introduced into the converter 11. At this time, the dephosphorizing agent is introduced while blowing oxygen into the converter 11 using a lance 12. The dephosphorizing agent may be, for example, a material containing quicklime (CaO). As a result, the phosphorus (P) in the molten steel M reacts with the dephosphorizing agent and oxygen (O) (3CaO + 2P + 5O- → 3CaO·P2O5). The reaction byproduct, 3CaO·P2O5, then rises to the surface and is absorbed by the slag SL floating on the surface of the molten steel M. In other words, the phosphorus (P) separated from the molten steel M is absorbed by the slag SL floating on the surface of the molten steel M. As a result, the phosphorus (P) content in the molten steel M decreases. In other words, dephosphorization occurs, which reduces the phosphorus (P) content in the molten steel M. At this time, at least one of the following is adjusted: the amount of dephosphorizing agent added, the oxygen injection flow rate, and the oxygen injection time, so that the phosphorus (P) content in the molten steel M is 0.025 wt% or less.

[0056] After decarburizing and dephosphorizing molten steel M by blowing oxygen into it, the oxygen (O) content in the molten steel M increases. The oxygen (O) in the molten steel M causes pinholes in the cast slab. In addition, the oxygen (O) in the molten steel reacts with the metal contained in the molten steel, causing the formation of metal oxide inclusions. These inclusions in the molten steel cause cracking defects in the cast slab.

[0057] Therefore, after the oxygen blowing is completed, deoxidation is performed to remove oxygen (O) from the molten steel M. For this purpose, a deoxidizing agent containing at least one of silicon (Si) and aluminum (Al) is introduced into the converter 11. At least one of an alloy containing silicon (Si) and an alloy containing aluminum (Al) can be used as the deoxidizing agent. In this case, the alloy containing silicon (Si) may be an Fe-Si alloy iron containing silicon (Si) and iron (Fe), with silicon (Si) contained at 70 wt% to 80 wt% and iron (Fe) contained at 20 wt% to 30 wt%. The alloy containing aluminum (Al) may be an alloy close to pure aluminum (Al) containing aluminum (Al) at 90 wt% to 95 wt%.

[0058] When a deoxidizing agent is added, the oxygen (O) contained in the molten steel M reacts with at least one of the silicon (Si) and aluminum (Al) contained in the deoxidizing agent. As a result, at least one of silicon oxides such as SiO2 and aluminum oxides such as Al2O3 are produced. The reaction byproducts of at least one of the silicon oxides and aluminum oxides are then absorbed by the slag SL floating on the surface of the molten steel M. As a result, the oxygen (O) content in the molten steel M decreases (deoxidation). At this time, the amount of deoxidizing agent added is adjusted so that the oxygen (O) content in the molten steel M is 0.001 wt% or less.

[0059] As explained above, at least one of a silicon (Si)-containing alloy and an aluminum (Al)-containing alloy is used as a deoxidizing agent. In this case, it is preferable to use a silicon (Si)-containing ferroalloy and an aluminum (Al)-containing ferroalloy in combination as deoxidizing agents, rather than using a silicon (Si)-containing alloy or an aluminum (Al)-containing alloy as a deoxidizing agent alone.

[0060] On the other hand, if the oxygen (O) content in the molten steel exceeds 0.001 wt%, there is a risk of pinhole defects occurring in the cast slab due to the oxygen (O), and cracking due to a large amount of inclusions. Therefore, the oxygen (O) content in the molten steel M is adjusted to 0.001 wt% or less during the deoxidation process.

[0061] As described above, when oxygen blowing is performed to remove carbon (C) and phosphorus (P) from molten steel M, the (S110) chromium (Cr) that was added to the molten steel M is oxidized, and thus becomes chromium oxide. The generated chromium oxide is then absorbed by the slag SL floating on the surface of the molten steel M. As a result, the chromium (Cr) content in the molten steel decreases. Therefore, it is necessary to reduce the chromium oxide contained in the slag SL back into chromium and supply it back to the molten steel M. For this purpose, a reducing agent is added to the inside of the converter 11 after deoxidation is complete. More specifically, the reducing agent is added to the slag SL. At this time, the reducing agent may be a material containing silicon (Si), and more specifically, it may be a silicon (Si)-containing ferroalloy. To give a more specific example, the reducing agent may contain 70 wt% to 80 wt% silicon (Si) and 20 wt% to 30 wt% iron (Fe).

[0062] When the reducing agent is added to the converter 11, the chromium oxide contained in the slag SL reacts with the silicon (Si) contained in the reducing agent. As a result, the chromium oxide in the slag SL is reduced to chromium (Cr), and the generated chromium (Cr) is absorbed or supplied to the molten steel. Therefore, the chromium (Cr) content in the molten steel increases. At this time, the amount of reducing agent added is adjusted so that the chromium (Cr) content in the molten steel is between 4.5 wt% and 5.5 wt%.

[0063] Once the reduction to chromium is complete, the composition and temperature of the molten steel M are checked. For example, molten steel M is taken from inside the converter 11 (or sampled), and the composition and temperature of the sampled molten steel are measured. Then, it is checked whether the composition of the measured molten steel M is within the target composition range, and whether the temperature of the measured molten steel M is within the target temperature range. Here, the target temperature may be, for example, 1650°C to 1750°C.

[0064] To explain with a more specific example, the content of each of the elements—chromium (Cr), carbon (C), phosphorus (P), sulfur (S), and oxygen (O)—is checked to see if it falls within the target content. If the content of each of the elements—chromium (Cr), carbon (C), phosphorus (P), sulfur (S), and oxygen (O)—is within the target content and the temperature of the molten steel is within the target temperature, the slag floating on the surface of the molten steel is removed (not shown). That is, the slag is removed from the surface of the molten steel. However, if the content of each of the elements—chromium (Cr), carbon (C), phosphorus (P), sulfur (S), and oxygen (O)—is not within the target content, or if the temperature of the molten steel is not within the target temperature, the process of adjusting the content of the elements or adjusting the temperature is repeated. Specifically, if the content of chromium (Cr), carbon (C), phosphorus (P), sulfur (S), and oxygen (O) in the molten steel does not meet the target levels, at least one of the following processes is carried out: addition of chromium (Cr) ferroalloy, decarburization, dephosphorization, desulfurization, deoxidation, and chromium reduction. Also, if the temperature of the molten steel M is below 1650°C, the molten steel M is heated to a temperature of 1650°C or higher. Conversely, if the temperature of the molten steel exceeds 1750°C, the temperature of the molten steel is reduced.

[0065] On the other hand, if the content of each component in the molten steel deviates from the target content, there is a risk that the quality of the cast slab S will deteriorate. Specifically, if the content of at least one of the following—chromium (Cr), carbon (C), phosphorus (P), sulfur (S), and oxygen (O)—deviates from the target content, there is a risk that the hardness of the manufactured cast slab will be low, or that pinholes and cracks will occur on the surface or inside the cast slab. This, in turn, can lower the hardness of the rolling rolls and contribute to the formation of pinholes and cracks on the surface or inside.

[0066] Furthermore, if the temperature of the molten steel M is below 1650°C, it may become difficult to raise the temperature of the molten steel M to the target temperature (the starting target temperature of the ladle smelting furnace (LF)) in the subsequent temperature control process. As a result, when supplying the molten steel M to the tundish, the temperature of the molten steel M may not reach the target casting temperature. In such a case, there is a risk that the nozzle that supplies the molten steel from the tundish to the mold may become blocked. Conversely, if the temperature of the molten steel M exceeds 1750°C, there is a risk that the refractory materials constituting the converter may be eroded and damaged by the high heat. Therefore, the temperature of the molten steel M is adjusted to be between 1650°C and 1750°C during the converter processing process.

[0067] Once the content of each component in the molten steel M is within the target range and the temperature of the molten steel M is within the target range, the slag floating above the surface of the molten steel M is removed (not shown).

[0068] After removing the slag SL from inside the converter 11, the molten steel M inside the converter 11 is tapped into the ladle 20. At this time, it is preferable to tap the molten steel M into the ladle 20 used in the carbon steelmaking process. This is because the equipment used in the subsequent processes uses the ladle 20 used in the carbon steelmaking process. Specifically, in the temperature control process, a ladle refining furnace (LF) is used as the temperature control device 30, and in the degassing process, a reflux vacuum degassing (RH: Rheinstaal Huttenwerke und Heraus) device is used as the vacuum device 40. At this time, the ladle refining furnace (LF) and the RH device are equipment used in the carbon steelmaking process and are connected to the ladle used in the carbon steelmaking process.

[0069] Furthermore, ladle smelting furnaces (LF) are not used in the stainless steel production process. In addition, while vacuum equipment is used in the stainless steel production process, this is a vacuum tank degasser (VTD), which is different from the RH equipment used in the carbon steel production process.

[0070] In this embodiment, when tapping the molten steel from inside the converter 11 into a ladle, the steel is tapped into a ladle 20 used in the carbon steelmaking process. That is, in order to use the equipment used in the carbon steelmaking process in the subsequent temperature control process and degassing process, the molten steel is tapped into a ladle 20 used in the carbon steelmaking process.

[0071] As described above, in this embodiment, a ladle smelting furnace is used as the temperature control device 30, and an RH device is used as the vacuum device 40. For this reason, in the following description, the temperature control device and the ladle smelting furnace will be given the same reference numeral "30" in the drawings, and the vacuum device and the RH device will be given the same reference numeral "40" in the drawings.

[0072] Once the tapping of molten steel M into the ladle 20 is complete, the ladle 20 containing the molten steel M is moved to the temperature control device 30, as shown in Figure 2(f), and the ladle 20 is connected to the temperature control device 30. That is, the ladle 20 is moved to the ladle refining furnace 30, which is a temperature control device 30 used in the carbon steelmaking process, and the ladle 20 is connected to the ladle refining furnace 30. The ladle refining furnace may be equipped with a cover 32 that covers the opening at the top of the ladle 20 and an electrode rod 31 that can be inserted into the inside of the ladle 20 by penetrating the cover 32, as shown in Figure 2(f). Then, in such a ladle refining furnace 30, desulfurization is performed to remove sulfur (S) from the molten steel, the carbon (C) and chromium (Cr) content is adjusted, and then the temperature of the molten steel is adjusted.

[0073] First, the desulfurization process using the ladle smelting furnace 30 will be explained. When the ladle 20 arrives at the ladle smelting furnace 30, the cover 32 of the ladle smelting furnace 30 is attached to the top of the ladle 20. Then, the desulfurizing agent is put into the ladle 20. At this time, the desulfurizing agent can be passed through the opening provided in the cover 32 and put into the ladle 20. As the desulfurizing agent, it is preferable to use at least one of a first material containing quicklime (CaO) and alumina (Al2O3) and a second material containing fluorite (CaF2). When the desulfurizing agent is put into the ladle 20, the desulfurizing agent reacts with the sulfur (S) in the molten steel to produce a reaction byproduct containing sulfur (S), and the produced reaction byproduct is absorbed into the slag SL on the surface of the molten steel M. As a result, the sulfur (S) content in the molten steel decreases (desulfurization). At this time, the sulfur (S) content in the molten steel should be kept below 0.015 wt%, which can be adjusted by controlling the amount of desulfurizing agent added.

[0074] Once desulfurization is complete, the molten steel M contained in the ladle 20 is sampled, and its carbon (C) and chromium (Cr) content is measured. Then, the carbon (C) and chromium (Cr) content in the molten steel M is adjusted according to the measured carbon (C) and chromium (Cr) content. For example, if the carbon (C) content is low, less than 0.75 wt%, a carbon (C)-containing carburizing agent is added to the ladle 20. The amount of carburizing agent added is then adjusted so that the carbon (C) content in the molten steel M is 0.75 wt% or higher. Conversely, if the measured carbon (C) content exceeds 0.95 wt%, solid oxygen, such as iron ore like FeO, is added to the ladle 20. At this time, the amount of solid oxygen added is adjusted so that the carbon (C) content in the molten steel M is 0.95 wt% or lower.

[0075] To give another example, if the measured chromium (Cr) content is low, less than 4.5 wt%, chromium (Cr)-containing iron alloy is added to the ladle 20. Conversely, if the measured chromium (Cr) content exceeds 5.5 wt%, solid oxygen, such as iron ore like FeO, is added to the ladle 20. At this time, the amount of solid oxygen added is adjusted so that the chromium (Cr) content in the molten steel is 5.5 wt% or less.

[0076] In the above, we have described the process of introducing solid oxygen into the ladle 20 connected to the ladle refining furnace 30 when the carbon (C) content exceeds 0.95 wt% or the chromium (Cr) content exceeds 5.5 wt%. However, the present invention is not limited thereto, and in subsequent processes, oxygen may be blown into the molten steel M in a vacuum device 40 to adjust the carbon (C) content to 0.95 wt% or less, or the chromium (Cr) content to 5.5 wt% or less.

[0077] Once molten steel M is tapped into ladle 20, ladle 20 is moved for the next process. However, the temperature of the molten steel M gradually decreases as ladle 20 moves. In other words, even if the temperature of the molten steel M is adjusted to 1650°C to 1750°C before tapping the molten steel from the converter 11 into ladle 20, the temperature of the molten steel M will decrease as ladle 20 moves to the next process.

[0078] Therefore, before moving the ladle 20 to the vacuum pump 40 used in the subsequent process, it is necessary to heat the molten steel M inside the ladle 20. For this purpose, power is supplied to the electrode rod 31 to generate an arc and heat from the electrode rod 31, and the molten steel is heated by the generated arc and heat. At this time, the molten steel M is heated so that its temperature reaches the starting target temperature, which may be 1560°C to 1600°C. Here, the starting target temperature refers to the target temperature of the molten steel M contained in the ladle 20 when the ladle 20, removed from the ladle refining furnace 30, departs for the subsequent process. Adjusting the temperature of the molten steel M to reach the starting target temperature can be done by controlling at least one of the amount of power supplied to the electrode rod 31 and the heating time of the molten steel using the electrode rod 31.

[0079] On the other hand, when the ladle 20 removed from the ladle refining furnace 30 departs for the subsequent process, if the temperature of the molten steel M (hereinafter referred to as the departure temperature) is less than 1560°C or exceeds 1600°C, the temperature of the molten steel M may deviate from the target casting temperature when the ladle 20 reaches the tundish of the casting apparatus. Here, the target casting temperature is the target temperature of the molten steel received in the tundish, and the target casting temperature may be between 1520°C and 1550°C. If the departure temperature is less than 1560°C, the temperature of the molten steel M may be less than 1520°C when the ladle reaches the tundish. Also, if the departure temperature is less than 1600°C, the temperature of the molten steel may exceed 1550°C when the ladle reaches the tundish.

[0080] If the temperature of the molten steel M is below 1520°C when the ladle 20 reaches the tundish, there is a risk that the nozzle supplying the molten steel M from the tundish to the mold may become blocked. Also, if the temperature of the molten steel exceeds 1600°C when the ladle 20 reaches the tundish, there is a risk of a breakout occurring when the molten steel solidifies in the casting apparatus, causing the solidified shell to rupture and the molten steel inside to spill out. Therefore, the starting temperature of the molten steel M in the ladle smelting furnace 30 is adjusted to be between 1560°C and 1600°C so that when the ladle 20 reaches the tundish, the temperature of the molten steel is between 1520°C and 1550°C.

[0081] The reason for using a ladle refining furnace (LF), which is used in the carbon steelmaking process, when carrying out the temperature control process (S130) is that it can effectively raise the temperature of the molten steel M without contaminating it. In other words, in the stainless steelmaking process, when raising the temperature of the molten steel, a metal such as aluminum (Al) is added to the molten steel to cause an exothermic reaction and raise the temperature. That is, in the stainless steelmaking process, no separate heating device is used when raising the temperature of the molten steel. For this reason, in this embodiment, the temperature of the molten steel M is adjusted using a ladle refining furnace 30, which is used to raise the temperature of the molten steel in the carbon steelmaking process. Therefore, the temperature of the molten steel M can be raised without adding any other materials to the molten steel M. In other words, the temperature of the molten steel can be increased without changing the composition of the molten steel M.

[0082] Once the composition and temperature in the ladle smelting furnace 30 have been adjusted, the ladle 20 is removed from the ladle smelting furnace 30. Next, the ladle 20 removed from the ladle smelting furnace 30 is moved to the vacuum device 40. Then, degassing is performed using the vacuum device 40 to remove nitrogen (N2) and hydrogen (H2) contained in the molten steel M (S140).

[0083] The vacuum device 40 is a reflux vacuum degassing (RH: Rheinstaal Huttenwerke und Heraus) device 40, and is an RH device 40 used in the carbon steelmaking process. Referring to Figure 2(g), the RH device 40 may include a vessel 41 having an internal space, a pump (not shown) connected to the vessel 41 so as to be able to adjust the pressure inside the vessel 41, a pair of reflux pipes 42a and 42b arranged in parallel on the left and right so as to be fitted inside the ladle 20 and connected to the bottom of the vessel 41, and a lance 43 fitted to the upper side of the vessel 41 for blowing in oxygen. Here, one of the pair of reflux pipes 42a and 42b, 42a, is a riser pipe through which the molten steel inside the ladle 20 rises, and the other reflux pipe 42b is a descender pipe through which the molten steel that has risen from the riser pipe descends towards the ladle 20.

[0084] The process of removing gas from molten steel M using such an RH apparatus 40 will now be described. First, a ladle 20 is positioned below a pair of reflux pipes 42a and 42b, and these are joined together to seal them. Then, the pressure inside the vessel 41 is reduced to a vacuum pressure, for example, 0.2 torr or less, and the ladle 20 is raised so that the pair of reflux pipes 42a and 42b are immersed in the molten steel inside the ladle 20. After this, an inert gas, for example, argon (Ar), is blown into the pair of reflux pipes 42a and 42b to circulate the molten steel M inside the vessel 41. The circulating molten steel is exposed to the vacuum atmosphere inside the vessel 41, and as a result, nitrogen (N2) and hydrogen (H2) gases in the molten steel are exhausted to the outside of the vessel 41. Therefore, the nitrogen (N) and hydrogen (H2) content in the molten steel M decreases, and at this time, the nitrogen (N2) content is reduced to 0.015 wt% or less, and the hydrogen (H2) content is reduced to 0.0005 wt% or less.

[0085] The following explains why the hydrogen (H2) content is adjusted to 0.0005 wt% or less during the degassing process (S140).

[0086] When manufacturing rolling rolls, it is necessary to adjust the hydrogen (H2) content in the rolling rolls to 0.0002 wt% or less. This is because hydrogen (H2) contained inside the rolling rolls tends to accumulate in inclusions and segregation, which can cause internal cracking in the rolling rolls when they are actually used. Here, "actual use of the rolling rolls" may refer to using the manufactured rolling rolls to roll an object to be rolled, such as a cast slab. For this reason, the hydrogen (H2) content in the rolling rolls is adjusted to 0.0002 wt% or less. When the hydrogen (H2) content in the rolling rolls is 0.0002 wt% or less, internal cracking due to hydrogen (H2) will not occur, or will be minimal. Furthermore, since it is practically difficult to completely remove hydrogen from rolling rolls, the hydrogen content is adjusted to 0.0002 wt% or less.

[0087] Thus, in order for the hydrogen (H2) content in the rolling rolls to be 0.0002 wt% or less, it is preferable to reduce the hydrogen (H2) content in the molten steel to 0.0005 wt% or less in the degassing process (S140). In other words, if the hydrogen (H2) content in the molten steel M cannot be adjusted to 0.0005 wt% or less in the degassing process (S140), it will be difficult to adjust the hydrogen (H2) content to 0.0002 wt% or less in the subsequent process of heating the rolling rolls to remove hydrogen (Figure 4(c)). In other words, it will be difficult to manufacture rolling rolls with a hydrogen (H2) content adjusted to 0.0002 wt% or less. Therefore, the hydrogen (H2) content in the molten steel is adjusted to 0.0005 wt% or less in the degassing process (S140).

[0088] Furthermore, in the degassing process (S140), the nitrogen (N2) content in the molten steel M is adjusted to 0.015 wt% or less. If the nitrogen (N2) content in the molten steel M exceeds 0.015 wt%, nitrogen (N2) precipitates will be generated when the cast slab is manufactured, which may cause a large amount of cracking in the cast slab. Therefore, the nitrogen (N2) content in the molten steel M is adjusted to 0.015 wt% or less using the degassing process (S130).

[0089] Thus, adjusting the hydrogen (H2) content in molten steel M to 0.0005 wt% or less and the nitrogen (N2) content to 0.015 wt% or less can be done by controlling the pressure and processing time of the vessel 41 of the RH apparatus 40. Specifically, by adjusting the pressure of the vessel 41 to 0.2 torr or less and maintaining this pressure for 20 minutes or more while processing the molten steel, it is possible to produce molten steel with a hydrogen (H2) content of 0.0005 wt% or less and a nitrogen (N2) content of 0.015 wt% or less.

[0090] The reason for using the RH device 40 as the vacuum device 40 when performing degassing treatment using the vacuum device 40 is that other types of vacuum devices have relatively low pressure control capabilities. Specifically, the RH device 40 used in the carbon steelmaking process can adjust the pressure inside the vessel 41 to 2 torr or less, while the vacuum device used in the stainless steelmaking process, the Vacuum Oxygen Decarburization (VOD) device, can only lower the pressure to a maximum of 3 torr to 4 torr. Furthermore, when removing hydrogen (H2) and nitrogen (N2) from molten steel, the lower the pressure, that is, the higher the vacuum, the more advantageous it is. For this reason, the RH device 40 used for degassing in the carbon steelmaking process is used. Consequently, hydrogen (H2) and nitrogen (N2) can be easily removed from the molten steel M, and hydrogen (H2) and nitrogen (N2) can be removed more effectively compared to using other vacuum devices, such as a Vacuum Oxygen Decarburization (VOD) device.

[0091] Thus, in the converter treatment process (S110), the converter 11 used in the stainless steelmaking process is used. That is, when preparing molten steel for the manufacture of rolling rolls with a high chromium (Cr) content, the converter 11 used in the stainless steelmaking process is used. Therefore, molten steel for the manufacture of rolling rolls with a high chromium (Cr) content can be prepared without contaminating converters for other types of steel. Furthermore, when preparing molten steel for the manufacture of stainless steel again using the same stainless steel converter that was used to prepare molten steel for the manufacture of rolling rolls, the chromium remaining in the stainless steel converter does not act as an impurity.

[0092] Furthermore, a ladle refining furnace 30, which is used in the carbon steelmaking process, is used as a device to adjust the composition and raise the temperature of the molten steel M tapped from the converter 11. In other words, the temperature of the molten steel M can be raised without adding any other materials to the molten steel. Therefore, the temperature of the molten steel can be increased without changing the composition of the molten steel.

[0093] Furthermore, when performing degassing treatment using the vacuum device 40, the RH device 40 used in the carbon steelmaking process is used. That is, degassing is performed using the RH device 40, which can be adjusted to lower the vessel pressure to 0.2 torr or less. Therefore, nitrogen (N2) and hydrogen (H2) can be effectively removed from the molten steel.

[0094] Furthermore, when preparing the molten steel M for the manufacture of rolling rolls, the converter 11 for stainless steel production, the ladle refining furnace 30 and RH device 40 for carbon steel production are used without separately installing a new converter, heating device, or vacuum device. As a result, it becomes unnecessary to install separate equipment for preparing the molten steel for the manufacture of rolling rolls, thus reducing associated costs.

[0095] Figures 3(a) to 3(d) show the operation of the casting apparatus of the present invention in sequence.

[0096] First, the casting apparatus 100 will be described based on Figures 3(a) to 3(d).

[0097] As shown in Figures 3(a) to 3(d), the casting apparatus 100 is a vertical casting apparatus that pulls out the cast slab S perpendicular to the ground when pulling it out of the mold 120. The casting apparatus according to this embodiment may be, for example, an apparatus capable of producing thick cast slabs (i.e., thick plates) having a thickness of about 700 mm.

[0098] As shown in Figures 3(a) to 3(d), the casting apparatus 100 includes a mold 120 into which molten steel M supplied to it can solidify, a support part 171 that can be inserted into the mold 120 and is movable up and down, a drive part 172 connected to the support part 171 to provide power for raising and lowering, a first magnetic field generating part 150a located on the outside of the mold 120 in the lateral direction, a second magnetic field generating part 150b located on the outside of the mold 120 in the lateral direction below the mold 120, and a heating part 160 located on the outside of the mold 120 in the lateral direction between the mold 120 and the second magnetic field generating part 150b.

[0099] Furthermore, the casting apparatus 100 includes a cooling unit 140 that extends perpendicularly to the ground below the mold 120 and is capable of solidifying the cast slab S that has been pulled out below the mold 120 by spraying cooling water into it; a rotating unit 190 positioned below the second magnetic field generating unit 150b so as to receive and rotate the cast slab S supported by the support unit 171; and a moving unit 180 positioned below the second magnetic field generating unit 150b so as to push and move the cast slab S supported by the support unit 171 toward the rotating unit 190.

[0100] Furthermore, the casting apparatus 100 may include a tundish 110 located above the mold 120 for supplying molten steel M to the mold 120, and a nozzle 130 connected to the lower part of the tundish 110 so that molten steel M can be supplied to the mold 120.

[0101] In Figure 3, for the sake of clarity, the rotating part 190 is shown only in Figure 3(d) and omitted in Figures 3(a) to (c). However, even in cases like those shown in Figures 3(a) to (c), the rotating part 190 is positioned below the cooling part, facing the moving part 180.

[0102] The mold 120 is a means for receiving molten steel M from the tundish 110 and allowing it to solidify into a specific shape. Such a mold 120 may have cooling water pipes (not shown) inside through which cooling water is circulated. Once molten steel is supplied to the mold 120 and solidified, it enters a semi-solid state in which a solidified region A and an unsolidified region B coexist.

[0103] The support portion 171 is inserted into the mold 120 so as to close the lower opening of the mold 120 before molten steel M is supplied to the mold 120. When molten steel is supplied into the mold 120 with the support portion 171 closed, the molten steel M begins to solidify on the support portion 171. As a result, the semi-solidified cast slab S is supported on the support portion 171. When the drive unit 172 is operated to lower the support portion 171, the support portion 171 descends to the lower side of the mold 120 while supporting the semi-solidified cast slab S. In other words, the descent of the support portion 171 pulls the cast slab S from inside the mold 120 to the lower side of the mold 120. Such a support portion may be in the shape of a plate.

[0104] The drive unit 172 is a means for raising and lowering the support unit 171 and is connectable to the lower part of the support unit 171. The drive unit 172 may also include a power source 172-1 that provides the driving force for raising and lowering, and a drive member 172-2 that connects the power source 172-1 and the support unit 171 so that the drive unit can be raised and lowered by the driving force transmitted from the power source 172-1.

[0105] The power source 172-1 may be a device equipped with a hydraulic piston. Needless to say, the power source 172-1 is not limited to the examples described above, and any means capable of raising and lowering the drive member 172-2 may be used.

[0106] The drive member 172-2 has one end connected to the power source 172-1 and the other end connected to the support portion 171. Such a drive member 172-2 may have a shape that extends in the vertical direction, for example. Alternatively, the height of the one end of the drive member 172-2 connected to the power source 172-1 may be fixed, while the height of the other end connected to the support portion 171 may be raised or lowered by the operation of the power source 172-1.

[0107] As described above, the drive unit 172 is a means for raising and lowering the support unit 171, and can adjust the speed at which the support unit 171 rises and falls. In particular, by adjusting the speed at which the support unit 171 falls, the speed at which the cast slab S supported by the support unit 171 is pulled out to the lower side of the mold 120 can be adjusted. In this case, the speed at which the cast slab S is pulled out to the lower side of the mold 120 may mean the casting speed. When the drive unit 172 adjusts the downward speed of the support unit 171, it adjusts its operation so that it falls at a speed of 0.04 m / min or less. More specifically, it adjusts its operation so that it falls at a speed of 0.01 m / min to 0.04 m / min. In other words, the drive unit 172 adjusts the downward speed of the support unit so that the casting speed is 0.04 m / min or less, more specifically, 0.01 m / min to 0.04 m / min.

[0108] Thus, adjusting the casting speed to 0.04 m / min or less is intended to suppress or prevent segregation in the cast slab S and to suppress or prevent a decrease in production rate. In other words, if the casting speed exceeds 0.04 m / min, the unsolidified molten steel M inside the cast slab S may not solidify sufficiently, resulting in the risk of segregation. Also, if the casting speed is less than 0.01 m / min, there is a problem of a decrease in the production rate of the cast slab S. Therefore, it is preferable to adjust the casting speed to between 0.01 m / min and 0.04 m / min.

[0109] The cooling unit 140 includes a plurality of rolls 141 arranged in the direction in which the support unit 171 moves up and down below the mold 120, and nozzles (not shown) located between the plurality of rolls 141 that spray cooling water onto the cast slab that has been pulled out to the bottom of the mold.

[0110] Multiple rolls 141 can be arranged so as to be aligned perpendicular to the ground. Furthermore, each of the multiple rolls 141 is provided so as to rotate due to the downward force of the cast slab S when it is lowered by the support portion 171. As a result, the cast slab S, which has been pulled out from the bottom of the mold 120, is lowered perpendicular to the ground by the lowering of the support portion 171 and the multiple rolls 141.

[0111] Nozzles for spraying cooling water are positioned between the multiple rolls 141. As a result, the cast slab S, which has been pulled out to the lower side of the mold 120, is secondarily cooled by the cooling water sprayed from the nozzles as it descends on the support portion 171.

[0112] When spraying cooling water onto the cast slab S that has been withdrawn to the lower side of the mold 120 to cause secondary solidification of the cast slab S, the flow rate of the cooling water is adjusted so that the surface temperature of the cast slab S is 800°C to 900°C. That is, the flow rate of the cooling water is adjusted so that the entire surface of the cast slab S located below the mold 120 is 800°C to 900°C. More specifically, the flow rate of the cooling water is adjusted so that the surface temperature from the top to the bottom of the cast slab S is uniformly 800°C to 900°C. To achieve this, the flow rate of the cooling water is adjusted so that the amount of cooling water sprayed decreases as the nozzle is positioned lower down in the vertical direction.

[0113] Adjusting the surface temperature of the cast slab S to 800°C to 900°C is to suppress or prevent the occurrence of surface cracks in the cast slab S and to prevent bulging. In other words, if the surface temperature of the cast slab S is below 800°C, there is a risk of cracks occurring on the surface of the cast slab S due to undercooling. Conversely, if the surface temperature of the cast slab S exceeds 900°C, there is a risk of bulging, where the solidified shell expands due to low strength of the solidified shell on the surface of the cast slab S. Therefore, the surface temperature of the cast slab S after it has been withdrawn from the mold 120 is adjusted to 800°C to 900°C.

[0114] If the temperature of the molten steel M supplied to the mold 120 is low, the molten steel M will solidify and become congested, which can cause segregation in the cast slab S. Therefore, in order to prevent the temperature of the molten steel from dropping, mold flux, which is a heat-retaining agent, is applied to the surface of the molten steel supplied to the mold 120. However, mold flux alone is not sufficient to prevent the temperature of the molten steel from dropping.

[0115] Therefore, a first magnetic field generating unit 150a is provided outside the mold 120 to allow the molten steel M inside the mold 120 to flow and suppress a drop in the temperature of the molten steel M. The first magnetic field generating unit 150a is located on the outside of the mold 120 in the lateral direction and generates a magnetic field. Here, the outside of the mold 120 in the lateral direction may mean the outside of the outer surface, which is the opposite surface of the inner surface of the mold 120 that the molten steel M contacts. In other words, the first magnetic field generating unit 150a is arranged outside the mold 120 so as to face the outer surface of the mold 120. To put it another way, the first magnetic field generating unit 150a can be arranged on the outside of the mold 120 in the lateral direction so as to surround the mold 120. For this purpose, the first magnetic field generating unit 150a may be provided in a hollow shape that extends along the outer surface of the mold 120. Such a first magnetic field generating unit 150a may include a coil disposed in the fuselage and inside the fuselage, which generates a magnetic field when supplied with power.

[0116] When a magnetic field is generated in the first magnetic field generating unit 150a, the generated magnetic field causes the molten steel M inside the mold 120 to flow. As a result, the molten steel M inside the mold 120 flows due to the magnetic field, which can suppress or prevent a drop in temperature due to the flow of the molten steel M. When the molten steel M flows, the components contained in the molten steel M are mixed uniformly or evenly. This can suppress or prevent the occurrence of segregation, which is formed in the inside of the cast slab by the accumulation or aggregation of specific components in predetermined areas.

[0117] The magnetic field generated in the first magnetic field generating unit 150a varies depending on the magnitude of the current supplied to the first magnetic field generating unit 150a, which corresponds to the power supplied or voltage applied to the unit. Therefore, the power supplied to the first magnetic field generating unit 150a or the voltage applied to the unit is adjusted so that a current of the target magnitude flows through the coil of the first magnetic field generating unit 150a. By causing current to flow through the first magnetic field generating unit 150a in this way, a magnetic field can be generated in the first magnetic field generating unit 150a. The magnetic field generated in the first magnetic field generating unit 150a can cause the molten steel M inside the mold 120 to flow, thereby suppressing or preventing a drop in the temperature of the molten steel M, and can also suppress or prevent the mold flux on the surface of the molten steel M from mixing into the molten steel.

[0118] On the other hand, if the current flowing through the first magnetic field generating unit 150a is too low, the molten steel M inside the mold 120 may cease to flow, causing the temperature of the molten steel M to drop and potentially leading to segregation in the cast slab S. Conversely, if the current flowing through the first magnetic field generating unit 150a is too high, the flow rate of the molten steel inside the mold 120 may be too fast, potentially causing mold flux to mix into the molten steel. Mold flux mixed into the molten steel M is an impurity and may cause cracking in the cast slab. Therefore, the magnitude of the current flowing through the first magnetic field generating unit 150a is adjusted by adjusting the magnitude of the power supplied to the first magnetic field generating unit 150a or the applied voltage, so that a magnetic field is generated that allows the molten steel inside the mold 120 to flow at an appropriate velocity.

[0119] When molten steel M solidifies inside the mold 120, the entire amount of molten steel M supplied to the mold 120 does not solidify simultaneously. Rather, solidification occurs sequentially from the peripheral edges in the width and length directions of the mold 120 toward the central region. Therefore, inside the mold 120, the peripheral edges in the width and length directions solidify into a solidified shell or solid state, while the central region in the width and length directions of the mold 120 remains in an unsolidified state where the molten steel M exists in a liquid state. In other words, a cast slab produced by the solidification of a portion of the molten steel inside the mold 120 is in a semi-solid state with a solidified region A and an unsolidified region B.

[0120] Furthermore, once the semi-solidified slab S is withdrawn from the bottom of the mold 120, the slab S is secondarily cooled by cooling water sprayed from the nozzle of the cooling unit 140. At this time, since the cooling unit 140 is located laterally to the slab S, solidification occurs sequentially from the peripheral edges in the width and length directions of the slab S toward the center. Therefore, the slab S withdrawn from the bottom of the mold 120 can be in a semi-solid state with a solidified region A and an unsolidified region B. Then, as time passes, the molten steel M in the unsolidified region B solidifies, producing a completely solidified slab without an unsolidified region B.

[0121] Furthermore, in the cast slab S withdrawn from the bottom of the mold 120, the accumulated solidification time is shorter as it moves towards the upper part closer to the mold 120, and longer as it moves towards the lower part. For this reason, in the cast slab S withdrawn from the bottom of the mold 120, the area of ​​the unsolidified region B is larger as it moves towards the upper part closer to the mold 120, and smaller as it moves towards the lower part. In other words, in the cast slab S withdrawn from the bottom of the mold 120, the area of ​​the solidified region A is smaller as it moves towards the upper part closer to the mold 120, and larger as it moves towards the lower part.

[0122] As described above, in the upper part of the cast slab S that has been withdrawn to the lower side of the mold 120, there is an unsolidified region B in which the molten steel M has not solidified. In other words, the cast slab S contains unsolidified molten steel M. When the cast slab S is withdrawn to the lower side of the mold 120, the cast slab S is solidified by the cooling water sprayed from the cooling section 140. However, if the unsolidified molten steel M present in the cast slab S solidifies without congestion, there is a risk of segregation occurring inside the cast slab S.

[0123] Therefore, a second magnetic field generating unit 150b is provided below the mold 120 to allow the unsolidified molten steel M inside the cast slab S that has been withdrawn to the lower side of the mold 120 to flow. The second magnetic field generating unit 150b is located below the mold 120, on the lateral side of the mold 120, and generates a magnetic field. More specifically, the second magnetic field generating unit 150b may be positioned below the mold 120 so as to face the first magnetic field generating unit 150a in the vertical direction. Even more specifically, the second magnetic field generating unit 150b may be positioned below the mold 120 so as to be on the lateral side of the cooling unit 140. For this purpose, the second magnetic field generating unit 150b may be provided in a hollow form. Furthermore, the second magnetic field generating unit 150b may be provided to have the same configuration as the first magnetic field generating unit 150a. In other words, the second magnetic field generating unit 150b may include the fuselage and a coil disposed inside the fuselage that generates a magnetic field when supplied with power.

[0124] When a magnetic field is generated in the second magnetic field generating unit 150b, the generated magnetic field is applied to the cast slab. As a result, the molten steel inside the cast slab S flows due to the magnetic field. Therefore, the molten steel M inside the cast slab S can solidify while flowing, thereby suppressing or preventing segregation from occurring inside the cast slab S.

[0125] The magnetic field generated in the second magnetic field generating unit 150b varies depending on the magnitude of the current supplied to the second magnetic field generating unit 150b or the applied voltage. Therefore, the power supplied to the second magnetic field generating unit 150b or the applied voltage is adjusted so that a current of the target magnitude flows through the coil of the second magnetic field generating unit 150b. By causing current to flow through the second magnetic field generating unit 150b in this way, a magnetic field can be generated in the second magnetic field generating unit 150b. The magnetic field generated in the second magnetic field generating unit 150b can cause the molten steel inside the cast slab S to flow, thereby suppressing or preventing the mixing of mold flux into the molten steel M.

[0126] On the other hand, if the current flowing through the second magnetic field generating unit 150b is too low, the molten steel M inside the cast slab S may stop flowing or not flow sufficiently, which may cause segregation inside the cast slab S. Conversely, if the current flowing through the first magnetic field generating unit 150a is too high, the flow rate of the molten steel M may be too fast, causing mold flux to mix into the molten steel. Mold flux mixed into the molten steel M is an impurity and may cause cracks in the cast slab S. Therefore, when generating a magnetic field using the second magnetic field generating unit 150b, the current flowing through the second magnetic field generating unit 150b is adjusted by adjusting the magnitude of the power supplied to the second magnetic field generating unit 150b or the applied voltage so that a magnetic field is generated that allows the molten steel M inside the cast slab S to flow at an appropriate flow rate.

[0127] Furthermore, if the time for which the second magnetic field generating unit 150b is operated to generate a magnetic field is too short, there is a risk that the cast slab S will not solidify sufficiently. In other words, there is a risk that the casting will end with unsolidified molten steel remaining inside the cast slab S. Conversely, if the time for which the second magnetic field generating unit 150b is operated to generate a magnetic field is too long, there is a risk that the magnetic field will be applied to areas where there is no unsolidified molten steel, i.e., to the bottom of the cast slab. In other words, there is a risk that the magnetic field will be applied to areas where it is not necessary. Therefore, when generating a magnetic field using the second magnetic field generating unit 150b, the time for which the magnetic field is applied to the cast slab is adjusted so that the unsolidified molten steel inside the cast slab S can be sufficiently solidified, while preventing the magnetic field from being unnecessarily applied to solidified areas.

[0128] As explained above, the area of ​​the unsolidified region of the cast slab drawn from the bottom of the mold 120 increases as it moves towards the top. Here, the lowest end of the cast slab S is the region that was first drawn from the mold 120, and the uppermost end of the cast slab S is the region that was last drawn from the mold 120. For this reason, in the cast slab drawn from the bottom of the mold 120, the uppermost end of the cast slab S is referred to as the end of the cast slab S.

[0129] When the cast slab S, which has been drawn out to the lower side of the mold 120, solidifies, the unsolidified molten steel at the end of the cast slab solidifies before the molten steel M located below the end of the cast slab. In this way, the molten steel M at the end of the cast slab solidifies before the molten steel M located below the end of the cast slab, resulting in shrinkage defects due to solidification shrinkage at the end of the cast slab. Since the end of the cast slab with shrinkage defects cannot be used as a product, the end of the cast slab with shrinkage defects is cut off after the completion of casting. Consequently, there is a problem that the actual yield of the cast slab decreases by the length of the cut end, and since the cut end is discarded, there is a problem that the amount of material corresponding to the length cut off is consumed with each operation, resulting in a waste of cost.

[0130] Therefore, a heating section 160 capable of heating the end portion of the cast slab is provided below the mold 120 to suppress or prevent solidification shrinkage of the end portion of the cast slab. The heating section 160 is positioned on the outside of the mold 120 in the lateral direction, between the mold 120 and the second magnetic field generating section 150b. More specifically, the heating section 160 may be positioned below the mold 120 so as to face the first magnetic field generating section 150a and the second magnetic field generating section 150b in the vertical direction. Furthermore, the heating section 160 may be positioned on the outside of the cooling section 140 in the lateral direction. For this purpose, the heating section 160 may be provided in a hollow form. Such a heating section 160 may include a body and a heating element disposed inside the body that generates heat when supplied with electricity.

[0131] When the heating unit 160 operates and generates heat, this heat heats or induces heating the molten steel M inside the end portion of the cast slab. This delays the solidification of the molten steel M at the end portion of the cast slab. In other words, the solidification of the molten steel at the end portion of the cast slab can be adjusted to solidify even more slowly than the molten steel below it. Therefore, the occurrence of shrinkage cavities at the end portion of the cast slab can be suppressed or prevented.

[0132] The heat generated in the heating section 160 varies depending on the power supplied to the heating section 160 or the applied voltage. Therefore, the power supplied to the heating section 160 is adjusted so that heat at the target temperature is generated in the heating section 160. In this way, by supplying power to the heating section 160 to generate heat, the end portion of the cast slab can be heated. This makes it possible to suppress or prevent solidification shrinkage at the end portion of the cast slab.

[0133] On the other hand, if the power supplied to the heating unit 160 is too low, the temperature of the heat generated in the heating unit 160 will be too low, and the molten steel M at the end of the cast slab will not be heated sufficiently. This may cause solidification shrinkage at the end of the cast slab, leading to shrinkage defects. Conversely, if the power supplied to the heating unit 160 is too high, the temperature of the heat generated in the heating unit 160 will be too high, causing the molten steel to be heated not only at the end of the cast slab but also below the end, resulting in remelting. Therefore, when heating the end of the cast slab using the heating unit 160, the power supplied to the heating unit 160 should be adjusted so that the end of the cast slab is heated sufficiently, but the molten steel M below the end of the cast slab is not heated and remelted.

[0134] Furthermore, if the heating time for the end portion of the cast slab using the heating unit 160 is too short, there is a risk that the end portion of the cast slab will not be sufficiently heated. As a result, the molten steel M at the end portion of the cast slab may solidify before the molten steel M at the lower end portion of the cast slab, causing solidification shrinkage at the end portion of the cast slab, which may lead to the occurrence of shrinkage cavities. Conversely, if the heating time for the heating unit 160 is too long, the molten steel at the end portion of the cast slab has already solidified, so there is no need to heat the end portion of the cast slab using the heating unit. Therefore, when heating the end portion of the cast slab using the heating unit 160, the heating time for the end portion of the cast slab should be adjusted so that the end portion of the cast slab is sufficiently heated while avoiding heating the end portion of the cast slab that has already solidified.

[0135] Thus, in this embodiment, when molten steel solidifies inside the mold 120, the first magnetic field generating unit 150a is used to cause the molten steel inside the mold 120 to flow. As a result, it is possible to suppress or prevent the temperature of the molten steel M inside the mold 120 from dropping, and thereby suppress or prevent segregation from occurring in the cast slab S.

[0136] Furthermore, when the cast slab withdrawn to the lower side of the mold 120 solidifies, the second magnetic field generating unit 150b, positioned below the mold 120, is used to flow the unsolidified molten steel inside the cast slab S. As a result, when the cast slab solidifies outside the mold 120, the unsolidified molten steel inside the cast slab S can solidify while flowing without congestion. This makes it possible to suppress or prevent segregation in the cast slab S caused by congestion of unsolidified molten steel.

[0137] On the other hand, conventionally, to prevent segregation from occurring in ingots for the manufacture of rolling rolls, the electro-slag remelting (ESR) method was used. The electro-slag remelting (ESR) method will be briefly explained below. First, molten steel intended for the manufacture of rolling rolls, with its top surface shaped, is solidified to produce an electrode rod. Then, an arc is generated using the manufactured electrode rod, and while remelting the electrode rod, the remelted molten steel is solidified by dripping it downwards in the shape of a water droplet to produce an ingot again. Using this process, it is possible to suppress or prevent segregation from occurring in the ingot, but it requires a complex process that involves the manufacturing of an electrode rod from the ingot produced as described above, the remelting of the electrode rod, and the resolidification of the remelted molten steel. Therefore, the time and cost required for the process to suppress segregation are enormous.

[0138] In contrast, the first and second magnetic field generating units M provided in the casting apparatus 100 can be used to flow the molten steel in the mold 120 and the unsolidified molten steel M in the cast slab S, thereby suppressing or preventing segregation from occurring inside the cast slab S. Therefore, compared to the conventional method of manufacturing ingots via electroslag remelting (ESR), the method according to this embodiment simplifies the process, shortens the time required, and reduces costs. Furthermore, in the conventional electroslag remelting (ESR) method, the amount of power supplied to operate the first and second magnetic field generating units is even smaller than the amount of power supplied to generate an arc in the electrode rod. Therefore, compared to the conventional method of manufacturing ingots via electroslag remelting (ESR), the amount of electrical energy consumed when manufacturing cast slabs can be reduced.

[0139] Furthermore, by heating the heating section 160 using the end portion of the cast slab, the solidification of the molten steel M at the end portion of the cast slab can be delayed. This suppresses or prevents solidification shrinkage at the end portion of the cast slab, thereby reducing the occurrence of shrinkage cavities at the end portion of the cast slab.

[0140] Returning to Figure 3, we will now describe the movable part 180 and the rotating part 190.

[0141] The movable part 180 is a means for pushing the cast slab S, which has been withdrawn from the lower side of the mold 120, from one side to move it toward the rotating part 190. That is, the movable part 180 is withdrawn from the lower side of the mold 120 and is supported vertically on the support part 171, and pushes the solidified cast slab S to transfer it to the rotating part 190. Such a movable part 180 may be a means that is driven horizontally with respect to the ground, for example, and the movable part may be equipped with a hydraulic or pneumatic cylinder.

[0142] The rotating part 190 receives the cast slab S that has been pulled away from the support part 171 by the moving part 180, and rotates the received cast slab S. In other words, the rotating part 190 receives the cast slab that is supported on the support part 171 in a direction perpendicular to the ground, and rotates the received cast slab parallel to the ground.

[0143] The rotating section 190 is positioned to face the moving section 180 in the horizontal direction. The rotating section 190 is capable of receiving and supporting the cast slab S that has been pulled away from the support section 171, and includes a rotatable rotary table 191 and a rotating member 192 connected to the rotary table 191 so that the rotary table 191 can rotate.

[0144] The rotary table 191 comprises a first table 191-1 extending in one direction and a second table 191-2 extending in a direction intersecting the direction of extension of the first table 191-1, with one end connected to the first table 191-1.

[0145] With respect to the cast slab S which is vertically supported on the support portion 171, the first table 191-1 is a means for supporting the side surface of the cast slab S, and the second table 191-2 is a means for supporting the lower surface of the cast slab S. The first table 191-1 may be provided so as to have a longer extension length than the second table 191-2. Preferably, the second table 191-2 is provided so as to have the same area as the lower surface of the cast slab S, or a larger area. The first table 191-1 may be provided with a plurality of rotatable rollers 191-3, and the plurality of rollers 191-3 are arranged in the direction in which the first table 191-1 extends.

[0146] One end of the first table 191-1 and one end of the second table 191-2 are connected to each other by a rotating member 192. The rotating table 191 can be rotated or tilted by the rotating member 192, as shown in Figure 3(d). That is, when the cast slab S is supported vertically on the support 171, the first table 191-1 of the rotating unit is perpendicular to the ground, and the second table 191-2 is positioned parallel to the ground. When the cast slab S supported on the support 171 is transferred to the rotating unit 190, the rotating unit 190 is rotated or tilted. That is, the rotating unit 190 is rotated so that the first table 191-1 is parallel to the ground and the second table 191-2 is perpendicular to the ground.

[0147] The above describes the production of a cast slab using a vertical casting apparatus. However, the present invention is not limited thereto, and a cast slab S can be produced using various types of casting apparatus equipped with a first magnetic field generating unit 150a disposed on the outside of the mold 120 in the lateral direction, a second magnetic field generating unit 150b disposed below the mold 120, and a heating unit 160.

[0148] Figures 4(a) to 4(c) are step-by-step process diagrams showing a method for manufacturing rolling rolls using cast slabs produced according to the present invention.

[0149] Once the cast slab S is manufactured, the manufactured cast slab S is heated to soften it (S300). For this purpose, the cast slab S is loaded into the first heating device 200. The first heating device 200 may include a furnace having an internal space and a heater for heating the furnace. Here, the heater may include, for example, a heating element that is disposed inside or outside the wall of the furnace and can generate heat with supplied electricity. Another example is that the heater may include a burner that generates heat by burning fuel.

[0150] When heating the cast slab S in the first heating device 200, the cast slab is heated to a temperature of 1100°C to 1250°C, preferably 1140°C to 1240°C. At this time, instead of placing the cast slab inside a furnace heated to 1100°C to 1250°C, the cast slab is placed inside a furnace adjusted to an even lower temperature, and then the temperature inside the furnace is gradually raised to 1140°C to 1240°C.

[0151] More specifically, first, the inside of the furnace is heated to 250°C to 350°C (first temperature), and this temperature is maintained for 3 to 5 hours, preferably 3 hours 30 minutes to 4 hours 30 minutes. After this, the inside of the furnace is heated to 450°C to 550°C (second temperature), and this temperature is maintained for 5 to 7 hours, preferably 5 hours 30 minutes to 6 hours 30 minutes. Next, the inside of the furnace is heated to 650°C to 750°C (third temperature), and this temperature is maintained for 3 to 5 hours, preferably 3 hours 30 minutes to 4 hours 30 minutes. Then, the inside of the furnace is heated to 1100°C to 1250°C (fourth temperature), and this temperature is maintained for 14 to 18 hours, preferably 15 hours 30 minutes to 17 hours 30 minutes. Furthermore, the time required to raise the temperature inside the furnace from a first temperature to a second temperature (first heating time) and the time required to raise the temperature from a second temperature to a third temperature are preferably 3 to 4 hours, and the time required to raise the temperature inside the furnace from a third temperature to a fourth temperature is preferably 9 to 10 hours. In this way, heating the inside of the furnace to the first to fourth temperatures and maintaining the temperature at the first to fourth temperatures means that the temperature of the cast slab placed inside the furnace is heated to the first to fourth temperatures and the temperature of the cast slab is maintained at the first to fourth temperatures.

[0152] When heating the cast slab S to 1100°C to 1250°C, the reason for gradually increasing the temperature, as described above, is that in the case of cast slab S containing a high amount of chromium (4.5 wt% or more), the hardness is high, and there is a risk of cracking during heating and cooling. Therefore, when heating the cast slab S to 1100°C to 1250°C, gradually increasing the temperature using the method described above can suppress or prevent cracking in the cast slab S.

[0153] Once the process of heating or heat-treating the cast slab S in the first heating device 200 is completed, the cast slab S is forged using the forging device 300 to produce rolling rolls. The forging device 300 may include, for example, an upper pressure lower section and a lower pressure lower section arranged apart in the vertical direction, and a drive unit connected to the upper pressure lower section and the lower pressure lower section so as to apply a predetermined force. Here, the drive unit may be a cylinder driven by hydraulics or pneumatics.

[0154] The following describes a method for forging a cast slab S using a forging apparatus 300. First, the cast slab is placed between the upper and lower pressure parts of the forging apparatus 300. Then, the drive unit is operated to lower the upper pressure part and raise the lower pressure part, reducing the distance between the upper and lower pressure parts. Next, the drive unit is operated to apply a further downward force to the upper pressure part and a further upward force to the lower pressure part. At this time, as time passes after the upper and lower pressure parts have been in contact with the cast slab S, the force with which the upper and lower pressure parts press against the cast slab increases. As a result, the cast slab S placed between the upper and lower pressure parts is compressed, and the thickness of the cast slab decreases. When the thickness of the cast slab has decreased to a target thickness, the upper and lower pressure parts are separated from the cast slab. Here, the target thickness may be 250 mm to 350 mm. This process is then repeated multiple times.

[0155] In this manner, the upper and lower pressure parts are brought into contact with the cast slab S and force is applied until the thickness of the cast slab S decreases by an amount corresponding to the target thickness. Once this reduction in thickness is achieved, the upper and lower pressure parts are separated from the cast slab S. This entire process is defined as "one pass." In this embodiment, the target thickness is set to 250 mm to 350 mm. The reduction in thickness of the cast slab S per pass is then adjusted to be between 250 mm and 350 mm. The above-described "one pass" is then repeated multiple times to manufacture the rolling roll.

[0156] On the other hand, if the thickness reduction of the slab S per pass is less than 250 mm, sufficient force may not be applied to the central region of the slab S in the thickness direction, potentially resulting in the failure to remove pores in the central region of the slab. If pores in the central region of the slab S in the thickness direction are not removed, this may lead to a decrease in the hardness of the rolling rolls. Conversely, if the thickness reduction of the slab S per pass exceeds 350 mm, cracking may occur on the surface of the slab, which can lead to defects in the rolling rolls.

[0157] Once the forging is complete and the rolling roll 141 is manufactured, the rolling roll 141 is heated to remove hydrogen (H2). For this purpose, the rolling roll 141 is placed in a second heating device 400 and heated using the second heating device 400. Here, the second heating device 400 may be the same as or different from the first heating device 200 described above.

[0158] When heating the rolling roll 141 using the second heating device 400, the rolling roll 141 is heated to 200°C to 400°C, more preferably to 250°C to 350°C. Furthermore, the temperature of the rolling roll 141 is maintained at 200°C to 400°C for 48 hours or more, more preferably 48 hours or more and 55 hours or less.

[0159] In this way, when the rolling roll 141 is heated to 200°C to 400°C, more preferably 250°C to 350°C, and held at this temperature for 48 hours or more, the hydrogen (H2) contained in or remaining in the rolling roll 141 diffuses into hydrogen gas, which is then exhausted to the outside. As a result, the hydrogen content in the rolling roll 141 decreases. At this time, it is preferable to make the hydrogen content in the rolling roll 141 0.0002 wt% or less (0 wt or more), which can be adjusted by controlling at least one of the heating temperature and the heat treatment time of the rolling roll 141.

[0160] On the other hand, hydrogen contained inside the rolling roll 141 tends to accumulate in the inclusions and segregation contained in the rolling roll 141, which may cause internal cracking in the rolling roll when it is actually used. Here, "actual use of the rolling roll" may refer to using the manufactured rolling roll 141 to roll an object to be rolled, for example, a cast slab S.

[0161] Therefore, the manufactured rolling mill 141 is heated at 200°C to 400°C for 48 hours or more to remove hydrogen so that the hydrogen content in the rolling mill 141 is 0.0002 wt% or less. At this time, if the hydrogen content in the rolling mill 141 is 0.0002 wt% or less, no cracks will occur inside the rolling mill 141 due to hydrogen. Furthermore, since it is practically difficult to completely remove hydrogen from the rolling mill 141, the hydrogen content is kept at 0.0002 wt% or less.

[0162] The following describes a method for manufacturing rolling rolls according to an embodiment of the present invention, based on Figures 1 to 4. Content that overlaps with what has been described above will be omitted or simplified.

[0163] First, molten steel M is prepared for the manufacture of rolling mill rolls (S100). To this end, molten steel M is first charged into a converter 11 for stainless steel production. Then, as shown in Figure 2(a), chromium (Cr) alloy ferroalloy is added to the converter 11. At this time, the amount of chromium (Cr) alloy ferroalloy added is adjusted so that the chromium (Cr) content in the molten steel inside the converter 11 is between 4.5 wt% and 5.5 wt%.

[0164] Next, as shown in Figure 2(b), oxygen is blown into the converter 11 using the lance 12. That is, oxygen is blown into the molten steel M in the converter 11 to remove carbon (C) and phosphorus (P). At this time, the carbon (C) content in the molten steel M is set to 0.75 wt% to 0.95 wt%, and the phosphorus (P) content is set to 0.025 wt% or less.

[0165] Next, as shown in Figure 2(c), a deoxidizing agent is introduced into the converter 11 to remove oxygen (O) from the molten steel M. At this time, at least one of an alloy containing silicon (Si) and an alloy containing aluminum (Al) can be used as the deoxidizing agent. The molten steel M is then deoxidized to a level where the oxygen (O) content is 0.001 wt% or less.

[0166] Once deoxidation is complete, a reducing agent, i.e., ferroalloy containing silicon (Si), is added to the converter 11, as shown in Figure 2(d). This causes a reaction between the chromium oxide in the slag SL and the silicon (Si) in the reducing agent. Consequently, the chromium oxide in the slag SL is reduced to chromium (Cr), and the resulting chromium (Cr) is absorbed or supplied to the molten steel M. This increases the chromium (Cr) content in the molten steel M. At this time, the amount of reducing agent added is adjusted so that the chromium (Cr) content in the molten steel M is between 4.5 wt% and 5.5 wt%.

[0167] Once the reduction to chromium is complete, the molten steel M inside the converter 11 is tapped into the ladle 20, as shown in Figure 2(e). At this time, the molten steel M is tapped into the ladle 20 for carbon steelmaking.

[0168] Then, the ladle 20 is moved to the temperature control device 30, i.e., the ladle smelting furnace 30, and the ladle 20 is attached to the cover 32 of the ladle smelting furnace 30 (Figure 2(f)). Next, a desulfurizing agent is added to the ladle 20 to remove sulfur (S) from the molten steel. At this time, the sulfur (S) content in the molten steel is kept below 0.015 wt%.

[0169] Once desulfurization is complete, the molten steel M contained in the ladle 20 is sampled and its carbon (C) and chromium (Cr) content is measured. Then, the carbon (C) and chromium (Cr) content in the molten steel M is adjusted according to the measured carbon (C) and chromium (Cr) content. At this time, depending on the measured carbon (C) and chromium (Cr) content, carburizing agents and ferroalloys containing chromium (Cr) are added, or solid oxygen such as iron ore is added, so that the measured carbon (C) content of the molten steel is 0.75 wt% to 0.95 wt% and the chromium (Cr) content is 4.45 wt% to 5.5 wt%.

[0170] Once the carbon (C) and chromium (Cr) content has been adjusted, the molten steel M is heated to a higher temperature. That is, an arc and heat are generated from the electrode rod 31 to heat the molten steel contained in the ladle 20. At this time, the temperature of the molten steel is set to 1560°C to 1600°C.

[0171] When the temperature of the molten steel M reaches 1560°C to 1600°C, the ladle 20 is removed from the ladle smelting furnace 30. Then, as shown in Figure 2(g), the ladle 20 is moved to the vacuum device, i.e., the RH device 40. The ladle 20 is then positioned below the pair of reflux pipes 42a and 42b, and they are connected to each other to seal the vessel. Next, the pump is operated to reduce the pressure inside the vessel 41 to a vacuum, for example, 0.2 torr or less, and then the ladle 20 is raised so that the pair of reflux pipes 42a and 42b are immersed in the molten steel inside the ladle 20. After this, argon (Ar) gas is blown into the pair of reflux pipes 42a and 42b to circulate the molten steel inside the vessel 41. The circulating molten steel is exposed to the vacuum atmosphere inside the vessel 41, and as a result, nitrogen (N2) and hydrogen (H2) gas in the molten steel are exhausted to the outside of the vessel 41. Therefore, the nitrogen (N) and hydrogen (H2) content in the molten steel decreases, and at this time, the nitrogen (N2) content is reduced to 0.015 wt% or less, and the hydrogen (H2) content is reduced to 0.0005 wt% or less.

[0172] After going through the processes (a) to (g) in Figure 2 described above, molten steel M for the manufacture of rolling rolls is prepared.

[0173] Once the molten steel M is ready, the ladle 20 is moved to the tundish 110 of the casting apparatus 100, and the molten steel M is supplied to the tundish 110 to start casting. To do this, first, the lower opening of the mold 120 is closed using the support part 171 of the casting apparatus 100. Then, as shown in Figure 3(a), the molten steel M from the tundish 110 is supplied to the mold 120 (S210). As a result, the molten steel M supplied to the mold 120 solidifies and begins to solidify from the top of the support part 171 (casting process) (S210). Then, while continuously supplying the molten steel M from the tundish 110 to the mold 120, the drive unit 172 is operated to lower the support part 171. As a result, as shown in Figure 3(b), the cast slab S inside the mold 120 is gradually pulled out to the bottom of the mold (S220).

[0174] As described above, while molten steel M is continuously supplied to the mold 120, the first magnetic field generating unit 150a, located outside the mold 120, is operated to generate a magnetic field. As a result, the magnetic field generated by the first magnetic field generating unit 150a is applied to the inside of the mold 120, causing the molten steel M inside the mold 120 to flow due to the magnetic field. This prevents or suppresses a drop in the temperature of the molten steel M inside the mold 120, and prevents or suppresses the mixing of mold flux on the surface of the molten steel M into the molten steel.

[0175] While molten steel is continuously supplied into the mold 120, the drive unit 172 is operated to gradually lower the support unit 171 to the underside of the mold 120. At this time, the speed at which the support unit 171 descends is adjusted to 0.04 m / min or less, more specifically to 0.01 m / min to 0.04 m / min. In other words, the casting speed is adjusted to 0.04 m / min or less, more specifically to 0.01 m / min to 0.04 m / min.

[0176] As shown in Figure 3(b), once the cast slab is withdrawn to the bottom of the mold 120, the withdrawn cast slab S is secondary solidified by cooling water sprayed from the nozzle of the cooling unit 140 (solidification process) (S220). The tundish 110 then continuously supplies molten steel M to the mold, and the support unit 171 continuously descends, thereby gradually increasing the length of the cast slab withdrawn to the bottom of the mold 120. Once a cast slab of the target length has been withdrawn to the bottom of the mold 120, the supply of molten steel to the mold 120 is interrupted. Then, as shown in Figure 3(c), the cast slab is withdrawn to the bottom of the mold until its uppermost end, i.e., its end (S230). Once the end of the cast slab has been withdrawn to the bottom of the mold, the second magnetic field generating unit 150b is activated to generate a magnetic field. Therefore, the unsolidified molten steel inside the cast slab S that has been withdrawn to the lower side of the mold 120 flows due to the magnetic field generated in the second magnetic field generating unit 150b. This prevents or inhibits the mixing of mold flux into the molten steel.

[0177] In the above, it was explained that when the end portion of the cast slab S is pulled out to the bottom of the mold, the second magnetic field generating unit 150b is activated to generate a magnetic field. However, the present invention is not limited to this, and it is also possible to activate the second magnetic field generating unit 150b to generate a magnetic field when the cast slab begins to be pulled out to the bottom of the mold 120.

[0178] When the end of the cast slab S is pulled out to the bottom of the mold, the heating unit 160 is activated to heat the end of the cast slab. This slows down the solidification of the unsolidified molten steel M at the end of the cast slab S. As a result, solidification shrinkage at the end of the cast slab can be suppressed or prevented, and other areas of the cast slab other than the end can be prevented from being remelted.

[0179] Once solidification is complete to the end of the cast slab S, the moving part 180 is operated to push the cast slab S, which is placed vertically on the support part 171, toward the rotating part 190, as shown in Figure 3(d). As a result, the cast slab S on the support part 171 is transported to the rotating part 190. At this time, the side surface of the cast slab S is supported by the first table 191-1 of the rotating part 190, and the bottom surface of the cast slab is supported by the second table 191-2. Next, the rotating part 190 is rotated, i.e., tilted (S240). More specifically, the rotating part 190 is rotated so that the first table 191-1 is parallel to the ground and the second table 191-2 is horizontal to the ground. As a result, the cast slab S rotates so that it is placed horizontally to the ground. The cast slab placed horizontally on the rotating part 190 is transported to the next process.

[0180] Once the cast slab S is manufactured, it is heated using the first heating device 200 (S300). At this time, the inside of the furnace into which the cast slab S is charged is gradually heated to 1140°C to 1240°C (target temperature) to heat the cast slab. More specifically, first the cast slab S is heated to 250°C to 350°C (first temperature) and held for 3 to 5 hours. After this, the cast slab S is heated to 450°C to 550°C (second temperature) and held for 5 to 7 hours. Next, the cast slab S is heated to 650°C to 750°C (third temperature) and held at the third temperature for 3 to 5 hours. Then, the cast slab S is heated to the target temperature of 1100°C to 1250°C (fourth temperature) and held for 14 to 18 hours. Thus, when heating the cast slab S to 1100°C to 1250°C (the fourth temperature), by gradually increasing the temperature from the first to the fourth temperature as described above, it is possible to suppress or prevent thermal cracking in cast slabs containing a large amount of chromium (Cr) of 4.5 wt% or more.

[0181] Once the process of heating the cast slab S in the first heating device 200 is complete, the cast slab is forged using the forging device 300 to manufacture rolling rolls (S400). At this time, the reduction in thickness of the cast slab S per pass is set to 250 mm to 350 mm, and this is repeated multiple times to manufacture rolling rolls 141.

[0182] Once the rolling roll R is manufactured, the rolling roll 141 is heated using the second heating device 400 to remove hydrogen (H2). At this time, the rolling roll 141 is heated at a temperature of 200°C to 400°C for 48 hours or more. This allows the hydrogen content in the rolling roll 141 to be adjusted to 0.0002 wt% or less (0 wt or more).

[0183] Table 1 is an evaluation table for rolling rolls manufactured by the method according to the embodiment of the present invention. For quality evaluation, a portion of the rolling roll manufactured by the method according to the embodiment was cut and used as a test piece.

[0184] Ultrasonic testing (UT) quality evaluation is a quality evaluation method used to detect internal defects such as pores and cracks. In other words, it is an evaluation method that transmits ultrasonic waves into the inside of a test specimen and uses the amount of ultrasonic energy reflected from discontinuous areas inside the specimen and the propagation time of the ultrasonic waves to detect the presence and amount of pores and cracks inside the specimen.

[0185] Macro quality assessment is a quality assessment method used to determine the presence and amount of coarse tissue. For the assessment, specimens were etched using corrosion, and then the internal structure of the specimens was observed using an optical microscope.

[0186] Inclusion quality evaluation is a quality assessment method for determining the quantity and size of inclusions present in a specimen. For evaluation, a portion of the specimen was polished, and then the size and quantity of inclusions were detected using an optical microscope.

[0187] Hardness is the hardness relative to the test specimen and was measured using a Brinell hardness tester.

[0188] [Table 1]

[0189] As shown in Table 1, the specimens produced by the method according to the embodiment all meet the acceptable standards for UT quality, macro quality, inclusion quality, and hardness quality. In other words, the rolling rolls produced by the method according to the embodiment all meet the acceptable standards for UT quality, macro quality, inclusion quality, and hardness quality. This indicates that by producing rolling rolls by the method according to the embodiment, it is possible to produce rolling rolls with fewer pores, cracks, and inclusions, a uniform structure, and high hardness.

[0190] Figures 5(a) and (b) show the results of cutting the cross-section of the rolling roll and etching the cross-section to check for the presence or absence of coarse segregation.

[0191] Here, Figure 5(a) shows a cross-section of the manufactured rolling roll, and Figure 5(b) shows a cross-section of the rolling roll manufactured by the comparative example method. The rolling roll manufactured by the comparative example method is a rolling roll manufactured via the electro-slag remelting (ESR) method.

[0192] Comparing Figures 5(a) and 5(b), neither the rolling roll nor the rolling roll from the comparative example showed coarse segregation. In other words, the rolling roll has a uniform structure equivalent to that of the rolling roll from the comparative example. This indicates that even when manufacturing rolling rolls without using the conventional electro-slag remelting (ESR) method, segregation can be sufficiently suppressed. That is, even when casting slabs using a method that flows molten steel using first and second magnetic field generating units during the casting process, segregation can be suppressed to a level equivalent to that of the conventional electro-slag remelting (ESR) method.

[0193] Furthermore, compared to the conventional electro-slag remelting (ESR) method, using first and second magnetic field generators during the casting process to suppress segregation results in a simpler process and a shorter processing time. In other words, it is possible to suppress segregation to the same level as the conventional method, while having the advantages of shorter processing steps and shorter processing time required to prevent segregation. [Industrial applicability]

[0194] According to the present invention, high-chromium (Cr) molten steel can be produced using converters used for the production of other types of steel, without contaminating those converters. Furthermore, when raising the temperature of the high-chromium (Cr) molten steel or performing degassing to exhaust gases, the temperature of the molten steel can be effectively raised, thereby improving degassing efficiency. [Explanation of Symbols]

[0195] 11 Converter 20 ladle 30 Temperature control device 31 Electrode rod 32 Cover 40 RH system, vacuum pump, vacuum oxygen decarburization (VOD) system 41 Vessel 42a, 42b Reflux tube 43 Lance 100 Casting apparatus, vertical casting apparatus 120 molds 140 Cooling section 141 Multiple rolls, rolling rolls 150a First magnetic field generation unit 150b Second magnetic field generation section 160 Heating section 171 Support part 172 Drive Unit 172-1 Power source 172-2 Drive Member 180 Mobile Unit 190 Rotating part 191 Rotating Table 191-1 First Table 191-2 Second Table 191-3 Multiple rollers 192 Rotating Member 200 First heating device 300 Forging equipment 400 Second heating device (S100) Process of preparing molten steel (S110) Converter process (S111) Process of adding ferroalloy (S112) Oxygen blowing process (S113) Deoxidation process (S114) Process of reducing chromium oxide to chromium (Cr) (S120) Process of pouring the hot steel into a ladle (S130) Temperature control process, degassing process (S140) Degassing process (S200) The process of solidifying molten steel to produce a cast slab. (S300) Process of heating the cast slab (S400) The process of forging a heated slab to manufacture a rolling mill roll. (S500) Process of heating the rolling mill rolls (LF) Ladle Refining Furnace (M) Molten steel (VTD) Vacuum Tank Degassing System

Claims

1. A method for producing high-chromium (Cr) molten steel having a chromium (Cr) content of 4.5 wt% to 5.5 wt%, The process of charging molten steel into the converter, The process involves introducing chromium (Cr)-containing chromium alloy iron into the converter so that the chromium (Cr) content in the molten steel is 4.5 wt% to 5.5 wt%, An oxygen blowing process is performed in which oxygen is blown into the converter into which chromium alloy iron is introduced to remove carbon (C) from the molten steel, The process of adding a deoxidizing agent to the converter to remove oxygen (O) from the molten steel, The process includes adding a reducing agent containing silicon (Si) to the converter to reduce chromium oxides contained in the slag floating on the surface of the molten steel to chromium (Cr), The aforementioned converter is a converter used to prepare molten steel for the manufacture of stainless steel, A method for producing high-chromium (Cr) molten steel, characterized in that the molten steel for the production of the aforementioned stainless steel has a chromium (Cr) content of 10.5 wt% to 11 wt%.

2. The process of pouring the molten steel from the converter into a ladle, A method for producing high-chromium (Cr) molten steel according to claim 1, characterized by comprising a temperature control step of heating molten steel received in a ladle using a ladle smelting furnace (LF), which is a heating device used in the steelmaking process of carbon steel.

3. The method for producing high-chromium (Cr) molten steel according to claim 2, characterized in that the temperature of the molten steel is adjusted to 1560°C to 1600°C during the temperature control process.

4. Using a reflux vacuum degassing (RH: Rheinstaal Huttenwerke und Heraus) apparatus, which is a vacuum device used in the carbon steelmaking process, hydrogen (H) in the molten steel received in the ladle is removed. ２ ) and nitrogen (N ２ This includes a degassing process to remove ) The method for producing high-chromium (Cr) molten steel according to claim 2, characterized in that the degassing process is carried out after the temperature control process is completed.

5. A method for producing high-chromium (Cr) molten steel according to any one of claims 2 to 4, characterized in that when tapping the molten steel from the converter into a ladle, the tapping is performed into a ladle used in the carbon steelmaking process.

6. The process of preparing high-chromium (Cr) molten steel containing 4.5 wt% to 5.5 wt%, A casting process comprising supplying molten steel to a mold of a casting apparatus, allowing the molten steel to solidify inside the mold, and producing a cast slab containing unsolidified molten steel, The process of withdrawing the cast slab produced in the casting process to the lower side of the mold, The process includes a solidification step in which a magnetic field is applied to a cast slab withdrawn from the lower side of the mold, causing the unsolidified molten steel contained in the cast slab to flow and solidify, thereby producing a cast slab. The process of preparing high-chromium (Cr) molten steel is as follows: The process involves introducing chromium (Cr)-containing chromium alloy iron into the converter so that the chromium (Cr) content in the molten steel is between 4.5 wt% and 5.5 wt%, and An oxygen blowing process is performed in which oxygen is blown into the converter into which chromium alloy iron is introduced to remove carbon (C) from the molten steel, The process of adding a deoxidizing agent to the converter to remove oxygen (O) from the molten steel, The process includes adding a reducing agent containing silicon (Si) to the converter to reduce chromium oxides contained in the slag floating on the surface of the molten steel to chromium (Cr), The aforementioned converter is a converter used to prepare molten steel for the manufacture of stainless steel, A method for manufacturing a cast slab, characterized in that the molten steel for the production of the aforementioned stainless steel has a chromium (Cr) content of 10.5 wt% to 11 wt%.

7. The method for manufacturing a cast slab according to claim 6, characterized in that the solidification process includes a process of heating the end portion of the cast slab that has been withdrawn from the bottom of the mold.

8. The method for manufacturing a cast slab according to claim 6, characterized in that the casting process includes a step of applying a magnetic field to the mold to cause the molten steel inside the mold to flow.

9. The method for manufacturing a cast slab according to claim 6, characterized in that the cast slab is withdrawn to the lower side of the mold at a speed of 0.04 m / min or less.

10. The solidification process includes the process of spraying cooling water onto the cast slab that has been withdrawn from the bottom of the mold. The method for manufacturing a cast slab according to claim 6, characterized in that when spraying cooling water onto the cast slab, the spraying is performed such that the surface temperature of the cast slab becomes 800°C to 900°C.

11. In the aforementioned extraction process, the cast slab is extracted from the mold so that it is perpendicular to the ground. A method for manufacturing a cast slab according to any one of claims 6 to 10, characterized in that the cast slab is solidified in a state in which it is positioned perpendicular to the ground during the solidification process.

12. A step of heating a cast slab produced by the method for producing a cast slab according to any one of claims 6 to 10, The process of forging a heated slab to form the shape of a rolling mill roll, The rolling rolls manufactured in the molding process are heated to release hydrogen (H) from the rolling rolls. ２ The process of removing ) and, A method for manufacturing a rolling roll, characterized in that the process of heating the cast slab includes a process of raising the temperature of the cast slab to a target temperature in multiple stages.

13. The process of heating the cast slab to the target temperature is as follows: The process involves heating the cast slab to a first temperature of 250°C to 350°C, The process involves heating the cast slab to a second temperature of 450°C to 550°C, The process involves heating the cast slab to a third temperature of 650°C to 750°C, A method for manufacturing a rolling roll according to claim 12, characterized by comprising the step of heating a cast slab to the target temperature of 1100°C to 1250°C.

14. When heating the cast slab to the first to third temperatures and the target temperature, The cast slab is kept at the first temperature for 3 to 5 hours. The cast slab is held at the second temperature for 5 to 7 hours. The cast slab is kept at the third temperature for 3 to 5 hours. The method for manufacturing a rolling roll according to claim 13, characterized in that the cast slab is held at the target temperature for 14 to 18 hours.

15. When forging the aforementioned cast slab, the cast slab, which has been heated to a temperature of 1100°C to 1250°C, is pressed down and forged. The method for manufacturing a rolling roll according to claim 14, characterized in that each time the cast slab is reduced using a reduction device, the thickness of the cast slab is reduced by 250 mm to 350 mm.

16. From the aforementioned rolling rolls, hydrogen (H ２ The method for manufacturing a rolling mill roll according to claim 12, characterized in that when removing the ) the rolling mill roll is heated to a temperature of 200°C to 400°C.

17. The method for manufacturing a rolling roll according to claim 16, characterized in that the rolling roll is heated to the temperature of 200°C to 400°C for 48 hours or more.

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