Method for manufacturing rolled material and heating furnace for hot rolling

Abstract

To provide a technique of manufacturing a rolled material by making the temperature difference between upper and lower surfaces in a distal end portion of a rolled material without being influenced by an operation condition.SOLUTION: Provided is a method for arranging a distal end portion of a rolled material so as to be supported by a skid in a heating furnace, in manufacturing a rolling material by using a hot rolling line including the heating furnace that heats the rolled material and a roller that rolls the heated rolled material. The heating furnace of the heat rolling line heats the rolled material to be rolled by the roller. In the heating furnace, the skid is arranged at a position of supporting the distal end portion of the rolled material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a rolled material by preventing the tip upward warping of the rolled material and a reheating furnace for hot rolling used in the method in a hot rolling line for rolling a rolled material heated in a heating furnace to a predetermined thickness by a rolling mill.

Background Art

[0002] Generally, hot-rolled steel strips are produced by heating a rolled material to a predetermined temperature in a heating furnace, rolling the heated rolled material to a predetermined thickness in a roughing mill to form a rough bar, heating the rough bar by a heating device such as an edge heater or a bar heater, and then performing finish rolling in a finishing mill composed of a plurality of rolling stands to roll it into a hot-rolled steel strip with a predetermined thickness. After cooling this hot-rolled steel strip by a cooling device on a hot run table, it is wound up by a coiler.

[0003] In such continuous hot rolling, shape defects such as "warping" may occur at the tip of the rough bar or the hot-rolled steel strip at each stand of the roughing mill or the finishing mill. When the tip of the rough bar or the hot-rolled steel strip warps upward, it contacts the equipment inside the rolling mill, resulting in equipment damage or the rolled material becoming a defective product. In such cases, the rolling of the subsequent cycle has to be stopped, and the operation productivity is significantly impaired.

[0004] Therefore, technologies for reducing the upward warping of the tips of such rough bars and hot-rolled steel strips have been developed. For example, Patent Document 1 discloses a technology for performing a cooling process between the roughing process and the finishing process. In the cooling process, cooling is performed by changing the water cooling conditions based on the steel type of the rolled material, the upper and lower surface temperatures of the rolled material at the time of cooling stop, etc. Also, in the finishing process, asymmetric cooling of the upper and lower surfaces of the rolled material is performed based on the warping state in the previous pass to control the tip warping that occurs in the subsequent pass.

[0005] Furthermore, Patent Document 2 discloses a technique for preventing upward warping of rolled material by a rolling mill by heating the material in a heating furnace so that there is a precise temperature difference between the front and back surfaces. In this heating furnace, the top and bottom surfaces are heated individually, and the temperature of the top and bottom surfaces is controlled by controlling the fuel. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 06-071326 [Patent Document 2] Japanese Patent Publication No. 2012-187602 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the above-mentioned conventional technology had the following problems. The technology described in Patent Document 1 does not take into account the upward curvature of the rolled material in the roughing mill. Furthermore, the investment required to install additional cooling equipment may be excessive. In the technology described in Patent Document 2, temperature control can be difficult when the target heating temperature differs in the longitudinal direction or on the upper and lower surfaces, and it can be difficult to control the temperature difference between the upper and lower surfaces when the rolled material remains in the heating furnace for a long time due to the rolling schedule. Therefore, it may not be possible to reliably prevent upward curvature of the leading edge of the rolled material.

[0008] The present invention has been made in view of the above, and aims to provide a manufacturing method that is not affected by operating conditions and reliably prevents the tip of a rolled material from warping upward at the tip by creating a temperature difference between the upper and lower surfaces of the tip of the rolled material, and a hot rolling heating furnace used in this method. [Means for solving the problem]

[0009] The present invention provides a method for manufacturing a rolled material that advantageously solves the above problems, and is characterized in that, when manufacturing a rolled material, a hot rolling line is used which includes a heating furnace for heating the material to be rolled and a rolling mill for rolling the heated material, and in the heating furnace, the leading edge of the material to be rolled is supported by a support material having a cooling function.

[0010] Furthermore, the method for manufacturing the rolled material according to the present invention is as follows: (a) With the thickness of the rolled material being t0, the center of the support material is positioned within a range of 0.8 × t0 to 1.0 × t0 from the tip in the longitudinal direction of the rolled material to provide support. (b) The support material is divided into multiple sections, with each section having a contact area of ​​80 to 120 cm² with respect to the rolled material. 2 The range shall be set such that the pitch of the support members in the width direction is in the range of 150 to 220 mm, and the contact rate with the rolled material in the width direction is in the range of 60 to 80%. These could be more preferable solutions.

[0011] The present invention provides a heating furnace for hot rolling that advantageously solves the above problems. This heating furnace is for a hot rolling line and heats a rolled material to be rolled by a rolling mill, characterized in that a support member having a cooling function is positioned to support the leading edge of the rolled material. An example of a support member having a cooling function is the skid 2 shown in Figure 1, and the cooling function may be in accordance with the common art of the art.

[0012] Furthermore, the heating furnace for hot rolling according to the present invention is (c) The support member is positioned such that its center is within a range of 0.8 × t0 to 1.0 × t0 from the leading edge of the rolled material, with the thickness of the rolled material being t0. (d) The support material is divided into multiple parts, and the area in contact with the rolled material is 80 to 120 cm² per part. 2 The range is such that the pitch of the support members in the width direction is in the range of 150 to 220 mm, and the contact rate with the rolled material in the width direction is in the range of 60 to 80%. These could be more preferable solutions. [Effects of the Invention]

[0013] According to the method for manufacturing a rolled material and the reheating furnace for hot rolling according to the present invention, without making excessive capital investment, regardless of the operating conditions, the temperature on the lower surface side of the tip of the material to be rolled can be made lower than that on the upper surface side at the outlet side of the reheating furnace. Therefore, the upward warping of the tip of the rolled material can be suppressed during the subsequent rolling process. Since the productivity is improved without operating troubles, it is industrially useful. The method for manufacturing a rolled material according to the present invention preferably arranges and supports the center of the support member within the range of 0.8×t0 to 1.0×t0 from the tip in the longitudinal direction of the material to be rolled, with the thickness of the material to be rolled being t0, in order to surely prevent the upward warping of the tip of the rolled material. This does not include the case where, due to restrictions such as the dimensions of the slab, the center of the support member is arranged and supported within the range of 0.8×t0 to 1.0×t0 from the tip in the longitudinal direction of the material to be rolled as a result.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic view showing the support state of the slab in the reheating furnace according to an embodiment of the present invention, where (a) is a schematic side view and (b) is a partially enlarged view taken along arrow A. [Figure 2] It is a schematic enlarged view showing a schematic cross-section along the longitudinal direction of the material to be rolled and the rolled material for each rolling schedule, where (a) is the state where the slab is supported in the reheating furnace, (b) is the state of the rough bar after rough rolling, and (c) is the state of the rough bar before finish rolling. [Figure 3] It is a graph showing the relationship between the actual overhang amount of the slab in the reheating furnace and the temperature difference ΔT between the upper and lower surfaces of the tip of the rough bar. [Figure 4] It is a graph showing the relationship between the actual overhang amount of the slab in the reheating furnace and the warping amount Lw of the tip rolled in the first stage of the finish rolling mill. [Figure 5] It is a schematic side view explaining the mechanism of tip warping during the rolling of the sheet material.

Embodiments for Carrying Out the Invention

[0015] [[ID=Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. The following embodiments illustrate devices and methods for embodying the technical idea of the present invention, and do not specify the configuration to the following. That is, the technical idea of the present invention can be variously modified within the technical scope described in the claims.

[0016] As a cause of the tip of the rolled material warping upward, there is a temperature difference generated in the thickness direction of the sheet bar (rough bar) on the entrance side of the rolling mill. Generally, the upper surface of the sheet bar is cooled by radiation and convective heat transfer to the atmospheric temperature, and by the retention of water from the scale breaker and the like. On the other hand, the lower surface often forms a closed space and is in a relatively high-temperature environment. Therefore, the upper surface of the sheet bar is more likely to have a lower temperature than the lower surface. Due to this temperature difference, the deformation resistance on the upper surface side and the lower surface side of the sheet bar becomes different, so that warping occurs at the tip of the rolled plate, for example, at the tip of a hot-rolled steel sheet, during rolling. FIG. 5 is a schematic side view for explaining the state where the tip warps upward during rolling of the sheet material. For example, when the upper surface temperature Tu of the sheet bar 11 is lower than the lower surface temperature Td (Tu < Td), the deformation resistance σu on the upper surface side of the sheet bar becomes larger than the deformation resistance σd on the lower surface side. Therefore, when the sheet bar 11, which is the material to be rolled, is passed through the rolling roll 10 by horizontal rolling, the lower surface side is extended more greatly in the rolling direction FD along the pass line plane PL than the upper surface side. Therefore, the tip 12A of the rolled material 12 is bent upward and warps upward. From the above considerations, the inventors considered that it is important to make the upper and lower surface temperatures of the tip portion of the material to be rolled such that the upper surface temperature Tu > the lower surface temperature Td in order to suppress the upward warping of the tip of the rolled material.

[0017] FIG. 1 shows the support state of the slab in the heating furnace according to the present embodiment. FIG. 1(a) is a schematic side view, and FIG. 1(b) is an enlarged cross-sectional view taken along arrow A, showing the operator side OP and the prime mover side DR. The slab 1 loaded into the heating furnace is supported by the skid 2 via the skid button 2A. A plurality of skids 2 are installed in the longitudinal direction of the slab 1 from the tip FE to the tail TE. Cooling water circulates inside the skid 2, and the lower surface of the slab 1 is cooled through the skid button 2A. Therefore, the periphery of the portion of the slab supported by the skid on the lower surface of the slab becomes lower in temperature than the other slab surfaces.

[0018] FIG. 2 shows a schematic cross-section along the longitudinal direction of the material to be rolled and the rolled material for each rolling schedule. FIG. 2(a) is a partially enlarged cross-sectional view showing the state where the tip of the slab 1 in the heating furnace is supported by the skid button 2A. A low temperature portion 1A is formed on the lower surface of the slab 1 that contacts the skid button 2A. Here, in the longitudinal direction of the slab 1, the distance from the tip of the slab 1 to the center of the skid button 2A is defined as the overhang amount. FIG. 2(b) shows the rough bar 11 after rough rolling. Due to rough rolling, the thickness becomes thinner (tb < t0), and the low temperature portion 11B on the lower surface is stretched. FIG. 2(c) shows the state of the sheet bar 11 immediately before being loaded into the finishing rolling mill. Since the tip unsteady portion of the sheet bar 11, that is, the crop portion CS is cut off, a substantially upper surface temperature Tu > lower surface temperature Td can be achieved at the tip portion 11A of the sheet bar 11.

[0019] The overhang amount is preferably 0.8 to 1.0 times the slab thickness t0. This allows the top surface temperature Tu at the leading edge of the slab after heating furnace extraction to be higher than the bottom surface temperature Td. As a result, the amount of warping Lw after the first stage of rolling in the finishing mill can be reduced. If the overhang amount is less than 0.8 times the slab thickness t0, there is a risk of the slab falling from the skid, so it is preferable that the overhang amount be 0.8 times the slab thickness t0 or more. On the other hand, if the overhang amount is 1.0 times the slab thickness t0 or more, it may be difficult to maintain top surface temperature Tu < bottom surface temperature Td at the leading edge. Therefore, it is preferable that the overhang amount be 0.8 to 1.0 times the slab thickness t0.

[0020] It is preferable for multiple skid buttons that contact the slab edge to make contact in the width direction, as this creates a temperature difference between the upper and lower surfaces. The contact area per skid button should be 80-120 cm². 2 A range of 80 cm² is preferred. This has the advantage of allowing for a greater temperature difference between the upper and lower surfaces. 2 If the contact area per skid button is less than 120 cm², the stability when the slab is placed on it may be compromised. 2 If the temperature exceeds this limit, excessive heat dissipation can occur, potentially leading to quality defects in the rolled slab. Therefore, the contact area per skid button should be 80-120 cm². 2 The following ranges are preferred. Furthermore, in the slab width direction, the contact width ws of the skid buttons is preferably in the range of 50 mm to 120 mm, and the pitch of the support material (pitch between skid buttons = contact width ws + spacing ds) is preferably in the range of 150 mm to 220 mm. The contact ratio CR in the width direction is preferably in the range of 60 to 80%. The contact ratio CR is defined as the percentage of the total contact length of the skid buttons in the width direction relative to the total width of the slab. By configuring the contact width ws of the skid buttons and the pitch between skid buttons in the slab width direction in this way, the slab can be heated without the skid buttons being damaged by thermal expansion and contraction, and without damaging the slab. [Examples]

[0021] In the heating furnace, the longitudinal arrangement of the skid and steel slab was varied, and heating was performed with different amounts of overhang (mm) at the tip of the steel slab. Figure 3 plots the temperature difference ΔTs (=Tu-Td) (°C) between the upper and lower surfaces of the rough bar tip after rough rolling against the actual value of the slab overhang (mm) in the heating furnace. The surface temperature of the upper and lower surfaces of the rough bar tip was measured using a radiation thermometer. From the results in Figure 3, it can be seen that the temperature difference ΔTs between the upper and lower surfaces of the rough bar tip tends to increase as the actual value of the overhang decreases. In particular, when the slab overhang ≤ 220 mm, the average of ΔT is positive, meaning that the upper surface temperature Tu of the rough bar tip is greater than the lower surface temperature Td.

[0022] Figure 4 shows the rough bar under the above conditions subsequently rolled in a finishing mill, and the tip curvature Lw (mm) after the first stage of rolling in the finishing mill is plotted against the actual value of the slab overhang in the heating furnace. The definition of curvature Lw is shown in Figure 5. It can be seen that when the actual value of the slab overhang in the heating furnace is 220 mm or less, the curvature Lw is reduced to 200 mm or less, less than half, and when the slab overhang is ≤ 180 mm, the curvature Lw approaches 0. [Industrial applicability]

[0023] The method for manufacturing rolled material and the heating furnace for hot rolling according to the present invention can reduce the upward curvature of the leading edge of the rolled material, thereby improving productivity and being industrially useful. [Explanation of Symbols]

[0024] 1. Rolled material (slab) 1A (Slab) Low-temperature section 2 Skid 2A Skid Button 10 Rolling Rolls 11. Sheet bar (rough bar, rough rolled material) 11A (After cropping) Coarse bar tip 11B (Seat bar) Low temperature section 12 (Finished) Rolled Material 12A (rolled material) tip ws (contact width of skid button) ds (spacing of skid buttons in the width direction) CR (Contact rate between skid and slab in the width direction) OP operator side DR (Driver side) FE (of the rolled material) tip TE (Tail end of rolled material) Lw (Warp amount at the exit of the first stage of the finishing rolling mill) Tu Top surface temperature Td bottom temperature FD rolling direction PL Pathline Plane CS (Crop portion of the rough bar to be cut)

Claims

1. When manufacturing rolled material using a hot rolling line equipped with a heating furnace for heating the material to be rolled and a rolling mill for rolling the heated material, In the heating furnace, the leading edge of the rolled material is supported by a support material having a cooling function. In the longitudinal direction of the rolled material, the overhang amount, which is the distance from the tip of the rolled material to the center of the support material, is set to 220 mm or less. A method for manufacturing a rolled material, wherein the support members are divided into multiple parts, the area in contact with the rolled material per part is in the range of 80 to 120 cm², the pitch of the support members in the width direction is in the range of 150 to 220 mm, and the contact rate with the rolled material in the width direction is in the range of 60 to 80%.

2. A method for manufacturing a rolled material according to claim 1, wherein the thickness of the rolled material is t0, and the center of the support material is positioned within a range of 0.8 × t0 to 1.0 × t0 from the tip in the longitudinal direction of the rolled material for support.

3. A heating furnace in a hot rolling line that heats the material to be rolled in a rolling mill, A support member having a cooling function is positioned to support the leading edge of the rolled material. In the longitudinal direction of the rolled material, the overhang amount, which is the distance from the tip of the rolled material to the center of the support material, is 220 mm or less. A heating furnace for hot rolling, wherein the support members are divided into multiple sections, the area in contact with the rolled material per section is in the range of 80 to 120 cm², the pitch of the support members in the width direction is in the range of 150 to 220 mm, and the contact rate with the rolled material in the width direction is in the range of 60 to 80%.

4. The heating furnace for hot rolling according to claim 3, wherein the support member is arranged such that its center is within a range of 0.8 × t0 to 1.0 × t0 from the leading edge of the rolled material, with the thickness of the rolled material being t0.

Images