Manufacturing method of 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 producing rolled material while preventing upward bowing of the tip end of the rolled material in a hot rolling line in which the rolled material is heated in a heating furnace and rolled to a predetermined thickness by a rolling mill, and to a hot rolling heating furnace used in this method. [Background technology]

[0002] In general, hot-rolled steel strips are produced by heating a material to be rolled to a predetermined temperature in a heating furnace, and then rolling the heated material to a predetermined thickness in a roughing mill to produce a rough bar. The rough bar is then heated by a heating device such as an edge heater or a bar heater, and is then finish-rolled in a finishing mill consisting of multiple rolling stands to produce a hot-rolled steel strip of a predetermined thickness. The hot-rolled steel strip is then cooled by a cooling device on a hot-run table and 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 hot rolled steel strip in each stand of the roughing mill or the finishing mill. If the rough bar or hot rolled steel strip has an upward warping at the tip, it will come into contact with the equipment inside the rolling mill, causing equipment damage and the rolled material to become a defective product. In such a case, rolling in the subsequent cycle must be stopped, and operational productivity is significantly impaired.

[0004] Therefore, a technology for reducing the upward warpage at the tip of such a rough bar or hot-rolled steel strip has been developed. For example, Patent Document 1 discloses a technology for performing a cooling process between the rough rolling process and the finish rolling process. In the cooling process, the water cooling conditions are changed based on the steel type of the rolled material, the temperatures of the top and bottom surfaces of the rolled material when cooling is stopped, etc., and in the finish rolling process, asymmetric cooling of the top and bottom surfaces of the rolled material is performed based on the warpage state in the previous pass to control the tip warpage that occurs in the latter pass.

[0005] Patent Document 2 discloses a technique for preventing upward warping of a material rolled by a rolling mill by heating the material in a heating furnace so that the front and back surfaces of the material have an appropriate temperature difference. The heating furnace is configured to heat the top and bottom surfaces separately, and the temperatures of the top and bottom surfaces are controlled by controlling the fuel. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 06-071326 [Patent Document 2] JP 2012-187602 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the above-mentioned conventional techniques have the following problems. The technology described in Patent Document 1 does not take into consideration the upward warping of the rolled material in the rough rolling mill. In addition, there is a risk that the investment required to install additional cooling equipment will be excessive. In the technology described in Patent Document 2, it may be difficult to control the temperature when the heating temperature target is different in the longitudinal direction or on the top and bottom surfaces, and it may be difficult to control the temperature difference between the top and bottom surfaces when the rolled material remains in the heating furnace for a long time due to the rolling schedule. Therefore, there are cases where it is not possible to reliably prevent the upward warping of the tip of the rolled material.

[0008] The present invention has been made in view of the above, and an object of the present invention is to provide a manufacturing method which is not influenced by operating conditions and which reliably prevents upward warping at the tip of the rolled material by creating a temperature difference between the top and bottom surfaces at the tip of the rolled material, and a hot rolling heating furnace for use in said method. [Means for solving the problem]

[0009] The method for producing rolled material of the present invention, which advantageously solves the above-mentioned problems, uses a hot rolling line equipped with a heating furnace for heating the rolled material and a rolling mill for rolling the heated rolled material, and is characterized in that, when producing rolled material, in the heating furnace, a support material having a cooling function is arranged to support the tip end of the rolled material.

[0010] The method for producing a rolled material according to the present invention is as follows: (a) 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 of the rolled material in the longitudinal direction of the rolled material to support the material; (b) The support material is divided into a plurality of pieces, and the area of ​​contact with the rolled material is set to 80 to 120 cm per piece. 2 the pitch of the support material 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%; This may be a more preferable solution.

[0011] The hot rolling heating furnace according to the present invention, which advantageously solves the above problems, is a heating furnace in a hot rolling line that heats a material to be rolled by a rolling mill, and is characterized in that a support member having a cooling function is arranged at a position that supports the tip end of the material to be rolled. An example of the support member having a cooling function is a skid 2 shown in Figure 1, and the cooling function may be any ordinary technology according to the common knowledge of a person skilled in the art.

[0012] The hot rolling heating furnace according to the present invention has the following features: (c) the support material is arranged so that its center is within a range of 0.8×t0 to 1.0×t0 from the tip of the rolled material, where t0 is the thickness of the rolled material; (d) The support material is divided into a plurality of pieces, and the area of ​​contact with the rolled material is 80 to 120 cm per piece. 2 the pitch of the support material 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%; This may be a more preferable solution. Effect of the Invention

[0013] According to the method for producing rolled material and the heating furnace for hot rolling of the present invention, the temperature of the lower surface side of the tip of the rolled material can be lower than that of the upper surface side at the outlet side of the heating furnace regardless of the operating conditions without making excessive capital investment. Therefore, the upward warping of the tip of the rolled material can be suppressed in the subsequent rolling process. Since there is no operational trouble and the productivity is improved, it is industrially useful. In the method for producing rolled material of the present invention, in order to reliably prevent the upward warping of the tip of the rolled material, it is preferable that the thickness of the rolled material is t0, and the center of the support material is arranged and supported within a range of 0.8×t0 to 1.0×t0 from the tip in the longitudinal direction of the rolled material. This does not include the case where the center of the support material is arranged and supported within a range of 0.8×t0 to 1.0×t0 from the tip in the longitudinal direction of the rolled material due to constraints such as the size of the slab. [Brief description of the drawings]

[0014] [Figure 1] 1A and 1B are schematic diagrams showing a supporting state of a slab in a heating furnace according to one embodiment of the present invention, in which (a) is a schematic side view, and (b) is a partially enlarged view viewed from the direction of arrow A. [Diagram 2] FIG. 1 is a schematic enlarged view showing the rolled material for each rolling schedule and a schematic cross section along the longitudinal direction of the rolled material, where (a) shows the state in which the slab is supported in a heating furnace, (b) shows the state of the rough bar after rough rolling, and (c) shows the state of the rough bar before finish rolling. [Diagram 3] 1 is a graph showing the relationship between the actual value of the overhang amount of the slab in the heating furnace and the temperature difference ΔT between the top and bottom surfaces of the tip of the rough bar. [Figure 4] 1 is a graph showing the relationship between the actual value of the amount of overhang of a slab in a heating furnace and the amount of warpage Lw of the tip portion rolled in the first stage of a finishing mill. [Diagram 5] FIG. 2 is a schematic side view illustrating the mechanism by which warpage occurs at the tip end when a plate material is rolled. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 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 be 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 that occurs in the thickness direction of the sheet bar (rough bar) on the inlet 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 or the like. On the other hand, the lower surface often forms a closed space and is in an environment with a relatively high temperature. 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 in which 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 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 charged 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 end 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 lower surface supported by the skid is at a lower 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 loading 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. In this way, the top surface temperature Tu at the front end of the slab after removal from the heating furnace can be made higher than the bottom surface temperature Td. As a result, the warpage amount Lw after the first stage rolling of the finishing mill can be reduced. If the overhang amount is less than 0.8 times the slab thickness t0, there is a risk that the slab will fall off the skid, so the overhang amount is preferably 0.8 times or more the slab thickness t0. On the other hand, if the overhang amount is 1.0 times or more the slab thickness t0, it may be difficult to make the top surface temperature Tu<the bottom surface temperature Td at the front end. Therefore, the overhang amount is preferably 0.8 to 1.0 times the slab thickness t0.

[0020] It is preferable that multiple skid buttons contact the leading edge of the slab in the width direction to create a temperature difference between the top and bottom surfaces. The contact area per skid button is 80 to 120 cm. 2 This has the advantage of creating a larger temperature difference between the top and bottom surfaces. The contact area per skid button is 80cm2. 2 If it is less than this, stability may be lost when a slab is placed on it. Also, if the contact area per skid button is less than 120 cm 2 If it exceeds this limit, the heat transfer will be too great, and the quality of the slab after rolling may be abnormal. Therefore, the contact area per skid button should be 80 to 120 cm 2 It is preferable that the contact width ws of the skid buttons in the slab width direction is 50mm to 120mm, and the pitch of the support material (pitch between skid buttons = contact width ws + spacing ds) is 150mm to 220mm in the slab width direction. It is preferable that the contact ratio CR in the width direction is 60% to 80%. The contact ratio CR is the percentage of the total widthwise contact length of the skid buttons relative to the total width of the slab. By configuring the contact width ws of the skid buttons in the slab width direction and the pitch between the skid buttons in this way, the slab can be heated without the skid buttons being damaged due to thermal expansion and contraction, and without causing scratches on the slab. EXAMPLES

[0021] In the heating furnace, the longitudinal arrangement of the skid and the steel slab was changed in various ways, and heating was performed with different overhang amounts (mm) at the tip of the steel slab. Figure 3 plots the temperature difference ΔTs (=Tu-Td) (°C) at the top and bottom surfaces of the tip of the rough bar after rough rolling against the actual overhang amount (mm) of the slab in the heating furnace. The surface temperatures of the top and bottom surfaces of the tip of the rough bar were measured with a radiation thermometer. The results in Figure 3 show a tendency for the temperature difference ΔTs at the top and bottom surfaces of the tip of the rough bar to increase as the actual overhang amount decreases. In particular, when the slab overhang amount is ≦220 mm, the average ΔT is positive, that is, the top surface temperature Tu of the tip of the rough bar is greater than the bottom surface temperature Td.

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

[0023] INDUSTRIAL APPLICABILITY According to the method for producing rolled material and the hot rolling heating furnace of the present invention, upward warping of the tip end of the rolled material can be reduced, 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 Mill 11 Sheet bar (rough bar, rough rolled material) 11A Rough bar tip (after cropping) 11B (Cold section of sheet bar) 12 (Finishing) Rolled material 12A (rolled material) tip ws (skid button) contact width ds (widthwise skid button spacing) CR (crosswise skid to slab) contact ratio OP operator side DR Prime Mover Side FE (end of rolled material) TE (Tail end of rolled material) Lw (finishing mill first stage exit side) warpage Tu Top surface temperature Td bottom temperature FD rolling direction PL Path Line Plane CS Crop (of the rough bar to be cut)

Claims

1. In producing rolled materials using a hot rolling line including a heating furnace for heating the rolled material and a rolling mill for rolling the heated rolled material, In the heating furnace, a support member having a cooling function is arranged to support the tip end of the rolled material.

2. The method for producing 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 x t0 to 1.0 x t0 from the tip in the longitudinal direction of the rolled material to support the material.

3. The support material is divided into a plurality of pieces, and the area of ​​contact with the rolled material is set to 80 to 120 cm per piece. ２ 3. The method for producing rolled material according to claim 1 or 2, wherein the support pitch 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. A heating furnace of a hot rolling line for heating a material to be rolled by a rolling mill, a support member having a cooling function is disposed at a position supporting the tip end of the rolled material.

5. The hot rolling heating furnace according to claim 4, wherein the support material is arranged so that the center is within a range of 0.8 x t0 to 1.0 x t0 from the tip of the rolled material, where t0 is the thickness of the rolled material.

6. The support material is divided into a plurality of pieces, and the area of ​​contact with the rolled material is 80 to 120 cm per piece. ２ 6. The hot rolling heating furnace according to claim 4 or 5, wherein the support pitch 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%.

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