JP2012166208A - Method for manufacturing thick and middle plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent extraction of a heating furnace by using a thin and long slab and preventing the hot deflection of the slab from increasing in the furnace in producing a thick intermediate plate without turning the slab. The present invention provides a method for producing a thick and medium plate in which the slab is heated so as not to occur, the rolling time of the slab extracted from the heating furnace is shortened to increase the rolling temperature, and the occurrence of misroll is suppressed.
SOLUTION: A two-tiered slab heated in a walking beam type heating furnace is extracted from the heating furnace, descaled as a two-tiered slab, and then the upper thick plate with a slab lifting device. The lower slab is lifted, the lower thick slab is transferred to a roughing mill and hot rolled.After the lower thick slab is transferred, the upper thin slab lifted by the slab lifting device is lowered. A method for producing a thick-middle plate, which is transferred to a finishing mill and hot-rolled to a thick-middle plate.
[Selection] Figure 6

Description

  The present invention uses a thin and long slab that is normally bent (heat-deflected) due to heat in the heating furnace and hinders extraction from the heating furnace. The present invention relates to a method for producing a thick and medium plate that is rolled to a thick and medium plate without rolling out, shortens the rolling time, increases the rolling temperature, and suppresses the occurrence of misroll.

  The thick plate is a hot-rolled steel plate having a thickness of 3 mm or more. Generally, the thick plate is classified as a medium plate and 3 mm or more as a thick plate, and may be collectively referred to as a thick plate. Thick and medium plates are widely used as steel structures such as shipbuilding, architecture, bridges, large diameter steel pipes.

  In the manufacturing process of the thick plate, since the rolled thickness of the thick plate is thin, the steel plate is easily cooled during rolling, so that the temperature deviation at each position of the steel plate becomes large. As a result, the hardness deviation tends to be large, so that the failure rate for misrolling is higher than that of a normal thick plate.

  In order to reduce the rejection rate, it can be solved by making the steel plate rolling temperature as high as possible. However, thick slabs are mainly rolled, especially because they are thin. Therefore, slabs with a small weight are used, but the continuous cast slab thickness and slab width obtained by continuously casting a slab with a small weight are charged into the heating furnace. A small slab for thick and medium plates that is not enough for the possible slab length, is unavoidably heavy, is rolled to a hot rolled slab thickness of about 1/3, and then cooled to the required length. The thick slab is manufactured by subjecting this small-sized slab to hot rolling (detent rolling and main rolling) again. Various apparatuses for lifting and rolling a slab for tenter rolling have been proposed (see, for example, Patent Documents 1 and 2).

  However, in the first hot rolling, not only the slab thickness is reduced to about 1/3, but if the final rolling width is set, it is necessary to use the normal rolling material for the main rolling. And the slab rolling at the table in front of the rolling mill accompanying it becomes unnecessary, and the rolling time can be shortened. As a result, although the rolling temperature can be increased, tenth rolling is performed in addition to the first rolling, so that the thickness of the slab is reduced, and the heating temperature is reduced in the heating furnace to ensure the rolling temperature before the main rolling. When the cut slab is heated, the hot deflection of the slab increases in the furnace, and this causes a problem in the extraction of the furnace.

  As a heating furnace for heating the slab, a walking beam furnace is usually used, and as a problem when the slab is heated by the walking beam furnace, a method of correcting the positional deviation of the slab in the furnace width direction (for example, Patent Document 3) and a method of covering the slab front and back surfaces to prevent decarburization of the slab surface layer (see, for example, Patent Document 4) have been proposed, but the hot deflection of the slab in the furnace in the heating furnace is proposed. No suppression technology has been proposed yet.

JP 2007-216278 A JP 2009-279630 A JP 2010-202965 A JP-A-7-284812

  Therefore, the present invention normally uses a thin and long slab that is bent due to heat in the heating furnace to hinder extraction, and is used to manufacture a thick intermediate plate without turning the slab. Heat the slab so that the hot deflection of the slab does not increase in the furnace, so that it does not interfere with the extraction of the heating furnace, the slab extracted from the heating furnace is rolled without performing tenter rolling, It is an object of the present invention to provide a method for producing a thick intermediate plate that can shorten the rolling time to increase the rolling temperature and suppress the occurrence of misroll.

  In order to solve the above-mentioned problems, the inventors of the present invention have developed a thin and long slab that is bent due to heat in the heating furnace to cause an obstacle to extraction. We have conducted intensive research on heating the slab so that hot deflection (heat dripping) does not increase. As a result, heat deflection (heat dripping) of thin chopped slabs is achieved by charging the slab into a heating furnace and heating it in two steps with the slabs for thick plates on top and the normal slabs on the bottom. I found out that it can be prevented. Then, the two-stage slab is extracted from the heating furnace, and the two slabs are separated by a slab lifting device between the roughing mill and the finishing mill. The slab for rolled material can be rolled with a rough rolling mill without rolling the slab, so that the rolling time of the slab for thick plate can be shortened and the rolling temperature can be increased. The present inventors have found a method for producing a thick medium plate (for example, a thickness of less than 3 to 6 mm) that can suppress the occurrence of misroll, and completed the present invention.

  The gist of the present invention is as follows.

  (1) In manufacturing a thick medium plate by heating the thin slab for thick medium plate in a walking beam heating furnace and hot rolling the thin slab for thick medium plate extracted from the heating furnace, A method for producing a thick-medium plate, characterized in that a thin slab is placed in an upper stage and a thick slab is placed in a lower stage in a two-tiered manner and charged in a walking beam heating furnace and heated.

  (2) After extracting the heated two-stage slab from the heating furnace into the walking beam furnace, the upper slab is lifted by the slab lifting device, and the lower thick slab is rough. After transporting to the rolling mill and hot rolling and transporting the lower thick slab, the upper thin plate slab that was lifted by the slab lifting device is lowered and transferred to the finishing mill to heat the thick plate. The method for producing a thick intermediate plate according to the above (1), characterized by performing hot rolling.

  (3) The scale according to (2) above, wherein the two-stage slab heated in the walking beam heating furnace is extracted from the heating furnace and then descaled as the two-stage slab. Manufacturing method of thick plate.

  (4) The method for producing a thick and medium plate according to (3), wherein the descaling is performed by injecting high-pressure water with a water scale breaker (HSB).

  (5) Each of the slabs is hot-rolled in a hot rolling line in which a slab lifting device is disposed between the rough rolling mill and the finishing mill. (1) to (4) above The manufacturing method of the thick inside plate in any one.

  In the present invention, when a heavy slab is first hot rolled, the slab thickness is reduced to about 1/3, and the final rolling width is set to a width necessary for a normal rolling material during main rolling. Thick and medium plates are manufactured without performing rolling out and slab rolling on the table in front of the rolling mill. For this reason, when a thin slab having the final rolling width is heated in a heating furnace, the slabs are stacked in two stages and charged into the heating furnace, and the slabs stacked after the heating furnace are separated, usually heating. Thin and long slabs that can be bent due to heat in the furnace and hinder the extraction can be used, and since the slabs are descaled in a two-layered state immediately after the extraction from the heating furnace, A temperature drop can be prevented. Furthermore, since it can be hot-rolled without performing slab rotation at the table in front of the rolling mill, the rolling time of the slab extracted from the heating furnace can be shortened to increase the rolling temperature, and the occurrence of misrolling is suppressed to prevent Can be manufactured. And manufacture of a thick steel plate can be performed using the existing several rolling mill and the hot rolling line which has a slab lifting apparatus (lamination slab separation apparatus).

It is a top view in a heating furnace (walking beam furnace). It is a figure for demonstrating the hot bending of the slab in a heating furnace in-furnace. It is a side view of a heating furnace extraction-portion site | part. It is a figure which shows the relationship between the heating temperature corresponding to slab thickness, and the amount of slab bending. It is a figure which shows the outline | summary of the hot rolling line in this invention. It is a figure which shows the outline | summary of the time transition of the manufacturing method of the thickness plate of this invention. It is a figure which shows a well-known slab lifting apparatus.

  Embodiments of the present invention will be described below.

  The present invention reduces the slab thickness to about 1/3 during the first hot rolling of a heavy slab, and at the final rolling width, usually due to heat deflection in the heating furnace ( The slab is made into a thin and long slab that causes a hindrance to the extraction by heat dripping), and this slab is reheated in the heating furnace so as to suppress the heat deflection of the slab generated in the heating furnace, and then from the heating furnace. Extraction and finish rolling are performed. For this reason, it has become possible to manufacture a thick and medium thickness plate by eliminating the need for tentering rolling to rotate the slab as in the prior art, shortening the rolling time of the slab and increasing the rolling temperature, and suppressing the occurrence of misroll.

  Hereinafter, the present invention will be described with reference to the drawings.

  First, the heating of the slab in the heating furnace will be described.

  FIG. 1 is a plan view of the inside of a heating furnace (walking beam furnace), FIG. 2 is a view for explaining hot deflection of a slab in the furnace, and FIG. 3 is a side view of a heating furnace extraction part. It is.

  For example, a continuously cast slab having a thickness of 250 mm was roughly rolled to 1/3 thickness, and after cooling, was divided into three parts to obtain a small slab having a thickness of 80 mm. As shown in FIG. 1, a case will be described in which a heating furnace (walking beam furnace) 1 is charged with this small slab 3 with a pusher 2 and heated and then extracted by an extraction device (extractor) 4.

  As a heating furnace that heats a slab to a predetermined temperature while sequentially transporting the slab from the charging side to the extraction side, a walking beam heating furnace is generally used. This walking beam type heating furnace consists of a walking beam (moving skid) whose hearth is movable up and down and a fixed walking beam (fixed skid). The slab is transported from the charging side to the extraction side by repeatedly transporting the slab in the heating furnace in the longitudinal direction in the furnace. Then, the slab that has reached the extraction standby position at the front end of the heating furnace extraction side is extracted out of the furnace by a slab extraction device (extractor) from the heating furnace and sent to the next process.

  The slab charged in the walking beam furnace is heated to 1200 to 1250 ° C. while moving on the stationary walking beam in the furnace by the vertically movable walking beam. As the temperature of the slab rises, the slab softens, and as shown in FIG. 2, the thin chopped slab 3 is movable up and down in a furnace in which a vertically movable walking beam 5 and a fixed walking beam 6 are installed. Both ends of the slab hang down outside the walking beam 5 and heat deflection occurs. When the deflection generated in the slab increases as described above, even if the slab is extracted by lifting the slab with the slab extractor (extractor) 4, the slab collides with the heating furnace extraction port if the deflection is higher than the lifting height. As a result, the extraction will be hindered. Or, even if it can be extracted by the slab extractor, when trying to place the slab on the table roll from the extractor, the slab's heat deflection part is caught on the edge of the extractor side table roll and cannot be placed on the table roll. is there. As described above, since the thin slab is heat-deformed at the time of heating, it has been difficult to heat it with a walking beam type heating furnace.

  Referring to FIG. 3, the slab 3 heated in the heating furnace 1 is lifted to a height hL by a slab extractor (extractor) 4 charged on the heating furnace extraction port side, and is lifted onto the table roll T. Moved to and placed. At this time, the thermal deflection of the slab is large. For example, when the thermal deflection becomes larger than the distance A between the lower edge of the heating furnace extraction port and the upper edge of the extractor, the thermal deflection portion of the slab collides with the lower edge of the heating furnace extraction port. This makes it impossible to extract slabs. Alternatively, when the slab 3 extracted from the heating furnace extraction port is moved and placed on the table roll T, the thermal deflection becomes larger than the distance B between the edge of the extractor side table roll and the upper edge of the extractor. The heat deflection part of the slab is caught on the edge of the table roll on the extractor side and cannot be placed on the table roll.

  The distance A between the lower edge of the heating furnace extraction port and the upper edge of the extractor and the distance B between the edge of the extractor-side table roll and the upper edge of the extractor vary depending on the heating furnace equipment, but in any case, the heat deflection of the slab If the amount of heat deflection is not smaller than the distance A and the distance B, the extraction of the slab from the heating furnace will be hindered.

  The amount of slab deflection in the heating furnace is calculated by the following equation (1) in consideration of the beam deflection theory and actual measurement values.

Where δ is the deflection (mm), E ₀ is the room temperature Young's modulus (200 Gpa), Te is the steel melting point (1500 ° C.), T is the heating temperature, Ls is the slab length (mm), and Lw is the movable walking beam width ( mm, for example, 1200 mm), L is the beam length (overhang), L = (Ls−Lw) / 2, h is the beam thickness (slab thickness) (mm), k is a coefficient, and k = 9.1. means.

  FIG. 4 is a diagram showing the relationship between the heating temperature corresponding to the slab thickness and the amount of slab deflection.

  As shown in FIG. 4, the higher the heating temperature, the greater the amount of thermal deflection of the slab, and the amount of deflection of the slab decreases as the thickness of the slab increases.

  Therefore, when the slab is extracted from the heating furnace, the amount of deflection δ calculated by the equation (1) is a height hL (distance A and distance B that secures the slab by the slab extractor (extractor). If it is smaller than s), the slab can be extracted from the heating furnace without hindrance, and the condition is as shown in the following equation (2).

Deflection amount δ + slab initial warpage C + marginal height R ≦ lifting height hL (2)
Here, it is obtained as an actual measurement value that the initial slab warpage C = 30 mm, the margin height R = 20 mm, and the lifting height hL = 162 mm.

  When the slab thickness is small like a small slab, the total amount of deflection δ + slab initial warpage C + room height R becomes larger than the height hL at which the slab extractor (extractor) lifts the slab. This will hinder the extraction of slabs from the slab.

  The present inventor believes that the increase in the amount of slab bending in the heating furnace is affected by the thin slab thickness as in the case of a small slab. Even if the slab has a long and thin slab length, the slab is loaded into the heating furnace in two stages and is usually bent due to heat in the heating furnace to cause an obstacle to extraction. It is found that the heat deflection of the slab can be eliminated, the slab extraction from the heating furnace is not hindered, and it is possible to heat in the heating furnace, and after the two-layer slab extraction from the heating furnace The present invention has been completed by finding that by separating and rolling the upper and lower slabs stacked in two stages, a thick intermediate plate can be produced without rolling the slab for tentering rolling.

Here, the amount of deflection of the lower slab when the two tiers are stacked is not corrected in the amount of warpage of the lower slab when the amount of deflection δu of the upper slab is smaller than the amount of deflection δd of the lower slab. δu when exceeding deflection amount .delta.d the lower slab since the lower slab is pressed in the upper slab, in consideration of the amount, the lower slab deflection of .delta.d ₂ when stacked two stages as shown in the following expression (3) Weighted average. However, the weight is replaced by the slab thickness.
Lower slab deflection amount δd ₂ = {(δu−δd) LuHu + δdLdHd} / LdHd (3)
Where δu: Upper slab deflection (mm), δd: Lower slab deflection (mm), δd ₂ : Weighted average lower slab deflection (mm), Lu: Upper slab beam length (mm), Ld : Lower slab beam length (mm), Hu: Upper slab thickness (mm), Hd: Lower slab thickness (mm).

Therefore, it is important to adjust the deflection amount δd ₂ of the two-stage slab so as to satisfy the following formula (4).

Deflection amount δd ₂ of two-stage slab + initial slab warpage C
+ Marginal height R ≤ Lifting height hL (4)
Here, the initial slab warpage C = 30 mm, the marginal height R = 20 mm, and the lifting height hL = 162 mm, but this value varies depending on the equipment.

  Next, a method for producing a thick intermediate plate according to the present invention will be described.

  FIG. 5 is a diagram showing an outline of a hot rolling line according to the present invention, and FIG. 6 is a diagram showing an overview of a time transition of the method for manufacturing a thick and medium plate according to the present invention.

  As shown in FIG. 5, the hot rolling line includes a heating furnace 1, a water scale breaker (HSB) 7, a rough rolling mill 8, a slab lifting device 9, a finishing rolling mill 10, a hot straightening machine 11, and a control cooling device. (Hardening etc.) It is arrange | positioned in order of 12 and it is comprised so that the hot-rolled steel plate cooled with the control cooling device may be sent to the shearing line 14 through the cooling bed 13.

  The manufacturing method of the thick plate will be described in the steps shown in time transition images (A-1) to (A-4) with reference to FIGS. 5 and 6. A heating furnace (walking beam furnace) 1 is provided with a slab that is stacked in two layers with a thick slab (thick slab) 15 on the bottom and a slab for thick medium plates (small slab) 16 on the top. And heated. By heating the slab as a two-layer stack, it was possible to prevent thermal sagging (thermal deflection) that occurred at the end of the slab for thick plate.

  In order to prevent thermal deflection (heat dripping) at the end of the thin slab, the width of the lower thick slab in the two-tiered slab should be the same as or wider than that of the upper thin slab. preferable.

  After the heated two-stage slab is extracted from the heating furnace (A-1), the scale (oxide) generated on the surface of the slab in the furnace is sprayed with high-pressure water by the water scale breaker (HSB) 7 And descaling (A-2). In the descaling process, since the slab thickness is increased in two layers, the slab is difficult to cool even when descaled by a high-pressure water flow, so that the temperature decrease of the slab can be suppressed. In addition, since heating is performed in a heating furnace in the form of a two-layer slab, scales are unlikely to be generated on the surface where the slabs overlap, and descaling of the overlapped surfaces is not necessary. For this reason, what is necessary is just to descal a slab with two steps piled up by injecting high pressure water with a water scale breaker (HSB).

  Next, the two-stage slabs after descaling are transferred to a slab lifting device (lap slab separating device) 9 installed between the rough rolling mill and the finishing mill of the hot rolling line, and the upper slab is thinned. The slab 16 is lifted by the slab lifting device 9 to separate the two slabs. The lower thick slab (normal material slab) 15 not lifted by the slab lifting device is transferred to the roughing mill 8 and rolled by the roughing mill as usual (A-3). On the other hand, the thin slab 16 lifted by the slab lifting device 9 is transferred to the hot rolling line after being transferred from the slab lifting device 9 to the finishing rolling mill 10 after the thick slab 15 is transferred, and is rolled and rolled by the finishing rolling mill 10. Let it be an intermediate plate (A-4).

  As the slab lifting device 9 used here, a known slab lifting device can be used. Although not limited as a slab lifting device, for example, a device having a mechanism for lifting and rolling a slab as shown in FIG. 7 can be used, and this device is a main body that grips the side surface of the slab H. 17 and a support structure 18 that supports the main body 17 and moves it up and down. The main body 17 includes a plate-like horizontal base 19, and two sets of gripping members (tongues) 20 that grip the slab H from both sides are attached to both sides thereof. A gate-shaped frame 21 is formed on the support structure portion 18, and a carriage 23 to which a wire 22 for suspending the main body portion 17 is connected is provided on the upper surface thereof. The carriage 23 is provided with a winch 24 for raising and lowering the wire 22, and the main body 17 can be moved up and down by raising and lowering the wire 21. The slab H can be lifted by gripping the side surface of the slab H with the gripping member 20 and operating the winch 24. In addition, this apparatus can also hold | grip and rotate the side surface of the slab H. FIG.

  In the above description, it is explained that a thin slab on the upper stage of a two-stage stack is lifted by a slab lifting device (stacked slab separating device) installed between a rough rolling mill and a finish rolling mill of a hot rolling line. However, this is a preferable example in which an apparatus for lifting and rolling a slab is installed in an existing hot rolling line, and this apparatus is used. Therefore, it is not always necessary to carry out the hot rolling line as a place where the upper thin slab is lifted.

  The present invention will be specifically described below based on examples.

  A 250 mm thick slab that was continuously cast was hot rolled into a 70 mm thick × 2100 mm wide slab, cooled, and then cut to prepare a 2100 × 3000 mm small slab for use as a thick slab. .

  In order to heat this 70 mm thickness × 2100 mm width × 3000 mm length thick slab for a medium plate to the rolling temperature, it was placed in a walking beam heating furnace and heated to 1200 ° C. The walking beam type heating furnace used for heating had a vertically movable walking beam width (Lw) of 1200 mm and a fixed walking beam width of 2600 mm. Heating was carried out in a walking beam heating furnace with a slab length (Ls) of 3000 mm.

  When the amount of thermal deflection of the small slab is calculated under the above conditions, the amount of deflection δu is 168 mm, which is 162 mm or more of the lifting height hL of the slab extractor (extractor), and does not satisfy the condition expressed by the equation (2). It can be seen that there is a problem in extraction from the heating furnace.

Therefore, the slabs were stacked in two stages and heated in a heating furnace.
Using a slab of 280 mm thickness x 2100 mm width x 3300 mm length as the lower slab, the calculated deflection amount of the lower slab of the two-tiered slab is (δu), 4 mm, and the deflection of the two-tiered slab The amount δd ₂ + the initial slab warpage C (30 mm) + the marginal height R (20 mm) is 39 mm, which is equal to or less than 162 mm of the required lifting height hL in the slab extractor (extractor). The conditions shown were satisfied, and it was found that there was no hindrance to the extraction of a two-layer slab.

  Therefore, the two-tiered slab is heated to 1200 ° C. in the heating furnace, the slab extracted from the heating furnace is descaled, and then transferred to the slab lifting device installed in the hot rolling line. I lifted it. The lower thick slab was transferred to a roughing mill and hot rolled to produce a thick plate. Next, the lower thick slab was transferred, and the suspended upper slab was lowered to a rolling line, transferred to a finishing mill, and rolled to produce a 4.6 mm thick plate.

  According to the present invention, it was possible to produce a thick and medium plate without performing tentering rolling as in the prior art. Further, by not performing the tentering rolling, it was possible to shorten the rolling time of the slab extracted from the heating furnace to increase the rolling temperature, and to suppress the occurrence of misrolls, thereby making it possible to produce a thick and medium plate.

1 Heating furnace 2 Pusher 3 Slab 4 Slab extractor (extractor)
5 Vertically movable walking beam 6 Fixed walking beam 7 Water scale breaker (HSB)
8 Coarse rolling mill 9 Slab lifting device 10 Finishing mill 11 Hot straightening machine 12 Controlled cooling device (quenching etc.)
13 Cooling bed 14 Shear line 15 Thick slab 16 Thin slab 17 Main body 18 Support structure 19 Plate-like horizontal base 20 Gripping member (tongue)
21 Gate type frame 22 Wire 23 Carriage 24 Winch H Slab A Distance between the lower edge of the heating furnace extraction port and the upper edge of the extractor B Distance between the edge of the table roll on the extractor side and the upper edge of the extractor T Table roll

Claims (5)

  The thin slab for thick and medium plates is produced by heating the thin slab for thick and medium plates in a walking beam heating furnace and hot rolling the thin slab for thick and medium plates extracted from the heating furnace. A method for producing a thick plate, characterized in that a thick slab is stacked in two steps on the upper stage and charged in a walking beam heating furnace and heated.   After extracting the heated two-stage slab from the heating furnace into the walking beam furnace, the upper slab is lifted by the slab lifting device, and the lower thick slab is transferred to the roughing mill. After transporting and hot-rolling, transporting the lower thick slab, lower the upper thick-slab thin slab that was lifted by the slab lifting device, transfer it to the finishing mill and hot-roll to the thick-medium plate The method for producing a thick intermediate plate according to claim 1.   3. The thick plate according to claim 2, wherein the two-stage slab charged in the walking beam heating furnace is extracted from the heating furnace and then descaled as the two-stage slab. Production method.   The said descaling is performed by injecting high pressure water with a water scale breaker (HSB), The manufacturing method of the thick plate | board of Claim 3 characterized by the above-mentioned.   The thickness according to any one of claims 1 to 4, wherein each slab is hot-rolled in a hot rolling line in which a slab lifting device is disposed between the rough rolling mill and the finish rolling mill. Manufacturing method of the intermediate plate.

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