JP2011079026A - Method for manufacturing thick plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thick plate capable of reducing the ride-up amount without adding any apparatus. <P>SOLUTION: In a hot rolling process of a thick plate for manufacturing the thick plate by the hot-rolling after heating a slab in a heating furnace, a shape of an end face of a preceding material to be rolled having its end face of a double-bulge shape along its rolling direction is measured. When the ride-up amount d1 on the surface side of the preceding material to be rolled is larger than the ride-up amount d2 on the back side of the preceding material, the heating amount on the back side of the slab in the heating furnace is increased. When the ride-up amount d1 on the surface side of the preceding material is smaller than the ride-up amount d2 on the back side of the preceding material, the heating amount on the back side of the slab in the heating furnace is decreased, and the succeeding slab is heated and then rolled. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for manufacturing a thick plate that reduces a turn-up (a turn-up amount, a turn-up difference) generated at an end of the metal plate during hot rolling in manufacturing a metal plate such as a thick steel plate.

  In the manufacture of thick plates, the material is heated to a certain temperature and then rolled to obtain a metal plate having a predetermined thickness. In particular, in the manufacture of thick steel plates, (1) a forming and rolling process in which several passes are rolled in the longitudinal direction on a slab as a raw material, (2) a predetermined width (= product width + ear margin) by turning the material to be rolled by 90 ° By adding three steps: a tenter rolling step for rolling into a rolling step, and (3) a finish rolling step for rolling the material to be rolled 90 ° in the longitudinal direction to a predetermined thickness and length. Thickness. Thereafter, the material to be rolled is cut by a cutting process through a cooling and heat treatment process, and becomes a thick steel plate as a final product.

  Considering the yield, it is desirable that the material cut off in the cutting process is small. Cutting is performed in order to eliminate shape defects formed at the end of the material to be rolled in the rolling process. Since the end of the material to be rolled is a free end, when the material to be rolled is rolled, the end of the material to be rolled has a unique shape. Specifically, by rolling, a single bulge shape having a convex portion at the central portion of the plate thickness or a double bulge shape having a concave portion at the central portion of the thickness is formed at the end of the material to be rolled.

  Here, the double bulge shape is particularly problematic in terms of the quality of the thick steel plate as the final product. The double bulge shape is generally referred to as “folding”. If this amount of curling up (hereinafter referred to as “the amount of curling up”) is excessive, even if both ends in the width direction of the thick steel plate after rolling are cut by a predetermined width, the width of the final product Concave portions remain on both end surfaces in the direction, and it may be forced to be “degraded” as a defective product.

  Conventionally, the following method has been proposed to reduce the amount of curling up to improve the yield and to prevent the occurrence of wrinkles in the thick steel plate. For example, in Patent Document 1, the shape of the end face along the rolling direction of the material to be rolled is measured in the middle of the hot rolling process of the steel sheet, and the steel slab surface side or the steel slab in the slab heating furnace is measured according to the shape. A method of hot rolling a steel sheet is disclosed, in which the amount of heating on the back surface side is changed and the subsequent steel slab is heated and then rolled. Further, in Patent Document 2, in all rolling passes or a plurality of rolling passes including at least one of the tenth rolling, a portion corresponding to the end in the width direction of the thick steel plate before rolling for each rolling pass. The manufacturing method of the thick steel plate without a seam flaw which heats and rolls only the front and back and side end surface of this, or the front and back of the site | part is disclosed. Moreover, in patent document 3, in the middle of a hot rolling process, the shape of the end surface along the rolling direction of a to-be-rolled material is measured, and according to the shape, the surface or back surface of a to-be-rolled material is cooled, and after cooling A hot rolling method that prevents rolling around a four-sided wrinkle is disclosed.

JP-A-8-112611 Japanese Patent Laid-Open No. 7-284811 JP-A-1-210113

  The production of thick plates is inevitable. In order to eliminate the shape defect of the final product, it is necessary to reduce the amount of curling up. On the other hand, it is important to reduce the amount of curling up from the viewpoint of yield.

As described above, techniques aimed at reducing the amount of curling up have already been disclosed, but these methods also have the following problems.
In the invention described in Patent Document 1, the end surface shape of the preceding material to be rolled is measured. When the end surface shape is a double bulge, the position of the inflection point is determined when the end surface shape is a single bulge. Depending on the above, the amount of heating on the steel slab surface side or the steel slab back side in the steel slab heating furnace is changed, and the subsequent steel slab is heated and then rolled. In such a method, since there is usually no complete correlation between the amount of change in heating amount and the amount of change in furnace temperature required for it, the furnace temperature tends to become unstable.
In the inventions described in Patent Document 2 and Patent Document 3, in order to heat or cool the material to be rolled in the rolling line, it is necessary to increase the equipment to the current rolling line. In addition, in these inventions, a part of the material to be rolled is heated or cooled, so that temperature unevenness occurs in the material to be rolled, and the design considering the uniform temperature distribution of the whole material to be rolled is not achieved.

  In view of the above problems, it is an object of the present invention to provide a method for manufacturing a thick plate that can reduce the amount of curling up without increasing new equipment.

The present invention will be described below.
In the hot rolling process of the thick plate manufactured by hot rolling after heating the slab in a heating furnace, the present invention has the shape of the end face along the rolling direction of the preceding rolled material whose end face has a double bulge shape. Measured, if the amount of turn up d1 on the front side of the preceding rolled material is larger than the amount of turn up d2 on the back side of the preceding rolled material, increase the amount of heating on the back side of the slab in the heating furnace, When the amount d1 of turning up on the front side of the material to be rolled is smaller than the amount of turning up d2 on the back side of the preceding material to be rolled, the amount of heating on the back side of the slab in the heating furnace is lowered and the subsequent slab is heated. And then rolling the thick plate.

  In the present invention, the “thick plate” is a concept that includes a thick steel plate as well as a metal plate (a plate made of a metal other than steel) having a thickness that allows the end surface to have a double bulge shape. Moreover, as shown in FIG. 1, the “bending amount d1 on the surface side of the preceding rolled material” means that the preceding rolled material is located on the surface side of the center in the plate thickness direction of the preceding rolled material. It refers to the amount d1 of curling up of the convex portion on the end face. Moreover, as shown in FIG. 1, “the amount of rolling d2 on the back side of the preceding rolled material” is the preceding rolled material that is located on the back side from the center in the plate thickness direction of the preceding rolled material. This refers to the amount d2 of curling up of the convex portion on the end face. In the present invention, “the back side of the slab in the heating furnace” corresponds to the back side of the preceding material to be rolled.

  Moreover, in the said invention, it is preferable that the heating amount by the side of the back surface of the slab in a heating furnace is determined based on the result of the temperature distribution calculation in the cross section of a preceding to-be-rolled material.

  Here, “calculation of temperature distribution in the cross section of the preceding rolled material” means a result of heat transfer calculation performed on all meshes formed by cutting the cross section of the preceding rolled material. In the present invention, it is preferable to perform temperature distribution calculation in consideration of heat transfer from skids (including moving skids and fixed skids) existing on the back side of the slab in the heating furnace.

  In the present invention, by controlling the amount of heating on the back side of the slab in the heating furnace, regardless of whether the amount of turning d1 on the front side of the preceding rolled material or the amount of turning d2 on the back side is large, Decrease the maximum amount of curling up. Therefore, according to the present invention, it is possible to provide a method of manufacturing a thick plate that can reduce the amount of rolling up without newly increasing equipment.

It is a figure explaining the amount of turning up. It is a figure which shows the production line of the thick board with which the manufacturing method of the thick board of this invention is applied. It is a flowchart of the manufacturing method of the thick board concerning this invention. It is a flowchart of the determination method of setting furnace temperature.

  Embodiments of the present invention will be described below.

  In the hot rolling process of the thick plate, the present invention changes the heating condition of the slab by changing the shape of the end face along the rolling direction of the preceding material to be rolled back to the subsequent thick plate production, and the amount of rolling up The present invention relates to a method of manufacturing a plank to be reduced.

  The occurrence of curling in the production of thick plates is caused by temperature variation (temperature unevenness) depending on the position of the heated slab. When there is a difference in temperature between the surface of the slab (hereinafter sometimes referred to as the “upper surface”) and the rear surface (hereinafter sometimes referred to as the “lower surface”), the surface with the higher temperature is stretched by rolling. As a result, there is a difference in shape between the upper and lower surfaces after rolling, that is, a large difference in turning amount (hereinafter, referred to as “turning difference” in some cases).

  FIG. 1 shows an example of turning up. FIG. 1 is a cross-sectional view of the preceding rolled material X whose end face shape is measured, and only the one end side in the plate width direction of the preceding rolled material X is extracted. The vertical direction in FIG. 1 is the plate thickness direction, the horizontal direction is the plate width direction, the upper side in FIG. 1 is the upper surface side, and the lower side is the lower surface side. In the example shown in FIG. 1, since the temperature on the upper surface side of the slab is relatively high, the amount of curling up d1 (surface side) of the convex portion positioned on the upper surface side from the center in the thickness direction of the preceding rolled material X The amount of curling up d1) is larger than the amount of curling up d2 (the amount of curling up on the back side d2) of the convex part located on the lower surface side of the center of the preceding rolled material X in the plate thickness direction. In the example of FIG. 1, d1-d2 is a turn-up difference.

  If the larger turn-up amount (d1 in the example of FIG. 1) is reduced to reduce the turn-up difference, an improvement in yield can be expected. In order to reduce the turn-up difference, the temperature difference between the upper and lower surfaces of the slab is simply reduced. However, since the degree of heat transfer is different between the upper surface side in contact with air and the lower surface side in contact with the production line, a temperature difference inevitably occurs. In order to avoid this, as in Patent Document 1, for example, the heating amount of the burner above or below the heating furnace is adjusted, and the slab is heated in advance by making a temperature difference between the upper and lower surfaces of the slab in the heating furnace. Just do it.

  On the other hand, the slab in the heating furnace has heat removal from the skid (slab moving device). That is, the temperature of the slab in the lower surface portion of the slab that comes into contact with the skid is lower than the temperature of the slab in other portions (the lower surface portion of the slab that does not come into contact with the skid and the upper surface of the slab). For this reason, it is difficult to make a temperature difference between the upper and lower surfaces uniformly.

  Therefore, in the present invention, the burner on the slab lower surface side of the slab heating furnace is appropriately controlled, and in particular by applying an appropriate temperature difference to the upper and lower surfaces of the subsequent slab based on the temperature distribution of the preceding rolled material, Provided is a method for producing a thick plate capable of producing a thick plate having a small amount and a small difference in turning up.

  In the following, the present invention will be described in detail by taking as an example the case of producing a thick steel plate.

  As described above, the production of the thick steel plate is performed by adding (1) a forming and rolling step, (2) a tenter rolling step, and (3) a finish rolling step to the slab to obtain a thick steel plate as a final product. For example, a slab having a length of about 5000 mm, a width of 2500 mm, and a thickness of about 250 mm is used. At this time, a series of rolling is performed by a rough rolling mill and a normal finish rolling mill from the viewpoint of production efficiency and rolling capacity, and a part of the above (1), (2) and (3) is performed by a rough rolling mill. In many cases, the rest of the above (3) is performed by a finishing mill.

  In the present invention, the shape of the end face along the rolling direction of the preceding rolled material is measured during the hot rolling process of the thick plate. At this time, the measurement of the end face shape may be performed during or after the above (2) or (3). The reason why the measurement may be performed during or after rolling is that the growth tendency of rolling up due to rolling does not always change during the rolling on both the upper and lower surfaces.

  In the present invention, the end face shape may be measured by an end face shape measuring instrument (end face shape measuring means) such as a laser distance meter. A well-known thing can be used suitably for an end surface shape measuring device. For example, if a laser is scanned with respect to the end face of the preceding rolled material whose end face has a double bulge shape, a profile having an end face shape can be output.

  FIG. 2 shows a simplified plank production line 10 to which the plank production method of the present invention is applied. As shown in FIG. 2, the thick plate production line 10 includes a heating furnace 1, a rough rolling mill row 2, and a finishing rolling mill row 3, and is provided between the rough rolling mill row 2 and the finishing rolling mill row 3. End face shape measuring means 4 is arranged. The end face shape measuring means 4 is a device that measures the end face shape of the material to be rolled by scanning a laser, and the measurement result by the end face shape measuring means 4 is sent to the control device 5. The control device 5 determines the magnitude relationship between the front side roll-up amount d1 and the back side turn-up amount d2 of the preceding rolled material whose end face shape has been measured, and the subsequent slab is determined based on the determination result. It is an apparatus for controlling the operation of the heating furnace 1 for heating. Specifically, when d1> d2, the operation of the heating furnace 1 is controlled by the control device 5 so as to increase the heating amount on the back surface side of the slab in the heating furnace 1. On the other hand, when d1 <d2, the operation of the heating furnace 1 is controlled by the control device 5 so as to reduce the heating amount on the back side of the slab in the heating furnace 1, and d1 = d2. First, the operation of the heating furnace 1 is controlled by the control device 5 so as to maintain the operating conditions of the heating furnace 1 when the preceding material to be rolled is heated.

  FIG. 3 shows a flowchart of a method for manufacturing a thick plate according to the present invention. Hereinafter, the present invention will be described with reference to FIGS.

  As shown in FIG. 3, the manufacturing method of the thick plate according to the present invention includes an end face shape measuring step (S1) for measuring the end face shape of the preceding rolled material, and a turn-up amount d1 on the surface side of the preceding rolled material. A first determination step (S2) for determining whether or not the amount d2 of turning on the back side of the preceding rolled material is larger, and the amount of turning d1 on the surface side of the preceding rolled material is the back side of the preceding rolled material A second determination step (S3) for determining whether or not the amount of curling up is smaller than d2. In the thick plate manufacturing method of the present invention, when an affirmative determination is made in step S2, a back surface side heating amount increasing step (S4) for increasing the heating amount on the back surface side of the slab in the heating furnace 1 is performed, and the subsequent slab Is heated in the heating furnace 1 controlled in the step S4 and then rolled. On the other hand, if a negative determination is made in step S2, step S3 is performed. When an affirmative determination is made in step S3, a back surface side heating amount reduction step (S5) for reducing the heating amount on the back surface side of the slab in the heating furnace 1 is performed, and the subsequent slab is a heating furnace controlled in the step S5. After being heated at 1, it is rolled. On the other hand, if a negative determination is made in step S3, it means that d1 = d2. In this case, a back surface side heating amount maintaining step (S6) for maintaining the operating condition (heating amount) of the heating furnace 1 when the preceding material to be rolled is heated is performed, and the subsequent slab is formed on the back surface side in the step S6. After being heated in the heating furnace 1 in which the heating amount is maintained, it is rolled.

  That is, in the present invention, the heating amount control of the burner disposed on the lower surface side of the slab is performed regardless of whether the tendency to curl up is large on the front surface side or on the back surface side. By performing such control, it is possible to adjust the temperature of the slab including the skid disposed below the slab heating furnace, so that the uniformity of the temperature on the lower surface of the slab can be particularly improved. Then, by controlling the heating amount of the burner that heats the subsequent slab by feedback from the end face shape of the preceding rolled material, it is possible to reduce the amount of rolling up of the subsequent rolled material.

  FIG. 4 shows a flowchart of an example of a method for determining the set furnace temperature. Usually, the heating furnace has a pre-tropical zone, a first heating zone, a second heating zone, and a soaking zone, and the heating amount of the burners on the upper and lower surfaces of each zone is set in consideration of the extraction temperature from each zone. It is common to do. In contrast, in the present invention, as shown in FIG. 4, the heating amount Cu (i) of the burner on the upper surface side of each band is determined in consideration of the extraction temperature of each band, while the burner on the lower surface side of each band. The heating amount Cd (i) is determined by correcting the heating amount Cu (i) of the burner on the upper surface side after feeding back the result of the end face shape of the preceding rolled material.

  In the present invention, the correction amount (ΔC in FIG. 4) may be determined from the result of performing temperature calculation on the slab before correcting the heating amount. Specifically, the slab cross section may be cut from a mesh and determined from the result of heat transfer calculation in each mesh.

  In actual slab heating, there is a lot of heat removal from the skid. In particular, the fixed skid has a longer contact time with the slab than the moving skid, and the amount of heat removal tends to increase. Therefore, the amount of heat removed from the fixed skid is a major factor that deteriorates the temperature uniformity on the lower surface of the slab. Therefore, in the present invention, it is preferable to determine the correction amount in consideration of heat transfer (heat removal) from the skid, particularly the fixed skid.

  A more accurate slab temperature distribution can be calculated by performing heat transfer calculations for the entire slab cross section. If the contact position between the slab and the skid is symmetrical, it is sufficient to perform heat transfer calculation for half of the slab cross section.

  In particular, the temperature distribution of the upper and lower surfaces of the slab at the end of the slab is greatly related to turning up. Therefore, the correction amount, that is, the heating amount on the lower surface side of the slab may be determined based on the temperature distribution result at the slab end. In the present invention, for example, the correction amount can be determined based on the temperature gradient of the slab end surface or the difference between the upper surface temperature and the lower surface temperature at the slab end portion so that the turn-up is minimized. In the present invention, the correction amount may be determined from the result of simulation calculation assuming the heating amount on the lower surface side of the slab, or may be determined from the empirical value already obtained. In the present invention, as described above, the correction amount is determined, and the heating amount on the slab lower surface side may be determined.

  In the above description related to the present invention, the form in which the end face shape measuring means 4 is arranged between the rough rolling mill row 2 and the finishing rolling mill row 3 is exemplified, but the present invention is not limited to this form. The end face shape measuring means for measuring the end face shape of the preceding material to be rolled may be arranged in the rough rolling mill row or the finish rolling mill row.

  A slab having a length of 4900 mm, a width of 2400 mm, and a thickness of 240 mm was slab-heated at a target temperature of 1100 ° C. in a heating furnace, the scale formed on the slab surface was removed by a descaler, and then a forming and rolling step and a tense rolling step were performed. The target thickness of the material to be rolled after the tentering rolling step was 142 mm. After the tentering rolling step, the end face shape of the preceding rolled material was measured with a laser distance meter (end face shape measuring step). As a result, the pre-rolled material has an upper surface side turn-up amount d1 of 20 mm, a lower face side turn-up amount d2 of 6 mm, and a turn-up difference of 14 mm. The profile was larger than the amount d2 (first determination step).

  Therefore, considering the amount of heat removed from the skid in the heating furnace existing on the bottom surface of the slab, the temperature distribution of the cross section of the slab cut by mesh was calculated, and the top surface temperature of the slab end was the bottom surface temperature of the slab end. It was found to be 50 ° C higher than. Therefore, heat transfer calculation was performed, and the heating temperature of the subsequent slab was corrected by correcting the heating amount of the burner on the slab lower surface side so that the lower surface side of the slab was 25 ° C. higher than the upper surface side of the slab (backside heating) Volume increasing step).

  As a result of correcting the heating amount of the burner on the lower surface side of the slab in this way, the subsequent rolled material finally rolled to a thickness of 142 mm has an upper surface amount of 11 mm and a lower surface amount of 4 mm. There was a difference of 7 mm. That is, according to the present invention, the amount of curling up and the curling up difference can be reduced. As a result, it was possible to manufacture a thick steel plate with a high yield.

  The present invention can be used for manufacturing thick steel plates.

d1 ... the amount of turn up on the front side d2 ... the amount of turn up on the back side X ... preceding rolled material 1 ... heating furnace 2 ... rough rolling mill row 3 ... finish rolling mill row 4 ... end face shape measuring means 5 ... control device 10 ... Thick plate production line

Claims (2)

After heating the slab in a heating furnace, in the hot rolling step of the thick plate manufactured by hot rolling, the shape of the end surface along the rolling direction of the preceding rolled material whose end surface is a double bulge shape is measured, When the amount d1 of turning up on the front side of the preceding rolled material is larger than the amount of turning up d2 on the back side of the preceding rolled material, increasing the amount of heating on the back side of the slab in the heating furnace, When the amount of curling up d1 on the front side of the preceding rolled material is smaller than the amount of curling up d2 on the back side of the preceding rolled material, the heating amount on the back side of the slab in the heating furnace is decreased, A method for producing a thick plate, comprising heating the subsequent slab and then rolling the slab. The method for manufacturing a thick plate according to claim 1, wherein the amount of heating on the back side of the slab in the heating furnace is determined based on a result of temperature distribution calculation in a cross section of the preceding rolled material. .

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