JP3764350B2 - Thick plate manufacturing method and rolling mill - Google Patents

Description

【００５４】
【表２】

【００５５】
得られた鋼板（厚さ２６．０ｍｍ、幅３０００ｍｍ、長さ１４２００ｍｍ）の各部位のスケール厚み及び温度は表３及び図４に示す通りである。この鋼板を水冷によって約５８０℃まで加速冷却した。加速冷却後の厚板の各部位の降伏強度を測定し、図５に示す。
【００５６】
【表３】

【００５７】
表３及び図４〜５から明らかなように、比較例では先端部の温度は高温部よりも約６０℃も低く、かつ高温部の温度が均一になるのは先端部から長さ約１０００ｍｍ以降の部分であるのに対して、実施例では先端部と高温部との温度差を約３０℃程度に半減でき、さらには先端部から長さ約５００ｍｍ以降の部分で温度を均一にできる。そのため比較例の厚板では先端部の降伏強度と高温部の降伏強度との差が約３５ＭＰａもあるのに対して、実施例では先端部の降伏強度と高温部の降伏強度との差を約１８ＭＰａ程度にまで低減できる。また高温部（降伏強度の定常部）から＋１０ＭＰａ程度までを鋼板として使用するとすると、比較例では先端から約７００ｍｍまでの部分を切り捨てる必要があるのに対して、実施例では先端から約４００ｍｍまでの部分だけを切り捨てればよく、切り捨て代を約３００ｍｍ程度低減できる。
【００５８】
【発明の効果】
本発明によれば、被圧延鋼板の先端部に対する水の噴射量を抑制すると共に、先端部から所定長さ以降の下流側部分に対しては水の噴射を強くしてスケーリングを略完全に除去しているため、厚板鋼板の平面方向（特に圧延方向）の温度差を低減でき、厚板の材質を略均一化できる。
【図面の簡単な説明】
【図１】図１は本発明のデスケーリング方法の一例を説明するための概略図である。
【図２】図２は本発明のデスケーリング方法の他の例を説明するための概略図である。
【図３】図３は本発明で使用する制御システムの一例を説明するための概略図である。
【図４】図４は実施例及び比較例で得られた鋼板の先端からの距離と表面温度との関係を示すグラフである。
【図５】図５は実施例及び比較例で得られた鋼板の先端からの距離と降伏強度との関係を示すグラフである。
【図６】図６は従来のデスケーリング方法を説明するための概略図である。
【符号の説明】
１ａ…圧延機
２…圧延ロール
４ａ、４ｂ…デスケーリングヘッダ
１６ａ、１６ｂ…制御手段
１１…検出手段
１５…コントロール手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a thick steel plate useful as a member of a steel structure (such as a ship), and a rolling mill used therefor.
[0002]
[Prior art]
When manufacturing a thick steel plate by hot rolling, there is a possibility that foreign matters such as a primary scale generated in the heating stage and a secondary scale generated in the rolling stage may get caught in the rolling roll. Therefore, high-pressure water is sprayed onto the steel plate before the front end of the steel plate bites into the rolling roll, and descaling is performed by continuing this injection to the rear end of the steel plate (plate material), thereby cleaning the surface of the steel plate. For example, FIG. 6 is a schematic diagram for explaining a conventional descaling method. In this method, a four-high rolling mill 1z composed of a pair of work rolls 2 for rolling a steel plate and a backup roll 3 for preventing deformation of the work rolls is used. A plurality of descaling nozzles 4 are arranged in a row in the width direction on the inlet side of the work roll 2, and the nozzles 4 are directed in a direction opposite to the entering direction of the steel plate (rolled material) 5. Yes. And before the to-be-rolled steel plate 5 bites into the work roll 2, high pressure water is sprayed from the nozzle 4, and descaling is performed from the front end to the rear end of the steel plate. However, when the descaling is performed in the hot reverse rolling in which the hot rolling is repeated for a plurality of passes, the four circumferential portions (the front end portion, the rear end portion, the both side portions) of the steel sheet to be rolled by air cooling during the rolling and the injection of the descaling water ) Is cooled more than the central portion, and the temperature difference becomes remarkable. Therefore, the material of the four peripheral portions (particularly, the front end portion and the rear end portion) and the material of the central portion are different.
[0003]
As a technique for reducing the temperature difference between the front end part and the rear end part and the central part, techniques disclosed in Japanese Patent Application Laid-Open Nos. 63-132715 and 5-104103 are known. In JP-A-63-132715, a descaling header (piping) is arranged before and after the rolling mill, and a high-pressure water injection nozzle (descaling nozzle) formed on the header is directed to the rolling mill side, A method is disclosed in which high-pressure water is jetted from the jet nozzle only after the tip of the material to be rolled passes through the position of the jet nozzle until the tail end of the material to be rolled passes through the rolling mill. However, when descaling by such a method, the scale removed by the nozzle in front of the rolling mill may be caught in the work roll and damage the surface of the material to be rolled. Therefore, in the embodiment of this publication, if high-pressure water is sprayed only from the nozzle after the rolling mill, there is no possibility that the scale removed by descaling may bite into the work roll. However, even if high-pressure water is sprayed only from the nozzle after the rolling mill, depending on the steel type and temperature of the material to be rolled, scale may occur during the idle time after rolling until rolling of the next pass. Then, since descaling is not performed before rolling, rolling is performed with the thick scale layer attached to the surface of the material to be rolled, the scale is crushed, the steel plate surface becomes red, and dust is generated. Further, the surface of the steel plate becomes rough, and the cooling of that portion is accelerated, resulting in temperature unevenness of the steel plate.
[0004]
Japanese Patent Application Laid-Open No. 5-104103 discloses a method of rolling a controlled rolled steel sheet in which tenth rolling is performed on a slab, followed by finish rolling. A method of performing descaling water cooling (center descaling) (figure (c) of the publication), rotating the steel sheet 90 degrees (figure (d) of the publication), and finishing rolling with the width direction as the rolling direction. It is disclosed. However, with this method, center descaling for temperature control (descaling in the center in the width direction) is performed at the time of tentering rolling, and because the steel plate is thick, temperature control (temperature uniformity) is difficult. It is difficult to make it uniform. Further, even if the temperature can be controlled in the tenter rolling process, the temperature difference may occur again because the finishing rolling process is performed.
[0005]
On the other hand, the steel sheet to be rolled has a part called a skid mark (or skid part). This portion is a portion that is in contact with the skid rail when the steel plate to be rolled is heated for hot rolling, and has a lower temperature than the surroundings. It is also important to reduce the temperature difference between the skid mark portion and other portions. For example, materials and processes, vol. 7 (1994), pp. 408 to 411, in order to reduce the temperature difference between the skid mark part and the other part, the subcutaneous primary scale is completely removed or the thickness of the scale layer during rolling is determined by the rolling conditions. It is suggested that the thickness should be reduced below the critical value determined by the above to prevent scale collapse. In this proposal, the temperature history when the rolling is repeated is different between the skid mark part and other parts, and tensile stress acts on the skid mark part, and the scale of the skid mark part peels off and becomes thin, in other words. For example, the parts other than the skid mark have a thick scale layer, and the thicker the scale layer, the higher the cooling speed (paradox of the heat insulation layer). The reason is that the speed is further accelerated, and therefore the temperature of the portion other than the skid mark is lowered, so that if the scale is completely removed and the scale thickness is made equal, the cooling speed becomes equal. However, this document also describes that even if the scale is completely removed, there is a limit to achieving uniform cooling by preventing uneven cooling of the accelerated cooling steel sheet.
[0006]
As described above, in the conventional technology, it is difficult to reduce the temperature difference between the front end portion and the rear end portion and the center portion of the thick steel plate, and the temperature difference between the skid mark portion and the other portions is difficult. Are also difficult to reduce. Therefore, the material varies and residual stress is generated. If the material varies, it is necessary to cut off the parts with different materials before shipping, which reduces the yield. Further, when the residual stress is generated, it is necessary to remove the residual stress by an additional operation such as a cold re-correction process, which is complicated.
[0007]
[Problems to be solved by the invention]
The present invention has been made paying attention to the above circumstances, and its purpose is to reduce the temperature difference in the plane direction of the thick steel plate when producing the thick plate by hot reverse rolling, It is in the point which makes the material of this substantially uniform.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have suppressed the amount of water injection to the end (tip) on the rolling roll entry side of the steel sheet to be rolled in reverse rolling. For example, the temperature difference from the other part (high temperature part) can be reduced, and further, if the scale layer is thin and substantially uniform with respect to the high temperature part, the cooling rate can be made substantially equal. The present invention was completed by discovering that the material of the material can be made substantially uniform.
[0009]
That is, the thick plate manufacturing method of the present invention that has achieved the above-mentioned object is to repeat the hot rolling of the steel sheet to be rolled a plurality of times and to descale by injecting water to the steel sheet to be rolled in at least one pass. In the method of manufacturing a thick plate by hot reverse rolling while hot rolling, the amount of water injection is suppressed at the rolling roll entry side end of the steel plate to be rolled in the descaling pass At the same time, the scale is removed almost completely by spraying water at a predetermined strength or more from the entry side end portion to the downstream side portion after the predetermined length. When there are a high portion and a low portion of the surface temperature in the downstream portion after a predetermined length from the entry side end of the steel plate to be treated, the water injection amount and the injection strength are divided into a high portion and a low portion. It is desirable to adjust the thickness. That is, for the part with a high surface temperature, the amount of water injection is increased and the injection strength is increased to reduce the temperature difference between the part with a high surface temperature and the part with a low surface temperature, and to make the scale thickness substantially uniform. Is desirable. Thereby, the amount of scale peeling in the cooling process after rolling can be made substantially the same between the portion having a high surface temperature and the portion having a low surface temperature, and the cooling rate can be made substantially the same. In the present invention, a plurality of descaling nozzles for injecting water are provided in the width direction on the inlet side of the rolling roll, and water is injected from each descaling nozzle in accordance with the surface temperature distribution in the width direction of the steel sheet. You may reduce the temperature difference of the direction substantially orthogonal to a rolling direction by adjusting quantity.
[0010]
The present invention includes a hot rolling roll, a descaling nozzle that is disposed on the inlet side of the rolling roll and that substantially completely removes the scale of the steel sheet to be rolled, and the amount of spray water supplied to the descaling nozzle And a control means capable of controlling the strength, and a detection means for detecting the biting timing of the steel sheet to be rolled in the rolling roll, in response to the biting timing detection signal of the detection means, While suppressing the amount of water injection to the end of the rolling roll entry side of the steel sheet, the strength is such that the scale can be almost completely removed from the entry side end to the downstream part after the predetermined length. Also included are rolling mills with control means for directing the supply of water.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a rolled steel sheet heated in the heating process is hot reverse-rolled and cooled after rolling (for example, accelerated cooling by water cooling or the like) [for example, thermo-mechanical control-process] ] To manufacture thick plates.
[0012]
In the heating step, heating is performed using a general-purpose heating furnace (batch furnace, continuous furnace, etc., particularly a continuous furnace). The present invention is advantageous when a continuous furnace using a skid rail (for example, a pusher type heating furnace, a walking beam type heating furnace or the like) is used. If these furnaces are used, a plurality of (for example, two) low-temperature portions called skid marks are generated in the longitudinal direction or width direction of the slab, but according to the present invention, the skid marks are used in the hot reverse rolling process described later. Since the temperature difference between the part and the other part (high temperature part) can be reduced, even if skid marks occur, the steel material can be made homogeneous and the occurrence of residual stress can be prevented, and the quality of the steel material can be made substantially uniform. .
[0013]
In addition, the heating temperature of the slab in the said heating process can be suitably selected according to the kind of steel plate, for example, is about 1000-1200 degreeC.
[0014]
In the hot reverse rolling, a pass for hot rolling the steel sheet to be rolled is repeated a plurality of times. In such reverse rolling, the temperature at the front end of the steel sheet in the rolling direction becomes too low, and the material in the rolling direction tends to be uneven. Also, in reverse rolling, the temperature of the steel sheet decreases while repeating the temperature reduction due to contact with the pressure roll and the subsequent reheating. Therefore, if the steel sheet has a low temperature part such as a skid mark part, the part is rolled. The temperature (A_c1Point A_c3The scale is easily peeled off, and a residual stress due to a temperature difference from the surroundings is generated, and the scale is further easily peeled off. When the scale is peeled off, the cooling rate in the subsequent cooling process becomes slow, the ambient temperature is rather lowered, and a temperature difference may occur. However, according to the present invention, since a specific descaling method is employed in rolling (described later), the temperature difference between the tip portion and the skid mark portion and other portions can be made substantially uniform even in reverse rolling. .
[0015]
That is, in the present invention, in hot reverse rolling, water is sprayed onto the steel plate to be scaled in at least one of the plurality of passes. The number of paths to be descaled is about 10 to 80% of all paths, preferably about 1.5 to 70%, and more preferably about 20 to 50%. Note that descaling is preferably performed approximately the same number of times in both the odd and even paths, rather than being shifted to either the odd or even path.
[0016]
A specific descaling method is employed in the descaling path. Hereinafter, further detailed description will be given with reference to the accompanying drawings.
[0017]
FIG. 1 is a schematic view showing an example of a rolling mill used in reverse rolling (descaling pass) and a descaling method using the rolling mill. The rolling mill 1a of FIG. 1 is a four-high rolling mill composed of a pair of work rolls 2 for rolling a steel plate and a backup roll 3 for preventing deformation of the work rolls. On the entrance side of the work roll 2, two rows (four rows in total) of descaling headers (not shown) are arranged on the front and rear sides, and each descaling header has a plurality of descaling headers. A scaling nozzle is formed. That is, the descaling nozzles 4a and 4b are arranged in two rows (a total of 4 rows) in front and rear in the vertical direction, and in each row, a plurality of descaling nozzles are arranged in the width direction. These nozzles 4 a and 4 b are directed in a direction opposite to the direction in which the rolled steel sheet 5 is rolled. By using such a rolling mill 1a, it is possible to perform descaling by the action described below, and it is possible to perform rolling while making the temperature difference in the plane direction of the steel material uniform.
[0018]
That is, before the steel plate 5 to be rolled bites into the work roll 2, when the jet of water from the descaling nozzles 4 a and 4 b is stopped and the steel plate 5 to be processed advances and bites into the work roll 2, the first row Water injection from the descaling nozzle 4a is started. In this way, the high pressure is applied only to the downstream portion after the predetermined length from the tip of the steel sheet to be rolled (for example, the portion after the length of 2000 mm, preferably 1500 mm or more, more preferably 1200 mm or more from the tip). Water can be applied, the temperature difference from the tip can be reduced, and the thickness of the scale layer can be made thin and substantially uniform. When the thickness of the scale layer is thin and substantially uniform, the difference in cooling rate due to the thickness of the scale can be reduced, so that the temperature difference after the cooling process (such as after the accelerated cooling process) can also be reduced. Therefore, the temperature can be made uniform from the front end portion to the rear end portion of the steel plate, and the material and quality of the steel plate (thick plate) can be made substantially uniform.
[0019]
Note that descaling is performed at the tip as long as the temperature difference between the tip and the downstream portion (hot portion) after a predetermined length from the tip is reduced and the scale of the hot portion can be removed almost completely. May be. FIG. 2 is a schematic diagram for explaining an example in which the tip portion is also descaled. In the example of FIG. 2, before the rolled steel plate 5 bites into the work roll 2, high-pressure water is injected only from the first row descaling nozzle 4a, and water is injected from the second row descaling nozzle 4b. Stop (see FIG. 2A). By spraying water from a part of the descaling nozzles, the scale of the end (tip part) on the entry side of the rolled steel sheet 5 can be removed, and water spraying of the other part of the descaling nozzles is stopped. As a result, it is possible to prevent the temperature of the tip portion from being excessively lowered.
[0020]
When the steel plate 5 to be processed moves forward and bites into the work roll 2, water is also ejected from the descaling nozzles in the second row (see FIG. 2B). That is, the amount of water injection is made larger than that of the tip portion from the tip portion of the steel sheet to be rolled to the downstream portion after a predetermined length. Therefore, the scale layer can be made thin and uniform almost completely by descaling, and the temperature difference from the tip portion having a low temperature can be reduced.
[0021]
Furthermore, if the rolling mill 1a of FIG. 2 is used, even if the to-be-processed steel plate 5 has a portion having a low surface temperature (for example, a skid mark) other than the tip portion, the amount of water injected in the low temperature portion is higher than that of the high temperature portion. By reducing the temperature (that is, by increasing the amount of water injected in the high temperature part from that in the low temperature part), the temperature difference from the other part (high temperature part) can be reduced while scaling the part. FIG.2 (c) is schematic which shows an example of the method of rolling the to-be-processed steel plate which has a part (skid mark etc.) with low surface temperature. In the example of FIG. 2C, a plurality of (for example, two) skid marks are formed in a direction substantially orthogonal to the rolling direction of the steel sheet to be rolled. When one of the plurality of skid marks 6 reaches the water injection region from the nozzles 4a and 4b, the water injection from the nozzles 4b in the second row is stopped, and the skid mark 6 is stopped. When the water passes through the water injection region, the water injection from the nozzle 4b is resumed. By stopping the jetting of water from the nozzle 4b only in a portion having a low surface temperature (such as a skid mark portion), this portion and other portions are removed while removing the scale of the portion having a low surface temperature (such as a skid mark portion). The temperature difference from the (high temperature part) can also be reduced. Reducing the temperature difference between the low temperature part and the high temperature part can suppress the occurrence of residual stress, so the amount of scale peeling in the cooling process (accelerated cooling process, etc.) can be made substantially equal between the low temperature part and the high temperature part. The speed can be substantially matched. Moreover, since there is almost no temperature difference before cooling, the temperature difference after cooling can be substantially eliminated by making the cooling rate substantially equal, and the material and quality of the steel plate (thick plate) can be made substantially uniform.
[0022]
Control of the amount and intensity of water shown in FIGS. 1, 2 (a) to (c), that is, water for the tip, the low temperature part (skid mark part, etc.), and other parts (high temperature part). The control of injection is organized as follows.
[0023]
Tip
The amount of water injection is reduced compared to the high temperature part to reduce the temperature difference from the high temperature part. The jetting strength of water may be such that the scale can be thinned, but may be such that the scale cannot be thinned, and the scale need not be removed.
[0024]
Specifically, the amount of water (the amount of water per 1 m width of the steel sheet and the amount of water per 1 m / s rolling speed) is, for example, 0 × 10.^-Fourm^Three6 × 10^-Fourm^ThreeThe following (preferably 4.5 × 10^-Fourm^ThreeOr less, more preferably 3 × 10^-Fourm^ThreeThe following). The water pressure is, for example, about 0 to 2.5 MPa.
[0025]
Low temperature part (skid mark part etc.)
The amount of water injection is reduced compared to the high temperature part to reduce the temperature difference from the high temperature part. In many cases, the jet strength of water is such that the scale can be removed almost completely.
[0026]
Specifically, the amount of water (the amount of water per 1 m width of the steel sheet and the amount of water per 1 m / s rolling speed) is, for example, 0 × 10.^-Fourm^ThreeOr more (preferably 3 × 10^-Fourm^ThreeAbove), 12 × 10^-Fourm^ThreeThe following (preferably 9 × 10^-Fourm^ThreeThe following). The water pressure is, for example, 0 MPa or more (preferably 1 MPa or more, more preferably 2.5 MPa or more), 6 MPa or less (preferably 4 MPa or less).
[0027]
High temperature part
The amount of water injection is increased as compared with the tip portion and the low temperature portion. Furthermore, the jet strength of water is such that the scale can be removed almost completely.
[0028]
Specifically, the amount of water (the amount of water per 1 m width of the steel sheet and the amount of water per 1 m / s rolling speed) is, for example, 0 × 10.^-Fourm^ThreeLarger (preferably 1 × 10^-Fourm^ThreeOr more, more preferably 6 × 10^-Fourm^ThreeAbove, especially 9 × 10^-Fourm^ThreeAbove), 12 × 10^-Fourm^ThreeIt is as follows. The water pressure is, for example, about 4 to 8 MPa.
[0029]
The thickness of the scale layer after removing the scale from the high temperature part is, for example, 20 μm or less, preferably 12 μm or less (particularly 5 μm or less). It is difficult to remove the scale layer truly completely, and it is usually 5 μm or more.
[0030]
Further, the temperature difference between the tip portion and the high temperature portion is a temperature difference after rolling (after completion of all passes), for example, 50 ° C. or less (preferably 45 ° C. or less, more preferably 40 ° C. or less), 0 ° C. or more (usually) 10 ° C. or higher, and more generally 20 ° C. or higher). The temperature difference between the low temperature part (skid mark part) and the high temperature part is the temperature difference after rolling (after completion of all passes), for example, 30 ° C. or less (preferably 20 ° C. or less, more preferably 10 ° C. or less), 0 ° C or higher (usually 10 ° C or higher, more generally 15 ° C or higher).
[0031]
The timing of switching the water injection from the front end portion to the high temperature portion (downstream portion after the predetermined length from the front end portion) may be performed based on the biting of the rolled steel sheet 5 into the work roll 2, for example, biting It may be before (for example, immediately before a predetermined time), when the rolled steel plate 5 is bitten, or after a predetermined time has passed after biting.
[0032]
Control of water injection may be performed by visual observation, but it is convenient to use a control system including a sensor or the like. FIG. 3 is a schematic diagram for explaining an example of a control system used for controlling the water injection shown in FIG.
[0033]
In the example of FIG. 3, the rolling mill 1 a includes detection means (load cell, optical sensor, etc., load cell in this example) 11 for detecting the biting of the rolled steel sheet 5 into the work roll 2, and rolling Detection means (in this example, a reduction position detector) 12 for detecting the plate thickness is attached, and the detection signal of biting and the detection signal of the plate thickness from these detection means are sent to the control means 15. It is done. The control means 15 includes a control circuit 13 and an input means (computer terminal or the like) 14. From the input means 14, information relating to rolling (rolling length, rolling width, descaling timing, number of headers used) Table, rolling speed, etc.) are entered as required. The control means 15 is also connected with a temperature sensor 17 for reading the surface temperature of the steel sheet to be processed and transmitting a temperature signal to the control means 15. The control means 15 uses the information from each of these detectors (or sensors) to control the descaling timing.
[0034]
More specifically, the first control valve 16a for controlling the amount of water supplied to the descaling nozzle 4a in the first row and the amount of water supplied to the descaling nozzle 4b in the second row are controlled. The control means composed of the second control valve 16b is used. The first and second control valves 16 a are connected to the control means 15, and the opening degree of the valves is adjusted according to instructions from the control means 15.
[0035]
For example, as shown in FIG. 2 (a), before the rolled steel plate 5 is engaged with the work roll 2, a non-engagement signal from the load cell is sent to the control means 13, and the instruction from the control means 13 is followed. The valve 16a leading to the first row descaling nozzle 4a is opened, and the valve 16b leading to the second row descaling nozzle 4b is closed.
[0036]
Further, as shown in FIG. 2 (b), when the rolled steel plate 5 is caught in the work roll 2, the valve 16b leading to the descaling nozzle 4b in the second row is opened according to the biting signal from the load cell. .
[0037]
When the low temperature portion (skid mark portion) approaches the water injection region as shown in FIG. 2 (c), the position and length (length in the rolling direction) are read by the temperature sensor 14, and the rolling speed, etc. Based on this information, the control means 13 calculates the timing of stopping and restarting the injection of the second row nozzle 4b, and sends an opening / closing signal to the valve 16b based on the calculation result.
[0038]
In the control system, the reduction position detector 12 is not always necessary. Further, when temperature control of the skid mark portion is not performed, the temperature sensor 17 is not necessarily required.
[0039]
Moreover, when performing control different from the example of FIG. 2, what is necessary is just to control according to the objective of each control. For example, as shown in FIG. 1, when only a part of the descaling nozzle is used and water is not injected to the tip, the valve 16b connected to the second row nozzle 4b may be normally closed. Furthermore, when only one row of nozzles is disposed as will be described later, only the first control valve is used and the opening degree thereof may be adjusted.
[0040]
In the present invention, the temperature difference in the width direction of the rolled steel sheet (direction substantially orthogonal to the rolling direction) may be reduced. In this case, the jet strength of water from the descaling header arranged in the width direction is covered. What is necessary is just to adjust according to the surface temperature distribution of the width direction of a rolled steel plate. For example, the width direction end of the steel sheet to be rolled is likely to have a temperature lower than the width direction center due to the two heat removal effects of air cooling and water cooling with descaling water, so the width direction center is increased toward the width direction end. In many cases, the injection amount and / or the injection strength (particularly, the injection amount) of water are suppressed. In addition, when there are a plurality of skid marks in a direction substantially parallel to the rolling direction of the steel sheet to be rolled, the water injection amount and / or the injection strength (particularly the injection amount) of the skid mark part is set to be higher than that other than the skid mark part. It may be suppressed. The suppression of the water amount may be performed intermittently, such as ON-OFF control.
[0041]
The rolling mill used in the present invention is not limited to a four-stage rolling mill, and any general-purpose rolling mill can be used.
[0042]
Further, the descaling nozzle may be disposed not only on the inlet side of the rolling mill but also on both the inlet side and the outlet side.
[0043]
Furthermore, the nozzles on the inlet side do not necessarily have to be arranged in two rows on the front and rear sides, but may be arranged in only one row (including the case where only one row is used by arranging a plurality of rows), and three or more rows are arranged. May be. Regardless of the number of nozzle rows, by controlling total water injection in each row, the amount and intensity of water injection and the timing of injection can be controlled in the same manner as in FIGS. .
[0044]
According to the present invention, since the scale is almost completely removed by descaling, it is possible to effectively prevent the occurrence of a temperature difference and the occurrence of residual stress even when using a steel type that is likely to generate a scale. And the quality can be made substantially uniform. Examples of steel types that can be advantageously used in the present invention (steel types that easily generate scales) include steels having the following component compositions.
[0045]
C: 0.1-0.2% by mass
Si: 0.1 to 0.5% by mass
Mn: 0.5 to 1.5% by mass
P: 0.03 mass% or less (excluding 0 mass%)
S: 0.02% by mass or less (excluding 0% by mass)
Al: 0.01 to 1.0% by mass
The balance may be substantially Fe and unavoidable impurities, and may contain other elements (Ti, Nb, etc.). When Ti and / Nb are contained, the amount of Ti may be about 0.05% by mass or less, and the amount of Nb may be about 0.05% by mass or less.
[0046]
Examples of steel types that are particularly prone to scale include the following steel types 1 and 2.
[0047]
[Steel grade 1]
C: 0.12-0.16 mass%
Si: 0.17 to 0.27% by mass
Mn: 1.00 to 1.15% by mass
P: 0.025 mass% or less (excluding 0 mass%)
S: 0.012 mass% or less (excluding 0 mass%)
Al: 0.018-0.05 mass%
The balance is Fe and inevitable impurities.
[0048]
[Steel grade 2]
C: 0.13-0.15 mass%
Si: 0.30-0.40 mass%
Mn: 1.20 to 1.30% by mass
P: 0.010% by mass or less (excluding 0% by mass)
S: 0.002 mass% (excluding 0 mass%)
Al: 0.02-0.05 mass%
Ti: 0.009 to 0.015 mass%
Nb: 0.005 to 0.01% by mass
Moreover, according to this invention, the material and quality of a thick board can be made substantially uniform. Therefore, there is no possibility that the thick plate is deformed even after the thick plate is cut, and the flatness of the steel plate can be increased. For example, a thick plate with a high flatness of about 9 to 100 mm (preferably about 15 to 70 mm) can be produced. Moreover, in this invention, since the temperature difference of the width direction can also be reduced, a different width steel plate (steel plate from which a width changes in a rolling direction) can be manufactured advantageously.
[0049]
The thick plate obtained by the present invention can be advantageously used as a member of a steel structure (a ship, a bridge, a pressure vessel, a large-diameter steel pipe, etc., especially a ship) because the material and quality are substantially uniform.
[0050]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.
[0051]
Example 1 and Comparative Example 1
Reverse rolling obtained by rolling out a slab (thickness 235 mm, width 1700 mm, length 2770 mm) heated to a surface temperature of 1140 ° C. (skid mark temperature 1120 ° C.) with a rough mill (rough rolling roll) The steel plate (thickness 66.0 mm, width 3000 mm, length 5600 mm) was used, and 10-pass hot reverse rolling was performed. Of the 10 passes, descaling was performed in the first pass, the third pass, and the fifth pass according to the descaling method shown in FIG. 2 (see Table 1). In addition, since only one side of the both ends in the rolling direction of the steel sheet is descaled, it is rare to perform descaling of only odd-numbered paths, but in this embodiment, in order to clarify the effect due to the difference in descaling method Descaling only odd paths.
[0052]
However, unlike the example of FIG. 2, water was not injected from the first row nozzle 4a to the tip portion. Control of water injection for the tip, skid mark part, and other parts (high temperature part) is as shown in Table 2 below.
[0053]
[Table 1]

[0054]
[Table 2]

[0055]
The scale thickness and temperature of each part of the obtained steel plate (thickness 26.0 mm, width 3000 mm, length 14200 mm) are as shown in Table 3 and FIG. This steel plate was accelerated to about 580 ° C. by water cooling. The yield strength of each part of the thick plate after accelerated cooling was measured and shown in FIG.
[0056]
[Table 3]

[0057]
As is clear from Table 3 and FIGS. 4 to 5, in the comparative example, the temperature of the tip portion is about 60 ° C. lower than that of the high temperature portion, and the temperature of the high temperature portion becomes uniform after about 1000 mm from the tip portion. In contrast, in this embodiment, the temperature difference between the tip and the high-temperature part can be halved to about 30 ° C., and the temperature can be made uniform in a part about 500 mm or longer from the tip. Therefore, in the thick plate of the comparative example, the difference between the yield strength of the tip portion and the yield strength of the high temperature portion is about 35 MPa, whereas in the example, the difference between the yield strength of the tip portion and the yield strength of the high temperature portion is reduced. It can be reduced to about 18 MPa. Further, if a steel plate is used from the high temperature part (steady part of yield strength) to about +10 MPa, in the comparative example, it is necessary to cut off a part from the tip to about 700 mm, whereas in the example, from the tip to about 400 mm. It is sufficient to cut off only the portion, and the cutting allowance can be reduced by about 300 mm.
[0058]
【The invention's effect】
According to the present invention, the amount of water injection to the tip of the steel sheet to be rolled is suppressed, and the water injection is strengthened from the tip to the downstream portion after a predetermined length to remove scaling almost completely. Therefore, the temperature difference in the plane direction (particularly in the rolling direction) of the thick steel plate can be reduced, and the material of the thick plate can be made substantially uniform.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining an example of a descaling method of the present invention.
FIG. 2 is a schematic diagram for explaining another example of the descaling method of the present invention.
FIG. 3 is a schematic diagram for explaining an example of a control system used in the present invention.
FIG. 4 is a graph showing the relationship between the distance from the tip of the steel sheet and the surface temperature obtained in the examples and comparative examples.
FIG. 5 is a graph showing the relationship between the distance from the tip of the steel sheet and the yield strength obtained in Examples and Comparative Examples.
FIG. 6 is a schematic diagram for explaining a conventional descaling method.
[Explanation of symbols]
1a ... rolling mill
2. Rolling roll
4a, 4b ... descaling header
16a, 16b ... control means
11: Detection means
15 ... Control means

Claims (6)

  A method of manufacturing a thick plate by hot reverse rolling in which a hot rolling of a steel plate to be rolled is repeated a plurality of times and water is sprayed to the steel plate to be rolled in at least one pass to perform hot rolling while descaling. In the descaling path, the amount of water injection is suppressed for the end portion on the rolling roll entry side of the rolled steel sheet, and for the downstream side portion after the predetermined length from the entry side end portion. A method for manufacturing a thick plate, in which water is sprayed at a predetermined strength or more to remove scale completely. The downstream portion after a predetermined length from the end portion on the entry side of the steel plate to be treated is divided into a skid mark portion and another portion to adjust the water injection amount and the injection strength, with respect to the other portion. In order to reduce the temperature difference between the other part and the skid mark part by increasing the amount of water jetted and increasing the jet strength, the scale thickness is made substantially uniform, so that the cooling process after rolling. The manufacturing method according to claim 1, wherein the amount of peeling of the scale is substantially the same between the other part and the skid mark part, and the cooling rate is substantially the same.   The manufacturing method of Claim 1 or 2 which strengthens the injection of the water with respect to the downstream part after predetermined length from the said entrance side edge part based on the timing of the biting of the steel plate to be rolled into a rolling roll.   The manufacturing method in any one of Claims 1-3 which arrange | position the descaling nozzle for injecting water at the entrance side of a rolling roll, and inject water toward the direction opposite to the approach direction of a to-be-rolled steel plate.   A plurality of descaling nozzles for injecting water are provided in the width direction on the inlet side of the rolling roll, and the amount of water injection from each descaling nozzle is adjusted in accordance with the surface temperature distribution in the width direction of the steel sheet. The manufacturing method in any one of Claims 1-4 which reduces the temperature difference of the direction substantially orthogonal to a rolling direction by.  A hot rolling roll, a descaling nozzle that is disposed on the inlet side of the rolling roll and substantially completely removes the scale of the steel sheet to be rolled, and the amount and strength of the spray water supplied to the descaling nozzle A control means that can be controlled, and a detecting means for detecting the biting timing of the rolled steel sheet in the rolling roll, and in response to the biting timing detection signal of the detecting means, the rolling roll of the rolled steel sheet While suppressing the amount of water injection to the end portion on the entry side, supply of water with a strength capable of removing the scale almost completely from the end portion on the entry side to the downstream portion after a predetermined length. A rolling mill comprising control means for indicating.

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