JP2015217411A - Method of manufacturing thick steel plate - Google Patents

Method of manufacturing thick steel plate Download PDF

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JP2015217411A
JP2015217411A JP2014102089A JP2014102089A JP2015217411A JP 2015217411 A JP2015217411 A JP 2015217411A JP 2014102089 A JP2014102089 A JP 2014102089A JP 2014102089 A JP2014102089 A JP 2014102089A JP 2015217411 A JP2015217411 A JP 2015217411A
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steel plate
thick steel
cooling device
temperature
accelerated cooling
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隆男 赤塚
Takao Akatsuka
隆男 赤塚
山崎 剛
Takeshi Yamazaki
剛 山崎
太基 宮野
Taiki Miyano
太基 宮野
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JFE Steel Corp
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JFE Steel Corp
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Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a steel plate having desired material characteristics with an excellent yield, by eliminating a temperature difference in the longitudinal direction of the steel plate after acceleration cooling.SOLUTION: In a method of manufacturing a thick steel plate by using hot rolling equipment having a reversible type rolling mill and cooling device and an accelerated cooling device arranged on the downstream side of the hot rolling equipment, in the hot rolling equipment, a conveyance speed when the thick steel plate passes through the cooling device, is increased toward an upstream side end part from a downstream side end part of the thick steel plate, the temperature of the upstream side end part of the thick steel plate just before the downstream side end part of the thick steel plate enters the accelerated cooling device, is set to be higher than the temperature of the downstream side end part to compensate a temperature drop in the upstream side end part until the upstream side end part enters the accelerated cooling device after the downstream side end part of the thick steel plate enters the accelerated cooling device, and a difference between the surface temperature of the thick steel plate when the downstream side end part of the thick steel plate enters the acceleration cooling device and the surface temperature of the thick steel plate when the upstream side end part enters the accelerated cooling device, is set to be 10°C or less.

Description

本発明は、熱間圧延を施し、材質の均一性に優れた厚鋼板を製造する方法に関し、特に、TMCP(制御圧延と制御冷却)により製造される引張強さ(TS)490MPa以上の強度を有する厚鋼板の製造方法に関する。   The present invention relates to a method of producing a thick steel plate having excellent material uniformity by hot rolling, and in particular, has a tensile strength (TS) produced by TMCP (controlled rolling and controlled cooling) of 490 MPa or more. The present invention relates to a method for manufacturing a thick steel plate.

近年、高施工性や安全性の観点から、材料に対し、高強度や、母材および溶接部の高靭性が求められており、そのための製造方法として、厚鋼板のTMCP(Thermomechanical Controlled Processing)技術が必要不可欠となっている。TMCP技術とは、制御圧延と制御冷却を組み合わせることによって、所望の材料特性を厚鋼板に持たせる技術である。 例えば特許文献1では、所望の材料強度を厚鋼板に持たせるために、加速冷却を利用して厚鋼板を製造している。   In recent years, from the viewpoint of high workability and safety, high strength and high toughness of base metal and welded parts are required for materials. As a manufacturing method therefor, TMCP (Thermal Mechanical Controlled Processing) technology for thick steel plates is required. Is indispensable. The TMCP technique is a technique for imparting desired material properties to a thick steel plate by combining controlled rolling and controlled cooling. For example, in Patent Document 1, a thick steel plate is manufactured using accelerated cooling in order to give the thick steel plate a desired material strength.

特開2001−200334号公報Japanese Patent Laid-Open No. 2001-200334

しかしながら、特許文献1のように加速冷却を利用した技術では、所望の材料強度を厚鋼板に持たせるために、加速冷却における冷却開始温度、冷却停止温度を厳密に制御しなければならない。   However, in the technique using accelerated cooling as in Patent Document 1, the cooling start temperature and the cooling stop temperature in accelerated cooling must be strictly controlled in order to give the thick steel plate the desired material strength.

図1は、従来の厚板圧延ラインの一例を示す概略図である。加熱炉2から抽出されたスラブは、可逆式圧延機3および冷却装置4からなる熱間圧延設備において、冷却装置4により冷却されながら、可逆式圧延機3により圧延され、所定板厚の厚鋼板1となる。そして、圧延後の厚鋼板1は、加速冷却装置5に搬送される。ここで、加熱炉2側を厚鋼板1の搬送方向上流側、加速冷却装置5側を厚鋼板1の搬送方向下流側とする。従来の加速冷却では、図3(a)に示すように、厚鋼板1が加速冷却装置5に入る直前では、厚鋼板1の下流側の端部Tの温度Tと上流側の端部Bの温度Tとは同じである(以下、搬送方向下流側の端部を端部T、上流側の端部を端部Bと記載する)。厚鋼板1の端部Tが加速冷却装置5の入口に到達してから、厚鋼板1の端部Bが加速冷却装置5の入口に到達するまでには時間差がある。このため、加速冷却装置5の入口に到達した時点での、端部Tの温度TをTとすると、空冷による温度降下により、加速冷却装置5の入口に端部Bが到達する時点での、端部Bの温度Tは、Tより低くなる(T<T)。また、加速冷却による温度低下量は端部T、端部Bとも同じであるので、加速冷却の開始温度が異なる端部T、端部Bの加速冷却終了温度も、当然、異なる。 FIG. 1 is a schematic view showing an example of a conventional thick plate rolling line. The slab extracted from the heating furnace 2 is rolled by the reversible rolling mill 3 while being cooled by the cooling apparatus 4 in a hot rolling facility comprising the reversible rolling mill 3 and the cooling device 4, and is a thick steel plate having a predetermined plate thickness. 1 Then, the rolled steel plate 1 is conveyed to the accelerated cooling device 5. Here, the heating furnace 2 side is the upstream side in the conveying direction of the thick steel plate 1, and the accelerated cooling device 5 side is the downstream side in the conveying direction of the thick steel plate 1. In the conventional accelerated cooling, as shown in FIG. 3A, immediately before the thick steel plate 1 enters the accelerated cooling device 5, the temperature T T at the downstream end T of the thick steel plate 1 and the upstream end B The temperature T B is the same (hereinafter, the end on the downstream side in the transport direction is referred to as end T, and the end on the upstream side is referred to as end B). There is a time difference between the end T of the thick steel plate 1 reaching the inlet of the accelerated cooling device 5 and the end B of the thick steel plate 1 reaching the inlet of the accelerated cooling device 5. Therefore, at the time it reaches the inlet of the accelerated cooling equipment 5, when the temperature T T of the end portion T and T S, the temperature drop due to cooling, to the inlet of the accelerated cooling equipment 5 at the time when the end portion B arrives The temperature T B at the end B is lower than T S (T B <T S ). In addition, since the temperature drop due to the accelerated cooling is the same for both the end T and the end B, the accelerated cooling end temperatures of the end T and the end B having different accelerated cooling start temperatures are naturally different.

すなわち、従来の加速冷却では、加速冷却の開始温度、終了温度が、端部Tと端部Bとで異なることとなり、加速冷却中および加速冷却後の変態挙動が、端部Tと端部Bとで異なるものとなる。その結果、得られる厚鋼板の端部Tから端部Bに向かって長手方向で、材料特性が変化することとなり、厚鋼板の一部分では所望の材料特性を満足できないという問題が生じることがあった。   That is, in the conventional accelerated cooling, the start temperature and the end temperature of the accelerated cooling are different between the end T and the end B, and the transformation behavior during the accelerated cooling and after the accelerated cooling is the end T and the end B. And will be different. As a result, the material properties change in the longitudinal direction from the end T to the end B of the resulting thick steel plate, and there is a problem that a desired material property cannot be satisfied in a part of the thick steel plate. .

本発明は上記実情に鑑みてなされたものであって、加速冷却の開始温度、終了温度を鋼板の長手方向で一定として材料特性を長手方向で均一にし、所望の材料特性を有する鋼板を歩留まり良く製造する方法を提供することを目的とする。   The present invention has been made in view of the above circumstances, and the starting temperature and ending temperature of accelerated cooling are made constant in the longitudinal direction of the steel sheet to make the material characteristics uniform in the longitudinal direction, and a steel sheet having desired material characteristics is obtained with a high yield. The object is to provide a method of manufacturing.

なお、ここでいう厚鋼板の温度は鋼板表面の温度であり、冷却装置による水冷を停止し、復熱が完了した後の鋼板表面温度である。復熱とは、水冷によって鋼板の表面温度が低下し、水冷停止後、鋼板内部の熱によって鋼板の表面温度が上昇する現象を指す。通常、水冷後の復熱は水冷停止から10〜15秒程度で完了する。以下、本明細書中で厚鋼板(鋼板)の温度という場合は、すべて、復熱が完了した後の、鋼板表面温度を指すものとする。   In addition, the temperature of a thick steel plate here is the temperature of the steel plate surface, and stops the water cooling by a cooling device, and is the steel plate surface temperature after completion of recuperation. Recuperation refers to a phenomenon in which the surface temperature of the steel sheet decreases due to water cooling, and after the water cooling stops, the surface temperature of the steel sheet increases due to heat inside the steel sheet. Normally, recuperation after water cooling is completed in about 10 to 15 seconds after the water cooling is stopped. Hereinafter, the temperature of the thick steel plate (steel plate) in this specification refers to the surface temperature of the steel plate after the recuperation is completed.

発明者らは上記課題を解決するために鋭意検討した結果、圧延終了後の厚鋼板において、下流側の端部Tの温度よりも上流側の端部Bの温度を意図的に高くすることにより、加速冷却開始時点において生じていた端部Tと端部Bの温度差を解消できることを見出した。また、冷却開始温度が等しくなることで、加速冷却終了時点において生じていた端部Tと端部Bの温度差も、当然、解消する。   As a result of intensive studies to solve the above problems, the inventors have intentionally made the temperature of the upstream end B higher than the temperature of the downstream end T in the thick steel plate after the end of rolling. It has been found that the temperature difference between the end T and the end B that has occurred at the start of accelerated cooling can be eliminated. Further, since the cooling start temperatures are equalized, the temperature difference between the end portion T and the end portion B that has occurred at the end of the accelerated cooling is naturally eliminated.

本発明は上記知見に基づくものであり、その特徴は以下の通りである。
[1]可逆式圧延機と冷却装置とを備えた熱間圧延設備と、前記熱間圧延設備の下流側に配置される加速冷却装置と、を用いて厚鋼板を製造する方法であって、前記熱間圧延設備において、厚鋼板が前記冷却装置を通過する際の搬送速度を、厚鋼板の下流側の端部から上流側の端部に向けて増加させ、前記加速冷却装置に厚鋼板の下流側の端部が入る直前の、厚鋼板の上流側の端部の温度を下流側の端部の温度よりも高くなるようにし、前記加速冷却装置に厚鋼板の下流側の端部が入る際の、厚鋼板の表面温度と、前記加速冷却装置に上流側の端部が入る際の、厚鋼板の表面温度との差を10℃以下とすることを特徴とする厚鋼板の製造方法。
[2]厚鋼板が前記冷却装置を通過する際の搬送速度を、厚鋼板の下流側の端部から上流側の端部に向けて段階的に増加させることを特徴とする[1]に記載の厚鋼板の製造方法。
The present invention is based on the above findings, and the features thereof are as follows.
[1] A method of producing a thick steel plate using a hot rolling facility including a reversible rolling mill and a cooling device, and an accelerated cooling device disposed on the downstream side of the hot rolling facility, In the hot rolling facility, the conveying speed when the thick steel plate passes through the cooling device is increased from the downstream end of the thick steel plate toward the upstream end, and the accelerated cooling device Immediately before the downstream end enters, the temperature of the upstream end of the thick steel plate is made higher than the temperature of the downstream end, and the downstream end of the thick steel plate enters the accelerated cooling device. A difference between the surface temperature of the thick steel plate and the surface temperature of the thick steel plate when the upstream end enters the accelerated cooling device is 10 ° C. or less.
[2] The conveyance speed when the thick steel plate passes through the cooling device is increased stepwise from the downstream end to the upstream end of the thick steel plate. Manufacturing method for thick steel plates.

本発明によれば、加速冷却中の厚鋼板の長手方向の温度差を解消して、厚鋼板の特性が長手方向で均一となり、所望の材料特性を有する厚鋼板を歩留まり良く製造することができる。   According to the present invention, it is possible to eliminate the temperature difference in the longitudinal direction of the thick steel plate during accelerated cooling, make the properties of the thick steel plate uniform in the longitudinal direction, and manufacture a thick steel plate having desired material characteristics with high yield. .

厚板圧延ラインの一例を示す概略図である。It is the schematic which shows an example of a thick plate rolling line. 本発明で使用する熱間圧延設備の一例を示す概略図である。It is the schematic which shows an example of the hot rolling equipment used by this invention. 冷却装置通過後から加速冷却装置に搬送される際の厚鋼板の端部の温度変化を示す概略図であり、(a)は従来の搬送時の厚鋼板の温度変化を示す図であり、(b)は本発明の搬送時の厚鋼板の温度変化を示す図である。It is the schematic which shows the temperature change of the edge part of the thick steel plate at the time of being conveyed to an acceleration cooling device after passing a cooling device, (a) is a figure which shows the temperature change of the thick steel plate at the time of the conventional conveyance, b) is a figure which shows the temperature change of the thick steel plate at the time of conveyance of this invention.

図1は、本発明の一実施の形態に係る厚鋼板の製造方法に使用する厚板圧延ラインの一例を示す概略図である。図1において、加熱炉2から抽出されたスラブは、可逆式圧延機3および冷却装置4からなる熱間圧延設備において、冷却装置4により冷却されながら、可逆式圧延機3により圧延され、所定板厚の厚鋼板1となる。冷却装置4による冷却は圧延の任意のパスにおいて行ってよい。そして、圧延後の厚鋼板1は加速冷却装置5に搬送される。   FIG. 1 is a schematic view showing an example of a thick plate rolling line used in the method of manufacturing a thick steel plate according to one embodiment of the present invention. In FIG. 1, a slab extracted from a heating furnace 2 is rolled by a reversible rolling mill 3 while being cooled by a cooling apparatus 4 in a hot rolling facility comprising a reversible rolling mill 3 and a cooling apparatus 4. A thick steel plate 1 is obtained. The cooling by the cooling device 4 may be performed in an arbitrary pass of rolling. Then, the rolled steel plate 1 is conveyed to the accelerated cooling device 5.

図2は、図1の厚板圧延ラインの一部である熱間圧延設備の一例を示す概略図である。図2において、厚鋼板1を可逆式に搬送するテーブルローラ6と、厚鋼板1を圧延する可逆式圧延機3と、冷却装置4とを備えている。   FIG. 2 is a schematic view showing an example of hot rolling equipment which is a part of the thick plate rolling line of FIG. In FIG. 2, the table roller 6 which conveys the thick steel plate 1 reversibly, the reversible rolling mill 3 which rolls the thick steel plate 1, and the cooling device 4 are provided.

冷却装置4は、厚鋼板1の上面側に棒状の冷却水を噴射する上ヘッダユニット7と、厚鋼板1の下面側に棒状の冷却水を噴射する下ヘッダユニット8とを備えている。また、冷却装置4の冷却水流量は一定とする。可逆式圧延機3は上流側、下流側のいずれの方向にも鋼板を搬送しながら圧延を行うため、冷却装置4は、可逆式圧延機3に対して上流側、下流側のいずれに配置してもよい。なお、冷却装置4は、本来、圧延時間の短縮を目的として設置するものである。冷却装置4により、圧延中に厚鋼板を冷却することで、目標とする圧延終了温度に短時間で到達でき、圧延時間の短縮を図れる。したがって、冷却装置4は可逆式圧延機3に近接して配置することが好ましい。すなわち、冷却装置4と可逆式圧延機3との距離が長いと、可逆式圧延機3と冷却装置4の間を、厚鋼板を往復搬送するのに時間がかかり、圧延時間の短縮を達成できない。このため、冷却装置4は可逆式圧延機3から近いほど望ましく、10m以内の位置に配置することが好ましい。冷却装置4の冷却能力としては、パス間温度降下量(1パスを通過する間に低下する鋼板温度)で10℃以上であることが好ましい。パス間温度降下量が10℃未満であると冷却能力が不足し、本発明が目的とする、厚鋼板温度を調整する効果が乏しいためである。   The cooling device 4 includes an upper header unit 7 that injects bar-shaped cooling water onto the upper surface side of the thick steel plate 1, and a lower header unit 8 that injects bar-shaped cooling water onto the lower surface side of the thick steel plate 1. The cooling water flow rate of the cooling device 4 is constant. Since the reversible rolling mill 3 performs rolling while conveying the steel sheet in both the upstream and downstream directions, the cooling device 4 is arranged on either the upstream side or the downstream side with respect to the reversible rolling mill 3. May be. The cooling device 4 is originally installed for the purpose of shortening the rolling time. By cooling the thick steel plate during rolling by the cooling device 4, the target rolling end temperature can be reached in a short time, and the rolling time can be shortened. Therefore, it is preferable to arrange the cooling device 4 in the vicinity of the reversible rolling mill 3. That is, if the distance between the cooling device 4 and the reversible rolling mill 3 is long, it takes time to reciprocate the thick steel plate between the reversible rolling mill 3 and the cooling device 4, and the reduction of the rolling time cannot be achieved. . For this reason, it is desirable that the cooling device 4 is closer to the reversible rolling mill 3, and it is preferable to arrange the cooling device 4 at a position within 10 m. The cooling capacity of the cooling device 4 is preferably 10 ° C. or more in terms of the temperature drop between passes (the temperature of the steel plate that decreases while passing through one pass). This is because if the temperature drop between passes is less than 10 ° C., the cooling capacity is insufficient and the effect of adjusting the temperature of the thick steel plate, which is the purpose of the present invention, is poor.

図2において、厚鋼板の端部Tが冷却装置4を通過する時の搬送速度をV(m/sec)、厚鋼板の端部Bが冷却装置4を通過する時の搬送速度をV(m/sec)とした時に、冷却装置4の冷却水流量は一定なので、厚鋼板の温度降下量は、厚鋼板の搬送速度に、ほぼ反比例する。したがって、V>Vとすることにより、冷却装置通過後、すなわち、加速冷却設備に搬送される際の厚鋼板の上流側の端部Bの温度TBを、厚鋼板の下流側の端部Tの温度Tより高くできる。 In FIG. 2, the conveying speed when the end T of the thick steel plate passes the cooling device 4 is V T (m / sec), and the conveying speed when the end B of the thick steel plate passes the cooling device 4 is V B. Since the cooling water flow rate of the cooling device 4 is constant when (m / sec), the temperature drop amount of the thick steel plate is almost inversely proportional to the conveying speed of the thick steel plate. Therefore, by setting V B> V T, after the cooling device passes, i.e., the temperature T B of the upstream end of the steel plate B as it is conveyed to accelerated cooling equipment, downstream of the end of the steel plate The temperature can be higher than the temperature T T of the part T.

なお、このように搬送速度を変化させて冷却することは、任意の圧延パスで行ってもよいが、圧延の途中のパスで行うことは好ましくない。これは、厚鋼板の端部Tと端部Bとに温度差があると、厚鋼板の端部Tと端部Bとで厚鋼板の変形抵抗が変わり、圧延が不安定となるためである。また、冷却装置4は可逆式圧延機3の上流側、下流側のいずれに配置してもよい。冷却装置4を下流側に配置する場合には、搬送速度を変化させて冷却するパスは最終パスとすることが好ましい。これは、冷却装置4が可逆式圧延機3の下流側に位置する場合には、最終パスにおいて圧延中に搬送速度を変化させても、冷却装置4は圧延の出側にあるため、圧延中の鋼板温度には影響しないからである。また、冷却装置4を可逆式圧延機3の上流側に配置する場合には、搬送速度を変化させて冷却するパスは、最終パスで、かつ、空パス(圧下をほとんどかけずに鋼板を搬送するだけのパス)とすることが好ましい。これは、冷却装置4が圧延の入側にあるため、圧延前に搬送速度を変化させながら冷却装置4に鋼板を通過させると、圧延時には厚鋼板の端部Tと端部Bとで温度差がある状態となるためである。   In addition, although cooling by changing a conveyance speed in this way may be performed by arbitrary rolling passes, it is not preferable to perform by a pass in the middle of rolling. This is because if there is a temperature difference between the end T and the end B of the thick steel plate, the deformation resistance of the thick steel plate changes between the end T and the end B of the thick steel plate, and the rolling becomes unstable. . Further, the cooling device 4 may be arranged on either the upstream side or the downstream side of the reversible rolling mill 3. When the cooling device 4 is arranged on the downstream side, it is preferable that the path for cooling by changing the conveying speed is the final path. This is because when the cooling device 4 is located downstream of the reversible rolling mill 3, even if the conveying speed is changed during rolling in the final pass, the cooling device 4 is on the exit side of rolling, This is because it does not affect the steel plate temperature. Further, when the cooling device 4 is arranged on the upstream side of the reversible rolling mill 3, the cooling path is changed by changing the conveyance speed, and the cooling path 4 is the final path and the empty path (the steel plate is conveyed with little reduction). It is preferable that the pass is a simple pass). This is because the cooling device 4 is on the entrance side of rolling, and if the steel plate is passed through the cooling device 4 while changing the conveying speed before rolling, the temperature difference between the end T and the end B of the thick steel plate during rolling. This is because there is a state.

すでに述べたように、厚鋼板の端部Tが加速冷却装置5の入口に到達してから、厚鋼板の端部Bが加速冷却装置5の入口に到達するまでには、時間差がある。このため、加速冷却開始温度を端部Tと端部Bとで等しくするためには、加速冷却装置5に厚鋼板の下流側の端部が入ってから上流側の端部が入るまでの、上流側の端部の温度低下を補償する必要がある。本発明では、図3(b)に示すように、厚鋼板の端部Tが加速冷却装置5の入口に到達した時点の端部Tの温度TをTとすると、空冷による温度降下の影響を考慮して、この時の端部Bの温度Tを、空冷による温度降下分だけ、Tより意図的に高くする。そうすると、テーブルローラ9上の、厚鋼板の端部Bが加速冷却装置5の入口に到達する時点の、端部Bの温度は、空冷により温度が降下して、端部Tが加速冷却装置5の入口に到達した時点の端部Tの温度と等しい温度になる(T=T)。厚鋼板の端部Bが加速冷却装置5の入口に到達する時点の、端部Bの温度は、端部Tが加速冷却装置5の入口に到達した時点の端部Tの温度と等しい温度であることが最も望ましいが、これらの温度の差が10℃以下であれば、材料特性に及ぼす影響は小さく、実用上、差し支えないため、これらの温度の差は10℃以下とする。好ましくは5℃以下である。また、加速冷却による温度低下量は端部T、端部Bとも等しいので、端部T、端部Bの加速冷却の開始温度が同じであれば、端部T、端部Bの加速冷却終了温度も、当然、等しくなる。 As already described, there is a time difference between the end T of the thick steel plate reaching the inlet of the accelerated cooling device 5 and the end B of the thick steel plate reaching the inlet of the accelerated cooling device 5. For this reason, in order to equalize the accelerated cooling start temperature at the end portion T and the end portion B, until the upstream end portion enters after the downstream end portion of the thick steel plate enters the accelerated cooling device 5, It is necessary to compensate for the temperature drop at the upstream end. In the present invention, as shown in FIG. 3B, if the temperature T T of the end T when the end T of the thick steel plate reaches the inlet of the accelerated cooling device 5 is T S , the temperature drop due to air cooling is reduced. effect in consideration of the temperature T B of the end portion B at this time, only the temperature drop due to cooling, intentionally higher than T S. If it does so, the temperature of the edge part B at the time of the edge part B of the thick steel plate on the table roller 9 reaching the inlet of the acceleration cooling device 5 will fall by air cooling, and the edge part T will become the acceleration cooling device 5 It becomes a temperature equal to the temperature of the end portion T when it reaches the inlet (T B = T S ). The temperature of the end B when the end B of the thick steel plate reaches the inlet of the accelerated cooling device 5 is equal to the temperature of the end T when the end T reaches the inlet of the accelerated cooling device 5. Although it is most desirable, if the difference between these temperatures is 10 ° C. or less, the effect on the material properties is small and may be practically used. Therefore, the difference between these temperatures is set to 10 ° C. or less. Preferably it is 5 degrees C or less. Further, since the temperature drop due to the accelerated cooling is the same for both the end T and the end B, if the start temperature of the accelerated cooling for the end T and the end B is the same, the accelerated cooling of the end T and the end B is completed. Of course, the temperature is also equal.

すなわち、加速冷却の開始温度、終了温度が、端部Tと端部Bとで等しくなり、加速冷却中および加速冷却後の厚鋼板の変態挙動が、端部Tと端部Bとで同じとなる。その結果、得られる厚鋼板の長手方向の材料特性が均一となり、歩留まりよく厚鋼板を製造することができる。   That is, the start temperature and the end temperature of the accelerated cooling are equal at the end T and the end B, and the transformation behavior of the thick steel plate during and after the accelerated cooling is the same at the end T and the end B. Become. As a result, the material properties in the longitudinal direction of the resulting thick steel plate become uniform, and the thick steel plate can be manufactured with a high yield.

加速冷却装置5の入口に厚鋼板の端部Tが到達してから、端部Bが加速冷却装置の入口に到達するまでの時間は、鋼板搬送速度と鋼板長さによるが、50〜120秒程度であり、この間の端部Bの温度低下は20〜40℃程度である。したがって、本発明では、厚鋼板の端部Tが加速冷却装置の入口の到達した時点の、端部Bの温度TB(℃)は、この時点の端部Tの温度T(℃)よりも20〜40℃程度高くする。端部Bの温度TB(℃)を端部Tの温度T(℃)よりも高くするために、端部Tが冷却装置4を通過する時の搬送速度Vから、端部Bが冷却装置4を通過する時の搬送速度Vまで搬送速度を増加させるが、連続的にVから増加させても、段階的に増加させてもよい。 The time from when the end T of the thick steel plate reaches the inlet of the accelerated cooling device 5 until the end B reaches the inlet of the accelerated cooling device depends on the steel plate conveyance speed and the steel plate length, but is 50 to 120 seconds. The temperature drop at the end B during this period is about 20 to 40 ° C. Therefore, in the present invention, the temperature T B (° C.) of the end B when the end T of the thick steel plate reaches the inlet of the acceleration cooling device is higher than the temperature T T (° C.) of the end T at this time. Is also increased by about 20-40 ° C. In order to make the temperature T B (° C.) of the end B higher than the temperature T T (° C.) of the end T , the end B is determined from the conveyance speed V T when the end T passes through the cooling device 4. increases the transport speed to the conveying speed V B when passing through the cooling device 4, be continuously increased from V T, it may be increased stepwise.

上記以外の熱間圧延条件、鋳造条件、加速冷却条件については、常法であればよい。また、本発明は、加速冷却時に温度差が生じる厚鋼板であれば、いかなる厚鋼板にも適用できるものであり、鋼の成分組成についても、限定されない。なお、ここで厚鋼板とは板厚5mm以上120mm以下の鋼板を指す。   About hot rolling conditions other than the above, casting conditions, and accelerated cooling conditions, what is necessary is just a conventional method. In addition, the present invention can be applied to any thick steel plate as long as it has a temperature difference during accelerated cooling, and the component composition of the steel is not limited. Here, the thick steel plate refers to a steel plate having a thickness of 5 mm to 120 mm.

可逆式圧延機の下流2mに冷却装置を備え、さらに下流に加速冷却装置を備える圧延、冷却ラインを用い、表1の成分組成を有する鋼素材を用いて、加熱温度1150℃、仕上げ圧延温度950℃で熱間圧延を行い、板厚25mm、長さ20mの厚鋼板を作製した。熱間圧延後、表2に示す条件で厚鋼板を冷却した。なお、厚鋼板の搬送方向下流側の端部Tが冷却装置を通過するときの搬送速度V(m/s)、厚鋼板の搬送方向上流側の端部Bが冷却装置を通過するときの搬送速度VB(m/s)については、表2に示す搬送速度とした。 Using a steel material having the composition shown in Table 1, using a rolling and cooling line equipped with a cooling device 2 m downstream of the reversible rolling mill and further equipped with an accelerated cooling device downstream, a heating temperature of 1150 ° C. and a finishing rolling temperature of 950 Hot rolling was performed at 0 ° C. to produce a thick steel plate having a plate thickness of 25 mm and a length of 20 m. After hot rolling, the thick steel plate was cooled under the conditions shown in Table 2. In addition, the conveyance speed V T (m / s) when the end T on the downstream side in the conveyance direction of the thick steel plate passes through the cooling device, and the end B on the upstream side in the conveyance direction of the thick steel plate passes through the cooling device. The conveyance speed V B (m / s) was the conveyance speed shown in Table 2.

Figure 2015217411
Figure 2015217411

得られた厚鋼板について、引張特性、衝撃特性をそれぞれ求めた。各試験方法は次の通りとした。
(1)引張特性
JIS Z 2201の規定に準拠して、JIS1A号全厚引張試験片を採取し、JIS Z 2241の規定に準拠して、引張試験を実施し、引張特性(引張強度TS)を求めた。全厚引張試験片は板幅中央で、端部T、端部Bからそれぞれ1mの位置より、圧延方向が引張り方向となるように採取した。目標とするTSは表2中に記載した。
(2)衝撃特性
板幅中央で、端部T、端部Bからそれぞれ1mの位置で、板厚(t)の1/4位置から、ノッチ方向が圧延方向となるように、JIS Z 2242に準拠して、Vノッチ衝撃試験片を採取し、シャルピー衝撃試験を実施した。試験温度:−40℃における吸収エネルギー(vE-40)を求め、衝撃特性を評価した。なお、吸収エネルギー値は、試験片3本の平均値とした。目標とするvE-40は表2中に記載した。得られた結果を表2に示す。
About the obtained thick steel plate, the tensile characteristic and the impact characteristic were calculated | required, respectively. Each test method was as follows.
(1) Tensile properties JIS 1A full-thickness tensile test specimens are collected in accordance with JIS Z 2201, and tensile tests are performed in accordance with JIS Z 2241 to obtain tensile properties (tensile strength TS). Asked. The full-thickness tensile test piece was sampled at the center of the plate width from a position 1 m from each of the end T and the end B so that the rolling direction was the tensile direction. The target TS is shown in Table 2.
(2) Impact characteristics At JIS Z 2242 at the center of the plate width, 1 m from each of the end T and end B, and from the 1/4 position of the plate thickness (t), the notch direction becomes the rolling direction. In accordance with this, a V-notch impact test piece was collected and a Charpy impact test was performed. Test temperature: Absorbed energy (vE -40 ) at -40 ° C was determined, and impact characteristics were evaluated. The absorbed energy value was an average value of three test pieces. The target vE- 40 is listed in Table 2. The obtained results are shown in Table 2.

Figure 2015217411
Figure 2015217411

表2から、本発明例はいずれも、厚鋼板の端部T、厚鋼板の端部Bにおける引張特性についてほとんど差がない。また、衝撃特性についてもほとんど差がなく、引張特性および衝撃特性のいずれも目標値を満足している。一方、比較例については、厚鋼板の端部Tと厚鋼板の端部Bでは引張特性および衝撃特性に大きな差があり、また、端部T、Bのいずれかで目標値を満足できていない。   From Table 2, all the examples of the present invention have almost no difference in the tensile properties at the end T of the thick steel plate and the end B of the thick steel plate. Also, there is almost no difference in impact characteristics, and both tensile characteristics and impact characteristics satisfy the target values. On the other hand, as for the comparative example, there is a large difference in tensile characteristics and impact characteristics at the end T of the thick steel plate and the end B of the thick steel plate, and the target value is not satisfied at either of the end T or B. .

1 厚鋼板
2 加熱炉
3 可逆式圧延機
4 冷却装置
5 加速冷却装置
6 テーブルローラ
7 上ヘッダユニット
8 下ヘッダユニット
9 テーブルローラ
DESCRIPTION OF SYMBOLS 1 Thick steel plate 2 Heating furnace 3 Reversible rolling mill 4 Cooling device 5 Accelerated cooling device 6 Table roller 7 Upper header unit 8 Lower header unit 9 Table roller

Claims (2)

可逆式圧延機と冷却装置とを備えた熱間圧延設備と、前記熱間圧延設備の下流側に配置される加速冷却装置と、を用いて厚鋼板を製造する方法であって、前記熱間圧延設備において、厚鋼板が前記冷却装置を通過する際の搬送速度を、厚鋼板の下流側の端部から上流側の端部に向けて増加させ、前記加速冷却装置に厚鋼板の下流側の端部が入る直前の、厚鋼板の上流側の端部の温度を下流側の端部の温度よりも高くなるようにし、前記加速冷却装置に厚鋼板の下流側の端部が入る際の、厚鋼板の表面の温度と、前記加速冷却装置に上流側の端部が入る際の、厚鋼板の表面の温度との差を10℃以下とすることを特徴とする厚鋼板の製造方法。   A method of manufacturing a thick steel plate using a hot rolling facility equipped with a reversible rolling mill and a cooling device, and an accelerated cooling device disposed downstream of the hot rolling facility, wherein the hot In the rolling equipment, the conveying speed when the thick steel plate passes through the cooling device is increased from the downstream end of the thick steel plate toward the upstream end, and the accelerated cooling device is provided on the downstream side of the thick steel plate. Immediately before the end enters, the temperature of the upstream end of the thick steel plate is made higher than the temperature of the downstream end, and when the downstream end of the thick steel plate enters the accelerated cooling device, A method of manufacturing a thick steel plate, characterized in that a difference between the temperature of the surface of the thick steel plate and the temperature of the surface of the thick steel plate when the upstream end enters the accelerated cooling device is 10 ° C or less. 厚鋼板が前記冷却装置を通過する際の搬送速度を、厚鋼板の下流側の端部から上流側の端部に向けて段階的に増加させることを特徴とする請求項1に記載の厚鋼板の製造方法。 The thick steel plate according to claim 1, wherein a conveying speed when the thick steel plate passes through the cooling device is gradually increased from a downstream end portion to an upstream end portion of the thick steel plate. Manufacturing method.
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