JP5098201B2 - Method for tempering thick steel plates - Google Patents

Method for tempering thick steel plates Download PDF

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JP5098201B2
JP5098201B2 JP2006097220A JP2006097220A JP5098201B2 JP 5098201 B2 JP5098201 B2 JP 5098201B2 JP 2006097220 A JP2006097220 A JP 2006097220A JP 2006097220 A JP2006097220 A JP 2006097220A JP 5098201 B2 JP5098201 B2 JP 5098201B2
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善道 日野
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JFE Steel Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

本発明は誘導加熱装置を用いた厚鋼板の焼戻し処理方法に関する。 The present invention relates to a method for tempering a thick steel plate using an induction heating device.

鋼板の搬送ライン上に誘導加熱装置を配置し、熱間圧延後の冷却から焼戻し処理までをオンラインで処理する厚板製造装置が実用化され、高強度ラインパイプ材等高性能厚鋼板の製造に供されている。   Introduced an induction heating device on the steel sheet conveyance line, and a steel plate manufacturing device that performs on-line processing from cooling after hot rolling to tempering has been put to practical use. It is provided.

誘導加熱は、１次コイル側に電流を流すことで磁界を発生させ、鋼板側に磁界にともなう誘導電流を発生させてジュール熱により加熱を行なうもので、強磁性体である鋼板の誘導加熱においては、鋼板表層のごく近傍に電流が流れ、その鋼板表層が発熱する。   Induction heating is a method in which a magnetic field is generated by passing an electric current to the primary coil side, and an induction current accompanying the magnetic field is generated on the steel sheet side to perform heating by Joule heat. Current flows very close to the steel sheet surface layer, and the steel sheet surface layer generates heat.

従って、厚鋼板の誘導加熱では、鋼板表層と中心部の温度が乖離する傾向にあり、板厚方向の材質安定性が損なわれる場合も生じるため、周波数と投入電力を調整して板厚方向で均一な鋼板温度が得られる誘導加熱方法が提案されている。   Therefore, in induction heating of thick steel plates, the temperature of the steel plate surface layer and the central part tend to deviate, and material stability in the plate thickness direction may be impaired. An induction heating method that provides a uniform steel plate temperature has been proposed.

特許文献１は被加熱素材である厚鋼板の誘導加熱方法に関し、被加熱素材を昇温させる加熱段階と均熱段階を有する、誘導加熱を用いた熱処理において、加熱段階と均熱段階の間に更に、準加熱段階を設けることが記載されている。   Patent Document 1 relates to an induction heating method for a thick steel plate that is a material to be heated, and includes a heating stage for raising the temperature of the material to be heated and a soaking stage. In the heat treatment using induction heating, between the heating stage and the soaking stage. Furthermore, it is described that a semi-heating step is provided.

加熱段階から直ちに均熱段階に移行すると板厚方向の温度均一性が十分でない場合も生じるので、準加熱段階は、加熱段階と同一周波数で、投入電力を下げた誘導加熱を行う。   Immediately from the heating stage to the soaking stage, the temperature uniformity in the plate thickness direction may not be sufficient. Therefore, the semi-heating stage performs induction heating at the same frequency as the heating stage and with reduced input power.

準加熱段階では、被加熱材の表面温度が一定に達した後も表面と中心の温度差が所定の範囲となるまで加熱するので、均熱段階での誘導加熱により板厚方向に均一な温度分布が得られる。   In the semi-heating stage, even after the surface temperature of the material to be heated reaches a certain level, heating is performed until the temperature difference between the surface and the center reaches a predetermined range. Distribution is obtained.

均熱段階では加熱段階よりも周波数を高くし、投入電力を下げて、被加熱材の表面部、特に端面における熱放散による温度低下を防止し、急激な温度変化を防止し、熱伝導による被加熱素材全体の温度偏差を熱伝導により解消する。
特許第３３７０４９９号公報 In the soaking stage, the frequency is set higher than in the heating stage, the input power is lowered, the temperature of the surface of the material to be heated, especially the end face, is prevented from lowering temperature due to heat dissipation, the rapid temperature change is prevented, and the heat conduction is reduced. The temperature deviation of the whole heating material is eliminated by heat conduction.
Japanese Patent No. 3370499

ところで、厚鋼板の製造においては、熱処理時間の短縮は重要な課題で、搬送ライン上に誘導加熱装置を設けた生産設備が開発されたが、一方、厚鋼板の需要分野では板厚拡大が進展し、誘導加熱における板厚方向の温度差の不均一性は助長される傾向にある。   By the way, in the manufacture of thick steel plates, shortening the heat treatment time is an important issue, and production equipment with induction heating devices on the transport line has been developed. However, the non-uniformity of the temperature difference in the thickness direction in induction heating tends to be promoted.

特許文献１記載の方法は、被加熱素材を一つの誘導加熱炉内において高温加熱し、さらに所定時間均熱保持する誘導加熱方法であり、被加熱素材を誘導加熱装置を通過させながら板厚方向の温度均一性を向上させることに関しては記載がない。   The method described in Patent Document 1 is an induction heating method in which a material to be heated is heated at a high temperature in one induction heating furnace, and is maintained at a constant temperature for a predetermined time. There is no description regarding improving the temperature uniformity.

そこで、本発明は、被加熱素材を誘導加熱装置を通過させながら加熱し、板厚方向の温度均一性を向上させる誘導加熱方法を提供することを目的とする。 Then, an object of this invention is to provide the induction heating method which heats a to-be-heated material, passing an induction heating apparatus, and improves the temperature uniformity of a plate | board thickness direction.

本発明の課題は、以下の手段により達成される。
１．厚鋼板が搬送ライン上の複数の誘導加熱装置を上流側から下流側に通過して所定の温度に加熱される厚鋼板の焼戻し処理方法であって、厚鋼板をＡｃ１点未満に加熱する前段の焼戻し処理と厚鋼板の一部または全部をＡｃ１点以上に加熱する後段の焼戻し処理を備え、後段の焼戻し処理は少なくとも最後に通過する誘導加熱装置によるものであり、複数の誘導加熱装置による加熱において、厚鋼板がＡｃ １ 点以上となる加熱時間の合計が１０秒以下であることを特徴とする厚鋼板の焼戻し処理方法。
２．厚鋼板の一部または全部をＡｃ１点以上に加熱する誘導加熱装置がソレノイド型誘導加熱装置で、前記ソレノイド型誘導加熱装置で加熱する際の周波数が１０００Ｈｚ以上で、エネルギー密度が前段の誘導加熱装置と同等以上であることを特徴とする請求項１記載の厚鋼板の焼戻し処理方法。 The object of the present invention is achieved by the following means.
1. A method of tempering a thick steel plate in which the thick steel plate passes through a plurality of induction heating devices on a conveyance line from the upstream side to the downstream side and is heated to a predetermined temperature, and is a pre-stage for heating the thick steel plate to less than Ac 1 point. Tempering treatment and a subsequent tempering treatment in which a part or all of the thick steel plate is heated to Ac 1 point or more, and the latter tempering treatment is at least by an induction heating device that passes last, and by a plurality of induction heating devices. A tempering method for a thick steel plate, characterized in that the total heating time for the thick steel plate to be Ac 1 point or higher in heating is 10 seconds or less .
2. The induction heating device that heats part or all of the thick steel plate to Ac 1 point or more is a solenoid induction heating device, and the frequency when heating with the solenoid induction heating device is 1000 Hz or more, and the energy density is the preceding induction heating. The method for tempering a thick steel plate according to claim 1, wherein the method is equal to or greater than that of the apparatus.

本発明によれば、厚鋼板製造における熱処理時間が短縮され、且つ板厚方向の材質均一性に優れる厚鋼板が得られ、産業上極めて有用である。   According to the present invention, it is possible to obtain a thick steel plate that shortens the heat treatment time in the production of the thick steel plate and is excellent in material uniformity in the plate thickness direction, which is extremely useful industrially.

本発明は鋼板を複数の誘導加熱装置を通過させて加熱し、少なくとも最後に通過する誘導加熱装置における加熱で所定の温度とすることを特徴とする焼戻し処理方法である。   The present invention is a tempering method characterized in that a steel sheet is heated by passing through a plurality of induction heating devices, and is heated to a predetermined temperature at least in the induction heating device that passes last.

図１は、本発明に係る焼戻し処理方法の実施に好適な厚板熱処理ラインを説明する図で、（ａ）は前加熱を実施中の厚板熱処理ライン、（ｂ）は最終加熱を実施中の厚板熱処理ラインを示し、図において１ａ，１ｂは後段の誘導加熱装置、２ａ，２ｂは前段の誘導加熱装置、３は被加熱鋼板、４は放射温度計、矢印ａは被加熱鋼板の搬送方向、ｂはパスラインを示す。尚、本発明において前段は上流側、後段は下流側を意味し、誘導加熱装置が前段、後段に各１台が配置される場合も含み、前段と後段の誘導加熱装置の台数に特に制限はない。   FIG. 1 is a diagram for explaining a thick plate heat treatment line suitable for carrying out the tempering method according to the present invention, where (a) is a thick plate heat treatment line during preheating, and (b) is during final heating. 1a and 1b are induction heating devices in the subsequent stage, 2a and 2b are induction heating devices in the previous stage, 3 is the steel plate to be heated, 4 is the radiation thermometer, and arrow a is the conveyance of the steel plate to be heated. Direction, b indicates a pass line. In the present invention, the preceding stage means the upstream side and the subsequent stage means the downstream side, including the case where one induction heating device is disposed in each of the preceding stage and the subsequent stage, and the number of induction heating devices in the preceding stage and the subsequent stage is not particularly limited. Absent.

図示した厚板熱処理ラインは複数の誘導加熱装置２ａ，２ｂ，１ａ，１ｂを所定の間隔を設けて配置し、前段の加熱を行う誘導加熱装置２ａ、２ｂの入側と出側、後段の加熱を行う誘導加熱装置１ａ、１ｂの入側、出側に鋼板表面の温度を測定する放射温度計４を其々配置する。   In the illustrated plate heat treatment line, a plurality of induction heating devices 2a, 2b, 1a, 1b are arranged at predetermined intervals, and the heating and heating of the induction heating devices 2a and 2b for heating the former stage are performed. The radiation thermometer 4 which measures the temperature of the steel plate surface is arrange | positioned at the entrance side and exit side of the induction heating apparatus 1a and 1b which perform this, respectively.

被加熱鋼板３は、所定の間隔を設けて配置された複数の誘導加熱装置２ａ，２ｂと１ａ，１ｂによって、パスラインｂ上を通過しながら加熱される。   The steel plate 3 to be heated is heated while passing over the pass line b by a plurality of induction heating devices 2a, 2b and 1a, 1b arranged at predetermined intervals.

本発明に係る厚鋼板の誘導加熱方法では、前段の誘導加熱装置２ａ，２ｂによる加熱は、目標加熱温度をＡｃ１点以下とし、後段の誘導加熱装置１ａ，１ｂによる加熱は、目標加熱温度をＡｃ１点以上とする。 In the induction heating method of the thick steel plate according to the present invention, the heating by the induction heating devices 2a and 2b in the first stage sets the target heating temperature to Ac 1 point or less, and the heating by the induction heating devices 1a and 1b in the latter stage sets the target heating temperature. Ac 1 point or more.

前段の誘導加熱装置２ａ，２ｂによる加熱は、後段の誘導加熱装置１ａ，１ｂによる、目標加熱温度をＡｃ１点以上とする加熱を行う際の誘導加熱装置への負荷を軽減し、被加熱鋼板３がＡｃ１点以上に加熱される時間を短縮するための、前加熱で４００〜６００℃を目標加熱温度とする。 The heating by the induction heating devices 2a and 2b in the first stage reduces the load on the induction heating device when performing the heating with the target heating temperature of Ac 1 point or more by the induction heating devices 1a and 1b in the subsequent stage, and the steel sheet to be heated 400 to 600 ° C. is set as the target heating temperature in the preheating for shortening the time during which 3 is heated to the Ac1 point or higher.

前段の誘導加熱装置２ａ，２ｂによる加熱は、可能な限り被加熱鋼板３の温度を高温とし、且つ鋼板の板厚方向の温度が均一となるように加熱条件を選定する。   For the heating by the induction heating devices 2a and 2b in the previous stage, the heating conditions are selected so that the temperature of the heated steel plate 3 is as high as possible and the temperature in the plate thickness direction of the steel plate is uniform.

後段の誘導加熱装置１ａ，１ｂによる加熱は、水冷などにより硬化した鋼板表面を軟化させ、板厚方向の材質を一様にするため、板厚目標加熱温度をＡｃ１点以上とし、被加熱鋼板３の一部または全部をＡｃ１点以上に加熱するが、Ａｃ１点以上に加熱される時間は材質劣化を防止するため１０秒以下とする。 Subsequent induction heating device 1a, the heating by 1b, to soften the hardened steel surface by water-cooling, in order to uniform the thickness direction of the material, the thickness target heating temperature was Ac 1 point or more, the heated steel sheet 3 of some or all heating above Ac 1 point, but the time to be heated above Ac 1 point is not more than 10 seconds to prevent the material deterioration.

前段の誘導加熱装置２ａ，２ｂによる加熱の際、一時的に鋼板表面温度がＡｃ１点を超える場合は、当該表面温度を超える時間を加算し、得られた合計時間が１０秒以下となるように後段の誘導加熱装置１ａ，１ｂによる加熱条件を調整する。 When heating with the induction heating devices 2a, 2b in the previous stage, if the steel plate surface temperature temporarily exceeds Ac 1 point, the time exceeding the surface temperature is added, and the total time obtained is 10 seconds or less. The heating conditions by the subsequent induction heating devices 1a and 1b are adjusted.

後段の誘導加熱装置１ａ，１ｂはソレノイド型誘導加熱装置を用い、周波数を１０００Ｈｚ以上、望ましくは４０００Ｈｚ以上で加熱する。   The induction heating devices 1a and 1b in the subsequent stage use solenoid type induction heating devices, and heat them at a frequency of 1000 Hz or more, preferably 4000 Hz or more.

目標加熱温度をＡｃ１点以上として加熱すると、鋼板表面温度が磁気変態点を超えた段階で、比透磁率が低下し、加熱効率が低下する。実験によれば、厚鋼板の誘導加熱では磁気変態点以下では比透磁率μｒが３〜１０であったものが、磁気変態点を超えると１となる。 When the target heating temperature is set at Ac 1 point or higher, the relative magnetic permeability is lowered and the heating efficiency is lowered when the steel sheet surface temperature exceeds the magnetic transformation point. According to the experiment, in the induction heating of the thick steel plate, the relative permeability μr is 3 to 10 below the magnetic transformation point, and becomes 1 when the magnetic transformation point is exceeded.

従って、加熱効率（電流の流れる空間分布、すなわち、スキンデプスで周波数ｆと比透磁率μｒの積）を一定とするため、磁気変態点以下の加熱で１０００Ｈｚの高周波とした場合、磁気変態点超えの加熱では３０００〜５０００Ｈｚとする。尚、高周波となるほど、水焼入れなどで硬化した鋼板表面が効果的に加熱されて好ましい。   Therefore, in order to keep the heating efficiency (space distribution through which current flows, that is, the product of the frequency f and the relative permeability μr at skin depth) constant, when the heating is below the magnetic transformation point and the high frequency is 1000 Hz, the magnetic transformation point is exceeded. In this heating, the frequency is set to 3000 to 5000 Hz. In addition, the higher the frequency, the more effectively the surface of the steel sheet hardened by water quenching or the like is effectively heated.

本発明は、鋼板がＡｃ１点を超えて加熱されても、短時間の場合、材質上の劣化が実用上無視できる程度であることを利用して、前段の誘導加熱装置２ａ，２ｂによる加熱や後段の誘導加熱装置１ａ，１ｂによる加熱条件を、所定温度に達するまでの昇温速度が速くなるように設定するので、熱処理時間が短縮される。 The present invention uses the fact that the deterioration of the material is practically negligible in a short time even when the steel sheet is heated to exceed Ac 1 point, and heating by the induction heating devices 2a and 2b in the previous stage is used. In addition, since the heating conditions by the induction heating devices 1a and 1b at the subsequent stage are set so that the temperature rising rate until reaching the predetermined temperature is increased, the heat treatment time is shortened.

また、前工程の水冷工程から搬出された鋼板が、直ちに前段の誘導加熱装置に搬入できるように、前段や最後の誘導加熱装置による加熱条件を調整すると生産性が向上して望ましい。   In addition, it is desirable to improve the productivity by adjusting the heating conditions of the previous and last induction heating devices so that the steel sheet unloaded from the previous water cooling step can be immediately carried into the previous induction heating device.

図１に示した厚板熱処理ラインを用いて、スラブ厚２５０ｍｍから板厚４０ｍｍに熱間圧延後、水冷を施した厚鋼板に焼戻し処理を施した。後段の誘導加熱装置１ａ，１ｂはソレノイド型誘導加熱装置とした。   Using the thick plate heat treatment line shown in FIG. 1, the hot-rolled thick steel plate was tempered after hot rolling from a slab thickness of 250 mm to a plate thickness of 40 mm. The latter induction heating devices 1a and 1b were solenoid type induction heating devices.

水冷後の鋼板温度は３００℃で、前段の誘導加熱装置２ａ，２ｂの目標加熱温度は５００℃とした。誘導加熱装置２ａ，２ｂによる加熱は、鋼板への投入電力密度（エネルギー密度）は３ＭＷ／ｍ２から１ＭＷ／ｍ２と順次低下させて均熱し、約８０秒で目標温度まで加熱した。 The steel plate temperature after water cooling was 300 ° C, and the target heating temperature of the induction heating devices 2a and 2b in the previous stage was 500 ° C. In the heating by the induction heating devices 2a and 2b, the input power density (energy density) to the steel plate was gradually decreased from 3 MW / m 2 to 1 MW / m 2 and soaked, and heated to the target temperature in about 80 seconds.

次に、後段の誘導加熱装置１ａ，１ｂで、目標加熱温度を８００℃として加熱を行った。周波数は１０００Ｈｚで、鋼板への投入電力は最大出力とし、出力調整は行わなかった。加熱当初、３ＭＷ／ｍ２であったものが、鋼板温度が磁気変態点を超え始めると鋼板の磁気特性に影響されて低下し、ソレノイド型誘導加熱装置１の加熱目標温度８００℃になった時点で、約２ＭＷ／ｍ２となった。 Next, heating was performed at a target heating temperature of 800 ° C. in the induction heating apparatuses 1a and 1b at the subsequent stage. The frequency was 1000 Hz, the input power to the steel plate was the maximum output, and the output was not adjusted. When heating was initially 3 MW / m 2 , but when the steel sheet temperature began to exceed the magnetic transformation point, it was affected by the magnetic properties of the steel sheet and decreased to reach the heating target temperature of 800 ° C. of the solenoid induction heating apparatus 1 Thus, it was about 2 MW / m 2 .

前段の誘導加熱装置２ａ，２ｂによって、加熱前の鋼板温度が一定に保たれるため、一定の送り速度で全長方向に均一な加熱が実現された。   Since the steel plate temperature before heating is kept constant by the induction heating devices 2a and 2b in the previous stage, uniform heating is realized in the full length direction at a constant feed rate.

図２に、前段の誘導加熱装置２ａ，２ｂ、後段の誘導加熱装置１ａ，１ｂの加熱による、鋼板特定部分における温度の時間的変化を示す。また、図３に焼戻し処理後の板厚方向の硬度分布を示す。尚、図において６００℃熱処理材は後段の誘導加熱装置１ａ，１ｂでの目標加熱温度を６００℃としたものである。   FIG. 2 shows temporal changes in temperature at a specific portion of the steel sheet due to heating by the induction heating devices 2a and 2b in the previous stage and the induction heating devices 1a and 1b in the subsequent stage. FIG. 3 shows the hardness distribution in the thickness direction after tempering. In the figure, the heat treatment material at 600 ° C. has a target heating temperature of 600 ° C. in the induction heating devices 1a and 1b in the subsequent stage.

図３より、本発明の焼戻し熱処理方法によれば、板厚方向に均一な鋼板の硬度分布が得られることが確認できた。尚、機械的特性は、６００℃熱処理材と本発明材では差がなかった。表面温度を放射温度計４で測定したところ、表面がＡｃ１点を超えた時間は８秒であった。 From FIG. 3, according to the tempering heat treatment method of the present invention, it was confirmed that a uniform steel plate hardness distribution was obtained in the plate thickness direction. The mechanical properties were not different between the heat-treated material at 600 ° C. and the material of the present invention. When the surface temperature was measured by the radiation thermometer 4, the time when the surface exceeded Ac 1 point was 8 seconds.

本実施例では、全長２０ｍの鋼板を加熱するのに６０秒を要し、加熱後に板厚で一様な温度になった時、板温が６３０℃であり、Ａｃ１点を超えた部分は板表面近傍であった。 In this example, it took 60 seconds to heat a steel plate having a total length of 20 m. When the plate thickness became uniform after heating, the plate temperature was 630 ° C., and the portion exceeding Ac 1 point was It was near the plate surface.

実施例１と同じ供試材を、前段の誘導加熱装置２ａ，２ｂに替えて雰囲気炉を用いて６００℃まで加熱後、後段の誘導加熱装置１ａ，１ｂで加熱して焼戻し処理を行った。   The same specimen as in Example 1 was heated to 600 ° C. using an atmospheric furnace instead of the preceding induction heating devices 2a and 2b, and then tempered by heating with the subsequent induction heating devices 1a and 1b.

後段の誘導加熱装置１ａ，１ｂでＡｃ１以上に加熱し、得られた鋼板は実施例１と同等の硬度分布であったが、６００℃まで加熱するのに約１時間を要し、能率を阻害した。 The subsequent steel plate was heated to Ac 1 or higher by induction heating devices 1a and 1b, and the obtained steel sheet had a hardness distribution equivalent to that of Example 1. However, it took about 1 hour to heat up to 600 ° C., and the efficiency was improved. Inhibited.

次に、雰囲気炉を１２００℃と高温に設定し、加熱時間を短縮したところ、炉内の温度分布に応じて、後段の誘導加熱装置１ａ，１ｂの加熱で、鋼板温度がＡｃ１を超えた所と超えなかった所ができた。 Next, when the atmosphere furnace was set to a high temperature of 1200 ° C. and the heating time was shortened, the steel sheet temperature exceeded Ac 1 due to the heating of the induction heating devices 1a and 1b in the subsequent stage according to the temperature distribution in the furnace. There was a place that did not exceed.

このため、水冷後に鋼板を一旦オフラインして、熱電対を多数設置し、同様の熱処理を施したところ、Ａｃ１を超えた累積時間が１０秒を超えていないと予想される場所は、実施例１と同等の材質が得られたが、超えたと予想される場所では材質劣化を生じていた。 For this reason, when the steel sheet was taken offline after water cooling, a number of thermocouples were installed, and the same heat treatment was performed, the place where the accumulated time exceeding Ac 1 is expected not to exceed 10 seconds is Although a material equivalent to 1 was obtained, the material was deteriorated at the place where it was expected to exceed.

従って、後段の誘導加熱装置１ａ，１ｂの前段において鋼板を加熱する装置は誘導加熱装置とする。   Therefore, the apparatus for heating the steel plate in the former stage of the latter induction heating apparatuses 1a and 1b is an induction heating apparatus.

本発明の適用に好適な厚板熱処理ラインを説明する図。The figure explaining the thick board heat processing line suitable for application of this invention. 本発明例Example of the present invention 本発明例Example of the present invention

符号の説明Explanation of symbols

１ａ，１ｂ 後段の誘導加熱装置
２ａ，２ｂ 前段の誘導加熱装置
３ 被加熱鋼板
４ 放射温度計
ａ 被加熱鋼板の搬送方向を示す矢印
ｂ パスライン 1a, 1b Subsequent induction heating device 2a, 2b Previous induction heating device 3 Heated steel plate 4 Radiation thermometer a Arrow indicating the conveyance direction of the heated steel plate b Pass line

Claims (2)

厚鋼板が搬送ライン上の複数の誘導加熱装置を上流側から下流側に通過して所定の温度に加熱される厚鋼板の焼戻し処理方法であって、厚鋼板をＡｃ１点未満に加熱する前段の焼戻し処理と厚鋼板の一部または全部をＡｃ１点以上に加熱する後段の焼戻し処理を備え、後段の焼戻し処理は少なくとも最後に通過する誘導加熱装置によるものであり、複数の誘導加熱装置による加熱において、厚鋼板がＡｃ １ 点以上となる加熱時間の合計が１０秒以下であることを特徴とする厚鋼板の焼戻し処理方法。 A method of tempering a thick steel plate in which the thick steel plate passes through a plurality of induction heating devices on a conveyance line from the upstream side to the downstream side and is heated to a predetermined temperature, and is a pre-stage for heating the thick steel plate to less than Ac 1 point. Tempering treatment and a subsequent tempering treatment in which a part or all of the thick steel plate is heated to Ac 1 point or more, and the latter tempering treatment is at least by an induction heating device that passes last, and by a plurality of induction heating devices. A tempering method for a thick steel plate, characterized in that the total heating time for the thick steel plate to be Ac 1 point or higher in heating is 10 seconds or less . 厚鋼板の一部または全部をＡｃ１点以上に加熱する誘導加熱装置がソレノイド型誘導加熱装置で、前記ソレノイド型誘導加熱装置で加熱する際の周波数が１０００Ｈｚ以上で、エネルギー密度が前段の誘導加熱装置と同等以上であることを特徴とする請求項１記載の厚鋼板の焼戻し処理方法。 The induction heating device that heats part or all of the thick steel plate to Ac 1 point or more is a solenoid induction heating device, and the frequency when heating with the solenoid induction heating device is 1000 Hz or more, and the energy density is the preceding induction heating. The method for tempering a thick steel plate according to claim 1, wherein the method is equal to or greater than that of the apparatus.
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