JP4923390B2 - Heat treatment apparatus and steel material manufacturing method - Google Patents

Description

  The present invention relates to a technique for heat-treating a steel material using an induction heating device.

  In the iron and steel process, various heat treatments such as quenching, tempering, and annealing are performed in order to improve properties such as strength and toughness of a steel material as a product, and to produce a stronger and tenacious steel material. These heat treatments are generally divided into a heating process and a cooling process. Among these, in the heating process, the transformation point temperature corresponding to the component of the steel material is the standard. For example, in the case of quenching, it must be heated to a temperature higher than the transformation point, and in the tempering and annealing, heating must be performed so as not to reach the transformation point.

  Therefore, it is necessary to heat accurately according to the purpose of heat treatment. Moreover, in order to suppress the dispersion | variation in quality within the same member, it is necessary to heat uniformly over the inside of steel materials. This heat treatment method is called uniform heating.

  In addition, steel materials that have been subjected to quenching and tempering heat treatment that are generally manufactured are subject to cooling mainly from the surface, and therefore the surface hardness tends to be higher than the inside. It is known that steel materials having such a hardness distribution in the thickness direction are vulnerable to corrosive environments and are prone to stress corrosion cracking (HIC) due to hydrogen sulfide when used in oil and natural gas pipelines. .

  Therefore, there is a case where the surface layer portion is softened by heating at a high temperature to reduce the hardness difference between the surface layer portion and the inside. This heat treatment method is called surface layer heating.

Conventionally, as a heating method for realizing these heating conditions, an induction heating device is used to heat the steel material in an induction heating furnace, and the steel is heated at a higher frequency than the heating stage and at a lower input power. An induction heating method has been proposed in which a quasi-heating stage is provided between the soaking stage and the induction heating at the same frequency as the induction heating in the heating stage, and the induction heating is performed by lowering the input power than the heating stage (for example, patents) Reference 1).
Japanese Patent Laid-Open No. 9-170021

  However, the technique disclosed in Patent Document 1 is not efficient because the heating time requires several tens of minutes. Moreover, since the frequency of the induction heating device is changed during the heating of the steel material, it is necessary to equip a mechanism for switching the frequency. Therefore, the apparatus becomes expensive and the structure of the apparatus becomes complicated. In addition, the calculation of input power for heating steel materials takes into account factors such as the induction current distribution inside the steel materials, heat removal by the atmosphere, efficiency of the heating device, specific heat of the steel materials, etc., which are necessary for achieving accurate temperature control. It has not been.

  For this reason, the idea of heat treatment on a rolling line using an induction heating apparatus has existed in the past, but has not been put to practical use. In addition to hardware problems such as lack of induction heating capability, there were also problems in software such as a problem solving method on how to specifically solve the heat treatment method. In order to perform the heat treatment, it is necessary to heat uniformly without making a temperature difference in the longitudinal direction and the thickness direction. For this purpose, it is necessary to accurately estimate the internal temperature of the steel during induction heating, and it is necessary to obtain the power for heating using this temperature estimation model. Furthermore, since the power during heating varies depending on the temperature before heating, it is necessary to perform these processes online. However, there is almost no literature which examined the calculation method of electric power and the method of determining the conveyance speed that gave a clear answer to these problems.

  The present invention has been made in view of such circumstances, and it is possible to accurately match the surface temperature and internal temperature of a steel material with a target, and to perform a heat treatment so that the steel material has desired properties. It is to provide a manufacturing method. In particular, in order to solve the above-described problem, the heat treatment efficiency is not affected without applying a calculation processing load.

The heat treatment apparatus according to claim 1 according to the present invention is a plurality of induction heating apparatuses installed on a rolling line of steel material and arranged at a subsequent stage of an accelerated cooling device that rapidly cools the rolled steel material, A straightening device for straightening the steel material installed between the accelerated cooling device and the plurality of induction heating devices on the steel material rolling line, and a temperature of the steel material installed on the rolling line are detected. At least one temperature detector, a size of the steel material, a conveying speed of the steel material, a heating target temperature of the steel material, and an actual temperature measured by the temperature detector of the steel material in a stage preceding the induction heating device, A calculation device that calculates the planned supply power to be supplied to the induction heating device, and a power supply device that supplies the planned supply power calculated by the calculation device to the induction heating device. The surface temperature of the steel material being heated by the induction heating device is equal to or lower than the first target temperature, and the difference between the temperature at a predetermined position inside the steel material thickness direction at the end of heating and the second target temperature is within a predetermined range. Power to be supplied to the induction heating device for heating so as to be inside, or the surface temperature of the steel material at the end of heating by the induction heating device is equal to or higher than a third target temperature, and the thickness direction of the steel material being heated The scheduled power supply to be supplied to the induction heating device is calculated for heating so that the temperature at a predetermined internal position is equal to or lower than the fourth target temperature.

Moreover, the heat processing apparatus of Claim 2 which concerns on this invention is the heat processing apparatus which is the said invention, The said arithmetic unit is a steel material after a heating based on the said steel material temperature measured with the said conveyance speed and the said temperature detector. and estimating means for estimating a temperature, when the estimated steel temperature is not within a predetermined temperature range, and repeating means to execute and repeat the estimation means by changing the conveying speed, estimated steel temperature is a predetermined temperature When it is within the range, it has power calculating means for calculating the supply power to be supplied to the induction heating device in order to heat the steel material to a target temperature based on the conveying speed.

The heat treatment apparatus according to a third aspect of the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is configured to calculate the steel material after induction heating from data including a conveyance speed of the steel material and the power to be supplied. Temperature estimation means for estimating the surface temperature and the internal temperature in the thickness direction, conformity determination means for determining whether or not the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature condition If the temperature condition is not satisfied, the temperature supply is corrected and the temperature estimation means and the fitness determination means are repeatedly executed. And a power determining unit that uses the scheduled power supply as power to be supplied to the induction heating device.

The heat treatment apparatus according to a fourth aspect of the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit calculates the steel material after induction heating based on data including a conveyance speed of the steel material and the power to be supplied. Temperature estimation means for estimating the surface temperature and the internal temperature in the thickness direction, conformity determination means for determining whether or not the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature condition If the temperature condition is not satisfied, the temperature supply is corrected and the temperature estimation means and the fitness determination means are repeatedly executed. On the basis of the planned supply power, it is determined whether or not the total power amount of each induction heating device used for heating the steel material meets a power condition that is a predetermined value or less. A force determination means, if it conforms to the power condition, a power determining unit that the power supplies supply scheduled power used for the operation on the induction heating device, not fit to the power condition, the supply Power condition determination processing means for correcting scheduled power and repeatedly executing the temperature estimation means and the conformity determination means .

The heat treatment apparatus according to claim 5 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is configured to calculate the steel material after induction heating from data including a conveyance speed of the steel material and the scheduled power supply. Temperature estimation means for estimating the surface temperature and the internal temperature in the thickness direction, conformity determination means for determining whether or not the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature condition If the temperature condition is not satisfied, the temperature supply is corrected by correcting the scheduled power supply and the temperature estimation means and the fitness determination means are repeatedly executed. If the temperature condition is satisfied, the temperature condition is satisfied. Among the planned supply power to be supplied, the planned supply power that minimizes the total amount of power of each induction heating device used for heating the steel material is the power supplied to the induction heating device. And a power determining unit.

  Moreover, the heat processing apparatus of Claim 6 which concerns on this invention is a heat processing apparatus which is the said invention, The said arithmetic unit is temperature which estimates the temperature distribution of the thickness direction of the said steel materials after the heating by the said induction heating apparatus. Distribution estimation means is further provided.

  Further, the heat treatment apparatus according to claim 7 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the temperature distribution estimation means is configured such that the steel material in the induction heating device is based on a conveyance speed of the steel material. A calorific value calculation means for calculating the amount of heat generated inside the steel material by obtaining an induction current distribution in the thickness direction, a radiated heat amount calculation means for calculating a radiated heat amount from the steel material to the atmosphere outside the induction heating apparatus, and the generated heat amount Temperature calculating means for calculating the surface temperature of the steel material and the internal temperature in the thickness direction by calculating the heat conduction to the inside of the steel material with the amount of heat dissipated as the boundary condition.

  The heat treatment apparatus according to claim 8 of the present invention is the heat treatment apparatus according to the above invention, wherein the temperature distribution estimation means estimates a temperature drop amount in the thickness direction of the steel material by the straightening device. Have means.

Moreover, the heat processing apparatus of Claim 9 which concerns on this invention is the heat processing apparatus which is the said invention, The said arithmetic unit was used for the heating of the said steel materials corresponding to each position of the longitudinal direction of the said steel materials It further has a heating history management means for managing the history of the electric power and the temperature detection value of the steel material.

  The heat treatment apparatus according to claim 10 of the present invention is the heat treatment apparatus according to the invention described above, wherein the top portion of the steel material detected by the temperature detector provided on the entrance side of the first stage induction heating apparatus. The target temperature calculation means for calculating the heating target temperature for each induction heating device for the head portion and the rear end portion of the steel material based on the temperature of the steel material, the measured temperature or estimated temperature of the rear end portion, and the conveying speed of the steel material And, at the head portion and the rear end portion of the steel material, the power supplied to each induction heating device is calculated based on the heating target temperature, and the power is adjusted in accordance with the movement of the head portion and the rear end portion of the steel material. Power supply means for controlling the power supply device and an intermediate portion sandwiched between the head portion and the rear end portion of the steel material, the measured temperature of the front portion of the steel material and the measured temperature of the rear end portion Alternatively, based on the estimated temperature and the measured or estimated temperature of the intermediate portion, the heating target temperature for each induction heating device of the top portion and the rear end portion of the steel material is corrected, and the induction heating device for each intermediate portion is corrected. Intermediate part target temperature calculation means for calculating the heating target temperature, and intermediate power supplied to each induction heating device based on the heating target temperature for each induction heating device of the intermediate part, and movement of the intermediate part of the steel material And intermediate power control means for controlling the intermediate power and supplying the intermediate power to the power supply device.

The heat treatment apparatus according to an eleventh aspect of the present invention is the heat treatment apparatus according to the above-described invention, wherein the temperature detector is provided before and after at least one of the induction heating devices, and the arithmetic device includes the induction device. Heating efficiency estimating means for estimating the heating efficiency of the induction heating device based on the electric power supplied to the heating device and the temperature rise of the steel material measured by the temperature detector, and then obtained for the steel material to be heat treated Correction calculating means for correcting the calculated power using the heating efficiency.

The heat treatment apparatus according to claim 12 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is a temperature drop that corrects an amount of heat dissipated into the atmosphere of the steel material in the rolling line by an actually measured temperature . Cooling for calculating a supply power for heating the steel material to a target temperature based on the amount of temperature drop estimated by the corrected amount of heat dissipated for the steel material to be heat treated next and the amount correction means Correction power calculation means.

  Moreover, the heat processing apparatus of Claim 13 which concerns on this invention is a heat processing apparatus which is the said invention, The said arithmetic unit is the temperature reduction amount by the said correction apparatus of the said steel materials in the said rolling line. Based on the temperature drop amount in the corrected straightening device, with respect to the steel material to be heat treated next, the temperature drop amount correction means for correcting by the actual temperature measured by the temperature detectors installed before and after, Cooling correction power calculation means for calculating a planned supply power for heating the steel material to a target temperature.

  The heat treatment apparatus according to claim 14 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the steel material has at least one temperature detector between the induction heating devices and is measured by the temperature detector. Feedback control means for controlling the power supplied to the induction heating device in the previous stage based on the difference between the temperature and the target temperature at the position given in advance, and the steel material temperature measured by the temperature detector, The apparatus further comprises feedforward control means for controlling the power supplied to the induction heating device at the subsequent stage based on the difference from the target temperature at that position.

  The heat treatment apparatus according to claim 15 of the present invention is the heat treatment apparatus according to the invention described above, wherein the steel material temperature measured by the temperature detector corresponding to each position in the longitudinal direction of the steel material is given in advance. The electric power supplied to the preceding induction heating device is controlled based on the difference from the target temperature at that position.

The heat treatment apparatus according to claim 16 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the feedforward control means is measured by the temperature detector corresponding to each position in the longitudinal direction of the steel material. The electric power supplied to the induction heating device at the subsequent stage is controlled based on the difference between the steel material temperature and the target temperature at the position given in advance.

A heat treatment apparatus according to claim 17 of the present invention includes a plurality of induction heating apparatuses that heat steel materials, and a correction apparatus that is installed in front of the plurality of induction heating apparatuses and that corrects the steel materials. Based on the size of the steel material, the conveyance speed of the steel material, the target heating temperature of the steel material, and the planned temperature of the steel material in the previous stage of the induction heating device, the planned supply power to be supplied to the induction heating device is An arithmetic device that calculates, and a power supply device that supplies the planned heating power calculated by the arithmetic device to the induction heating device, wherein the arithmetic device has a surface temperature of the steel being heated by the induction heating device. Supply to the induction heating device for heating so that the difference between the temperature at a predetermined position in the thickness direction of the steel material at the end of heating and the second target temperature is within a predetermined range at or below the first target temperature. The planned power or the surface temperature of the steel material at the end of heating by the induction heating device is equal to or higher than the third target temperature, and the temperature at a predetermined position inside the thickness direction of the steel material being heated is equal to or lower than the fourth target temperature. The power to be supplied to the induction heating device for heating is calculated.

The heat treatment apparatus according to claim 18 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the induction heating device is installed on a rolling line of the steel material and is rapidly moved by an accelerated cooling device after rolling. The steel material cooled and further straightened by the straightening device is heated.

  Moreover, the heat processing apparatus of Claim 19 which concerns on this invention is a heat processing apparatus which is the above-mentioned invention. WHEREIN: The conveyance speed of the said steel materials is a conveyance speed predetermined based on the size of the said steel materials.

Further, the heat treatment apparatus according to claim 20 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is the steel material after induction heating from data including a conveyance speed of the steel material and the planned supply power. Temperature estimation means for estimating the surface temperature of the steel and the internal temperature in the thickness direction, conformity determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature If the condition is not met, use the temperature condition determination processing means for correcting the scheduled power supply and executing the temperature estimation means and the suitability determination means repeatedly; Power determining means for using the supplied scheduled power to be supplied to the induction heating device.

The heat treatment apparatus according to claim 21 according to the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is configured to calculate the steel material after induction heating from data including a conveyance speed of the steel material and the power to be supplied. Temperature estimation means for estimating the surface temperature of the steel and the internal temperature in the thickness direction, conformity determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature If the condition is not met, use the temperature condition determination processing means for correcting the scheduled power supply and executing the temperature estimation means and the suitability determination means repeatedly; Based on the supplied power to be supplied, it is determined whether or not the total power amount of each induction heating device used for heating the steel material meets a power condition that is equal to or less than a predetermined value. A power amount determination unit that, if it conforms to the power condition, a power determining unit that the power supplies supply scheduled power used for the operation on the induction heating device, not fit to the power condition, Power condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the conformity determination means .

The heat treatment apparatus according to claim 22 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is configured to calculate the steel material after induction heating from data including a conveyance speed of the steel material and the power to be supplied. Temperature estimation means for estimating the surface temperature of the steel and the internal temperature in the thickness direction, conformity determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature If the condition is not satisfied, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the conformity determination means; and if the temperature condition is satisfied, the temperature condition is The power to supply the induction heating device with the planned supply power that minimizes the total power amount of the induction heating devices used for heating the steel material among the appropriate supply power to be supplied. And a power determining means to.

  Moreover, the heat processing apparatus of Claim 23 which concerns on this invention is a heat processing apparatus which is the said invention, The said arithmetic unit is temperature which estimates the temperature distribution of the thickness direction of the said steel materials after the heating by the said induction heating apparatus. A distribution estimation means is further provided.

  The heat treatment apparatus according to claim 24 of the present invention is the heat treatment apparatus according to the invention described above, wherein the temperature distribution estimation means obtains an induction current distribution in the thickness direction of the steel material in the induction heating apparatus. The generated heat amount calculating means for calculating the generated heat amount inside the steel material, the dissipated heat amount calculating means for calculating the dissipated heat amount from the steel material to the atmosphere outside the induction heating device, and the generated heat amount and the dissipated heat amount as boundary conditions. Temperature calculating means for calculating the heat conduction to the inside of the steel material and estimating the surface temperature of the steel material and the internal temperature in the thickness direction.

  The heat treatment apparatus according to claim 25 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the temperature distribution estimation means estimates a temperature drop amount in the thickness direction of the steel material by the straightening device. Have means.

The heat treatment apparatus of claim 26 according to the present invention, in the invention a is a heat treatment device described above, the arithmetic unit divides the steel in the longitudinal direction of the plurality of virtual partitions, in this compartment units It further has a heating history management means for managing the history of the electric power used for heating the steel material and the temperature detection value of the steel material.

Moreover, the heat treatment apparatus according to claim 27 of the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is configured to calculate the steel material after induction heating from data including a conveyance speed of the steel material and the power to be supplied. Temperature estimation means for estimating the surface temperature of the steel and the internal temperature in the thickness direction, conformity determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature If the condition is not satisfied, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the conformity determination means; and if the temperature condition is satisfied, the temperature condition is A power determination unit configured to supply power to be supplied to the induction heating device as power to be supplied to the induction heating device, which is the maximum supply speed of the steel material among the suitable power supply to be supplied

Further, the heat treatment apparatus according to claim 28 according to the present invention is the heat treatment apparatus according to the above-described invention, wherein the arithmetic unit is configured to calculate the steel material after induction heating from data including a conveyance speed of the steel material and the power to be supplied. Temperature estimation means for estimating the surface temperature of the steel and the internal temperature in the thickness direction, conformity determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition, and the temperature If the condition is not met, use the temperature condition determination processing means for correcting the scheduled power supply and executing the temperature estimation means and the suitability determination means repeatedly; Based on the supplied power to be supplied, it is determined whether or not the total power amount of each induction heating device used for heating the steel material meets a power condition that is equal to or less than a predetermined value. A power amount determination unit that, if it conforms to the power condition, the temperature estimating means uses the new conveying speed increases the transport speed, the adaptation judgment unit, the temperature condition determination processing unit, wherein the power amount determination repeatedly running means until no conform to the temperature condition, the conveying speed calculating means for acquiring the transport speed used for matching the final operation to the power condition and the temperature condition as the new transport speed, the power If the condition is not met, the apparatus has power condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means .

Moreover, the heat treatment apparatus according to claim 29 according to the present invention includes a plurality of induction heating apparatuses installed on a steel material rolling line and arranged at a subsequent stage of an accelerated cooling apparatus that rapidly cools the rolled steel material. A straightening device for straightening the steel material installed between the accelerated cooling device and the plurality of induction heating devices on the steel material rolling line; and a temperature of the steel material installed on the rolling line. The induction based on at least one temperature detector to be detected, the size of the steel material, the conveying speed of the steel material, the target heating temperature of the steel material, and the expected temperature of the steel material in the previous stage of the induction heating device. A first computing device that computes a first scheduled power to be supplied to the heating device, a size of the steel material, a conveyance speed of the steel material, a heating target temperature of the steel material, and a preceding stage of the induction heating device; Based on the measured temperature measured by the temperature detector of the steel, the induction and the second arithmetic device for calculating a second supply scheduled power supplied to the heating device, the measured temperature of the predetermined temperature and the steel of the steel The first scheduled power supply is selected as the scheduled power supply, and if the difference between the planned temperature of the steel material and the measured temperature of the steel material is not within the predetermined range, the first scheduled power supply is selected. A power selection device that selects the scheduled supply power of 2 as the planned supply power, and a power supply device that supplies the planned supply power selected by the power selection device to the induction heating device, the first and second The arithmetic device is such that the surface temperature of the steel material being heated by the induction heating device is equal to or lower than a first target temperature, and the difference between the temperature at a predetermined position inside the steel material thickness direction at the end of heating and the second target temperature is predetermined. Add to be within range To be supplied to the induction heating device or the surface temperature of the steel material at the end of heating by the induction heating device is equal to or higher than a third target temperature, and the temperature at a predetermined position inside the thickness direction of the steel material being heated. Is calculated to supply power to be supplied to the induction heating device in order to heat so that the temperature becomes equal to or lower than the fourth target temperature.

  A method for manufacturing a steel material according to a thirty-third aspect of the present invention is manufactured by performing a heat treatment using the heat treatment apparatus according to the above-described invention.

  ADVANTAGE OF THE INVENTION According to this invention, the surface temperature of steel materials and internal temperature can be matched with a target accurately, and the heat processing which a steel material has the target property can be performed. Moreover, it becomes possible to provide a uniform temperature distribution in the longitudinal direction of the steel sheet. Furthermore, economical and highly efficient heat treatment can be performed by minimizing electric power and maximizing the conveyance speed.

  In general, a steel material is heated to around 1200 ° C. in a heating furnace, and then hot-rolled to a predetermined size by a rolling mill. In order to improve strength and toughness after rolling, cases of rapid cooling by an accelerated cooling device are increasing. The rapidly cooled steel sheet is tempered and heat-treated in a gas heat treatment furnace as necessary, and then cut and shipped.

  FIG. 1 is a side view showing a schematic configuration of a steel material production line to which the present invention is applied. This steel material production line includes a heating furnace 2 that heats a steel material 1, a rolling mill 3 that performs rough rolling and finishing rolling, an accelerated cooling device 4, a straightening device 5, an induction heating device 6, and a temperature detector that measures the temperature of the steel material 1. 7.

  In this steel material production line, after the rolling process and the cooling process, the straightening device 5 is used to correct the warping and bending of the steel material 1, and then the tempering process is performed by the induction heating device 6 installed on the line.

  In this steel material production line, heat treatment is performed using an induction heating device 6 installed on the line, instead of the conventional heat treatment by the gas combustion furnace installed offline. Therefore, since the tempering process can be performed after the quenching process online, the efficiency can be dramatically improved. Moreover, by using the induction heating device 6, the accuracy of the heating temperature can be increased as compared with the case where a gas combustion furnace is used. Therefore, it is possible to control the temperature distribution in the thickness direction with high accuracy.

  It is essential that the induction heating device 6 has an ability to heat the steel material 1 to a predetermined temperature. When heat treatment on the rolling line is performed using the induction heating device 6, the heat treatment efficiency is inferior to the rolling efficiency due to the conveyance speed limitation of the induction heating device 6, and as a result, productivity may be hindered. Therefore, in order to increase the conveyance speed, it is necessary to increase the number of induction heating devices 6, but the facility becomes large, the cost of equipment and installation space increases, the power consumption increases, and the operating cost also increases. Therefore, it is difficult to apply to actual machines. Therefore, in the present invention, even when the number of the induction heating devices 6 is small, the heating method is performed in which the steel material 1 is reciprocated a plurality of times and heated so that the rolling efficiency is not inferior, productivity is not hindered, and cost is reduced. .

  In this case, it is necessary not only to avoid deteriorating the efficiency of the steel material production line including rolling, but also to improve the temperature control accuracy of the steel material 1. Accordingly, it is necessary to appropriately select the number of reciprocations (the number of passes) and the conveyance speed.

  In addition, the heating method includes surface heating and uniform heating depending on the target steel material 1.

In either case, the surface temperature and the internal temperature of the steel material 1 are heated to different target temperatures. The internal temperature may be an average temperature in the thickness direction (average temperature), a temperature at the center of the thickness (center temperature), or an arbitrary depth from the plate surface (for example, a thickness of 1/3) , 1/4 depth).

  In the case of surface layer heating, the surface temperature at the end of heating is heated to a target temperature or higher. In that case, heating is performed so that the internal temperature during the heating process does not exceed the upper limit temperature. By performing such surface heating, the hardness of the surface can be made the same as the inside, problems in applications such as pipelines can be avoided, and material deterioration due to an excessive increase in internal temperature can be suppressed.

  In the case of uniform heating, heating is performed so that the temperature of the entire steel material (inside) reaches the target temperature range at the end of heating, while preventing the surface temperature during the heating process from exceeding a predetermined value (for example, the Ac1 transformation point). Do. By such uniform heating, it is possible to ensure desired characteristics and suppress quality variations among the same members, and to suppress material changes due to surface overheating.

  In order to perform surface layer heating, the surface is heated to a target temperature before the surface and the internal temperature become uniform by heat transfer from the heated surface to the inside from the induction heating device 6 and heat radiation from the surface. It is necessary. Conversely, in order to perform uniform heating, it is necessary to prepare a plurality of induction heating devices 6 and gradually heat them while repeating the heating process and the cooling process. For example, after passing the steel material through the induction heating apparatus with a plurality of passes, the process of transporting the steel material in the opposite direction and heating again is repeated for the number of designated passes. At this time, while passing through the induction heating device, the vicinity of the surface is heated by the skin effect, and after exiting the induction heating device 6, it becomes a cooling process until it reverses, radiating heat from the surface and entering the inside Due to heat transfer, the surface and internal temperatures become uniform.

In the present invention, both surface heating and uniform heating are performed in accordance with A. Steel inside the induction heating current distribution model, B. A heat transfer model based on the heat conduction equation , C.I. A heat transfer model based on radiation and convection with the atmosphere ; An efficiency estimation model with a learning function that estimates the heating efficiency and reflects it in the next material was created, the temperature change inside the steel material was modeled, and the accuracy of the heat treatment method was improved.

  In the present invention, three variations of heat treatment methods are used in order to improve heat treatment accuracy. In the following description of the embodiment, the contents of these three heat treatment methods will be referred to as appropriate.

  The first heat treatment method corresponds to the invention of claims 1 to 16, the second heat treatment method corresponds to the invention of claims 17 to 28, and the third heat treatment method of claim 29. Corresponds to the invention.

(1) First heat treatment method When performing the above calculation, the steel material temperature after accelerated cooling differs depending on the operation conditions under the same manufacturing conditions. For this reason, the steel material temperature after accelerated cooling or before heating is measured for each steel material, and the heating power, conveyance speed, etc. are determined online based on the measured values, and the heating temperature is set to the target temperature. Match. In the first heat treatment method, a mechanism for further improving accuracy is constructed using this method.

  The first heat treatment method has the following features.

(i) After rolling or accelerating cooling based on the manufacturing conditions of the steel material, the steel material is conveyed to the entrance of the induction heating device.

(ii) The steel material temperature before heating is measured, and the heating power to be given to the induction heating device 6 and the conveying speed of the steel material are determined based on the measured values.

  (iii) The power consumption should be as small as possible.

  (iv) It is necessary to perform heat treatment at a conveyance speed that does not impede operation.

(2) Second heat treatment method When performing the above calculation, the processing capability of the arithmetic processing unit or the like may not be sufficient, and it may take too much calculation load, that is, calculation processing time. In such a case, measuring the temperature of the steel material immediately before the start of heating and then performing the calculation process results in poor heat treatment efficiency and inferior rolling efficiency, which is another online process, and the overall online efficiency. The problem of lowering occurs. In order to avoid this, in the second heat treatment method, a mechanism for determining heating power, conveyance speed, and the like in advance is constructed.

  The second heat treatment method has the following features.

  (i) The starting temperature of induction heating of the steel material is estimated from the manufacturing conditions up to the induction heating device such as rolling and cooling conditions of the steel material.

  (ii) Obtain electric power and conveyance speed that satisfy the target and limit of the heating temperature.

  Furthermore, the following contents are taken into consideration for practical use.

  (iii) The power consumption should be as small as possible.

  (iv) It is necessary to perform heat treatment at a conveyance speed that does not impede operation.

(3) Third heat treatment method In performing the above calculation, the processing capability of the arithmetic processing unit or the like may not be sufficient, and it may take too much calculation load, that is, calculation processing time. In such a case, measuring the temperature of the steel material immediately before the start of heating and then performing the calculation process takes too much time for the calculation process, so the heat treatment efficiency deteriorates, and the rolling efficiency which is another online process Will cause problems that reduce overall online efficiency. In order to avoid this, it is sufficient to build a mechanism that determines the heating power, conveyance speed, etc. in advance, but for that purpose, it is not necessary to measure the steel temperature immediately before the heat treatment, and the rolling and cooling conditions of the steel material. It is necessary to estimate the starting temperature of the induction heating of the steel material from the manufacturing conditions up to the induction heating device.

  However, even under the same manufacturing conditions, the temperature of each steel material after accelerated cooling may vary depending on the operating conditions. For this reason, rather than preparing electric power in advance with a table or the like, the steel material temperature after accelerated cooling or before heating is actually measured for each steel material, and the heating power, conveyance speed, etc., depending on the value, It is necessary to construct a mechanism that improves the accuracy for determining and determining the heating temperature online to match the heating temperature with the target temperature. Therefore, in the third heat treatment method, in order to execute the calculation more efficiently and more accurately, the temperature is predicted in advance, and the predicted temperature is corrected when it differs from the actually measured temperature. Build a mechanism.

  The third heat treatment method has the following features.

  (i) The starting temperature of induction heating of the steel material is estimated from the manufacturing conditions up to the induction heating device such as rolling and cooling conditions of the steel material.

  (ii) Obtain electric power and conveyance speed that satisfy the target and limit of the heating temperature.

  (iii) Measure the steel material temperature before heating, and correct and determine the heating power to be applied to the induction heating device 6, the conveying speed of the steel material, etc. based on the difference between the temperature predicted in advance and the temperature measured immediately before heating. To do.

  Furthermore, the following points are taken into consideration for practical use.

  (iv) The power consumption should be as small as possible.

  (v) It is necessary to perform heat treatment at a conveyance speed that does not impede operation.

  The heat treatment apparatus according to the embodiment of the present invention has the following functions.

  1) In order to accurately estimate the internal temperature of the steel material 1 during induction heating, a differential equation in the thickness direction is adopted, the permeability and penetration depth are estimated from the steel material temperature and power, and the thickness direction induction of the steel material 1 is induced. Obtain the current distribution and estimate the calorific value.

  2) In order to obtain the heating power setting, since there are a plurality of temperature conditions, a plurality of manipulated variables (power), and the model is nonlinear, the calculation is performed by nonlinear programming. As a result, the surface temperature and the internal temperature are not independent variables, but they can be regarded as being independent to some extent by heating multiple units, making it possible to set targets separately.

  3) Using the objective function of nonlinear programming as the sum of power consumption, find the power that minimizes power consumption while satisfying the temperature condition.

  4) After obtaining the power setting at a certain speed, calculation is repeated while changing the transport speed within a heatable range, and the transport speed that does not hinder the operation is obtained while satisfying the temperature condition.

  5) In the first heat treatment method, in order to further improve the accuracy of temperature control, the power and speed are calculated from the measured temperature of the steel material measured with a thermometer at the end of accelerated cooling or immediately before induction heating treatment.

  6) In the second heat treatment method, in order to obtain the power and speed online, the starting temperature of induction heating of the steel material is estimated from the manufacturing conditions up to the induction heating device such as rolling and cooling conditions of the steel material in the initial setting, Prepare a framework for setting power and transport speed in advance.

  7) In the third heat treatment method, in order to obtain the power and speed online, the starting temperature of induction heating of the steel material is estimated from the manufacturing conditions up to the induction heating device such as rolling and cooling of the steel material in the initial setting, Power is set in advance, and in order to improve the accuracy of heating temperature control, correction calculation of power and speed is performed based on the measured temperature of the steel material measured with a thermometer at the end of accelerated cooling or immediately before induction heating treatment Prepare a framework.

  Specific processing contents are described below.

(1) Setting calculation function The conveyance speed and electric power for heating the steel material 1 are the following three processes. Pre-processing method, B. Measurement processing method, C.I. After the pre-calculation, it is determined by any one of the combination methods for actual measurement correction. Note that the first heat treatment method described above is described in B.I. An actual measurement processing method is employed, and the second heat treatment method described above is described in A. The pretreatment method is adopted, and the third heat treatment method described above is C.I. A combination method is used in which the actual measurement is corrected after pre-calculation.

A. Pre-treatment method The heating start schedule of the steel material 1 set in advance based on the size of the steel material 1 and the operating conditions and past results in the heating furnace, rolling mill, cooling device, straightening machine before reaching the induction heating device The conveyance speed and the number of passes are determined from the temperature and the heating target temperature, and the electric power necessary for heating is calculated based on the values. The steel material 1 is heated with the electric power set by the induction heating device 6 while being transported at the determined transport speed. Even if the temperature of the steel material 1 is not measured, it is possible to efficiently perform the processing without including the calculation time in the heat treatment by performing the processing with a huge calculation load in advance by accurately obtaining the estimated temperature.

B. Measurement processing method The temperature before the heating start of the steel material 1 is measured, and the electric power necessary for the heating is calculated based on the measured temperature before the heating start and the conveyance speed. An accurate power value can be calculated by performing a calculation based on the measured temperature of the steel material 1.

C. Combination method for measuring and correcting after pre-calculation This is a method combining A and B above. As described above, the heating power and the conveyance speed are calculated in advance based on the manufacturing conditions, and the temperature before the heating of the steel material 1 is started by the thermometer set after the cooling is completed or immediately before the induction heating device. Is actually measured. When the measured temperature is close to the heating start scheduled temperature, a. Heating is performed at the conveyance speed and power calculated by the pretreatment method. If the measured temperature is different from the planned temperature, b. It corrects with the conveyance speed and electric power which were calculated | required by the measurement processing system, and heats. According to this method, it is possible to process highly accurate calculations in a short time.

(2) Tracking processing function The steel material 1 is divided into virtual parts in the longitudinal direction, the heating power calculated by the setting calculation function is set for each virtual part, and according to the conveyance of the steel material 1 in the power supply device Output. Thereby, the temperature non-uniformity in the longitudinal direction of the steel material 1 can be eliminated, and the same material can be produced at all positions of the steel material 1.

(3) Heating power correction function The temperature of the steel material 1 is measured by the temperature detectors 7 provided before and after the induction heating device 6. The heating power is corrected based on the actually measured temperature. FF (feed forward) control and FB (feedback) control are provided.

(4) Model learning function A steel material heat transfer model for obtaining heating power, an efficiency estimation model by induction heating, a temperature drop model in a straightening device, and the like are corrected at an actually measured temperature. This is because the temperature obtained as a result of the treatment in the above (1) to (3) is measured, the temperature difference with the target temperature is compared, and the treatment with the next steel material 1 is performed so that the temperature difference disappears. Therefore, the calculation process is corrected to improve the accuracy.

  Hereinafter, these functions will be described.

I. Setting calculation function First, the calculation method of the electric power when the heating start temperature and conveyance speed of the steel material 1 are given is demonstrated.

  FIG. 2 is a side view showing a schematic configuration of the heat treatment apparatus according to the first embodiment of the present invention.

  The steel material 1 is heated while moving in the induction heating device 6. At the entrance of each induction heating device 6, a temperature detector 7 for detecting the temperature of the steel material is provided. The temperature signal obtained by the temperature detector 7 is input to the control device 10. The control device 10 calculates the power to be supplied to the induction heating device 6 based on the actually measured temperature of the steel material 1 or the scheduled heating start temperature and the conveyance speed, and outputs the value to the power supply device 12.

  Note that the power calculation method differs depending on the first to third heat treatment methods.

  In the first heat treatment method, calculation is performed using the actually measured temperature at the start of heating among the aforementioned temperatures. The power supply device 12 controls the output of the induction heating device 6 so that the supplied power becomes a value given from the control device 6.

  In the second heat treatment method, calculation is performed using the expected temperature at the start of heating among the above-mentioned temperatures. The power supply device 12 controls the output of the induction heating device 6 so that the supplied power becomes a value given from the control device 6.

  In the third heat treatment method, among the above-mentioned temperatures, the estimated temperature at the start of heating is used for calculation in advance, and the measured temperature is used for correction and correction calculation based on the temperature difference from the estimated temperature. I do. The power supply device 12 controls the output of the induction heating device 6 so that the supplied power becomes a value given from the control device 6.

  When the steel material 1 is heated by the induction heating device 6, the induced current flows in a concentrated manner on the steel material surface, so that the surface is mainly heated. And the inside of steel materials is heated mainly by the heat transfer from the surface.

Therefore, the induction current distribution inside the steel material when heating by the induction heating device 6 is obtained. The current distribution inside the steel material is expressed by the penetration depth. The penetration depth differs depending on the frequency and the relative magnetic permeability, and is expressed by equation (1).

  When the penetration depth δ is large, an induced current flows to the inside of the steel material. When the penetration depth δ is small, the induction current is concentrated on the surface, so that the heating is also concentrated on the surface, and the inside of the steel material is heated by heat conduction from the surface. Therefore, even if the same power is applied, the surface heating temperature changes if the penetration depth is different. Therefore, the penetration depth is obtained based on the formula (1) to determine the current density distribution inside the steel material. From this current distribution, the heating power to the induction heating device 6 is determined.

In general, the relationship between the distance z from the steel material surface and the induced current I (z) at that position is expressed by equation (2). α is a constant.

Therefore, the ratio of the power consumption at the position z from the steel surface is expressed by equation (3).

That is, equation (3) can be considered to represent the power distribution during induction heating.

Next, the temperature change of the steel material during heating using the induction heating device 6 is expressed by a mathematical formula. Equations (4) to (6) are obtained from the difference equation of the heat conduction equation.

Rewriting Equations (4) to (6), Equation (7) is obtained as a temperature difference equation obtained by dividing the steel material into three parts in the thickness direction.

Q _{1 in} equation (4) is composed of heat transfer with the atmosphere, which is a boundary condition, and the amount of heat supplied from the heating device, and is represented by equation (8).

Here, the equation (9) is linearized with respect to x _{i, j} . The temperature of the steel material is x _0, and the x _{i, j} ⁴ term in the equation (9) is linearly approximated using x _{0 up} to the first order term of the Taylor expansion with x ₀ as the center. The Taylor expansion up to the first order is expressed by equation (11).

Using equation (11), we obtain equation (12)

Therefore, Equation (9) becomes Equation (14).

Using Equation (14), Equation (7) is rearranged to obtain Equation (15).

In Expression (15), Expression (20) is obtained by multiplying the inverse matrix of the matrix E from the left side.

  It is.

Equation (20) is the basic equation for the temperature change of the steel material 1 . If u _b = 0 in this equation, the equation represents the temperature change during the cooling process by the atmosphere.

  Next, an equation representing a temperature change from the position of the temperature detector 7 installed in front of the induction heating device 6 to the position of the temperature detector 7 on the exit side of the induction heating device is created.

FIG. 3 is a diagram illustrating symbols used in a formula representing a temperature change.

The length of each induction heating device 6 from the position of the temperature detector 7 in front of the induction heating device 6 to the temperature detector position on the exit side of the induction heating device 6 is li, and the interval between the induction heating devices is si, The electric power input to each induction heating device 6 is represented by ui. And the induction heating apparatus entrance side temperature of the steel material 1 is represented by x ₀ , the induction heating apparatus exit side temperature is represented by x ^* _N , and the temperatures before and after each induction heating apparatus are represented by x _i and x ′ _i .

  The number of steps in the difference equation is obtained by setting the length of the induction heating device to li, the interval to si, and the conveyance speed to v.

ni = li / (v × dt) (24)
mi = si / (v × dt) (25)
However, dt: step time, ni, mi: number of steps Then, the temperature at each position when the steel material 2 is sequentially heated by the induction heating device is expressed by the equation (26).

far.

The temperature change between the induction heating devices, for example, the temperature change between x0 and x1 is expressed by equation (27).

Further, the temperature as a result of heating by the first induction heating device, that is, the outlet side temperature x ′ ₁ of the induction heating device is expressed by Expression (28).

Substituting equation (27) into equation (28) yields equation (29).

When this calculation is repeated one after another, the temperature distribution of the steel material 1 at the position of the outlet side thermometer of the Nth induction heating apparatus is expressed as in Expression (30).

If this is rearranged, it becomes a linear expression of u ₁ ,..., U _N as shown in Expressions (31) and (32).

By using equation (32), heating power u _1, ..., a u _N, the temperature distribution after induction heating x1, ..., can be determined by calculating the x *.

  In addition, depending on the temperature range of the material to be heated, the heating temperature may be affected by the temperature change of specific heat or thermal conductivity. FIG. 23 shows an example in which the specific heat of the heated material changes with temperature, and FIG. 24 shows an example in which the thermal conductivity of the heated material changes with temperature. In such a case, the specific heat cp, the thermal conductivity λ, and the temperature are treated as variables, and the difference calculation is performed using equations (4) to (7), whereby the temperature distribution x1 of the steel material after heating is performed. , ..., x * can be obtained.

  FIG. 25 is a flowchart showing a procedure for estimating the temperature of the material to be heated.

  By calculating the difference between the equations (4) to (7), the temperature is calculated every certain time dt, and the temperature is estimated from the start of heating to the end of heating. At this time, the material to be heated is heated by a plurality of induction heating devices while moving at a given speed. By incorporating this condition, the temperature change of the material to be heated is sequentially calculated. The calculation ends when the steel material passes through the induction heating device.

  Increasing the number of divisions of the material to be heated in this calculation increases the accuracy of temperature estimation, but it takes time to calculate.If the number is decreased, the calculation time is shortened but accuracy of temperature estimation deteriorates. The number of divisions is determined according to the thickness.

  The calculation method described above can be realized in the control device 10. FIG. 4 is a flowchart showing a schematic procedure for obtaining the steel material temperature distribution after heating from the heating power.

  In step T1, the power distribution inside the steel material to be heated is obtained by equation (3). In step T2, the calorie distribution supplied from the induction heating device 6 is obtained from equations (8) to (10) based on the power distribution. In step T3, the amount of heat dissipated into the atmosphere is determined by equation (14). In step T4, using the obtained results, coefficients represented by equations (21), (22), and (23) for obtaining a temperature change inside the steel material are calculated.

  In step T5, the temperature distribution of the steel material 1 is calculated | required from the electric power which the induction heating apparatus 6 supplies using the number of the induction heating apparatuses 6, the length of this apparatus, the space | interval between these apparatuses, and the conveyance speed of steel materials. At this time, the temperature distribution of the steel material 1 may be obtained by applying the equations (27) to (30), and the temperature distribution of the steel material 1 may be obtained by applying the equation (32).

  Next, a method for performing a desired heat treatment using this calculation method, that is, a procedure for determining the heating power so that the steel material 1 has a target temperature distribution will be described. This procedure can be realized in the control device 10 having the above calculation procedure.

  FIG. 5 is a diagram showing a schematic flow of power calculation processing for obtaining heating power.

In step S1, appropriate initial power values u ₁ ,..., U _N are determined. In step S2, the heating temperature distribution x1, ..., x * on the outlet side of the induction heating device is calculated according to the above calculation procedure (steps T1 to T4). In step S3, the heating temperature in each induction heating device is compared with a temperature condition that is a target temperature range, and it is determined whether the temperature condition is satisfied.

In the case of Yes in step S4, that is, if the temperature condition is met, the calculation ends with the heating power as the final heating power. In the case of No in step S4, that is, when it is not suitable, new induction heating power u ₁ ,..., U _N are given and the temperature calculation is performed again.

By repeatedly performing the above processing, if the target temperature distribution x * at the outlet side of the induction heating device is given, the electric power u ₁ ,..., U _N that realizes the target temperature distribution can be obtained. As a method for giving new heating powers u ₁ ,..., U _N , a general method such as linear programming or nonlinear programming may be applied. If the temperature condition is feasible, the solution can be obtained by a finite number of calculations.

  In the present embodiment, the temperature inside the steel material can be calculated using an arbitrary number of induction heating devices 6. Therefore, the internal temperature of the steel material 1 can be obtained for each induction heating device in the heat treatment line, and the internal temperature of the steel material 1 can be obtained for a plurality of induction heating devices.

  Thereby, the frequency | count of letting the induction heating apparatus 6 pass in multiple times can change the conveyance speed for every optimal number of passes and every pass, or the number of the induction heating apparatuses 6 used for every pass can be changed. .

  Therefore, the surface temperature of the steel material 1 during heating can be controlled to be equal to or lower than the target surface temperature, and the temperature at a predetermined position inside the steel material 1 at the end of heating can be controlled to fall within a predetermined range with respect to the target internal temperature. A power setting value, that is, a power setting value for the uniform heating process can be determined. Moreover, the power set value which can control the surface temperature of the steel material 1 during heating to be equal to or higher than the target surface temperature, and control the temperature at a predetermined position inside the steel material 1 at the end of heating to be equal to or lower than the target internal temperature, That is, the power setting value for the surface heat treatment can be determined.

  Next, a heat treatment apparatus according to the second embodiment will be described. The present embodiment is characterized in that the heating power that minimizes the amount of power consumption is obtained in the power calculation processing of the first embodiment. Therefore, since the other configuration is the same as that of the first embodiment, detailed description thereof is omitted.

  FIG. 6 is a diagram illustrating a schematic flow of power calculation processing for obtaining heating power according to the second embodiment.

In step S11, appropriate initial value powers u ₁ ,..., U _N are determined. In step S12, the heating temperature distribution x1,..., X * on the outlet side of the induction heating device is calculated according to the calculation procedure of steps T1 to T4. In step S13, the heating temperature in each induction heating device is compared with a temperature condition that is a target temperature range, and it is determined whether the temperature condition is satisfied.

In the case of No in step S14, that is, when it is not suitable, new induction heating powers u ₁ ,..., U _N are given and the temperature calculation is performed again. In the case of Yes in step S14, that is, if the temperature condition is met, in step S15, the total power consumption that is the sum of the power consumption in each induction heating device 6 is obtained, and the total power consumption is minimized. Judge whether or not. That is, the heating power that minimizes the total power consumption in the induction heating device 6 is obtained.

  In the case of No in step S16, that is, when the total power consumption does not meet the condition equal to or less than the predetermined amount, new induction heating power is given and the temperature calculation is performed again. In the case of Yes in step S16, that is, if the total power consumption meets the condition of a predetermined amount or less, the calculation is ended with the heating power as the final heating power.

The condition for processing so that the heating power becomes the minimum value is expressed by Expression (33).

  That is, u (i) satisfying these conditions means that the surface temperature of the steel material 1 at all points in the heating process does not exceed the upper limit temperature, and the internal temperature after the heating process is heated within the internal temperature target range. Among the power settings for the uniform heating process, the heating power consumes the least amount of power.

  In addition, among the power settings of the surface layer heating process in which the surface temperature of the steel material 1 at all points in the heating process is heated to a target surface temperature or higher, and the internal temperature after the heating process is ended to a target internal temperature or lower. Heating power with low power consumption.

Note that the new heating power u _1, ..., a method of providing a u _N is linear programming, be a common method such as nonlinear programming, or may be applied optimization techniques such as genetic algorithms.

  Next, the heat processing apparatus of 3rd Embodiment is demonstrated. The present embodiment is characterized in that the optimum heating power obtained in the second embodiment is processed using a nonlinear programming method with constraints such as a sequential quadratic programming method. Accordingly, since the other configuration is the same as that of the second embodiment, detailed description thereof is omitted.

  First, the heating conditions of the steel material 1 in the first embodiment and the second embodiment are expressed by mathematical formulas.

Conditional expressions related to the target temperature are expressed by Expression (34) and Expression (35).

Since the center temperature is a heating target, it is expressed by the condition of the equation. Since the surface temperature is highest on the exit side of the induction heating device, the temperature on the exit side of the induction heating device is used. Moreover, since it is a heating upper limit, it is represented by an inequality. However, in the center temperature target, it is also possible to specify a range as shown in Expression (36).

Based on Formula (34) to Formula (36), in the case of surface layer heating, the target temperature is the surface temperature and the upper limit temperature is the internal temperature.
Surface temperature condition: │Ts-Tr│ <cc is a constant Internal temperature condition: Tu-Ti> 0
However, Ts: surface temperature maximum value, Tr: heating target temperature, Tu: upper limit temperature, Ti: internal temperature maximum value, v: transfer speed On the other hand, in the case of uniform heating, the target temperature is the internal temperature and the upper limit temperature is To make the surface temperature
Internal temperature condition: │Ti-Tr│ <cc is a constant Surface temperature condition: Tu-Ts> 0
These are the limiting conditions for determining the power of each induction heating device 6. Furthermore, since the capability of the induction heating device 6 is also limited, this is expressed by the equations (37) and (38) as the constraint conditions.

Furthermore, in the constraints of the equations (34) and (35), the temperatures T _N and T _1s in the constraints can be expressed using the heating power u ₁ ,..., U _N of the induction heating device 6. That is, using the expression (32), the constraint condition expressions (34) and (35) are expressed by the heating power u ₁ ,..., U _N.

First, equation (34), which is an equal heating condition, is expressed by equations (39) and (40).

Furthermore, the constraint condition of the inequality can be expressed by the equations (41) to (44).

From these, since the objective function and the constraint conditions are all expressed by the heating powers u ₁ ,..., U _N , the sequential quadratic programming method of the optimization method can be applied. The following is a summary of the above.

  When this problem setting is optimized using a sequential quadratic programming method, the minimum heating power distribution that satisfies the temperature condition is obtained. That is, the target of the surface temperature and the internal temperature at the time of heating can be realized with the minimum necessary power.

  Next, a method for determining the conveyance speed and power, which is a setting calculation function, is described.

  The conveyance speed and electric power for heating the steel material 1 are the following three treatments: Pre-processing method, B. Measurement processing method, C.I. After the pre-calculation, it is determined by any one of the combination methods for actual measurement correction. Note that the first heat treatment method described above is described in B.I. An actual measurement processing method is employed, and the second heat treatment method described above is described in A. The pretreatment method is adopted, and the third heat treatment method described above is C.I. A combination method is used in which the actual measurement is corrected after pre-calculation.

A. Pre-Processing Method FIG. 7 is a configuration diagram of a system that realizes the pre-processing method. Since the structure of the production line of the steel material 1 is the same as the above-mentioned structure, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  From the production management computer 13, data related to the steel material 1 to be manufactured is transmitted to the preprocessing arithmetic device 14. The data includes the size (width, thickness, length) of the steel material 1, the heating method, the heating start scheduled temperature, the heating target temperature, and the like. Here, the preprocessing arithmetic device 14 is provided in the control device 10.

  The preprocessing arithmetic unit 14 determines the conveyance speed, the number of passes, and the power during heating based on this data. Then, the determined transport speed is output to the transport speed setting device 15, and the determined power is output to the power supply device 12.

  Here, as a method for determining the conveyance speed, there are a method of extracting from the table and a method of convergence calculation.

a. Method for Extracting Conveying Speed from Table FIG. 8 is a diagram showing a correspondence table of the size, the conveying speed, and the number of passes of the steel material 1.

  Based on this table, the preprocessing arithmetic unit 14 extracts the conveyance speed and the number of passes from the width, thickness, and length as the size of the steel material 1. If the values of the specifications do not match the item values in the table, the values in the preceding and following tables are interpolated.

  Further, the table may be configured to extract the conveyance speed and the number of passes based on at least one of the width, thickness, and length as the size of the steel material 1.

b. Method for Determining Conveyance Speed by Convergence Calculation FIG. 9 is a flowchart showing a schematic procedure for determining a conveyance speed by convergence calculation. This method is characterized in that the conveyance speed is determined so that the time required for the heat treatment is the shortest among the heating power satisfying the condition of the heating temperature.

  In addition, when the steel material 1 is heated by reciprocating the induction heating device group a plurality of times, the conveyance speed can be set for each pass. Therefore, the conveyance speed is defined by the following equation.

V0 = [V01, V02, V03,..., V0n]
However, V0: transport speed initial value,
V0i (i = 1 to n): initial value of the i-th transport speed In step S20, an initial value is set as the transport speed. Here, the initial value V0 may be an arbitrary value or may be determined based on the actual value.

  In step S21, the power calculation shown in FIGS. 5 and 6 is performed using the transport speed to obtain the heating power. In step S22, it is investigated whether the post-heating temperature of the steel material 1 satisfies the constraint conditions under this heating condition. This constraint condition is the same as the temperature determination condition in step S3 in FIG. 5 and step S13 in FIG. 6, and checks whether the surface temperature and the internal temperature of the steel material 1 are within a predetermined temperature range, respectively.

  In the case of Yes in step S22, that is, when the constraint condition is satisfied, it means that the power calculation has been properly executed. Therefore, even if the transport speed is increased, an appropriate amount of power can be obtained. May be required. Therefore, in step S23, the conveyance speed is increased by a predetermined amount. The transport speed may be increased at a predetermined rate instead of a predetermined amount, or the transport speed may be increased based on a predetermined function.

  In step S24, electric power calculation is performed again using the increased conveyance speed, and in step S25, it is checked whether the temperature after heating of the steel material 1 satisfies the constraint condition. If Yes in step S25, that is, if the constraint condition is satisfied, steps S23 to 25 are further repeated. As a result, a higher transport speed can be set.

  In the case of No in step S25, that is, when the constraint condition is not satisfied, the processing from step S26, which will be described later, is performed, but the constraint condition used in the previous calculation without proceeding to this processing. It is also possible to adopt a conveyance speed that satisfies the above.

  In the case of No in step S22, that is, when the surface temperature and the internal temperature of the steel material 1 are not within the predetermined temperature ranges, it means that the power calculation has not been performed correctly. Here, the case where the power calculation is not performed correctly is a case where the temperature of the steel material 1 is low because the conveyance speed is too high. This is because when the temperature of the steel material 1 is high, the temperature can be lowered by lowering the amount of electric power, so that the amount of electric power can always be obtained.

  Therefore, in this case, since the temperature heating of the steel material 1 is insufficient, in step S26, the conveyance speed is decreased by a predetermined amount. Note that the conveyance speed is not a predetermined amount but may be slowed at a predetermined rate, or may be decelerated based on a predetermined relational expression or function.

  And in step S27, electric power calculation is performed again using the decelerated conveyance speed, and in step S28, it is investigated whether the temperature after heating of the steel material 1 satisfies constraint conditions.

  If No in step S28, that is, if the constraint condition is not satisfied, steps S26 to S28 are further repeated. In the case of Yes in step S28, that is, when the constraint condition is satisfied, this transport speed is adopted in step S29.

  According to this method, the heating condition with the fastest conveyance speed among the electric power satisfying the predetermined constraint conditions can be obtained as the final result, and therefore, the heat treatment condition with the shortest treatment time can be obtained.

  In this method, the convergence calculation is performed from the initial value of the conveyance speed. However, power calculation may be performed based on a plurality of conveyance speed values, and the fastest conveyance speed among the conveyance speeds satisfying the constraint conditions may be obtained. Moreover, based on the combination of the past conveyance speed actual value and the specifications of the steel material 1 (for example, thickness, width, etc.), the conveyance speed corresponding to the specifications of the steel material 1 to be heated is calculated by the internal dividing point method. May be.

  A method for determining the conveyance speed in the case of multiple passes will be described.

  (1) The first method is a method in which the ratio of the conveyance speed of each path is determined in advance and the convergence calculation is performed in accordance with the ratio.

  For example, in the case of 3 passes, the speed ratio for each pass is determined in advance as shown by the following equation.

v (2) = 1.5 × v (1)
v (3) = 1.2 × v (1)
When various conditions for heating are given and the speed is determined, a coefficient α is obtained, and a value corrected by the coefficient α as shown in the following equation is set as the conveyance speed.

V ′ (i) = α × V (i)
FIG. 26 is a flowchart showing a procedure for obtaining the coefficient α. First, an initial value is given to α, and the calculation is repeatedly performed while changing the value sequentially so that α becomes a large value within a range where the power calculation result satisfies the constraint condition. Thereby, conditions with a large conveyance speed can be determined among the power constraint conditions.

  (2) In the second method, the transport speed of each pass is changed, and the combination with the fastest speed is selected.

  The case of 3 passes will be described as an example. The maximum value of the speed is Vmax, the step width of the speed change is ΔV, and v (1), v (2), and v (3) are defined by the following equations.

v (1) = Vmax−i × ΔV, i = 1,.
v (2) = Vmax−j × ΔV, j = 1,.
v (3) = Vmax−k × ΔV, k = 1,.
Then, i, j, and k are increased from 1, respectively, and the fastest speed is finally extracted while satisfying the constraint condition.

  FIG. 27 is a flowchart showing a procedure for obtaining the conveyance speed. i, j, and k are increased from 1, and a combination that satisfies the power calculation constraint condition is obtained while changing the speed of each path within a range equal to or higher than a predetermined minimum speed (Vmin). Then, the combination that gives the fastest speed is selected. Here, as a criterion for determining the fastest speed, a combination having the largest v (1) + v (2) + v (3) can be selected. Alternatively, a combination having the largest value obtained by multiplying each speed by a weighting coefficient can be selected.

  And based on the conveyance speed decided here, the above-mentioned electric power setting calculation is performed and heating electric power is calculated | required. Then, the obtained heating power is sent to the power supply device 12 and the conveyance speed is sent to the conveyance speed setting device 15 to cause the steel material 1 to be heated.

  In addition, a. A method of extracting the conveyance speed from the table, b. In both methods of determining the conveyance speed by convergence calculation, a combination of conveyance speeds having different numbers of passes can be obtained and determined immediately before heating. For example, the transport speed in the case of 1 pass, the transport speed in the case of 3 passes, the transport speed in the case of 5 passes are obtained in advance, and one of them is selected immediately before heating based on the current efficiency and other criteria. You can also.

  Next, a method for obtaining the influence coefficient of the conveyance speed when the heating start scheduled temperature and the heating target temperature are changed will be described.

  FIG. 10 is a flowchart showing a procedure for obtaining an influence coefficient when the scheduled heating start temperature is changed. By this procedure, when the heating start scheduled temperature is Ti, the heating start scheduled temperature change amount is ΔTi, and the heating start scheduled temperature is Ti + ΔTi, the coefficient of how much the conveyance speed obtained above should be changed Ask for.

  This procedure is the same as the procedure for determining the conveyance speed shown in FIG. The treatment is started with an influence coefficient of 1, and the influence coefficient is adjusted so that heating is possible and the treatment time is the shortest.

When the value of the influence coefficient obtained in this way is q, the conveyance speed v ′ when the actual heating start scheduled temperature is Ti + ΔT can be obtained by Expression (45).

  Similarly, a speed change coefficient when the heating target temperature is changed is also obtained.

  FIG. 11 is a flowchart showing a procedure for obtaining an influence coefficient when the heating target temperature is changed. By this procedure, when the heating target temperature is Tr, the heating target temperature change amount is ΔTr, and the heating target temperature is Tr + ΔTr, the coefficient of how much the conveyance speed obtained above should be changed is obtained.

  This procedure is the same as the procedure for determining the conveyance speed shown in FIG. The process is started with an influence coefficient of 1, and the influence coefficient is adjusted so that heating is possible and the processing time is the shortest.

When the value of the influence coefficient thus obtained is q, the conveyance speed v ′ when the actual heating start temperature is Tr + ΔT is obtained by the following equation (46).

  This influence coefficient is a process described later. Measurement processing method and C.I. Used in combination processing.

B. Actual Measurement Processing Method FIG. 12 is a diagram illustrating a system configuration related to the actual measurement processing method. Since the structure of the production line of the steel material 1 is the same as the above-mentioned structure, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  This process is a process of actually measuring the heating start temperature of the steel material 1 after accelerated cooling, determining the conveying speed and calculating the heating power based on the temperature.

  This is done by the following procedure.

(I) Acquisition of heating start temperature and determination of heating target temperature
The heating start temperature of the steel material 1 is obtained by actual measurement with at least one temperature detector installed from the cooling device delivery side to the induction heating device entry side. Further, the actual measurement processing arithmetic device 16 determines the heating target temperature based on the data from the production management computer 13.

(Ii) Determination of transfer speed
Next, the conveyance speed is determined. The conveyance speed can also be obtained by interpolating the table values shown in FIG. In addition, b. In the convergence calculation, it can be calculated by replacing the expected heating start temperature with the actual heating start temperature. In addition, based on the expected heating start temperature in advance, b. When using the conveyance speed obtained by the method described in the convergence calculation, use Equation (45) or Equation (46) based on the temperature difference between the expected heating start temperature and the actual measurement result of the heating start temperature. Therefore, the calculation time can be shortened.

  In addition, a. A method of extracting the conveyance speed from the table, b. In both methods of determining the conveyance speed by convergence calculation, a combination of conveyance speeds having different numbers of passes can be obtained and determined immediately before heating. For example, the transport speed in the case of 1 pass, the transport speed in the case of 3 passes, the transport speed in the case of 5 passes are obtained in advance, and one of them is selected immediately before heating based on the current efficiency and other criteria. You can also.

(Iii) Calculation of heating power at the tip and tail ends of the steel material 1
Since the heating power differs between the tip portion and the tail end portion, the heating power at the tip end and the tail end is calculated according to the above-described method, that is, the procedure for obtaining the power shown in FIGS.

(Iv) Calculation of the temperature reached by each induction heating device 6 at the tip and tail ends of the steel material 1
Further, the temperatures reached on the entry side and the exit side of each induction heating device 6 when heated with this electric power are also stored for the tip and tail ends. This reached temperature is a target value when performing FF and FB control.

(V) Interpolation of power and temperature
And the heating power and ultimate temperature of the intermediate part of the steel material 1 are calculated | required by interpolating the heating power and ultimate temperature of the front-end | tip part and tail part which were already calculated | required.

C. Combination Processing Method FIG. 13 is a diagram illustrating a system configuration according to the combination processing method. Since the structure of the production line of the steel material 1 is the same as the above-mentioned structure, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  First, the preprocessing arithmetic unit 14 executes the preprocessing method. That is, the conveyance speed and electric power are obtained based on the scheduled heating start temperature of the steel material 1. The obtained conveyance speed and electric power are sent to the actual measurement processing arithmetic unit 16.

  On the other hand, the temperature detector 7 measures the heating start temperature before the induction heating device of the steel material 1 after the cooling process is finished. The measured temperature is input to the measured processing arithmetic device 16.

  When the actually measured heating start temperature is close to the planned heating temperature, for example, when Equation (47) is satisfied, heating is performed at the conveyance speed and heating power obtained in the pre-processing.

| Tr0-Tr1 | <= α (47)
Tr0: Expected heating start temperature, Tr1: Actual heating start temperature, α is a predetermined value, for example, 10 ° C
On the other hand, when the equation (48) is established, the actual measurement processing device 16 performs the above-described actual measurement calculation, corrects the conveyance speed, and sets the heating power as the new conveyance speed. Obtain by calculation.

| Tr0-Tr1 |> α formula (48)
The transport speed and power thus determined are transmitted to the transport speed setting device 15 and the power supply device 12, respectively, and the steel material 1 is heated.

  As described above, by combining the pre-processing and the correction processing by the actual measurement processing, it is possible to perform heating using an efficient and optimum transport speed and heating power. In addition, calculations that require a processing load in advance can be corrected online based on the measured temperature at the end of accelerated cooling only when the power setting is set in advance in the initial setting and only when different from the initial setting. Processing can be realized.

II. Tracking processing function Since the steel material 1 after cooling has a temperature difference in the longitudinal direction, it is necessary to change the power setting in the longitudinal direction. Moreover, the heating target temperature may be changed in the longitudinal direction of the steel material 1 depending on the difference in the cooling state after heating at the longitudinal position. A method for enabling online processing in the present invention will be described below. It is possible to estimate or actually measure the temperature at each position in the longitudinal direction and perform the above-described set power calculation at each position. However, this increases the processing load and makes online processing a reality. Not right. In this process, power setting, FF control, and FB control are performed for the steel material 1 in correspondence with the position in the longitudinal direction. FIG. 14 is a diagram for explaining the operation of the tracking process.

  In the tracking process, the current position in the longitudinal direction of the steel material 1 is estimated as needed based on the rotation speed signal input from the transport roll and the temperature detection signal of the temperature detector 7. Then, when the corresponding position in the longitudinal direction of the steel material 1 enters each induction heating device 6, electric power corresponding to the position is output to each induction heating device 6.

  There are the following three calculation procedures.

(1) Measure the temperatures at the leading and trailing ends, calculate the power based on the measured temperatures, and interpolate the power at the intermediate portion.

The procedure is as follows. (I) As shown in FIG. 20, before the steel material 1 enters the induction heating device or when it exits the cooling device, the temperature detector 7 detects the tip of the steel material 1 (traveling direction). Measure the temperature. Here, the temperature detector 7 is installed at a position where the temperature of the tail end can be measured before the tip of the steel material 1 enters the induction heating device 6.

  (Ii) Based on the measured actual temperature of the tip of the steel material 1, the heating power of the tip is calculated.

  (Iii) As shown in FIG. 21, as the steel material 1 is transported and the longitudinal position of the steel material 1 changes, the temperature at each position in the longitudinal direction of the steel material 1 is measured, and the longitudinal direction of the steel material 1 is measured. Save the measured temperature corresponding to the position.

  (Iv) As shown in FIG. 22, the temperature of the rear end portion of the steel material 1 is measured.

  (V) Based on the measured actual temperature of the tail end of the steel material 1, the heating power of the tail end is calculated.

  (Vi) The heating power at the intermediate portion in the longitudinal direction of the steel material 1 is obtained by interpolating the power at the tip and tail ends from the measured temperatures at the tip portion and the tail end portion and the measured temperatures at each of the intermediate portions in the longitudinal direction.

Pi = (Pt-Pb) / (Tt-Tb) * (Ti-Tt) + Pt
Pt: leading edge power, Pb: trailing edge power, Pi: intermediate power
Tt: Front end temperature, Tb: Rear end temperature, Ti: Intermediate part temperature,
(Vii) Before the steel material 1 enters the induction heating device 6, the power calculation of (v) is completed, and when the steel material 1 enters the induction heating device 6, the corresponding power is changed depending on the part of the steel material 1. And give.

According to this method, since it is based on the measured temperature from the tip portion to the tail end portion, there is an advantage of good accuracy. However, in order to measure the temperature of the tip portion and the tail end portion, the installation position of the temperature detector 7 is provided. Needs to be farther from the induction heating device than the length of the steel material, and there is a restriction on the installation space in order to cope with the long steel material 1. Alternatively,
(2) The temperature of the tip is measured, and thereafter the power is corrected by the temperature difference from the tip.

  (I) Before the steel material 1 enters the induction heating device 6 or exits the cooling device, the temperature of the tip portion (traveling direction) of the steel material 1 is measured by the temperature detector 7.

  (Ii) Based on the measured actual temperature of the tip of the steel material 1, the heating power of the tip is calculated.

  (Iii) As the steel material 1 is conveyed and the longitudinal position of the steel material 1 changes, the temperature at each position in the longitudinal direction of the steel material 1 is measured and stored.

  (Iv) Based on the measured actual temperature of the intermediate part of the steel material 1, the heating power at each position of the intermediate part is calculated.

Pi = Pt + ΔPi
ΔPi is power that gives ΔT = Ti-Tt temperature increase amount Pt: leading edge power, Pb: trailing edge power, Pi: intermediate power
Tt: Front end temperature, Tb: Rear end temperature, Ti: Intermediate part temperature,
(V) Before the steel material 1 enters the induction heating device 6, the power calculation of (iv) is completed, and when the steel material 1 enters the induction heating device 6, the corresponding power is changed depending on the part of the steel material 1. Give.

According to this method, since there is no restriction on the installation space because it is based on the measured temperatures of the tip and intermediate portions, the calculation error increases as the position of the tail end portion when the steel material 1 has a large temperature change in the longitudinal direction. A problem occurs. As another method, (3) power is calculated by actually measuring the temperatures at the front and rear ends, and the power at the intermediate portion is interpolated.

  (I) Before the steel material 1 enters the induction heating device 6 or exits the cooling device, the temperature of the tip portion (traveling direction) of the steel material 1 is measured by the temperature detector 7.

  (Ii) The temperature of the rear end portion of the steel material 1 is estimated. If the temperature estimation method of the tail end is the same time, the temperature of the tip end after cooling and the temperature of the tail end are the same, and the tip end and tail end until entering the same position, that is, the induction heating device 6 Estimate how much the temperature drop is cooled from the time difference. In addition, in order to raise a precision more, the temperature difference of the front-end | tip part and tail end part of the steel material 1 of the same conditions was memorize | stored in the past, and the temperature estimation of a tail end part from a front-end | tip part is performed based on the value In some cases.

  (Iii) Calculate the power at the front and rear ends.

  (Iv) As the steel material 1 is conveyed and the longitudinal position of the steel material 1 changes, the temperature of each position in the longitudinal direction of the steel material 1 is measured and stored.

  (V) The heating power of the intermediate portion in the longitudinal direction of the steel material 1 is obtained by interpolating the power at the tip and the tail by the measured temperature at the tip, the estimated temperature at the tail, and the measured temperatures at the middle in the longitudinal direction. Ask.

Pi = (Pt-Pb) / (Tt-Tb) * (Ti-Tt) + Pt
Pt: leading edge power, Pb: trailing edge power, Pi: intermediate power
Tt: Tip temperature, Tb: Estimated tail temperature, Ti: Intermediate temperature,
According to this method, the measured temperature of the tip portion and the intermediate portion, since the calculation based on the temperature of the tail end which is estimated from the measured temperature of the tip, without being restricted by the installation space, setting further calculates power calculation Accuracy can be secured.

  (4) The temperature at the tip is measured, and the tail is estimated from the table set value (constant) or the temperature difference at the end of the previous process (rolling or rapid cooling).

  (I) Before the steel material 1 enters the induction heating device 6 or exits the cooling device, the temperature of the tip portion (traveling direction) of the steel material 1 is measured by the temperature detector 7.

  (Ii) Based on the measured actual temperature of the tip of the steel material 1, the heating power of the tip is calculated.

  (Iii) The tail end is estimated from a table value set in advance according to size, steel type, or the temperature difference at the end of the previous step (rolling or rapid cooling).

  (Iv) The heating power at the tail end is calculated from the estimated tail end temperature.

  (V) The heating power at each position of the intermediate portion is obtained by interpolation using the following formula for the power at the tip and tail.

Pi = (Pt−Pb) / (ni−1) * (i−1) + Pt
i = 1,..., ni
Pi: i-th power from the top, Pt: tip power, Pb: tail power,
ni: Number of blocks in the longitudinal direction of the steel material (vi) Before the steel material 1 enters the induction heating device 6, the power calculation of (v) is completed, and when the steel material 1 enters the induction heating device 6, Change the power depending on the part and give it.

  According to this method, since the power setting calculation of the entire steel material can be performed without waiting for the tail end to pass through the temperature detector 7, it is also applied when the distance between the temperature detector 7 and the induction heating device 6 is relatively short. be able to.

In the above description, the explanation is based on the actually measured temperature. When the preliminary processing function is used, the tracking processing function can be realized based on the heating start scheduled temperature, the heating target temperature, and the like, instead of the actually measured temperature .

  Any of the four methods described above may be used, and may be selected in consideration of each merit and demerit in accordance with the layout of the apparatus configuration, the capacity of the arithmetic unit, and the type of the steel material 1.

III. Heating power correction function (FF control and FB control)
As described above, when temperature estimation and power setting are performed using a mathematical model, an error may occur in the temperature due to a mathematical model error. For this reason, electric power is correct | amended with the measured temperature of the steel material 1 measured with the temperature detector 7 installed in the induction heating apparatus entrance side and exit side.

  15 and 16 are diagrams showing the configuration of the FF control. The FF control power calculation device 18 corrects the power based on the measurement signal of the temperature detector 7 installed on the entrance side of each induction heating device 6.

The power correction value of the j-th induction heating device 6 at the i-th portion from the tip of the steel material 1 is given by the equation (51).

  Note that the FF control power calculation device 18 may be provided for each induction heating device 6, or the entire induction heating device 6 may be controlled as a single unit.

17 and 18 are diagrams illustrating the configuration of the FB control. The FB control power calculation device 19 corrects the power based on the measurement signal of the temperature detector 7 installed on the exit side of each induction heating device 6. This electric power correction value is calculated | required by Formula (52).

  Note that the FB control power calculation device 19 may be provided for each induction heating device 6, or the entire induction heating device 6 may be controlled as a single unit.

It is also effective to sequentially estimate the heating efficiency described later and reflect it in the results of FF control and FB control. The heating correction power in this case is

As described above, the temperature control accuracy can be improved by performing the correction based on the actually measured temperatures by the temperature detectors 7 provided before and after the induction heating device 6.

IV. Model Learning Function FIG. 19 is a diagram for explaining the entire learning function. This model learning function has the following three learning functions.

A. B. Learning of the heating efficiency for estimating the heating efficiency of the induction heating device 6 C. Air cooling learning to estimate temperature drop due to air cooling Temperature drop estimation amount and model learning in the correction device for estimating the temperature drop amount in the correction device 5 Hereinafter, these learning methods will be described.

A. Learning of heating efficiency The distances of section 1, section 2, and section 3 in FIG. 2 are l1, l2, and l3, respectively, and the passing speeds of the sections are v1, v2, and v3, respectively. And the temperature distribution x (k) inside the steel material 1 is defined by the following formula.

The temperature at the end of section 1 is expressed by equation (56).

When the power supplied by the induction heating device 6 and u _b, the temperature at the end of the section 2 is expressed by formula (58).

Further, the temperature at the end of section 3 is expressed by equation (61).

Since u _b may be determined so that this becomes equal to the target temperature _Tr , the equation (62) relating to learning is obtained.

From the learning equation (62), the amount of electric power supplied to the induction heating device 6 for heating to the target temperature _Tr is given by the equation (63).

  However, because of the power loss in the induction heating device 6 and the heating loss when the supplied power amount raises the temperature of the steel material 1, the power amount given by the equation (63) is supplied to the induction heating device 6. In many cases, however, the temperature increase amount of the steel material 1 does not reach the target temperature increase amount.

  For this reason, the heating efficiency exerted on the temperature rise of the steel material 1 by the amount of supplied power is calculated by obtaining the actual heating amount, and the target heating amount is obtained in consideration of the heating efficiency of the induction heating device 6. The power supply amount is calculated.

  From the conveyance speed of the steel material 1 and the installation intervals of the temperature detectors 7 installed on the entry side and the exit side of the induction heating device 6, the time required for a portion to be heated to pass between the temperature detectors is obtained.

As shown in Fig. 2, if the moving speeds in the i-th section 1, section 2, and section 3 from the tip are ν1 (i), ν2 (i), and ν3 (i), the passing time between temperature detectors is It calculates | requires by the following formula | equation (64).

Therefore, the temperature detector 7 on the entry side and the exit side of the induction heating device 6 detects the temperature at the same position of the steel material 1 with a time difference t _b (i). Then, the temperature difference detected by the temperature detector 7 at that time becomes the actual temperature increase amount of the steel material 1. Furthermore, the temperature rise amount of the whole steel material 1 is detectable by performing the detection of the temperature detector 7 periodically.

It is assumed that the detected temperature in the i-th section from the tip of the steel material 1 is T _bi (i), and the temperature distribution at the entrance temperature detector position is uniform.

In Equation (30), when the i-th efficiency is β (i) and the supply electric energy u _b (i) is given, the temperature T _b0 (i) at the outlet temperature detector position is given by Equation (66). Become.

The heating efficiency is a ratio of the amount of electric power that is actually used for heating in a given electric power supply amount, and is expressed by equation (67) by modifying equation (66).

Then, using the estimated heating efficiency, the amount of power supplied to the induction heating device 6 at the next stage is given by the following equation (68).

  The control device 10 in FIG. 2 performs the above calculation for each period, and supplies it to the induction heating device 6 as a target power amount.

  That is, the measurement with the temperature detector 7 is periodically performed to estimate the heating efficiency. And the estimation result of this heating efficiency is reflected in the input electric power calculation in the induction heating apparatus 6 through which the present steel material 1 passes next. Thereby, the accuracy of temperature control of the steel material 1 can be improved.

The efficiency β (i) obtained above can also be used when calculating the input power of the next block in the induction heating device 6. That is, the heating efficiency and the input power are expressed by the following formulas (69) and (70).

  Efficiency estimation considering the temperature distribution of the steel material 1 is performed and the result is reflected in the next block, so the accuracy of temperature control can be improved.

B. Air cooling learning In the temperature estimation calculation shown in Equation (9), the heat transfer calculation of steel is learned by estimating the amount of heat removal due to convection with the atmosphere and heat transfer.

As shown in the equation (71), Q ′ obtained by multiplying the amount of heat Q by the adjustment coefficient γ is defined as the amount of heat removed from the atmosphere. The temperature calculation is performed while changing the adjustment coefficient γ, and the convergence calculation is performed so that the measured temperature and the estimated temperature are close to each other.

  It is conceivable that γ is classified and stored according to the size of steel and the type of steel.

C. Estimating the temperature drop in the straightening device and model learning The temperature drop in the straightening device 5 is determined by taking into account heat removal by the roll of the straightening device 5, heat removal by the atmosphere in the straightening device, and heat removal by the cooling water. And can be calculated by the equation (72).

However, these temperature estimation values are greatly affected by changes over time such as measurement errors associated with actual measurement, roll wear, and cooling water application. Therefore, corrections are made to these estimation equations using the temperatures obtained before and after the correction device 5. The correction formula is given by formula (77).

  By using the adjustment coefficient obtained by the equation (78), it is possible to correct the error of the temperature estimation formula of the correction device 5 and correct the secular change of the temperature drop amount.

  The adjustment coefficient α obtained in this way is used when determining the heating power for the next and subsequent materials. Moreover, it classify | categorizes and preserve | saves according to the thickness of the steel material 1, width | variety, and temperature rising amount, and it can use it for the steel material of the same heating conditions after the following material.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

The side view which shows schematic structure of the manufacturing line of the steel materials to which this invention is applied. The side view which shows schematic structure of the heat processing apparatus of 1st Embodiment which concerns on this invention. The figure showing the symbol used for the formula showing a temperature change. The flowchart which shows the general | schematic procedure of calculating | requiring the steel material temperature distribution after a heating from heating electric power. The figure which shows the outline flow of the electric power calculation process which calculates | requires heating electric power. The figure which shows the outline flow of the electric power calculation process which calculates | requires heating electric power based on other embodiment. The block diagram of the system which implement | achieves a pre-processing system. The figure which shows the correspondence table of the size of steel materials, a conveyance speed, and the number of passes. The flowchart which shows the general | schematic procedure which determines a conveyance speed by convergence calculation. The flowchart which shows the procedure which calculates | requires the influence coefficient when heating start temperature is changed. The flowchart which shows the procedure which calculates | requires the influence coefficient when heating target temperature is changed. The figure which shows the structure of the system which concerns on a correction process system. The figure which shows the structure of the system which concerns on a combination processing system. The figure explaining operation | movement of a tracking process. The figure which shows the structure of FF control. The figure which shows the structure of FF control. The figure which shows the structure of FB control. The figure which shows the structure of FB control. The figure explaining the whole learning function. The figure explaining the interpolation procedure of the electric power by the measurement temperature of steel materials. The figure explaining the interpolation procedure of the electric power by the measurement temperature of steel materials. The figure explaining the interpolation procedure of the electric power by the measurement temperature of steel materials. The figure which shows the relationship between the specific heat of a to-be-heated material, and temperature. The figure which shows the relationship between the heat conductivity of a to-be-heated material, and temperature. The flowchart which shows the procedure for estimating the temperature of a to-be-heated material. The flowchart which shows the procedure which calculates | requires coefficient (alpha). The flowchart which shows the procedure which calculates | requires conveyance speed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steel material, 2 ... Heating furnace, 3 ... Rolling mill, 4 ... Accelerated cooling device, 5 ... Straightening device, 6 ... Induction heating device, 7 ... Temperature detector, 10 ... Control device, 11 ..., 12 ... Power supply device , 13 ... Production management computer, 14 ... Pre-processing arithmetic device, 15 ... Conveyance speed setting device, 16 ... Correction processing arithmetic device, 18 ... FF control power arithmetic device, 19 ... FB control power arithmetic device.

Claims (30)

A plurality of induction heating devices installed on the rolling line of steel material and arranged at the subsequent stage of the accelerated cooling device for rapidly cooling the rolled steel material;
A straightening device for straightening the steel material installed between the accelerated cooling device and the plurality of induction heating devices on a steel material rolling line;
At least one temperature detector installed on the rolling line for detecting the temperature of the steel material;
Based on the size of the steel material, the conveyance speed of the steel material, the target heating temperature of the steel material, and the actual temperature measured by the temperature detector of the steel material in the previous stage of the induction heating device, the induction heating device An arithmetic unit for calculating the supply power to be supplied;
A power supply unit that supplies the planned heating power calculated by the arithmetic unit to the induction heating unit;
The arithmetic unit is:
The surface temperature of the steel material being heated by the induction heating device is equal to or lower than the first target temperature, and the difference between the temperature at a predetermined position inside the steel material thickness direction at the end of heating and the second target temperature is within a predetermined range. Power to be supplied to the induction heating device for heating, or the surface temperature of the steel material at the end of heating by the induction heating device is equal to or higher than a third target temperature, and a predetermined value inside the thickness direction of the steel material being heated A heat treatment apparatus for calculating a supply power to be supplied to the induction heating apparatus for heating so that a temperature at a position is equal to or lower than a fourth target temperature. The arithmetic unit is:
An estimation means for estimating a steel material temperature after heating based on the steel material temperature measured by the conveyance speed and the temperature detector;
When the estimated steel temperature is not within a predetermined temperature range, a repeating unit that repeatedly executes the estimating unit by changing the conveyance speed;
When the estimated steel material temperature is within a predetermined temperature range, power calculating means for calculating the supply power to be supplied to the induction heating device for heating the steel material to a target temperature based on the conveying speed is provided. The heat treatment apparatus according to claim 1. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
2. The heat treatment apparatus according to claim 1, further comprising: a power determining unit configured to supply power to be supplied to the induction heating apparatus when the temperature condition is met, to supply power to the induction heating apparatus. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
When the temperature condition is met, based on the planned supply power used for the calculation, the power condition where the total amount of power of each induction heating device used for heating the steel material is equal to or less than a predetermined value Electric energy determination means for determining whether or not the
If the power condition is met, the power determining means for setting the power to be supplied to the induction heating device to be supplied power used for the calculation ,
Power condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the conformity determination means when the power condition is not satisfied. Item 2. The heat treatment apparatus according to Item 1. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
If the temperature condition is met, the planned supply power that minimizes the total power amount of each induction heating device used for heating the steel material among the planned supply power that meets the temperature condition is induced. The heat treatment apparatus according to claim 1, further comprising a power determination unit configured to supply power to the heating apparatus. The arithmetic unit is:
The heat treatment apparatus according to any one of claims 1 to 5, further comprising temperature distribution estimation means for estimating a temperature distribution in a thickness direction of the steel material after being heated by the induction heating apparatus. The temperature distribution estimating means includes
Based on the conveying speed of the steel material, the generated heat amount calculating means for calculating the generated heat amount inside the steel material by obtaining the induction current distribution in the thickness direction of the steel material in the induction heating device;
A dissipated heat amount calculating means for calculating a dissipated heat amount from the steel material to the atmosphere outside the induction heating device;
Temperature calculation means for calculating heat conduction to the inside of the steel material using the generated heat amount and the dissipated heat amount as a boundary condition to estimate the surface temperature of the steel material and the internal temperature in the thickness direction is provided. The heat treatment apparatus according to claim 6.   The heat treatment apparatus according to claim 6 or 7, wherein the temperature distribution estimation means includes cooling temperature estimation means for estimating a temperature drop amount in the thickness direction of the steel material by a straightening device. The arithmetic unit is:
The heating history management means for managing the history of the electric power used for heating the steel material and the temperature detection value of the steel material corresponding to each position in the longitudinal direction of the steel material. The heat treatment apparatus according to claim 8. Based on the temperature of the head portion of the steel material detected by the temperature detector provided on the entrance side of the first stage induction heating device, the measured or estimated temperature of the rear end portion, and the conveying speed of the steel material, Target temperature calculation means for calculating the heating target temperature for each induction heating device for the head portion and the rear end portion of
In the head portion and the rear end portion of the steel material, power supplied to each induction heating device is calculated based on the heating target temperature, and the power is controlled in accordance with the movement of the head portion and the rear end portion of the steel material. Power supply means for supplying to the power supply device,
In the intermediate portion sandwiched between the head portion and the rear end portion of the steel material, the measured temperature of the head portion of the steel material, the measured temperature or estimated temperature of the rear end portion, and the measured temperature or estimated temperature of the intermediate portion Based on the intermediate part target temperature calculation means for correcting the heating target temperature for each induction heating device of the intermediate part by correcting the heating target temperature for each induction heating device of the leading portion and the rear end portion of the steel material,
The intermediate power supplied to each induction heating device is calculated based on the heating target temperature for each induction heating device of the intermediate portion, and the intermediate power is controlled in accordance with the movement of the intermediate portion of the steel material to the power supply device. The heat treatment apparatus according to claim 9, further comprising intermediate power control means for supplying the heat treatment apparatus. Having the temperature detector before and after at least one induction heating device;
The arithmetic unit is:
Heating efficiency estimation means for estimating the heating efficiency of the induction heating device based on the power supplied to the induction heating device and the temperature rise of the steel material measured by the temperature detector;
11. The heat treatment apparatus according to claim 1, further comprising a correction calculation unit that corrects the electric power obtained for the steel material to be heat-treated using the heating efficiency. The arithmetic unit is:
A temperature drop amount correcting means for correcting the amount of heat dissipated into the atmosphere of the steel material in the rolling line by an actually measured temperature ;
Next, with respect to the steel material to be heat-treated, based on the amount of temperature drop estimated by the corrected amount of heat dissipated, cooling correction power calculation means for calculating power to be supplied for heating the steel material to a target temperature; The heat treatment apparatus according to claim 7 , comprising: The arithmetic unit is:
A temperature drop amount correcting means for correcting the temperature drop amount of the steel material in the rolling line by the correction device by an actual temperature measured by a temperature detector installed before and after the correction device;
Next, with respect to the steel material to be heat-treated, it has cooling correction power calculation means for calculating power to be supplied for heating the steel material to a target temperature based on the temperature drop amount in the corrected straightening device. The heat treatment apparatus according to claim 1, wherein the heat treatment apparatus is a heat treatment apparatus. Having at least one temperature detector between the induction heating devices;
Feedback control means for controlling the power supplied to the induction heating device of the previous stage based on the difference between the steel material temperature measured by the temperature detector and the target temperature at the position given in advance;
A feedforward control means for controlling electric power supplied to a subsequent induction heating device based on a difference between a steel material temperature measured by the temperature detector and a target temperature at the position given in advance; The heat treatment apparatus according to claim 1, wherein the heat treatment apparatus is a heat treatment apparatus. The feedback control means includes
The electric power supplied to the induction heating device of the previous stage is controlled based on the difference between the steel material temperature measured by the temperature detector corresponding to each position in the longitudinal direction of the steel material and the target temperature at that position given in advance. The heat treatment apparatus according to claim 14. The feedforward control means includes
The electric power supplied to the induction heating device in the subsequent stage is controlled based on the difference between the steel material temperature measured by the temperature detector corresponding to each position in the longitudinal direction of the steel material and the target temperature at that position given in advance. The heat treatment apparatus according to claim 14. A plurality of induction heating devices for heating steel materials;
Straightening device installed in the front stage of the plurality of induction heating devices, for straightening the steel material,
Based on the size of the steel material, the conveying speed of the steel material, the target heating temperature of the steel material, and the planned temperature of the steel material in the previous stage of the induction heating device, the planned supply power to be supplied to the induction heating device is calculated. An arithmetic unit to
A power supply unit that supplies the planned heating power calculated by the arithmetic unit to the induction heating unit;
The arithmetic unit is:
The surface temperature of the steel material being heated by the induction heating device is equal to or lower than the first target temperature, and the difference between the temperature at a predetermined position inside the steel material thickness direction at the end of heating and the second target temperature is within a predetermined range. Power to be supplied to the induction heating device for heating, or the surface temperature of the steel material at the end of heating by the induction heating device is equal to or higher than a third target temperature, and a predetermined value inside the thickness direction of the steel material being heated A heat treatment apparatus for calculating a supply power to be supplied to the induction heating apparatus for heating so that a temperature at a position is equal to or lower than a fourth target temperature.   The said induction heating apparatus is installed on the rolling line of the said steel materials, is rapidly cooled by the accelerated cooling apparatus after rolling, and further heats the said steel materials corrected by the said straightening apparatus. Heat treatment equipment.   The heat treatment apparatus according to claim 17 or 18, wherein the conveyance speed of the steel material is a conveyance speed predetermined based on a size of the steel material. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
20. When the temperature condition is satisfied, the apparatus includes a power determining unit that uses the scheduled supply power used for the calculation as power to be supplied to the induction heating device. Heat treatment equipment. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
When the temperature condition is met, based on the planned supply power used for the calculation, the power condition where the total amount of power of each induction heating device used for heating the steel material is equal to or less than a predetermined value Electric energy determination means for determining whether or not the
If the power condition is met, the power determining means for setting the power to be supplied to the induction heating device to be supplied power used for the calculation ,
Power condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the conformity determination means when the power condition is not satisfied. Item 20. The heat treatment apparatus according to any one of Items 17 to 19. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
If the temperature condition is met, the planned supply power that minimizes the total power amount of each induction heating device used for heating the steel material among the planned supply power that meets the temperature condition is induced. The heat treatment apparatus according to any one of claims 17 to 19, further comprising a power determination unit configured to supply power to the heating apparatus. The arithmetic unit is:
The heat treatment apparatus according to any one of claims 17 to 22, further comprising temperature distribution estimation means for estimating a temperature distribution in a thickness direction of the steel material after being heated by the induction heating apparatus. The temperature distribution estimating means includes
A calorific value calculation means for calculating a calorific value generated in the steel material by obtaining an induction current distribution in the thickness direction of the steel material in the induction heating device;
A dissipated heat amount calculating means for calculating a dissipated heat amount from the steel material to the atmosphere outside the induction heating device;
Temperature calculation means for calculating heat conduction to the inside of the steel material using the generated heat amount and the dissipated heat amount as a boundary condition to estimate the surface temperature of the steel material and the internal temperature in the thickness direction is provided. The heat treatment apparatus according to claim 23.   The heat treatment apparatus according to claim 23, wherein the temperature distribution estimation means includes cooling temperature estimation means for estimating a temperature drop amount in the thickness direction of the steel material by a straightening device. The arithmetic unit is:
The steel material is further divided into a plurality of virtual sections in the longitudinal direction , and further has a heating history management means for managing the history of the electric power used for heating the steel material and the temperature detection value of the steel material in this section unit. The heat treatment apparatus according to any one of claims 17 to 25. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
When the temperature condition is met, power determining means for setting the power to be supplied to the induction heating device, which is the supply power that maximizes the conveying speed of the steel material, among the power to be supplied that meets the temperature condition. The heat treatment apparatus according to claim 17 or 18, characterized by the above. The arithmetic unit is:
Temperature estimation means for estimating the surface temperature of the steel material and the internal temperature in the thickness direction after induction heating from the data including the conveyance speed of the steel material and the scheduled power supply;
Suitability determination means for determining whether the surface temperature of the steel material and the internal temperature in the thickness direction meet a predetermined temperature condition;
If the temperature conditions are not met, the temperature condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the suitability determination means;
When the temperature condition is met, based on the planned supply power used for the calculation, the power condition where the total amount of power of each induction heating device used for heating the steel material is equal to or less than a predetermined value Electric energy determination means for determining whether or not the
When the power condition is met, the temperature estimation means, the conformity determination means, the temperature condition determination processing means, and the power amount determination means are adapted to the temperature condition using a new transport speed obtained by increasing the transport speed. Repetitively executing until it stops, a transport speed calculating means for acquiring the transport speed used for the final calculation that matches the temperature condition and the power condition as a new transport speed ;
Power condition determination processing means for correcting the scheduled power supply and repeatedly executing the temperature estimation means and the conformity determination means when the power condition is not satisfied. Item 19. A heat treatment apparatus according to Item 17 or 18. A plurality of induction heating devices installed on the rolling line of steel material and arranged at the subsequent stage of the accelerated cooling device for rapidly cooling the rolled steel material;
A straightening device for straightening the steel material installed between the accelerated cooling device and the plurality of induction heating devices on a steel material rolling line;
At least one temperature detector installed on the rolling line for detecting the temperature of the steel material;
A first supply schedule to be supplied to the induction heating device based on the size of the steel material, the conveyance speed of the steel material, the target heating temperature of the steel material, and the planned temperature of the steel material in the previous stage of the induction heating device. A first computing device for computing power;
Based on the size of the steel material, the conveyance speed of the steel material, the target heating temperature of the steel material, and the actual temperature measured by the temperature detector of the steel material in the previous stage of the induction heating device, the induction heating device A second computing device that computes a second scheduled supply power to be supplied;
If the difference between the estimated temperature of the steel material and the measured temperature of the steel material is within a predetermined range, the first scheduled power supply is selected as the scheduled supply power, and the estimated temperature of the steel material and the measured temperature of the steel material A power selection device that selects the second scheduled power supply as the planned power supply if the difference is not within a predetermined range;
A power supply device that supplies the planned heating power selected by the power selection device to the induction heating device;
The first and second arithmetic units are:
The surface temperature of the steel material being heated by the induction heating device is equal to or lower than the first target temperature, and the difference between the temperature at a predetermined position inside the steel material thickness direction at the end of heating and the second target temperature is within a predetermined range. Power to be supplied to the induction heating device for heating, or the surface temperature of the steel material at the end of heating by the induction heating device is equal to or higher than a third target temperature, and a predetermined value inside the thickness direction of the steel material being heated A heat treatment apparatus for calculating a supply power to be supplied to the induction heating apparatus for heating so that a temperature at a position is equal to or lower than a fourth target temperature.   30. A method for producing a steel material, wherein the steel material is produced by performing a heat treatment using the heat treatment apparatus according to any one of claims 1 to 29.

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