JP4333283B2 - Manufacturing method of high-strength steel sheet - Google Patents

Description

  The present invention is a steel plate used for machine structures, architectural civil engineering, line pipes, etc., and has high strength with excellent cutting cracking resistance, which does not cause cracks on the cut surface when cut with a shearing machine. The present invention relates to a method of manufacturing a steel plate.

  A thick steel plate rolled to a predetermined thickness by hot rolling is cooled in a cooling bed and then a measuring operation is performed. The measured thick steel plate is cut into a predetermined width and length. This cutting is performed by cutting with a shearing machine or gas cutting. Usually, a thick steel plate having a thickness less than about 50 mm is cut by a shearing machine, and if it exceeds that, gas cutting is performed. The shearing machine includes a crop shear that cuts the top and bottom portions of the thick steel plate, a side shear that cuts the ear, a slitter that divides the width direction of the thick steel plate into two parts, and an end shear that cuts the length direction into a predetermined dimension. By passing through a cutting line composed of these shearing machines, the steel sheet is cut into a thick steel plate having a predetermined size.

  Defects on the cut surface by a shearing machine include sagging, burrs, mechanical cracks, cutting, stepping, etc. If these occur, they cannot be used as they are, and require maintenance such as grinder grinding or recutting. Thus, the yield is reduced and the manufacturing cost is increased. Various proposals have been made as countermeasures for these cut surface defects.

  For example, it is proposed that the equipment conditions of the shearing machine are managed at appropriate values, assuming that these cut surface defects are largely determined by the equipment conditions of the shearing machine (see Non-Patent Document 1, for example). Further, as a method of reducing sagging, a method of preheating a crop part including a cutting line and then cutting with a shearing machine has been proposed (for example, see Patent Document 1).

  However, with high-toughness and high-strength steel sheets with a tensile strength of about 550 MPa or more used for mechanical structures, civil engineering, and line pipes, even if the equipment conditions of the shearing machine are managed at appropriate values, the frequency of occurrence is Although there are few, the cut surface may have a crack (hereinafter referred to as “cut crack”) along the center of the plate thickness. When such shear cutting cracks occur, it is necessary to remove the cracks, and the yield decreases. Furthermore, in order to prevent cutting cracks, it is necessary to use a gas cutter, resulting in a significant reduction in productivity compared to shear cutting.

  For the purpose of preventing cut cracking by such a shearing machine, that is, improving the resistance to cut cracking, a high toughness and high strength thick steel sheet having a specified chemical component has been proposed (for example, see Patent Document 2). In this technique, the C content, S content, and Pcm value are kept low, and the addition of Ca significantly improves the cutting ability with a shearing machine.

  On the other hand, a method for preventing hydrogen cracking at the time of shearing of a high-strength steel sheet, in which the hot-rolled steel sheet is dehydrogenated while being passed through a high-temperature heat treatment apparatus has been disclosed (for example, see Patent Document 3).

Moreover, the method of reheating the steel plate after hot rolling with the induction heating apparatus installed on the line is disclosed (for example, refer patent document 4).
JP-A-6-190627 JP 2000-309845 A JP 2000-119744 A JP 2002-256339 A Edited by Japan Iron and Steel Institute, Steel Handbook, Volume 3 (1) Rolled Foundation / Steel, 3rd Edition, page 285

  However, these conventional techniques have the following problems.

  First, in the technique described in Patent Document 1, it is necessary to preheat the crop part before cutting with a shearing machine, and there is a problem that the efficiency of the shearing work is reduced.

  Moreover, in the technique of the said patent document 2, since a chemical component is limited, there exists a problem that it is difficult to apply to the steel material of a wide use, and also raises a raw material cost.

  And in the technique of the said patent document 3, since it dehydrogenates at 550-700 degreeC, material deterioration, such as a strength fall and DWTT characteristic, will be caused.

  Furthermore, although the idea of the in-line heat processing technique using the induction heating apparatus described in Patent Document 4 has existed conventionally, it has not been put into practical use. The reason for this was not only hardware problems such as insufficient induction heating capacity, but also soft problems. 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 sheet at the time of induction heating, and it is necessary to calculate 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 are no literatures on how to calculate the power and how to determine the transport speed that give a clear answer to these problems.

  The present invention has been made in view of the above circumstances, and in steel sheets that are accelerated or cooled or quenched after hot rolling, even if they are cut with a shearing machine, no cut cracks are generated on the cut surfaces, and excellent cut resistance It aims at providing the manufacturing method of the high strength steel plate which has the property.

  As a result of diligent research on cutting cracks by a shearing machine, the present invention is accelerated in order to prevent diffusible hydrogen present in steel causing cutting cracks from adhering to various defects in steel. This is based on the knowledge that it is most effective to reheat with an induction heating device installed on the line after cooling or quenching. In order to perform in-line heat treatment using an induction heating device, it is important to accurately estimate the surface layer temperature and internal temperature of the steel sheet during induction heating, and to set the power and conveyance speed that satisfy the target value of the heating temperature. I found out that there was.

  The present invention has been made based on the above findings and has the following characteristics.

[1] In a method for producing a steel sheet, which is reheated on a line using an induction heating device after hot rolling, after accelerated cooling or direct quenching,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is met, a supply step of supplying the induction heating device with the electric power used for the calculation;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet.

[2] In a method for manufacturing a steel sheet, after hot rolling, accelerated cooling or direct quenching and then reheating on the line using an induction heating device,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is met, based on the power used for the calculation, the total power value of each induction heating device used for heating the steel sheet meets a power condition that is equal to or less than a predetermined value. A power determination step for determining whether to
When the temperature condition is met, a supply step of supplying the induction heating device with the electric power used for the calculation;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet.

[3] In the method of manufacturing a steel sheet, after hot rolling, accelerated cooling or direct quenching and then reheating on the line using an induction heating device,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is satisfied, the calculation step, the determination step, and the determination processing step are repeatedly performed using the new transfer speed obtained by increasing the transfer speed until the temperature condition is not satisfied. An extraction step to extract the power and transport speed used for the final operation that fits;
A supply step of supplying the extracted electric power to the induction heating device while conveying the steel sheet at the extracted conveyance speed;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet.

[4] In the method for manufacturing a steel sheet, which is reheated on the line using an induction heating apparatus after hot rolling, after accelerated cooling or direct quenching,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is met, based on the power used for the calculation, the total power value of each induction heating device used for heating the steel sheet meets a power condition that is equal to or less than a predetermined value. A power determination step for determining whether to
When the temperature condition is satisfied, the calculation step, the determination step, and the determination processing step are repeatedly performed using the new transfer speed obtained by increasing the transfer speed until the temperature condition is not satisfied. An extraction step to extract the power and transport speed used for the final operation that fits;
A supply step of supplying the extracted electric power to the induction heating device while conveying the steel sheet at the extracted conveyance speed;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet.

[5] In the method for manufacturing a high-strength steel sheet according to [3] or [4], the steps from the calculation step to the extraction step are performed until the heating start temperature in the induction heating device is determined. Then, the electric power and the conveyance speed are extracted in advance, and when the heating start temperature is determined, based on the amount of change from the heating start temperature predicted in the calculation step to the determined heating start temperature, Correct the transport speed extracted before the article to make it a newly extracted transport speed, and newly extract the power obtained by recalculating the power at the newly extracted transport speed A method for producing a high-strength steel sheet, wherein the supplying step is performed using the newly extracted conveyance speed and the newly extracted electric power.
[ 6 ] The method for producing a high-strength steel sheet according to any one of [1] to [ 5 ], wherein the steel sheet is reheated by an induction heating device before being cooled to 150 ° C. or lower.

  In the present invention, after accelerated cooling or quenching of the steel sheet after rolling, reheating before the steel sheet temperature falls below a predetermined temperature prevents hydrogen from adhering to defects in the steel. It is possible to sufficiently remove hydrogen. Therefore, hydrogen does not accumulate on the cut surface, and cracking can be prevented. According to the present invention, it is possible to stably produce a steel plate that does not generate a cut crack on the cut surface even if it is cut by a shearing machine, and as a result, industrially beneficial effects such as yield improvement and production cost reduction are brought about. It is.

  In addition, highly accurate heat treatment can be performed with an induction heating apparatus installed on the line, so that productivity is greatly improved and industrially beneficial effects can be obtained.

  The constituent requirements of the present invention and the reasons for limitation will be described below. First, the steel material to be used in the present invention is a steel plate that is accelerated or cooled or quenched after hot rolling. This is because the steel plate that has been accelerated or cooled is generally high in strength and cut by a shearing machine. This is because there is a high possibility of causing breakage.

  In general, a steel plate that has been accelerated or quenched is cooled in a cooling bed or the like, but in the present invention, reheating is performed before cooling to a predetermined temperature. This facilitates removal of diffusible hydrogen in the steel. Reheating is performed before the steel sheet temperature is cooled to 150 ° C. or lower. The reason is that when cooled to 150 ° C. or lower, diffusible hydrogen in the steel is fixed to various defects such as dislocations, point defects, or grain boundaries, and thus is difficult to be removed in the subsequent heat treatment. is there. Therefore, in the present invention, after accelerated cooling or quenching, reheating is performed before the steel sheet temperature is cooled to 150 ° C. or lower.

  Thereafter, diffusible hydrogen is removed by reheating to a temperature of 200 ° C. or higher and lower than 500 ° C. When the reheating is performed at a temperature lower than 200 ° C., removal of diffusible hydrogen is insufficient, and cutting cracks are likely to occur when cutting with a shearing machine. On the other hand, diffusible hydrogen is sufficiently removed when the reheating is performed at a temperature of 500 ° C. or higher, so that cracking does not occur at the time of shear cutting, but rather the amount of decrease in strength due to annealing becomes rather large rather than tempering. A sufficient strength cannot be obtained. Therefore, the reheating temperature is specified to be 200 ° C. or higher and lower than 500 ° C.

  In this invention, since it is necessary to reheat before steel plate temperature is cooled to 150 degrees C or less, reheating is performed with the induction heating apparatus installed on the same line as rolling equipment and cooling equipment.

  Hereinafter, a control method at the time of reheating by the induction heating apparatus will be described.

  Heating methods using an induction heating device include surface heating and uniform heating.

  In both cases, the surface temperature and the internal temperature of the steel sheet are heated to different targets. The internal temperature includes an average temperature in the thickness direction (average temperature), a temperature at the center of the thickness (center temperature), and the like.

  In the case of surface layer heating, the surface temperature is heated to the target temperature at the end of heating. In that case, heating is performed so that the internal temperature during the heating process does not exceed the upper limit temperature.

  In the case of uniform heating, the internal temperature is heated to the target temperature at the end of heating. In that case, heating is performed so that the surface temperature during the heating process does not exceed the upper limit temperature.

  In order to perform uniform heating, it is necessary to prepare a plurality of induction heating devices and gradually heat them while repeating the heating process and the cooling process.

  Further, heating may be performed by reciprocating the induction heating device group a plurality of times. In order to increase the conveyance speed so as not to hinder the rolling efficiency, it is necessary to increase the heating capacity (maximum power) and prepare a large number of units, because this increases the cost of the apparatus and the installation space.

  Furthermore, even under the same manufacturing conditions, the steel plate temperature after accelerated cooling differs depending on the operating conditions. For this reason, it is necessary to construct a mechanism for obtaining the power online after actually measuring the temperature of the steel plate after accelerated cooling, rather than preparing power in advance using a table or the like.

In order to accurately perform the heat treatment online with an induction heating apparatus, there are the following problems.
(A) The internal temperature of the steel sheet during induction heating is accurately estimated.
(B) The power and the conveyance speed that satisfy the target and limit of the heating temperature are obtained.
Furthermore, in practical use,
(C) Reduce power consumption as much as possible.
(D) Heat treatment is performed at a conveyance speed that does not impede operation.
(E) The steel plate temperature before heating is measured, and the heating power, the conveyance speed, etc. are determined based on the measured values.

  In the present invention, the following means are used to solve the above problems.

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

(B) 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, calculation is performed by nonlinear programming. As a result, the surface temperature and the internal temperature are not independent variables, but by placing a plurality of induction heating devices and heating them, they can be regarded as independent to some extent and can be set separately.
This is expressed as follows.
Variable: Power P given to each induction heating device P = [p1,..., Pi,.
Internal temperature condition: | Ti-Tr | <c (c is a constant)
Surface temperature condition: Tu-Ts> 0
Objective function: Sum of power consumption (kWh) Σ (pi * v)
However, Ts: surface temperature maximum value, Tr: heating target temperature, Tu: upper limit temperature, Ti: internal temperature maximum value, v: transport speed.

  (C) By using the objective function of nonlinear programming as the sum of power consumption, the power that minimizes the power consumption can be found while satisfying the temperature condition.

  (D) By obtaining the power setting at a certain speed and then repeatedly performing the calculation while changing the transport speed within a heatable range, a transport speed that does not hinder the operating conditions can be obtained while satisfying the temperature condition.

  (E) In order to obtain the power and speed online, power setting is performed in advance in the initial setting to simplify the optimization calculation. Further, by performing a correction calculation of the electric power and the conveyance speed based on the actually measured temperature at the end of the accelerated cooling, it is possible to control with higher accuracy.

  The temperature distribution of the steel material by induction heating is obtained as follows.

The current distribution inside the steel material is represented by the penetration depth. The penetration depth is expressed by a frequency and a relative magnetic permeability as shown in Equation (2).
δ = 50.3 * SQRT * (R / μ / fx) / 100 (2)
However, δ: penetration depth, R: specific resistance, μ: relative permeability, fx: frequency When the penetration depth is large, the induced current flows to the inside of the steel material, but when the penetration depth is small, Since the induced current is concentrated on the surface, the heating is also concentrated on the surface, and the inside of the steel material is heated by heat transfer from the surface. Therefore, even when the same electric power is applied, the surface heating temperature varies depending on the penetration depth. Therefore, the penetration depth is obtained from the relative permeability, the current distribution inside the steel material is calculated from the penetration depth, and the temperature distribution inside the steel material is obtained from the current distribution.

In general, the relationship between the distance z from the steel material surface and the induced current I (z) is expressed by equation (3). α is a constant.
I (z) = αexp (-z / δ) (3)
Therefore, the ratio of the power consumption at the distance z from the steel material surface is expressed by Expression (4).
E ₀ (z) = I (z) ² / ∫I (z) ² ...... (4)
That is, Equation (4) can be considered as the power distribution during induction heating.

Next, the temperature change of the steel material in the heating process using the induction heating apparatus is expressed by a mathematical formula. Equation (5) is obtained from the difference equation of the heat conduction equation.

By using the equations (5) to (8), the temperature distribution of the steel material after heating (x _{1, j} x _{2, j} ... x _{nb-1, j} x _{nb, j} ) Can be requested. The calculation flow is shown in FIG. The calculation ends when the steel material passes through the induction heating device.

  Next, FIG. 4 shows how to obtain the heating power using this temperature model.

First, an appropriate initial value power u _{k, j} is given, and the heating temperature distribution x _{i, j} on the induction heating device outlet side is calculated. And the heating temperature and temperature conditions in each induction heating apparatus are compared, and it is determined whether the temperature conditions are satisfied. If the temperature condition is met, the calculation ends with the heating power as the final heating power. If they do not match, a new heating induction heating power is given and the temperature calculation is repeated. The method for giving the new heating power u _{k, j} may be a general method such as linear programming or nonlinear programming. If the temperature condition is feasible, it converges with a finite number of calculations.

Furthermore, the sum of the power consumption in each induction heating apparatus is given as an objective function. After determining whether or not the steel material temperature after heating meets the temperature condition, it is also determined whether or not the power consumption in each induction heating device is minimized. That is, the heating power required by this process minimizes the power consumption in the induction heating device. Also in this case, the method for giving the new heating power u _{k, j} may be a general method such as linear programming or non-linear programming. This calculation flow is shown in FIG.

  To determine the transport speed, the number of passes is determined first, and convergence calculation as shown in FIG. 6 is performed. Start with an appropriate initial speed and perform power setting calculations. Depending on the speed, heating may not be possible depending on the upper limit of the power capacity and temperature conditions. In that case, the power setting calculation is performed at a reduced speed. If heating is possible, increase the transfer speed and calculate the power setting. Find the fastest speed within the heatable range.

  And based on the conveyance speed decided here, heating electric power is calculated | required using the electric power setting calculation of the preceding clause. The steel material is heated using the obtained heating power and conveyance speed.

  The heating power and transfer speed obtained in this way can be calculated in advance and stored in a table, etc., or used online, or calculated online when the accelerated cooling of the steel has been completed and the heating start temperature has been determined. Can also be requested.

  However, if calculated in advance, the temperature at the end of the accelerated cooling may be different from the schedule. In addition, since the convergence calculation is repeatedly performed using a complicated model, the calculation amount is enormous, and the calculation may not be in time on-line. In such a case, the following correction method is effective. In this method, the heating power and the conveyance speed are calculated in advance, the conveyance speed is corrected with the actual temperature after the completion of the accelerated cooling, and the power is recalculated. This is shown below.

First, after calculating in advance the conveyance speed shown in FIG. 6, the influence coefficient of the conveyance speed when the heating start temperature is changed is obtained. This procedure is shown in FIG. The heating start temperature is Ti, the change amount of the heating start temperature is ΔTi, and a coefficient of how much the conveyance speed should be changed when the heating start temperature is Ti + ΔTi is obtained. Starting from the influence coefficient of 1, the influence coefficient is adjusted so that heating is possible and the processing time is the shortest. When this value is q, the conveyance speed v ′ when the actual heating start temperature is Ti + ΔT is obtained by the following equation (9).
v ′ (n _p ) = (qΔT + 1) v (n _p ) (9)
However, n _p : number of passes, v ′ (n _p ): corrected transport speed, v (n _p ): speed determined in advance, q: influence coefficient Accelerated cooling is terminated, and actual temperature is detected At this point, the conveyance speed is corrected in this way. Further, the power calculation shown in FIG. 3 or 4 is performed again at the corrected speed. If only the convergence calculation of the power calculation, it will not take much time. By using the correction method, the most efficient conveyance speed can be obtained, and the heating power can be set with high accuracy.

  FIG. 2 is a side view showing a schematic configuration of a heat treatment apparatus to which the method for producing a high-strength steel plate according to the present invention is applied.

  The steel material 2 is heated while being moved by the conveyance roller 11 in the induction heating device 5. A temperature detector 9 for detecting the temperature of the steel material 2 is provided at the entrance of the induction heating device 5. The temperature signal obtained by the temperature detector 9 is input to the control device 13. The control device 13 calculates the power to be supplied to the induction heating device 5 based on the temperature of the steel plate 2 or the scheduled heating start temperature and the conveyance speed, and outputs the value to the power supply device 12. The power supply device 12 controls the output of the induction heating device 5 so that the supplied power becomes a value given from the control device 13.

Examples of the present invention will be described below. Table 1 shows the chemical composition of the test steel. These steels were melted by a combination of a converter and an RH vacuum degassing apparatus, and slab slabs were formed by a continuous casting method. The slab was rolled into a steel plate having a thickness of 13 to 25 mm by hot rolling, and then cooled using a water-cooled accelerated cooling facility.

  Table 2 shows the rolling end temperature and the cooling stop temperature at this time. Then, it reheated using the induction heating apparatus installed on the same line as the cooling facility.

  FIG. 1 is a schematic diagram of equipment arrangement in this embodiment. After the steel plate 2 rolled by the hot rolling mill 3 arranged on the rolling line 1 is cooled by the accelerated cooling device 4, the steel plate 2 is re-started by the three solenoid induction heating devices 5 arranged in series on the same line 1. Heated. Then, after correction by the hot leveler 6, shear cutting is performed by the shearing machine 7. These reheating conditions are also shown in Table 2.

  The conveyance speed and electric power for heating a steel plate were determined by the pre-processing system about No.1. That is, the conveyance speed and the number of passes were determined in advance from the heating start scheduled temperature and the heating target temperature of the steel sheet, and the electric power required for heating was calculated based on the values.

No. 2 to No. 7 were determined by the correction processing method. That is, the temperature before starting heating of the steel sheet was measured, and the electric power necessary for heating was calculated based on the actually measured temperature before starting heating and the conveyance speed. In this calculation, the desired power was obtained while correcting the conveyance speed as necessary. As the internal temperature, the average temperature in the thickness direction was used.

  After the reheated steel plate was cooled to a temperature of 100 ° C. or lower, each steel plate was cut at 10 locations by a shearing machine, and a cut crack test was performed. In the test, the steel plate cut end face was investigated by magnetic particle flaw detection, and the number of cut portions (end face) where cut cracks were observed was determined. Here, even when a plurality of cracks could be confirmed in one end face, the number of occurrences of cut cracks was set to 1 because there was one end face. The tensile strength was measured by a tensile test using a full thickness test piece. The above test and measurement results are also shown in Table 2.

  Examples No. 1 to No. 4, which are examples of the present invention, are all reheated in the range of 300 to 500 ° C. before the steel plate temperature becomes 150 ° C. or lower after cooling, and the occurrence of cracks at the cut end faces is recognized. I couldn't. When No. 1 and No. 2 were compared, the internal temperature after reheating was closer to the target temperature in No. 2 which was set by actually measuring the steel plate temperature after cooling.

  On the other hand, No. 5, which is a comparative example, had a reheating temperature exceeding 500 ° C. and did not cause shear cutting cracking, but the strength reduction was significant. In No. 6, the steel plate temperature before reheating was 150 ° C. or less, and in No. 7, the reheating temperature was less than 300 ° C., and cracks occurred at the cut end faces.

  In the present invention example, the surface temperature and the internal temperature of the steel sheet during induction heating were accurately estimated and the power was set, so the surface was not overheated beyond the Ac1 transformation point, and the internal temperature was also 300 to 500 ° C. I was able to hold it accurately. In addition, because the conveyance speed when reheating with the induction heating device is optimized, the steel plate to be heat treated next can be efficiently heat treated without waiting in front of the induction heating device or hindering rolling efficiency. It was.

The schematic diagram of the equipment arrangement | positioning in the Example of this invention. The side view which shows schematic structure of the heat processing apparatus with which the manufacturing method of the high strength steel plate which concerns on this invention is applied. The calculation flow figure of the temperature distribution in embodiment of this invention. The power calculation flow figure in the embodiment of the present invention. The power consumption optimization flowchart in the embodiment of the present invention. The conveyance speed optimization flowchart in the embodiment of the present invention. The influence coefficient calculation flow figure in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling line 2 Steel plate 3 Hot rolling mill 4 Accelerated cooling apparatus 5 Induction heating apparatus 6 Hot leveler 7 Shearing machine 9 Temperature detector 11 Conveyance roller 12 Power supply apparatus 13 Control apparatus

Claims (6)

In the method of manufacturing a steel sheet after hot rolling, reheating on the line using an induction heating device after accelerated cooling or direct quenching,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is met, a supply step of supplying the induction heating device with the electric power used for the calculation;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet. In the method of manufacturing a steel sheet after hot rolling, reheating on the line using an induction heating device after accelerated cooling or direct quenching,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is met, based on the power used for the calculation, the total power value of each induction heating device used for heating the steel sheet meets a power condition that is equal to or less than a predetermined value. A power determination step for determining whether to
When the temperature condition is met, a supply step of supplying the induction heating device with the electric power used for the calculation;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet. In the method of manufacturing a steel sheet after hot rolling, reheating on the line using an induction heating device after accelerated cooling or direct quenching,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is satisfied, the calculation step, the determination step, and the determination processing step are repeatedly performed using the new transfer speed obtained by increasing the transfer speed until the temperature condition is not satisfied. An extraction step to extract the power and transport speed used for the final operation that fits;
A supply step of supplying the extracted electric power to the induction heating device while conveying the steel sheet at the extracted conveyance speed;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet. In the method of manufacturing a steel sheet after hot rolling, reheating on the line using an induction heating device after accelerated cooling or direct quenching,
A calculation step of estimating the surface temperature of the steel sheet and the temperature in the thickness direction after induction heating from data including the conveyance speed of the steel sheet and the power to be supplied to the induction heating device,
A determination step of determining whether the maximum temperature of the surface of the steel sheet is less than the Ac1 transformation point and whether the temperature in the thickness direction is 300 ° C. or more and less than 500 ° C .;
If the temperature condition is not met, a determination processing step of correcting the power and repeatedly executing the calculation step and the determination step;
When the temperature condition is met, based on the power used for the calculation, the total power value of each induction heating device used for heating the steel sheet meets a power condition that is equal to or less than a predetermined value. A power determination step for determining whether to
When the temperature condition is satisfied, the calculation step, the determination step, and the determination processing step are repeatedly performed using the new transfer speed obtained by increasing the transfer speed until the temperature condition is not satisfied. An extraction step to extract the power and transport speed used for the final operation that fits;
A supply step of supplying the extracted electric power to the induction heating device while conveying the steel sheet at the extracted conveyance speed;
A method for producing a high-strength steel sheet having excellent shear cutting cracking characteristics, comprising: a cutting step of performing shear cutting on a line after reheating the steel sheet. In the manufacturing method of the high-strength steel plate according to claim 3 or 4, before the heating start temperature in the induction heating device is determined, each step from the calculation step to the extraction step is performed, Extracted in advance based on the amount of change from the heating start temperature predicted in the calculation step to the determined heating start temperature when the conveyance speed is extracted and the heating start temperature is determined The transport speed is corrected to the newly extracted transport speed, and the power obtained by recalculating the power at the newly extracted transport speed is used as the newly extracted power. A method for producing a high-strength steel sheet, characterized in that the supplying step is performed using the extracted conveyance speed and newly extracted electric power. The method for producing a high-strength steel sheet according to any one of claims 1 to 5 , wherein the steel sheet is reheated by an induction heating device before being cooled to 150 ° C or lower.

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