Method for manufacturing hot-rolled steel sheet, method for predicting temperature history of hot-rolled steel sheet, and method for predicting hardening portion of hot-rolled steel sheet

Abstract

The present invention aims to provide a method for manufacturing a hot-rolled steel sheet capable of predicting a temperature history of a convex-concave of an end face of a spiral. A method for manufacturing a hot-rolled steel sheet according to an aspect of the present invention includes a step of measuring a surface temperature of a hot-rolled strip-shaped steel material, a step of calculating a temperature history in a natural cooling state after winding, assuming that the strip-shaped steel material is wound into a spiral shape in which a convex-concave does not exist in an end face, based on the surface temperature measured in the above measuring step, a step of actually winding the strip-shaped steel material after the above measuring step into a spiral shape, a step of scanning an end face of a spiral wound in the above winding step using a displacement meter and deriving a size of a convex-concave of the end face within a range of a radius of the spiral, and a step of predicting a temperature history in a natural cooling state of the convex-concave using the temperature history calculated in the above calculating step and the size of the convex-concave derived in the above deriving step.

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of a hot-rolled steel sheet, a temperature history prediction method of a hot-rolled steel sheet, and a hardening portion prediction method of a hot-rolled steel sheet. BACKGROUND

[0002] A hot-rolled steel sheet is manufactured by winding a hot-rolled strip-shaped steel material into a coil shape and cooling the wound coil to a normal temperature level. The hot-rolled steel sheet is again extracted in a strip shape and subjected to pickling and cold rolling, and becomes a cold-rolled steel sheet. As a problem point in the manufacture of the cold-rolled steel sheet, the fracture of the steel material at the time of threading can be cited. When the fracture of the steel material occurs, it is necessary to stop the threading line and perform a recovery work, the cost for recovery is high, and the production efficiency is reduced. In addition, the fracture of the steel material also becomes a cause of equipment failure.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-593

[0006] Patent Document 2: Japanese Patent Application Publication No. 2010-112958 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] As one of the causes of the fracture at the time of cold rolling of the steel material which is high in quenching property, the cracking of the end portion of the steel material can be cited. When the cracking of the end portion of the steel material occurs in the cold rolling, stress is concentrated at the cracked portion at the time of threading, the crack grows, and the fracture of the steel material is easily caused.

[0009] As the cause of the cracking, the winding shape defect of the coil after hot rolling can be cited. That is, when the winding defect exists in the coil after hot rolling, the unevenness of the end surface of the coil becomes large. When a large protrusion exists in the end surface of the coil, the protrusion functions as a fin, and thus the cooling speed of the protrusion becomes fast at the time of cooling of the coil. When the cooling speed of the protrusion becomes fast, hard phases such as bainite and martensite are easily mixed in the protrusion. As a result, a gap is generated at the time of cold rolling of the steel material, and the gap grows, and thus the cracking of the end portion is easily caused.

[0010] From such a viewpoint, the present inventors have found that, by predicting the temperature history of the unevenness (particularly, the protrusion) of the end surface of the coil, it is possible to previously recognize the possibility of the fracture of the steel material in the subsequent process.

[0011] Note that in Patent Document 1, it is described that the temperature unevenness on the run-out table (ROT) of the rolled steel sheet after hot rolling is predicted, and the manufacturing conditions of the rolled steel sheet before being wound by the winding machine are controlled in such a manner that the predicted temperature unevenness becomes small.

[0012] Further, in Patent Literature 2, there is described a technique in which, when the distance between the range finder and the end face of the metal plate coil is measured to calculate the telescope amount of the end face of the coil, it is identified whether the measurement value of the end portion of the coil is a tang shape or a telescope shape. In Patent Literature 2, it is described that, when the difference between the measured distances of the innermost coil metal plates at both ends of the inner diameter of the coil and the difference between the measured distances of the outermost coil metal plates at both ends of the outer diameter of the coil exceed threshold values, respectively, the coil is determined to be a coil in which the end portion of the metal plate is measured as a tang shape, and the telescope amount of the coil is calculated excluding the innermost coil and / or outermost coil distance data measured as the tang shape.

[0013] However, in Patent Literatures 1 and 2, the relationship between the concave-convex of the end face of the coil and the cracking of the end portion of the coil is not studied.

[0014] The present application is made based on the above-described circumstances, and aims to provide a hot-rolled steel sheet manufacturing method capable of predicting the temperature history of the concave-convex of the end face of the coil and a hot-rolled steel sheet temperature history prediction method. Further, the present application aims to provide a hardening portion prediction method of a hot-rolled steel sheet capable of predicting the presence or absence of cracking of the steel material in a subsequent process based on the temperature history of the concave-convex of the end face of the coil.

[0015] Solution to the problem

[0016] The hot-rolled steel sheet manufacturing method according to one aspect of the present application includes: a measurement step of measuring the surface temperature of a hot-rolled strip-shaped steel material; a first calculation step of calculating a temperature history in a natural cooling state after winding, assuming that the strip-shaped steel material is wound into a coil shape in which there is no concave-convex on the end face, based on the surface temperature measured by the measurement step; a winding step of actually winding the strip-shaped steel material after the measurement step into a coil shape; a derivation step of scanning the end face of the coil wound by the winding step with a displacement meter and deriving the size of the concave-convex of the end face in the range of the radius of the coil; and a first prediction step of predicting the temperature history in the natural cooling state of the concave-convex using the temperature history calculated by the first calculation step and the size of the concave-convex derived by the derivation step.

[0017] The hot-rolled steel sheet manufacturing method can predict the temperature history in the natural cooling state of the concave-convex of the end face of the coil formed by winding the strip-shaped steel material.

[0018] Preferably, the method for manufacturing a hot-rolled steel sheet further includes a second calculating step of calculating a phase change rate using the temperature history predicted by the first predicting step, and a second predicting step of predicting a hardened portion of the strip-shaped steel material using the phase change rate calculated by the second calculating step. The method for manufacturing a hot-rolled steel sheet can predict the presence or absence of a fracture of the steel material in a subsequent step by having the second calculating step and the second predicting step.

[0019] Preferably, in the deriving step, the size of the irregularity is derived based on a central value of the measured values measured by the displacement meter. Thus, by deriving the size of the irregularity based on the central value of the measured values measured by the displacement meter in the deriving step, the temperature history of the end surface of the scroll in a natural cooling state can be easily and accurately predicted.

[0020] Preferably, in the deriving step, the size of the irregularity is derived using a two-dimensional coordinate system defined by the protruding direction of the irregularity and the scanning direction of the displacement meter. Thus, by deriving the size of the irregularity using the two-dimensional coordinate system defined by the protruding direction of the irregularity and the scanning direction of the displacement meter in the deriving step, the temperature history of the end surface of the scroll in a natural cooling state can be easily and accurately predicted.

[0021] The temperature history prediction method of a hot-rolled steel sheet according to another aspect of the present application includes a measuring step of measuring a surface temperature of a hot-rolled strip-shaped steel material, a first calculating step of calculating a temperature history in a natural cooling state after winding, assuming that the strip-shaped steel material is wound into a scroll shape in which an irregularity is not present on an end surface, based on the surface temperature measured by the measuring step, a winding step of actually winding the strip-shaped steel material after the measuring step into a scroll shape, a deriving step of scanning an end surface of a scroll wound by the winding step using a displacement meter and deriving a size of an irregularity of the end surface within a range of a radius of the scroll, and a first predicting step of predicting a temperature history in a natural cooling state of the irregularity using the temperature history calculated by the first calculating step and the size of the irregularity derived by the deriving step.

[0022] The temperature history prediction method of a hot-rolled steel sheet can predict a temperature history in a natural cooling state of an irregularity of an end surface of a scroll formed by winding the strip-shaped steel material.

[0023] The hardening portion prediction method of the hot-rolled steel sheet according to still another aspect of the present application includes: a measurement step of measuring a surface temperature of a hot-rolled strip-shaped steel material; a first calculation step of calculating a temperature history in a natural cooling state after coiling, assuming that the strip-shaped steel material is coiled into a scroll shape in which there is no unevenness in an end surface; a coiling step of actually coiling the strip-shaped steel material after the measurement step into a scroll shape; an extraction step of extracting a size of the unevenness of the end surface of the scroll coiled in the coiling step in a range of a radius of the scroll; a first prediction step of predicting a temperature history in a natural cooling state of the unevenness using the temperature history calculated in the first calculation step and the size of the unevenness extracted in the extraction step; a second calculation step of calculating a phase change rate using the temperature history predicted in the first prediction step; and a second prediction step of predicting a hardening portion of the strip-shaped steel material using the phase change rate calculated in the second calculation step.

[0024] The hardening portion prediction method of the hot-rolled steel sheet can predict the presence or absence of a crack in the steel material in a subsequent step based on the temperature history of the unevenness of the end surface of the scroll.

[0025] Effects of Invention

[0026] As described above, the manufacturing method of the hot-rolled steel sheet according to one aspect of the present application and the temperature history prediction method of the hot-rolled steel sheet according to another aspect of the present application can predict the temperature history of the unevenness of the end surface of the scroll. In addition, the hardening portion prediction method of the hot-rolled steel sheet according to still another aspect of the present application can predict the presence or absence of a crack in the steel material in a subsequent step based on the temperature history of the unevenness of the end surface of the scroll. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flowchart showing the manufacturing method of the hot-rolled steel sheet according to one embodiment of the present application.

[0028] Figure 2 is a schematic view showing a manufacturing apparatus of the hot-rolled steel sheet used in the manufacturing method of the hot-rolled steel sheet according to Figure 1

[0029] Figure 3 is a schematic view showing a scanning position of the end surface of the scroll by the displacement meter in the extraction step of the manufacturing method of the hot-rolled steel sheet according to Figure 1

[0030] Figure 4 is a schematic view showing a scanning position of the end surface of the scroll by the displacement meter in the extraction step of the manufacturing method of the hot-rolled steel sheet according to Figure 1

[0031] Figure 5 is a schematic view showing a scanning position of the end surface of the scroll by the displacement meter in the extraction step of the manufacturing method of the hot-rolled steel sheet according to Figure 1 ​​​Explanatory view of the derivation step of the size of the unevenness in the derivation process of the manufacturing method of the hot-rolled steel sheet.

[0032] Figure 6 is a flowchart showing a manufacturing method of a hot-rolled steel sheet in a different manner from the manufacturing method of the hot-rolled steel sheet. Figure 1

[0033] Figure 7 is a graph showing a temperature history of the upper end surface of the imaginary scroll based on the first calculation process of No. 1 in a natural cooling state after just being wound.

[0034] Figure 8 is a graph showing a measurement result of the shape of the unevenness of the end surface of the scroll measured by the displacement meter in the derivation process of No. 1 and a derivation result of the size of the unevenness of the end surface of the scroll derived by the derivation section.

[0035] Figure 9 is a graph showing a temperature history of the end surface of the scroll in a natural cooling state after just being wound predicted by the first prediction process of No. 1 and a measured value of the temperature of the end surface.

[0036] Figure 10 is a graph showing a temperature history of the upper end surface of the imaginary scroll in a natural cooling state after just being wound calculated by the first calculation process of No. 2.

[0037] Figure 11 is a graph showing a measurement result of the shape of the unevenness of the end surface of the scroll measured by the displacement meter in the derivation process of No. 2 and a derivation result of the size of the unevenness of the end surface of the scroll derived by the derivation section.

[0038] Figure 12 is a graph showing a temperature history of the end surface of the scroll in a natural cooling state after just being wound predicted by the first prediction process of No. 2 and a measured value of the temperature of the end surface. DETAILED DESCRIPTION

[0039] Hereinafter, an embodiment of the present application will be described in detail with appropriate reference to the accompanying drawings.

[0040] [First Embodiment]

[0041] [Manufacturing Method of Hot-Rolled Steel Sheet]

[0042] Figure 1 ​A manufacturing method of a hot-rolled steel sheet includes a step of measuring a surface temperature of a hot-rolled strip-shaped steel material (measurement step S1), a step of calculating a temperature history in a natural cooling state after winding, assuming that the strip-shaped steel material is wound in a scroll shape in which there is no concave-convex on an end surface, based on the surface temperature measured by the measurement step S1 (first calculation step S2), a step of actually winding the strip-shaped steel material after the measurement step S1 in a scroll shape (winding step S3), a step of scanning an end surface of a scroll wound by the winding step S3 with a displacement meter and deriving a size of a concave-convex of the end surface in a range of a radius of the scroll (derivation step S4), and a step of predicting a temperature history in a natural cooling state of the concave-convex using the temperature history calculated by the first calculation step S2 and the size of the concave-convex derived by the derivation step S4 (first prediction step S5). The measurement step S1, the first calculation step S2, the winding step S3, the derivation step S4, and the first prediction step S5 constitute a temperature history prediction method of a hot-rolled steel sheet according to an aspect of the present application. Note that the "scroll shape" refers to a spiral shape as viewed in an axial direction. The "end surface of a scroll" is a surface of a scroll that is perpendicular to a central axis. That is, the "end surface of a scroll" refers to a surface formed by an end in a width direction of a strip-shaped steel material.

[0043] According to the manufacturing method of a hot-rolled steel sheet, by predicting a temperature history of a concave-convex of an end surface of a scroll, it is possible to previously recognize a possibility of a fracture of a steel material when a cold-rolled sheet is manufactured using the hot-rolled steel sheet.

[0044] In describing the manufacturing method of a hot-rolled steel sheet, first, refer to Figure 2 A manufacturing apparatus 1 of a hot-rolled steel sheet (hereinafter, also simply referred to as "manufacturing apparatus 1") capable of implementing the manufacturing method of a hot-rolled steel sheet will be described.

[0045] [Manufacturing apparatus of hot-rolled steel sheet]

[0046] Figure 2A manufacturing apparatus 1 for a steel sheet includes a hot rolling device 2 that has a plurality of pairs of rolling rolls 2a, a conveyance unit 2b that conveys a strip-shaped steel material X hot-rolled by the rolling rolls 2a, and a winding machine 2c that winds the strip-shaped steel material X conveyed to the conveyance unit 2b into a spiral shape, and constitutes a hot rolling line; a measuring device 3 that measures a surface temperature of the strip-shaped steel material X conveyed by the conveyance unit 2b; a calculating device 4 that calculates a temperature history in a natural cooling state of a spiral (imaginary spiral) assumed to be a case where the strip-shaped steel material X is wound into a spiral shape in which a concave-convex does not exist on an end surface, on the basis of the surface temperature of the strip-shaped steel material X measured by the measuring device 3; an deriving device 5 that derives a size of a concave-convex of an end surface E of a spiral X1 wound by the winding machine 2c in a range of a radius of the spiral X1 and constitutes a deriving line; and a predicting device 6 that predicts a temperature history in a natural cooling state of the concave-convex using the temperature history calculated by the calculating device 4 and the size of the concave-convex derived by the deriving device 5. In addition, the manufacturing apparatus 1 includes a natural cooling device 7 that performs natural cooling on the spiral X1 after the deriving line. Note that the manufacturing apparatus 1 can further include a cold rolling device that cold-rolls the spiral X1 after the natural cooling by the natural cooling device 7, an annealing device that anneals the strip-shaped steel material after the cold rolling by the cold rolling device, and the like.

[0047] The hot rolling device 2 conveys the strip-shaped steel material X to the winding machine 2c by the conveyance unit 2b after rough rolling and finish rolling are performed on a thick steel plate heated by a heating furnace (not shown), and winds the strip-shaped steel material X into a spiral shape by the winding machine 2c. The conveyance unit 2b has, for example, a plurality of conveyance rolls.

[0048] The measuring device 3 has a non-contact temperature sensor 3a such as a thermographic camera. The measuring device 3 measures a surface temperature of the strip-shaped steel material X after hot rolling and before winding by the winding machine 2c. The measuring device 3 measures the temperature of the entire area (total length and total width) of the surface of the strip-shaped steel material X.

[0049] The calculating device 4 is constituted by, for example, a computer. The calculating device 4 assumes a spiral (imaginary spiral) in which a concave-convex does not exist on an end surface, which is formed by winding the strip-shaped steel material X, to be a cylinder, and calculates a temperature history in a natural cooling state of the imaginary spiral by a two-dimensional model of a polar coordinate system.

[0050] The deriving device 5 has a conveyor 5a that carries the scroll Xl wound by the winding machine 2c, a displacement meter 5b that scans the end face E of the scroll Xl carried on the conveyor 5a and measures the shape of the end face E, and a deriving section 5c that derives the magnitude of the unevenness of the end face E of the scroll Xl based on the shape measured by the displacement meter 5b. The displacement meter 5b measures the shape of the end face E of the scroll Xl in the range of the radius of the scroll Xl, and preferably in the range of the diameter. As the displacement meter 5b, for example, a laser displacement meter is used. The displacement meter 5b has a laser irradiation section that irradiates laser light to the end face E of the scroll Xl and a light receiving element that receives a part of the light reflected by the end face E. The displacement meter 5b reads the reflected light of the laser light irradiated from the laser irradiation section to the end face E by the above-mentioned light receiving element. The displacement meter 5b is configured to be able to measure the shape of the end face E of the scroll Xl by a triangulation method. The deriving section 5c is configured, for example, by a computer. The displacement meter 5b and the deriving section 5c can also be integrally configured.

[0051] The prediction device 6 is configured, for example, by a computer. The prediction device 6 predicts the temperature history of the unevenness of the end face E of the scroll Xl in the case where the scroll Xl assumed to be actually wound by the winding machine 2c is naturally cooled by the natural cooling device 7 or the like.

[0052] The natural cooling device 7 naturally cools the scroll Xl of which the shape of the end face E is measured by the deriving device 5. In the manufacturing apparatus 1, the scroll Xl after the winding by the winding machine 2c is heated to the degree of 500°C or more. The natural cooling device 7 air-cools the heated scroll Xl to the normal temperature. The manufacturing apparatus 1 naturally cools the scroll Xl wound by the winding machine 2c, and thus when a large convex portion exists in the end face E of the scroll Xl, the cooling speed of the convex portion is likely to be faster than that of other portions.

[0053] 〔Strip Steel Material〕

[0054] The strip steel material X is formed by heating and hot-rolling a slab. The strip steel material X has, for example, a composition of carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, molybdenum, and copper, and the remaining portion is iron and inevitable impurities. In the case where the strip steel material X is subjected to cold-rolling, the winding temperature in the winding process S3 can be set to be equal to or higher than the Ms (martensite transformation start temperature) of the strip steel material X.

[0055] As an upper limit of the carbon equivalent Ceq of the strip-shaped steel material X represented by the following formula (1), 0.75% is preferable, and 0.70% is more preferable. When the carbon equivalent Ceq of the strip-shaped steel material X exceeds the above upper limit, the possibility of generation of the phase of martensite can be high in the case where the cooling speed at the time of natural cooling is high. On the other hand, as a lower limit of the above carbon equivalent Ceq, there is no particular limitation, but for example, it can be set to 0.55%. When the above carbon equivalent Ceq does not satisfy the above lower limit, the transformation is completed approximately before the winding process S3, and thus the phase of martensite is difficult to generate, and the possibility of generation of edge cracks in the scroll X1 in the subsequent processes is low. Therefore, the method of manufacturing the hot-rolled steel sheet is preferably used in the case where the carbon equivalent Ceq of the strip-shaped steel material X is equal to or higher than the above lower limit.

[0056] Ceq [%] = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 (1)

[0057] wherein [C], [Si], [Mn], [Ni], [Cr], [Mo], and [V] represent the contents (mass %) of C, Si, Mn, Ni, Cr, Mo, and V, respectively.

[0058] (Measurement Process)

[0059] The measurement process S1 is performed by the measurement device 3. In the measurement process S1, the surface temperature of the strip-shaped steel material X after the hot-rolling and before the winding by the winding machine 2c is measured in the range of the entire area (total length x total width) of the surface of the strip-shaped steel material X.

[0060] (First Calculation Process)

[0061] The first calculation process S2 is performed by the calculation device 4. In the first calculation process S2, for example, a scroll (imaginary scroll) in which the end face where the convex and concave are not present is formed by winding the strip-shaped steel material X is assumed to be a cylindrical shape, and the temperature history in the natural cooling state of the imaginary scroll is calculated by a two-dimensional model of a polar coordinate system. The first calculation process S2 can be performed before the winding process S3, or can be performed after the winding process S3. In addition, the first calculation process S2 can be performed after the derivation process S4.

[0062] Reference Figure 3 An example of the calculation step of the temperature history in the natural cooling state of the imaginary scroll X2 performed by the first calculation process S2 will be described. In the first calculation process S2, the temperature history in the natural cooling state of the imaginary scroll X2 is calculated using a two-dimensional model of a polar coordinate system in which the end face of one side of the imaginary scroll X2 (the end face of the side where the convex and concave are not present) is assumed to be a cylindrical shape. Figure 3The coordinates of the intersection of the imaginary plane (the upper end surface of the imaginary scroll X2) and the central axis of the imaginary scroll X2 are set as the origin O (0, 0), the coordinate of the central axis direction with the origin O as the reference is set as z [m], and the coordinate of the radial direction with the origin O as the reference is set as r [m] in a two-dimensional model of a polar coordinate system, and the temperature history of the natural cooling state of the imaginary scroll X2 is calculated. In the first calculation process S2, a plurality of calculation points are provided in the central axis direction and the radial direction of the imaginary scroll X2, and the temperature history of the natural cooling state is calculated for each calculation point. Specifically, in the first calculation process S2, the following equation (2) is used for the calculation point inside the imaginary scroll X2 (the calculation point of the portion not exposed to the outside air), the following equation (3) is used for the calculation point of the portion exposed to the outside air, the temperature of the calculation point of the imaginary scroll X2 at t time after the winding is set as Φ [°C] with the winding immediately after the winding as the reference, and the temperature history of the natural cooling state of the imaginary scroll X2 is calculated.

[0063] [Mathematical expression 1]

[0064]

[0065] [Mathematical expression 2]

[0066]

[0067] Note that in the above equation (2) and the above equation (3), the meanings are as follows, that is, H: enthalpy [kcal / kg], p: density [kg / m 3 ] of the portion of the strip-shaped steel material corresponding to the calculation point, λ r : radial thermal conductivity [kcal / m / hr / °C], λ z : axial thermal conductivity [kcal / m / hr / °C], ε: emissivity [-], σ: Stefan-Boltzmann constant [kcal / m 2 / hr / °C 4 ], F 12 : form factor [-], α: natural convection heat transfer rate [kcal / hr / m 2 / °C], V: volume [m 3 ] of the portion of the strip-shaped steel material corresponding to the calculation point, A: surface area [m 2 ] of the portion of the strip-shaped steel material corresponding to the calculation point. In the above equation (3), q is a boundary condition. With respect to the inner peripheral surface of the imaginary scroll X2, the boundary condition is given by the following equation (4), and with respect to the end surface and the outer peripheral surface of the imaginary scroll X2, the boundary condition is given by the following equation (5). In the above equation (4) and the above equation (5), the meanings are as follows, that is, T: surface temperature [°C] of the portion corresponding to the calculation point measured by the measurement process S1, T f : atmospheric temperature [°C] at the time of natural cooling.

[0068] [Mathematical Expression 3]

[0069] q=εσF 12 (T 4 -T f 4 )+α(TT f ) 1.25 ···(4)

[0070] [Mathematical Expression 4]

[0071] q=εσ(T 4 -T f 4 )+α(TT f ) 1.25 ···(5)

[0072] (Winding process)

[0073] In the winding process S3, the strip steel X, whose surface temperature was measured in the measurement process S1, is wound into a spiral shape at a high temperature using a winding machine 2c. From the viewpoint of preventing the formation of martensitic phases, the winding temperature in the winding process S3 is preferably above the Ms temperature of the strip steel X. As a lower limit of the above winding temperature, 400°C is preferred, more preferably 500°C, and even more preferably 560°C. On the other hand, as an upper limit of the above winding temperature, 700°C is preferred, and more preferably 670°C. When the winding temperature is below the lower limit, the strength of the strip steel X is too high, and the load on the equipment in subsequent processes such as cold rolling may increase. Conversely, when the winding temperature exceeds the upper limit, the proportional thickness of the surface of the strip steel X may increase. It should be noted that "winding temperature" refers to the surface temperature of the strip steel X before winding.

[0074] (Export process)

[0075] The export process S4 is performed by the export device 5. For example... Figure 2 as well as Figure 4 As shown, in the outgoing process S4, the end face E of the scroll X1 being transported on the conveyor 5a is scanned using a displacement gauge 5b, and the shape of the unevenness of the end face E is measured within the radius of the scroll X1, preferably within the diameter. Furthermore, in the outgoing process S4, the size of the unevenness of the end face E is determined using the outgoing section 5c and a two-dimensional coordinate system defined by the protruding direction of the unevenness (the direction of the central axis of the scroll X1) and the scanning direction of the displacement gauge 5b (the radial direction of the scroll X1). This method of manufacturing hot-rolled steel sheet, by using the aforementioned two-dimensional coordinate system to determine the size of the unevenness of the end face E, allows for easy and accurate prediction of the temperature history of the unevenness of the end face E of the scroll X1 under natural cooling conditions using the first prediction process S5 described later.

[0076] In the deriving step S4, the size of the concave-convex of the end face E is preferably derived based on the central value of the measured values measured by the displacement meter 5b. Specifically, in the deriving step S4, after the end face E of the coil Xl is continuously measured in the range of the radius by the displacement meter 5b, the size of the concave-convex of the end face E is derived based on the central value of the measured values measured by the displacement meter 5b using the deriving section 5c. The manufacturing method of the hot-rolled steel sheet derives the size of the concave-convex of the end face E based on the above-described central value, so that even in the case where a large protruding portion (crimping) due to winding deviation is formed at the end portion of the outer circumferential side and / or the inner circumferential side of the coil Xl, the size of the concave-convex of the entire coil Xl can be appropriately measured. As a result, it is easy to easily and accurately predict the temperature history of the concave-convex of the end face E of the coil Xl in the natural cooling state using the first predicting step S5.

[0077] Referring to Figure 4 and Figure 5 An example of the deriving step of the size of the concave-convex of the end face E of the coil Xl by the deriving step S4 will be described. First, in the deriving step S4, the end face E of the coil Xl carried on the conveyer 5a is scanned by the displacement meter 5b, and the shape of the concave-convex of the end face E is measured in the range of the radius of the coil Xl. Next, the reference surface R of the end face E is set based on the central value of the measured values measured by the displacement meter 5b. Next, using a two-dimensional model of a polar coordinate system in which the coordinates of the intersection of the central axis Z of the coil Xl and the reference surface R are set as the origin O (0, 0), the coordinates in the central axis direction from the origin O are set as z [m], and the coordinates in the radial direction from the origin O are set as r [m], the size of the concave-convex of the end face E is derived. Specifically, after the coil Xl is divided into a plurality of regions in the radial direction, the size of the concave-convex is averaged for each region, and the average value is made to fall into the two-dimensional coordinate system, thereby deriving the size of the concave-convex of the region. At this time, the lengths of the regions in the radial direction of the coil Xl can also be made different. For example, the lengths of a pair of regions located at both ends in the radial direction can be set smaller than those of the other regions, so as to easily reflect the concave-convex due to crimping. In addition, a constant threshold value can also be set, and the protruding amount below the threshold value is treated as a protruding amount that does not correspond to the concave-convex.

[0078] (First predicting step)

[0079] The first predicting step S5 is performed by the predicting device 6. In the first predicting step S5, the temperature history of the concave-convex of the end face E of the coil Xl in the natural cooling state is predicted based on the immediately after winding state. In the first predicting step S5, the temperature history of the concave-convex of the end face E in the natural cooling state is predicted using the above-described equations (2) to (5). At this time, with respect to the reference surface R, the boundary condition of the above-described equation (3) is given by the above-described equation (5).

[0080] <Advantages>

[0081] The hot-rolled steel sheet manufacturing method can predict the temperature history of the concave-convex of the end surface E of the vortex X1 formed by winding the strip steel material X in the natural cooling state. Therefore, according to the hot-rolled steel sheet manufacturing method, it is possible to anticipate in advance the possibility of steel material breakage when a cold-rolled sheet is manufactured using the strip steel material X.

[0082] The hot-rolled steel sheet temperature history prediction method can predict the temperature history of the concave-convex of the end surface E of the vortex X1 formed by winding the strip steel material X in the natural cooling state. Therefore, according to the hot-rolled steel sheet temperature history prediction method, it is possible to anticipate in advance the possibility of steel material breakage when a cold-rolled sheet is manufactured using the strip steel material X.

[0083] [Second Embodiment]

[0084] <Hot-rolled steel sheet manufacturing method>

[0085] Figure 6 The hot-rolled steel sheet manufacturing method includes a step of measuring the surface temperature of a hot-rolled strip steel material (measurement step S11), a step of calculating the temperature history in the natural cooling state after winding, assuming that the strip steel material is wound into a vortex shape in which there is no concave-convex on the end surface, based on the above surface temperature measured by the measurement step S11 (first calculation step S12), a step of actually winding the strip steel material after the measurement step S11 into a vortex shape (winding step S13), a step of scanning the end surface of the vortex wound by the winding step S13 using a displacement meter and deriving the size of the concave-convex of the above end surface within the range of the radius of the vortex (derivation step S14), a step of predicting the temperature history in the natural cooling state of the above concave-convex using the temperature history calculated by the first calculation step S12 and the size of the concave-convex derived by the derivation step S14 (first prediction step S15), a step of calculating the phase transformation rate (ferrite-pearlite transformation rate) using the temperature history predicted by the first prediction step S15 (second calculation step S16), and a step of predicting the hardened portion of the strip steel material using the phase transformation rate calculated by the second calculation step S16 (second prediction step S17). The measurement step S11, the first calculation step S12, the winding step S13, the derivation step S14, the first prediction step S15, the second calculation step S16, and the second prediction step S17 constitute the hot-rolled steel sheet hardened portion prediction method of one aspect of the present application. As for the measurement step S11, the first calculation step S12, the winding step S13, and the derivation step S14, it is possible to use the same as the measurement step S11, the first calculation step S12, the winding step S13, and the derivation step S14 of the hot-rolled steel sheet temperature history prediction method of the first embodiment. Figure 1The steps of the measurement process S1, the first calculation process S2, the winding process S3, and the derivation process S4 are the same as those of the first prediction process S5, and thus the description thereof is omitted. Note that, in the first calculation process S12, the temperature history can also be calculated using the following Equation (6) instead of the above-described Equation (2) and using the following Equation (7) instead of the above-described Equation (3), in the same manner as in the first prediction process S15 described later.

[0086] (First prediction process)

[0087] In the first prediction process S15, the allotropic heat Q t [kcal / m 3 / hr] calculated by the second calculation process S16 described later is added to calculate the temperature history of the strip-shaped steel material. Specifically, in the first prediction process S15, the temperature history is predicted using the following Equation (6) instead of the above-described Equation (2) and using the following Equation (7) instead of the above-described Equation (3). The first prediction process S15 can be performed in the same manner as the first prediction process S5 of the first embodiment except that the following Equation (6) is used instead of the above-described Equation (2) and the following Equation (7) is used instead of the above-described Equation (3). Figure 1

[0088] [Equation 5]

[0089]

[0090] [Equation 6]

[0091]

[0092] (Second calculation process)

[0093] The second calculation process S16 can be performed by a computer, for example. In the second calculation process S16, the phase change rate is calculated from an isothermal transformation equation including the influence of the γ grain diameter. In the second calculation process S16, the allotropic heat Q t corresponding to the calculated phase change rate is also calculated. Specifically, in the second calculation process S16, the phase change rate X [-] is calculated using the following Equation (8) and the following Equation (9), and the allotropic heat Q t [kcal / m 3 / hr] of the time t is calculated using the following Equation (10). The allotropic heat Q t calculated by the second calculation process S16 is used for the prediction of the temperature history in the first prediction process S15 described above. The allotropic heat Q t can also be used for the calculation of the temperature history in the first calculation process S12 described above.

[0094] [Equation 7] ​

[0095]

[0096] [Equation 8]

[0097]

[0098] [Equation 9]

[0099] Q t = Q total ΔX•••(10)

[0100] Note that in the above Equations (8) to (10), the meanings are as follows, i.e., S: a nucleation area term, K: a temperature-dependent term, Q total : total transformation heat [kcal / m 3 / hr], T: temperature [°C] of the calculation point calculated by the first calculation process S12 or the first prediction process S15. Further, a, b, c, m, n in the above Equations (8) to (10) are constants adjusted according to the type of the steel material. These constants are determined, for example, by making a TTT diagram using a hot-rolled crop after rough rolling, and adjusting them in such a manner that the calculated values agree with the experimental values. However, the transformation rate is affected by the state of the prior structure such as austenite grain size, and thus varies depending on the hot-rolling conditions. Therefore, the value of c is adjusted according to the hot-rolling conditions.

[0101] (Second prediction process)

[0102] The second prediction process S17 can be performed by a computer, for example. In the second prediction process S17, the hardening portion of the end surface of the spiral wound by the winding process S13 is predicted using the transformation ratio calculated by the second calculation process S16. In the second prediction process S17, for example, the relationship between the transformation ratio and the hardness is previously obtained, and the hardening portion is predicted from the calculated transformation ratio. In the second prediction process S17, for example, a threshold value of the hardness at which the steel material is likely to be fractured in the subsequent process such as the cold-rolling process can be previously set, and the calculated transformation ratio is compared with the threshold value, thereby predicting the presence or absence of the fracture of the steel material in the subsequent process. Further, in the second prediction process S17, a threshold value of the transformation ratio at which the steel material is likely to be fractured in the subsequent process such as the cold-rolling process can be previously set, and the calculated value is compared with the threshold value, thereby predicting the presence or absence of the fracture of the steel material.

[0103] <Advantages>

[0104] The method of manufacturing a hot-rolled steel sheet can predict the presence or absence of the fracture of the steel material in the subsequent process using the transformation ratio calculated by the second calculation process S16. According to the method of manufacturing a hot-rolled steel sheet, by previously cutting out the hardening portion that becomes the cause of the fracture in the subsequent process, the risk of the fracture of the steel material at the time of passing through the roll can be reduced.

[0105] The method for predicting the hardening of hot-rolled steel sheets can use the phase transformation rate calculated by the second calculation process S16 to predict whether the steel will fracture in subsequent processes.

[0106] [Other Implementation Methods]

[0107] The above embodiments do not limit the structure of the present invention. Therefore, the above embodiments can be modified by omitting, substituting, or adding constituent elements of each part based on the description in this specification and common technical knowledge, and these modifications should be interpreted as falling entirely within the scope of the present invention.

[0108] For example, in the above-described derivation process, the size of the unevenness of the end face can be determined based on the average value, mode, etc. of the unevenness of the end face of the scroll. However, as described above, from the viewpoint that the overall size of the unevenness of the scroll can be appropriately measured even in the case of large protrusions such as overlap in the above-described derivation process, it is preferable to determine the size of the unevenness of the end face of the scroll based on the center value of the measured value.

[0109] In the above-described derivation process, it is also possible to determine the size of the concavity / convexity without using a two-dimensional coordinate system defined by the protruding direction of the concavity / convexity of the end face of the scroll and the scanning direction of the displacement gauge. For example, in the above-described derivation process, the measurement result measured by the displacement gauge can be directly used as the size of the concavity / convexity of the end face of the scroll for derivation.

[0110] Example

[0111] The present invention will be further described in detail below through embodiments, but the present invention is not limited to these embodiments.

[0112] [No.1]

[0113] use Figure 2 The manufacturing equipment 1 shown manufactured a hot-rolled steel sheet. First, using a non-contact temperature sensor 3a (FLIR thermal imager "CPA-SC7100"), the surface temperature of the strip steel X after hot rolling and before winding by the winding machine 2c was measured over the entire area (total length and total width) of the surface of the strip steel X (measurement step). Next, the temperature history under natural cooling conditions of a spiral (imaginary spiral) assuming that the strip steel X is wound into a spiral shape without any concave or convex end faces was calculated using the above formulas (2) to (5) (first calculation step). In this first calculation step, 10 calculation points were set in the central axis direction of the imaginary spiral and 50 points were set in the radial direction (total: 10 × 50), and the temperature history under natural cooling conditions was calculated for each calculation point. Figure 7Fig. 6 shows a temperature history in a natural cooling state after winding of an upper end surface 410 mm away from the center axis in the radial direction in the above-mentioned imaginary vortex.

[0114] Next, the strip steel X was actually wound using the winding machine 2c (winding step). Next, the end surface E of the wound vortex Xl was scanned in the diameter range using the displacement meter 5b (laser displacement meter "IL-2000" manufactured by Keyence Corporation), and the shape of the convexities and concavities of the end surface E of the vortex Xl was measured. Further, after the reference surface of the end surface E was set based on the central value of the measured values measured by the displacement meter 5b, the size of the convexities and concavities of the end surface E was derived using a two-dimensional coordinate system defined by the protruding direction of the convexities and concavities and the scanning direction of the displacement meter 5b using the derivation unit 5c (derivation step). Note that the convexities and concavities of the end surface E of the vortex Xl were set to be positive when protruding toward the displacement meter 5b side and to be negative when being concave toward the conveyor 5a side. In this derivation step, the vortex Xl was divided into 13 regions in the radial direction, and the size of the convexities and concavities was averaged for each region, and the average value was plotted in the two-dimensional coordinate system and derived as the size of the convexities and concavities of the region. In this derivation step, the length of a pair of regions located at both ends in the radial direction was set to be smaller than the length of the other regions so as to easily reflect the convexities and concavities due to the collapse. Specifically, the length of the regions located at both ends in the radial direction was set to be 1 / 2 of the length of the other regions. Further, the threshold value of the convexities and concavities was set to be 10 mm, and with respect to the average value of the convexities and concavities of each region, values smaller than 10 mm were discarded. In Figure 8 Fig. 7 shows the measurement results of the shape of the convexities and concavities of the end surface E of the vortex Xl measured by the displacement meter 5b in the derivation step and the derivation results of the size of the convexities and concavities of the end surface E of the vortex Xl derived by the derivation unit 5c.

[0115] Next, with respect to the convexities and concavities of the end surface E of the vortex Xl derived in the derivation step, the temperature history in the natural cooling state after winding was predicted using the calculation results calculated in the first calculation step and the above-mentioned equations (2) to (5) (first prediction step). In Figure 9 Fig. 8 shows the prediction results of the end surface E of the vortex Xl at a position 410 mm away from the center axis in the radial direction predicted by the first prediction step. Further, Fig. 9 shows the measured values of the temperature of the end surface E of the vortex Xl 23 minutes after the winding in the position corresponding to the position predicted by the first prediction step. Figure 9

[0116] [No. 2]

[0117] The same manufacturing apparatus 1 as in No. 1 was used, and the measurement step, the first calculation step, the winding step, the derivation step, and the first prediction step were performed in the same manner as in No. 1. In Figure 10 ​The diagram shows the temperature history of the upper surface of the hypothetical vortex, located 410 mm radially away from the central axis, under natural cooling conditions, based on the initial winding state. Additionally, in... Figure 11 The diagram shows the measurement results of the shape of the concavity / convexity of the end face E of the volute X1 measured by the displacement gauge 5b in the above-mentioned export process, and the export results of the size of the concavity / convexity of the end face E of the volute X1 exported by the export section 5c. Furthermore, in Figure 12 The diagram shows the prediction result of the first prediction process for the end face E of the scroll X1 located 410 mm away from the central axis in the radial direction, as well as the measured temperature of the end face E of the scroll X1 corresponding to the position predicted by the first prediction process 24 minutes after winding.

[0118] like Figures 7 to 12 As shown, No. 1, which was determined to have unevenness by the above-described derivation process, and No. 2, which was determined not to have unevenness, are both prediction results from the first prediction process that are approximately consistent with the measured values. Therefore, it can be concluded that both No. 1 and No. 2 can accurately predict the temperature history of unevenness on the end face E of the vortex X1.

[0119] [No.3]

[0120] Using the same manufacturing apparatus 1 as No.1, a measurement process, a first calculation process, a winding process, a decoupling process, and a first prediction process were performed. Furthermore, in No.3, the phase transformation rate of the end face of the spiral was calculated using the aforementioned equations (8) and (9), and the heat of change (second calculation process) was calculated using the aforementioned equation (10). In No.3, the temperature history was predicted using the aforementioned equations (6) and (7) in the first calculation process and the first prediction process. Furthermore, in No.3, the Vickers hardness [Hv] at the location (calculation point) where the phase transformation rate was calculated in the second calculation process was measured was also measured. Table 1 shows the phase transformation rate calculated by No.3 and the Vickers hardness measured by No.3.

[0121] [Table 1]

[0122]

[0123] As shown in Table 1, the calculated point A, with a lower phase transformation rate, has a higher Vickers hardness compared to calculated points B and C, which have higher phase transformation rates. This indicates that the phase transformation rate is related to the hardness of the spiral. Therefore, by calculating the phase transformation rate using the second calculation process, the hardened portion of the spiral can be predicted. Furthermore, by pre-setting a threshold for hardness or phase transformation rate that may cause steel fracture in subsequent processes such as cold rolling, and comparing this threshold with the calculated phase transformation rate, it is possible to predict whether steel fracture will occur in subsequent processes.

[0124] Industrial applicability

[0125] As explained above, the manufacturing method of the hot-rolled steel sheet according to one aspect of the present application is suitable for detecting in advance the possibility of the fracture of the steel material at the time of manufacturing the cold-rolled sheet or the like.

[0126] Explanation of Reference Signs:

[0127] 1 Manufacturing apparatus of hot-rolled steel sheet

[0128] 2 Hot-rolling device

[0129] 2a Rolling roll

[0130] 2b Conveyance section

[0131] 2c Coiler

[0132] 3 Measuring device

[0133] 3a Non-contact temperature sensor

[0134] 4 Calculating device

[0135] 5 Deriving device

[0136] 5a Conveyor

[0137] 5b Displacement meter

[0138] 5c Deriving section

[0139] 6 Predicting device

[0140] 7 Natural cooling device

[0141] X Steel strip

[0142] X1 Spiral

[0143] X2 Imaginary spiral

[0144] E End surface

[0145] O Origin

[0146] R Reference surface of end surface of spiral

[0147] Z Center axis of spiral

Claims

1. A method for manufacturing hot-rolled steel plate, wherein, The method for manufacturing the hot-rolled steel plate includes: The measurement process involves measuring the surface temperature of hot-rolled strip steel. The first calculation process calculates the temperature history of the strip steel under natural cooling conditions after winding, assuming that the strip steel is wound into a spiral shape without any unevenness at the end face, based on the surface temperature measured by the measurement process. The winding process involves actually winding the strip steel after the measurement process into a spiral shape. In the export process, a displacement gauge is used to scan the end face of the spiral wound in the winding process, and the size of the unevenness of the end face is exported within the radius of the spiral; and The first prediction step uses the temperature history calculated by the first calculation step and the size of the bumps derived by the derivation step to predict the temperature history of the bumps under natural cooling conditions.

2. The method for manufacturing hot-rolled steel plate according to claim 1, wherein, The method for manufacturing the hot-rolled steel plate further includes: The second calculation step uses the temperature history predicted by the first prediction step to calculate the phase transition rate; and The second prediction step uses the phase transformation rate calculated by the second calculation step to predict the hardened portion of the strip steel.

3. The method for manufacturing hot-rolled steel sheet according to claim 1 or 2, wherein, In the export process, the size of the concavity and convexity is determined based on the center value of the measured value determined by the displacement gauge.

4. The method for manufacturing hot-rolled steel sheet according to claim 1 or 2, wherein, In the export process, the size of the concave and convex surfaces is determined using a two-dimensional coordinate system defined by the protruding direction of the concave and convex surfaces and the scanning direction of the displacement gauge.

5. A method for predicting the temperature history of hot-rolled steel plates, wherein, The method for predicting the temperature history of hot-rolled steel plates includes: The measurement process involves measuring the surface temperature of hot-rolled strip steel. The first calculation process calculates the temperature history of the strip steel under natural cooling conditions after winding, assuming that the strip steel is wound into a spiral shape without any unevenness at the end face, based on the surface temperature measured by the measurement process. The winding process involves actually winding the strip steel after the measurement process into a spiral shape. In the export process, a displacement gauge is used to scan the end face of the spiral wound in the winding process, and the size of the unevenness of the end face is exported within the radius of the spiral; and The first prediction step uses the temperature history calculated by the first calculation step and the size of the bumps derived by the derivation step to predict the temperature history of the bumps under natural cooling conditions.

6. A method for predicting the hardened portion of hot-rolled steel plates, wherein, The method for predicting the hardened portion of hot-rolled steel plates includes: The measurement process involves measuring the surface temperature of hot-rolled strip steel. The first calculation process calculates the temperature history of the strip steel under natural cooling conditions after winding, assuming that the strip steel is wound into a spiral shape without any unevenness at the end face, based on the surface temperature measured by the measurement process. The winding process involves actually winding the strip steel after the measurement process into a spiral shape. In the export process, a displacement gauge is used to scan the end face of the vortex formed by the winding process, and the size of the concavity and convexity of the end face is exported within the radius of the vortex. The first prediction step uses the temperature history calculated by the first calculation step and the size of the bumps derived by the derivation step to predict the temperature history of the bumps under natural cooling conditions. The second calculation step uses the temperature history predicted by the first prediction step to calculate the phase transition rate; and The second prediction step uses the phase transformation rate calculated by the second calculation step to predict the hardened portion of the strip steel.

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