JP5515411B2 - Steel heating method, heating control device and program - Google Patents

Description

  The present invention relates to a steel material heating method, a heating control device, and a program for preventing generation of scale soot due to internal oxidation.

  For example, the heating in a continuous billet furnace ensures the temperature at which the properties required for the product, such as material, surface quality, dimensional accuracy such as width and thickness, etc., are created in the subsequent steel rolling mill. To be done. Therefore, it is very important to heat the steel material under appropriate conditions in the heating furnace.

  However, during this heating process, selective oxidation along the grain boundaries of the steel surface layer portion (hereinafter also referred to as “grain boundary oxidation”), and point-like oxides (hereinafter “ May also be called “subscale”. This grain boundary oxidation and subscale layer (hereinafter also referred to as “internal oxide layer” together) may remain after rolling, and surface defects in hot-rolled steel sheets, cold-rolled steel sheets, surface-treated steel sheets ( It is also called “scale 疵”. This internal oxide layer is a spot that appears on the surface when the steel material is heated and extracted, but it is a spot of less than 1 mm, but it is around 100 mm when rolled from a steel slab to a steel plate approximately 100 times in the longitudinal direction. In the case of a cold-rolled steel sheet or a surface-treated steel sheet as a product, the length may be 300 to 1000 mm.

  In particular, steel materials having a low C concentration such as C = 0.005 to 0.05% by mass% are often used for automobile exterior steel plates, beverage cans and the like because of their excellent workability. Since this steel material requires a high level of appearance, it is not possible to ship the large scale bottles as described above at the product stage, resulting in a decrease in yield and a delay in delivery to the user due to such a drop in yield. This leads to a further increase in costs, such as an increase in product inventory so as not to cause problems.

  Therefore, in order to prevent such scale wrinkling, for example, heating methods such as Patent Document 1 and Patent Document 2 have been developed. In the heating method of Patent Document 1, the atmosphere condition in the furnace is controlled when heating the slab for ordinary steel before hot rolling, the slab heating temperature is 1050 to 1250 ° C., and the air ratio is 1.0 to 1.2. By doing so, the manifestation of grain boundary oxidation, which is the starting point of wrinkles, is prevented, and the linear scale wrinkles and pattern defects that occur during hot rolling are reduced.

  In the heating method of Patent Document 2, after heating the slab to 1150 to 1250 ° C. using a heating furnace, the slab is roughly rolled using a roughing mill to form a sheet bar, which is arranged on the entry side of the finishing mill. Descaling is performed by setting the surface temperature of the seat bar in the range of 950 to 1050 ° C. on the entrance side of the installed descaler.

Japanese Patent Application Laid-Open No. 2004-10954 JP 2002-66606 A JP 61-292528 A JP-A-62-22089 JP 2005-134153 A

  With these heating methods, it is possible to prevent scale wrinkles from occurring to some extent. However, in the case of Patent Document 1, C: 0.20% or less, Si: 0.1% or less, Mn: 1.0% or less, P: 0.050% or less, S: 0.02% or less, other Fe And the normal steel slab which consists of an unavoidable element is heated in the atmosphere of 1.0-1.2 by air ratio, and slab heating temperature within the range of 1050 to 1250 degreeC. Although it is possible to operate at an air ratio of 1.0 or more, the heating furnace opens and closes the door for charging and extraction of slabs or steel materials, and intrusion air enters the heating furnace and oxygen in the furnace Concentration increases. Therefore, the actual air ratio including the intruding air that affects the surface oxidation behavior of the slab or steel may exceed 1.2. With the technique described in Patent Document 1, only the internal oxide layer including the grain boundary oxidation is scaled. It is difficult to make it below the generation limit.

  Moreover, in patent document 2, in the hot rolling method of the slab containing 0.03-0.8 mass% of Si, after heating to the said slab 1150-1250 degreeC range using a heating furnace, using a rough rolling mill The slab was roughly rolled into a sheet bar and descaled using the descaler with the surface temperature of the sheet bar in the range of 950 to 1050 ° C. on the entry side of the descaler disposed on the entry side of the finish rolling mill. Thereafter, finish rolling is performed using the finish rolling mill. As described in Patent Document 2, if the surface temperature is maintained in the range of 950 to 1050 ° C. and descaling is performed, the peelability of the firelite is improved, but the internal oxide layer including grain boundary oxidation is a steel structure. In reality, it is difficult to prevent the generation of scale defects sufficiently even if only the descaling conditions are improved.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to heat a steel material while further reducing the probability of occurrence of scale soot due to internal oxidation.

In order to solve the above-described problems, according to a certain aspect of the present invention, there is provided a steel material heating method for preventing the generation of scale soot due to internal oxidation , wherein C = 0.005 to 0.00. 25%, Si ≦ 0.5%, Mn = 0.1 to 1.5%, P = 0.005 to 0.03%, S ≦ 0.03%, Al = 0.005 to 0.18%, Regarding steel materials containing N ≦ 0.02% (the rest are elements inevitably contained except for Fe), the distribution of the surface temperature within the field of view of the temperature measuring device for measuring the surface temperature of the steel material On the basis of the temperature control point, the highest temperature portion, and on the surface of the steel material, a value obtained by calculating the weighted average surface temperature Tm at the temperature control point at which the temperature is 1150 ° C. or higher by the following formula 0 is Ts1 (° C.). When the heating time when Ts1 is 1150 ° C. or higher is t1 (minutes) To, meet the following equation 1, and, subject material is other than SULC (Super Ultra Low Carbon) material, the weighted average surface temperature Tm formula 0 follows at the temperature control point temperature of 1075 ° C. or higher When the value calculated in step Ts2 (° C.) and the heating time when Ts2 is 1075 ° C. or more is t2 (minutes), heating is performed under the conditions satisfying the following formula 2, or the target material is SULC (Super It is an Ultra Low Carbon) material, and the weighted average surface temperature Tm at the temperature control point where the temperature is 1115 ° C. or higher is defined as Ts2 (° C.), and the heating time when Ts2 is 1115 ° C. or higher. Is t2 (minutes) , a steel heating method is provided in which heating is performed under conditions that satisfy the following expression 3 .

Tm = Σ (T _i × Δt _i ) / ΣΔt _i , (i = 1,..., N) (Equation 0)
Ts1 + 0.857 × t1 <1270 (Formula 1)
1175 ≦ Ts2 + 0.857 × t2 (Formula 2)
1215 ≦ Ts2 + 0.857 × t2 (Formula 3)

Here, in Formula 0, n represents the number of arbitrary time constants Δt selected.

  The steel material may further contain at least one of Ti ≦ 0.15%, B ≦ 0.006%, Nb ≦ 0.1%, and Cr ≦ 0.1% by mass%.

  The surface temperature of the steel material being heated in a heating furnace is measured, and based on the measured surface temperature, the furnace temperature of the heating furnace and the conveyance speed of the steel material in the heating furnace are set so as to satisfy the condition It is preferable to control at least one.

  An object having a known temperature for correcting stray light in the heating furnace is installed in the vicinity of the luminance measuring unit, and in the surface temperature measurement of the steel material, the luminance measuring unit is used to absorb and emit by the gas in the furnace. The temperature of the steel material may be obtained by measuring the radiant energy of the steel material and the temperature-known object with a monochromatic luminance having a wavelength at which no occurrence occurs, and correcting the measured monochromatic luminance with stray light.

  When determining the temperature of the steel material, the stray light amount is calculated based on the radiant energy of the temperature known object and the temperature of the temperature known object, and based on the calculated stray light amount and the radiant energy of the steel material. Thus, the temperature of the steel material may be calculated.

  The brightness measurement unit is an imaging device that captures a monochromatic brightness distribution of radiant energy of the steel material and the temperature known object as an image having a predetermined number of pixels, and the temperature known object is in an image captured by the imaging device. It may be arranged at a position where the occupied area is 25 pixels or more.

  The temperature known object may be arranged at a position where an area occupying in an image captured by the imaging device is 100 pixels or more.

  The emissivity of the temperature known object may be within a range of 0.1 before and after the emissivity of the steel material.

  Using the luminance measurement unit, further measure the radiant energy of the furnace inner wall of the heating furnace, record the difference in radiant energy between the furnace inner wall and the temperature known object, based on the recorded difference in radiant energy The presence or absence of a change with time in the emissivity of the temperature-known object may be grasped.

  When the emissivity of the known temperature object changes with time, the emissivity after change with time may be calculated, and the stray light correction may be performed using the emissivity after change with time.

  The temperature known object is preferably arranged at a position that satisfies at least one of the following conditions (A), (B), and (C).

(A) A position where the stray light distribution in the furnace is substantially the same as the position of the steel material, and a position separated from the furnace wall by a distance where the stray light amount is substantially the same. (C) Position where no flame is sandwiched between the steel materials

Moreover, in order to solve the above-mentioned problem, according to another aspect of the present invention, a heating control apparatus for controlling a heating furnace that heats the steel material while conveying the steel material in the furnace length direction, in mass% , C = 0.005-0.25%, Si ≦ 0.5%, Mn = 0.1-1.5%, P = 0.005-0.03%, S ≦ 0.03%, Al = 0 .005 to 0.18%, N ≦ 0.02% (the rest are elements inevitably contained except for Fe), which are arranged and passed through a plurality of locations along the conveying direction of the steel material. A plurality of temperature measuring devices for measuring the temperature distribution of the steel material surface;
Based on the temperature distribution of the surface of the steel material measured by the one temperature measuring device, a portion having the highest temperature in a range passing through the visual field of the temperature measuring device is determined among the surface of the steel material, and the temperature management of the steel material A position determination unit that is a temperature management point that is a part used for the measurement, and the position and temperature of the temperature management point in the measurement result of each temperature measurement device are specified based on the temperature management point determined by the position determination unit Based on the temperature history of the steel material in the measurement results of the management point specifying unit and each temperature measuring device , the temperature management point is a predetermined temperature (1150 ° C. in the following formula 1, 1075 ° C. in the formula 2, and formula 3 1115 ° C.) It is determined that the temperature control point is equal to or higher, and the weighted average surface of the temperature control point is equal to or higher than the predetermined temperature within the time. A determination unit for calculating the degree Tm, was converted, the temperature control points which are transmitted based on said weighted average surface temperature Tm and the time is equal to or higher than the predetermined temperature from the determination unit, the target material SULC (Super Ultra Low Carbon In the case of materials other than materials, the heating furnace is controlled so as to satisfy the following equations 1 and 2, and when the target material is a SULC (Super Ultra Low Carbon) material, the following equations 1 and 3 are used. There is provided a heating control device having a heating furnace control section for controlling the heating furnace so as to satisfy the above.

Tm = Σ (T _i × Δt _i ) / ΣΔt _i , (i = 1,..., N) (Equation 0)
Ts1 + 0.857 × t1 <1270 (Formula 1)
1175 ≦ Ts2 + 0.857 × t2 (Formula 2)
1215 ≦ Ts2 + 0.857 × t2 (Formula 3)

Here, in Formula 0, n represents the number of arbitrary time constants Δt selected. Further, Ts (° C.) in the formulas 1 to 3 is the weighted average surface temperature Tm calculated by the formula 0, and the Ts1 (° C.) in the formula 1 is the steel material having a temperature of 1150 ° C. or higher. The weighted average surface temperature Tm calculated using the above formula 0 for the temperature control point, t1 (minutes) is the heating time when the temperature of the temperature control point is 1150 ° C. or higher, and Ts2 ( ° C) is a weighted average surface temperature Tm calculated using Equation 0 for the temperature control point at which the temperature is 1075 ° C or higher in the steel material, and t2 (min) is the temperature of the temperature control point is 1075. Is the heating time at or above C., and Ts2 (° C.) in Equation 3 is a weighted average surface calculated using Equation 0 for the temperature control point at which the temperature of the steel is 1115 ° C. or more. The temperature Tm, and t2 (min) is the heating time when the temperature at the temperature control point is 1115 ° C. or higher .

In order to solve the above problems, according to still another aspect of the present invention, in mass% , C = 0.005 to 0.25%, Si ≦ 0.5%, Mn = 0.1-1. 0.5%, P = 0.005 to 0.03%, S ≦ 0.03%, Al = 0.005 to 0.18%, N ≦ 0.02% (the remainder is unavoidably contained except for Fe) And controlling the heating furnace that heats the steel material while conveying the steel material containing the steel material in the furnace length direction, respectively, and arranged at a plurality of locations along the conveying direction of the steel material in the heating furnace, a plurality of computer capable of communicating with the temperature measuring device for measuring the temperature distribution of the steel material surface to pass, on the basis of the temperature distribution of the steel material surface in which one of the temperature measuring device is measured, the temperature measurement of the steel material surface The hottest part in the range that passes through the field of view of the device A position determination function that is determined and used as a temperature management point that is a part used for temperature management of the steel material, and the temperature management in the measurement result of each temperature measurement device with the temperature management point determined by the position determination function as a reference Based on the management point specifying function for specifying the position and temperature of the point, and the temperature history of the steel material in the measurement result of each temperature measuring device , the temperature management point is a predetermined temperature (1150 ° C. in the following Equation 1 and Equation 2 1075 ° C. and 1115 ° C. in Equation 3.) It is determined that the temperature control point is equal to or higher than the predetermined temperature, and the temperature control point is equal to or higher than the predetermined temperature within the time. weighted average surface temperature Tm, and calculates a determination function, and the temperature control points which are transmitted based on said weighted average surface temperature Tm and the time is equal to or higher than the predetermined temperature from the determined features, the subject Is a material other than a SULC (Super Ultra Low Carbon) material, the heating furnace is controlled to satisfy the following formulas 1 and 2, and when the target material is a SULC (Super Ultra Low Carbon) material: A heating furnace control function for controlling the heating furnace so as to satisfy the following formulas 1 and 3 is provided.

Tm = Σ (T _i × Δt _i ) / ΣΔt _i , (i = 1,..., N) (Equation 0)
Ts1 + 0.857 × t1 <1270 (Formula 1)
1175 ≦ Ts2 + 0.857 × t2 (Formula 2)
1215 ≦ Ts2 + 0.857 × t2 (Formula 3)

Here, in Formula 0, n represents the number of arbitrary time constants Δt selected. Further, Ts (° C.) in the formulas 1 to 3 is the weighted average surface temperature Tm calculated by the formula 0, and the Ts1 (° C.) in the formula 1 is the steel material having a temperature of 1150 ° C. or higher. The weighted average surface temperature Tm calculated using the above formula 0 for the temperature control point, t1 (minutes) is the heating time when the temperature of the temperature control point is 1150 ° C. or higher, and Ts2 ( ° C) is a weighted average surface temperature Tm calculated using Equation 0 for the temperature control point at which the temperature is 1075 ° C or higher in the steel material, and t2 (min) is the temperature of the temperature control point is 1075. Is the heating time at or above C., and Ts2 (° C.) in Equation 3 is a weighted average surface calculated using Equation 0 for the temperature control point at which the temperature of the steel is 1115 ° C. or more. The temperature Tm, and t2 (min) is the heating time when the temperature at the temperature control point is 1115 ° C. or higher .

  According to such a configuration, the computer program is stored in the storage unit included in the computer, and is read and executed by the CPU included in the computer, thereby causing the computer to function as the heating control device. A computer-readable recording medium in which a computer program is recorded can also be provided. The recording medium is, for example, a magnetic disk, an optical disk, a magneto-optical disk, a flash memory, or the like. Further, the above computer program may be distributed via a network, for example, without using a recording medium.

  As described above, according to the present invention, it is possible to heat a steel material while further reducing the probability of occurrence of scale soot due to internal oxidation.

It is explanatory drawing explaining the heating furnace and heating control apparatus which concern on the 1st Embodiment of this invention. It is explanatory drawing explaining the heating furnace and heating control apparatus which concern on the same embodiment. It is explanatory drawing explaining the heating furnace which concerns on the same embodiment. It is explanatory drawing explaining the steel materials heating method which concerns on the same embodiment. It is explanatory drawing explaining the steel materials heating method which concerns on the same embodiment. It is explanatory drawing explaining the Example of the steel materials heating method which concerns on the same embodiment. It is explanatory drawing explaining the Example of the steel materials heating method which concerns on the same embodiment. It is explanatory drawing explaining the Example of the steel materials heating method which concerns on the same embodiment. It is explanatory drawing explaining the characteristic 2 which the temperature measuring method which concerns on the embodiment has. It is explanatory drawing explaining the characteristic 3 which the temperature measuring method which concerns on the embodiment has. It is explanatory drawing explaining the characteristic 3 which the temperature measuring method which concerns on the embodiment has. It is explanatory drawing explaining the characteristic 4 which the temperature measuring method which concerns on the embodiment has. It is explanatory drawing explaining the condition 1 of the characteristic 5 which the temperature measuring method which concerns on the embodiment has. It is explanatory drawing explaining the condition 2 of the characteristic 5 which the temperature measuring method which concerns on the embodiment has. It is explanatory drawing explaining the characteristic 5 which the temperature measurement method which concerns on the embodiment has. It is explanatory drawing explaining the Example of the temperature measurement method which concerns on the embodiment. It is explanatory drawing explaining the Example of the temperature measurement method which concerns on the embodiment. It is explanatory drawing for demonstrating the temperature measuring method which concerns on related technology. It is explanatory drawing for demonstrating the temperature measuring method which concerns on related technology.

  In the following, in order to facilitate understanding of the embodiment and the like of the present invention, first, the outline of the embodiment of the present invention will be described, and then the steel heating method according to the embodiment of the present invention will be described in detail. . Then, an example of the effect by embodiment of this invention is demonstrated with an Example.

  Moreover, the heating furnace used with the steel material heating method of embodiment of this invention has the temperature measurement apparatus which can measure the surface temperature of the steel materials which are to-be-heated materials. As the temperature measuring device, various devices can be used as long as they can measure the surface temperature of the steel material. In the embodiment of the present invention, however, in order to enhance the effect, the steel material may be used. A temperature measuring method and apparatus capable of accurately measuring the surface temperature of the glass are used. By using this temperature measuring method and apparatus, the effect in the embodiment of the present invention can be remarkably enhanced. Therefore, after explaining the above contents, the temperature measuring device will be described in detail.

That is, the following will be described in the following order so that the embodiment of the present invention can be easily understood.
1. 1. Outline of first embodiment 2. Details of the steel heating method About Example 4. About temperature measuring method and apparatus according to embodiments

  In the following, for convenience of explanation, a “continuous billet heating furnace” will be described as an example of the heating furnace. However, the heating furnace controlled by the present invention is not limited to the continuous billet heating furnace. That is, it goes without saying that the heating furnace may be various ones usually used for heating steel materials.

(1. Overview of the first embodiment)
1A and 1B are explanatory diagrams for explaining the configuration of a heating control device and a heating furnace according to a first embodiment of the present invention. Here, FIG. 1B has shown sectional drawing which cut | disconnected the heating furnace 1 in FIG. 1A by the AA line. In addition, as shown to FIG. 1A, each structure of the heating furnace 1 does not necessarily exist on the same plane (for example, the burner 2 and the temperature measurement apparatus 100). However, in FIG. 1B, for convenience of explanation, each main component is shown on the same sectional view. As above-mentioned, below, the case where the heating control apparatus which concerns on each embodiment of this invention is applied to the continuous billet heating furnace is mentioned as an example, and is demonstrated. First, the heating furnace will be described.

<1-1. Heating furnace>
As shown in FIG. 1A, the heating furnace 1 heats the steel material F while conveying the steel material F, which is an example of a steel material, in the furnace length direction (also referred to as an x-axis direction or a conveyance direction). That is, the steel material F shown in FIG. 1A has one side of the heating furnace 1 (charging side, negative on the x axis) so that the furnace width direction (also referred to as y-axis direction) is the longitudinal direction as shown in FIG. 1B. It is also referred to as the direction side.) It is charged from the charging inlet IN provided in the furnace wall at the end. And the steel material F is extracted from the extraction port OUT provided in the furnace wall of the other side (extraction side, x-axis positive direction side) end part of the heating furnace 1 with a conveying apparatus.

  In addition, although it does not specifically limit as a conveying apparatus, In the heating furnace 1 which concerns on this embodiment, the example using a walking beam is shown. As shown in FIG. 1A, the walking beam type conveying apparatus is configured such that a skid beam 3 having the same length as the furnace length direction is supported by a plurality of skid posts 4, and a steel material F is placed on the skid beam 3. Is placed. The combination of the skid beam 3 and the skid post 4 is also called a skid. As shown in FIG. 1B, a plurality of skids are arranged in the furnace width direction.

  This skid is classified into a fixed skid and a movable skid, and the fixed skid and the movable skid are alternately arranged as shown in FIG. 1B. The movable skid moves back and forth in the furnace length direction (x-axis direction) while moving up and down in the furnace height direction (also referred to as the z-axis direction). As a result, the steel material F is transported forward while the movable skid moves forward from the state supported by the skid beam 3 of the movable skid. Thereafter, when the movable skid moves downward, the steel material F is now supported by the fixed skid. Then, after the movable skid moves forward, the movable skid moves backward and then rises to support the steel material F again. By repeating the operation of the movable skid, the steel material F is sequentially conveyed in the furnace length direction.

  A plurality of burners 2 are arranged in the heating furnace 1, and the burners 2 are cooked. Accordingly, the steel material F is heated by the frame (flame) ejected from the burner 2 while being transported to the transport device, that is, in the furnace. In the heating furnace 1 shown in FIG. 1A and FIG. 1B, a frame is formed in the furnace width direction while forming a pair so as to be opposed to both furnace walls in the furnace width direction as shown in FIG. A “side burner” is used to form However, the arrangement position of the burner 2 is not particularly limited, and may be a so-called “axial burner” that is arranged on the furnace ceiling or the hearth and forms a frame in the conveying direction. The type of the burner 2 is not particularly limited, and various burners such as a gas fuel burner, a liquid fuel burner, and a regenerative burner can be used.

  In the heating furnace 1, the heating state of the steel material F is controlled mainly by adjusting the conveying speed of the steel material F by the conveying device, the combustion amount of each burner 2, and the like by a control device (not shown).

The heating furnace 1 according to the first embodiment of the present invention has been described above.
Next, the steel material heated by the heating furnace 1 according to the first embodiment of the present invention will be described in detail.

<1-2. About Steel>
The steel material F heated by the heating furnace 1 described above is C = 0.005 to 0.25%, Si ≦ 0.5%, Mn = 0.1 to 1.5%, P = 0.005% by mass. It is a steel material containing -0.03%, S≤0.03%, Al = 0.005-0.18%, N≤0.02%. In addition, the steel material containing the said component may contain the element contained unavoidable except Fe other than the said component.

  C is an element that reduces the elongation and the r value related to breath processability, and is preferably smaller from the viewpoint of processability. However, in order to reduce it to less than 0.0005%, it is costly from the steelmaking process and is not practical in operation. Moreover, it is more preferable to add to some extent from the viewpoint of ensuring strength. However, if the C content exceeds 0.25%, workability is impaired, so the upper limit of the C content needs to be 0.25%.

  Si is an element that improves the strength of steel. However, when the Si content increases, Si oxide is formed on the surface of the steel material, and non-plating occurs during hot-dip plating or plating adhesion is reduced. Moreover, since the external appearance is deteriorated by the Si oxide except for the galvanized steel sheet, the upper limit of the Si content needs to be 0.5%.

  Mn is an element that improves the strength of steel, and its effect can be obtained with a content of 0.1% or more. On the other hand, when Mn is contained exceeding 1.5%, the steel material is hardened and the workability is lowered, and Mn oxide is generated on the surface of the steel material, and the hot dipping property is impaired. Therefore, the upper limit of the Mn content needs to be 1.5%.

  P is an element having a large ability to improve the strength of steel, and has less adverse effects on workability than Si, Mn, etc., and is a useful element for strengthening steel. However, if the content is less than 0.005%, the above-described effects cannot be obtained. Further, P is an element that slows the alloying reaction of hot dip galvanizing, and is an element that generates a linear pattern on the plating surface and deteriorates the surface properties or adversely affects spot weldability. Therefore, the upper limit of the P content needs to be 0.03%.

  S is an impurity inevitably contained in the steel, and is preferably smaller from the viewpoint of deep drawability. However, if it is 0.03% or less, there is no substantial adverse effect, and from the viewpoint of deep drawability. Is also an acceptable content. Therefore, the upper limit of the S content needs to be 0.03%.

  Al is an element contained as a deoxidizing element for steel, and if it is less than 0.005%, a sufficient deoxidizing effect cannot be obtained. However, if the content exceeds 0.18%, the workability is lowered, so the upper limit of the Al content needs to be 0.18%.

  N is preferable to reduce the content in steel materials that require workability, but may be added to steel materials that require strength securing. However, even if added over 0.02%, the effect is saturated and cracking during continuous casting or hot rolling is likely to occur. Therefore, the upper limit of the N content may be 0.02%. is necessary.

  Further, the steel material F may further contain at least one of Ti ≦ 0.15%, B ≦ 0.006%, Nb ≦ 0.1%, and Cr ≦ 0.1% by mass%. .

  Ti is an element that improves workability by fixing N in steel as TiN and reducing the amount of solute N. When Ti is added in excess of 0.15%, the effect is saturated, rather, TiC is formed and workability is deteriorated. Therefore, when adding Ti, it is preferable to make the upper limit of the content 0.15%. From the viewpoint of improving workability, when adding Ti, it is preferable to add 0.015% or more.

  B has a strong affinity for N, and has the effect of forming a nitride during solidification or hot rolling, reducing N dissolved in the steel and improving workability. However, if the content exceeds 0.006%, the welded part and its heat-affected zone harden during welding, and the toughness deteriorates. In addition, the strength of the hot-rolled sheet is increased, and the load during cold rolling is increased. Furthermore, as the recrystallization temperature increases, the in-plane anisotropy of the r value, which is an index of workability, increases and press formability deteriorates. Therefore, when adding B, it is preferable to make B content 0.006% or less.

  Nb has a strong affinity with C and N, and forms carbonitrides during solidification or hot rolling, and has the effect of reducing workability by reducing C and N dissolved in the steel. However, if the content exceeds 0.1%, the recrystallization temperature increases, and as a result, the in-plane anisotropy of the r value, which is an index of workability, increases and press formability deteriorates. Moreover, the toughness of the welded portion is also deteriorated. Therefore, when Nb is added, the Nb content is preferably 0.1% or less.

  Cr is a useful element that can refine the steel structure and can strengthen the steel by solid solution, and is added according to the required strength. However, if Cr is added in excess of 0.1%, the effect is saturated and the hardening is increased, which makes rolling difficult. Therefore, when adding Cr, the Cr content is preferably 0.1% or less.

  Examples of steel materials containing the above-described elements include tin-based (low-carbon Al-K-based) steel materials, and SULC (Super Ultra Low Carbon) -based steel materials such as hot-dip galvanized steel sheets and cold-rolled thin sheets.

The steel material heated by the heating furnace 1 according to the first embodiment of the present invention has been described above.
Next, the configuration of the heating control apparatus 10 according to the first embodiment of the present invention will be described with reference to FIGS. 1A and 1B.

<1-3. Configuration of Heating Control Device>
As shown in FIGS. 1A and 1B, the heating control device 10 includes a temperature measurement device 100, a storage unit 142, a position determination unit 11, a management point specifying unit 12, a management point storage unit 13, and a determination unit 14. And a heating furnace control unit 15.

  The temperature measuring devices 100 are respectively arranged at a plurality of locations along the conveying direction of the steel material F, that is, the furnace length direction. And the temperature measuring apparatus 100 measures the temperature distribution of the surface of the steel material F which passes the arrange | positioned location.

  In FIG. 1A, the case where the temperature measuring device 100 is arrange | positioned at each of five places along a conveyance direction is illustrated. Here, in order to distinguish each temperature measuring device 100, the temperature measuring device 100 arrange | positioned at each location is also called temperature measuring device 100A-100E, respectively. And when it says the temperature measuring apparatus 100, arbitrary temperature measuring apparatuses 100A-100E shall be shown.

  The number of the temperature measuring devices 100 arranged is not particularly limited, but at least two are arranged. And the arrangement position of the temperature measuring apparatus 100 will not be specifically limited if it arranges along the conveyance direction.

  The temperature measuring device 100 is preferably a temperature measuring device that performs radiation temperature measurement, for example. However, as described above, the temperature measuring device 100 is not particularly limited as long as the temperature distribution on the surface of the steel material F can be measured. However, the temperature measuring apparatus 100 used in the present embodiment, which will be described in detail later, can accurately measure the temperature distribution on the surface of the steel material F. Therefore, it is desirable to use the temperature measuring apparatus 100 described later in detail. 1A and 1B show an example in which a temperature measuring device 100 described later in detail is used. Therefore, the temperature measuring apparatus 100 mainly performs radiation temperature measurement. Therefore, the imaging device 110 of the temperature measuring device 100, the temperature known object 120, and the like are arranged at a position where the radiation light from the steel material F can be imaged.

  The temperature measuring device 100 is controlled by the heating control device 10 and measures the temperature distribution of the steel material F at a predetermined timing. That is, when the steel material F enters the temperature measurement region Ar, the temperature measurement device 100 images the radiance of the steel material F and images the surface temperature distribution. Therefore, it is desirable that the heating control device 10 itself always keeps track of which position the steel material F is being conveyed. Further, the temperature measuring devices 100A to 100E are controlled so as to sequentially measure the temperature of at least the same steel material F. That is, when one steel material F with a temperature measuring device 100A is imaged, the temperature measuring devices 100B to 100E measure the temperature of the steel material F when the steel material F passes through each arrangement location (temperature measurement region Ar). I do. As a result, a certain steel material F is measured at each location by all or two or more temperature measuring devices 100. The steel material F to be temperature-measured may be all the steel materials F that are transported and heated, but may be one or more steel materials F selected by the heating control device 10.

  The temperature measurement result is recorded in the storage unit 142 by each temperature measurement device 100. At this time, it is preferable that the temperature measurement results for a certain steel material F are collectively recorded in the storage unit 142. That is, the temperature measurement results obtained by the temperature measuring devices 100A to 100E are associated with each other or are all associated with one steel material F that is a temperature measurement object. As a result, a plurality of temperature measurement results for one steel material F and a plurality of temperature measurement results for another steel material F are distinguished from each other. In addition, since this heating control apparatus 10 can control the heating degree for every steel material F, below, operation | movement, a process, etc. with respect to one steel material F are demonstrated, and the same with respect to the other steel materials F is demonstrated. A description of the operation and processing will be omitted as appropriate.

  The position determining unit 11 is based on the distribution of the surface temperature of the steel material F measured by a certain temperature measuring device (for example, the temperature measuring device disposed in the heating furnace 1 at the position closest to the charging inlet IN). The part with the highest temperature in the predetermined region is determined and set as a temperature management point which is a part used for temperature management of the steel material F.

  This temperature management point may be determined based on, for example, an operation record or the like, but may be obtained from actual measurement by the temperature measurement device 100A. A temperature management point will be described for each of these determination methods.

First, the determination method based on the operation performance etc. in the heating furnace 1 is demonstrated.
It is rare that a steel material F that has been charged in the heating furnace 1 and has not been heated until now becomes a heating target. Therefore, in this case, the position determination unit 11 determines the temperature management point based on the past operation results. The operation results include, for example, product quality results such as a state before heating, a state during heating, a state after heating, and a state after subsequent processing for the steel material F that has been heated in the past. For example, when there is a track record in which the quality of the steel material F has deteriorated after heating or after a subsequent rolling step, the surface temperature of the steel material F is highest at least before, during or after heating. This maximum temperature position is recorded in advance as an operation result. According to the heating control device 10 according to the present embodiment, this position is specified based on the temperature distribution measurement result because the temperature measurement device 100 can measure the temperature distribution of the steel material F. Can do. And the position determination part 11 sets this highest temperature position to the position which should manage temperature in order to maintain quality favorable. Since the data about such a maximum temperature position varies depending on the steel type, size, and the like of the steel material F, the position determination unit 11 stores the maximum temperature position in advance as a database in advance for each steel type, size, etc. of the steel material F. . This database may be included in the position determination unit 11 itself, or may be recorded in another storage device (for example, the storage unit 142). And the position determination part 11 acquires characteristic information like identification information, a steel type, size, etc. about the steel material F which is a heating control object from the higher-order control apparatus which controls the heating furnace 1, for example. Then, the position determination part 11 specifies steel material F from a database based on characteristic information, and determines the highest temperature position matched with the steel material F to the said temperature control point.

Next, a determination method based on actual measurement by the temperature measurement apparatus 100A will be described.
The temperature measuring device 100 </ b> A is disposed relatively to the charging side of the heating furnace 1 among the plurality of temperature measuring devices 100 provided in the heating furnace 1, that is, at a location closest to the charging port IN. The temperature measuring device 100A measures the surface temperature distribution of the steel material F that has passed below the temperature measuring device 100A. Although depending on the heating performance by the heating furnace 1, the highest temperature position on the surface of the steel material F is expected to be relatively high during heating by the heating furnace 1 as compared with other positions. As a result, the temperature is expected to be higher than other reference positions. Then, the position determination part 11 determines the highest temperature position in the surface of the steel material F as a temperature control point based on the temperature distribution which the temperature measurement apparatus 100A measured. The maximum temperature position means a position where the temperature of the steel material F measured by the temperature measuring device 100A is the highest temperature, and is the highest compared to all other positions during or after heating. It does not have to be temperature. As described above, this maximum temperature position is a position that is expected to be higher than other reference positions as a result of being relatively higher than other positions or higher than a desired temperature. Means.

  However, when performing position determination based on this actual measurement, an abnormal temperature position is generated in the surface temperature distribution measured by the temperature measuring device 100A, which is not suitable for determination as a reference point because the temperature is locally high or low due to some abnormality. It is also possible to do. In this case, in order to prevent the position determination unit 11 from selecting such an abnormal temperature position as a temperature management point, the area of the position where the temperature is the highest based on the surface temperature distribution measured by the temperature measurement device 100A. (It may be the number of pixels). Then, when the area is less than the predetermined threshold, the position determination unit 11 confirms whether or not the area is equal to or higher than the threshold at the next highest temperature position. As a result, the position determining unit 11 can determine the highest temperature position where the area is equal to or greater than the threshold value as the highest temperature position. The abnormal temperature position has a smaller area than the surface area of other normal steel materials F, and the area varies depending on the specifications of the heating furnace 1, the characteristics of the steel materials F, the heating state, and the like. Therefore, it is desirable to previously obtain a threshold value (for example, the maximum area) for the area of the abnormal temperature position based on actual measurement.

  In determining the temperature control point, it is possible to appropriately set whether the temperature management point is based on the actual operation value or the actual measurement value. For example, when the operation result for the steel material F is in the database, the temperature control point is determined based on the operation result, and when the operation result is not in the database, it can be determined based on the actual measurement value. . Or, for example, the determination based on the operation results only when the credibility that it is preferable to maintain the product quality is determined based on the operation results, etc., based on the past operation results, control results, etc. It is also possible to perform. The same applies to the case of actual measurement values. However, when the temperature management point is determined based on the actual measurement value, that is, the measurement result by the temperature measuring device 100A, it is not necessary to prepare a database in advance, and since it is actually determined at the highest temperature position, it is easier and easier. A reliable position can be determined.

  The position determination unit 11 uses information regarding the position of the temperature management point determined in this way (for example, the position in the plane of the steel piece, the position in the imaging range of the imaging device, etc.) as described later. Output to.

  The management point specifying unit 12 specifies the position and temperature of the temperature management point in the measurement results of the temperature measuring devices 100A to 100E with the temperature management point determined by the position determining unit 11 as a reference. That is, the management point specifying unit 12 is based on the information regarding the position of the temperature management point transmitted from the position determination unit 11, and the position of the temperature management point in the measurement results of the temperature measuring devices 100 </ b> A to 100 </ b> E acquired from the storage unit 142. , And the temperature at the specified position is obtained from the corresponding measurement result. Moreover, when the management point specific | specification part 12 specifies the position of the temperature management point in the measurement result of each temperature measuring apparatus 100A-100E, the information showing the position of the steel material F in the heating furnace 1 acquired separately is put together. Can be used.

The management point specifying unit 12 determines the position and temperature of the temperature management point specified from each measurement result,
The temperature measuring devices 100A to 100E that have been specified and the position in the transport direction (the location where the temperature measuring device 100 is installed) and the steel material F are associated with each other and recorded in the management point storage unit 13.

The determination part 14 determines the average temperature of the steel material in the predetermined area | region containing the temperature control point in the measurement result of each temperature measuring apparatus 100A-100E, and the heating time in the said average temperature. More specifically, the determination unit 14 pays attention to the temperature of the temperature management point in the measurement results of each of the temperature measuring devices 100A to 100E, and the measurement result having the temperature management point of 1150 ° C. or higher is expressed by the following formula 11. Based on this, a weighted average surface temperature _Tm is calculated.

・・・（式１１）

... (Formula 11)

Here, Δt _i in Equation 11 is a time interval determined as follows. That is, the heating control device 10 takes the elapsed time from the charging of the steel material F into the heating furnace 1 to the measurement time of the temperature control point in each temperature measuring device 100A to 100E on the horizontal axis, and each temperature measuring device 100A to 100E. A graph with the vertical axis representing the temperature at the temperature control point is generated. Here, the determination unit 14 divides the region where the temperature management point is 1150 ° C. or higher into arbitrary time intervals Δt _i , and determines the average temperature T _i at this time interval Δt _i . Subsequently, the determination unit 14 calculates the weighted average temperature T _m using the above equation 11 using the determined T _i and Δt _i .

  Moreover, the determination part 14 determines the heating time which is the time when the temperature control point is 1150 degreeC or more using the above-mentioned graph figure.

  Furthermore, the determination part 14 determines a weighted average temperature and heating time similarly about the area | region where the temperature control point is 1075 degreeC or more using the above-mentioned method.

  The determination unit 14 outputs the obtained weighted average temperature and heating time to the heating furnace control unit 15 described later.

  The heating furnace control unit 15 controls the heating state of the heating furnace 1 based on the following formula 12 using the weighted average temperature and the heating time output from the determination unit 14. Here, Ts1 in the following formula 12 is a weighted average temperature in a heating region of 1150 ° C. or higher, and t1 is a heating time in which Ts1 is 1150 ° C. or higher.

    Ts1 + 0.857 × t1 <1270 (Formula 12)

  By controlling the heating furnace 1 so that the heating furnace control unit 15 satisfies the condition represented by the above formula 12, generation of scale soot that occurs when the steel material F is heated in the heating furnace 1 can be prevented. it can. In addition, the generation | occurrence | production limit of a scale flaw is "C = 0.005-0.25% by mass%, Si <= 0.5%, Mn = 0.1-1.5%, P = 0.005-0. 03%, S ≦ 0.03%, Al = 0.005 to 0.18%, N ≦ 0.02%, and the rest is an element inevitably contained except for Fe ” Since it is determined by the generation temperature of the firelight and the infiltration depth of the inner oxide layer (which depends on the temperature and time), it is not affected by the components of the steel material F to be heated. In addition, for solid solution element fixation, crystal grain control, solid solution strengthening, and the like, Ti and Nb may be included in total by 0.1 mass% or less. Moreover, about 0.002 mass% of B may be included in order to improve hardenability and secondary work brittleness. In addition, Cr, Ni, Cu, Mo, and V may be contained in an amount of about 1% by mass. The present invention can be applied to any steel material that includes a steel plate for containers and is generally referred to as ordinary steel.

  Moreover, it is preferable that the heating furnace control unit 15 controls the heating state of the heating furnace 1 so as to satisfy not only the condition represented by the above expression 12 but also the condition represented by the following expression 13 or 14: . Here, Ts2 in the following formula 13 is a weighted average temperature in a heating region of 1075 ° C. or higher, and t2 is a heating time in which Ts2 is 1075 ° C. or higher. Moreover, Ts2 in the following formula 14 is a weighted average temperature in a heating region of 1115 ° C. or higher, and t2 is a heating time in which Ts2 is 1115 ° C. or higher. However, in the following formula 13, it is important that the minimum value of Ts2 does not fall below 1075 ° C., and in the following formula 14, it is important that the minimum value of Ts2 does not fall below 1115 ° C.

1175 ≦ Ts2 + 0.857 × t2 (Formula 13)
1215 ≦ Ts2 + 0.857 × t2 (Formula 14)

  Generally, in a heating furnace, when the heating time is shortened, the steel material is not sufficiently heated to the inside, and even if the surface temperature measured by the temperature measuring device has increased to the target value, the internal temperature has not sufficiently increased. This can happen. As a result, when the steel material is extracted from the heating furnace and subjected to the rolling process, the temperature drop during the rolling process increases. When this temperature drop becomes larger than a certain level, it becomes difficult to secure the temperature necessary for the rolling process. Further, there is a possibility that the temperature on the exit side of the rolling process is not more than the Ar3 transformation point, so that the required material may not be ensured. Therefore, the heating furnace control unit 15 controls the heating state of the heating furnace 1 so as to satisfy the condition expressed by the above formula 13 or 14 according to the component of the steel material F to be heated. Therefore, it is possible to ensure the temperature required for finish rolling, and to secure the material required for the steel material. Here, since the temperature of the Ar3 transformation point changes according to the component of the steel material F to be heated, for example, when the tin-based steel material F is heated, the heating state of the heating furnace 1 is set so as to satisfy the above expression 13. It is preferable to control. In addition, when heating a SULC-based steel material F such as a hot-dip galvanized steel plate or a cold-rolled thin plate, it is preferable to control the heating state of the heating furnace 1 so as to satisfy the above formula 14.

  Various methods can be used as the heating state control method for satisfying the above Equation 12 and Equation 13 or Equation 12 and Equation 14, and in particular, “furnace temperature adjustment by the burner 2” and “ It is preferable to control at least one of “adjustment of conveyance speed”. Which of the two heating adjustments is performed is preferably determined by the heating furnace control unit 15 based on the temperature distribution of the steel material F, the energy efficiency, the heating time limit, and the like. In order to perform this heating adjustment, the heating furnace control unit 15 further includes a furnace temperature control unit 16 and a conveyance speed control unit 17 as shown in FIG. 1A. Each heating adjustment method and characteristic examples will be described in each configuration, and these configurations will be described below.

  The furnace temperature control unit 16 controls the furnace temperature of the heating furnace 1 based on the average heating temperature and the heating time transmitted from the determination unit 14. More specifically, the furnace temperature control unit 16 determines how much the atmospheric temperature needs to be adjusted based on the furnace atmospheric temperature and the above formulas 12 and 13, and sets the atmospheric temperature by the determined amount. In order to adjust, the fuel flow rate of the burner 2 is adjusted. The adjustment amount of the combustion flow rate is preferably determined in advance corresponding to the average heating temperature and the temperature distribution based on the operation results, the adjustment results, the experimental results, and the like.

  When the heating adjustment by the furnace temperature control unit 16 is performed, it is possible to perform the heating control of the steel material without reducing the productivity because the conveyance speed is not lowered as compared with other heating adjustments. In addition, when the lower limit of steel material surface temperature is provided and the transmitted average temperature is less than the lower limit, the furnace temperature control part 16 will control the burner 2 so that atmospheric temperature may rise. .

  The conveyance speed control unit 17 controls the conveyance speed of the steel material F by the conveyance device based on the average heating temperature and the heating time transmitted from the determination unit 14. That is, the conveyance speed control unit 17 adjusts the in-furnace time for each steel material F. It is desirable that the adjustment amount of the conveyance speed is determined in advance corresponding to the average heating temperature and the temperature distribution based on the operation results, the adjustment results, the experimental results, and the like.

  When controlling both the furnace temperature and the conveyance speed, the furnace temperature control unit 16 and the conveyance speed control unit 17 are expressed by Expression 12 and Expression 13 or Expression 12 and Expression 14 in cooperation with each other. The heating furnace is controlled so as to satisfy the conditions.

  The configuration of the heating control apparatus 10 according to the first embodiment of the present invention has been described above. According to this heating control device 10, the maximum temperature position, which is the portion having the highest temperature, is detected as the temperature control point from the temperature distribution of the steel material F in the temperature measurement region Ar of each of the temperature measurement devices 100A to 100E. By paying attention to the temperature control point, it is possible to control the heating of the steel slab in the heating furnace.

  The method of heating a steel material using such a temperature control point is based on the actual measurement values by the temperature measuring devices 100A to 100E, and compared with the determination of the mature heat based on the simulation and the determination of the mature heat based on the atmospheric temperature of the heating furnace 1. Thus, the heat of maturation of the steel material F can be determined more accurately.

  Moreover, in the position determination part 11 which determines the temperature management point used as a reference | standard, the determination based on the operation performance etc. or the determination based on actual measurement is performed as mentioned above. When determining the reference temperature management point, the position determination unit 11 according to the present embodiment determines the position having the highest temperature in the region whose area is equal to or greater than a predetermined threshold as the temperature management point. It is possible. Therefore, it is possible to prevent a location where the temperature is locally high due to some abnormality being determined as the reference point.

  In addition, as an example of the cause of such a locally high temperature, when the heating target is the steel material F, a blister scale is cited. The surface of the steel material F is heated and heated to raise the temperature, and is covered with an oxide scale generated by the oxidation. The surface temperature of the steel material F in the present embodiment usually indicates the temperature of the scale surface, but is not limited to the scale surface temperature. A part of this scale may swell locally due to a difference in thermal expansion from the ground iron, and may be lifted from the ground iron. This swollen state is called a blister. In the lifted state, the heat received by the scale from the surroundings is less likely to be taken away by the ground iron, resulting in a higher temperature than the scale surface in contact with the ground iron. Therefore, if the maximum temperature position is simply determined as the temperature control point, the blister scale may be selected as the reference point. However, such a blister scale has a smaller area than other scale surfaces. Therefore, by excluding the abnormal temperature position such as the blister scale by a predetermined area (threshold), it is possible to prevent the accuracy of the heating control of the steel material from being lowered.

  In order to perform accurate heating control in this way, it is very important that each of the temperature measuring devices 100A to 100E can measure an accurate surface temperature distribution. Therefore, it is desirable to use the temperature measuring device 100 using the principle of radiation temperature measurement, which will be described in detail later, as this temperature measuring device 100. When this temperature measuring device 100 is used, the accuracy of the heating control of the steel material is further improved. It is possible to improve.

(2. Details of steel heating method)
Subsequently, the steel material heating method according to the first embodiment of the present invention will be described in detail with reference to FIGS. 2-4 is explanatory drawing for demonstrating the steel material heating method which concerns on this embodiment.

  The present inventor has eagerly studied to prevent the scale flaw caused by grain boundary oxidation that occurs during heating in the steel slab heating furnace. In the experimental furnace as shown in FIG. 2, the steel material is heated and extracted with high-pressure water after extraction. An experiment to simulate the internal oxidation state similar to the actual machine was performed by descaling and cooling.

First, the experimental furnace used in the above-described experiment will be described with reference to FIG.
As shown in FIG. 2, the experimental furnace used in this simulation experiment controls the temperature rise of the steel material with an electric heater. In order to reproduce the oxidizing atmosphere of the actual furnace, the furnace is divided into a combustion chamber (left side of the furnace), the fuel supplied to the combustion chamber and the combustion air are mixed and burned, and the heating chamber in which the steel material is placed It was sent to (right side in the furnace). Moreover, after oxidizing the surface of the steel material heated by the electric heater in the same manner as the actual machine and performing predetermined temperature raising, heating and holding processes, the steel material was extracted from the experimental furnace. After cooling, the steel surface was descaled using high-pressure water. Subsequently, the steel material was allowed to cool for a considerable amount of time before being subjected to steel material rolling after descaling with an actual machine, and then naturally cooled in a sealed container in a nitrogen atmosphere. A sample of a predetermined size was cut out from the steel material that had been allowed to cool to room temperature, and the cross section perpendicular to the heated surface was polished, and then the thickness of the remaining internal oxide layer was investigated.

  In addition, the steel material used for the above-mentioned experiment is a tin-based steel material, and its components are as shown in Table 1 below. Also, the presence or absence of the remaining internal oxide layer was determined by observing a sample with a polished cross section under a microscope.

  FIG. 3 shows the relationship between the average steel material temperature Ts in the heating region where the steel material surface temperature is 1150 ° C. or higher and the heating time t1 of 1150 ° C. or higher and the presence or absence of the internal oxide layer. In FIG. 3, “◯” indicates “no remaining internal oxide layer”, and “×” indicates “with internal oxide layer remaining”. Looking at the presence or absence of the remaining internal oxide layer shown in FIG. 3, it can be seen that the higher the heating temperature and the longer the heating time, the easier the internal oxide layer remains. Further, when the boundary line expression representing the remaining limit of the internal oxide layer was calculated using the least square method, the following expression 15 was obtained.

    Ts <1270−0.857 × t1 (Expression 15)

  Based on this knowledge, we investigated the presence or absence of scale flaws in the product process when the heating temperature and heating time changed during actual operation. Here, the presence or absence of scale wrinkles was determined by visually checking and confirming the rolled steel material in an inspection process that is a post-rolling process. When the steel piece surface layer is internally oxidized, the internal oxide layer extends in the rolling direction and is confirmed as a linear flaw. Steel materials with such linear wrinkles were judged to have scale wrinkles, and steel materials without linear wrinkles were judged to have no scale wrinkles.

  The obtained results are shown in FIG. As is clear from FIG. 4, under the conditions in which internal oxidation was not recognized in the experimental results in the experimental furnace of FIG. 3 (conditions of Formula 15), the scale soot caused by internal oxidation was also observed under the actual machine operating conditions (product plate). Occurrence was not observed. Therefore, it has been found that the above equation 15 can be used as an equation representing the limit of scale wrinkling. Therefore, by operating the heating furnace so as to satisfy Formula 15, it is possible to eliminate the remaining of the internal oxide layer after descaling and to prevent scale soot due to internal oxidation. I understood.

  In addition, according to past knowledge, concentration of [Si] and [S] is recognized in a site where internal oxidation occurs. In addition, the concentration of [Si] and [S] is also observed in the scale soot on the product plate as in the portion where internal oxidation occurs. Therefore, instead of visually confirming the presence or absence of scale wrinkles, the presence or absence of concentration of [Si] and [S] may be used as the determination condition for the presence or absence of scale wrinkles.

  By the way, it is possible to prevent the generation of scale flaws by heating the steel material so as to satisfy the condition expressed by the above formula 15 (that is, formula 12). If it is too low, the temperature required for finish rolling cannot be ensured, and a problem may occur in the material of the steel material. Then, this inventor examined the conditions which should be satisfied in order to ensure the temperature required for finish rolling from the actual machine finish rolling mill delivery side steel temperature record and the structure investigation result of the steel sample collected after rolling. As a result, it was found that by operating the heating furnace so as to satisfy the following expression 16, it is possible to secure the temperature necessary for finish rolling, and to avoid material problems that may occur in the steel material.

    Ts ≧ 1175−0.857 × t2 (Expression 16)

  Here, in the above formula 16, Ts is an average steel material temperature (° C.) in a heating region where the steel material surface temperature is 1075 ° C. or higher, and t2 is a heating time (minute) of 1075 ° C. or higher.

  The above equation 16 is shown together with FIG. As apparent from FIG. 4, by controlling the heating furnace 1 so as to satisfy Expression 15, it becomes possible to prevent the generation of scale soot, and the heating furnace 1 so as to satisfy both Expression 15 and Expression 16. By controlling, it becomes possible to prevent the occurrence of scale wrinkles while ensuring the temperature required for finish rolling.

  Needless to say, the above equation 15 can be obtained by modifying the above equation 15. Needless to say, the above equation 16 can be obtained by modifying the above equation 16.

  Moreover, the steel material to be used was changed into SULC type steel materials (hot-dip galvanized steel sheet and cold-rolled thin sheet), and the experiment was similarly performed. As a result, it is possible to prevent the occurrence of scale flaws by heating the steel material so as to satisfy the condition expressed by the above formula 15 (that is, the formula 12), similarly to the tin-based steel material. I understood.

  In hot-dip galvanized steel sheets and cold-rolled thin sheets, there are limits for securing materials in finish rolling, as with tin-based steel materials. SULC-based steel materials such as hot-dip galvanized steel sheets and cold-rolled thin plates have a lower carbon concentration than tin-based steel materials, and the Ar3 transformation point on the finishing side is higher than tin-based steel materials. About these steel materials, as a result of examining the temperature for securing the material in the finish rolling in the same manner, the temperature required for the finish rolling can be secured by operating the heating furnace so as to satisfy the following Expression 17. Thus, it was found that the material problems that can occur in the steel material can be avoided.

    Ts ≧ 1215−0.857 × t2 (Expression 17)

  Here, in Formula 17, Ts is an average steel material temperature (° C.) in a heating region where the steel material surface temperature is 1115 ° C. or higher, and t2 is a heating time (min) of 1115 ° C. or higher.

  Needless to say, the above equation 17 is obtained by modifying the above equation 17.

The steel material heating method according to the present embodiment has been described above.
Then, the Example of the steel material heating method which concerns on this embodiment is described in detail.

(3. About Example)
Below, the Example of the steel material heating method which concerns on this embodiment is described in detail, referring FIGS. 5-6B. 5-6B is explanatory drawing for demonstrating the Example of the steel material heating method which concerns on this embodiment.

  In this example, the heating control of the steel materials shown in Table 1 was performed using the heating furnace 1 as shown in FIG. 1A in which the temperature measuring devices 100 were provided at five locations. The steel materials shown in Table 1 were subjected to temperature raising, heating, and holding steps suitable for the steel materials, and the steel materials were extracted from the heating furnace 1. After cooling, the steel surface was descaled using high-pressure water. Subsequently, finish rolling suitable for the steel materials shown in Table 1 was performed, and the presence or absence of scale wrinkles was determined.

  First, in FIG. 5, the temperature measurement result of the steel materials shown in Table 1 by the temperature measuring devices 100A to 100E is shown. The horizontal axis of FIG. 5 is the elapsed time (minutes) from the charging of the steel material into the heating furnace 1 to each temperature control point measurement time, and the elapsed time corresponding to the position where the temperature measuring devices 100A to 100E are provided, It is also described. Moreover, the vertical axis | shaft of FIG. 5 is the temperature of each temperature control point.

  As is clear from FIG. 5, the slopes of the straight lines between the temperature measuring devices 100A to 100B and between the temperature measuring devices 100B to 100C have a positive slope, and between the temperature measuring devices 100C to 100E, It can be seen that the straight line is almost flat. This indicates that the steel materials are still being heated at the positions of the temperature measuring devices 100A and 100B. At the positions of the temperature measuring devices 100C, 100D and 100E, the heating of the steel materials is completed, It shows that it has become.

  When the presence or absence of scale wrinkles in the steel material heated as shown in FIG. 5 was confirmed, there was no scale wrinkles in the steel material after finish rolling.

  Here, in the heating state shown in FIG. 5, the weighted average surface temperature Tm in the temperature range of 1150 ° C. or higher was calculated by the above equation 11, and the heating time at the calculated weighted average surface temperature was determined. It was found that the heating conditions shown in (1) belong to a region where scale wrinkles can be prevented.

  Subsequently, using the steel materials shown in Table 2 below, the same experiment was performed while changing the steel material heating time and the steel material heating temperature.

  The results using the two types of tin steel shown in Table 2 are shown together with FIG. 6A. Moreover, the result using the hot-dip galvanized steel sheet and cold-rolled thin sheet shown in Table 2 is shown together with FIG. 6B.

  As shown in FIG. 6A, for both of the two types of tin-based steel materials, the combination of the conditions of the steel material heating time and the steel material heating temperature exceeds the scale soot generation limit shown in FIG. 6A, Many of the steel materials after heating had scale flaws. Moreover, the scale flaw did not generate | occur | produce about what the combination of the conditions of steel material heating time and steel material heating temperature did not exceed the scale flaw generation limit shown to FIG. 6A. Moreover, as shown in FIG. 6B, the combination of the conditions of the steel material heating time and the steel material heating temperature for both of the two types of steel materials, the hot-dip galvanized steel sheet and the cold-rolled thin sheet, has the scale flaw occurrence limit shown in FIG. 6B. In the case of exceeding this, there were many cases in which scale flaws occurred in the steel material after heating. Moreover, the scale flaw did not generate | occur | produce about what the combination of the conditions of steel material heating time and the steel material heating temperature did not exceed the scale flaw generation limit shown to FIG. 6B.

  As is clear from this result, it was found that the generation of scale flaws can be prevented by heating the steel material so as to satisfy the condition represented by the above formula 12.

(4. Temperature measuring method and apparatus according to this embodiment)
Next, a temperature measurement method used in the embodiment of the present invention and an apparatus for performing the method will be described. In addition, as above-mentioned, in embodiment of this invention, various things can be used for the temperature measuring method and apparatus, if the temperature of the steel material surface is measured. However, the temperature measurement method and apparatus described below can measure the temperature very accurately compared to other temperature measurement methods and apparatuses. Since it becomes possible to accurately measure the surface temperature, the steel material heating method and the heating control device according to the embodiment of the present invention further enhance the effects as described above, and more accurately determine the ripe heat of the steel material. It becomes possible. Therefore, in the following, this temperature measurement method and apparatus will be described in detail with reference to FIGS.

  In the following, in order to facilitate understanding of how this temperature measurement method and apparatus can accurately measure temperature compared to other temperature measurement methods and apparatuses according to related technology, A related technique will be described, and then a temperature measurement method used in the embodiment of the present invention will be described. Then, after describing a temperature measuring device for realizing this method, examples of the temperature measuring method and device used in the embodiment will be described. Furthermore, an example of the effect of the temperature measurement method and apparatus used in this embodiment will be described in comparison with Patent Documents 3 to 5.

That is, below, the temperature measurement method and apparatus used in the present embodiment will be described in the following order 4-1. Related technology 4-2. Outline of temperature measurement method according to this embodiment 4-3. Example of temperature measuring apparatus according to this embodiment 4-4. Measurement example by temperature measuring apparatus according to this embodiment 4-5. Examples of effects of temperature measuring device according to this embodiment

<4-1. Related Technology>
The related art will be described with reference to FIGS. 16 and 17. 16 and 17 are explanatory diagrams for explaining a temperature measurement method according to the related art.

  When measuring the surface temperature of a steel material in a heating furnace in a non-contact manner, generally, a method of measuring thermal radiation energy from the object surface such as a radiation thermometer is used. However, in the heating furnace, there is radiant energy radiated from the inner wall of the furnace, a flame or the like. This radiant energy is reflected by the surface of the steel material and enters a sensor such as a radiation thermometer. Therefore, the radiation thermometer etc. displays the temperature corresponding to the sum of the thermal radiant energy radiated from the steel material and the reflected energy reflected from the surface of the steel material by the radiant energy radiated from the inner wall or flame, etc. A temperature error corresponding to the reflected energy occurs. This reflected energy is called by various names such as stray light, reflected light, external light, back light, stray light noise, etc., all of which are the same, and is hereinafter referred to as “stray light”.

  For example, in measurement under outdoor air conditions or room temperature conditions, the radiant energy emitted from the atmosphere or indoor walls is smaller than the radiant energy of a high-temperature steel material, so stray light errors do not become a problem. However, in a heating furnace having a high-temperature flame or a furnace wall, errors due to stray light are large, and therefore accurate temperature measurement is difficult.

  Therefore, a method for correcting the influence of stray light and obtaining a true object temperature has been developed. According to the method related to this related art, as shown in FIG. 16, first, a temperature known object 912 is placed in a heating furnace 911, and is calculated by the heat radiation theory from the known temperature of the object 912 by the calculation means 918. Based on the difference between the surface brightness and the measured value of the apparent brightness of the object 912, the amount of stray light in the heating furnace 911 is quantified. Further, the true radiant energy of the steel material is obtained by subtracting the amount of stray light in the heating furnace 911 from the apparent brightness of the steel material 913 measured by the optical surface temperature measuring means 914 such as a radiation type thermometer having a camera. To obtain the temperature. The temperature is displayed by the temperature display unit 919. As such a related technique, for example, Patent Document 5 is cited.

  In this method, an easily conceivable form is to place a known temperature object in the vicinity of the steel material and to compare the steel material with the known temperature object in order to reduce the stray light correction error.

However, such a form has the following problems.
Problem 1: When a steel material moves, it is difficult to place an object with a known temperature in the vicinity thereof.
Problem 2: If an object with a known temperature is placed near the steel, that is, away from the camera, the number of pixels of the object with a known temperature in the image is reduced.

The problem 1 will be described.
When the steel material moves, for example, in a walking beam type heating furnace or the like, there is a possibility that an object having a known temperature is damaged by the movement of the steel material. As a countermeasure, if a mechanism for moving the shielding plate according to the movement of the steel material is provided, the measurement system itself becomes complicated, which is not practical.

The problem 2 will be described.
For example, in order to arrange a steel material at a distant position or measure the temperature of a relatively small steel material, it is necessary to use an imaging device having a certain degree of resolution so that the steel material can be imaged. For example, when a 400,000-pixel camera is used as the imaging device, the viewing angle of one pixel is a small region having a width of 0.08 degrees and a height of about 0.08 degrees. When a temperature-known object is placed at a position away from the camera, the area of the temperature-known object that occupies the image becomes very small. Therefore, the output of one pixel is affected by spatial fluctuations, temporal fluctuations, signal processing system disturbances, etc. Will cause some variation.

  FIG. 17 shows an example of output variations in units of pixels. As shown in FIG. 17, there is a large variation in the output of one pixel unit, and there is a possibility that the measurement accuracy is lowered due to this variation. Therefore, in order to obtain high measurement accuracy, it is necessary to define an area instead of a single pixel and take the average value of the pixels in the area, and at least 5 × 5 pixels, preferably an average of 10 × 10 pixels or more Should be taken.

  However, considering a case where an object with a known temperature is placed in the vicinity of a steel material 6 meters away from the camera, for example, the width corresponding to a viewing angle of 0.08 degrees per pixel is about 10 millimeters. In order to take an average of 10 × 10 pixels, an area of 100 × 100 millimeters must be averaged.

  On the other hand, as the temperature known object 912, as shown in FIG. 16, it is practical to use a thermocouple thermometer 916 with a protective tube 917, which usually has a diameter of about 20 to 30 millimeters. As such, it is impractical to install a large temperature known object of 100 × 100 millimeters.

  As a result of earnest research on the conventional temperature measuring device and the temperature measuring device related to this related art, the present inventors have come up with the problems 1 and 2 as described above. In response to this problem, the inventors have further improved the effect of stray light by installing a temperature-known object, for example, a thermocouple with a protective tube, in the vicinity of the imaging device, not in the vicinity of the steel material, by means such as the following. Invented a temperature measurement method that can be corrected automatically, and found that the effect can be remarkably improved when used in the heating furnace according to the above embodiment.

<4-2. Overview of Temperature Measurement Method According to this Embodiment>
Hereinafter, an outline of the temperature measurement method according to the embodiment of the present invention will be described.
This temperature measuring method has the following features 1 to 3 roughly based on the temperature measuring method according to the related art described above.

Feature 1: When a temperature-known object for correcting stray light is installed in the vicinity of the imaging device and the radiation energy of the steel material is measured, a wavelength that does not cause absorption and emission by the gas in the furnace is selected, and its monochromatic color The luminance is measured, and the temperature obtained by correcting the obtained monochromatic luminance with stray light.
Feature 2: The temperature-known object is arranged at a position where the size is at least 25 pixels, preferably 100 pixels or more, in terms of the number of pixels of the imaging device.
Characteristic 3: The object whose temperature is known uses a material whose emissivity is in the range of 0.1 before and after the emissivity of the steel material.

  The temperature measurement method according to the present embodiment will be described while sequentially explaining these features.

[4-1-1. Feature 1]
Feature 1: When a temperature-known object for correcting stray light is installed in the vicinity of the imaging device and the radiation energy of the steel material is measured, a wavelength that does not cause absorption and emission by the gas in the furnace is selected, and its monochromatic color The luminance is measured, and the temperature obtained by correcting the obtained monochromatic luminance with stray light.

  In this feature 1, “the wavelength at which absorption and emission by the furnace gas do not occur” does not mean that absorption and emission do not occur completely, but a wavelength at which absorption and emission are less likely to occur compared to other wavelengths. means. Further, “monochromatic luminance” and “single wavelength” mean that they are not all wavelengths, and include, for example, luminance of a wavelength having a predetermined width depending on wavelength selection accuracy. The temperature measurement process by the feature 1 and the temperature measurement method according to the present embodiment will be described as follows.

  For example, if the object with known temperature and the steel are close to each other, the amount of stray light incident on both is almost equal, so the stray light obtained from the measurement result of the object with known temperature is also irradiated to the steel. What is necessary is just to correct | amend the radiant energy of the made steel. However, when both are separated as in the present embodiment, the equality of stray light amounts is not necessarily guaranteed.

  Therefore, in the method of the present embodiment, the following means are roughly used in order to ensure the equality of the stray light amount between the temperature known object and the steel material.

Means 1: Select a wavelength at which absorption and emission by the gas in the furnace do not occur, and measure a single wavelength.
Mean 2: The stray light correction calculation formula is created by strictly applying the theory of radiant heat transfer in order to enable theoretical evaluation of errors due to temperature distribution in the furnace.

(Means 1)
Each means will be specifically described below.
In the combustion furnace, there are carbon dioxide and water vapor generated by the combustion of fuel. These gas bodies absorb the radiant energy in the furnace and radiate energy according to their temperature. Since the gas temperature varies depending on the position in the furnace, the amount of stray light in the furnace varies depending on the position. However, the energy absorbed and emitted by gases such as carbon dioxide and water vapor is limited to some specific wavelength ranges in the spectrum. Therefore, stray light correction that does not include the influence of the gas in the furnace is possible by measuring the wavelength that avoids both the absorption / radiation wavelength region of carbon dioxide and the absorption / radiation wavelength region of water vapor.

  Therefore, in the present embodiment, by measuring a wavelength satisfying the above conditions, for example, a single wavelength of 1 μm, it is possible to correct stray light under a condition in which the position of the temperature-known object and the steel material is separated. As in this embodiment, there is no precedent for an example in which the single wavelength condition is essential for the purpose of stray light correction.

(Means 2)
The calculation for correcting stray light in accordance with the use of a single wavelength uses the Plank equation for calculating radiant energy of a single wavelength, not the Stefan-Bolzmann equation used in general radiant heat transfer calculation. Specifically, the calculation is performed according to the following procedures 1 to 7.

  Procedure 1: In advance, an off-line blackbody standard furnace is used to create a relational expression between the output of the imaging device and the blackbody luminance.

  First, the temperature of the blackbody standard furnace is maintained at T [K]. The black body luminance E at the temperature T is calculated according to Planck's law (the following equation 101).

・・・（式１０１）

... (Formula 101)

Here, each constant of the above-mentioned formula 101 is as follows.
E: Black body luminance of wavelength λ [W / m ³ ]
λ: wavelength [m]
T: Temperature [K]
C1: Constant 3.74 × 10 ⁻¹⁶ [W / m ² ]
C2: Constant 0.014387 [μm · K]

  Next, the standard temperature point of the blackbody standard furnace is measured by the imaging device, and the output L of the imaging device is obtained. The same measurement is sequentially performed by changing the temperature T, and a relational expression between E and L is created by the least square method or the like. Here, the relational expression between E and L is represented by the following expression 102.

・・・（式１０２）

... (Formula 102)

  Since the relational expression represented by the expression 102 means a characteristic expression specific to each imaging apparatus, it is necessary to create it for each imaging apparatus when a new imaging apparatus is introduced. However, since this is a characteristic unique to the imaging apparatus, once this procedure 1 is performed, it is not necessary to perform it again thereafter. In the present embodiment, for example, a wavelength of 1 μm is used as the measurement wavelength λ, and an optical filter can be used to select this wavelength. However, the measurement wavelength λ may be other wavelengths, and the wavelength selection method may be, for example, using an imaging element that captures only a specific wavelength, or a specific wavelength included in the imaging device, in addition to the optical filter. It goes without saying that various methods can be used such as extracting the wavelength by image analysis.

Procedure 2: In an actual furnace, a black body luminance E ₁ is calculated from Planck's law from the temperature T ₁ [K] of a thermocouple with a known temperature, for example, a thermocouple with a protective tube, as shown in Equation 103 below.

・・・（式１０３）

... (Formula 103)

Step 3: The image pickup device measures the temperature known object, obtaining an output L _1. The above characteristic equation created off-line (wherein 102), calculates the luminance corresponding to the output L _1.

The luminance calculated in this procedure 3 is an apparent luminance including reflection of stray light, and corresponds to a quantity called emissivity in the field of radiant heat transfer. This is represented as _{G 1.} That is, the luminance G ₁ is expressed by the following formula 104.

・・・（式１０４）

... (Formula 104)

Procedure 4: The stray light amount J is calculated from E ₁ and G _{1 according} to the following equation 105.

・・・（式１０５）

... (Formula 105)

In this equation 105, ε ₁ is the emissivity of an object with a known temperature.
Here, the derivation process of Equation 105 will be described. The monochromatic radiation amount A radiated from the object surface at temperature T is obtained by multiplying the black body luminance E calculated from Planck's law by the emissivity ε of the object surface. That is, the monochromatic radiation amount A is expressed by the following formula 106.

・・・（式１０６）

... (Formula 106)

  Further, the amount B of the in-furnace stray light (external irradiation) J reflected from the object surface is expressed by the following formula 107 from the radiant heat transfer theory.

・・・（式１０７）

... (Formula 107)

  The “apparent luminance” G measured by the imaging apparatus is the sum of A and B, and is expressed by the following formula 108.

・・・（式１０８）

... (Formula 108)

By transforming this formula, formula 109 for calculating the stray light amount J is obtained. Therefore, by substituting E ₁ , G ₁ and ε ₁ into this equation 109, the above equation 105 is derived.

・・・（式１０９）

... (Formula 109)

Step 5: The image pickup device measures the steel to obtain an output L _2. Then, the above characteristic equation (equation 102), calculates the luminance corresponding to the output _{L 2.} This luminance is an apparent luminance including reflection of stray light. This is represented as _{G 2.} That is, the luminance G ₂ is expressed by the following formula 110.

…（式１１０）

... (Formula 110)

The output L ₂ as measured by the imaging device here is expressed as a distribution to the surface of the steel material. That is, the output L ₂ for a given point in the captured image of the imaging apparatus corresponds to a locus of the steel that is captured in the captured image, output L ₂ takes a different value for each position in the captured image sell. Accordingly, the luminance G ₂ calculated from the output L ₂ is also a distribution with respect to the steel material. Incidentally, for convenience of explanation, the luminance G ₂ is, be described as the average luminance of the luminance or more points of one point in the luminance distribution. However, the subsequent calculation or the like for the luminance G _2, by performing each position corresponding to a steel material in the captured image, in this temperature measuring method, it is needless to say that can measure the temperature distribution.

Step 6: From the _{G 2} and the procedure stray light amount J calculated in item 4 (Formula 105), calculates the blackbody intensity _{E 2} of the steel by Equation 111 below.

・・・（式１１１）

... (Formula 111)

In the above formula 111, ε ₂ is the emissivity of the steel material.
Here, the derivation process of this equation will be described.
Using the following expression 112 (the above expression 108) derived in the above step 4 and modifying this expression to obtain the black body luminance E, the above expression 111 is obtained.

・・・（式１１２）

... (Formula 112)

Procedure 7: From this E ₂ , the temperature T ₂ [K] of the steel material is obtained using the inverse function (equation 113) of the following Planck's law.

・・・（式１１３）

... (Formula 113)

Here, in the above equation 113, the base of Log is a natural logarithm.
By using the stray light correction method (procedure 1 to procedure 7) described here, the temperature of the steel material can be obtained even when the temperature-known object and the steel material are separated. The reason will be described below.

  The radiant energy from the object of known temperature and the steel material is the sum of the amount of radiation from the object itself and the amount of reflection of stray light received from inside the furnace. As in the equation 108 derived in the above-mentioned procedure 4, the radiant energy of the temperature known object and the steel material is expressed by the following equations 114 and 115.

・・・（式１１４）

・・・（式１１５）

... (Formula 114)

... (Formula 115)

  Here, the subscript 1 represents a temperature known object, and the subscript 2 represents a steel material. The first term on the right side of each equation is the amount of radiation from the object itself, and the second term is the amount of reflection of stray light from the furnace on the object surface.

In the related art, correction is performed by adding or subtracting the difference ΔG (= G ₂ −G ₁ ) of the radiant energy, and the relationship between the apparent luminance G and the black body luminance E in the above two formulas 114 and 115. The brightness E is obtained by using the same, and the temperature of the steel material is obtained. Therefore, in the method of the related art, it is necessary that ε ₁ and ε _{2 in} the above two expressions are equal, and (1-ε ₁ ) J ₁ and (1-ε ₂ ) J ₂ are equal. That is, since it is a requirement that the emissivity of the object having the known temperature and the steel material are equal and the total of the stray light amount J over the measurement wavelength band is equal, it is necessary to place both in the vicinity where it is clear that the stray light is equal. It is.

On the other hand, in the temperature measurement method of the present embodiment, as shown in the description of the correction calculation procedure, the equality of both types is not a requirement. That is, since a single wavelength with a small difference in stray light amount is used in the furnace, the second term (1-ε ₁ ) J ₁ and (1-ε ₂ ) J _{2 in} the above equation do not have to be equal, and the emissivity Even if ε and stray light J differ depending on the position, the measurement error can be reduced.

In general, the material heated in the heating furnace has a high emissivity because the surface is oxidized in the case of a metal material, and the emissivity of the material itself is high in the case of a nonmetallic material. Usually, the emissivity of the object to be heated is a value exceeding 0.8. Therefore, (1-ε) is smaller than ε, and the second term (1-ε) J is smaller than the first term εE in the above equation. Therefore, even if there is little difference in the stray J ₂ of the stray light J ₁ and a steel position of the temperature known object position, is only a difference in the second term relatively value is small occurs, the influence of the expression of the calculation result Is small. In the present embodiment, the measurement wavelength λ is set to a wavelength with less absorption / radiation by the furnace gas. Therefore, it is possible to very small difference between the stray J ₂ of the stray light J ₁ and a steel position of the temperature known object position. Therefore, in this embodiment, it is possible to calculate as J ₁ = J ₂ without arranging the temperature known object and the steel material close to each other. Even if the difference between J ₁ and J ₂ is different by about 10%, there is no significant effect on the error. This is because if the emissivity is about 0.8 and the difference in J is about 0.2, the difference on the right side of the above equation is only about (1−0.8) × 10% = 2%. It is.

  For the above reasons, if the temperature measurement method of this embodiment that performs single wavelength measurement is used, even if a temperature known object is placed at a position where there is a slight difference in stray light, temperature measurement can be performed without greatly reducing accuracy. is there. That is, it is not necessary to place an object with a known temperature near the steel material.

[4-1-2. Feature 2]
Feature 2. The temperature-known object is arranged at a position where the size is at least 25 pixels, preferably 100 pixels or more, in terms of the number of pixels of the imaging device.

The feature 2 will be described as follows.
As shown in Problem 2 above, in the related technology, since the area occupied by one pixel of the imaging device is small, the output of one pixel is affected by, for example, spatial and temporal fluctuations, disturbance of the signal processing system, and the like. Some variation occurs. FIG. 7 shows an actual measurement value of an output of an object of a known temperature in units of one pixel.

  When the standard deviation of the actually measured values shown in FIG. 7 was calculated, σ = 11 ° C. Therefore, it is clear that if the stray light correction is performed using the measurement value of only one pixel, the error is large and it is not practical. Therefore, in the temperature measurement method of this embodiment, such a problem can be solved by taking an average value of a plurality of pixels and performing correction calculation using the average value.

Hereinafter, specific conditions will be described based on the considerations of the inventors who have derived this feature 2.
As described above, the standard deviation of one pixel unit was 11 ° C. Since the standard deviation when n average values are taken is inversely proportional to the square root of the number, if the average of 25 pixels is taken, the standard deviation is about 2 ° C., which is 1/5. If the average value of 100 pixels is taken, it is inversely proportional to the square root 10 of 100, so it is about 1/10 of 1/10.

  In the temperature measurement in the furnace, a standard deviation of 2 ° C. is almost practical, and 1 ° C. is sufficient. Therefore, it is necessary to place a temperature known object at a position where the number of pixels of at least 25 pixels (for example, 5 × 5 pixels), preferably 100 pixels (for example, 10 × 10 pixels) or more can be obtained.

  For example, it is appropriate to use a thermocouple with a protective tube as a known temperature object. Since the outer diameter of the thermocouple with a protective tube used in the heating furnace is about 20 to 30 mm, the measurement range is about 10 mm in the vertical and horizontal directions and about 10 mm in the case of the circular shape.

  On the other hand, for example, in a commonly used CCD camera having about 400,000 pixels, the viewing angle of one pixel is about 0.08 degrees × 0.08 degrees. Therefore, the viewing angle when viewing 5 × 5 = 25 pixels is 0.4 ° × 0.4 °. Since tan 0.4 degree = 0.070, in order to capture a range of 10 mm × 10 mm at a viewing angle of 0.4 degree × 0.4 degree, it should be placed closer to the camera than 10 mm / 0.0070 = 1400 mm. I must.

  Although the calculation is performed for the case where the measured portion of the temperature-known object is 10 mm, if the same calculation is performed when the size is different, the position where the temperature-known object is to be placed is the size Y of the measured portion. On the other hand, it is desirable that the distance X from the imaging device satisfies the following expression 116.

・・・（式１１６）

... (Formula 116)

  Based on such considerations, the present inventors have derived Feature 2 described above. Therefore, in this embodiment, the temperature-known object has a position where the size is at least 25 pixels (for example, 5 × 5 pixels), preferably 100 pixels (for example, 10 × 10 pixels) or more in the number of pixels of the imaging device. Placed in. In other words, for a temperature known object, if the size of the measured part of the temperature known object is Y and the distance from the imaging device is X, X is set so as to satisfy Equation 116 above. More specifically, X is set to a value smaller than 1400 mm when a CCD camera having about 400,000 pixels is used as the imaging device and Y is 10 mm. As a result, in the temperature measurement method according to the present embodiment, the measurement error of the imaging apparatus can be reduced and the temperature measurement accuracy can be improved.

[4-1-3. Feature 3]
Feature 3. The material whose temperature is known uses a material whose emissivity is in the range of 0.1 before and after the emissivity of the steel material.

The feature 3 will be described as follows.
The inventors of the present invention theoretically examined the measurement results when the measurement conditions were variously changed, that is, the error in the temperature after stray light correction, with respect to the temperature measurement method of the present embodiment.

  The examination conditions are as follows. In a combustion furnace having a length of 12 m and a height of 2.5 m, the inner wall temperature is 1200 ° C., the temperature of the steel placed on the hearth is 900 ° C., and the emissivity of the steel is 0.86. Heat transfer calculation was performed, and the theoretical values of the amount of radiant heat transfer and the amount of reflected stray light on each surface under the conditions satisfying the above characteristics 1 and 2 were obtained. The calculation method is described by Yoshio Kato, “Introduction to Heat Transfer” (Yokendo) p. 377-p. The procedure shown in 382 was used.

  By applying the stray light correction calculation method described in the above feature 1 to the calculation result, the position of the temperature known object is set to the left wall position in the furnace in the furnace width direction as the origin 0 m point, and from the 0 m point to the right 12 m point The stray light correction value when changed every 2 m was calculated. The position of the imaging device was the left 0 m point, and the position of the steel material was the center in the furnace width direction, that is, the 6 m point. The calculation results are shown in FIG. The emissivity ε shown in FIG. 8 is an emissivity of an object whose temperature is known, and the emissivity of the steel material is fixed at 0.86.

  As shown in FIG. 8, according to this calculation result, for example, when the emissivity of the known temperature object is equal to the emissivity 0.86 of the steel material, the corrected temperature of the steel material is The difference is within 3 ° C. with respect to the true temperature of 900 ° C. of the steel material.

  However, when there is a difference in emissivity ε between the steel material and the temperature-known object, it can be seen that the temperature difference becomes large. In the range of emissivity ε = 0.86 of the steel material and emissivity of the object having a known temperature of 0.81 to 0.91, that is, around 0.05, it is ± 6 ° C with respect to the true temperature of 900 ° C When the emissivity of an object having a known temperature is in the range of 0.76 to 0.96, that is, about 0.1 to about ± 13 ° C.

  If an error up to about 10 ° C. is allowed in consideration of practicality, the emissivity of an object with a known temperature varies slightly depending on the temperature and emissivity level, but a material that is within about 0.1 before and after the steel emissivity is selected. The measurement error should be further reduced if it is preferably within about 0.05 or so.

  On the other hand, in the related technology, a method of correcting stray light based on the luminance of an object whose temperature is known is adopted. In this related technique, the positional relationship between the steel material and the temperature-known object is not clearly shown, but in the drawings illustrated as examples, the temperature-known object is placed in the vicinity of the steel material, and both are placed in the vicinity as an embodiment. It is thought that this is assumed.

  According to the knowledge of the inventors, as described above, when there is a large difference between the temperature of the steel and the furnace inner wall, for example, the temperature of the steel is 900 ° C. and the temperature of the furnace inner wall is 1200 ° C., the vicinity of the furnace wall Then, it is strongly affected by stray light from the furnace wall. However, when the emissivity of an object whose temperature is known and the emissivity of a steel material are approximately the same, the effect becomes small. This is shown in FIG. FIG. 9 shows the calculation result when the emissivity ε of the known temperature object in FIG. 8 is 0.86, which is equal to that of the steel material, and the calculation result when the emissivity ε is 0.76 away from the value. That is, in FIG. 9, the ● plot is an example in the case where the emissivity of the steel material and the temperature known object is approximately the same, and the x plot is an example in which the emissivity of the temperature known object is different from that of the steel material. Again, the steel was placed in the center of the furnace, i.e. 6 m.

  As shown in FIG. 9, when the emissivity is different, not only the temperature error increases, but also the difference between the vicinity of the furnace wall and the center increases. For this reason, in the related art, since there is no regulation of emissivity, although it is not clearly shown, it is considered that, as an embodiment, a temperature known object has to be placed in the vicinity of the steel material.

  However, in this embodiment, by regulating the emissivity of the temperature known object, as shown in the ● plot of FIG. 9, even if the temperature known object is placed at a position away from the steel material at the 6 m point, the error is small. Measurement is possible.

  The features 1 to 3 included in the temperature measurement method according to the embodiment of the present invention have been described above. The temperature measurement method according to this embodiment has the following features 4 and 5 in addition to the above features 1 to 3 in order to maintain and improve the measurement accuracy.

Feature 4: Dealing with time-dependent changes in emissivity Feature 5: Position of an object with a known temperature defined by the stray light quantity distribution in the furnace

  Next, features 4 and 5 will be described.

[4-1-4. Feature 4]
Feature 4: Dealing with changes in emissivity over time

The feature 4 will be described as follows.
When a thermocouple with a metal protective tube is used as a known temperature object, the emissivity of the known temperature object may change slightly due to the effect of oxidation due to long-term use or the like. Further, when a thermocouple with a ceramic protective tube is used, there is no fear of oxidation, but the possibility of emissivity change due to adhesion of soot and furnace dust cannot be excluded. Therefore, in the temperature measurement method according to the present embodiment, such a change with time of the emissivity of the known temperature object can be dealt with by the following means.

Means 1: Method for Grasping Change in Emissivity over Time Generally, in order to measure the emissivity on the surface of an object, it is necessary to measure the temperature and luminance of the object under conditions without stray light. Therefore, it is difficult to grasp the emissivity if the object is installed in the furnace. However, if the operating conditions of the furnace are constant, the stray light quantity distribution in the furnace does not vary, and the relationship between the radiance from the object whose temperature is known and the radiance from the inner wall of the furnace is considered to be constant. Using this phenomenon, the difference between the furnace inner wall brightness in the field of view of the imaging device and the temperature known object brightness is recorded over a long period of time, and the presence or absence of emissivity changes with time is grasped by managing the trend under the same temperature conditions. Can be managed. For example, it can be determined that the emissivity of the temperature known object has changed when the change in the difference between the furnace inner wall brightness and the temperature known object brightness exceeds a predetermined threshold. And when emissivity changes, in order to maintain temperature measurement precision, the countermeasure by the following means 2 can be taken.

Mean 2: How to cope with change in emissivity with time. The best means is to replace an object having a known temperature with a new one. When the exchange is impossible and the change value of the emissivity can be estimated from the trend management data of the means 1, the following method may be used for correction. That is, in the following equation 117 (the above equation 105) for calculating the stray light amount J derived by the means 2 of the above feature 1, the equation 118 using the emissivity ε _x after change with time instead of the standard emissivity ε. Thus, the amount of stray light J is calculated.

・・・（式１１７）

・・・（式１１８）

... (Formula 117)

... (Formula 118)

  After calculating the stray light amount J, the procedure 5 and subsequent items of the above feature 1 are calculated according to the above-described calculation procedure, and the temperature after the stray light correction is calculated. FIG. 10 shows an example in which the correction calculation for the emissivity change with time is performed by this method. As shown in FIG. 10, when the emissivity of an object having a known temperature increases with time with respect to the reference emissivity of 0.86, the corrected temperature decreases. However, according to the temperature measurement method according to the present embodiment, an output with a correct temperature of 900 ° C. can be obtained by calculating using the above feature 4.

  That is, the temperature measurement method according to the present embodiment has the feature 4 to reduce the influence of the emissivity of the temperature known object over time, etc., and improve the temperature measurement accuracy even for long-term use. Can be maintained.

Emissivity after change over time ε _x
It should be noted that the emissivity ε _x after time change used here can be derived as follows.
As described above, the means 1 records the difference between the furnace inner wall luminance and the temperature known object luminance in the field of view of the imaging device over a long period of time. At this time, the difference between the brightness of the part of the furnace where the change in emissivity with time is considered to be relatively stable and hardly changed, for example, the brightness of the furnace wall that has not been repaired or repaired for a long time, and the known temperature of the object is also included. Record. Hereinafter, this site is also referred to as “comparison site”. When the furnace inner wall is a comparison part, the furnace inner wall brightness recorded by the means 1 can be set as the brightness of the comparison part.

Here, the apparent luminance of the comparison portion is Gw, and the temperature known object luminance is Gt. That is, a change in the difference ΔG (= Gt−Gw) between the comparison site luminance Gw and the temperature-known object luminance Gt is recorded for a long period. Note that the “apparent luminance G” measured by the imaging apparatus is expressed by the above formula 108, so that the initial temperature known object (Gt ₁ ), the initial comparison site (inner wall, etc.) (Gw ₁ ), and long-term elapsed The apparent luminances of the later known temperature object (Gt ₂ ) and the comparison part (Gw ₂ ) after a long period of time are as follows.

・・・（式Ａ１）

... (Formula A1)

In this formula A1, Et is the black body luminance of the temperature known object, Jt is the stray light amount of the temperature known object, ε _w , the emissivity of the comparison part, Ew is the black body luminance of the comparison part, and Jw is the comparison part. Is the amount of stray light. Here, since the comparison site is a site where the change in emissivity with time is relatively stable and considered almost unchanged, the emissivity of the comparison site becomes constant at ε _w before and after the elapse of the period. Further, by making the temperature at the time of measurement constant, the black body luminance Et of the known object does not change before and after the lapse of the period. Furthermore, since the in-furnace stray light condition is rarely changed, the stray light amount Jt of the known object and the stray light amount Jw of the comparison part do not change before and after the passage of the period.

From this equation A1, the initial luminance difference ΔG ₁ and the luminance difference ΔG ₂ after the elapse of the period are expressed by the following equations A2 and A3.

・・・（式Ａ２）

・・・（式Ａ３）

... (Formula A2)

... (Formula A3)

Therefore, the temporal change amount (ΔG ₂ −ΔG ₁ ) of the luminance difference ΔG can be calculated as in the following formula A4.

・・・（式Ａ４）

... (Formula A4)

From this formula A4, it can be seen that the amount of change in emissivity (ε _x −ε) of an object whose temperature is known is proportional to the amount of change in apparent luminance over time (ΔG ₂ −ΔG ₁ ).

Here, if the proportionality constant between (ε _x −ε) and (ΔG ₂ −ΔG ₁ ) is K (= Et−Jt), the proportionality constant K can be obtained as follows.

  Since Et is the black body luminance of an object whose temperature is known, it can be calculated from the known temperature value according to the above equation 103. On the other hand, Jt is the amount of stray light received by an object whose temperature is known, and therefore can be calculated from the output L of the imaging apparatus using the above formulas 104 and 105. Therefore, the proportionality constant K (= Et−Jt) can be obtained by performing these measurements and calculations in advance. Further, the equation A4 can be calculated as the following equation A5.

・・・（式Ａ５）

... (Formula A5)

Therefore, by substituting the calculated proportionality constant K and the temporal change amount of the apparent luminance difference (ΔG ₂ −ΔG ₁ ) into the equation A5, the emissivity ε _x of the temperature known object after the temporal change is obtained. Can do. In addition, since the comparison calculation after a long period of time is performed under the in-furnace condition for which the proportional constant K is calculated, Et and Jt can be kept unchanged. It can be used until it is exchanged.

Note that the emissivity ε _x of the temperature-known object after the change with time needs to be calculated using data in which the conditions in the furnace (temperature and stray light amount) are equivalent. Therefore, of the long-term data measured and recorded, the known thermometer temperature and the temperature of the comparison site (furnace wall inner surface, etc.) are almost the same as the initial stage, and the furnace operating conditions (furnace stray light conditions) are It is desirable to extract a large number of data in time zones that are substantially the same, and calculate the emissivity ε _x using the average value. It is also possible to test the certainty of the results by statistical methods based on the variance of the data.

[4-1-5. Feature 5]
Feature 5: Position of an object with a known temperature defined by the stray light quantity distribution in the furnace

The feature 5 will be described as follows.
As described above, in this embodiment, the object whose temperature is known does not need to be arranged in the vicinity of the steel material by using a wavelength that does not cause reflection / absorption by the furnace gas or the like. The stray light inside has a distribution according to the position. Therefore, in the temperature measurement method according to the present embodiment, the temperature known object is placed at a position where the stray light amount is equivalent to the stray light amount at the steel material position in order to further improve the measurement accuracy. The restriction of the position of the temperature known object due to the stray light distribution or the like is defined by the following three conditions.

Condition 1: Position where the stray light amount is substantially the same as the position of the steel material in the distribution of stray light in the furnace Condition 2: A position where the angle with respect to the measurement surface of the steel material is not less than an angle at which the emissivity of the steel material does not change Condition 3: With the steel material Position where no flame is sandwiched between

  Each condition will be described below.

Condition 1: A position where the stray light distribution is almost the same as the position of the steel material in the furnace stray light distribution. If there is a temperature distribution on the inner wall of the furnace, the vicinity of the inner wall of the furnace is strongly affected by the temperature of the nearby inner wall of the furnace. The amount of light may be different from the general part in the furnace. FIG. 11 shows the result of calculating the stray light amount based on the data of the inventors when some of the furnace wall temperatures are different. This is the stray light distribution when a part of the inner walls of the furnace is 1100 ° C. in a furnace maintained at a furnace inner wall temperature of 1200 ° C. The horizontal axis in FIG. 11 is the distance from the furnace wall at 1100 ° C. The amount of stray light in an area less than 0.25 m from the furnace inner wall is significantly different from the amount of stray light at other positions. Therefore, in the temperature measurement method according to the present embodiment, the influence of the stray light distribution in the furnace due to the temperature distribution of the furnace inner wall is reduced by arranging the temperature known object at a position separated by 0.25 m or more from the furnace inner wall, Measurement accuracy can be further improved.

Condition 2: The position where the angle of the steel material with respect to the measurement surface is equal to or greater than the angle at which the emissivity of the steel material does not change. Generally, depending on the substance, the surface emissivity may vary depending on the radiation direction. This is illustrated, for example, in Figure 2.81 of the Chemical Engineering Handbook 3rd edition. On the other hand, in the temperature measurement method according to this embodiment, a temperature-known object and a steel material are placed in the same field of view of the imaging device, and correction calculation is performed by comparing the brightness. Therefore, in order to prevent the emissivity of the steel material from changing with respect to the emissivity of the object with known temperature, place the object with known temperature at the position where the angle with respect to the measurement surface of the steel material is an angle within the range where the emissivity does not change. Must be within the field of view of the imaging device.

  The inventors who have come up with such a problem use steel materials (steel materials), place temperature-known objects at various angles, measure the temperature of the steel materials by the method described above, and determine the angle from the size of the error. Judged the limit of. As a result, as shown in FIG. 12, it was concluded that this angle needs to be 13 degrees or more.

  Therefore, in the temperature measurement method according to the present embodiment, the influence on the temperature measurement due to the change in the emissivity of the steel material is reduced by arranging the temperature known object at a position where the angle with respect to the measurement surface of the steel material exceeds 13 degrees. Thus, the temperature measurement accuracy can be further improved.

Condition 3: Position where no flame is sandwiched between steel materials In this embodiment, since monochromatic light, for example, radiation having a wavelength of 1 μm, which avoids the radiation spectrum of carbon dioxide and water vapor, which are thermal radiation gases in the combustion gas, is measured, Compared with wavelength radiation measurement type thermometers, it is less susceptible to flames. However, since the flame contains free radicals or the like that are thermally radioactive, stray light correction errors may occur if a flame is interposed between the flame and the steel material. Therefore, in the temperature measurement method according to the present embodiment, the influence of the flame is reduced by maintaining the positional relationship in which the flame is not sandwiched between the steel material, the temperature known object, and the imaging device. This positional relationship is defined by the positional relationship between the steel material of the furnace to which the present technology is applied and the flame. Specifically, as shown in FIG. 13, the horizontal distance from the measured point (steel) to the flame end is X ₁ , the height from the measured point to the flame lower end is Y ₁ , and the temperature is known from the measured point. When the horizontal distance to the object is X ₀ and the height is Y ₀ , the position of the temperature known object is set so as to satisfy the following equation 119.

・・・（式１１９）

... (Formula 119)

  As described above, the position of the temperature known object, which is defined by the stray light distribution in the furnace, by combining the conditions 1 to 3, is shown as follows.

In other words, this position is
Condition 1: The distance from the inner wall of the furnace is 0.25 m or more,
Condition 2: The angle formed between the measured point and the temperature known object is 13 degrees or more with respect to the surface of the measured point,
Condition 3: The horizontal distance from the measured point to the end of the flame is X ₁ , the height from the measured point to the flame is Y ₁ , the horizontal distance from the measured point to the temperature known object is X ₀ , and the height is Y When it is set to ₀ , it is set so as to satisfy the above equation 119.

  An example of the position of this temperature known object is the hatched area in FIG. The temperature measurement method according to the present embodiment can further improve the temperature measurement accuracy of the steel material by disposing a temperature known object within this range.

The temperature measuring method used in the embodiment of the present invention has been described above.
Next, an example of a temperature measuring apparatus according to the present embodiment that actually executes such a method will be described.

<4-3. Example of temperature measuring apparatus according to this embodiment>
As shown in FIG. 13, the temperature measuring device 100 measures the temperature of the steel material F arranged in the heating furnace 1. In FIG. 13, as the heating furnace 1, a furnace that performs heating by a burner 2 (an example of various burners such as a regenerative burner, a side burner, a roof burner, and an axial burner) is illustrated, but the temperature according to this embodiment is illustrated. The heating furnace 1 to which the measuring apparatus 100 can be applied is not limited to this example. When the temperature measuring device 100 is used in the embodiment of the present invention, it is desirable to insert the imaging device 110 and the temperature known object 120 from the furnace side wall or the furnace ceiling. That is, in this case, the horizontal direction shown in FIG. 13 corresponds to the furnace width direction.

  As shown in FIG. 13, the temperature measurement device 100 includes an imaging device 110, a temperature known object 120, a calculation unit 130, a display unit 141, and a storage unit 142.

  The imaging device 110 is an example of a luminance measurement unit, and is arranged so that the steel material F and the temperature-known object 120 can be captured in the same visual field. Although FIG. 13 shows a case where the imaging device 110 is inserted into the heating furnace 1, in this case, the imaging device 110 has a heat resistant structure. The imaging device 110 only needs to be able to image the inside of the heating furnace 1. For example, the imaging device 110 may be disposed outside the heating furnace 1 by providing a window in the heating furnace 1 with heat-resistant glass or the like. Is possible.

  In addition, the imaging device 110 includes, for example, a wavelength selection filter (not shown) so as to be able to capture the luminance of a predetermined wavelength so as to satisfy the above feature 1. This wavelength selection filter is an example of a wavelength selection unit, and transmits light of a predetermined wavelength. The wavelength selection unit is not limited to the wavelength selection filter. For example, the imaging device 110 can capture the luminance of all wavelength bands (or a predetermined wavelength band) that can be imaged, and the image analysis unit 131 can extract only light of a predetermined wavelength. In this case, the image analysis unit 131 also serves as a wavelength selection unit. In addition, as an image pickup element of the image pickup apparatus 110, an element that picks up only a single color luminance of a predetermined wavelength can be used. In this case, the imaging device 110 also serves as a wavelength selection unit.

  As such an imaging device 110, for example, a camera using an image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) can be used. For example, an IP (imaging plate) can be used. As long as the luminance value in the captured image can be accumulated, any configuration may be used. And from such an imaging device 110, the luminance value received by each pixel in the captured image is output as an electrical signal.

  On the other hand, the temperature-known object 120 is disposed at a position satisfying the above-described features 1, 2, and 5, and includes, for example, a protective tube and a thermometer inserted inside the protective tube. The protective tube is made of, for example, a material that satisfies the emissivity defined in the above feature 3. When the metal material is a steel material F, examples of such a material include ceramic materials such as alumina, alumina / silica, silicon carbide, and quartz, and metal materials such as Inconel, Hastelloy, and stainless steel. Moreover, as a thermometer, contact-type thermometers, such as a thermocouple thermometer and a resistance thermometer, can be used, for example. Examples of the thermocouple thermometer include a platinum-platinum rhodium thermocouple, and examples of the resistance thermometer include a platinum resistance thermometer. However, these thermometers are appropriately changed according to the temperature of the heating furnace 1 and the temperature band to be measured. The temperature of the known temperature object 120 is output to the calculation unit 130 (stray light calculation unit 22).

  The calculation unit 130 analyzes the image captured by the imaging device 110 and calculates the temperature of the steel material F from the monochromatic luminance of the steel material F. At that time, the calculation unit 130 corrects this temperature as described above. Therefore, as shown in FIG. 13, the calculation unit 130 includes an image analysis unit 131, a stray light calculation unit 132, a stray light correction unit 133, a temperature calculation unit 134, an emissivity change unit 135, and a storage unit 136. Have

  The image analysis unit 131 analyzes a captured image (an image including a single wavelength luminance value) captured by the imaging device 110, and corresponds to an output value corresponding to the luminance value of the temperature known object 120 and a luminance value of the steel material F. The output value is calculated. Then, each of the image analysis units 131 outputs an output value for the temperature known object 120 to the stray light calculation unit 132 and outputs an output value for the luminance value of the steel material F to the stray light correction unit 133. At this time, the image analysis unit 131 calculates the output value corresponding to the luminance value of the temperature known object 120 from the average value of a plurality of pixels, because the temperature known object 120 is arranged at the position having the characteristics 1 and 2. Similarly, the average value can be used for the steel material F. Therefore, temperature calculation accuracy errors can be reduced.

  The stray light calculation unit 132 calculates the stray light amount J by executing the procedure 2 to the procedure 4 of the feature 1 based on the output value corresponding to the luminance value of the temperature known object 120. Note that the procedure 1 has already been processed, and the above formulas 1 and 2 are already recorded in the stray light calculation unit 132. The stray light calculation unit 132 uses the recorded formulas 1 and 2. Then, Step 2 to Step 4 are executed.

  The stray light correction unit 133 executes Step 5 and Step 6 of the above feature 1 based on the output value corresponding to the luminance value of the temperature-known object 120 and the stray light amount J calculated by the stray light calculation unit 132 to correct stray light. Then, the black body luminance of the steel material F is calculated.

  Based on the black body luminance of the steel material F calculated by the stray light correction unit 133, the temperature calculation unit 134 calculates the temperature of the steel material F subjected to the stray light correction by executing the procedure 7 of the above feature 1. The calculation result is displayed on the display unit 141 or recorded in the storage unit 142. The display unit 141 includes, for example, a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display (PDP), a field emission display (FED), and an organic display. An electroluminescence display (organic EL, OELD: Organic Electroluminescence Display), a video projector, or the like can be used.

  On the other hand, the image analysis unit 131 further extracts an output value corresponding to the brightness of the furnace inner wall of the heating furnace 1 and outputs it to the emissivity changing unit 135. Then, the emissivity changing unit 135 calculates the furnace inner wall luminance from the output value, and records the difference between the furnace inner wall luminance and the temperature known object luminance in the storage unit 136. The emissivity changing unit 135 and the storage unit 136 execute the above feature 4 by using these pieces of information, and appropriately update the radiance of the temperature known object 120 used by the stray light calculation unit 132.

  Note that the arithmetic unit 130 may be configured by, for example, a general-purpose or dedicated computer. The computing unit 130 can be configured by causing the computer to execute a program that realizes the functions of the above-described configurations. The computer includes a CPU (Central Processing Unit), a recording device such as an HDD (Hard Disk Drive), a ROM (Read Only Memory), a RAM (Random Access Memory), and a LAN (Local Area Network). Communication devices connected to the computer, input devices such as a mouse / keyboard, magnetic disks such as flexible disks, optical disks such as various CDs (Compact Discs), MOs (Magneto Optical) disks, DVDs (Digital Versatile Discs), and semiconductors Drives that read and write to removable storage media such as memory, display devices such as monitors, speakers, headphones, etc. And an output device such as an audio output device. And this computer can implement | achieve the function of each structure of the calculating part 130 by running the program recorded on the recording device and the removable storage medium, or the program acquired via the network.

<4-4. Measurement Example Using Temperature Measuring Device According to this Embodiment>
Next, the example which measured the steel material F surface temperature arrange | positioned in a combustion furnace (an example of the heating furnace 1) as a metal material with the temperature measuring method and temperature measuring apparatus which concern on embodiment of this invention is shown. The combustion furnace used here has a length of 8 m (corresponding to the furnace width direction in the case of the heating furnace 1), a width of 2 m, and a height of 2 m, and heats the steel material F by LNG (Liquid Natural Gas). The steel material F is approximately 5 m and has a thickness of 50 mm. The imaging device 110 used a CCD camera with 380,000 pixels. The CCD camera has a wavelength filter function, and using this wavelength filter function, single wavelength radiation with a wavelength of 1.0 ± 0.2 μm was measured. At this time, since the wavelength filter function has a width of about ± 0.2 μm, the imaging device 110 actually measures only the radiated light having a wavelength of 0.8 to 1.2 μm. However, a wavelength having such a width can be regarded as a single wavelength for practical use and industrial use. Therefore, the imaging device 110 does not need to capture strict single-wavelength light, and only needs to capture light having a wavelength that can be regarded as an industrially single wavelength.

  A radiation thermometer tester was commissioned to test the relationship between the temperature of the thermometer test blackbody furnace and the output value of the CCD camera. The verification temperature range is 900 ° C to 1250 ° C. Using the obtained test data, a fitting calculation by the least square method is performed, and the following expression 21 is obtained as a specific form of the characteristic expression 20 (the expression 102) of the imaging device 110 in the stray light correction calculation procedure. It was.

・・・（式２０）

・・・（式２１）

... (Formula 20)

... (Formula 21)

  Here, G is the gain setting value of the CCD camera, SS is the shutter speed setting value, L is the output of the CCD camera, E is the luminance corresponding to the temperature of the black body furnace, and the temperature at which the test was performed , 900 ° C., 1000 ° C., 1100 ° C., 1200 ° C., and 1250 ° C., the values calculated by the Planck equation described above. As a specific calculation method, five coefficients in the equation were determined by a nonlinear least square method with E as a dependent variable and G, SS, and L as independent variables. This characteristic formula is specific to the CCD camera used in this embodiment, and must be created individually when the CCD camera model is different or when the imaging device 110 other than the CCD camera is used.

  As shown in FIG. 14, the CCD camera was inserted obliquely downward from a measurement port opened in the side wall of the furnace. The horizontal distance from the farthest measurement point (position 1) of the steel material F to the camera is 6 m, and the height from the horizontal plane on which the steel material F is placed to the CCD camera is 1.6 m. This is a positional relationship in which no flame enters the line connecting the tip of the CCD camera and the farthest measurement point (position 1) of the steel material F. The center line of the CCD camera is directed toward the center (position 2) of the steel material F, specifically, the depression angle is 21 degrees. This dip angle is selected in order to keep the entire surface of the steel material F, that is, from position 1 to position 3 in the field of view of the camera, and may be appropriately determined in consideration of the shape of the furnace and the position where the steel material is placed. Thus, the temperature measuring device 100 can measure the temperature distribution of the entire surface of the steel material F by keeping the entire surface of the steel material F within the field of view.

  The temperature known object 120 uses a thermocouple with a protective tube and has an outer diameter of 17 mm. This thermocouple with a protective tube is inserted horizontally at a position 0.2 m below the CCD camera tip, protrudes 0.3 m from the inner surface of the furnace wall into the furnace, and the tip is within the field of view of the CCD camera. . If the positional relationship is within the visual field of the CCD camera, it is not always necessary to insert it horizontally. Depending on the structure of the furnace, it may be advantageous in terms of strength to open the ceiling and insert it vertically. Since this thermocouple works as an object having a known temperature, the protective tube covering the outside must have a known emissivity. In this embodiment, an alumina / silica ceramic protective tube having an emissivity of 0.85 was used.

  In this example, since the emissivity of the steel material F was 0.86, it is almost the same as the emissivity of the thermocouple protective tube, but the emissivity is different as long as it is within the range satisfying the above feature 3. May be. The type of thermocouple used was a JISB type thermocouple. The type of thermocouple may be appropriately selected depending on the temperature used. Further, instead of the thermocouple, another temperature sensor such as a platinum resistance thermometer may be used.

  The viewing angle of the CCD camera is sufficiently large at 60 degrees on the left and right and 45 degrees on the top and bottom. The brightness of the inner wall of the furnace and the brightness of the surface of the thermocouple protection tube are stored for a long time by the storage unit 136 connected to the thermocouple, and the trend of the difference is managed to change the emissivity of the thermocouple protection tube over time. If the change is detected, the temperature known object emissivity used for the stray light calculation is corrected so that the difference in luminance is equal. In this correction, among the stored data, the furnace temperature is a certain temperature (in this embodiment, a range of 1190 ° C. to 1210 ° C.), and the temperature of the known temperature object is a certain temperature (this implementation). In the example, only the data in the range of 1170 ° C. to 1190 ° C. was extracted, and the heat radiation conditions in the furnace were equivalent.

  The luminance measurement range of the object having a known temperature in the CCD camera was a circular portion having a surface of about 10 mm in diameter, and an average value of about 200 pixels was measured. The temperature of the steel material F is in the range from 900 ° C to 1250 ° C. Three points of position 1, position 2, and position 3 shown in FIG. 14 were measured. Position 1 is about 6 m in horizontal distance from the CCD camera, position 2 is about 4 m, and position 3 is about 2 m away.

  FIG. 15 shows the result of performing the stray light correction calculation by the temperature measurement method according to the present embodiment and comparing it with the temperature measured by the thermocouple thermometer embedded in each position of the steel material F. In FIG. 15, the vertical axis represents the measured temperature obtained by performing the stray light correction calculation by the temperature measuring method according to the present embodiment, and the horizontal axis represents the embedded thermocouple measured temperature. Further, a solid line in FIG. 15 represents a line (horizontal axis = vertical axis) in which the measured temperature (after correction of stray light) by the present method and the measured temperature of the embedded thermocouple coincide. As shown in FIG. 15, the measurement points at positions 1 to 3 were located on the solid line, and the embedded thermocouple measured temperature and the measured temperature (after stray light correction) by this method showed good agreement. Therefore, it can be seen that the temperature measurement method according to the present embodiment can accurately measure the temperature of the steel material F. In addition, the temperature measuring method according to the present embodiment further measures the surface temperature distribution of the steel material F by measuring the temperature at each location in the captured image of the steel material F as in positions 1 to 3. It is possible to measure well.

<4-5. Examples of effects of temperature measuring device and the like according to this embodiment>
Finally, examples of advantageous effects on the above Patent Documents 3 to 5 will be described so that the effects of the temperature measurement method used in the embodiment of the present invention can be easily understood. However, it is needless to say that the effects described here are merely examples and do not limit the effects of the temperature measurement method according to the present embodiment.

[4-5-1. Patent Document 3]
In the temperature measurement method described in Patent Document 3, a shielding plate is provided on the surface of the temperature measurement object to block stray light in the furnace. The shielding plate is cooled with water to prevent thermal radiation from the shielding plate itself. The error due to the radiation emitted by the shielding plate is obtained by actually measuring the temperature T _{2 of the} shielding plate and obtaining a corrected true temperature T ₁ from the apparent radiation energy G _{1 according} to the following equation 22. Eb (T) represents radiant energy at temperature T.

・・・（式２２）

... (Formula 22)

  In Patent Document 3, it is necessary to place a shielding plate near the steel material. However, when the steel material moves, for example, in a walking beam heating furnace, the shielding plate may be damaged by the movement of the steel material. If a mechanism for moving the shielding plate according to the movement of the steel material is provided, the measurement system itself becomes complicated. In addition, it is difficult to completely block stray light with the light shielding plate, and the accuracy may decrease depending on the path of stray light.

  On the other hand, in the temperature measurement method and the like described in the present embodiment, there is no need to place a structure near the steel material. Therefore, the temperature measurement method and the like described in the present embodiment do not require the use of a shielding plate, a water cooling device, a complicated measurement system, or the like with respect to Patent Document 3, and measures temperature with a simple device configuration. be able to. Further, in this temperature measurement method and the like, the amount of stray light is calculated and stray light correction is performed, so that the influence of stray light that cannot be blocked by the light shielding plate can be reduced, and high-precision temperature measurement is possible. .

[4-5-2. Patent Document 4]
In the temperature measurement method described in Patent Document 4, the surface temperature T corrected from the apparent temperature S of the radiation thermometer is obtained by the following equation representing the luminance L using the measured temperature Tw and the effective temperature Tw ′ of the furnace wall. .

・・・（式２３）

... (Formula 23)

  At this time, the furnace wall effective temperature Tw ′ is calculated by the primary expression 24 of the brightness of the actually measured temperatures Tw1, Tw2,... Twn of two or more thermometers installed on the furnace wall.

・・・（式２４）

... (Formula 24)

Coefficient a ₁ of the linear _expression, a 2, _... a _n is previously set to a value adapted to the dimensions of the pre-furnace body shape and steel by experiments or the like.

In Patent Document 4, stray light sources in the furnace are mainly a flame and a furnace wall. However, in this patent document 4, although the influence of the stray light from the furnace wall can be corrected to some extent, it is difficult to correct when the radiant energy from the flame changes. Stray temperature and size of the furnace or flame emanating always from the flame if constant heating furnace without using a flame, the coefficients a _1, a 2, _... is included as a constant value to a _n, if flame fluctuation The coefficients a ₁ , a ₂ ,... _An are considered to change. In general, in a heating furnace, the amount of combustion in the combustion device is appropriately adjusted in order to appropriately control the temperature in accordance with the amount of the object to be heated and the reached temperature, so that the flame state changes with time. On the other hand, Patent Document 2 does not show a correction means corresponding to a change in flame. Therefore, it is difficult to apply this Patent Document 4 to a heating furnace using a flame.

  On the other hand, in the temperature measurement method and the like described in the present embodiment, the temperature known object is arranged in the furnace space so that both the stray light emitted from the furnace wall and the stray light emitted from the flame are irradiated to the temperature known object. Further, the positional relationship between the flame, the steel material, and the temperature known object is defined as shown in the feature 5 above. Therefore, in the temperature measurement method described in the present embodiment, it is possible to appropriately correct the fluctuation of the radiant energy of the flame.

[4-5-3. Patent Document 5]
Patent Document 5 is as described in the related art, and the effects and the like according to the embodiment of the present invention have been described in detail in the above description. However, the temperature measurement device according to the embodiment of the present invention further includes a temperature. By installing a known object in the vicinity of the camera away from the steel material and imaging the monochromatic luminance of the wavelength at which absorption and emission by the furnace gas do not occur, various obstacles due to the movement of the steel material described in Patent Document 3 are avoided. At the same time, it is possible to increase the angle of view of a temperature known object, which is usually a small object, to obtain a sufficient number of pixels, and to improve the stray light correction accuracy.

  In the above description, the features of the temperature measurement method and the like according to an embodiment of the present invention are described separately from features 1 to 5 so that the features can be easily understood. However, the features 1 to 5 do not limit the features of the embodiment of the present invention, and the features of the embodiment of the present invention are described in detail in the features 1 to 5 described above. Needless to say, each feature is also included.

  As mentioned above, although preferred embodiment of this invention was described in detail, referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Burner 10 Heating control apparatus 11 Position determination part 12 Control point specific | specification part 13 Control point memory | storage part 14 Judgment part 15 Heating furnace control part 16 Furnace temperature control part 17 Conveyance speed control part 100 Temperature measuring device 110 Imaging device 120 Temperature Known object 130 Calculation unit 131 Image analysis unit 132 Stray light calculation unit 133 Stray light correction unit 134 Temperature calculation unit 135 Emissivity change unit 136 Storage unit 141 Display unit 142 Storage unit F Steel bill

Claims (13)

A steel heating method for preventing the generation of scale flaws due to internal oxidation,
% By mass , C = 0.005 to 0.25%, Si ≦ 0.5%, Mn = 0.1 to 1.5%, P = 0.005 to 0.03%, S ≦ 0.03% , Al = 0.005 to 0.18%, N ≦ 0.02% (the rest are elements inevitably contained except for Fe) ,
Based on the distribution of the surface temperature in the field of view of the temperature measuring device that measures the surface temperature of the steel material, the temperature control point is the highest temperature part, and the temperature control point at which the temperature is at least 1150 ° C. weighted average surface temperature Tm and Ts1 a value calculated by the equation 0 follows (° C.), when the heating time in Ts1 is 1150 ° C. or more and t1 (min), meet the following equation 1, and the,
The target material is a material other than SULC (Super Ultra Low Carbon) material, and the temperature calculated at the temperature control point at which the temperature is 1075 ° C. or higher is calculated as Ts2 (° C.) as Ts2 (° C.). When the heating time at 1075 ° C. or higher is t2 (minutes), heating is performed under the conditions satisfying the following formula 2, or
The target material is a SULC (Super Ultra Low Carbon) material, and the weighted average surface temperature Tm at the temperature control point where the temperature is 1115 ° C. or higher is defined as Ts2 (° C.). A steel material heating method, wherein heating is performed under conditions satisfying the following expression 3 when a heating time at 1115C or higher is t2 (minutes) .

Tm = Σ (T _i × Δt _i ) / ΣΔt _i , (i = 1,..., N) (Equation 0)
Ts1 + 0.857 × t1 <1270 (Formula 1)
1175 ≦ Ts2 + 0.857 × t2 (Formula 2)
1215 ≦ Ts2 + 0.857 × t2 (Formula 3)

Here, in Formula 0, n represents the number of arbitrary time constants Δt selected. The steel material further contains at least one component of Ti ≦ 0.15%, B ≦ 0.006%, Nb ≦ 0.1% and Cr ≦ 0.1% by mass%. The steel material heating method according to claim 1 . Measure the surface temperature of the steel being heated in the heating furnace,
Based on the measured surface temperature, so as to satisfy the condition, the a furnace temperature of the heating furnace, and controlling at least one of the conveying speed of the heating furnace of the steel, according to claim 1 or 2. The steel heating method according to 2. A temperature known object for correcting stray light in the heating furnace is installed in the vicinity of the luminance measuring unit,
In the surface temperature measurement of the steel material,
Using the luminance measurement unit, by measuring the radiant energy of the steel material and the temperature known object by monochromatic luminance having a wavelength at which absorption and emission by the furnace gas do not occur,
The steel material heating method according to claim 3 , wherein the temperature of the steel material is obtained by correcting the measured monochromatic luminance with stray light. When determining the temperature of the steel material,
Based on the radiant energy of the temperature known object and the temperature of the temperature known object, the amount of stray light is calculated,
The steel material heating method according to claim 4 , wherein the temperature of the steel material is calculated based on the calculated stray light amount and the radiant energy of the steel material. The luminance measuring unit is an imaging device that images a monochromatic luminance distribution of radiant energy of the steel material and the temperature known object as an image of a predetermined number of pixels,
The steel material heating method according to claim 4 or 5 , wherein the temperature known object is arranged at a position where an area occupying in an image captured by the imaging device is 25 pixels or more. The steel material heating method according to claim 6 , wherein the temperature-known object is arranged at a position where an area occupying in an image captured by the imaging device is 100 pixels or more. The steel material heating method according to any one of claims 4 to 7 , wherein an emissivity of the temperature known object is in a range of 0.1 before and after the emissivity of the steel material. Using the brightness measurement unit, further measure the radiant energy of the inner wall of the heating furnace,
Record the difference in radiant energy between the furnace inner wall and the temperature known object,
The method for heating steel according to any one of claims 4 to 8 , wherein the presence or absence of a change with time in the emissivity of the temperature known object is grasped based on the recorded difference in the radiant energy. When a change with time of the emissivity of the temperature known object occurs, calculate the emissivity after the change with time,
The steel material heating method according to claim 9 , wherein the stray light correction is performed using the emissivity after the change with time. The said temperature known object is arrange | positioned in the position which satisfy | fills at least any one among the conditions of the following (A), (B) and (C), It is any one of Claims 4-10 characterized by the above-mentioned. The steel material heating method as described in 2.
(A) A position where the stray light distribution in the furnace is substantially the same as the position of the steel material, and a position separated from the furnace wall by a distance where the stray light amount is substantially the same. (C) Position where no flame is sandwiched between the steel materials A heating control device for controlling a heating furnace for heating the steel material while conveying the steel material in the furnace length direction,
% By mass , C = 0.005 to 0.25%, Si ≦ 0.5%, Mn = 0.1 to 1.5%, P = 0.005 to 0.03%, S ≦ 0.03% , Al = 0.005 to 0.18%, N ≦ 0.02% (the rest are elements inevitably contained except for Fe), respectively, at a plurality of locations along the conveying direction of the steel material A plurality of temperature measuring devices for measuring the temperature distribution of the steel material surface disposed and passed;
Based on the temperature distribution of the surface of the steel material measured by the one temperature measuring device, a portion having the highest temperature in a range passing through the visual field of the temperature measuring device is determined among the surface of the steel material, and the temperature management of the steel material A position determination unit as a temperature control point that is a part used for
A management point identifying unit that identifies the position and temperature of the temperature management point in the measurement result of each temperature measurement device, with the temperature management point determined by the position determination unit as a reference,
Based on the temperature history of the steel material in the measurement results of each temperature measuring device, the temperature control point is a predetermined temperature (1150 ° C. in the following formula 1, 1075 ° C. in the formula 2, and 1115 ° C. in the formula 3. And a determination unit that calculates a time during which the temperature management point is equal to or higher than a predetermined temperature and a weighted average surface temperature Tm of the temperature management point that is equal to or higher than the predetermined temperature within the time. ,
When the target material is other than a SULC (Super Ultra Low Carbon) material based on the time when the temperature control point transmitted from the determination unit is equal to or higher than a predetermined temperature and the weighted average surface temperature Tm, The heating furnace is controlled so as to satisfy 1 and Expression 2, and when the target material is a SULC (Super Ultra Low Carbon) material, the heating furnace is controlled so as to satisfy the following Expression 1 and Expression 3. A furnace control unit;
A heating control device comprising:

Tm = Σ (T _i × Δt _i ) / ΣΔt _i , (i = 1,..., N) (Equation 0)
Ts1 + 0.857 × t1 <1270 (Formula 1)
1175 ≦ Ts2 + 0.857 × t2 (Formula 2)
1215 ≦ Ts2 + 0.857 × t2 (Formula 3)

here,
In the above formula 0, n represents the number of arbitrary time constants Δt selected.
Further, Ts (° C.) in the formulas 1 to 3 is the weighted average surface temperature Tm calculated by the formula 0,
Ts1 (° C.) in the formula 1 is a weighted average surface temperature Tm calculated using the formula 0 for the temperature control point where the temperature of the steel is 1150 ° C. or more, and t1 (min) is the temperature It is the heating time when the temperature of the control point is 1150 ° C. or higher,
Ts2 (° C.) in the equation 2 is a weighted average surface temperature Tm calculated using the equation 0 for the temperature control point where the temperature of the steel is 1075 ° C. or more, and t2 (min) is the temperature It is the heating time when the temperature of the control point is 1075 ° C. or higher,
Ts2 (° C.) in Equation 3 is a weighted average surface temperature Tm calculated using Equation 0 for the temperature control point at which the temperature of the steel material is 1115 ° C. or more, and t2 (min) is the temperature This is the heating time when the temperature of the control point is 1115 ° C. or higher .
% By mass , C = 0.005 to 0.25%, Si ≦ 0.5%, Mn = 0.1 to 1.5%, P = 0.005 to 0.03%, S ≦ 0.03% , Al = 0.005 to 0.18%, N ≦ 0.02% (the rest are elements inevitably contained except for Fe) while conveying the steel material in the furnace length direction. A computer that controls a heating furnace that heats the steel and that is capable of communicating with a plurality of temperature measuring devices that are arranged at a plurality of locations along the conveying direction of the steel material in the heating furnace and that measure the temperature distribution of the surface of the steel material that passes therethrough In addition,
Based on the temperature distribution of the surface of the steel material measured by the one temperature measuring device, a portion having the highest temperature in a range passing through the visual field of the temperature measuring device is determined among the surface of the steel material, and the temperature management of the steel material A position determination function as a temperature control point, which is a part used for
A management point specifying function for specifying the position and temperature of the temperature management point in the measurement result of each temperature measuring device with reference to the temperature management point determined by the position determination function ;
Based on the temperature history of the steel material in the measurement results of each temperature measuring device, the temperature control point is a predetermined temperature (1150 ° C. in the following formula 1, 1075 ° C. in the formula 2, and 1115 ° C. in the formula 3. And a determination function for calculating a time during which the temperature control point is equal to or higher than a predetermined temperature and a weighted average surface temperature Tm of the temperature control point equal to or higher than the predetermined temperature within the time. ,
Based on the time when the temperature control point transmitted from the determination function is equal to or higher than a predetermined temperature and the weighted average surface temperature Tm , if the target material is other than a SULC (Super Ultra Low Carbon) material, the following formula The heating furnace is controlled so as to satisfy 1 and Expression 2, and when the target material is a SULC (Super Ultra Low Carbon) material, the heating furnace is controlled so as to satisfy the following Expression 1 and Expression 3. Furnace control function,
A program to realize

Tm = Σ (T _i × Δt _i ) / ΣΔt _i , (i = 1,..., N) (Equation 0)
Ts1 + 0.857 × t1 <1270 (Formula 1)
1175 ≦ Ts2 + 0.857 × t2 (Formula 2)
1215 ≦ Ts2 + 0.857 × t2 (Formula 3)

here,
In the above formula 0, n represents the number of arbitrary time constants Δt selected.
Further, Ts (° C.) in the formulas 1 to 3 is the weighted average surface temperature Tm calculated by the formula 0,
Ts1 (° C.) in the formula 1 is a weighted average surface temperature Tm calculated using the formula 0 for the temperature control point where the temperature of the steel is 1150 ° C. or more, and t1 (min) is the temperature It is the heating time when the temperature of the control point is 1150 ° C. or higher,
Ts2 (° C.) in the equation 2 is a weighted average surface temperature Tm calculated using the equation 0 for the temperature control point where the temperature of the steel is 1075 ° C. or more, and t2 (min) is the temperature It is the heating time when the temperature of the control point is 1075 ° C. or higher,
Ts2 (° C.) in Equation 3 is a weighted average surface temperature Tm calculated using Equation 0 for the temperature control point at which the temperature of the steel material is 1115 ° C. or more, and t2 (min) is the temperature This is the heating time when the temperature of the control point is 1115 ° C. or higher .

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