JPH0468045B2 - - Google Patents

Description

[Detailed description of the invention]

In order to set the optimum transformation coiling temperature when hot rolling steel materials, the present invention grasps changes in the transformation state of each steel type based on various measurement data, and sets the transformation start location and transformation completion location of each steel material at any desired location. The present invention relates to a method and apparatus for controlling the transformation coiling temperature in a hot rolling mill by positionally controlling the temperature. Generally, in hot rolling of carbon steel and alloy steel, hot rolled steel material after leaving the finishing mill undergoes transformation when it reaches a transformation temperature point where the γ iron austenite structure transforms into the α iron pearlite structure by cooling. This results in the occurrence of fever B phenomenon. The calorific value of such transformation is primarily determined by the carbon content, but the location where the transformation starts and where the transformation is completed varies depending on the use of the steel material, destination, etc. To illustrate this situation based on FIGS. 1 to 4, the untransformed winding temperature control in FIG. 1 extends the incubation time to obtain a coarse pearlite structure and controls the start of transformation after the winding time _T1 . is the second
The coiling temperature control during transformation shown in the figure controls the start of transformation at the coiling thermometer in order to obtain a spherical pearlite structure, and the coiling temperature control at the completion of transformation shown in Fig. 3 obtains a homogeneous fine pearlite structure. In order to obtain a homogeneous pearlite structure, the transformation is completed at the winding thermometer and then the winding is performed after the transformation is completed. , the transformation temperature is controlled to be maintained at a substantially constant level so that the transformation is completed at the winding thermometer. Although the transformation state varies depending on the steel type, in conventional hot rolling, operations were performed by controlling only the target coiling temperature, which can be seen in the above drawing. There are three identical temperatures associated with transformation, and for the operator, the temperature can be interpreted in three different transformation states: untransformed, metamorphosed, and
Since the steel was wound without knowing whether the transformation had been completed or not, variations in the steel structure occurred, making it difficult to obtain a product with uniform mechanical properties. The present invention solves these difficulties and measures the temperature distribution and winding temperature at each position of the strip as it passes through the finishing mill and moves on the hot run table, and winds the product according to its destination. The present invention provides a method and apparatus for controlling the transformation winding temperature, in which cooling water is injected into the strip at any time to control the target temperature and the transformation state. The present invention targets carbon steel or alloy steel with a carbon content of 0.10 to 1.7%, but this is problematic in rolling operations (transformation If the carbon content exceeds 1.7%, the steel sheet becomes an extremely hypereutectoid steel, which is not practical as a thin steel sheet. An embodiment of the transformation coiling temperature control method and device in a hot rolling mill according to the present invention will be explained based on the drawings. A hot rolling finishing mill 1, a cooling device 2, and a winding device 3 are arranged along the moving direction of the strip 4. Between the device 2 and the
A pulse oscillator 19 attached to the No. 6 stand, a thickness gauge 20, and a finishing outlet thermometer 5 for measuring the strip temperature are installed respectively. In addition, each water injection nozzle 9 that injects water into the water injection banks 8 and 8 arranged above and below the hot run table 21 in the cooling device 2 has a water flow control valve 1, respectively.
0 to enable free flow control, and an intermediate thermometer 6 for measuring the strip temperature is also installed at any intermediate location within the cooling device 2. Further, a winding thermometer 7 is installed between the cooling device 2 and the winding device 3, and various control devices, that is, an initial setting device 11, a host computer 12, Cooling information receiving device 13, required bank number calculation device 14, water injection matrix creation device 15, water injection bank control device 1
6. Feedback control device 17, learning device 18
A transformation coiling temperature control device in a hot rolling mill is configured by providing the following. Here, various temperature drop models due to cooling at each moving position of the steel material are shown below. 1 Temperature drop model in air cooling area dθ/dt=-B/h {(θ+273) ⁴ -(θA+273) ⁴ }-Ac/h(θ-θA) Aλ/h(θ-θw)+qt/Cρ 2 Water-cooling area Temperature drop model dθ/dt=-Au/h(θ-θw)-Al/h(θ-θw)-Aλ/h(θ-θw)+qt/Cρ 3 Temperature drop in the water cooling area of the lower bank only Model dθ/dt=-B/h {(θ+273) ⁴ −(θA+273) ⁴ }-Ac/h(θ-θA) -Al/h(θ-θw)+qt/Cρ However, θ: Material temperature °C t: Time sec B: Radiation constant mm/sec・deq ³ Al: Lower bank water cooling constant mm/sec Ac: Air cooling constant mm/sec Aλ: Heat transfer constant to table roller mm/sec θA: Air temperature °C h: Plate thickness mm qt: Transformation heat generated per unit time kcal/ ^m3・
sec C: Specific heat kcal/Kg ρ: Specific gravity Kg/m ³ Au: Upper bank water cooling constant θw: Water temperature °C. The coefficients B, Au, Ak, Ac, and Aλ of the model equation are obtained by off-line calculation of actual operation data, and the transformation heat is determined by the transformation time determined by the steel type and transformation start temperature, and the transformation total heat value that depends only on the steel type. Find from. It is known that consumption during the incubation period due to continuous cooling and consumption during the incubation period due to constant temperature maintenance are different, but if the consumption amount is the same and the temperature is the same, they exhibit almost the same transformation behavior. Therefore, in the present invention, the transformation start timing is determined by calculating from the isothermal transformation curve using the Manning-LORIG method. That is, the transformation start timing during cooling in the hot-transform table is determined from the isothermal transformation curve (TTT curve). FIG. 6 shows an example of a isothermal transformation curve. This sixth
In the figure, for example, the material is rapidly cooled from 800℃ to 650℃,
This shows that when held at 650°C, metamorphosis begins after 2.4 seconds and ends after 21 seconds. In experiments to determine the TTT curve, very small test pieces are used to minimize the influence of mass effects. However, when cooling a material at a certain cooling rate, such as cooling in a hot run table, the timing of the start of transformation cannot be determined from the TTT curve. This is a well-known fact. The Manning-Roritzk method is based on the idea that metamorphosis begins when the amount of incubation period defined by the first equation reaches "0.1" in the supercooled state leading up to the start of metamorphosis. I=∫1/Vc・1/Z(T)dt...(1) However, T is the temperature of the rolled material, and Z(T) is the temperature at the temperature T.
This is the start time of metamorphosis in the TTT curve. Vc in the first equation is the cooling rate. Expressing the first equation using the amount of incubation period △I between minute time △t, the second equation
It becomes like the formula. I (T ₁ → T ₂ ) = _o 〓 ^j=1 △Ij＝ _o 〓 ^j=1 △tj／Zj …(2) However, j is one of the two parts of the material temperature T ₁ to T ₂ In the division, △Ij represents the amount of latent period in the j-th calculation section, △tj represents the latent time in the j-th temperature section, and Zj represents the average latent time in the j-th temperature section. Further, there are various methods for determining the metamorphosis end timing, but for example, the metamorphosis end timing may be determined by finding the metamorphosis time at the metamorphosis start temperature from the TTT curve and adding it to the metamorphosis start time. Furthermore, the method for calculating the latent heat during transformation is based on the fact that the latent heat of transformation is determined by the composition of the rolled material. That is, the latent heat is determined by experiment, and the latent heat is calculated according to the components of the material to be rolled. The heat of transformation generated per unit time is determined by dividing the latent heat of transformation by the transformation time. Changes in the metamorphosis state can be understood from the relationship between the amount of incubation period and the heat capacity of metamorphosis. That is, untransformed Incubation period amount < 1.0 Metamorphosis Incubation period amount = 1.0 and Metamorphosis heat capacity = 0 (Metamorphosis time has not elapsed since the metamorphosis start time.) Metamorphosis completed Incubation period amount = 1.0 and Metamorphosis heat capacity = 0 (Metamorphosis time has elapsed since the metamorphosis start time) ) In addition, cooling water injection that takes into account the transformation heat capacity, transformation start temperature, and transformation time is based on the above-mentioned temperature drop model in the air cooling area dθ/dt=-B/h{(θ+273) ⁴ −(θA+273 ) ⁴ }-Ac/h(θ-θA)-Aλ/h(θ-θw)+qt/Cρ In, the transformation heat capacity and transformation time are used to determine the transformation heat qt generated per unit time.
That is, qt=transformation heat capacity/transformation time. Further, the transformation start temperature is the temperature when the amount of latent period becomes 1.0, and the transformation time is determined by taking into account the heat of transformation and determining the temperature drop. In the manner described above, cooling water is injected based on dθ/dt of the temperature drop model so that the desired transformation state and coiling temperature are achieved. Furthermore, the same applies to the temperature drop model in the water cooling area described above and the temperature drop model in the water cooling area of only the lower bank described above. Furthermore, the measured value of the finishing exit thermometer is used as the initial material temperature (θ), as shown in FIG. That is,
Temperature drop model in air cooling area dθ/dt = -B/h {(θ+273) ⁴ -(θA+273) ⁴ }-Ac/h (θ-θA) -Aλ/h (θ-θw) + qt/Cρ Material temperature The same applies to the temperature drop model in the water cooling area used as (θ) and the temperature drop model in the water cooling area of only the lower bank. Furthermore, an intermediate thermometer and a winding thermometer are used to verify the transformation state as shown in FIGS. 9 to 11. The measured value of the winding thermometer is used in feedback control (correction control based on the deviation between the target winding temperature and the actual temperature). Furthermore, the measured values of the finishing exit thermometer, intermediate thermometer, and winding thermometer are also used for performance management. The necessary data of various numerical values thus obtained are inputted into the cooling information receiving device 13 as cooling information and transformation information of the strip 4. When performing actual transformation coiling temperature control, the moved strip 4 is placed in the finishing rolling mill 1.
When you insert the No. 1 stand, first the initial setting device 11
is activated, and calculates the number of water injection banks and water injection pattern required for the tip portion of the strip 4 based on various cooling information and transformation information of the strip 4 received by the cooling information receiving device 13 via the host computer 12. Then, the water injection bank control device 16 is activated, and a water flow control valve 10 installed in each water injection nozzle 9 that injects water into the upper and lower water injection banks 8, 8 in the cooling device 2.
Outputs opening/closing commands. Further, the movement of the strip 4 progresses and the finishing rolling mill 1
From the moment the bank is inserted into the No. 6 stand, the pulse transmitter 19 generates an interrupt signal every pitch of a certain length, and the required bank number calculation device 14 is activated. Cooling information from the cooling information device 13 takes into account various data measured at this point, such as each temperature measured by the finishing exit thermometer 5, intermediate thermometer 6, and winding thermometer 7, as well as other data such as material speed, plate thickness, water injection pattern, etc. The required number of water injection banks directly below the finishing outlet thermometer 5 is calculated based on the information on the finishing exit side thermometer 5, and the next water injection matrix creation device 15 creates a water injection matrix that takes bank response delay, passage time, etc. into consideration. The water injection bank control device 16 is operated to output opening/closing commands for each water flow control valve 10 as described above. As the strip 4 moves further and the tip reaches the winding thermometer 7, the feedback control device 17 is activated to control the winding thermometer 7 to reach the target winding temperature. Further, the learning device 9 is operated to appropriately control fluctuations between the coils. In this way, the temperature distribution of the strip 4 is determined by taking into account the measurement data from various measuring instruments and the data of each transformation state of each steel type, etc., and the cooling water is applied to the strip 4.
By pouring water into the hot run table 21, the transformation heat generation phenomenon on the hot run table 21 can be freely controlled. Here, a method for calculating the required number of banks will be explained.
As shown in Figure 1, there are three points at the same temperature, but there are differences at each point: (1) before the start of transformation, (2) during transformation, and (3) after completion of transformation. In order to distinguish this, for example, information on the target winding temperature and the transformation state (before transformation, during transformation, after completion of transformation) may be provided from a host computer to the winding temperature control device. FIG. 7 schematically shows a method for calculating the required number of banks in a hot run table, and also shows an example of winding after completion of transformation. FIG. 7A schematically represents the amount of incubation period until the rolled material undergoes transformation, and shows that transformation begins at the timing when the amount of incubation period reaches 1.0. In this example, when the water injection banks are set from No. ₁ to No. ₃ , transformation starts at timing If up to, timing x ₃
Transformation begins at a temperature Tct ₃ lower than the target winding temperature.
When the water injection banks are set from No. 1 to No. 4, transformation starts at timing X ₂ and winding occurs at a temperature Tct ₂ near the target winding temperature. That is, the required number of banks calculating device calculates the required number of banks that satisfy the conditions of the target winding temperature and the transformation state (before, during, and after completion of transformation) while increasing the number of water injection banks sequentially from No. 1, for example. As described above, the method for controlling the transformation coiling temperature in a hot rolling mill according to the present invention is effective when the carbon content is 0.10 to 0.10.
In the method of hot rolling 1.7% carbon steel or alloy steel, the temperature distribution of the strip 4 moving from the hot rolling finishing mill 1 to the winding machine 3 via the cooling device 2 is shown on the finishing exit side. The cooling water is measured by a thermometer 5, an intermediate thermometer 6 in the cooling device 2, and a winding thermometer 7, and further takes into account the transformation heat capacity, transformation start temperature, and transformation time depending on the steel type, and then cools the strip 4. By pouring water, the transformation start place and the transformation end place can be controlled to arbitrary places, and the temperature distribution in the winder 3 can be controlled to be in an untransformed state, a transformation state, and a transformation completed state according to the required steel characteristics, and The start of transformation is controlled at the position of the intermediate thermometer. Similarly, the transformation coiling temperature control device includes a finishing outlet side thermometer 5 for measuring the strip temperature between the hot rolling finishing mill 1 and the cooling device 2, which are arranged along the moving direction of the strip 4. Cooling device 2
An intermediate thermometer 6 in the cooling device for measuring the strip temperature is installed at an arbitrary point in the middle of the strip, and a winding gauge 7 is installed between the cooling device 2 and the winding machine 3. A water injection bank control device 16 that controls the flow rate of the water flow rate control valve 10 is configured to receive signals from the finishing outlet thermometer 5, the intermediate thermometer 6, and the winding thermometer 7. Figure 12 shows machine structural steel S45C with a plate thickness of 4.0 mm C 0.42~0.48 (wt%) Si 0.15~0.35 (wt%) Mn 0.6~0.9 (wt%) P 0.03 or less (wt%) S 0.035 or less (weight %), the cooling state of the hot-rolled steel strip and the accompanying transformation state of the strip during rolling according to the present invention, and the state during the period from passing through the final stand of the finishing mill to the winding machine. show. Table 1 shows the mechanical properties of S45, which is the mechanical structural steel, when it is wound before transformation, during transformation, and after completion of transformation.

[Table] Figure 13 shows carbon steel S45C for machine structures. ) was rolled to a plate thickness of 1.6 mm, and the finishing temperature at the point where it left the final finishing mill was 800℃, and by applying coiling temperature control,
This figure shows the cooling curve of the hot-rolled steel strip on the hot line table when it is cooled, and the transformation has been completed and the steel strip is wound up. The rolling speed at this time is
At 550mpm, the temperature of the cooling water is 25℃, and the amount of cooling water is
250m ³ /Hr. By controlling the transformation coiling temperature during hot rolling, the present invention guarantees the hardness desired by the user when controlling the coiling temperature before transformation and during transformation, and the shear workability of the product when controlling the coiling temperature after transformation. Furthermore, it has become possible to omit some cold rolling and TPO annealing processes. It is also effective against coil deformation, and the coil deformation of the total production amount is 1.5.
% to 0.3%, and furthermore, the transformation winding start control has the effect of changing the structure to a tough and fine structure similar to that of patenting treatment on a hot run table, so the heat treatment process can be omitted, improving the mechanical properties of the product. It has many excellent effects in improving the quality of life.

[Brief explanation of the drawing]

The drawings show an embodiment of the transformation coiling temperature control method and device in a hot rolling mill according to the present invention, and FIGS. 1 to 4 show various transformation states caused by cooling of general hot rolled steel. This explains the changes. Figure 1 shows the untransformed winding, Figure 2 shows the transformed winding,
Fig. 3 is a graph explaining the transformation completed winding, and Fig. 4 is a graph explaining the transformation completed winding and the winding point in each temperature control. Fig. 5 is a block diagram explaining the entire transformation winding temperature control method and the same device. Figure 6 is an example of a isothermal transformation curve, Figure 7 is a schematic diagram of the method for calculating the required number of banks, Figure 8 is an explanation of how to use the finishing exit thermometer,
9 to 11 are graphs for explaining the use of the intermediate thermometer and the winding thermometer. FIG. 12 is a graph of one embodiment, and FIG. 13 is a graph of another embodiment. DESCRIPTION OF SYMBOLS 1... Hot rolling finishing mill, 2... Cooling device, 3... Winding device, 4... Strip, 5... Finish exit side thermometer, 6
... Intermediate thermometer, 7... Winding thermometer, 9... Water injection nozzle, 10... Water flow control valve.

Claims (1)

[Claims] 1. In a method of hot rolling carbon steel or alloy steel with a carbon content of 0.10 to 1.7%, the steel is moved from a hot finishing mill to a winding machine via a cooling device. Measure the temperature distribution of the strip using a finish exit thermometer, an intermediate thermometer in the cooling device, and a winding thermometer.
Furthermore, by injecting cooling water into the strip, taking into account the transformation heat capacity, transformation start temperature, and transformation time, which depend on the steel type, the transformation start and end locations can be controlled to desired locations, and the desired steel characteristics can be controlled. A transformation coiling temperature control method in a hot rolling mill, characterized by controlling the temperature distribution in the coiler to an untransformed state, a transforming state, and a transformation completed state, and controlling the transformation start at the position of an intermediate thermometer. 2. A finishing outlet thermometer for measuring the strip temperature is installed between the hot rolling finishing mill and the cooling device, which are arranged along the direction of movement of the strip, and a cooling device for measuring the strip temperature is installed at an arbitrary point in the middle of the cooling device. In addition, a winding thermometer is provided between the cooling device and the winding machine, and a water injection bank control device that controls the flow rate of the water flow control valve for each water injection nozzle in the cooling device is provided. A transformation coiling temperature control device for a hot rolling mill, characterized in that it is configured to receive signals from an exit side thermometer, an intermediate thermometer, and a coiling thermometer.