JP5226965B2 - Steel plate cooling method and steel plate continuous heat treatment equipment - Google Patents

Description

  The present invention relates to a steel plate cooling method in which a steel plate is gradually cooled and then rapidly cooled in a steel plate continuous heat treatment facility, and a steel plate continuous heat treatment facility for carrying out this method.

  Steel plate continuous heat treatment equipment is used to heat and cool a traveling steel plate and continuously anneal it (Patent Document 1).

  FIG. 4A is a schematic view of a steel plate continuous heat treatment facility, and FIG. 4B is a schematic view of a steel plate continuous heat treatment facility of a hot dip galvanizing facility.

  In FIG. 4 (a), the steel plate 2 is introduced from the deflector roll 1 into the furnace, and heated zone 4, soaking zone 5, slow cooling zone 6, quench zone 7, The aging zone 8, the secondary cooling zone 9, and the tertiary cooling zone 10 are sequentially conveyed, and are conveyed to the next process via the quench device 11.

  4B, the steel sheet 2 introduced into the furnace is sequentially conveyed to the heating zone 4, the soaking zone 5, the slow cooling zone 6, the quenching zone 12, and the adjustment zones 13 and 14. Then, it is hot dip galvanized in the plating pot 16 through the snout 15.

  FIG. 5 is a schematic view showing an example of a slow cooling zone and a rapid cooling zone.

  In FIG. 5, in the slow cooling zone 6 and the quenching zone 12, a plurality of cooling wind boxes 17 for blowing cooling gas to the steel plate 2 with the traveling steel plate 2 interposed therebetween are arranged at intervals, and each cooling wind box is arranged. 17 is supplied with a cooling gas by a cooling blower 18. In the slow cooling zone 6 and the rapid cooling zone 12, the cooling blower 18 blows a cooling gas from the cooling wind box 17 to both sides of the steel plate 2 so that the outlet temperature of the steel plate becomes a predetermined temperature. .

  The inlet side plate temperature of the slow cooling zone 6 is measured by the plate temperature detector 21, the outlet side plate temperature of the slow cooling zone 6 is measured by the plate temperature detector 19, and the outlet side plate temperature of the rapid cooling zone is measured by the plate temperature detector 20. From the temperature pattern for each steel type and the steel plate size, the plate passing speed that can be processed in each furnace zone is calculated, and the lowest plate passing speed is calculated as the maximum plate passing speed for that steel type and size. Restricted.

  The steel sheet 2 is gradually cooled from a heating / soaking annealing temperature by the annealing zone 6 and then rapidly cooled by the quenching zone 12 so that predetermined mechanical characteristics can be obtained.

As a cooling method of the cooling zone, Patent Document 2 discloses a primary cooling zone after soaking of the steel plate continuous annealing equipment, and a gas jet cooling device that cools the surface of the steel plate by blowing a gas from a nozzle is provided in the plate direction. In addition, it is disclosed that the cooling capacity of the multi-stage cooling unit can be controlled independently so that the cooling unit on the front stage side can be gradually cooled, and the cooling unit on the rear stage side can be cooled rapidly (see Patent Document 2). ).
JP 2005-226157 A JP 2006-124817 A

  In the method of slow cooling and quenching in the primary cooling zone after soaking in Patent Document 2, the boundary between the slow cooling zone and the quenching zone is fixed, and a method for compensating for the lack of cooling capacity in the slow cooling zone is presented. However, if the ability of the slow cooling zone becomes a bottleneck, the feeding speed cannot be increased beyond the maximum feeding speed of the slow cooling zone.

  Therefore, in the present invention, in the cooling zone composed of the slow cooling zone and the subsequent rapid cooling zone, when the cooling capacity limit of the slow cooling zone limits the plate passing speed, that is, the slow cooling to the outlet temperature set in the slow cooling zone. In cooling the steel sheet when the temperature on the entrance side to the quenching zone becomes high without being able to perform the cooling, the sheet passing speed is increased by using a part of the preceding cooling device disposed in the quenching zone for slow cooling. It is possible to provide a steel plate cooling method and a steel plate continuous annealing facility that can improve production efficiency.

  The steel sheet cooling method of the present invention is a steel sheet continuous heat treatment facility in which a slow cooling zone and a rapid cooling zone each include a cooling zone composed of a plurality of stages of cooling devices. A steel plate cooling method that rapidly cools in the quench zone, and if the cooling zone alone cannot cool to the target plate temperature on the outlet side of the slow zone, a part of the cooling device in the preceding stage of the quench zone is used for slow cooling. The plate temperature is controlled by using the side as a virtual annealing zone exit side.

  The maximum plate passing speed of the cooling zone is obtained in the following procedures 1 to 3 to control the plate passing speed.

Step 1:
The cooling load TD _A of the cooling device in the slow cooling zone and the rapid cooling zone is obtained from the following formula 1, and the cooling load TD _A by the device capacity is calculated from the following two formulas as the cooling load TD _S by the passing plate condition. The speed Ls is obtained.

Coolable load TD _A due to equipment capacity
TD _A = 2 · Lf · α _max / (m · C)... Formula 1 Cooling load TD _S depending on plate passing conditions
TD _S = h · Ls · ln {(T _S1 −T _g ) / (T _S2 −T _g )}...
h: Plate thickness (m)
Ls: Plate speed (m / sec)
T _S1 : Entrance side plate temperature (° C)
T _g : Cooling gas temperature (° C)
T _S2 : Delivery side plate temperature (° C)
Lf: Effective furnace length (m)
α _max : Heat transfer coefficient (kcal / m ² · sec · ° C)
C: Specific heat of steel plate (kcal / kg · ° C)
m: Steel sheet density (kg / m ³ )

Step 2:
Determine the number of steps in the quenching zone where the maximum plate speed of the slow cooling zone obtained in step 1 can be passed, determine the number of cooling units that can be used for quenching in the quenching zone, and use this number of cooling units in the quenching zone The number of stages that can be switched for slow cooling is obtained by subtracting from the total number of stages.

Step 3:
For the number of stages in all cases that can be switched determined in the procedure 2, the plate passing speed is determined according to the procedure 1, and among the maximum plate passing speeds in the slow cooling zone and the quenching zone obtained after switching, The minimum maximum plate passing speed is obtained, and this is defined as the maximum plate passing speed of the cooling zone that combines the slow cooling zone and the quench zone. At this time, the heat transfer coefficient of the quenching zone to be switched to slow cooling is corrected to the equivalent of the slow cooling zone, and the maximum value of the maximum feeding speed of the cooling zone and the number of switching steps are obtained among the switching steps of all cases. .

Further, the plate temperature T (t) on the virtual slow cooling zone outlet side is calculated from the following equations 3 and 4 to control the plate temperature.
T (t) = {K · α · (T _g −T _o / 2) · t + h · C · T _o } / (K · α · t / 2 + h · C) (3 formulas)
α∝ln {(T _o −T _g ) / (T _s −T _g )} (4 formulas)
T (t): Plate temperature (° C)
K: 2 / (7.85 g / cm ³ × 3600 sec / hr) = 7.1 × 10 ⁻⁵
α: Heat transfer coefficient (kcal / m ² · hr · ° C)
T _g : Cooling gas temperature (° C)
T _o : inlet side plate temperature (° C) = actual plate temperature on the equipment slow cooling side t: time (sec)
h: Plate thickness (mm)
C: Specific heat of steel plate (kcal / kg · ° C)
T _s : Outlet plate temperature

  Moreover, the steel plate continuous heat treatment facility of the present invention is a steel plate continuous heat treatment facility in which a slow cooling zone for slowly cooling a heated steel plate and a quenching zone for rapid cooling are arranged in a cooling zone composed of multiple stages of cooling devices. It is characterized by having a control device that controls the plate temperature by using a part of the cooling device in the previous stage of the quenching zone as a virtual annealing zone when it cannot be cooled to the target cooling zone outlet side temperature only by the slow cooling zone. To do.

  The control device calculates the maximum plate passing speed of the cooling zone according to the procedures 1 to 3 and controls the plate passing speed, and sets the virtual plate temperature T (t) on the outlet side of the slow cooling zone to three types and 4 It is a control device that controls the plate temperature by calculating from the equation.

  Usually, each plate temperature is managed on the slow cooling zone exit side and the quenching zone exit side. In the heat treatment furnace, the maximum plate passing speed may be determined by the slow cooling zone cooling capacity, the maximum cooling plate cooling capacity may be determined by the quench zone cooling capacity, or the maximum by the capacity of other heating zones. In some cases, the plate speed is determined. Of the maximum speeds of the heating zone, the soaking zone, the slow cooling zone, and the rapid cooling zone, when the slow cooling zone is the lowest speed, the lowest speed of the slow cooling zone becomes the maximum heat treatment furnace speed.

  In the present invention, in the cooling zone composed of the slow cooling zone and the subsequent rapid cooling zone, when the cooling capacity limit of the slow cooling zone limits the plate passing speed, that is, the outlet side temperature set in the slow cooling zone can be gradually cooled. In the cooling of steel sheets when the temperature on the entrance side to the quenching zone is high, it is possible to increase the sheet feeding speed by using a part of the previous stage cooling device arranged in the quenching zone for slow cooling. And improve production efficiency.

  If the cooling speed limit of the slow cooling zone limits the plate feeding speed and there is a margin in the cooling capacity of the quenching zone, use a part of the cooling device in the previous stage of the quenching zone for slow cooling to maximize the plate passing speed. Since the plate temperature can be controlled by calculating the number of switching stages of the slow cooling use that can be performed and setting the exit side as the hypothetical slow cooling zone exit side, the plate passing speed in this case can be made larger than before, so heat treatment equipment can be efficiently Can operate.

  The present invention is illustrated by examples.

  In the present invention, in order to perform slow cooling in the preceding stage of the rapid cooling zone after the slow cooling zone, the maximum plate passing speed and the number of switching stages in the cooling zone are calculated according to the following procedure.

  FIG. 1 is a schematic diagram showing the arrangement of cooling devices (wind boxes) in a slow cooling zone and a rapid cooling zone.

(1) As the plate passing condition, the plate passing size, the slow cooling zone entry side target plate temperature, the slow cooling zone exit side target plate temperature (same as the quenching zone entry side plate temperature), and the rapid cooling zone exit side target plate temperature are read.

In this example, the plate thickness h: 1 mm, T _S1 : annealing zone plate temperature T _S1 : 800 ° C, annealing zone exit side plate temperature (same as quenching zone entry side plate temperature) T _S2 : 700 ° C, quenching zone exit side plate temperature : 400 ° C., cooling gas temperature T _g : 50 ° C., steel plate specific heat C: 0.134 kcal / kg · ° C., steel plate density: 7850 kg / m ³ .

(2) The calculation of the number of switching stages for slow cooling in the preceding stage of the quenching zone and the plate passing speed of the cooling zone is obtained by the above formulas 1 and 2 for the next cooling load TD.
Coolable load TD _A due to equipment capacity
TD _A = 2 · Lf · α _max / (m · C)... Formula 1 Cooling load TD _S depending on sheet passing conditions
TD _S = h · Ls · ln {(T _S1 −T _g ) / (T _S2 −T _g )}... 2 type Each wind box (SCF 1 to 6) of the slow cooling zone from the above 1 type, quench zone TD _A of each of the wind boxes (RCF 1 to 6) is obtained, and TD _A = TD _S , and from the LS of the above two formulas, the plate feed speed (Vscf 1 to 6, SCF 1 to 6, RCF 1 to 6) Vrcf1 to 6) are obtained. Here, for example, Vscf3 is the maximum speed at which a predetermined plate thickness and temperature cycle can be achieved by using 1 to 3 stages of a cooling device in the slow cooling zone, and Vrcf4 is from behind the cooling device in the quenching zone. The maximum speed at which a predetermined plate thickness and temperature cycle can be achieved using four stages.

Table 1 shows the plate passing speed obtained by calculation.

(3) From Table 1, the number of stages n required for quenching in the quenching zone is calculated from the maximum plate speed in the current slow cooling zone. In Table 1, the maximum speed in the slow cooling zone is 266 mpm,
246 mpm (Vrcf3) <266 mpm ≦ 328 mpm (Vrcf4)
To the wind box RCF4 (fourth stage) in the quenching zone, that is, the subsequent four wind boxes must be used for quenching (n = 4).

(4) Calculation of the maximum number of stages that can be switched to slow cooling The switchable stage number I is obtained by subtracting the number of stages n required for rapid cooling from the total number N of quenching zones (I = N−n). The number of possible stages I = 6−4 = 2, and up to two stages before the quenching zone, that is, one or two stages can be switched for slow cooling.

(5) Obtain the maximum plate passing speed of the slow cooling zone and the maximum plate passing speed of the quench zone for each number of stages to be switched to slow cooling (in this embodiment, one or two stages), and calculate the maximum plate passing speed of the cooling zone. Ask. At this time, the heat transfer coefficient of the quenching zone used for slow cooling is corrected in the same manner as that of the slow cooling zone.

Table 2 shows the calculation results in the case of two-stage switching.

Table 3 shows the calculation results in the case of one-stage switching.

  Of the maximum plate passing speeds in the slow cooling zone and the rapid cooling zone after switching, the minimum plate passing speed is the maximum speed limit in the cooling zone.

If the two-stage switching, from Table 2, the maximum speed 328mpm of RCF3 the rapid cooling zone than the maximum speed 443mpm of RCF2 corresponding to slow cooling zone after switching is small, the maximum rate 328mpm the rapid cooling zone is a slow cooling zone and the rapid cooling zone It becomes the maximum plate speed in the cooling zone.

  In the case of one-stage switching, from Table 3, the maximum speed 354 mpm of RCF 1 corresponding to the slow cooling zone after switching is smaller than the maximum speed 410 mpm of RCF 2 in the quenching zone, so the maximum speed 354 mpm of the slow cooling zone is the slow cooling zone. And the maximum plate passing speed in the cooling zone that combines the quenching zone.

  Comparing the case of one-stage switching and the case of two-stage switching, in this case, the one-stage switching increases the plate passing speed, and the maximum plate passing speed 354 mpm is obtained.

  (6) In the case of the heating zone, the soaking zone, and the one-stage switching obtained in 5 above, the maximum speeds of the slow cooling zone and the quenching zone after switching are compared, and the maximum speed of the lowest value is obtained. This lowest maximum speed is the maximum speed limit in the heat treatment furnace. The maximum speed 354 mpm of the cooling zone in the case of one-stage switching is the lowest value compared to the maximum speed 370 mpm of the heating zone and the maximum speed 420 mpm of the soaking zone, so 354 mpm is the maximum speed limit of the heat treatment furnace.

  From the above results, as shown in the temperature history of FIG. 2, the first-stage windbox (RCF1) in the preceding stage of the rapid cooling zone is switched to slow cooling, and the exit side of this windbox (RCF1) is the virtual slow cooling zone exit. Become the side.

  Moreover, in this invention, the plate | board temperature T (t) of the virtual slow cooling zone exit side is calculated from said 3 type | formula and 4 type | formula, and plate | board temperature is controlled.

T (t) = {K · α · (T _g −T _o / 2) · t + h · C · T _o } / (K · α · t / 2 + h · C) (3 formulas)
α∝ln {(T _o −T _g ) / (T _s −T _g )} (4 formulas) The rotational speed of the blower in the quenching zone switched to slow cooling is controlled collectively with the blower in the slow cooling zone To. Since the cooling capacity of the quenching zone cooling device and that of the slow cooling zone are different, when using the preceding stage of the quenching zone for slow cooling, the number of rotations of the quenching zone cooling device is reduced and the slow cooling zone It is necessary to control so as to be equal to the heat transfer coefficient. The control range when using the first stage of the quenching zone for slow cooling is the relationship between the heat transfer coefficient of the slow cooling zone and the rotational speed of the cooling device, the thermal heat transfer coefficient of the slow cooling zone, and the rotational speed of the cooling device. It can be obtained from the relationship.

  FIG. 3 is a graph showing the relationship between the heat transfer coefficient, the slow cooling zone, and the rotational speed of the cooling device.

  For example, in FIG. 3, the heat transfer coefficient (α) is 100 when the rotational speed of the blower in the slow cooling zone (SCF) is 100%, and the rotational speed of the blower in the rapid cooling zone (RCF) corresponding to this is 20 %. Corresponding to the rotational speed command value 0-100% for the slow cooling blower, the control range is set so that the rotational speed of the rapid cooling blower switched to slow cooling is controlled at 0-20%. .

It is a schematic diagram which shows arrangement | positioning of the cooling device (wind box) of a slow cooling zone and a rapid cooling zone. It is a figure which shows the calculated temperature history. It is a graph which shows the relationship between a heat-heat transfer coefficient, a slow cooling zone, and the rotation speed of a cooling device. (A) is the schematic of a steel plate continuous heat treatment equipment, (b) is the schematic of the steel plate continuous heat treatment equipment of a hot dip galvanization equipment. It is the schematic of a slow cooling zone and a rapid cooling zone.

Explanation of symbols

1: Deflector roll 2: Steel plate 3: Transport roll 4: Heating zone 5: Soaking zone 6: Slow cooling zone 7: Primary cooling zone 8: Overaging zone 9: Secondary cooling zone 10: Third cooling zone 11: Quench Device 12: Rapid cooling zone 13, 14: Cooling adjustment zone 15: Snout 16: Plating pot 17: Winding box 18 for cooling 18: Cooling blower 19, 20: Temperature detector

Claims (4)

Steel sheet cooling method in which a steel sheet is continuously cooled in a slow cooling zone and then rapidly cooled in a rapid cooling zone in a steel sheet continuous heat treatment facility in which a slow cooling zone and a rapid cooling zone are each composed of a cooling device having a plurality of stages. However, if the cooling zone alone cannot cool to the target cooling zone outlet side plate temperature, a part of the cooling device in the preceding stage of the quenching zone is switched to the annealing zone, and the maximum feeding speed of the cooling zone is set. A steel plate cooling method characterized by controlling the plate temperature by obtaining the number of switching stages for switching the rapid cooling zone required for realizing the maximum plate passing speed to the slow cooling zone in the following procedures 1 to 3.
Step 1:
The cooling load TD _A of the cooling device of the slow cooling zone and the rapid cooling zone is obtained from the following formula 1, and the cooling load TD _A by the device capacity is calculated from the following two formulas = the cooling load TD _S by the passage condition is the number of stages used in each cooling zone Then, a plate speed Ls that can be achieved is obtained.
Coolable load TD _A due to equipment capacity
TD _A = 2 · Lf · α _max / (m · C)... Formula 1 Cooling load TD _S depending on sheet passing conditions
TD _S = h · Ls · ln {(T _S1 −T _g ) / (T _S2 −T _g )}...
h: Plate thickness (m)
Ls: Plate speed (m / sec)
T _S1 : Entrance side plate temperature (° C)
T _g : Cooling gas temperature (° C)
T _S2 : Delivery side plate temperature (° C)
Lf: Effective furnace length (m)
α _max : Heat transfer coefficient (kcal / m ² · sec · ° C)
C: Specific heat of steel plate (kcal / kg · ° C)
m: Steel sheet density (kg / m ³ )
Step 2:
If the maximum plate feeding speed of the slow cooling zone is the maximum plate feeding speed of the furnace, the maximum plate feeding speed of the slow cooling zone obtained in step 1 is determined in which number of stages of the quenching zone can be passed. The number of stages of the cooling device that can be used for rapid cooling is obtained, and the number of stages that can be switched for slow cooling is obtained by subtracting the number of stages from the total number of stages of the cooling device in the quenching zone.
Step 3:
For the number of stages in all cases that can be switched determined in the procedure 2, the plate passing speed is determined according to the procedure 1, and among the maximum plate passing speeds in the slow cooling zone and the quenching zone obtained after switching, The minimum maximum plate passing speed is obtained, and this is defined as the maximum plate passing speed of the cooling zone that combines the slow cooling zone and the quench zone. At this time, the heat transfer coefficient of the quenching zone to be switched to slow cooling is corrected to the equivalent of the slow cooling zone, and the maximum value of the maximum feeding speed of the cooling zone and the number of switching steps are obtained among the switching steps of all cases. . Calculate the plate temperature T (t) on the exit side of the virtual slow cooling zone from the following formulas (3) and (4) based on the actual plate temperature on the exit side of the equipment slow cooling zone measured by the thermometer on the exit side of the equipment slow cooling zone. The steel sheet cooling method according to claim 1 , wherein the steel sheet temperature is controlled.
T (t) = {K · α · (T _g −T _o / 2) · t + h · C · T _o } / (K · α · t / 2 + h · C) (3 formulas)
α∝ln {(T _o −T _g ) / (T _s −T _g )} (4 formulas)
T (t): Plate temperature (° C)
K: 2 / (7.85 g / cm ³ × 3600 sec / hr) = 7.1 × 10 ⁻⁵
α: Heat transfer coefficient (kcal / m ² · hr · ° C)
T _g : Cooling gas temperature (° C)
T _o : inlet side plate temperature (° C) = actual plate temperature on the equipment slow cooling side t: time (sec)
h: Plate thickness (mm)
C: Specific heat of steel plate (kcal / kg · ° C)
T _s : Outlet plate temperature In the steel plate continuous heat treatment facility in which a slow cooling zone for gradually cooling the heated steel plate and a rapid cooling zone for rapid cooling are arranged in a cooling zone composed of multiple stages of cooling devices,
The control device for controlling the plate temperature by using a part of the cooling device in the preceding stage of the quenching zone as a virtual annealing zone when the cooling zone alone cannot cool to the target cooling zone outlet side plate temperature. A steel plate continuous heat treatment facility, which is a control device that controls the plate passing speed by calculating the maximum plate passing speed of the cooling zone in accordance with steps 1 to 3 of the steel plate cooling method. The control device calculates the plate temperature T (t) on the imaginary annealing zone exit side of the steel sheet cooling method according to claim 2 from Formulas 3 and 4 of the steel plate cooling method according to Claim 2, and controls the plate temperature. The steel plate continuous heat treatment facility according to claim 3, wherein the steel plate continuous heat treatment facility is a control device.

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