JP4903073B2 - Cooling pattern display method - Google Patents

Description

  The present invention relates to a cooling pattern display method for displaying a cooling temperature history and a cooling rate in a cooling zone of a continuous annealing furnace for heat-treating a steel plate.

  A continuous annealing furnace 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 continuous annealing furnace, and FIG. 4B is a schematic view of a continuous annealing furnace of a hot dip galvanizing facility. In FIG. 4 (a), the steel plate 2 is introduced into the furnace from the deflector roll 1 and heated zone 4, soaking zone 5, slow cooling zone 6, primary cooling zone 7 by the upper and lower conveying rolls 3 in the furnace. Then, the overaging zone 8, the secondary cooling zone 9, and the tertiary cooling zone 10 are sequentially conveyed and conveyed to the next process through the quench device 11 outside the furnace.

  Further, in the hot dip galvanizing equipment shown in FIG. 4 (b), the steel sheet 2 introduced into the furnace is sequentially supplied to the heating zone 4, the soaking zone 5, the slow cooling zone 6, the quenching zone 12, and the cooling adjustment zones 13 and 14. It is conveyed and hot-dip galvanized in the plating pot 16 through the snout 15.

  In the cooling zone, the steel sheet is cooled from the austenite state at a predetermined cooling rate and transformed into ferrite bainite or martensite to give predetermined workability and toughness.

  FIG. 5 is a schematic view of the cooling zone. In the cooling zone 7 of the slow cooling zone and the quenching zone, a plurality of cooling window boxes 17 for blowing cooling gas to the steel plate 2 with the traveling steel plate 2 interposed therebetween are arranged at intervals in the vertical direction, and each cooling window is arranged. A cooling gas is supplied to the box 17 by a cooling blower 18. In the cooling zone, cooling is controlled by blowing a cooling gas from both sides of the steel plate by a cooling blower so that the outlet temperature of the steel plate becomes a predetermined temperature. The inlet side plate temperature is measured by a plate temperature detector 19, and the outlet side plate temperature is measured by a plate temperature detector 20.

The DCS and process computer in the operation room include {(exit side plate temperature one inlet side plate temperature) from the inlet side plate temperature and the outlet side plate temperature, the inlet side and outlet side plate temperatures, the cooling zone length and the plate passing speed. / (Cooling zone length / feeding plate speed)} is displayed.
JP 2005-226157 A

  Conventionally, cooling in the cooling zone is controlled by the process computer or DCS outlet side plate temperature control, with the air flow of the cooling blower being controlled with the priority given to setting the outlet side plate temperature to a predetermined temperature. The actual delivery side plate temperature displayed on the is monitored.

  The metallurgical structure and mechanical characteristics of the steel sheet are affected by the cooling temperature history and cooling rate in the cooling zone. The cooling rate and the cooling temperature history are affected by the plate passing speed, the inlet and outlet plate temperatures, and the cooling length. Depending on the steel plate and steel plate size, the maximum plate passing speed differs from the throughput and heat transfer conditions, and the cooling length depends on how many cooling blowers achieve the outlet side plate temperature depending on the plate passing speed, temperature conditions, and steel plate size. change. Therefore, the cooling temperature history and the cooling rate change depending on the plate passing condition and the operating condition.

  On the conventional operation screen, the information regarding the cooling rate in the cooling zone is such that the average cooling rate obtained from (exit side plate temperature / inlet side plate temperature) / (cooling zone length / plate passing rate) is displayed.

  However, the actual cooling rate history of the steel sheet is unknown only by the average cooling rate obtained using the outlet side and inlet side plate temperatures, and the plate speed, temperature conditions, cooling length, inlet side plate temperature, outlet side The effect on the metallurgical structure and mechanical properties of the steel sheet due to differences in the actual cooling temperature history and cooling rate due to changes in the side plate temperature could not be accurately grasped.

  Therefore, the present invention calculates the cooling rate and cooling temperature history during the running of the cooling zone on the display panel of the cooling zone operation panel, displays it on the continuous cooling transformation diagram of steel, and reflects it in the quality control of the steel sheet coil. The present invention provides a method for displaying a cooling pattern in a cooling zone of a continuous heat treatment furnace for steel plates.

The present invention provides a cooling temperature pattern display method for displaying a cooling temperature history and a cooling rate actual value in a cooling zone of a continuous heat treatment furnace for continuously heat-treating a traveling steel plate in a continuous cooling transformation diagram of the steel plate ,
The cooling temperature history {T (t)} and the cooling rate actual value {Rc (t)} are calculated by the following equation (1) including the heat transfer coefficient calculated by the following equation (4) and the following equation (2). In determining the heat transfer coefficient (α ₁ ) obtained from the following equation (3) from the outlet plate temperature obtained by calculation and the heat transfer coefficient obtained from the following equation (3) from the actual outlet temperature obtained from the measurement ( α ₂ ) and the ratio {heat transfer coefficient (α ₂ ) / heat transfer coefficient (α ₁ )} multiplied by the heat transfer coefficient calculated by the following equation (4) to correct the calculated output side plate temperature Calculates the cooling temperature history {T (t)} and the cooling rate actual value {Rc (t)} that match the actual plate temperature,
The cooling speed actual value and the cooling temperature history obtained to display in the drawing CCT of the steel.

In the present invention, the cooling temperature {T (t)} and the cooling rate {Rc (t)} are obtained by the following equations (1), (2) , (3), and (4) , and the continuous cooling transformation is performed. Display on the diagram.

T (t) = {K · α · (Tg−T _o / 2) · t + h · C · T _o } / (K · α · t / 2 +
h · C) (1)
Rc (t) = K · α · (Tg−T _o / 2) · (K · α · t / 2 + h · C) ⁻¹
− (K · α / 2) · {K · α (Tg−T _o / 2) · t + h · C · T _o } ·
{(K · t / 2) + h · C} ⁻² (2)
α∝ln {(T _o −Tg) / (Ts−Tg)} (3)
α = A · N ^m (4)
However,
K: 2 / (7.85 g / cm ³ × 3600 sec / hr) = 7.1 × 10 ⁻⁵
h: Plate thickness (mm)
C: Specific heat of steel plate (kcal / kg · ° C)
T _o: entry side temperature (℃)
T (t): Plate temperature (° C)
Rc (t): Cooling rate (° C / sec)
t: Time (sec)
α: Heat transfer coefficient (kcal / m ² · hr · ° C)
α ₁ : Heat transfer coefficient obtained by calculation (kcal / m ² · hr · ° C)
α ₂ : heat transfer coefficient (kcal / m ² · hr · ° C)
Tg: Cooling gas temperature (° C)
Ts: Outboard plate temperature
A: Constant (depending on the cooling device)
N: Blower speed
m: Constant (depending on the cooling device)

  According to the present invention, by calculating and displaying the cooling temperature history and cooling rate, it is possible to know the influence of the cooling temperature history and cooling rate of the steel sheet on the metallurgical structure and mechanical properties. It becomes.

For each cooling device, an approximate function of the rotational speed of the blower and the heat transfer coefficient can be created from the theoretical formula and experimental formula of forced convection heat transfer. this is,
α = A ・ N ^m
As shown, the heat transfer coefficient can be approximated to an exponential function of the rotational speed of the blower. here,
α: Heat transfer coefficient A: Constant (depending on cooling device)
N: Blower rotation speed m: Constant (depending on cooling system)
The heat transfer coefficient α of each cooling device can be calculated from the actual rotational speed N of each blower, and the cooling temperature history T (t) is sequentially calculated from the formulas (1) and (2) for the steel strip in the course of traveling through the cooling zone. The cooling rate Rc (t) can be calculated.

Here, on-line measurement with the outlet side plate temperature calculated as described above from the error factors such as the approximate expression of the heat transfer coefficient α of the cooling device, the arithmetic mean temperature difference of equation (1), and the plate temperature measurement error. This is not exactly the same as the delivery side temperature. Therefore, the heat transfer coefficient α is corrected by the following equation (3).
α∝ln {(T _o −Tg) / (Ts−Tg)} (3)
here,
T _o : inlet side plate temperature Tg: blowing gas temperature Ts: outlet side plate temperature For example, as shown in FIG. 2, when each blower is rotated uniformly, the inlet side plate temperature is 677 ° C and the outlet side plate temperature is 400 ° C. Assume that the outlet side plate temperature is 388 ° C. In order to correct the plate temperature of 388 ° C. to the actual 400 ° C., α ₁ ∝ln {(677-50) / (388-50)} = 0.617 used in the calculation and the actual α ₂ ∝ln {(677 -50) / (400-50)} = 0.583 and 0.583 / 0.6179 = 0.944, and 0.943 is calculated for each blower (the above-mentioned “α = A · N ^m )) Multiplied by α used for correction.

In addition, as shown in FIG. 3, when the pre-stage blower is preferentially operated and the inlet side plate temperature is 677 ° C. and the outlet side plate temperature is 400 ° C., the plate temperature obtained by calculation is 422 ° C. and the outlet side plate temperature is Suppose that it became 408 degreeC. In order to correct this delivery side plate temperature of 408 ° C. to the actual 400 ° C., α ₁ ∝ln {(677-50) / (422-50)} = 0.522 and α ₂ ∝ln {(422 −50) / (408-50)} = 0.038, (α ₁ + α ₂ ) ∝0.560 is obtained, and α∝ln {(677-50) / (400-50)} = 0. The ratio 0.583 / 0.560 = 1.04 with respect to 583 is obtained, and 1.04 is multiplied by α used for the calculation of each blower to correct it.

  As described above, by correcting α, it is possible to calculate the cooling temperature history and the cooling rate at which the calculated delivery side plate temperature matches the actual plate temperature.

In an example of a certain cooling zone, the display of the calculation result under the plate operating conditions in Table 1 is shown in FIG. Table 1 is a table showing an example of the inlet side plate temperature, the outlet side plate temperature, the plate thickness, the plate passing speed, and the operation mode of the cooling device for each steel type in actual operation.

When cooling is performed under the conditions shown in Table 1, the sheet temperature T (t) and the cooling rate Rc (t) for each steel type displayed on the continuous cooling transformation diagram , the vertical axis is the temperature (° C.), and the horizontal axis is the time ( When displayed on figure t), it will curve as shown in FIG.

  In the continuous cooling transformation diagram, the state of transformation that occurs in the process of continuous cooling from the austenite state is shown, so by displaying the cooling rate and cooling temperature history in this continuous cooling transformation diagram, It becomes possible to know the transformation state of retained austenite, ferrite and bainite. Information on the product coil is stored in the process computer, and the cooling rate and cooling temperature history during the running of the steel sheet are determined by comparing the cooling rate and cooling temperature history with the information on the product coil. The influence on the characteristics can be examined to help the quality control of the steel sheet.

Vertical axis Temperature (° C.), the horizontal axis indicates time diagram on the cooling temperature history T of (t) (t), is a diagram showing a cooling rate Rc (t). It is explanatory drawing of correction | amendment of the heat transfer coefficient (alpha). It is explanatory drawing of correction | amendment of the heat transfer coefficient (alpha). (A) is the schematic of a continuous annealing furnace, (b) is the schematic of the continuous annealing furnace of a hot dip galvanization installation. It is the schematic of a 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 (1)

In the cooling temperature pattern display method for displaying the cooling temperature history and the cooling rate actual value in the cooling zone of the continuous heat treatment furnace for continuously heat-treating the traveling steel plate in the continuous cooling transformation diagram of the steel plate ,
The cooling temperature history {T (t)} and the cooling rate actual value {Rc (t)} are calculated by the following equation (1) including the heat transfer coefficient calculated by the following equation (4) and the following equation (2). In determining the heat transfer coefficient (α ₁ ) obtained from the following equation (3) from the outlet plate temperature obtained by calculation and the heat transfer coefficient obtained from the following equation (3) from the actual outlet temperature obtained from the measurement ( α ₂ ) and the ratio {heat transfer coefficient (α ₂ ) / heat transfer coefficient (α ₁ )} multiplied by the heat transfer coefficient calculated by the following equation (4) to correct the calculated output side plate temperature Calculates the cooling temperature history {T (t)} and the cooling rate actual value {Rc (t)} that match the actual plate temperature,
A cooling pattern display method, wherein the obtained cooling temperature history and actual cooling rate value are displayed on the continuous cooling transformation diagram of the steel.
T (t) = {K · α · (Tg−T _o / 2) · t + h · C · T _o } / (K · α · t / 2 +
h · C) (1)
Rc (t) = K · α · (Tg−T _o / 2) · (K · α · t / 2 + h · C) ⁻¹
− (K · α / 2) · {K · α (Tg−T _o / 2) · t + h · C · T _o } ·
{(K · t / 2) + h · C} ⁻² (2)
α∝ln {(T _o −Tg) / (Ts−Tg)} (3)
α = A · N ^m (4)
However,
K: 2 / (7.85 g / cm ³ × 3600 sec / hr) = 7.1 × 10 ⁻⁵
h: Plate thickness (mm)
C: Specific heat of steel plate (kcal / kg · ° C)
T _o: entry side temperature (℃)
T (t): Plate temperature (° C)
Rc (t): Cooling rate (° C / sec)
t: Time (sec)
α: Heat transfer coefficient (kcal / m ² · hr · ° C)
Tg: Cooling gas temperature (° C)
Ts: Outboard plate temperature
A: Constant (depending on the cooling device)
N: Blower speed
m: Constant (depending on the cooling device)

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