JPS62166014A - Cooling method for hot steel plate with different thickness - Google Patents

Abstract

PURPOSE:To uniformly cool steel plate parts in the vicinity of a thickness changing line by obtaining an optimum cooling condition based on a temp. at plural dividing points in the longitudinal direction of the plate and controlling a plate passing speed in accordance with a thickness of the plate. CONSTITUTION:A radiation thermometer 12 measures a temp. at plural dividing points in the longitudinal direction of a hot steel plate S prior to insertion of the plate S into a cooler 3. An optimum cooling condition at each dividing point is calculated a controlling calculator 4 based on the measured value. When the plate is cooled with its thicker part at the head, a passing speed is lowered to supplement a shortage of a cooling time for the thicker part prior to insertion of the thickness changing line into the cooler 3. The passing speed is accelerated up to the speed for a thinner part passing at the instant when the thickness changing line enters the cooler 3. In the case of the thinner part at the head, the speed is first accelerated and then decelerated. In this method, both the thicker and thinner parts around the thickness changing line are uniformly cooled to the target temp.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a method of cooling a steel plate surface by a certain amount while feeding a differential thickness hot steel plate whose steel thickness changes in a stepwise manner in the longitudinal direction. This relates to a differential thickness heat-A temporary cooling method carried out by supplying water.

(Prior art) In hot rolling fI4 temporary forced water cooling, the cooling end temperature affects the steel sheet material, so in order to obtain one sheet metal having a uniform and desired material quality, each part of the steel sheet must be predetermined and nine sheets must be cooled with high precision. A method for controlling the temperature at the end of cooling of a hot plate is proposed in Japanese Patent Application Laid-open No. 87914/1983. In this method, the cooling start and end temperatures are Ti, T
When φ5 cooling rate fVc and cooling zone length fLc, v*=νclILc/(Ti-Tφ)...
...The threading speed obtained in (1) is set to the standard threading speed v6, and the cooling start temperature difference due to the difference in cooling start time in the longitudinal direction of the steel plate is corrected by ink that accelerates the threading speed between the cooling zone lengths. be.

In Zaraani %m No. 6O-938F11, a method of correcting the threading speed by taking in strange sounds just before the start of cooling is also proposed. Concept 1 of these threading speed control is shown in Fig. 7.

V in the figure is the standard threading speed obtained by the above il1 formula.

ΔV represents a change in the threading speed due to acceleration to compensate for the difference in cooling start temperature in the longitudinal direction, and Δν2 represents a modification of the threading speed by taking in the cooling start temperature VCL. The sheet threading speed control shown in FIG.
When 1+Δv2 is smaller than ν, fP is practically sufficient for a constant-thickness steel plate where the ice-frost cooling rate in the longitudinal direction of the steel plate can be considered constant! Every time? I'm doing M.

In addition, differential thickness steel plates are used for ships with snow, etc., and many non-forced cooling types have already been manufactured.

[Problem that the invention seeks to solve]

Problems when performing forced water cooling while supplying a constant amount of cooling water and temporarily passing n1 are: ■ The effect on the cooling end temperature by keeping the threading speed unchanged is that the cooling zone of the entire length of the steel plate is affected. Appears in long length.

■ Starting cooling in the longitudinal direction of the steel plate There are two points that are affected by the threading speed.

Furthermore, as a problem specific to differential thickness steel plates, ■ Cooling start temperature deviation due to longitudinal air cooling speed difference ■ Longitudinal water cooling speed difference There is.

The reason for ■ above is that the length of the cooling zone out of the total length of the steel plate is always in the cooling process at the same time.

Cooling end temperature system of patent application Shofig-93861? I11
'l be.

Although this point is used in reverse, this control method is effective when the stock of differentially thick steel plates has a difference in water cooling speed in the longitudinal direction and smooth acceleration or deceleration of the threading speed is required. This causes a deviation in the MA degree at the end of cooling in the longitudinal direction.

The reason for this will be considered with respect to points P and Q (Fig. 8) in the longitudinal direction of the steel plate. As shown in FIG. 8(a), the interval between points P and Q is assumed to be short, as is the length S of the cooling zone.

Points P and Q are cooled when they are open for a certain period of time. points P and Q
As shown in Figure 8 (b), the velocity Vp in the cooling zone is
By threading the plate at , VQ, it is cooled to the target cooling end temperature at 1. By the way, since points P and Q are in the cooling zone when opened during the above time t, during this time, V, vQ
must be equal.

Now, suppose that the point Q is just before the start of cooling and it is found that the sheet threading speed VQ cannot cool the sheet to the target cooling end temperature, and the sheet threading speed is changed to Vζ shown by the broken line in FIG. 8 and set to 9. At this time, the sheet passing speed vP is no longer vP (the cooling end temperature at the point P deviates from the target value).

Therefore, if the threading speed is corrected in order to adjust the cooling end temperature at a certain point in the longitudinal direction of the steel plate to the target value, it will act as a disturbance at other points, and the cooling end temperature f within the steel plate will be reduced. It will lower it.

Moreover, the above-mentioned (2) is due to the difference in cooling start time in the longitudinal direction during sheet passing.

In addition, the above-mentioned ■ and ■ are caused by the difference in plate thickness in the longitudinal direction. In differential thickness steel plates, the plate thickness changes discontinuously at the difference thickness line, so the cooling start temperature and water cooling cooling rate are discontinuous near the difference thickness line. becomes.

A constant amount of water is supplied with the thick side as the tip, as shown in Figure 9 (a). (The cooling end temperature when cooling is performed at a constant sheet threading speed is shown in Figure 9 (b). In this case The cooling end temperature of the thin part is lower than the cooling end temperature of the thick part.

What is the cooling end temperature when the threading speed is ? It is shown in FIG. 10(b). In this case, the side of the differential thickness line of the thin section cooling medium thick section is inside the cooling equipment, and the cooling time of the circulating section decreases by the amount of speed increase, and as a result, the thick section cooling end temperature is on the side close to the differential thickness line. It exhibits the division of a triangle. In either case, since the plate thickness changes stepwise, a cooling end temperature gap occurs at the edge difference thickness line due to the difference in cooling start temperature and water cooling rate between the thick and thin parts.

Therefore, the mechanical properties fluctuate greatly near the differential thickness portion, making it impossible to obtain the desired mechanical properties and the quality is not uniform over the entire length.

This invention was developed in order to solve the above-mentioned problems.In order to cool steel plates with different thicknesses, it is possible to improve the predicted cooling start temperature in the longitudinal direction of the steel plate. It is an object of the present invention to provide a cooling method for obtaining a uniform differential thickness steel plate 1 having a desired material quality by obtaining a desired cooling end temperature.

Means for Solving Problem 1] The gist of the present invention is to forcibly cool a hot-rolled steel plate to a predetermined temperature by reducing the cooling start temperature, % cooling end temperature, and the sound of the cooling water. In the process of cooling by setting the cooling zone length and the threading speed during cooling in advance, measurements are taken at multiple dividing points in the longitudinal direction of the steel sheet before loading it into the cooling equipment, and the actual values are used. Based on this, the optimum cooling conditions for each division point are calculated, and when the thick section is used as the tip, the speed is decelerated just before the start of differential thickness edge cooling, and then the speed is accelerated to the thin section. When threading as a gold advance, the difference in thickness is I%l.
This is a method for cooling a differential thickness heated steel sheet, which is characterized by accelerating the speed before the start of cooling and then decelerating the threading speed of the thick section.

[Effect]

The conveyance and cooling of the steel plate is carried out, for example, in the following manner. That is, it is conveyed by roller tables placed before and after the cooling equipment.

Cooling water is supplied from nine nozzles located on the top of the roller table in the cooling equipment.

The operation will be explained below with reference to FIG. Curve 7 in FIG. 1 shows the relationship between the cooling start temperature Ti and the sheet passing speed V, which is determined from the sheet passing speed. Preliminary here! 11 Cooling start temperature Ti is determined, for example, as the cooling start temperature of the tip of a constant thickness steel plate surrounding the plate thickness at the predicted position. Now, if the predicted cooling start temperature is T, then
The plate threading speed v is determined from the target cooling end temperature, plate thickness, and cooling water 11-. Next, the sheet passing speed V and the cooling start time at the predicted position are determined, and the cooling start temperature T,1 is calculated from the air-resistant cooling rate. As shown in Fig. 1, in the case of T, >T, the predicted cooling amount starting temperature is increased to Ti2 and the one-thread speed v2)
The cooling start criticality Ti2 is determined. This operation sequentially? Repeat,
The threading speed v at which the difference between both cooling start temperatures &T, and Ti is less than the allowable value? demand. If Ti,<T,1, perform the opposite operation.

Improve the accuracy of predicting the cooling start temperature of each section in the longitudinal direction of a steel plate with a difference in edge thickness in convergence calculations, and improve the accuracy of the cooling end temperature in parts excluding the vicinity of the difference thickness section.

In addition, for the vicinity of the differential thickness section, the sheet is first fully threaded at a speed determined from the thin section cooling conditions. Since the required cooling time for the thin part of ft1l is long when the thick part is required to be cooled, the threading speed is reduced before the differential thickness wire enters the cooling equipment to compensate for the insufficient cooling time for the thick part. Next, the moment the differential thickness wire enters the cooling equipment, it is accelerated to the thin section threading speed. As a result, both the thick and thin portions near the differential thickness portion can be uniformly cooled to the target temperature, making it possible to manufacture a differential thickness steel plate that has the desired mechanical properties kW that are uniform throughout the steel plate. Furthermore, when cooling the thin section, the cooling water t7j is combined with shielding to reduce the acceleration/deceleration rate of the strip threading speed, making it possible to finely control the cooling time, and to ensure uniform cooling especially near the differential thickness section. It can be improved.

[Example-1] FIG. 2 is an equipment configuration diagram showing an example of rolling and cooling equipment for implementing the present invention. A hot steel plate S rolled by a finishing mill 1 is flattened by a hot leveler 2 and then forcedly cooled by water in a cooling equipment 3.

The cooling equipment 3 includes a plurality of cooling zones 7, and each cooling zone 7 has a plurality of upper and lower roll pairs 5 and cooling water nozzles 8 arranged therein. The steel plate S is conveyed to an open roller table 6 of each equipment, and a pair of upper and lower rollers 5. The table rollers 6 are each driven by a motor 9, 10, 11. A radiation thermometer 12 is installed between the finishing rolling mill 1 and the cooling installation 1iiiia, and a radiation thermometer 13 and a steel plate detector are installed immediately after the cooling installation 3. 14 are arranged respectively. These detected values are input to the control computer 4.

In the nine facilities configured as described above, cooling control is performed according to the procedure shown in FIG. First, cooling conditions such as the end temperature of quenching, water cooling rate, and plate thickness are set in the control computer 4. The control computer 4 performs calculation 7 of the amount of cooling water and the length of the cooling zone based on these cooling conditions.

Next, for the case of the tip of the thick section, find the threading speed of the thick section from the low cooling conditions that show how to determine the threading speed, and then calculate the threading speed of the thick section from the difference thickness line toward the tip using the formula shown below. .

In general, the set speed k Vxl when the position X from one plate tip iη) enters the cooling equipment, the cooling time ′frt(xi
, the cooling zone length fLc, the following equation holds true.

V(x
By determining i, the differential thickness steel plate can be cooled to the target temperature.

The thickness of the thick part is 2g, and the threading speed of the thick part until the tip (thick part) enters the cooling equipment and the 9th difference thickness line enters the cooling equipment is ν eyebrow x),
The threading speed of the thick section after the thick wire enters the cooling equipment is expressed as VU (X
), and when rIJj is expressed as hesitation during the required cooling of the thick part, equation (2) is.

becomes.

The cooling start temperature and cooling end temperature of the thin part are T and U, respectively.
, TφU, water cooling cooling rate is VcU, then Vg(x)
=・Lcxv(fi”/(THU-T4.y)・
...-f41! Vσfx) is obtained.

Expressing the -th term on the left side of equation (3) as Σ, and performing the integration of the second term.

Here, i=1 is the tip of the steel plate, i=j is the position of the steel plate where the threading speed is to be determined, and i=N+1 is the position of the difference in thickness line. (See Figure 4) The -th term on the left side of equation (5) is i
= j and i = j + 1 to N+1.

(6) Formula f j = N + I Xi> is applied up to j=1 to find vA(xj').

vA (engineering, ) and VU metal fitting m-renroku-) give the target continuous plate threading of the number of steels with different thicknesses, and also incorporate the acceleration and deceleration before slow cooling of the different thicknesses.

Next, the cooling start temperature Tirxl' of each part in the longitudinal direction of the steel plate is determined using the nine plate speeds obtained above, and the comparison with the predicted value Ti(x) at the same position is performed.

Based on the tip cooling start temperature of a constant thickness steel plate with plate thickness at all predicted positions of Tifxl, the value is the sum of the deviation ΔT,
Temperature and reaction results at the end of E rolling at the same position' TFix) 'Air cooling cooling rate geva(x) 'The time from the end of rolling to the start of tip cooling. Then, Ti(x) = TF? x) −' o ×vjxl+Δ
T......(7) On the other hand, Ti(x) is as follows. Therefore, here α is a permissible value. Cooling start temperature ■ Pre-crushing 11th place IJ
lx=x; (6) for (i-1, 2,...),
(7).

Using equation (9), calculate v(x)1r convergence.

Threading speed Fkf' (xl￥
i control computer 47D ≧ upper and lower rollers - 5 and respective driving motors of table rollers 6 9 + 10
.

11, and the difference thickness - plate Sv cooling end temperature 1iTφ is controlled.

FIG. 5 shows an example of measuring the cooling end temperature when cooling is performed with the thick side as the tip. Is straight line a the target value or actual value? fMb
is the actual measured value when cooling E (l control 1) is applied to this invention, and the straight line C is the actual measured value when cooling is performed 7 times at the rate shown in FIG.

The steel plate size for both actual measurements is 23m thick.

The thickness of the thin part is 18mm, the length is 14m, and the width is 3000m.

[Example-2] Another example of this invention is shown below. Same equipment configuration and procedure as Example-1? When used, Iv part is resistant to cooling.

In this example, a portion of the cooling water was blocked. Figure 6 shows the simulation results for one-sheet passing and counterfeiting at this time. In the figure, arfi is the sheet passing speed in this example [hh is Example-1
This is the threading speed of the method. In addition.

The cooling conditions including the cooling start temperature and the cooling end temperature and the steel plate size are the same as in Example-1.

[Effect of investigation]

In this invention, the temperature at which the steel plate starts to be scraped at each part in the longitudinal direction is predicted n.
By combining the same control with shutting off the cooling water or cooling the thin section when cooling the thin section, it is possible to uniformly bring the differential thickness steel plate to the target temperature in the longitudinal direction. Multiply the effect of being able to cool down to.

Does this result in desired mechanical properties? Does the steel plate have uniform quality along its entire length? Obtainable.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between cooling start temperature and sheet threading speed, Figure 2
Is the diagram this invention? An equipment configuration diagram showing an example of the rolling and cooling equipment to be carried out, Fig. 3 is a flowchart showing the cooling control procedure, Fig. 4 is a clear view of the plate threading speed determination formula (6), and Fig. 5 is a differential thickness steel plate. An example of measuring the cooling end temperature? FIG. 6 is a diagram showing the simulation effect of the sheet threading speed in the case of another embodiment. FIG. 7 is a schematic diagram showing the concept of conventional sheet threading speed control. FIG. 8 is a diagram showing the cooling state of each part in the longitudinal direction of the steel plate. Figure 9 is a schematic diagram of the cooling end temperature at 9 o'clock when a steel plate of different thickness is cooled at an adjusted threading speed. Formula % Figure 3 71'40 Consultation 5 Figure Time Piece 6 Off Figure (A) i80 W Secret Crab Slut Account

Claims (3)

[Claims] (1) To forcefully cool a hot rolled steel plate to a predetermined temperature, the cooling start temperature, cooling end temperature, amount of cooling water, cooling zone length, and sheet threading speed during cooling are set in advance. In the cooling process, before loading the steel plate into the cooling equipment, the temperature at multiple division points in the longitudinal direction of the steel plate is actually measured, and the optimum cooling conditions for each division point are calculated based on the measured values, and the thick part is used as the tip. When threading, reduce the speed just before starting to cool the differential thickness wire,
Thereafter, the threading speed of the thin wall portion is accelerated, and when threading the thin wall portion as the tip, the speed is accelerated immediately before the cooling of the differential thickness line starts, and then the threading speed is decelerated to the thick wall portion. Cooling method for differential thickness heated steel plates. (2) To set the strip threading speed, first measure the temperature of the steel strip before loading it into the cooling equipment, and cool the steel strip at multiple division points in the longitudinal direction, taking into account the difference in air cooling rate within the strip due to the difference in plate thickness. Predict the starting temperature, find the threading speed, then calculate the cooling start time at the predicted position from this threading speed to find the cooling start temperature, and check if the difference between this cooling start temperature and the previously predicted value is less than the allowable value. A method for cooling a differential thickness heated steel plate according to claim 1, wherein the threading speed is set by performing convergence calculation so that the following is achieved. (3) The differential thickness heated steel sheet according to claim 1, wherein part or all of the cooling water supply is shielded or cut off during the threading of thin-walled parts to correct part or all of the threading speed setting. Cooling method.