JP2002028712A - Method of manufacturing for steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing the generation of defective thickness and insufficient flatness by preventing peak load at the tailing-off of a material in the finish rolling of a hot-rolled steel sheet and thick steel plate. SOLUTION: In the rolling of the hot-rolled steel sheet, the difference ΔP between the rolling load in the stational part of a material to be rolled and the peak load in the rear end part is preliminarily determined about the pass at each stand of a finishing mill 4, temperature rising for canceling ΔPmax from the maximum value of ΔP (=ΔPmax) of the rolling-load difference of each stand and, after heating the rear end part of the material to be rolled based on this temperature rising, finish rolling is performed. In the rolling of the thick steel plate, the ΔP is preliminarily determined about each pass of the finish rolling with a single stand and the temperature rising is decided from the maximum value ΔPmax of the ΔP of each pass.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for hot rolling a hot rolled steel strip or a thick steel plate (collectively referred to as a steel plate).
The present invention relates to a method for preventing a peak load generated at the front and rear ends of a steel plate.

[0002]

2. Description of the Related Art The longitudinal distribution of a rolling load in producing a hot-rolled steel plate or a thick steel plate shows an excessive load when the bottom is removed.

FIG. 1 is a graph showing an example of a rolling load in a final pass of finish rolling of a thick steel plate. When such a peak load occurs, when rolling is performed at the same rolling reduction value, the peak load generating portion cannot be reduced to a target thickness, and a thickness defect occurs, and in the finish rolling process in which the thickness is reduced,
Flatness failure occurs and causes rolling troubles such as narrowing.

[0004] As described above, the peak load causes various operation hindrance factors such as the occurrence of defective thickness and the occurrence of defective flatness.
Conventionally, a method of heating a material to be rolled so as to compensate for the temperature drop has been proposed as a cause of the peak load being caused by a decrease in the temperature of the material to be rolled.

[0005] For example, Japanese Patent Application Laid-Open No. Hei 10-192910 discloses that a steel slab after rough rolling is heated so that the surface temperature of the coldest part (usually the front and rear ends) becomes 850 ° C or higher.
A method of finish rolling is disclosed.

[0006]

However, the present inventors have conducted a detailed study, and found that even when a steel sheet having a uniform temperature without a temperature-reducing portion at the front and rear ends is rolled, a peak load is generated at the time when the buttocks are removed. It turned out to be.

FIG. 2 is a graph showing an example of a rolling load of a steel plate test piece at a uniform temperature in a lab test.
In this lab test, a test piece having a thickness of 20 mm and a width of 150 mm was rolled immediately after heating to 1150 ° C. In this case, unlike the actual operation, the time from heating furnace extraction to rolling is short, and since water cooling such as descaling is not performed,
Although it is considered that the temperature of the material to be rolled is substantially uniform, a peak load still occurs when the bottom is removed.

As described above, since a peak load is generated even when the temperature of the material to be rolled is uniform, a method of actually measuring the material temperature and heating the whole material to be uniform as in the method described in the prior art. In this case, the heating of the front and rear ends is insufficient, and the generation of the peak load cannot be prevented. Conversely, if the front and rear end portions are excessively heated, the load at these portions will be extremely reduced, causing problems such as poor thickness reduction and poor flatness.

It is an object of the present invention to provide a method for preventing a peak load at the time of material erosion in hot rolling of a steel sheet, thereby preventing a thickness defect and a flat defect from occurring.

[0010]

Means for Solving the Problems The inventors have obtained the following findings and completed the present invention.

(A) In the case of a hot-rolled steel sheet, the peak load observed at the end of the bottom of the finish rolling is the peak load pattern over a wide range of steel types and sizes, excluding the effect of the load caused by the temperature drop at the rear end. There is a typological tendency. The reason why the peak load occurs at the rear end of the uniformly heated material is that the plastic flow in the width direction is greater at the rear end, which has more free surfaces, than at the steady part, which causes the width to expand, and as compared with the steady part. This is considered to be caused by the increase in the width of the plate at the rear end. This suggests that the rear end can be particularly heated to prevent peak loads.

(B) In the case of a thick steel plate, a load peak is observed at the leading and trailing ends of the material to be rolled in each pass of the reversible rolling. There is a typical trend in peak load patterns over a wide range of steel types and dimensions.

In order to manage the above-mentioned peak load, in the reversible rolling mill, since the trailing edge direction changes for each pass with respect to the conveying direction, it is necessary to manage both the front and rear ends of the material to be rolled. .

(C) In an actual process, it is not necessary to strictly distinguish between the load increase at the front and rear ends and the load increase due to the temperature decrease, which are observed in the above-mentioned uniform heating material. That is, as a means for preventing the peak load including both, the material may be heated so as to compensate for the difference corresponding to the difference between the rolling load in the steady part and the load in the peak part.

(D) In the actual process, since the heating is performed immediately before the finish rolling, the compensation heating amount may be obtained by assuming in advance the load difference between the steady portion and the peak portion generated during the finish rolling.

The present invention has been completed based on the above findings, and the gist thereof is as follows.

(1) In a method of manufacturing a hot-rolled steel sheet by using a continuous hot rolling mill having a plurality of stands, which has a heating device for reheating the material to be rolled after the rough rolling, the respective stands of the finishing mill The difference ΔP between the rolling load at the steady portion of the material to be rolled and the peak load at the rear end is determined in advance, and from the maximum value (= ΔPmax) of the rolling load difference ΔP at each stand, ΔP
A method for producing a steel sheet, comprising determining a heating amount for canceling max, heating the rear end of the material to be rolled based on the heating amount, and then finish rolling.

(2) In a method of manufacturing a thick steel plate using a reversible rolling mill having a heating device for reheating a material to be rolled after rough rolling, in each pass of finish rolling, rolling of a steady portion of the material to be rolled is performed. The difference ΔP between the load and the peak load at the front and rear ends is obtained in advance, and the maximum value of the rolling load difference ΔP (= Δ
Pmax), a heating amount for canceling ΔPmax is determined, and then the rear end of the material to be rolled is heated based on the heating amount and finish-rolled.

Here, the stationary portion of the material to be rolled means a portion where the rolling load is substantially constant at the center in the longitudinal direction of the material to be rolled.

The rear end (or front end) of the material to be rolled is
It means a portion where the peak load appears at the rear end (or the front end) in the length direction of the material to be rolled (including a portion at the foot of the peak, that is, a portion where the load increases as compared with the steady portion).

[0021]

FIG. 3 is a schematic view showing an arrangement of a continuous hot rolling mill for hot-rolled steel sheets provided with a heating device for heating a material to be rolled.

The material heated in the heating furnace 1 is supplied to a roughing mill 2
, And is rolled to a product thickness by the finishing mill 4, and then passes through the cooling device 5 and is finally wound by the down coiler 6.

The problem with peak loads is in finish rolling, which directly affects the quality of the product. Therefore, it is necessary to heat the rear end of the material to be rolled, which corresponds to the trailing edge, before finish rolling. Therefore, in FIG. 3, the heating device 3 is arranged before the finish rolling mill.

The finishing mill 4 is provided with a process computer 7 for determining the rolling conditions of each stand and controlling the plate thickness and tension.

In the process computer 7, the difference between the peak load P at the time when the tail is removed and the load P0 at the steady portion = ΔP is stored for each stand. ΔP is stored as a table value for each category of rolling conditions such as steel type, plate thickness, plate width, rolling temperature, and rolling speed. However, instead of the above table values, ΔP may be obtained in a functional form for the sheet thickness, sheet width, rolling temperature, and rolling speed.

Hereinafter, the procedure of the embodiment of the present invention relating to a hot-rolled steel sheet will be described.

After the material has passed through the roughing mill 2, the process computer 7 calculates the reduction setting of each stand of the finishing mill. At this time, ΔP is also obtained from a table value stored for each stand, and the maximum value ΔPmax of ΔP of each stand is determined.

Next, the amount of temperature rise ΔT of the heating device 3 for canceling ΔPmax is determined.

The rolling load P is the thickness HI of the incoming side and the thickness H of the outgoing side.
P = f (HI, HO, R, K, T) (1) as a function of O, roll radius R, steel type K, and rolling temperature T.

The rolling load fluctuation ΔP when the rolling temperature T fluctuates by ΔT is as follows: ΔP = (∂f / ∂T) ΔT = g (ΔT) (2) The quantity ΔT can be expressed as ΔT = g ⁻¹ (ΔPmax) (3)

After the amount of temperature increase ΔT is determined, the rear end of the material to be rolled, which corresponds to the trailing edge, is heated by ΔT by the heating device 3.
Normally, the rear end of the material to be rolled heated by ΔT has a temperature higher than the steady portion temperature. The heating device is not particularly limited, but it is preferable to use an induction heating device or an electric heating device having excellent control response.

After passing through the heating device 3, it is rolled to a product thickness by a finish rolling mill and wound up by a down coiler. By proper heating of the rear end, a peak load does not occur at the rear end of each stand during finish rolling, and a product with good plate thickness accuracy and flatness can be obtained. In the stands other than the stand in which ΔPmax occurs, the amount of temperature rise at the rear end is larger than the appropriate value, but the difference is small, and it does not reach the point where poor thickness and poor flatness occur.

Next, reversible rolling by a single-stand rolling mill for producing a thick steel plate will be described.

FIG. 4 is a schematic view showing an arrangement of a single-stand rolling mill for a thick steel plate provided with a heating device for heating a material to be rolled. The same elements as those in FIG. 3 are denoted by the same reference numerals.

The material heated in the heating furnace 1 is supplied to a roughing mill 2
, Is rolled to a predetermined thickness and width, and is rolled to a product thickness by a finishing mill 4, and then is sent to a cooling floor 8 through a cooling device 5. The finishing mill is provided with a process computer 7 for determining the rolling conditions for each pass.

The process computer 7 stores the difference between the peak load P at the time of the trailing edge of each pass and the load P0 of the steady portion = ΔP. ΔP is stored as a table value for each rolling condition such as steel type, plate thickness, plate width, rolling temperature, and rolling speed.

Hereinafter, the procedure for implementing the present invention example relating to a thick steel plate will be described.

After the material passes through the roughing mill 2, the process computer 7 calculates rolling conditions for each reversible pass in the finishing mill. At this time, ΔP is also obtained from a table value stored for each pass. ΔP obtained in each pass is divided into normal rotation (rolling from the heating furnace 1 to the cooling floor 8 in FIG. 4) and reverse rotation, and the maximum values ΔPsmax, ΔP
Determine Pgmax.

Next, the heating amounts ΔTs and ΔTg of the heating device 3 for canceling ΔPsmax and ΔPgmax are determined.

ΔTs = g ⁻¹ (ΔPsmax) (4) ΔTg = g ⁻¹ (ΔPgmax) (5) After the amount of temperature rise is determined, the material to be rolled using the heating device 3 and hitting the buttocks in the forward rotation The rear end is heated by ΔTs, and the front end of the material to be rolled, which corresponds to the buttocks during reverse rotation, is heated by ΔTg.

After passing through the heating device 3, the product is rolled to a product thickness by a finish rolling mill. By proper heating of the front and rear ends, a peak load does not occur at the end of each pass during finish rolling. A product with good plate thickness accuracy and flatness can be obtained.

As a table of ΔP values (or a parameter of a function for obtaining ΔP) stored in the process computer, after initial values are set, learning is carried out successively by actual measurement of rolling loads to follow the latest process state. It is preferred that

In this case, it is necessary to define the positions of the stationary part and the front and rear end parts when the actual measurement data of the rolling load is collected by the process computer. For example, it is better to define as follows.

Steady-state part: The position in the longitudinal direction of the material to be rolled is defined and determined according to the characteristics of each process. For example, it is defined as “a part excluding the 1/10 length of the front and rear ends of the entire rolling length”. The data of the rolling load may be obtained from the average value of the steady portion.

Front and rear end portions: The position in the longitudinal direction of the material to be rolled is defined and determined according to the characteristics of the process. For example, it is defined as "1/15 of the rear end (or the front end) of the entire rolling length". As the peak load, the maximum load value in the section at the front and rear ends may be obtained.

It is preferable to define the above-mentioned length position so that the stationary portion and the front and rear end portions do not overlap. Further, in the above example, the length positions defining the stationary portion, the front and rear end portions are not all constant, and the characteristics of the material (slab dimensions, heating furnace conditions, finishing temperature conditions), and the characteristics of rough rolling (rough rolling dimensions, Temperature conditions) and the conditions for tent rolling of thick steel plates may be used as variables.

As a standard method of learning, actual values of the load at the steady portion and the peak load difference at the front and rear ends are sampled, and the table values of the correction coefficients stratified by the rolling conditions are integrated, integrated, exponentially smoothed or moving averaged. It is good to adopt a method of updating sequentially. For example, the calculation is performed as follows.

As described above, for a given material to be rolled, the amount of temperature increase ΔT is determined from the equation (3) for the value of ΔP found from a table or function. It is assumed that a load difference ΔPm is actually measured for the material to be rolled with respect to the temperature increase ΔT. The error ΔΔP of the load difference is obtained as ΔΔP = ΔPm−ΔP (6)

The temperature rise correction amount Δ for this load error ΔΔP
ΔT is obtained using equation (3). The sign at this time is ΔΔ
When P is negative (insufficient heating), the heating correction amount ΔΔT is made positive.

The temperature increase correction amount ΔΔT is obtained as a learning term as
It is stored in a 1: 1 correspondence with the table value of ΔP.
In the learning method, for example, α is the weight of the integration method, and the suffix i is obtained as ΔΔT _{i + 1} = αΔΔT _i + ΔΔT _i-1 (7), with the rolling order number of the material to be rolled.

For the next (i + 1) -th material to be rolled, ΔP is found from the load difference table, and the temperature increase Δ
After obtaining T, the temperature rise correction amount ΔΔT _{i + 1 in} equation (7) is further obtained.
The value obtained by adding the above may be used as the set amount of temperature rise to the heating device.

When ΔP is obtained from the function formula, the learning method differs depending on the form of the function. Generally, the learning term is modified by a parameter in the function by an integration method, a moving average method, or the like.

[0053]

EXAMPLES The present invention and comparative examples were subjected to the following rolling simulation experiments using a lab test and a computer.

(1) A high-tensile slab having a thickness of 270 mm and a width of 1250 mm was rolled to a product thickness of 2 mm by a continuous hot rolling mill shown in FIG. The work roll diameter of the finishing mill is about φ750 mm. After the rough rolling was completed, ΔPmax was determined by a process computer, and the rear end of the material to be rolled was heated using an induction heating device. Table 1 shows the experimental results
Shown in Table 1 also shows comparative examples in which the amount of temperature rise by the induction heating device was variously changed.

In Example A of the present invention in which ΔPmax was predicted and the temperature was raised appropriately, ΔPmax hardly occurred.
Sheet thickness accuracy and flatness were also good.

On the other hand, under the conditions of Comparative Examples B to D in which the temperature was raised in the heating device without estimating ΔPmax and the conditions of Comparative Example E in which the temperature was not raised, the occurrence of ΔPmax could not be eliminated. , Plate thickness deviation and flatness were all poor.

[0057]

[Table 1] Here, ΔPmax = maximum value of (stand-through load−steady portion load) of each stand, Finished plate thickness deviation = Rear end plate thickness of finished material after finish rolling—
Steady part thickness.

[0058] (2) thickness 240 mm, assuming a slab of tensile strength 490 N / mm ² class steel plate width 2260 mm, 4
Was rolled to a product thickness of 8 mm with a single-stand hot rolling mill shown in (1). Work roll diameter of finishing mill is φ1000mm
It is. After rough rolling is completed, ΔP
The maximum was determined, and the front and rear ends of the material to be rolled were heated using an induction heating device. Table 2 shows the experimental results. Table 2 also shows comparative examples in which the amount of temperature rise by the induction heating device was variously changed.

In Example F of the present invention in which ΔPmax was predicted and the temperature was raised appropriately, ΔPmax hardly occurred.
Sheet thickness accuracy and flatness were also good. On the other hand, ΔPma
The conditions of Comparative Examples GI in which the temperature was raised without predicting x,
Under the conditions of Comparative Example J in which the temperature was not raised, the occurrence of ΔPmax could not be eliminated, resulting in poor thickness deviation and flatness.

[0060]

[Table 2] Here, ΔPmax = maximum value of (pass through load−steady portion load) of each pass, Finished plate thickness deviation = Rear end plate thickness of finished material after finish rolling—
The thickness of the stationary part.

[0061]

According to the present invention, in the finish rolling of a hot-rolled steel plate or a thick steel plate, it is possible to prevent the occurrence of an excessive load at the time of material bottom-out, and to achieve the plate thickness accuracy over the entire length of the material to be rolled.
Products with good flatness can be stably manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a rolling load in a finishing pass of a thick steel plate.

FIG. 2 is a graph showing an example of a rolling load of a steel sheet test piece having a uniform temperature in a lab test.

FIG. 3 is a schematic diagram showing an arrangement of a continuous hot rolling mill for a hot-rolled steel sheet provided with a heating device for heating a material to be rolled.

FIG. 4 is a schematic diagram showing a line configuration diagram using a single-stand rolling mill in an example of the present invention.

[Explanation of symbols]

 1: Heating furnace 2: Rough rolling mill 3: Heating device 4: Finish rolling mill 5: Cooling device 6: Down coiler 7: Cooling floor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B21B 37/18 BBM B21B 37/00 132B 45/00 37/12 BBJ BBM

Claims (2)

[Claims] 1. A method for producing a hot-rolled steel sheet using a continuous hot rolling mill comprising a plurality of stands, comprising a heating device for reheating a material to be rolled after rough rolling, wherein each stand of a finishing mill is The difference ΔP between the rolling load at the steady portion of the material to be rolled and the peak load at the rear end is obtained in advance, and ΔPmax is calculated from the maximum value (= ΔPmax) of the rolling load difference ΔP at each stand.
A method for producing a steel sheet, comprising: determining a temperature increase amount for canceling the above, heating the rear end of the material to be rolled based on the temperature increase amount, and then finish rolling. 2. A method for producing a steel plate using a reversible rolling mill having a heating device for reheating a material to be rolled after rough rolling, wherein a rolling load of a steady portion of the material to be rolled is provided for each pass of finish rolling. ΔP between the rolling load difference ΔP and the peak load at the front and rear ends is determined in advance, and the maximum value (= ΔPma
x) determining a heating amount for canceling ΔPmax, heating the rear end of the material to be rolled based on the heating amount, and finish-rolling the steel sheet.