JPH02229609A - Method for preventing necking in hot rolling - Google Patents

Abstract

PURPOSE:To improve the yield of a product by providing a transformation rate sensor to detect the transformation rate from phase gamma to phase alpha in steel stock, estimating generating positions of necking based on this transformation rate, correcting a model formula based on this result and estimating positions of change and variation in the dimension of a sectional area. CONSTITUTION:In each of (n) transformation rate sensor 7, an exciting coil 71 and a detecting coil 72 are arranged face to face in both sides and in the middle of a strip 3 and excited by alternating current. Since, in carbon steel, phase alpha is ferromagnetic and phase gamma is non-magnetic, the magnetic sensor 7 detects the change of magnetic characteristics, therefore, the transformation rate. An output from the transformation rate 7 is given to a computer 9 to calculate the transformation rate from the information concerning the chemical component, rolling and cooling of the strip 3 based on the model formula. The model formula is corrected and the generating positions of necking are estimated accurately in comparison with measured values and aperture signals PS to control the width rolling reduction of an edger 2 are outputted based on the estimated value. In this way, it is possible to accurately estimate the generating position of necking, reduce the range of an width expanded part and improve the yield of the product.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preventing necking that occurs during hot strip rolling of steel materials, and particularly to a method for predicting the location where necking occurs.

[Conventional technology]

In hot strip rolling such as in a hot strip mill, excessive tension is generated in the strip when the tip of the strip is wound around the winder in order to wind the rolled strip knob with the winder. This phenomenon in which local cross-sectional dimension changes occur is called nesoking. Here, local changes in cross-sectional dimensions include changes in plate width and plate thickness, and below, a change in plate width, that is, a case where the plate width becomes narrower, will be explained.

FIG. 5 is a graph showing the relationship between temperature and yield stress of carbon steel used for the strip, with yield stress plotted on the vertical axis and temperature on the horizontal axis.

As shown in Fig. 5, the yield stress of carbon steel during high-temperature tensile deformation generally decreases significantly in the region between the transformation start temperature Ts at which the transformation from T phase to α phase begins and the transformation end temperature Te. , becomes minimum at the end of metamorphosis.

The rolled strip is usually water-cooled on an exit table to lower its temperature, and after completing the γ-α transformation, it is wound up. Therefore, when the tip of the strip is wound around the winder, necking occurs on the strip due to tensile deformation in a range where the stress Fs due to the tension is greater than the yield stress. This necking is most likely to occur in the part that has completed its metamorphosis at the time of wrapping. In order to prevent this necking, the strip width near the portion where necking is expected to occur may be increased in advance, but if the strip width is expanded over too wide a range, the yield will be poor.

Therefore, in order to improve yield, it is important to accurately predict the location where necking will occur.

As a conventional technology to solve such problems,
There is an invention disclosed in Publication No. 43460. This uses the strip composition, width and thickness, winding machine lead speed, and cooling conditions as variables, and predicts the necking occurrence position and amount of change using a model equation as a function, and then calculates the width near the relevant part in advance. This is a way to expand it.

Furthermore, in order to improve the necking position prediction accuracy, Japanese Patent Application Laid-Open No. 62-68617 installs width gauges on the exit side of the finishing rolling mill and the entrance side of the winding machine, and compares these measured values to detect necking. Know the actual location and amount of change,
A method has been disclosed which attempts to perform learning of a predictive model formula.

[Problem to be solved by the invention]

However, these conventional techniques have the following problems. That is, in the former case, the transformation phenomenon of steel that causes necking changes in a complicated manner due to various factors, so it is difficult to accurately predict the position and amount of change in necking using only a model equation.

Furthermore, the latter method can be learned only when necking actually occurs, and cannot be learned when necking does not occur, making predictions by the prediction model uncertain. In addition, the plate width varies over the entire length of the strip, and it is difficult to accurately determine the location where nesoking occurs by comparing the measurements from two width gauges. Furthermore, since the width gauge normally measures optically, there is a risk that it will malfunction due to the influence of the surrounding environment such as cooling water, and as a result, there is a possibility that the necking position will be detected incorrectly.

Therefore, when the necking position is predicted by the conventional method, the error in the predicted position becomes large, and a certain amount of margin is required in the range in which the width is expanded in advance. Furthermore, since this portion will eventually be cut, if the range of the portion to be widened in advance is large, the yield of the product will decrease.

This invention was made in view of the above circumstances, and the purpose of this invention is to estimate the position where necking occurs using a transformation rate sensor installed on the exit side of the finishing rolling mill, and to detect the occurrence of necking regardless of whether or not necking occurs. An object of the present invention is to provide a method for preventing necking in hot rolling, which can predict the necking occurrence position, reduce the widening range, and improve the yield.

[Means to solve the problem]

The method for preventing necking in hot rolling according to the present invention uses a model formula to predict the position and amount of change in local cross-sectional dimensions due to necking caused by tension generated when steel material rolled in a rolling mill is wound. In the method for preventing necking in hot rolling in which necking is prevented by changing the cross-sectional dimension in advance by an amount commensurate with the amount of change at the change position, transformation from the γ phase to the α phase of the steel material is carried out on the exit side of the rolling machine. A metamorphosis rate sensor is provided to detect the metamorphosis rate, which is the ratio of
The present invention is characterized in that the necking occurrence position is estimated based on the transformation rate, the model formula is corrected based on the estimation result, and the change position and amount of change in the cross-sectional dimension are predicted.

[Effect]

In this invention, the location where necking occurs is estimated by measuring the transformation rate of the steel material, and based on the estimation results, a model formula for predicting the transformation time is repeatedly revised based on the chemical composition of the steel material, rolling conditions, and cooling conditions. The prediction accuracy can be improved, and the prediction accuracy of the change position and change rate of the cross-sectional dimension of the steel material before rolling can be improved, and the widening range near the necking occurrence position can be reduced.

〔Example〕

The method for preventing necking in hot rolling according to the present invention will be described below.
An embodiment will be explained based on the drawings.

FIG. 1 is a schematic diagram showing the configuration of a hot rolling finishing line to which this method is applied. In the figure, 1 is a stand of a hot finishing mill that rolls a strip 3;
A finishing edger 2 for reducing the width of the strip 3 is provided on the upstream side of the strip 3. A runout table 4 consisting of a roller table is provided on the downstream side thereof. The runout table 4 conveys the rolled strip 3 to the pinch rolls 5 provided downstream thereof, and the strip 3 caught by the pinch rolls 5 is wound up by a winder 10. In addition, n metamorphosis rate sensors 7 are installed between the rollers of the runout table 4 to detect the metamorphosis rate of the rope.
, 7... are provided.

FIG. 2 is a sectional view taken along line 1-1 in FIG. 1, showing the configuration of the transformation rate sensor. The transformation rate sensor 7 includes excitation coils 71, 71, 71 and detection coils 72, 72. 72, and the excitation coils 71, 71.71 are excited by alternating current. In this transformation rate sensor 7, the magnetic properties of the α phase and the γ phase of carbon steel are different in the temperature range below the magnetic transformation point Tc, and the α phase is ferromagnetic, while the γ phase is nonmagnetic. This is utilized to detect changes in magnetic properties as changes in magnetic flux distribution, and to detect the transformation rate from γ phase to α phase. Therefore, unlike an optical sensor, it is not affected by water from the cooling device, and detection is possible even in cooling water.

Further, the output from the transformation rate sensor 7 is given to the computer 9,
Based on the chemical composition, rolling and cooling information of the strip 3 given therein, the time required for the transformation rate to reach a predetermined value is calculated using the model formula described later, and the time required for the transformation rate to reach a predetermined value is calculated, and the model formula is corrected by comparing it with the actual value from the transformation rate sensor 7. , accurately determine the location of necking.
The opening signal ps for controlling the width reduction amount of the edger 2 is output based on the predicted value.

Next, the operation of this line will be explained.

FIG. 3 is a graph showing the relationship between the strip position, strip temperature T, transformation rate X (%), and yield stress σ when cooling is performed by the method of this invention. The axis in Figure 3 (a) is the strip temperature T.
1 Figure 3(b) shows the transformation rate X, and Figure 3(C) shows the yield stress σ.
My husband and I have As shown in FIG. 3(a), the strip 3 is gradually cooled by the cooling device 6, but when it is cooled to the transformation start temperature Ts, as shown in FIG. 3(b), γ
The transformation from phase to α phase starts, and the transformation rate X rapidly increases.
At the same time, the yield stress σ decreases as shown in FIG. 3(C).

When further cooled to the transformation end temperature Te, the transformation ends and the yield stress σ becomes minimum. Thereafter, the yield stress σ increases as the strip temperature T decreases. When the tip of the strip 3 is wound up by the winder 10, the stress Fs due to the tension is greater than the yield stress σ (Ln =
Necking occurs between Ls).

That is, the tips of the strips 3 are connected to the transformation rate sensors 7, 7...
Detection of the metamorphosis rate X starts from the time when the strip passes upstream of
The metamorphosis end position Le is determined based on the distribution of .

Now, the transformation rate of strip 3 that has finished finish rolling is X
The time required for this to occur (the elapsed time after leaving the final finishing stand 1) can be predicted as a function of the chemical composition of the strip 3, rolling conditions, and cooling conditions, as shown in the following model equation.

r=f (X, H, h, Tt.Cc + C.l
1, q, ") where τ: Prediction time Cooling rate {circle around (2)}=Strip speed If the distance from the stand 1 to the i-th transformation rate sensor 7 is L., the elapsed time τl from the stand 1 is given by the following formula.

L. τ · = 6 Then, the actually measured transformation rate X. at the i-th transformation rate sensor 7. i
Then, the time required to reach the transformation rate X &i is τ positive.

On the other hand, the required time τ▲ according to the above model formula at the transformation rate xml is τi = f(X&i+ H+ h+ Tt r
Ccr CMI%l ql (2) Then, the coefficient a+b+1 is determined from the actual measured values of the plurality of metamorphosis rate sensors 7, 7, . . . so that τ5ak+bk=τi.

This is calculated for each strip 3, and the coefficient ak+b,
will be corrected.

a;=γmam+(1-γla:-1 bi:=γb bk+ (ITb) b:-r where γ, .γb: smoothing gain (0≦γ, .γ,≦1) Corrected in this way The metamorphosis start time and metamorphosis end time are determined by the model formula.

The metamorphosis start time τ is the metamorphosis rate x. ,=0.05, and τZ
* = f (X.* + H + h + T
t + C c + C I4111 Q + V)
a; +b: The metamorphosis end time τSf is the metamorphosis rate X. r
=0.95, and τ'at= f C”ctr+H.
+ h+Tt + Cc + CMRI qt v)
a: +B Metamorphosis start time τ' determined by the above formula. 3, the transformation end time τ2, and the stripping speed V, the transformation start position 1 and the transformation end position W. L=t is as follows.

L *. s ”τz3・V L Z,= τ′:Xf ” If the distance from the stand 1 to the winder 10 is Lc, and the total length of the strip 3 is L, then the necking position LD+n is Lo. ．． = (Lc - L':,t)/Ls Also the length of necking. , a are considered to be approximately proportional to the metamorphosis interval, so t, o. ．． = ((5,1L,.)/t,s)
・R Here, R: It is sufficient to target the constant interval.

Further, the amount of necking ΔWf can be determined by calculating the yield stress σ at the transformation point.

Next, we will explain how to widen the area near the predicted nesting position. Figure 4 is a graph explaining the widening method.
The horizontal axis shows the strip length before finish rolling, the vertical axis shows the edger opening S in Fig. 4(a), the strip width W on the exit side of the stand in Fig. 4(b), and Fig. 4(C) respectively indicate the strip width W at the entrance side of the winding machine. Necking position LO+1, 'necking length L0 predicted by the method described above
、． By expanding in advance the strip width at the position corresponding to the predicted necking position L6111 based on the necking amount ΔWf, it is possible to prevent the occurrence of a narrow portion due to necking.

The widening of the position corresponding to the predicted necking position L (bl1) is performed by the edger 2 installed on the entrance side of the stand 1.

The necking correction start position LIS and end position Llf are determined by the following equations, where L is the length of the strip before finish rolling.

Las = (Lo.- - Ll1.-
) ・LmLst= (Lo.y+ +
Lo. m) - Increase the edger opening S of the edger 2 by ΔS between Lll and Lllf from the tip of the strip 3 before Lll rolling to widen the width. Here, ΔS may be determined by the following formula from the predicted necking amount ΔWf and the esher plate width adjustment efficiency η.

η As shown in FIG. 4, by widening the edger opening degree S by ΔS in accordance with the predicted necking position LO+1%, the width reduction amount becomes smaller, and the strip width immediately after exiting the stand 1 becomes wider accordingly.

(Figure 4(b)). Therefore, even if necking occurs at the predicted necking position Wto, - during winding, the strip width at the narrow portion will not become narrower than the target finished width, and the required strip width can be secured.

〔effect〕

As explained above, according to the present invention, the position where necking occurs can be accurately predicted based on the measured value of the transformation rate, regardless of whether or not necking occurs, and the length of necking that occurs there and the amount of necking can be predicted with accuracy. Therefore, excellent effects such as reducing the range of the widened portion and improving product yield can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a hot rolling finishing line to which the hot rolling necking prevention method according to the present invention is applied;
Figure 2 is a cross-sectional view taken along line nn in Figure 1 showing the configuration of the transformation rate sensor, Figure 3 is a graph showing the relationship between strip position, strip temperature, transformation rate and yield stress, and Figure 4 is widening. A graph explaining the method, FIG. 5, is a graph showing the relationship between temperature and yield stress of carbon steel. 1... Stand 2... Edger 3... Strip 7... Metamorphosis rate sensor 9... Calculator 10...
・Rewinder patent applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Noboru Kono Zuzu

Claims (1)

[Claims] 1. Predicting the position and amount of change in local cross-sectional dimensions due to necking caused by tension generated when a steel material rolled in a rolling mill is rolled up using a model formula,
In the hot rolling necking prevention method of preventing necking by changing the cross-sectional dimension in advance by an amount corresponding to the amount of change at the change position, A metamorphosis rate sensor that detects a certain metamorphosis rate is provided, and a necking occurrence position is estimated based on the metamorphosis rate,
A method for preventing necking in hot rolling, comprising correcting a model formula based on the estimation result and predicting a change position and amount of change in the cross-sectional dimension.