JP4710237B2 - Method for predicting deformation of thick steel plate and method for manufacturing the same - Google Patents

Description

  The present invention relates to a deformation amount prediction method for a thick steel plate that predicts a deformation amount when a thick steel plate cooled after hot rolling is cut, and a method for manufacturing the thick steel plate using the prediction method.

  In recent years, an accelerated cooling technique for obtaining a high-strength, high-toughness steel sheet by strongly cooling the steel sheet after controlled rolling has been widely performed in a thick steel sheet manufacturing process. Accelerated cooling can not only greatly reduce the manufacturing cost by reducing the conventional additive element components, but also can produce a steel sheet having excellent weldability. In accelerated cooling, cooling water is sprayed from the cooling nozzle onto the surface of the hot steel sheet, and the convection boiling heat transfer phenomenon on the surface of the steel sheet achieves a high cooling rate several hundred times that of natural cooling, resulting in a finer crystal structure. It is possible to manufacture a steel plate having a high strength, a high toughness.

  However, because of the high cooling capability of accelerated cooling, slight non-uniform factors during cooling such as the water content density of the cooling water, the surface temperature of the steel plate, and the surface properties of the steel plate such as the scale thickness cause large temperature unevenness of the steel plate. In particular, in the vicinity of the end of the plate, the steel plate is apt to cool and the temperature rapidly decreases. When such temperature unevenness occurs, not only does the mechanical properties of the steel sheet vary, but also shape defects such as ear stretch and belly stretch, and lateral bending due to residual stress, that is, a cut camber occurs. To do.

  Residual stress generated in steel sheets can be eliminated by post-processing such as heat treatment and cold straightening. However, applying such treatment to all steel sheets reduces production efficiency and manufacturing costs. Will lead to a significant increase.

In order to solve such a problem, for example, “analysis of temperature, thermal stress, and shape defect during accelerated cooling of thick steel plate”, Iron and Steel Vol.1.83, No.2 (1997) (Non-Patent Document 1) ) Describes a technique for predicting the residual stress of the steel sheet and the amount of the cut camber. This is because the temperature distribution in the width direction of the steel sheet is calculated from the initial temperature distribution at the end of rolling, taking into account the phase transformation by calculating heat removal and heat conduction during water cooling and air cooling, yield stress, Young's modulus and linear expansion coefficient. This is a technique for predicting a cut camber by performing an elasto-plastic stress analysis in consideration of the temperature dependence of material property values such as the above, and finding that the difference in thermal expansion due to temperature unevenness of the steel sheet is exposed as residual stress. On the other hand, in Japanese Patent Application Laid-Open No. 61-262428 (Patent Document 1) and Japanese Patent Application Laid-Open No. 4-66271 (Patent Document 2), the temperature such as the maximum temperature and the minimum temperature difference, the temperature difference between the center portion of the plate width and the edge portion, respectively. A technique using the difference itself as a criterion is disclosed.
"Analysis of temperature, thermal stress, and shape defects during accelerated cooling of thick steel plates", Iron and Steel Vol.1.83, No.2 (1997) JP 61-262428 A JP-A-4-66271

   In the above conventional technique (Non-patent Document 1), the process of calculating the camber amount from the steel plate temperature distribution is complicated, and it may be necessary to perform repeated calculations. However, there is a problem that a great deal of labor is required to perform the calculation and the calculation load is heavy. In addition, the conventional techniques (Patent Documents 1 and 2) have a problem in that the accuracy of determination is not conspicuous because not only the temperature difference but also the temperature distribution form affects the cut camber.

  The present invention has been made in order to solve the above-described problems, and a deformation amount prediction method for a thick steel plate that can accurately predict the deformation amount without performing complicated theoretical calculation. An object of the present invention is to provide a method of manufacturing a thick steel plate that makes the deformation amount within an allowable value by performing an additional determination in a subsequent process based on the predicted deformation amount.

The method for predicting the deformation amount of a thick steel plate according to the present invention includes a step of measuring the temperature distribution in the plate width direction of the hot-rolled thick steel plate, and a temperature difference from a reference temperature point of the temperature distribution in the plate width direction. And multiplying the distance and integrating to obtain an evaluation index. The temperature distribution is obtained by measuring the temperature at a predetermined pitch in the plate width direction of the thick steel plate and further averaging the temperature in the longitudinal direction.
Moreover, the deformation amount prediction method for a thick steel plate according to the present invention further includes a step of predicting the deformation amount after cutting of the thick steel plate based on the evaluation index.
Further, the method for predicting the amount of deformation of a thick steel plate according to the present invention measures the temperature distribution in the plate width direction of the cutting region of the thick steel plate, determines the evaluation index of the cutting region, or determines the thickness of the thick steel plate after cutting. The deformation amount is predicted.
Moreover, deformation of the prediction method of thick steel sheet according to the present invention, that measure the hot straightening before or temperature distribution in the plate width direction after the hot straightening of the thick steel plates.
Moreover, the deformation amount prediction method of the thick steel plate according to the present invention predicts the camber amount as the deformation amount of the thick steel plate.

Moreover, the manufacturing method of the thick steel plate according to the present invention is obtained by the deformation amount prediction method for the thick steel plate, and whether or not to perform cold correction or heat treatment on the rear stage side based on the evaluation index or the deformation amount. Or set the conditions.
Moreover, the manufacturing method of the thick steel plate which concerns on this invention performs cold correction after a cutting | disconnection, when it is judged that the said evaluation index or the said deformation | transformation amount is larger than a predetermined reference value.

  According to the present invention, it is possible to calculate an evaluation index (parameter) that can be directly determined from the measurement result of the steel plate temperature distribution without complicated calculation logic. Can be done.

  FIG. 1 is an explanatory view showing an example of a production line to which a method for predicting a deformation amount of a thick steel plate and a method for producing a thick steel plate according to the present invention are applied. In FIG. 1, 1 is a rolling mill, 2 is an accelerated cooling device, 3 is a hot leveler, 4 is a plate width direction thermometer, 5 is a deformation amount prediction computer, 6 is a sorting device, and 7 is a cold leveler (cold straightening). Machine). The deformation amount prediction computer 5 performs a calculation process for predicting a deformation amount after the thick steel plate 10 is cut. The principle of the calculation process will be described below with reference to FIGS.

  In the production line of FIG. 1, for example, a thick steel plate 10 having a plate thickness of 19 mm and a plate width of 2060 mm is manufactured via the rolling mill 1, the accelerated cooling device 2, and the hot leveler 3. The residual stress distribution was measured, and for example, the cutting process was performed with a cutting width of 150 mm and a cutting length of 10 m, and the cutting camber amount d was measured.

  FIG. 2 is a characteristic diagram combining the measurement result of the residual stress and the measurement result of the steel plate temperature distribution on the outlet side of the hot leveler 3. The temperature distribution and residual stress distribution of the steel plate on the outlet side of the hot leveler 3 are similar to each other. This is because the thermal stress generated before the hot leveler 3 is removed by the hot leveler 3, so that the temperature deviation is exposed as the thermal stress difference, that is, the residual stress according to the following equation (1).

ここで、Δσ（ｘ）：残留応力差、α：線膨張係数、Ｅ：ヤング率、ΔＴ（ｘ）：温度偏差であり、ｘは板幅方向の位置を表す。

Here, Δσ (x): residual stress difference, α: linear expansion coefficient, E: Young's modulus, ΔT (x): temperature deviation, and x represents a position in the plate width direction.

  FIG. 3 is a conceptual diagram of a line-cut camber. When a region indicated by a broken line is cut out from a thick steel plate, the residual stress generated in the steel plate is released by cutting and is generated as follows. It can be calculated by the formula. That is, the bending moment M acting on the steel plate is calculated by the following equation (2).

曲率Ｋは、次の（３）式で計算される。

The curvature K is calculated by the following equation (3).

  Here, I: sectional moment of inertia. Assuming that the camber is an arc, the camber amount d is expressed by the following equation (4).

  Here, L is the cut length, and W is the cut width. Substituting equation (1) into equation (4) yields the following equation (5).

  FIG. 4 is a characteristic diagram showing the temperature distribution in the width direction of the thick steel plate, and the temperature data corresponding to the section of 10 m of the cut length is averaged in the rolling length direction from the measurement result of the steel plate temperature. . In the first embodiment, based on the above knowledge, the parameter (evaluation index) Ω shown in the following equation (6) is set using n pieces of temperature data within the cutting range as shown in FIG. calculate.

  Here, Ti: average value in the longitudinal direction of temperature measurement values at each position in the sheet width direction, Tc: temperature corresponding to the center part of the strip width (reference temperature), xi: temperature measurement position in the strip width direction, Δx: temperature measurement pitch .

FIG. 5 is a characteristic diagram showing the relationship between the parameter Ω and the measured value of the cut camber. There is a correlation between the parameter Ω and the camber. Assuming that L = 10000 mm and α = 1.4 × 10 ⁻⁵ 1 / ° C., the slope of the approximate straight line in the least square method shown in FIG. 5 is 3L ³ α / 2 (= 2100).

  As described above, by calculating the parameter Ω from the measurement result of the steel plate temperature at the cut width portion, the cut camber amount can be predicted easily and accurately.

  FIG. 6 is a flowchart showing the process of the deformation amount prediction computer 5 of FIG. The deformation amount prediction computer 5 takes in the data of the temperature distribution in the plate width direction from the plate width direction thermometer 4 arranged on the outlet side of the hot leveler 3 (S1), and performs the arithmetic processing of the above equation (6). The parameter Ω is calculated (S2). At this time, the plate width direction thermometer 4 measures the temperature at a predetermined pitch in the width direction of the thick plate steel plate 10, and the deformation amount prediction computer 5 is, for example, the region indicated by a broken line in FIG. ), And the corresponding parameter Ω is calculated. Then, the deformation amount predicting computer 5 determines whether or not the parameter Ω satisfies the relationship of parameter Ω ≦ allowable value (S3). The command is output, and the sorting device 6 is transferred to the next process of the thick steel plate 10 (S4). In the example of FIG. 1, the correction by the cold leveler 7 is omitted, and the process proceeds to the subsequent processing. When the above relational expression is not satisfied, for example, the cutting camber amount is not within an allowable range when cutting at the customer site, and in the example of FIG. 1, the thick steel plate 10 is transferred to the cold leveler 7 side by the sorting device 6. Then, correction by the cold leveler 7 is performed to suppress deformation of the product (S5).

  Here, the example in which the plate width direction thermometer 4 is provided on the exit side of the hot leveler 3 has been described, but the plate width direction thermometer 4 may be provided on the entry side of the hot leveler 3. The correction by the hot leveler 3 is mainly correction of the shape or warpage of the steel plate 10 at that time and has little effect on suppressing the residual stress. Therefore, the temperature distribution in the width direction on the entry side of the hot leveler 3 is obtained. However, the deformation amount after cutting of the steel sheet can be predicted in the same manner. Moreover, when the above relational expression is not satisfied, the example in which the correction by the cold leveler 7 is performed to suppress the deformation of the product has been described. However, instead of or in addition to this, heat treatment may be performed in the subsequent process.

  In the above example, the example of predicting the amount of the cut camber has been described. However, as long as the temperature distribution is obtained appropriately, the amount of deformation after cutting of an arbitrary shape can be similarly predicted. In the above example, the parameter Ω is obtained to determine whether the value is less than the allowable value. However, the deformation amount is obtained from the parameter Ω, and whether the deformation amount is less than the allowable value. You may make it judge about. Moreover, although the example of the strip width center part was demonstrated as a reference | standard temperature point, it is not limited to a strip width center part, For example, the position of the vicinity may be sufficient.

  An accelerated coolant having a plate thickness of 14 to 25 mm and a plate width of 2200 to 3200 mm was subjected to cutting under various conditions of a cutting width of 150 mm to 400 mm and a cutting length of 10 to 15 m. At that time, whether or not the cut-off camber is within the allowable range is determined using the present invention and the conventional method (maximum temperature deviation within the cut-off width), respectively, and the result of comparison with the actually measured cut-off camber amount. Are shown in FIG. 7 (present invention) and FIG. 8 (conventional method), respectively. In the conventional method, a large camber is determined to be good and a small one is determined to be bad. However, according to the present invention, it is possible to accurately determine the defect of the cut camber without complicated calculation. Can be done.

Explanatory drawing which showed an example of the production line of the thick steel plate to which this invention was applied. The figure which shows the measurement result of the temperature distribution in a residual stress and a hot leveler delivery side. The conceptual diagram of a line cutting camber. The characteristic view which showed the temperature distribution of the width direction of a thick steel plate. The figure which shows the relationship between parameter (omega) and the measured value of a line cutting camber. The flowchart which showed the process of the deformation | transformation amount prediction computer. The figure which shows the result of having performed the determination of a line cutting camber by this invention. The figure which shows the result of having determined the line cutting camber by the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling machine, 2 Accelerated cooling device, 3 Hot leveler (hot straightening machine), 4 Sheet width direction thermometer, 5 Deformation amount prediction computer, 6 Sorting device, 7 Cold leveler (cold straightening machine), 10 Thick plate steel plate .

Claims (7)

A step of measuring the temperature distribution in the plate width direction of the hot-rolled thick steel plate,
A step of obtaining an evaluation index by multiplying the temperature difference from the reference temperature point of the temperature distribution in the plate width direction and the distance and integrating the temperature difference, and
A method for predicting a deformation amount of a thick steel plate, wherein the temperature distribution is obtained by measuring the temperature at a predetermined pitch in the plate width direction of the thick steel plate and further averaging the temperature in the longitudinal direction . 2. The method for predicting a deformation amount of a thick steel plate according to claim 1, further comprising a step of predicting a deformation amount after cutting the thick steel plate based on the evaluation index.   The temperature distribution in the plate width direction of the cutting region of the thick steel plate is measured, the evaluation index of the cutting region is obtained, or the deformation amount of the thick steel plate after cutting is predicted. The deformation amount prediction method for the thick steel plate described.   The method for predicting a deformation amount of a thick steel plate according to any one of claims 1 to 3, wherein a temperature distribution in the plate width direction of the thick steel plate before hot correction or after hot correction is measured. The method of predicting a deformation amount of a thick steel plate according to any one of claims 1 to 4 , wherein a cutting camber amount is predicted as the deformation amount of the thick steel plate. Whether or not to perform cold correction or heat treatment on the rear stage side based on the evaluation index obtained by the deformation amount prediction method of the thick steel plate according to any one of claims 1 to 5 or the deformation amount of the thick steel plate or A method for producing a thick steel plate, characterized by setting conditions. The method for producing a thick steel plate according to claim 6, wherein cold correction is performed when it is determined that the evaluation index or the deformation amount is larger than a predetermined reference value.

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