JP2008013839A - Method for predicting material quality of heat-treated rolled-steel plate, and method for operating continuous annealing line utilizing this prediction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique with which even in the case of existing the unevenness of material quality caused by the former process, the material quality of a heat-treated rolled-steel plate can be stabilized. <P>SOLUTION: An extension ratio, tension, load value of rolling, thickness and width of the steel plate in a heat-treating rolling mill 2 disposed at the outlet side of a continuous annealing furnace 1 are obtained by measuring or from a host computer, and based on these values, the prediction of the material quality, such as the yield point YP and the tensile strength YS, etc., is performed. Based on the predicted values of these material qualities, the operational conditions of the continuous annealing furnace 1, are feedback-controlled and then, even in the case that the unevenness of the material quality caused by the former process, such as the variation of the steel plate composition, etc., exists, the occurrence of a non-standardized article can be prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for predicting the quality of a temper rolled steel sheet in a continuous processing line having a continuous annealing furnace, for example, a continuous processing line in which a temper rolling mill is disposed on the outlet side of a continuous annealing facility or a hot dipping plating facility, and a continuous process using the same. The present invention relates to an operation method of an annealing line, and is particularly effective for a material prediction method and an operation method of a high-tensile steel plate having a tensile strength of 780 MPa or more.

  In a continuous annealing line in which a temper rolling mill is arranged on the exit side of the continuous annealing furnace, the heating / soaking plate temperature in the furnace or the slow cooling furnace exit side plate temperature greatly affects the material of the temper rolled steel sheet. For this reason, conventionally, efforts have been made to make the temperature control inside the continuous annealing furnace highly accurate and stabilize the material. However, for example, in the case where there is a material variation due to the previous process such as a change in the steel plate component, even if the plate temperature control of the continuous annealing furnace is simply made highly accurate, the material variation cannot be avoided. Particularly in recent years, from the viewpoint of improving the molding accuracy of automobile parts, there has been a demand for reduction in material variation of high-tensile materials (high-strength steel plates), particularly high-tensile materials having a tensile strength of 780 MPa or more, and in particular, stabilization of tensile strength. The manufacturer's request could not be fully met.

Patent Document 1 discloses a technique for providing a steel plate temperature control means between a continuous annealing furnace and a temper rolling mill to stabilize the material quality of the temper rolled steel plate by eliminating the influence of the environmental temperature. However, this method also has no effect when there is material variation due to the previous process.
Patent Document 2 proposes a method of controlling the annealing temperature by the amount of tension fluctuation of the temper rolling apparatus. However, this method focuses only on the tension fluctuation, and the temper rolling load needs to be constant, and there is a problem in prediction accuracy when the rolling load fluctuates.
Moreover, in order to roll the temper rolling load under a certain condition, it depends on the ability of the temper rolling device, but generally it is a method that can be established only in a very limited range for a relatively low tensile strength steel plate. it is conceivable that.
Further, no specific description of the tensile strength level is found in the examples, and the effect on the steel plate having a high tensile strength is not proved at all. Therefore, the technical content is different from that of the present invention, and it cannot be said to be an effective method for a high-tensile steel plate having a tensile strength of 780 MPa or more.

For this reason, conventionally, a method has been adopted in which the material of the temper rolled steel sheet after being manufactured is inspected off-line and the result is fed back to the manufacturing conditions of the continuous annealing line. However, since this method takes time for feedback, a large amount of non-standard products may occur.
JP-A-6-344019 JP-A-6-10055

  The present invention solves the above-mentioned conventional problems, and even when there is material variation due to the previous process such as fluctuation of the steel plate component, it is possible to promptly feed back to the continuous annealing line, An object of the present invention is to provide a technology capable of stabilizing the material of a temper rolled steel sheet, particularly a high-tensile steel sheet having a tensile strength of 780 MPa or more, while suppressing generation to a minimum.

  In order to solve the above-mentioned problems, the invention of claim 1 is directed to the elongation rate, tension, rolling load value, steel plate thickness, and plate width in a temper rolling mill arranged on the outlet side of the continuous annealing furnace. Is obtained by measurement or obtained from a higher-order computer, and based on these values, the material prediction of the temper rolled steel sheet is performed. The elongation rate, tension, rolling load value, steel plate thickness and width are continuously measured over the entire length of the steel plate or obtained from a host computer, and the material prediction of the temper rolled steel plate is based on these values. It is preferable to use the prediction formula to calculate the yield point of the steel sheet from the values of elongation rate, tension, rolling load in the temper rolling mill, and the thickness and width of the steel sheet. It is preferable to carry out.

  The invention of claim 4 relates to an operation method of the continuous annealing line, and predicts the material quality of the temper rolled steel sheet by any of the methods of claims 1 to 3, and operates the continuous annealing furnace based on the prediction result. It is characterized by feedback control of conditions. The operating conditions for feedback control are preferably one or more of the heating furnace plate temperature, the soaking furnace plate temperature, and the slow cooling furnace outlet plate temperature of the continuous annealing furnace.

  According to the inventions of claims 1 to 3, even when there is material variation due to the previous process, the material is immediately determined from the values of elongation rate, tension, rolling load in the temper rolling mill, the plate thickness of the steel plate, and the plate width. Predictions can be made. In addition, according to the inventions of claims 4 to 5, the temper rolled steel sheet is controlled while performing the feedback control of the operation condition of the continuous annealing furnace so that the predicted material becomes constant, thereby minimizing the occurrence of nonstandard products. The material can be stabilized. In addition, according to the present invention, even when an abnormality occurs in the plate thermometer of the continuous annealing furnace, the occurrence of the abnormality can be detected immediately, and the generation of nonstandard products can be suppressed.

Hereinafter, preferred embodiments of the present invention will be described.
FIG. 1 is a diagram schematically showing a continuous annealing line of a steel sheet, wherein 1 is a continuous annealing furnace, and 2 is a temper rolling mill arranged on the outlet side thereof. The continuous annealing furnace 1 is roughly divided into a heating furnace 3, a primary soaking furnace 4, a secondary soaking furnace 5, and a cooling furnace 6. The steel sheet delivered from the delivery reel 7 is heated and annealed to a temperature suitable for the material of the steel sheet while traveling in the heating furnace 3, the primary soaking furnace 4, and the secondary soaking furnace 5 in sequence. The material is quenched in the cooling furnace 6 from the outlet temperature of the next soaking furnace 5, temper-rolled by the temper rolling mill 2, and wound on the take-up reel 8. In addition, surface treatment equipment such as an overaging furnace, a cooling furnace, a hot dipping equipment for manufacturing surface-treated steel sheets, an alloying equipment, and an electroplating equipment is attached between the cooling furnace 6 and the temper rolling mill 2. Also good. The above configuration is not different from the conventional one, and the plate temperature of each part is controlled with high accuracy as described above.

  In the temper rolling mill 2, temper rolling is performed by light reduction, but in the present invention, the rolling load, tension, and elongation rate in the temper rolling mill 2 are continuously detected to predict the material. In the present invention, in order to accurately perform the material prediction of the high-tensile steel sheet having a tensile strength of 780 MPa or more in particular, the material prediction is performed by incorporating not only the tension and elongation of the temper rolling mill but also the rolling load of the temper rolling mill. There is a special feature. 2 and 3 show the correlation between the rolling load of a high-tensile steel sheet having a tensile strength of 780 MPa or more and the yield point of the high-tensile steel sheet. 4 and 5 show the correlation between the rolling load and tensile strength of the high-tensile steel plate. That is, according to the results data, if the elongation is the same as shown in FIGS. 2 and 3, the yield point (YP) of the temper rolled steel sheet increases as the rolling load and tension increase, and FIGS. As shown in FIG. 5, the tensile strength (TS) is also increased. Even if the rolling load or tension is constant, the yield point (YP) and the tensile strength (TS) increase as the elongation rate is lower. From this, it can be seen that there is a strong correlation between the rolling load, tension, elongation, and material (YP, TS) of the temper rolled steel sheet.

  Therefore, based on past operational results, a material prediction formula for temper rolled steel sheet was created. The ROBERTS formula, known as the theoretical formula for temper rolling, includes many influential factors such as material (YP, TS), elongation, tension, friction coefficient, thickness, rolling speed, roll diameter, etc. Since the material can be accurately predicted by using the above factor with high accuracy, the following material prediction formula was created as an example of the present invention. The influential factors are calculated from the elongation (%) of the temper rolling mill, the tension (MPa) of the temper rolling mill, the sheet thickness (mm), the rolling load of the temper rolling mill and the sheet width of the steel sheet. Line load (ton / m) is used.

YP = a * Elongation rate (%) + b * (Average tension MPa) + c * (Steel sheet thickness mm * Line load ton / m) + d
In this equation, YP is the yield point, the unit is MPa, SPM% is the elongation rate, and the line load is a value obtained by dividing the rolling load by the width of the steel sheet. The coefficients included in this equation are determined by multiple regression analysis, but the specific numerical values of a, b, c, d in the above equation and the form of the equation are determined by the characteristics of each line and the strength of the steel plate to be passed Needless to say, the present invention is not limited to the above. By the way, when temper rolling with a constant rolling load, which is often performed on mild steel sheets, is applied to high-tensile steel sheets of 780 MPa or more, adjustment with excessive rolling load and tension balance close to the limit of equipment specifications due to the high tension of the steel sheets. It becomes quality rolling, the rolling itself becomes extremely unstable, and in the worst case, troubles such as plate breakage may occur.

  As for the tension, in actual operation, there is a tension on the entry side and the exit side of the temper rolling mill, but both are in a proportional relationship, and the values used for material prediction use the entry side or the exit side. It is preferable to use after averaging. As for the thickness and width of the steel sheet, either the value on the entry side or the value on the exit side of the temper rolling mill may be measured or obtained from the host computer, and the steel sheet in the annealing furnace may be used. It is preferable to use the value on the outlet side of the temper rolling mill from the influence of the elongation of the steel.

The reason why TS can be predicted extremely accurately as will be described later when the material prediction of a tempered rolled steel sheet, particularly a high-tensile steel sheet having a TS of 780 MPa or more, adopts the rolling load of the temper rolling mill as an influencing factor is as follows. Conceivable. In general soft steel plates, because the steel plate is soft, the rolling load of the temper rolling mill and the equipment capacity of the tension have room for the soft steel plate, so either one of the rolling load or tension (for example, rolling) When the (load) fluctuates, the other one (for example, tension) can be controlled to make the elongation constant constant by rolling control of the temper rolling mill, and there is no significant difference even if only tension is used as an influencing factor. However, a high-tensile steel sheet having a TS of 780 MPa or more has a margin in equipment capacity for rolling load and tension of a temper rolling mill compared to the high-strength steel sheet, and is often operated at the limit of each equipment capacity. If one of the rolling load and tension fluctuates, the other may not be able to absorb, and the prediction accuracy cannot be improved by using only one of the rolling load or tension. It is thought that it is necessary to predict the composite load from the elongation rate.

  In addition, as an influencing factor for predicting the material, the precision considering one or more of the temper rolling mill work roll diameter, the friction coefficient between the temper rolling mill work roll and the steel plate, and the temper rolling mill rolling speed are considered. It is also preferable to improve. When it is difficult to determine the temper rolling mill work roll diameter and the friction coefficient between the temper rolling mill work roll and the steel sheet, values determined or determined in advance may be used. The temper rolling mill rolling speed may be either the value on the entry side or the value on the exit side of the temper rolling mill.

  As shown in FIG. 6, it was confirmed that the YP predicted by this equation was in good agreement with the actual YP (multiple correlation coefficient 0.925). Since there is a strong correlation between YP and TS of the temper rolled steel sheet as shown in FIG. 7, TS is predicted using the relationship of TS = e * YP + f shown in FIG. When the relationship with the record TS is confirmed, it is as shown in FIG. As is obvious to those skilled in the art, since the relationship between TS and YP also changes depending on the steel type, an expression corresponding to the steel type, for example, an expression using higher-order expressions or various functions may be used. It is not limited to the form. Also in the case of the above formula, e and f in the formula are not particularly limited as they are determined by the characteristics of each line and the steel type.

In an example of the present invention, the rolling load, tension, and elongation rate continuously detected in the temper rolling mill 2, and the thickness gauge 11 and the sheet width meter 12 located behind the temper rolling mill 2 are continuously measured. The detected plate thickness and width are input to the process computer 9 shown in FIG. 1 and are calculated by substituting into the YP calculation formula and TS calculation formula of the tempered rolled steel sheet input to the process computer 9 and are calculated in real time. The material of the steel plate during rolling can be grasped.

  Note that the values of the plate thickness and the plate width may be obtained from the vidicon 10 which is a host computer of the process computer 9. Furthermore, in order to further improve the material prediction accuracy, the temper rolling is added with one or more of the temper rolling mill work roll diameter, the friction coefficient between the temper rolling mill work roll and the steel plate, and the temper rolling mill rolling speed. You may use the YP calculation formula and TS calculation formula of a rolled steel plate. The temper rolling mill work roll diameter and the friction coefficient value between the temper rolling mill work roll and the steel sheet are directly input to the process computer 9 by the operator or pre-input, and the temper rolling mill rolling speed is temper rolling. Rotational speed of the work roll or bridle roll installed before and after the temper rolling mill (not shown) is detected from the roll capable of detecting the rotational speed in or near the temper rolling mill and input to the process computer 9 That's fine.

  For this reason, when fluctuations occur in the calculated YP and TS of the temper rolled steel sheet, an alarm of occurrence of abnormality can be immediately issued, and a large number of off-standard products are not generated as in the prior art. In addition, even when the cause of the abnormality is a material variation due to a previous process such as a steel plate component variation, it appears as a variation in rolling load, tension, and elongation rate, so that the occurrence of the abnormality can be immediately grasped. The use of the temper rolling mill 2 as a material fluctuation monitor in this way is a novel technique that has never been seen before.

  As described above, since the material of the temper rolled steel sheet can be accurately grasped using the temper rolling mill 2 as a monitor, in the invention of claim 4, the temper rolling obtained by the method of claims 1 to 3 is used. Based on the result of predicting the material of the steel plate, the plate temperature inside the continuous annealing furnace 1 is feedback-controlled. The process computer 9 shown in FIG. 1 receives coil pre-process information from a vidicon 10 that controls the process of the entire factory, and based on the predicted value of the material, the heating / soaking plate temperature of the continuous annealing furnace 1, the temperature at the outlet side of the slow cooling furnace, etc. Feedback control.

Specific feedback destinations are as follows.
That is, steel sheets intended to control the structure (phase fraction) of ferrite, martensite, bainite, retained austenite, etc. (generally, high-tensile steel sheets and ultra-high-strength steel sheets with a tensile strength of 440 to 1600 MPa, especially TS Is 780 MPa or more), the feedback destination is one or more of the plate temperature of the heating furnace 3 and the soaking furnace 4 for determining the phase fraction and the outlet side plate temperature of the slow cooling furnace 5 for determining the quenching start temperature. And In particular, in an ultra-high-strength steel sheet, since there is a steel type in which the outlet side plate temperature of the slow cooling furnace 5 has the greatest influence on the fluctuation of YP, it is effective to control this.

  In addition, the strengthening mechanism of ultra low carbon steel, low carbon steel and steel is metallurgically annealed (solid grain control, texture control, etc.) such as solid solution strengthening type and precipitation strengthening type high tensile strength, precipitate morphology, For steel plates for the purpose of controlling the dispersion state (generally, TS is 270 to 980 MPa mild steel plate, high-tensile steel plate and ultra-high strength steel plate, especially TS is 780 MPa or more), the feedback destination is the heating furnace 3, One or more plate temperatures of the soaking furnace 4 and the slow cooling furnace 5 are set.

  If such feedback control is performed, even if material variations due to the previous process or material variations due to fluctuations in the plate temperature in the continuous annealing furnace occur, automatic correction is made immediately and the material stability of the temper rolled steel sheet is improved. Can be planned. This has made it possible to meet the demands from automobile manufacturers for reducing material variations in high-tensile materials (high-strength steel plates).

It is a schematic diagram of a continuous annealing line. It is a graph which shows the correlation of rolling load and YP. It is a graph which shows the correlation between rolling tension and YP. It is a graph which shows the correlation with a rolling load and TS. It is a graph which shows the correlation between rolling tension and TS. It is a graph which shows the correlation with prediction YP and performance YP. It is a graph which shows the relationship between YP and TS. It is a graph which shows the correlation with prediction TS and track record TS.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Continuous annealing furnace 2 Temper rolling mill 3 Heating furnace 4 Soaking furnace 5 Slow cooling furnace 6 Cooling furnace 7 Dispensing reel 8 Take-up reel 9 Process computer 10 Vidicon 11 Thickness gauge 12 Sheet width gauge

Claims (5)

  Measure the elongation rate, tension, and rolling load values of the temper rolling mill located on the outlet side of the continuous annealing furnace, and measure the thickness and width of the steel plate from a higher-level computer, or obtain a temper based on these values. A method for predicting the material of a tempered rolled steel sheet, wherein the material prediction of the rolled steel sheet is performed.   The elongation rate, tension, rolling load value, steel plate thickness, and plate width are continuously measured over the entire length of the steel plate or obtained from a host computer, and the material prediction of the temper rolled steel plate is performed based on these values. The method for predicting material quality of a temper rolled steel sheet according to claim 1.   Predicting the material quality of temper rolled steel sheet by using the prediction formula to calculate the yield point of steel sheet from the values of elongation rate, tension, rolling load in temper rolling mill and the thickness and width of steel sheet The method for predicting the material of a temper rolled steel sheet according to claim 1 or 2.   A method for operating a continuous annealing line, wherein the material prediction of the temper rolled steel sheet is performed by the method according to any one of claims 1 to 3, and the operation conditions of the continuous annealing furnace are feedback controlled based on the prediction result.   5. The continuous annealing line according to claim 4, wherein the operating condition for feedback control is one or more of a heating furnace plate temperature, a soaking furnace plate temperature, and a slow cooling furnace outlet temperature of the continuous annealing furnace. Operating method.

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