JP2006274404A - Annealing method for cold-rolled steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an annealing method for a cold-rolled steel plate capable of measuring the yield point of the steel plate in an on-line manner with excellent accuracy, and suppressing the dispersion of the yield point of the steel plate in a coil to be low by performing the feedback to an annealing condition. <P>SOLUTION: The annealing method of the cold-rolled steel plate in a continuous annealing process of the steel plate comprises an iron loss value measuring step of measuring the iron loss value in the longitudinal direction of the steel plate by totaling the iron losses, a yield point estimation step of estimating the yield point from the iron loss value measured in the iron loss value measurement step and information on the kind and the thickness of the steel plate based on the correlation between the iron loss value and the yield point which are obtained in advance for each steel kind and thickness, and an annealing temperature adjustment step of adjusting the annealing temperature so that the yield point estimated by the yield point estimation step is within a predetermined range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an annealing method in a continuous annealing facility for cold-rolled steel sheets.

  In general, cold-rolled steel sheets are manufactured by subjecting hot-rolled steel sheets that have been hot-rolled to each step of pickling, cold rolling, electrolytic cleaning, annealing, temper rolling, and recoil. It is done by. In recent years, a continuous annealing facility in which the steps of electrolytic cleaning, annealing, and temper rolling are combined has become mainstream.

  In the continuous annealing process of a cold-rolled steel sheet by a continuous annealing facility, the mechanical properties of the cold-rolled steel sheet to be processed vary greatly depending on the heat treatment conditions of heating and cooling. Therefore, control of the heat treatment conditions for heating and cooling is important.

  Therefore, in the continuous annealing process of cold-rolled steel sheet, in order to obtain desired mechanical properties, a predetermined annealing temperature is set according to the standard of the steel sheet, the steel type, etc., so that the set annealing temperature is constant. Control is taking place.

  As described above, in the conventional continuous annealing process, control is performed so as to be constant with respect to a preset annealing temperature, so that variations in steel plate components, for example, hot rolling conditions such as finishing temperature and coiling temperature, etc. Due to variations in the mechanical properties, the mechanical characteristics, particularly the yield point, vary within the coil, which may result in out-of-specification.

For such a problem, Japanese Patent Application Laid-Open No. 2002-294351 (Patent Document 1) describes a rolling load P ₀ per unit width of a steel sheet to be rolled in a temper rolling mill disposed on the outlet side of a continuous annealing facility. And the tensile strength TS _{0 of the} steel sheet to be rolled were previously determined for each plate thickness of the steel sheet, and were measured in the temper rolling mill based on the relationship between the rolling load P ₀ and the tensile strength TS ₀ . The tensile strength TS _{1 of the} steel plate to be rolled is calculated from the rolling load P ₁ per unit width of the steel plate to be rolled, and the quenching temperature and / or the steel plate is set so that the calculated tensile strength TS ₁ becomes a desired tensile strength. Alternatively, a method for controlling the tempering temperature is described.
JP 2002-294351 A

However, the method described in Patent Document 1 is a method of calculating the tensile strength TS ₁ of the rolled steel sheet using the rolling load P ₁ per unit width of the rolled steel sheet actually measured in the temper rolling mill. but since refining factors affecting the rolling load P ₁ in the rolling is not only tensile strength, there can be a problem in terms of estimation accuracy, variations in the mechanical properties especially yield point in the coil, the occurrence of specifications out It could not be completely prevented.

  In addition, the tensile test for guaranteeing the yield point, which is the mechanical property of the steel sheet, is performed at a representative position of the coil, for example, at one position where the coil is divided, and the total length of the coil cannot always be guaranteed.

  In order to suppress the variation in yield point due to variations in steel plate components and hot rolling conditions, it is necessary to accurately monitor and measure the yield point of the steel plate online and feed it back to the annealing conditions.

  Therefore, the present invention provides a method for annealing a cold-rolled steel sheet that can accurately measure the yield point of the steel sheet online and feed back to the annealing conditions, thereby suppressing variations in the yield point of the steel sheet in the coil. The purpose is to provide.

  The present inventors diligently studied a method capable of measuring the yield point of a steel sheet online. As described above, since the measurement of the yield point is generally performed by a tensile test, it has been considered that online measurement is impossible.

  Therefore, while investigating various possibilities, it is not possible to use an iron loss meter that is used in manufacturing equipment for electromagnetic steel sheets and is used to monitor the total length of iron loss, which is a magnetic property, in the longitudinal direction of the steel sheet. I came to think that.

Therefore, we collected data and examined whether there was any correlation between the iron loss value and the yield point. FIG. 1 shows that in mass%, C contains 0.0025%, Si 1.2%, Mn 1.0%, P 0.07%, Al 0.5%, the balance being substantially Fe. The result of having _{calculated |} required the correlation of iron loss _{W15 / 50} and a yield point is shown about the cold-rolled steel plate after annealing which has thickness 1.0mm. Here, the iron loss W _15/50 refers to the energy loss consumed in the steel sheet per unit mass when magnetized so that the magnetic flux density is 1.5 T (Tessler) with an AC frequency of 50 Hz. The unit is expressed in W / kg. The energy loss consists of both hysteresis loss and eddy current loss in the magnetization process.

  As shown in FIG. 1, it was found that there is a certain correlation between the iron loss value and the yield point if the steel type and the plate thickness are the same.

  That is, it has been found that if the correlation between the iron loss value and the yield point is obtained in advance, the yield point can be monitored by the iron loss meter.

The present invention has been made based on the above findings and has the following characteristics.
[1] A method for annealing a cold-rolled steel sheet in a continuous annealing process of a steel sheet,
Iron loss value measurement step for measuring the iron loss value in the longitudinal direction of the steel sheet with an iron loss meter,
Yield from the iron loss value measured by the iron loss value measurement step and the steel type and thickness information of the steel sheet based on the correlation between the iron loss value and the yield point obtained in advance for each steel type and sheet thickness. A yield point estimation step for estimating a point;
An annealing method for a cold-rolled steel sheet, comprising: an annealing temperature adjustment step for adjusting the annealing temperature so that the yield point estimated by the yield point estimation step falls within a predetermined range.

  According to the present invention, there is provided a method for annealing a cold-rolled steel sheet that can accurately measure the yield point of a steel sheet online and feed back to the annealing conditions, thereby suppressing variations in the yield point of the steel sheet in the coil. Provided.

  Hereinafter, an example of the best mode for carrying out the present invention will be described.

  FIG. 2 is a schematic view showing an example of the configuration of annealing equipment in a continuous annealing process of a steel sheet to which the method for annealing a cold-rolled steel sheet according to the present invention is applied.

  In FIG. 2, the steel sheet paid out from the pay-in reel 1 on the entry side is first annealed at a predetermined temperature in the annealing equipment 2, then cooled, and then passed through the temper rolling equipment 3 to the tension reel on the exit side. 4 is wound around the coil. Further, an iron loss meter 5 is provided at an arbitrary position between the outlet of the annealing equipment 2 and the tension reel 4, and the iron loss value in the longitudinal direction of the passing steel plate is continuously measured. In addition, as an installation position of the said iron loss meter 5, although providing in the exit vicinity of the annealing equipment 2 shown in FIG. 2 or the exit side of the temper rolling equipment 3 is preferable, it is not limited to the said position. When provided in the vicinity of the outlet of the annealing equipment 2, it is possible to speed up feedback for controlling the annealing temperature in the annealing equipment 2 based on the measurement result of the iron loss value of the iron loss meter 5. Have advantages. Moreover, when it provides in the exit side of the temper rolling equipment 3, it has the advantage that the value of the yield point of final product itself can be controlled directly.

  In such an apparatus configuration, the annealing method according to the present invention is an annealing method in a continuous annealing process of a steel sheet, and an iron loss value measuring step of measuring an iron loss value in the longitudinal direction of the steel sheet by the iron loss meter 5; Based on the correlation between the iron loss value obtained for each steel type and sheet thickness and the yield point, the yield point is determined from the iron loss value measured in the iron loss value measurement step and the steel type and sheet thickness information of the steel sheet. And a annealing temperature adjustment step for adjusting the annealing temperature so that the yield point estimated by the yield point estimation step falls within a predetermined range.

  Thus, the iron loss value measured by the iron loss meter 5 is converted into the yield point of the steel sheet, and the annealing point in the annealing facility 2 is set so that the yield point value is within the range of the required specification of the steel sheet. By performing feedback control on the temperature, it becomes possible to suppress the variation in the yield point of the steel sheet in the coil, and quality control can be performed with high accuracy.

  The adjustment of the annealing temperature in the annealing equipment 2 can be performed, for example, by adjusting the output of the annealing equipment or adjusting the plate feed speed in the annealing equipment.

  Here, the correlation between the iron loss value and the yield point needs to be obtained for each steel sheet having a different steel type and thickness, and in particular, the required specification that needs to suppress the variation of the yield point. Do this for severe steel grades and plate thicknesses.

  The above steps are preferably performed continuously over the entire length of the coil, but may be performed once in the entire length of the coil, preferably twice or more. However, in order to perform feedback to the annealing temperature of the coil, it is preferable to execute at least once on the coil tip side.

  In the continuous annealing equipment shown in FIG. 2, C contains 0.0025% by mass, 1.2% Si, 1.0% Mn, 0.07% P, 0.5% Al, and the balance. Is substantially made of Fe, and the steel plates having thicknesses of 1.0 mm and 1.2 mm were annealed.

  In advance, the correlation between the iron loss value and the yield point was determined for each of the steel sheets.

As an example of the present invention, the measured value of the iron loss W _15/50 in the iron loss meter provided in the vicinity of the outlet of the annealing equipment so as to satisfy the required specification of the yield point in the steel sheet is within the range of 11 to 13 W / kg. Annealing was performed while controlling the temperature of the annealing equipment. At that time, the annealing temperature in the annealing equipment was 790 ° C. to 830 ° C., and the sheet feeding speed was 40 to 60 m / min.

  Moreover, as a comparative example, annealing was performed while controlling the annealing temperature in the annealing equipment at a constant 810 ° C. and a sheet feeding speed of 50 m / min as in the past.

As a result of measuring the yield point in the longitudinal direction of the steel sheet for each of the inventive examples and the comparative examples, in the comparative example, the yield point varied in the range of 32 to 40 kgf / mm ^2. In the invention example, the yield point was 32 to 36 kgf / mm ^2, and the variation could be reduced to half.

It is a figure which shows an example of the result of having calculated | required the correlation of an iron loss value and a yield point about the cold-rolled steel plate after annealing. It is the schematic which shows an example of the structure of the annealing equipment in the continuous annealing process of the steel plate to which the annealing method of the cold rolled steel plate concerning this invention is applied.

Explanation of symbols

1 Payoff reel 2 Annealing equipment 3 Temper rolling equipment 4 Tension reel 5 Iron loss meter

Claims (1)

A method for annealing a cold-rolled steel sheet in a continuous annealing process of a steel sheet,
Iron loss value measurement step for measuring the iron loss value in the longitudinal direction of the steel sheet with an iron loss meter,
Yield from the iron loss value measured by the iron loss value measurement step and the steel type and thickness information of the steel sheet based on the correlation between the iron loss value and the yield point obtained in advance for each steel type and sheet thickness. A yield point estimation step for estimating a point;
An annealing method for a cold-rolled steel sheet, comprising: an annealing temperature adjustment step for adjusting the annealing temperature so that the yield point estimated by the yield point estimation step falls within a predetermined range.