JP2005232482A - Method for continuously heat-treating hot-rolled steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously heat-treating a hot-rolled steel plate, which controls a pate temperature more precisely than ever. <P>SOLUTION: This continuous heat treatment method is a technology that has improved the same method of connecting a steel strip in a preceding coil to a steel strip in the following coil, which have the same plate thicknesses in a specification after having been hot-rolled, and continuously passing them through a heat treatment apparatus which controls an atmospheric temperature to a predetermined one, specifically by connecting the head of the preceding steel strip in a hot rolling direction to the head of the following steel strip in the hot rolling direction, or connecting the end of the preceding steel strip in the hot rolling direction to the end of the following steel strip in the hot rolling direction; and further specifically, by preparing a forwardly wound coil which has wound up the steel strip in the hot rolling direction and a reversely wound coil which has rewound the steel strip so as to reverse the top to the end in the rolling direction, sequentially alternately connecting the steel strip from each coil, and heat-treating them. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for continuous heat treatment of a hot-rolled steel strip, and in particular, even when the junction point between the steel strip rear end of the preceding coil and the steel strip front end of the subsequent coil passes through the heating zone of the continuous heat treatment apparatus. The present invention relates to a heat treatment technology for a hot-rolled steel strip that can stably control the temperature.

  One of the heat treatments for hot-rolled steel strip is to wind a steel strip manufactured by hot rolling into a coil shape, and then unwind the coil (about 10 tons) with an uncoiler. There is a method in which the end and the steel strip tip of the succeeding coil are sequentially welded to run in the heat treatment apparatus. For example, when annealing is performed as a heat treatment, a continuous annealing apparatus as shown in FIG. 3 is used. The furnace 4 in which a large number of radiant tubes (not shown) are arranged as indirect heating sources is divided into heating zones 5, soaking zones 6 and cooling zones 7, and the steel strip 1 passing through each zone is set to a predetermined range. The temperature is maintained and a constant thermal cycle is given to the steel strip 1.

  However, since the steel type, plate thickness, and plate width of the coiled steel strip to be heat-treated are different, it is necessary to change the ambient temperature of each zone according to the coil to be processed. Moreover, even if the steel type, plate thickness, and plate width of the coiled steel strip are the same standard, there are variations in the longitudinal direction of the steel strip. Therefore, in order to keep the steel strip passing through the furnace at a predetermined temperature, temperature control is strictly performed in each zone.

For example, in a continuous heat treatment furnace that gives a predetermined heat cycle to a steel plate, when the heat load such as the plate thickness and the plate temperature changes, feed forward control is performed to change the heating condition based on the heat transfer equation at a predetermined timing. In addition, a plate temperature control method has been proposed in which after a predetermined time has elapsed, feedback control for correcting the heating condition according to the plate temperature deviation is performed using the heating condition set value as an initial value (see Patent Document 1). Moreover, in the steel strip temperature control method for a continuous annealing furnace in which the temperature of the strip (steel strip) is controlled by adjusting the fuel flow rate in the radiant tube disposed in the furnace, Find the furnace temperature difference to be changed from the current furnace temperature of the preceding board in the zone passing plate and the target set furnace temperature of the succeeding board, find the fuel flow difference corresponding to the furnace temperature difference, and achieve the fuel difference in the minimum time Therefore, temporarily find the time to burn at the maximum fuel flow or the time to burn at the minimum fuel flow, and if the load on the trailing plate is higher than the load on the preceding plate, change the strip plate. Before the point passes through the inlet of the heating zone, the maximum combustion is performed for the maximum time to be burned. On the other hand, when the load on the trailing plate is lower than the load on the preceding plate, the plate change point of the strip is Immediately after passing through the tropics, continuous annealing is performed for minimum combustion for the minimum combustion time. Strip temperature control method of is also disclosed. With these prior arts, control to the target plate temperature can be performed with considerably high accuracy. However, the control may still have unsatisfactory results. Therefore, in order to increase the accuracy of sheet temperature control before and after the steel strip change position, coils with the same standard thickness, i.e., coils with the same target thickness after hot rolling, are sequentially joined in the heat treatment apparatus. Attempts were made to pass through and avoid changes in the thermal load due to changes in plate thickness, but sufficient results have not yet been obtained.
Japanese Patent Laid-Open No. 6-49546 JP-A-61-113728

  In view of such circumstances, an object of the present invention is to provide a continuous heat treatment method for a hot-rolled steel strip capable of controlling the plate temperature with higher accuracy than before.

  In view of such circumstances, the inventor has reviewed the conventional continuous heat treatment method and embodied the result in the present invention.

  That is, the present invention continuously joins a preceding steel strip having the same thickness and a subsequent steel strip manufactured by hot rolling and continuously controls the atmospheric temperature to a predetermined temperature. In the continuous heat treatment method of the hot-rolled steel strip to be passed, the hot rolling direction tip of the preceding steel strip and the hot rolling direction tip of the subsequent steel strip are joined or the hot rolling direction of the preceding steel strip A continuous heat treatment method for a hot-rolled steel strip, characterized in that a rear end and a rear end in the hot rolling direction of a subsequent steel strip are joined.

  The present invention also provides a continuous heat treatment apparatus that joins a preceding steel strip and a subsequent steel strip manufactured by hot rolling to the same standard and controls the ambient temperature to a predetermined temperature. In the continuous heat treatment method of the hot-rolled steel strip to be passed, the normal winding coil that has wound the steel strip along the rolling direction of the hot rolling, and the rewinding with the front and rear ends of the steel strip reversed in the rolling direction This is a continuous heat treatment method for hot-rolled steel strips, characterized in that reverse-wound coils are prepared and steel strips from the respective coils are alternately and sequentially joined.

  Furthermore, these methods can be preferably applied when the steel type and plate width of the steel strip are the same standard, or when the heat treatment is annealing.

  In the present invention, the coil of the hot-rolled steel strip having the same standard thickness is re-rolled every other production so that the leading and trailing ends are reversed, and then sequentially joined, and then passed through the heat treatment apparatus. As a result, steep plate thickness fluctuations at the joints are eliminated, and plate temperature control is performed smoothly. In particular, the effect is effective when heat treating steel strips of the same standard steel type, thickness and width.

  Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.

  First, the inventor sought the cause of unstable plate temperature control in the conventional heat treatment method. As a result, when the steel strip 1 is joined by changing the coil, as shown schematically in FIG. 2 in the cross section of the plate, the joining (welding) portion between the steel strip rear end of the preceding coil and the steel strip front end of the succeeding coil It was found that a step 2 occurred. This level difference 2 is due to the fact that when manufacturing a steel strip by hot rolling, the thickness at the front end becomes thinner than the rear end along the rolling direction (for example, a steel strip having a target thickness of 2.2 mm). And the difference (Δt) between the front and rear ends is about 0.1 mm). Such a level difference is within an allowable range as the thickness of the product, so that no consideration was given to the heat treatment.

  However, the inventor regarded this phenomenon as very important for the plate temperature control in the heat treatment. It was thought that such a sudden change in the plate thickness had a great influence on the responsiveness in the plate temperature control. In other words, in the conventional plate thickness feedforward control, even if the fuel flow rate of the heating furnace was adjusted with a steep plate thickness variation, the response was slow, and the accuracy of the plate temperature control could not be improved.

  In view of this, the present inventor has considered that in order to eliminate the step 2, a joining portion as schematically shown in FIG. This is because the change in the plate thickness at the joint becomes smooth. That is, the leading end in the hot rolling direction of the preceding steel strip and the leading end in the hot rolling direction of the following steel strip are joined, or the trailing end of the preceding steel strip in the hot rolling direction and the heat of the following steel strip The rear end of the intermediate rolling direction is joined after the direction is changed before joining. Specifically, a steel strip 1 manufactured by hot rolling is prepared by winding up the front end and the rear end in the hot rolling direction opposite to the normal one (referred to as a reverse winding coil). This preparation is possible if you have a set of rewinding machines offline. And when the coil wound up by normal hot rolling (referred to as a forward winding coil) and the two types of the above-mentioned reverse winding coil were rewound alternately and joined together and tried to heat treatment, Since good plate temperature control could be carried out, the present invention was completed on the requirement that such a joint be used.

  In the hot rolling process, a carbon steel strip having a plate thickness of 2.2 mm and a plate width of 100 mm was produced and wound into a coil. The length of the steel strip for one coil is 500 m. The coils were sequentially supplied to a continuous annealing apparatus as shown in FIG. 3 and annealed. At that time, the heat treatment method according to the present invention was applied. That is, using a pair of uncoilers and coilers provided off-line, half of the manufactured coils were rewound so that the front and rear ends of the steel strips were reversed to form the reverse-wound coil. And the said normal winding coil and the said reverse winding coil which were not rewinded were joined and supplied to the line of the continuous annealing apparatus alternately. In this case, as the plate temperature control method, the technique described in Patent Document 1 is adopted. Moreover, the target atmospheric temperatures in the heating zone 5 and the soaking zone 6 are 1100 ° C. and 1020 ° C., respectively, and the temperature in the cooling zone is sequentially reduced in the range of 200 to 300 ° C.

  Example of plate temperature control in the heating zone 5 when the present invention is applied, the horizontal axis indicates the steel strip length (or time), and the vertical axis indicates the temperature deviation (the target temperature and the actual temperature for each of the plate temperature and the furnace temperature). 4 is shown in FIG. For comparison, continuous annealing without applying the present invention was also performed. FIG. 5 shows an example of the plate temperature control in that case. Furthermore, a non-contact type radiation thermometer is used for measuring the plate temperature.

  4 and 5, conventionally, only the plate temperature control in which the plate temperature deviation exceeds ± 10 ° C. was possible in the vicinity of the joint (welding position). However, if the present invention is applied, it can be reliably controlled at ± 10 ° C. Is clear. As a result, variation in the characteristics (tensile strength, strain, etc.) in the longitudinal direction of the annealed material when the present invention was applied was reduced, and the product quality was significantly improved as compared with the prior art.

  In addition, although the said Example is a case where the coiled steel strip of the same specification steel grade, board thickness, and board width is joined, if the board thickness is the same, the standard of steel grade and board width will differ. You may apply when joining coiled steel strips. This is because the accuracy of the plate temperature control is improved also in such a case. Further, the heat treatment method in the present invention is not necessarily limited to “annealing”. It may be used for “normalization”.

It is sectional drawing which shows typically the joining state of the steel strip in the continuous heat processing of the steel strip which concerns on this invention. It is sectional drawing which shows typically the joining state of the steel strip in the continuous heat processing of the conventional steel strip. It is a longitudinal cross-sectional view which shows the continuous annealing apparatus of a general steel strip. It is a figure which shows the board temperature control condition at the time of applying the continuous annealing method of the steel strip which concerns on this invention. It is a figure which shows the board temperature control condition in the conventional continuous annealing method of a steel strip.

Explanation of symbols

1 Steel strip 2 Step 3 Roller 4 Furnace 5 Heating zone 6 Soaking zone 7 Cooling zone

Claims (4)

A hot-rolled steel strip that joins a preceding steel strip with the same thickness and a subsequent steel strip manufactured by hot rolling and continuously passes through a heat treatment device that controls the ambient temperature to a predetermined temperature. In the continuous heat treatment method, the leading end in the hot rolling direction of the preceding steel strip and the leading end in the hot rolling direction of the following steel strip are joined, or the trailing end in the hot rolling direction of the preceding steel strip is followed. A method for continuous heat treatment of a hot-rolled steel strip, characterized by joining a rear end in a hot rolling direction of the steel strip. A hot-rolled steel strip that joins a preceding steel strip with the same thickness and a subsequent steel strip manufactured by hot rolling and continuously passes through a heat treatment device that controls the ambient temperature to a predetermined temperature. In the continuous heat treatment method of
Preparing a normal winding coil wound around the steel strip along the rolling direction of the hot rolling, and a reverse winding coil rewinded with the front and rear ends of the steel strip reversed with respect to the rolling direction. A continuous heat treatment method for hot-rolled steel strips, characterized by alternately joining steel strips one after another. The method for continuous heat treatment of a hot-rolled steel strip according to claim 1 or 2, wherein the preceding steel strip and the following steel strip have the same steel grade and sheet width. The said heat processing is annealing, The continuous heat processing method of the hot-rolled steel strip in any one of Claims 1-3 characterized by the above-mentioned.

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