JP5834775B2 - Manufacturing equipment and manufacturing method for continuous hot-dip galvanized steel sheet - Google Patents

Description

  The present invention relates to a production facility and a production method for a continuous hot-dip galvanized steel sheet.

  The production equipment for continuous hot-dip galvanized steel sheets is a facility that continuously anneals steel strips, which are strip-shaped steel sheets, in a continuous annealing furnace, and then directly sends them from the snout on the outlet side of the continuous annealing furnace to the galvanizing bath for hot dip galvanization. is there. A continuous annealing furnace usually includes a heating zone for heating a steel plate being conveyed in an airtight furnace to approximately 800 to 1000 ° C. in a high-temperature gas atmosphere, and then a cooling zone for cooling to approximately 300 to 600 ° C. by blowing low-temperature gas. Have. There is also one in which a soaking zone for soaking the steel strip after heating is installed at the subsequent stage of the heating zone. In some cases, a pre-tropical zone that preheats the steel strip before heating is installed in the preceding stage of the heating zone.

  Patent Document 1 relates to a bright annealing furnace (no snout). In particular, in order to make it possible to significantly shorten the startup time (seasoning time) at the start of operation of the new furnace and at the time of restart after repair, The gas inside the furnace is discharged out of the furnace through a ventilation pipe arranged at the boundary between the lining refractory and the outer wall skin, and the exhausted gas is sucked out of the furnace and the impurity component in the gas It is described that an in-furnace gas circulation device is re-supplied into the furnace after being removed and cleaned.

  In Patent Document 2, in a continuous reducing atmosphere annealing apparatus for a metal strip (no snout), a refiner (a moisture removal apparatus, referred to as a refining apparatus in Patent Document 2) is used in front of the heating zone. Techniques are described in which installed pre-tropical gas is blown into the cooling zone to improve cooling efficiency, or conversely, cooling zone gas is blown into the pre-tropical zone to improve preheating efficiency.

JP-A-4-116127 JP 11-236623 A

  In continuous hot-dip galvanized steel sheet manufacturing equipment, it is necessary to remove the moisture in the continuous annealing furnace and reduce the dew point in order to improve the plateability. Conventionally, a cooling zone using a refiner provided outside the furnace The dew point is controlled by sucking the gas in the furnace, removing the moisture, and returning it to the heating zone. However, this method cannot secure high plating properties stably. The reason is described below.

  Addition of Si, Mn, etc. is known to be effective for improving the strength of steel materials. However, since Si, Mn is a component that inhibits zinc plating properties, There is a limit. FIG. 2 is a schematic diagram showing the relationship between the amount of surface oxidation of a component that inhibits plating properties and the atmospheric gas dew point obtained by the inventors' experimental investigation. In the general dew point range, which is the normal operating range, there is a large amount of surface oxidation, and as the annealing temperature becomes higher, the concentration tends to proceed, but as shown in FIG. 2, by reducing the dew point in the furnace, plating Since the surface concentration of the component that inhibits the property is suppressed, the plating property can be ensured even under high temperature annealing. In other words, in the general dew point control range, the surface concentration of the component that inhibits the plating property cannot be suppressed, and the plating property is lowered. For example, when the relationship between the surface concentration of each component of a steel sheet containing 1.5% by mass Si or 2.0% by mass Mn in steel and the dew point in the furnace was investigated, the dew point was −45 ° C. or less and Mn It was found that surface concentration was greatly suppressed, and Si surface concentration was greatly suppressed at −50 ° C. or lower. That is, in order to suppress the surface concentration of Si and Mn and to ensure stable high plating properties, it is necessary to control the dew point in the furnace to −50 ° C. or lower. In the method of using the refiner to suck the gas in the furnace from the cooling zone, remove the moisture, and return it to the heating zone, the dew point can only be lowered to about -40 ° C, and it is difficult to ensure high plating properties stably. there were.

On the other hand, in the case of a continuous hot dip galvanizing facility having a hot dip galvanizing bath, as for the dew point of the atmospheric gas in the snout, the hot dip zinc vaporizes as the dew point decreases in the snout as the dew point decreases in the furnace. There was a problem of sticking to the belt and causing quality defects.
As described above, in the conventional continuous hot dip galvanized steel sheet manufacturing equipment, the dew point of the continuous annealing furnace cannot be controlled to -50 ° C. or less, and it is difficult to ensure stable plating properties. When the temperature is lowered, the molten zinc vaporized in the snout adheres to the steel strip and causes a quality defect, and there is a problem that it is not possible to ensure both high quality and plating product quality.

The inventors diligently studied the means for solving the above-mentioned problems and made the present invention having the following gist configuration.
(1) Continuous annealing in which the furnace is divided into all three zones: a heating zone that heats the steel strip, which is a strip-shaped steel plate to be passed through, a soaking zone that soaks, and a cooling zone that cools. In a production facility for continuous hot dip galvanized steel sheets, in which a furnace is directly connected to a hot dip galvanizing bath with a snout, which is a closed space for direct feeding of steel strips from the furnace into the plating bath, at least a total of three zones are added. In the tropics and soaking zones, a dew point meter and furnace gas inlet and outlet are connected to a refiner, which is a moisture removing device provided outside the furnace, and the refiner is connected to each of the connected zones independently. The gas circuit is formed without joining in the refiner, the refiner operates so that the measured value of the dew point meter of the connected zone matches the target dew point for each formed gas circuit, and the snout Same as dew point meter A continuous hot-dip galvanized steel sheet, wherein the humidifier is configured to operate so that a measured value of the dew point meter of the snout matches a target dew point of the snout. production equipment.
(2) The snout is provided with a gas outlet and a blow-in port for the gas inside the snout, and these are connected to the refiner to form a gas circulation path between the inside of the snout and the measured value of the dew point meter of the snout is The equipment for producing a continuous hot-dip galvanized steel sheet according to (1), wherein the refiner operates in addition to the humidifier so as to coincide with the target dew point.
(3) Using the continuous hot-dip galvanized steel sheet manufacturing equipment described in (1) or (2) above, the target dew point of the furnace is −50 ° C. or lower, and the target dew point of the snout is −35 to −10 ° C. A method for producing a continuous hot-dip galvanized steel sheet, characterized in that the plating operation is performed as

  According to the present invention, both the quality of the plated product and the plating property can be secured with high stability.

It is a schematic diagram which shows one example of embodiment of this invention. It is a schematic diagram which shows the relationship between the surface oxidation amount of the component which inhibits plating property, and the atmospheric gas dew point in a furnace. It is a schematic diagram which shows one example (an example different from the previous figure) of embodiment of this invention.

  In the present invention, for example, as shown in FIG. 1, a heating zone 1 for heating a steel strip S, which is a strip-shaped steel plate to be passed through, in order from the upstream side of the feed path, a soaking zone 2 for soaking, and cooling. Assuming that the continuous annealing furnace divided into all three zones of the cooling zone 3 is directly connected to the hot dip galvanizing bath 5 by the snout 4 which is a closed space for direct feeding of the steel strip from the furnace into the plating bath. To do. Sealing rolls 9 for preventing atmospheric mixing between different processing zones are arranged at the required points from the cooling zone 3 to the snout 4 and the entrance of the heating zone 1 is prevented from entering the furnace. A seal roll 10 is provided for this purpose. There is a case where a heater is provided in the downstream portion of the cooling zone 3 to be used for overaging treatment. Such premise itself is within the scope of well-known conventional techniques.

Under this assumption, in the present invention, it provided the least be pressurized tropical 1 in all three zones, the dew 6 and furnace gas to a total of two zones of the soaking zone 2 and a suction outlet 7 and blow port 8, These are connected to a refiner 11 which is a moisture removing device provided outside the furnace, and gas circulation paths 12 and 13 are formed with the refiner 11 independently for each connected zone, and connected to each formed gas circulation path. The refiner 11 operates so that the measured value of the dew point meter in the zone that matches the target dew point, and the dew point meter 6 and the humidifier 14 for humidifying the inside of the snout 4 are provided in the snout 4. The humidifier 14 is configured to operate so that the measured value of the dew point meter 6 matches the target dew point of the snout 4.

In addition, although the case where the suction port 7 and the suction port 8 are each provided in a pair in the heating zone 1 and the soaking zone 2 is shown in FIG. 1, the dew point is easier to adjust if a plurality of installations are provided. Two or more pairs of suction ports 8 may be provided, and may be appropriately adjusted to achieve a target dew point.
The gas circulation paths 12 and 13 connected to different zones are independent from each other, and there is no merging in the refiner 11. For each gas circuit, the refiner 11 performs an operation of removing moisture from the gas in the gas circuit so that the dew point measurement value of the zone connected to the gas circuit matches the target dew point. On the other hand, the humidifier 14 performs an operation of humidifying (supplying moisture) in the snout so that the measured dew point value in the snout matches the target dew point (which is higher than the target dew point in the furnace zone). .

  In this way, a part of the gas is sucked out from the divided zone in the furnace and blown into the same zone after removing moisture, and the inside of the snout is humidified with a humidifier, so that the dew point in the furnace is −50 ° C. or less. The dew point in the furnace and the dew point in the snout can be controlled independently of each other so that both hot-dip galvanized steel sheet quality and plateability can be secured at a high level. become.

  The in-furnace zone in which the dew point meter 6, the suction port 7, and the inlet 8 are provided may be at least one zone among all three zones, but is preferably the soaking zone 2. Soaking zone 2 is a zone where the furnace temperature is higher than the other two zones and the surface concentration of Si and Mi is likely to occur. Therefore, a dew point meter, a suction port and a blow-in port are preferentially provided for this zone. The low dew point control is suitable for high plating stability. Of course, most preferably, it is provided in all three zones.

  Further, in the example shown in FIG. 3, in addition to the example of FIG. 1, the snout 4 is provided with a gas outlet 7 and an air inlet 8 for the gas in the snout, and these are connected to the refiner 11 to circulate the gas between the inside of the snout. In this example, the path 15 is formed and the refiner 11 is operated in addition to the humidifier 14 so that the measured value of the dew point meter of the snout becomes the target dew point of the snout. According to this, the dew point in the snout can be controlled with higher accuracy, the zinc adhesion in the snout can be more effectively prevented, and the high stability of the plated product quality is further improved.

  In the plating operation using the equipment of the present invention, the target dew point in the furnace is preferably set to −50 ° C. or lower in order to suppress the surface concentration of Si and Mn as described above. Such low dew point control is achieved by using the equipment of the present invention, so that surface concentration of Si and Mn can be effectively prevented, and the plating property can be secured at a high level. On the other hand, the dew point in the snout can be controlled independently of the inside of the furnace by using the equipment of the present invention. The target dew point in the snout is preferably −35 ° C. or higher in order to effectively prevent vaporized zinc from adhering to the steel strip in the snout. However, if it is too high, a zinc oxide film is formed on the bath surface, which is disadvantageous in that it adheres to the steel strip.

  An example in which the present invention is applied to the continuous hot-dip galvanized steel sheet production line in the same embodiment as the example shown in FIG. 3 will be described. In this line, conventionally, the dew point in the furnace was controlled by using a refiner provided outside the furnace to suck the gas in the furnace from the cooling zone, remove the moisture, and return it to the heating zone. The lower limit is about −40 ° C., and the dew point is not controlled in the snout. For this reason, in the plating operation of high-strength steel sheets to which Si and Mn are added, it has not yet been possible to sufficiently suppress non-plating and surface property defects of plated products. In contrast, in the examples, the soaking zone dew point can be stably controlled to −50 ° C. or lower, and the dew point in the snout can be stably controlled to −35 ° C. to −10 ° C. Thus, the occurrence frequency of non-plating decreased to 10 and the occurrence frequency of defective surface properties of the plated product decreased to 20, respectively, and the effects of the present invention were remarkably exhibited.

DESCRIPTION OF SYMBOLS 1 Heating zone 2 Soaking zone 3 Cooling zone 4 Snout 5 Hot dip galvanizing bath 6 Dew point meter 7 Suction port 8 Inlet 9 and 10 Seal roll 11 Refiner 12, 13, 15 Gas circulation path 14 Humidifier S Steel strip

Claims (3)

A continuous annealing furnace divided into all three zones: a heating zone that heats a steel strip that is a strip-shaped steel plate to be passed through, a soaking zone that soaks, and a cooling zone that cools, in order from the upstream side of the feeding path. In a continuous hot-dip galvanized steel sheet manufacturing facility directly connected to a hot-dip galvanizing bath with a snout, which is a closed space for direct feeding of the steel strip from the furnace to the plating bath, at least the heating zone in all three zones is uniform. In the tropics , a dew point meter and a furnace gas inlet and outlet are connected to a refiner which is a moisture removing device provided outside the furnace, and a gas circulation path to the refiner independently for each connected zone. was formed without merging in the refiner, for each gas circulation path and the formation, the measured value of the dew-point meter zone and connected to the refiner is operated so as to coincide with the target dew point, and dew-point instrument the snout And in the same snout And a humidifier for humidity provided, manufacturing equipment of a continuous hot-dip galvanized steel sheet which measured value of dew-point instrument of the snout is characterized in that a configuration in which the humidifier is operated so as to coincide with the target dew point of the snout.   The snout is provided with a gas outlet and a gas inlet for the gas inside the snout, and these are connected to the refiner to form a gas circulation path between the inside of the snout and the measured value of the dew point meter of the snout is the target dew point of the snout. The equipment for producing a continuous hot-dip galvanized steel sheet according to claim 1, wherein the refiner is operated in addition to the humidifier so as to match the above.   Plating operation using the continuous hot-dip galvanized steel sheet manufacturing facility according to claim 1 or 2, wherein the target dew point of the furnace is -50 ° C or lower, and the target dew point of the snout is -35 to -10 ° C. A method for producing a continuous hot-dip galvanized steel sheet.

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