JP6825593B2 - Hot-dip galvanizing equipment and manufacturing method of hot-dip galvanized steel sheet - Google Patents

Description

The present invention relates to a steel sheet manufacturing facility, a steel sheet manufacturing method, and a dew point control method.

In recent years, in the fields of automobiles, home appliances, building materials, etc., there is an increasing demand for high-strength steel sheets that can contribute to weight reduction of structures. It is known that this high-strength steel sheet can be produced by adding Si to the steel to produce a high-strength steel sheet having good hole expandability and ductility.

The alloyed hot-dip galvanized steel sheet is obtained by heating and annealing the base steel sheet at a temperature of about 600 to 900 ° C. in a reducing atmosphere or a non-oxidizing atmosphere, then performing hot-dip galvanizing treatment on the steel sheet, and further heating the galvanized steel sheet. Manufactured by alloying. However, when an alloyed hot-dip galvanized steel sheet is manufactured using a high-strength steel sheet containing a large amount of Si (particularly 0.2% by mass or more) as a base material, there are the following problems.

Si in steel is an easily oxidizing element, and is selectively oxidized even in a generally used reducing atmosphere or non-oxidizing atmosphere to concentrate on the surface of the steel sheet and form an oxide. This oxide reduces the wettability with hot-dip zinc during the plating process and causes non-plating. Therefore, as the Si concentration in the steel increases, the wettability drops sharply and non-plating occurs frequently. Further, even if non-plating is not achieved, there is a problem that the plating adhesion is inferior. Further, when Si in the steel is selectively oxidized and concentrated on the surface of the steel sheet, there is a problem that a significant delay in alloying occurs in the alloying process after hot dip galvanizing, which significantly impairs productivity.

In response to such a problem, for example, in Patent Document 1, a mixed gas of a humidifying gas and a dry gas and a dry gas are introduced into the uniform tropical zone, and the volume of the uniform tropical zone and the gas flow rate of the humidifying gas supplied to the uniform tropical zone. Alloyed hot-dip zinc plating characterized in that the water content, the gas flow rate of the dry gas supplied to the average tropical zone, the gas flow rate of the dry gas supplied to the cooling zone, and the average temperature inside the average tropical zone satisfy a predetermined relationship. The manufacturing method of the steel plate is described. With this technique, the alloying temperature is reduced by suppressing the surface concentration of Si and internally oxidizing it.

Japanese Unexamined Patent Publication No. 2016-17192

According to the method described in Patent Document 1, it is possible to obtain a good plating appearance with high plating adhesion of a high-strength steel sheet, and it is possible to suppress a decrease in tensile strength by lowering the alloying temperature. is there. However, it is more useful if the alloying temperature can be reduced more efficiently and the decrease in tensile strength can be suppressed.

Further, in the method of Patent Document 1, the dew point cannot be controlled stably, and after the humidifying gas is blown into the inlet side of the tropics more than necessary, the oxide scale adheres to the roll in the annealing furnace and the steel plate is formed. There is a concern that a flaw (so-called pickup defect) may occur.

A first object of the present invention is to provide a steel sheet manufacturing facility, a steel sheet manufacturing method, and a dew point control method for suppressing the pickup defect.

A second object of the present invention is to provide a steel sheet manufacturing facility, a steel sheet manufacturing method, and a dew point control method capable of efficiently reducing the alloying temperature and suppressing a decrease in tensile strength.

The present inventors have made extensive studies to solve the above problems. As a result, by controlling (adjusting) the humidification amount of the atmosphere in the latter stage of the solitary tropics where the steel sheet becomes hot so as to be different from the humidification amount in the earlier stage, the dew point can be stably controlled and pickup defects can be suppressed. , It has been found that it is possible to efficiently reduce the alloying temperature and suppress the decrease in tensile strength.

A steel sheet manufacturing facility having an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are juxtaposed in this order is adjusted in the amount of humidification by a humidified atmospheric gas introduced in the latter stage of the soaking zone, and this is adjusted in the previous stage. The first problem can be solved by manufacturing the steel sheet with equipment that can be controlled differently from the humidification amount to be adjusted.

Further, the steel sheet manufacturing facility for solving the first problem is further provided with a hot-dip galvanizing facility adjacent to the cooling zone and an alloying facility for alloying the hot-dip galvanizing to manufacture the steel sheet. The second problem can be solved.

Specifically, the present invention provides the following.

[1] A steel plate manufacturing facility having an incubator in which a heating zone, a soaking zone, and a cooling zone are juxtaposed in this order, and a humidified atmospheric gas provided after the soaking zone is charged. Humidification by charging one inlet, a second inlet for charging a humidified atmospheric gas, which is provided in front of the first inlet in the solitary tropics, and the atmospheric gas being charged from the first inlet. The first humidification amount adjusting unit has a first humidification amount adjusting unit for adjusting the amount and a second humidification amount adjusting unit for adjusting the humidification amount by inputting the atmospheric gas from the second input port. A steel plate manufacturing facility comprising a control unit that controls the humidification amount to be adjusted and the humidification amount adjusted by the second humidification amount adjustment unit to be different.

[2] The control unit is characterized in that the flow rate of the atmospheric gas charged into the first inlet is controlled to be larger than the flow rate of the atmospheric gas charged into the second inlet. Steel plate manufacturing equipment.

[3] The steel sheet manufacturing facility according to [1] or [2], further comprising a dew point meter provided in the latter stage of the tropics.

[4] Further, the first inlet and the second inlet, which are necessary for controlling to a desired dew point based on the dew point meter provided in the latter stage of the average tropical zone and the measurement result of the dew point meter. A ratio setting that determines the flow rate ratio of atmospheric gas to the first input port and the second input port based on the calculation result of the total amount calculation unit that calculates the total amount of atmospheric gas charged into the first input port and the second input port. The steel plate manufacturing facility according to [2], which comprises a vessel and a container.

[5] The boundary between the front stage and the rear stage of the average tropics is set in the range of 1/3 to 2/3 of the length in the direction of the plate of the average tropics from the entrance side end of the average tropics [5]. The steel sheet manufacturing facility according to any one of 1] to [4].

[6] The steel sheet manufacturing facility according to any one of [1] to [5], further comprising a hot-dip galvanizing facility adjacent to the cooling zone.

[7] The steel sheet manufacturing facility according to [6], further comprising an alloying facility for alloying hot dip galvanizing.

[8] The control unit is described in any one of [2] to [7], wherein the control unit controls based on a correlation in which the faster the line speed of the steel sheet, the greater the amount of humidification in the latter stage of the soaking tropics. Steel plate manufacturing equipment.

[9] There is a steel sheet manufacturing method in which a steel sheet is manufactured by a steel sheet manufacturing facility having an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are juxtaposed in this order. The faster the line speed of the steel sheet, the more the solitary tropical A steel sheet manufacturing method characterized by increasing the amount of humidification in the subsequent stage.

[10] The increase in the amount of humidification is performed by the injection of the humidified atmospheric gas in the latter stage of the uniform tropical zone, and in the uniform tropical zone, the humidified atmospheric gas in the stage before the injection position of the atmospheric gas. The steel plate manufacturing method according to [9], wherein the gas is charged to adjust the flow rate of the atmospheric gas.

[11] The steel sheet manufacturing method according to [10], wherein the flow rate of the atmospheric gas in the latter stage is made larger than the flow rate of the atmospheric gas in the previous stage in the tropics.

[12] The method for producing a steel sheet according to any one of [10] and [11], wherein the flow rate of the atmospheric gas is adjusted so that the dew point in the latter stage of the solitary tropics is within a desired range.

[13] One of [10] to [12], wherein the total amount of the atmospheric gas to be charged is calculated based on the line speed, and the flow rate of the atmospheric gas is adjusted based on the calculation result. The steel sheet manufacturing method described.

[14] The steel sheet manufacturing method according to any one of [10] to [13], wherein the flow rate of the atmospheric gas is adjusted according to the type of the steel sheet to be manufactured.

[15] The steel sheet manufacturing method according to any one of [9] to [14], wherein hot-dip galvanizing treatment is performed after cooling in the cooling zone.

[16] The steel sheet manufacturing method according to [15], wherein an alloying treatment is performed after the hot dip galvanizing treatment.

[17] When the measurement result of the dew point in the latter stage of the solitary tropics deviates from the desired dew point, the total amount of the humidified atmospheric gas charged into the first and second stages of the solitary tropics is required to obtain the desired dew point. The ratio of the atmospheric gas to be charged in the first stage and the atmosphere gas to be charged in the latter stage is set, and the amount of the atmospheric gas to be charged in the first stage and the second stage of the average tropics is adjusted to adjust the amount of the atmosphere gas to be input in the first stage and the second stage of the average tropics. A dew point control method characterized by controlling the dew point of.

[18] Manufacture of a steel sheet in which the steel sheet is annealed using the steel sheet manufacturing facility according to any one of [1] to [8], and the annealed steel sheet is plated by a hot dip galvanizing facility adjacent to the cooling zone. Method.

According to the present invention, it is possible to suppress the occurrence of dents (so-called pickup defects) on the steel sheet due to the adhesion of the oxide scale to the roll in the furnace.

Further, according to the present invention, the alloying temperature can be efficiently reduced and the decrease in tensile strength can be suppressed.

FIG. 1 is a schematic view schematically showing the steel sheet manufacturing equipment of the embodiment. FIG. 2 is a diagram schematically showing details of the tropics of the steel sheet manufacturing equipment of the embodiment. FIG. 3 is a schematic view of a part of the latter part of the tropics to explain the adjustment of the atmospheric gas flow rate in the embodiment. FIG. 4 is a diagram showing the results of Example 3, FIG. 4 (a) is a diagram showing the results of a comparative example in which a steel sheet is manufactured using a conventional steel sheet manufacturing facility, and FIG. 4 (b) is a diagram showing the results of a comparative example. It is a figure which shows the result of the invention example which manufactured the steel sheet using the steel sheet manufacturing facility shown in FIGS.

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

FIG. 1 is a schematic view schematically showing the steel sheet manufacturing equipment of the present embodiment. FIG. 2 is a diagram schematically showing the details of the soothing tropics of the steel sheet manufacturing equipment of the present embodiment. FIG. 3 is a schematic view of a part of the latter part of the tropics to explain the adjustment of the atmospheric gas flow rate in the present embodiment.

The steel sheet manufacturing facility 1 shown in FIG. 1 includes an annealing furnace 2, a snout 3, a hot-dip galvanizing bath 4 as a hot-dip galvanizing facility, and an alloying facility 5. The direction of the white arrow shown in FIG. 1 is the through plate direction.

The annealing furnace 2 has a configuration in which a heating zone 20, a soaking zone 21, and a cooling zone 22 are arranged in this order. Each band 20, 21, 22 is provided with one or more hearth rolls at the top and bottom. When the steel sheet is folded 180 degrees from the Haas roll, the steel sheet is conveyed in the vertical direction a plurality of times inside a predetermined band of the annealing furnace 2 to form a plurality of paths. A hearth roll may be used in which the steel plate is moved at a right angle without being folded back. The number of hearth rolls is not particularly limited and may be set as appropriate.

Adjacent bands communicate with each other via a communication section that connects the upper or lower parts of the bands. In the present embodiment, the first heating zone 20A and the second heating zone 20B communicate with each other via a throat (squeezing portion) 23A connecting the upper portions of the respective bands. The second heating zone 20B and the solitary tropics 21 communicate with each other via a throat 23B connecting the lower parts of the respective zones. The solitary tropics 21 and the first cooling zone 22A communicate with each other via a throat 23C connecting the lower portions of the respective zones. The first cooling zone 22A and the second cooling zone 22B communicate with each other via a throat 23D that connects the lower portions of the respective zones. The height of each throat may be appropriately set, but since the diameter of the hearth roll is about 1 m, it is preferably 1.5 m or more. However, from the viewpoint of enhancing the independence of the atmosphere of each band, it is preferable that the height of each communication portion is as low as possible.

The tip of the snout 3 is immersed in the hot-dip galvanizing bath 4, and the cooling zone 22 of the annealing furnace 2 and the hot-dip galvanizing bath 4 are connected by this immersion. An alloying facility 5 for heat-alloying zinc plating is provided after the hot-dip galvanizing bath 4.

As shown in FIGS. 2 and 3, the leveling tropical 21 of the steel plate manufacturing facility of the present embodiment includes a pipe 200, a humidifying gas inlet 201, a humidifying device 202, a dew point meter 203 for humidifying gas, and a flow rate adjustment for humidifying gas. Valve 204, flow meter 205, dew point meter 206 in the furnace, dew point indicator controller (DIC: Dew point indicator controller) 207, ratio setter 208, flow indicator controller (FIC: Flow indicator controller) 209. It has a flow control valve 210 for dry gas and a dry gas inlet 211.

As shown in FIG. 2, in the present embodiment, the boundary between the front stage and the rear stage of the tropics 21 is set to 1/2 of the length in the plate-passing direction of the tropics from the entrance side end of the tropics. .. As will be described later, in the latter stage of the soothing tropics 21 where the temperature of the steel sheet becomes high, the water consumption due to the internal oxidation reaction of Si increases and the dew point tends to fluctuate. Therefore, in the present invention, at least 2 in the latter and earlier stages of the soaking tropics. Since the amount of humidification is adjusted at each location and measures are taken to suppress fluctuations in the dew point in the latter stage of the uniform tropical 21, it is necessary to consider the uniform tropical 21 separately in the first stage and the second stage. Therefore, where to set the boundary between the front stage and the rear stage of the uniform tropical 21 may be determined in consideration of where in the uniform tropical 21 the steel sheet becomes hot and the problem of dew point fluctuation is likely to occur. From this point of view, it is preferable that the latter stage is a region where the temperature of the steel sheet is 700 ° C. or higher. The position of the boundary between the front stage and the rear stage of the tropics 21 will be determined as appropriate, but usually, the length from the entrance side end of the tropics to the plate direction of the tropics is 1/3 to 2/3. Often set in the range of.

In the present embodiment, the pipe 200 is branched at a branch A point into a humidifying gas pipe 200A through which the humidifying gas passes and a dry gas pipe 200B through which the dry gas passes. The humidifying gas pipe 200A further has a branch B and a branch C for connecting to each of the humidifying gas inlets 201A, 201B, and 201C, which will be described later. The dry gas pipe 200B has three connecting holes for connecting to the dry gas inlet described later. The type of the atmosphere gas is not particularly limited, for _example, an H 2 -N ₂ mixed gas or _{N 2} gas. The dry gas is usually an atmospheric gas having a dew point of about −60 to −50 ° C.

In the present embodiment, the humidifying gas inlet 201 is composed of three humidifying gas inlets 201A, 201B, and 201C. The humidifying gas inlet 201B and the humidifying gas inlet 201C are provided in the latter stage of the tropics, and the humidifying gas inlet 201C is provided in the later stage of the humidifying gas inlet 201B. The humidifying gas inlet 201A is provided in front of the tropics 21. The three humidifying gas inlets 201A, 201B, and 201C are all connected to the humidifying gas supply pipe 200A. The humidifying gas inlet 201C corresponds to the first inlet. Further, the humidifying gas inlet 201B corresponds to the second inlet. If the distance (distance in the plate-passing direction) between the humidifying gas inlet 201C and the humidifying gas inlet 201B is within the range of 6 to 10 m, the flow rate of the humidified gas charged from the humidified gas inlet 201B described later is adjusted. The effect of doing this will be enhanced. In the present embodiment, the number of humidifying gas inlets in the latter stage of the uniform tropical 21 is 2, but the number of humidifying gas inlets in the latter stage may be one. When there is one humidifying gas inlet in the latter stage, at least one humidifying gas inlet is provided in the front stage of the average tropical 21. Further, it is not necessary to provide a humidifying gas inlet in the front stage of the uniform tropical 21. When the humidifying gas inlet is not provided in the front stage of the tropics 21, two or more humidifying gas inlets are provided in the rear stage of the tropics 21. However, the number of humidifying gas inlets in the latter stage of the solitary tropics 21 is preferably 2 or more, and it is preferable to provide 1 or more humidifying gas inlets in the front stage of the solitary tropics 21.

The humidifying device 202 is provided between the branch A and the branch B on the humidifying gas pipe 200A to humidify the atmospheric gas.

The dew point meter 203 for humidifying gas is located on the downstream side in the atmospheric gas supply direction and is arranged between the branch A and the branch B, and measures the dew point of the atmospheric gas humidified by the humidifying device 202.

The humidifying gas flow rate adjusting valve 204 is composed of three humidifying gas flow rate adjusting valves 204A, 204B, and 204C. The humidifying gas flow rate adjusting valve 204A is provided between the branch B and the humidifying gas inlet 201A, whereby the amount of humidified gas sent to the humidifying gas inlet 201A can be adjusted. The humidifying gas flow rate adjusting valve 204B is provided between the branch C and the humidifying gas inlet 201B, whereby the amount of humidified gas sent to the humidifying gas inlet 201B can be adjusted. The humidifying gas flow rate adjusting valve 204C is provided between the branch B and the humidifying gas inlet 201C, whereby the amount of humidified gas sent to the humidifying gas inlet 201C can be adjusted. The flow rate adjusting valve 204C for humidifying gas corresponds to the first humidifying amount adjusting section. The flow rate adjusting valve 204B for humidifying gas corresponds to the second humidifying amount adjusting section.

As described above, in the present embodiment, the humidifying device 202, the dew point meter 203 for the humidifying gas, and the flow rate adjusting valve 204 for the humidifying gas are arranged in this order.

The flow meter 205 is composed of three flow meters 205A, 205B and 205C. The flow meter 205A is provided between the humidifying gas flow rate adjusting valve 204A and the humidifying gas inlet 201A, whereby the flow rate of the humidified gas adjusted by the humidifying gas flow rate adjusting valve 204A can be measured. The flow meter 205B is provided between the humidifying gas flow rate adjusting valve 204B and the humidifying gas inlet 201B, whereby the flow rate of the humidified gas adjusted by the humidifying gas flow rate adjusting valve 204B can be measured. The flow meter 205C is provided between the humidifying gas flow rate adjusting valve 204C and the humidifying gas inlet 201C, whereby the flow rate of the humidified gas adjusted by the humidifying gas flow rate adjusting valve 204C can be measured.

The in-core dew point meter 206 is provided after the solitary tropics 21 so that the dew point in the furnace of the soaking tropics 21 can be measured. The installation position of the dew point meter 206 in the furnace is preferably a position where the temperature of the steel plate becomes high. The temperature of the steel sheet becomes high is 700 ° C. or higher. Since the high position on the outlet side of the furnace is included in the region where the temperature of the steel sheet becomes high, it is in this range in the present embodiment as shown in the figure. Further, as in the steel sheet manufacturing facility 1 of the present embodiment, the number of dew point totals 206 in the furnace is preferably one.

The dew point indicator controller 207 is connected to the dew point meter 206 in the furnace, receives the measurement result of the dew point measured by the dew point meter 206 in the furnace, and is based on the difference between the preset target dew point and the above measurement result. , Calculate the total amount of humidifying gas required to reach the target dew point. The dew point indicator controller 207 corresponds to the total amount calculation unit.

The ratio setting device 208 is connected to the dew point indicator controller 207, receives the total amount of humidifying gas calculated by the dew point indicator controller, and based on this, of the humidifying gas supplied to the humidifying gas inlets 201A, 201B, 201C. Set the ratio. At this time, the ratio setting device 208 is adjusted by the amount of humidification adjusted by the input of the atmospheric gas from the humidifying gas input port 201C in the latter stage of the tropics and by the input of the atmospheric gas from the humidifying gas input port 201B in the previous stage. The amount of humidification to be applied is controlled to be different. Therefore, in the present embodiment, the ratio setting device 208 also has a role as a control unit.

The flow rate indicator 209 is composed of flow rate indicator 209A, 209B, and 209C, each of which is connected to the ratio setting device 208. The flow rate indicator 209A is connected to the flow meter 205A and can receive the measurement result of the flow rate measured by the flow meter 205A. The flow rate indicator 209A is also connected to the humidifying gas flow rate adjusting valve 204A, and the humidifying gas flow rate adjusting valve 204A is operated based on the flow rate measurement result and the ratio set by the ratio setting device 208. , Adjust the flow rate. The flow rate indicator 209B is connected to the flow meter 205B and can receive the measurement result of the flow rate measured by the flow meter 205B. The flow rate indicator 209B is also connected to the humidifying gas flow rate adjusting valve 204B, and the humidifying gas flow rate adjusting valve 204B is operated based on the flow rate measurement result and the ratio set by the ratio setting device 208. , Adjust the flow rate. The flow rate indicator 209C is connected to the flow meter 205C and can receive the measurement result of the flow rate measured by the flow meter 205C. The flow rate indicator 209C is also connected to the humidifying gas flow rate adjusting valve 204C, and the humidifying gas flow rate adjusting valve 204C is operated based on the flow rate measurement result and the ratio set by the ratio setting device 208. , Adjust the flow rate.

The dry gas flow rate adjusting valve 210 is provided in the dry gas pipe 200B and is sent to the dry gas inlet 211 to adjust the flow rate of the dry gas. By adjusting the flow rate of this dry gas, the pressure inside the furnace is maintained at the set value.

The dry gas input port 211 is composed of the dry gas input ports 211A, 211B, and 211C, and is connected to the connecting hole formed in the dry gas pipe 200B from the dry gas pipe 200B to the dry gas input port 211. Dry gas is sent.

Next, a method of manufacturing a steel sheet using the steel sheet manufacturing facility 1 of the present embodiment will be described. The steel sheet moves on the hearth rolls of the heating zone 20, the soaking zone 21, and the cooling zone 22 of the annealing furnace 2, passes through the snout 3, is hot-dip galvanized in the hot-dip galvanizing bath 4, and is alloyed in the alloying facility 5. To.

The steel sheet manufacturing equipment 1 of the present embodiment can be used for manufacturing steel sheets having various component compositions. Therefore, the composition of the steel sheet applied to the steel sheet manufacturing facility 1 is not particularly limited. However, even a steel sheet having a composition that tends to cause problems such as pickup defects and an increase in alloying temperature is characterized in that the occurrence of these problems can be suppressed. Therefore, the effect of the present invention is remarkably exhibited in a steel sheet having a component composition in which problems such as pickup defects and an increase in alloying temperature are likely to occur. The component composition in which the effect of the present invention is more clearly exhibited is the component composition of high-tensile steel or ordinary steel, and the component composition of high-tensile steel is, for example, C: 0.015 to 0.35%, Si: 0 as the essential component. 0.01 to 2.5%, Mn: 1.5 to 4.0%, P: 0.10% or less, S: S: 0.01% or less, optional component Al: 0.001 to 1.000% , Cr: 0.001 to 1.000%, Ni: 0.05 to 1.00%, Cu: 0.05 to 1.00%, Mo: 0.05 to 1.00%, Ti: 0.005 ~ 0.080%, Nb: 0.005 to 0.050%, B: 0.001 to 0.005%, Sb: 0.001 to 0.200%, the balance is Fe and unavoidable impurities. If the above optional element is contained below the lower limit, the optional element shall be included as an unavoidable impurity. The composition of ordinary steel is, for example, C: 0.0001 to 0.004%, Si: 0.001 to 0.10%, Mn: 0.01 to 0.50%, P: 0.10%. Hereinafter, S: S: 0.01% or less is contained, and the balance is Fe and unavoidable impurities. In addition, high-tensile means steel having a tensile strength of 590 MPa or more, and ordinary steel means steel having a tensile strength of less than 590 MPa.

The heating method in the heating zone 20 is not particularly limited, and either direct heating or indirect heating may be used. The heating temperature may be appropriately determined by a usual method, but is often set to 550 to 900 ° C.

The steel sheet heated in the heating zone 20 enters the tropics 21 and is heated. The heating method in the tropics 21 is not particularly limited, and either indirect heating or direct heating may be used. Further, the heating temperature in the tropics 21 is not particularly limited, but the outside temperature of the tropics 21 is in the range of 750 to 900 ° C., and the temperature of the inside of the tropics 21 is 300 to 300 to higher than the above-mentioned outside temperature. It is often set as low as 500 ° C. Further, as will be described later, when the temperature reaches 700 ° C. or higher, a problem due to surface concentration of Si, which is a problem solved by the present invention, tends to occur. Therefore, the present invention is particularly effective when the heating temperature in the tropics 21 is 700 ° C. or higher.

The dew point in the tropical 21 is appropriately set according to the type of steel sheet to be manufactured and the like. The dew point is adjusted by adjusting the flow rate of the dry gas sent from the dry gas pipe 200B and the flow rate of the humidifying gas sent from the humidifying gas pipe 200A to the dry gas flow rate adjusting valve 210 and the humidifying gas flow rate adjusting valve 204. It is done by adjusting. In carrying out the present invention, the dew point is preferably set in the range of 25 to 0 ° C.

Adjusting the dew point in the soaking zone 21 above -25 ° C., the inside of oxygen is supplied from the iron oxide, even after the internal oxide of Si is formed, Si by oxygen supplied from of H _{2 O} atmosphere Due to the continued oxidation, more internal oxidation of Si occurs. Then, the amount of solid solution Si decreases in the inner region of the surface layer of the steel sheet on which internal oxidation is formed. When the amount of solid solution Si decreases, the surface layer of the steel sheet behaves as if it were low Si steel, the subsequent alloying reaction is promoted, and the alloying reaction proceeds at a low temperature. As a result of the lower alloying temperature, the retained austenite phase can be maintained at a high fraction, which improves ductility. In addition, the desired strength can be obtained without the tempering softening of the martensite phase progressing. In the average tropics 21, when the dew point becomes 10 ° C or higher, the steel strip iron begins to oxidize, so the temperature should be sufficiently lower than 10 ° C for the reason of minimizing the dew point distribution uniformity and the dew point fluctuation range in the average tropics 21. More specifically, the upper limit of the dew point is preferably controlled at 0 ° C.

By using the steel sheet manufacturing equipment 1 of the present embodiment, in addition to the above-mentioned overall dew point adjustment, the dew point can be adjusted in more detail by the following method.

When the steel sheet being transported is heated in the solitary tropics 21, the dew point is measured by the dew point meter 206 in the furnace. As will be described later, the dew point tends to fluctuate in the latter stage of the average tropical 21, and the following adjustment of the dew point is an adjustment of the dew point for suppressing the fluctuation of the dew point in the latter stage of the average tropical 21. Therefore, the dew point measured here can be regarded as the dew point in the tropics 21, but is regarded as the dew point in the latter stage of the tropics 21.

The measurement result of the dew point measured by the dew point meter 206 in the furnace is sent to the dew point indicator controller 207. The dew point indicator controller 207 calculates the total amount of humidifying gas required to reach the target dew point based on the difference between the preset target dew point and the above measurement result, for example, by PID control. The target dew point is preferably set to 25 to 0 ° C.

The total amount of required humidifying gas calculated by the dew point indicator controller 207 is sent to the ratio setting device 208. The ratio setting device 208 sets the ratio of the humidifying gas to be charged into the humidifying gas inlets 201A, 201B, and 201C in order to control the target dew point. The ratio may be determined in advance by a plurality of tests or by a method of making a prediction based on the past test results of similar cases.

Each of the flow rate indicator 209A, 209B, and 209C has a flow rate adjusting valve for humidifying gas based on the measurement result of the flow rate measured by the flow rate meters 205A, 205B, 205C so that the ratio is determined by the ratio setting device 208. The 204A, 204B, and 204C are adjusted to adjust the flow rate of the humidifying gas to be charged into the humidifying gas inlets 201A, 201B, and 201C. As a result, the humidifying gas required to reach the target dew point is charged from the humidifying gas inlets 201A, 201B, and 201C.

The measurement of the dew point meter 206 in the furnace may be performed intermittently, and the above-mentioned soaking tropical operation may be performed only when the dew point is measured.

In the above operation in the tropics 21, the flow rate adjusting valve 210 for dry gas is used for adjusting the pressure in the furnace and controlling the dew point in the tropics 21. If the flow rate of the humidifying gas is increased by the flow control valve 204 for the humidifying gas during the dew point control in the latter stage of the soaking tropic 21, the pressure inside the furnace may fluctuate or the dew point of the entire furnace may fluctuate. However, the adjustment of the dew point in the latter stage of the above-mentioned leveling tropical 21 is a fine adjustment, and even if the pressure in the furnace fluctuates or the dew point in the entire furnace fluctuates, it is within the permissible range, which is a problem. There is no.

The steel sheet heated in the tropics 21 is sent to the cooling zone 22 and cooled. The cooling method in the cooling zone 22 is not particularly limited, and either air cooling or water cooling may be used. The temperature of the steel sheet after cooling may be appropriately set according to the type of the steel sheet and the like, but is usually cooled to 500 ° C. or lower. When the plating treatment is performed after cooling as in the steel sheet manufacturing equipment of the present embodiment, it is preferable to cool to 470 to 500 ° C.

The steel sheet cooled by the cooling zone 22 passes through the snout 3 and enters the hot-dip galvanizing bath 4. As a result, the steel sheet is galvanized. The conditions of the zinc plating treatment are not particularly limited, and the plating bath temperature and the plating bath composition may be appropriately set. Usually, the temperature of the zinc plating bath is in the range of 450 to 470 ° C., the composition of the plating bath contains a small amount of Al (0.5% by mass or less), and the balance is Zn and unavoidable impurities.

After galvanizing in the hot-dip galvanizing bath 4, alloying is performed in the alloying facility 5. The alloying treatment conditions are not particularly limited, but usually, the alloying temperature is 470 to 600 ° C., and the alloying treatment time is 1 second or more.

Next, the effect of the steel sheet manufacturing equipment 1 of the present embodiment will be described.

In order to efficiently suppress fluctuations in the dew point and suppress pickup defects in the steel sheet manufacturing facility 1 that is continuously annealed at a predetermined line speed, it depends on the atmospheric gas introduced in the subsequent stage of the uniform tropical 21 according to the line speed. It is necessary to adjust the amount of humidification appropriately. For example, it is effective to increase the amount of humidifying gas input in the latter stage of the tropics because the outlet side where the steel sheet becomes hot consumes more water due to the internal oxidation reaction of Si and the dew point tends to fluctuate. .. Further, it is necessary to suppress the burden on the furnace body due to the excessive amount of humidifying gas in the subsequent stage. Specifically, in addition to the above adjustment of the humidification amount, the humidification amount is also adjusted in the earlier stage. The steel sheet manufacturing facility 1 of the present embodiment has a humidifying gas inlet 201C and a flow rate adjusting valve 204C for humidifying gas after the soaking tropics 21. By adjusting the flow rate adjusting valve 204C for humidifying gas, an appropriate amount of humidifying gas can be input to the latter stage of the tropics, and the humidifying amount can be appropriately controlled. As a result, the fluctuation of the dew point is reduced, and the pickup defect can be suppressed. Here, the "appropriate amount of humidifying gas" may be obtained experimentally, may be obtained by simulation using a computer or the like, or may be determined from past trouble cases. Further, since the steel sheet manufacturing equipment 1 of the present embodiment has the humidifying gas input port 201B and the ratio setting device 208 serves as a control unit, the flow rate of the humidifying gas input to the humidifying gas input port 201B is set as described above. It can be adjusted by the humidifying gas flow rate adjusting valve 204B so as to be different from the humidifying amount adjusted in the subsequent stage. In addition to adjusting the input amount of humidifying gas at the humidifying gas input port 201C and the flow rate adjusting valve 204C for humidifying gas, by adjusting the input amount of humidifying gas in the previous stage, the humidifying gas in the latter stage becomes excessive. As a result, it is possible to suppress the burden on the furnace body. If the amount of humidification can be made different, the ratio setting device 208 does not have to be used. For example, it may be controlled by a computer or the like that selects conditions for different humidification amounts from the allowable range of an appropriate amount of humidifying gas.

As described above, the outlet plate temperature of the average tropics 21 is usually 750 to 900 ° C., and the entrance plate temperature of the average tropics is often set to 300 to 500 ° C. lower than the exit side. Here, Si added to the steel sheet is remarkably concentrated on the surface of the steel sheet at a high temperature of 700 ° C. or higher, and the surface concentration of Si becomes an inhibitory factor of the alloying reaction of the steel sheet. In order to suppress this surface thickening, the dew point on the soaking tropics side where the steel sheet has the highest temperature may be set to 25 to 0 ° C. As described above, the steel sheet manufacturing equipment 1 of the present embodiment has the humidifying gas inlet 201C and the flow rate adjusting valve 204C for humidifying gas, so that the fluctuation of the dew point in the subsequent stage of the soaking tropics 21 can be reduced. As a result, it is easy to adjust the dew point on the soaking tropical side to the range of 25 to 0 ° C. Therefore, when hot-dip galvanizing is performed in the hot-dip galvanizing bath 4 and alloying is performed in the alloying facility 5, Si is a steel plate. Oxide is formed inside, the thickening of the surface of the steel sheet is suppressed, the alloying reaction occurs efficiently, and the alloying temperature can be reduced.

Further, if the line speed, which is the transport speed of the steel plates, is increased, more steel plates will be charged into the uniform tropical 21 even at the same time than before the increase. Then, the steel sheet absorbs moisture more easily, and the dew point becomes more variable. Therefore, in order to suppress the fluctuation, it is necessary to further increase the flow rate of the humidified gas. The fluctuation of the dew point also becomes particularly large in the latter stage of the average tropics 21. As described above, since the steel sheet manufacturing equipment 1 of the present embodiment has the humidifying gas input port 201C and the flow rate adjusting valve 204C for humidifying gas, the flow rate of the humidifying gas to be input to the subsequent stage of the soaking tropical 21 is adjusted according to the line speed. It can be increased or decreased. As a result, fluctuations in the dew point due to changes in the line speed can be effectively suppressed. As described above, the correlation between the appropriate value of the humidified amount of the humidified atmospheric gas (flow rate of the atmospheric gas in this embodiment) and the line speed tends to increase as the line speed increases. is there.

From the viewpoint of obtaining the effect of the present invention, when the number of the humidifying gas inlet and the flow rate adjusting valve for the humidified gas is a plurality, the flow rate can be controlled independently at each inlet as in the present embodiment. There is no need. However, if the flow rate can be adjusted independently at each inlet, finer dew point control becomes possible. Further, as described above, considering the possibility of dew point fluctuation in the latter stage, the effect of the present invention is enhanced by increasing the flow rate of the atmospheric gas in the latter stage.

Further, the steel sheet manufacturing facility 1 of the present embodiment has an in-core dew point meter 206, which is a dew point meter, at the subsequent stage of the soaking tropics 21. As mentioned above, if it is known that the dew point fluctuates easily in the latter stage of the average tropical 21 and the flow rate of the humidifying gas to be input in the latter stage of the average tropical 21 is known, check with the in-core dew point total 206. The dew point fluctuation can be reduced without doing this, but if there is a dew point meter 206 in the furnace, it is possible to manufacture while checking the change in the dew point. Therefore, the dew point fluctuation should be suppressed to an extremely small value while appropriately adjusting the flow rate. Is possible.

Further, as described above, since moisture is easily absorbed and the dew point is liable to fluctuate in the latter stage of the tropics 21, the dew point meter 206 in the furnace is installed in the latter stage of the tropics 21 so that the dew point is liable to fluctuate. The dew point can be grasped appropriately, and it becomes easier to suppress the dew point fluctuation. Further, in the upper part of the average tropics 21, the specific gravity of water vapor is light, so that a high dew point is likely to occur. Therefore, especially in the upper part of the latter stage, water is most easily absorbed and the dew point fluctuation is likely to be large. Therefore, if the position of the dew point total 206 in the furnace is set to the latter stage and the upper part of the uniform tropical 21, the effect is further enhanced. The "upper part" means a position of 1/2 or more in the height direction of the tropical 21.

Further, in the steel sheet manufacturing facility 1 of the present embodiment, the number of dew point totals 206 in the furnace is one. When there are multiple humidifying gas inlets and humidifying gas flow rate adjusting valves, there are no partitions inside the soaking tropics 21, so each humidifying gas flow rate adjusting valve has its own control loop to control the dew point in the furnace. Then, the influence of the humidifying gas input from one of the regulating valves becomes the disturbance influence of the control loop of the other regulating valve. When there are a plurality of humidifying gas inlets and humidifying gas flow rate adjusting valves, and when there is one dew point meter 206 in the furnace as in this embodiment, the flow rate can be adjusted without being affected by other locations. This facilitates proper control of the dew point.

Further, in the present embodiment, since the humidifying gas dew point meter 203 is provided, the humidifying device 202, the humidifying gas dew point meter 203, and the humidifying gas flow rate adjusting valve 204 are arranged in this order. The dew point of the atmospheric gas humidified by the humidifying device 202 is measured by the dew point meter 203 for the humidifying gas to confirm that the dew point is the desired point, or to quickly adjust the dew point when the dew point deviates from the desired point. be able to.

The steel sheet manufacturing equipment 1 of the present embodiment includes an in-core dew point meter 206, a dew point indicator controller 207, and a ratio setter 208. The dew point in the tropics 21 is measured, and based on this, the dew point indicator controller 207 calculates the total amount of humidifying gas required to stabilize the dew point, and each humidification is performed by the ratio determined by the ratio setting device 208. By determining the input amount for each gas input port, it is possible to smoothly control the dew point during manufacturing.

Further, in the present embodiment, since the humidifying gas can be supplied to the preceding stage as well, there is an effect of reducing the burden on the furnace body. In addition, when humidifying gas is not supplied to the previous stage, it is necessary to raise the dew point rapidly when switching the steel sheet to be manufactured from ordinary steel to high-tensile steel, and at the start of high-tensile steel plate, the ratio of the previous stage is made larger than 0. Then the ratio needs to be switched to 0. On the other hand, if the humidifying gas is also supplied to the previous stage, it is not necessary to switch the ratio at the time of passing the high-tensile steel plate, and the control can be simplified.

The steel plate manufacturing equipment 1 of the present embodiment has an in-core dew point meter 206, a dew point indicator controller 207, and a ratio setter 208, and further has three flow meters 205A, 205B, 205C, and three flow rate indicator adjusters. It has a total of 209A, 209B, and 209C. With the flow meters 205A, 205B, 205C, the flow rate before adjustment can be grasped more accurately, and the flow rate can be adjusted by the flow rate indicator regulators 209A, 209B, 209C based on the accurately grasped flow rate. .. Therefore, according to the steel sheet manufacturing equipment 1 of the present embodiment, strict dew point adjustment is possible by grasping the flow rate and adjusting the flow rate extremely accurately.

Further, the steel sheet manufacturing facility 1 of the present embodiment has a humidifying gas inlet 201A in front of the soaking tropics 21. As described above, it is effective to directly inject the humidifying gas into the latter stage of the flatulent tropics 21 by the humidifying gas inlet 201C and the humidified gas inlet 201B provided in the latter stage of the flatulent tropics 21. By providing the humidifying gas inlet 201A in the tropics 21, it is also useful for adjusting the dew point in the latter stage of the flatulence 21. In particular, when the number of humidifying gas inlets that can be provided after the solitary tropics 21 is small, it is effective to provide the humidifying gas inlets in the front stage of the soothing tropics 21. Specifically, when there are about 1 to 3 humidifying gas inlets that can be provided after the solitary tropics 21, it is particularly effective to provide the humidifying gas inlets at the front stage of the soothing tropics 21.

Further, in the manufacture of steel sheets, the type of steel sheet to be manufactured may be switched in the middle. Among the steel sheets, there are steel sheets that do not need to be charged with humidifying gas during manufacturing and steel sheets that should not be charged with humidifying gas. In particular, the humidifying gas is charged after the steel sheet that should not be charged with humidifying gas. When producing a required steel sheet (high-tensile material, etc.), it is necessary to sharply raise the dew point in the humidified tropical 21. However, it is difficult to suddenly change the dew point in the tropical 21 in the steel sheet manufacturing facility in which the humidifying gas inlet is provided only in the latter stage of the tropical 21. Since the steel sheet manufacturing facility 1 of the present embodiment has a humidifying gas input port 201A in front of the soothing tropical 21, a steel sheet (high-tensile material or the like) in which the humidifying gas must be charged after the steel sheet to which the humidifying gas should not be charged. ) Can be rapidly raised, and can be preferably applied regardless of the type of steel sheet to be switched. Examples of steel sheets that do not need to be charged with humidifying gas and steel sheets that should not be charged with humidifying gas can be exemplified by ordinary steel.

The effects of the steel sheet manufacturing equipment 1 of the present embodiment are as described above. In the above description, an example in which the humidification amount is adjusted by the flow rate of the humidified atmospheric gas is shown, but the present invention is not limited to this. For example, control may be performed to change the dew point of the humidified atmospheric gas in the first stage and the second stage. Specifically, it can be realized by changing the mixing ratio of the humidifying gas and the drying gas between the first stage and the second stage of the tropics. However, flow rate control is desirable from the viewpoint of control followability.

[Example 1]
It is a steel sheet manufacturing facility with an annealing furnace in which the heating zone, the solitary tropics, and the cooling zone are juxtaposed in this order. The length is set to 1/2 of the length in the through plate direction.) There are two humidification gas inlets, one in one place and one in the previous stage, and the humidification is injected into these humidification gas inlets. Steel sheets were manufactured using a steel sheet manufacturing facility having a flow control valve for humidifying gas that regulates the flow rate of gas and a control unit that controls the amount of humidification. Here, the composition of the steel sheet to be produced was the composition of ordinary steel and high-tensile steel.

The line speed was about 90 mpm, the target dew point was -15 ° C, and automatic control was performed to adjust the flow control valve for humidifying gas so that the dew point was within ± 5 ° C. On the other hand, the dew point fluctuated greatly unless the flow rate was controlled by the flow rate adjusting valve for humidifying gas. Based on the above, the flow rate of the humidified gas inlet, which is the first inlet for the humidified atmospheric gas, and the flow rate of the atmospheric gas to be injected into the humidified gas inlet, are adjusted. If there is a flow rate adjusting valve for humidifying gas, which is the first flow rate adjusting unit, the effect of stabilizing the dew point can be obtained. As a result, the effect of suppressing pickup defects could be enhanced by the present invention.

Further, in each case, hot-dip galvanizing was performed and alloying was performed. When the humidifying gas input amount was adjusted with the humidifying gas flow rate adjusting valve, the alloying temperature could be reduced.

[Example 2]
In Example 2, the steel sheet was manufactured by using the steel sheet manufacturing equipment shown in FIGS. 1 to 3 and the conventional steel sheet manufacturing equipment. FIG. 4 is a diagram showing the results of this embodiment, FIG. 4 (a) is a diagram showing the results of a comparative example in which a steel sheet is manufactured using a conventional steel sheet manufacturing facility, and FIG. 4 (b) is a diagram showing the results of a comparative example. It is a figure which shows the result of the invention example which manufactured the steel sheet using the steel sheet manufacturing facility shown in FIGS.

When steel sheets are manufactured using conventional steel sheet manufacturing equipment, no individual flow control valve is installed at the humidification gas inlet, and the flow rate of the dry gas before it is charged into the humidifier is adjusted to blow the humidified gas into the tropics. The amount is adjusted. As shown in FIG. 4A, the test time was set to 3 hours, and the target dew point in the furnace was set to −20 ° C. to −10 ° C. If you check the dew point trend in the furnace, you can see that there are some timings that deviate from the target dew point range in the furnace. In addition, although it is within the target dew point range in the furnace, the dew point trend fluctuates up and down within the target dew point range in the furnace, and the dew point in the furnace cannot be controlled stably.

As shown in FIG. 4 (b), when the steel sheet is manufactured by the steel sheet manufacturing equipment of FIGS. 1 to 3, the equipment configuration is such that a flow control valve is installed for each humidifying gas inlet as shown in FIG. ing. There are two humidification gas inlets in the latter part of the tropics, and each has a flow control valve. The flow rate ratio setting device was set to 40% on the front stage side and 60% on the rear stage side. The test time was set to 3 hours, and the target dew point in the furnace was set to -20 ° C to -10 ° C. If you check the dew point trend in the furnace, you can see that the dew point in the furnace is controlled within the target dew point range in the furnace. Further, at the start of dew point control, the dew point fluctuates up and down, but the dew point fluctuation gradually decreases, and it can be seen that the dew point in the furnace can be controlled stably. Therefore, it can be seen that the occurrence of pickup defects can be suppressed.

In addition, paying attention to the fact that the dew point fluctuation is larger in the latter stage, by setting the dew point observation point as the latter stage and making the control sensitivity (ratio) of the latter stage larger than that in the first stage, follow-up as shown in FIG. 4 (b). I was able to improve my sex.

When the steel sheet is manufactured by the steel sheet manufacturing equipment shown in FIGS. Therefore, the target dew point can be controlled by supplying a large amount of humidifying gas to the subsequent stage. As a result, the dew point fluctuation can be stabilized as shown in FIG. 4 (b).

1 Steel plate manufacturing equipment 2 Abrasive furnace 20 Heating zone 21 Normal tropical 22 Cooling zone 23 Throat 200 Piping 201 Humidifying gas inlet 202 Humidifying device 203 Dew point meter for humidifying gas 204 Flow control valve for humidifying gas 205 Flow meter 206 Dew point meter in furnace 207 Dew point indicator regulator 208 Ratio setter 209 Flow indicator regulator 210 Flow control valve for dry gas 211 Dry gas inlet 3 Snout 4 Molten zinc plating bath 5 Alloying equipment

Claims (5)

A heating zone, a soaking zone, and cooling zone is a galvanized production facility this have a juxtaposed annealing furnace in the order, the steel sheet subjected to galvanizing treatment to Tsuban the annealing furnace,
The first inlet for charging the humidified atmospheric gas, which is provided in the latter region where the solitary tropical steel sheet reaches 700 ° C. or higher ,
Than the subsequent regions of the soaking zone was provided before the region of the upstream side of the sheet passing direction, a second input port for introducing humidified atmosphere gas,
A first humidification amount adjusting unit that adjusts the humidification amount by inputting the atmospheric gas from the first inlet
A second humidification adjusting unit that adjusts the humidification amount by introduction of the ambient gas from the second input port,
A dew point meter provided in the latter region of the tropics,
Have a control unit which humidification amount and is adjusted humidification amount is adjusted by the first humidification adjusting unit and in the second humidification adjusting unit is controlled to be different,
The control unit
A total amount calculation unit that calculates the total amount of atmospheric gas charged into the first inlet and the second inlet based on the dew point in the latter region measured by the dew point meter and the preset target dew point. When,
Based on the calculation result in the total amount calculation unit, the first inlet and the said so that the flow rate of the atmospheric gas charged into the first inlet is larger than the flow rate of the atmospheric gas charged into the second inlet. A ratio setting device that determines the flow rate ratio of atmospheric gas at the second inlet,
Hot-dip galvanizing equipment characterized by having. The hot-dip galvanizing facility according to claim 1, wherein the target dew point is set to 25 to 0 ° C. The hot-dip galvanizing facility according to claim 1 or 2 , further comprising an alloying facility for alloying hot-dip galvanizing . Wherein, the faster line speed of the steel sheet, molten zinc according to any one of claims 1 to 3, characterized in that control is based on a correlation of increasing the amount of humidification of a subsequent stage of the soaking zone Plating equipment . Annealing the steel sheet using a hot-dip galvanizing installation according to any one of claims 1-4,
A method for manufacturing a hot-dip galvanized steel sheet in which a hot-dip galvanized steel sheet is subjected to hot-dip galvanized steel sheet .