JP2018048388A - Alloying method of molten zinc plated layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alloying method of a molten zinc plated layer that can alloy a molten zinc plated layer of a steel plate of a plurality of steel types and/or a steel plate of a different thickness in the same apparatus without lowering productivity and can alloy that of a steel plate of a steel type having a high nonmagnetic material ratio.SOLUTION: In an alloying method of a molten zinc plated layer, a steel plate H is galvanized with molten zinc and heated in an alloying furnace 7 to alloy a molten zinc plated layer. The steel plate H galvanized with molten zinc is heated in a vertical magnetic flux method (TF method) of induction heating to alloy the molten zinc plated layer of the steel plate of a steel type having a nonmagnetic material index of 40 or higher.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for alloying a hot dip galvanized layer of a steel sheet.

In a hot dip galvanizing line, which is a line for galvanizing a steel plate, the steel plate is passed through a hot dip galvanizing bath and heated to form an alloyed layer of zinc and iron on the surface layer of the hot dip galvanized layer. Heating of the steel sheet during alloying is performed by induction heating that is heated by a high-frequency current. Generally, an LF (Longitudinal Flux: parallel magnetic flux) system is adopted as induction heating (see Patent Document 1). In the LF method, a high-frequency current (primary current) is passed through an induction coil that surrounds the periphery of the steel plate, so that a magnetic flux is generated in parallel with the direction of travel of the steel plate and is generated on the surface of the steel plate in a direction that cancels this magnetic flux. As the eddy currents accumulate, an induced current is generated in a direction opposite to the primary current, thereby heating the steel sheet in a non-contact manner.
Further, as a heating method other than the LF method, a method using a high temperature gas is known.

JP-A-6-330276

  However, when heating by LF induction heating at the time of alloying after hot dip galvanizing as disclosed in Patent Document 1, a steel type (for example, high-strength steel or ultra-high-strength steel) having a higher ratio of non-magnetic material is heated. Efficiency is reduced. This is because, when it is assumed that the nonmagnetic material is uniformly present in the steel sheet, if the nonmagnetic material ratio is high, the current penetration depth of the induced current becomes large, and the penetration depth is larger than ½ of the thickness of the steel plate. This is because the induced currents generated on the front and back of the steel plate interfere with each other and no induced current is generated on the cross section of the steel plate.

In addition, high-strength steel and ultra-high-strength steel originally have a low interdiffusion rate of iron and zinc, and therefore must be alloyed at a higher temperature or at a lower temperature than mild steel.
Therefore, the alloying of high-strength steel or ultra-high-strength steel by LF induction heating is an operating condition of higher cost and lower production.
Furthermore, since the ultra-high strength steel having increased strength in recent years has a very high non-magnetic ratio, the LF method cannot be heated to a desired temperature suitable for alloying.

Furthermore, in the current steel industry, because there are many needs, there are many steel types that are sold, and it is common to produce steel sheets of multiple steel types with one line / equipment, although some orders are produced together. It is. When steel sheets of different steel types with different non-magnetic ratios are continuously galvanized and alloyed, heating with the LF method results in changes in optimum operating conditions, especially the plate feed speed, resulting in a significant loss of productivity. It becomes.
Moreover, even if it is the same steel type, when the thickness of a steel plate differs, when heating by LF system, it is necessary to change a plate passing speed.

  A heating method using a high-temperature gas known as a heating method other than the induction heating of the LF method can be heated regardless of the ratio of the non-magnetic material. However, the heating efficiency is lower than that of induction heating, and the heating method is very long. It is not realistic because it requires tropical or very slow plate speeds.

  This invention is made | formed in view of this point, and does the alloying of the hot dip galvanizing layer, without reducing productivity with respect to the steel plate of several steel types and / or various thickness steel plate with the same apparatus. An object of the present invention is to provide a method for alloying a hot dip galvanized layer, which can be alloyed with a steel sheet of a steel type having a high nonmagnetic ratio.

  In order to achieve the above object, the present invention is a method for alloying a hot dip galvanized layer, which comprises hot dip galvanizing a steel plate, heating the hot dip galvanized steel plate, and alloying the hot dip galvanized layer. The hot-dip galvanized steel sheet is heated by vertical magnetic flux induction heating, and the hot-dip galvanized layer of the steel sheet having a nonmagnetic index of 40 or more is alloyed.

  It is preferable to suppress the vibration of the steel sheet passing through the induction heating device that performs induction heating by the vertical magnetic flux method.

  According to the alloying method of the hot dip galvanized layer of the present invention, the hot dip galvanized layer is alloyed on the steel plate of a plurality of steel types and / or steel plates of various thicknesses with the same apparatus without reducing the productivity. be able to. Further, the above alloying can be performed on a steel sheet having a high nonmagnetic ratio, that is, a steel sheet having a high nonmagnetic index.

It is a figure which shows the outline of the continuous hot dip galvanizing apparatus which concerns on embodiment of this invention. It is a figure which shows the outline of the alloying heating furnace of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of a continuous hot dip galvanizing apparatus according to an embodiment of the present invention. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

In the continuous hot dip galvanizing apparatus 1 of FIG. 1, the steel plate H is introduced into the hot dip galvanizing bath 2 after being annealed in an unillustrated annealing furnace.
The steel sheet H introduced into the hot dip galvanizing bath 2 is turned upward by the sink roll 3 provided in the bath 2 and the warp is corrected by the support roll 4, and then drawn out from the hot dip galvanizing bath 2. It is.
The hot dip galvanized steel sheet H is sprayed with a wiping gas from the gas wiping nozzle 5 toward both surfaces thereof to adjust the plating adhesion amount.

The steel plate H whose plating adhesion amount is adjusted is passed through a vibration damping device 6 that suppresses vibration of the steel plate H. The damping device 6 may have a function of defining the angle of the steel sheet H with respect to the alloying heating furnace 7 in addition to the function of suppressing the vibration of the steel sheet H.
As a method for suppressing vibrations and regulating the angle by the vibration damping device 6, a method in which a high-temperature gas (for example, 450 ° C. or more) is sprayed on the end of the steel sheet H can be considered. Moreover, the system by electromagnetic force may be used.
Furthermore, for example, the roller heated to 450 ° C. or more may be in contact with the end of the steel plate H to suppress the vibration of the steel plate H and define the angle of the steel plate H. In addition, although the hot dip galvanized layer of the steel plate H is deformed by contact with a roller or the like, since the viscosity of the hot dip galvanized layer is lowered while the steel plate H is being passed through the alloying heating furnace 7, The deformed portion of the galvanized layer returns to the state before deformation. The width of the roller is, for example, 5 to 10 mm.

In addition, without providing the above-described vibration damping device 6, the vibration of the steel sheet H may be suppressed or the angle may be defined by the wiping gas from the gas wiping nozzle 5.
Further, without providing the vibration damping device 6, the intermesh amount (roll pushing amount) of the support roll 4 may be adjusted to suppress the vibration of the steel sheet H and to regulate the angle.

After passing through the vibration damping device 6, the steel plate H is heated in the alloying heating furnace 7, and is heated to, for example, 550 ± 10 ° C. until the steel plate H reaches the upper roll 8. The layer is alloyed.
The alloyed steel sheet H is cooled by a cooling device (not shown), and the sheet passing direction is changed by the upper roll 8.

  By alloying the hot-dip galvanized layer in this way, the weldability, corrosion resistance, pressability and the like of the steel sheet H can be improved.

  FIG. 2 is a diagram showing an outline of the alloying heating furnace 7, FIG. 2 (A) is a schematic side view of the alloying heating furnace 7, and FIG. 2 (B) is a sheet width of the steel plate H of the alloying heating furnace 7. It is a schematic cross section in the direction center part.

For example, as shown in FIG. 2, the alloying heating furnace 7 is provided such that E-shaped cores 71 and 72 are opposed to each other with the steel plate H interposed therebetween in a side view and a cross-sectional view.
The E-shaped cores 71 and 72 are made of a ferromagnetic core such as ferrite, laminated electromagnetic steel sheets, and amorphous alloys. In addition, the E-shaped cores 71 and 72 have induction coils 73 and 74 wound around the central convex portions 71a and 72a.

  The induction coils 73 and 74 are made of a conductor such as copper, and are connected to a power source (not shown). The magnetic flux M generated by the induction coils 73 and 74 penetrates the steel plate H in the thickness direction. In the alloying heating furnace 7, an induction current perpendicular to the magnetic flux M is generated in the plate surface of the steel plate H, and the steel plate H is heated by the induction current. That is, the alloying heating furnace 7 heats the steel sheet H by induction heating using a TF (Transverse Flux) method. In addition to the method shown in FIG. 2, the same heating effect can be obtained as long as the method generates a magnetic flux that penetrates the steel plate H in the thickness direction.

  Conventionally, since all steel types of steel sheets could be heated by LF induction heating during alloying, TF induction heating was not introduced into the alloying technology. As described above, the steel plate H is heated by TF induction heating in the alloying heating furnace 7 during alloying. Therefore, unlike the case of heating by LF induction heating, induced currents generated on the front and back of the steel sheet H do not interfere with each other. More specifically, in the case of heating by TF type induction heating, an induction current circulating in the plane direction of the steel sheet H is generated, so the induction current is the end of the steel sheet H, which is characteristic of the LF type induction heating. Unlike the induced current that goes around the part from the front surface to the back surface, no interference or cancellation occurs. Therefore, even if it is a steel type that cannot be heated by LF induction heating and has a high nonmagnetic ratio, the steel sheet H can be heated and alloyed with high efficiency.

Moreover, in the continuous hot dip galvanizing apparatus 1, not only a steel type with a high nonmagnetic material ratio but also a low steel type can be heated with high efficiency to alloy hot dip galvanizing. And the heating efficiency does not depend on the nonmagnetic material ratio. Therefore, in the continuous hot dip galvanizing apparatus 1, it is not necessary to change the sheet passing speed in accordance with the nonmagnetic material ratio of the steel plate H.
Therefore, in the continuous hot dip galvanizing apparatus 1, the hot dip galvanized layer can be alloyed with a single apparatus without reducing the productivity of steel sheets of a plurality of steel types.

Furthermore, in the continuous hot dip galvanizing apparatus 1, the steel plate H is heated by the TF induction heating in the alloying heating furnace 7, so even if the plate thickness changes, the high frequency power depends on the plate thickness of the steel plate H. If the high frequency power is changed according to the outlet temperature of the alloying heating furnace 7 measured with a radiation thermometer or the like, it is not necessary to change the plate passing speed according to the plate thickness.
Therefore, in the continuous hot dip galvanizing apparatus 1, the hot dip galvanized layer can be alloyed to a plurality of thickness steel sheets with the same apparatus without reducing the productivity.

  In addition, the form of induction heating of the TF method in the alloying heating furnace 7 is not limited to the above-described example. For example, it is a magnetic core that concentrates the magnetic flux generated from the induction coil and is provided freely in the plate width direction of the steel plate. Alternatively, TF induction heating may be performed using the core. In this case, the heating distribution in the plate width direction can be adjusted by adjusting the position of the magnetic core in the plate width direction. Therefore, since it is not necessary to change the plate passing speed according to the plate width of the steel plate, the hot dip galvanized layer can be appropriately alloyed without reducing productivity even if the plate width is changed.

  Moreover, since the continuous hot dip galvanizing apparatus 1 is provided with the vibration damping device 6, the distance between the steel sheet H and the E-shaped cores 71 and 72 in the alloying heating furnace 7 can be made constant and close, Heating to a desired temperature suitable for alloying can be performed more reliably and efficiently.

Table 1 below shows the results of calculating the temperature of the steel sheet when induction heating was performed on a plurality of steel types having different nonmagnetic ratios based on the operation results of the actual machine. The nonmagnetic material ratio is indicated by a nonmagnetic material index, which will be described later, representing the ratio, and the temperature of the steel sheet after heating is 550 ° C., which is one of the temperatures set when alloying the high-strength material. This is expressed as a ratio (%) when 100% is taken from the hot dip galvanizing bath and the temperature of the steel sheet when reaching the alloying heating furnace is 400%. The plate width is 1500 mm, the plate thickness is 0.8 mm, and the induction heating capacity is a maximum of 2000 kW. The examples show the calculation results when induction heating is performed by the TF method as in the above-described continuous hot dip galvanizing apparatus 1 and compared. The example shows the calculation result when induction heating is performed by the LF method.
Here, the non-magnetic index is given by (1−magnetic permeability) × 100. Moreover, the acquisition method of the magnetic permeability is as follows. That is, according to the standard of JIS C 2550-1: 2011 “Electromagnetic steel strip test method”, the magnetic field strength (H) and magnetic flux density (B) are measured by Epstein measurement used in the standard, and the measurement is performed. The magnetic permeability is calculated from the result and the formula of μ (magnetic permeability) = B (magnetic flux density) / H (magnetic field strength).

In Comparative Example 1, a steel sheet of a steel type having a very low nonmagnetic material ratio, that is, a nonmagnetic material index of 0, was heated by a plate feed speed of 150 m / min and LF induction heating. In Comparative Example 1, the temperature of the steel plate after passing through the alloying heating furnace, that is, the temperature of the steel plate after heating was 100%.
In Comparative Examples 2, 3, and 4, steel sheets of non-magnetic material index of 20, 40, and 80 are heated by LF induction heating, and at that time, the output from the power source used for induction heating and the plate passing speed Was the same as in Comparative Example 1. In these Comparative Examples 2, 3, and 4, the temperature of the steel sheet after heating in the alloying heating furnace was 80%, 50%, and 18%, and was not sufficiently heated.

  In Comparative Examples 5, 6, and 7, a steel sheet of a steel type having a nonmagnetic index of 20, 40, and 80 is heated by LF induction heating, and the output from the power source used for induction heating is adjusted at that time. 1 and the plate passing speed was the same as in Comparative Example 1. In Comparative Examples 5 and 6, the temperature of the steel sheet after heating in the alloying heating furnace was 100% and 99%, but in Comparative Example 7, the output was 1.5 times that in Comparative Example 1. The temperature of the steel plate after the heating was only obtained up to 25%.

  In Comparative Example 8, a steel sheet having a nonmagnetic index of 80 is heated by LF induction heating, and the output from the power source used for induction heating is 1.5 times that in Comparative Example 1, and The plate speed was set to 50 m / min, which is the lowest speed at which no problems occur during alloying. Nevertheless, in Comparative Example 8, the temperature of the steel sheet after heating in the alloying heating furnace was only obtained up to 70%.

  In Comparative Example 6, the temperature of the steel sheet after heating is almost 100% in the calculation. However, when the steel type having the same non-magnetic material ratio as Comparative Example 6 is heated by LF induction heating with an actual machine, resonance occurs. Became insufficient, and large temperature unevenness occurred in the plate width direction. Normally, optimization (matching operation) according to the non-magnetic ratio of the steel type is required, but changing the internal space (gap and width) of the coil and changing the frequency etc. for each steel type It is unrealistic and Comparative Example 6 is a measure of the post-heating temperature that can be achieved in a line that produces a single steel grade or a limited steel grade.

  In Examples 1, 2, and 3, a steel type having a nonmagnetic index of 40, 60, and 80, that is, a steel type having a high nonmagnetic ratio, was heated by TF induction heating. Further, the output from the power source used for induction heating and the plate passing speed were common among the examples. The plate passing speed was 150 m / min. In Examples 1, 2, and 3, the temperature of the steel sheet after heating in the alloying heating furnace was 100%. As described above, when the TF method is adopted for induction heating, a hot dip galvanized steel sheet can be used even if the nonmagnetic material ratio is high or the output and the plate feed speed are not changed according to the nonmagnetic material ratio. It can be heated in an alloying heating furnace to a temperature suitable for alloying.

  Moreover, unlike the case where the steel type having the same nonmagnetic index as in Comparative Example 6 is heated by LF induction heating with an actual machine, the steel type having the same nonmagnetic index as in Examples 1 to 3 is heated by TF induction with an actual machine. When heated, an appropriate resonance occurs regardless of the nonmagnetic index, that is, the nonmagnetic ratio, so that temperature unevenness does not occur in the plate width direction. Appropriate resonance occurs regardless of the non-magnetic ratio. In the LF method, the induced current flows in opposite directions on the front and back of the steel sheet, so the non-magnetic ratio increases and the current depth increases. In the TF method, the induced current flows through the entire thickness of the steel plate in parallel with the plate surface of the steel plate, so that the induced current is not canceled as in the LF method. .

  The present invention is useful for a technique for alloying a hot-dip galvanized layer of a steel sheet by TF induction heating.

DESCRIPTION OF SYMBOLS 1 ... Continuous hot dip galvanizing apparatus 2 ... Hot dip galvanizing bath 3 ... Sink roll 4 ... Support roll 5 ... Gas wiping nozzle 6 ... Damping device 7 ... Alloying furnace 71, 72 ... E-shaped core 73, 74 ... Induction Coil 8 ... Upper roll

Claims (2)

A method of alloying a hot dip galvanized layer by hot dip galvanizing a steel plate and heating the hot dip galvanized steel plate to alloy the hot dip galvanized layer,
The heating of the hot dip galvanized steel sheet is performed by induction heating of a vertical magnetic flux system,
A method of alloying a hot-dip galvanized layer, comprising alloying a hot-dip galvanized layer of a steel sheet having a nonmagnetic index of 40 or more. The method for alloying a hot-dip galvanized layer according to claim 1, wherein vibrations of the steel sheet passing through an induction heating device that performs induction heating by the vertical magnetic flux method are suppressed.

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