JP2018168435A - Galvanized steel sheet, and production method of galvanized steel sheet - Google Patents

Abstract

To provide a galvanized steel sheet having high glossiness; and to provide a production method of the galvanized steel sheet capable of producing easily and inexpensively the galvanized steel sheet having high glossiness.SOLUTION: In a galvanized steel sheet, an orientation ratio of a (002) plane of Zn crystal on the surface of a galvanized layer is 45% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hot dip galvanized steel sheet and a method for producing a hot dip galvanized steel sheet.

  Conventionally, in hot dip galvanized steel sheet, as a method of increasing the glossiness of the surface, a method of adding a trace metal such as Sb to the components in the hot dip zinc bath (see Patent Document 1), or the surface roughness of the hot dip galvanized base plate A method of adjusting the roughness (see Patent Document 2), a method of changing the roughness of the SK roll used in temper rolling after plating (SK treatment) (see Patent Document 3), and the like have been proposed.

JP-A-5-320848 JP-A-9-263967 JP 2004-143505 A

  However, in the method proposed in Patent Document 1, it is necessary to prepare a molten zinc bath containing a trace metal such as Sb separately from a normal molten zinc bath not containing a trace metal such as Sb, and depending on the steel plate. Therefore, there is a problem that switching loss occurs. Moreover, since the method proposed by patent document 1 cannot switch a molten zinc bath unless a line is once stopped, application was difficult in the actual operation.

  In addition, the methods proposed in Patent Documents 2 and 3 have a problem that the cost increases with the change to the roll whose roughness is adjusted.

  The present invention has been made in view of the above, and a hot dip galvanized steel sheet having high glossiness and a hot dip galvanized steel sheet capable of easily and inexpensively manufacturing a hot dip galvanized steel sheet having high glossiness. It is an object of the present invention to provide a manufacturing method.

  In order to solve the above-described problems and achieve the object, the hot dip galvanized steel sheet according to the present invention has a (002) plane orientation ratio of 45% or less of Zn crystal on the surface of the hot dip galvanized layer. Features.

  In order to solve the above-described problems and achieve the object, the manufacturing method of the hot dip galvanized steel sheet according to the present invention includes a plating step of immersing the steel sheet in a hot dip galvanized bath in which the aluminum concentration is controlled to 0.160% or less. It is characterized by performing.

  Moreover, the manufacturing method of the hot dip galvanized steel sheet which concerns on this invention is a heating process which heats the said steel plate so that the exit side plate temperature of a heating furnace may become 430 degreeC-455 degreeC after the said plating process in the said invention. It is characterized by performing.

  The hot-dip galvanized steel sheet according to the present invention has high glossiness because the orientation ratio of the (002) plane of Zn crystals on the surface of the hot-dip galvanized layer is controlled to 45% or less. Moreover, according to the manufacturing method of the hot dip galvanized steel sheet which concerns on this invention, by plating a steel plate with the hot dip zinc bath which controlled aluminum concentration to 0.160% or less, Zn crystal | crystallization on the surface of a hot dip galvanized layer is carried out. The orientation ratio of the (002) plane can be controlled to 45% or less, and a hot dip galvanized steel sheet having a high glossiness can be produced easily and at low cost.

Drawing 1 is a figure showing the important section of hot dip galvanizing line 1 used for the manufacturing method of the hot dip galvanized steel sheet concerning the embodiment of the present invention. FIG. 2 is a graph showing the relationship between the orientation ratio of the (002) plane of Zn crystals on the surface of the hot dip galvanized steel sheet and the surface gloss of the hot dip galvanized steel sheet. FIG. 3 is a diagram for explaining an oblique pattern generated in the steel plate. FIG. 4 is a graph showing the relationship between the heating temperature of the steel sheet after plating and the oblique pattern.

  A hot-dip galvanized steel sheet and a method for producing a hot-dip galvanized steel sheet according to the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

  As shown in FIG. 1, a hot dip galvanizing line 1 for producing a hot dip galvanized steel sheet according to the present embodiment includes a hot dip galvanizing pot 10, a sink roll 20, a pair of support rolls 30, and a pair of wiping nozzles. 40 and an alloying furnace 50. And in the manufacturing method of the hot dip galvanized steel plate using this hot dip galvanizing line 1, a plating process, an adhesion amount adjustment process, and a heating process are implemented.

  In the plating step, the hot-dip zinc pot is passed through the inside of a snout (not shown) so that the steel plate S, which has been subjected to a predetermined heat treatment before the plating step (not shown) and whose surface is cleaned and activated, is not exposed to the outside air. 10 enters the molten zinc bath 11 held at 10. Then, the steel sheet S that has entered the molten zinc bath 11 is changed in the direction of conveyance substantially vertically upward by the sink roll 20 in the bath, and pulled up from the molten zinc bath 11 by the support roll 30.

  Subsequently, in the adhesion amount adjusting step, by blowing high-pressure gas from the wiping nozzle 40 to the steel sheet S immediately after being pulled up from the molten zinc bath 11, the excess molten zinc adhering to the steel sheet S is squeezed downward. The zinc adhesion amount of the steel sheet S is adjusted.

  When manufacturing hot dip galvanizing, it is usually unnecessary to use the alloying furnace 50 which is a subsequent heating step (reheating step), but in this embodiment, the oblique pattern on the surface of the steel sheet S to be described later is improved. Therefore, the steel sheet S is heated (reheated) so that the outlet side plate temperature of the alloying furnace 50 falls within a predetermined range. A small amount of aluminum is added to the molten zinc bath 11.

  In order to increase the glossiness of hot dip galvanizing, the present inventors have tried various production conditions and found that there are conditions that increase the glossiness. Further, as a result of various investigations of steel sheets having different glossiness levels, it has been newly found that the glossiness has a correlation with the orientation ratio of the (002) plane.

  Here, FIG. 2 shows the relationship between the orientation ratio of the (002) plane of Zn crystal on the surface of the hot dip galvanized layer and the glossiness of the surface of the hot dip galvanized layer in the hot dip galvanized steel sheet. The horizontal axis represents the orientation ratio of the (002) plane, and the vertical axis represents the glossiness (G value).

  As shown in FIG. 2, the present inventors show that the lower the orientation ratio of the (002) plane of the Zn crystal on the surface of the hot dip galvanized layer, the higher the glossiness (G value) of the surface of the hot dip galvanized layer. I found out that For example, when “high glossiness” is defined as “glossiness (G value) of 300 or more”, the (002) plane of Zn crystal on the surface of the hot dip galvanized layer as shown in the dot portion of FIG. It can be seen that the glossiness (G value) of the hot-dip galvanized steel sheet after manufacture can be controlled to 300 or more by controlling the orientation ratio of the steel sheet to 45% or less. Furthermore, as a result of intensive studies, the inventors have reduced the aluminum concentration of the molten zinc bath 11 in order to reduce the orientation ratio of the (002) plane of Zn crystals on the surface of the hot dip galvanized layer. I found a good thing.

  In this embodiment, based on the above knowledge, in the plating process, the steel sheet S is immersed in the hot dip zinc bath 11 in which the aluminum concentration is controlled to 0.160% or less to perform plating. Thereby, the orientation ratio of the (002) plane of the Zn crystal on the surface of the hot dip galvanized layer of the hot dip galvanized steel sheet after manufacture is controlled to 45% or less, and the glossiness (G value) of the surface of the hot dip galvanized layer. Becomes 300 or more. The aluminum concentration in the molten zinc bath 11 is more preferably 0.140% or less.

  Here, the orientation ratio R (hk · l) of the (002) plane of the Zn crystal on the surface of the hot dip galvanized layer of the hot dip galvanized steel sheet is based on the diffraction peak intensity obtained by X-ray diffraction measurement. It can be defined as (1).

R (hk · l) = [I (hk · l) / Is (hk · l)] / Σ [I (hk · l) / Is (hk · l)] (1)

  However, in the above formula (1), I (hk · l) is the diffraction peak intensity value (cps) of each crystal plane (hk · l) of the hot-dip galvanized layer obtained by X-ray diffraction measurement, and Is ( hk · l) is a diffraction peak intensity value (cps) of each crystal plane (hk · l) of the standard zinc powder. In addition, Σ in the above formula (1) is ten kinds of crystal planes necessary for the evaluation, that is, (00 · 2), (10 · 0), (10 · 1), (10 · 2), (10 · 3). ), (11.0), (11.2), (20.1), (10.4), (20.3) means summing up the values for the crystal planes.

  Further, the glossiness (G value) of the surface of the hot dip galvanized steel sheet is 60 degrees specular glossiness (G value) with a gloss meter based on, for example, “JIS Z 8741 (1997)”. It can be obtained by measuring.

  In the plating step, if the aluminum concentration of the molten zinc bath 11 is too low, dross is generated in the bath, which may affect the quality. Therefore, it is desirable to control the aluminum concentration of the molten zinc bath 11 to 0.100% or more.

  Here, when plating is performed while controlling the aluminum concentration of the molten zinc bath 11 to 0.160% or less in the plating step, the initial alloy layer formed on the surface when the steel sheet S enters the molten zinc bath 11 is formed. In some cases, the surface of the steel sheet S grows and irregularities are formed. Then, when the high pressure gas is blown from the wiping nozzle 40 in the adhesion amount adjusting step, the unevenness grows by the unevenness promotion effect (Bernoulli's theorem) due to the collision of the high pressure gas. Thereby, as shown in FIG. 3, for example, a plurality of diagonal patterns (wrinkles) P are formed on the surface of the steel sheet S, and the possibility that the quality of appearance decreases as the operation speed increases.

  Therefore, in this embodiment, the heating process is performed after the plating process. In this heating step, the steel sheet S is heated in the alloying furnace 50 so that the outlet side plate temperature of the alloying furnace 50 is 430 ° C to 455 ° C. Thereby, the surface of the steel plate S is leveled, and the occurrence of the oblique pattern P as shown in FIG. 3 is suppressed. If the temperature is lower than 430 ° C., the improvement effect is insufficient, and if it exceeds 455 ° C., alloying proceeds at the interface between the zinc and the steel sheet S, resulting in alloyed hot dip galvanizing, so the heating temperature is 430 ° C. to 455 ° C. It is preferable to make it into the range of ° C.

  FIG. 4 shows the relationship between the heating temperature of the steel sheet S after plating (the temperature at the outlet side of the alloying furnace 50) and the oblique pattern P formed on the surface of the steel sheet S. As shown in the figure, by controlling the heating temperature of the steel sheet S after plating to 430 ° C. to 455 ° C., is there no oblique pattern P formed on the surface of the steel sheet S (see “◎” on the horizontal axis)? Alternatively, although the diagonal pattern P is formed to some extent, it can be kept within a range that does not affect the quality (see “◯” on the horizontal axis). On the other hand, as shown in the figure, when the steel plate S after plating is not heated, an oblique pattern P that affects the quality is formed on the surface of the steel plate S (see “X” on the horizontal axis).

  In addition, the objective of this invention of raising the glossiness of hot dip galvanization can be achieved by implementing the above-mentioned plating process, and implementation of a heating process is not essential. For example, even if the diagonal pattern P is formed on the plated steel sheet S because the heating process is not performed or the heating temperature in the heating process is outside the range of 430 ° C. to 455 ° C., the diagonal pattern P is generated. It can be used as a product by cutting off the part. That is, in this embodiment, in order to suppress the yield fall when the diagonal pattern P generate | occur | produces in the steel plate S after plating, in addition to a plating process, a heating process is implemented.

  After the heating step, the steel sheet S is cooled so that the molten zinc adhering to the steel sheet S is solidified, and subjected to processing such as shape correction, chemical conversion treatment, and oil coating as necessary. Thereby, manufacture of a hot dip galvanized steel plate is completed.

  According to the manufacturing method of the hot dip galvanized steel sheet according to the present embodiment as described above, the steel sheet S is melted by plating with the hot dip zinc bath 11 in which the aluminum concentration is controlled to 0.160% or less. A hot-dip galvanized steel sheet having high glossiness (glossiness (G value) of 300 or more) can be controlled by controlling the orientation ratio of the (002) plane of Zn crystals on the surface of the galvanized layer to 45% or less. can do. Moreover, it can suppress that the defect generate | occur | produces on the surface of the steel plate S by heating the steel plate S after plating so that the delivery side plate temperature of the alloying furnace 50 may be 430 degreeC-455 degreeC.

  Moreover, since the manufacturing method of the hot dip galvanized steel sheet which concerns on this embodiment does not need to prepare the hot dip zinc bath containing special components like Sb like patent document 1, and there is no switching loss, patent documents Compared with 1, hot-dip galvanized steel sheet can be easily manufactured. Furthermore, the manufacturing method of the hot dip galvanized steel sheet according to the present embodiment changes the roughness of the finish roll during cold rolling and the roll of temper rolling after plating (SK treatment) as in Patent Documents 2 and 3. Since it is not necessary, it is possible to manufacture a hot-dip galvanized steel sheet at a lower cost than Patent Documents 2 and 3.

  Further, in the hot-dip galvanized steel sheet manufactured by the method for manufacturing a hot-dip galvanized steel sheet according to the present embodiment, the orientation ratio of the (002) plane of Zn crystal on the surface of the hot-dip galvanized layer is controlled to 45% or less. Therefore, it has high glossiness (glossiness (G value) of 300 or more).

  Hereinafter, the effect of the present invention will be described while comparing the present invention example that satisfies the constituent requirements of the present invention with the comparative example that does not satisfy the constituent requirements of the present invention.

  In this example, No. 1 shown in Table 1 was used. 1-No. The steel sheet of No. 5 is subjected to part or all of the manufacturing method of the hot dip galvanized steel sheet, that is, the plating step, the adhesion amount adjusting step, and the heating step, and the glossiness (G value) and the presence or absence of an oblique pattern Evaluation was performed. In Table 1, the underline shown below the numerical value indicates that the numerical value satisfies the constituent requirements of the present invention. Also, in the column of “oblique pattern” in Table 1, “◎” indicates that no oblique pattern is formed, and “◯” indicates that the oblique pattern is slightly formed but does not affect the quality. An object having an oblique pattern is shown by x.

  As shown in Table 1, no. Steel plate No. 1 has an aluminum concentration in the bath that indicates the aluminum concentration in the molten zinc bath of more than 0.160%, and the (002) plane orientation ratio is as high as 51%, so the glossiness (G value) is less than 300. And the target glossiness (G value) has not been reached. In addition, No. Although the heating process (heating in an alloying furnace) is not performed after the plating process, the steel sheet No. 1 has a high AL concentration in the bath, and therefore has no oblique pattern on the surface.

  Next, no. Steel plate No. 2 was hot dip galvanized with the AL concentration in the bath indicating the aluminum concentration of the hot dip bath being 0.160% or less, and the (002) plane orientation ratio was 40%, and the glossiness (G value) ) Achieved over 300. However, when the line speed (steel sheet conveying speed) was set to 80 mpm and heating was not performed in the alloying furnace, an oblique pattern to the extent that the quality was affected was generated. Therefore, no. When using the steel plate No. 2, it was necessary to cut off the portion where the diagonal pattern was generated, and the yield decreased.

  The present inventors diligently studied a method using an alloying furnace as a method of improving the oblique pattern generated when the AL concentration is lowered as described above. As a result, no. In the case of steel plate 3, After hot-dip galvanizing under the same plating conditions as in No. 2, heating was performed at a heating temperature of 430 ° C. in the heating process (alloying plate temperature of the alloying furnace), and the oblique pattern was improved to such an extent that the quality was not affected. .

  No. In the steel plate No. 4, no. After hot dip galvanizing under the same plating conditions as in No. 2, heating was performed at a heating temperature in the heating step (alloying plate temperature of the alloying furnace) of 445 ° C., and the oblique pattern was further improved and a good appearance was obtained. .

  In addition, No. In the case of steel plate No. 5, no. After hot dip galvanization under the same plating conditions as in No. 2, heating was performed at a heating temperature in the heating process (outside plate temperature of the alloying furnace) of 465 ° C., but the oblique pattern improved and a good appearance was obtained. As a result, alloying progressed and alloyed hot dip galvanizing was achieved, and the plating was changed to a plating different from the intended hot dip galvanizing. Thus, no. Through the experimental results of No. 5 steel plate, it was confirmed that the heating temperature (outside plate temperature of the alloying furnace) had to be 455 ° C. or lower in order to avoid alloying hot dip galvanization.

  As described above, when the line speed is increased by carrying out the heating process after the plating process, the problem that an oblique pattern tends to appear on the surface of the hot dip galvanized layer is solved. It was confirmed that the occurrence of was suppressed.

  As mentioned above, although the hot-dip galvanized steel sheet and the manufacturing method of the hot-dip galvanized steel sheet according to the present invention have been specifically described by the embodiments and examples for carrying out the invention, the gist of the present invention is limited to these descriptions. Rather, it should be construed broadly based on the claims. Needless to say, various changes and modifications based on these descriptions are also included in the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Hot dip galvanizing line 10 Hot dip pot 11 Hot dip zinc bath 20 Sink roll 30 Support roll 40 Wiping nozzle 50 Alloying furnace S Steel plate

Claims (3)

  A hot dip galvanized steel sheet, wherein the orientation ratio of the (002) plane of Zn crystals on the surface of the hot dip galvanized layer is 45% or less.   A method for producing a hot dip galvanized steel sheet, comprising performing a plating step of immersing the steel sheet in a hot dip galvanizing bath whose aluminum concentration is controlled to 0.160% or less.   The method for producing a hot-dip galvanized steel sheet according to claim 2, wherein a heating process for heating the steel sheet is performed after the plating process so that the outlet side plate temperature of the heating furnace is 430 ° C to 455 ° C. .

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