JP6772930B2 - Manufacturing method of hot-dip galvanized steel sheet and hot-dip galvanized steel sheet - Google Patents

Description

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

Conventionally, as a method of increasing the surface gloss of a hot-dip galvanized steel plate, a method of adding a trace metal such as Sb to a component in a hot-dip galvan bath (see Patent Document 1) or a surface roughness of a hot-dip galvanized original plate (See Patent Document 2) and a method of changing the roughness of the SK roll used in temper rolling (SK treatment) after plating (see Patent Document 3) have been proposed.

Japanese Unexamined Patent Publication No. 5-320848 Japanese Unexamined Patent Publication No. 9-263967 Japanese Unexamined Patent Publication No. 2004-143505

However, in the method proposed in Patent Document 1, it is necessary to prepare a hot-dip galvanized bath containing a trace metal such as Sb separately from a normal hot-dip zinc bath not containing a trace metal such as Sb, and depending on the steel sheet. Since it is necessary to switch between the two, there is a problem that switching loss occurs. Further, the method proposed in Patent Document 1 cannot be switched between hot-dip zinc baths unless the line is temporarily stopped, so that it is difficult to apply the method in actual operation.

Further, the methods proposed in Patent Documents 2 and 3 have a problem that the cost increases with the change to the roll having the roughness adjusted.

The present invention has been made in view of the above, and a hot-dip galvanized steel sheet having a high glossiness and a hot-dip galvanized steel sheet having a high glossiness can be manufactured easily and at low cost. It is an object of the present invention to provide a method of manufacturing the above.

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

In order to solve the above-mentioned problems and achieve the object, the method for producing a hot-dip galvanized steel sheet according to the present invention involves 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 doing.

Further, in the method for producing a hot-dip galvanized steel sheet according to the present invention, in the above invention, after the plating step, a heating step of heating the steel sheet is performed so that the temperature of the outlet side plate of the heating furnace becomes 430 ° C. to 455 ° C. It is characterized by doing.

The hot-dip galvanized steel sheet according to the present invention has a high glossiness because the orientation ratio of the (002) plane of the Zn crystal on the surface of the hot-dip galvanized layer is controlled to 45% or less. Further, according to the method for producing a hot-dip galvanized steel sheet according to the present invention, the Zn crystals on the surface of the hot-dip galvanized layer are formed by plating the steel sheet in a hot-dip zinc bath in which the aluminum concentration is controlled to 0.160% or less. The orientation ratio of the (002) surface can be controlled to 45% or less, and a hot-dip galvanized steel sheet having high gloss can be easily manufactured at low cost.

FIG. 1 is a diagram showing a main part of a hot-dip galvanized line 1 used in the method for manufacturing a hot-dip galvanized steel sheet according to an 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 glossiness of the surface of the hot-dip galvanized layer. FIG. 3 is a diagram for explaining an oblique pattern generated on 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 method for manufacturing a hot-dip galvanized steel sheet and a hot-dip galvanized steel sheet according to the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments. In addition, the components 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, the hot-dip galvanized line 1 for manufacturing the hot-dip galvanized steel sheet according to the present embodiment includes a hot-dip galvanized pot 10, a sink roll 20, a pair of support rolls 30, and a pair of wiping nozzles. It is provided with 40 and an alloying furnace 50. Then, in the method for producing a hot-dip galvanized steel sheet using the hot-dip galvanized line 1, a plating step, an adhesion amount adjusting step, and a heating step are carried out.

In the plating step, the hot-dip galvanized pot S, which has been subjected to a predetermined heat treatment in the pre-process of the plating step (not shown) and whose surface has been cleaned and activated, is passed through a snout (not shown) so as not to come into contact with the outside air. It invades the hot-dip galvanized bath 11 held in 10. Then, the steel plate S that has penetrated into the hot-dip galvanized bath 11 is changed in the transport direction substantially vertically upward by the sink roll 20 in the bath, and is pulled up from the hot-dip galvanized bath 11 by the support roll 30.

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

When producing hot-dip galvanizing, it is usually not necessary 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, which will be described later, is improved. Therefore, the steel plate S is heated (reheated) so that the temperature of the exit side plate of the alloying furnace 50 is within a predetermined range. A small amount of aluminum is added to the hot-dip zinc bath 11.

The present inventors have tried various production conditions in order to increase the glossiness of hot-dip galvanizing, and have found that there are conditions for increasing the glossiness. Further, as a result of various investigations of steel sheets having different glossiness, it was 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 crystals on the surface of the hot-dip galvanized steel sheet and the glossiness of the surface of the hot-dip galvanized layer. 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 have a higher gloss (G value) on the surface of the hot-dip galvanized layer as the orientation ratio of the (002) plane of the Zn crystal on the surface of the hot-dip galvanized layer is lower. I found that it would be. Then, for example, when "high glossiness" is defined as "glossiness (G value) of 300 or more", the (002) plane of the Zn crystal on the surface of the hot-dip galvanized layer is shown in the dot portion of the figure. It can be seen that the glossiness (G value) of the hot-dip galvanized steel sheet after production can be controlled to 300 or more by controlling the orientation ratio of 45% or less. Furthermore, as a result of diligent studies, the present inventors, in order to reduce the orientation ratio of the (002) plane of the Zn crystal on the surface of the hot-dip galvanized layer, it is necessary to reduce the aluminum concentration of the hot-dip zinc bath 11. I found a good thing.

In the present embodiment, based on the above findings, in the plating step, 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. As a result, the orientation ratio of the (002) plane of the Zn crystal on the surface of the hot-dip galvanized steel sheet after production is controlled to 45% or less, and the glossiness (G value) of the surface of the hot-dip galvanized layer is controlled. Is 300 or more. The aluminum concentration of the hot-dip 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 steel sheet is calculated by the following formula based on the diffraction peak intensity obtained by the 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 a 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 the diffraction peak intensity value (cps) of each crystal plane (hk · l) of the standard zinc powder. Further, Σ in the above formula (1) is 10 kinds of crystal planes necessary for evaluation, that is, (00.2), (10.0), (10.1), (10.2), (10.3). ), (11.0), (11.2), (20.1), (10.4), (20.3) means to sum the values for each crystal plane.

Further, the glossiness (G value) of the surface of the hot-dip galvanized steel sheet of the hot-dip galvanized steel sheet is, for example, based on "JIS Z 8741 (1997)", and the glossiness meter measures the glossiness (G value) of 60 degrees. It can be obtained by measuring.

If the aluminum concentration of the hot-dip zinc bath 11 is too low in the plating step, dross may occur in the bath, which may affect the quality. Therefore, it is desirable to control the aluminum concentration of the hot-dip zinc bath 11 to 0.100% or more.

Here, when plating is performed by controlling the aluminum concentration of the hot-dip zinc bath 11 to 0.160% or less in the plating step, an initial alloy layer formed on the surface of the steel sheet S when it invades the hot-dip zinc bath 11 is formed. It may grow and unevenness may be formed on the surface of the steel sheet S. Then, when the high-pressure gas is blown from the wiping nozzle 40 in the adhesion amount adjusting step, the unevenness grows due to the unevenness promoting effect (Bernoulli's theorem) due to the collision of the high-pressure gas. As a result, for example, as shown in FIG. 3, a plurality of diagonal patterns (wrinkles) P are formed on the surface of the steel sheet S, and the higher the operation speed, the higher the possibility that the appearance quality deteriorates.

Therefore, in the present embodiment, the heating step is carried out after the plating step. Then, in this heating step, in the alloying furnace 50, the steel plate S is heated so that the output side plate temperature of the alloying furnace 50 becomes 430 ° C. to 455 ° C. As a result, the surface of the steel sheet S is leveled and the occurrence of the diagonal pattern P as shown in FIG. 3 is suppressed. If the temperature is lower than 430 ° C, the improvement effect is insufficient, and if the temperature exceeds 455 ° C, alloying proceeds at the interface between zinc and the steel sheet S, resulting in alloyed hot-dip galvanizing. Therefore, the heating temperature is 430 ° C to 455 ° C. It is preferably in the range of ° C.

FIG. 4 shows the relationship between the heating temperature of the steel sheet S after plating (the temperature of the exit side of the alloying furnace 50) and the diagonal 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., no diagonal pattern P is formed on the surface of the steel sheet S (see “◎” on the horizontal axis). Alternatively, the diagonal pattern P can be limited to a range (see “◯” on the horizontal axis) that does not affect the quality although it is formed to some extent. On the other hand, as shown in the figure, when the steel sheet S after plating is not heated, an oblique pattern P to the extent that affects the quality is formed on the surface of the steel sheet S (see “x” on the horizontal axis).

The object of the present invention of increasing the glossiness of hot-dip galvanizing can be achieved by carrying out the above-mentioned plating step, and it is not essential to carry out the heating step. For example, even if the diagonal pattern P is formed on the steel sheet S after plating because the heating step is not performed or the heating temperature in the heating step 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 plated part. That is, in the present embodiment, in order to suppress a decrease in yield when a diagonal pattern P is generated on the steel sheet S after plating, a heating step is carried out in addition to the plating step.

After the heating step, the steel sheet S is cooled so that the molten zinc adhering to the steel sheet S solidifies, and if necessary, shape correction, chemical conversion treatment, oil coating, and the like are performed. This completes the production of the hot-dip galvanized steel sheet.

According to the method for producing a hot-dip galvanized steel sheet according to the present embodiment as described above, the steel sheet S is melted by plating the steel sheet S in 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 a high glossiness (glossiness (G value) of 300 or more) can be manufactured by controlling the orientation ratio of the (002) plane of Zn crystals on the surface of the zinc plating layer to 45% or less. can do. Further, by heating the plated steel sheet S so that the temperature of the exit side of the alloying furnace 50 becomes 430 ° C. to 455 ° C., it is possible to suppress the occurrence of defects on the surface of the steel sheet S.

Further, in the method for producing a hot-dip galvanized steel sheet according to the present embodiment, unlike Patent Document 1, it is not necessary to prepare a hot-dip galvanized bath containing a special component such as Sb, and there is no switching loss. Compared with No. 1, it is possible to easily manufacture a hot-dip galvanized steel sheet. Further, in the method for producing a hot-dip galvanized steel sheet according to the present embodiment, as in Patent Documents 2 and 3, the roughness of the finish roll during cold rolling and the roll roughness of temper rolling (SK treatment) after plating is changed. Since it is not necessary, it is possible to manufacture a hot-dip galvanized steel sheet at a lower cost as compared with Patent Documents 2 and 3.

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

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

In this embodiment, No. 1 shown in Table 1 is shown. 1-No. The above-mentioned method for producing a hot-dip galvanized steel sheet, that is, a part or all of a plating step, an adhesion amount adjusting step, and a heating step was carried out on the steel sheet of 5, and the glossiness (G value) and the presence or absence of an oblique pattern were obtained. 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. In addition, in the "diagonal pattern" column in Table 1, those with no diagonal patterns formed are marked with ◎, and those with some diagonal patterns formed but do not affect the quality are marked with ○, which affects the quality. Those with diagonal patterns formed to the extent of the effect are indicated by x.

As shown in Table 1, No. The steel sheet of No. 1 has an AL concentration in the bath, which indicates the aluminum concentration of the hot-dip zinc bath, exceeds 0.160%, and the (002) plane orientation ratio is as high as 51%, so that the glossiness (G value) is less than 300. Therefore, the target glossiness (G value) has not been reached. In addition, No. Although the steel sheet of No. 1 was not subjected to a heating step (heating in an alloying furnace) after the plating step, the diagonal pattern on the surface was not generated because the AL concentration in the bath was high.

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

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

In addition, No. In the steel plate of No. 4, No. After hot-dip galvanizing under the same plating conditions as in 2, heating was performed with the heating temperature (outside plate temperature of the alloying furnace) set to 445 ° C., and the diagonal pattern was further improved and a good appearance was obtained. ..

In addition, No. In the steel plate of No. 5, No. After hot-dip galvanizing under the same plating conditions as in 2, heating was performed with the heating temperature (outside plate temperature of the alloying furnace) set to 465 ° C., and the diagonal pattern was improved and a good appearance was obtained. As the alloying progressed, it became alloyed hot-dip galvanizing, and the plating changed to a different plating from the target hot-dip galvanizing. In this way, No. Through the experimental results of the steel plate of No. 5, it was confirmed that the heating temperature (outside plate temperature of the alloying furnace) must be 455 ° C. or lower in order to avoid alloying hot-dip galvanizing.

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

The method for producing a hot-dip galvanized steel sheet and a hot-dip galvanized steel sheet according to the present invention has been specifically described above with reference to embodiments and examples for carrying out the invention, but the gist of the present invention is limited to these descriptions. It must be broadly interpreted based on the description of the scope of claims. Needless to say, various changes, modifications, etc. based on these descriptions are also included in the gist of the present invention.

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

Claims (3)

The orientation ratio of the (002) plane of the Zn crystal on the surface of the hot-dip galvanized layer is 36% to 45 % .
A hot-dip galvanized steel sheet having a glossiness (G value) of 300 to 435. By the aluminum concentration perform plating step of immersing the steel sheet in a molten zinc bath that is controlled at 0.13 5%, and characterized in that gloss (G value) to produce a hot-dip galvanized steel sheet is 300 to 435 A method for manufacturing a hot-dip galvanized steel sheet. The method for producing a hot-dip galvanized steel sheet according to claim 2, wherein after the plating step, a heating step of heating the steel sheet is performed so that the temperature of the outlet side plate of the heating furnace becomes 430 ° C. to 455 ° C. ..

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