KR19980702926A - Zinc and zinc-alloy hot-dip galvanized steel sheet with few empty spots and excellent coating adhesion and manufacturing method thereof - Google Patents

Abstract

Zinc and zinc-alloy hot-dip steel sheets and galvanized zinc and zinc-alloy hot-dip steel sheets for use in automobiles, and methods for producing these steel sheets. Zinc and zinc-alloy hot-dip galvanized steel sheets with an oxide of an element that can be easily oxidized directly under the coating and exhibit a reduced number of vacant spots and good coating adhesion. According to the method, during hot rolling the cooling is performed at a slow-cooling rate so that the temperature for coiling is set at 600 ° C. or higher and the oxide is maintained after the subsequent steps.

Description

Zinc and zinc-alloy hot-dip galvanized steel sheet with few empty spots and excellent coating adhesion and manufacturing method thereof

Zinc and zinc-alloy hot-dip galvanized steel sheets are mainly used in automobile bodies because of their low cost and good corrosion resistance, and in addition to the corrosion resistance due to coating, coating adhesion during press working is required to apply the steel sheet to automobile bodies. When the coating adhesion deteriorates, the coated layers are peeled off in powder or mass, which sometimes causes galling in press molding or degrades the corrosion resistance of the parts where the coating layers are peeled off; Stripped fragments also adversely scratch the steel sheet.

As a prior art for improving the coating adhesion, Japanese Patent Laid-Open No. 61-276961 discloses a technique in which Zn and Fe are alloyed after zinc hot dip coating at a high temperature of 700 to 850 ° C. However, at high temperatures, the alloy not only leads to high costs but also to increased costs for installations such as rolls.

Further, in Japanese Patent Laid-Open No. 3-232926, the steel contains at least one of Zr, La, Ce, Y, and Ca, and the cooling rate from recrystallization annealing to coating is 50 ° C. It is set to / sec or more. The cost increases due to the addition of Zr to the steel and the productivity decreases because the cooling capacity has to decrease the sheet feed rate.

In Japanese Patent Laid-Open No. 2-163356, O, Al, and N contents in the steel are set to 0.0045% by weight or less, (25 x N% by weight) to 0.15% by weight, and 0.0030% or less, respectively. Moreover, limitations on Ti, Si, and P contents, and Si (wt%) + P (wt%)> Ti (wt%) must be satisfied according to Japanese Patent Laid-Open No. 6-81101. In any case, the desired steel sheet properties, such as strength and elongation, cannot always be achieved by this content limitation, and there is a possibility that coating adhesiveness will be degraded due to errors in certain composition ranges.

In Japanese Patent Laid-Open No. 4-333552, coating adhesion is improved by performing Ni pre-plating before plating. In general, however, continuous plating lines (hereinafter referred to as CGL) do not have such equipment, and a large investment cost is required to improve the equipment and the like.

On the other hand, automobile bodies are required to be lighter due to recent regulations on exhaust gas. The thinning of the steel sheet is a method for lightening the automobile body. According to this method, it is necessary to increase the steel sheet strength corresponding to the thickness reduction in order to ensure safety. Therefore, high tensile strength steel sheet has been developed to strengthen the steel sheet by increasing the steel content of elements such as Si, Mn, and P. Since automotive steel sheets are press formed, good material properties are required with high r-values (high Lankford values), in particular the addition of these elements is essential for high tensile strength steel sheets.

In the case of zinc plated coating of such steel sheets, recrystallization annealing at a high temperature of about 700 to 900 ° C. is necessary to obtain excellent material properties. In CGL, recrystallization annealing is generally carried out in a nitrogen atmosphere in the presence of hydrogen (hereinafter referred to as reducing annealing), which is a reducing atmosphere for Fe, but with some elements such as Si, Mn, and P Against oxidizing atmosphere. Thus, elements such as Si, Mn, and P, which are more oxidative than Fe (referred to as the easily oxidized element), diffuse outward during reduction annealing and are bonded to oxygen on the surface of the steel sheet to refer to oxides (called surface separation layers). ). Since these oxides significantly inhibit the wettability between the molten zinc and the steel sheet, so-called empty spots, that is, defects that occur when zinc does not adhere to the steel sheet, appear.

In order to overcome this problem, Japanese Patent Laid-Open No. 61-9386 proposes a method of preplating the surface of the steel sheet with Ni before the zinc hot dip coating process. According to this method, however, at least 10 g / m 2 of Ni plating when the steel contains at least Si and at least one element from 0.2 to 2.0 wt% of Si, 0.5 to 2.0 wt% of Mn, and 0.1 to 20 wt% of Cr. This is necessary and results in increased costs. In addition, while this large amount of Ni plating improves the wettability between the zinc hot-dip coating and the steel sheet, unfortunately, defects caused by Si and Ni on the coated surface frequently appear during the alloying process.

For example, Japanese Patent Laid-Open No. 57-70268 proposes a method of preplating the surface of a steel sheet with Fe before the zinc hot dip coating process. According to this method, empty spots in the Si-containing steel can be prevented by preplating, but more than 5 g / m 2 of Fe plating is required, which is extremely uneconomical.

In addition, other methods are disclosed in Japanese Patent Laid-Open Nos. 55-122865 and 4-254531. In these methods, the steel sheet is oxidized in advance to form a Fe oxide film on the surface of the steel sheet, followed by reduction annealing. However, according to these methods, alloying elements such as Si are separated on the surface and an oxide film is formed due to excessive reduction during reduction annealing, which causes a problem of poor coating. In order to prevent such excessive reduction, a large amount of Fe oxide is required. However, if the amount of the Fe oxide film is very large, the Fe oxide film is peeled off due to rolling or the like, and conversely, an insufficient surface coating or working side effect is produced because a surface separation layer is produced and fragments of the peeled Fe oxide film are scattered in the furnace. Brings about.

In addition, in connection with known proposals for steel compositions and hot rolling conditions for zinc hot-dip coating of high tensile steel sheets, Japanese Patent Publication No. 6-158172 contains Si ≦ 0.2 and Mn ≦ 1.5 by weight. A method of winding a steel at a temperature of at least 650 ° C. followed by pickling, cold rolling, annealing, and zinc hot dip coating is disclosed. In Japanese Patent Laid-Open No. 6-179943, a steel containing 0.10 to 1.5% by weight of Si and 1.00 to 3.5% by weight of Mn is wound at a temperature of 500 ° C. to 680 ° C. including a positive limit, followed by pickling, cold rolling, and annealing. Rings and methods of zinc hot dip coating are disclosed.

These methods provide specific process conditions, such as steel composition and hot rolling conditions, for a series of manufacturing steps, but cannot inhibit surface separation layers formed during reducing annealing or improve empty spot or coating adhesion.

The present invention relates to zinc and zinc-alloy hot-dip galvanized steel sheets with few bare spots and excellent coating adhesion, and a method of manufacturing the same.

1 is an EPMA analysis chart of oxide observed just below the scale during hot rolling.

FIG. 2 is a graph showing the results of elemental analysis of conventional unannealed cold rolled steel sheets, the analysis being performed by GDS up to about 10 μm in the depth direction from the surface.

3 is an element analysis result of the annealing cold rolled steel sheet of the present invention, a graph showing an element analysis result performed by GDS up to about 10 μm in the depth direction from the surface.

4 is an element analysis result of a conventional annealed cold rolled steel sheet, a graph showing the result of the element analysis performed by GDS up to about 10 ㎛ in the depth direction from the surface.

5 is an elemental analysis result of the annealed cold rolled steel sheet of the present invention, a graph showing the result of the elemental analysis performed by GDS up to about 10 μm in the depth direction from the surface.

FIG. 6 is a cross-sectional optical micrograph taken at magnification x1,000, showing an oxide located directly below the scale of a hot rolled sheet of one embodiment. FIG.

FIG. 7 is a cross-sectional optical micrograph taken at magnification x1,000, showing an oxide located just below the scale of a conventional hot rolled sheet.

FIG. 8 is a cross-sectional optical micrograph taken at a magnification x1,000 showing an oxide-zinc alloy galvanized steel sheet containing an example.

9 is a cross-sectional optical micrograph taken at a magnification x1,000 showing a conventional zinc alloyed hot dip galvanized steel sheet containing no oxides.

FIG. 10 is an SEM photograph taken at a magnification x1,500 showing the steel sheet of the example in which the coating layer was dissolved.

FIG. 11 is a SEM photograph taken at magnification x15,000, showing a conventional steel sheet with a coating layer dissolved therein. FIG.

Explanation of symbols for main parts of the drawings

1. Untreated steel sheet 2. Scale

3. oxide 4. coating layer

5. Oxide

As a result of detailed experiments, the inventors of the present invention have found that by providing an oxide of an element that can be easily oxidized directly under the coating layer of zinc and zinc-alloy hot-dip coated steel sheets, the spot and coating adhesion are greatly improved.

In other words, the present invention provides zinc and zinc-alloy hot-dip steel sheets with oxides of elements that can be easily oxidized directly under the coating layer.

Moreover, in the zinc and zinc-alloy hot dip steel sheets, the oxygen concentration is preferably 1 ppm or more, more preferably 2 to 2 in the region up to 3 μm deep in the sheet-thickness direction in the surface layer of the steel sheet substrate immediately below the coating layer. 200 ppm, and more preferably 3 to 100 ppm.

In addition, this hot dip galvanized steel sheet is preferably heat-alloyed after zinc hot dip coating, whereby excellent zinc alloyed and zinc-alloy hot dip steel sheet is obtained. In addition, in the zinc alloyed and zinc-alloy hot dip steel sheets, the oxygen concentration is preferably 1 ppm or more, more preferably 2 to 2 in a region up to 3 μm deep in the sheet-thickness direction in the surface layer of the steel sheet substrate immediately below the coating layer. 200 ppm, and more preferably 3 to 100 ppm.

In addition, each zinc and zinc-alloy hot dip steel sheet and alloyed zinc and zinc-alloy hot dip steel sheet preferably contain at least one element selected from Si, Mn, and P as steel components in the following ranges:

0.001 ≤ Si ≤ 3.0 wt%

0.05 ≤ Mn ≤ 2.0 wt%

0.005 ≤ P ≤ 0.2 wt%

In addition, the present invention provides a method for producing the above-mentioned zinc and zinc-alloy hot-dip steel sheet or alloyed zinc-alloy hot-dip steel sheet which exhibits reduced number of empty spots and excellent coating adhesion. In other words, the present invention provides a method consisting of the following steps:

Step A for forming oxide directly under the scale, while coiling the hot rolled steel strip, the temperature of the steel strip is set to at least 600 ° C. and the average slow-cool rate to 540 ° C. (CT-540) Forming an oxide from an element that can be more oxidized than iron by setting it to ^0.9 ÷ 40 (° C./min) or less; And

Step B for zinc and zinc-alloy hot-dip coating of steel strips. According to this method, step B follows step A and the remaining steps can also be used between steps A and B. In general, steps such as pickling, degreasing, cold rolling, annealing and the like can be suitably used as this intermediate step.

In addition, according to the process of the present invention, the oxide formed in step A is preferably maintained until the treatment carried out in the annealing furnace immediately before step B after the pretreatment step carried out after step A.

Further, according to these methods, the hot rolled slab preferably contains at least one element selected from Si, Mn, and P as steel components in the following ranges:

0.001 ≤ Si ≤ 3.0 wt%

0.05 ≤ Mn ≤ 2.0 wt%

0.005 ≤ P ≤ 0.2 wt%

Moreover, according to the above-mentioned method, zinc alloyed zinc and zinc-alloy hot dip steel sheets can be produced using heat-alloying after step B.

Next, an oxide of an easily oxidizable element located directly below the coating layer will be described.

These oxides of easily oxidizable elements are formed during hot rolling, in particular, oxides are grown during coiling when the temperature is high (hereinafter referred to as CT) and the cooling rate after coiling is low.

Oxides formed during hot rolling are observed just below the scale, as shown in FIG. 6. On the other hand, in the conventional hot rolled sheet, as shown in Fig. 7, no oxide is observed just below the scale. Oxides observed during hot rolling are analyzed using an electron probe microanalyzer (hereafter referred to as EPMA) and the results are shown in FIG. 1. Since Mn, P, Al, and O show peaks, it is understood that oxides of these elements are formed. The steel plates shown in FIGS. 6 and 1 contain 0.1 wt% Mn, 0.006 wt% P, and 0.03 wt% Al, and they do not contain particularly high amounts of Mn, P, or Al.

The zinc hot-dip steel sheet or galvanized zinc hot-dip steel sheet of the present invention is manufactured so that an oxide formed directly under the scale during the hot rolling process is maintained even after a post-treatment step such as pickling and coating.

The mechanism for producing oxide directly below the scale is as follows: In a scale layer consisting essentially of iron oxide formed during hot rolling, oxygen diffuses internally into the steel during or after the coiling process and then forms an oxide of an element that can be easily oxidized in the steel. Form. Thus, oxides are formed even when only traces of easily oxidizable elements are contained in the steel.

Oxides of elements that may be more oxidized than iron are present directly below the zinc and zinc-alloy melt coatings according to the invention, but oxides of elements that may be less oxidized than iron oxide or iron may also be contained. In addition, such an oxide is preferably formed at the grain boundaries of the hot rolled steel sheet.

As a result of studies and investigations conducted on various types of steel sheets, the inventors of the present invention have found oxides of Si-O, Mn-O, Al-O, P-O, and Fe-Si-O in the steel sheets.

FIG. 2 shows the results of elemental analysis for a conventional steel sheet and FIG. 3 shows the results of an annealed cold rolled steel sheet in which oxides were observed. The analysis was performed here by glow-discharge spectroscopy (hereinafter referred to as GDS) in the region up to about 10 μm in the depth direction at the surface of each steel sheet. The peaks of Mn, Al, P, and O observed at depths of about 0.3 to 4 μm in the surface layer correspond to oxides.

FIG. 4 shows the results of elemental analysis for the conventional steel sheet, and FIG. 5 shows the results of the annealed cold rolled steel sheet in which oxides were observed. The analysis was performed here by GDS in the region up to about 10 μm in the depth direction from the surface of each steel sheet. A large amount of surface separation material produced by reduction annealing is observed in the conventional steel sheet of FIG. 4, while the production of surface separation products in the steel sheet with oxides produced during hot rolling is suppressed and not observed at all.

Next, the oxide of the present invention present in the steel sheet surface layer directly below the coating layer (the surface layer of the steel sheet substrate) can be observed by optical-microscopy by etching the steel sheet with a 1% nital solution for a few seconds to several tens of seconds.

8 (photo) and 9 (photo) respectively show a conventional zinc alloyed hot-dip steel sheet containing no oxide and an alloyed zinc hot-dip steel sheet containing oxides of the present invention. 8 and 9 are cross-sectional optical micrographs of a zinc alloyed galvanized steel sheet taken at a magnification x1,000. The black ribbon-like material observed just below the coating layer is an oxide (indicated by arrow).

In addition, the formation of oxides can also be confirmed by analyzing the oxygen contained in the steel. Regarding the technique, after coiling, a steel sheet obtained by dissolving only a coating layer of a hot rolled steel sheet, a zinc and zinc-alloy hot-dip steel sheet, in which the scale layer has been removed by pickling, a cold rolled steel sheet, or an annealed sheet Analyzing the oxygen in the steel in the entire sheet-thickness direction using the method, and comparing the numerical value obtained with the numerical value of the steel sheet obtained by polishing the surface layer on which the oxide is formed. Compared to the value of the polished sheet, the steel sheet on which the oxide is formed has a higher oxygen value analyzed in the entire sheet-thickness direction.

Next, a mechanism for improving coating adhesion with the vacant spot by forming an oxide directly under the coating layer will be studied.

Initially, with respect to the improvement in the empty spot, as mentioned above, the surface separation of elements that can be easily oxidized when oxides are produced just below the scale by internal oxygen diffusion during or after coiling is CGL. Was found to be inhibited during reduction annealing at.

This phenomenon is believed to be due to:

The amount of elements that can be easily oxidized in the surface layer is reduced because the elements that can be easily oxidized are already precipitated as oxides during or after coiling; The oxide formed prevents the transition (external diffusion) of elements that can be easily oxidized from the bulk steel to the steel plate surface; Oxidation-reduction takes place inside the steel sheet, in other words, the Fe-containing oxide produced during or after coiling is converted into an oxide of an element that can be easily oxidized during reduction annealing.

Therefore, the surface separation material of the element which can be easily oxidized is greatly reduced, thereby significantly improving the empty spot. This material here inhibits the wettability between the molten zinc and the steel sheet.

Next, the coating adhesion will be explained.

It is known that the coating peels off mainly due to tack stress during press molding.

Since the coating layer, i.e., the steel sheet with an oxide directly under the steel sheet of the present invention, has a space between the oxide crystals, zinc penetrates into the steel sheet more easily than the conventional steel sheet containing no oxide. As a result, the interface between the coating layer and the steel sheet is considerably roughened so that the coating layer can be adhered to the steel sheet densely. As a result, both the hot dip galvanized steel sheet and the galvanized zinc hot dip steel sheet according to the present invention obtain excellent coating adhesion during press molding.

10 and 11 show the coating of the steel sheet to expose the steel sheet in accordance with the galvanostatic process (4% methyl salicylate, 1% salicylic acid, and 10% potassium iodide / methanol solution; 5 cc / cm 2). The observation result obtained by using SEM from the steel plate which was forcibly dissolved by the potential is shown. It is understood that the interface between the coating layer and the steel sheet is apparently rougher compared to conventional steel sheets that do not contain oxides.

In addition, the technique disclosed by the present invention has a better effect when the steel sheet contains at least one component selected from Si, Mn, and P as steel components in the following ranges:

0.001 ≤ Si ≤ 3.0 wt%

0.05 ≤ Mn ≤ 2.0 wt%

0.005 ≤ P ≤ 0.2 wt%

Problems such as empty spots and reduced coating adhesion do not occur at all in the steel sheet containing no such elements, so the lower limits for these elements are preferably 0.001% by weight for Si, 0.05% by weight for Mn, and P 0.005% by weight. On the other hand, the upper limit for each element is determined in consideration of the preferred range for both the maximum effect on reinforcement and expense.

In addition, the technique disclosed by the present invention shows that zinc and zinc-alloy hot-dip steel sheets in which a small amount of oxides are etched by 1% nital have sufficient effects on both the empty spot and the coating adhesion even when observed by optical microscope in cross section. Indicates.

In addition, the oxygen analysis of the steel shows a sufficient effect, especially on the spot and coating adhesion, which is empty when the value of the following equation is more than 1 ppm:

(Oxygen in steel sheet with coating removed by hydrochloric acid and antimony method)-(Oxygen in steel sheet with coating surface removed by hydrochloric acid and antimony method and then the surface layer was polished to remove 3 μm of the surface layer)

Next, the manufacturing technique of the coated steel sheet described above will be disclosed. The high temperature for coiling after hot rolling and slow cooling after coiling is required. Details are as follows.

The temperature for coiling after hot rolling should be 600 ° C or higher to produce oxide, and the cooling rate up to 540 ° C after coiling should be below the following conditions:

(CT-540) ^0.9 ÷ 40 (℃ / min)

The oxide is not formed below 540 ° C. even when slow-cooling is further performed.

In addition, pickling and / or polishing is generally performed to descale prior to coating, and sometimes equipment for electrolytic degreasing or pickling is also provided at the CGL inlet side, but during or during coiling in a hot rolling process. The oxide produced in the surface layer of the steel sheet should remain after the treatment.

Zinc and zinc-alloy hot dip coating of the present invention is a generic term for hot dip zinc containing zinc and may include galfan and galvalume as well as zinc hot dip coating, both in Si Is contained in zinc. Moreover, Pb, Mg, Mn and the like may further be contained. Therefore, the conditions for the zinc bath are not particularly limited.

Other conditions for the coating layer are not particularly limited, but considering the corrosion resistance and the like, the preferred amount of zinc and zinc-alloy coating is about 25 to 90 g / m 2 and the preferred zinc content in the coating layer in the galvanized zinc hot-dip steel sheet is 8 to 13 Weight percent.

In addition, both hot rolled steel sheets and cold rolled steel sheets can be used as coating materials.

Examples of the present invention are presented below:

Each sample shown in Table 1 was melted by a converter and formed into slabs by continuous casting. Each slab obtained was hot rolled at a slab-heating temperature of 1150 to 1200 ° C., and as a finishing temperature of 900 to 920 ° C., and at a thickness of 1.2 to 3.5 mm at the coiling temperature and cooling rate shown in Table 2. The sheet thus obtained was pickled at 5O < 5 > C for 5 to 15 seconds in an aqueous 5% HCl solution to remove the scale layer, and then separated into two groups, one group was immediately CGL treated and the other was cold rolled to a thickness of 0.7 mm. In addition, on the CGL inlet side, the following method was used in combination with pretreatment for removing the surface layer of the steel sheet, if necessary.

Electrolytic degreasing: electrolysis at 60 ° C. for about 10 seconds in 3% aqueous NaOH solution.

Pickling: Pickling at 60 ° C. for about 3 seconds in a 5% aqueous HCl solution.

Brushing roll: Brushing roll with abrasive grains.

In CGL, both the hot rolled sheet and cold rolled sheet were annealed at 800 to 850 ° C. and then hot plated at 470 ° C. In addition, an alloyed zinc hot-dip steel sheet was obtained by subjecting the annealed sheet to an alloying process which was continuously performed at 480 to 530 ° C. for 15 to 30 seconds.

○ Evaluation method for oxide

Observation of Oxides in Hot Rolled Sheets

The cross section of each hot rolled sheet with scale was polished and an optical microscope was observed to measure the oxide penetration depth without etching. The preferred magnification of the optical microscope was 1,000.

Quantitative Evaluation of Oxides in Hot Rolled Sheets

The following values were obtained:

(Intra-cavity oxygen analyzed in the total sheet-thickness direction of the hot rolled sheet descaled by pickling)-(Intra-cavity oxygen of the steel plate polished to reach the oxide penetration depth in the sheet-thickness direction after descaling)

Quantitative Evaluation of Oxides in Coating Sheets

Each coating sheet was immersed in the following solution until the end of the dissolution reaction of the coating and then the concentration of oxide-derived oxygen in the region up to 3 μm in the sheet-thickness direction at the surface of the steel sheet was calculated according to the following equation:

(Oxygen in steel sheet peeled off by hydrochloric acid and antimony method)-(Oxygen in steel sheet peeled off by hydrochloric acid and antimony method and then the surface layer was polished to remove 3 μm)

1% nital solution 1% by volume HNO ₃ -ethanol solution

Hydrochloric acid / antimony method Sb ₂ O ₃ (20 g) + 35% HCl (1 L)

○ Evaluation method for empty spots

Each covering sheet was evaluated by visual observation.

Free spot not observed: rank 1

Slightly observed: rank 2

A small number observed: rank 3

Observed: Rank 4

○ Test for coating-adhesive evaluation

Each coated sheet was subjected to a Dupont impact test using a 1 / 2-inch punch and peeling was confirmed by visual observation.

No peeling observed: ○

Peel Observation: ×

Each alloyed zinc alloy hot-dip plated steel sheet was bent at 90 °, then re-rolled, and then the compressed surface of the steel sheet was peeled off with a tape to measure the peeled amount of zinc by fluorescence X-rays.

Count Number:

Less than 500: Rank 1 (good)

500 or more and less than 1,000: Rank 2

1,000 or more and less than 2,000: Rank 3

2,000 or more and less than 3,000: Rank 4

3000 and above: Rank 5

Table 3 shows the results of the hot dip galvanized steel sheet and Table 4 shows the results of the zinc alloy hot dip galvanized steel sheet.

Sample-Steel Composition sign Cwt% Siwt% Mnwt% Pwt% A 0.105 0.010 0.08 0.008 B 0.070 0.10 0.10 0.01 C 0.070 0.50 2.0 0.07 D 0.010 1.50 0.10 0.05 E 0.003 0.003 0.05 0.005 F 0.003 0.01 0.20 0.01 G 0.003 0.30 0.50 0.04 H 0.003 0.05 1.95 0.20

Coiling conditions, oxide penetration depth into hot rolled sheet, and amount of oxide in hot rolled sheet Sample steel CT ℃ Average cooling rate up to 540 ℃℃ / min Hot Rolled Citrooxide Penetration Depthμm Amount of oxide in hot rolled sheet Sample river number A 540 1.0 0 0 One A 600 1.0 One One 2 A 600 1.5 0 One 3 A 700 2.0 7 5 4 B 650 1.5 8 8 5 C 650 1.5 6 7 6 D 580 1.0 0 0 7 D 620 1.2 One One 8 E 650 1.2 5 5 9 E 650 1.6 One One 10 E 650 1.8 0 One 11 F 650 1.0 10 11 12 G 650 1.0 12 15 13 H 600 1.8 0 0 14 H 650 1.0 12 18 15

Example and Comparative Example (Zinc Hot-Plated Steel Sheet) Examples and Comparative Examples Corresponding Sample Steel Numbers in Table 2 Hot Rolled Oxide Cold rolled steel Surface removal by pretreatment at CGL inlet side g / ㎡ Plating amount g / ㎡ Amount of oxide in the plated sheet ppm Free spot rank DuPont Test Results Comparative Example 1 One Not observed Perform 0.1 40 0 2 × Example 1 2 Observed Perform 0.1 50 One One ○ Example 2 2 Observed Do not perform 0.1 50 One One ○ Example 3 4 Observed Perform 0.5 70 5 One ○ Comparative Example 2 4 Observed Perform 8.0 70 0 4 × Example 4 4 Observed Do not perform 0.5 70 3 One ○ Example 5 5 Observed Perform 0.1 60 7 One ○ Example 6 6 Observed Perform 3.5 60 2 One ○ Comparative Example 3 7 Not observed Perform 0.1 50 0 One × Example 7 8 Observed Perform 0.1 90 One One ○ Example 8 9 Observed Perform 0.5 50 5 One ○ Example 9 10 Observed Perform 0.3 40 One One ○ Comparative Example 4 10 Observed Perform 1.0 40 0 3 × Example 10 12 Observed Perform 0.2 50 10 One ○ Example 11 13 Observed Perform 0.2 50 11 One ○ Comparative Example 5 14 Not observed Perform 0.2 50 0 4 × Example 12 15 Observed Perform 0.2 50 16 One ○

Example and Comparative Example (alloyed zinc hot-dip galvanized steel sheet) Examples and Comparative Examples Corresponding Sample Steel Numbers in Table 2 Hot Rolled Oxide Cold rolled steel Surface removal by pretreatment at CGL inlet side g / ㎡ Plating amount g / ㎡ Fe content in plating Amount of oxide in the plated sheet ppm Free spot rank Powder test results Comparative Example 1 One Not observed Perform 0.1 40 10.5 0 One 4 Example 1 2 Observed Perform 0.1 40 10.3 One One One Example 2 4 Observed Perform 0.5 40 11.4 3 One One Example 3 6 Observed Perform 0.2 70 9.6 6 One 2 Example 4 6 Observed Do not perform 0.2 70 9.1 5 One 2 Example 5 6 Observed Perform 0.1 30 10.1 7 One One Comparative Example 2 7 Not observed Do not perform 0.1 60 11.5 0 2 5 Example 6 8 Observed Perform 0.1 60 11.0 One One 2 Example 7 10 Observed Do not perform 0.1 40 9.9 One One One Example 8 10 Observed Do not perform 1.0 40 10.8 One One 2 Comparative Example 3 10 Observed Do not perform 3.0 40 9.0 0 One 3 Example 9 13 Observed Perform 0.2 60 10.1 14 One 2 Example 10 13 Observed Perform 5.0 60 10.5 5 One 2 Example 11 13 Observed Perform 15.0 60 9.2 2 One One Comparative Example 4 13 Observed Perform 25.0 60 10.5 0 3 4 Comparative Example 5 14 Not observed Perform 1.0 40 11.8 0 3 5 Example 12 15 Observed Perform 0.2 30 11.1 15 One One Example 13 15 Observed Perform 0.2 60 10.4 15 One 2

The technique disclosed by the present invention relates to a zinc hot-dip steel sheet and an alloyed zinc hot-dip steel sheet which exhibit a reduced number of empty spots and excellent coating adhesion, and are mainly suitably used for steel sheet of automobile bodies.

Claims (10)

A zinc and zinc-alloy hot-dip steel sheet comprising an oxide formed of an element more oxidative than iron, just below the coating layer. The zinc and zinc-alloy hot dip steel sheet according to claim 1, wherein the oxygen concentration is 1 ppm or more in the region up to 3 占 퐉 in the sheet-thickness direction from the surface layer of the steel sheet substrate immediately below the coating layer. 2. The zinc and zinc-alloy hot dip steel sheet according to claim 1, wherein the steel sheet is further heat-alloyed. 4. The zinc and zinc-alloy hot dip steel sheet according to claim 3, wherein the oxygen concentration is 1 ppm or more in the region up to 3 占 퐉 in the sheet-thickness direction from the surface layer of the steel sheet substrate immediately below the coating layer. The zinc and zinc-alloy hot-dip steel sheet according to any one of claims 1 to 4, comprising at least one element selected from Si, Mn, and P as a steel component in the following ranges: 0.001 ≤ Si ≤ 3.0 wt% 0.05 ≤ Mn ≤ 2.0 wt% 0.005 ≤ P ≤ 0.2 wt% While coiling the steel strip, by setting the temperature of the steel strip to at least 600 ° C and the hot rolled steel strip to an average slow-cooling rate of up to 540 ° C (CT-540) below ^0.9 ÷ 40 (° C / min) Step A for forming an oxide formed from an element more oxidizing than iron just below the scale; And A method for producing a zinc and zinc-alloy hot-dip steel sheet comprising the step B of zinc and zinc-alloy hot-plating the steel strip. The zinc and zinc-alloy melting according to claim 6, wherein the oxide formed in step A remains after the pre-treatment step carried out after the step A and immediately before step B until the annealing treatment is carried out. Method for producing galvanized steel sheet. The zinc and zinc-alloy hot-dip steel sheet according to any one of claims 6 to 7, wherein the hot-rolled slab contains at least one element selected from Si, Mn, and P as steel components in the following ranges. Way: 0.001 ≤ Si ≤ 3.0 wt% 0.05 ≤ Mn ≤ 2.0 wt% 0.005 ≤ P ≤ 0.2 wt% 8. A method according to any one of claims 6 and 7, wherein the zinc and zinc-alloy hot dip steel sheets are heat-alloyed after step B. 10. The method of claim 9, wherein the hot-rolled slab contains at least one element selected from Si, Mn, and P as steel components in the following ranges: 0.001 ≤ Si ≤ 3.0 wt% 0.05 ≤ Mn ≤ 2.0 wt% 0.005 ≤ P ≤ 0.2 wt%