WO1998030729A1

WO1998030729A1 - Hot dip galvanized steel sheet reduced in defects derived from failed plating and excellent in contact plating adhesion and process for producing the same

Info

Publication number: WO1998030729A1
Application number: PCT/JP1997/000045
Authority: WO
Inventors: Nobue Fujibayashi; Kazuaki Kyono; Motonori Miyaoka; Nobuo Totsuka
Original assignee: Kawasaki Steel Corporation
Priority date: 1997-01-13
Filing date: 1997-01-13
Publication date: 1998-07-16
Also published as: CA2215110A1; CA2215110C; KR19980702926A; DE69728389D1; EP0900857A1; DE69728389T2; EP0900857B1; EP0900857A4; KR100325755B1

Abstract

A hot dip galvanized steel sheet for use as steel sheets for automobiles, an alloyed hot dip galvanized steel sheet, and a process for producing the same. The galvanized steel sheet is reduced in the defects derived from failed plating and excellent in contact plating adhesion, and is characterized by having oxides of elements, more oxidizable than iron just under the plating, the oxides being formed during hot rolling. According to the production process, the temperature of coiling at the time of hot rolling is 600 °C or above, the cooling is carried out at a low rate, and the oxides are left intact also in the subsequent steps.

Description

Hot-dip galvanized steel sheet with few non-plating defects and excellent plating adhesion, and its manufacturing method

TECHNICAL FIELD The present invention relates to a hot-dip galvanized steel sheet having few non-plating defects and excellent adhesion and a method for producing the same.

Akira Background technology

Hot-dip zinc-coated steel sheets are mainly used for automobile bodies because they are inexpensive and have excellent corrosion resistance.However, in addition to corrosion resistance due to plating, the adhesion of plating during press working is required as the performance of steel sheets for automobile bodies. Have been. If the adhesion of the plating deteriorates, the plating layer peels off in powder or lump form, causing mold seizure, deteriorating the corrosion resistance of the peeled part, and causing scratches due to the peeled plating pieces. Was.

As a conventional technique for improving the plating adhesion, Japanese Patent Application Laid-Open No. 61-269691 discloses that Fe and Zn are applied at a high temperature of 700 to 850 ° C after hot-dip galvanizing. Need to be alloyed. However, alloying at high temperatures not only increases costs, but also increases the burden on equipment such as rolls.

In Japanese Patent Application Laid-Open No. Hei 3-232926, steel contains at least one of Zr, La, Ce, Y, and Ca, and is cooled from recrystallization annealing to plating. The speed is specified at 50 ° CZ seconds or more. Addition of Zr and the like to steel increased costs, and the productivity was poor because the speed of passing through had to be reduced due to the problem of cooling capacity.

Further, in Japanese Patent Application Laid-Open No. 2-163630, particularly, the components of steel in 0, Al, and N are respectively 0.0045 wt% or less, and (25 XN wt%) to 0.15 wt%. , 0.03 It is specified as 0 wt% or less. Also, in Japanese Patent Application Laid-Open No. 6-81101, the content of Ti, Si, and P in steel is limited and the content of Si (wt%) + P (wt%) ≥ Ti (wt%) is satisfied. Must. In any case, the regulation by the component does not always achieve the steel sheet performance such as the desired strength and drawability, and the adhesion from the specified component range may be reduced due to the deviation from the specified component range.

In Japanese Patent Laid-Open No. 4-333552, the plating adhesion is improved by performing Ni pre-plating before hot-dip galvanizing. However, there is no such facility in the ^ _ continuous molten zinc plating line (abbreviated as CGL), and a large investment is required for improving the facilities. On the other hand, recent emission regulations require lighter automobile bodies. One method for reducing the weight of an automobile body is to reduce the thickness. In this method, it is necessary to increase the strength of the board by the reduced thickness to ensure safety. For this reason, high-strength steel sheets have been developed that increase the content of elements such as Si, Mn, and P in steel to increase the strength of the steel sheets. Since automotive steel sheets are subjected to breath processing, high r-value (high Rankford value) steel sheets with improved material properties are required. In particular, the addition of these elements is essential for high-strength steel sheets. Has become.

In applying such hot-dip galvanizing to a steel sheet, recrystallization annealing must be performed at a high temperature of about 700 to 900 ° C. in order to obtain excellent material properties. Usually, in CGL, recrystallization annealing is performed in a nitrogen atmosphere in the presence of hydrogen (referred to as reduction annealing). Although this atmosphere is a reducing atmosphere for Fe, it is not suitable for elements such as SiMn and P. It is an oxidizing atmosphere. Therefore, elements that are more easily oxidized than Fe (such as Si, Mn, and P) during the reduction annealing (called oxidizable elements) diffuse out and combine with oxygen on the steel sheet surface to form oxides ( This is called surface thickening). These oxides significantly impair the wettability between the molten zinc and the steel sheet, so that a defect called non-plating in which zinc does not adhere to the steel sheet occurs. As one method of overcoming these problems, Japanese Patent Publication No. Sho 61-93386 proposes a method of pre-plating Ni on the surface of a steel sheet prior to hot-dip galvanizing. ing. However, in this method, S i: 0.2 to 2 · Ow t%, Mn: 0.5 to 2.0 w t%, and C r: 0.1 to 20 w t% when intended for the steel containing more than one kind, the adhesion amount is required to be subjected to 1 O gZm ² or more N i plating had invited an increase in cost. When such a large amount of Ni plating is applied, hot-dip galvanizing and the wettability of the steel sheet are improved, but defects caused by Si and Ni on the plating surface during the alloying process. There was a problem of frequent occurrence.

For example, Japanese Patent Application Laid-Open No. 57-70268 proposes a method of pre-plating Fe on the surface of a steel sheet prior to hot-dip galvanizing. According to this method, it is possible to prevent non-plating defects of the Si-added steel by pre-plating, but this requires the application of Fe plating of 5 gZm ² or more, which is extremely uneconomical. Was.

Further, as another method, there is a method disclosed in Japanese Patent Application Laid-Open No. 55-122285 and Japanese Patent Application Laid-Open No. Hei 4-254531. In these methods, a steel sheet is oxidized in advance to form a Fe oxide film on its surface, and then subjected to reduction annealing. However, in these methods, there is a problem that the alloy element such as Si is excessively reduced during the reduction annealing, the surface is concentrated, and an oxide film is formed, resulting in poor plating properties. To prevent this over-reduction, a large amount of Fe oxide is required. However, if the amount of Fe oxide film is too large, the Fe oxide film will be peeled off by a roll, etc., and instead the surface will thicken, impairing the plating property, and the peeled Fe oxide film will be scattered in the furnace. And adversely affect the operation.

Regarding the hot-dip galvanizing of high-strength steel sheets, a known proposal regarding the composition of the steel and the conditions of hot rolling (also abbreviated as hot rolling) is disclosed in Disclosure of methods for winding steel containing S i ≤ 0.2 and Mn ≤ 1.5 at a temperature of 650 ° C or higher, followed by pickling, cold rolling, annealing and hot-dip galvanizing According to Japanese Patent Application Laid-Open No. 6-179943, steel containing Si: 0 · 10− to 1.5 wt% and Mn: l. It discloses a method of winding and pickling at a temperature of 80 or less, followed by cold rolling annealing and hot-dip galvanizing.

However, in these methods, although the processing conditions for a series of steps such as the composition of the components in the steel and the hot rolling conditions are specified, the surface thickened film during reduction annealing is suppressed to prevent non-plating defects. It does not provide good adhesion. Disclosure of the invention

As a result of detailed experiments, the inventors found that non-plating defects and plating adhesion were dramatically improved by having an oxide of an easily oxidizable element directly under the coating layer of a hot-dip zinc-coated steel plate. Was found.

That is, the present invention provides a hot-dip galvanized steel sheet having an oxide of an element that is more easily oxidized than iron, immediately below the plating layer.

Further, in the hot-dip galvanized steel sheet, the oxygen concentration in a range of 3 μm in the thickness direction from the surface layer of the base steel sheet below the plating layer is preferably 1 ppm or more, and more preferably 2 ppm. 200200 ppm is preferred, and 3 to 100 ppm is more preferred.

Further, it is preferable that these hot-dip galvanized steel sheets are further subjected to a heat-alloying treatment after being subjected to the zinc plating, whereby an excellent alloyed hot-dip galvanized steel sheet is provided. Also in the case of the alloyed molten zinc-based plated steel sheet, the oxygen concentration in a range of 3 m from the surface layer of the base steel sheet below the plated layer in the thickness direction is preferably 1 ppm or more. Preferably, it is 2 to 200 ppm, more preferably 3 to 100 ppm.

Further, in any of the above-mentioned hot-dip galvanized steel sheets or alloyed hot-dip galvanized steel sheets, at least one selected from the group consisting of Si, Mn and P is used as the steel sheet component. 0.00 1 ≤ S i ≤ 3.0w t% ―

0. 05≤Mn≤ 2.0 w t%

0.005 ≤ P≤ 0.2 wt%

It is preferable to contain in the range of.

Further, the present invention also provides a method for producing a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet having few non-plating defects and excellent plating adhesion. Ie

Process A: When the hot-rolled steel strip is wound into a coil, the temperature of the steel strip

Set to 600 ° C or higher, and the average cooling rate up to 540 ° C (steel strip winding temperature – 540) ° · ⁹ ÷ 40 (° C / min) or less, oxides of elements that are more easily oxidized than iron immediately below the scale Forming a, and

Process B: Process of applying molten zinc plating

Is a manufacturing method having the following process sequence. In this manufacturing method, it is sufficient that step B is provided after step A, and another processing step may be provided between step A and step B. Usually, as such an intermediate treatment, an acid pickling step, a degreasing step, a cold rolling step, an annealing step and the like are appropriately used.

Further, in the manufacturing method of the present invention, it is preferable that the oxide formed in the step A is left in a pretreatment step performed after the step A and before an annealing furnace treatment immediately before the step B.

Further, in these production methods, at least one slab to be subjected to the hot rolling is selected from the group consisting of Si, Mn and P as components.

0.001 ≤ S i ≤ 3.0 w t%

0. 05≤Mn≤ 2.0 w t%

0.005 ≤ P≤ 0.2 wt%

It is preferable to use those contained in the range of.

Further, in any of the above-described manufacturing methods, after the step B, the heat alloying treatment is performed. Can produce an alloyed hot-dip galvanized steel sheet

Next, the oxide of the easily oxidizable element immediately below the plating layer in the present invention will be described.

This oxide is generated during hot rolling, and can be grown and formed particularly when the temperature during coil winding (abbreviated as CT) is high and the cooling rate is low thereafter.

The oxide formed during the hot rolling is observed immediately below the scale as shown in Fig. 6. On the other hand, as shown in Figure 7, the conventional hot-rolled sheet shows no oxide immediately below the scale. Fig. 1 shows the results of the analysis of the acid sardines found at the hot-rolled B temple using an electron probe microanalyzer (abbreviated as EPMA). Peaks are observed in Mn, P, A, and O, indicating that these oxides are formed. In the steel sheets used in Fig. 6 and Fig. 1, the components in the steel are Mn: 0.1 wt%, P: 0.06 wt%, A1: 0.03 wt%, especially Mn, P, A 1 is not a steel sheet with a large amount.

In the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet according to the present invention, the oxide immediately below the plating layer is the oxide immediately below the scale formed in the hot-rolling stage, and the subsequent treatment step such as pickling and plating. Are left even after passing through.

The mechanism by which oxides are formed immediately below the scale is that the oxygen in the scale layer mainly composed of iron oxide generated during hot rolling diffuses inside the steel after winding the steel strip, and then diffuses into the steel. To form an oxide of an easily oxidizable element. Therefore, it is formed even if the content of steel is very small.

In the present invention, as described above, an oxide of an element that is more easily oxidized than iron exists immediately below the molten zinc-based plating, but other oxides of an element that are less easily oxidized than iron oxide or iron Oxides may be included. In the present invention, it is more preferable that this oxide is formed at the crystal grain boundary of the hot-rolled sheet. The present inventors have studied and prepared various steel sheets. As a result, as oxides, si—O system, Mn—O system, Al—O system, P—O system, and Fe—S including Fe i — O-based oxides are detected.

Fig. 2 shows a conventional steel sheet, and Fig. 3 shows a Glow dis charge spectroscopy (abbreviated as GDS) in the depth direction from the surface layer of the unannealed sheet after cold rolling where oxides are observed to about 10 m. 2) shows the results of elemental analysis measurement by. The peaks of Mn, Al, P, and O appearing at a depth of about 0.3 to 4 ^ t m from the surface layer in FIG. 3 correspond to oxides.

Fig. 4 shows the results of a conventional steel sheet, and Fig. 5 shows the results of elemental analysis by GDS in the depth direction from the surface layer after cold rolling annealing to about 10 / im where oxides are observed. In the conventional steel sheet in Fig. 4, a large amount of surface condensate generated by reduction annealing is observed, while in the steel sheet with oxide generated during hot rolling, as shown in Fig. 5, Production is suppressed and hardly observed.

Next, in the present invention, the oxide present on the surface layer of the steel sheet immediately below the plating layer (the surface layer of the base steel sheet) can be observed with an optical microscope by etching with 1% nital solution for several seconds to several tens of seconds. .

Fig. 8 (Photo) and Fig. 9 (Photo) show observation examples of the conventional alloyed hot-dip galvanized steel sheet without oxides and the present invention, which is an alloyed hot-dip galvanized steel sheet having oxides. FIGS. 8 and 9 are cross-sectional optical micrographs of the alloyed hot-dip galvanized steel sheet at a magnification of 1000. The black strips (indicated by-) observed immediately below the plating layer are oxides.

Oxide formation can also be confirmed by performing oxygen analysis in steel. The method used is to remove the scale layer by pickling after hot-rolling, remove the scale layer of hot-dip galvanized steel sheet, or use a cold-rolled unannealed or annealed sheet. It is sufficient to compare the analysis value of oxygen in steel in the direction with the analysis value of oxygen in steel of a steel sheet from which the surface layer where oxide is formed is removed by grinding or the like. In the case of oxide-producing steel sheets, the total thickness direction analysis value is larger than the analysis value of the ground plate. Next, the mechanism by which non-plating defects and plating adhesion are improved by forming an oxide directly under the plating layer is discussed. First, as for the improvement of non-plating defects, as described above, oxide is generated immediately below the scale by internal diffusion of oxygen at the time of coiling and after coiling, thereby making it easier to reduce oxidation in CGL. It was found that the surface concentration of the oxidizing element was suppressed.

This is due to the fact that the oxidizable element has already been precipitated as an oxide after winding and the oxidizable element in the surface layer has been reduced, and that the oxidizable element has been transferred from Balta to the steel sheet surface. The movement (external diffusion) is hindered by the formed oxide, and the oxidation-reduction reaction inside the steel sheet, that is, the oxide containing Fe generated during winding or after rolling is reduced during reduction annealing. It is presumed to be due to the change to oxides of easily oxidizable elements.

As a result, it is thought that the concentration of easily oxidizable elements on the surface of the molten zinc that inhibits the wettability of the steel sheet is extremely reduced, and that non-plating defects are dramatically improved. Next, the adhesion will be described.

It is known that plating is exfoliated mainly by compressive stress during press working.

In the steel sheet having an oxide immediately below the plating layer according to the present invention, zinc is easily permeated because there is a gap between oxide crystals as compared with a conventional steel sheet having no oxide. As a result, the unevenness of the interface between the plating layer and the steel sheet becomes severe, and the plating layer can firmly adhere to the steel sheet. As a result, in the hot-dip galvanized steel sheet and the galvannealed steel sheet disclosed by the present invention, the adhesion of the plating during the press working is excellent.

The plating layer is forcibly dissolved to the iron potential by the galvanostatic method (4% methyl salicylate, 1% salicylic acid, 10% methanol solution of potassium iodide Z, 5 mA / cm ² ). The results are shown in Figs. 10 and 11 when the steel plate is exposed and the steel plate is exposed and observed by SEM. It can be seen that the roughness of the interface between the plating layer and the steel sheet is clearly greater than that of the conventional oxide-free steel sheet. In addition, the technology disclosed in the present invention includes, as a component in steel, at least one component selected from the group consisting of Si, Mn, and P;

0. 0 0 1≤ S i ≤ 3.0 .0 w t%

0 .0 5≤M n≤ 2.0 .0 w t%

0. 0 0 5≤ P≤ 0 .2 w t%

More excellent effects are observed in steel sheets containing in the range of. Since problems such as non-plating defects and poor adhesion are unlikely to occur in steel sheets that do not contain these elements, the lower limits of each element are as follows: Si: 0.001 wt%, Mn: 0.05 wt%, P: preferably 0.05 wt%. On the other hand, the upper limit of each element is set as a preferable range from the viewpoint of saturation of the effect of strengthening and cost. In addition, the technology disclosed by the present invention has a sufficient effect on both the non-plating defect and the plating adhesion if a small amount is observed by etching with 1% nital in the cross-section observation of the hot-dip galvanized steel sheet using an optical microscope. It has been seen. Also, in the oxygen analysis in steel,

(Oxygen analysis value of steel sheet peeled off by antimony hydrochloride / antimony method) 1 (Oxygen analysis value of steel sheet after 3 μΐη of surface layer was removed by plating after hydrochloric acid * antimony method)

A value of 1 ppm or more has been found to have a sufficient effect especially on non-plating defects and plating adhesion. Next, a technique for manufacturing the above-described plated steel sheet will be disclosed. It is a necessary condition that the temperature at the time of hot rolling is high and that it is gradually cooled thereafter. Give a detailed explanation. ―

If the hot-rolling coiling temperature is not higher than 600 ° C, oxides will not be generated, and the cooling rate to 540 ° C after winding will be reduced.

^{(CT- 5 4 0) 0.} 9 ÷ 4 0 (° CZ min)

Must be: At 540 ° C or lower, no oxide is formed even if the cooling is further performed.

In addition, when plating, pickling and Z or polishing are usually performed to remove scale, and facilities such as electrolytic degreasing and pickling are sometimes performed on the CGL entry side. After the heat treatment, during the winding in the hot rolling process, the oxides on the surface layer of the steel sheet generated after the winding must remain.

The molten zinc-based plating of the present invention refers to molten zinc containing zinc as a whole, and may be galvanized or galvanized containing Si in zinc as well as the molten zinc plating. Further, Pb, Mg, Mn, etc. may be included. Therefore, the conditions of the zinc bath are not particularly limited.

Is not particularly limited for conditions other plating layer, coating weight of the zinc-based plated over any corrosion resistance aspect ² 5~9 0 g / m 2 approximately, plating of the alloying molten zinc plated steel sheet An appropriate iron content in the bed is 8 to 13 wt ° / o.

Also, the hot rolled sheet and the cold rolled sheet may be used as the original plate for plating. BRIEF DESCRIPTION OF THE FIGURES

[Figure 1] EPMA analysis of oxides just below the scale observed during hot rolling.

FIG. 2 is a graph of a depth direction elemental analysis of a conventional cold-rolled unannealed sheet from the surface layer to about 10 μm by GDS.

[Fig. 3] From the surface layer by GDS of the unannealed sheet after cold rolling in the example to the range of about 10 / im It is a graph of a depth direction elemental analysis result. ―

FIG. 4 is a graph of a depth direction elemental analysis of about 10 μm from the surface layer by GDS after conventional cold rolling annealing.

FIG. 5 is a graph of the results of elemental analysis in the depth direction from the surface layer to about 10 μm by GDS after cold rolling annealing in the example.

FIG. 6 is a cross-sectional optical micrograph of the oxide immediately below the scale of the hot-rolled sheet of Example at a magnification of 1000 times.

FIG. 7 is a cross-sectional optical microscope photograph of a conventional hot-rolled sheet at a magnification of 100 × just below the scale.

FIG. 8 is a cross-sectional optical micrograph of the alloyed hot-dip galvanized steel sheet having an oxide of Example at a magnification of 1000 times.

FIG. 9 is a cross-sectional optical microscope photograph of a conventional oxide-free galvannealed steel sheet at a magnification of 1000 ×.

FIG. 10 is a 3 × 1 photograph of a steel sheet in which a plating layer is melted in an example at a magnification of 150 ×.

[Fig. 11] This is an SEM photograph of a conventional steel sheet in which a plating layer is melted at a magnification of 1500.

[Explanation of symbols]

1 Steel plate base 2 Scale 3 Oxide 4 Plating layer 5 Oxide Best mode for carrying out the invention

Hereinafter, an example of the present invention will be described.

After smelting the test materials shown in Table 1 in a converter, they were made into slabs by continuous forming. This slab was hot-rolled at a slab heating temperature of 1150 to 1200 ° C, a finishing temperature of 900 to 900 ° C, a coil winding temperature and a cooling rate shown in Table 2. 2-3 .5 mm thick. After that, the scale layer is removed by pickling for 5 to 15 seconds in a 5% HC1 aqueous solution at 80 ° C for 5 seconds. Then, CGL is directly passed through the plate and cold-rolled to a thickness of 0.7 mm. And created. In addition, the following methods were combined as necessary as a pretreatment method in which the steel sheet surface layer was removed by pretreatment on the CGL entry side.

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

Pickling: Pickling in 60%, 5% HC1 aqueous solution for about 3 seconds

Brush mouth: Brush roll with abrasive grains

The hot-rolled sheet and the cold-rolled sheet were both annealed at 800-850 ° C and then hot-dipped at 470 ° C in CGL. In the case of heat alloying, alloying was continued at 480 to 530 ° C for 15 to 30 seconds.

〇Oxide evaluation method

Observation method of oxide on hot rolled sheet:

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

Measurement of oxide content in hot rolled sheet:

(Analytical value of oxygen in steel in the thickness direction of hot-rolled sheet from which scale has been removed by pickling) i (Analytical value of oxygen in steel of steel sheet that has been ground in the thickness direction to the depth of oxide penetration after scale removal) I asked.

Measurement of oxide content on plated plate:

Immerse in the following solution until the dissolution reaction is completed, and determine the oxygen concentration in the range of 3 μm in the thickness direction from the surface of the steel sheet derived from oxides by the formula: (Oxygen analysis value of steel sheet) It was obtained from (Oxygen analysis value of steel sheet in which 3 μιη of the surface layer was removed by polishing after peeling off by the antimony method using hydrochloric acid). % Nital solution 1 vol% HN0 ₃ one ethanol solution of hydrochloric acid _{_{• S b 2 0 3 (20}} g) + 35% HC 1 (1 1)

評価 Non-plating defect evaluation method

The plated plate was visually observed and evaluated.

No plating defect None · · · Rank 1

Slightly present · · · · 2

Small quantity · · · 3

Yes ... 4

〇Plating adhesion evaluation test

For the hot-dip galvanized steel sheet, a DuPont peel test was performed using a 1/2 inch hammer, and the presence or absence of peeling was visually confirmed.

No peeling

Peeled · · · The X-alloyed hot-dip zinc-coated steel sheet was bent and bent 90 °, the tape was peeled off on the press-bonded side, and the amount of peeled zinc was measured by X-ray fluorescence.

Count less than 500: Rank 1 (good)

500 or more and less than 1 000: 2

1 000 or more and less than 2000: 3

2000 or more and less than 3000: 4

3000 or more: 5 Table 3 shows the results for hot-dip galvanized steel sheets and Table 4 shows the results for galvannealed steel sheets. VI

m ^ lara

S 刚 0 / m 6Jf / I d 6 0 £ / 86 OAX Table 2 Winding conditions, oxide penetration depth of hot-rolled sheet and measured value of oxide amount in hot-rolled sheet Sample steel CT Average cooling up to 540 ° C Oxide of hot-rolled sheet oxide amount in hot-rolled sheet Test steel

. C speed ° c / min Penetration depth ^ m Measured value p p m number

A 54 0 1.0.0 0 0 1

A 6 0 0 1. 0 1 1 2

A 60 0 1.5 0 <1 3

A 70 0 2.0 7 5 4

B 65 0 1.5 8 8 5

C 6 5 0 1.5 6 7 6

D 58 0 1.0.0 0 0 7

D 6 2 0 1.2 <1 <18

E 65 0 1.2 5 5 9

E 6 5 0 1.6 <1 1 1 0

E 65 0 1.8 0 <1 1 1

F 65 0 1.0 1 0 1 1 1 2

G 650 1.01 1 2 1 5 1 3

H 60 0 1.8 0 0 1 4

H 65 0 1. 0 1 2 1 8 1 5

Table 3 Examples and Comparative Examples (Steel sheets with hot-dip galvanized steel) Examples and Table 2 show the presence or absence of cold rolling by hot rolling. CGL side plating Unplated plated plate Dupont Comparative example Surface oxide content Defects

Steel number Presence or absence Removal amount g / m ² g / m ² ppm Rank Comparative example 1 1 No Yes <0.140 0 2 X Example 1 2 Yes Yes <0.1.50 1 1 Ο

2 2 Yes No <0.1.50 1 1 〇

3 4 Yes Yes 0.5 70 5 1 比較 Comparative Example 2 4 Yes Yes 8.70 0 4 X Example 4 4 Yes No 0.5 70 3 1 〇

5 5 Yes Yes 0.1 0.1 60 7 1 〇

6 6 Yes Yes 3.5 5 60 2 1 〇 ^^ J 3 7 Ϊ

None 0.15 0 1 X Example 7 8 Yes Yes <0.190 <1 1 〇

8 9 Yes Yes 0,5 50 5 1 〇

9 1 0 Yes Yes 0.3 4 1 1 〇 Comparative Example 4 1 0 Yes Yes 1. 0 40 0 3 X Protrusion 1 0 1 2 Yes Yes 0.2 50 1 0 1 〇

1 1 1 3 Yes Yes 0.2501 1 1 比較 Comparative Example 5 14 No Yes 0.2 50 0 4 X Example 1 2 1 5 Yes Yes 0.250 1 6 1

Table 4 Examples and comparative examples (alloyed hot-dip galvanized steel sheet)

Example 1 and Example 2 Example of hot-rolled and cold-rolled side without CGL plating Plating During plating Unplated paddle pad Comparative example Sample surface oxide deposited by pretreatment of oxides Iron content Oxide content Defects Test result Steel No.Presence or removal g / m ² g / m ² % PP m Rank Comparative example 1 1 No Yes 0.1 40 1 0.5.0 0 1 4 Example 1 2 Yes Yes 0.1 40 1 0.3 1 1 1

2 4 Yes Yes 0.5 40 1 1.4 3 1 1

3 6 Yes Yes 0.2 70 9.6 6 1 2

4 6 Yes No 0.2 0.2 70 9. 1 5 1 2

5 6 Yes Yes <0.1 30 10.1 7 1 1 Comparative Example 2 7 No No 0.16 1 1.5 1 5 Example 6 8 Yes Yes 0.16 1 1.0 <1 1 2

7 1 0 Yes No <0.1.40 9.99 1 1

8 1 0 Yes No 1.0 40 1 0.8. <1 2 Comparative Example 3 1 0 Yes No 3.0 40 9.00 0 3 Example 9 1 3 Yes Yes 0.2 60 1 0.1 1 4 2

1 0 1 3 Yes Yes 5.60 10.5 0.55 2

1 1 1 3 Yes Yes 1 5.60 60 9.2 2 1 Comparative Example 4 1 3 Yes Yes 25.0 60 1 0.5.04

5 1 4 No Yes 1.0 40 1 1.80 5 Example 1 2 1 5 Yes Yes 0.2 30 1 1.1 1 5 1

1 3 1 5 Yes Yes 0.2 60 10.4 1 5 2

Industrial applicability-

The technology disclosed in the present invention relates to a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet having few non-plating defects and excellent plating adhesion, and is suitable mainly for use in a steel sheet for an automobile body.

Claims

The scope of the claims -

1. Hot-dip galvanized steel sheet characterized by having an oxide of an element that is more easily oxidized than iron immediately below the plating layer

2. The plated steel sheet according to claim 1, wherein an oxygen concentration in a range of 3 m in a thickness direction from a surface layer of the base steel sheet below the plating layer is 1 ppm or more. Hot-dip galvanized steel sheet

3. The galvanized steel sheet according to claim 1, further comprising a heat alloying treatment.

4. The plated steel sheet according to claim 3, wherein the oxygen concentration in the range of 3 μΐη from the surface of the base steel sheet below the plating layer in the thickness direction is 1 ppm or more. Hot-dip galvanized steel sheet

5. The plated steel sheet according to any one of claims 1 to 4, wherein at least one selected from the group consisting of Si, Mn, and P as the steel sheet component,

0.001 ≤ S i ≤ 3.0 w t%

0. 05≤Mn≤ 2.0 w t%

0.005 ≤ P≤ 0.2 wt%

Hot-dip galvanized steel sheet characterized by containing in the range of

6. Process A: When the hot-rolled steel strip is wound into a coil, the temperature of the

600 ° C or higher, and the average cooling rate up to 540 ° C (steel strip winding temperature-540) ° · ⁹ ÷ 40 (° CZ min.) Forming, and

Process B: Process of applying molten zinc plating

For producing a hot-dip galvanized steel sheet characterized by having the following process sequence:

7. The manufacturing method according to claim 6, wherein in the pretreatment step performed after the step A and before the annealing furnace treatment immediately before the step B, the oxide formed in the step A is Method for producing hot-dip galvanized steel sheet characterized by remaining

8. The method according to any one of claims 6 to 7, wherein the slab to be subjected to the hot rolling is at least one selected from the group consisting of Si, Mn, and P as a component. To

0.001 ≤ S i ≤ 3.0 w t%

0. 05≤Mn≤ 2.0 w t%

0.005 ≤ P≤ 0.2 wt%

Method for producing a hot-dip galvanized steel sheet characterized by containing in the range of

9. The manufacturing method according to any one of claims 6 to 7, wherein after the step B, a heat-alloying treatment is performed.

10. The production method according to claim 9, wherein the slab subjected to the hot rolling is at least one selected from the group consisting of Si, Mn, and P as a component.

0.001 ≤ S i ≤ 3.0 w t%

0. 05≤Mn≤ 2.0 w t%

0.005 ≤ P≤ 0.2 wt%