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1. (WO2016072475) HOT-DIP GALVANIZED STEEL SHEET

PCT Biblio. Data
Full Text
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Book Details
The title of the invention
Technical field
0001
Background technique
0002 0003 0004 0005 0006 0007 0008 0009 0010 0011
CITATION
Patent Document
0012
Summary of the Invention
Problems that the Invention is to Solve
0013
Means for Solving the Problems
0014 0015 0016
Effect of the Invention
0017
BRIEF DESCRIPTION OF THE DRAWINGS
0018
DESCRIPTION OF THE INVENTION
0019 0020 0021 0022 0023 0024 0025 0026 0027 0028 0029 0030 0031 0032 0033 0034 0035 0036 0037 0038 0039 0040 0041 0042 0043 0044 0045 0046 0047 0048 0049 0050 0051 0052 0053 0054 0055 0056 0057 0058 0059 0060 0061 0062 0063 0064 0065 0066 0067 0068 0069 0070 0071 0072 0073 0074 0075 0076 0077 0078 0079 0080 0081 0082 0083 0084 0085 0086 0087 0088 0089 0090 0091 0092 0093 0094 0095 0096 0097 0098 0099 0100 0101 0102 0103 0104 0105 0106 0107 0108 0109 0110 0111 0112 0113 0114 0115 0116
Example
0117 0118 0119 0120 0121 0122 0123 0124 0125 0126 0127 0128 0129 0130 0131 0132 0133 0134 0135 0136 0137 0138 0139 0140 0141 0142 0143 0144 0145 0146 0147 0148 0149 0150 0151 0152 0153 0154 0155 0156 0157 0158 0159 0160 0161 0162 0163 0164 0165 0166 0167 0168 0169 0170 0171 0172 0173 0174 0175 0176 0177 0178 0179 0180
Industrial Applicability
0181
The scope of the claims
1 2 3 4 5
Drawing
1 2
Book Details
The name of the invention: hot-dip galvanized steel sheet
Technical field
[0001]
　The present invention relates to an excellent hot-dip galvanized steel sheet in the plating adhesion.
　The present application, on November 05, 2014, claiming priority based on Japanese Patent Application No. 2014-225398, filed in Japan, the contents of which are incorporated here.
Background technique
[0002]
　Mainly for steel sheet used in the frame member of an automobile, there has been a growing demand for higher strength. In these high-strength steel sheets, for obtaining an excellent moldability high strength, it is common to add alloying elements typified by contributing Si and Mn for improving the strength. However, alloying elements typified by Si and Mn also has effects of lowering the coating adhesion.
　As for the automobile steel sheet, since the commonly used outdoors, that is superior corrosion resistance required is usually.
[0003]
　However, in applications such as the outer plate of the motor vehicle, subjected to a severe bending a peripheral portion of the plate by press working (bending heme) it is usual. Further not only the automobile outer plate, in other applications, harsh bending or by pressing, is often used by applying such hole expansion processing. When subjected to such harsh bending and hole expansion processing on conventional galvanized steel sheet, in its working portion, the plating layer was sometimes peeled off from the base material steel plate. If the plating layer is peeled off in this way, the corrosion resistance of the change is lost, there is early corrosion base steel sheet, rusting occurs problems. Also even does not lead to peeling of the plating layer, the plating layer and in adhesion between the base steel sheet is lost, if Shojire voids even slightly in that portion, and the outside air or moisture penetrates into the gap, plating anti-corrosion function is lost by layer. As a result, the same early corrosion to the base steel sheet, rusting occurs.
　These problems, as the high-strength steel sheet used is subjected to such severe bending, plated steel sheet having a galvanized layer has excellent adhesion of the plating layer to the base material steel plate is strongly desired there.
[0004]
　To enhance the adhesion of the plating layer, for example, as typified by Patent Documents 1 to 3, to generate an internal oxidation of the steel sheet, the base steel causing plating peeling an oxide of the interface between the plating layer how to reduce have been proposed. However, if for generating such oxides steel surface layer, the carbon of the steel sheet surface layer is gasified combine with oxygen. As a result, the detached from carbon steel, the strength of the area where the carbon is separated is significantly reduced. If the strength of the steel sheet surface layer is decreased, fatigue resistance which depends strongly on the properties of the surface layer portion deteriorates, there is a concern that the fatigue strength is significantly reduced.
[0005]
　Alternatively, in order to improve the adhesion of the plating layer, Patent Document 4, by performing adding a new annealing process and pickling step prior to the general annealing process, modify the base steel sheet surface, plating how to improve adhesion have been proposed. However, in the method described in Patent Document 4, with respect to the production method of general high strength plated steel sheet, since the process is increased, there is a problem in terms of cost.
[0006]
　Further, in Patent Document 5, to remove the carbon from the surface layer portion of the base steel sheet, a method of increasing the adhesiveness of the plating has been proposed. However, in the method described in Patent Document 5, significantly reduced the strength of the region to remove the carbon. Therefore, the method described in Patent Document 5, fatigue resistance is deteriorated strongly dependent on the characteristics of the surface layer portion, there is a concern that the fatigue strength is significantly reduced.
[0007]
　In Patent Document 6, 7, Mn in the coating layer, controlling the Al and Si amount to a preferred range, the steel sheet having improved plating adhesion have been proposed. The steel sheet described in Patent Documents 6 and 7, it is necessary to control the element content in the coating layer during manufacture with high precision, large load on operation, there is a problem in cost.
[0008]
　As a method to improve the coating adhesion, Patent Document 8, a high-strength steel sheet has been proposed microstructure of the steel sheet is composed of only ferrite. However, the steel sheet described in Patent Document 8, since the microstructure is only soft ferrite, not sufficiently high strength can be obtained.
[0009]
　Here, galvannealed steel sheets subjected to alloying treatment is widely used after galvanizing treatment. Alloying treatment, the plated layer is heated to a temperature above the melting point of Zn, a large amount of Fe atoms are diffused in the plating layer during the base steel sheet during the certain plating layer in the process of a layer of Zn-Fe alloy mainly . For example, Patent Document 9,10,11 excellent galvannealed steel sheet coating adhesion have been proposed. However, to fully alloyed plating layer, it is necessary to heat the steel plate to a high temperature. Heating the steel to a high temperature, the steel sheet inside the microstructure altered easily generated particularly coarse iron-based carbides, due to that the characteristics of the steel sheet is impaired, which is undesirable.
[0010]
　Patent Document 12, galvanized steel sheet basis steel sheet comprises Si, Mn, one or more selected from the group consisting of Al is described. Patent Document 12, in the manufacturing process, it is described that control the plating bath penetration temperature of base steel sheet. Further, Patent Document 12, defining the area ratio of the cross section of the alloy layer formed at the interface between the base steel sheet and the plated layer, and excellent hot-dip galvanized steel sheet in a plating adhesion and spot weldability is disclosed there.
[0011]
　Patent Document 12, Si in the surface, the steel sheet Mn oxide is present, when the invaded by molten zinc plating bath, non-plating galvanizing is not performed is mentioned that a large amount occurs. However, Patent Document 12, Si, reduce the Mn oxide before the start plating technique is not disclosed. In Patent Document 12, the plating bath penetration temperature of the base steel sheet, higher than hot-dip galvanizing bath temperature. Depending on the Al content in the molten zinc plating bath, the plating bath penetration temperature of the base steel sheet at a minimum, to 4 ° C. ultra higher than hot-dip galvanizing bath temperature is increased up to 28 ° C.. Therefore, in Patent Document 12, there is a case where uniformity of characteristics bath temperature stability and hence product becomes insufficient.
CITATION
Patent Document
[0012]
Patent Document 1: Japanese Laid-Open Patent Publication No. 2008-019465
Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-060742
Patent Document 3: Japanese Laid-Open Patent Publication No. 9-176815
Patent Document 4: Japanese Patent Laid-Open 2001-026853 Publication No.
Patent Document 5: Japanese Laid-open Patent Publication No. 2002-088459
Patent Document 6: Japanese Laid-open Patent Publication No. 2003-055751
Patent Document 7: Japanese Laid-open Patent Publication No. 2003-096541
Patent Document 8: Japanese Patent Laid-open 2005 Publication No. -200750
Patent Document 9: Japanese Unexamined Patent Publication No. 11-140587
Patent Document 10: Japanese Laid-open Patent Publication No. 2001-303226
Patent Document 11: Japanese Laid-open Patent Publication No. 2005-060743
Patent Document 12: Japanese Laid table No. 2013-541645 Gazette
Summary of the Invention
Problems that the Invention is to Solve
[0013]
　In view of the situation described above, the present invention is, strength, ductility, hole expandability, it is an object to provide a good molten zinc-plated steel sheet spot weldability coating adhesion.
Means for Solving the Problems
[0014]
　The present inventors have conducted extensive studies in order to obtain good galvanized steel sheet coating adhesion. As a result, the present inventors have, zeta phase in the plating layer (FeZn 13 were found to suppress the plating peeling by incorporating) Thus, without performing the alloying treatment of the plating layer, excellent hot-dip galvanized steel sheet in the plating adhesion can be obtained.
[0015]
　The present invention was completed on the basis of this finding, the embodiment is as follows.
[0016]
(1) consists of a galvanized layer formed on at least one surface of said base steel sheet and the base steel sheet,
　the galvanized layer on the surface of the steel sheet, Fe content of 0% super-5 % or less and is the Al content is 0% or less super to 1.0%, including columnar crystals composed of ζ phase, further, more than 20% of the total interface between the galvanized layer and the base steel sheet there is covered in ζ phase, all the interface in the galvanized layer, the interface formed between ζ crystal grains and the base material steel plate there is a coarse oxides of ζ crystal grains, and the ζ phase and the base steel sheet is 50% or less with respect to,
the base material steel plate containing, by
　　mass%, C:
　　0.040 ~ 0.400%,
　　Si: 0.05 ~ 2.50%, Mn: 0.50 ~ 3.50
　　Pasento, P:
　　0.0001 ～ 0.1000 Pasento, S: 0.0001 ～
　　0.0100 Pasento, Al: 0.00 The
　　~
　　1.500% 1, N: 0.0001 ~ 0.0100%, O: 0.0001
　　~ 0.0100%, Si + 0.7Al ≧ 0.30 (element symbol in the formula, the content of the element ( represents the mass%).) satisfied, it has the chemical composition and the balance being Fe and inevitable impurities,
　has a fine layer in direct contact with the interface between the galvanized layer and the base steel sheet, the fine an average thickness of 0.1 ~ 5.0 .mu.m of layer, the average particle size of the ferrite phase in the finer layer is the 0.1 ~ 3.0 [mu] m, wherein one of Si and Mn in fine layer or comprise two or more oxides, the maximum diameter of the oxide is 0.01 ~ 0.4 .mu.m,
　Wherein the 1/8 thickness 1-3 / 8 thickness in the range of 1/4 thickness around from the surface of the base material steel plate, in a volume fraction, galvanized steel sheet having residual austenite phase at least 1%.
　(2) For the galvanized layer, the coating weight of one surface of the base material steel plate is 10 g / m 2 or more, 100 g / m 2 hot-dip galvanized steel sheet according to or less (1).
(3) the base material steel plate contains, by mass%,
　　further,
　　Ti: 0.001 ~ 0.150%,
　　Nb: 0.001 ~ 0.100%, V: 0.001 ~ 0.300%,
of the hot-dip galvanized steel sheet according to contain one or more selected from (1) or (2).
(4) the base material steel plate contains, by mass%,
　　further,
　　Cr: 0.01 ~
　　2.00%, Ni: 0.01 ~ 2.00%, Cu: 0.01 ~
　　2.00%, Mo:
　　~ 2.00% 0.01, B:
　　0.0001 ~ 0.0100%, W: 0.01 ~ 2.00%,
containing one or two or more species selected from among (1) - hot-dip galvanized steel sheet according to any one of (3).
(5) the base material steel plate contains, by mass%,
furthermore, Ca, Ce, Mg, Zr, La, contain from 0.0001 to 0.0100% in total of one or more of REM (1) ~ hot-dip galvanized steel sheet according to any one of (4).
Effect of the Invention
[0017]
　According to this aspect of the present invention can provide strength, ductility, hole expandability, spot weldability, excellent hot-dip galvanized steel sheet in the plating adhesion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
[Figure 1] of the cross section of the hot-dip galvanized steel sheet according to the present embodiment is a scanning electron microscope (SEM) photograph of a cross section including and neighboring galvanized layer / base steel sheet surface.
FIG. 2 is a field emission scanning electron microscope (FE-SEM) photograph of a section of the galvanized steel sheet according to the present embodiment.
DESCRIPTION OF THE INVENTION
[0019]
　Galvanized steel sheet according to the embodiment of the present invention, the base steel sheet (hereinafter, simply referred to as steel.) And galvanized layer formed on at least one surface of the steel sheet (hereinafter, simply referred to as a plating layer.) consisting of.
　Plating layer, Fe content is not more than 0% Ultra-5% Al content is not more than 0% super% to 1.0%, including columnar crystals composed of ζ phase. Plating layer, the plating layer and the base material more than 20% of the total interface between the steel sheet is coated on the zeta phase, zeta phase and the matrix there is coarse oxides of the interface between the steel sheet zeta grains and the matrix the proportion of the interface formed between the steel sheet is 50% or less.
[0020]
　First, a description will be given zinc plating layer constituting the hot-dip galvanized steel sheet according to the embodiment of the embodiment of the present invention. Note that [%] in the following description are [mass%].
[0021]
(Plating layer)
　in embodiments of the present invention, the galvanized layer, Fe content is not more than 0% super-5.0%, Al content is 0% or less super to 1.0%. Further, the galvanized layer Ag, B, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Ge, Hf, I, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni , Pb, Rb, Sb, Si , Sn, Sr, Ta, Ti, V, W, Zr, or may be one or containing two or more REM, or mixed. Thus, galvanized layer, contain one or two or more of said elements, or even those mixed, the effect of the present invention is not impaired, the corrosion resistance and workability by the content If such is improved preferably also.
　In the present embodiment, galvanized layer includes columnar crystals composed of ζ phase, characterized in that more than 20% of the total interface between the plated layer and the base steel sheet is covered with the ζ phase .
　Further, the adhesion amount of hot-dip galvanizing layer on one surface of the base material steel plate is 10 g / m 2 or more, 100 g / m 2 is preferably less.
[0022]
: [Fe content in galvanized layer 0% Ultra to 5.0% or less]
　Since the coating adhesion and the Fe content is increased to deteriorate the galvanized layer, and a Fe content of 5.0% or less There is a need to. To enhance the coating adhesion Further, Fe content in the coating layer is preferably set to 4.0% or less, more preferably 3% or less. The lower limit of the Fe content in the plating layer is 0 percent. The Fe content is less than 0.5%, the ζ phase may not be sufficiently obtained needed to improve the adhesion. Therefore, Fe content in the coating layer is preferably 0.5% or more, further preferably 1.0% or more.
[0023]
: [Al content in the galvanized layer 0% super% to 1.0% or less]
　Since the coating adhesion between the Al content is increased to deteriorate the galvanized layer, and an Al content of 1.0% or less There is a need to. To enhance the coating adhesion Further, Al content in the coating layer is preferably set to 0.8% or less, further preferably 0.5% or less. The lower limit of the Al content in the plating layer is 0 percent. The Al content to less than 0.01%, it is necessary to lower the Al concentration in the plating bath excessively. When extremely lowered Al concentration in the plating bath, the plating adhesion alloying increasingly Fe content in the coating layer by excessively progress of the plating layer is degraded. Therefore, Al content of the plating layer is preferably 0.01% or more. In this respect, Al content of the plating layer is more preferably 0.05% or more.
[0024]
　さらに、溶融亜鉛めっき層はＡｇ、Ｂ、Ｂｅ、Ｂｉ、Ｃａ、Ｃｄ、Ｃｏ、Ｃｒ、Ｃｓ、Ｃｕ、Ｇｅ、Ｈｆ、Ｉ、Ｋ、Ｌａ、Ｌｉ、Ｍｇ、Ｍｎ、Ｍｏ、Ｎａ、Ｎｂ、Ｎｉ、Ｐｂ、Ｒｂ、Ｓｂ、Ｓｉ、Ｓｎ、Ｓｒ、Ｔａ、Ｔｉ、Ｖ、Ｗ、Ｚｒ、ＲＥＭの１種または２種以上を含有、あるいは混入するものであってもよい。溶融亜鉛めっき層が、上記の元素の１種または２種以上を含有、あるいは混入するものであっても、本発明の効果は損なわれず、その含有量によっては耐食性や加工性が改善される等好ましい場合もある。
[0025]
"Ζ phase"
　in Figure 1 shows a scanning electron microscope (SEM) photograph of a cross section of the galvanized steel sheet according to the present embodiment. As shown in FIG. 1, galvanized layer of the present invention, zeta phase is an alloy of Fe and Zn (FeZn 13 including columnar crystals made of). Particularly among all the interface between the plated layer and the base steel sheet, the ratio of the interface ζ phase is in contact with the base steel sheet is characterized in that 20% or more. Thus, coarse oxides over longer diameter 0.2μm containing Si and / or Mn can serve as a starting point for peeling is taken into ζ phase from the base steel sheet surface. This coarse oxides by becomes difficult act as starting points of fracture to improve the adhesion of the plating layer. From this viewpoint, it is preferable that the interface ζ phase and the base steel sheet is plated layer and the ratio for all of the interface between the base steel sheet is 25% or more, more preferably 30% or more. Incidentally, the interface of the ζ phase and the base steel sheet is the upper limit of the percentage of all of the interface between the plating layer and the base steel sheet is not particularly defined, but may be 100%. Incidentally, when the major axis of the oxide containing Si and / or Mn is 0.2 [mu] m or more, cracks starting from the oxide becomes significant, when the major axis is less than 0.2 [mu] m, less likely serve as a starting point of cracks . This degree of stress concentration at the time of deformation of the galvanized steel sheet, in order to vary the size of the oxide. Specifically, as the oxide is large (major axis is long), the stress is easily concentrated during deformation, the plating layer is likely to peel.
[0026]
　On the other hand, not taken into coarse oxides ζ phase containing Si and / or Mn, the interface coarse oxides of ζ phase and the base steel sheet is present, the effect of improving the plating adhesion by ζ phase is not sufficiently obtained , which is not preferable. Therefore, coarse oxides zeta exists grains and the ratio of the interface between the base steel sheet (coarse oxides containing zeta grains), zeta phase and the base steel sheet of the crystal of zeta phase (zeta grain) to 50% or less for all of the interface between. If the ratio of the interface between the coarse oxide-containing ζ crystal grains and the base material steel plate is 50% or less, coarse oxide is sufficiently reduced containing Si and / or Mn are present without being incorporated into the ζ phase. The ratio of the interface between the coarse oxide-containing ζ crystal grains and the base material steel plate is preferably 35% or less for all of the interface between the ζ phase and the base steel sheet. The interface between the ζ phase and the base steel sheet, preferably as or more coarse oxides diameter 0.2μm less. Of all the interface between the ζ phase and the base steel sheet, it is most preferred ratio of surfactants coarse oxide-containing ζ grain makes with the base steel sheet is 0%.
[0027]
　Moreover, galvanized layer δ1 phase (FeZn 7 may also contain a). However, to increase the fraction of δ1-phase, was immersed base steel sheet in the plating bath, it is necessary to advance the alloying of the plating layer by heating the base steel sheet, tensile properties of the base material steel plate is deteriorated by heating to. It is preferable from this point of view, the fraction of δ1 phase is small. Particularly among all the interface between the plating layer and the base steel sheet, it is preferable that the ratio of the interface δ1 phase is in contact with the base material steel plate is 20% or less.
[0028]
　Proportion interface between the ζ phase and the base steel sheet in the present invention accounts for all of the interface between the plating layer and the base steel sheet and the interface δ1 phase and the base steel sheet is occupied by all of the interface between the plating layer and the base steel sheet ratios can be determined in the following manner.
　That is, a sample is taken from the hot-dip galvanized steel sheet, as an observation plane parallel to sheet thickness cross section in the rolling direction of the base material steel plate. The viewing surface was mirror-polished, field emission scanning electron microscope (FE-SEM: Field Emission Scanning Electron Microscope) using a total L of the length of the interface between the plating layer and the base steel sheet was observed 200μm or more and to observe until. The sum L of the lengths interface is observed until the above 200 [mu] m is to the inside of one thickness section L may be observed until more than 200 [mu] m, a plurality of plate thickness in a cross section L is 200 [mu] m or more and it may be observed until.
[0029]
　In the same field as the field of observation of the L, the crystal grains exhibit columnar is ζ phase or δ1 phase, measuring the total L1 of the ζ phase and δ1 phases and the length of the interface between the base steel sheet. Subsequently, in the same field as the field of observation of the L1, perform high-resolution crystal orientation analysis by EBSD (Electron Bach-Scattering Diffraction) method using a FE-SEM, it performs identification of .delta.1 phase, .delta.1 phase and the matrix the sum is L2 length of the interface of the steel sheet.
　(L1-L2) / L with ζ phase and the interface of the base material steel plate is regarded as a percentage of all of the interface between the plating layer and the base steel sheet.
　Similarly, the interface between the δ1 phase and the base steel sheet with a L2 / L is considered as a percentage of all of the interface between the plating layer and the base steel sheet.
　Incidentally, separation of the ζ phase and δ1 phase, may be performed by a method other than the above EBSD method. For example, field emission electron probe micro-analyzer: by (FE-EPMA Field Emission Electron Probe MicroAnalyser), performed Zn element mapping in the plating layer, it may be performed to determine the difference Zn amount of ζ-phase and δ1 phases Absent.
[0030]
　Also, among the crystals of zeta phase (zeta grains), the rate of the interface of coarse oxide zeta exists grains and (coarse oxides containing zeta grains) and the base steel sheet is obtained in the following manner. That is, in the same field as the field of observation of the L, zeta phase and the base material interface to the observation of the steel sheet, zeta phase and the base steel sheet and the interface over long diameter 0.2μm coarse oxide is zeta grain (coarse obtaining an oxide containing ζ grains). Oxide existing in an interface between the ζ phase and the base steel sheet of the plating layer appear dark compared to the surrounding in backscattered electron (BSE) image of the SEM. Therefore, whether oxides at the interface between the ζ phase and the base steel sheet of the plating layer is present, by observing the reflected electron (BSE) image of the SEM in the same field as the field of view observed L, and the periphery determining the difference in brightness between the. Further, each oxide is determined by measuring the major axis on the observation plane, the major axis is determined more than 0.2μm coarse oxides. Then, a length of the interface between the coarse oxide-containing ζ crystal grains and the base steel sheet to obtain a total L ** length of the interface. By determining the L ** / (L1-L2), of all the interface between the ζ phase and the base steel sheet, the ratio of surface coarse oxide-containing ζ grain makes with the base steel sheet is obtained.
[0031]
　In order to clearly revealing the ζ phase, the observation surface of the sample after mirror polishing, may be subjected to a corrosion of the observation plane by using the etchant such as nital.
[0032]
[Adhesion amount of hot-dip galvanizing: 10 ~ 100 g / m 2 ]
　is not sufficient corrosion resistance is obtained with a small amount of adhesion to the base material steel plate one surface of galvanized layer fear. Therefore, adhesion of the base material steel plate one surface of the plating layer is 10 g / m 2 preferably not less than. From the viewpoint of corrosion resistance, coating weight 20 g / m 2 and more preferably at least, 30 g / m 2 or more is more preferable. On the other hand, when the amount is large adhesion of the plating layer becomes severe electrode wear when performing spot welding, there is a possibility that the deterioration of the decrease and welded joint strength of the welding nugget diameter when subjected to welding continuously occurs. Therefore, the coating weight of the plating layer 100 g / m 2 is preferably not more than. In view of the continuous weldability, coating weight 93 g / m 2 , more preferably at most, 85 g / m 2 and more preferably not more than.
[0033]
　Galvanized steel sheet of the present invention includes the plated layer, has a fine layer of the base steel sheet is shown below.
　The fine layer, the average particle size of the ferrite phase present in the outermost layer is a region that is 1/2 or less of the average particle size of the ferrite phase in the lower layer. The average particle size of the ferrite phase in the finer layer, the extra half to become a boundary of an average particle size of the ferrite phase in the lower layer, define the boundary of the fine layer and the underlying.
[0034]
　Finer layer is in direct contact with the interface between the base steel sheet galvanized layer. The average thickness of the finer layer is 0.1 ~ 5.0 .mu.m. The average particle size of the ferrite phase in the finer layer is 0.1 ~ 3.0 [mu] m. Miniaturization layer contains one or more oxides of Si and Mn, the maximum diameter of the oxide is 0.01 ~ 0.4 .mu.m.
[0035]
　If the average thickness of the finer layer is 0.1μm or more, when processing galvanized steel sheet, occurrence and spreading of cracks can be suppressed. Therefore, the average thickness of the finer layer is not less than 0.1 [mu] m, it is preferable to 1.0μm or more. The average thickness of 5.0μm or less finer layer can be formed while suppressing excessive alloying in the plating bath. Therefore, Fe content in the coating layer can be prevented the deterioration of coating adhesion due to excessively large. Therefore, the average thickness of the finer layer is not more than 5.0 .mu.m, it is preferable to 3.0μm or less.
[0036]
　By the average particle size of the ferrite phase of the finer layer and above 0.1 [mu] m, when processing galvanized steel sheet, occurrence and spreading of cracks can be suppressed. Therefore, the average grain size of the ferrite phase of the finer layer is not less than 0.1 [mu] m, it is preferable to 1.0μm or more. Further, when the average particle size of the ferrite phase of the finer layer and 3.0μm greater than the effect of suppressing the generation and extension of cracks is limited. Therefore, the average grain size of the ferrite phase of the finer layer is set to 3.0μm or less, it is preferable to 2.0μm or less.
[0037]
　The one or more oxides of Si and Mn contained in the finer layer, e.g., SiO 2 , Mn 2 SiO 4 , MnSiO 3 , Fe 2 SiO 4 , FeSiO 3 selected from among, MnO one or two or more thereof.
　When the maximum diameter of the one or more oxides of Si and Mn contained in the finer layer is in 0.01μm or more, to form a fine layer, generation of ζ phase is sufficiently promoted a plating layer can be formed. Maximum diameter of the oxides is preferably 0.05μm or more. Further, the fine layer maximum diameter of 0.4μm or less of the above oxides can be formed while suppressing excessive alloying of the plating layer. Maximum diameter of the oxides is preferably 0.2μm or less.
[0038]
　The average particle size of the ferrite phase in an average thickness and miniaturization layer of finer layer is measured by the following methods. From galvanized steel sheet, a sample is taken as an observation plane parallel plate thickness cross section in the rolling direction of the base material steel plate. The observation surface of the sample is processed by CP (Cross section polisher) device, a reflection electron image at FE-SEM (Field Emission Scanning Electron Microscopy) was observed at 5000-fold, measured.
[0039]
　Maximum diameter of the one or more oxides of Si and Mn contained in the fine layer is measured by the following methods. From galvanized steel sheet, a sample is taken as an observation plane parallel plate thickness cross section in the rolling direction of the base material steel plate. The observation surface of the sample FIB (Focused Ion Beam) is processed to produce a thin film sample. Thereafter, the thin film sample is observed at a magnification of 30000 times with a FE-TEM (Field Emission Transmission Electr on Microscopy). 5-field observation of each film sample, the maximum diameter of oxides measured by the total field of view, the maximum diameter of the oxide in the thin film sample.
[0040]
　Chemical composition of the base material steel plate constituting the hot-dip galvanized steel sheet according to the present embodiment in the following (composition) will be described. Note that [%] in the following description are [mass%].
[0041]
[C: 0.040 ~ 0.400%]
　C is an element added to enhance the strength of the base material steel plate. However, if the content of C exceeds 0.400%, and the spot weldability is deteriorated, not preferable, C content is at most 0.400%. In view of the spot weldability, the content of C is less than 0.300%, more preferably at most 0.220%. On the other hand, when the content of C is less than 0.040%, strength is lowered, it becomes difficult to secure a sufficient tensile maximum strength, C content is 0.040% or more. In order to increase the strength further, it is preferable that the content of C is more than 0.055%, and more preferably not less than 0.070%.
[0042]
[Si: 0.05 ~ 2.50%]
　Si suppresses the formation of iron-based carbides in the base material steel plate, is an element to increase the strength and formability. However, Si is also an element embrittle the steel, when the content exceeds 2.50%, troubles such as cast slab cracking tends to occur. Therefore, the Si content should be not more than 2.50%. Moreover, Si is an oxide formed on the surface of the base steel sheet in the annealing step, significantly impair the adhesion of the plating. From this viewpoint, the content of Si is preferably not more than 2.00%, more preferably at most 1.60%. On the other hand, is less than 0.05% content of Si, in the plating step of the hot-dip galvanized steel sheet, coarse iron-based carbide is produced in large quantities, the strength and the formability deteriorates. Therefore, the Si content is 0.05% or more. Incidentally, from the viewpoint of suppressing the formation of iron-based carbides, the content of Si is 0.10% or more, more preferably 0.25% or more.
[0043]
[Mn: 0.50 ~ 3.50%]
　Mn is added to increase the strength by enhancing the hardenability of the base steel sheet. However, if the content of Mn exceeds 3.50%, the coarse Mn concentrated portion in the plate thickness central portion of the base steel sheet occurs, embrittlement is likely to occur, the troubles such as cast slab cracking It occurs more easily. Therefore, the content of Mn should be not more than 3.50%. Also it deteriorates spot weldability if the content of Mn is increased. Therefore, the content of Mn is less than 3.00%, more preferably at most 2.80%. On the other hand, when the content of Mn is less than 0.50%, since the soft tissue is formed in large quantities during the cooling after annealing, it is difficult to ensure a sufficiently high maximum tensile strength. Therefore, the Mn content is 0.50% or more. For greater strength, the content of Mn is 0.80% or more, more preferably 1.00% or more.
[0044]
[P: 0.0001 ~ 0.1000%]
　P is an element which embrittle the steel is even when the content of P is more than 0.1000%, tends to occur problems such as cast slab cracking . Therefore, the P content is not more than 0.1000%. Also, P is also an element embrittle the melted portion caused by spot welding, in order to obtain a sufficient welded joint strength, the content of P is preferably set to less 0.0400%, or less 0.0200% it is more preferable to be. Meanwhile, when the content of P less than 0.0001% is accompanied by a significant increase in manufacturing cost. Therefore, the P content is set to 0.0001% or more, preferably 0.0010% or more.
[0045]
[S: 0.0001 ~ 0.0100%]
　S is combined with Mn to form coarse MnS, which is an element to lower the ductility, formability such stretch flangeability and bendability. Therefore, the content of S and 0.0100% or less. The S is also an element degrading the spot weldability. Therefore, S content is preferably set to 0.0060% or less, and more preferably to less 0.0035%. Meanwhile, when the content of S to less than 0.0001% is accompanied by a significant increase in manufacturing cost. Therefore, the S content is set to 0.0001% or more, preferably not less than 0.0005%, and more preferably 0.0010% or more.
[0046]
[Al: 0.001 ~ 1.500%]
　Al is an element to embrittle steel. When the content of Al exceeds 1.500%, the more likely to occur troubles such as cast slab cracking, the content of Al is less 1.500%. Also, since the spot weldability if the content of Al is increased to deteriorate, the content of Al is preferably set to less 1.200%, and more preferably 1.000% or less. On the other hand, although even lower limit of the content of Al is not particularly defined effect of the present invention is exhibited, Al is inevitable impurities present in trace amounts in the raw material, the content thereof to less than 0.001% is accompanied by a significant increase in the production cost. Therefore, Al content is 0.001% or more. The Al is an effective element as a deoxidizing agent, the effect of deoxidation, in order to obtain more fully, the content of Al is preferably set to 0.010% or more.
[0047]
[N: 0.0001 ~ 0.0100%]
　N forms coarse nitrides, ductile, because it is an element that degrades the formability such stretch flangeability and bendability, it is possible to suppress the amount preferable. When the content of N exceeds 0.0100% since the formability deterioration becomes remarkable, the upper limit of the N content is 0.0100%. The excessive addition of N, since the cause of blowholes during welding, the content is small is better. From these viewpoints, it is preferable that the N content is not more than 0.0070%, and more preferably 0.0050% or less. On the other hand, the lower limit of the N content, the effect of the present invention are exhibited without particularly, when the content of N to less than 0.0001% leads to a significant increase in manufacturing cost. Therefore, the lower limit of the N content is 0.0001% or more. Preferably N content is 0.0003% or more, more preferably 0.0005% or more.
[0048]
[O: 0.0001 ~ 0.0100%]
　O forms an oxide, ductility, from degrading the formability such stretch flangeability and bendability, it is preferable to suppress the content. When the content of O exceeds 0.0100% since the formability deterioration becomes remarkable, the upper limit of the O content is 0.0100%. More preferably the content of O is 0.0050% or less, more preferably 0.0030% or less. O lower limit of the content of, the effect of the present invention without particularly setting is exhibited, when the content of O and less than 0.0001% is accompanied by a significant increase in manufacturing cost. Therefore, the lower limit 0.0001%. Preferably O content is 0.0003% or more, more preferably 0.0005% or more.
[0049]
[Si + 0.7Al ≧ 0.30]
　Si and Al are element for suppressing generation of carbides due to the bainite transformation. To obtain a residual austenite, it is preferable to add Si and / or Al more than a certain amount. The addition amount and the addition amount of Al Si In this respect, it is necessary to satisfy the following formula 2. Preferably the value of the formula 2 on the left side (Si + 0.7Al) is 0.45 or more, more preferably 0.70 or more.
　　Si + 0.7Al ≧ 0.30 ··· (Equation 2)
　However, Si and Al of the formula 2 and the addition amount of each element (mass%).
[0050]
　Furthermore, the base steel sheet of galvanized steel sheet according to the embodiment of the present invention may be added the following elements as required.
　Specifically, in addition to the above chemical components, Ti: 0.001 ~ 0.150%, Nb: 0.001 ~ 0.100%, V: 0.001 ~ 0.300%, selected from among it may contain one or two or more.
[0051]
[Ti: 0.001 ~ 0.150%]
　Ti is precipitation strengthening, fine grain strengthening by ferrite grain growth inhibition, and the dislocation strengthening through suppression of recrystallization, contribute to the strength increase of the base material steel plate it is an element. However, if the content of Ti exceeds 0.150%, the deterioration of the formability deposition number is in the carbonitride content of Ti is preferably not more than 0.150%. From the viewpoint of moldability, the content of Ti is more preferably less 0.080%. On the other hand, the lower limit of the content of Ti, the effect of the present invention are exhibited without particularly. In order to obtain a strength increasing effect by Ti addition sufficiently, the content of Ti is preferably 0.001% or more. For even higher strength of the base material steel plate, the content of Ti is more preferably 0.010% or more.
[0052]
[Nb: 0.001 ~ 0.100%]
　Nb is precipitation strengthening, by dislocation strengthening through suppression of fine grain strengthening and recrystallization of a ferrite grain growth suppression, contribute to the strength increase of the base material steel plate element it is. However, if the content of Nb exceeds 0.100%, the deterioration of the formability deposition number is in the carbonitride, Nb content is more preferably 0.100% or less. From the viewpoint of formability, the Nb content is more preferably 0.060% or less. On the other hand, the lower limit of the content of Nb, the effect of the present invention are exhibited without particularly. To obtain the strength increasing effect of Nb added sufficiently, the content of Nb is preferably 0.001% or more. For even higher strength of the base material steel plate, the content of Nb is more preferably 0.005% or more.
[0053]
[V: 0.001 ~ 0.300%]
　V is precipitation strengthening, by dislocation strengthening through suppression of fine grain strengthening and recrystallization of a ferrite grain growth suppression, contribute to the strength increase of the base material steel plate element it is. However, if the content of V exceeds 0.300% formability increasingly precipitation of carbonitrides degrades. Therefore, the content of V is less than 0.300%, more preferably not more than 0.200%. On the other hand, the lower limit of the V content, the effect of the present invention are exhibited without particularly. To obtain the strength increasing effect due to the addition of V sufficiently, it is preferable that the content of V is 0.001% or more, more preferably 0.010% or more.
[0054]
　In the base material steel plate of the present embodiment, furthermore, Cr: 0.01 ~ 2.00%, Ni: 0.01 ~ 2.00%, Cu: 0.01 ~ 2.00%, Mo: 0.01 ~ 2.00%, B: 0.0001 ~ 0.0100%, W: 0.01 ~ 2.00%, 1 kind or may contain two or more species selected from among.
[0055]
[Cr: 0.01 ~ 2.00%]
　Cr suppresses phase transformation at high temperature, an effective element for high strength, may be added instead of a part of the C and / or Mn . However, when the content of Cr exceeds 2.00%, workability is impaired productivity in hot drops. Therefore, the content of Cr is preferably set to 2.00% or less, more preferably not more than 1.20%. On the other hand, the lower limit of the content of Cr, the effect of the present invention are exhibited without particularly. To obtain the effect of increasing the strength by adding Cr sufficiently, it is preferable that the content of Cr is 0.01% or more, further preferably 0.10% or more.
[0056]
[Ni: 0.01 ~ 2.00%]
　Ni suppresses phase transformation at high temperature, an effective element for high strength, may be added instead of a part of the C and / or Mn . However, when the content of Ni exceeds 2.00%, weldability is impaired. Therefore, the content of Ni is preferably set to 2.00% or less, more preferably not more than 1.20%. On the other hand, the lower limit of the content of Ni, the effect of the present invention are exhibited without particularly. To obtain a sufficient effect of strengthening by Ni added, the Ni content is preferably 0.01% or more, further preferably 0.10% or more.
[0057]
[Cu: 0.01 ~ 2.00%]
　Cu is an element to increase the strength by the presence in the steel as fine particles, can be added in place of part of C and / or Mn. However, when the Cu content exceeds 2.00%, weldability is impaired. Therefore, the Cu content is preferably set to 2.00% or less, more preferably not more than 1.20%. On the other hand, the lower limit of the Cu content, the effect of the present invention are exhibited without particularly. To obtain a sufficient effect of strengthening by Cu addition, the content of Cu is preferably 0.01% or more, further preferably 0.10% or more.
[0058]
[Mo: 0.01 ~ 2.00%]
　Mo suppresses phase transformation at high temperature, an effective element for high strength, may be added instead of a part of the C and / or Mn . However, when the content of Mo exceeds 2.00%, workability is impaired productivity in hot drops. Therefore, the content of Mo is preferably set to 2.00% or less, more preferably not more than 1.20%. On the other hand, the lower limit of the content of Mo, the effect of the present invention are exhibited without particularly. To obtain the effect of increasing the strength by adding Mo sufficiently, it is preferable that the content of Mo is 0.01% or more, more preferably 0.05% or more.
[0059]
[B: 0.0001 ~ 0.0100%]
　B suppresses phase transformation at high temperature, an effective element for high strength, may be added instead of a part of the C and / or Mn . However, when the content of B exceeds 0.0100% since the workability is impaired productivity in hot drops, the content of B is preferably set to 0.0100% or less. From the viewpoint of productivity, the content of B is more preferably 0.0050% or less. On the other hand, the lower limit of the B content, the effect of the present invention are exhibited without particularly. To obtain a sufficient effect of strengthening the by the addition of B, and the content of B is preferably set to 0.0001% or more. For further increasing the strength, the content of B is more preferably 0.0005% or more.
[0060]
[W: 0.01 ~ 2.00%]
　W suppresses phase transformation at high temperature, an effective element for high strength, may be added instead of a part of the C and / or Mn . However, when the content of W exceeds 2.00%, workability is impaired productivity in hot drops. Therefore, the content of W is preferably not more than 2.00%, more preferably not more than 1.20%. On the other hand, the lower limit of the content of W, the effect of the present invention is exhibited without being specifically defined. To obtain a sufficient high strength by the W, preferably W content is 0.01% or more, further preferably 0.10% or more.
[0061]
　Further the base material steel plate in the molten zinc plated steel sheet of an embodiment of the present invention, as other elements, Ca, Ce, Mg, Zr , La, 0.0001 ~ 1 kind or two or more kinds in total REM 0. it may contain 0100%. Added reason for these elements are as follows.
　It is to be noted that the REM, is an abbreviation of Rare Earth Metal, it refers to the elements belonging to the lanthanide series. In an embodiment of the present invention, the REM and Ce which is often added in misch metal, it may contain a composite elements of the lanthanoid series in addition to La and Ce. As inevitable impurities, the effect of the present invention is exhibited as containing elements of the lanthanide series other than those La and Ce. Moreover, the effect of the present invention is exhibited as the addition of metal La and Ce.
[0062]
　Ca, Ce, Mg, Zr, La, REM is an element effective for improvement of moldability may be added alone or in combination. However, Ca, Ce, Mg, Zr, La, if the total of one or more of the content of REM exceeds 0.0100%, it may impair the ductility. Therefore, it is preferable that the total amount of each element is 0.0100% or less, more preferably not more than 0.0070%. On the other hand, Ca, Ce, Mg, Zr, La, the lower limit of one or more of the content of REM, the effect of the present invention are exhibited without particularly. To obtain the effect of improving the formability of the base material steel plate sufficiently, it is preferable that the total content of these elements is 0.0001% or more. From the viewpoint of moldability, Ca, Ce, Mg, Zr, La, a total of one or more of the content of REM is more preferably at 0.0010% or more.
[0063]
　In the chemical components in the base material steel plate of the plated steel sheet according to the present embodiment, the remainder of the elements described above are Fe and unavoidable impurities. Incidentally, the above-described Ti, Nb, V, Cr, Ni, Cu, Mo, B, for the W, both to contain trace amounts of less than each of the lower limit as an impurity is allowed. Further, Ca, Ce, Mg, Zr, La, for also REM, to contain trace amounts of less than the lower limit of the total amount as an impurity is permitted.
[0064]
(Microstructure)
　will now be described microstructure of the base material steel plate of such hot-dip galvanized steel sheet to an embodiment of the present invention.
"Residual austenite"
　base steel sheet of such hot-dip galvanized steel sheet to an embodiment of the present invention includes a retained austenite phase. Residual austenite, the strength - a ductility balance largely increase tissue. The volume fraction of retained austenite in the 1/8 thickness 1-3 / 8 thickness range around the 1/4 thickness from the surface of the base steel sheet is less than 1%, the strength - is less effective to increase the ductility balance. Therefore, the volume fraction of retained austenite is 1% or more. Strength - To increase the ductility balance, volume fraction of retained austenite is preferably 3% or more, more preferably 5% or more. On the other hand, to obtain a large amount of residual austenite, it is necessary to increase the amount of C to be added significantly, as a result, there is significantly impair concerned weldability by a large amount of C. Therefore, the volume fraction of residual austenite preferably 25% or less. Further, the residual austenite is transformed into hard martensite with the deformation, the martensite by acting as starting points of fracture, stretch flangeability is degraded. Therefore, the volume fraction of the retained austenite is more preferably not more than 20%.
[0065]
　The base steel sheet of the galvanized steel sheet according to the embodiment of the present invention, in addition to the residual austenite, granular ferrite, acicular ferrite, non-recrystallized ferrite, pearlite, bainite, bainitic ferrite, martensite, tempered martensite site may have one or microstructure consisting of two or more of coarse cementite. The base steel sheet, in order to obtain characteristics according to application of the galvanized steel sheet, each phase, breakdown of the volume fraction of each tissue, the tissue size can be appropriately selected placement.
[0066]
　The volume fraction of each tissue contained in the base steel sheet of the galvanized steel sheet according to the embodiment of the present invention can be measured, for example, by the following method.
[0067]
　The volume fraction of retained austenite contained in the base material steel sheet structure of galvanized steel sheet of the present embodiment is evaluated by X-ray diffraction method. In 1/8 thickness 1-3 / 8 thickness ranging from a thickness of the surface finish a plane parallel mirror to the plate surface, to measure the area fraction of FCC iron by X-ray diffractometry, it with a volume of residual austenite a fraction.
[0068]
　Base steel sheet structure ferrite included, bainitic ferrite, bainite, tempered martensite, fresh martensite volume fraction of pearlite and coarse cementite galvanized steel sheet of the present embodiment is calculated by the following method . As the observation plane parallel plate thickness cross section in the rolling direction of the base material steel plate, a sample is taken. Polishing the observation surface of the sample, to nital etching. 1/4 of the plate thickness of the observation plane around 1/8 thickness 1-3 / 8 thickness range field emission scanning electron microscope (FE-SEM: Field Emission Scanning Electron Microscope) area fraction was observed with the measure, regarded as the volume fraction have it.
[0069]
　Further, in the hot-dip galvanized steel sheet according to the present embodiment, the thickness of the base material steel plate is not particularly limited, the flatness of the hot-dip galvanized steel sheet, from the viewpoint of controllability of cooling, the thickness of the base material steel plate 0 .6mm above, it is preferable the range of less than 5.0 mm.
[0070]
(Method of manufacturing a galvanized steel sheet)
　will be described in detail how to manufacture a galvanized steel sheet according to the embodiment of the present invention.
[0071]
　Method for producing a coated steel sheet according to the present embodiment, the annealing step, a plating step, and a post-plating cooling step, between the plating step and the annealing step, and / or, in the plating after the cooling step, residual austenite performing bainite transformation process described later to obtain the.
　Annealing step, the base steel sheet, the average heating rate between 600 ~ 750 ° C. as 1.0 ° C. / sec or more, heating to 750 ° C. or higher. Plating process, 450 ~ 470 ° C. The plating bath temperature, the steel plate temperature 440 ~ 480 ° C. at the time of plating bath enters, base material steel plate under the condition that the effective Al amount in the plating bath and 0.050 to 0.180 wt% by immersion in a galvanizing bath to form a plating layer with galvanized surface of the steel sheet. After plating cooling step after the plating step, satisfying the following formula course of cooling until 350 ° C. is described below (1).
[0072]
　To produce the hot-dip galvanized steel sheet according to the embodiment of the present invention, first to produce the base material steel plate.
　The base steel sheet is to cast a slab that was added alloy elements in accordance with the characteristics, subjected to hot rolling, is produced by applying a cold rolling.
　Follows is a detailed description of each manufacturing step.
[0073]
"Casting process"
　First of all, casting a slab to be subjected to hot rolling. It is preferable chemical composition of the slab (composition) is a component of the above. Slab subjected to hot rolling, it is possible to use those produced by such a continuous casting slab or thin slab caster.
[0074]
"Hot rolling process"
　in the hot rolling step, for suppressing the anisotropy of the crystal orientation due to casting, it is preferable that the heating temperature of the slab 1080 ° C. or higher. The heating temperature of the slab, more preferably, to 1150 ° C. or higher. The upper limit of the heating temperature of the slab is not particularly defined. To heat the slab exceed 1300 ° C., it is necessary to introduce a large amount of energy, leading to a significant increase in manufacturing cost. Therefore, the heating temperature of the slab is preferably set to 1300 ° C. or less.
[0075]
　After heating the slabs, performing hot rolling. The completion temperature of hot rolling (rolling completion temperature) of less than 850 ° C., increased rolling reaction force, it is difficult to get a thickness of a specified stable. Therefore, completion temperature of hot rolling is preferably set to 850 ° C. or higher, more preferably 870 ° C. or higher. On the other hand, the completion temperature of the hot rolling in a 980 ° C. than the apparatus for heating the steel sheet in the process from the end of heating of the slab until the completion of hot rolling is required, it requires high costs. Therefore, it is preferable to a completion temperature of the hot rolling and 980 ° C. or less, and more preferably set to 960 ° C. or less.
[0076]
　Then, taking up the hot-rolled steel sheet after hot rolling as a coil. The average cooling rate in the course of cooling until winding from hot rolling is preferably set to 10 ° C. / sec or more. This is because the advancing more transformation at low temperature, to a fine particle size of the hot-rolled steel sheet, in order to refine the effective crystal grain size of the base material steel plate after cold rolling and annealing.
[0077]
　Coiling temperature of hot-rolled steel sheet is preferably set to 350 ° C. or higher 750 ° C. or less. This is the microstructure of the hot-rolled steel sheet, perlite and / or major axis is generated by dispersing a more coarse cementite 1 [mu] m, the distortion introduced by cold rolling to localize, various crystal orientations in the annealing step in order to reverse transformation to austenite. This is, refining the effective crystal grains of the base material steel plate after annealing. When the coiling temperature is below 350 ° C., it may pearlite and / or coarse cementite is not generated, which is not preferable. Furthermore, lowering the strength of the hot rolled steel sheet, for performing easily cold rolling, it is more preferable to increase the coiling temperature above 450 ° C.. On the other hand, when the coiling temperature exceeds 750 ° C., pearlite and ferrite are produced in a long strip shape in the rolling direction, respectively, the effective crystal grain of the base material steel plate to produce a ferrite portion after cold rolling and annealing is extended in the rolling direction There tends to be as coarse, undesirable. Further, in order to fine the effective crystal grain size of the base material steel plate after annealing, it is more preferable to reduce the coiling temperature to 680 ° C. or less.
[0078]
　Next, the pickling of hot rolled steel sheet manufactured in this way. Pickling, since it is intended to remove oxide on the surface of the hot-rolled steel sheet, it is important for plating improvement of the base material steel plate. Pickling, may be the one time, it may be performed a plurality of times.
[0079]
"Cold process"
　Next, obtain a cold-rolled steel sheet by performing cold rolling on the hot-rolled steel sheet after pickling.
　In cold rolling, the total rolling reduction exceeds 85%, ductility of the steel sheet is lost, increases risk of the steel sheet during cold rolling is broken. Therefore, the total reduction rate is preferably set to 85% or less. From this viewpoint, the total reduction ratio is more preferably be 75% or less, more preferably 70% or less. Lower limit of the total reduction ratio in the cold rolling step is not particularly defined. The total reduction ratio is less than 0.05%, the shape of the base material steel plate becomes inhomogeneous, plating does not uniformly adhered, appearance is impaired. Therefore, preferably 0.05% or more and more preferably be 0.10% or more. Incidentally, the cold rolling is preferably performed in multiple passes, the distribution of rolling reduction to the number of passes and each pass of the cold rolling is not limited.
[0080]
　Further, reduction rate sum of 10% of the cold rolling, in the range of less than 20%, then recrystallization does not proceed sufficiently in the annealing step, coarse crystals lost malleable contains a large amount of dislocations grain remains near the surface, there are cases where the bending resistance and the fatigue characteristics deteriorate. To avoid this, to reduce the total rolling reduction, it is effective to in the minor accumulation of dislocations in the crystal grains leave malleable grains. Alternatively, to increase the total rolling reduction, sufficiently advanced recrystallization in annealing step, it is effective to a worked structure in the storage is small recrystallized grains of dislocation therein. From the viewpoint of the minor accumulation of dislocations in the crystal grains, it is preferable that the total reduction ratio is 10% or less in the cold rolling step, more preferably it is 5.0% or less. On the other hand, sufficiently proceed recrystallization in annealing step, it is preferable that the total reduction ratio of 20% or more, further preferably 30% or more.
[0081]
"Annealing step"
　in the embodiments of the present invention, subjected to annealing cold-rolled steel sheet. In an embodiment of the present invention, it is preferable to use a continuous annealing plating line having a preheating zone and reduction zone and the plating zone. Then, a preheating zone while annealing step is passed through a reducing zone, exit the annealing step until arriving to the plating zone, it is preferable to perform the plating process in the plating zone.

The scope of the claims
[Claim 1]
　Consists of a base steel sheet and the base material galvanized layer formed on at least one surface of steel sheet,
　the galvanized layer on the surface of the steel sheet, Fe content of 0% Ultra and 5% or less There, Al content is not more than 0% super% to 1.0%, including columnar crystals composed of ζ phase, further, the galvanized layer of 20% or more of ζ phase of the total interface between the base steel sheet the coated, in the galvanized layer, the interface formed between ζ crystal grains and the base material steel plate there is a coarse oxides of ζ crystal grains with respect to the total interface between the ζ phase and the base steel sheet 50% or less,
the base material steel plate containing, by
　　mass% C:
　　0.040 ~
　　0.400% Si: 0.05 ~ 2.50% Mn: 0.50 ~
　　3.50% P : 0.0001
　　～ 0.1000 Pasento, S: 0.0001
　　～ 0.0100 Pasento, Al: 0.001 ～ 1
　　% .500,
　　N: 0.0001 ~ 0.0100%, O: 0.0001
　　~ 0.0100%, Si + 0.7Al ≧ 0.30 (element symbol in the formula, the content of the element (mass%) the expressed.) satisfied, has the chemical composition and the balance being Fe and inevitable impurities,
　has a fine layer in direct contact with the interface between the galvanized layer and the base steel sheet, the fine layer an average thickness of 0.1 ~ 5.0 .mu.m, the mean particle size of the ferrite phase in the finer layer is the 0.1 ~ 3.0 [mu] m, 1 kind or two kinds of Si and Mn in the fine layer It contains more oxides, the maximum diameter of the oxide is 0.01 ~ 0.4 .mu.m,
　Wherein the 1/8 thickness 1-3 / 8 thickness in the range of 1/4 thickness around from the surface of the base material steel plate, in a volume fraction, galvanized steel sheet having residual austenite phase at least 1%.
[Claim 2]
　For the galvanized layer, the coating weight of one surface of the base material steel plate is 10 g / m 2 or more, 100 g / m 2 hot-dip galvanized steel sheet according to claim 1 or less.
[Claim 3]
Characterized in that said base material steel plate contains, by mass%,
　　further,
　　Ti: 0.001 ~ 0.150%,
　　Nb: 0.001 ~ 0.100%, V: 0.001 ~ 0.300%,
selected from among hot-dip galvanized steel sheet according to claim 1 or claim 2 containing one or more was.
[Claim 4]
Characterized in that said base material steel plate contains, by mass%,
　　further,
　　Cr: 0.01
　　~ 2.00%, Ni: 0.01 ~ 2.00%, Cu: 0.01
　　~ 2.00%, Mo: 0.01
　　2.00% ~, B:
　　0.0001 ~ 0.0100%, W: 0.01 ~ 2.00%,
one of the claims 1 to 3 containing one or more selected from among galvanized steel sheet according to an item or.
[Claim 5]
Characterized in that said base material steel plate contains, by mass%,
furthermore, Ca, Ce, Mg, Zr, La, any of claims 1 to 4 containing from 0.0001 to 0.0100% of one or two or more kinds in total of REM galvanized steel sheet according to an item or.