The name of the invention: hot-dip galvanized steel sheet
Technical field
[0001]
　The present invention relates to a galvanized steel sheet. The present invention is particularly ductility, bendability, excellent coating adhesion during hole expandability and bending deformation, and to high-strength galvanized steel sheet having excellent continuous bending fatigue properties.
　The present application, on November 5, 2014, claiming priority based on Japanese Patent Application No. 2014-225525, filed in Japan, the contents of which are incorporated here.
Background technique
[0002]
　Recently, there has been increasing mainly demand for high strength of the steel sheet used in the frame members of automobiles. In these high-strength steel sheet, the ductility in order to obtain a complicated member shape, moldability such bendability and stretch flange formability is required. Further, since the constantly subject to vibration when used as automotive parts, high fatigue resistance is also obtained. In addition, for automotive steel sheets, 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, and a loss of adhesion between the plating layer and the base steel sheet, if the gap even slightly that portion Shojire, outside air or moisture from entering in a gap therebetween. Thus, anti-corrosion function is lost by the plating layer, the similarly early corrosion 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 form oxides in the interior of the steel sheet, reducing the oxide at the interface of the base steel and the plating layer which causes the plating peeling methods have been proposed. However, if for generating such oxides steel sheet surface layer, gasified linked carbon of the steel sheet surface layer and oxygen, the result, carbon is removed from the steel sheet. Therefore, in the technique described in Patent Documents 1 to 3 have the strength of a region where the carbon is separated is significantly reduced in the steel plate. 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 limit strength is significantly decreased.
[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. In this case, in 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 limit strength is significantly decreased.
[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 according to 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, since the steel sheet described in Patent Document 8 is microstructure only soft ferrite, sufficient strength can not be obtained.
[0009]
　Here, after galvanizing treatment, galvannealed steel sheet which has been subjected to alloying treatment is widely used. 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, the coated steel sheet of Patent Document 9-11, 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.
Patent Document 12, in the manufacture of hot-dip galvanized steel sheet Si-Mn-Al-containing matrix, and controls the entering material temperature, by regulating the galvanized and sectional area ratio in the interface alloy layer of the base steel sheet, technique for improving coating adhesion and spot weldability is disclosed.
The steel sheet described in Patent Document 12, Si-Mn oxide it has been stated that adversely affect the plating adhesion. However, a technique for reducing the Si-Mn oxide before the start plating is not disclosed in patent document 12. In Patent Document 12, (depending higher bath temperature plus 4 ° C., the bath temperature plus 28 ℃ at maximum a minimum the Al of the plating bath) for entering material temperature to be higher than the bath temperature for, the bath temperature stability , thus, leaving a problem in uniformity of the properties of the product.
CITATION
Patent Document
[0010]
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
[0011]
　In view of the situation described above, the present invention is particularly bendability and stretch flange formability (hereinafter, simply referred to as stretch flangeability.) Excellent moldability of the steel sheet represented by, fatigue resistance, weldability, there is provided a high-strength galvanized steel sheet excellent in corrosion resistance and plating adhesion.
Means for Solving the Problems
[0012]
　The present inventors have found that the moldability of the bendability and the steel sheet represented by stretch flangeability, fatigue properties, weldability, intensive studies in order to obtain a high strength galvanized steel sheet excellent in corrosion resistance and plating adhesion the superimposed. As a result, the present inventors have improved stretch flangeability (the hole expandability) by controlling the microstructure of the steel sheet to the proper tissue fraction. Further, the present inventors have improved the plating layer and the base material boundary from bending by controlling the volume fraction of the base material steel plate side of the hard phase of the steel sheet and fatigue resistance. Furthermore, the present inventors have found that the plating layer during ζ phase (FeZn 13 ) to produce a suppressed plating peeling by incorporating an origin and a coarse oxide breakdown therein. These by the present inventors, without performing alloying treatment of plating layer, ductility, and formability of the bendability and the steel sheet represented by stretch flangeability, fatigue properties, weldability, corrosion resistance and plating adhesion excellent galvanized steel sheet has been found that the resulting.
[0013]
　The present invention was completed on the basis of this finding, it is an aspect as follows.
[0014]
(1) consists of a galvanized layer formed on at least one surface of said base steel sheet and the base steel sheet, the base material steel plate is a
　mass%, C: 0.040 ~
　0.280%, Si :
　0.05
　~ 2.00%, Mn: 0.50
　~ 3.50%, P: 0.0001 ~ 0.1000%, S: 0.0001
　~ 0.0100%, Al: 0.001 ~ 1
　% .500,
　N: 0.0001 ~ 0.0100%, O: 0.0001 ~ 0.0100%,
the balance has a chemical composition consisting of Fe and impurities, further
quarter thickness from the surface of the steel sheet in 1/8 thickness 1-3 / 8 thickness range around the,
volume fraction, 0-50% and a ferrite phase, the bainite and bainitic ferrite phase and fresh martensite phase and tempered martensite phase of rigid assembly consisting of one or more Woven and a 50% or more in total, the residual austenite phase 0 to 8% the sum of the pearlite phase and coarse cementite phase is 0-8% and the interface between the galvanized layer and the base steel in the surface layer ranging from up to steel sheet direction depth 20 [mu] m,
residual austenite is 0-3%,
around a volume fraction V1 of the hard tissue in the surface layer range, a quarter thickness from the steel sheet surface 1/8 thickness 1-3 / 8 which is the ratio of the volume fraction V2 of the hard tissue in the range of thickness V1 / V2 to have limited the microstructure in the range of 0.10 to 0.90, the galvanized layer is, Fe content was 0% ultra-5% Al content is 0% super% to 1.0%, including columnar crystals composed of ζ phase, further,
the galvanized layer and the base steel sheet interface between the ζ phase and the base steel sheet of the total surfactant (a) with A *) the ratio of ((A * / A) × 100) is not less than 20%, the fine layer on the surface side in the base steel sheet is formed, the average thickness of the finer layer is 0. 1 ~ 5.0 .mu.m, the an average particle diameter of 0.1 ~ 3.0 [mu] m of the ferrite phase in the finer layer, one or more oxides of Si and Mn are contained in the fine layer , hot-dip galvanized steel sheet maximum diameter of 0.01 ~ 0.4 .mu.m of the oxide.
(2) the steel sheet contains, by mass%,
　Ti: 0.001 ~ 0.150%,
　Nb: 0.001 ~ 0.100%, V: 0.001 ~ 0.300%,
selected from among galvanized steel sheet according to (1) containing one or more kinds.
(3) the steel sheet contains, by
　mass%,
　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%,
containing one or more selected from among the above (1) or (2) hot-dip galvanized steel sheet according to.
(4) The steel sheet contains, by
mass%, Ca, the (1 Ce, Mg, Zr, La, characterized by containing 0.0001 to 0.0100% in total of one or more of REM ) hot-dip galvanized steel sheet according to any one of - (3).
(5) In the above hot-dip galvanized layer, the interface between ζ crystal grains and the base material steel plate there is a coarse oxides of ζ crystal grains, 50% relative to the total interface between the ζ phase and the base steel sheet galvanized steel sheet according to any one of the following in the above (1) to (4).
(6) for the hot-dip galvanizing layer, a coating weight of one surface of the steel sheet is 10 g / m 2 or more, 100 g / m 2 molten zinc according to any one of the following in the above (1) to (5) plated steel sheet.
Effect of the Invention
[0015]
　According to the aspect of the present invention can provide formability, fatigue resistance, weldability, hot-dip galvanized steel sheet excellent in corrosion resistance and plating adhesion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016]
[1] Figure 1, of the cross section of the hot-dip galvanized steel sheet according to the present embodiment, an enlarged structural photograph including and neighboring galvanized layer / base steel sheet surface.
[Figure 2] of the cross section of the galvanized steel sheet according to the present embodiment, an enlarged photograph of a sectional structure of the vicinity including the galvanized layer / base steel sheet surface.
DESCRIPTION OF THE INVENTION
[0017]
　Galvanized steel sheet according to the present embodiment, by mass%, C: 0.040 ~ 0.280% , Si: 0.01 ~ 2.00%, Mn: 0.50 ~ 3.50%, P: 0.0001 ~ 0.100%, S: 0.0001 ~ 0.0100%, Al: 0.001 ~ 1.500%, O: 0.0001 ~ 0.0100%, N: 0.0001 ~ 0. containing 0100% balance base steel sheet having a chemical composition consisting of Fe and impurities (hereinafter, also simply referred to as steel.) the surface of galvanized layer (hereinafter, also simply referred to as a plating layer.) is formed it become one.
　Incidentally, the thickness of the base material steel plate is 0.6mm or more, it is suitable less than 5.0 mm. When the thickness of the base material steel plate is less than 0.6 mm, it becomes difficult to maintain the shape of the base material steel plate flat, not suitable. Further, when the thickness of the base material steel plate is 5.0mm or more, it becomes difficult to control the cooling in the manufacturing process, moldability without predetermined microstructure is obtained may be deteriorated.
[0018]
　First described chemical components of the base material steel plate constituting the hot-dip galvanized steel sheet according to the embodiment of the present invention (composition). Note that [%] in the following description are [mass%].
[0019]
[C: 0.040 ~ 0.280%]
　C is contained in order to increase the strength of the base material steel plate. However, if the content of C exceeds 0.280%, because the spot weldability is deteriorated, C content is at most 0.280%. In view of the spot weldability, the content of C is less than 0.250%, 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%.
[0020]
[Si: 0.05 ~ 2.00%]
　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 2.00%, troubles such as cast slab cracking tends to occur. Therefore, the amount of Si should be 2.00% or less. 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 less 1.500%, more preferably at most 1.200%. On the other hand, the content of Si is less than 0.05%, in the plating step of the hot-dip galvanized steel sheet, coarse iron-based carbide is produced in large quantities, since the deterioration of the strength and moldability, the content of Si is 0. to 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.
[0021]
[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 deteriorates spot weldability of galvannealed steel sheets with 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 content of Mn should be 0.50% or more. For greater strength galvanized steel sheet, the content of Mn is 0.80% or more, more preferably 1.00% or more.
[0022]
[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% and more preferably it is. Meanwhile, when the content of P less than 0.0001%, since with a significant increase in manufacturing cost, the P content is the lower limit of 0.0001%. The content of P is preferably set to 0.0010% or more.
[0023]
[S: 0.0001 ~ 0.0100%]
　S is combined with Mn to form coarse MnS, ductility, since an element to lower the moldability such stretch flangeability and bendability, the content of S to 0.0100% or less. The S is also an element degrading the spot weldability. Therefore, the content of S 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, the lower limit value of 0.0001%. The content of S is preferably set to 0.0005% or more, and more preferably 0.0010% or more.
[0024]
[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 more preferably to less 1.200%, still more preferably 1.000% or less. On the other hand, the effect of the present embodiment even the lower limit of the content of Al is not particularly setting is exerted. However, Al is an impurity present in trace amounts in the raw material, the content thereof to less than 0.001% is because it involves a significant increase in manufacturing costs, and 0.001% or more. Although Al is an element effective as a deoxidizer, the effect of deoxidation, in order to obtain more fully, the content of Al is more preferably set to 0.010% or more.
[0025]
[N: 0.0001 ~ 0.0100%]
　N forms coarse nitrides, ductile, because it is an element that degrades the formability such stretch flangeability and bendability, is necessary to suppress the amount added is there. 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 content of N is even without particularly setting effect of this embodiment is exhibited, 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.
[0026]
[O: 0.0001 ~ 0.0100%]
　O forms an oxide, ductility hot-dip galvanized steel sheet, from degrading the formability such stretch flangeability and bendability, it is necessary 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 embodiment is exhibited without particularly, when the content of O and less than 0.0001% is accompanied with significant increase in manufacturing cost, 0 the lower limit .0001%. Preferably O content is 0.0003% or more, more preferably 0.0005% or more.
[0027]
　Additional, the base steel sheet of the galvanized steel sheet according to the present embodiment, may be added the following elements as required.
[0028]
　In the steel sheet according to the present embodiment, further, 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.
[0029]
[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, contributes to increasing strength of the galvanized steel sheet 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%. In contrast, the lower limit of the content of Ti is the effect of the present embodiment is exhibited without particularly, in order to obtain a sufficient strength increasing effect by addition of Ti, the Ti content 0.001% or more there it is preferable. For even higher strength galvanized steel sheet, the content of Ti is more preferably 0.010% or more.
[0030]
[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 galvanized steel sheet it is an element. However, if the content of Nb exceeds 0.100% is possible for the deterioration of the formability of the galvanized steel sheet deposition number is in the carbonitride, Nb content is 0.100% or less more preferable. 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 is the effect of the present embodiment is exhibited without particularly, in order to obtain a sufficient strength increasing effect by the addition of Nb, the Nb content is 0.001% or more it is preferable. For even higher strength galvanized steel sheet, the content of Nb is more preferably 0.005% or more.
[0031]
[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 galvanized steel sheet it is an element. 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 content of V is the effect of the present embodiment is exhibited without particularly, in order to obtain a sufficient strength increasing effect due to the addition of V, the content of V is 0.001% or more it is preferably, more preferably 0.010% or more.
[0032]
　In the steel sheet according to 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.
[0033]
[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%, since the workability is impaired productivity in hot drops, the content of Cr is preferably set to 2.00% or less, 1 and more preferably .20 percent. On the other hand, the lower limit of the content of Cr is the effect of the present embodiment is exhibited without particularly, in order to obtain a sufficient effect of strengthening due to addition of Cr, the content of Cr is 0.01% preferably or more, more preferably 0.10% or more.
[0034]
[Ni: 0.01 ~ 2.00%]
　Ni suppresses phase transformation at high temperature, an effective element for high strength galvanized steel sheet, instead of a part of the C and / or Mn it may be added. However, when the content of Ni exceeds 2.00%, since the weldability is impaired, the content of Ni is preferably set to 2.00% or less, even more preferably less 1.20% . On the other hand, the lower limit of the Ni content is the effect of the present embodiment is exhibited without particularly, in order to obtain a sufficient effect of strengthening by Ni added, the Ni content is 0.01% or more it is preferably, more preferably 0.10% or more.
[0035]
[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%, since the weldability is impaired, the content of Cu is preferably set to 2.00% or less, even more preferably less 1.20% . On the other hand, the lower limit of the content of Cu is effective in the present embodiment is exhibited without particularly, in order to obtain a sufficient effect of strengthening by Cu addition, the Cu content more than 0.01% it is preferably, more preferably 0.10% or more.
[0036]
[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, if it exceeds 2.00% content of Mo, since the workability is impaired productivity in hot drops, the content of Mo is preferably set to 2.00% or less, 1 and more preferably .20 percent. On the other hand, the lower limit of the content of Mo is the effect of the present embodiment is exhibited without particularly, in order to obtain a sufficient effect of strengthening by Mo addition, the content of Mo is 0.01% preferably or more, more preferably 0.05% or more.
[0037]
[B: 0.0001 ~ 0.0100%]
　B suppresses phase transformation at high temperature, an effective element for high strength galvanized steel sheet, instead of a part of the C and / or Mn it may be added. 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, even if the lower limit of the content of B is not particularly defined, but the effect of this embodiment is exhibited, in order to obtain a sufficient effect of strengthening due to the addition of B, the content of B 0.0001% it is preferable that the above. For further increasing the strength, the content of B is more preferably 0.0005% or more.
[0038]
[W: 0.01 ~ 2.00%]
　W suppresses phase transformation at high temperature, an effective element for high strength galvanized steel sheet, instead of a part of the C and / or Mn it may be added. However, when the content of W exceeds 2.00%, since the productivity workability impaired by between heat is reduced, the content of W is preferably from 2.00%, 1.20% by more preferably less. On the other hand, the lower limit of the content of W is the effect of the present embodiment is exhibited without particularly determined, in order to obtain a high strength by W sufficiently, the content of W is 0.01% or more it is preferable, more preferably 0.10% or more.
[0039]
　Further the base material steel plate in the molten zinc plated steel sheet of the present embodiment, as other elements, Ca, Ce, Mg, Zr , La, 0.0001 ~ 0.0100% in one or more the sum of REM it may be contained. 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 the present embodiment, 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 an impurity, the effect of the present embodiment is exhibited as containing elements of the lanthanide series other than those La and Ce. Moreover, the effect of the present embodiment is exhibited as the addition of metal La and Ce.
[0040]
　Ca, Ce, Mg, Zr, La, REM is an element effective for improving the formability of galvannealed steel sheets 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%, the may impair the ductility, the total of the content of each element is preferably 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 embodiment is exhibited without particularly, formability of galvannealed steel sheets in order to obtain a sufficient effect of improving, 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.
[0041]
　In the chemical components in the hot-dip galvanized 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.
[0042]
　Why organization defined the base steel sheet of the galvanized steel sheet according to the embodiment of the present invention is as follows.
[0043]
(Microstructure)
　microstructure in the base material steel plate of such hot-dip galvanized steel sheet to an embodiment of the present invention, the 1/8 thickness 1-3 / 8 thickness range around the 1/4 thickness from the surface of the base material steel plate , the ferrite phase (hereinafter, referred to as ferrite) is not less than 50% in the volume fraction, bainite (hereinafter, bainite hereinafter) and bainitic ferrite phase (hereinafter, referred to as bainitic ferrite) and fresh martensite phase (hereinafter , flash called martensite) and tempered martensite phase (hereinafter, the total of hard tissue comprising one or more of) that tempered martensite is 50% or more by volume fraction, the residual austenite phase (hereinafter, residual austenite hereinafter) of from 0 to 8% volume fraction (including 0%), pearlite (hereinafter, referred to as pearlite) and crude Cementite phase (hereinafter, referred to as cementite) are those sum of is not more than 8% by volume fraction.
[0044]
"Ferrite"
　ferrite is an organization that has excellent ductility. However, ferrite is due to low intensity since it is soft, not obtained sufficient stretch flangeability of galvanized steel sheet when the volume fraction of the ferrite is 50 percent. Therefore, the volume fraction of ferrite is 50% or less. To increase the stretch flangeability, the volume fraction of the ferrite is preferably 45% or less, more preferably 40% or less. Effects of this embodiment without the lower limit of the volume fraction of the ferrite is specifically defined is exerted, may volume fraction be 0%. In order to increase ductility, it is preferable that the ferrite fraction is 5% or more, more preferably 10% or more.
[0045]
"Residual austenite"
　residual austenite strength galvanized steel sheet - an organization to improve the ductility balance. On the other hand, the residual austenite is transformed into hard martensite with the deformation, to serve as starting points of fracture, since the stretch flangeability is degraded, and 8% the upper limit of the volume fraction of retained austenite. From the viewpoint of formability of hot-dip galvanized steel sheet, it is preferable volume fraction of residual austenite is small, preferably 5% or less, more preferably 0 to 3% (including 0%). The volume fraction of retained austenite of galvanized steel sheet is smaller preferably, may be 0%.
[0046]
"Hard tissue"
　to increase the maximum tensile strength and stretch flangeability of galvanized steel sheet, the volume fraction of hard structures consisting of one or more of bainite and bainitic ferrite and fresh martensite and tempered martensite 50% there needs to be more. To increase the stretch flangeability of the steel sheet, the volume fraction of hard structures is preferably set to 58% or more, still more preferably 65% or more. On the other hand, the upper limit of the volume fraction of hard microstructures is exerted the effect of the present embodiment without specifically defined, but may volume fraction be 100%. Lowering the yield stress, to increase the shape fixability, it is preferable that the volume fraction of hard microstructures is less 93%, more preferably 85% or less.
[0047]
"Bainitic ferrite and / or bainite"
　bainitic ferrite and / or bainite is the excellent tissue balance formability and strength of the galvanized steel sheet, the total volume fraction of the bainitic ferrite and bainite there may be a 100%. Further, bainitic ferrite and / or bainite, soft ferrite and hard martensite, a microstructure having an intermediate intensity of tempered martensite and residual austenite, it contained more than 5% from the viewpoint of the stretch flangeability still more preferably, it is more preferably contained by 10% or more. On the other hand, if the bainitic ferrite and / or volume fraction of bainite is more than 90%, increases excessively the yield stress is not preferable because the shape fixability is concerned to degrade.
[0048]
"Tempered martensite"
　tempered martensite, in terms of the tensile strength of the galvanized steel sheet, the volume fraction is preferably 5% or more. The tempered martensite is a structure to improve the tensile strength increased, the volume fraction may be 100%. On the other hand, if the volume fraction of tempered martensite contained in the steel sheet structure is more than 90% increase excessively the yield stress, the shape fixability is feared that degradation, the volume fraction of tempered martensite is 90 % is preferably not greater than.
[0049]
"Fresh martensite"
　fresh martensite, tensile but to strength is greatly improved, while the order degrading stretch flangeability become starting points of fracture, to contain 30% or less at a volume fraction in the steel sheet structure preferable. Particularly more preferable that the volume fraction of fresh martensite is 20% or less in order to increase the hole expandability, further preferably 10% or less.
[0050]
"Other microstructure"
　The steel sheet structure of galvanized steel sheet according to the present embodiment, may include pearlite and / or coarse cementite like other than the tissue. However, the greater the perlite and / or coarse cementite steel sheet structure of the base material steel plate, the ductility deteriorates. Therefore, the volume fraction of pearlite and / or coarse cementite contained in the steel sheet structure is 8% or less in total. Incidentally, it is also preferred that the total of pearlite and / or coarse cementite is 5% or less.
[0051]
　Further, the steel sheet structure of galvanized steel sheet according to the present embodiment, the surface layer ranging to a depth 20μm of the steel sheet direction starting from the interface of the plating layer and the base steel, the volume fraction of residual austenite is 0-3% ( together is limited to including 0%), the volume fraction of the hard microstructures in the surface layer range "V1", the 1/8 thickness 1-3 / 8 thickness range around the 1/4 thickness from the steel sheet surface in 0.90 times or less in the range 0.10 times the volume fraction of said hard tissue "V2".
[0052]
"Retained austenite in the vicinity of the interface between the plated layer and the base steel"
　residual austenite in the vicinity of the interface between the plated layer and the base steel galvanized steel sheet, transformed into hard martensite due to deformation, galvanized steel sheet since serve as starting points of fracture when large strain is applied bending deformation near the surface of the, thereby contributing to the deterioration of bending property and fatigue resistance. From this viewpoint, in the surface layer ranging steel direction depth 20μm originating from the interface between the plating layer and the base steel, it is necessary to limit the volume fraction of retained austenite and 0-3%. The volume fraction of retained austenite in the surface layer ranges preferably as low, it may be 0%.
[0053]
"Hard tissue in the vicinity of the interface between the plated layer and the base steel"
　hard structures in the vicinity of the interface between the plating layer and the base steel sheet of the galvanized steel sheet, increasing the strength in the surface layer of the molten zinc plated steel sheet, the fatigue limit strength the significantly improved, which contributes tissue to improve the fatigue resistance. In this respect, "V1" the volume fraction of hard microstructures in the surface range of the interface of the plating layer and the base steel sheet to the steel sheet direction depth 20μm originating, around a quarter thickness from the surface of the steel sheet 1 / 8 thick case of the "V2" the total volume fraction of 1-3 / 8 range of thickness, the V1 / V2 is these ratios as 0.10 or more, sufficient strength in the surface layer of the molten zinc plated steel sheet it is necessary to improve. Note that to sufficiently improve the fatigue properties, it is preferred that the V1 / V2 is 0.20 or more, more preferably 0.30 or more, further preferably 0.40 or more. On the other hand, the interface of the plating layer and the base steel to suppress the fraction of hard microstructures in the surface layer ranging steel direction depth 20μm originating improves the local ductility by reducing the intensity of hot-dip galvanized steel sheet near the surface by, it is also possible to improve the bending property. From this point of view, to obtain good bendability, V1 / V2 is set to 0.90 or less, preferably set to 0.85 or less, and more preferably to 0.80 or less.
[0054]
　Further, the surface layer range of the interface of the plating layer and the base steel sheet of the galvanized steel sheet according to the present embodiment to the steel sheet direction depth 20μm originating, Si and the BCC crystal grain boundaries and / or the crystal grains of iron / or it may have a fine oxide containing Mn. It is to produce in advance the fine oxides on the steel sheet inside a surface layer ranges, including steel sheet surface serving as a starting point for peeling of the plating layer, namely the Si and / or Mn at the interface of the plating layer and the base steel sheet locations, iron it is possible to suppress the generation of oxide.
[0055]
　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.
[0056]
　Ferrite contained in the steel sheet structure of galvanized steel sheet of the present invention, bainitic ferrite, bainite, tempered martensite, fresh martensite volume fraction of pearlite and coarse cementite thickness cross section parallel to the rolling direction of the steel sheet the sample was taken as a viewing surface, polished viewing surface, and nital etching, 1/8 thickness 1-3 / 8 thickness range around a quarter of the plate thickness, or plating layer and the base steel sheet ( the range up to the steel sheet direction depth 20μm originating from the interface between the base steel) each field emission scanning electron microscope (FE-SEM: field emission scanning observed by electron microscope) the area fraction measured, it it can be regarded as the volume fraction have. However, if the plating layer is removed by nital etching, it may be regarded as the interface between the plated layer and the base steel with a surface of the sample.
[0057]
　The volume fraction of retained austenite included in the steel sheet structure of galvanized steel sheet of the present embodiment, by using a FE-SEM, performs high-resolution crystal orientation analysis by EBSD (Electron Bach-Scattering Diffraction) method, to evaluate.
　First, mirror-finished parallel plate thickness cross section in the rolling direction, 1/8 thickness 1-3 / 8 thickness in the range 1/4 thickness around from the surface of the base material steel plate, or the plating layer and the base steel in each ranging steel direction depth 20μm originating from the interface, a measuring step and 0.15μm or less, 10000 in total 2 to measure the crystal orientation in the above areas. Then, it is determined which of the iron iron or FCC (face-centered cubic structure) of each measurement point BCC (body-centered cubic structure), a point that is determined to FCC iron and residual austenite, the area of retained austenite the fraction can be measured and the volume fraction with it.
Incidentally, when measuring the sufficiently large area for area fraction is the volume fraction equivalent, 10000 in total if the above-mentioned 2 volume fraction the area fraction of retained austenite by measuring the crystal orientation at least in the region it can be a rate.　
[0058]
Galvanized steel sheet of the present embodiment has a fine layer on the interface with the plating layer in the base steel sheet. A portion near the plating layer in the refinement layer is in direct contact with the plating layer.
　The fine layer, present in the outermost layer of the base steel sheet, the average particle size of the ferrite phase constituting the fine layer, an average particle size of the ferrite phase in the lower layer side than the finer layer in the base material steel plate 1 / is an area that is 2 or less. 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.
　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.
[0059]
　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, and more preferably to 1μm or more. The average thickness of the finer layer is not more than 5.0 .mu.m, 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.
[0060]
　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, and more preferably to 1μm or more. Further, when the average particle size of the ferrite phase of the finer layer and 3μm 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 3μm or less, it is preferable to 2μm or less.
[0061]
　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. When the maximum diameter of the oxides is 0.4μm or less, it can be formed while suppressing excessive alloying of the plating layer. Therefore, to form a fine layer, it is possible to prevent deterioration of coating adhesion due to the Fe content in the coating layer is too large. Maximum diameter of the oxides is preferably 0.2μm or less.
[0062]
　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) is observed at 5000-fold.
[0063]
　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.
[0064]
(Plated layer)
　hot-dip galvanized steel sheet of an embodiment of the present invention is hot-dip galvanizing layer on the surface of the base material steel plate is formed.
　In embodiments of the present invention, the galvanized layer, Fe content was 0% super-5.0%, Al content is 0% 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 embodiment is not impaired, corrosion resistance and workability by the content there is sometimes such preferred are improved.
　Moreover, galvanized layer includes columnar crystals composed of ζ phase, 20% or more of the total interface between the plated layer and the base steel is characterized in that it is coated on 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 or less.
[0065]
[Fe content in galvanized layer: 5.0% or less]
　Since the coating adhesion and the Fe content is increased in the galvanized layer is deteriorated, it is necessary that the Fe content of 5.0% or less . 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. Although not provided the lower limit of the Fe content in the coating layer, in particular, since it is less than 0.5% may ζ phase can not be sufficiently obtained necessary in order to improve the adhesion, the Fe content in the coating layer preferably 0.5% or more, further preferably 1.0% or more.
[0066]
[Al content in the galvanized layer: 1.0%]
　Since the coating adhesion between the Al content is increased to deteriorate the galvanized layer, it is necessary to set the Al content is 1.0% or less . 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 coating layer is not particularly provided, in order to less than 0.01% must be reduced extremely the Al concentration in the plating bath, as a result, the alloying of the plating layer is too since the Fe content in the coating layer is deteriorated plating adhesion increasing by proceeds, Al content in the coating layer is preferably set to 0.01% or more. In this respect, Al content in the coating layer is preferably 0.05% or more.
[0067]
　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、本実施形態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。
[0068]
"Ζ phase"
　in FIG. 1, according to the present embodiment, showing a cross-sectional enlarged structure photograph of galvanized steel sheet. As shown in FIG. 1, galvanized layer of the present embodiment is a plated layer which is coated on the surface of the base steel sheet (base steel), zeta phase is an alloy of Fe and Zn (FeZn 13 consists of) In particular, the galvanized steel sheet of the present embodiment, the ratio of the interface of all the interface between the galvanized layer and the base steel sheet (A), the ζ phase is in contact with the base material steel plate (A *) (( a * / a) × 100) is equal to or less than 20%. Thus, coarse oxides over longer diameter 0.2μm containing Si and / or Mn can serve as a starting point of peeling, taken into the ζ phase from the base steel sheet surface, whereby the starting point of the coarse oxides destruction as it becomes difficult work, improving the adhesion of the plating layer. From this viewpoint, it is preferable that the interface ζ phase and the base steel is more than 25% proportion accounted for all of the interface between the plating layer and the base steel sheet, and 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 plated layer and the base steel is not particularly defined, but may be 100%.
[0069]
　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, the ratio of the interface of coarse oxides exists zeta crystal grains and (coarse oxides containing zeta grains) and the base steel of in zeta phase crystal (zeta crystal grains) is, zeta phase and the base steel sheet preferably 50% or less for all of the interface between, and more preferably 35% or less. Preferably the fewer coarse oxide at the interface of the base material steel plate of the zeta phase, zeta phase and of all of the interface between the base steel sheet, coarse oxides containing zeta grains land at the interface between the zeta phase and the base steel sheet it is most preferred ratio of the interface formed between the iron is 0%.
[0070]
When the long diameter of oxide including the 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 it serves 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.
[0071]
　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.
[0072]
　Ratio of the interface ζ phase and the base steel sheet in the present embodiment accounts for all of the interface between the plated layer and the base steel sheet can be obtained in the following manner.
That is, a sample was taken as an observation plane parallel plate thickness cross section in the rolling direction of the base material steel plate, the viewing surface was mirror-polished, first, field emission scanning electron microscope (FE-SEM: Field Emission Scanning Electron Microscope) the use, the total L of the length of the observed surface is observed until more than 200 [mu] m. 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, the separation of the ζ phase and δ1 phases may be carried out by a method other than the 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.
[0073]
　In order to clearly revealing the ζ phase, it may be subjected to a corrosion of the observation plane of the viewing surface of the sample using the etchant nital like after mirror polishing.
The presence or absence of long diameter 0.2μm or more coarse oxides, performing sectional SEM observation in the manner described above, to determine by measuring the major axis of the photographed oxide.
[0074]
Note that the oxide-containing ζ crystal grains, interfacial alloy layer taken by a BSE image (backscattered electron image), can be determined by the difference of tones. Reflection electron image to become more larger the atomic number, oxides appear dark compared to the surrounding. Position which can oxide depends annealing dew point, and generates the internal side of the surface layer of the higher dew point is high (about 0 ℃ or higher) instead of the surface of the steel sheet steel. After formation of the plating layer, the process proceeds alloying, as Fe in the base steel sheet surface layer is diffused in the plating layer, oxides of internal sequentially from the surface is taken into the plating layer between the plating layer and the base steel sheet . Furthermore, in the oxides having determined, by measuring the major axis on the observation plane, the major axis is determined more than 2μm and coarse oxides.
[0075]
[Adhesion amount of hot-dip galvanizing: 10 ~ 100 g / m 2 ]
　since no sufficient corrosion resistance can not be obtained with a small amount of adhesion to the base material steel plate one surface of galvanized layer, to the base steel sheet one surface of the plating layer coating weight 10 g / m 2 and more. From the viewpoint of corrosion resistance, coating weight 20 g / m 2 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, electrode wear when performing spot welding is severe, degradation of loss and welded joint strength of the welding nugget diameter occurs when performing welding continuously. Therefore, the coating weight of the plating layer 100 g / m 2 or less. In view of the continuous weldability, coating weight 93 g / m 2 is preferably not more than, 85 g / m 2 and more preferably less.
[0076]
(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.
　Method for manufacturing a galvanized steel sheet according to the present embodiment, a slab having the above chemical components is heated to 1080 ° C. or higher, the hot-rolled steel sheet subjected to hot rolling to a rolling completion temperature in the range of 850 ~ 980 ° C. and then, a step of winding then as a coil, a hot rolling step of controlling so as to satisfy the equation (1) described below the temperature of the hot-rolled steel sheet in the course of cooling until 300 ° C. after rolling the hot, the hot rolled after pickling following step, a cold rolling step of performing cold rolling to a reduction ratio in total 85% or less, the steel sheet after the cold rolling step, the average heating rate between 600 ~ 750 ° C. 1.0 ° C. / s or higher, the maximum heating temperature (Ac3-60) ℃ or higher and heated as 750 ° C. or more temperature range, then the average cooling rate between 720 ~ 650 ℃ 2.5 ℃ / sec or higher, 650 ° C. ~ the average cooling rate between 500 ° C. 5 And annealing step of cooling as 0 ° C. / sec or more, after the annealing step, 450 ~ 470 ° C. The plating bath temperature, 440 ~ 480 ° C. The temperature of the steel sheet during the plating bath enters, an effective Al amount in the plating bath 0. by immersing the steel sheet in the plating conditions to from 050 to 0.180 wt% in the plating bath, the plating step of forming a plating layer with galvanized surface of the steel sheet, after the plating step, cooling to 350 ° C. and after plating cooling step satisfying the equation (2) that the process will be described later, the steel sheet further 100 ° C. until the later diameter 50 ~ 800 mm roll total of two or more bending with cooling below - processing steps of performing deformation by bending back and , comprising a.
　Follows is a detailed description of each manufacturing step.
[0077]
　To produce the hot-dip galvanized steel sheet according to the embodiment of the present invention produces first a base steel sheet steel.
　In order to manufacture the steel plate, first, casting a slab having the above chemical components (composition). Slab subjected to hot rolling, it is possible to use those produced by such a continuous casting slab or thin slab caster.
[0078]
"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. More preferably, the heating temperature of the slab to 1150 ° C. or higher. On the other hand, the upper limit of the heating temperature of the slab is not particularly defined, since it leads to a significant increase in manufacturing cost must be turned a large amount of energy to heat beyond 1300 ° C., be 1300 ° C. or less preferable.
[0079]
　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, and more preferably set to 870 ° C. or higher. On the other hand, the completion temperature of the hot rolling in a 980 ° C. greater, because the device 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, hot the completion temperature of the rolled and 980 ° C. or less, and more preferably set to 950 ° C. or less.
[0080]
　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.
　Coiling temperature of hot-rolled steel sheet is preferably set to 450 ° C. or higher 650 ° C. or less. This pearlite and / or major axis to the microstructure of the hot rolled steel sheet is produced by dispersing a more coarse cementite 1 [mu] m, in order to localize the distortion introduced by the cold rolling. Thus, by the inverse transform to austenite various crystal orientations in the annealing step, in order to refine the effective crystal grains of the base material steel plate after annealing. When the coiling temperature is below 450 ° C., it may pearlite and / or coarse cementite is not generated, which is not preferable. On the other hand, when the coiling temperature exceeds 650 ° C., pearlite and ferrite is formed in a long strip shape in the rolling direction, respectively. Thus, there is a tendency that the effective crystal grain of the base material steel plate to produce a ferrite portion after cold rolling and annealing becomes coarse, which extends in the rolling direction is undesirable.
[0081]
　Here, the surface of the base material steel plate after annealing, in order to control the hard tissue to a predetermined volume fraction, in the hot rolling process, it is necessary to moderately decarburizing the base steel sheet surface. Decarburization behavior from the base steel sheet is not may be controlled by controlling the atmosphere, a large-scale equipment is required, a large load in terms of cost. Therefore, in this embodiment, in the interval from the finish rolling completion (hot rolling finished) up to 300 ° C., by controlling the steel sheet temperature by controlling the cooling rate, to control the decarburization behavior.
　Temperature control of the base material steel plate, out of the zone up to 300 ° C. from the finish rolling completion is performed in a range where BCC phase of iron in the base steel sheet surface is temperature Ae3 * below which will become stable. This decarburization from BCC phase of iron is to advance faster than the decarburization from FCC phase is stable phase at high temperature. In the present embodiment, the temperature range lower than the temperature of the steel strip is 300 ° C., the rate of diffusion of oxygen is sufficiently slow, since considered not to affect the decarburization behavior also advancing speed of the decarburization, the mother in the hot rolling process temperature range of the temperature control of the timber steel sheet is a section of up to 300 ° C..
　It should be noted, Ae3 * can be determined using the following formula.
[0082]
　Ae3 * [℃] = 885 + 31.7Si-29.3Mn + 123.2Al-18.2Cr-40.0Ni-21.0Cu + 12.6Mo
[0083]
　In the above formulas, C, Si, Mn, Al, Cr, Ni, Cu, Mo is the amount of the respective elements (mass%).
[0084]
　Further, decarburization behavior of the steel sheet is controlled separately in the second phase of the first phase to winding the coil from the finish rolling completion, the wound in coils up to the room temperature. This is the first phase whereas progresses decarburization under air, in the second phase, wound in close contact steel plates by a coil, decarburization in outside air intrusion little conditions There to proceed, because the rate of progression of decarburization in both differ significantly.
[0085]
　Specifically, in order to appropriately decarburizing the steel sheet surface layer portion, in the course of cooling up to 300 ° C. from the finish rolling completion, to control the temperature of the steel strip to a range satisfying the following formula (1). Equation (1) is a formula related to the degree of progress of decarburization behavior, indicating that the higher the decarburization value of expression (1) is greater progresses. Note that each term in equation (1), t [sec] is the time elapsed from the finish rolling completion, t1 [s] is the time elapsed until the finish rolling completion Ae3 * temperature, t2 [s ] is the elapsed time until the wound into the coil from the finish rolling completion, t3 [s] is the time elapsed from the finish rolling completion until the steel sheet temperature reaches 300 ° C.. Further, T (t) [℃] is steel temperature, W Si [mass%] and W Mn [wt%] is the average content of each element of Si, Mn in the whole steel sheet, respectively. Furthermore, alpha, beta, gamma, each term of δ is a constant term, respectively × 10 8.35 8 , 2.20 × 10 4 , 1.73 × 10 10 , 2.64 × 10 4 is.
[0086]
[Number 1]

[0087]
　In the above formula (1), first integral term in parentheses is a term related to the degree of progress of decarburization during the cooling of the first stage, second integral term progression of decarburization during the cooling of the second phase degree and is a term to which it is related. In either term, decarburization high base steel sheet temperature, and dwell time progresses longer. Particularly, in the second phase, oxygen is an element to promote the decarburization is hardly present in the atmosphere, for the progress of decarburization by oxygen attracted by the Si and Mn in the steel from the surface of the scale layer, the second integration the term includes the impact of the content of Si and Mn, the value of the expression 1 the more Si and Mn content in steel increases, indicating that the decarburization proceeds.
[0088]
　In the course of cooling after the finish rolling completion, the value of the above formula (1) is less than 0.8, the base steel sheet surface layer portion hardly decarburization, the volume ratio V1 of the hard tissue of the surface layer portion, the thickness of the since the volume ratio ratio of V2 of the hard tissue around the 1/4 thickness from the surface V1 / V2 exceeds 0.90, the bending property is deteriorated, the value of the above formula (1) is 0.8 or more and for cooling in such a way that. From this viewpoint, it is preferable to cool such that the value of the above formula (1) is 1.0 or more, more preferably be 1.3 or more. On the other hand, when the value of the above formula (1) is more than 20.0, excessive decarburization steel plate surface layer portion, V1 / V2 is less than 0.30, since the fatigue resistance of the steel sheet is remarkably deteriorated, the formula the value of (1) to cool so that 20.0. From this viewpoint, it is preferable to cool such that the value of the above formula (1) is 15.0 or less, and more preferably be 10.0.
[0089]
　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.
[0090]
"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 base steel sheet is lost, because the increasing risk of the base steel sheet during cold rolling is broken, 85% or less of total reduction ratio to. From this viewpoint, the total rolling reduction is preferably set to 75% or less, more preferably 70% or less. For lower limit of the total reduction ratio in the cold rolling step is not particularly defined, which is less than 0.05% will heterogeneity shape of the base material steel plate, plating is not uniformly adhere the appearance is impaired, 0.05 preferably be at least%, more preferably it is 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.
[0091]
　Further, reduction rate sum of 10% of the cold rolling, in the range of less than 20%, recrystallization does not proceed sufficiently in the subsequent annealing step. Thus, coarse crystal grains that have lost malleable contains a large amount of dislocations remains near the surface, in some cases bending resistance and fatigue resistance of the galvanized steel sheet is degraded. To avoid this, to reduce the total rolling reduction, or in the minor accumulation of dislocations in the crystal grains leave malleable grains, or by increasing the total reduction ratio, the recrystallization in the annealing step sufficiently advanced, it is effective to a worked structure within the accumulation of dislocation is small recrystallized grains. 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.

The scope of the claims
[Claim 1]
It consists of a galvanized layer formed on at least one surface of the steel sheet and the steel sheet,
said steel sheet contains, by
　mass%, C:
　0.040 ~ 0.280%, Si: 0.05 ~ 2.00% ,
　Mn:
　0.50
　～ 3.50 Pasento, P: 0.0001
　～ 0.1000 Pasento, S: 0.0001 ～ 0.0100 Pasento, Al: 0.001
　～ 1.500 Pasento, N: 0.0001
　0.0100% ~, O: 0.0001 ~ 0.0100%,
has a chemical composition balance consisting of Fe and impurities, further
1/8 thickness around a quarter thickness from the surface of the steel sheet - 3/8 in a range of thickness,
volume fraction, and 0-50% of ferrite phase,
the hard tissue comprising one or more of bainite and bainitic ferrite phase and fresh martensite phase and tempered martensite phase a total of more than 50% And a top, the residual austenite phase 0 to 8% the sum of the pearlite phase and coarse cementite phase is 0-8%
and the steel sheet direction depth 20μm from the interface of the galvanized layer and the base steel in the surface layer ranging,
0 to 3% residual austenite,
and the hard tissue volume fraction V1 in the surface layer range, 1/8 thickness 1-3 / 8 thickness around the 1/4 thickness from the steel sheet surface having said hard tissue microstructure that limits the ratio of the volume fraction V2 V1 / V2 to the range of 0.10 to 0.90 of the range of
the galvanizing layer, Fe content is 5% or less, and the Al content is 1.0% or less, includes a columnar crystal composed of ζ phase, further,
the ζ phase of the total surfactant (a) between the galvanized layer and the base steel sheet percentage and occupied by the interface of the base material steel plate (a *) ((a / A) × 100) is not less than 20%, the fine layer on the surface side in the base steel sheet is formed, the is 0.1 ~ 5.0 .mu.m average thickness of the fine layer, the fine layer the average particle size of the ferrite phase is 0.1 ~ 3.0 [mu] m in said one or more oxides of Si and Mn contained in the finer layer, the maximum diameter of the oxide is 0. hot-dip galvanized steel sheet is 01μm ~ 0.4μm.
[Claim 2]
The steel sheet contains, by
　mass%,
　Ti: 0.001 ~ 0.150%,
　Nb: 0.001 ~ 0.100%, V: 0.001 ~ 0.300%,
1 kind or selected from among the hot-dip galvanized steel sheet according to claim 1 containing two or more.
[Claim 3]
The steel sheet contains, by
　mass%,
　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%,
containing one or more selected from among the claims 1 or according to 2 galvanized steel plate.
[Claim 4]
The steel sheet contains, by
mass%, Ca, Ce, Mg, Zr, La, in any one of claims 1 to 3 containing from 0.0001 to 0.0100 percent of one or two or more kinds in total of REM hot-dip galvanized steel sheet according.
[Claim 5]
In the hot-dip galvanizing layer, claim ζ interface between coarse ζ oxides are present crystal grains and the base steel of the crystal grains, 50% or less is the total interface between the ζ phase and the base steel galvanized steel sheet according to any one of 1-4.
[Claim 6]
Wherein the galvanized layer, coating weight is 10 g / m in one side of the steel plate 2 or more, 100 g / m 2 galvanized steel sheet according to any one of claims 1 to 5 or less