The present invention, ductility, bendability, excellent coating adhesion during hole expandability and bending deformation, and, to a high strength galvanized steel sheet having excellent continuous bending fatigue properties.
BACKGROUND
[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]
　On the other hand, for example, in the galvanized steel sheet described in Patent Document 12, the appearance unevenness was occur derived from the non-uniformity of the Fe content of the plating layer in the width direction.
CITATION
Patent Document
[0011]
Patent Document 1: JP 2008-019465 Patent Publication
Patent Document 2: JP 2005-060742 Patent Publication
Patent Document 3: JP-A-9-176815
Patent Document 4: JP 2001-026853 Patent Publication
Patent Document 5: JP 2002-088459 JP
Patent Document 6: JP 2003-055751 Patent Publication
Patent Document 7: JP 2003-096541 JP
Patent Document 8: JP 2005-200750 JP
Patent Document 9: JP-A 11-140587 JP
Patent Document 10: JP 2001-303226 JP
Patent Document 11: JP 2005-060743 JP
Patent Document 12: WO 2016/072477
Summary of the Invention
Problems that the Invention is to Solve
[0012]
　In view of the situation described above, the present invention is, ductility, excellent formability of the bendability and the steel sheet represented by stretch flangeability, appearance uniformity of the plating, fatigue resistance, weldability, corrosion resistance and plating adhesion there is provided a high-strength galvanized steel sheet having excellent.
Means for Solving the Problems
[0013]
　The present inventors have ductility, and formability of the bendability and the steel sheet represented by stretch flangeability, fatigue properties, weldability, in order to obtain a high strength galvanized steel sheet excellent in corrosion resistance and plating adhesion intensive extensive investigations. As a result, the present inventors have improved ductility and hole expandability (the stretch flangeability) 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 steel sheet and the boundary from bending by controlling the volume fraction of the base material steel plate side of the hard phase of the fatigue resistance. Furthermore, the present inventors have found that even when using a steel sheet containing Si and Mn in a large amount as be plated, immediately below the plating layer and the base steel sheet and Fe-Al alloy layer formed at the interface it is possible to suppress the crack generation and propagation during processing by forming a specific refinement layer electrode composed of fine grains of the ferrite phase, it was found that could suppress the plating peeling as a starting point. Further, by controlling the thickness of the fine layer and Fe-Al alloy layer in the steel plate width direction to a specific range, found that it is possible to obtain a galvanized steel sheet excellent in appearance uniformity not only the coating adhesion It was.
[0014]
　The present invention was completed on the basis of this finding, the embodiment is as follows.
[0015]
(1) A hot dip galvanized steel sheet having a galvanized layer on at least one side of the base material steel plate,
　the base material steel plate is a
　　mass%, C: 0.040% ~
　　0.280%, Si:
　　%
　　~ 2.00 0.05%, Mn: 0.50% ~
　　3.50%, P: 0.0001% ~ 0.1000%, S: 0.0001% ~
　　0.0100%, Al: 0.
　　%
　　~ 1.500 001%, N: 0.0001% ~ 0.0100%,
　　O: 0.0001% ~ 0.0100%, Ti:
　　0% ~ 0.150%, Nb: 0% ~ 0.100
　　Pasento,
　　V:
　　0 Pasento ～ 0.300 Pasento, Cr: 0 Pasento
　　～ 2.00 Pasento, Ni: 0 Pasento ～ 2.00 Pasento, Cu:
　　0 Pasento ～ 2.00 Pasento, Mo: 0 Pasento ～ 2.00
　　%, B: 0%
　　~ 0.0100%, W: 0% ~ 2.00%, and
　　Ca, Ce, Mg, Zr, La, and REM: 0% to 0.0100% in total
comprises a
　balance having a chemical composition consisting of Fe and impurities,
　The total thickness of the base material steel plate, the at 1/8 thickness 1-3 / 8 thickness in the range of 1/4 thickness around from the surface of the base material steel plate,
　ferrite phase at a volume fraction of 50% or more 97 % or less,
　the total of hard tissue comprising one or more of the bainite phase and bainitic ferrite phase and fresh martensite phase and tempered martensite phase at a volume fraction of 3% or more,
　the residual austenite phase volume fraction 0% to 8%,
　0% to 8% in the total volume fraction of the pearlite phase and coarse cementite phase,
　the surface layer portion from the interface between the galvanized layer and the base steel sheet to the steel sheet direction depth 20μm in,
　0 to 3% residual austenite volume fraction,
　and the hard tissue volume fraction V1 in the surface layer portion, 1/8 thickness around a quarter thickness from the steel sheet surface 1-3 / 8 wherein the range of thicknesses hard Which is the ratio V1 / V2 of the volume fraction V2 tissue has the microstructure in the range of 0.10 to 0.90,
　Fe content in the galvanizing layer is 0% and 3.0% or less, and the Al content is 0% or less than 1.0%,
　the interface between the galvanized layer and the base steel sheet, the average thickness is 0.1 [mu] m ~ 2.0 .mu.m, steel width the difference between the maximum thickness and the minimum thickness in the direction having an Fe-Al alloy layer is within 0.5 [mu] m,
　To the base material in the steel sheet has a fine layer in direct contact with the Fe-Al alloy layer, wherein the 0.1 [mu] m ~ 5.0 .mu.m average thickness of the finer layer, the average of the ferrite phase in the finer layer particle size is 0.1 [mu] m ~ 3.0 [mu] m, the contains one or more oxides of Si and Mn in fine layer, the maximum diameter of 0.01 [mu] m ~ 0.4 .mu.m of the oxide , and the wherein the difference between the maximum thickness and the minimum thickness of the fine layer of the steel plate width direction is within 2.0 .mu.m, galvanized steel sheet.
(2) the coating weight per one side of the galvanized layer is 10 g / m 2 or more, 100 g / m 2 and equal to or less than, hot-dip galvanized steel sheet according to (1).
(3) the base material steel plate contains, by mass%,
　　further,
　　Ti: 0.001% ~ 0.150%, Nb: 0.001% ~ 0.100%, and
　　V: 0.001% ~ 0.300 %,
　characterized in that it contains one or more selected from the group consisting of hot-dip galvanized steel sheet according to (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:
　　0.01 Pasento ～ 2.00 Pasento, B: 0.0001 Pasento ～ 0.0100 Pasento, and
　　W: 0.01% ~ 2.00%,
　characterized in that it contains one or more selected from the group consisting of any one of (1) to (3) Melt zinc-plated steel plate.
(5) the base material steel plate contains, by mass%,
　furthermore, Ca, Ce, Mg, Zr, La, and 0.0001% - selected from the group consisting of REM 1 or two or more in total 0. characterized in that it contains 0,100%, hot-dip galvanized steel sheet according to any one of (1) to (4).
The invention's effect
[0016]
　According to the aspect of the present invention can provide the appearance uniformity of the plating, formability, fatigue resistance, weldability, hot-dip galvanized steel sheet excellent in corrosion resistance and plating adhesion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017]
[1] Figure 1 is a diagram showing an example of a schematic view of a sectional structure of a molten zinc plated steel sheet of the present invention.
DESCRIPTION OF THE INVENTION
[0018]
　Galvanized steel sheet according to the embodiment of the present invention, in 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: containing between 0.0001% 0.0100%, the remainder being the base steel sheet having a chemical composition consisting of Fe and impurities (. hereinafter, simply also referred to as a steel plate) surface galvanized layer (hereinafter, simply also referred to as a plating layer.) in which is formed.
　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.
　Plating layer, Fe content is not more than 0% and 3.0%, Al content is 0% or less than 1.0%.
[0019]
　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 those except those where there is a special description means the mass%.
[0020]
[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%.
[0021]
[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, the content of Si exceeds 2.00%, it tends to occur problems such as cast slab cracking. 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.
[0022]
[Mn: 0.50% ~ 3.50%]
　Mn is contained in order 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.
[0023]
[P: 0.0001% ~ 0.1000%]
　P is an element which embrittle steel, further the content of P is more than 0.1000%, or cracking the cast slab, the slab during rolling because tends to occur troubles such as cracked, 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 value of 0.0001% to 0.0010% or more it is preferable.
[0024]
[S: 0.0001% ~ 0.0100%]
　S is combined with Mn to form coarse MnS, ductility, since an element to lower the moldability such hole expandability (stretch-flange formability) and bendability , the content of S and 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 0.0001% as the lower limit value, preferably set to 0.0005% or more, and more preferably 0.0010% or more.
[0025]
[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, accompanied by a substantial increase in production cost to the content thereof less than 0.001%. Therefore, Al content is 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.
[0026]
: [N 0.0001% ~ 0.0100%]
　Since N forms coarse nitrides, ductility, is an element degrading the formability such hole expandability (stretch-flange formability) and bending resistance, the it is necessary to suppress the content. 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 content 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.
[0027]
[O: 0.0001% ~ 0.0100%]
　O forms an oxide, ductility hot-dip galvanized steel sheet, from degrading the formability such hole expandability (stretch-flange formability) and bendability, O it is necessary to suppress the content of. 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.
[0028]
　Additional, the base steel sheet of the galvanized steel sheet according to the present embodiment, may be contained the following elements as required.
[0029]
　First, in the base steel sheet according to the present embodiment, further, Ti: 0.001% ~ 0.150%, Nb: 0.001% ~ 0.100%, and V: 0.001% ~ 0.300 %, it may contain one or more selected from the group consisting of.
[0030]
[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, the increasing strength of the galvanized steel sheet an element which contributes. However, if the content of Ti exceeds 0.150%, the deterioration of the formability deposition number is in the carbonitride, Ti content should be not more than 0.150%. From the viewpoint of moldability, the content of Ti is preferably not more than 0.080%. On the other hand, 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 Ti, the content of Ti is 0.001% or more it is preferable. For even higher strength galvanized steel sheet, the content of Ti is more preferably 0.010% or more.
[0031]
[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, the content of Nb exceeds 0.100%, the deterioration of the formability of the galvanized steel sheet deposition number is in the carbonitride, the content of Nb is set to 0.100% or less. From the viewpoint of formability, the Nb content is 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, to obtain a sufficient strength increasing effect by Nb, the content of Nb is 0.001% or more It is preferred. For even higher strength galvanized steel sheet, the content of Nb is more preferably 0.005% or more.
[0032]
[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 0.300%. The content of V is 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 strength increasing effect by V sufficiently, it is preferable that the content of V is 0.001% or more, more preferably 0.010% or more.
[0033]
　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%, and W: 0.01% ~ 2.00%, 1 kind selected from the group consisting of two or it may contain more.
[0034]
[Cr: 0.01% ~ 2.00%]
　Cr 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 contain Te. However, the content of Cr is more than 2.00%, since the workability is impaired productivity in hot drops, the Cr content is not more than 2.00%. The content of Cr is preferably not more than 1.20%. On the other hand, the effect of the content of the lower limit in this embodiment even without particularly setting of Cr is exerted in order to obtain a sufficient effect of strengthening by Cr, the content of Cr is 0.01% or more it is preferably, more preferably 0.10% or more.
[0035]
[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 contain Te. However, when the content of Ni exceeds 2.00%, since the weldability is impaired, the Ni content is not more than 2.00%. The content of Ni is preferably not more than 1.20%. In contrast, although even lower limit of the content of Ni is not particularly setting effect of this embodiment is exhibited, in order to obtain a sufficient effect of strengthening by Ni, the Ni content is 0.01% or more preferably there, more preferably 0.10% or more.
[0036]
[Cu: 0.01% ~ 2.00%]
　Cu is an element to increase the strength of the galvanized steel sheet by the presence in the steel as fine particles, instead of a part of the C and / or Mn it can be contained. However, when the Cu content exceeds 2.00%, since the weldability is impaired, the Cu content is not more than 2.00%. The content of Cu is preferably not more than 1.20%. On the other hand, the lower limit of the content of Cu is effective in the present embodiment is exhibited without particularly, to obtain a sufficient effect of hot-dip galvanized steel sheet and high strength by Cu, the content of Cu is 0. is preferably 0.1% or more, more preferably 0.10% or more.
[0037]
[Mo: 0.01% ~ 2.00%]
　Mo 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 contain Te. However, the content of Mo is if it exceeds 2.00%, since the workability impaired by productivity in hot drops, the content of Mo should be not more than 2.00%. The content of Mo is preferably not more than 1.20%. On the other hand, the effect of the present embodiment also the lower limit of the content is not particularly setting of Mo is exerted in order to obtain a sufficient effect of strengthening by Mo, the content of Mo is 0.01% or more it is preferably, more preferably 0.05% or more.
[0038]
[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 contain Te. However, the content of B exceeds 0.0100% since the workability is impaired productivity in hot drops, the content of B is set to 0.0100% or less. From the viewpoint of productivity, the content of B is preferably not more than 0.0050%. On the other hand, the effect of the content of the lower limit in this embodiment even without particularly setting of B is exerted, in order to obtain a sufficient effect of strengthening due to the B, the content of B 0.0001% or more and it is preferable to. For increasing the strength of the additional hot-dip galvanized steel sheet, the content of B is more preferably 0.0005% or more.
[0039]
[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 contain Te. However, the content of W is more than 2.00%, since the workability is impaired productivity in hot drops, the content of W is set to 2.00% or less. The content of W is preferably not more than 1.20%. 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.
[0040]
　0 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, and one member selected from the group consisting of REM or two or more kinds in total .0001% may be contained 0.0100%. Containing reasons 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, REM and Ce it is often contained in mischmetal, which 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 these La and Ce. Moreover, the effect of the present embodiment are exhibited as containing metal La or Ce.
[0041]
　Ca, Ce, Mg, Zr, La, and REM are elements effective in improving the formability of hot-dip galvanized steel sheet may contain one or two or more. However, Ca, Ce, Mg, Zr, La, and the total of one or more content selected from the group consisting of REM exceeds 0.0100%, the may impair the ductility, the the total content of the element is set to 0.0100% or less. It is preferable that the total content of each of these elements is less than 0.0070%. On the other hand, Ca, Ce, Mg, Zr, La, and one or more content lower limit selected from the group consisting of REM is the effect of the present embodiment is exhibited without particularly, to obtain the effect of improving the formability of hot-dip galvanized steel sheet 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, and the sum of one or more content selected from the group consisting of REM is more preferably at 0.0010% or more.
[0042]
　In the chemical components in the hot-dip galvanized steel sheet according to the present embodiment, the remainder of the elements described above is Fe and 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.
[0043]
　Why organization defined the base steel sheet of the galvanized steel sheet according to the embodiment of the present invention is as follows.
[0044]
(Microstructure)
　for microstructure of the base material steel plate of the hot-dip galvanized steel sheet according to the embodiment of the present invention will be described. Although the characteristics of the steel varies with microstructure, when quantifying microstructure, over the entire region of the steel material to quantify microstructure, it is not practical to define. Therefore, the present invention illustrating a typical microstructure of the steel material to quantify the microstructure of 1/8 thickness 1-3 / 8 thickness around the 1/4 thickness from the surface of the base steel sheet, specified. Mid-thickness portion, since the microstructure is changed by strong solidification segregation, it can not be said microstructure representative of steel. Site close to the surface layer of the steel sheet in order to change the microstructure by reaction with local temperature changes or the outside air, it can not be said microstructure representative of steel.
　A microstructure base steel sheet of the galvanized steel sheet according to the embodiment of the present invention, 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, ferrite phase ( hereinafter, ferrite hereinafter) is at a volume fraction of 40% or more and 97% or less, bainite phase (hereinafter, bainite hereinafter) and bainitic ferrite phase (hereinafter, referred to as bainitic ferrite) and fresh martensite phase (hereinafter , fresh referred martensite) and tempered martensite phase (hereinafter, the total of hard tissue comprising one or more of) that tempered martensite is not less than 3% by volume fraction, the residual austenite phase (hereinafter, referred to as the residual austenite ) is 0% to 8% in the volume fraction (including 0%), pearlite (hereinafter, referred to as pearlite) coarse Mentaito phase (hereinafter, referred to as cementite) Total and is what is 0% to 8% volume fraction (including 0%).
[0045]
"Ferrite"
　ferrite is an organization that has excellent ductility. However, ferrite is due to low intensity since it is soft, not obtained galvanized steel sheet sufficient tensile maximum strength when the volume fraction of the ferrite is 97 percent. Therefore, the volume fraction of ferrite is 97% or less. To increase the maximum tensile strength of the galvanized steel sheet, the volume fraction of ferrite is preferably set to less 92%, and more preferably 85% or less. Furthermore, the maximum tensile strength is obtained a galvanized steel sheet of more than 950 MPa, more preferably to the volume fraction of ferrite and 80% or less, more preferably 70% or less. Meanwhile, the volume fraction of the ferrite is sufficient ductility is not obtained at less than 50%, the volume fraction of ferrite is 50% or more. It is preferable that the volume fraction of ferrite and 55% or more, more preferably 60% or more.
[0046]
"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%.
[0047]
"Hard tissue"
　to increase the maximum tensile strength of the 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 in total more than 3% there needs to be. To increase the maximum tensile strength of the galvanized steel sheet, the volume fraction of hard structures is preferably set to 7% or more, more preferably 15% or more. On the other hand, limits since the ductility of the hot-dip galvanized steel sheet excessively increase the volume fraction of hard structures is deteriorated, the volume fraction of hard structures to 60% or less. In this respect, the volume fraction of hard structures is preferably set to 55% or less, more preferably 50% or less.
[0048]
"Bainitic ferrite and bainite"
　bainitic ferrite and bainite is an excellent tissue balance formability and strength of the galvanized steel sheet, 60% or less of the bainitic ferrite and / or bainite volume fraction There is preferably contained in the steel sheet structure. Further, bainitic ferrite and bainite are microstructure having soft ferrite and hard martensite, an intermediate strength of tempered martensite and retained austenite, and more may be included more than 5% from the viewpoint of the stretch flangeability 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 60%, increases excessively the yield stress is not preferable because the shape fixability is concerned to degrade.
[0049]
"Tempered martensite"
　tempered martensite is a structure to improve the tensile strength of the galvanized steel sheet increases, it may be contained less than 60% volume fraction in the steel sheet structure. From the viewpoint of tensile strength, the volume fraction of tempered martensite is preferably 5% or more. On the other hand, if the volume fraction of tempered martensite contained in the steel sheet structure is more than 60%, increases excessively the yield stress is not preferable because the shape fixability is concerned to degrade.
[0050]
"Fresh martensite"
　fresh martensite is included but greatly improve the tensile strength of the galvanized steel sheet, on the one hand in order to degrade the stretch flangeability become starting points of fracture, 30% or less at a volume fraction in the steel sheet structure it is preferred that the. 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.
[0051]
"Other microstructure"
　The steel sheet structure of galvanized steel sheet according to the embodiment of the present invention, may be contained pearlite and / or coarse cementite like other than the tissue. However, pearlite and / or coarse cementite becomes large, ductility deteriorates the steel sheet in the tissue of the molten zinc steel plate. 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 preferable that the volume fraction of pearlite and / or coarse cementite is 5% or less in total.
[0052]
　Further, the steel sheet structure of galvanized steel sheet according to the embodiment of the present invention, the plating layer and the surface layer portion interface of up to steel sheet direction depth 20μm originating in the base steel sheet (base steel), the volume fraction of retained austenite with rate is limited to 3% or less, the volume fraction of the hard microstructures in the surface layer "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".
[0053]
"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 sheet of the galvanized steel sheet is transformed into hard martensite due to deformation, molten zinc since they serve as starting points of fracture when large strain is applied bending deformation in the vicinity of the surface of the plated steel sheet, a bending resistance and contributes tissue degradation of fatigue resistance. From this viewpoint, in the surface layer portion to the steel plate direction depth 20μm originating from the interface between the plating layer and the base steel sheet, to limit the volume fraction of residual austenite 0% to 3% (including 0%) There is a need. The volume fraction of retained austenite in the surface layer portion preferably as low, it may be 0%.
[0054]
"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 (base steel) galvanized steel sheet, the strength in the surface layer of the molten zinc plated steel sheet enhanced fatigue limit strength significantly improved, which contributes tissue to improve the fatigue resistance. In this respect, "V1" the volume fraction of hard microstructures in the surface layer up to the steel plate direction depth 20μm originating from the interface between the plated layer and the base steel, 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 fraction of hard microstructures in the surface layer up to the steel plate direction depth 20μm originating from the interface between the plated layer and the base steel to some extent, local ductility by reducing the strength of the galvanized steel sheet surface near by improved, it is 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.
[0055]
　Further, the surface layer portion of the interface between the plated layer and the base steel of the hot-dip 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. Be to produce in advance the fine oxides on the steel sheet inside a surface portion, the steel sheet surface serving as a starting point for peeling of the plating layer, i.e., oxide containing Si and / or Mn at the interface between the plating layer and the base steel sheet it is possible to suppress the occurrence of things.
[0056]
　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.
[0057]
　Volume fraction of molten zinc ferrite contained in the steel sheet structure of the plated steel sheet, bainitic ferrite, bainite, tempered martensite, fresh martensite, pearlite and coarse cementite present invention can be measured by the following method. First, a sample is taken as an observation plane parallel plate thickness cross section in the rolling direction of the steel sheet, polished viewing surface to nital etching. Then, 1/8 thickness 1-3 / 8 thickness range around a quarter of the thickness, or, plated layer and the base steel sheet (base steel) and the interface of up to steel sheet direction depth 20μm originating in range each field emission scanning electron microscope: observed with (FE-SEM field emission scanning electron microscope) the area fraction measured can be regarded to have it as a volume fraction. 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.
[0058]
　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.
[0059]
　As shown in FIG. 1, molten zinc plated steel sheet of the present embodiment has a Fe-Al alloy layer 30 at the interface between the galvanized layer 10 and the base material steel plate 20, fine below the base material steel plate 20 having a layer 40 and decarburized layer 50.
　Refinement layers and the decarburized layer is a layer that generates by progresses decarburization reaction conditions controlled in a specific atmosphere at a specific temperature range in the annealing step as described below. Therefore, miniaturization layer and decarburized in the constituent phases with the exception of oxide and inclusion particles are substantially ferrite phase 60 is mainly tissue. Specifically, it is the volume fraction of the ferrite phase is 70% or more, the austenite phase remaining structure, bainite phase, martensite phase, and is one or more occupied mixed structure of pearlite It refers to the layer.
　Definition of the fine layer has an average particle size of the ferrite phase in the outermost part of the base material steel plate, if it is 1/2 or less of the average particle size of the ferrite phase in the decarburized layer is defined as finer layer is present . 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 decarburized layer is defined as the boundary between the fine layer and decarburized layer.
[0060]
　Finer layer is in direct contact with the Fe-Al alloy layer. An average thickness of 0.1 [mu] m ~ 5.0 .mu.m finer layer, the average particle size of the ferrite phase in the finer layer is 0.1 [mu] m ~ 3.0 [mu] m, the miniaturization layer, one of Si and Mn or comprise two or more oxides, the maximum diameter of the oxide is 0.01 [mu] m ~ 0.4 .mu.m.
[0061]
　The average thickness of the finer layer is 0.1 [mu] m ~ 5.0 .mu.m. It can not be obtained the effect of improving the crack generation and extension suppressing effect is not coating adhesion obtained with less than 0.1μm average thickness of the fine layer. If it is 5.0μm greater, alloying of the plating layer (Zn-Fe alloying) proceeds, Fe content in the coating layer increases, plating adhesion is degraded. The average thickness of the preferred fine layer is 0.2 [mu] m ~ 4.0 .mu.m, more preferably from 0.3 [mu] m ~ 3.0 [mu] m.
[0062]
　And the difference between the maximum thickness and the minimum thickness of the fine layer of the steel plate width direction is within 2.0 .mu.m. Here the maximum thickness of the fine layer of the steel sheet width direction and the minimum thickness respectively measure the thickness of the fine layer of eight points with the location and therebetween 50mm from both edges 7 aliquoted and maximum thickness therein It is to show that the minimum thickness. Alloying as the thickness of the finer layer is thick plating layer (Zn-Fe alloying) because the advances easily, when the difference in the thickness of the fine layer of the steel plate width direction is large, it becomes uneven alloying, plating adhesion and it may adversely affect the uniformity of the coating appearance. Preferably the difference between the maximum thickness and the minimum thickness of the fine layer of the steel plate width direction from the viewpoint of the uniformity of the plating adhesion and plating appearance is 1.5μm or less, further not more 1.0μm or less preferable.
[0063]
　The average particle size of the ferrite phase in the finer layer is 0.1 [mu] m ~ 3.0 [mu] m. Average particle diameter of the cracking and spreading effect of suppressing the effect of improving the coating adhesion is not obtained in the less than 0.1μm of the ferrite phase is not obtained. The average particle size of the ferrite phase can not be obtained the effect of improving the coating adhesion as a 3.0μm greater. The average particle diameter of the preferred ferrite phase is 0.1 [mu] m ~ 2.0 .mu.m.
[0064]
　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.
　Maximum diameter of the one or more oxides of Si and Mn contained in the fine layer is 0.01 [mu] m ~ 0.4 .mu.m. The oxides, as described later, the present invention is formed inside the base steel sheet at a particular temperature range during annealing, the growth of the ferrite phase crystal of the base material steel plate surface layer is suppressed by the oxide particles, fine layer There is formed. Maximum diameter formed to be smaller than 0.01μm fine layer of oxide can not be sufficiently, plating adhesion is degraded. Maximum diameter of the oxide is ferrite phase coarsened to be 0.4μm greater, with the formation of the fine layer is insufficient, the oxide itself plating adhesiveness to become a starting point of the plating peeling decreases. A preferred range of the maximum diameter of the oxide is 0.05 .mu.m ~ 0.2 [mu] m.
[0065]
　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.
[0066]
　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.
[0067]
(Fe-Al alloy layer)
　In an embodiment of the present invention, the interface between the plated layer and the steel sheet Fe-Al alloy layer is formed. The formation of the Fe-Al alloy layer, the plating layer can be inhibited from alloying (Zn-Fe alloying), inhibiting the plating adhesion decreases. In addition, it is possible to suppress the generation of appearance irregularities caused by uneven alloying. Appearance unevenness due to uneven alloying is than galvannealed steel sheet which has been subjected to alloying treatment after hot-dip galvanizing process, is likely to occur towards the galvanized steel sheet without alloying treatment. The thickness of the Fe-Al alloy layer is set to 0.1 [mu] m ~ 2.0 .mu.m. It may be less than 0.1μm coating adhesion and appearance is reduced in some cases to lower the coating adhesion as a 2.0μm greater. Preferably from 0.1μm ~ 1.0μm.
[0068]
　The difference between the maximum thickness and the minimum thickness of the Fe-Al alloy layer in the steel sheet width direction is within 0.5 [mu] m. Here, the maximum thickness and the minimum thickness of the Fe-Al alloy layer in the steel sheet width direction respectively measure the thickness of the Fe-Al alloy layer of eight places located between them a 7 equal to 50mm from both edges, the indicates that the maximum thickness and the minimum thickness in the. Fe-Al alloy of the thickness of the alloy layer is thin enough plating layer (Zn-Fe alloying) for tends advances, the large difference in thickness of Fe-Al alloy layer in the steel sheet width direction, it becomes uneven alloying , it may adversely affect the uniformity of the plating adhesion and plating appearance. From the viewpoint of uniformity of the plating adhesion and plating appearance, it is preferable that the difference between the maximum thickness and the minimum thickness of the Fe-Al alloy layer in the steel plate width direction is 0.4μm or less, is 0.3μm or less it is more preferable.
[0069]
(Plating layer)
　in embodiments of the present invention, the galvanized layer, Fe content is not more than 0% and 3.0%, Al content is 0% or less than 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, depending on its content corrosion resistance and workability If such is improved preferably also.
　In the present embodiment, galvanized layer ζ phase (FeZn 13 may include a columnar crystal made of),
　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.
[0070]
[Fe content in galvanized layer: 0% and 3.0% or less]
　The Fe content in galvanized layer is not more than 0% and 3.0%. Fe content of 0% is substantially difficult to manufacture. Fe content is decreased coating adhesion exceeds 3.0%. The Fe content is less than 0.3%, the plating adhesion property may deteriorate, the preferable range of Fe content in terms of plating adhesion securing is 0.3% to 2.5%, more preferably is 0.5% to 2.0%.
[0071]
[Al content in the galvanized layer: 0% and 1.0%]
　of Al content in the galvanized layer is not more than 0% and 1.0%. If the plating bath does not contain Al, or extremely when the content is less proceeds alloying of the plating layer, since the plating adhesion is degraded, Al content in the plating layer is 0.1% or more it is preferable. Here refers to Fe atoms and alloying of the plating layer is diffused in the plating layer, Zn-Fe alloy is formed. Al content is lowered coating adhesion exceeds 1.0%. A preferred range of Al content in terms of plating adhesion securing is 0.1% to 0.8%, more preferably from 0.2% to 0.5%.
[0072]
: [Amount of adhered galvanized 10 g / m 2 ~ 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 reduction and the weld 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.
[0073]
(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.
[0074]
　Method for manufacturing a galvanized steel sheet according to the present embodiment, hot rolling the slab having the above chemical components is heated to 1080 ° C. or higher, subjected to hot rolling to a rolling completion temperature in the range of 850 ° C. ~ 980 ° C. and the steel sheet, 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 cooling process after hot rolling to 300 ° C., the hot rolling process then after pickling, and cold rolling step of performing cold rolling to a reduction ratio in total 85% or less, the steel sheet after cold rolling step, the average heating rate between 600 ℃ ~ 750 ℃ 1.0 ℃ / s or more, the maximum heating temperature (Ac1 + 25) ℃ above Ac3 ° C. or less, and heated as a temperature region above 750 ° C., then, 760 ° C. ~ 700 ° C. the average cooling rate 0.1 ° C. / s ~ between 5.0 flat between ℃ / s, 650 ℃ ~ 500 ℃ And annealing step of cooling the cooling rate as 1.0 ° C. / s or more, after the annealing step, the plating bath temperature 440 ℃ ~ 470 ℃, 430 ℃ ~ 480 ℃ the temperature of the steel sheet during the plating bath enters, in the plating bath by immersing the effective Al amount in the plating bath steel sheet a plating condition to 0.180 to 0.250 wt%, the plating step of forming a plating layer with galvanized surface of the steel sheet, after the plating step, steel sheet 100 ° C. until a total of two or more bent using a roll having a diameter of 50 mm ~ 800 mm after cooling below - and a processing step of performing deformation by bending back.
　It follows is a detailed description of each manufacturing step.
[0075]
　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 containing the alloying elements in accordance with the characteristics, subjected to hot rolling, is produced by applying a cold rolling.
　It follows is a detailed description of each manufacturing step.
[0076]
"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.
[0077]
"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.
[0078]
　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. 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, the completion temperature of the hot rolling and 980 ° C. or less, and more preferably set to 950 ° C. or less.
[0079]
　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.
[0080]
　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, the effective crystal grains of the base material steel plate after annealing can miniaturization. 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.
　Also, after winding the hot-rolled steel sheet, there is a case where the internal oxide layer underneath the scale layer is nonuniformly (toward the center portion than the edge portion is thick) is formed. If the coiling temperature exceeds 650 ° C. it becomes remarkable. Step (pickling, cold rolled) After the inner oxide layer will be described later if they are not removed even leads to uneven formation of the fine layer and Fe-Al alloy layer, adverse effects on the uniformity of the coating adhesion and appearance there is a possibility to exert. Therefore, the coiling temperature from the viewpoint of the uniformity of the plating adhesion and appearance is preferably lowered to 650 ° C. or less.
[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 becomes lower than the temperature Ae3 * ° C. which results in a stable. This decarburization from BCC phase of iron is to advance faster than the decarburization from FCC phase is stable phase at high temperature. Note in the present embodiment, the temperature range lower than the base steel sheet temperature of 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 hot rolling process temperature range of the temperature control of the base material steel plate is a section of up to 300 ° C. in.
　Incidentally, Ae3 * [℃] can be obtained by using the following equation.
[0082]
　Ae3 * [℃] = 885 + 31.7Si-29.3Mn + 123.2Al-18.2Cr-40.0Ni-21.0Cu + 12.6Mo
[0083]
　In the above formula, C, Si, Mn, Al, Cr, Ni, Cu, Mo are the contents 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, the steel sheet temperature is controlled 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 more Si and Mn content in steel formula (1) 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 it is 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. Internal oxide layer to be generated under the scale layer will enhance pickling, uniform formation as possible the removed towards miniaturization layer and Fe-Al alloy layer is preferable from the viewpoint of ensuring a uniform appearance due it. If the internal oxide layer is removed, pickling conditions are not particularly limited, for example, the use of hydrochloric acid is preferred from the viewpoint of the pickling efficiency and economy. The conditions for removing the internal oxide layer, for example, the concentration of hydrochloric acid, 5% by mass or more as hydrogen chloride, pickling temperature 80 ° C. or higher, pickling time is given as recommended conditions more than 30 seconds.
[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 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 the number of paths and reduction ratio for 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%, 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 fatigue resistance are degraded. 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.
[0092]
"Annealing step"
　in the embodiments of the present invention, subjected to annealing cold-rolled steel sheet. In embodiments of the present invention, it is preferable to use a continuous annealing plating line having a preheating zone and a soaking zone and the plating zone. Then, passed through a preheating zone while annealing step and the soaking zone, exit the annealing step until arriving to the plating zone, it is preferable to perform the plating process in the plating zone.
[0093]
　As described above, when using a continuous annealing plating line annealing process and plating process, for example, it is preferable to use a method described below.
　In particular, important in ensuring the atmosphere, control of the heating system, while appropriate, to uniformly generate a control miniaturization layer and Fe-Al alloy layer of the atmosphere in the soaking zone, the coating adhesion and appearance uniformity in the preheating zone it is.
[0094]
　In the preheating zone, the water vapor partial pressure P (H 2 O) and hydrogen partial pressure P (H 2 is a Log value of the ratio of the) Log (P (H 2 O) / P (H 2 a)) -1. 7 in an atmosphere controlled to ~ -0.2, using a preheating burner in which the air ratio of 0.7 to 1.0 is Tsuban while heating the steel sheet temperature of 400 ° C.-800 ° C..
　In the preheating zone, the water vapor partial pressure P (H 2 O) and hydrogen partial pressure P (H 2 by adjusting the ratio between)
　This is because, in the preheating zone by adjusting the air ratio, suppress the production of the steel sheet surface of the oxide film of the strong deoxidizing element such as Si. Simultaneously, water vapor partial pressure P (H 2 O) and hydrogen partial pressure P (H 2 by adjusting the ratio of) In this, in a subsequent plating process, thereby suppressing the excessive Fe-Zn alloy reaction at the grain boundary of the steel sheet surface, Fe-Al alloy reaction to selectively occurs as. Fe-Al in alloy reaction selectively occurs it encourages the formation of a uniform Fe-Al alloy layer, it is possible to obtain excellent plating adhesiveness, appearance uniform. Log (P (H 2 O) / P (H 2 )) is more than -0.2 when the Fe-Zn alloying is liable to occur in the subsequent plating step, Fe concentration in the plating is increased. Thereby, plating adhesion property is lowered, also tends to occur appearance unevenness. On the other hand, Log (P (H 2 O) / P (H 2 If)) is less than -1.7, the carbon concentration on the surface of the steel sheet is possible high part, since no form fine layer on the surface, plating adhesion sex is reduced.
　The "air ratio", and the volume of air contained in the mixed gas per unit volume is the ratio of air volume to be theoretically required to fully combust the fuel gas contained in the mixed gas per unit volume, represented by the following formula.
　[Volume of air contained in the unit volume gas mixture (m air ratio = 3 )] / [volume of air to be theoretically required to fully combust the fuel gas contained in the mixed gas per unit volume (m 3 ) ]
[0095]
　When the air ratio of the is too large beyond 1.0, excess Fe oxide film is generated on the steel sheet surface layer portion, the decarburized layer after annealing bloated, also excessively generated fine layer. Whereby proceeds alloying excessively plating, plating adhesion, chipping resistance, powdering resistance decreases. Therefore, it is preferable that the air ratio above is 1.0 or less, more preferably 0.9 or less. When the air ratio is too small and less than 0.7 is not fine layer is formed, plating adhesion is degraded. Therefore, the air ratio is 0.7 or more, preferably 0.8 or more.
　Further, the steel sheet temperature to Tsuban preheating zone when less than 400 ° C., it is impossible to form a sufficiently fine layer. Therefore, the steel sheet temperature for Tsuban the preheating zone is set to 400 ° C. or higher, preferably to 600 ° C. or higher. On the other hand, in the high-temperature steel sheet temperature for Tsuban the preheating zone exceeds 800 ° C., oxide containing coarse Si and / or Mn is produced on the surface of the steel sheet, plating adhesion is degraded. Therefore, the steel sheet temperature for Tsuban the preheating zone is set to 800 ° C. or less, preferably set to 750 ° C. or less.
　Internal oxidation proceeds heating rate in the preheating zone is slow, coarse oxides within the steel sheet is produced. In particular, 600 heating rate at ° C. ~ 750 ° C. is important to avoid excessive decarburization of the steel sheet surface layer portion, coarse to suppress the formation of oxides of average heating rate during this period 1.0 ° C. / sec or higher there needs to be. If the average heating rate during this period is less than 1.0 ° C. / sec, coarse oxides are formed in the finer layer, coating adhesion and powdering resistance is lowered. To avoid generation of excessive decarburization, and coarse oxides of the steel sheet surface layer portion, the average heating rate between 600 ° C. ~ 750 ° C. preferably set to 1.5 ° C. / sec or more, 2.0 ° C. / sec it is more preferably not less than. Average heating rate at 600 ° C. ~ 750 ° C. is to ensure a processing time in the preheating zone, preferably in the 50 ° C. / sec or less. When the average heating rate is less than 50 ° C. / sec, even more easily miniaturized layer is obtained, the plating layer is obtained having excellent uniformity in coating adhesion and appearance.
[0096]
　The maximum heating temperature in the annealing step, in order to control the fraction of the microstructure involved in formability of the steel sheet in a predetermined range is an important factor. When the maximum heating temperature is low, undissolved coarse iron-based carbide in the steel, the formability deteriorates. In the less than the maximum heating temperature is 750 ° C., without coarse iron carbide is sufficiently soluble in the hot-rolled steel sheet, remains until the plate and a product may impair significantly the ductility. The iron-based carbide is sufficiently dissolved, to increase the moldability, the maximum heating temperature was (Ac1 point +25) ° C. or higher and 750 ° C. or higher, preferably in the (Ac1 point +50) ° C. or higher. On the other hand, the maximum heating temperature is more than Ac3 point, since the ferrite fraction in the steel is significantly reduced, the maximum heating temperature is less Ac3 point. In view of coating adhesion, to reduce the oxide of the base steel surface, the maximum heating temperature is low it is preferable. Is preferably not more than the maximum heating temperature is 850 ° C. From this viewpoint, it is more preferable to 830 ° C. or less.
[0097]
　The Ac1 point and Ac3 point of the steel sheet is the starting point and completion point of the respective austenite reverse transformation, specifically, cut small pieces from the steel sheet after hot rolling, heating to 1200 ° C. at 10 ° C. / sec, during which obtained by measuring the volume expansion.
[0098]
　Maximum heating temperature (750 ° C. or higher) in the annealing step, to reach the soaking zone. Atmosphere in the soaking is Log (P (H 2 O) / P (H 2 for controlling)) to -1.7 ~ -0.2. Log (P (H 2 O) / P (H 2 )) is not formed miniaturization layer is less than -1.7, plating adhesion is degraded. Log (P (H 2 O) / P (H 2 )) progresses excessively decarburization exceeds -0.2, together with the base steel sheet surface layer of the hard phase is significantly reduced, miniaturization layer coarse oxides are formed, the plating adhesion and powdering resistance is lowered.
[0099]
　As described above, Log in soaking (P (H 2 O) / P (H 2 )) is the is -1.7 ~ -0.2, Si and Mn oxide serving as a starting point for plating peeling the outermost surface without forming the layer, fine oxides of Si and / or Mn maximum diameter of 0.05 .mu.m ~ 0.4 .mu.m in the interior of the steel sheet surface layer is formed. Fine oxides of Si and / or Mn suppresses the growth of Fe recrystallization during annealing. Also, water vapor in the annealing atmosphere for decarburized surface layer base material, the base material surface layer after annealing is a ferrite. As a result, the surface layer of the base material after annealing, the average thickness of a 0.1 [mu] m ~ 5.0 .mu.m, the mean particle size of the ferrite phase is 0.1 [mu] m ~ 3.0 [mu] m, the maximum diameter of 0. refinement layer containing an oxide of a 01μm ~ 0.4μm Si and / or Mn is formed.
[0100]
　Of annealing step, the pre-plating after reaching the maximum heating temperature up to the plating bath cooling (before cooling step plating), the temperature range from 760 ° C. to 700 ° C., a temperature range from 650 ° C. to 500 ° C. in two stages with by controlling the temperature of the steel sheet, it is possible to obtain a predetermined microstructure. First, in order to promote the formation of ferrite sufficiently define the average cooling rate of between 760 ° C. to 700 ° C.. If the average cooling rate from 760 ° C. to 700 ° C. is more than 5.0 ° C. / sec, there are cases in which the ferrite of the product does not proceed sufficiently, the average cooling rate to 5.0 ° C. / sec or less. In order to promote generation of ferrite sufficiently, the average cooling rate is preferably set to 3.5 ° C. / sec or less, and more preferably set to 2.5 ° C. / sec or less. On the other hand, the average cooling rate from 760 ° C. to 700 ° C. is because at less than 0.3 ° C. / sec may produce a large amount of pearlite, the average cooling rate 0.3 ° C. / sec or more. To avoid the formation of pearlite, it is preferable that the average cooling rate 0.5 ° C. / sec or more, and more preferably set to 0.7 ° C. / sec or more.
[0101]
　Next, in order to avoid the generation of excessive pearlite and / or coarse cementite, defining the cooling rate from 650 ° C. to 500 ° C.. Is less than the average cooling rate is 1.0 ° C. / sec from 650 ° C. to 500 ° C., since the pearlite and / or coarse cementite is produced in large quantities, the average cooling rate to 1.0 ° C. / sec or more. Since it is preferable to perlite and / or coarse cementite is not included in the steel, in order to avoid these production sufficiently, the average cooling rate is preferably set to 2.0 ° C. / sec or more, 3.0 ° C. / and more preferably in a second. Although 650 upper limit of the average cooling rate in the temperature range of 500 ° C. from ° C. is not particularly provided, in order to obtain an excessively large average cooling rate, the refrigerant that does not interfere with the special cooling equipment or plating step is required, preferably Absent. In this respect, the average cooling rate in the above temperature range is preferably set to 100 ° C. / sec or less, more preferably to 70 ° C. / sec or less.
[0102]
　Following plating before cooling step, to obtain the tempered martensite, until the steel sheet temperature reaches the plating bath after reaching the 500 ° C., and the steel sheet was a the predetermined time staying in a predetermined temperature range as the martensitic transformation process it may be. Martensitic transformation treatment temperature, a martensitic transformation start temperature Ms point is the upper limit, it is more preferable that the upper limit is (Ms point -20) ° C.. Martensitic transformation treatment is preferably the lower limit 50 ° C., and more preferably the lower limit and 100 ° C.. Further, the martensitic transformation treatment time is preferably 1 second to 100 seconds, more preferably 10 seconds to 60 seconds. Note that martensite obtained by martensitic transformation process is changed to the tempered martensite by entering the high temperature of the plating bath at a plating step.
[0103]
　Incidentally, Ms point is calculated by the following equation.
　Ms point [℃] = 541-474C / (1 -VF) -15Si-35Mn-17Cr-17Ni + 19Al
[0104]
　In the above formula, VF represents the volume fraction of the ferrite, C, Si, Mn, Cr , Ni, Al is the content of the respective elements (mass%).
　Incidentally, it is difficult to measure the volume fraction of the ferrite directly during manufacture. Therefore, in determining the Ms point in the present invention, cut out pieces of the previous cold-rolled steel sheet to Tsuban a continuous annealing line, annealing at the same temperature history as if was Tsuban the small pieces to a continuous annealing line Te, and measuring the change in volume of the piece of ferrite, has a numerical value calculated using the result as the volume fraction VF of the ferrite.
[0105]
　Further, to advance the formation of bainite, during a period from the steel sheet temperature reached 500 ° C. up to the plating bath, it may also be a certain time staying in a temperature range of the steel sheet given a bainite transformation treatment. Since bainite transformation treatment temperature progresses formation of pearlite and / or coarse cementite exceeds 500 ° C., bainite transformation treatment temperature is set to 500 ° C. or less. Further, when the bainite transformation treatment temperature is below 350 ° C., since the transformation does not proceed sufficiently, bainite transformation treatment temperature is set to 350 ° C. or higher. Bainite transformation treatment time, to advance the transformation sufficient, and 10 seconds or more, in order to suppress the formation of pearlite and / or coarse cementite, the following 500 seconds. Incidentally, after the pre-plating cooling step, when performing both the bainite transformation treatment and martensite transformation treatment, for enforcement order to be carried out and bainite transformation treatment and martensite transformation treatment.
[0106]
"Plating step"
　will be immersed base material steel plate obtained in this manner in the plating bath.
　Plating bath composed mainly of zinc, the effective Al amount is a value obtained by subtracting the total amount of Fe from the total amount of Al in the plating bath having a composition of 0.180% 0.250%. The effective amount of Al in the plating bath is below 0.180% formation of Fe-Al alloy layer is not sufficient, since the invasion of Fe in the plating layer progresses, coating adhesion is impaired, 0.180 there needs to be greater than or equal to%. In this respect, the effective amount of Al in the plating bath is preferably at least 0.185%, more preferably at least 0.190%. On the other hand, if the effective Al amount in the plating bath is more than 0.250%, Fe-Al alloy layer of the base steel sheet and the plating layer is excessively generated, the coating adhesion is impaired. In this respect, the effective amount of Al in the plating bath is required to be less 0.250%, preferably to less 0.240%, further preferably not more than 0.230%.
[0107]
　Plating bath, 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, may be those one or more elements of REM is mixed, the content of each element, If such preferred corrosion resistance and workability of the galvanized layer is improved also.
[0108]
　The temperature of the plating bath is preferably set to 440 ℃ ~ 470 ℃. Is less than the plating bath temperature of 440 ° C., increases excessively, the viscosity of the plating bath, it is difficult to control the thickness of the plating layer, disfiguring galvanized steel sheet. Accordingly, the temperature of the plating bath is preferably at least 440 ° C., more preferably it is 445 ° C. or higher. On the other hand, a large amount of fumes is generated and the plating bath temperature exceeds 470 ° C., it is difficult to safely manufactured. Therefore, the plating bath temperature is preferably 470 ° C. or less, more preferably be 460 ° C. or less.
[0109]
　If the lower temperature of the steel strip is 430 ° C. at the time of the base steel sheet enters the plating bath, in order to stabilize the plating bath temperature at 440 ° C. or higher, since it is necessary to provide a large amount of heat in the plating bath, practically it is not suitable. On the other hand, if it exceeds the temperature of the steel strip is 480 ° C. at the time of the base steel sheet enters the plating bath, in order to stabilize the plating bath temperature to 470 ° C. or less, necessary to introduce the facility for heat removal a large amount of heat from the plating bath There are, it is not suitable in terms of production cost. Therefore, in order to stabilize the bath temperature of the plating bath, the temperature of the plating bath entrance of the base material steel plate 430 ° C. or higher, and 480 ° C. or less. In addition, in order to properly control the Fe-Al alloy layer, the temperature of the plating bath ingress of the base steel sheet is 440 ° C. or more, and more preferably limited to 470 ° C. or less.
[0110]
　Temperature of the plating bath is preferably stable at a temperature in the range of 440 ℃ ~ 470 ℃. When the temperature of the plating bath is unstable, Fe content of Fe-Al alloy layer and the plating layer becomes uneven, leading to non-uniformity of appearance and adhesion of the plated layer. In order to stabilize the temperature of the plating bath, it is preferable to substantially match the temperature of the plating bath and the steel sheet temperature at the time of the plating bath entrance. Specifically, the temperature control of the limits of the actual production facility, it is preferable that the steel sheet temperature at the time of the plating bath enters within ± 10 ℃ plating bath temperature, be within ± 5 ℃ plating bath temperature more preferable.
[0111]
　Incidentally, after the plating bath immersion, for a proper coating weight, spraying high-pressure gas mainly composed of nitrogen on the surface of the steel sheet, it is preferred to remove the excess zinc surface. Then it cooled to room temperature. At that time, diffusion of Fe atoms from the base material steel plate into the plating layer is hardly proceed, is 1 ° C. / sec or more is coating adhesion ensure proper cooling rate to a temperature 350 ° C. to produce the ζ phase is substantially stopped preferable from the point of view.
[0112]
　Further, after cooling to 350 ° C., to obtain a hard tissue, it may be cooled to 250 ° C. or less at an average cooling rate of more than 1.0 ° C. / sec. To obtain fresh martensite phase and / or tempered martensite phase is preferably in the average cooling rate 3.0 ° C. / sec or more, and even more preferably to a 5.0 ° C. / sec or more.
[0113]
　Further, after cooling to 250 ° C. or less, may be subjected to a reheating treatment in order to obtain the tempered martensite. Treatment temperature and the treatment time of the re-heat treatment may be appropriately set according to the target properties. However, re-heating temperature is sufficient effect can not be obtained is less than 250 ° C., while the Beyond the 350 ° C., since there is a concern that the plating layer is altered, plating adhesion is degraded, reheating temperature it is preferable that the 250 ° C. or higher 350 ° C. or less. Further, since the re-heating time is saturated with treatment effect exceeds 1000 seconds, the processing time is preferably 1000 seconds or less.
[0114]
　Further, after cooling to 350 ° C., to obtain a residual austenite, may be subjected to bainitic transformation process applied to retention of 15 seconds to 500 seconds at a temperature range of 250 ° C.-350 ° C.. Is less than the bainite transformation treatment temperature is 250 ° C., retained austenite generated martensite is not sufficiently obtained. Therefore, the bainite transformation treatment temperature is preferably 250 ° C. or higher, and more preferably set to 300 ° C. or higher. On the other hand when the bainite transformation treatment temperature exceeds 350 ° C., the diffusion of Fe atoms from the base material steel plate into the plating layer proceeds, plating adhesion is degraded. Therefore, the bainite transformation treatment temperature is preferably 350 ° C. or less, and more preferably set to 330 ° C. or less.
　When bainite transformation treatment time is 15 seconds or more, the effect of performing the bainite transformation treatment is sufficiently obtained. It is more preferable bainite transformation treatment time is 25 seconds or more. When bainite transformation treatment time is less than 500 seconds, it is possible to perform the bainite transformation treatment efficiently. It is more preferable bainite transformation treatment time is 300 seconds or less.
[0115]
　Further, in order to further stabilize the residual austenite, after cooling to 250 ° C. or less, may be subjected to a reheating treatment. Treatment temperature and the treatment time of the re-heat treatment may be appropriately set according to the target properties. However, re-heating temperature is sufficient effect can not be obtained is less than 250 ° C.. Therefore, re-heating temperature is preferably set to 250 ° C. or higher, more preferably to 280 ° C. or higher. When reheating temperature exceeds 350 ° C., the diffusion of Fe atoms from the base material steel plate into the plating layer proceeds, plating adhesion is degraded. Therefore, re-heating temperature is preferably set to 350 ° C. or less, and more preferably set to 330 ° C. or less.
　Further, since the re-heating time is saturated with treatment effect exceeds 1000 seconds, the processing time is preferably 1000 seconds or less.
[0116]
"Processing step"
　Then, after cooling the steel sheet temperature to 100 ° C. or less, for reducing the residual austenite of the base material steel plate surface, bending the plated steel sheet - unbending subjected to deformation. Bending can be performed using a roll of 50 mm ~ 800 mm in diameter. Since roll diameter is less than 50 mm, a large amount of strain in the surface layer base material steel plate is introduced by bending deformation, formability of the steel sheet is impaired. Further, the roll diameter 800mm than small strain amount in the base steel sheet surface layer, no residual austenite is reduced sufficiently. Bending - unbending deformation, to reduce the residual austenite in the front and back surfaces of the base material steel plate, the deformation of the outer bend the front and back surfaces, it is necessary to perform each one or more times, the bending of more than 2 times in total - it is necessary to the deformation by bending back performed. This makes it possible to keep the residual austenite in the front and back surfaces of the base material steel plate into a predetermined range.
[0117]
　Although it is possible to manufacture a galvanized steel sheet according to the present embodiment by the manufacturing method described above, the present invention is not limited to the above embodiment.
[0118]
　For example, in the embodiment of the present invention, it may on the surface of the galvanized layer of the galvanized steel sheet obtained by the method described above, be given a coating composed of a composite oxide containing phosphorus oxide and / or phosphorus Absent.
　Film comprising phosphorus oxide and / or composite oxide containing phosphorus, can function as a lubricant when processing galvanized steel sheet, to protect the galvanized layer formed on the surface of the base material steel plate can.
[0119]
　Further, in this embodiment, it may be subjected to the molten zinc plated steel sheet was cooled to room temperature, cold rolling at a reduction rate of 3.00% or less for the straightening.
[0120]
　The manufacturing method of hot-dip galvanized steel sheet according to the embodiment of the present invention have been described above, the thickness of the base material steel plate is 0.6mm or more, to be applied to the manufacture of hot-dip galvanized steel sheet is less than 5.0mm It is preferred. 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, it may not be appropriate. Further, when the thickness of the base material steel plate is 5.0mm or more, there is a case where the control of the cooling in the annealing step and the plating step becomes difficult.
Example
[0121]
　Examples of the present invention will be described. The conditions of the present embodiment is an example of conditions adopted for confirming the workability and effects of the present invention. The present invention is not limited to this single example of conditions. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention may employ various conditions.
[0122]
"Example 1"
　casting a slab having a chemical composition of A-BY shown in Tables 1 to 3 (composition), thermal hot-rolled process conditions shown in Table 4 to Table 7 (slab heating temperature, rolling completion temperature) and during rolling, tables 4 to hot-rolling process conditions shown in Table 7 (average cooling rate from the hot rolling finished to coiling, the coiling temperature, equation (1)) was cooled in to obtain hot-rolled steel sheet.
　Then, (immersed in 10% hydrochloric acid 80 ° C., immersion time are shown in Tables 4 to 7) in hot-rolled steel sheet pickling cold subjected to cold-rolled process conditions shown in Table 4 to Table 7 (rolling reduction) subjected to during rolling to obtain a cold-rolled steel sheet.
[0123]
　Then, the air ratio in the heating process conditions (preheating zone in the annealing step shown the resulting cold rolled steel sheet in Tables 8 to 11, Log in preheating zone atmosphere (P (H 2 O) / P (H 2 )), Log equalizing in tropical atmosphere (P (H 2 O) / P (H 2 )), the average heating rate in a temperature range of 600 ℃ ~ 750 ℃, was annealed at a maximum heating temperature). Condition indicating this steel sheet Tables 8 to 11 (average cooling rate of an average cooling rate), temperature range of the cooling rate 2 (650 ° C.-500 ° C. in a temperature range of cooling rate 1 (760 ° C.-700 ° C.), martensitic transformation treatment conditions (treatment temperature, treatment time), the bainite transformation treatment of the conditions (treatment temperature, treatment time) the cooling process performed by), to obtain a base steel sheet for plating.
　Then, the conditions shown in Table 12 to Table 15 were immersed in the galvanizing bath (effective Al amount, the plating bath temperature, penetration temperature of the steel sheet), to under the conditions shown in Table 12 to Table 15 (cooling rate 3 (350 ° C. the average cooling rate), average cooling rate in the temperature range of the cooling rate 4 (350 ℃ ~ 250 ℃) , conditions of the bainite transformation treatment 2 (treatment temperature, treatment time), reheating treatment conditions (treatment temperature, treatment time) plated after the cooling process in). Then, bending under the conditions shown in Table 12 to Table 15 (roll diameter, machining pass) - unbending giving the process, further subjected to cold rolling under the conditions shown in Table 12 to Table 15 (rolling reduction), Experiment to obtain a galvanized steel sheet 1-202 (however, in some experimental examples, some of which it was interrupted experiment).
[0124]
　Samples were then taken as an observation plane parallel plate thickness cross section in the rolling direction of the base material steel plate from each galvanized steel sheet, high by microstructure observation and EBSD method using a field emission scanning electron microscope (FE-SEM) performs resolution crystal orientation analysis, 1/4 1/8 thickness 1-3 / 8 range (1/4 thickness) of the thickness around the plate thickness, and, starting from the interface between the plating layer and the base steel sheet the surface portion to a depth of 20μm and volume fraction of the microstructure in the (base steel surface layer) were measured. Incidentally, in Tables 16 to 19 as "martensite" indicates the fresh martensite, among microstructure in Tables 16 to 19 and "other" indicates pearlite and / or coarse cementite. In addition, the "hard phase", is a hard tissue comprising one or more of the bainite and bainitic ferrite and fresh martensite and tempered martensite.
[0125]
　Coating weight of plating is to melt the plated layer by using a hydrochloric acid inhibitor containing, it was determined by comparing the weights before and after melting. By quantifying Fe, the Al by ICP simultaneously, Fe concentration in the plating layer was measured Al concentration.
[0126]
　Further, the plated steel sheet, a sample was taken as an observation plane parallel plate thickness cross section in the rolling direction of the base material steel plate, the using the measuring method described above, the interface between the base steel sheet galvanized layer Fe- the average thickness of the thickness difference in the width direction of the Al alloy layer, and, it the thickness difference of the average thickness and width directions of the direct contact with the fine layer, the average particle size of the ferrite phase in the fine layer (ferrite phase average grain size) to determine the maximum diameter of the one or more oxides of Si and Mn in the fine layer (maximum diameter oxides). The results are shown in Table 20 through Table 23.
[0127]
　Then, in order to examine the characteristics of the plated steel sheet, a tensile test, a hole expansion test, bending test, fatigue test, adhesion evaluation test, spot welding test, corrosion test, chipping resistance test, powdering resistance test, the plate appearance uniformity rating went. Table 24 to Table 31 show the characteristics in each of the experimental examples.
[0128]
　Tensile test, creates a No. 5 test piece described from plated steel sheet in JIS Z 2201, performed by the method described in JIS Z2241, it was calculated yield strength YS, tensile maximum strength TS, total elongation El. The tensile properties, tensile maximum strength TS and rated the case of more than 550MPa as good.
　Hole expansion test was conducted by the method described in JIS Z 2256. Among the formability, ductility (total elongation) El and hole expandability λ will vary with the maximum tensile strength TS, and good strength, ductility and hole expandability if it meets the following formula (2).
　TS 1.5 × El × lambda 0.5　≧ 2.0 × 10　　6 · · · formula (2)
[0129]
　Bending test, creates a No. 5 test piece described in JIS Z 2201 from the galvanized steel sheet, using the V-block method described in JIS Z 2248, was 90 ° V bending test. The radius at the bottom of the V-block was varied 0.5mm increments from 1.0mm to 6.0 mm, cracks in the specimen was the minimum bend radius r [mm] of the smallest radius that did not occur. Bending resistance, the minimum bend radius r normalized by the thickness t [mm], and evaluated by the "r / t", were evaluated if "r / t" is 2.0 or less as good bending resistance.
[0130]
　Fatigue test, creates a No. 1 test piece described in JIS Z 2275 from the galvanized steel sheet was subjected to pulsating plane bending fatigue test according to JIS Z 2273. The maximum number repeated as 10 million times, and evaluating the fatigue limit DL and fatigue ratio DL / TS, fatigue limit ratio was good fatigue resistance in the case of 0.30 or more.
[0131]
　Plating adhesion, compared plated steel sheet had a tensile strain uniaxial 5%, was subjected to DuPont impact test. The plated steel sheet after the impact test joining the adhesive tape, then peeling, plating is particularly the case in which not peeled well (◎), a case where the plating is peeled off by 5% or more and poor (×), peeling of the plating where less than 5% was considered good (○). DuPont impact test, using the shot type that the radius of curvature of the tip and 1/2 inch, was performed by dropping a 3kg of the weight from a height of 1 m.
[0132]
　Spot weldability was evaluated by a continuous RBI test. In welding conditions the diameter of the molten portion is 5.3 times to 5.7 times the thickness square root, continuously performed 1000 times spot welding. Then, the diameter of the molten portion first point d 1 and 1000 goal d 1000 compared with a, d 1000 / d 1 passed if is not less than 0.90 (○), the case of less than 0.90 not It was passed (×).
[0133]
　The evaluation of the corrosion resistance, using a test piece cut out a plated steel sheet to 150 mm × 70 mm. The test piece was subjected to dip-type chemical conversion treatment of zinc phosphate, followed subjected to cationic electrodeposition coating 20μm, the further intermediate coating 35 [mu] m, it was subjected to overcoating 35 [mu] m, the back surface and the end was sealed with electrical tape. The corrosion resistance test, using the CCT to one cycle SST6hr → dry 4hr → wet 4hr → freezing 4hr. Evaluation of corrosion resistance after painting is subjected to crosscut reaching the base steel sheet with a cutter to painted surfaces, it was measured blister width after CCT60 cycles. Evaluated as acceptable if the width 3.0mm or less swelling (○), was unacceptable in the case of 3.0mm greater (×).
[0134]
　Chipping resistance was evaluated using a test piece cut out plated steel sheet 70 mm × 150 mm. First, the test piece, degreasing automotive, formation of chemical conversion film, the three-coat painting steps were performed. Then, while cooling holding the test piece to -20 ° C., air pressure 2 kgf / cm 2 was irradiated with crushed stone (0.3g ~ 0.5g) 10 pieces of vertically. Irradiation of crushed stone was repeated five times for each specimen. Thereafter, each test piece, and observing the total of 50 chipping traces were evaluated according to the following criteria depending on the position of the peeling interface. Peeling boundary is above the plating layer as acceptable is (plated layer - intercoat interface painting - interface conversion coating or electrodeposition coating,) (○), the plating layer - interfacial peeling even one in base iron things were judged as failure (×).
[0135]
　Powdering property, in order to evaluate the workability of the plating layer was evaluated using the V bending (JIS Z 2248). The plated steel sheet was cut into 50 × 90 mm, a molded body formed by 1R-90 ° V-shaped die press and the specimen. In valleys of each specimen were performed tape peeling. Specifically, detached by pressing a cellophane tape having a width of 24mm on the bent portion of the specimen was determined length 90mm portion of the cellophane tape was visually. The evaluation criteria were as follows. Peeling of the plating layer is evaluated as acceptable ones less than 5% relative to the processing unit area (○), peeling of the plating layer was unacceptable to most 5 percent relative to the processing unit area (×).

WE claims

[Requested item 1]
　A galvanized steel sheet having on at least one side of the galvanized layer of the base material steel plate,
　the base material steel plate is a
　　mass%, C: 0.040%
　　~ 0.280%, Si: 0.05
　　～
　　2.00 Pasento Pasento, Mn:
　　0.50 Pasento ～ 3.50 Pasento, P: 0.0001 Pasento ～ 0.1000 Pasento, S: 0.0001
　　Pasento ～ 0.0100 Pasento, Al: 0.001 Pasento ～
　　% 1.500,
　　N: 0.0001%
　　~ 0.0100%, O: 0.0001% ~ 0.0100%,
　　Ti: 0% ~ 0.150%, Nb: 0% ~
　　0.100%, V :
　　0%
　　~ 0.300%, Cr:
　　0% ~ 2.00%, Ni: 0% ~ 2.00%,
　　Cu: 0% ~ 2.00%, Mo: 0% ~
　　2.00%, B : 0%
　　~ 0.0100%, W: 0% ~ 2.00%, and
　　Ca, Ce, Mg, Zr, La, and REM: total % ~ 0.0100%
comprise
　the remainder has a chemical composition consisting of Fe and impurities,
　The total thickness of the base material steel plate, the at 1/8 thickness 1-3 / 8 thickness in the range of 1/4 thickness around from the surface of the base material steel plate,
　ferrite phase at a volume fraction of 50% or more 97 % or less,
　the total of hard tissue comprising one or more of the bainite phase and bainitic ferrite phase and fresh martensite phase and tempered martensite phase at a volume fraction of 3% or more,
　the residual austenite phase volume fraction 0% to 8%,
　0% to 8% in the total volume fraction of the pearlite phase and coarse cementite phase,
　the surface layer portion from the interface between the galvanized layer and the base steel sheet to the steel sheet direction depth 20μm in,
　a 0-3% residual austenite volume fraction,
　and the hard tissue volume fraction V1 in the surface layer portion, 1/8 thickness 1-3 / 8 thickness around the 1/4 thickness from the steel sheet surface the hard in the range of The V1 / V2 is a ratio of the volume fraction V2 woven has the microstructure in the range of 0.10 to 0.90,
　Fe content in the galvanizing layer is 0% and 3.0% or less, and the Al content is 0% or less than 1.0%,
　the interface between the galvanized layer and the base steel sheet, the average thickness is 0.1 [mu] m ~ 2.0 .mu.m, steel width the difference between the maximum thickness and the minimum thickness in the direction having an Fe-Al alloy layer is within 0.5 [mu] m,
　To the base material in the steel sheet has a fine layer in direct contact with the Fe-Al alloy layer, wherein the 0.1 [mu] m ~ 5.0 .mu.m average thickness of the finer layer, the average of the ferrite phase in the finer layer particle size is 0.1 [mu] m ~ 3.0 [mu] m, the contains one or more oxides of Si and Mn in fine layer, the maximum diameter of 0.01 [mu] m ~ 0.4 .mu.m of the oxide , and the wherein the difference between the maximum thickness and the minimum thickness of the fine layer of the steel plate width direction is within 2.0 .mu.m, galvanized steel sheet.
[Requested item 2]
　The coating weight per one side of the galvanized layer is 10 g / m 2 or more, 100 g / m 2 and equal to or less than, hot-dip galvanized steel sheet according to claim 1.
[Requested item 3]
　Characterized in that said base material steel plate contains, by mass%,
　　further,
　　Ti: 0.001% ~ 0.150%, Nb: 0.001% ~ 0.100%, and
　　V: 0.001% ~ 0.300%,
　from characterized in that it contains one or more selected from the group consisting, hot-dip galvanized steel sheet according to claim 1 or 2.
[Requested item 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:
　　% ~ 2.00 0.01%, B: 0.0001% ~ 0.0100%, and
　　W: 0.01% ~ 2.00%,
　containing one or two or more selected from the consisting of group hot-dip galvanized steel sheet according to the feature that any one of claims 1 to 3 to.
[Requested item 5]
　Characterized in that said base material steel plate contains, by mass%,
　furthermore, Ca, Ce, Mg, Zr, La, and 0.0001% - 0.0100% content selected from the group consisting of REM 1 or two or more in total hot-dip galvanized steel sheet according to the feature that any one of claims 1 to 4 to.