INDUSTRIAL APPLICABILITY The present invention is a high-strength alloyed hot-dip galvanized steel sheet having a strength of 590 MPa (preferably 980 MPa) or more, which is suitable as a steel sheet for automobiles to be press-processed, and excellent in extensibility, perforation property, and fatigue characteristics. Regarding galvanized steel sheets.
Background technology
[0002]
　In recent years, awareness of environmental issues has increased, and in the automobile industry, it is important to reduce the weight of the vehicle body in order to improve fuel efficiency. On the other hand, in order to ensure safety in the event of a collision, it is also necessary to increase the strength of the vehicle body. In order to achieve both the weight reduction of the vehicle body and the improvement of safety, a high-strength material may be used, but the higher the strength, the more difficult the press molding becomes. Further, in order to improve the pressing performance, it is preferable that the characteristics of the steel sheet in the width direction are homogeneous.
[0003]
　This is because, in general, as the strength of the steel material increases, the yield strength increases and the extensibility and hole expansion property decrease. Further, the higher the strength, the lower the fatigue limit ratio, which makes it difficult to further increase the strength.
[0004]
　In high-strength hot-dip galvanized steel sheets, bainite is formed during the slow cooling of the conventional annealing process. Therefore, for example, a steel sheet containing ferrite mainly composed of martensite as disclosed in Patent Document 1 has been conventionally known, but a hot-dip galvanized steel sheet having sufficient formability has been realized. There wasn't.
[0005]
　Patent Document 2 discloses a technique for optimizing the size of the austenite low-temperature transformation phase to improve extensibility and flangeability, but has not achieved both strength and extensibility. Regarding the improvement of extensibility, for example, Patent Documents 3 and 4 disclose steel sheets (hereinafter referred to as TRIP steels) utilizing the process-induced transformation of retained austenite.
[0006]
　However, ordinary TRIP steel sheets require a large amount of Si in order to suppress the formation of cementite, but when a large amount of Si is added, the hot-dip galvanizing property of the steel sheet surface deteriorates, so the applicable steel materials are limited. Will be done. Further, a large amount of C is required to secure high strength, but if a large amount of C is added, welding problems such as nugget cracking occur.
[0007]
　Regarding the hot-dip galvanizing property of the steel sheet surface, Patent Document 5 discloses that Si is reduced in TRIP steel, and although improvement in hot-dip galvanizing property and ductility can be expected, the above-mentioned weldability remains a problem. ..
[0008]
　In DP steel that can be produced with a smaller amount of C than TRIP steel, if the amount of Si is large, the ductility becomes high as described later. However, as in the case of TRIP steel, there remains a problem in plating property. As a solution to the problem of deterioration of plating property due to high Si, for example, Patent Document 6 discloses that the atmosphere at the time of annealing is controlled to remove C from the surface layer of the steel sheet. By removing the C from the surface layer of the steel sheet, plating is possible even if Si exceeds 1% by mass, but since the surface layer of the steel sheet becomes soft, there arises a problem that fatigue characteristics are significantly deteriorated. In addition, since the ultra-high-tensile steel sheet with a strength of 980 MPa or more has a high microstructure strength, it is easily affected by cooling and reduction equal width direction fluctuations during manufacturing, and a steel sheet having uniform characteristics in the width direction can be used. There was a problem that it was difficult to make.
Prior art literature
Patent documents
[0009]
Patent Document 1: Japanese Patent No. 5305149
Patent Document 2: Japanese Patent No. 4730056
Patent Document 3: Japanese Patent Application
Laid-Open No. 61-157625 Patent Document 4: Japanese Patent Application Laid-Open No. 2007-063604
Patent Document 5: Japanese Patent Application Laid-Open No. 2000-345288 No.
Patent Document 6: Patent No. 5370104
Patent Document 7: International Publication No. 2013/047755
Outline of the invention
Problems to be solved by the invention
[0010]
　In view of the current state of the prior art, the present invention enhances extensibility, hole expandability, and fatigue characteristics in an alloyed hot-dip galvanized steel sheet having a strength of 590 MPa or more (preferably 980 MPa or more), and the width of the steel sheet. An object of the present invention is to make the characteristics in the direction uniform, and an object of the present invention is to provide an alloyed hot-dip galvanized steel sheet that solves the problem.
Means to solve problems
[0011]
　The present inventors have diligently studied a method for solving the above problems and have obtained the following findings.
[0012]
　(w) After cold rolling, heat treatment is performed in a two-phase region or a single-phase region, and then cooled or maintained at a temperature higher than the bainite formation temperature to suppress bainite transformation and have a low bainite fraction. Moreover, by forming a composite structure of ferrite and martensite, ductility can be improved.
[0013]
　By adding (x) Si, the ferrite fraction can be stably increased to improve ductility, and by strengthening the solid solution, the strength can be improved, so that an excellent strength-ductility balance can be ensured. ..
[0014]
　(y) The deterioration of plating property due to the addition of Si is dealt with by conventional atmosphere control, but martensite in the de-C layer, which is generated by atmosphere control and hinders fatigue characteristics, is replaced with martensite with a small aspect ratio. If so, the fatigue characteristics can be enhanced. By applying a leveler to the hot-rolled steel sheet before and after pickling the hot-rolled steel sheet, the martensite in the de-C layer can be made into martensite having a small aspect ratio.
[0015]
　(z) In addition to applying a leveler, in the annealing process after cold rolling, the heating rate in the required temperature range is controlled within the required range to suppress uneven distribution of ferrite, and the ferrite mass in which ferrite grains are accumulated is harmless. When homogenized to the above-mentioned form, the hole-expandability is improved, both extensibility and hole-expandability can be achieved, and the characteristics of the steel sheet in the width direction including the plating state can be made uniform.
[0016]
　The present invention has been made based on the above findings, and the gist thereof is as follows.
[0017]
　(1) The composition of the steel plate is by mass%,
C: 0.06% or more, 0.22% or less,
Si: 0.50% or more, 2.00% or less,
Mn: 1.50% or more, 2 .80% or less,
Al: 0.01% or more, 1.00% or less,
P: 0.001% or more, 0.100% or less,
S: 0.0005% or more, 0.0100% or less,
N: 0 .0005% or more, 0.0100% or less,
Ti: 0% or more, 0.10% or less,
Mo: 0% or more, 0.30% or less,
Nb: 0% or more, 0.050% or less,
Cr: 0 %
Or more, 1.00% or less, B: 0% or more, 0.0050% or less,
V: 0% or more, 0.300% or less,
Ni: 0% or more, 2.00% or less,
Cu: 0% or more , 2.00% or less,
W: 0% or more, 2.00% or less,
Ca: 0% or more, 0.0100% or less,
Ce: 0% or more, 0.0100% or less,
Mg: 0% or more, 0 .0100% or less,
Zr: 0% or more, 0.0100% or less,
La: 0% or more, 0.0100% or less,
REM: 0% or more, 0.0100% or less,
Sn: 0% or more, 1.000% or less,
Sb: 0% or more, 0.200% or less,
balance: Fe and impurities, alloyed and melted on the surface of the steel plate In an alloyed hot-dip zinc-plated steel sheet having a zinc-plated layer,
　the microstructure in the range of 1/8 plate thickness to 3/8 plate thickness centered on 1/4 plate thickness in the plate thickness direction from the surface of the steel plate is the area ratio. , Ferrite: 15% or more, 85% or less, Retained austenite: Less than 5%, Martensite: 15% or more, 75% or less, Pearlite: 5% or less, and balance (including 0%): Bainite, as
　described above. the number of the following ferrite lumps thickness direction of the thickness of 20μm is not less than 50% of the total number of ferrite lumps,
　the steel sheet surface layer portion, and following deprotection C layer 150μm thickness greater than 10μm is formed,
　the de-C An alloyed hot-dip zinc-plated steel sheet having a ferrite particle size of 30 μm or less in the layer and 50% or less of martensite having an aspect ratio of 5 or more.
[0018]
　(2) The above-mentioned (1), wherein a miniaturized layer having an average thickness of 0.1 μm to 5.0 μm is further provided between the alloyed hot-dip galvanized layer and the de-C layer. Alloyed hot-dip galvanized steel sheet.
[0019]
　(3) The difference in Fe concentration in the width direction in the alloyed hot-dip galvanized layer is less than 1.0% in mass%, and the difference in the proportion of martensite having the aspect ratio of 5 or more in the width direction. The alloyed hot-dip galvanized steel sheet according to (1) or (2) above, wherein the content is 10% or less.
[0020]
　(3) The composition of the components is
Ti: 0.01% or more, 0.10% or less,
Mo: 0.01% or more, 0.30% or less,
Nb: 0.005% or more, 0. 050% or less,
Cr: 0.01% or more, 1.00% or less,
B: 0.0002% or more, 0.0050% or less,
V: 0.001% or more, 0.300% or less,
Ni: 0. 01% or more, 2.00% or less,
Cu: 0.01% or more, 2.00% or less,
W: 0.01% or more, 2.00% or less,
Ca: 0.0001% or more, 0.0100% Below,
Ce: 0.0001% or more, 0.0100% or less,
Mg: 0.0001% or more, 0.0100% or less,
Zr: 0.0001% or more, 0.0100% or less,
La: 0.0001% above, 0.0100% or
less, REM: 0.0001% or more, 0.0100% or
less, Sn: 0.001% or more 1.000% or
less, Sb: 0.001% or more, or less 0.200%
of
The alloyed hot-dip zinc-plated steel sheet according to any one of (1) to (3) above, which comprises one type or two or more types .
The invention's effect
[0021]
　According to the present invention, it is possible to provide a high-strength alloyed hot-dip galvanized steel sheet which is excellent in extensibility, hole expandability, and fatigue characteristics and has uniform characteristics in the width direction of the steel sheet.
Forms for carrying out the invention
[0022]
　The alloyed hot-dip zinc-plated steel sheet of the present embodiment has a composition of the steel sheet in mass%,
C: 0.06% or more, 0.22% or less,
Si: 0.50% or more, 2.00% or less,
Mn: 1.50% or more, 2.80% or less,
Al: 0.01% or more, 1.00% or less,
P: 0.001% or more, 0.100% or less,
S: 0.0005% or more, 0.0100% or less,
N: 0.0005% or more, 0.0100% or less,
Ti: 0% or more, 0.10% or less,
Mo: 0% or more, 0.30% or less,
Nb: 0% or more, 0.050% or less,
Cr: 0% or more, 1.00% or less,
B: 0% or more, 0.0050% or less,
V: 0% or more, 0.300% or less,
Ni: 0% or more, 2. 00% or less,
Cu: 0% or more, 2.00% or less,
W: 0% or more, 2.00% or less,
Ca: 0% or more, 0.0100% or less,
Ce: 0% or more, 0.0100% Below,
Mg: 0% or more, 0.0100% or less,
Zr: 0% or more, 0.0100% or less,
La: 0% or more, 0.0100% or less,
REM: 0% or more, 0.0100% or less,
Sn: 0% or more, 1.000% or less,
Sb: 0% or more, 0.200% or less,
balance: In an alloyed hot-dip zinc-plated steel sheet composed of Fe and impurities and having an alloyed hot-dip zinc-plated layer on the
　steel sheet surface, the thickness is 1/8 to 3/8 thick centering on 1/4 thickness in the plate thickness direction from the steel sheet surface. The microstructure of the range is ferrite: 15% or more, 85% or less, retained austenite: less than 5%, martensite: 15% or more, 75% or less, pearlite: 5% or less, and the balance (0%). including): consists bainite,
　the following numbers ferrite lumps the thickness direction of the thickness of 20μm is not less than 50% of the total number of ferrite lumps,
　the steel sheet surface layer portion, the thickness of 10μm or more 150μm following de-C layer There are formed,
　the grain size of the ferrite of the de-C layer is not less 30μm or less, of the martensite, the aspect ratio is the ratio of 5 or more martensite is equal to or less than 50%.
[0023]
　Hereinafter, the alloyed hot-dip galvanized steel sheet of the present embodiment and the manufacturing method of the present embodiment will be sequentially described.
[0024]
　In conventional DP (Dual Phase) type ultra-high-tensile steel (DP steel), it is common to control the steel material by appropriately adjusting the microstructure fraction such as ferrite and martensite. be. Increasing the ferrite fraction improves ductility, but increasing ferrite causes (a) a decrease in strength due to an increase in the fraction of the soft structure, and (b) a decrease in ductility due to agglomeration of ferrite grains. It was found that the required strength-ductility balance could not be obtained.
[0025]
　In the alloyed hot-dip galvanized steel sheet of the present embodiment, the present inventors have made ferrite characteristics and existing forms, and other structural characteristics and existing states in order to enhance extensibility, hole-expandability, and fatigue characteristics. I focused on this and repeated diligent research. As a result, it was found that in DP steel (including the case where a small amount of retained austenite is contained), the ductility and the hole-expanding property do not decrease even if the strength is increased by hardening the soft ferrite and controlling the morphology. This will be described below.
[0026]
　It was found that when the amount of Si in the steel was 0.5% in order to reduce the degree of decrease in strength in (a) above, the strength-ductility-drilling property balance was improved. The reason for this is not clear, but the martensite fraction can be reduced by the solid solution strengthening of (a1) ferrite, the starting point of cracks is reduced, the local ductility is improved, and (a2) ferrite It is considered that the reason is that the plastic instability region is reduced and the uniform ductility is improved by the solid solution strengthening.
[0027]
　However, on the other hand, as the amount of Si increased, the scale of the surface layer increased and the plating property deteriorated, which made it difficult to manufacture a plated steel sheet. Therefore, a method was used in which the atmosphere was controlled and an oxide was formed inside the steel sheet instead of the surface layer of the steel sheet to ensure good plating properties. However, in this method, de-C progresses on the surface layer of the steel sheet at the same time as the formation of oxides inside the steel sheet, so that the surface layer of the steel sheet becomes soft and fatigue cracks easily propagate, and the fatigue limit ratio is significantly reduced. I have.
[0028]
　While diligently studying a method for solving the problem of the present invention, the present inventors have found that the steel sheet used for the leveler after the completion of hot rolling and the steel sheet obtained by grinding the surface layer of the steel sheet have good fatigue characteristics. I found it. Further, it was found that when the steel sheet is bent in the annealing process, the fatigue characteristics are further improved.
[0029]
　The reason for this is not clear, but the aspect ratio of martensite present in the de-C layer formed on the surface of the steel sheet has become smaller, and the surface structure has become finer, making it difficult for fatigue crack propagation to occur. It can be considered as a factor.
[0030]
　As described above, the addition of Si improved the strength-ductility balance, but even if the ferrite fraction increased, the degree of improvement in the strength-ductility balance and the degree of improvement in the strength-ductility balance were small.
[0031]
　In general, ferrite, which is a soft phase, has a large amount of deformation in a low strain region as it is responsible for deformation in DP steel. However, the ferrite existing in the vicinity of martensite is constrained by martensite at the time of deformation, and the amount of deformation is small.
[0032]
　The present inventors focused on this phenomenon and investigated the optimum conditions for restraining the deformation of ferrite. Then, by optimizing the deformation restraint state that ferrite receives from the adjacent hard phase (martensite) while maintaining the ferrite fraction that can improve the extensibility, it is possible to obtain both extensibility and hole expansion property. I arrived.
[0033]
　Until now, the mainstream of microstructure control has been to examine the correlation between grain boundaries and properties. It is obvious that in the case of single-phase steel, the influence of grain boundaries with different characteristics is large, but the present inventors have widened holes in a composite structure in which structures with significantly different characteristics such as ferrite and martensite coexist. When examining the improvement of properties, it was thought that the grain size in each structure does not make a big sense, and the existence form of the same phase greatly contributes to the characteristics.
[0034]
　Based on the above idea, the present inventors have described an aggregate of ferrite grains surrounded by a hard phase (having a plurality of ferrite grains and having a plurality of ferrite grains) adjacent to the hard phase (bainite, martensite). We confirmed the importance of evaluation using "ferrite lumps") and found the optimum conditions for restraining the deformation of ferrite.
[0035]
　The mechanism by which the material is improved under the above-mentioned proper conditions is not clear, but if the thickness of the ferrite block in the plate thickness direction is thin, the deformation of the ferrite is more constrained by the deformation restraint by the hard phase, and the ferrite is pseudo-cured. However, it is considered that it acted significantly on the maintenance of strength, suppressed the occurrence of cracks due to local giant deformation, and effectively improved the hole-spreading property.
[0036]
　The thickness of the ferrite lump is the maximum value of the thickness in the direction perpendicular to the plate surface in each of the ferrite lumps surrounded by the hard phase.
[0037]
　Since the extensibility depends on the deformability of ferrite and linearly correlates with the ferrite fraction, it is possible to achieve both extensibility and hole expansion by controlling the ferrite fraction and the existence form of ferrite. Become.
[0038]
　The alloyed hot-dip galvanized steel sheet of the present embodiment has been made based on the above findings found by the present inventors, and the characteristic requirements of the alloyed hot-dip galvanized steel sheet of the present embodiment will be described below.
[0039]
　First, the reason for limiting the component composition will be described. Hereinafter,% related to the component composition means mass%.
[0040]
　Component composition
　C: 0.06% or more and 0.22% or less
　C is an element that increases the hardness of martensite and contributes to the improvement of strength. If C is less than 0.06%, the addition effect cannot be sufficiently obtained, so C is set to 0.06% or more. It is preferably 0.07% or more. On the other hand, if C exceeds 0.22%, the formation of cementite is promoted and the hole-expanding property and weldability are lowered. Therefore, C is set to 0.22% or less. C is preferably 0.17% or less.
[0041]
　Si: 0.50% or more and 2.00% or less
　Si is an element that contributes to the improvement of strength and fatigue strength by solid solution strengthening without lowering ductility. If Si is less than 0.50%, the addition effect cannot be sufficiently obtained, so Si is set to 0.50% or more. It is preferably 0.80% or more, more preferably 1.00% or more. On the other hand, if Si exceeds 2.00%, ductility and spot weldability deteriorate, so Si is set to 2.00% or less. Si is preferably 1.80% or less, more preferably 1.60% or less.
[0042]
　Mn: 1.50% or more and 2.80% or less
　Mn is an element that contributes to the improvement of strength by strengthening solid solution and improving hardenability. If Mn is less than 1.50%, the addition effect cannot be sufficiently obtained, so Mn is set to 1.50% or more. It is preferably 1.80% or more. On the other hand, when Mn exceeds 2.80%, the weldability is lowered, the formation of ferrite is suppressed and the ductility is lowered, and the segregation is expanded and the hole expanding property is also lowered. Therefore, the Mn is 2. 80% or less. Mn is preferably 2.50% or less.
[0043]
　Al: 0.01% or more and 1.00% or less
　Al is an element necessary for deoxidation, suppresses the formation of harmful carbides, and contributes to the improvement of extensibility and hole-expanding property. In particular, it is an element that contributes to the improvement of chemical conversion treatment property without reducing ductility in a low Si component system.
[0044]
　If Al is less than 0.01%, the addition effect cannot be sufficiently obtained, so Al is set to 0.01% or more. On the other hand, if Al exceeds 1.00%, the addition effect is saturated and the chemical conversion treatment property and spot weldability are lowered. Therefore, Al is set to 1.00% or less. From the viewpoint of improving the chemical conversion treatment, 0.80% or less is preferable.
[0045]
　P: 0.001% or more and 0.100% or less
　P is an element that contributes to the improvement of strength and is an element that enhances corrosion resistance in coexistence with Cu. If P is less than 0.001%, the addition effect cannot be sufficiently obtained and the steelmaking cost increases significantly. Therefore, P is set to 0.001% or more. In terms of steelmaking cost, P is preferably 0.010% or more. On the other hand, if P exceeds 0.100%, weldability and workability deteriorate, so P is set to 0.100% or less. When corrosion resistance does not matter and workability is important, P is preferably 0.050% or less.
[0046]
　S: 0.0005% or more and 0.0100% or less
　S is an element that forms a sulfide (MnS or the like) that is the starting point of cracking and inhibits the hole-expanding property and the total extensibility. The smaller the S, the better, but if the S is reduced to less than 0.0005%, the steelmaking cost will increase significantly, so the S is set to 0.0005% or more. On the other hand, if S exceeds 0.0100%, the hole-expanding property and the total extensibility are remarkably lowered, so S is set to 0.0100% or less. Preferably S is 0.0060% or less.
[0047]
　N: 0.0005% or more and 0.0100% or less
　N is an element that inhibits processability. Further, N is an element that reduces the effective amount of Ti and / or Nb by forming a nitride (TiN and / or NbN) that inhibits extensibility and hole-expanding property when coexisting with Ti and / or Nb. be.
[0048]
　It is better that N is small, but if N is reduced to less than 0.0005%, the steelmaking cost will increase significantly, so N is set to 0.0005% or more. On the other hand, if N exceeds 0.0100%, the workability, extensibility, and hole expanding property are remarkably lowered, so N is set to 0.0100% or less. Preferably N is 0.0060% or less.
[0049]
　The composition of the plated steel sheet of the present invention has Ti: 0.01% or more, 0.10% or less, Mo: 0.01% or more, 0.30% or less, Nb: 0.005, as appropriate, for the purpose of improving characteristics. % Or more, 0.050% or less, Cr: 0.01% or more, 1.00% or less, B: 0.0002% or more, 0.0050% or less, V: 0.001% or more, 0.300% or less , Ni: 0.01% or more, 2.00% or less, Cu: 0.01% or more, 2.00% or less, W: 0.01% or more, 2.00% or less, Ca: 0.0001% or more , 0.0100% or less, Ce: 0.0001% or more, 0.0100% or less, Mg: 0.0001% or more, 0.0100% or less, Zr: 0.0001% or more, 0.0100% or less, La : 0.0001% or more, 0.0100% or less, REM: 0.0001% or more, 0.0100% or less, Sn: 0.001% or more, 1.000% or less, Sb: 0.001% or more, 0 .200% or less of 1 type or 2 or more types may be contained.
[0050]
　Ti: 0.01% or more and 0.10% or less
　Ti is an element that delays recrystallization and contributes to the formation of unrecrystallized ferrite, and also forms carbides and / or nitrides, and contributes to the improvement of strength. Is.
[0051]
　If the Ti content is less than 0.01%, the content effect cannot be sufficiently obtained. Therefore, the Ti content is preferably 0.01% or more. On the other hand, if it exceeds 0.10%, the moldability is lowered, so Ti is set to 0.10% or less. Ti is preferably 0.05% or less.
[0052]
　Mo: 0.01% or more and 0.30% or less
　Mo is an element that delays recrystallization, contributes to the formation of unrecrystallized ferrite, enhances hardenability, and contributes to the control of martensite fraction. .. In addition, Mo segregates at the grain boundaries, suppresses zinc from invading the structure of the welded portion during welding, contributes to the prevention of cracks during welding, and produces pearlite during cooling in the annealing process. It is an element that also contributes to suppression.
[0053]
　If Mo is less than 0.01%, the content effect cannot be sufficiently obtained, so Mo is preferably 0.01% or more. More preferably, Mo is 0.04% or more. On the other hand, if Mo exceeds 0.30%, the moldability deteriorates, so Mo is set to 0.30% or less. Mo is preferably 0.25% or less.
[0054]
　Nb: 0.005% or more and 0.050% or less
　Nb is an element that delays recrystallization and contributes to the formation of unrecrystallized ferrite, and also forms carbides and / or nitrides, and contributes to the improvement of strength. Is. If Nb is less than 0.005%, the content effect cannot be sufficiently obtained, so Nb is preferably 0.005% or more. More preferably, Nb is 0.010% or more. On the other hand, if Nb exceeds 0.050%, the moldability is lowered, so Nb is set to 0.050% or less. Preferably, Nb is 0.030% or less.
[0055]
　Cr: 0.01% or more and 1.00% or less
　Cr is an element that delays recrystallization, contributes to the formation of unrecrystallized ferrite, and contributes to the suppression of pearlite formation during cooling in the annealing step. If Cr is less than 0.01%, the content effect cannot be sufficiently obtained, so Cr is preferably 0.01% or more. More preferably, Cr is 0.05% or more. On the other hand, if Cr exceeds 1.00%, the moldability is lowered, so Cr is set to 1.00% or less. Cr is preferably 0.50% or less.
[0056]
　B: 0.0002% or more, 0.0050% or less,
　B is an element that delays recrystallization, contributes to the formation of unrecrystallized ferrite, enhances hardenability, and contributes to the control of martensite fraction. be. Further, B segregates at the grain boundaries, suppresses zinc from invading the structure of the welded portion during welding, contributes to prevention of cracking during welding, and generates pearlite during cooling in the annealing step. It is an element that also contributes to suppression.
[0057]
　If B is less than 0.0002%, the content effect cannot be sufficiently obtained, so B is preferably 0.0002% or more. More preferably, B is 0.0010% or more. On the other hand, if B exceeds 0.0050%, the moldability is lowered, so B is set to 0.0050% or less. B is preferably 0.0025% or less.
[0058]
　V: 0.001% or more and 0.300% or less
　V is an element that contributes to the improvement of strength by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and strengthening dislocations by suppressing recrystallization. Is. If V is less than 0.001%, the strength improving effect cannot be sufficiently obtained, so V is preferably 0.001% or more. More preferably, V is 0.010% or more. On the other hand, if V exceeds 0.300%, the carbonitride is excessively precipitated and the moldability is lowered. Therefore, V is set to 0.300% or less. V is preferably 0.150% or less.
[0059]
　Ni: 0.01% or more and 2.00% or less
　Ni is an element that suppresses phase transformation at high temperatures and contributes to the improvement of strength. If Ni is less than 0.01%, the content effect cannot be sufficiently obtained, so Ni is preferably 0.01% or more. More preferably, Ni is 0.10% or more. On the other hand, if Ni exceeds 2.00%, the weldability deteriorates, so Ni is set to 2.00% or less. Ni is preferably 1.20% or less.
[0060]
　Cu: 0.01% or more and 2.00% or less
　Cu is an element that exists as fine particles and contributes to the improvement of strength. If the Cu content is less than 0.01%, the content effect cannot be sufficiently obtained. Therefore, the Cu content is preferably 0.01% or more. More preferably, Cu is 0.10% or more. On the other hand, if Cu exceeds 2.00%, the weldability deteriorates, so Cu is set to 2.00% or less. Cu is preferably 1.20% or less.
[0061]
　W: 0.01% or more and 2.00% or less
　W is an element that suppresses phase transformation at high temperature and contributes to improvement of strength. If W is less than 0.01%, the content effect cannot be sufficiently obtained, so W is preferably 0.01% or more. More preferably, W is 0.10% or more. On the other hand, if W exceeds 2.00%, the hot workability is lowered and the productivity is lowered, so the W is set to 2.00% or less. W is preferably 1.20% or less.
[0062]
　Ca: 0.0001% or more, 0.0100% or less
　Ce: 0.0001% or more, 0.0100% or less
　Mg: 0.0001% or more, 0.0100% or less
　Zr: 0.0001% or more, 0.0100 %
　Or less La: 0.0001% or more, 0.0100% or less
　REM: 0.0001% or more, 0.0100% or less
　Ca, Ce, Mg, Zr, La, and REM contribute to the improvement of moldability. It is an element. If Ca, Ce, Mg, Zr, La, and REM are each less than 0.0001%, the content effect cannot be sufficiently obtained, so that each element is preferably 0.0001% or more. More preferably, each element is 0.0010% or more.
[0063]
　On the other hand, if Ca, Ce, Mg, Zr, La, and REM each exceed 0.0100%, the ductility may decrease, so all the elements are set to 0.0100% or less. Preferably, each element is 0.0070% or less.
[0064]
　REM is an abbreviation for Rare Earth Metal and refers to an element belonging to the lanthanoid series. REM and Ce are often contained in the form of misch metal, but in addition to La and Ce, elements of the lanthanoid series may be contained in combination. Even if an element of the lanthanoid series other than La and Ce is contained as an impurity, the property is not impaired. Further, the metal La or Ce may be contained.
[0065]
　Sn: 0.001% or more and 1.000% or less
　Sn is an element that suppresses the coarsening of the structure and contributes to the improvement of the strength. If Sn is 0.001% or more, the content effect cannot be sufficiently obtained, so Sn is preferably 0.001% or more. More preferably, Sn is 0.010% or more. On the other hand, if Sn exceeds 1.000%, the steel sheet may become excessively brittle and the steel sheet may break during rolling, so Sn is set to 1.000% or less. Sn is preferably 0.500% or less.
[0066]
　Sb: 0.001% or more and 0.200% or less
　Sb is an element that suppresses the coarsening of the structure and contributes to the improvement of the strength. If Sb is less than 0.001%, the content effect cannot be sufficiently obtained, so Sb is preferably 0.001% or more. More preferably, Sb is 0.005% or more. On the other hand, if Sb exceeds 0.200%, the steel sheet becomes excessively brittle and the steel sheet may break during rolling, so Sb is set to 0.200% or less. Preferably, Sb is 0.100% or less.
[0067]
　In the composition of the alloyed hot-dip galvanized steel sheet of the present embodiment, the balance excluding the above elements is Fe and impurities. The impurity is an element that is inevitably mixed from the steel raw material and / or in the steelmaking process, and is an element that is allowed to exist within a range that does not impair the characteristics of the alloyed hot-dip galvanized steel sheet of the present embodiment.
[0068]
　For example, Ti, Mo, Nb, Cr, B, V, Ni, Cu, W, Ca, Ce, Mg, Zr, La, REM, Sn, and Sb are all alloyed hot-dip zinc of the present embodiment. If the amount is less than the lower limit specified by the composition of the plated steel sheet, it is acceptable as an unavoidable impurity.
[0069]
　As impurities, H, Na, Cl, Sc, Co, Zn, Ga, Ge, As, Se, Y, Tc, Ru, Rh, Pd, Ag, Cd, In, Te, Cs, Ta, Re, Os. , Ir, Pt, Au, and Pb are allowed in the range of 0.010% or less in total.
[0070]
　Next, the microstructure of the alloyed hot-dip galvanized steel sheet of the present embodiment will be described.
[0071]
　In the alloyed hot-dip galvanized steel sheet of the present embodiment, the strength, ductility, hole expandability, and fatigue characteristics are each controlled by controlling the fraction and morphology of ferrite and martensite and controlling the surface structure. The balance with can be obtained at a high level.
[0072]
　In general, increasing the ferrite fraction improves ductility, but since ferrite is soft, its strength and hole expandability decrease. In the present embodiment, the hard phase restrains the deformation of the soft phase, so that the characteristics and functions of ferrite can be effectively utilized.
[0073]
　Limited range of microstructure: 1/8 plate thickness centered on 1/4 plate thickness in the
　plate thickness direction from the steel plate surface to 3/8 plate thickness 1/4 plate thickness centered on the plate thickness direction from the steel plate surface 1 The microstructure of / 8 to 3/8 thickness is mainly responsible for the mechanical properties of the entire steel sheet. Therefore, in the present embodiment, the range in the plate thickness direction that defines the structure fraction is "1/8 plate thickness to 3/8 plate thickness centered on 1/4 plate thickness". The percentage of the tissue fraction is the area ratio.
[0074]
　Ferrite: 15% or more, 85% or less If the
　ferrite content is less than 15%, it becomes difficult to secure the required extensibility, so the ferrite content is set to 15% or more. The ferrite content is preferably 20% or more. On the other hand, if the ferrite exceeds 85%, it becomes difficult to secure the required strength, so the ferrite is set to 85% or less. Ferrite is preferably 75% or less.
[0075]
　Pearlite: 5% or less If
　pearlite exceeds 5%, the extensibility and hole-spreading property will decrease, so the pearlite should be 5% or less. The lower limit includes 0%.
[0076]
　Residual austenite:
　It is effective to use retained austenite as a supplement in terms of ensuring extensibility of less than 5%. However, retained austenite causes hydrogen cracking depending on the conditions of use, so retained austenite. Is less than 5%. The lower limit includes 0%.
[0077]
　Martensite: 15% or more, 75% or less If
　martensite is less than 15%, it is difficult to secure the required strength, so martensite should be 15% or more. Preferably martensite is 20% or more. On the other hand, if martensite exceeds 75%, it becomes difficult to secure the required elongation, so martensite should be 75% or less. Preferably martensite is 65% or less.
[0078]
　Bainite: The residual
　bainite may be produced as a residual structure as a structure for adjusting the fraction of martensite, but may be 0%. In order to secure ferrite and martensite at their respective lower limit fractions, the upper limit of the balance is 70%.
[0079]
　Here, a method of calculating the area ratio will be described.
[0080]
　A sample is taken with a plate thickness cross section parallel to the rolling direction as an observation surface, the observation surface is polished, nightal etching is performed, and observation is performed with an optical microscope or a scanning electron microscope (SEM). The area ratio is calculated using the captured image or the image analysis software in the device. For the area ratio, one field of view in the image is 200 μm in length and 200 μm or more in width, image analysis is performed for each of 10 or more different fields of view, the area ratio of each tissue is calculated to obtain the average value, and the average value is the area ratio. And.
[0081]
　Using the above image, the thickness of the ferrite mass is measured. In the above field of view, the longest thickness in the plate thickness direction of the ferrite block is defined as the thickness of the ferrite block.
[0082]
　Using the above image, the aspect ratio of martensite in the de-C layer described later can be calculated. In the thickness of martensite, the long part and the short part are measured, and the thickness of the long part divided by the thickness of the short part is defined as the aspect ratio. Further, among the martensites in the visual field having an area of ​​200 μm in length and 200 μm in width or more, the number ratio of martensite having an aspect ratio of 5 or more is calculated.
[0083]
　When martensite is difficult to discriminate by night game etching, repeller etching can also be used.
[0084]
　Next, a method for measuring retained austenite will be described.
[0085]
　The area ratio of retained austenite can be measured by electron backscatter diffraction (EBSD) method or X-ray diffraction method. When measuring by the X-ray diffraction method, the diffraction intensity of the (111) plane of ferrite (α (111)) and the diffraction intensity of the (200) plane of retained austenite (γ (200)) are measured by using Mo-Kα rays. , The diffraction intensity of the (211) plane of ferrite (α (211)) and the diffraction intensity of the (311) plane of retained austenite (γ (311)) were measured, and the area ratio of retained austenite (f) was calculated by the following equation. A ) can be calculated.
　f A = (2/3) {100 / (0.7 × α (111) / γ (200) +1)}
　　+ (1/3) {100 / (0.78 × α (211) / γ (311) ) +1)}
[0086]
　Thickness of ferrite lumps in the plate thickness direction: 20 μm or less
　Number of ferrite lumps with the above thickness of 20 μm or less: 50% or more of the total number of ferrite lumps In
　the alloyed hot-dip galvanized steel sheet of the present embodiment, the required hole expandability is ensured. Above, the thickness and number of ferrite masses are important.
[0087]
　If the thickness of the ferrite mass in the plate thickness direction exceeds 20 μm, the constraining of the adjacent hard phase (martensite, bainite) to the ferrite mass does not sufficiently act, and excessive deformation occurs at the center of the ferrite mass. Since the deformation limit is easily reached, local deformation occurs in the steel sheet, and the effect of improving the hole expanding property cannot be obtained, the thickness of the ferrite block in the plate thickness direction is set to 20 μm or less. It is preferably 16 μm or less.
[0088]
　If the number of ferrite lumps having a thickness of 20 μm or less in the plate thickness direction is less than 50% of the total number of ferrite lumps, it is difficult to obtain the effect of improving the hole expanding property at a level having a superior difference. The number of ferrite lumps having a thickness of 20 μm or less in the thickness direction shall be 50% or more of the total number of ferrite lumps. It is preferably 70% or more.
[0089]
　Thickness of de-C layer on the surface layer of the steel sheet: 10 μm or more and 150 μm or less The
　de-C layer is formed by the reaction of C on the surface layer of the steel sheet with oxygen in the atmosphere to become CO or CO 2 and escape into the atmosphere. NS. Since it is difficult to obtain a hard structure in the surface layer portion where C is reduced, the structure becomes softer than that inside the steel sheet.
[0090]
　The thickness of the C-de-C layer is determined as follows.
[0091]
　In the plate thickness direction, the hardness is measured in the range of 1/8 plate thickness to 3/8 plate thickness centering on 1/4 plate thickness, and the average value is used as the reference hardness of the hardness of the steel plate. Measure the hardness from 1/8 of the steel sheet thickness toward the surface layer of the steel sheet, insert points that are 0.9 or less of the standard hardness, and determine the distance from the point that is 0.9 or less to the surface of the steel sheet. The thickness of the de-C layer is used.
[0092]
　In the alloyed hot-dip galvanized steel sheet of the present embodiment, the presence of a de-C layer having a thickness of 10 μm or more and 150 μm or less on the surface layer of the steel sheet is important in order to secure the required hole expandability and fatigue characteristics. The formation of the C-de-C layer will be described later.
[0093]
　If the thickness of the C-de-C layer is less than 10 μm, the plating property and the hole-expanding property are deteriorated. Therefore, the thickness of the C-de-C layer is set to 10 μm or more. It is preferably 20 μm or more, more preferably 30 μm or more. On the other hand, if the thickness of the de-C layer exceeds 150 μm, even if the morphology of martensite in the de-C layer is controlled, the fatigue characteristics do not improve and the fatigue characteristics and strength decrease. The thickness of is 150 μm or less. It is preferably 120 μm or less, more preferably 100 μm or less.
[0094]
　In the de-C layer, the grain size of ferrite is set to 30 μm or less, and the proportion of martensite having an aspect ratio of 5 or more is set to 50% or less in order to secure the required fatigue characteristics. This will be described below.
[0095]

　Grain size of ferrite in de-C layer 　: 30 μm or less In the de-C layer, if the particle size of ferrite exceeds 30 μm, the fatigue characteristics deteriorate, so the particle size of ferrite is set to 30 μm or less. The reason why the fatigue characteristics decrease is not clear, but it is considered that when the grain size of ferrite is large, the fraction of adjacent martensite becomes small and fatigue cracks easily propagate. The smaller the particle size of ferrite, the more preferably 25 μm or less, and more preferably 20 μm or less. Here, the particle size of ferrite represents the average particle size. For example, observe a region with an area of ​​40,000 μm 2 or more, write a line segment parallel to the rolling direction, divide the total length of the line segment by the number of intersections of the line segment and the grain boundary, and divide the average value by the number of intersections of the line segment and the grain boundary. And.
[0096]
　Ratio of martensite having an aspect ratio of 5 or more: 50% or less In
　martensite having an aspect ratio of 5 or more, fatigue cracks are considered to occur along the martensite and easily propagate. In the hot-dip zinc-plated steel plate, the proportion of martensite in the de-C layer having an aspect ratio of 5 or more is reduced to further improve the fatigue characteristics.
[0097]
　If the proportion of martensite in the de-C layer having an aspect ratio of 5 or more exceeds 50%, the fatigue characteristics are significantly reduced, so the proportion is set to 50% or less. It is preferably 40% or less, more preferably 30% or less. Further, in order to make the characteristics in the width direction more uniform, the difference in the proportions of martensite having an aspect ratio of 5 or more in the width direction is preferably 10% or less. More preferably, it is 6% or less.
[0098]
　Next, the miniaturized layer existing between the de-C layer and the alloyed hot-dip galvanized layer will be described. The miniaturized layer is a layer formed by the progress of an oxidation or decarburization reaction under conditions controlled to a specific atmosphere during annealing as described later. Therefore, the structure constituting the miniaturized layer is substantially mainly a ferrite phase except for oxides and inclusion particles. The boundary between the miniaturized layer and the de-C layer is a boundary in which the average grain size of ferrite in the miniaturized layer is less than 1/2 of the average grain size of ferrite in the de-C layer.
[0099]
　The average thickness of the miniaturized layer is preferably 0.1 μm to 5.0 μm. If the average thickness of the miniaturized layer is less than 0.1 μm, the effect of suppressing the occurrence and elongation of cracks cannot be obtained, and the effect of improving the plating adhesion cannot be obtained. If it exceeds 5.0 μm, alloying of the plating layer (Zn—Fe alloy formation) proceeds, the Fe content in the alloyed hot-dip galvanized layer increases, and the plating adhesion deteriorates. The average thickness of the finer layer is more preferably 0.2 μm to 4.0 μm, and even more preferably 0.3 μm to 3.0 μm.
[0100]
　The average thickness of the miniaturized layer is measured by the method shown below. From the alloyed hot-dip galvanized steel sheet, a sample is taken with the cross section parallel to the rolling direction of the base steel sheet as the observation surface. The observation surface of the sample is processed by a CP (Cross section polisher) device, and a reflected electron image by FE-SEM (Field Emission Scanning Electron Microscopy) is observed and measured at a magnification of 5000.
[0101]
　The refined layer contains one or more oxides of Si and Mn. Examples of the oxide include one or more selected from the group consisting of SiO 2 , Mn 2 SiO 4 , MnSiO 3 , Fe 2 SiO 4 , FeSiO 3 , and MnO. As will be described later, this oxide is formed in the base steel sheet in a specific temperature range during annealing. Since the oxide particles suppress the growth of ferrite phase crystals on the surface layer of the base steel sheet, a miniaturized layer is formed.
[0102]
　Next, the alloyed hot-dip galvanized layer will be described.
[0103]
　The alloyed hot-dip galvanizing layer is a plating layer obtained by alloying a hot-dip galvanizing layer formed under normal plating conditions (including a plating layer formed by hot-dip galvanizing a zinc alloy) under normal alloying treatment conditions.
[0104]
　The plating adhesion amount of the alloyed hot-dip galvanized layer is not particularly limited to a specific amount, but the single-sided adhesion amount is preferably 5 g / m 2 or more from the viewpoint of ensuring the required corrosion resistance .
[0105]
　Further, in order to reduce the unevenness of the appearance, it is preferable that the difference in Fe concentration in the width direction in the alloyed hot-dip galvanized layer is less than 1.0% in mass%. More preferably, it is 0.7 or less.
[0106]
　In the alloyed hot-dip galvanized steel sheet of the present embodiment, upper layer plating (for example, Ni plating) may be performed on the alloyed hot-dip galvanized layer for the purpose of improving coatability and weldability. Further, for the purpose of improving the surface properties of the alloyed hot-dip galvanized layer, various treatments such as chromate treatment, phosphate treatment, lubricity improvement treatment, weldability improvement treatment and the like may be performed.
[0107]
　The tensile strength of the alloyed hot-dip galvanized steel sheet of the present embodiment is preferably 590 MPa or more. A high-strength steel sheet having a tensile strength of 590 MPa or more is suitable as a material steel sheet for automobile members.
[0108]
　The plate thickness of the alloyed hot-dip galvanized steel sheet of the present embodiment is not particularly limited to a specific plate thickness range, but is preferably 0.1 to 11.0 mm. A high-strength thin steel sheet having a plate thickness of 0.1 to 11.0 mm is suitable as a material steel sheet for an automobile member manufactured by press working. Further, the high-strength thin steel plate having the above-mentioned plate thickness can be easily manufactured on the thin plate production line.
[0109]
　Next, the manufacturing method of the present embodiment will be described.
[0110]
　The manufacturing method for producing the alloyed hot-dip zinc-plated steel sheet of the
present embodiment is, for example, (a) hot rolling by heating a cast slab having a component composition of the alloyed hot-dip zinc-plated steel sheet of the present embodiment to 1100 ° C. or higher. subjecting, to exit the hot rolling at a finishing temperature above Ar3 point, the hot-rolled steel sheet after hot rolling finished wound in a temperature range of 680 ° C. or less,
the hot-rolled steel sheet was wound (b), prior to the pickling And / or later, the hot-rolled steel sheet was leveled and then subjected to cold rolling at a rolling ratio of 30% or more and 70% or less to obtain a cold-rolled steel sheet, and
(c) a cold-rolled steel sheet,
　(c-1). It consists of 1 to 10% by volume of H 2 , and N 2 , H 2 O, and the balance of one or more of O 2 , and the ratio of water pressure to hydrogen partial pressure in pre-tropical and average-tropical regions is log (P H2 O / P H2 in), -1.7 or -0.2 at below atmosphere,
　(c-2) 500 ° C. or higher, an average heating rate of the temperature range of maximum temperature -50 ° C. 1 At ° C./sec or higher, heat to the maximum reaching temperature of 720 ° C. or higher and 900 ° C. or lower, hold for 30 seconds or longer and 30 minutes or lower, and after holding,
　(c-3) From the maximum reached temperature of -50 ° C to the cooling stop temperature T (° C) that satisfies the following formula (B) at an average cooling rate of X (° C / sec) or higher that satisfies the following formula (A). while cooling, bending the bending radius 800mm below annealed to perform one or more times,
galvanized in (d) of the steel sheet after annealing, then subjected to alloying treatment in galvanized
, characterized in that ..
[0111]
　X ≧ (Ar3-350) / 10 a　　　　　　　　　　　　　　　　　　　... (A)
　a = 0.6 [C] +1.4 [Mn] +1.3 [Cr] +3.7 [Mo] -100 [B] -0. 87
　T ≧ 730-350 [C] -90 [Mn] -70 [Cr] -83 [Mo] ・ ・ ・ (B)
　　[Element]: Mass% of element
[0112]
　Hereinafter, the process conditions of the manufacturing method of the present embodiment will be described.
[0113]
　(a) Process
　Heating temperature of casting slab: 1100 ° C or higher
　Finishing hot rolling temperature: Ar 3 points or higher
　Winding temperature: 680 ° C or lower
[0114]
　A cast slab having a component composition of the alloyed hot-dip galvanized steel sheet of the present embodiment is prepared according to a conventional method. Once the cast slab is cooled, it is heated to 1100 ° C. or higher and subjected to hot rolling. If the heating temperature of the cast slab is less than 1100 ° C, the homogenization of the cast slab and the dissolution of the carbonitride become insufficient, resulting in a decrease in strength and workability. Therefore, the heating temperature of the cast slab is 1100 ° C or higher. And. It is preferably 1150 ° C. or higher.
[0115]
　On the other hand, when the heating temperature of the cast slab exceeds 1300 ° C., the production cost rises, the productivity decreases, and the particle size of the initial austenite locally increases to form a mixed grain structure, resulting in a decrease in ductility. There is a risk of doing. Therefore, the heating temperature of the cast slab is preferably 1300 ° C. or lower. More preferably, it is 1250 ° C. or lower.
[0116]
　The cast slab may be directly subjected to hot rolling at a high temperature (1100 ° C. or higher, preferably 1300 ° C. or lower) immediately after the cast slab is cast.
[0117]
　Hot rolling is completed at a temperature of 3 Ar points or higher. If the finish hot rolling temperature is less than Ar 3 points, the steel sheet may crack in the next cold rolling and the material may deteriorate. Therefore, the finishing hot rolling temperature is set to Ar 3 points or more. It is preferably (Ar3 + 15) ° C. or higher.
[0118]
　Since the finish hot-rolling temperature may be appropriately set in the temperature range of Ar 3 points or more according to the composition, material, etc. of the hot-rolled steel sheet, the upper limit of the finish hot-rolling temperature is not particularly set.
[0119]
　The Ar3 points may be calculated by the following formula.
　　　Ar3 = 901-325 x [C] +33 x [Si] +287 x [P] +40 x [
　　　　　　Al] -92 ([Mn] + [Mo])
　　　　[Element]: Mass% of element
[0120]
　The hot-rolled steel sheet that has been hot-rolled is wound at a temperature of 680 ° C. or lower. When the winding temperature exceeds 680 ° C., cementite becomes coarse and the annealing time becomes long, and the grain size of ferrite in the surface de-C layer exceeds 30 μm, so the winding temperature is set to 680 ° C. or lower. It is preferably 630 ° C or lower, more preferably 580 ° C or lower.
[0121]
　The lower limit of the take-up temperature is not particularly set, but if it is less than 400 ° C., the strength of the hot-rolled steel sheet increases too much and the rolling load in cold rolling increases. Therefore, the take-up temperature is preferably 400 ° C. or higher. ..
[0122]
　(b) Process
　Rolling rate: 30% or more and 70% or less The
　hot-rolled steel sheet is pickled to remove the scale layer, and then the hot-rolled steel sheet is subjected to cold rolling. When the rolling ratio is less than 30%, the formation of recrystallized nuclei is unlikely to occur, the grain growth starts due to the coarsening of the recovered grains, the recrystallization becomes insufficient, the ductility decreases, and the thickness in the plate thickness direction increases. Since the ratio of the number of ferrite lumps of 20 μm or less is reduced, the rolling ratio is set to 30% or more.
[0123]
　The rolling ratio is preferably higher in order to reduce the area ratio of unrecrystallized ferrite and further improve the extensibility of the steel sheet, but the rolling load also increases as the rolling ratio increases, so the rolling ratio is 70%. It is as follows. If the rolling load is high, there is a concern that the shape accuracy of the steel sheet may decrease, so the rolling ratio is preferably 65% ​​or less.
[0124]
　Further, in order to improve the uniformity of the structure in the width direction, the hot-rolled steel sheet is leveled before and / or after pickling the hot-rolled steel sheet. By this treatment, it is possible to reduce the number ratio of martensite having an aspect ratio of 5 or more in the martensite in the de-C layer.
[0125]
　By applying the leveler, the strain of the leveler is added to the strain of the cold rolling and remains even after the cold rolling. Due to the strain accumulated on the surface layer of the steel sheet, ferrite recovers and recrystallizes during annealing and approaches equiaxed, then reverse transformation to austenite with a small aspect ratio, and cooling to martensite with a small aspect ratio. It is estimated that the distribution is also uniform in the width direction. Therefore, when the leveler is not applied, the proportion of maltensites having an aspect ratio of 5 or more becomes high, and the difference in the proportions in the width direction becomes large (for example, martens having an aspect ratio of 5 or more in the width direction). (The difference in the ratio of the sites is more than 10%), so that the difference in the fatigue limit ratio becomes large and the fatigue characteristics decrease.
[0126]
　Further, when the surface layer structure that is uniform in the width direction as described above is subjected to plating treatment and alloying treatment, it becomes easy to alloy uniformly, and the difference in Fe concentration in the width direction in the alloyed hot-dip galvanized layer becomes large. It becomes smaller.
[0127]
　In addition, by applying the leveler, the strain of the leveler is added in the range near the 1/4 plate thickness in the width direction, although it is not as high as that of the surface layer. Crystallize. Then, at the time of retention, austenite is precipitated from the fine ferrite grain boundaries, whereby a large lump of ferrite grains is dispersed. As a result, the number of ferrite lumps having a thickness of 20 μm or less in the plate thickness direction is 50% or more of the total number of ferrite lumps, and the required hole expandability can be ensured. Further, when the leveler is applied, the rolling in the width direction becomes uniform in the subsequent cold rolling, and the strain of the leveler remains uniform in the width direction. Therefore, the ferrite structure is also dispersed in the range of about 1/4 thickness in the width direction. And the uniformity of the tissue is improved. For example, if the amount of strain introduced into the surface layer of the steel sheet by the roll leveler is 0.2% or more at the maximum, it is considered that the structural change of the surface layer can be affected.
[0128]
　(c) Step The
　annealing step is the most important step in creating the microstructure of the alloyed hot-dip galvanized steel sheet of the present embodiment. Hereinafter, each process condition will be described.
[0129]
　(c-1) Burning atmosphere
　Atmosphere composition: 1 to 10% by volume of H 2 , and one or more of
　　　　　　　N 2 , H 2 O, and O 2
　Remaining water pressure and hydrogen partial pressure in the tropical zone ratio: log (P H2 O / P H2 in), -1.7 or -0.2 or less
[0130]
　In the ablation step, an ablation atmosphere is formed with 1 to 10% by volume of H 2 , and N 2 , H 2 O, and the balance of one or more of O 2 , and the moisture pressure in the average tropics. the ratio of hydrogen partial pressure, log (P H2 O / P H2 in), -1.7 or more controls to -0.2 or less.
[0131]
　When the steel sheet is annealed in the above annealing atmosphere, the scale of the surface layer of the steel sheet disappears and oxides are generated inside the steel sheet. As a result, the plating property of the steel sheet can be ensured, and the hot-dip galvanized layer can be formed on the surface of the steel sheet with good adhesion in the plating step described later.
[0132]
　H 2 If is less than 1 vol%, log (P in the soaking zone H2 O / P H2 becomes difficult to make) in the range of -1.7 ~ -0.2, since plating of the steel sheet is reduced , H 2 is 1% by volume or more. It is preferably 3% by volume or more. If H 2 exceeds 10% by volume, the atmosphere cost increases, so H 2 is set to 10% by volume or less. It is preferably 7% by volume or less.
[0133]
　Log in soaking (P H2 O / P H2 If) is less than -1.7, the thickness of the de-C layer is less than 10 [mu] m, since the plating is degraded, log in soaking (P H2 O / P H2 ) Is -1.7 or higher. It is preferably −1.3 or higher, more preferably -1 or higher. When the log (P H2O / PH2 ) in the tropics exceeds -0.2, the thickness of the de-C layer exceeds 150 μm and the fatigue characteristics decrease. Therefore, the log ( PH2O / PH2 ) in the tropics is It shall be -0.2 or less. It is preferably −0.5 or less, more preferably −0.7.
[0134]
　If it is possible to control the thickness of the de-C layer, for example, the ratio of the partial pressure of carbon dioxide to the partial pressure of carbon monoxide can be controlled instead of the ratio of the water pressure and the partial pressure of hydrogen. May be good.
[0135]
　The conditions of the annealing atmosphere is a condition in the soaking zone, log (P even preheating zone H2 O / P H2 in), -1.7 or more controls to -0.2 or less. In the pre-tropical zone, adjusting the ratio of the water vapor partial pressure PH2O to the hydrogen partial pressure PH2 can be used to adjust the thickness of the de-C layer, the thickness of the refined layer, the aspect ratio of martensite, the uniformity of Fe concentration in the width direction, and It affects the surface texture of the steel sheet before plating.
[0136]
　As described above, even after cold rolling, the strain of the leveler is added to the strain of cold rolling in the width direction and remains. Water vapor partial pressure P in yet preheating zone H2O and hydrogen partial pressure P H2 by adjusting the ratio between, since lowering of the surface layer of the C concentration is suppressed and recrystallization is prevented from excessively progress, re at Atsushi Nobori The crystallized ferrite becomes finer. As a result, austenite is finely precipitated on the surface layer during subsequent annealing in the tropics, the aspect ratio of martensite produced after cooling becomes small, and ferrite becomes fine. Thus subjecting the leveler, further log (P in preheating zone H2 O / P H2 in), -1.7 or more, by controlling the -0.2 or less, the aspect ratio of the martensite de C layer is improved Will be done.
[0137]
　Also, log (P in preheating zone H2 O / P H2 in), -1.7 or more, by controlling the -0.2 or less, to suppress excessive decarbonization at the steel sheet surface, the subsequent plating step and alloys In the conversion process, excessive Fe—Zn alloy reaction at the grain boundaries on the surface of the steel sheet is suppressed. As a result, in the alloyed hot-dip galvanized layer, the formation of a uniform Fe—Al alloy layer is promoted to make the Fe concentration in the width direction uniform, and excellent plating adhesion and appearance uniform can be obtained.
[0138]
　When the log ( PH2O / PH2 ) exceeds −0.2 in the pretropical zone, decarburization on the surface of the steel sheet becomes excessive, the thickness of the de-C layer exceeds 150 μm, and the fatigue characteristics deteriorate. Therefore, the log ( PH2O / PH2 ) in the pretropical zone should be -0.2 or less. It is preferably −0.5 or less, more preferably −0.7. On the other hand, in the preheating zone log (P H2 O / P H2 If) is less than -1.7, the carbon concentration on the surface of the steel sheet is possible high part, since no fine layer on the surface is formed, and the Fe concentration in the width direction It tends to be non-uniform, and the plating adhesion is further reduced. Therefore, log in preheating zone (P H2 O / P H2 ) is set to -1.7 or more. It is preferably −1.3 or higher, more preferably -1 or higher.
[0139]
　(c-2) Heating / holding
　Average heating speed in the temperature range of 500 ° C or higher and maximum ultimate temperature of -50 ° C: 1 ° C / sec or higher
　Maximum ultimate temperature: 720 ° C or higher, 900 ° C or lower
　Retention at maximum ultimate temperature: 30 In the
　annealing step of seconds or more and 30 minutes or less, the average heating rate in the temperature range of 500 ° C. or higher and the maximum temperature reached −50 ° C. is important in forming the desired form of ferrite.
[0140]
　As the steel sheet is heated, ferrite begins to be formed at 500 ° C. or higher. Therefore, the lower limit of the temperature range that defines the average heating rate is set to 500 ° C. Finally, the steel sheet is heated to a maximum temperature of 720 ° C. or higher and 900 ° C. or lower and held for 30 seconds or longer and 30 minutes or shorter, but in a temperature range of heating at an average heating rate of 1 ° C./sec or higher. The maximum temperature reached is -50 ° C.
[0141]
　In terms of controlling the morphology of ferrite, the average heating rate in the above temperature range should be high. When the average heating rate is less than 1 ° C./sec, nucleation starts from the priority nucleation position and the ferrite mass becomes large, and the number ratio of the ferrite mass having a thickness of 20 μm or more in the plate thickness direction exceeds 50%. Therefore, the hole expanding property is lowered, so the average heating rate in the above temperature range is set to 1 ° C./sec or more. It is preferably 5 ° C./sec or higher.
[0142]
　When the steel sheet contains Ti, Nb, V, etc. that form carbides, when the steel sheet is heated, it stays in the temperature range of 550 to 760 ° C for 30 seconds, and then it is heated to the maximum temperature of -50 ° C to reach the maximum. When annealing is performed at a temperature of 720 to 900 ° C., carbides such as TiV, NbC, and VC can be finely precipitated in the steel sheet structure.
[0143]
　The maximum temperature reached in the annealing step is 720 or more and 900 ° C or less. If the maximum temperature reached is less than 720 ° C, austenite cannot be sufficiently formed, martensite cannot be sufficiently secured, cementite remains undissolved, and tensile strength (TS) and hole expandability (λ) decrease. Therefore, the maximum temperature reached is 720 ° C or higher. The maximum temperature reached is preferably 770 ° C. or higher in terms of sufficiently forming austenite, sufficiently dissolving cementite, and ensuring the required tensile strength (TS) and perforation property (λ).
[0144]
　When the maximum temperature reached exceeds 900 ° C., the austenite grains become coarse, the subsequent formation of ferrite is delayed, and the ductility decreases. Therefore, the maximum temperature reached is set to 900 ° C. or lower. The maximum temperature reached is preferably 850 ° C. or lower in order to secure the required ductility and further enhance the strength-ductility balance.
[0145]
　The holding time at the maximum temperature reached is 30 seconds or more and 30 minutes or less. If the retention time is less than 30 seconds, austenite cannot be sufficiently formed, martensite cannot be sufficiently secured, and cementite remains undissolved. The decrease in martensite reduces the tensile strength (TS), and the presence of undissolved cementite does not increase the ductility and hole-spreading property (λ) even though the strength has decreased, so that TS × λ decreases. The holding time is 30 seconds or more. It is preferably 60 seconds or more.
[0146]
　When the holding time exceeds 30 minutes, the austenite grains become coarse and the thickness of the ferrite mass becomes larger than the specified range, so that the hole expanding property is lowered and the value of strength × λ is lowered. Therefore, the holding time is set to 30 minutes or less. It is preferably 20 minutes or less.
[0147]
　The holding time is the time for holding in the temperature range of the maximum reached temperature to the maximum reached temperature of −50 ° C.
[0148]
　(c-3) Cooling / bending
　Cooling temperature range: Maximum reached temperature -50 ° C ~ Cooling stop temperature T (° C) that satisfies the following formula (B)
　Average cooling rate: X (° C / sec) that satisfies the following formula (A) )
　Or more Bending process with a radius of 800 mm or less during cooling: 1 time or more
[0149]
　Following the above holding, the steel sheet is cooled from a maximum temperature of −50 ° C. to a cooling stop temperature T that satisfies the following formula (B) at an average cooling rate of X (° C./sec) or higher that satisfies the following formula (A). While cooling to (° C.), the steel sheet is bent at least once with a bending radius of 800 mm or less.
[0150]
　The following formula (A) is an empirical formula that defines the average cooling rate (° C./sec) that can suppress the formation of pearlite in relation to the component composition. The following formula (B) is an empirical formula that defines the lower limit of the temperature range in which the formation of bainite can be suppressed and a sufficient amount of martensite can be secured in relation to the component composition.
[0151]
　If the cooling shutdown temperature T (° C.) does not satisfy the following equation (B), a large amount of bainite is generated, a sufficient amount of martensite cannot be obtained, and the required strength cannot be secured. Therefore, the cooling shutdown temperature T (° C.) is a temperature that satisfies the following formula (B).
[0152]
　If the average cooling rate up to the cooling stop temperature T (° C.) is slow, pearlite that inhibits extensibility and hole expansion is generated during cooling, so cooling is stopped in order to suppress the pearlite fraction to 5% or less. The average cooling rate X (° C./sec) up to the temperature T (° C.) is an average cooling rate that satisfies the following formula (A).
[0153]
　X ≧ (Ar3-350) / 10 a　　　　　　　　　　　　　　　　　　　... (A)
　a = 0.6 [C] +1.4 [Mn] +1.3 [Cr] +3.7 [Mo] -100 [B] -0. 87
　T ≧ 730-350 [C] -90 [Mn] -70 [Cr] -83 [Mo] ・ ・ ・ (B)
　　[Element]: Mass% of element
[0154]
　While the steel sheet is being cooled, the steel sheet is bent at least once with a bending radius of 800 mm or less. By this bending process, the particle size of the surface layer of the steel sheet can be made finer, and the particle size of ferrite in the de-C layer can be made 30 μm or less. Although the reason for this is not clear, it is considered that nucleation of crystal grains having different crystal orientations is promoted and the crystal grain size of the surface layer of the steel sheet obtained after annealing becomes smaller.
[0155]
　If the bending radius exceeds 800 mm, the amount of strain introduced into the surface layer of the steel sheet is small, nucleation of crystal grains does not occur, and the effect of grain refinement cannot be obtained. Therefore, the bending radius is set to 800 mm or less. The larger the bending amount (processing amount), the more nucleation is promoted and the effect of grain refinement can be obtained. Therefore, the bending radius is preferably 730 mm or less. More preferably, it is 650 mm or less.
[0156]
　Since the bending radius may be appropriately set based on the thickness of the steel plate and the load specifications of the equipment, the lower limit of the bending radius is not particularly set.
[0157]
　(d) Step
　Hot-dip galvanizing
　　Plating bath temperature: 440 to 480 ° C
　　Steel plate temperature: 430 to 490 ° C
　Hot-dip galvanizing including hot-dip galvanizing of zinc alloy on the surface of the steel sheet by immersing the steel sheet after the annealing process in the plating bath. To apply.
[0158]
　The plating bath is a plating bath mainly composed of molten zinc, and Al, Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, Sc, I, It may contain one kind or two or more kinds of Cs and REM. The amount of Al may be appropriately adjusted depending on the ease of alloying.
[0159]
　The plating bath temperature is preferably 440 to 480 ° C. If the plating bath temperature is less than 440 ° C, the viscosity of the plating bath rises excessively, it becomes difficult to properly control the thickness of the plating layer, and the appearance of the steel sheet and the plating adhesion deteriorate. The bath temperature is preferably 440 ° C. or higher. More preferably, it is 450 ° C. or higher.
[0160]
　On the other hand, if the plating bath temperature exceeds 480 ° C., a large amount of fume is generated, the working environment is deteriorated, and safe operation is hindered. Therefore, the plating bath temperature is preferably 480 ° C. or lower. More preferably, it is 470 ° C. or lower.
[0161]
　If the temperature of the steel sheet that penetrates into the plating bath is less than 430 ° C, it becomes difficult to stably maintain the temperature of the plating bath at 450 ° C or higher. Therefore, the temperature of the steel sheet that enters the plating bath is preferably 430 ° C or higher. .. More preferably, it is 450 ° C. or higher.
[0162]
　On the other hand, if the temperature of the steel sheet that penetrates into the plating bath exceeds 490 ° C, it becomes difficult to stably maintain the temperature of the plating bath at 470 ° C or lower. Therefore, the temperature of the steel sheet that penetrates into the plating bath should be 490 ° C or lower. preferable. More preferably, it is 470 ° C. or lower.
[0163]
　After plating, the hot-dip galvanized steel sheet cooled to room temperature may be cold-rolled with a reduction ratio of 3% or less. By this cold rolling, the shape of the hot-dip galvanized steel sheet can be corrected, and the proof stress and ductility of the steel sheet can be adjusted. If the reduction rate exceeds 3%, the ductility decreases, so the reduction rate is preferably 3% or less.
[0164]
　Alloying of hot-dip galvanizing
　　Heating temperature: 470 to 620 ° C.
　　Heating time: 2 to 200 seconds The
　hot-dip galvanizing layer formed by immersing a steel sheet in a plating bath is alloyed to form an alloyed hot-dip galvanizing layer. Formed on the surface of the steel plate.
[0165]
　If the alloying treatment temperature is less than 470 ° C., alloying does not proceed sufficiently, so the alloying treatment temperature is preferably 470 ° C. or higher. More preferably, it is 490 ° C. or higher. On the other hand, when the alloying treatment temperature exceeds 620 ° C., coarse cementite is formed and pearlite is formed, and the strength is lowered. Therefore, the alloying treatment temperature is preferably 620 ° C. or lower. More preferably, it is 600 ° C. or lower.
[0166]
　If the alloying treatment time is less than 2 seconds, the alloying of the hot-dip galvanized layer does not proceed sufficiently, so the alloying treatment time is preferably 2 seconds or more. More preferably, it is 5 seconds or longer. On the other hand, if the alloying treatment time exceeds 200 seconds, pearlite is generated and the plating layer is overalloyed. Therefore, the alloying treatment time is preferably 200 seconds or less. More preferably, it is 150 seconds or less.
[0167]
　The alloying treatment may be performed immediately after the steel sheet is pulled out of the plating bath, or the plated steel sheet may be cooled to room temperature and then reheated.
[0168]
　After the alloying treatment, the alloyed hot-dip galvanized steel sheet cooled to room temperature may be cold-rolled with a reduction ratio of 3% or less. By this cold rolling, the shape of the alloyed hot-dip galvanized steel sheet can be corrected, and the proof stress and ductility of the steel sheet can be adjusted. If the reduction rate exceeds 3%, the ductility decreases, so the reduction rate is preferably 3% or less.
Example
[0169]
　Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is described in this one condition example. It is not limited. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
[0170]
　(Example 1)
　The molten steel having the composition shown in Table 1 was continuously cast according to a conventional method to obtain a cast slab. In Table 1, the component compositions of reference numerals A to T satisfy the component compositions of the present invention.
[0171]
　In the component composition of reference numeral a, C and Mo do not satisfy the component composition of the present invention, in the component composition of reference numeral b, Mn and P do not satisfy the component composition of the present invention, and in the component composition of reference numeral c, Al and Nb. Does not satisfy the component composition of the present invention, and in the component composition of reference numeral d, C and Mn do not satisfy the component composition of the present invention.
[0172]
　In the component composition of reference numeral e, Si and S do not satisfy the component composition of the present invention, in the component composition of reference numeral f, N and Ti do not satisfy the component composition of the present invention, and the component composition of reference numeral g is Si, N. , And Ti does not satisfy the component composition of the present invention, Cr does not satisfy the component composition of the present invention, and B does not satisfy the component composition of the present invention.
[0173]
[table 1]

[0174]
　The cast slab having the composition shown in Table 1 was heated, subjected to hot rolling, pickled, leveled, and then subjected to cold rolling to produce a steel sheet having a thickness of 1.6 mm. Under the conditions shown in 6 to 6, it was annealed, cooled, cooled, and then plated.
[0175]
[Table 2]

[0176]
[Table 3]

[0177]
[Table 4]

[0178]
　The processing numbers (alphabet + number) shown in Tables 2 to 4 and Tables 5 to 7 described later indicate the steels having the component compositions shown in Table 1 in the alphabet, and the numbers indicate the numbers of the examples. For example, the treatment number "A1" indicates that it is the first example carried out using the steel A whose component composition is shown in Table 1.
[0179]
　Tables 2 to 4 show the casting slab heating temperature, Ar3, hot rolling finish temperature, winding temperature, hot-rolled steel sheet treatment before pickling, cold rolling rolling ratio, annealing furnace atmosphere, annealing process. The heating rate, reached temperature (maximum temperature), holding time, average cooling rate in the cooling process, and cooling stop temperature are shown. In addition, the values ​​on the right side of the equations (A) and (B) are also shown. In the examples of the invention and some of the comparative examples, a strain of up to 0.2% or more was applied to the surface by a leveler.
[0180]
　Further, the bending radius and the number of times of bending during annealing, the zinc plating bath temperature, and the temperature of the plate entering the plating bath are shown. Further, the alloyed product indicates the alloying treatment temperature and the alloying treatment time.
[0181]
　After the steel sheet was subjected to the treatment under the conditions shown in Tables 2 to 4, the aspect and mechanical properties of the microstructure were measured and evaluated.
[0182]
　The fraction of each structure in the microstructure, the thickness of the ferrite mass, and the thickness of the de-C layer were determined by the above-mentioned method. The ferrite grain size in the de-C layer and the number density of martensite in the de-C layer having an aspect ratio of 5 or more were calculated by observing with a scanning electron microscope as follows.
[0183]
　In the region outside half the thickness of the de-C layer in the de-C layer, observe a region with an area of ​​40,000 μm 2 or more, write a line segment parallel to the rolling direction, and set the total length of the line segment as the line segment. The average value divided by the number of intersections of the grain boundaries was taken as the ferrite particle size.
[0184]
　Find the number of martensites and the lengths of the minor and major axes of each martensite, and divide the length of the major axis by the length of the minor axis as the aspect ratio. The number density was calculated by dividing the number of In addition, as the difference in texture in the width direction, the difference in number density obtained by dividing the number of martensites having an aspect ratio of martensite of 5 or more in the de-C layer by the total number of martensites was also calculated.
[0185]
　The appearance of the plating was evaluated by visually judging the difference in Fe concentration in the width direction of the plating layer and the occurrence of non-plating. “X” indicates that non-plating having a diameter of 0.5 mm or more is observed and deviates from the permissible range in appearance. “◯” indicates that no non-plating having a diameter of 0.5 mm or more was observed, but unevenness occurred when the difference in Fe concentration in the width direction was 1.0% or more. In addition, "◎" is a case other than that.
[0186]
　The plating adhesion during processing in which compressive stress was applied was evaluated in the peeling state after the 60 ° V bending test. “X” indicates a case where the peeling width is 7.0 mm or more and is not practically acceptable, and “◯” indicates a case other than that.
[0187]
　The test was carried out according to JIS Z 2241, and the mechanical properties (yield stress, tensile strength, elongation, yield point elongation) were evaluated. The hole expandability was tested in accordance with JIS Z 2256. Fatigue characteristics were measured in a flat bending fatigue test. As the test piece, a JIS No. 1 test piece was used, and the stress ratio was set to -1. Repetition frequency is set to 25 Hz, the maximum repetition number × 10 2 6 was times. The value obtained by dividing the fatigue limit strength by the maximum tensile strength was defined as the fatigue limit ratio. In addition, the difference in fatigue limit ratio in the width direction was also calculated as an index of whether or not the characteristics of the steel sheet in the width direction were uniform.
[0188]
　Tables 5 to 7 show the measurement results and the evaluation results.
[0189]
[Table 5]

[0190]
[Table 6]

[0191]
[Table 7]

[0192]
　In the embodiment, in order to clarify the quality of the steel grade, the cases where TS × EL ≧ 16000 MP%, TS × EL × λ ≧ 480000 MP%%, fatigue limit ratio ≧ 0.40, and fatigue limit ratio difference ≦ 0.10. Labeled as invention steel.
[0193]
　In the steel sheets of processing numbers A1 and F7, the rolling ratio was low, the "rate of ferrite ingot thickness of 20 μm or less" was low, and TS × EL × λ was low. In the steel sheet of process number A6, the winding temperature was high, the ferrite grain size in the C-de-C layer was large, and the fatigue limit ratio was low. In the steel sheet of process number A9, the bending radius of the bending process was large, the ferrite grain size in the C-de-C layer was large, and the fatigue limit ratio was low.
[0194]
　Since the steel sheets of treatment numbers A11 and B6 were not bent, the ferrite grain size in the C-de-C layer was large and the fatigue limit ratio was low. In treatment number A12, the log ( PH2O / PH2 ) of the atmosphere in the furnace in the pretropical zone was high, the thickness of the de-C layer was thick, and the fatigue limit ratio was low. In the treatment number A13, the log ( PH2O / PH2 ) of the atmosphere in the furnace in the pre-tropical zone was low, the surface became uneven, and the plating adhesion was lowered. Moreover, since the proportion of martensite having an aspect ratio of 5 or more in the C-de-C layer exceeded 50%, the fatigue limit ratio decreased.
[0195]
　In the steel sheet of process number B1, since the cooling rate was slow, the pearlite fraction was high and TS × EL and TS × EL × λ were low. In the steel sheet of process number C1, since the holding time at the time of heating was short, the microstructure fraction did not fall within the range of the present invention, and TS × EL and TS × EL × λ became low.
[0196]
　In the steel sheet of process number C3, TS × EL × λ was low because the holding time during heating was long. In the steel sheet of treatment number C5, the log ( PH2O / PH2 ) of the atmosphere in the furnace in the tropical zone was low, and the thickness of the de-C layer was less than 10 μm, so that the appearance of plating and the plating adhesion were deteriorated. .. In the steel sheet of treatment number C6, the log ( PH2O / PH2 ) of the atmosphere in the furnace in the tropical zone was high, the thickness of the de-C layer was thick, and the TS × EL × λ and the fatigue limit ratio were low.
[0197]
　In the steel sheet of process number D1, the maximum temperature reached was low, the microstructure fraction did not fall within the range of the present invention, and TS × EL and TS × EL × λ were low. In the steel sheet of treatment number D4, the alloying treatment temperature was high, the appearance of plating was deteriorated, and the amount of pearlite was large, so that TS × EL and TS × EL × λ were low. In the steel sheet of treatment number D5, the alloying treatment time was short and the appearance of plating was deteriorated.
[0198]
　In the steel sheet of treatment number D8, the alloying treatment time was long and the appearance of plating was deteriorated. Moreover, since the amount of pearlite was large, TS × EL and TS × EL × λ became low. In the steel sheets of treatment numbers G1 and E1, the heating rate was slow, the "rate of ferrite lump thickness of 20 μm or less" was low, and TS × EL × λ was low.
[0199]
　In the steel sheet of process number E5, the cooling shutdown temperature was low, the bainite transformation proceeded too much, the martensite fraction was low, and TS × EL and TS × EL × λ were low. In the steel sheet of process number F1, the maximum temperature reached was high, the ferrite fraction was low, and TS × EL and TS × EL × λ were low. In the steel sheet of process No. F5, the winding temperature was high, the ferrite grain size in the C-de-C layer was large, and the fatigue limit ratio was low.
[0200]
　In the steel sheet of process No. F6, the bending radius of the bending process was large, the ferrite grain size in the C-de-C layer was large, and the fatigue limit ratio was low. In the steel sheets of treatment numbers G5 and H2, the zinc plating bath temperature was low and the appearance of the plating was deteriorated, but the extensibility, hole expansion property, and fatigue characteristics were excellent, and the characteristics in the width direction of the steel sheet were also uniform. rice field. In the steel sheet of process number L2, the heating temperature was low, the martensite fraction was out of the range of the present invention, and TS × EL and TS × EL × λ were low.
[0201]
　The steel sheets of treatment numbers B4, C9, G3 and G9 were not leveled before and / or after pickling. Therefore, the number of ferrite lumps having a thickness of 20 μm or less in the plate thickness direction is less than 50% of the total number of ferrite lumps, and the proportion of martensite having an aspect ratio of 5 or more in the de-C layer exceeds 50%. Was there. As a result, the difference in the proportions of martensite having an aspect ratio of 5 or more in the width direction exceeded 10%, and the difference in structure in the width direction during the de-C layer became large, so that the difference in fatigue limit ratio was also large. became. In addition, TS × EL × λ was low and the fatigue limit ratio was small.
[0202]
　In the steel sheets of process numbers a1, b1, c1, d1, e1, f1, g1, h1, and i1, the composition of the components is out of the scope of the present invention, so that TS × EL, TS × EL × λ, etc. are low. ing. Regarding other conditions, the structure is within the scope of the present invention, and the differences in surface quality (appearance, plating adhesion), TS × EL, TS × EL × λ, fatigue limit ratio, and fatigue limit ratio are good. ..
Industrial applicability
[0203]
　As described above, according to the present invention, it is possible to provide a high-strength alloyed hot-dip galvanized steel sheet having excellent extensibility, hole-expanding property, and fatigue characteristics, and having uniform characteristics in the width direction of the steel sheet. can. Therefore, the present invention is highly applicable in the steel sheet manufacturing industry, the automobile manufacturing industry, and other machine manufacturing industries.
The scope of the claims
[Claim 1]
　The composition of the steel sheet is by mass%,
C: 0.06% or more, 0.22% or less,
Si: 0.50% or more, 2.00% or less,
Mn: 1.50% or more, 2.80%. Below,
Al: 0.01% or more, 1.00% or less,
P: 0.001% or more, 0.100% or less,
S: 0.0005% or more, 0.0100% or less,
N: 0.0005% Above, 0.0100% or less,
Ti: 0% or more, 0.10% or less,
Mo: 0% or more, 0.30% or less,
Nb: 0% or more, 0.050% or less,
Cr: 0% or more, 1.00% or less,
B: 0% or more, 0.0050% or less,
V: 0% or more, 0.300% or less,
Ni: 0% or more, 2.00% or less,
Cu: 0% or more, 2. 00% or less,
W: 0% or more, 2.00% or less,
Ca: 0% or more, 0.0100% or less,
Ce: 0% or more, 0.0100% or less,
Mg: 0% or more, 0.0100% Below,
Zr: 0% or more, 0.0100% or less,
La: 0% or more, 0.0100% or less,
REM: 0% or more, 0.0100% or less,
Sn: 0% or more, 1.000% or less,
Sb: 0% or more, 0.200% or less,
balance: Fe and impurities, alloyed and melted on the surface of the steel plate In an alloyed hot-dip zinc-plated steel sheet having a zinc-plated layer,
　the microstructure in the range of 1/8 plate thickness to 3/8 plate thickness centered on 1/4 plate thickness in the plate thickness direction from the surface of the steel plate is the area ratio. , Ferrite: 15% or more, 85% or less, Retained austenite: Less than 5%, Martensite: 15% or more, 75% or less, Pearlite: 5% or less, and balance (including 0%): Bainite, as
　described above. the number of the following ferrite lumps thickness direction of the thickness of 20μm is not less than 50% of the total number of ferrite lumps,
　the steel sheet surface layer portion, and following deprotection C layer 150μm thickness greater than 10μm is formed,
　the de-C An alloyed hot-dip zinc-plated steel sheet having a ferrite particle size of 30 μm or less in the layer and 50% or less of martensite having an aspect ratio of 5 or more.
[Claim 2]
　The alloyed hot-dip zinc according to claim 1, further comprising a miniaturized layer having an average thickness of 0.1 μm to 5.0 μm between the alloyed hot-dip galvanized layer and the de-C layer. Plated steel plate.
[Claim 3]
　The difference in Fe concentration in the width direction in the alloyed hot-dip galvanized layer is less than 1.0% in mass%, and the difference in the proportion of martensite having an aspect ratio of 5 or more in the width direction is 10%. The alloyed hot-dip galvanized steel sheet according to claim 1 or 2, characterized in that it is as follows.
[Claim 4]
　The composition of the components is
Ti: 0.01% or more, 0.10% or less,
Mo: 0.01% or more, 0.30% or less,
Nb: 0.005% or more, 0.050% or less in mass%. ,
Cr: 0.01% or more, 1.00% or less,
B: 0.0002% or more, 0.0050% or less,
V: 0.001% or more, 0.300% or less,
Ni: 0.01% or more , 2.00% or less,
Cu: 0.01% or more, 2.00% or less,
W: 0.01% or more, 2.00% or less,
Ca: 0.0001% or more, 0.0100% or less,
Ce : 0.0001% or more, 0.0100% or less,
Mg: 0.0001% or more, 0.0100% or less,
Zr: 0.0001% or more, 0.0100% or less,
La: 0.0001% or more, 0 .0100% or
less, REM: 0.0001% or more, 0.0100% or
less, Sn: 0.001% or more 1.000% or
less, Sb: 0.001% or more, less 0.200%
one or
The alloyed hot-dip zinc-plated steel sheet according to any one of claims 1 to 3, which comprises two or more kinds .