0001]The present invention relates to a steel sheet and plated steel sheet.
BACKGROUND
[0002]In recent years, it is being used more high-strength steel sheets to automobile. This is in order to reduce the emissions of carbon dioxide, fuel efficiency through weight reduction is required, also the time of collision, absorb the impact energy, because the vehicle body which can ensure occupant protection and safety is determined .
[0003]
　However, in general, the moldability is lowered if high strength steel sheets. Therefore, elongation required for drawing or stretch forming, and decreases the hole expandability required burring workability. Therefore, conventionally, techniques to achieve both high strength and elongation or hole expandability have been proposed (e.g., Patent Documents 1-9, reference).
[0004]
　For example, JP 2006-274318 (Patent Document 1) and JP-A 2013-181208 (Patent Document 2), the metal structure of the steel sheet, bainite composite structure is ferrite and the hard tissue is soft tissue as a technique to ensure a high elongation high strength is disclosed.
[0005]
　The JP 2011-225941 (Patent Document 3), a precipitation strengthening ferrite by controlled precipitation distribution mainly by precipitation phenomena occurring in grain boundary diffusion (interphase surface deposition) in the transformation in the phase interface from austenite to ferrite the main phase, techniques to achieve both strength and elongation is disclosed.
[0006]
　JP-A-2012-026032 (Patent Document 4), a steel sheet structure to a ferrite single-phase structure, to strengthen the ferrite fine carbides, techniques to achieve both strength and elongation is disclosed.
[0007]
　The JP 2011-195956 (Patent Document 5), in the high strength thin steel sheet, a ferrite phase, bainite phase, and austenite grains having the required C concentration in martensite and austenite grains at the interface of 50% as above, there is disclosed a technique for securing elongation and hole expandability.
[0008]
　The JP 2014-141703 (Patent Document 6) and JP 2011-184788 (Patent Document 7), the metal structure of the steel sheet as a composite structure of martensite is ferrite and the hard tissue is soft tissue , a technique for ensuring high elongation even at a high strength is disclosed.
[0009]
　The JP 2011-195956 (Patent Document 8) and WO 2014/185405 (Patent Document 9), the metal structure of the steel sheet, ferrite, bainite, and, by the martensite, inter-organizational by reducing the difference in hardness, it is disclosed a technique for improving the hole expansion. Also, WO 2016/132549 (Patent Document 10) and WO 2016/133222 (Patent Document 11), the metal structure of the steel sheet, ferrite, bainite, and, as martensite, misorientation 5 the proportion of the crystal grains is ~ 14 °, by 10 to 60% area ratio, while a high strength, stretch flangeability, a technique for ensuring the fatigue properties and corrosion resistance after painting notch has been disclosed .
[0010]
　For the hole expandability improvement of, in Non-Patent Document 1, in the single tissue, hole expansion if reduce hardness difference between the tissue is disclosed to be improved.
CITATION
Patent Document
[0011]
Patent Document 1: JP 2006-274318 Patent Publication
Patent Document 2: JP 2013-181208 Patent Publication
Patent Document 3: JP 2011-225941 Patent Publication
Patent Document 4: JP 2012-026032 Patent Publication
Patent Document 5: JP 2011-195956 JP
Patent Document 6: JP 2014-141703 Patent Publication
Patent Document 7: JP 2011-184788 JP
Patent Document 8: JP 2011-195956 JP
Patent Document 9: WO 2014/185405
Patent Document 10: WO 2016/132549 Patent
Patent Document 11: International Publication No. WO 2016/133222
Non-patent literature
[0012]
Non-Patent Document 1: Kato et al., Steel research (1984) vol. 312, p. 41
Summary of the Invention
Problems that the Invention is to Solve
[0013]
　In the technique disclosed in Patent Documents 1 and 2, the steel sheet structure is a composite structure of the soft tissue and the hard tissue, the interface of soft tissue and hard tissue during hole expansion, to facilitate the development of a crack.
[0014]
　In Patent Documents 3 and 4 to the technique disclosed, precipitates hard tissue dispersed in the soft tissues, during hole expansion, since the starting point of cracking, in either technique, strength, elongation, stretch flangeability both of it is difficult.
[0015]
　The technique disclosed in Patent Document 5, but the tissue is difficult to control can ensure excellent elongation and hole expandability.
[0016]
　In the technology disclosed in Patent Document 6 and Patent Document 7, since the hardness difference between the soft tissue and the hard tissue is large, and promote crack propagation during spreading interface of these tissues holes, poor hole expandability.
[0017]
　Patent Document 8, Patent Document 9, the technology disclosed in Patent Document 10 and Patent Document 11, since a crack is generated from the inside of bainite during hole expansion, hole expandability improvement margin is small. This is because the starting point of cracks cementite included in the bainite.
[0018]
　In the technique disclosed in Non-Patent Document 1, the conditions for forming a single organization, it is difficult to apply to industrial scale manufacturing process of the hot rolled steel sheet, also remains a problem in terms of high strength there.
[0019]
　The present invention aims to tensile strength to provide a high strength of at least 590 MPa, the steel sheet and plated steel sheet having excellent hole expandability.
Means for Solving the Problems
[0020]
　The present inventors have collateral in order to solve the above problems, the tensile strength of 590MPa or more DP (Dual Phase) steel, a high strength by improvement of ductility and hard tissues by soft tissue (ferrite) (martensite) while, made extensive study design guidelines and manufacturing method thereof microstructure improved hole expansion is. In this research process, while maintaining excellent ductility and tensile strength of more than 590Ma, it was possible to develop a steel sheet having excellent hole expansion. Results of the examination of tissue characteristics of developed steel, the microstructure is constituted by a metal phase 1 to the metal phase 3, which is defined on the basis of an indicator K and Y values, the upper included in the prior art DP steel bainite, lower bainite, pearlite, tissue corresponding to cementite and residual austenite (this organization is also the organization corresponding to the metal phase 4 below.) revealed that generation of is suppressed. That is, by optimizing the manufacturing conditions, if control of the presence form of a metal phase 1 to the metallic phase 3, while maintaining high strength and high ductility, have found that it is possible to improve the hole expandability significantly.
[0021]
　The gist of the present invention is as follows.
[0022]
　(1) in
mass%,
C:
0.01 ~ 0.20% Si: 0.005 ~ 0.10%,
Mn: 0.60 ~ 4.00%, Al: 0.10 ~ 3.00%,
P: 0.10% or
less, S: 0.03% or
less, N: 0.01% or
less, O: 0.01% or
less, Ti:
0 ~ 2.00%, Nb: 0 ~ 2.00%, V:
0 ~ 0.30% Cu: 0 ~ 2.00%, Ni: 0 ~ 2.00%, Mo: 0 ~ 1.00%, Cr: 0 ~ 2.00% B: 0 ~ 0.01 % Ca: 0 ~ 0.010%, Mg: 0 ~ 0.010%, Zr: 0 ~ 0.050%, REM: 0 ~ 0.1%, Sb: 0 ~ 0.10%, Sn: 0 ~ % 0.10, as: 0 ~ 0.5%, the balance has a chemical composition of Fe and 　impurities, one crystal regions surrounded by 5.0 ° or more grain boundaries measured by EBSD analysis grain and ,

10 　to the average value of Image Quality in the grain -3 a value obtained by multiplying a K value,
　the average misorientation in the crystal grains (°) and Y values,
　a metal the K value is less than 4.000 the phases and metal phases 1,
　wherein the K value is at 4.000 or more, and the Y value is a metal phase and a metal phase 2 is 0.5-1.0,
　the K value be 4.000 or more and the Y value to a metal phase and a metal phase 3 is less than 0.5,
　when the metal phase that does not belong to any of the metallic phase 1-3 and metal phase 4, in area%,
　the metal phase 1: less than 1.0% or more 35.0%,
　the metal phase 2: 30.0% or more 80.0% or less,
　metallic phase 3: 50.0% 5.0% or more or less,
　the metal phase 4: 5.0% or less microstructure comprising a steel sheet is.
[0023]
　(2) the metal phase 4 comprises a microstructure is 0%,
the steel sheet of the above (1).
[0024]
　(3) or more 60.0% of the boundary of the metal phase 1 and another metal phase is a boundary between the metal phase 2,
the steel sheet of the above (1) or (2).
[0025]
　(4) a thickness of 0.8 ~ 3.6 mm,
one of the steel sheet of the above (1) to (3).
[0026]
　(5) a tensile strength of a steel sheet is not less than 780 MPa,
　in area%,
　the metal phase 1: less than 1.0% or more 35.0%,
　the metal phase 2: 30.0% or more 80.0% or less,
　metallic phase 3: less than 5.0% or more 35.0%,
　the metal phase 4: comprising a microstructure is 5.0% or less,
one of the steel sheet of the above (1) to (4).
[0027]
　(6) a tensile strength of a steel sheet to less than 590 MPa 780 MPa,
　the metal phase 1: less than 1.0% or more 30.0%,
　the metal phase 2: 35.0% or more 70.0 or less,
　the metal phase 3: 35.0% or more 50.0% or less,
　the metal phase 4: comprising a microstructure is 5.0% or less,
one of the steel sheet of the above (1) to (4).
[0028]
　(7) on the surface of one of the steel sheet of the above (1) to (6), comprising a galvanized layer,
plated steel sheet.
[0029]
　(8) on the surface of one of the steel sheet of the above (1) to (6), and a galvannealed layer,
plated steel sheet.
The invention's effect
[0030]
　According to the present invention, high strength of tensile strength of at least 590 MPa (more than 780 MPa), the steel sheet and plated steel sheet having excellent hole expandability is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031]
An example of FIG. 1 microstructure is a diagram schematically illustrating.
DESCRIPTION OF THE INVENTION
[0032]
　　1. Chemical composition
　described chemical composition of the steel sheet according to the present invention. In the following description, "%" for the content means "mass%".
[0033]
　C: 0.01 ~ 0.20%
　C is an element necessary for obtaining the metal phase 1 of a predetermined amount. If it is less than 0.01%, it is difficult to more than 1.0% of the metal phase 1 of a predetermined amount in area fraction. Therefore, the lower limit of 0.01%. To increase the area of the metal phase 1, 0.03% or more may be 0.04% or more, or 0.05% or more.
[0034]
　On the other hand, excessive it is difficult to 1.0% or more metallic phase 1 at an area fraction is added. Therefore, the upper limit is 0.20%. To increase the area of ​​the metal phase 1, 0.10%, 0.08% or less, may be 0.07% or less, or 0.06% or less.
[0035]
　Si: 0.005 ~
0.10% Si is an element necessary for obtaining the metal phase 3 of a predetermined amount. If it is less than 0.005%, it is difficult to obtain a metallic phase 3 of a predetermined amount. Therefore, the lower limit of 0.10%. To increase the area of the metal phase 3, 0.015% or more and 0.020% or more, may be 0.025% or more, or 0.030% or more.
[0036]
　On the other hand, excessively when the area of ​​the metal phase 3 is too high addition, it is difficult to more than 1.0% by area fraction of metal phase 1. Therefore, the upper limit to 0.10%. In order to optimize the area of ​​the metal phase 1 and the metal phase 3 0.060% or less, may be 0.050% or less, or 0.040% or less.
[0037]
　Mn: 0.60 ~
　4.00% Mn is an element necessary for obtaining the metal phase 1 of a predetermined amount. If it is less than 0.60, it becomes difficult to more than 1.0% of the metal phase 1 in area fraction. Therefore, the lower limit 0.60%. Preferably 0.60% or more, more preferably 0.90% or more, more preferably 1.10% or more, more preferably 1.30% or more.
[0038]
　On the other hand, excessive it is difficult to 1.0% or more metallic phase 1 at an area fraction is added. Therefore, to 4.00% of the upper limit. Preferably 3.00% or less, more preferably 2.50% or less, more preferably 2.00% or less, more preferably not more than 1.80%.
[0039]
　Al: 0.10 ~
　3.00% Al is an element necessary for obtaining the metal phase 3 of a predetermined amount. If it is less than 0.10%, it becomes difficult to obtain a metallic phase 3 of a predetermined amount. Therefore, the lower limit of 0.10%. Preferably 0.20% or more, more preferably 0.30% or more, more preferably 0.40% or more, further preferably 0.55% or more.
[0040]
　On the other hand, excessively area ratio of the metal phase 3 is high is added, it is difficult to more than 1.0% of the metal phase 1 in area fraction. Therefore, a 3.00% limit. Preferably 2.00% or less, more preferably 1.50% or less, more preferably 1.00% or less, more preferably 0.80%.
[0041]
　P: 0.10% or less
　P is an impurity element, or segregated in the grain boundary, inhibit hole expansion to form a coarse phosphides. It exceeds 0.10%, since the segregation becomes remarkable, limited to not more than 0.10%. Preferably, 0.02% or less. P as less preferably, the lower limit is not particularly necessary to limit, the lower limit is 0%. However, be reduced to less than 0.0001%, because it is economically disadvantageous, it may limit 0.0001%.
[0042]
　S: 0.03% or less
　S is an impurity element, inhibit hole expandability and forms coarse sulfides. It exceeds 0.03%, since the decrease in the hole expandability and excessively generated sulfide becomes remarkable, limited to not more than 0.03%. More preferably 0.005% or less. S as less preferably, the lower limit is not particularly necessary to limit, the lower limit is 0%. However, when reduced to less than 0.0001%, the manufacturing cost is greatly increased, 0.0001% is substantially the lower.
[0043]
　N: 0.01% or less
　N is an impurity element, inhibit hole expandability and forms coarse nitrides. Exceeds 0.01%, the nitride is excessively generated decrease in hole expandability and becomes remarkable, limited to 0.01% or less. More preferably 0.0030% or less. N as less preferably, the lower limit is not particularly necessary to limit, the lower limit is 0%. However, when reduced to less than 0.0001%, the manufacturing cost is greatly increased, 0.0001% is substantially the lower.
[0044]
　O: 0.01% or less
　O is an impurity element, inhibit hole expandability and forms coarse oxides. Exceeds 0.01%, the oxides are excessively generated decrease in hole expandability and becomes remarkable, limited to 0.01% or less. More preferably 0.0050% or less. O as less preferably, the lower limit is not particularly necessary to limit, the lower limit is 0%. However, when reduced to less than 0.0001%, the manufacturing cost is greatly increased, 0.0001% is substantially the lower.
[0045]
　Ti: 0 ~ 2.00%
　Ti, since then fine crystal grains is an element for improving the hole expansion, may be incorporated as appropriate. It exceeds 2.00%, nitrides and carbides mainly composed of Ti is excessively formed, for hole expansion property deteriorates, and 2.00% the upper limit. Preferably 0.50% or less, more preferably 0.10% or less, more preferably not more than 0.05%. Not necessarily to contain Ti, the lower limit is 0%. It may be contained 0.04% or more for the hole expansion improvement.
[0046]
　Nb: 0 ~ 2.00%
　Nb, since then fine crystal grains is an element for improving the hole expansion, may be incorporated as appropriate. It exceeds 2.00%, nitrides and carbides mainly composed of Nb is excessively formed, for hole expansion property deteriorates, and 2.00% the upper limit. Preferably 0.20% or less, more preferably 0.05% or less, more preferably not more than 0.03%. Not necessarily to contain Nb, the lower limit is 0%. For hole expansion improvement may contain more than 0.005%.
[0047]
　V: 0 ~ 0.30%
　V, since then fine crystal grains is an element for improving the hole expansion, may be incorporated as appropriate. Exceeds 2.00%, nitrides and carbides mainly composed of V is excessively formed, for hole expansion property deteriorates, and 2.00% the upper limit. Preferably 0.50% or less, more preferably 0.10% or less, more preferably not more than 0.05%. Not always necessary to include V, the lower limit is 0%. For hole expansion improved, it may be contained 0.04% or more.
[0048]
　Cu: 0 ~
　2.00% Cu in order to have the effect of increasing the area ratio of the metal phase 1, it may be incorporated as appropriate. It exceeds 2.00%, it becomes difficult to obtain a metallic phase 3 of a predetermined amount. Therefore, a 2.00% limit. Preferably 1.00% or less, more preferably 0.50% is less, more preferably 0.20% or less, more preferably not more than 0.05%. Not necessarily to contain Cu, the lower limit is 0%. If necessary, it may be contained 0.01% or more.
[0049]
　Ni: 0 ~
　2.00% Ni, in order to have the effect of increasing the area ratio of the metal phase 1, may be incorporated as appropriate. It exceeds 2.00%, it becomes difficult to obtain a metallic phase 3 of a predetermined amount. Therefore, a 2.00% limit. Preferably 1.00% or less, more preferably 0.50% is less, more preferably 0.20% or less, more preferably not more than 0.05%. Not necessarily to contain Cu, the lower limit is 0%. If necessary, it may be contained 0.01% or more.
[0050]
　Mo: 0 ~
　1.00% Mo in order to have the effect of increasing the area of the metal phase 3, may be contained as appropriate. It exceeds 1.00%, it is difficult to secure more than 1% of the metal phase 1 in area fraction. Therefore, a 1.00% limit. Preferably 0.5% or less, more preferably from 0.3% or less, more preferably 0.1% or less, more preferably not more than 0.05%. Not necessarily to contain Mo, the lower limit is 0%. If necessary, it may be contained 0.01% or more.
[0051]
　Cr: 0 ~
　2.00% Cr, in order to have the effect of increasing the area of the metal phase 3, may be contained as appropriate. It exceeds 2.00%, it is difficult to secure more than 1% of the metal phase 1 in area fraction. Therefore, a 2.00% limit. Preferably 1.00% or less, more preferably 0.5% or less, more preferably 0.25% or less, more preferably 0.10% or less, more preferably not more than 0.05%. Not necessarily to contain Cr, the lower limit is 0%. If necessary, it may be contained 0.01% or more.
[0052]
　B: 0 ~ 0.01%
　B is to have an effect of increasing the area ratio of the metal phase 1, it may be incorporated as appropriate. Exceeds 0.01%, B nitrides and carbides mainly is excessively generate, for hole expansion deteriorates, so the upper limit is made 0.01%. Preferably 0.0025% or less, more preferably 0.0015% or less, more preferably 0.0010% or less, more preferably not more than 0.0004%. Not necessarily to contain B, the lower limit is 0%. If necessary, it may be contained 0.0003% or more.
[0053]
　Ca: 0 ~ 0.010% Ca
　is by suppressing the formation of coarse oxides and sulfides, since an element which contributes to improvement of the hole expandability, does not inhibit the other characteristics of the steel sheet according to the present invention it may be added in a range. It exceeds 0.010%, Ca and oxides generated excessively mainly composed of, for degradation hole expanding property, the upper limit is made 0.010%. Preferably 0.005% or less, more preferably 0.002% or less, more preferably not more than 0.0005%. Not always necessary to include Ca, the lower limit is 0%. If necessary, it may be contained 0.0003% or more.
[0054]
　Mg: 0 ~ 0.010% Mg
　is by suppressing the formation of coarse oxides and sulfides, since an element which contributes to improvement of the hole expandability, does not inhibit the other characteristics of the steel sheet according to the present invention it may be added in a range. It exceeds 0.010%, Mg mainly an oxide is excessively formed that the order to degrade hole expanding property, the upper limit is made 0.010%. Preferably 0.005% or less, more preferably 0.002% or less, more preferably 0.001% or less, more preferably not more than 0.0004%. Not necessarily to contain Mg, the lower limit is 0%. If necessary, it may be contained 0.0003% or more.
[0055]
　Zr: 0 ~ 0.050% Zr
　is by suppressing the formation of coarse oxides and sulfides, since an element which contributes to improvement of the hole expandability, does not inhibit the other characteristics of the steel sheet according to the present invention it may be added in a range. Exceeds 0.050%, Zr mainly an oxide is excessively formed that the order to degrade hole expanding property, the upper limit 0.050%. Preferably not more than 0.005%. Not always necessary to include Zr, the lower limit is 0%. If necessary, it may be contained more than 0.0005%.
[0056]
　REM: 0 ~ 0.1% REM
　is by suppressing the formation of coarse oxides and sulfides, since an element which contributes to improvement of the hole expandability, does not inhibit the other characteristics of the steel sheet according to the present invention it may be added in a range. It exceeds 0.1%, REM mainly an oxide is excessively formed that the order to degrade hole expanding property, the upper limit is made 0.1%. Preferably not more than 0.005%. Need not necessarily be contained REM, the lower limit is 0%. If necessary, it may be contained more than 0.0005%.
[0057]
　Incidentally, REM is, Sc, is a generic name for a total of 17 elements Y and lanthanoid, and the content of REM means the total amount of the element. REM, which is often added in misch metal, there is a case to be added in the composite elements of the lanthanide series in addition to the La and Ce. Again, the steel sheet according to the present invention exerts the effect of the steel sheet according to the present invention. Also by adding a metal REM such as metal La and Ce, steel sheet according to the present invention exerts the effect of the steel sheet according to the present invention.
[0058]
　Sb: 0 ~ 0.10% Sb
　is allowed to suppress the formation of coarse oxides and sulfides, since an element which contributes to improvement of the hole expandability, does not inhibit the other characteristics of the steel sheet according to the present invention it may be added in a range. Exceeds 0.10%, Sb mainly an oxide is excessively formed that the order to degrade hole expanding property, the upper limit is made 0.10%. Preferably not more than 0.005%. Not necessarily to contain Sb, the lower limit is 0%. If necessary, it may be contained 0.0002% or more.
[0059]
　Sn: 0 ~ 0.10% Sn
　is by suppressing the formation of coarse oxides and sulfides, since an element which contributes to improvement of the hole expandability, does not inhibit the other characteristics of the steel sheet according to the present invention it may be added in a range. Exceeds 0.10%, Sn mainly an oxide is excessively formed that the order to degrade hole expanding property, the upper limit is made 0.10%. Preferably not more than 0.005%. Not necessarily to contain Sn, the lower limit is 0%. If necessary, it may be contained more than 0.0005%.
[0060]
　As: 0 ~ 0.5% As
　is to suppress the formation of coarse oxides and sulfides, since an element which contributes to improvement of the hole expandability, does not inhibit the other characteristics of the steel sheet according to the present invention it may be added in a range. Exceeds 0.5% oxide based on As is excessively formed, for hole expansion deteriorates, so the upper limit is made 0.5%. Preferably not more than 0.005%. Not necessarily to contain As, the lower limit is 0%. If necessary, it may be contained more than 0.0005%.
[0061]
　Steel sheet according to the present invention contains the elements described above, the balance has a chemical composition of Fe and impurities. Note that the impurities, in producing the steel industrially, refers to the components to be mixed ores, from a source other factors scraps.
[0062]
　　2. Microstructure
　in the steel sheet of the present invention, in order to distinguish in response to the dislocation density contained the crystal grains constituting the microstructure therein, K and Y values are used as an index.
[0063]
　First, EBSD method following GAIQ method measured value measured in (Grain average image quality) 10 to GAIQ value obtained by analyzing at -3 to define the value obtained by multiplying the a K value. Further, the GAM values measured value measured was obtained and analyzed by Grain Average Misorientation (GAM) method described in EBSD method is defined as a Y value. K value is an index showing the height of the crystalline, is a useful indicator to evaluate the dislocation density contained in the crystal. Y values are useful indicators for evaluating the orientation difference in the crystal grains. Therefore, the steel sheet according to the present invention, is a combination of K and Y values to identify the microstructure.
[0064]
　Next, a method of calculating the GAIQ method. For rolling direction vertical section of the 1/4 depth position of the sheet thickness t from the surface of the steel sheet (1 / 4t part), 200 [mu] m in the rolling direction, EBSD analysis measurement interval 0.2μm regions of 100μm in the rolling surface normal direction get the crystal orientation information by. Here EBSD analysis, using a thermal field emission scanning electron microscope (JEOL Ltd. JSM-7001F) and EBSD detector (TSL manufactured DVC5 type detector) constructed by the apparatus, supplied with the EBSD analyzer "TSL OIM Data the Collection 6 ", is measured with an exposure time of 60mm seconds. Next, the crystal orientation information obtained, the orientation difference 5 ° or more regions is defined as grains, it calculates the average value of Image Quality value in the crystal grain by GAIQ method. Here, the Image Quality value, is one of the analysis parameters mounted on EBSD analysis apparatus supplied software "OIM Analysis (TM) Version 7.0.1", the crystallinity in the measurement region height It is shown. That is, the dislocation density of the high region, since the disturbance in the crystallinity occurs, Image Quality value decreases.
[0065]
　Next, a method of calculating the average misorientation of the crystal grains (°). The obtained crystal orientation information, the misorientation 5 ° or more regions is defined as the crystal grain, the GAM method to determine the average crystal misorientation in the crystal grains. Average misorientation in the crystal grains, EBSD analysis apparatus in the provided software "OIM Analysis (TM) Version 7.0.1" is one of the mounted analysis parameters in "Grain Average Misorientation (GAM)" value the points, after calculating the misorientation between the adjacent measuring points, in which an average value for the grain in all measuring points.
[0066]
　Based on the K and Y values obtained as described above, it can be classified metal phase as follows.
Metallic phase 1: K value metal phase is less than 4.000
metal phase 2: the K value is 4.000 or more, and the metal phase Y value of 0.5-1.0
metallic phase 3: K value There is at 4.000 or more, and Y value metal phase is less than 0.5
metal phase 4: metal phase that does not belong to any of the metallic phase 1-3
[0067]
　Metallic phase 1: 1.0% or more 35.0% less
　metal phase 1 is tissue required to secure the strength of the steel sheet. When the area fraction is less than 1.0%, since to secure the minimum tensile strength is difficult, the lower limit is 1.0%. Preferably 2.0% or more, more preferably 3.0% or more, further preferably 5.0% or more. On the other hand, when an area fraction greater than or equal to 35.0%, of the boundary of the metal phase 1 and another metal phase, the ratio of the boundary between the metal phase 2 is likely to be less than 60.0%, the hole expanding property is deteriorated because fear is, to be less than 35.0%. Preferably less than 32.0%, more preferably less than 30.0%, more preferably less than 25.0%.
[0068]
　The metal phase 1, when an area fraction greater than or equal to 30.0%, since the tensile strength becomes difficult to less than 780 MPa, is desired to obtain a "steel tensile strength is less than or more 590 MPa 780 MPa" case, it is less than 30.0%. If the tensile strength is desired to obtain a steel sheet "is not less than 780MPa may remain less than 1.0% or more 35.0%.
[0069]
　Metallic phase 2: 30.0% or more 80.0% or less
　of the metal phase 2, which is an important organization in order to obtain excellent hole expansion required at the time of press molding. When the area fraction is less than 30.0%, it becomes difficult to secure a predetermined hole expansion, the lower limit and 30.0%. Preferably 40.0% or more, more preferably 50.0% or more, more preferably 60.0% or more. On the other hand, when it exceeds 80.0% by area fraction, the austenite untransformed too reduced, can not be obtained metal phase 1 of 1.0% or more, to ensure a minimum tensile strength since it is difficult, the upper limit is 80.0%. Preferably 78.0% or less, more preferably 76.0% or less, more preferably not more than 75.0%.
[0070]
　Note that in the "steel tensile strength is less than or more 590 MPa 780 MPa" is a metal phase 2, of less than 35.0% in area fraction, there is a possibility that a problem that hole expanding deteriorates occurs, 70 when it exceeds 2.0%, there is a possibility that problems that the elongation deteriorates. Therefore, when it is desired to obtain a "steel tensile strength is less than 780MPa or 590MPa" is a metal phase 2 may not more than 70.0 35.0% or more. If the tensile strength is desired to obtain a steel sheet "is not less than 780MPa may less 80.0% 30.0% or more.
[0071]
　Metallic phase 3: 5.0% or more 50.0% less
　metal phase 3 is required tissue to ensure excellent ductility required in press molding. When the area fraction is less than 5.0%, since it is difficult to obtain a predetermined ductility, and 5.0% lower limit. Preferably 10.0% or more, more preferably 15.0% or more, 20.0% or more. On the other hand, when the area fraction is 50.0% or more, too reduced austenite untransformed is not possible to obtain more than 1.0% of a metal phase 1 to ensure minimum tensile strength since it is difficult, the upper limit is 50.0%. Preferably not more than 45.0%, more preferably not more than 40.0%, more preferably is not more than 30.0%.
[0072]
　The metal phase 3, the case of more than 35.0% in area fraction, since it is difficult to obtain a tensile strength of not less than 780MPa, when it is desired to obtain a "steel tensile strength is not less than 780MPa" it is a metallic phase 3 preferably set to less than 35.0% 5.0% or more. Conversely, when it is desired to obtain a "steel tensile strength is less than 780MPa or 590MPa" is a metallic phase 3 preferably set to less 50.0% 35.0% or more.
[0073]
　Metal phase 4: 5.0% or less
　metal phase 4 that does not belong to any of the metallic phase 1-3 are the hard tissue, become starting points of cracking at the time of spread holes, reducing the hole expansion. Therefore, the metal phase 4 is limited to 5.0% or less in total of the area fraction. Preferably 4.0% or less, more preferably 3.0% or less, more preferably 2.0% or less, more preferably 1.2% or less, and most preferably 0%. Note that the metal phase 4 was subjected to structural observation with an optical microscope, upper bainite, lower bainite, pearlite, were cementite and residual austenite. Conversely, upper bainite, lower bainite, pearlite, and was subjected to EBSD analysis of the present invention to cementite and residual austenite, it is determined that all the metal phase 4.
[0074]
　As described above, the microstructure of the steel sheet according to the present invention is provided with the metal phase 1 to the metal phase 4 (the metal phase 4 may be 0%). In particular, while maintaining the tensile strength, in order to improve the hole expanding property, be more than 60.0% of the boundary of the metal phase 1 and another metal phase is a tissue which is a boundary between the metal phase 2 preferable. Proportion of the boundary between the metal phase 2 of the boundary of the metal phase 1 and another metal phase is preferably 70.0% or more, more preferably 80.0% or more, more preferably 90.0% or more . By limiting such a range, while maintaining the tensile strength, the reason can improve hole expansibility but under investigation, is generally thought to be due to the following mechanism.
[0075]
　Figure 1 is an example of a microstructure of the steel sheet according to the present invention is schematically shown. In the microstructure illustrated in FIG. 1, the reference numeral 1 is a metal phase 1, the reference numeral 2 denotes a metal phase 2, reference numeral 3 is meant respectively the metallic phase 3. In the example shown in FIG. 1, no metal phase 4 is present.
[0076]
　In the example shown in FIG. 1, it is the hardest phase metallic phase 1, a soft phase metallic phase 3, the metal phase 2 is the phase having an intermediate hardness of the metal phase 1 and the metal phase 3. Thus, since if the microstructure is a boundary of more than 60.0% of the boundary of the metal phase 1 and another metal phase and a metal phase 2, a hardness difference at the interface between adjacent crystal structure is small, the steel sheet even when subjected to harsh processing such as hole expansion processing, since the stress concentration is alleviated, broken at the interface of adjacent grain structure is suppressed, hole expandability is remarkably improved.
[0077]
　In order to form a microstructure shown in FIG. 1, the metal phase 1: less than 1.0% or more 35.0%, the metal phase 2: 30.0% or more 80.0% or less, metallic phase 3: 5 50.0% 2.0% or more or less, the metal phase 4: it is necessary to microstructure is 5.0% or less.
[0078]
　Plated steel sheet according to the present invention, the surface of the steel sheet according to the present invention, a conventional method, a steel sheet formed with galvanized layer or galvannealed layer. The galvanized layer or a galvannealed layer, for example, preferably from below.
(a) Fe is less than 7 mass%, the balance being Zn, galvanized layer composed of Al and impurities or the plating layer plating layer alloyed
(b) in Fe is 7 to 15 mass%, the balance being Zn, molten zinc comprising Al and impurities plating layer or a plating layer of the plated layer alloyed
[0079]
　The present invention, tensile strength is a 980MPa or less of the steel sheet than 590MPa primarily intended. It may optionally be the upper limit as 960MPa or 930 MPa. Is primarily a 0.8 ~ 3.6mm of thickness of the steel plate. If necessary, the lower limit 1.0 mm, 1.8 mm, may be 2.0mm or 2.2 mm, or the upper limit 3.4 mm, as 3.2mm or 2.0mm.
[0080]
　3. Manufacturing method
　following, a method for manufacturing the steel sheet according to the present invention. The present inventors have confirmed that having the above chemical composition, and be manufactured at least the following conditions are satisfied way, the microstructure of the present invention is obtained.
[0081]
　Billet subjected to hot rolling may be a slab produced by a conventional method, but is not limited to steel strips having a specific chemical composition and properties. For example, the continuous cast slab may be a slab produced by a general method such as thin slab caster.
[0082]
　(1) rough rolling process before processing
　before rough rolling step, subjected to processing such as reduction ΔW of length in the width direction of the steel strip is 30 to 60%. This step can be introduced uniformly lattice defects in the slab. Then, this uniform lattice defects as will facilitate the austenite grains recrystallization in 1 pass before the rolling of the hot finish rolling. When reduction ΔW is less than 30%, it is difficult to introduce a uniform lattice defects in the slab, it is difficult to obtain 30.0% or more metallic phase 2 in area fraction. Reduction ΔW, to the extent capable of reducing the width of the steel strip width direction, since it is appropriately set, the upper limit is not particularly limited, about 60% for reasons of manufacturability is substantial upper limit.
[0083]
　(2) hot-rolling process
　rolling one pass before (2a) hot finish rolling, a temperature: 880 ~ 950 ° C., rolling reduction: 15 carried out at ~ 25% of conditions.
　By this step, to form a lattice defect is small austenite grains uniform lattice defects introduced in the above described process of (1) as a driving force. If the temperature or if reduction ratio of less than 880 ° C. is more than 25%, an excessively lattice defects will be introduced, it is difficult to obtain 30.0% or more metallic phase 2 in area fraction in the austenite . Further, if or reduction ratio temperature exceeds 950 ° C. If there is less than 15%, austenite grains are coarsened, recrystallized austenite grains is inhibited. As a result, it is impossible to obtain a lattice defect is small austenite grains, to obtain 30.0% or more metallic phase 2 in area fraction difficult.
[0084]
　(2b) hot finish rolling, a temperature: 870 ~ 940 ° C., rolling reduction: 6 carried out at ~ 10% of conditions.
　This step introduces an appropriate amount of lattice defects in the austenite grains. This small amount of lattice defects in the subsequent cooling step, acts as a phase transformation nuclei to the metal phase 2. If the temperature or if reduction ratio of less than 870 ° C. is more than 10%, excess lattice defects in austenite will be introduced, it is difficult to obtain 30.0% or more metallic phase 2 in area fraction. Further, if or when the rolling reduction temperature exceeds 940 ° C. of less than 6%, lattice defects introduced into the austenite grains become excessively small, it is difficult to obtain 30.0% or more metallic phase 2 in area fraction Become.
[0085]
　(3) cooling step
　(3a) the time from the finish rolling end to the water-cooling start is within 0.5 seconds.
　After finish rolling hot starts water cooling within 0.5 seconds. After completion of rolling, by immediately starting the water cooling, it is possible to suppress the coarsening of austenite grains, after the cooling step, it is possible to obtain a metallic phase 3 of a predetermined amount. If the time until the water cooling start is more than 0.5 seconds, is strained pull coarsening of austenite grains, to reduce nucleation sites of the metal phase 3, it is difficult to obtain a metallic phase 3 of a predetermined amount. Since the time from the finish rolling end to the water-cooling start, in coolable range, may be appropriately set, the lower limit is not particularly limited, it is difficult in the real operation to less than 0.01 seconds, about 0.01 seconds is a substantial lower limit.
[0086]
　(3b) average cooling rate in the temperature range of 870 ~ 720 ° C. is a 50 ~ 140 ° C. / sec.
　If the average cooling rate in a temperature range of 870 ~ 720 ° C. is less than 50 ° C. / sec, it is strained pull the coarsening of austenite grains, to reduce the nucleation sites of the metal phase 3, the metallic phase 3 of a predetermined amount get it is difficult. On the other hand, the average when the cooling rate exceeds 140 ° C. / sec, too is suppressed diffusion of carbon, because austenite is stabilized, that in a subsequent step to obtain a metal phase 3 of a predetermined amount becomes difficult.
[0087]
　(3c) 720 ° C. or less 630 ° C. greater than the cooling time in the temperature range of 2 to 10 seconds. That is, the average cooling rate in this temperature range is set to 45 ~ 9 ° C. / sec.
　This step can be generated metallic phase 3 of a predetermined amount. Here, the cooling time is in the case of less than 2 seconds, transformation to the metal phase 3 does not proceed sufficiently, it is impossible to obtain a metallic phase 3 of a predetermined amount. On the other hand, if the cooling time exceeds 10 seconds, it proceeds excessively transformation from austenite to metallic phase 3, after the step to obtain a metal phase 1 of a predetermined amount becomes difficult in the.
[0088]
　Here, when the cooling time is 5 seconds or more at 720 ° C. or less 630 ° C. than the temperature range of not out making the metallic phase 3 in an area fraction of less than 35.0%. Therefore, when the tensile strength is desired to obtain a steel sheet is not less than 780MPa, the the cooling time is less than 5 seconds, when it is desired to obtain a steel sheet tensile strength is less than or more 590 MPa 780MPa is the cooling time and 5 seconds or more.
[0089]
　(3d) 630 ° C. or less 600 ° C. greater than the cooling time in the temperature range of, and less than 2 seconds or more 6 seconds. That is, the average cooling rate in this temperature range is set to 15 ~ 5 ° C. / sec.
　This step can be produced a metal phase 2. If the cooling time is less than 2 seconds, since the carbon contained in the untransformed austenite can not be sufficiently diffused, the metal phase 4 will be produced in large amounts. On the other hand, if the cooling time is more than 6 seconds, the metal phase 4 from austenite causes a large amount produced, leading to hole expansion degradation.
[0090]
　(3e) average cooling rate at 600 ° C. or less 450 ° C. than the temperature range of the cooling so that 50 ~ 100 ° C. / sec (e.g., water cooling) is.
　This step can be metallic phase 4 below 5.0%. If the average cooling rate is less than 50 ° C. / sec, the area ratio of the metal phase 4 becomes too high, the hole expansion properties are deteriorated. On the other hand, the average when the cooling rate exceeds 100 ° C. / sec, too is suppressed diffusion of carbon, because austenite is stabilized, that in a subsequent step to obtain a metal phase 1 of a predetermined amount becomes difficult.
[0091]
　(4) winding process
　the steel sheet is wound at a temperature of 400 ° C. 25 ° C. or higher. It can cause transformation to the metal phase 1 from austenite by this process. If the coiling temperature exceeds 400 ° C., it becomes impossible to metallic phase 4 below 5.0%, the hole expanding property is deteriorated. In actual operation, since it is difficult to wind at room temperature or below, the lower limit to 25 ° C..
[0092]
　(5) Other steps
　pickled rewind the wound steel sheet in the step (4) may be subjected to a cold rolling steel plate. By subjecting to remove oxides of the steel sheet surface with pickling the cold rolling, it is possible to achieve tensile strength increase, improve chemical conversion treatability, improvement and the like of the plating properties. Incidentally, pickling may be a single, or may be performed a plurality of times.
[0093]
　Rolling reduction in cold rolling is preferably 30-80%. When the rolling reduction is less than 30%, the tensile strength is not improved, the reduction ratio of 30% or more. Preferably 40% or more. On the other hand, when the reduction ratio exceeds 80%, the tensile strength is excessively increased to the ductility and hole expandability drops, the reduction ratio be 80% or less. Preferably 70% or less.
[0094]
　The steel sheet according to the present invention, the microstructure defined by K and Y values ​​are, since in tissue obtained by the process of the above (1) to (4), be subjected to cold rolling steel plate, K values ​​and Y values ​​are not changed significantly, microstructure almost remains unchanged after cold rolling. Therefore, even if the increase in tensile strength by subjecting a cold-rolled steel sheet, hole expandability is not reduced.
[0095]
　Subjecting the steel sheet after cold rolling to continuous annealing line may be annealed at 750 ~ 900 ° C.. The present inventors have found that by annealing 750 ~ 900 ° C., K and Y values ​​was confirmed experimentally that does not change significantly. Therefore, even when subjected to annealing the steel sheet after cold rolling, hole expandability is not reduced. Annealing temperature, in terms of minimizing the change of the K value and the Y value is preferably 800 ~ 850 ° C..
[0096]
　Annealing time is not particularly limited. Annealing time is within a range that does not suppressed as much as possible changes in the K and Y values ​​may be set as appropriate.
[0097]
　In the production method of a plated steel sheet according to the present invention, the steel sheet manufactured by the manufacturing method of the steel sheet according to the present invention, subjected to hot-dip galvanizing in a conventional manner. In the production method of the present invention alloyed coated steel sheet, the steel sheet manufactured by the manufacturing method of the steel sheet according to the present invention, subjected to galvannealing according to a conventional method.
[0098]
　Plating temperature and in a conventional method, at the alloying temperature, K and Y values ​​of the microstructure does not change, not drop hole expandability of the steel sheet.
Example
[0099]
　Next, a description will be given of an embodiment of the present invention, conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is, in this single condition example the present invention is not limited. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0100]
　(Example 1)
　from Table 1 and the steel strip compositions shown in Table 2 were prepared steel sheet under the conditions shown in Table 3 and Table 4.
[0101]
[Table 1]

[0102]
[Table 2]

[0103]
[table 3]

[0104]
[Table 4]

[0105]
　In Table 3 and Table 4, step (1) means a process of pre-rough rolling step shows a decrease ΔW of length in the width direction of the steel strip (%) in the table. Step (2a) includes one pass before the rolling of the hot finish rolling, step (2b) is hot finish rolling means, respectively, show the respective temperatures shown in Table (℃) and reduction rate (%) there. Step (3a) is held from the end of the final rolling up water cooling start, the table shows the holding time. Step (3b) is a cooling step at a temperature range of 870 ~ 720 ° C., The table shows the average cooling rate (° C. / sec) at that temperature range. Step (3c) is a cooling step in a temperature range of 630 ° C. than 720 ° C. or less, the table shows the cooling time (in seconds) in this temperature range. Step (3d) is a cooling step in a temperature range of 600 ° C. than 630 ° C. or less, the table shows the cooling time (in seconds) in this temperature range. Step (3e) is a cooling step at a temperature range of 450 ° C. than 600 ° C. or less, the table shows the average cooling rate (° C. / sec) at that temperature range. Step (4) is a winding process, the table shows the coiling temperature (° C.).
[0106]
　The resulting steel sheet metal structure, to measure the mechanical properties and hole expansion.
[0107]

　for rolling direction vertical section of the 1/4 depth position of the sheet thickness t from the surface of the steel sheet (1 / 4t part), 200 [mu] m in the rolling direction, 0.2 [mu] m area of 100μm in the rolling surface normal direction obtaining the crystal orientation information by EBSD analysis by the measurement interval. Here EBSD analysis, using a thermal field emission scanning electron microscope (JEOL Ltd. JSM-7001F) and EBSD detector (TSL manufactured HIKARI detector) device constituted by, carried in the analysis speed of 200 to 300 points / sec to. Next, the obtained crystal orientation information, the misorientation 5 ° or more regions is defined as the grain, it calculates the mean misorientation in the grain particle, orientation difference in grain 0.5 ° less, or to determine the proportion of crystal grains is 0.5 ~ 1.0 °.
[0108]
　Definitive present invention "average misorientation in the crystal grains" is the average value of the azimuthal distribution of the crystal grains "Grain Average Misorientation (GAM)", after calculating the misorientation between adjacent measurement points, crystal in which the average value was determined for grains in all measuring points. GAM values ​​were calculated using the software that came with the EBSD analyzer "OIM Analysis (registered trademark) Version 7.0.1".
[0109]
　The "average value of Image Quality in the crystal grains" in the present invention, in fact, refers to the average of the values obtained by analyzing with a measured value measured in EBSD method GAIQ (Grain average image quality) method.
GAIQ, to the crystal orientation information obtained by the EBSD analysis, when defining the orientation difference 5 ° or more regions with grain, average dislocation density in the crystal grains determined the percentage of the crystal grains is less than 4000. The value of GAIQ can be calculated using the software provided with EBSD analyzer "OIM Analysis (TM) Version 7.0.1".
[0110]
　Based on the K and Y values obtained as described above were classified metal phase as follows.
Metallic phase 1: K value metal phase is less than 4.000
metal phase 2: the K value is 4.000 or more, and the metal phase Y value of 0.5-1.0
metallic phase 3: K value There is at 4.000 or more, and Y value metal phase is less than 0.5
metal phase 4: metal phase that does not belong to any of the metallic phase 1-3
[0111]

　Tensile strength and elongation, right angle taken JIS5 test piece No. in the rolling direction of the steel sheet, subjected to tensile test in accordance with JIS Z 2242, tensile strength and (TS) total elongation (El) is measured and is evaluated.
[0112]

　For hole expandability, performs compliance with hole expanding test in Japan Iron and Steel Federation standard JFS-T1001-1996, it is evaluated by measuring the hole expansion ratio (HER).
[0113]
　The results are shown in Table 5.
[0114]
[table 5]

[0115]
　As shown in Table 5, the steel sheet of the present invention example has a higher tensile strength and sufficient hole expandability 590 MPa.
[0116]
　(Example 2)
　from Table 6 and billet compositions shown in Table 7, were prepared steel sheet under the conditions shown in Table 8 and Table 9.
[0117]
[Table 6]

[0118]
[Table 7]

[0119]

[Table 8]

[0120]
[Table 9]

[0121]
　In Table 8 and Table 9, step (1) means a process of pre-rough rolling step shows a decrease ΔW of length in the width direction of the steel strip (%) in the table. Step (2a) includes one pass before the rolling of the hot finish rolling, step (2b) is hot finish rolling means, respectively, show the respective temperatures shown in Table (℃) and reduction rate (%) there. Step (3a) is held from the end of the final rolling up water cooling start, the table shows the holding time. Step (3b) is a cooling step at a temperature range of 870 ~ 720 ° C., The table shows the average cooling rate (° C. / sec) at that temperature range. Step (3c) is a cooling step in a temperature range of 630 ° C. than 720 ° C. or less, the table shows the cooling time (in seconds) in this temperature range. Step (3d) is a cooling step in a temperature range of 600 ° C. than 630 ° C. or less, the table shows the cooling time (in seconds) in this temperature range. Step (3e) is a cooling step at a temperature range of 450 ° C. than 600 ° C. or less, the table shows the average cooling rate (° C. / sec) at that temperature range. Step (4) is a winding process, the table shows the coiling temperature (° C.).
[0122]
　The resulting steel sheet metal structure, to measure the mechanical properties and hole expansion.
[0123]

　for rolling direction vertical section of the 1/4 depth position of the sheet thickness t from the surface of the steel sheet (1 / 4t part), 200 [mu] m in the rolling direction, 0.2 [mu] m area of 100μm in the rolling surface normal direction obtaining the crystal orientation information by EBSD analysis by the measurement interval. Here EBSD analysis, using a thermal field emission scanning electron microscope (JEOL Ltd. JSM-7001F) and EBSD detector (TSL manufactured DVC5 type detector) constructed by the apparatus, supplied with the EBSD analyzer "TSL OIM Data the Collection 6 ", is measured with an exposure time of 60mm seconds. Next, the obtained crystal orientation information, the misorientation 5 ° or more regions is defined as the grain, it calculates the mean misorientation in the grain particle, orientation difference in grain 0.5 ° less, or to determine the proportion of crystal grains is 0.5 ~ 1.0 °.
[0124]
　Definitive present invention "average misorientation in the crystal grains" is the average value of the azimuthal distribution of the crystal grains "Grain Average Misorientation (GAM)", after calculating the misorientation between adjacent measurement points, crystal in which the average value was determined for grains in all measuring points. GAM values ​​were calculated using the software that came with the EBSD analyzer "OIM Analysis (registered trademark) Version 7.0.1".
[0125]
　The "average value of Image Quality in the crystal grains" in the present invention, in fact, refers to the average of the values obtained by analyzing with a measured value measured in EBSD method GAIQ (Grain average image quality) method.
GAIQ, to the crystal orientation information obtained by the EBSD analysis, when defining the orientation difference 5 ° or more regions with grain, average dislocation density in the crystal grains determined the percentage of the crystal grains is less than 4000. The value of GAIQ can be calculated using the software provided with EBSD analyzer "OIM Analysis (TM) Version 7.0.1".
[0126]
　Based on the K and Y values obtained as described above were classified metal phase as follows.
Metallic phase 1: K value metal phase is less than 4.000
metal phase 2: the K value is 4.000 or more, and the metal phase Y value of 0.5-1.0
metallic phase 3: K value There is at 4.000 or more, and Y value metal phase is less than 0.5
metal phase 4: metal phase that does not belong to any of the metallic phase 1-3
[0127]

　Tensile strength and elongation, right angle taken JIS5 test piece No. in the rolling direction of the steel sheet, subjected to tensile test in accordance with JIS Z 2242, tensile strength and (TS) total elongation (El) is measured and is evaluated.
[0128]

　For hole expandability, performs compliance with hole expanding test in Japan Iron and Steel Federation standard JFS-T1001-1996, it is evaluated by measuring the hole expansion ratio (HER).
[0129]
　The results are shown in Table 10.
[0130]
[Table 10]

[0131]
　As shown in Table 10, the steel sheet of the present invention example has a higher tensile strength and sufficient hole expandability 780 MPa.
Industrial Applicability
[0132]
　According to the present invention, high strength of tensile strength of at least 590 MPa (more than 780 MPa), the steel sheet and plated steel sheet having excellent hole expandability is obtained.
DESCRIPTION OF SYMBOLS
[0133]
　Crystal structure of 1 K value of less than 4
　in 2 K value of 4 or more, the crystal structure of Y values 0.5-1.0
　at 3 K value of 4 or more, Y value is less than 0.5 crystal structure

WE CLAIM

[Requested item 1]
　By
mass%,
C:
0.01 ~ 0.20%, Si: 0.005 ~
0.10%, Mn: 0.60 ~ 4.00%, Al: 0.10 ~
3.00%, P:
0.10%, S: 0.03% or
less, N: 0.01% or
less, O: 0.01% or
less,
Ti: 0 ~ 2.00%, Nb: 0 ~
2.00%, V:
~ 0.30%
0
Cu: 0 ~ 2.00%, Ni: 0 ~
2.00%, Mo: 0 ~ 1.00%,
Cr: 0 ~ 2.00% B: 0 ~
0.01% Ca :
0
~ 0.010%,
Mg: 0 ~ 0.010%, Zr: 0 ~
0.050%, REM: 0 ~ 0.1%, Sb: 0 ~
0.10%, Sn: 0 ~ 0.
% 10, as: 0 ~ 0.5%,
the balance has a chemical composition of Fe and
　impurities, and the crystal grain of the region surrounded by 5.0 ° or more grain boundaries measured by EBSD analysis ,
10 　to the average value of Image Quality in the grain -3 a value obtained by multiplying a K value,
　the average misorientation in the crystal grains (°) and Y values,
　a metal the K value is less than 4.000 the phases and metal phases 1,
　wherein the K value is at 4.000 or more, and the Y value is a metal phase and a metal phase 2 is 0.5-1.0,
　the K value be 4.000 or more and the Y value to a metal phase and a metal phase 3 is less than 0.5,
　when the metal phase that does not belong to any of the metallic phase 1-3 and metal phase 4, in area%,
　the metal phase 1: less than 1.0% or more 35.0%,
　the metal phase 2: 30.0% or more 80.0% or less,
　metallic phase 3: 50.0% 5.0% or more or less,
　the metal phase 4: 5.0% or less microstructure comprising a steel sheet is.
[Requested item 2]
　Wherein the metal phase 4 comprises a microstructure is 0%,
the steel sheet according to claim 1.
[Requested item 3]
　Or 60.0% of the boundary of the metal phase 1 and another metal phase is a boundary between the metal phase 2,
the steel sheet according to claim 1 or claim 2.
[Requested item 4]
　Thickness of 0.8 ~ 3.6 mm,
the steel sheet according to any one of claims 1 to 3.
[Requested item 5]
　A steel sheet tensile strength is greater than or equal to 780 MPa,
　in area%,
　the metal phase 1: less than 1.0% or more 35.0%,
　the metal phase 2: 30.0% or more 80.0% or less,
　the metal phase 3 : less than 5.0% or more 35.0%,
　the metal phase 4: comprising a microstructure is 5.0% or less,
the steel sheet according to any one of claims 1 to 4.
[Requested item 6]
　A steel tensile strength is less than or more 590 MPa 780 MPa,
　the metal phase 1: less than 1.0% or more 30.0%,
　the metal phase 2: 35.0% or more 70.0 or less,
　the metal phase 3:35 50.0% 2.0% or more or less,
　the metal phase 4: comprising a microstructure is 5.0% or less,
the steel sheet according to any one of claims 1 to 4.
[Requested item 7]
　On the surface of the steel sheet according to any one of claims 1 to 6, comprising a galvanized layer,
plated steel sheet.
[Requested item 8]
　On the surface of the steel sheet according to any one of claims 1 to 6, comprising a galvannealed layer,
plated steel sheet.