Technical field
[0001]
　The present invention relates to a cold-rolled steel sheet and a manufacturing method thereof, automobile parts, etc. as the main purpose, ductility, hole expandability, and a high-strength cold-rolled steel sheet and a manufacturing method thereof excellent in punching fatigue properties. The present application, to 02 May 24, 2015, and Japanese Patent Application No. 2015-034137, filed in Japan, on 02 May 24, 2015, and Japanese Patent Application No. 2015-034234, filed in Japan, 07 May 2015 13 on the day, and the Japanese Patent application No. 2015-139888, filed in Japan, on 07 May 13, 2015, claiming priority based on has been and Japanese Patent application No. 2015-139687, filed in Japan, the contents of which are here incorporated to.
Background technique
[0002]
　To suppress the emission of carbon dioxide gas from automobiles, and weight reduction of automobile bodies is advanced by application of high-strength steel sheet. Also, for safety of the occupant is also the automobile body have come to a high-strength steel sheets are often used in place of mild steel plate.
[0003]
　In the future, in order to further promote weight reduction of automobile bodies must increase the intensity level of the high-strength steel sheet more than ever. However, if high strength generally steel, formability decreases. To the steel sheet and automotive parts, it is necessary to go through a variety of molding process, for molding of high strength steel sheets to automobile members, in addition to strength, formability is essential to improve is there.
[0004]
　In addition, the weight of parts for machine structure constituting the automobile or the like, together with thinning of the component thickness due to the high strength of the steel to be used, the volume reduction of the part itself by forming pierced holes are valid. However, the formation of the pierced hole, the industrial Although adoption of punching is preferred, the end face of the punching unit concentrates excessive stress and strain. Therefore, especially in high-strength steel sheets, when performing punching, the generated voids in the boundary of the low-temperature transformation phase and the residual austenite, punching fatigue properties there is a problem of a decrease.
[0005]
　For example, when using a high-strength steel sheet skeletal system component, the steel sheet as moldability mentioned above, it is required and elongation and hole expandability. Therefore, conventionally, in the high strength thin steel sheet, several means for improving the expandability elongation and hole have been proposed.
[0006]
　For example, Patent Document 1, high-strength thin steel sheet by utilizing residual austenite as the steel sheet of the metal structure to improve the ductility is disclosed. The thin steel sheet of Patent Document 1, by increasing the stability of the residual austenite, it is disclosed that the ductility of the high strength thin steel sheet are improved. However, is not considered punching fatigue properties, elongation, form optimal metal structure in order to improve the hole expandability and punching fatigue properties is not clear, also, a control method is not disclosed.
[0007]
　In Patent Document 2, in order to improve the hole expandability, cold-rolled steel sheet is disclosed with reduced texture of steel sheet metal structure. However, it is not considered punching fatigue properties, elongation, tissue and control technology for improving hole expandability and punching fatigue properties is not disclosed.
[0008]
　In Patent Document 3, in a steel sheet containing retained austenite and ferrite and bainite, to improve the local elongation, a low-temperature transformation product phase and the main phase, and high-strength cold-rolled steel sheet having a reduced fraction of the ferrite is disclosed there. However, the cold-rolled steel sheet of Patent Document 3, the metal structure of the steel sheet for mainly the low temperature transformation product phase, voids are generated at the boundary of the low-temperature transformation product phase and residual austenite in the plate end face portion at the time of stamping, punching fatigue environment stress repeatedly in the hole is loaded, it is difficult to secure a high fatigue characteristics.
[0009]
　As described above, conventionally, the high strength steel sheet, increasing the ductility and hole expandability simultaneously, further, it was extremely difficult to ensure the fatigue properties of fatigue environment that stress repeatedly punched holes are loaded (punching fatigue properties) .
CITATION
Patent Literature
[0010]
Patent Document 1: Japanese Patent Publication No. 5589893
Patent Document 2: Japanese Patent Publication No. 5408383
Patent Document 3: Japanese Patent Publication No. 5,397,569
Summary of the Invention
Problems that the Invention is to Solve
[0011]
　As described above, in order to promote future weight reduction of automobile bodies must increase the use intensity level of high-strength steel sheet more than ever. Further, for example, the use of high-strength steel sheets for automobile bodies of the skeletal system parts must achieve both high elongation and hole expandability. Further, even it excels in elongation and hole expandability, the punching fatigue properties decrease, which is undesirable as a scaffold system parts of the automobile body.
[0012]
　Also, especially in the skeletal system component, the members such as the side sill, after being molded as a member, the collision safety is required. That is, the member, such as a side sill, excellent workability is required is when molding the member, after being molded as a member, the collision safety is required.
　To ensure crashworthiness are not only high tensile strength, it is also required high 0.2% proof stress. However, in high-strength automotive steel sheets, high tensile strength, 0.2% proof stress higher, excellent ductility, it is very difficult to satisfy all of excellent hole expandability.
[0013]
　In view of the state of the prior art, tensile strength more than 980 MPa, 0.2% proof stress a high-strength steel sheet of more than 600 MPa, while ensuring sufficient punching fatigue properties, good elongation and hole expandability It was an object to provide a high-strength cold-rolled steel sheet manufacturing method thereof. In the present invention, and it is excellent in elongation, indicating that total elongation is 21.0 percent, and is excellent in hole expandability, show that hole expansion ratio is 30.0% or more.
Means for Solving the Problems
[0014]
　We have now, assuming a manufacturing process that can be achieved using conventional is between successive hot and rolling equipment and continuous annealing equipment employed, while ensuring punching fatigue properties, high strength, high elongation, and good In order to ensure the hole expandability, and extensive research. As a result, it led to obtain the following findings.
[0015]
　(A) tensile strength in the above high-strength cold-rolled steel sheet 980 MPa, by controlling the area ratio of polygonal ferrite in the metal structure of the steel sheet, further controls the form of the residual austenite, to express excellent ductility it can. Specifically, local elongation is improved by increasing the structural fraction of the ferrite, the retained austenite, uniform elongation is improved. Therefore, the combination of these metal structure, it is possible to significantly improve the ductility with the conventional high strength steel sheets.
[0016]
　(B) a form control of the residual austenite by the controlling the placement of the hard tissue, it is possible to ensure a higher ductility and excellent hole expandability. Specifically, by the form of the residual austenite to control the production conditions so that the particulate, during hole expansion, it is possible to suppress the generation of voids at the interface between the soft tissue and hard tissue. Usually, residual austenite contained in the high strength thin steel sheet to become a plate shape, stress is concentrated on the edge portion of the plate-like austenite, resulting in occurrence from the interface between the ferrite of voids during hole expansion. In other words, voids generated from the interface is particularly likely to occur from the austenite edge after transformation to martensite. Therefore, by setting the retained austenite granulated, since stress concentration is relieved, even with a high ferrite fraction, it is possible to prevent the hole expandability deterioration.
[0017]
　(C) Further, by controlling the dispersion state of the hard tissue in the metal structure of the steel sheet, hole expandability can be improved. As described above, voids generated during hole expansion is, edge portions of the hard tissue, generated from the connection portion of the hard tissue, the cracks this void linked. Cracks occur from the edge portion of hard tissue, by controlling the form of residual austenite can be suppressed. Specifically, as connection of the hard tissue is lowered, by controlling the arrangement of the hard tissue, it is possible to suppress cracks generated from the connecting portion of hard tissue, it can be improved further hole expandability. Further, by controlling so that connectivity is low, is excellent in punching fatigue properties.
[0018]
　The present invention has been made based on the above findings and has as its gist is as follows.
[0019]
(1) cold-rolled steel sheet according to one embodiment of the present invention, the chemical composition, in mass%, C: 0.100% to less than 0.500%, Si: 0.8% to less than 4.0% , Mn: 1.0% to less than 4.0%, P: less than 0.015%, S: less than 0.0500%, N: less than 0.0100%, Al: less than 2.000%, Ti: 0 .020% to less than 0.150%, Nb: 0% to less than 0.200%, V: 0% to less than 0.500%, B: 0% to less than 0.0030%, Mo: 0 % or more and less than 0.500%, Cr: 0% to less than 2.000%, Mg: 0% to less than 0.0400%, Rem: 0% to less than 0.0400%, and Ca: 0% above, containing less than 0.0400%, the balance is iron and impurities, the total content of Si and Al 1.000% or more Ri, metal structure, polygonal ferrite of 40.0% or more by area ratio of less than 60.0%, bainitic ferrite 30.0% or more, the residual austenite 10.0% or more, or less 25.0% the martensite containing 15.0% of the residual austenite, and an aspect ratio of 2.0 or less, at 1.0μm or less in length 1.0μm or less and the length of the minor axis of the major axis a proportion of the residual austenite is at 80.0% or more, of the bainitic ferrite, and an aspect ratio of 1.7 or less, and the area of ​​the crystal orientation difference is surrounded by 15 ° or more grain boundaries the average value of the crystal orientation differences 0.5 ° or more, the ratio of bainitic ferrite is less than 3.0 ° is at 80.0% or more, the residual O and the martensite and the bainitic ferrite And a connectivity D value with Tenaito is 0.70 or less, a tensile strength of at least 980 MPa, 0.2% proof stress above 600 MPa, the total elongation of 21.0 percent or more and hole expansion ratio is 30.0% or more characteristics having.
[0020]
　(2) cold-rolled steel sheet according to the above (1), the connectivity D value is 0.50 or less, the hole expansion ratio may be 50.0% or more.
[0021]
　(3) cold-rolled steel sheet according to (1) or (2), the chemical composition, by mass%, Nb: 0.005% to less than 0.200%, V: 0.010% or more, less than 0.500%, B: 0.0001% to less than 0.0030%, Mo: 0.010% to less than 0.500%, Cr: 0.010% to less than 2.000%, Mg: 0.0005% to less than 0.0400%, Rem: 0.0005% to less than 0.0400%, and Ca: 0.0005% or more, containing less than 0.0400%, one or more it may be.
[0022]
　(4) hot-rolled steel sheet according to another aspect of the present invention is a hot rolled steel sheet for use in the production of cold-rolled steel sheet of any one of the above (1) to (3), chemical composition, by mass% in, C: 0.100% to less than 0.500%, Si: 0.8% to less than 4.0%, Mn: 1.0% to less than 4.0%, P: 0.015% less, S: less than 0.0500%, N: less than 0.0100%, Al: less than 2.000%, Ti: 0.020% to less than 0.150%, Nb: 0% or more, 0.200% less, V: 0% to less than 0.500% B: 0% to less than 0.0030%, Mo: 0% to less than 0.500%, Cr: 0% to less than 2.000%, mg: 0% to less than 0.0400%, Rem: 0% to less than 0.0400%, and Ca: 0% to less than 0.0400%, the free And the balance is iron and impurities, the total content of Si and Al is 1.000% or more, the metal structure comprises a bainitic ferrite, 15 ° or more grains of the bainitic ferrite field surrounded by the mean value of the crystal orientation differences of regions 0.5 ° or more and 3.0 area ratio of the bainitic ferrite is less than ° is 80.0% or more, connectivity E value of pearlite it is 0.40 or less.
[0023]
　Method for producing a cold-rolled steel sheet according to another aspect of (5) The present invention, the chemical composition, C: 0.100% to less than 0.500%, Si: 0.8% to less than 4.0% , Mn: 1.0% to less than 4.0%, P: less than 0.015%, S: less than 0.0500%, N: less than 0.0100%, Al: less than 2.000%, Ti: 0 .020% to less than 0.150%, Nb: 0% to less than 0.200%, V: 0% to less than 0.500% B: 0% to less than 0.0030%, Mo: 0% or more and less than 0.500%, Cr: 0% to less than 2.000%, Mg: 0% to less than 0.0400%, Rem: 0% to less than 0.0400%, and Ca: 0% or more , containing less than 0.0400%, balance being iron and impurities, der total content of Si and Al 1.000% or more A casting step of casting a steel ingot or slab; and rough rolling step of performing reduction in total 40% or more at a first temperature range of 1000 ° C. or higher 1150 ° C. or less in the steel ingot or slab, in the following formula (a) when the temperature determined by the component and T1, and the total reduction ratio of 50% or more in the second temperature range of T1 ° C. or more T1 + 0.99 ° C. or less, hot rolling finished hot rolled at T1-40 ° C. or higher in the hot rolled to process hot rolled steel sheet after up to a third temperature range of 600 ~ 650 ℃ 20 ℃ / s or higher 80 ° C. / s or less in the cooling rate; and finish rolling to obtain a steel plate, hot rolling process and containing a first cooling step of cooling; the hot rolled steel sheet after the first cooling step, to dwell 600 ~ 650 ° C. the third temperature range by the following formula (b), in determining the time t seconds 10.0 seconds a retaining step; the hot rolled steel sheet after the residence step 600 ° C. A second step of cooling to below, the hot-rolled steel sheet at 600 ° C. or less, in the microstructure of the steel sheet after coiling, connectivity E value of pearlite 0.40 or less and of bainitic ferrite , the average value of the crystal orientation difference of a region surrounded by 15 ° or more grain boundaries than 0.5 °, as the proportion of bainitic ferrite is less than 3.0 ° is 80.0% or more winding taken, the winding step and obtaining a hot-rolled steel; said hot-rolled steel sheet pickling and for pickling; the hot-rolled steel sheet after the pickling step, the cumulative reduction of 40.0% or more 80.0% or less cold rolling process and to obtain a cold-rolled steel sheet subjected to cold rolling such that the rate; the cold-rolled steel sheet after the cold rolling step, the temperature was raised to the fourth temperature range of T1-50 ° C. or higher 960 ° C. or less Te, annealing step and that for 30 to 600 seconds in the fourth temperature region; said cooling after said annealing step The rolled steel sheet, the third cooling step and the cooling in the following cooling rate 1.0 ° C. / s or higher 10.0 ° C. / s until the fifth temperature zone of 600 ° C. or higher 720 ° C. or less; 10.0 ° C. / s or higher having; 60.0 ° C. / s and following cooling to a sixth temperature zone of 0.99 ° C. or higher 500 ° C. or less at a cooling rate, the heat treatment step of holding the following 600 seconds 30 seconds.
　T1 (° C.) = 920 + 40 × C 2 -80 × C + Si 2 + 0.5 × Si + 0.4 × Mn 2 -9 × Mn + 10 × Al + 200 × N 2 -30 × N-15 × Ti ... formula (a)
　　t (seconds) = 1.6 + (10 × C + Mn-20 × Ti) / 8 ... formula (b)
　each element symbol in the formulas represents the content by mass percent of the element.
[0024]
　(6) The method of producing a cold rolled steel sheet according to (5), in the winding process, the steel sheet may be wound up at 100 ° C. or less.
[0025]
　(7) A method of manufacturing a cold-rolled steel sheet according to (6), said during the winding step and the pickling step, the hot-rolled steel sheet, 400 ° C. or higher, the seventh temperature below A1 transformation point raised to pass heated, it may have a holding step of holding for 10 seconds or more 10 hours or less.
[0026]
　(8) (5) The method of producing a cold rolled steel sheet according to any one of (1) to (7), in the heat treatment step, after cooling the cold-rolled steel sheet to a sixth temperature zone, more than one second before holding, it may be reheated to a temperature range of 0.99 ° C. or higher 500 ° C. or less.
[0027]
　(9) above (5) to a manufacturing method of a cold-rolled steel sheet according to any one of (8), after the heat treatment step, further comprising by a plating step of performing hot-dip galvanizing to the cold-rolled steel sheet it may be.
[0028]
　(10) A method of manufacturing a cold-rolled steel sheet according to (9), after the plating process, have an alloying treatment step of performing heat treatment in the eighth temperature range of 450 ° C. or higher and 600 ° C. or less good.
Effect of the Invention
[0029]
　According to this aspect of the present invention, suitable as a structural member, such as an automobile, a tensile strength above 980 MPa, yield strength greater than 600 MPa 0.2%, punching fatigue properties, high strength cold-rolled with excellent elongation and hole expandability it is possible to provide a steel sheet and a manufacturing method thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030]
It is a graph showing the relationship between FIG 1] D value and the hole expansion rate (%).
It is a graph showing the relationship between FIG. 2] D value and E values.
3 is a graph showing the relationship between a D value and the punching fatigue (test piece: thickness 1.4 mm).
DESCRIPTION OF THE INVENTION
[0031]
　Hereinafter, the cold-rolled steel sheet according to an embodiment of the present invention (sometimes referred to as steel sheet according to the present embodiment) will be described.
　First described metal structure and form of the steel sheet according to the present embodiment.
[0032]
　[An area ratio, the polygonal ferrite of 40.0% or more to less than 60.0%]
　is polygonal ferrite contained in the metal structure of the steel sheet, easily deformed because it is soft tissue, it contributes to the improvement of ductility. To improve both the uniform elongation and local elongation, and 40.0% the lower limit of the area ratio of polygonal ferrite. On the other hand, when the polygonal ferrite is 60.0% or more, 0.2% proof stress is remarkably deteriorated. Therefore, the area ratio of polygonal ferrite is less than 60.0%. Preferably, less than 55.0%, more preferably less than 50.0%.
　Coarse ferrite exceeding 15μm is surrendered before the fine ferrite, causing microscopic plastic instability. Therefore, in the polygonal ferrite favorably it has a maximum grain size is 15μm or less.
[0033]
　[An area ratio, residual austenite 10.0% or higher, 25.0% or less]
　retained austenite to deformation-induced transformation, which contributes metal structure to the improvement of uniform elongation. To obtain this effect, and the area ratio of residual austenite 10.0% or more. Preferably 15.0% or more. When the area ratio of residual austenite is less than 10.0%, sufficient effect can not be obtained, it is difficult to obtain a ductility purposes. On the other hand, the 0.2% yield strength when the area ratio of residual austenite exceeding 25.0% is for less than 600 MPa, the upper limit is 25.0%.
[0034]
　[An area ratio, bainitic ferrite or more 30.0%]
　bainitic ferrite is an effective organization in order to secure the 0.2% proof stress. To ensure the above 0.2% yield strength 600 MPa, a bainitic ferrite is 30.0% or more. Further, bainitic ferrite is also a metallic structure necessary for ensuring the predetermined amount of retained austenite. The steel sheet according to the present embodiment, by transformation from austenite to bainitic ferrite occurs, carbon is diffused into the non-transformed austenite and concentrated. When the carbon concentration increases by enrichment of carbon, the temperature of transformation occurs from austenite to martensite is less room temperature can exist stably as residual austenite at room temperature. To ensure the retained austenite in the area ratio as a metal structure of the steel sheet 10.0% or more, it is preferable to secure a bainitic ferrite 30.0% or more in area ratio.
　When bainitic ferrite area ratio is less than 30.0%, with 0.2% yield strength decreases, the carbon concentration in the retained austenite is lowered, it tends to occur transformation to martensite at room temperature. In this case, it is impossible to obtain a predetermined amount of retained austenite, to obtain the ductility of interest difficult.
　On the other hand, when the area ratio of the bainitic ferrite is 50.0% or more, it becomes impossible to secure the polygonal ferrite and 10.0% or more of residual austenite of more than 40.0%, the upper limit 50.0 % is preferably not greater than.
[0035]
　[Martensite is 15.0% by area ratio]
　In the present embodiment, the martensite shows fresh martensite and tempered martensite. Hard martensite, by adjacent to the soft tissue, during machining, to crack the interface easily occurs. Furthermore, the interface itself between the soft tissue and promote crack propagation, significantly degrade the hole expandability. Therefore, it is desirable to reduce the area ratio of martensite as much as possible, the upper limit of the area ratio as 15.0%. Martensite 0%, i.e., it may not be contained.
　In martensite area ratio throughout the thickness is preferably not more than 10.0%, particularly preferably martensite in the range of 200μm from the surface layer is not more than 10.0%.
[0036]
　[Of residual austenite, and an aspect ratio of 2.0 or less, it is more than 80.0% the proportion of residual austenite is 1.0μm or less or less and the length of the minor axis 1.0μm length of the major axis]
　during hole expansion, voids are generated from the interface between the soft tissue and hard tissue. Void generated from the interface, in particular, it tends to occur from the austenite of edge after the transformation to martensite. The reason is that typically, retained austenite contained in the high strength thin steel sheet is present between the bainite lath, the form to become a plate shape, because the stress tends to concentrate on the edges.
　The steel sheet according to the present embodiment, by granulated form of residual austenite, suppresses the formation of voids at the interface between the soft tissue and hard tissue. By the residual austenite granular, even with a high ferrite fraction, it is possible to prevent the hole expandability deterioration. More specifically, when the residual austenite length of there long axis aspect ratio of retained austenite of 2.0 or less is 1.0μm or less is 80.0% or more, the tissue content of polygonal ferrite even when the rate is 40% or more, hole expandability is not deteriorated. On the other hand, if the proportion of residual austenite with the above characteristics is less than 80.0%, hole expandability is remarkably deteriorated. Therefore, among the retained austenite, the aspect ratio is 2.0 or less, residual austenite length of the major axis is 1.0μm or less or less and the length of the minor axis 1.0μm to 80.0% or more . Preferably it is greater than or equal to 85.0%. Here, the length of the major axis has a limited percentage of the following residual austenite 1.0μm, the residual austenite is 1.0μm greater length of the major axis, the distortion is concentrated excessively during deformation, void This is because lowering the production and hole expandability of. The major axis is the maximum length of each of the residual austenite to be observed in a two-dimensional cross-section after the polishing, the minor axis is a maximum length of retained austenite in the direction perpendicular to the long axis.
　When the average carbon concentration in the residual austenite is less than 0.5%, the stability decreases with respect to the processing, the average carbon concentration in the retained austenite is preferably 0.5% or more.
[0037]
　[Of bainitic ferrite, the aspect ratio is 1.7 or less, the average value of the crystal orientation difference in the crystal orientation difference is surrounded by 15 ° or more the grain boundary area is 0.5 ° or more, 3.0 ratio of less than ° is bainitic ferrite 80.0% or higher]
　by the crystal orientation difference is controlled to an appropriate range the crystal orientation differences of a region surrounded by the grain boundaries of above 15 °, 0.2% it is possible to improve the strength.
　Further, the form of the residual austenite is greatly influenced by the form of bainitic ferrite. That is, when the transformation from the untransformed austenite to bainitic ferrite takes place, area remaining without transformation is residual austenite. Therefore, in terms of morphology control of the residual austenite, it is necessary to perform shape control of bainitic ferrite.
[0038]
　Bainitic ferrite bulk (i.e., the aspect ratio is close to 1.0) when produced, residual austenite will remain in granular at the interface of bainitic ferrite. The aspect ratio is said to be massive if 1.7 or less. Furthermore, the bainitic ferrite, the crystal orientation difference in the crystal orientation difference is surrounded by 15 ° or more grain boundary regions than 0.5 °, by controlling to less than 3.0 °, higher in the crystal grains 0.2% proof stress increases by sub-grain boundaries existing in density prevent movement of the dislocations. This massive bainitic ferrite, the population of the crystal orientation difference is small bainitic ferrite (lath) is, due to the recovery of dislocations at the interface (sub-boundaries of the product), became one of the grain a result, is because it is generated to the metal structure. Such in order to produce a bainitic ferrite having crystallographic characteristics, it is necessary to fine austenite before transformation.
[0039]
　Bay of bainitic ferrite, and an aspect ratio of 1.7 or less, the average value of the crystal orientation difference in the crystal orientation difference is surrounded by 15 ° or more the grain boundary area is 0.5 ° or more, 3.0 ° If the proportion of the a bainitic ferrite below is 80.0% or more, a high 0.2% proof stress is obtained. In this case, the form of the residual austenite, length 1.0μm or less and yet the length of the minor axis of there long axis aspect ratio of 2.0 or less is 1.0μm or less. On the other hand, if the bainitic ferrite having the above characteristics is less than 80.0%, it becomes impossible to obtain a high 0.2% proof stress can not be obtained a predetermined amount of residual austenite with a form of interest. Therefore, the aspect ratio is 1.7 or less, the average value of the crystal orientation difference in the crystal orientation difference is surrounded by 15 ° or more the grain boundary area is 0.5 ° or more and less than 3.0 ° Beini the lower limit of the proportion of tick ferrite and 80.0%. As the ratio of such a bainitic ferrite is high, while improving the 0.2% proof stress, it is possible to secure a large amount of residual austenite with the form of interest, the preferred ratio of the bainitic ferrite having the above characteristics it is at least 85%.
[0040]
　[Connectivity D value of martensite and bainitic ferrite and residual austenite is 0.70 or less]
　martensite contained in the steel sheet microstructure, bainitic ferrite, residual austenite, tensile strength of the steel sheet, 0.2 it is required tissue to ensure% proof stress. However, since these tissues are harder than the polygonal ferrite at the time of hole expansion, voids are easily generated from the interface. In particular, if these hard tissue is generated by concatenating, voids are easily generated from the connecting portion. Generation of voids causes the hole expandability is remarkably deteriorated.

The scope of the claims
[Claim 1]
　Chemical composition, in
　　mass% C: 0.100% to less than
　　0.500% Si: 0.8% to less than
　　4.0%, Mn: 1.0% to less than 4.0%,
　　P: less than
　　0.015%, S: less than
　　0.0500%, N: less than
　　0.0100%, Al: less than
　　2.000%, Ti: 0.020% to less than
　　0.150%, Nb: 0% or more and less than 0.200%,
　　V: 0% to less than
　　0.500%, B: 0% to less than
　　0.0030%, Mo: 0% to less than
　　0.500%, Cr: 0% or more, less than
　　2.000% Mg: 0% to less than
　　0.0400%, Rem: 0% to less than 0.0400%, and
　　Ca: 0% to less than 0.0400%,
containing, balance iron and an
　impurity, and the total content of Si and Al 1.000% or more,
　the metal structure, the area ratio In polygonal ferrite of 40.0% or more to less than 60.0%, bainitic ferrite 30.0% or more, the residual austenite 10.0% or higher, 25.0% or less, the martensite 15.0% contains the following,
　the out of retained austenite, and an aspect ratio of 2.0 or less, the proportion of residual austenite length of the long axis is 1.0μm or less or less and the length of the minor axis 1.0μm is 80. and 0% or more,
　of the bainitic ferrite, the aspect ratio is 1.7 or less, and the average value of the crystal orientation difference in the crystal orientation difference is surrounded by 15 ° or more the grain boundary region 0 .5 ° or more, the ratio of bainitic ferrite is less than 3.0 ° is at 80.0% or higher,
　the martensite and connectivity D value of the bainitic ferrite and the residual austenite There is 0.70 or less,
　a tensile strength of at least 980 MPa, 0.2% proof stress above 600 MPa, the total elongation of 21.0 percent or more and hole expansion ratio has a 30.0% or more properties
, characterized in that cold-rolled steel sheet.
[Claim 2]
　The connectivity D value is 0.50 or less, cold-rolled steel sheet according to claim 1, wherein the hole expansion ratio is characterized in that 50.0 percent or more.
[Claim 3]
　The chemical composition, by
　mass%, Nb: 0.005% to less than
　0.200%, V: 0.010% to less than
　0.500%, B: 0.0001% to less than 0.0030% or ,
　Mo: 0.010% to less than
　0.500%, Cr: 0.010% to less than
　2.000%, Mg: 0.0005% to less than
　0.0400%, Rem: 0.0005% or more , less than 0.0400%, and
　Ca: 0.0005% to less than 0.0400%,
the cold-rolled steel sheet according to claim 1 or 2 containing one or more.
[Claim 4]
　A hot rolled steel sheet for use in the production of cold-rolled steel sheet of any one of claims 1 to 3,
　chemical composition, in
　　mass%, C: 0.100% to less than
　　0.500%, Si: 0 .8% to less than
　　4.0%, Mn: 1.0% to less than
　　4.0%, P: less than
　　0.015%, S: less than
　　0.0500%, N: less than
　　0.0100%, Al : less than
　　2.000%, Ti: 0.020% to less than 0.150%,
　　Nb: 0% to less than
　　0.200%, V: 0% to less than
　　0.500%, B: 0% or more , less than
　　0.0030%, Mo: 0% to less than
　　0.500%, Cr: 0% to less than
　　2.000%, Mg: 0% to less than
　　0.0400%, Rem: 0% or more, 0 less than .0400%, and
　　Ca: 0% to less than 0.0400%,
containing, balance being iron and impurities,
　The total content of Si and Al is 1.000% or more,
　the metal structure comprises a bainitic ferrite,
　crystal orientation difference of a region surrounded by more than 15 ° of the grain boundary of the bainitic ferrite mean value of 0.5 ° or more, the area ratio of the bainitic ferrite is less than 3.0 ° is at 80.0% or more,
　connectivity E value of pearlite is 0.40 or less
and wherein the hot-rolled steel sheet to be.
[Claim 5]
　Chemical composition, C: 0.100% to less than 0.500%, Si: 0.8% to less than 4.0%, Mn: 1.0% to less than 4.0%, P: 0. less than 015%, S: less than 0.0500%, N: less than 0.0100%, Al: less than 2.000%, Ti: 0.020% to less than 0.150%, Nb: 0% or more, 0. less than 200%, V: 0% to less than 0.500% B: 0% to less than 0.0030%, Mo: 0% to less than 0.500%, Cr: 0% to less than 2.000% , Mg: 0% to less than 0.0400%, Rem: 0% to less than 0.0400%, and Ca: 0% or more, and contains less than 0.0400%, balance being iron and impurities, Si and a casting step of the total content of Al is cast steel ingot or slab is 1.000% or more;
　the steel ingot or A rough rolling step of performing reduction in total 40% or more at a first temperature range of 1000 ° C. or higher 1150 ° C. or less in Love, when the temperature determined by the components in the following equation (1) T1, T1 ℃ or higher the total rolling reduction in a second temperature range of T1 + 0.99 ° C. or less and 50% or more, and hot rolling step including a finish rolling to obtain a hot rolled steel sheet to exit the hot rolling at T1-40 ° C. or higher;
　a first step of cooling in the hot rolled to process hot rolled steel sheet after up to a third temperature range of 600 ~ 650 ℃ 20 ℃ / s or higher 80 ° C. / s or less cooling rate;
　after the first cooling step the hot-rolled steel sheet, a retention step of dwell time t seconds 10.0 seconds specified by the following formula (2) to a third temperature range of 600 ~ 650 ° C.;
　the hot rolled steel sheet after the residence step 600 ℃ and second cooling step of cooling to below;
　the hot-rolled steel sheet, 6 At 0 ℃ below, in the microstructure of the steel sheet after coiling, connectivity E value of pearlite 0.40 or less and of bainitic ferrite, crystal orientation difference of a region surrounded by 15 ° or more grain boundaries mean value of 0.5 ° or more, 3.0 percentage of bainitic ferrite is less than ° the winding so that 80.0% or more, and coiling process to obtain a hot-rolled steel sheet;
　the hot-rolled steel sheet pickling and for pickling;
　the hot-rolled steel sheet after the pickling step, obtaining a cold-rolled steel sheet subjected to cold rolling such that the cumulative rolling reduction of 80.0% or less 40.0% or more cold rolling step and,
　a cold-rolled steel sheet after the cold rolling step, it was heated to a fourth temperature range of T1-50 ° C. or higher 960 ° C. or less, held for 30 to 600 seconds in the fourth temperature region annealing step a;
　the said cold-rolled steel sheet after annealing, the fifth temperature region between 600 ° C. or higher 720 ° C. or less In 1.0 ° C. / s or higher 10.0 ° C. / s and a third step of cooling in the following cooling rate;
　10.0 ° C. / s or higher 60.0 ℃ / s 150 ℃ or more of the following cooling rate 500 ° C. ; following sixth cooled to a temperature range, a heat treatment step of holding 30 seconds to 600 seconds
manufacturing method of cold-rolled steel sheet characterized by having a.
　T1 (° C.) = 920 + 40 × C 2 -80 × C + Si 2 + 0.5 × Si + 0.4 × Mn 2 -9 × Mn + 10 × Al + 200 × N 2 -30 × N-15 × Ti ... Equation
　　(1) t (seconds) = 1.6 + (10 × C + Mn-20 × Ti) / 8 ... equation (2)
　element symbol in the formulas represents the content by mass percent of the element.
[Claim 6]
　In the winding process, a manufacturing method of a cold-rolled steel sheet according to claim 5, characterized in that winding the steel sheet at 100 ° C. or less.
[Claim 7]
　During the winding step and the pickling step, it has a holding step of said hot-rolled steel sheet, 400 ° C. or higher, the temperature was raised to a seventh temperature range below A1 transformation point, holding 10 seconds to 10 hours or less method for producing a cold-rolled steel sheet according to claim 6, characterized in that.
[8.]
　In the heat treatment step, after said cold-rolled steel sheet was cooled to a sixth temperature range, prior to holding more than one second, it claims 5-6, characterized in that reheating to a temperature range of 0.99 ° C. or higher 500 ° C. or less method for producing a cold-rolled steel sheet according to 7 any one of.
[Claim 9]
　After the heat treatment step, the manufacturing method of the cold-rolled steel sheet according to any one of claims 5-8, characterized by further comprising a plating step of performing hot-dip galvanizing to the cold-rolled steel sheet.
[Claim 10]
　After the plating step, the manufacturing method of the cold-rolled steel sheet according to claim 9, characterized in that it comprises an alloying treatment step of performing heat treatment in the eighth temperature range of 450 ° C. or higher and 600 ° C. or less