Specification [Title oftl1elnvention] HOT-ROLLED STEEL SHEET [Technical Field ofthe Invention] [0001] Theptesent invention relates to a hot-rolled steel sheet excellent in workability and particularly relates to a hoHolled steel sheet having a composite structure and excellent in stretch flangeability. [Related Art] [0002] In reqent years, in response to the demand for reduction in weight of various members for the purpose of improving fuel economy of vehicles, a reduction in thickness was accomplished byinereasingthe strength of a steel sheet. such as an iron alloy used forthe members, and application of light metals such as an AI alloy to the various members have been proceeded. Howevet~ as compared with heavy metals such as steel, the light metals such as an AI alloy have an advantage of high specific strength, but are extremely expensive. For this reason, the application of the light metal such as an AI alloy is limited to special applications. Accordingly, in order to apply the reducti.on in the wdght of the various members to a cheaper and wider range, it is required to reduce the thickness by increasing the strength of the steel sheet. [0003] When the steel sheet is strengthened, the material properties such as formability (workability) are generally deteriorated. Thus, in the developing of the high-strength steel sheet, it is an important problem to achieve the high strength ofthe steel sheet witl1out deteriorating tl1e materialproperties. Particularly, stretch-flange formability, bun-ing workability, ductility, fatigue durability, impact resistance, - 1 - corrosion resistance, and the like are required for the steel sheet used as vehicle members such. as au inner plate member, a structural member, and a suspension member, depending on 1he. application, and it is important to realize both ofmaterial properties aud strength. [0004] For example, among1hevehicle members, the steel sheets used for the stru.ctU:ral member, the suspension member, and 1he like, which account for about 20% of the vehicle body weight are press-formed mainly based on stretch flange processing and burring processing after performing blanking and drilling by shearing or punching. For this reason, excellent stretch ilaugeability is required for such steel sheets. [0005] With respect to the above-described problem., for example, Patent Document 1 discloses a hot-rolled steel sheet .in which 1he fraction aud 1he size ofthe martensite, the number density, and the average gap between martensite is specified, audis excellent in elongation aud hole expansibility. Patent Document 2 discloses a hotrolled steel sheet in which average particle diameters offerrite.and a second phase and a carbon concentration ofthe second phase are limited, and is excellent in burring workability. Patent Document Jdisclose.s a hot-rolled steel sheet which .is obtained by coiling the steel sheet at a low temperature after being. kept at a temperature in a range of750°C to 600°C for 2 to 15 seconds, and is excellent in workability, surface tex-ture, and plate flatness. [0006] However, in Patent Document 1, since a primary cooling rate should be set to be equal to or higher tban 50°C/s after completing the hot rolling, the load applied on an apparatus becom~s higher. In addition, in a case of setting the primary cooling rate - 2 - to be equal to or higher than 50°C/s, there is a problem in that unevenness in material properties is caused by unevenness in the cooling rate, [0007] Inaddition, as described above, in recent years, the demand for the highstrength steel sheet to the a:11ton10bile members have been required. In a case where the high,strength steel sheet is press-formed by cold working, cracks likely to occur at an edge of a portion which is subjected to the stretch flange forming during the forming process. The reason for this is that work hardening occurs only on .an edge portion due to the strain which is introduced to a punched end surface at the time of blanking. In the related art, as a method of evaluation a test of the stretch flangeability, a hole expansion test has been used. However, in the hole expansion test, breaking occurs without the strains in the circumferential direction are hardly distributed; however, in the actual process ofcoinponents, strain distribution is present, and thus a gradient of the strain and the stress in the vicinity ofthe broken portion affects. a breaking limit. Accordingly, regardingthe high-strength steel sheet, even if the stretch flangeability is sufficient in the hole expansion test, in a case ofperforming cold pressing, the breaking may occur due to the strain distribution. [0008] The techuiques disclosed in Patent Documents 1 to 3 disclose that in all of the inventions, the hole expansibility is improved by specifYing only the stiuctures observed nsing an optical microscope. However, it is not clear whether or not snfficient stretch flangeability can be secured even in consideratior1 of the strain disti·ibntion. [Prior Art Document] [Patent Document] - 3 - [0009] [Patent Document 1] Japanese Unexamined Patent Application, First Publication No; 2013-19048 [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2001-303186 [Patent Docl.l!llent3] Japanese Unexamined Patent Application, First Publication No. 2005-213566 [Disclosure ofthe Invention] [Problems to be Solved bythe Invention] [0010] TI1e present invention has been. made in consideration of the above-described circumstance. An object of the present invention is to provide a hig!Htrength hot-rolled steel sheet which is excellent in the str.etch flangcability and can be applied to a member which requires high strength and the strict stretch flangeability. In the present invention, the stretch flangeability means a value evaluated by .a product oflimit forming height H (mm) and tensile strength TS (MPa) of the flange obtained as a result ofthe test by the saddle type s1ret.;;h flange test method, which is an index of the stretch flangeability in consideration of the strain distribution. In addition, the excellent stretch .flangeability means that the product ofthe limit forming height H (mm) and the tensile strengthTS (MPa) is equal to or greater than 19500(mm·MPa). In addition, the high strength means that the tensile strength is equal to or greater than .590 MPa. There is no need to particularly setthe upper limit of the s1rength; however, in the range of the structure defined in the present invention, it is difficult to secure a strength of greater than 1470 MPa. - 4 - [Means for Solving the Problem] [0011] According to the related art, the improvement of the stretch flangeability (hole expansibility) has been performed by inclusion control, homogenization of structure, uni:(ication of structure, and/orredllction in hardness difference between structure, as disclosed in Patent Documents 1 to 3. In other words, in therehted art, hole expansibility, workability, or the like have been improved by controlling the structure which can. be observed using an optical microscope. [0012] :W this regard, the present inventors made an intensive study by focusing an intragranular orientation difference in grains in consideration thatthe stretch flangeabilityunder the presence ofthe Strain distribution cannot b~: improved even by controlling only the structure observed using an optical microscope. As a result, it was found that it is possible to greatly improve the stretch flangeability by controlling the ratio of the grains in which the intragranular orientation difference is in a range of 5° to 14° with respectto the entire grains to be within a certain range. [0013] The present invention is configured on the basis ofthe above findings, and the gists thereof are as follows. [0014] (1) A hot"rolled. steel sheet according to one aspect of the present invention includes, as a chemical composition, by mass%, C: 0.04%to0.1&%, Si: 0.10%to 1.70%, Mn: 0.50%to3.00%, AI: 0.010%to l.OO%,B: 0%to0.005%, Cr: 0%to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 2.0%, Ni: 0% to 2.0%, Mg: O%to 0.05%, REM: 0% to 0;05%, Ca: O%to 0.05%, Zr: 0%to 0.05%, P: limited to equal to or less than 0.050%, - 5 - S: limited to equal to or less than 0. 010%, and N: limited to equal to or less than 0.0060%, with the remainder including of Fe and impurities; and a stiucture which includes, by arearatio, a ferrite :md a bainite in a range of75%to 95% in total, and a martensite in a range of 5% to 20%, in which in the stiuctute, in a case where a boundary having an orientation difference of equal to or greater than 15° is defmed as agrain boundary, and an area which is surrounded by the grain boundary and has an equivalent circle diameter of equal to or greater than 0.3 f1Jh is defined as a grain, the ratio ofthe grains having an intragranular orientation difference in a range of 5° to 14° is, by area mtio, in a range of 10% to 60%. (2) In the hot-rolled steel sheet describedin the above (1 ), a tensile strength may be equ, it is concernedthat surface flaws occur. Fortlus reason, even in the case of containing Cu, the uppet.limit of the Cu content is preferably set to 2.0%, and is further preferably set to 1.0%. [0031] Ni: O.Ol%to 2.0% Ni is an element winch enhances the strength and improves the toughness of the steel sheet. In. order to obtain such effects, the Ni. content is preferably equal to or greater than 0. 01% On the other hand, when the Ni content is greater than 2. 0%, the ductility is deteriorated. For this reason, even in the case of contaitung Ni, the upper linut of the Ni content is preferably set to 2.0%. [0032] Ca: 0.0001%to 0.05% Mg: 0,0001%to0.05% - 13 - Zr: O.DOOlo/oto 0,05% REM: 0.0001%to 0.05% All of Ca, Mg, Zr, and REM are elements which improve the toughness by controlling the shape of sulfides and oxides. Accordingly, in order to .obtain such effects, each of one or more of these elements is preferably equal to or greater than 0.0001%, and is further preferably equal to or greater than 0.0005%. However, when the amount of these elements is excessively high, the stretch flangeability is deteriorated, For this reason, even .. inthe case of containing these elements, the upper limit of each content is preferably setto 0.05%. [0033] Next, the structure (metallographic structure) of the hot-rolled steel.sheet according to the present embodimentwiU he described. It is necessary that the· hot-rolled steel sheet according to the present embodiment cmttain, by area ratio, :ferrite and bainite in arange of75%to 95% in total, and martensite in a range of 5%to 20%, in the structure observed usirig an optical nucroscope. With such a composite structure, it is possible to improve the strength and the stretch flangeability in good balance. When the total amount of the ferrite and the bainite is less than. 75% by area ratio, the stretch flangeability is deteriorated. In addition, when the totaL area ratio of the ferrite and the bainite is greater than95%, the strength is deteriorated, the ductility is deteriorated, and thereby it is difficult to secure the properties which are generally required for the vehicle members. Although each of the fraction (the area ratio) of the ferrite and the bainite is not necessarily limited, when the.fraction ofthe ferrite is greater than 90%, sufficient strength cannot he obtained in some cases, and tlms the fraction of the ferrite is preferably equal to less than90%, and is further preferably less than 70%. On the other hand, \\l1en the - 14 - fraction ofthe bainite is greater than 60%, the ductility may be deteriorated, and thus the fraction ofthe. bainite is preferably less than 60%, and is further preferably less than 50%, In the hot-ro1led,steel sheet according to the present embodiment, the structures of the remainders other than the ferrite, bainite, and martensite are not particularly limited, and for example, it rnay be residual austenite, pearlite, or the like. However, when the structures ofthe remainder other than the ferrite, bainite, and martensite are greater than 5% in total, the stretchflangeability and the ductility are deteriorated. For this reason, theratio ofthe. structures of the remainders is preferably eqnal to or less than 5%, further preferably equal to or less than 3%, and still further preferably 0%, by area ratio, (003.4] The structure fraction (the area tatio) can be obtained using the following method. First, a sample collected from the hot-rolled steel sheet is etched using nita!. After etching, a structUre photograph obtained at a 1/4 thickness. position in. a visual field of 300 f!m x 300 jJ.m using an optical microscope is subjected to image analysis, and thereby the area ratio of ferrite and pearlite, and the total area ratio bainite and mattensite are obtained. Then, a sample etched by LePera solution, the structure photograph obtained at a 114 thickness positionin the visual field of 300 f!ill x 300 f!111 using the optical microscope is subjected to the image analysis, and thereby the total area ratio ofresidua\ austenite and martensite is calculated. Further, with a sample obtained by grinding the surface to a depth of 114 thickness from the normal direction to the rolled surface, the volume fi·action of the residual austenite is obtained through X-ray diffraction measurement. The volume fi·actjon of the residual austenite is equivalent to the area ratio, and thus is set as the - 15 - area ratio ofthe residual austenite. With such a method, it is possible to obtain the arearatio of each offerrite, bainite, martensite', residual aust!"'nite, and pearlite. [003.5] In the hot-rolled steel sheet according to the present ~mbodiment, it is necessary to control the stfucture observed using the optical microscope to be within the above~described range, and to control the ratio of the grains having an intragranular orientation difference-in a range of SO to l4°,obtained using an EBSDmethod (electron beam back scattering diffraction pattern analysis method) frequently used for the crystal orientation analysis. Specifically, in a case where a boundary having the orientation difference of equal to or higher than 15° isdefmed as a grain boundary, and an area which is surrounded by the grain boundary and hagan equivalent circle diarueter of equal to or greater than 0.3 J.Lm is defined as a grain, the taiio of the grains having an intragranular orientation difference ina range of 5° to 14" is set to be in a range of 10% to.60% by area ratio, with respect to the entire grains. The grains having such intragrannlar orientation difference.are effective to obtain the steel sheet which has the strength and the workability in the .excellent balance, and thus when the ratio is controlled, it is possible to greatly improve the stretch flangeability while maintaining a desired steel. sheet strength. When the ratio of the grains having an intra granular orientation difference in a range of so to 14° is less than 10% by area ratio, the stretch flangeability is deteriorated. In addition, when the ratio of the grains having an intragranular orientation difference in a range of 5° to 14° is greater than 60% by area ratio, the ductility is deteriorated. Here, it is considered that an intragranular orientation difference is related to a dislocation density contained in the grains. Typically, the increase in the intragranular - 16 - dislocation density causes the workability to be deteriorated while bringing about the improvement of the strength. However, in the grain in which the intragranular orientation difference is controlled to beinarange of5° to 14°, it is possible to improve the strength without deteriorating the workability. For this.reason, in the hot-rolled steel sheet according to the presentembodiment, the ratio ofthe grains having an intragranular orientation difference in a range of5° to 14° is controlled to be in a range of 10% to :60%. The grains havmg a!l intragranular orientation difference of less lower 5° are excellent in the workability, but are hard to be highly strengthened, and the grams havmg anintragranular orientation difference of greater than 14° have different deformations therein, and thus do not contribute to the improvement ofthe stretch flangeability. {003.6] The ratio ofthe grams having an intragratmlar orientation difference in a range of 5° to 14° can be measured by the following.method. First, at a position of depth of 114 (1/4t portion) thicknesst frotn sutface of the steel sheet in a cross section vertical to a rolling direction, an area of200 jl11l in the rolling direction, and 100 jl11l in the normal direction to the rolled surface is subjected to EBSD analysis at a measurement pitch of0.2 jl11l so as to obtain crystal orientation infotmation. Here, the EBSD analysis is performed using ap. apparatus which is configured to include a thermal field emission scanning. electron microscope (JSM- 700 lF, manufactured by JEOL) and an EBSD detector (HIKARI detector manufactured by TSL), at an analysis speed in a range of200 to 300 points per second. Then, with respect to the obtained crystal orientation information, an area having the orientation difference of eqnal to or greater than 15° and an equivalent circle diameter of equal to or greater than 0.3 J.tm is defined as a grain~ the average intragranular - 17 - orientation difference ofthe grains is calculated, and the ratio of the grains having an intragranular orientation difference in a range of 5° to 14 ° is obtained. The grain defmed as described above and the ~tverage intragranular orientation difference can be calculated using software "OIM Analysis (trademark)" attached to an EBSD analyzer. The ''intragranulat orientation difference" of the present invention means "Grain Orientation Spread {GOS)" which is an orientation .disp¢rsion in the grains, and the value thereofis obtained as an average value of reference crystal orientations and misorientations ofall ofthe measurement points vvithin the same grain as disclosed in "Misorientation Analysis of Plastic Deformation of Stainless Steel by EBSD and X· Ray Diffraction Methods", KIMURAHidehiko, journal ofthe Japan Society of Mechanical Engineers (Series A) Vol.71, No.712, 2005, p. 1722 to 1728. In the present emllodiment, the reference crystal orientation is an orientation obtained by averaging all of the measurement points in the same grail], a value ofGOS can be calculated using "OIM Analysis (trademark) Version 7.0.1" whichis software attached to the EBSD analyzer. [0037] FIG 1 is an example of an EBSD analysis result of an area of 100 !J-ill x 100 !J-ill at 1/4t portion in the cross section vertical to therolling direction of the hot-rolled steel sheet according to the pre.sent embodiment. In FIG. 1, art area ..ill which a boundary having the orientation difference of equal to or greater than 15° is indicated as a grain boundary in a range of 5° to 14° is shown in gray. In the drawing, an area shown in black indicates martensite. [0038] In the present embodiment, the stretch flangeability is evaluated using the saddle type stretch flange test method in whichthe saddle-shaped formed pwduct is - 18 - used. Specifically, the saddle-shaped fonned product simulating the stretch flange shape formed of a linear portion and an arc portion as illustrated in FIG 2 is pressed, and the stretch flangeability is evaluated using a lilnit forming height at this tilne. In the saddle type stretch flange test of the present embodiment, the limit forming height B (mm) when a clearance atthe time of]Ju11ching a comer portion is set to 11% is measure<;! using the saddle-type formed product in which a radius of curvature R of a comer is set to be in a range of 50 to 60 tum, and ati opening angle e is set to l2D0 • Here, the clearance indicates the ratio of a gap between a punching die and a punch, and the thickness ofthe test piece, Actually,the clearance is determined by combination of a punching tool and the sheetthickness, and thus the value ofl 1% means a range ofl05% to 11.5%. The ~:xistence of the cracks having a length of 1/3 of the sheet thickness are visually observed aft'€[ forming, and then a forming height of the limit in which the cracks are not present is detennined as the limit forming height. [0039] In a hole expansion test which is used as a test method to evaluate the stretch flange formability in the related art, breaking occurs without strains are mostly :distributed in the circumferential direction, and thus the strain and the gradient of stress in the vicinity of the· broken portion during hole expansion test are different from that in the case of actually fonningthe stretch flange. In additiot1, in the hole expansion test, the evaluation reflecting the original stretch flange fonning is not performed since, the evaluation is performed when the rupture of the thickness penetration occmred. On the other hand, in the saddle type stretch flange test used in the present embodiment, it is possible to evaluate the stretch flangeability in consideration of the strain distribution, and thus the evaluation reflecting the original stretch flange forming can be performed. - 19 - [0040] In the hot-rolled steel sheet according to the present embodiment, the area ratio of each of the structures ofth~ ferrite and bainite wlrich are observed using the optical microscope is not directly related. to the ratio offhe grains having an intragranular otientatioh difference ina range of 5° to 14°. In other words, for example, eveniftbere are hot-rolled steel sheets i1l which the area ratio of ferrite and bainite afethe same each other, the ratio ofthe grains having an intragranular orientation. difference in a range of 5° to 14 ° are not necessarily the same. Accordingly, it is not possible to obtain the properties corresponding to the hot-rolled steel sheet according to the present embodiment only by controllingtheferrite area ratio; the bainite area ratio, and the martensite area ratio. Details for this will be described in Examples below [0041] The hot-rolled steel sheet according to the present embodiment can be obtained using a manufacturing method incltidirtg a hot rolling process artd a cooling process as follows. [0042] In the hot tolling process, the hot-rolled steel. sheet is obtained by heating and hot.rolling a slab having the above-described chemical composition. The sla.b heating temperature is preferably in a range of1050°C to 1260°0. When the slab heating temperature is lower than 1050°0, it is difficult to secure the hot rolling finishing temperature, which is not preferable. On the other hand, when the slab heating temperature is equal to or higher than 1260°0, the yield is decreased due to the scale off, and thus the heating temperature is preferably equal to or! ower than 1260°C. - 20 - [0043] In a case where the ratio of the grains having an intragranular orientation difference ina t In the hot-rolled steel sheet which was subjected to the hot rolling controlled as described above is Cooled. In the Cooling process, the hot-rolled steel sheet after completing the hot rolling is cooled (first cooling) down to a temperature range in a range of650°C to 750°C at a cooling rate of equal to orgreatertban 10°C/s, and tbe temperature is kept for 3 to 10 seconds in the temperature range, and thereafter,. the hot-rolled steel sheet is cooled (second cooling) down to the temperature of equal to or lower than l00°C at a cooling rate of equal to or greater than 30°C/s. When the cooling rate in the frrst cooling islower than 1 0°C/s, the ratio of the grains having an intragranular orientation differencejn a range of5° to 14 ° is less than 10%, which is not preferable. In addition, whe.n a cooling stoppingtemperatute inihe frrst cooling is l!)wer than 650°C, the ratio of the grains having an ihttagranular orientation difference in a range of5° to 146 is less than 10%, which .is not preferable. On .the other hand, when the cooling stopping teinperattlre in the first cooling is higher than 750°C, the martensite fractionis excessively low, the strength is decreased, and the ratio of the. grains having an intragranular orientation difference in a range of 5° to 14° is greater than 60%, which is.not preferable. When the retention time is shorter than. three seconds at a temperature range of 65Q°Cto 750°C, the martensite fraction is excessively high, the ductility is .deteriorated, and. the ratio of the grains having an intragrannlar orientation difference in a range of 5° to 14° is less than 10%, which is not preferable. When the retention time at a temperature range of 650°C to 750°C is longer than 10 seconds, the martensite fraction is decreased, the strength is deteriorated, and the ratio of the. grains having an intragranular orientation difference in a range of 5° to 14 ° is less than 10%, which is not preferable. In - 24 - addition, when the cooling rate of the second cooling is lowerthan 30°C/s, the martensite fraction is decreased, the strength is deteriorated, andthe ratio of the grains having an intra granular orientation difference in .a range of5 ° to 14° is greater than 60%, which is not preferable. When the cooling stoppingtemperature ofthe second cooling is higher than 1 00°C, the ratio of the grmposllimrs {mlus'i,ll, renlaimler .l'eand ~tnpuriri.i!!~) Ar3 No: c Si Mn I' s AI N B Cr J\1j) Cu Nt Mg ftli;M () 'lr ('Cj ,\ 0.{:!6 () 90 1 'lj.() ll. Ol8 0.00~ O:l5 O.llOUl 825 lJ QJ)(;, uo 1:2:!) 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Q.lWi1 l!J.11 sz S:l1J 6 46· 7U 3-2 J) 911J 1161:1 9U '12 {1631 H!J.Q 2~~ 000 * ,Hl 40 '3] I! 336 nzo $!i~! "~· 0-JJ$4 9$:2 l9 lf'\11! l M $0 34 H 1136 113f'l ;\]9\) ;::-4 {_1_1,1~:2 9~0 3' 1>70 16 l1 611 ;;; 0 ~?-5 1 ill' $9:5 Zl' Ml1 lOH! JS 'i()l} 7 2 ~" Yi I 0" $75 Wl(l '?Of :r:a \),69): !fJQO Zl of+l) & :;a ~{!I) • 31 • [0052] Withrespect to the obtained hot-rolled steeLsheet, each strnctnre fraction (the area ratio), and the ratio of the grains having an intragranJ.Jlar qt-ientation difference in a range of So to 14° Were obtained. The structure fraction (the arearatio)was obtained J.Jsing the following lnethod. First, a sample collectedfromthe hot-rolled steel 'Sheet was etched J.Jsing nita!. After etching, a stmctnre photograph obtained at a 114 thickness positionin a visJ.Jal field of300 !-lin x 300.1-1111 using an optical microscOpe was subjeCted to image analysis, and thereby the area ratio offerrite and pearlite, and the total area ratio bainite and martensite were obtained. Then, With a sample etched by LePera solution, the structnre photograph obtained at al/4 thickness position in the visual field of300 1-lffi x 300 1-lffi J.JSingthe optical microscope was subjected iothe image analysis, and thereby the total area ratio of residual austenite and martensite wall calculated. Further, with a sample obtained by grinding the surfaceto a depth of 114 thickness in the normal direction to the rolled surface, the volume fraction of the residual austenite was obtained through X-ray diffraction measurement. The volume fraction of the residual a4stenite was equivalentto the area ratio, and thus was set as the axea ratio of the residual austenite. With such a method, the area ratio of e.ach of ferrite, bainite, martensite, residual austenite, and pearlite was obtained. Further, the ratio of the grains having an intragranular orientation difference in a range of so to 14° was measured using the following method. First, at a position of depth of 1/4 (114t portion) thickness t from surface ofthe steel sheet in a cross section vetiical to a rolling direction, an area of200 1-1m in the rolling direction, and 100 1-1m in the normal direction to the rolled surface was subjected to EBSD analysis at a - 32 - measurement pitch of0.2 ~J-m so as to obtain crystal orientation information. Here, the EBSD analysis was performed using an apparatus vvhich is configured to include a thermal field emission scanning electronmicroscope (JSM-7001F, manufactured by JEOL) and an EBSD detector (HIKARl detector manufactured by TSL), at an analysis speed in a range of200 to 300 points persecond. Then, with resp()ct to the obtained crystal orientation information, an areahaving the orientation difference of equalto or greaterthan 15° and an equivalent circle diameter of equal to or greater than 0.3 ~J-m was defined as a grain, the average intragranular orientation difference of the grains was calculated, and the ratio ofthe grains having an intragranular orientation difference inarange of 5° to 14° was obtained. The gr;tin defmed as described above and the. average intragrannlar orientation difference can he calculated using software "DIM Analysis (tradelllillkT attached to an EBSD analyzer. [0053] Next, the yield strength and the tertsile strength were obtained in the tensile test, and the limit forming height was obtained by the saddle tyPe .stretch flange test. In addition, a product of tensile strength (MPa) and limit forming height (mm) was evaluated as an index ofthe str.etch flangeability, and in a case where the product thereof is equal to or greaterthan 19500 mm·MPa, it was determined that the steel sheet was excellent in the stretch flangeability. The tensile test was performed based on JIS Z 2241 using tensile test pieces No.5 ofJIS which were col!ectedin the.longitudinal direction. which is orthogonal to tl1e rolling direction. Further, the saddle type stretch flange test was conducted by setting a clearance at the time ofpunchihg a corner portion to 11% using a saddle-type formed product in which a radius of curvature R of a corner was set to 60 mm, and an opening - 33 - angle e was set to 120°. In addition, the existence ofthe cracks having a length of 1/3 of the $heet thickness were visually observed after forming, and then a forming height of the limit in which the cracks·were not present was· determined as the limit forming height. The results are indicated in Table 3. - 34 - ~- Ratio"''":_$"''"'"'""" Ferrite 1:.U.mit.e.t~1M f\>tdJ&.+ 00tt\)-1eat;~.,"ft Yt~b;t Ten:ri!tt Ten ~lant\nittc.atca t%fWtn:tm rt3 1 Jl ;ii';t £Q2 21612 .t¢1'{Jit1ltJfu ;qf l'f¢$1:1)t' {fi\:efM#.\ft ' l.l 33' es !:i 41 5Al a1> ;!I)Q.1~. tt~lQf¢£1( llrt*cm. itWOtltitm 4 90 l Yl ' x; 41l (t1lk lt1lli r:xanlptc ()f'l'resJtnt irtvf!ilic# l 'H! 16 :¢5 J 41 450 6:S1 'J~~ J~SJt!llfl~1){11u.mcut tnvcmi:ol'r " 5·6 34 "" '" 46 5-P: IIllO 21@\l -~lp1;:ofl1n'Sttit :i!:wc;nkia 9 61 24 "' 51 47 306 711'1 IHZ40 inver~tmn jl) J$ 5-1 Z-~f II 21 lll t\31/ :H:t50 n 42 rt-1 9} 7 ;m ;.<1') tpD 21)7;50 E::-.Arn~ of Presmr irm~M~C!t 12 2& & ~~ 6 59 i:!f) 640 ~:241:!-0 l!:>:.:atllpte of ~tmr {nventro:" i-"d IW g 93 7 \1 411 61'1 2£»1511H 52 :;a 9!) ID 5l ~lf) &10 2'!)2;:1!) Cxam!)l~r£-pf'I!!{Cfit illn"tlttN~ 15 cs 4 'Jl n 46 :1'19 6U9 211124 1\.\'.!}.mple r4' Pft'!{et'\1' i.~~vtt\!Wn Jf,-, ,",,, 1~ 81 13 :r.t l9J r;N5 ll!!:vtw 16xurqp~.of -J~em:tK tiW<~lLWn. l7 &3 ' l\li !l l7 512 600 ;rf.i4fl!) l':JiX'i!l'lpk\- od" ~t inYi.iJMti\111 l$ 0 (I Q lli& " 91$ 1~!7 3\\iS .,, ... , 1.9 ?3 !1] }4 __ 419 "!l""'' 21) J "' s: 1121! 21. ,s 21 71 4i;~.e_~ 2S 7!}' 4 .:$3 17 j J1ll S9J l'J'l~?(l C.~tat$v~:JLmm~pt~ .J 29 73 M "' g l 401 tl(),l 17$4::5 e~:pttv%, Cr:O.{)l%to LO%, Mo: 0.{)1% tOLO%, Cu: {L01%to 2..0%; and Ni: O.OI%to2.0%. 4. 11J.e hot-rolled Steel sheetaccording.to any one ofClaims 1 io .3, v.>herein,the chelllical oow.positio.n contains, .by mass%, one or more selected from the group.consisting of: Mg: o.0001%to omo/o, REM: 0.0001%to 0.05%, Ca: 0.0001 %to 0.05%, and Zr: 0:000.1% to 0.05%;