DESCRIPTION HOT-ROLLED STEEL SHEET AND MANUFACTURNG METHOD FOR SAME Technical Field [0001] This invention relates to a precipitation-strengthened hot-rolled steel sheet having excellent formability and excellent fatigue properties of a sheared edge, and a method of manufacturing the steel sheet. This application claims priority fro111 Japanese Patent Application No. 2012-004554, tlie disclosure of which is incorporated herein by reference. Background Art [0002] In recent years, an attempt to reduce the weight of automobiles or various machine parts has been niade. The reduction in weight can be realized by the optitnization design of the part's sliape to ensure rigidity. In the case of liollow parts such as press-formed parts, the reduction in weight can be directly realized by reducing the plate thickness. Howevel; in order to maintain the static fracture strength and the yield strength while reducing tlie plate thickness, it is necessary to use a high-strength tnaterial for the parts. For this purpose, an attempt to apply a steel sheet having a tensile strength of 590 MPa or more to a low-cost steel tnaterial having excellent strength properties has been made. Meanwhile, in order to highly strengthen the inaterial, it is necessary to satisfy both of high strength and formability such as fracture liniit during sliape forming or burring fornlability. Fullliennore, when the parts are applied to chassis parts, a steel sheet based on precipitation-strengthening by the addition of micro-alloy elements has been developed in order to ensure toughness of an arc-welded part and to suppress HAZ softening. In addition to this, various steel sheets have been developed (for exaoiple, see Patent Documents 1 to 5). [0003] The above-described tnicro-alloy ele~nentsp romote the precipitation of coherent precipitates of approxitnately several nanometers to several tens of nanometers in size at a temperature below the Acl temperature. In the process of tnanufacturing the hot-rolled steel sheet, the strength of the steel sheet can be significantly improved by such coherent precipitates, but thete is a problem in that fine cracks are generated at a sheared edge and the sheared edge. In Non-patent Document I, this problem was solved by utilizing microstructure strengthening while using alloy constituents to which micro-alloy elenients were added. However, when the niicrostructure strengthening is utilized, it is difficult to 1 achieve a high yield strength required for the parts, a~idth e suppressiou ofthe deterioratiou of the sheared edge of the precipitation-streugthened hot-rolled steel sheet remains an issue. [0004] Patent Document 1: Japanese Patent Application Laid-Ope11 (JP-A) No. 2002-161340 Patent Document 2: JP-ANo. 2004-27249 Patent Document 3: JP-A No. 2005-314796 Patent Docutnetlt 4: JP-A No. 2006-1611 12 Patent Document 5: JP-A No. 2012-1775 Non-patent Document 1: Kunishige et al., TETSU-TO-HAGANE, vol. 71, No. 9, pp.1140-1146 (1985) SUMMARY OF INVENTION Technical Problem [0005] The invention can solve the above-described problem relating to the deterioration of fomlability and fatigue properties of a sheared edge in a precipitation-strengthened hot-rolled steel sheet. The invention provides a hot-rolled steel sheet having excellent forlllability and fatigue properties of a sheared edge with a tensile strength of 590 MPa or more, and a method of ~nanufacturingth e steel sheet. Solution to Problem [0006] The inventors achieved the soppression of the deterioration of a sheared edge in the above-described steel sheet contai~ii~pigre cipitated elements by adjusting the individual contetlts of ~nicm-alloye lements and carbon to their respective appropriate ranges and controlling a crystal orientation. The sutnmary of the invention is as follows. (I) A hot-rolled steel sheet including, in terms of % by mass, 0.030% to 0.120% of C, 1.20% or less of Si, 1.00% to 3.00% of Mn, 0.0 1% to 0.70% ofAl, 0.05% to 0.20% of Ti, 0.01% to 0.10% ofNb, 0.020% or less of P, 0.010% or less of S, and 0.005% or less ofN, and a balance consisting of Fe and impurities, in which 0.106 > (C% -Ti% * 12/48 - Nb% * 12/93) 2 0.012 is satisfied; a pole density of {I l2)(110) at a position of 114 plate thickness is 5.7 or less; an aspect ratio (long axis/short axis) of prior austenite grains is 5.3 or less; a density of (Ti, Nb)C precipitates having a size of 20 nm or less is 1 o9 pieces/mm3 or more; a yield ratio YR, which is the ratio of a tensile strength to a yield stress, is 0.80 ortnore; and a tensile strength is 590 MPn o!. [0007] (2) The hot-rolled steel sheet accordiug to (I), fi~rtherin cluding, ill terms of % by mass, olie or more of 0.0005% to 0.0015% ofB, 0.09% or less of Cr, 0.01% to 0.10% of V, or 0.01% to 0.2% ofMo, 2 inwhichO.l06>(C%-Ti%* 12148-Nb%* 12193-V%* 12/51)>0.012is satisfied in a case where the hot-rolled steel sheet contains V. [0008] (3) A method of manufacturing a hot-rolled steel sheet, the method including: heating a steel to 1250°C or higher, the steel including, in terms of % by mass, 0.030% to 0.120% of C, 1.20% or less of Si, 1.00% to 3.00% of Mn, 0.01% to 0.70% ofAl, 0.05% to 0.20% of Ti, 0.01 %to 0.10% of Nb, 0.020% or less of P, 0.010% or less of S, and 0.005% or less ofN, and a balance consisting of Fe and impurities, in which 0.106 ? (C% - Ti% * 12/48 - Nb% * 12/93) ? 0.012 is satisfied; hot rolling the heated steel at a final rolling temperature of 96OoC or higher in finish rolling with a total of rolling reductions at two stands fiom a last stand of 30% or more when a Ti content is in a range of 0.05% (C%-Ti%* 12148-Nb%* 12193-V%* 12/51)>0.012is satisfied in a case where the steel contains V. Advantageous Effects of Invention [OOIO] According to the invention, a hot-rolled steel sheet having excellent formability and fatigue properties of a sheared edge in which generation of fine cracks is suppressed at a sheared edge of a precipitation-strengthened hot-rolled steel sheet having a tensile strength of 590 MPa or tnore can be provided. BRIEF DESCRIPTION OF DRAWINGS [0011] Fig. 1 shows an examination result of a relationship between an excessive C content and a rate of separation development. Fig. 2 shows an exatnination of the effect of an aspect ratio of prior austenite grains and a pole density of {112}(110) at a position of 114 plate thickness on the separation Fig. 3 shows an observation result of separation at a sheared edge of sample steel sheet A having an aspect ratio of prior austenite grains of more than 5.3. Fig. 4 shows an observation result of separation at a sheared edge of sample steel sheet B having an aspect ratio of prior austenite grains of 5.3 or less and a pole density of {1 12}(110) at a position of 114 plate thickness of 5.7 or Inore. Fig. 5 shows an obse~vationre sult of separation at a sheared edge of sample steel sheet C in which all of microstrc~cturacl haracteristics of a metal according to the invention-a balance of C, Ti, and Nb, a pole density of {112)(110) at a positiotl of 114 plate thickness, an aspect ratio of prior austenite grains, and a size and a deusity of (Ti, Nb)C precipitates-are satisfied. Fig. 6 is a graph showing results of punching fatigue tests for sample steel sheets A, B, and C. Fig. 7 is a comparison of fatigue fracture surfaces behveen sample steel sheet A and sample steel sheet C. Fig. 8 shows an exatnitlatiotl result of effects of a final rolling temperature and a total rolling reduction at the last hvo stands on a pole density of {I l2}(ll0) when the Ti content is 0.05% to 0.10%. Fig. 9 shows an exatniuation result of effects of a final rolling temperature and a total rolling reduction at the last hvo stands on an aspect tatio of prior austenite grains when the Ti content is 0.05% to 0.10%. Fig. 10 shows an examinatiotl result of effects of a final rolling temperature and a total rolling reduction at the last hvo stands on a pole density of {112}(110) when the Ti content is more than 0.10% and 0.20% or less. Fig. 11 shows an examination result of effects of a final rolling temperature and a total rolling reduction at the last two stands on an aspect ratio of prior austetlite grains when the Ti co~ltetltis more than 0.10% and 0.20% or less. Fig. 12 shows an examination result of a relationship between a density of precipitates having a size of 20 nnl or less and a coiliug temperature. Fig. 13 shows an exatnination result of a relationship between a density of precipitates having a size of 20 nm or less aud a yield ~atioY R. Fig. 14 shows an examination result of an effect of the inve~ltiotbl ased on a relationship between a fatigue strength op at 10' cycles and a tensile strength TS, in a steel according to the invention whicll satisfied all of the characteristics of ingredients aud metal satisfy all of the characteristics of ingredients aud metal tnicmstructi~rea nd in which separation developed. DESCRIPTION OF EMBODIMENTS [0012] Hereinbelow, the details of the invetitioti are described. Conventionally, the~eha s been a p~oblenli n that fine cracks are generated at a sheared edge atld formability and fatigue properties are deteriorated when precipitation strengthening by micro-alloy elements is utilized. In order to solve this problem, it is necessary to strengthen the steel sheet by utilizing ~nicrostructurals trengthening using ~na~le~isori tleo wer bainite. The inventors explored appropriate values with respect to the individual contents of micro-alloy elements and carbon in a precipitation-strengthened steel sheet, and foutld that the deterioration of the slieared edge of the precipitation-strengthened steel, ~vllichh as been cotlventionally difficultt o suppress, can be suppressed by controlling the ~nicrostruct~tranl orphology oft he metal atld the crystal orientation thereof,t hereby successfi~llyd eveloping a hot-rolled steel sheet. [0013] Hereinbelow, the reasons for limiting the ingredients of the hot-rolled steel sheet, which is a feature of the invention, are explained. Wlien the content of C is less than 0.030%, the desired strength cannot be obtained. Furthermore, the deficiency of C content relative to the lower limits ofTi and Nb contents for obtaining the desired strength causes a sho~lageo fC precipitated at a grain boundary. As a result, the strength oft he crystal grain boundary is dec~easeda nd ro~~ghneossf t he sheared edge is significantly increased, whereby separation is developed at the sheared edge. Wlien the content of C exceeds 0.120%, a density of cementite is increased. As a result, elongation propetlies and burring fomlability are deteriorated and separation is developed at the sheared edge due to the formation of a pearlite microstructure. Therefore, the content of C is set to from 0.030% to 0.120%. [0014] Si is an effective element for supplessing coarsening of cementite and providing solid-solution strengthening. However, when the content of Si exceeds 1.20%, separation is developed at the sheared edge. Therefore, the co~ltenot f Si is set to 0.120% or less. Since Si provides solid-solution strengthening and is effective as a deoxidizing agent, it is preferable to contain 0.01% or Inole of Si. [OOI 51 The content of Mn is set to from 1.00% to 3.00%. Since Mn is an element for providing solid-solution strengthening, it is essential to contain 1.00% or Inore of Mn in order suifide is formed in a MI^ segregation pollton, whereby elongatton propelttes are sslgn~ticatltly deteriorated. Therefore, the content of Mn is set to 3.00% or less. [0016] A1 is added as a deoxidizitlg elemetlt and is an effective element for reducing oxide in a steel and improving elongatiotl properties by accelerating the transformation of ferrite. 5 Therefore, the content of Al is set to 0.01% or more. When the content ofAl exceeds 0.70%, a tensile strength of 590 MPa or more cannot be achieved, and further, a yield ratio YR of 0.80 or more cannot be achieved. Therefore, the content ofAl is set to from 0.01% to 0.70%. [0017] Ti provides precipitation strengthening by the formation of a carbide. It is necessary to contain more than 0.05% of Ti in order to achieve a steel strength of 590 MPa or more. In particula~; when precipitated at a temperature below the Acl temperature, fine precipitation strengthening due to coherent precipitation can be provided. However, when the C content is low, the content of solute C is decreased, whereby the strength of the crystal grain boundary is decreased and roughness of the sheared edge is significantly increased, and separation is developed at the sheared edge. [0018] In the invention, it was found that the deterioration of the sheared edge is suppressed and the separation is suppressed when the Ti content and the C content satisfy the following Fonnula (I), and the characteristics of the ~nicrostructural morphology of the metal described below are satisfied. Here, in the following Fonnula (I), "*" indicates "x (multiplication)". Fortnuia (1): 0.106 L (C% -Ti% * 12/48 - Nb% * 12/93) L 0.012 [0019] The relationship between the rate of separation developnlent and the excessive C is shown in Fig. 1. The rate of separation develop~nenwt as 100% when the excessive C content was less than 0.012 or exceeded 0.106, which revealed an appropriate range of the excessive C. Sa~nplehs aving excessive C contents within the appropriate range exhibit rates of separation developtnent of 50% or less, even when the content of another element is outside the range specified therefor. Therefore, it was confirmed that a separation suppression effect is obtained by satisfying the excessive C content specified by Fornlitla (I). Meanwhile, the rate of separation development exceeded 0% even in some satnples having contents of ingredients within their respective ranges specified by the invention. It was found that the separation developtnent in such satnples results fiotn the microstructure of the metal. The details are described below. Here, the excessive C tneans the excessive C content calciilated according to "(C% - [0020] The rate of separation development is a value detertnined by cutting a blank having a clearance of lo%, and observing the punched surface. 111 a case in which separation is developed at the sheared edge, the fracture surface of the sheared edge exhibits a shelf-like texture with a step, and the maximuni I~eightn easured with a roughness meter in the shear 6 direction is 50 pm or tiiore. Therefore, the separatioti develop~nent is defined by a step-like texture of the sheared edge and a maxitnum height of 50 ptii or tnore. Here, the rate of separation developtnent is a frequency of tlie separation development in tlie ten punching tests. [0021] When tlie content of Ti exceeds 0.20%, it is difficult to form a solid solution ofTi completely even by a solution treatment. Furthennore, when the content of Ti exceeds 0.20%, tlie t~nsolidifiedT i fortiis coarse carbonitride together with C and N in a slab. The coarse carbonitride remains in the produced plate, whereby toughness is significantly deteriorated and separation is developed at the sheared edge. Therefore, tlie content of Ti is set to frotn 0.05% to 0.20%. In order to ensure the toughness of a hot-rolled slab, the content of Ti is preferably set to 0.1 5% or less. [0022] Nb can fort11 a carbide of Nb alone and can also form a solid solution of (Ti, Nb)C in Tic, thereby reducing the size of carbide and exerting an extremely high precipitation strengthening ability. When the content ofNb is less than 0.01%, no precipitation strengthening effect can be obtained. On the other hand, when tlie content of Nb exceeds 0.10%, the precipitation strengthening effect is satitrated. Therefore, the content ofNb is set to from 0.01% to 0.10%. [0023] P is an element for solid-solution strengthening. When tlie content of P in the steel exceeds 0.020%, P segregates to the crystal grain boundaiy. As a result, the strength of the grain boundary is decreased, and separation is developed it1 the steel, atid in addition to this, toughness is decreased, and tlie resistance to secondary wolkitig etnbrittletnent is decreased. Therefore, the content of P is set to 0. 020% or less. The lower litnit of tlie P content is not particularly limited, and is preferably set to 0.001 % in terms of cost of depliosphorizatioti and productivity. [0024] S deteriorates stretch flange-ability by tlie fortnation of a cotiipound with Mn. Therefore, tlie contetit of S is preferably as low as possible. When tlie content of S exceeds 0.010%, the separation is developed at the sheared edge due to the band-like segregation of MnS. Therefore, tlie content of S is set to 0.010% or less. Tlie lower limit of the S content is not pat.ticularly limited, and is preferably set to 0.001% in terms of cost and productivity. [0025] N forms TiN before hot rolling. TiN has an NaC1-type crystal stracture, and has a non-coherent interface with base imn. Therefore, crack$ originating finm TiN are ge~ipratecl exceeds 0.005%, it is difficult to suppress the separation at the sheared edge. Tlielefote, the content ofN is set to 0. 005% or less. Tlie lower litnit of the N content is not particularly limited, and is preferably 5 ppm% from the viewpoint ofcost of denitrification and productivity. [0026] Hereinbelow, optional elements are explained. B can form a solid solution at the grain bol~tldarya nd suppresses the segregation of P to the grain boundary, thereby itnprovitlg the strength of the grain boundary and reducing the roughness of the sheared edge. A B content of 0.0005% or Inore is preferable, since a strength of 1080 MPa or more can be achieved and the separation at the sheared edge can be suppressed. Even when the content of B exceeds 0.0015%, no improvement effect associated with the inclusion is observed. Therefore, it is preferable that the content of B is set to from 0.0005% to 0.0015%. [0027] Cr can form a solid solution in MC similar to V, and can provide strengthening through the formation of a carbide of Cr alone. When the content of Cr exceeds 0.09%, the effect is saturated. Therefore, the content of Cr is set to 0.09% or less. It is preferable that the content of Cr is set to 0.01% or more, in terms of securing the product strength. [0028] V is replaced with Tic and precipitates in the form of (Ti, V)C, thereby realizing a high-strength steel sheet. When the content of V is less than 0.01%, no effect is produced. On the other hand, when the content of V exceeds 0.10%, surface cracking of a hot-rolled steel sheet is accelerated. Therefore, the content of V is set to from 0.01% to 0.10%. When the formula of 0.1 06 2 (C% - Ti% * 12/48 - Nb% * 12/93 - V% * 12/51) 2 0.012 is not satisfied, the content of solute C is decreased, whereby the strength of the ciystal grain boundary is reduced and the roughness of the sheared edge is significantly increased, and thus, separation is developed at the sheared edge. [0029] Mo is also an element for precipitation. When the content of Mo is less than 0.01%, no effect is produced. On the other hand, when the content of Mo exceeds 0.2%, elongation properties are deteriorated. Therefore, the content of Mo is set to fiotn 0.01% to 0.2%. [0030] Next, the characteristics of the invention, that is, the microstructure and the texture, are described. When the steel sheet according to the invention satisfies the above-described ranges ofthe ingredients and the pole density of {I 12}(110) at a position of 114 plate thickness is 5.7 or less, the separation at the sheared edge can be suppressed. { I 17}(110) is a crystal orientation developed in a rolling prncess, and determined from an electron back-scattering pattern obtained using an electron bean1 accelerated by a voltage of 25 kV or more (electron back-scattering pattern by an EBSP method), and using a sample in which surface strains of the surface to be measured have been eliminated by electrochen~icapl olishing of the rolling-direction section of the steel sheet using 5% 8 perchloric acid. Here, the measurement is perfonned in a range of 1000 ptn or more in the rolling direction and 500 pm in the plate thickness direction, and a measurement interval is preferably 3lnn to 5 ptn. Other identification methods suc11 as a method based on diffraction pattern by TME or X-ray diffraction are inadequate as the measurement method, since it is i~npossibleto specify the measurement position by such methods. [0031] With regard to the morphology of prior austenite grains, it was found that the separation at the sheared edge can be suppressed when the aspect ratio (long axis/sl~orta xis) thereof is 5.3 or less. Therefore, the aspect ratio is set to 5.3 or less. [0032] The relationship of the separation development to the aspect ratio and the pole density of (1 12)(110) is shown in Fig. 2. In this figure, a circle indicates that the rate of separation development is 0% in the evaluation of the separation, and a cross mark indicates that the rate of separation development exceeds 0%. Even when the contents of the ingredients fell witl~inth eir respective appropriate ranges, an aspect ratio exceeding 5.3 resulted in separation development at any pole densities. On the other hand, none of the samples having contents of the ingredients within their respective appropriate ranges, an aspect ratio of 5.3 or less, and a pole density of 5.7 or less exhibited separation development. Here, in a tnethod to reveal the prior austenite grains, it is preferable to use dodecylbet~ze~~e sulfonate, picric acid, or oxalic acid. [0033] The observation result of the separation at the sheared edge of sample steel sheet A having an aspect ratio of prior austenite grains of more than 5.3, using the above-described method to reveal the prior austenite grains is shown in Fig. 3. The separation at the sheared edge was exhibited as a shelf-like crack surface developed in a direction intersecting with the shear direction. As a result of the detailed observation, it was found that the crack extended along the grain boundary of the prior austenite. On the other hand, as shown in'Fig. 4, in sample steel sheet B having an aspect ratio of prior austenite grains of 5.3 or less and a pole density of (1 12)(110) of 5.7 or more, the atea of separation decreased according to the aspect ratio, but the separation was not completely suppressed. Howevel; as sho\vn in Fig. 5, in satnple steel sheet C which satisfies all the cha~acteristicso f the microstructure of the metal according to the invention, that is, the balance of C, Ti, and Nb, the pole density of ( 1 12)(110) at a position of 114 plate thickness, the aspect ratio of prior austenite grains, and the size and tlie density of (Ti: Nb)C precipitates; suppression of the separation was fo~rnd, [0034] The results of the tests for punching fatigue of test steels A, B, and C are shown in Fig. 6. The tests for punching fatigue were perfor~ned with a Shank type fatigue tester, and the evaluation was carried out using a test piece which had been subjected to a punching shear 9 processing of 10 tntn-diameter with a side clearance of 10% at the center portion of the stuooth test piece according to JISZ2275. Each of test steels A, B, and C has a tensile strength of about 980 MPa. In contrast to steel C in which the separation was suppressed, the fatigue strength at lo5 cycles in test steelsA and B was decreased by about 50 MPa. The comparison of fatigue fracture surfaces between test steel A and test steel C is shown in Fig. 7. In test steel C, it was found that fatigue cracks were generated from the separated portion and that the decrease in the fatigue strength at finite life was caused by the separation development. In tlie shearing process, cracks initiated from the punch and die edges run in the sheet thickness direction along the strokes of the punch and combined together to fonn a sheared edge. It has been thought tliat, in a steel sheet strengthened by coherent precipitates based on Ti, the separation development cannot be suppressed because of a decrease in toughness. In the invention, the separation was observed in detail, the mechanism of the separation development was clarified, and it was found that the separation at the sheared edge can be suppressed and the fatigue strength of the sheared edge can be improved by appropriately adjusting the composition of the ingredients and controlling the microstructure of the metal to have appropriate crystal orientation and crystal grain morphology. [0035] The density of (Ti, Nb)C precipitates having a size of 20 nm or less in the ~i~icrostroctuoref the metal is required to be 1 o9 pieces/tntn3 more. This is because a yield ratio YR, of the tensile strength and tlie yield stress, of 0.80 or more cannot be achieved when the density of (Ti, Nb)C precipitates having a size of 20 11111 or less is less than lo9 pieces/mm3. On the other hand, the density of the precipitates is preferably 10'' pieces/mm3 or less. It is preferable that the precipitates are measured by the observation of 5 or Inore fields by a transmission electron nlicroscope at a high magnification of 10000-fold or more, using a replica sample prepared with a method described in JP-A 2004-3 17203. Here, the size of the precipitate refers to the equivalent circular diameter of the precipitate. A precipitate having a size of 1 nm to 20 nm is selected for the measurement of the precipitation density. [0036] Hereinbelow, the characteristics of the method of tlianufacturing the steel sheet according to the invention are described. In the method of manufacturing the hot-rolled steel sheet according to the invention, the slab heating temperatnre is preferably 1250°C or higher, in order to sufficiently solidify the precipitated elenients contained. On the other hand, when it was found tliat there is an appropriate range of the finish rolling condition that varies with the content of Ti. When the Ti content is in a range of 0.05% 5 Ti 5 0.10%, the final lulling teniperature in finish rolling is required to be set to 960°C or highel; and tlie total of the 10 rolling reductions at two stands from the last stand is required to be set to 30% or more. When the Ti content is in a range of 0.10% riota. ustenite grains tnay he in a range of 1.42 to 5.25, an ' pieces/mtn3 to 3.10 x 10" pieces/mm 3 . [0040] In the method of tnanufacturing a hot-rolled steel sheet according to the invention, the final rolling temperature in finish rolling may be in a range of 963°C to 98S°C in a Ti content range of 0.05% 5 Ti < 0.1 0%, the total ofthe rolling reductions at two stands fion~th e last stand may be in a ratige of 32.5% to 43.2% in a Ti content rauge of 0.05% 5 Ti < 0.10%, tlie final rolling temperature in finish rolling may be in a range of 98loC to 105S°C in a Ti content range of 0.10% 0.012 is satisfied; hot rolling the heated steel at a final rolling tenlperature of 960°C or higher in finish rolli~lgw it11 a total ofrolling reductions at two stands fiun~a last stand of 30% or more when a Ti content is ill a range of 0.05% 0.012 is satisfied it1 a case \diere the steel cot~tainsV . Dated tllis 29"' day of July, 2014 M J N A MEHTA-DUTT] OF REWRY & SAGAR ATTORNEY FOR THE APPLICANT[S]