Specification [Title of the Invention] PLASTIC WORKING METHOD OF METALS AND PLASTIC WORKING APPARATUS [Technical Field of the Invention] [OOOl] The present invention relates to a plastic working method and a plastic working apparatus, in which steel including austenite can be formed while suppressing necking or breaking. welated Art] [0002] Hitherto, various plastic working niethods capable of improving the forniability of steel have been proposed. For example, in a plastic working method disclosed in Patent Document 1, first, before the press-forniing of steel, steel is preheated to anAC3 transformation point or higher, which is an austenite single phase region of about 750°C to 1000°C, in a heating filmace or tlie like. This steel in the austenite single phase state is press-formed and is quenched by being rapidly cooled using heat transfer from the steel to a mold. As a result, a press-formed product with high strength and has excellent dimensional accuracy is produced. [0003] In addition, in a plastic working method disclosed in Patent Document 2, steel including austenite is drawn by heating a die of a mold while cooling a punch of the mold. As a result, a part of steel which forms a flange after fonning is heated by heat transfer fro111 the die so as to decrease defonnation resistance thereof, and the other part of steel is cooled by heat transfer from the puncli so as to increase deforniation resistance thereof, thereby enabling tlie steel to be drawn. Accordingly, the steel call be drawn while preventing wrinkles and breaking. [0004] In addition, in a plastic working method disclosed in Patent Document 3, in a metallographic structure of steel as a workpiece, a space factor of bauiitic ferrite and/or granular bainitic ferrite as a pritnary phase is controlled to be 70% or more, and a space factor of retained austenite as a secondary phase is controlled to be 5% to 30%, and a C concentration in the retained austenite is controlled to be 1.0 mass% or more. As a result, the total elongation value of the steel, which is 7% at room temperature, is 20% at 250°C, and thus formability at this temperature is improved. [0005] With these conventional tecbnologies of the related art, the formability of steel including austenite is improved to some extent. However, currently, further improvement of formability has been required because the shapes of components are more complicated and the thicknesses thereof are more decreased. [Prior Art Document] patent Docun~ent] [0006] [Patent Document I] Japanese Unexamitied Patent Application, First PublicationNo. 2005-177805 [Patent Document 21 Japanese Unexamined Patent Application, First Publication No. 2007-111765 [Patent Document 31 Japanese ~nexamiiiedP atent Application, First Publication No. 2004-190050 [Disclosure of the Invention] [Problems to be Solved by the Invention] [0007] -~ The present invention has been made in consideration of the above-described problems, and an object thereof is to provide a plastic working method and a plastic working apparatus, in which, when steel including austenite is used as a workpiece, necking or breaking can be suppressed and the formability of the steel can be improved. [Means for Solving the Problem] [OOOS] The scope of the present invention is as follows. (1) According to a first aspect of the present invention, there is provided a plastic working method of a steel including austenite, the method including: physical property analyzing process of ~neasuringT p, oLp, and oHp for each of strain ratios P, when Tp represents a strain-induced-transformation-maxi- in the unit of "C which is changed depending on the strain ratio p, oLp represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio P on a lower temperature side than To, and oHp represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio on a higher temperature side than Tp; deformation mode analyzing process of analyzing a strain ratio px to be selected from among the strain ratios P, when the strain ratio px is a strain ratio of an estimated breaking point w11ich is specified during plastic deformation of the steel; heating process of heating such that a local temperature TI,I is within a first temperature range indicated by the following expression 1 after selecting Tpx fronl anlong the To, selecting oLps from among the oLp, and selecting oHp, from anlong the oHD respectively, when the Tp, represents a straininduced-~ ansformation-maximum-ductility-temperatuirne t he unit of "C for the strain ratio px, the oLpx represents a standard deviation of a fitted curve of critical equivalent strain ~vl~icdehp ends on the strain ratio Px on a lower temperature side than To,, the oHp, represents a standard deviation of a fitted curve of critical equivalent strain \vhich depends on the strain ratio px on a higher temperature side than Tp,, and TI,,,I represents a local temperature in the unit of "C of the estimated breaking point; and working process of plastically deforming the steel after the heating: Tp,-2x~Lpx~~,,~5Tp.2,+5x1o Hpx . . . (Expression 1). (2) In plastic working method according to (I), in the deformation mode analyzing process, a change in temperature ATl,d may be further analyzed, when the AT!-I represents a change ~ItIe mperature in the unit of "C of the local temperature TI,,[ which is changed during the plastic deformation of the steel; and in the heating process, heating may be performed such that the local temperature TI,[ is within a second temperature range indicated by the following expression 2: Tpx-AT~,,~-2~~Lpx5T~OCa~<.r25pXxo-HApTx ~OC.a. . ~ +1 (Expression 2). (3) In the plastic working method according to (1) or (2), in the heating process, at least one of the steel, a mold, and a surrounding space around the steel may be heated such that the local temperature TI,,^ is within the temperature range. (4) In the plastic working method according to (1) or (2), in the heating process, a heating medium may be heated such that the local temperature TI,,I is within the temperature rage; aid in the ~vorkingp rocess, the steel may be plastically deformed using the pressure of the heating medium. (5) In the plastic working method according to any one of (1) to (4), in the deformation mode analyzing process of analyzing the estimated breaking point, the strain ratio px, and the change in temperatnre ATI,,~ may be analyzed wing a plastic working sin~ulation. (6) According to another aspect of the present invention, there is provided a plastic working apparatus which performs the plastic working method according to any one of (1) to (3) and (5), tlie apparatus including: a housing unit that acconltnodates the steel and a mold; a heating unit that heats at least one of the steel, tlie niold, and a surrounding space around tlie steel; and a working unit that plastically deforms the steel, wliich is heated by the heating unit, using the mold. (7) The plastic working apparatus according to (6) may further include an insulating member that is arranged to cover the housing unit. (8) The plastic working apparatus according to (6) or (7) may further include a temperature measuring unit tliat measures respective temperatures of the steel, the mold, and an internal space of tlie housing unit. (9) According to still another aspect of the present invention, there is provided a plastic working apparatus which performs the plastic working method according any one of (I), (2), (4), and (5), the apparatus including: a housing unit that accomniodates the steel and a mold; a heating medium introducing unit tliat introduces the heating medium into tlie niold; a heating unit that heats at least one of the steel, tlie mold, a surrounding space around the steel and the heating medium; and a working unit that plastically deforms the steel, which is heated by the heating unit, using a pressure of the heating medium. (10) Tlie plastic working apparatus according to (9) may further include an insulating member tliat is arranged to cover the housing unit. (1 1) The plastic working apparatus according to (9) or (10) may fi~rther include a temperature measuring unit tliat measures respective te~nperatureso f the steel, the niold, and an internal space of tlie housing unit, and tlie heating medium. [Effects of the Invention] [0009] According to tlie above-described aspects of the present invention, steel including austenite is plastically deformed in a temperature range including a strainit~ duced-hansfomation-maxin~um-ductility-tetnperatwurheic h corresponds to the strain ratio of an estimated breaking point of the steel. Therefore, the transfor~nation induced plasticity phenomenon exhibited in this steel can be utilized to the maximum. As a result, it is possible to provide a plastic \\lorking method and a plastic working apparatus, in which necking or breaking can be suppressed and formability can be improved. [Brief Description of the Drawing] [OOl 01 FIG 1 is a schematic diagram showing tlie trausformatio~iln duced plasticity phenomenon. FIG. 2 is a schematic diagram showing uniaxial tension, plane strain tension, and equal biaxial tension. FIG. 3 is a diagram showing a temperature dependence of a critical equivalent strain of low carbon steel at each strain ratio P. FIG. 4 is a diagram showing a normal distribution fitted curve of the temperature dependence of tlie critical equivalent strain when P=O in FIG. 3. FIG 5 is a partially cutaway front view showing a scliematic configuration of a plastic working apparatus according to an embodiment of the present invention. FIG. 6 is a partially cutaway front view showing a schematic configuration of a plastic working apparatns according to another embodiment of the present invention. FIG. 7 is a schematic diagram showing forming by square cylinder drawing. [Embodiments of the Invention] [OOll] Aplastic working method and a plastic working apparatus according to embodiments of the present invention will be described in detail. However, the present invention is not limited to the configurations of the following embodiments, and various modifications can be made wvithin a range not departing from the scope of the present invention. [0012] First, a plastic working method accordiug to an embodi~nenot f the present invention will be described. In the plastic working method according to the embodin~etits, teel including austenite is used as a ~vorkpiecea, nd the transformation induced plasticity phenomenon exhibited in this steel is utilized to the maximum. [0013] Here, the transformation induced plasticity (TRIP) phenomenon will be described. FIG. 1 is a schematic diagram showing the TRIP phenornenon. As sho\vn in FIG. 1, for example, when steel including austenite (TRIP steel) is tensely deformed, necking occurs after the deformation progresses to some extent, Wllen necking occurs, a stress applied to a neck increases. Due to this stress, stress induced transformation (indicated by A in FIG. 1) in which retained austenite is transformed into martensite occurs. Since martensite has a higher strength than other microstructures, the neck is reinforced by the stress induced transfonnation co~npared to other regions, and the deformation of the neck does not progress. As a result, deformation in the vicinity regions of the neck, where has a relatively low strength, progresses. Aphenomenon in ~vhichn ecking caused by stress induced transformation and suppression of defomlation are repeated is referred to as the transfonnation induced plasticity (TRIP) plienomenot~. As a result, the inside of a material is unifor~nlyd efol-tned, and superior ductility is obtained. [0014] - However, the above-described TRP phenomenon depends on temperature. Improvement of ductility by this TRIP phenomenon is obtained only in a specific temperature range. 111 addition, a temperature (hereinafter referred to as "straininduced- transformation-maxin~t~m-ductility-tetnperaturea"t) w hich maximum ductility is obtained by the TRIP phenomenon (stress induced transformation) depends on a chemical structure and a metallographic structure of TRIP steel. Further, as a result of a thorough study, the present inventors found that this strain-inducedtransformation-~~~ axirnum-ductility-tehmaps a strain ratio P dependency (plastic deformation mode dependency) in which a value thereof is changed by a strain ratio P (plastic deforrnation mode) during plastic deformation. [0015] The strain ratio P described herein is expressed by, when biaxial strains in a biaxial stress state are a maxin~unp~ri ncipal strain EI and a ~nit~in~purimnc ipal strain ~ 2 : PZ EZ-.E I. In this expression, ~ 1 2 ~ 2I.n particularly, a state where P=-0.5 is referred to as a uniaxial tension state, a state where P=O is referred to as a plane strain tension state, and a state where P=1.0 is referred to as an equal biaxial tension state. FIG. 2 is a schematic diagram showing uniaxial tension, plane strain tension, and equal biaxial tension. As sho~vnin FIG. 2, uniaxial tension where P=-0.5 is a deformation mode where steel is stretched in a 61 direction and is cotnpressed in a 62 direction in the FIG. 2, and this deformation mode corresponds to plastic working such as draw fonning. Plane strain tension where P=O is a deforrnation mode where steel is stretched in the ~1 direction and is not deformed in the 62 direction in the FIG. 2, and this deformation mode corresponds to plastic working such as bending. Equal biaxial tension where fi=l.O is a deformation mode ~vheres teel is stretched in the 61 direction and is stretched in the EZ direction in the FIG 2, and this deformation mode corresponds to plastic working such as stretch forming. [0016] In order to effectively utilize the TRIP phenomenon to improve plastic deformability, it is necessary that both factors be considered at the same time, the factors including: the strain-induced-transformation-maximum-ductility-te~nperat~~re which is a value unique to each type of steel; and the strain ratio I) (plastic deformation mode) during plastic deformation which affects this strain-induced-transformationmaximum- ductility-temperature. However, in the above-described conventional technology of the related art, these factors are not considered. The strain-inducedtransfor~ nation-maximum-ductility-temper is a value which depends on the strain ratio (3 and thus, hereinafter, will be represented by "Tp". For example, when the strain ratio I) is -0.5, the strain-induced-transformation-1naximum-ducti1ity-temperature thereof will be represented by T.0.5. [0017] FIG. 3 sliows the temperature dependence of a critical equivalent strain h. c",ical at each strain ratio ~vhenlo w carbon steel is examined. In FIG. 3, a square-dot line indicates the results of (3=-0.5, a triangle-two dot chain line indicates the results of P=O, and a circle-solid line indicates the results of p=1.0. In addition, an equivalent strain E, refers to a strain ~vhichis calculated from the following expression A when biaxial strains in a biaxial stress state are a maximum principal strain and a ~nitiimunpi rincipal strain EZ. This equivalent strain E, refers to an equivalent uniaxial stress-strain coniponent which is converted from a stress -strain component in the multiaxial stress state. This equivalent strain &, is used to compare different plastic defonnation modes, that is, to compare plastic deformability (ductility) at different strain ratios P. The critical equivalent strain &q.critical refers to an equivalent strain E, at which breaking occurs in steel as a workpiece. &s={4+3x(~12+~22+I~n ~&~)) .. . (Expression A) [OOlX] As shown in FIG. 3, the values of the critical equivalent strain &q.,"li,,l (ductility) increase in a specific temperature range. As described above, this improvement of ductility is caused by tlle TRIP phenomenon. In this way, the improvement of ductility by the TRIP phenomenon depends on temperature. For exarnple, when e=-0.5, a strait~-induced-transfor~iiation-maxinium-ductili~- temperature T.o.5 is 150°C, and the critical equivalent strain at this temperature is the highest valne. [0019] In addition, FIG. 3 shows that the strain-induced-transformation-maxi~iiumductility- temperature Tp is changed depending on the strain ratio 0. For example, as described above, wlien P=-0.5, a strain-induced-trsuisformation-~~iaxiniu~n-ductilitytemperature T.o.5 is 150°C, but, when P=O, a straia-indnced-transformation-maximumductility- temperature TO is 200°C; and when P=1 .O, a strain-induced-transformationmaximum- ductility-temperature T1.o is 250°C. In this way, the strain-inducedtransforination- maximum-ductility-tempatwe Tp depends on the strain ratio P. [0020] In FIG. 4, the temperature dependence of the critical equivalent strain ~ e ~ - ~ ~ i ~ i ~ ~ when P=O in FIG. 3 is indicated by a two-dot chain line, and a fitted curve which is plotted on the assumption that the temperature dependence follows a normal distribution curve is indicated by a dot line. As described above, when the strain ratio p is 0, a temperature at which the critical equivalent strain E,.,"~~,,I is improved to the highest value due to the TRIP phenomenon is 200°C ~vhicliis the straiti-inducedtransformation- maxin~um-ductility-temperaT o. However, as shown in FIG. 4, a temperature at which the critical equivalent strain &,.,",i,l is improved has a specific range. This temperature range in xvliich the critical equivalent strain ~ ~ . , , i , i , ~ li s improved can be obtained from the fitted curve which is plotted on the assu~nptionth at the temperature range follows the nonnal distribution curve indicated by the dot line in FIG. 4. [0021] Amethod of obtaining the temperature range, in which the critical equivalent strain is improved by the above-described TRIP phenomenon, from the fitted curve (approximate function) will be described below. First, on the assumption that the temperature dependence of the critical equivalent strain follows the nornial distribution curve, the temperature dependence is approximated to a probability density hnctiot~re presented by the following expressions B and C. Here, the following expression B in which 0 represents the strain ratio expresses an approximate function (fitted curve of critical equivalent strain which depends on tlie strain ratio P on a lower temperature side than Tp) of the temperature dependence of the critical equivalent strain %<"tical on a lower temperature side than the strain-induced-transformationmaximum- ductility-temperature Tp at which the critical equivalent strain &qsritie.ll is improved to the highest value. The following expression C in which 0 represents the strain ratio expresses an approximate function (fitted curve of critical equivalent strain Tvhich depends on tlie strain ratio P on a higher temperature side than Tp) of tlie temperature dependence of the critical equivalent strain &q.critica~ on a higher temperature side than the strain-induced-h.ansfomation-maxinium-d~~ctilitytetnperature Tp at which the critical equivalent strain ~+,.,"~i,,l is improved to the l~igl~evsatl ue. In the expressions B and C, the respective synlbols denote the following: &q.cri,icacl:r itical equivalent strain T: tenlperahire TD: strain-i1~duced-transformation-ma,~in~u1n-di~~ti1ity-temperat11re OLDs: tandard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio 0 on a lower temperature side than Tp 013~s: tandard deviation of a fitted curve of critical equivalent strain wvhich depends on the strain ratio on a higher temperature side than Tp e: nah~ralo garithm n: circular constant CI to C4: constant (Expression B) (Expression C) [0022] When the matliematical definition of the probability density function is taken into consideration, the tetnperati~rer ange in which the critical equivalent strain ~ e q - ~ " ~ i ~ ~ l is improved by the TRIP phenonlenon can be expressed using OLD and OHD described above. That is, this temperature range can be expressed by, for example, (Tp-3xuLP) to (TP+3xoHp), (Tp-2xoLP) to (TP+2xoHp), or (Tp-uLp) to (TP+oHp). Here, the range of (Tp-3xuLp) to (Tp+3xuHp) mathematically represents an integrated value of the probability density function being 0.9974, the range of (Tp-2x0Lp) to (TP+2xoHp) mathematically represents an integrated value of the probability density function being 0.9544, and the range of (Tp-oL~t)o (Tp+oHp) n~atl~ematicalrlyep resents an integrated value of the probability density function being 0.6826. [0023] In this way, the temperature range in which the critical equivalent strain &, ,,iti,l is improved by the TRIP pheno~nenonc an be expressed using oLg and oHp which are the standard deviations of the fitted curve (fitted curve of critical equivalent strain) which is plotted on the assu~nptionth at the temperature range follows the normal distribution curve. The values of oLp and oHp depend on the strain ratio p. Hereinafter, for example, when the strain ratio is 0, uLp and uHp will be represented by oLo and oHo. When P=O, as sllowvn in FIG 4, the strain-induced-transformationmaximum- ductility-temperature To is 200°C, and o h is 55°C and OHO is 19°C as a result of analyzing the fitted curve. The analysis of the fitted curve for obtaining aLp and uHp can be performed using a general data analysis and graph making application or a spread sheet application having a general making function of graph. [0024] In FIG. 4, for example, the temperature range in which the critical equivalent strain ~ e q . ~ "i~s ii~m~plro ved by the TRIP phenonlenon can be expressed as 35°C to 257°C in the case of ( T , J - ~ x oto~ ()T 0+3xaHo), 90°C to 238°C in the case of (TO- 2xoLo) to (To+2xoHo), 145°C to 219OC in the case of (TO-OLt~o) (To+oHo), or the like. However, as a result of a thorough study on various steels and various strain ratios, the present inventors found that, when (Tp-2xuLp) to (Tp+l.25xuHp) is adopted as the temperature range, the temperature range in lv11ich the critical equivalent strait1 ~ ~ ~ . ~ ~ i is improved by the above-described TRIP phenomenon can be preferably expressed without excess and deficiency. Accordingly, in the plastic working method according to the embodiment, (To-2xoLp) to (TD+l.25xoHp)is adopted as the temperature range in which the critical equivalent strain &q-,,itiot is improved by the above-described TRIP phenotnenon. Otherwise, optionally, the lower limit of this temperature range may be set as (Tp-1 .75xcrLp), (Tp-1.5xoLp), or (Tp-1.25xoLp). Likewise, the upper limit of this temperature range may be set as (Tp+l.20xoHp), (Tp+l. 15xcrHp), or (Tb- 1.lOxoLp). [0025] When the strain ratio 0 is 0, and when the temperature range is set as (Tp- 2xoLo) to (Tp+1.25xoHo),t he temperature rat~geit1 ~vl~itchhe critical equivalent strain h.ccitical is improved by the above-described TRIP pllenomenon is 90°C to 223.75OC. That is, it can be seen that, in the case of low carbon steel, plastic working needs to be performed in a temperature range of 90°C to 223.75'C.to itnprove plastic defor~nabilityi n a plastic deformation mode where the strain ratio p is 0. [0026] It cat] be seen from above that the following plastic working method needs to be adopted in order to fortn steel (TRIP steel) iucluding austenite as a workpiece while suppressing necking or breaking to the maximum. This method may itlclude: (1) previously measuring the strain-induced-transfomation-maximum-ductilitytemperature Tp (OC) of steel, ~vllichis a workpiece, at each of strain ratios P, measuring the standard deviation oLp of the fitted curve of critical equivalent strain which depends on the strain ratio p on a lower temperature side than Tpas the standard ofTp, aud measuring the standard deviation oHp of the fitted curve of critical equivalent strain wl~icldi epends on the strain ratio (1 on a higher temperature side than Tp as the standard of Tp; (2) previously specifying a plastic defonnation rnode of a local region of the steel where necking or breaking is tilost likely to occur during forming, that is, specifying a strain ratio px of this local region; (3) controlling the temperature of the local region to be within a temperature range (Tpx-2xoLp,) to (Tpx+l.25xoHp,) suitable for the strain ratio Ox; and (4) plastic working of the steel is performed under conditions where the temperature of the local region is within this tetnperature range. In this range, (1x represents the strain ratio (1 being x (P=x); Tpx represents a straininduced- transfom~ation-~naxin~t~t~~-dnctility-tetnpwerhaetnn trhee strain ratio (1 is x; oLpy represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio px on a lower temperature side than Tp, as the standard of Tp.; and oHp, represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio px on a higher temperature side than Tp, as the standard ofTp,. Tp,, oLps, and oHpx are previously measured for each of the strain ratios and are included in Tp, oLp, and oHp. Accordingly, methods of measuring and analyzing Tpx, oLpx, and oHpx are tlle sane as those of Tp, oL6, and oHp. [0027] Specifically, in the plastic working tnethod according to the embodiment, steel including austenite is used as a workpiece, the method including: a physical property analyzing process of measuring Tp, oLp, and oHp for each of strain ratios p, when Tp represents a strain-induced-transfort~~ation-maximun~-d~ctii-temperoaf tthree steel in the unit of "C ~ v l ~ iisc clh~a nged depending on the strain ratio (1, oLp represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio p on a lower temperature side than Tp, and oHp represents a standard deviation of a fitted curve of critical equivalent strain wl~icdl~ep ends on the strain ratio p on a higher temperature side than Tp; a defor~nationm ode analyzing process of analyzing a strain ratio px to be selected from among tlie strain ratios p, when tlie strain ratio px is a strain ratio of an estimated breaking point which is specified during plastic deformation of the steel; a heating process of heating a steel such that a local tenlperature TI,,I is within a first temperature range indicated by tlie follo~ving expression D after selecting the To, froni among the Tp, selecting the oLpx from among the oLp, and selecting the oHp, from among the oHp respectively , when Tax represents a strain-induced-transformation-maxi~~~u~n-ductility-te~npoerf athteur set eel in the unit of "C for the strain ratio px, ohx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio px on a lower temperature side than Tps, oHp, represents the standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio px on a higher temperature side than To,, and TI,,I represents a local tenlperature in the unit of "C of the estimated breaking point; and a working process of plastically defonning the steel after the heating process. T b , - 2 x o L ~ x ~ ~ , , ~ ~.2b5sxo+1l3 px .. . (Expression D). [0028] In the physical property analyzing process, the strain-induced-transfon~iationmaximum- ductility-temperature of the steel in the unit of "C used as the workpiece at each of the strain ratios 0 is measured. Ametl~odo f measuring the strain-inducedtransformation- maximum-ductility-teniperature Tp is not particularly limited. For example, a spherical stretch forming test in which an end of a test piece is fixed while changing the horizontal and vertical dimension of the test piece may be performed at each temperature. The temperature at which the critical equivalent strain (ductility) is improved to the highest value is set as the strain-induced-transformationmaxitnurn- ductility-temperature Tp at the strain ratio p thereof. Next, for each of tlie steel ratios, the standard deviation of a fitted curve of critical equivalent strain wl~ich depends on the strain ratio B on a lower temperature side that1 Tg and the standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio (3 on a higher temperature side than To are obtained from the above-described fitted curve analysis. [0029] In the deformation mode analyzing process, when the steel is plastically deformed, a local region (estimated breaking point) of the steel where neckiug or breaking is most likely to occur is specified, and a strain ratio (3x is specified as a plastic deformation mode of the local region. This strain ratio Bx is selected from among the strain ratios measured in the physical property analyzing process. A method of measuring the estimated breaking point and the strain ratio px thereof is not particularly limited. For example, a scribed circle test may be performed. The scribed circle test is a method including: depicting a circular pattern or a lattice pattern on a surface of a workpiece before working; specifying a local region (estimated breaking point) where necking or breakiug is likely to occur due to plastic deformation; and measuring the pattern shape of this local region in order to specify a plastic deformation mode (strain ratio Bx) of the local region. Based on the results of the scribed circle test, the plastic deformation mode of the local region can be classified as uniaxial tension (P=-0.5), a drawing region (-0.5- a, 9- m n L E(D m m Q X EW 0 0 Example 1 Example 2 Example 3 Example 4 Example 5 Austen i te Fraction/% 100 17. 12 4, Properties of Workp iece Optimum Temperature Optimum Temperature Tg Of Stress Induced Transformation Optimum Temperature Tp Of Stress Induced Transformat ion ?C) 2 x a Lp (OC) 1.25xaHg ('C) Optimum Temperature Tp Of Stress Induced Transformation PC) 2 x a Lp (OC) 1.25~a Hp (OC) Optimum Temperature Tp Of Stress Induced Transformat ion ("C) 2 x a Lp ("C) 1.25a~H g ("C) .Optimum Temperature Tp Of Stress Induced Transformation ("C) 2 x a Lp (OC) 1.25xaHp ("C) Optimum Temperature Tp Of Stress Induced Transformat ion ("C) 2 x a Lp ("C) 1.25~a Hp ("C) Tp Of Stress Induced Transformation B =-0.5 75 90 75 50 90 76 150 110 69 175 62 62 60 150 Strain B =O 100 100 44 75 140 68 200 110 24 225 160 25 25 30 114 fi =-0.25 100 130 58 50 160 88 175 106 56 200 120 38 25 40 114 Ratio ,B B =0.25 125 140 50 100 100 64 225 140 38 225 140 25 50 30 100 B =O. 5 125 130 64 125 150 44 225 160 38 250 180 19 75 50 75 B -1.0 150 86 38 150 100 50 250 150 19 250 120 19 100 90 38 Table 3 Local Temperature Tlocal of Estimated [Document Type] CLAIMS - [Claim 11 A plastic working method of steel including austenite, the method comprising: physical property analyzing process of tneasuring Tp, oLp, and oHs for each of strain ratios (3, when Tp represents a strain-induced-transfonnation-maximum-ductilitytemperature in the unit of "C which is changed depending on the strain ratio P, oLp represents a standard deviation of a fitted curve of critical equivalerit strain which depends on the strain ratio (3 on a lower temperature side than the Tp, oHp represents a standard deviation of a fitted curve of critical equivalent strain \vl~iclid epends on the strain ratio a on a higher temperature side than the Tp; deformation mode analyzing process of analyzing a strain ratio (3x to be selected from among the strain ratios (3, when the strain ratio ax is a strain ratio of a11 estimated breaking point which is specified during plastic deformation of the steel; heating process of heating the steel such that a local temperature TI,,^ is within a first temperature range indicated by the following expression 1 after selecting Tgx fiom among the Tp, selecting oLps from among the oLp, and selecting oHp, fiom among the oHD, when Tp, represents a strain-induced-transformation-maximutnductility- temperature in the unit of "C for the strain ratio px, oLp, represents a standard deviation of a fitted curve of critical equivalent strain wvhicli depends on the strain ratio ax on a lower temperature side than the Ts,, oHgx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio px on a higher temperature side than the Tp,, and the T~,,I represents a local temperature ("C) of the estimated breaking point; and working process of plastically defortning the steel after the heating: Tpx-2xoLpx3~,,~3p,+.215 x(sHpX. . . (Expression 1). [Claim 21 The plastic working method according to Claim 1, wherein in the defortnation mode analyzing process, a change in temperature ATl,, is filrther analyzed, when theATl,,~ represents a change in temperature in the unit of "C of the local temperature TI,,,I which is changed during the plastic deformation of the steel in the wvorking process, and wherein in the heating process, heating is performed such that the local temperature TI,^ is within a second temperature range indicated by the folloxving expression 2: Tp,-ATl,,~-2x~Lg.5Tl,a~~p,-AT~1. ~2+5x oHp, .. . (Expression 2). [Claim 31 The plastic working nlethod according to Claim 1, wherein in the heating process, at least one of the steel, a mold, and a surrounding space around the steel is heated such that the local temperature TI,^ is within the first temperature rage. [Claim 4) The plastic working method according to Claim 1, wherein in the heating process, a heating medium is heated suc11 that the local temperature TI,,^ is within the first temperature range, and wherein in the working process, the steel is plastically defonned using a pressure of the heating medium. [Claim 51 The plastic working method according to Claim 2, wherein in the physical property analyzing process, the estimated breaking point, the strain ratio px, and the change in temperature ATI,,I are analyzed using a plastic working simulation. [Claim 61 Aplastic working apparatus which performs the plastic working method according to Claim 1, the apparatus comprising: a housing unit that accommodates the steel and a mold; a heating unit that heats at least one of the steel, the mold, and a surroundir~g space around the steel; and a working unit that plastically deforms the steel, which is heated by the heating unit, using the mold. [Claim 71 The plastic working apparatus according to Claim 6, further comprising an insulating member that is arranged to cover the housing unit. [Claim 81 The plastic working apparatus according to Claim 6, further comprising a temperature measuring unit that measures respective temperatures of the steel, the mold, and an internal space of the housing unit. [Claim 91 A plastic working apparatus which performs the plastic working method according to Claim 4;-the apparatus comprising: a housing unit that accommodates the steel and a mold; a heating medium introducing unit that introduces the heating medium into the mold; a heating unit that heats at least one of the steel, the mold, and the surrounding space around the steel and the heating medium; and a working unit that plastically deforms the steel, which is heated by the heating unit, using a pressi~reo f the heating medium. , [Claim 101 The working apparatus according.to Claim 9, further comprising an insulating member that is arranged to cover the housing unit. [Claim 111 The plastic working apparatus according to Claim 9, further comprising .\ a temperature measnring unit that measures respective temperatures of the steel, the mold, an internal space of the housing unit, and the heating medium.