Document Tjrpe] Specification [Title of the Invention] BEARING PART, STEEL FOR BEARING PART AND METHOD FOR PRODUCING THEREOF [Tecl~nicalF ield of the Invcntion] [OOO l] The present invention relates to a bearing part such as needle bearings, roller bearings and ball bearings, steel for a beating part w11ich is a material for the bearing part, and a neth hod for producing thereof Priority is claimed on Japanese Patent Application No. 2014-3338, filed on January 10,2014, and Japanese Patent Application No. 2014-84952, filed on April 16, 2014, the contents of which are incorporated herein by reference. [Related Art] [0002] Bewing~parts.stach =.needle bearings, roller bearings and ball bearings are continually used under a situatio~w~h ere a foreign material such as burr or abrasion powder is mixed into lubricating oil, that is, are continually used even in contaminated environments. Therefore, it is important to improve rolling contact fatigue life of a bearing part in contaminated environments. In order to improve the rolling contact fatigue life of the bearing part in contaminated enviro~unents, it is known that an increase in retained austenite is effective. Accordingly, steel for the bearing part is subjected to a surface treatment such as a carbt~rizingo r nitriding. [0003] However, there are some problems that not only a surrace treatment suc11 as carburizing or nitriding for the steel for the bearing parts is high cost, but also a variation in qualities of a bearing part occurs due to the influence of variations in the treatment atmosphere. For example, Patent Document I discloses a bearing part including large amount of retained austenite manufactured by quenching and tempering and without carburizing or a nitriding. A bearing part disclosed in the Patent Docnment 1 secures the amount of retained austenite by lowering the martensite start temperature (Ms point) by including C, Mn and Ni, or Mo into the steel. Ho~vever, when a content of Mn, xvhich is added to the steel, is increased in order to secnre the amount of retained austenite, the hardenability of the steel is raised. As a result, a supercooled structure such as martensite is generated during cooling after hot rolling, and the \\rorkability, ductility and toughness of hot rolled wire rod is deteriorated. [0004] In addition, the Patent Document 2 discloses a method of generating retained austenite \vhile suppressing grain coarsening by using spherical cementite. Ho\\cever, in the method disclosed in Patent Doctument 2, spheroidizing at high tenlperahlre is performed for long period of time. As a result, C is solid-soluted into an austenite phase and the number density of spherical cementite is insufficient. Further~noret, he grain size of austu~ite.isc oarsened and an improvement effect of rolling contact fatigue life cannot be obtained sufficiently. [OOOS] Since the treatment time of spheroidizing annealing is long, when the nn~nbero f times of the annealing is increased, it is ktlown that production efficiency is deteriorated by increasing a ananufacturing cost. To solve this problem, for example, the Patent Document 3 discloses a high-carbon steel rolled wire rod for bearing parts that was invented by some of the present inventors and the high-carbon steel rolled wire rod for bearing parts is capable of wire drawing \vithout spheroidizing annealing. [0006] In addition, conventionally, spheroidizing annealing is performed before or after the wire drawing. Among the spheroidizing annealing, Patent Document 4 discloses a alethod in which the rolletl wire rod is subjected to the wire dra\ving after the hot rolling is completed and the spheroidizing annealing is perfornled so that the spheroidizing annealing before the wire drawing can be omitted. I-Iowever, the method disclosed in the Patent Document 4 is not intended to shorten the treatment time of the splleroidizing an~lealing. [Prior Art Docurne~~t] [Patent Document] [0007] [Patent Document 11 Japanese Unexatnined Patent Application, First Publication No. 2004-124215 [Patent Docunlent 21 Japanese Unexamined Patent Application, First Publication No. 2007-077432 [Patent Docu~nen3t1 PCT International Publication WO 2013/108828 Publicatio~~N2o0. 04-100016 [Disclosure of the Inve~~tio~~] [Proble~nsto be.-Sol.vcd by the Invention] [OOOS] However, as in Patent Document 1, when the content of MII in the steel is increased, it is difficult to process the hot rolled wire rod by o~nittiugsp heroidizing annealing, and it is necessary to perform spheroidizing several times so as to obtain the bearing part for the foregoing reasons. In addition, the present i~lve~ltofrosu nd that it is necessary to control the ~nicrostruch~trher ough the use of wire dra~vinga nd quenching where the quenching temperature is controlled, in order to manufacture a bearing part having an excelle~r~otl ling contact fatigue life in contaminated e~lvironmentsu sing the material disclosed in Patent Docun~en3t . [0009] The present illvention has been made in view of such circutnstances, and the aim of the present invention is to provide a bearing part having an excellent rolling contact fatigue life in em~ironmenitn cluding contaminated environments, steel for a bearing part which is a material for the bearing part, and a method for manufacturing them, ill wliicli the uomber of spheroidizing annealing is only one and n~l~ictahk es a sliort amount of time. [Means for Solvi~igth e Problem] [OOlO] The present inventors found that the average grain size of prior-aostenite of a bearing part can be refined by subjecti~igs teel including Cr in wliicli the ~~ietallograpl~ic struch~rec o~~sist. and, [C], [Si], [tvh], [Cu], [Nij, [Cr], [Mo], [All and [B] in the equation 2 represent, by mass%, the content of C, tlie content of Si, the content of MI, tlie content of Cu, the content of Ni, the content of Cr, the cor~teriot f Mo, the content ofAl and the content of B, respectively, in the hot rolled wire rod, Al=750,8-26.6x[C]+17.6x[Si]-11.6x~1i]-22.9x[Cuj-23.Ox[Ni]+24.1x[Cr]+22. 5x[Mo]-l69.4x[AI]-894.7x[B] (Equation.2).