[0002] 近年來，鋼板的輥軋技術係有明顯的進步，隨著這種趨勢，輥軋用輥子的使用環境也更為嚴酷化。尤其是在最近，高強度鋼板和薄型化製品之類的輥軋負荷大且被要求具有優異的表面品質之鋼板的生產量不斷的增大當中。 [0003] 因而，針對於冷軋用工作輥子，係被要求具有優異的耐磨損性以及用來提供該種耐磨損性之高硬度。一般而言，耐磨損性的提昇，大都借助於輥子材料的高合金化，然而，輥子材料高合金化的結果，有時候會導致研磨切削性的惡化或者發生輥子事故時之被害的增大(耐事故性變差)，因此，必須採用兼具研磨切削性與耐事故性的材料。此外，想要製造優異的表面品質的鋼板的話，必須預先就將與鋼板進行直接接觸的輥子採用具有均質且細微的表面性狀者，具體而言，係採用具有高淨度且細微的顯微組織之鑄鐵、鑄鋼來作為輥子材質。 [0004] 此外，在熱軋用工作輥子身上，發生輥子磨損和在表面產生粗糙的話，勢必對於輥軋製品的材質和尺寸上的輥軋製程產生限制，而且也難以減少輥子的更換頻率，因此，輥子耐用度的下降，將成為阻礙生產性的提昇和阻礙成本的削減之瓶頸之一。因此，對於熱軋用工作輥子，必須要求：減少磨損和減少在表面產生粗糙，以資提昇輥子的耐用度。 [0005] 基於這種理由，針對於所使用的輥軋用輥子，乃熱切期望能夠提昇其特性，尤其是提昇耐磨損性。輥軋用輥子的耐磨損性的提昇，在鋼板的製造上，是與鋼板品質的提昇以及生產性的提昇，有直接關聯性的重要課題。 [0006] 針對於這種想要提昇輥軋用輥子的耐磨損性的要求，已經有人開發出例如非專利文獻1、非專利文獻2所揭示的高速工具鋼系輥子，其外層的組成分是採用與高速度工具鋼的組成分類似的組成分，並且散佈著大量的硬質碳化物，而可顯著提昇耐磨損性。此外，例如在專利文獻1中所揭示的熱軋用複合輥子，是在鋼製的芯材的外周，利用連續堆積厚度法來形成外層。專利文獻1所揭示的熱軋用複合輥子，外層材的組成分，以重量%計，係含有C：1.0~4.0%、Si：3.0%以下、Mn：1.5%以下、Cr：2~10%、Mo：9%以下、W：20%以下、V：2~15%、P：0.08%以下、S：0.06%以下、B：0.0500%以下，其餘部分是Fe以及不可避免的雜質，其金屬組織，以面積比計，是含有粒狀碳化物5~30%、非粒狀碳化物6%以上的組織所組成，基質的硬度是維氏硬度(Hv)550以上。再者，該外層材亦可又含有Ni：5.0%以下、Co：5.0%以下、Nb：5.0%以下。如此一來，可藉由某一既定量以上的非粒狀碳化物的存在，即使有裂隙產生時，亦可抑制裂隙進展到達輥子的深部，因而可提昇耐熱龜裂性，並且因為含有VC系的硬質碳化物，耐磨損性也很良好。 [0007] 這種高速工具鋼系輥子外層材，為了要提昇耐磨損性，就必須使多量的硬質碳化物分散在基質中。但是，高速工具鋼系組成分所生成的硬質碳化物，一般而言，其比重較之基質的比重更輕，在鑄造中很容易產生偏析。尤其是在因生產性、經濟性都優異而成為具有代表性的輥子外層材的鑄造方法，也就是離心鑄造法中的話，比重較輕的相受到離心力的作用而很容易集積和偏析在內側，因此高速工具鋼系輥子外層材是很難以利用離心鑄造法來進行製造。 [0008] 然而，專利文獻2所揭示的技術，是用來提供：即使應用離心鑄造法也不會產生偏析等之耐磨損性和耐龜裂性優異的輥軋用輥子外層材的技術，這種輥子外層材的組成分，以質量%計，含有C：1.5~3.5%、Si：1.5%以下、Mn：1.2%以下、Ni：5.5%以下、Cr：5.5~12.0%、Mo：2.0~8.0%、V：3.0~10.0%、Nb：0.5~7.0%，並且是以Nb、V以及C的含量是必須符合特定的關係，同時Nb與V之兩者的比值必須落在特定的範圍內的方式來含有Nb以及V。 [0009] 又，專利文獻3所揭示的輥子外層材的組成分，以質量%計，含有C：1.5~3.5%、Si：1.5%以下、Mn：1.2%以下、Cr：5.5~12.0%、Mo：2.0~8.0%、V：3.0~10.0%、Nb：0.5~7.0%，並且是以Nb、V以及C的含量必須符合特定的關係，同時Nb與V之兩者的比值必須落在特定的範圍內的方式來含有Nb以及V。藉由採用這種組成分，即使應用離心鑄造法來進行製造，亦可抑制生成於輥子外層材中的偏析，而可提昇耐磨損性與耐龜裂性，對於提昇熱軋的生產性有很大的貢獻。 [0010] 又，專利文獻4是揭示離心鑄造複合輥子。專利文獻4所揭示的離心鑄造複合輥子，是由外層與鑄鐵的內層或鑄鋼的內層所構成，外層的組成分，以重量%計，是含有C：1.0~3.0%、Si：0.1~3.0%、Mn：0.1~2.0%、Cr：2.0~10.0%、Mo：0.1~10.0%、V：1.0~10.0%、W：0.1~10.0%，而且符合Mo+W：10.0%以下的關係之合金成分，其餘部分是Fe和不可避免的雜質。專利文獻4所揭示的技術，係可抑制：容易引起凝集和偏析之M6
C型碳化物的結晶出現，而成為只有MC型+M7
C3
型碳化物析出的外層，因而係可利用離心鑄造法來進行製造。 [0011] 又，例如專利文獻5是揭示：輥軋輥子用離心鑄造外層材。專利文獻5所揭示的輥軋輥子用離心鑄造外層材的組成分，以質量%計，是含有C：4.5~9%、Si：0.1~3.5%、Mn：0.1~3.5%、V：18~40%，其金屬組織優選是在維氏硬度為HV550~900的基質中，以面積率計，MC碳化物是以面積率為20~60%的範圍分散於基質中的金屬組織。根據專利文獻5所揭示的技術，是積極地利用：比重較小的MC碳化物集中濃化在內面側之離心鑄造偏析現象，在離心鑄造之後，進行切削工作而只保留MC碳化物集中濃化的層，如此一來，就可以較低成本確實地形成MC碳化物較多的輥子外層。 [0012] 已知的具有極優異的耐磨損性的材料，係有超硬合金。一般而言，已知的超硬合金例如：係有如非專利文獻3所揭示的這樣，將碳化鎢(WC)與當作黏結劑的Co一起進行成形和燒結的超硬合金。 [0013] 將這種超硬合金應用於輥軋用輥子的技術，係有如專利文獻6、專利文獻7、專利文獻8、專利文獻9、專利文獻10等所揭示的。 [0014] 專利文獻6是揭示：熱軋輥子以及熱軋導引輥子用鎢碳化物基超硬合金。專利文獻6所揭示的技術之鎢碳化物基合金，鉻相對於鈷與鎳的合計量之重量比落在1/1~1/99；鈷相對於鎳的重量比落在9/1~1/9；而且鎢碳化物是88重量%以下；鈷與鎳與鉻的總和是12~65重量%。在專利文獻6中是揭示出將這種超硬合金應用在普通鋼材(線材)之熱軋用輥子的例子。 [0015] 又，專利文獻7是揭示出：由超硬合金所構成的熱間線材用輥子。根據專利文獻7所記載的技術，所使用的超硬合金，其金屬組織是由：硬質碳化物相與三元合金結合相所形成的，該硬質碳化物相是具有平均粒徑為1μm至5μm之WC(碳化鎢)，或者將WC的其中一部分利用TiC、TaC、NbC之中的一種以上來進行置換，且置換量是10重量%以下；而該三元合金結合相，則是該結合相中的Cr相對於Ni與Co的合計量是在0.30以下，且相對於全結合相是在0.05以上，再者，Ni相對於Ni與Co的合計量是0.33至0.90，分極電位相對於冷卻一般工業用水則是在0.3V以上。藉由採用這種超硬合金，可製作成耐表面粗糙性優異的熱間線材用輥子。 [0016] 又，專利文獻8所揭示的輥軋用複合輥子，是在由鋼系或鐵系材料所形成的內層的外周上，隔介著中間層而與由超硬合金所形成的外層接合在一起，該中間層是由：使用平均粒徑3μm以下的WC原料粉末所形成的超硬合金來形成的。並且優選是將中間層的WC粒子的含量，以重量比率計，予以控制在70%以下。如此一來，可製作成耐磨損性優異且強度上的可靠性很高之超硬合金製輥軋用輥子。 [0017] 又，專利文獻9所揭示的超硬合金製輥軋用輥子，其外層是利用耐磨損性優異的超硬合金來形成，並且又具備由含有WC與Ni的超硬合金所形成的中間層，因此在強度上的可靠性很高。 [0018] 此外，專利文獻10所揭示的板輥軋用超硬合金製複合輥子，是在由鋼系材料或鐵系材料所形成的內層的外周，接合著由超硬合金所形成的外層而構成的板輥軋用超硬合金製複合輥子，該外層材料的超硬合金，以R=σc(1-ν)/Eα(此處的σc是抗彎強度、ν是縱橫應變比、E是楊氏係數、α是熱膨脹係數)的數式來表示的熱衝撃係數R，是符合400以上的條件之超硬合金。如此一來，可改善輥子的耐磨損性、耐表面粗糙性，能夠減少在輥軋事故時所產生的熱龜裂，以及龜裂的進展。 ［先前技術文獻］ ［專利文獻］ [0019] 專利文獻1：日本特開平04-141553號公報 專利文獻2：日本特開平04-365836號公報 專利文獻3：日本特開平05-1350號公報 專利文獻4：日本特開平08-60289號公報 專利文獻5：國際專利申請案WO2006/030795號 專利文獻6：日本特公昭57-6502號公報 專利文獻7：日本特公昭58-39906號公報 專利文獻8：日本特開2004-243341號公報 專利文獻9：日本特開2006-175456號公報 專利文獻10：日本特開2004-268140號公報 ［非專利文獻］ [0020] 非專利文獻1：鎌田等數人合著之日立評論 Vol. 72， No. 5(1990)，p69 非專利文獻2：橋本等數人合著之製鐵研究 第338號(1990)，p62 非專利文獻3：門間改三著：「鐵鋼材料學改訂版」實教出版(1981)，p368[0002] In recent years, there has been a marked improvement in the rolling technology of steel sheets, and with this trend, the use environment of the rolls for rolling has become more severe. In particular, recently, high-strength steel sheets and thin-formed products have a large rolling load and are required to have an increasing production volume of steel sheets having excellent surface quality. [0003] Therefore, for the work rolls for cold rolling, it is required to have excellent wear resistance and high hardness for providing such wear resistance. In general, the improvement in wear resistance is largely due to the high alloying of the roller material. However, as a result of the high alloying of the roller material, sometimes the grinding machinability is deteriorated or the damage of the roller accident is increased. (The accident resistance is deteriorated. Therefore, it is necessary to use a material that has both abrasive machinability and accident resistance. In addition, in order to manufacture a steel sheet having excellent surface quality, it is necessary to adopt a uniform and fine surface property for a roller which is in direct contact with the steel sheet, in particular, a high-purity and fine microstructure. Cast iron and cast steel are used as the material of the roller. [0004] In addition, in the work rolls for hot rolling, if the roller wears and the surface is rough, it is bound to limit the roll rolling process in the material and size of the rolled product, and it is also difficult to reduce the frequency of replacement of the rolls. The decline in the durability of the roller will be one of the bottlenecks that hinder productivity improvement and hinder cost reduction. Therefore, for work rolls for hot rolling, it is required to reduce wear and reduce roughness on the surface to improve the durability of the rolls. [0005] For this reason, it is desirable to be able to improve the characteristics of the rolls for rolling used, in particular, to improve the wear resistance. The improvement of the wear resistance of the roll for rolling is an important issue that is directly related to the improvement of the quality of the steel sheet and the improvement of productivity in the production of the steel sheet. [0006] In response to such a demand for improving the wear resistance of a roll for a roll, a high-speed tool steel roll disclosed in, for example, Non-Patent Document 1 and Non-Patent Document 2 has been developed, and the composition of the outer layer thereof has been developed. It uses a composition similar to that of high-speed tool steel and is spread with a large amount of hard carbides, which can significantly improve wear resistance. Further, for example, in the composite roll for hot rolling disclosed in Patent Document 1, the outer layer is formed on the outer periphery of a steel core material by a continuous deposition thickness method. In the composite roll for hot rolling disclosed in Patent Document 1, the composition of the outer layer material is C: 1.0 to 4.0%, Si: 3.0% or less, Mn: 1.5% or less, and Cr: 2 to 10% by weight %. Mo: 9% or less, W: 20% or less, V: 2 to 15%, P: 0.08% or less, S: 0.06% or less, B: 0.0500% or less, and the rest are Fe and unavoidable impurities, and the metal thereof The structure is composed of a structure containing 5 to 30% of granular carbides and 6% or more of non-granular carbides, and the hardness of the matrix is 550 or more in Vickers hardness (Hv). Further, the outer layer material may further contain Ni: 5.0% or less, Co: 5.0% or less, and Nb: 5.0% or less. In this way, by the presence of a certain amount of non-granular carbide or more, even when cracks are generated, the crack progress can be suppressed from reaching the deep portion of the roller, thereby improving the heat crack resistance and containing the VC system. The hard carbides are also very good in abrasion resistance. [0007] Such a high-speed tool steel roll outer layer material must disperse a large amount of hard carbide in the matrix in order to improve wear resistance. However, the hard carbides formed by the high-speed tool steel component are generally lighter in specific gravity than the matrix, and segregation is likely to occur during casting. In particular, in the casting method of the representative outer layer of the roller which is excellent in productivity and economy, that is, in the centrifugal casting method, the phase having a light specific gravity is easily accumulated and segregated on the inner side by the centrifugal force. Therefore, the high speed tool steel roll outer layer is difficult to manufacture by centrifugal casting. [0008] However, the technique disclosed in Patent Document 2 is to provide a technique for rolling the roll outer layer material which is excellent in abrasion resistance and crack resistance, such as segregation, even when the centrifugal casting method is applied. The composition of the outer layer of the roll contains C: 1.5 to 3.5%, Si: 1.5% or less, Mn: 1.2% or less, Ni: 5.5% or less, Cr: 5.5 to 12.0%, and Mo: 2.0, by mass%. ~8.0%, V: 3.0~10.0%, Nb: 0.5~7.0%, and the content of Nb, V and C must conform to a specific relationship, and the ratio of Nb to V must fall within a specific range. The way inside contains Nb and V. Further, the composition of the outer layer of the roller disclosed in Patent Document 3 contains, by mass%, C: 1.5 to 3.5%, Si: 1.5% or less, Mn: 1.2% or less, and Cr: 5.5 to 12.0%. Mo: 2.0 to 8.0%, V: 3.0 to 10.0%, Nb: 0.5 to 7.0%, and the content of Nb, V, and C must conform to a specific relationship, and the ratio of Nb to V must fall within a specific relationship. The way to range contains Nb and V. By using such a composition, even if the centrifugal casting method is used for manufacturing, segregation generated in the outer layer of the roll can be suppressed, and wear resistance and crack resistance can be improved, and the productivity of hot rolling can be improved. Great contribution. Further, Patent Document 4 discloses a centrifugally cast composite roller. The centrifugally cast composite roller disclosed in Patent Document 4 is composed of an outer layer and an inner layer of cast iron or an inner layer of cast steel, and the composition of the outer layer, in terms of % by weight, contains C: 1.0 to 3.0%, Si: 0.1. ~3.0%, Mn: 0.1~2.0%, Cr: 2.0~10.0%, Mo: 0.1~10.0%, V: 1.0~10.0%, W: 0.1~10.0%, and in line with Mo+W: 10.0% or less The alloy composition, the rest is Fe and inevitable impurities. The technique disclosed in Patent Document 4 suppresses the occurrence of crystallization of M 6 C-type carbide which is liable to cause aggregation and segregation, and becomes an outer layer in which only MC type + M 7 C 3 type carbide is precipitated, and thus it is possible to use centrifugation. Casting method to manufacture. Further, for example, Patent Document 5 discloses that the outer layer of the rolled roll is centrifugally cast. The composition of the centrifugally cast outer layer material for a rolled roll disclosed in Patent Document 5 contains C: 4.5 to 9%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, and V: 18% by mass%. 40%, the metal structure is preferably in a matrix having a Vickers hardness of HV550 to 900. The MC carbide is a metal structure dispersed in a matrix in an area ratio of 20 to 60% in terms of area ratio. According to the technique disclosed in Patent Document 5, the centrifugal casting segregation phenomenon in which the MC carbide concentrate having a small specific gravity is concentrated and concentrated on the inner surface side is performed, and after the centrifugal casting, the cutting work is performed and only the MC carbide concentration is retained. In this way, the outer layer of the roller having more MC carbide can be reliably formed at a lower cost. [0012] Known materials having extremely excellent wear resistance are superhard alloys. In general, a known superhard alloy is, for example, a superhard alloy in which tungsten carbide (WC) is formed and sintered together with Co as a binder as disclosed in Non-Patent Document 3. [0013] The technique of applying such a superhard alloy to a roll for rolling is disclosed in Patent Document 6, Patent Document 7, Patent Document 8, Patent Document 9, Patent Document 10, and the like. [0014] Patent Document 6 discloses a tungsten carbide-based superhard alloy for a hot rolling roll and a hot rolling guide roll. In the tungsten carbide-based alloy of the technique disclosed in Patent Document 6, the weight ratio of chromium to the total amount of cobalt and nickel falls between 1/1 and 1/99; and the weight ratio of cobalt to nickel falls at 9/1 to 1 /9; and the tungsten carbide is 88% by weight or less; the sum of cobalt and nickel and chromium is 12 to 65% by weight. Patent Document 6 discloses an example in which such a cemented carbide is applied to a roll for hot rolling of a general steel material (wire). Further, Patent Document 7 discloses a roller for a hot wire rod made of a cemented carbide. According to the technique described in Patent Document 7, the superhard alloy used has a metal structure formed by a combination of a hard carbide phase and a ternary alloy having an average particle diameter of 1 μm to 5 μm. WC (tungsten carbide), or a part of WC is replaced by one or more of TiC, TaC, and NbC, and the substitution amount is 10% by weight or less; and the ternary alloy bonded phase is the combined phase The total amount of Cr relative to Ni and Co is 0.30 or less, and is 0.05 or more with respect to the total bonded phase. Further, the total amount of Ni with respect to Ni and Co is 0.33 to 0.90, and the polarization potential is generally relative to cooling. Industrial water is above 0.3V. By using such a superhard alloy, it is possible to produce a roll for a hot wire which is excellent in surface roughness resistance. Further, the composite roll for rolling disclosed in Patent Document 8 is an outer layer formed of a cemented carbide layer on the outer periphery of an inner layer formed of a steel-based or iron-based material via an intermediate layer. Bonded together, the intermediate layer is formed of a superhard alloy formed using a WC raw material powder having an average particle diameter of 3 μm or less. Further, it is preferable that the content of the WC particles of the intermediate layer is controlled to 70% or less by weight. In this way, it is possible to produce a roller for a super-hard alloy rolling which is excellent in abrasion resistance and high in reliability. Further, the roll for a superalloy roll disclosed in Patent Document 9 is formed of a superhard alloy excellent in abrasion resistance and further formed of a superhard alloy containing WC and Ni. The middle layer is therefore highly reliable in terms of strength. [0018] Further, the super-hard alloy composite roller for sheet rolling disclosed in Patent Document 10 is an outer layer formed of a cemented carbide material or an iron-based material, and is bonded to an outer layer formed of a cemented carbide. The super-hard alloy composite roller for the plate rolling is composed of the superhard alloy of the outer layer material, and R=σc(1-ν)/Eα (where σc is the bending strength, ν is the aspect ratio, E It is a thermal hardness coefficient R expressed by a numerical formula of Young's modulus and α is a thermal expansion coefficient, and is a superhard alloy which satisfies the condition of 400 or more. In this way, the wear resistance and surface roughness of the roller can be improved, and the thermal cracking generated during the rolling accident and the progress of the crack can be reduced. [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 04-141553 (Patent Document No. Hei. Japanese Patent Laid-Open Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. Japanese Unexamined Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. 2004-175. Hitachi Review Vol. 72, No. 5 (1990), p69 Non-Patent Document 2: Hashimoto et al., No. 338 (1990), p62 Non-Patent Document 3: Change between doors: Iron and Steel Materials Science Revision Edition" Practical Education Publishing (1981), p368
［發明所欲解決的技術課題］ [0021] 然而，專利文獻1所揭示的技術，因為是在鋼製芯材的外周，利用連續堆積法來形成外層，因而存在著：生產性低，且成本較高的問題。又，專利文獻2、3所揭示的技術，主要是將Nb、V以及C的含量限定在特定範圍，並且使MC型碳化物均勻地分散，以資謀求提昇耐磨損性與耐龜裂性。但是，實際上，含有許多Cr和Mo之M7
C3
型碳化物和M6
C型碳化物也有相當多的量存在，如果想要更進一步提昇特性的話，只從將MC型碳化物做均勻分散的觀點來考量的話，還是不夠的。此外，專利文獻4所揭示的技術，為了減少容易引起凝集和偏析的M6
C型碳化物的結晶出現，乃將Mo+W的含量限定為10.0%以下，如此一來，就可以利用離心鑄造法來製造輥子外層材。然而，限制Mo、W的含量的結果所衍生的問題，則是無法符合近年來之業界所要求之對於耐磨損性的更進一步的提昇。 [0022] 此外，使用離心鑄造法來製造輥軋用輥子的話，因Mo、V、W之類的碳化物形成元素的增量而形成的碳化物較輕，因而所形成的碳化物容易集積在內面側，而凝集在與內層之間的境界處，因而會有導致境界的接合強度變差之虞慮。 [0023] 又，專利文獻5所揭示的技術，雖然可提昇輥子的耐磨損性，但不僅必須實施除去MC型碳化物變少之外面側領域的作業，而且良率非常低，會有喪失離心鑄造法原本的高生產性與低成本的優勢之問題。 [0024] 又，使用超硬合金之專利文獻6和專利文獻7所揭示的技術，是以線材輥軋用的小型輥子作為對象，因此，難以將這種技術直接適用到冷軋用輥子和熱軋用輥子之類的大型輥子的製造上。而且，與離心鑄造製品相較，必須實施昂貴的製程也就是HIP處理，因此，雖然說是小型製品，但是卻有製造成本偏高的問題。 [0025] 使用超硬合金來作為板輥軋用輥子的外層材之專利文獻8、專利文獻9、以及專利文獻10所揭示的技術，都是想定為：以燒結暨HIP法來成形出外層材，因此，存有製造成本極高的問題。此外，這些的技術，係使用軟質的Co和Ni來作為結合劑，因此也會有：在輥軋時很容易生成凹痕瑕疵(凹部)之問題，無法達到實用化。 [0026] 本發明是想要解決上述習知技術的問題，其目的是要以較低廉的成本來提供：與傳統技術相較可顯著地提昇耐磨損性之耐磨損性優異的輥子外層材以及使用該輥子外層材之輥軋用複合輥子。 ［用以解決課題之技術方案］ [0027] 本發明人等，為了達成上述的技術課題，乃針對於：能夠利用生產性暨經濟性都優異的離心鑄造法，來製造具有與超硬合金同等程度之極高耐磨損性的輥軋用輥子的條件，不斷努力地加以檢討。其結果，找到了一種創見，就是：在進行離心鑄造時，如果能夠利用作用在熔融金屬液以及結晶析出相的離心力，來使得硬質碳化物密集和濃化在輥子的外表面側的話，即可顯著地提昇以離心鑄造法製的輥軋用輥子的耐磨損性。此外，又更進一步的檢討，而找到了另一種創見，就是：在離心鑄造時，如果想要使得硬質的碳化物密集和濃化在輥子的外表面側的話，只要能夠找到：可從正在受到離心力作用的液相中，讓比重較液相更大的碳化物作為初晶而結晶出來的條件即可。 [0028] 換言之，正在受到離心力作用的液相中，如果有較液相的比重更大的碳化物晶析出來的話，將會有朝外周方向的離心力作用在碳化物身上。這個時候，如果碳化物與其周圍的γ相不產生共晶凝固，而是由碳化物作為初晶直接從液相中晶析出來的話，碳化物的周圍還是處在液相狀態，因此碳化物就可很容易往外周側移動和集積。 [0029] 因此，乃著眼於比重較大的W，來作為可符合這種條件之碳化物形成元素，而且想到要含有較多量的W，不斷反覆地進行各種澆鑄實驗，並且活用狀態圖的計算等，因而找到了下列兩種創見： (1)將含有多量之比重較大的W的W-Co基合金，熔製成含有0.6質量%以上的C之熔融金屬液的話，W濃化後的M6
C型碳化物將作為初晶，而晶析出來。 (2)如果將這種W-Co基合金熔融金屬液進行離心鑄造的話，即可獲得：作為初晶而晶析出來的M6
C型碳化物，將會高濃度地偏析在外層材的外表面側的組織形態。 [0030] 此外，也找到一種創見，就是：如果使用Fe基合金來當作基質合金的話，將可促進W系共晶碳化物的形成，而會阻礙M6
C型碳化物晶析出來作為初晶。此外，也找到多種創見，就是：如果使用可提高碳的活性之 W-Co基合金來當作基質合金的話，將可減少W系共晶碳化物的形成，而會在熔融金屬液中晶析出來大量的W濃化後的M6
C型碳化物作為初晶；此外，如果C含量低於0.6質量%的話，無法晶析出來M6
C型碳化物作為初晶，另一方面，如果C含量高於3質量%的話，液相線溫度變得太高，不僅難以熔解和鑄造之外，而且非常容易龜裂的MC型碳化物、M2
C型碳化物將會成長而變粗大化，因此，很容易導致輥子斷裂。 [0031] 本發明是基於以上的各種創見，進一步加以檢討而開發完成的。換言之，本發明的要旨係如下所述。 (1) 一種輥軋用輥子外層材，其係W-Co基合金製輥軋用輥子外層材，其組成分是W含量從輥子外周側往內周側沿著徑向降低之具有含量斜度的組成分，而在相當於輥軋使用時的最大徑的位置之外層材表面的組成分，以質量%計，係含有：W：25~70%、Co：5~45%、C：0.6~3.5%、Si：0.05~3%、Mn：0.05~3%、Mo：1~15%，而其餘部分則是不可避免的雜質。 (2) 一種如(1)所述的輥軋用輥子外層材，其中，除了前述組成分之外，又含有以質量%計，從Fe：5~40%、Cr：0.1~10%、V：0.1~6%、Nb：0.1~3%之中所選出的一種或兩種以上。 (3) 一種如(1)或(2)所述的輥軋用輥子外層材，其中，除了前述組成分之外，又含有以質量%計，Ni：0.05~3%。 (4) 一種如(1)或(2)或(3)所述的輥軋用輥子外層材，其中，前述輥軋用輥子外層材是離心鑄造製的。 (5) 一種輥軋用複合輥子，其係由外層、與該外層融合一體化的內層所構成的輥軋用複合輥子，前述外層是如(1)或(2)或(3)之任一項所述之輥軋用輥子外層材。 (6) 一種輥軋用複合輥子，其係由外層、與該外層融合一體化的中間層、與該中間層融合一體化的內層所構成的輥軋用複合輥子，前述外層是如(1)或(2)或(3)之任一項所述之輥軋用輥子外層材。 (7) 一種如(5)或(6)所述的輥軋用複合輥子，其中，前述外層是離心鑄造製的。 ［發明之效果］ [0032] 根據本發明，係可以便宜的價格且很容易製造出：適合作為熱軋用或冷軋用輥子使用之耐磨損性明顯優異的輥軋用輥子，尤其是以離心鑄造法製造的輥軋用輥子，而可達成產業上特優的效果。[Technical Problem to be Solved by the Invention] However, in the technique disclosed in Patent Document 1, since the outer layer is formed on the outer circumference of the steel core material by the continuous deposition method, there is a low productivity and a cost. Higher problem. Further, the techniques disclosed in Patent Documents 2 and 3 mainly limit the content of Nb, V, and C to a specific range, and uniformly disperse MC type carbides in order to improve wear resistance and crack resistance. . However, in fact, M 7 C 3 type carbides and M 6 C type carbides containing many Cr and Mo are also present in considerable amounts, and if it is desired to further improve the characteristics, only the MC type carbides are made uniform. It is not enough to consider the scattered views. Further, in the technique disclosed in Patent Document 4, in order to reduce the occurrence of crystallization of M 6 C-type carbide which is liable to cause aggregation and segregation, the content of Mo + W is limited to 10.0% or less, and thus, centrifugal casting can be utilized. The method is to manufacture a roller outer layer. However, the problem derived from the result of limiting the content of Mo and W is that it cannot meet the further improvement of wear resistance required by the industry in recent years. Further, when the roll for rolling is produced by the centrifugal casting method, the carbide formed by the increase in the carbide forming elements such as Mo, V, and W is light, and thus the formed carbide is easily accumulated. The inner side is agglomerated at the boundary between the inner layer and the inner layer, and thus there is a concern that the joint strength of the boundary is deteriorated. Further, in the technique disclosed in Patent Document 5, although the wear resistance of the roller can be improved, it is not only necessary to perform work in the field of removing the surface of the MC-type carbide, and the yield is extremely low, and there is a loss. The original high productivity and low cost advantages of centrifugal casting. Further, the technique disclosed in Patent Document 6 and Patent Document 7 of the super-hard alloy is targeted for a small-sized roller for wire rolling, and therefore it is difficult to directly apply this technique to the roller and heat for cold rolling. The manufacture of large rolls such as rolls for rolling. Moreover, compared with the centrifugally cast product, an expensive process, that is, a HIP process, must be performed. Therefore, although it is a small product, there is a problem that the manufacturing cost is high. [0025] The techniques disclosed in Patent Document 8, Patent Document 9, and Patent Document 10, which use a superhard alloy as an outer layer material for a roll for sheet rolling, are all intended to form an outer layer material by a sintering and HIP method. Therefore, there is a problem that the manufacturing cost is extremely high. Further, since these techniques use soft Co and Ni as a binder, there is a problem that dents (concave portions) are easily formed during rolling, and practical use cannot be achieved. The present invention is intended to solve the above-mentioned problems of the prior art, and an object thereof is to provide an outer layer of a roller excellent in abrasion resistance which can remarkably improve wear resistance as compared with the conventional art. And a composite roll for rolling using the outer layer of the roll. [Technical Solution to Solve the Problem] The inventors of the present invention have been able to manufacture a product which is equivalent to a superhard alloy by a centrifugal casting method excellent in both productivity and economy. The conditions of the roller for rolling, which is extremely high in abrasion resistance, are constantly being reviewed. As a result, a finding was found that, in the centrifugal casting, if the centrifugal force acting on the molten metal liquid and the crystal precipitation phase can be utilized to make the hard carbide dense and concentrated on the outer surface side of the roller, The wear resistance of the roll for rolling by the centrifugal casting method is remarkably improved. In addition, after further review, another finding was found: in centrifugal casting, if you want to make hard carbide dense and concentrated on the outer surface side of the roller, as long as you can find: In the liquid phase in which the centrifugal force acts, the carbide having a larger specific gravity than the liquid phase may be crystallized as a primary crystal. [0028] In other words, in the liquid phase which is subjected to centrifugal force, if carbide having a larger specific gravity than the liquid phase is crystallized, centrifugal force in the outer circumferential direction acts on the carbide. At this time, if the carbide does not produce eutectic solidification with the surrounding γ phase, but the carbide is directly crystallized from the liquid phase as the primary crystal, the periphery of the carbide is still in the liquid phase, so the carbide is It can be easily moved and accumulated on the outer circumference. [0029] Therefore, attention is paid to W, which has a large specific gravity, as a carbide-forming element that can satisfy such a condition, and it is thought that a large amount of W is required, and various casting experiments are continuously performed repeatedly, and the calculation of the state diagram is utilized. Then, the following two kinds of ideas were found: (1) When a W-Co-based alloy containing a large amount of W having a large specific gravity is melted to a molten metal liquid containing 0.6% by mass or more of C, the concentration of W is concentrated. The M 6 C type carbide will be crystallized as a primary crystal. (2) If the W-Co-based alloy molten metal solution is subjected to centrifugal casting, it is obtained that the M 6 C-type carbide crystallized as the primary crystal is segregated at a high concentration outside the outer layer material. The tissue morphology on the surface side. [0030] In addition, a finding is also found that if a Fe-based alloy is used as a matrix alloy, the formation of W-based eutectic carbides can be promoted, and the crystallization of M 6 C-type carbides can be hindered as an initial crystal. In addition, a number of original ideas have been found, that is, if a W-Co-based alloy capable of increasing the activity of carbon is used as a matrix alloy, the formation of W-based eutectic carbides can be reduced, and crystallization is performed in molten metal. A large amount of M 6 C-type carbide after W concentration is used as the primary crystal; in addition, if the C content is less than 0.6% by mass, the M 6 C-type carbide cannot be crystallized as the primary crystal, and on the other hand, if C When the content is more than 3% by mass, the liquidus temperature becomes too high, and it is not only difficult to melt and cast, but MC-type carbides and M 2 C-type carbides which are very likely to be cracked will grow and become coarser. Therefore, it is easy to cause the roller to break. [0031] The present invention has been developed based on the above various findings and further reviewed. In other words, the gist of the present invention is as follows. (1) A roll outer layer material for rolling, which is a W-Co-based alloy roll outer layer material, and has a compositional component having a W content which decreases in the radial direction from the outer peripheral side to the inner peripheral side of the roll. The composition of the surface of the layer other than the position of the maximum diameter at the time of rolling use, in mass%, contains: W: 25 to 70%, Co: 5 to 45%, C: 0.6 ~3.5%, Si: 0.05~3%, Mn: 0.05~3%, Mo: 1~15%, and the rest are inevitable impurities. (2) The outer layer material for a roll for rolling according to (1), which, in addition to the aforementioned component, contains, by mass%, from Fe: 5 to 40%, Cr: 0.1 to 10%, V : 0.1 to 6%, Nb: 0.1 to 3% of one or more selected. (3) The outer layer material for a roll for rolling according to (1) or (2), further comprising, in addition to the aforementioned component, Ni: 0.05 to 3% by mass. (4) The roll outer layer material for rolling according to (1), wherein the roll outer material for rolling is centrifugally cast. (5) A composite roll for rolling, which is a composite roll for rolling which is composed of an outer layer and an inner layer which is integrated with the outer layer, and the outer layer is as (1) or (2) or (3) An outer layer of a roller for rolling as described. (6) A composite roll for rolling, which is a composite roll for rolling formed by an outer layer, an intermediate layer integrated with the outer layer, and an inner layer which is integrated with the intermediate layer, and the outer layer is as (1) The rolled outer layer material for rolling according to any one of (2) or (3). (7) A composite roll for rolling according to (5) or (6), wherein the outer layer is centrifugally cast. [Effects of the Invention] According to the present invention, it is possible to easily manufacture a roll for rolling which is excellent in abrasion resistance which is suitable for use as a roll for hot rolling or cold rolling, particularly at a low price, especially The roller for rolling manufactured by the centrifugal casting method can achieve an industrially superior effect.
[0034] 本發明的輥軋用輥子外層材，是離心鑄造製的。此處所稱的「離心鑄造製輥軋用輥子外層材」係指：採用以往被作為輥軋用輥子的製造方法使用的離心鑄造法來製造後的狀態之輥軋用輥子外層材之意。使用離心鑄造法來製造的輥軋用輥子外層材(「離心鑄造製」的輥軋用輥子外層材)，與使用其他的製造方法所製造的輥軋用輥子彼此之間，就「物」的本身而言，就有很明顯的區別，而且想要利用構造或特性來界定該「離心鑄造製」的輥軋用輥子外層材，需要耗費很大的勞力，因此不合實際。 [0035] 本發明的輥軋用輥子外層材是W-Co基合金製，其組成分是W含量從輥子外周側往內周側沿著徑向降低之具有含量斜度的組成分，而在相當於輥軋使用時的最大徑的位置之外層材表面的組成分，以質量%計，含有W：25~70%、Co：5~45%，並且含有C：0.6~3.5%、Si：0.05~3%、Mn：0.05~3%、Mo：1~15%，其餘部分是不可避免的雜質。此外，上述的組成分，即使是在：相當於對外層材總體積而言，至少為外表面側之20%的體積量之徑向位置處，例如：若為外徑250mm、內徑140mm之套筒的話，則是從相當於輥軋使用時的最大徑位置起算朝內周側沿著徑方向至少9mm的位置處，也能夠符合這種組成分的條件為宜。 [0036] 再者，此處所稱的「相當於輥軋使用時的最大徑的位置處的外層材表面」，係指：將澆鑄時形成在外層材的外表面的層(因為熔融金屬液與鑄模接觸時受到急速冷卻而凝固的部位等)予以車削除去，相當於剛開始可供輥軋使用時的製品輥子徑的最大徑的位置之外層材表面而言，換言之，相當於可作為製品(輥子外層材)來使用時的最大徑的位置之外層材表面。此外，所稱的「相當於輥軋使用時的最大徑的位置之外層材表面」係包含：將澆鑄時形成在外層材的外表面的層予以車削除去，而從相當於剛開始可供輥軋使用的製品輥子徑的最大徑的位置的外層材表面起算朝內周側，對於外層材總體積而言，至少佔據體積量20%之位於外表面側的範圍。 [0037] 又，對於外層材表面的組成分之分析，係可採用：利用螢光X射線分析、發光分光分析之類的機器分析方法，或者亦可利用破壞性檢查的方式，從包含該外層材表面的位置採取：在輥子徑向上的厚度為小於10mm的塊狀試料，再將該試料進行化學分析的方法。 [0038] 首先，說明限定本發明的輥軋用輥子外層材的組成分之理由。以下，有關於組成分的質量%，都單純只以%來記載。 [0039] C：0.6~3.5% C係可與W、以及Mo、Cr、V、Nb之類的碳化物形成元素結合而形成硬質碳化物，具有提昇耐磨損性的作用之元素。隨著C含量的多寡，碳化物的形態和晶析量以及晶析溫度都會改變。C含量大於等於0.6%的話，M6
C型碳化物將會作為初晶而晶析出來，而在離心鑄造時可獲得M6
C型碳化物偏析在外表面側的組織形態，而可提昇耐磨損性。此外，C含量低於0.6%的話，作為初晶而晶析出來的M6
C型碳化物量不足而導致耐磨損性變差。另一方面，C含量很多而超過3.5%的話，不僅難以當作外層材來進行製造，並且會生成非常容易龜裂的M2
C碳化物和MC碳化物而變得粗大化，因而在進行輥軋時，將很容易發生輥子破壞。基於上述的理由，乃將C含量限定在0.6~3.5%的範圍。再者，合宜的C含量是1.0~3.0%。更好的C含量是1.2~2.8%。 [0040] Si：0.05~3% Si是可當作脫氧劑來作用並且也具有基質強化作用的元素。想要獲得這種效果，Si含量必須在0.05%以上。另一方面，Si含量超過3%的話，不僅效果已趨飽和，而且會出現片狀的石墨，而導致韌性變差。因此，乃將Si含量限定在0.05~3%的範圍。此外，合宜的Si含量是0.1~2%。更好的Si含量是0.2~1.8%。 [0041] Mn：0.05~3% Mn是可藉由形成MnS而將S予以固定下來，而具有可將S對於材質造成的不良影響予以無害化的作用之元素。又，Mn可固溶於基質中而對於提昇淬火硬化性有所幫助。想要獲得這種效果的話，Mn含量必須是0.05%以上。另一方面，Mn含量超過3%的話，不僅上述的效果趨於飽和，而且也會導致材質變差。因此，乃將Mn含量限定在0.05~3%的範圍。此外，合宜的Mn含量是0.1~1%。更好的Mn含量是0.2~0.8%。 [0042] Mo：1~15% Mo是可與C結合而形成碳化物之碳化物形成元素，在本發明中尤其是可固溶於W濃化的初晶碳化物亦即硬質的M6
C型碳化物中，可將碳化物予以強化，而具有增加輥子外層材的耐破壞性的作用。又，Mo係可在熱處理時提昇淬火硬化性，對於增加輥子外層材的硬度有所幫助。此外，Mo是比Co更重的元素，也具有：不會妨礙初晶碳化物朝向外表面側進行離心分離，或者促進初晶碳化物朝向外表面側進行離心分離的效果。想要獲得這些效果的話，Mo含量必須是1%以上。另一方面，Mo含量過多而超過15%的話，將會出現以Mo為主體之又硬又脆的碳化物，導致耐磨損性變差。因此，乃將Mo含量限定在1~15%的範圍。此外，合宜的Mo含量是2~10%。更好的Mo含量是4~10%。 [0043] W：25~70% W是在本發明中最重要的元素，係設定成含量高達25%以上的合金組成分。如此一來，可大量地晶析出來W濃化後的硬質M6
C型碳化物來作為初晶，因而可製作出耐磨損性明顯提昇之輥軋用輥子外層材。此外，W含量若低於25%的話，就難以獲得符合本發明之目的之耐磨損性優異的輥軋用輥子外層材。另一方面，W含量超過70%的話，不僅M6
C型碳化物變粗大化而且變脆，熔融金屬液的融點上昇而變得難以熔解、鑄造等。因此，乃將W含量限定在25~70%的範圍。此外，合宜的W含量是30~65%。更好的W含量是35~55%。 [0044] Co：5~45% Co與W都是在本發明中的重要元素。藉由含量大量的Co與W，可以增加C的活量，可以促進出現許多W濃化後的硬質碳化物(M6
C型或M2
C型和MC型等)來作為初晶，對於提昇輥軋用輥子外層材的耐磨損性有所幫助。想要獲得這種效果的話，Co含量必須是5%以上。另一方面，Co含量太多而超過45%的話，γ相將趨於穩定化，基質變成軟質，若當作輥軋用輥子來使用的話，將會導致發生許多的凹痕瑕疵(凹部)，耐磨損性明顯變差。因此，乃將Co含量限定在5~45%的範圍。此外，合宜的Co含量是10~40%。更好的Co含量是15~35%。 [0045] 上述的成分是基本的成分，除了基本組成分之外，亦可因應必要選擇性地又含有：從Fe：5~40%、Cr：0.1~10%、V：0.1~6%、Nb：0.1~3%之中所選出的一種或兩種以上，或者又含有Ni：0.05~3%，或者同時含有從Fe：5~40%、Cr：0.1~10%、V：0.1~6%、Nb：0.1~3%之中所選出的一種或兩種以上以及Ni：0.05~3%。 [0046] 從Fe：5~40%、Cr：0.1~10%、V：0.1~6%、Nb：0.1~3%之中所選出的一種或兩種以上 Fe、Cr、V、Nb都是碳化物形成元素，係可固溶於碳化物而具有強化碳化物的作用之元素，可因應必要而選擇性地含有其中一種或兩種以上。 [0047] Fe除了可固溶於碳化物，也同時可固溶於基質，對於基質的強化有所幫助，具有：作為輥軋用輥子使用時，可防止形成凹痕瑕疵(凹部)的作用。想要獲得這種效果的話，合宜的Fe含量是5%以上。另一方面，Fe含量超過40%的話，作為初晶而出現的硬質M6
C型碳化物量將會減少，脆弱的M3
C型碳化物將會增加，耐磨損性將會變差。因此，若想含有Fe的話，係將Fe含量限定在5~40%的範圍為宜。此外，更好的Fe含量是10~35%。更優的Fe含量是12~30%。 [0048] 關於在基質中含有Fe即可強化W-Co基合金的基質的機轉(理由)，在目前尚未明確，可能是因為產生了：Co所達成的γ相穩定化作用與Fe所達成的α相穩定化作用互相抵消，其結果將使得基質的強度上昇，或者是因為Fe所導致的α相穩定化作用比較大，基質變成硬質的麻田散鐵或變韌鐵組織，或者又在這種基質中出現了已析出細微碳化物的組織，之類的基質強化現象的緣故。 [0049] Cr是強力的碳化物形成元素，主要是可形成共晶碳化物，並且具有可提昇所形成的碳化物的強度之效果。共晶碳化物將會結晶出現於初晶也就是M6
C型碳化物的間隙中，因此，就結果而言，具有可強化M6
C型碳化物的間隙之作用。又，Cr也具有可減少石墨的出現之作用。W-Co基合金是因為C的活量係數很高，所以很容易出現石墨，石墨出現的話，韌性將會變差。為了抑制石墨的出現以資謀求能夠穩定地當作輥軋用輥子來使用，在本發明中是因應必要來含有Cr為宜。想要獲得這種效果的話，Cr的合宜含量是0.1%以上。另一方面，Cr含量超過10%的話，Cr系共晶碳化物將會大量出現而導致韌性變差。因此，若想要含有Cr的話，將Cr含量限定在0.1~10%的範圍為宜。此外，更好的Cr含量是在1~8%。更優的Cr含量是在1.5~7%。 [0050] V是可與C結合而形成硬質的VC(包含Mo、Nb、Cr、W等在內的MC型碳化物)之元素，所形成的MC型碳化物係作為初晶而結晶出來，而成為W濃化後的M6
C型碳化物的晶出核，可促進M6
C型碳化物的出現，並且具有可使細微的M6
C型碳化物高密度地分散之作用。想要獲得這種效果的話，將V含量設在0.1%以上為宜。另一方面，V含量太多而超過6%的話，即使是含有很多W，低比重的V系MC型碳化物還是會增加，而且變粗大化，在進行離心鑄造時，將會被離心分離到輥子外層材的內面側。因此，在外面側將會因為硬質的M6
C型碳化物量不足，而導致當作輥子外層材使用時的耐磨損性變差。此外，被離心分離到內面側的V系MC型碳化物太多的話，與輥子內層或與中間層之間的境界強度將會變差。因此，若想要含有V的話，是將V含量限定在0.1~6%的範圍為宜。此外，更好的V含量是在1~5%。更優的V含量是在1.5~4%。 [0051] Nb與C的結合力極高，是強力的碳化物形成元素，很容易與V或W形成複合碳化物。這種Nb與V或W的複合碳化物，將成為當作初晶而晶析出來之W濃化後的M6
C型碳化物的晶出核，可促進M6
C型碳化物的出現，而且也具有可使細微的M6
C型碳化物高密度分散的作用。想要獲得這種效果的話，Nb的含量必須是在0.1%以上。另一方面，Nb含量過多而超過3%的話，將會形成低密度的Nb系MC型碳化物且變粗大化，在進行離心鑄造時，碳化物很容易被離心分離到輥子外層材的內面側，並且外層材內面側的MC型碳化物的量會增加。而且被離心分離到外層材內面側的MC型碳化物的量太多的話，與輥子內層或與中間層之間的境界強度將會變差，因此，內面側的品質將會變差。因此，若想要含有Nb的話，將Nb含量限定在0.1~3%的範圍為宜。此外，更好的Nb含量是在0.5~2%。更優的Nb含量是在0.6~1.8%。 [0052] Ni：0.05~3% Ni是具有可提昇淬火硬化性的作用之元素，例如：如果想要解決大型輥子的淬火硬化性不足的問題的話，可因應必要來含有。想要獲得這種效果的話，將Ni含量設在0.05%以上為宜。此外，如果只是如同雜質般的程度之低於0.05%的話，則無法發揮其效果。另一方面，Ni含量超過3%的話，γ相將會趨於穩定化，而變得無法確保所期望的淬火硬化性。因此，若想要含有Ni的話，將Ni含量設定在0.05~3%的範圍為宜。更好的Ni含量是在0.1~2.5%。 [0053] 上述的成分以外之其餘部分是不可避免的雜質。不可避免的雜質係可舉出：P、S、N、B。此外，P會偏析於粒界而造成導致材料脆化之類的不良影響，因此，作為雜質而言，最好是儘量減少，但如果是在0.05%以下的話，則可許容其存在。又，S也是與P同樣地會偏析於粒界，而造成導致材料脆化之類的不良影響，因此，作為雜質而言，最好是儘量減少，但如果是在0.05%以下的話，其中的一部分將會與Mn進行化合而變成硫化物系夾雜物存在，而成為無害化，因此可被許容。此外，如果是一般通常的熔解方法的話，將會有0.01~0.1%程度的N混入作為雜質。但是，其含量只有這種程度的話，並不會對於本發明的效果產生影響。然而，N會有可能在複合輥子之外層與中間層或與內層的境界上產生氣泡缺陷，因此將N含量限定在低於0.07%為宜。此外，B有時候會從熔解原料的回收廢料或從鑄造用助熔劑混入而被視為不可避免的雜質元素含有B。B會固溶在碳化物或基質中而改變碳化物的性質，或者固溶於基質中而對於基質的淬火硬化性造成影響，因而導致製品品質的不穩定。因此，B含量是要極力減少為宜，但如果是0.1%以下的話，則對於本發明的效果不會造成不良影響。因此，上述的不可避免的雜質元素，是將其合計含量予以調整為低於1%為宜。 [0054] 其次，說明本發明輥軋用輥子外層材之合宜的製造方法。 [0055] 在本發明中，基於生產性、以及製造成本的觀點考量，是將輥軋用輥子外層材，採用使鑄造用鑄模進行旋轉的形式之離心鑄造法來進行製造。如此一來，可以較低廉的價格來製造耐磨損性優異的輥軋用輥子外層材。 [0056] 首先，是在旋轉中的鑄模內注入具有上述的輥子外層材組成分的熔融金屬液達到既定的厚度，來進行離心鑄造，而製成輥軋用輥子外層材。此外，通常為了要保護鑄模，一般的作法是在鑄模內面，披覆著以鋯石等作為主材料的耐火物。此外，在本發明中，是以將離心力達到120~250G的方式來調整旋轉數之後，進行離心鑄造為宜。藉由賦予高離心力，可提高在外表面側之大比重的硬質碳化物的分散密度。 [0057] 在本發明中，亦可將所製得的輥軋用輥子外層材，當作單體的套筒，並且將軸材嵌合在該套筒中而製作成輥軋用輥子。又，所製得的輥軋用輥子外層材，亦可在其內側設置融合成一體化的中間層，而成為具有中間層的套筒，並且將軸材嵌合在該套筒中而製作成輥軋用輥子。此外，中間層，是在輥子外層材的凝固途中或完全凝固之後，將鑄模進行旋轉，同時注入具有中間層組成分的熔融金屬液，藉由進行離心鑄造而形成的為宜。中間層的材料係可舉出例如：石墨鋼、C含量為1~2質量%之高碳鋼、亞共晶鑄鐵等。此外，這些輥軋用輥子的軸材，並未特別地限定，是採用另外單獨製造的鍛鋼品(軸)、鑄鋼品(軸)、鑄鐵品(軸)為宜。 [0058] 此外，在本發明中，既可以製作成：將上述的輥軋用輥子外層材當作外層，而由該外層與融合一體化的內層所形成的複合輥子，也可以製作成：將上述的輥軋用輥子外層材當作外層，而由該外層與融合一體化的中間層、與該中間層融合一體化的內層所形成的複合輥子。 [0059] 在形成中間層的情況下，是在輥子外層材凝固途中或完全凝固之後，將鑄模旋轉的同時，注入具有中間層組成分的熔融金屬液，進行離心鑄造為宜。此外，中間層材係採用：石墨鋼、C含量為1~2質量%的高碳鋼、亞共晶鑄鐵等為宜。中間層與外層融合成一體，外層的成分將會在10~90%程度的範圍內混入中間層。基於抑制外層成分混入到內層的混入量之觀點考量，最好是預先就儘量地減少外層的成分混入到中間層的混入量。 [0060] 一般而言，是在外層或中間層完全凝固之後，停止鑄模的旋轉，並且將鑄模豎立起來之後，才將內層材進行靜置鑄造來形成內層。此處，用來進行靜置鑄造的內層材，係採用：鑄造性與機械性質優異的球狀石墨鑄鐵、芋蟲狀石墨鑄鐵(CV鑄鐵)等為宜。此外，如果是不具有中間層，而是由外層與內層融合成一體的複合輥子的話，外層材的成分有1~10%的程度混入到內層的情況很多。外層材中所含的W、Cr、V等，是強力的碳化物形成元素，如果這些元素混入到內層的話，將會導致內層變得脆弱。因此，在本發明中，是將外層成分之混入到內層的混入率抑制在低於5%為宜。 [0061] 上述的輥軋用輥子外層材、輥軋用複合輥子，在鑄造後，又實施熱處理為宜。熱處理，優選是實施一次以上之先加熱到1000~1200℃並且保持5~40小時之後，放置在爐內冷卻或者進行空冷或吹風空冷的工序；以及再加熱到400~600℃並保持之後，進行冷卻的工序。此外，本發明的輥軋用輥子外層材、輥軋用複合輥子的硬度，係因應其用途而調整在79~100 HS的範圍內為宜。最好是以能夠穩定的確保這種硬度的方式來調整鑄造後的熱處理為宜。 ［實施例］ [0062] 利用高頻感應加熱爐，熔製出具有表1所示的組成分的熔融金屬液，並且利用離心鑄造法，鑄造成作為試驗材之套筒狀的輥子外層材(外徑：250mmφ，徑向厚度：55mm)。此外，將澆鑄溫度設定在1450~1550℃，將離心力設定成重力倍數之140~220G。在其中一部分的試驗材(熔融金屬液No.S)中，產生了朝向內面之明顯的碳化物偏析現象，因此，基於減少這種偏析之目的，而將離心力設定為60G。鑄造後，再加熱到1050~1200℃並且保持10小時之後，又實施了一次或重複兩次之：進行冷卻至100℃以下的淬火硬化處理、以及加熱至400~560℃並保持後，進行冷卻之回火處理。如此一來，可將試驗材之從外表面起算在厚度方向上5mm位置處的硬度，予以調整成落在85~100 HS。此外，也熔製出：具有可作為鋼鐵的熱間精製輥軋用輥子使用之市售的離心鑄造製外層材的組成分(高速工具鋼輥子系組成分：2.2%C-0.4%Si-0.4%Mn-5.3%Cr-5.2%Mo-5.6%V-1.1%Nb)之熔融金屬液(熔融金屬液No.V)，同樣的進行鑄造成套筒狀的輥子外層材，鑄造後也實施了熱處理，來作為傳統例(試驗材No.22)的試驗材(硬度85 HS)。 [0063] 從已經實施了上述熱處理後的試驗材，採取出：分析組成分用試驗片、磨損試驗用試驗片。此外，試驗材No.19，因為非常容易裂開因而試驗材的採取極為困難。 [0064] 此外，分析組成分用試驗片，是先從上述的熱處理後的試驗材的外表面起算，朝徑向將5mm的厚度予以車削除去，再從該車削後的外表面採取分析組成分用試驗片，該試驗片的厚度是從外表面起算深入徑向5mm，該試驗片的大小則是從與外表面平行的面採取10mm×10mm的大小。使用所取得的試驗片，進行各成分元素的分析。分析方法是採用化學分析，C是利用燃燒法；Si、W是利用重量法；Mn、Cr、Mo是利用原子吸光法；Co是利用容量法；Fe是利用容量法或原子吸光法。 將所獲得的結果顯示於表2。 此外，磨損試驗片(外徑60mmφ×寬度10mm)，則是從上述的熱處理後的試驗片，以磨損試驗片的寬度中央位置剛好是位在從該試驗材的外表面起算之在徑向上的10mm位置處的方式，來採取出磨損試驗片。此外，磨損試驗，是如第2圖所示般地，利用試驗片(磨損試驗片)與對手材(材質：S45C、外徑190mmφ×寬度15mm)之兩個圓盤，以打滑轉動的方式來進行該磨損試驗。 [0065] 磨損試驗，是在將試驗片進行水冷的同時，又對於以700rpm(周速為2.1m/s)的迴轉數來進行旋轉中的該試驗片，將已加熱到850℃的對手片施以980N的荷重壓迫在該試驗片上，以打滑率為14.2%的條件，來使該對手片進行轉動。試驗片的轉動圈數，每到達21000次時，就將對手片進行更新，當累積迴轉數到達168000次時，就停止轉動。在試驗結束後，檢查該磨損試驗片的磨損減量。針對於所獲得的磨損減量，以傳統例(試驗材No.22)的磨損減量當作基準(1.0)，計算出相對於基準之各試驗材的磨損減量的比值(耐磨損比=(傳統例的磨損減量)/(該試驗材的磨損減量))，來評量其耐磨損性。如果耐磨損比是3以上的話，就標註記號為「◎」、耐磨損比是2以上且低於3的話，就標註記號為「○」；耐磨損比低於2的話，就標註記號為「×」，記號◎係表示非常良好；記號○係表示良好；記號×係表示不良。 將所獲得的結果顯示於表3。 [0066][0067][0068][0069] 本發明例的耐磨損比，都是在2.1以上，與傳統例(高速工具鋼輥子)相較，耐磨損性有明顯提昇。另一方面，落在本發明的範圍之外的比較例，有的是在試驗中途發生龜裂，有的則是耐磨損比並未達到2，與傳統例相較，耐磨損性的改善很少。 [0070] 此外，將所觀察到的本發明例(No.13、No.5)的組織予以顯示在第1圖。以可使得從熱處理後的試驗材外表面起算在徑向上5mm的位置剛好成為觀察面的方式，採取了組織觀察用試驗片，利用掃描型電子顯微鏡(倍率為250倍)進行觀察，而獲得反射電子像。可確認出白色領域是初晶碳化物(W濃化後的M6
C型碳化物)。可以看出：在本發明例的試驗材(套筒狀輥子外層材)外表面側，係高密度地分散著初晶碳化物。 [0071] 此外，作為比較參考之用，針對於試驗材No.11(本發明例)，係在從熱處理後的試驗材(套筒狀輥子外層材)外表面起算之在徑向上18mm的位置(18mm位置)以及38mm的位置(38mm位置)處，從該位置處採取分析組成分用試驗片，該試驗片的厚度是往徑向深入5mm，大小則是從與外表面平行的面採取10mm×10mm的大小。並且進行化學分析來對於各位置處的組成分進行了分析。將所獲得的結果也一起標示於表2。 [0072] 此外，針對於試驗材No.11(本發明例)，則是以可使得磨損試驗片的試驗面，剛好是位於：從熱處理後的試驗材外表面起算在徑向上18mm的位置(18mm位置)以及38~48mm的範圍的位置(38mm位置)的方式，來採取了磨損試驗片。與上述的條件同樣地實施了磨損試驗，測定了磨損減量。將所獲得的結果，一起標示於表3。 [0073] 從表2可以看出：在試驗材(套筒狀輥子外層材)外表面，主要是有W濃化於此處，在從外表面起算在徑向上距離18mm的位置(18mm位置)處、在從外表面起算在徑向上距離38mm(38mm位置)的位置處，W的比率減少，Co、Fe等的比率增加，很明顯地是形成了具有含量斜度的組成分。因此，從表3可以看出：在從外表面起算在徑向上距離18mm的位置(18mm位置)處、在從外表面起算在徑向上距離38mm(38mm位置)的位置處，其耐磨損性是比從外表面起算在徑向上距離10mm為止的領域內的耐磨損性更為降低。[0034] The outer layer of the roll for rolling of the present invention is obtained by centrifugal casting. The "roller outer layer material for a centrifugal casting roll" as used herein refers to a roll outer material of a roll which has been conventionally produced by a centrifugal casting method used as a method for producing a roll for rolling. The roll outer layer material for rolling ("roller roll outer layer material for "centrifugal casting") manufactured by the centrifugal casting method and the roll for rolling manufactured by using another manufacturing method are "object" In fact, there is a clear distinction, and it is unrealistic to use a structure or a characteristic to define the "roller casting" roll outer layer material for rolling, which requires a lot of labor. [0035] The outer layer of the roll for rolling of the present invention is made of a W-Co-based alloy, and its composition is a component having a content gradient in which the W content decreases from the outer peripheral side to the inner peripheral side of the roll in the radial direction, and The composition of the surface of the layer other than the position of the maximum diameter at the time of rolling use, in terms of mass%, contains W: 25 to 70%, Co: 5 to 45%, and contains C: 0.6 to 3.5%, Si: 0.05~3%, Mn: 0.05~3%, Mo: 1~15%, and the rest are inevitable impurities. Further, the above composition is even at a radial position corresponding to a total volume of the outer layer of at least 20% of the outer surface side, for example, if the outer diameter is 250 mm and the inner diameter is 140 mm. In the case of the sleeve, it is preferable to carry out the condition of at least 9 mm in the radial direction toward the inner peripheral side from the maximum diameter position at the time of rolling use. [0036] Here, the term "the surface of the outer layer material at the position corresponding to the maximum diameter at the time of rolling use" means a layer formed on the outer surface of the outer layer material at the time of casting (because molten metal and The part which is rapidly cooled and solidified when the mold is in contact with the mold is removed by turning, and corresponds to the position of the maximum diameter of the product roll diameter when the roll is used for rolling, in other words, it can be used as a product. (roller outer layer material) The surface of the material outside the position of the largest diameter when used. In addition, the term "layer surface other than the position of the maximum diameter at the time of rolling use" includes: turning off the layer formed on the outer surface of the outer layer material during casting, and the equivalent is just available. The surface of the outer layer material at the position of the largest diameter of the product roll diameter used for rolling is on the inner peripheral side, and the total volume of the outer layer material is at least 20% of the volume on the outer surface side. [0037] Moreover, the analysis of the composition of the surface of the outer layer material may be performed by using a machine analysis method such as fluorescent X-ray analysis or luminescence spectrometry, or may also utilize a destructive inspection method from the outer layer. The position of the surface of the material is a method in which a sample having a thickness of less than 10 mm in the radial direction of the roller is subjected to chemical analysis. [0038] First, the reason for limiting the composition of the outer layer of the roll for rolling of the present invention will be described. Hereinafter, the mass % of the component is described in terms of only %. C: 0.6 to 3.5% C is an element which can form a hard carbide by combining with W, and a carbide forming element such as Mo, Cr, V, or Nb, and has an effect of improving wear resistance. With the amount of C, the morphology and crystallization amount of the carbide and the crystallization temperature change. When the C content is 0.6% or more, the M 6 C type carbide will be crystallized as a primary crystal, and in the centrifugal casting, the microstructure of the M 6 C type carbide segregated on the outer surface side can be obtained, and the wear resistance can be improved. Damage. Further, when the C content is less than 0.6%, the amount of the M 6 C-type carbide crystallized as the primary crystal is insufficient to cause deterioration of the abrasion resistance. On the other hand, when the C content is a large amount and exceeds 3.5%, it is not only difficult to manufacture as an outer layer material, but also M 2 C carbides and MC carbides which are very likely to be cracked are coarsened, and thus the rolls are rolled. Rolling will easily occur when rolling. For the above reasons, the C content is limited to the range of 0.6 to 3.5%. Further, a suitable C content is 1.0 to 3.0%. A better C content is 1.2 to 2.8%. [0040] Si: 0.05 to 3% Si is an element which acts as a deoxidizer and also has a matrix strengthening effect. In order to obtain this effect, the Si content must be 0.05% or more. On the other hand, when the Si content exceeds 3%, not only the effect is saturated, but also flake graphite occurs, resulting in deterioration of toughness. Therefore, the Si content is limited to the range of 0.05 to 3%. In addition, a suitable Si content is 0.1 to 2%. A better Si content is 0.2 to 1.8%. Mn: 0.05 to 3% Mn is an element which can fix S by forming MnS, and has an effect of imparting harmless effects to S on the material. Further, Mn can be dissolved in the matrix to contribute to the improvement of quench hardenability. In order to obtain such an effect, the Mn content must be 0.05% or more. On the other hand, when the Mn content exceeds 3%, not only the above-described effects tend to be saturated, but also the material may be deteriorated. Therefore, the Mn content is limited to the range of 0.05 to 3%. Further, a suitable Mn content is 0.1 to 1%. A better Mn content is 0.2 to 0.8%. [0042] Mo: 1 to 15% Mo is a carbide-forming element which can form a carbide in combination with C, and in the present invention, in particular, a primary crystal carbide which is soluble in W and concentrated, that is, a hard M 6 C In the type carbide, the carbide can be reinforced, and the effect of increasing the fracture resistance of the outer layer of the roller can be obtained. Moreover, the Mo system can improve the quench hardenability during heat treatment, which is helpful for increasing the hardness of the outer layer of the roll. Further, Mo is an element heavier than Co, and has an effect of preventing the primary carbide from being centrifugally separated toward the outer surface side or promoting the centrifugal separation of the primary carbide toward the outer surface side. In order to obtain these effects, the Mo content must be 1% or more. On the other hand, if the Mo content is too large and exceeds 15%, hard and brittle carbides mainly composed of Mo will occur, resulting in deterioration of wear resistance. Therefore, the Mo content is limited to the range of 1 to 15%. In addition, a suitable Mo content is 2 to 10%. A better Mo content is 4 to 10%. W: 25 to 70% W is the most important element in the present invention, and is set to an alloy composition having a content of up to 25% or more. In this way, the hard M 6 C-type carbide which has been concentrated by the crystallization can be crystallized in a large amount as the primary crystal, and the roll outer layer material for rolling can be produced with a marked improvement in abrasion resistance. Further, when the W content is less than 25%, it is difficult to obtain an outer layer of a roll for rolling which is excellent in abrasion resistance in accordance with the object of the present invention. On the other hand, when the W content is more than 70%, not only the M 6 C type carbide becomes coarse and brittle, but the melting point of the molten metal liquid rises and it becomes difficult to melt, cast, and the like. Therefore, the W content is limited to the range of 25 to 70%. In addition, a suitable W content is 30 to 65%. A better W content is 35 to 55%. Co: 5 to 45% Co and W are both important elements in the present invention. By the large amount of Co and W, the activity of C can be increased, and many hard carbides (M 6 C type, M 2 C type, MC type, etc.) after W concentration can be promoted as primary crystals for lifting. The abrasion resistance of the roll outer layer material for rolling is helpful. To achieve this effect, the Co content must be 5% or more. On the other hand, if the Co content is too much and exceeds 45%, the γ phase tends to be stabilized, and the matrix becomes soft. If it is used as a roll for rolling, many dents (concave portions) will occur. The wear resistance is significantly deteriorated. Therefore, the Co content is limited to the range of 5 to 45%. In addition, a suitable Co content is 10 to 40%. A better Co content is 15 to 35%. [0045] The above-mentioned components are basic components, and may optionally contain, in addition to the basic components, from Fe: 5 to 40%, Cr: 0.1 to 10%, and V: 0.1 to 6%. Nb: one or more selected from 0.1 to 3%, or contains Ni: 0.05 to 3%, or both from Fe: 5 to 40%, Cr: 0.1 to 10%, and V: 0.1 to 6 %, Nb: one or more selected from 0.1 to 3% and Ni: 0.05 to 3%. [0046] One or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, and Nb: 0.1 to 3% are Fe, Cr, V, and Nb. The carbide-forming element is an element which can be dissolved in a carbide and has an action of strengthening a carbide, and may optionally contain one or two or more kinds as necessary. [0047] In addition to being soluble in carbides, Fe can be dissolved in a matrix at the same time, which contributes to the strengthening of the matrix, and has a function of preventing the formation of dents (concave portions) when used as a roller for rolling. In order to obtain such an effect, a suitable Fe content is 5% or more. On the other hand, when the Fe content exceeds 40%, the amount of hard M 6 C-type carbide which appears as a primary crystal will be reduced, the fragile M 3 C-type carbide will increase, and the abrasion resistance will be deteriorated. Therefore, if it is desired to contain Fe, it is preferred to limit the Fe content to a range of 5 to 40%. In addition, a better Fe content is 10 to 35%. The preferred Fe content is 12 to 30%. [0048] The mechanism (reason) for strengthening the matrix of the W-Co-based alloy by containing Fe in the matrix is not clear at present, probably because the γ phase stabilization achieved by Co is achieved with Fe. The α phase stabilization cancels each other out, and the result is that the strength of the matrix is increased, or because the α phase stabilization caused by Fe is relatively large, the matrix becomes a hard granulated iron or a tough iron structure, or A matrix strengthening phenomenon such as a structure in which fine carbides have precipitated appears in the matrix. [0049] Cr is a strong carbide-forming element, mainly capable of forming a eutectic carbide, and has an effect of enhancing the strength of the formed carbide. The eutectic carbide will crystallize in the gap between the primary crystal and the M 6 C-type carbide, and as a result, has the effect of reinforcing the gap of the M 6 C-type carbide. Further, Cr also has the effect of reducing the appearance of graphite. W-Co-based alloys are very prone to graphite because of the high coefficient of activity of C. If graphite appears, the toughness will deteriorate. In order to suppress the occurrence of graphite, it is desirable to use it stably as a roll for rolling, and in the present invention, it is preferable to contain Cr as necessary. In order to obtain such an effect, the suitable content of Cr is 0.1% or more. On the other hand, when the Cr content exceeds 10%, Cr-based eutectic carbides will appear in a large amount to deteriorate the toughness. Therefore, if Cr is desired, the Cr content is preferably in the range of 0.1 to 10%. In addition, a better Cr content is between 1 and 8%. The preferred Cr content is between 1.5 and 7%. [0050] V is an element which can form a hard VC (MC type carbide including Mo, Nb, Cr, W, etc.) in combination with C, and the formed MC type carbide crystallizes as a primary crystal. Further, the crystal nucleus of the M 6 C-type carbide which is concentrated by W promotes the appearance of the M 6 C-type carbide and has a function of dispersing the fine M 6 C-type carbide at a high density. In order to obtain such an effect, it is preferred to set the V content to 0.1% or more. On the other hand, if the V content is too large and exceeds 6%, even if it contains a lot of W, the V-based MC type carbide having a low specific gravity will increase and become coarser, and will be centrifugally separated when performing centrifugal casting. The inner side of the outer layer of the roller. Therefore, on the outer side, the wear resistance of the outer layer of the roll may be deteriorated due to the insufficient amount of the hard M 6 C type carbide. Further, if there are too many V-based MC-type carbides which are centrifugally separated to the inner surface side, the boundary strength with the inner layer of the roller or the intermediate layer will be deteriorated. Therefore, if V is desired, it is preferable to limit the V content to the range of 0.1 to 6%. In addition, a better V content is between 1 and 5%. The better V content is between 1.5 and 4%. [0051] The binding strength of Nb to C is extremely high, and it is a strong carbide-forming element, and it is easy to form a composite carbide with V or W. The composite carbide of Nb and V or W is a crystal nucleus of M 6 C-type carbide which is crystallized as a primary crystal and can promote the appearance of M 6 C-type carbide. Moreover, it also has a function of dispersing fine M 6 C type carbides at a high density. In order to obtain this effect, the content of Nb must be 0.1% or more. On the other hand, when the Nb content is too large and exceeds 3%, a low-density Nb-based MC-type carbide is formed and coarsened, and when centrifugal casting is performed, carbides are easily separated by centrifugation into the inner surface of the outer layer of the roll. On the side, and the amount of MC-type carbide on the inner surface side of the outer layer material increases. Further, if the amount of the MC-type carbide which is centrifugally separated to the inner surface side of the outer layer material is too large, the boundary strength with the inner layer of the roller or the intermediate layer will be deteriorated, and therefore, the quality of the inner surface side will be deteriorated. . Therefore, if it is desired to contain Nb, it is preferred to limit the Nb content to the range of 0.1 to 3%. In addition, a better Nb content is 0.5 to 2%. A better Nb content is between 0.6 and 1.8%. [0052] Ni: 0.05 to 3% Ni is an element having an effect of improving quench hardenability. For example, if it is intended to solve the problem of insufficient hardenability of a large roll, it may be contained as necessary. In order to obtain such an effect, it is preferred to set the Ni content to 0.05% or more. In addition, if it is only less than 0.05% as much as an impurity, the effect cannot be exerted. On the other hand, when the Ni content exceeds 3%, the γ phase tends to be stabilized, and the desired quench hardenability cannot be ensured. Therefore, if Ni is desired, it is preferable to set the Ni content in the range of 0.05 to 3%. A better Ni content is between 0.1 and 2.5%. [0053] The rest of the above components are inevitable impurities. Examples of unavoidable impurities include P, S, N, and B. Further, P segregates at the grain boundary to cause an adverse effect such as embrittlement of the material. Therefore, it is preferable to reduce the amount of impurities as much as possible, but if it is 0.05% or less, it is allowed to exist. In addition, S is segregated at the grain boundary in the same manner as P, and causes adverse effects such as embrittlement of the material. Therefore, it is preferable to reduce the amount of S as an impurity as much as possible, but if it is 0.05% or less, A part of it will be combined with Mn to become a sulfide-based inclusion, and it will become harmless, so it can be allowed. In addition, if it is a general melting method, there will be 0.01 to 0.1% of N mixed as an impurity. However, if the content is only such an extent, it does not affect the effect of the present invention. However, N may cause bubble defects in the outer layer of the composite roll and the intermediate layer or the boundary of the inner layer, so it is preferable to limit the N content to less than 0.07%. In addition, B sometimes contains B from an impurity element which is considered to be unavoidable from the recycled waste material of the molten raw material or mixed with the casting flux. B will solidify in the carbide or matrix to change the properties of the carbide, or be dissolved in the matrix to affect the quench hardenability of the matrix, thus leading to instability of the quality of the product. Therefore, the B content is preferably reduced as much as possible, but if it is 0.1% or less, the effect of the present invention is not adversely affected. Therefore, it is preferable that the above-mentioned unavoidable impurity element is adjusted to a total content of less than 1%. Next, a suitable method for producing the outer layer of the roll for rolling of the present invention will be described. In the present invention, the outer layer of the roll for rolling is manufactured by a centrifugal casting method in which the casting mold is rotated, in view of productivity and production cost. In this way, the outer layer of the roll for rolling which is excellent in abrasion resistance can be produced at a relatively low price. [0056] First, a molten metal liquid having the above-described composition of the outer layer of the roller is injected into a rotating mold to obtain a predetermined thickness, and centrifugal casting is performed to obtain a roll outer layer material for rolling. Further, in general, in order to protect the mold, it is common practice to coat the inner surface of the mold with a refractory material containing zircon or the like as a main material. Further, in the present invention, it is preferable to perform centrifugal casting after adjusting the number of rotations so that the centrifugal force reaches 120 to 250 G. By imparting high centrifugal force, the dispersion density of the hard carbide having a large specific gravity on the outer surface side can be increased. In the present invention, the obtained roll outer layer material for rolling may be used as a single sleeve, and a shaft material may be fitted into the sleeve to form a roll for rolling. Further, the obtained roll outer layer material for rolling may be provided with an intermediate layer which is fused and integrated on the inner side thereof to form a sleeve having an intermediate layer, and the shaft member is fitted into the sleeve to be formed. Roller for rolling. Further, the intermediate layer is formed by rotating the mold while the roll outer layer is solidified or completely solidified, and simultaneously injecting the molten metal having the intermediate layer composition by centrifugal casting. The material of the intermediate layer may, for example, be graphite steel, high carbon steel having a C content of 1 to 2% by mass, hypoeutectic cast iron or the like. Further, the shaft material of these rolls for rolling is not particularly limited, and it is preferable to use separately forged steel products (shafts), cast steel products (shafts), and cast iron products (shafts). Further, in the present invention, the above-mentioned roll outer layer material for rolling may be formed as an outer layer, and the composite roll formed by the outer layer and the inner layer integrated with the fusion may be produced as follows: The above-mentioned roll outer layer material for rolling is referred to as an outer layer, and a composite roll formed of the outer layer and the inner layer integrated with the fusion and the inner layer which is integrated with the intermediate layer. [0059] In the case of forming the intermediate layer, it is preferable to inject the molten metal having the intermediate layer composition while rotating the mold while the outer layer of the roll is solidified or completely solidified. In addition, the intermediate layer is preferably graphite steel, high carbon steel having a C content of 1 to 2% by mass, hypoeutectic cast iron or the like. The intermediate layer is integrated with the outer layer, and the outer layer component is mixed into the intermediate layer in the range of 10 to 90%. From the viewpoint of suppressing the amount of mixing of the outer layer component into the inner layer, it is preferable to reduce the amount of the mixture of the outer layer mixed into the intermediate layer as much as possible in advance. [0060] Generally, after the outer layer or the intermediate layer is completely solidified, the rotation of the mold is stopped, and after the mold is erected, the inner layer is subjected to static casting to form an inner layer. Here, the inner layer material used for the static casting is preferably spherical graphite cast iron or worm-like graphite cast iron (CV cast iron) excellent in castability and mechanical properties. Further, in the case of a composite roll in which the outer layer and the inner layer are integrated without the intermediate layer, the composition of the outer layer material is mixed into the inner layer to the extent of 1 to 10%. The W, Cr, V, etc. contained in the outer layer material are strong carbide forming elements, and if these elements are mixed into the inner layer, the inner layer becomes weak. Therefore, in the present invention, it is preferred that the mixing ratio of the outer layer component to the inner layer is suppressed to less than 5%. [0061] The above-mentioned roll outer layer material for rolling and the composite roll for rolling are preferably subjected to heat treatment after casting. The heat treatment is preferably carried out by heating to 1000 to 1200 ° C for more than one time and holding for 5 to 40 hours, then cooling in the furnace or performing air cooling or air cooling; and reheating to 400 to 600 ° C and maintaining The process of cooling. Further, the hardness of the roll outer layer material for rolling and the composite roll for rolling according to the present invention is preferably adjusted within the range of 79 to 100 HS depending on the application. It is preferable to adjust the heat treatment after casting in such a manner that the hardness can be stably ensured. [Examples] [0062] A molten metal liquid having the composition shown in Table 1 was melted by a high-frequency induction heating furnace, and was cast into a sleeve-like roll outer layer material as a test material by centrifugal casting ( Outer diameter: 250mmφ, radial thickness: 55mm). In addition, the casting temperature is set at 1450 to 1550 ° C, and the centrifugal force is set to 140 to 220 G of the gravity multiple. In some of the test materials (molten metal No. S), a significant carbide segregation phenomenon toward the inner surface was generated. Therefore, the centrifugal force was set to 60 G for the purpose of reducing such segregation. After casting, after heating to 1050 ~ 1200 ° C and holding for 10 hours, it is carried out once or twice: cooling to 100 ° C or less after quench hardening treatment, and heating to 400 ~ 560 ° C and maintaining, cooling Tempering treatment. In this way, the hardness of the test material from the outer surface at a position of 5 mm in the thickness direction can be adjusted to fall at 85 to 100 HS. In addition, it is also melted: a component of a commercially available centrifugally cast outer layer which can be used as a hot-rolled refining roll for steel (high-speed tool steel roll system component: 2.2% C-0.4% Si-0.4 The molten metal liquid (molten metal No. V) of %Mn-5.3%Cr-5.2%Mo-5.6%V-1.1%Nb) was similarly cast into a sleeve-shaped outer layer of the roll, and was also cast after casting. The heat treatment was carried out as a test material (hardness 85 HS) of a conventional example (test material No. 22). [0063] From the test material after the above heat treatment, the test piece for analysis composition and the test piece for abrasion test were taken. Further, the test material No. 19 was extremely difficult to take because of the fact that it was very easy to crack. [0064] Further, the test piece for analyzing the component is firstly turned from the outer surface of the heat-treated test material described above, and the thickness of 5 mm is turned away in the radial direction, and then the analysis is performed from the outer surface after the turning. A test piece was used, and the thickness of the test piece was 5 mm in the radial direction from the outer surface, and the size of the test piece was 10 mm × 10 mm from the surface parallel to the outer surface. The analysis of each component element was performed using the obtained test piece. The analysis method is chemical analysis, C is a combustion method; Si and W are by weight method; Mn, Cr, and Mo are atomic absorption methods; Co is a volumetric method; and Fe is a volumetric method or atomic absorption method. The results obtained are shown in Table 2. Further, the abrasion test piece (outer diameter 60 mm φ × width 10 mm) is the test piece after the heat treatment described above, and the center position of the width of the abrasion test piece is just in the radial direction from the outer surface of the test piece. At the 10mm position, the wear test piece was taken out. In addition, as shown in Fig. 2, the abrasion test is performed by using a test piece (abrasion test piece) and two disks of a material (material: S45C, outer diameter 190 mmφ × width 15 mm) in a slipping manner. This abrasion test was carried out. [0065] The abrasion test was performed while the test piece was subjected to water cooling, and the test piece which was rotated at a number of revolutions of 700 rpm (peripheral speed of 2.1 m/s) was used, and the hand piece which had been heated to 850 ° C was used. The load of 980 N was applied to the test piece, and the hand piece was rotated under the condition of a slip ratio of 14.2%. The number of revolutions of the test piece is updated every 21,000 times, and when the cumulative number of revolutions reaches 168,000 times, the rotation is stopped. After the end of the test, the wear reduction of the worn test piece was examined. With respect to the obtained wear reduction, the wear reduction of the conventional test piece (test material No. 22) was used as a reference (1.0), and the ratio of the wear reduction of each test material with respect to the reference was calculated (wear resistance ratio = (traditional The wear reduction of the example / (the wear reduction of the test material)) was used to evaluate the wear resistance. If the wear resistance ratio is 3 or more, the mark is "◎", and the wear resistance ratio is 2 or more and less than 3, the mark is "○"; if the wear resistance ratio is less than 2, the mark is marked. The symbol is "X", the symbol ◎ indicates very good; the symbol ○ indicates good; the symbol × indicates poor. The results obtained are shown in Table 3. [0066] [0067] [0068] [0069] The wear resistance ratio of the examples of the present invention is all above 2.1, and the wear resistance is remarkably improved as compared with the conventional example (high speed tool steel roll). On the other hand, in the comparative examples falling outside the scope of the present invention, cracks occurred in the middle of the test, and the wear resistance ratio did not reach 2, and the abrasion resistance was improved as compared with the conventional example. less. Further, the organization of the observed examples (No. 13, No. 5) of the present invention is shown in Fig. 1. The test piece for tissue observation was taken in such a manner that the position on the outer surface of the test material after the heat treatment was 5 mm in the radial direction, and the observation piece was observed by a scanning electron microscope (magnification: 250 times) to obtain a reflection. Electronic image. It was confirmed that the white region was a primary crystal carbide (M 6 C-type carbide after W concentration). It can be seen that in the outer surface side of the test material (sleeve-shaped roll outer layer material) of the present invention, the primary crystal carbide is dispersed at a high density. [0071] In addition, as a comparative reference, the test material No. 11 (inventive example) was placed at a position of 18 mm in the radial direction from the outer surface of the heat-treated test material (sleeve-shaped roll outer layer material). From the position (18 mm position) and the position of 38 mm (38 mm position), the test piece for analysis is taken from this position, and the thickness of the test piece is 5 mm deep in the radial direction, and the size is 10 mm from the surface parallel to the outer surface. ×10mm size. Chemical analysis was also performed to analyze the composition at each position. The results obtained are also shown together in Table 2. Further, with respect to the test material No. 11 (example of the present invention), the test surface which can make the abrasion test piece is located at a position of 18 mm in the radial direction from the outer surface of the test material after the heat treatment ( A wear test piece was taken in a manner of a position (38 mm position) in the range of 38 to 48 mm and a range of 38 to 48 mm. The abrasion test was carried out in the same manner as the above conditions, and the wear reduction was measured. The results obtained are shown together in Table 3. [0073] It can be seen from Table 2 that on the outer surface of the test material (sleeve-shaped roller outer layer material), mainly W is concentrated here, and the distance from the outer surface is 18 mm in the radial direction (18 mm position). At a position at a distance of 38 mm (38 mm position) in the radial direction from the outer surface, the ratio of W decreases, and the ratio of Co, Fe, etc. increases, and it is apparent that a composition having a content gradient is formed. Therefore, it can be seen from Table 3 that the wear resistance is at a position (18 mm position) at a distance of 18 mm in the radial direction from the outer surface at a position of 38 mm (38 mm position) in the radial direction from the outer surface. The wear resistance in the field of 10 mm in the radial direction from the outer surface is further lowered.