TW201812028A - Roll outer layer material for hot rolling and composite roll for hot rolling - Google Patents

Roll outer layer material for hot rolling and composite roll for hot rolling Download PDF

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TW201812028A
TW201812028A TW106123209A TW106123209A TW201812028A TW 201812028 A TW201812028 A TW 201812028A TW 106123209 A TW106123209 A TW 106123209A TW 106123209 A TW106123209 A TW 106123209A TW 201812028 A TW201812028 A TW 201812028A
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outer layer
hot rolling
roll
content
iron
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TW106123209A
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TWI655295B (en
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岩田直道
鈴木健史
松村祥一
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Ｊｆｅ鋼鐵股份有限公司
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D19/00—Casting in, on, or around objects which form part of the product
    • B22D19/08—Casting in, on, or around objects which form part of the product for building-up linings or coverings, e.g. of anti-frictional metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D13/00—Centrifugal casting; Casting by using centrifugal force
    • B22D13/02—Centrifugal casting; Casting by using centrifugal force of elongated solid or hollow bodies, e.g. pipes, in moulds rotating around their longitudinal axis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D19/00—Casting in, on, or around objects which form part of the product
    • B22D19/16—Casting in, on, or around objects which form part of the product for making compound objects cast of two or more different metals, e.g. for making rolls for rolling mills
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use
    • B21B27/02—Shape or construction of rolls
    • B21B27/03—Sleeved rolls
    • B21B27/032—Rolls for sheets or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D5/00—Heat treatments of cast-iron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/38—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for roll bodies
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

The purpose of the present invention is to provide a roll outer layer material for hot rolling and a composite roll for hot rolling, whereby wear resistance is ensured, pit-shaped flaws on the roll surface are reduced, and excellent surface roughing resistance is obtained. A roll outer layer material characterized by having a composition containing, in terms of mass%, 2.0-3.0% C, 0.2-1.0% Si, 0.2-1.0% Mn, 4.0-7.0% Cr, 3.0-6.5% Mo, 5.0-7.5% V, 0.5-3.0% Nb, 0.05-3.0% Ni, 0.2-5.0% Co, and 0.5-5.0% W, the content of C, Cr, Mo, V, Nb, Ni, and W satisfying expression (1), and the remainder comprising Fe and unavoidable impurities, at least 85% of the matrix structure of the roll outer layer material being a tempered martensite and/or bainite structure, and the minor axis of the tempered martensite or bainite being 0.5-3.0 [mu]m. (1): 0.05 ≤ (%C - %V * 0.177 - %Nb * 0.129 - %Cr * 0.099 - %Mo * 0.063 - %W * 0.033) + (%Ni) ≤ 4.0. In expression (1), the terms %C, %V, %Nb, %Cr, %Mo, %W, and %Ni are the content (mass%) of each element.

Description

熱軋用輥子外層材以及熱軋用複合輥子    Outer layer of hot rolling roll and composite roll for hot rolling   

本發明是關於熱軋用複合輥子，尤其是關於適用於鋼板的熱軋精製輥軋機的熱軋用輥子外層材以及熱軋用複合輥子。 The present invention relates to a composite roll for hot rolling, and more particularly to an outer layer of a roll for hot rolling and a composite roll for hot rolling, which are suitable for use in a hot rolling finishing roll mill for a steel sheet.

近年來，隨著鋼板熱軋技術的進步，軋輥的使用環境也更趨嚴酷化，此外，高強度鋼板和薄型鋼板之類的輥軋負荷較大的鋼板的生產量也在增加中。因此，在輥軋用工作輥子身上發生：起因於輥軋面的疲勞所致的表面粗糙現象和缺損瑕疵的問題變多，因而必須要求具有較之以往更高水準的耐表面粗糙性和耐缺損性。目前是在熱軋時，大多採用：藉由添加數%量的V來形成大量的硬質碳化物，而可提昇耐磨損性的高速度工具鋼系輥子。 In recent years, with the advancement of hot rolling technology of steel plates, the use environment of rolls has become more severe. In addition, the production volume of steel plates with high rolling loads such as high-strength steel plates and thin steel plates is also increasing. For this reason, the work rolls for rolling have many problems such as surface roughness and defects due to the fatigue of the rolling surface. Therefore, it is necessary to have a higher level of surface roughness and defect resistance than before. Sex. At present, during hot rolling, high-speed tool steel-based rollers that can increase wear resistance by forming a large amount of hard carbides by adding a few% of V are mostly used.

關於這種高速度工具鋼系輥子的外層材，例如：專利文獻1所提案的輥軋用輥子外層材，是含有C：1.5~3.5%、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%，且Nb以及V的含量必須符合Nb、V以及C含量的特定關係，同時Nb與V之兩者的比值必須落在特定的範圍內。如此一來，係 可成為：即使應用離心鑄造法來進行製造時，亦可抑制外層材中的硬質碳化物的偏析，而且耐磨損性與耐龜裂性優異的輥軋用輥子外層材。又，專利文獻2所提案的輥軋用輥子外層材，係含有C：1.5~3.5%、Cr：5.5~12.0%、Mo：2.0~8.0%、V：3.0~10.0%、Nb：0.5~7.0%，並且Nb以及V的含量，必須是Nb、V以及C的含量符合特定的關係，並且Nb與V之兩者的比值落在特定範圍內。如此一來，係可成為：即使應用離心鑄造法來進行製造時，亦可抑制外層材中的硬質碳化物的偏析，而且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貢獻的輥軋用輥子外層材。 Regarding the outer layer material of such high-speed tool steel-based rollers, for example, the roll outer layer material proposed in Patent Document 1 contains C: 1.5 to 3.5%, Ni: 5.5% or less, Cr: 5.5 to 12.0%, Mo: 2.0 ~ 8.0%, V: 3.0 ~ 10.0%, Nb: 0.5 ~ 7.0%, and the content of Nb and V must conform to the specific relationship of the content of Nb, V, and C, and the ratio of Nb and V must fall Within a specific range. In this way, even when the centrifugal casting method is used for manufacturing, it is possible to suppress the segregation of hard carbides in the outer layer, and to provide a roll outer layer having excellent abrasion resistance and crack resistance. The outer layer of the roll for rolling proposed in Patent Document 2 contains C: 1.5 to 3.5%, Cr: 5.5 to 12.0%, Mo: 2.0 to 8.0%, V: 3.0 to 10.0%, and Nb: 0.5 to 7.0. %, And the content of Nb and V must be such that the content of Nb, V, and C meet a specific relationship, and the ratio of both Nb and V falls within a specific range. In this way, even when the centrifugal casting method is used for manufacturing, the segregation of hard carbides in the outer layer can be suppressed, and the abrasion resistance and crack resistance can be improved, which can improve the production of hot rolling. The outer layer of the roll for rolls, which greatly contributes to its properties.

另一方面，基於提昇熱軋製品的品質與提昇生產性的觀點考量，熱軋用輥子的使用環境更加嚴酷化，鋼板的連續輥軋量也在增加中。此外，對於熱軋製品的表面品質的更為嚴格。因此，比考慮到輥子的磨損性更為優先考慮的要如何抑制表面粗糙之類的輥子表面的疲勞損傷，已經成為重大的技術課題。針對於這種課題，專利文獻3所提案的離心鑄造製複合輥子，係將C、Mo、V、Nb的含量，在C：2.2~2.6%、Cr：5.0~8.0%、Mo：4.4~6.0%、V：5.3~7.0%、Nb：0.6~1.3%的範圍內，進一步調整為落在符合Mo+V、C-0.24V-0.13Nb的關係之特定範圍內，而成為在熱軋環境下之輥子表層的耐疲勞性優異的複合輥子。此外，專利文獻4所提案的輥軋用輥子外層材，係含有C：1.3~2.2%、Si：0.3~1.2%、Mn： 0.1~1.5%、Cr：2.0~9.0%、Mo：9.0%以下、V：4.0~15.0%、以及從W：20.0%以下、Ni：5.0%以下、Co：10.0%以下之中所選出的其中一種或兩種以上，其餘部分實質上是Fe以及不可避免的雜質，並且將在其組織中分散的碳化物的尺寸，選定在特定的範圍內。專利文獻4，係減少很容易形成粗大的碳化物之共晶碳化物的數量，因而可減少凹坑狀的瑕疵。 On the other hand, from the viewpoint of improving the quality of hot-rolled products and improving productivity, the use environment of hot-rolling rollers is becoming more severe, and the continuous rolling amount of steel sheets is also increasing. In addition, the surface quality of hot-rolled products is more stringent. Therefore, how to suppress fatigue damage on the surface of the roller, such as rough surface, has been given a higher priority than considering the abrasion of the roller, and it has become a major technical issue. In response to such a problem, the centrifugal casting composite roller proposed in Patent Document 3 contains C, Mo, V, and Nb content in C: 2.2 to 2.6%, Cr: 5.0 to 8.0%, and Mo: 4.4 to 6.0. %, V: 5.3 ~ 7.0%, Nb: 0.6 ~ 1.3%, further adjusted to fall within a specific range that meets the relationship of Mo + V, C-0.24V-0.13Nb, and becomes a hot rolling environment Composite roller with excellent fatigue resistance on the surface of the roller. In addition, the roll outer layer material proposed in Patent Document 4 contains C: 1.3 to 2.2%, Si: 0.3 to 1.2%, Mn: 0.1 to 1.5%, Cr: 2.0 to 9.0%, and Mo: 9.0% or less. , V: 4.0 ~ 15.0%, and one or two or more selected from W: 20.0% or less, Ni: 5.0% or less, Co: 10.0% or less, and the rest is essentially Fe and unavoidable impurities , And the size of the carbides dispersed in its structure is selected within a specific range. Patent Document 4 reduces the number of eutectic carbides that easily form coarse carbides, thereby reducing pit-like defects.

[先前技術文獻]     [Prior technical literature]     [專利文獻]     [Patent Literature]    

專利文獻1：日本特開平04-365836號公報 Patent Document 1: Japanese Patent Application Laid-Open No. 04-365836

專利文獻2：日本特開平05-1350號公報 Patent Document 2: Japanese Patent Application Laid-Open No. 05-1350

專利文獻3：日本特開2009-221573號公報 Patent Document 3: Japanese Patent Application Laid-Open No. 2009-221573

專利文獻4：日本特許第3962838號 Patent Document 4: Japanese Patent No. 3962838

然而，近年來的輥軋技術，係朝向：輥軋鋼板的高品質化與高級化，以明顯的速度不斷地進步當中。同時，對於輥軋也嚴格地追求低成本化，因而輥子的使用環境愈趨嚴酷。所以傳統之只著眼在碳化物身上之輥子材質的設計，已經無法減輕凹坑狀瑕疵的發生了。 However, in recent years, the rolling technology has been oriented towards the improvement of the quality and advancement of rolled steel sheets, which are constantly progressing at an obvious rate. At the same time, the cost of rolling is also strictly pursued, so the use environment of rollers is becoming more severe. Therefore, the traditional design of the roller material focused on the carbide body has been unable to alleviate the occurrence of pit-like defects.

本發明是有鑒於上述情事而進行開發完成的，其目的是要提供：可確保耐磨損性，並且可減輕輥子 表面的凹坑狀瑕疵之耐表面粗糙性優異的熱軋用輥子外層材以及熱軋用複合輥子。 The present invention has been developed in view of the foregoing circumstances, and an object thereof is to provide a hot rolling roll outer layer material which can ensure abrasion resistance and reduce pit-like flaws on the surface of the roll, and has excellent surface roughness resistance, and Compound roll for hot rolling.

本發明人等乃針對於：形成在熱軋用輥子表面的凹坑狀瑕疵的發生處所進行詳細的調查。其結果，得知：凹坑狀的瑕疵，共晶碳化物(主要是M2C系、M6C系、M7C3系以及M23C6系碳化物)所產生的龜裂在基質組織中進行傳播，而缺損形成凹坑狀。因此，想出了：若要減輕凹坑狀瑕疵的話，除了以往所著眼的碳化物種類、大小之外，有效的作法，是要降低在基質組織中進行傳播之龜裂的傳播速度，進而完成了本發明。換言之，針對於：影響輥子外層材的耐熱間轉動疲勞性和基質組織的尺寸的各種因素進行研究的結果，獲得了以往未知的創見，就是：藉由各元素的成分範圍的調整、以及將各元素的含量調整成可使得各元素符合特定的關係，係可顯著地提昇熱軋時的耐疲勞性。此外，也獲得了另一種創見，就是：藉由控制基質組織的尺寸，可更顯著地提昇熱軋時的耐疲勞性。 The present inventors have conducted detailed investigations into the occurrence of pit-like flaws formed on the surface of a hot-rolling roll. As a result, it was found that crater-like defects and cracks generated by eutectic carbides (mainly M 2 C-based, M 6 C-based, M 7 C 3- based, and M 23 C 6- based carbides) were in the matrix. The tissue spreads, and the defects form pits. Therefore, I came up with the following idea: In order to reduce the pit-like defects, in addition to the types and sizes of carbides that have been focused on in the past, an effective method is to reduce the propagation speed of cracks that propagate in the matrix tissue, and then complete This invention. In other words, the results of research on various factors affecting the thermal fatigue resistance of the outer layer of the roller and the size of the matrix structure have obtained previously unknown ideas: by adjusting the composition range of each element, and The content of the elements is adjusted so that each element conforms to a specific relationship, and the fatigue resistance during hot rolling can be significantly improved. In addition, another idea was obtained: by controlling the size of the matrix structure, the fatigue resistance during hot rolling can be significantly improved.

首先，說明作為本研究的基礎之實驗結果。 First, the experimental results that are the basis of this study will be described.

先利用高頻感應加熱爐熔解出熔融金屬液，該熔融金屬液的組成分，以質量%計，是將各元素含量在下列範圍內加以改變，Si：0.1~1.5%、Mn：0.1~1.5%、C：1.6~3.5%、Cr：3.5~9.0%、Mo：2.1~7.0%、V： 4.1~8.5%、Nb：0.3~4.6%、Ni：0.02~3.6%、Co：0.3~8.0%、W：0.2~8.0%，其餘部分是Fe以及不可避免的雜質，並且利用離心鑄造法進行鑄造成：與輥子外層材相當的環狀輥子材(外徑：250mm 、寬度：65mm、厚度：55mm)。此外，將澆鑄溫度設在1450℃~1530℃，將離心力設在：180G，剛好是環狀輥子材的外周部的重力倍數。鑄造後，實施淬火硬化處理、回火處理，將硬度製作成HS：78~86。此外，淬火硬化處理，是先將溫度加熱到1070℃，然後進行空冷。此外，回火處理是以530~570℃的溫度，根據熔融金屬液成分的不同，分成兩次或三次來實施，以使得殘留沃斯田鐵量低於低於10體積%。 First, a high-frequency induction heating furnace is used to melt out the molten metal liquid. The composition of the molten metal liquid is changed by mass% in the following ranges: Si: 0.1 to 1.5%, Mn: 0.1 to 1.5. %, C: 1.6 ~ 3.5%, Cr: 3.5 ~ 9.0%, Mo: 2.1 ~ 7.0%, V: 4.1 ~ 8.5%, Nb: 0.3 ~ 4.6%, Ni: 0.02 ~ 3.6%, Co: 0.3 ~ 8.0% , W: 0.2 ~ 8.0%, the rest is Fe and unavoidable impurities, and is cast by centrifugal casting method: ring-shaped roller material equivalent to the outer layer of the roller (outer diameter: 250mm , Width: 65mm, thickness: 55mm). In addition, the casting temperature was set between 1450 ° C and 1530 ° C, and the centrifugal force was set at 180G, which is exactly the gravity multiple of the outer peripheral portion of the ring-shaped roller material. After casting, quench hardening treatment and tempering treatment are performed, and the hardness is HS: 78 ~ 86. In addition, in the hardening treatment, the temperature is first heated to 1070 ° C and then air-cooled. In addition, the tempering treatment is performed at a temperature of 530 to 570 ° C. in two or three times depending on the composition of the molten metal liquid, so that the residual amount of iron in the Vastfield is less than 10% by volume.

從所製得的環狀輥子材身上採取熱軋疲勞試驗片(外徑60mm 、厚度10mm)，實施了曾經在日本特開2010-101752公報中所揭示的熱軋疲勞試驗，該熱軋疲勞試驗係顯示出：實際的熱軋用作業輥子的耐疲勞性具有良好的再現性。此外，藉由使用直徑為0.2mm 的焊線的放電加工(焊線切割)法，在疲勞試驗片的外周面上的兩個地方，進行切割而導入如第1圖所示的凹口(深度t：1.2mm、周方向長度L：0.8mm)。此外，在疲勞試驗片的滾動面的端部，實施了1.2C的倒角加工。 A hot-rolled fatigue test piece (outer diameter: 60 mm) was taken from the obtained ring-shaped roller material. (Thickness: 10 mm). The hot-rolling fatigue test disclosed in Japanese Patent Application Laid-Open No. 2010-101752 was performed. This hot-rolling fatigue test system shows that the fatigue resistance of actual hot-rolling work rolls has good repeatability . In addition, by using a diameter of 0.2mm The electrical discharge machining (wire cutting) method of the welding wire is performed at two places on the outer peripheral surface of the fatigue test piece to introduce a notch (depth t: 1.2 mm, length L in the circumferential direction) as shown in FIG. 1. : 0.8mm). In addition, the end of the rolling surface of the fatigue test piece was chamfered at 1.2C.

如第1圖所示，熱軋疲勞試驗，是將具有凹口的試驗片(熱軋疲勞試驗片)與被加熱後的對手材之兩個圓盤，旋轉暨打滑轉動方式來進行的。亦即，如第1圖所示，將試驗片(熱軋疲勞試驗片)1利用冷卻水2一邊進行 水冷，一邊使其以700rpm的迴轉數進行旋轉。同時，將利用高頻感應加熱線圈3加熱至800℃的對手片(材質：S45C，外徑：190mm ，寬度：15mm)4，以施加980N的荷重的條件下，抵接在旋轉中的該試驗片1，並且在打滑率為9%的條件下，使對手片進行轉動。在這種狀態下，使熱軋疲勞試驗片1進行轉動，直到被導入在其外周面上的兩個凹口5折損為止，分別求出各凹口折損時的轉動迴轉數，將兩者的平均值當作熱軋疲勞壽命。並且，將熱軋疲勞壽命超過35萬轉的情況，評判為：熱軋疲勞壽命非常優異。 As shown in FIG. 1, the hot rolling fatigue test is performed by rotating and slipping the two discs of a test piece (hot rolling fatigue test piece) having a notch and a heated opponent. That is, as shown in FIG. 1, the test piece (hot rolling fatigue test piece) 1 was cooled with cooling water 2 while being rotated at a rotation number of 700 rpm. At the same time, the hand piece (material: S45C, outer diameter: 190mm) heated to 800 ° C by the high-frequency induction heating coil 3 (Width: 15mm) 4, under the condition of applying a load of 980N, abut the test piece 1 in rotation, and rotate the opponent piece under the condition of a slip ratio of 9%. In this state, the hot-rolled fatigue test piece 1 is rotated until the two notches 5 introduced into the outer peripheral surface thereof are broken, and the number of rotation revolutions when each notch is broken is calculated. The average value is taken as the hot rolling fatigue life. In addition, when the hot rolling fatigue life exceeds 350,000 revolutions, it is judged that the hot rolling fatigue life is very excellent.

此外，針對於所製得的環狀輥子材，進行組織觀察。組織觀察，是從自環狀輥子材的外表面起算朝內10mm的內部任意位置，採取10×10×5mm(5mm是在環狀輥子材的厚度方向)的組織觀察試驗片，並且針對於10×10mm的面進行鏡面研磨，使用硝酸蝕刻液(5體積%硝酸+乙醇)進行10秒左右的腐蝕之後，使用光學顯微鏡來進行觀察。 The structure of the obtained annular roller material was observed. The structure observation is a 10 × 10 × 5mm (5mm is the thickness direction of the endless roller material) arbitrary position from the inside of the endless roller material from the outer surface of the inner surface. The × 10 mm surface was mirror-polished, and then etched using a nitric acid etching solution (5 vol% nitric acid + ethanol) for about 10 seconds, and then observed using an optical microscope.

此外，為了測定回火麻田散鐵或回火變韌鐵的短徑(短軸長度)，從所製得的環狀輥子材的外表面起算朝內10mm的內部任意位置，採取測定試驗片(5mm×10mm×5mm)，針對於5mm×10mm的面進行鏡面研磨，實施了電子背向散射繞射(EBSD)測定。利用電子背向散射繞射法(EBSD)，以加速電壓為15kV，步進量為0.1μm的條件，針對10000μm2以上的領域進行了測定。 在與相鄰的測定點之間的方位差為15°以上之處畫上境界線，如第2圖所示，將被境界線所圍繞的領域視為一個結晶，在測定面上對於長徑為5μm以上之20個結晶的短徑進行測定，並且算出其平均值。 In addition, in order to measure the short diameter (short axis length) of tempered Asada loose iron or tempered toughened iron, an arbitrary position inside 10 mm inward from the outer surface of the obtained annular roller material was taken, and a measurement test piece ( 5 mm × 10 mm × 5 mm), mirror polishing was performed on a 5 mm × 10 mm surface, and electron backscatter diffraction (EBSD) measurement was performed. The electron backscatter diffraction method (EBSD) was used to measure an area of 10,000 μm 2 or more under the conditions of an acceleration voltage of 15 kV and a step size of 0.1 μm. Draw the boundary line where the azimuth difference from the adjacent measurement point is 15 ° or more. As shown in Figure 2, the area surrounded by the boundary line is regarded as a crystal. The short diameter of 20 crystals of 5 μm or more was measured, and the average value was calculated.

針對於得到的結果，將熱軋疲勞壽命與(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)之關係顯示於第3圖，將熱軋疲勞壽命與回火麻田散鐵或回火變韌鐵的短徑之關係顯示於第4圖。 Based on the results obtained, the relationship between the hot rolling fatigue life and (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) is shown in FIG. 3 shows the relationship between the fatigue life of hot rolling and the short diameter of tempered Asada iron or tempered and toughened iron.

從第3圖可以得知：(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)的數值如果是0.05以上或4.0以下的話，熱軋疲勞壽命係有顯著的提昇。此處，V、Cr、Mo、Nb、W是很容易形成碳化物的元素，(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)是表示：固溶在基質中的碳量。因此，(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)就是：固溶在基質中的碳量與Ni量的總和，藉由將這個值調整到適正的範圍，基質中的龜裂的傳播速度將會變慢，而可獲得熱軋疲勞壽命優異的輥子外層材。此外，藉由控制成符合上述成分範圍，且將基質組織的回火麻田散鐵或變韌鐵的結晶大小控制在第4圖所示的範圍內，可顯著地提昇熱軋疲勞壽命。 It can be known from Figure 3: (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) if the value is above 0.05 or 4.0 In the following, the hot rolling fatigue life is significantly improved. Here, V, Cr, Mo, Nb, and W are elements that easily form carbides (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) Yes means: the amount of carbon solid-dissolved in the matrix. Therefore, (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) is: the amount of carbon dissolved in the matrix and the amount of Ni In sum, by adjusting this value to a proper range, the propagation speed of cracks in the matrix will be slower, and a roll outer layer having excellent hot rolling fatigue life can be obtained. In addition, by controlling the composition to conform to the above-mentioned composition range, and controlling the crystal size of the tempered Asada loose iron or the toughened iron in the matrix structure within the range shown in Fig. 4, the hot rolling fatigue life can be significantly improved.

本發明是基於上述創見而開發完成的，其要旨如下所述。 The present invention has been developed based on the aforementioned ideas, and the gist thereof is as follows.

[1]一種熱軋用輥子外層材，其特徵為：其組成分以質量%計，含有C：2.0~3.0%、Si：0.2~1.0%、Mn：0.2~1.0%、Cr：4.0~7.0%、Mo：3.0~6.5%、V：5.0~7.5%、Nb：0.5~3.0%、Ni：0.05~3.0%、Co：0.2~5.0%、W：0.5~5.0%，並且C、Cr、Mo、V、Nb、Ni、W的含量，係符合下列數式(1)的關係，其餘部分是Fe以及不可避免的雜質，基質組織的85%以上是回火麻田散鐵組織及回火變韌鐵組織之其中至少一種組織，回火麻田散鐵或回火變韌鐵的短徑是0.5~3.0μm，0.05≦(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)≦4.0 數式(1) [1] An outer layer of a roll for hot rolling, characterized in that its composition is in mass% and contains C: 2.0 to 3.0%, Si: 0.2 to 1.0%, Mn: 0.2 to 1.0%, and Cr: 4.0 to 7.0 %, Mo: 3.0 to 6.5%, V: 5.0 to 7.5%, Nb: 0.5 to 3.0%, Ni: 0.05 to 3.0%, Co: 0.2 to 5.0%, W: 0.5 to 5.0%, and C, Cr, Mo The content of, V, Nb, Ni, and W is in accordance with the following formula (1). The rest is Fe and inevitable impurities. More than 85% of the matrix structure is tempered Asada loose iron structure and tempered and toughened. At least one of the iron structures, the short diameter of tempered Asada loose iron or tempered toughened iron is 0.5 ~ 3.0μm, 0.05 ≦ (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) ≦ 4.0 Equation (1)

此處的%C、%V、%Nb、%Cr、%Mo、%W、%Ni是表示各元素的含量(質量%)。 Here,% C,% V,% Nb,% Cr,% Mo,% W, and% Ni represent the content (mass%) of each element.

[2]一種熱軋用複合輥子，其係外層與內層融合一體化而成的熱軋用複合輥子，其特徵為：前述外層是由上述[1]所述的熱軋用輥子外層材所形成的。 [2] A hot-rolling composite roll, which is a hot-rolling composite roll formed by integrating an outer layer and an inner layer, wherein the outer layer is made of the outer layer material of the hot-rolling roller described in [1] above. Forming.

根據本發明，可製造出：龜裂的傳播速度明顯地降低的熱軋用輥子外層材以及熱軋用複合輥子。其結果，也可獲得：可減少表面粗糙和缺損之類的因為進行熱軋而產生的輥子表面損傷，而可達成延長連續輥軋的距離和提昇輥子壽命之效果。 According to the present invention, a hot rolling roll outer layer and a hot rolling composite roll with significantly reduced crack propagation speed can be produced. As a result, it is possible to reduce the surface damage of the roller caused by hot rolling such as surface roughness and defects, and to achieve the effects of extending the continuous rolling distance and improving the life of the roller.

1‧‧‧試驗片(熱軋疲勞試驗片) 1‧‧‧test piece (hot rolled fatigue test piece)

2‧‧‧冷卻水 2‧‧‧ cooling water

3‧‧‧高頻感應加熱線圈 3‧‧‧ high frequency induction heating coil

4‧‧‧對手片 4‧‧‧ Opponents

5‧‧‧凹口 5‧‧‧ notch

第1圖是將熱間轉動疲勞試驗使用的試驗機的結構、熱間轉動疲勞試驗用試驗片(疲勞試驗片)、以及被導入在熱間轉動疲勞試驗用試驗片(疲勞試驗片)的外周面的凹口的形狀、尺寸，以示意方式顯示的說明圖。 Fig. 1 shows the structure of a test machine used for the thermal rotation fatigue test, the test piece (fatigue test piece) for the thermal rotation fatigue test, and the outer periphery of the test piece (fatigue test piece) introduced into the thermal rotation fatigue test. The shape and size of the notches on the surface are schematically illustrated.

第2圖是顯示：將本發明的實施方式的熱軋用輥子外層材以EBSD法進行測定的結果之圖。 FIG. 2 is a graph showing the results of measuring the outer layer of a hot-rolling roll according to the embodiment of the present invention by the EBSD method.

第3圖是顯示：熱軋疲勞試驗中的熱軋疲勞壽命與(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)之關係的圖。 Figure 3 shows the hot rolling fatigue life and (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni ).

第4圖是顯示：熱軋疲勞試驗中的熱軋疲勞壽命與回火麻田散鐵或變韌鐵的短徑之關係的圖。 FIG. 4 is a graph showing the relationship between the hot rolling fatigue life and the short diameter of tempered Asada loose iron or toughened iron in the hot rolling fatigue test.

本發明的熱軋用輥子外層材，是利用公知的離心鑄造法或連續澆鑄堆積法之類的鑄造法來製造的，雖然也可以直接就當作：環形輥子、套筒輥子，但是，比較適合用來作為：熱間精製輥軋用的熱軋用複合輥子的外層材。又，本發明的熱軋用複合輥子，是由：外層、以及與該外層融合一體化的內層所構成的。此外，亦可在外層與內層之間，配置有中間層。換言之，亦可以：與外層融合一體化的中間層以及該中間層融合一體化的內層，來取代 與外層融合一體化的內層。在本發明中，雖然並未特別限定內層、中間層的組成分，但是，內層是採用球狀石墨鑄鐵(球墨鑄鐵)或鍛鋼為宜；中間層是採用C：1.5~3.0質量%的高碳材為宜。 The outer layer of the hot-rolling roll of the present invention is manufactured by a casting method such as a known centrifugal casting method or a continuous casting stacking method. Although it can also be directly used as a ring roller or a sleeve roller, it is more suitable. It is used as the outer layer of hot rolling composite rolls for hot-rolled refining rolls. The hot-rolled composite roll of the present invention is composed of an outer layer and an inner layer that is integrated with the outer layer. In addition, an intermediate layer may be disposed between the outer layer and the inner layer. In other words, it is also possible to replace the inner layer integrated with the outer layer by the intermediate layer integrated with the outer layer and the inner layer integrated with the middle layer. In the present invention, although the composition of the inner layer and the intermediate layer is not particularly limited, it is preferable that the inner layer is made of nodular graphite cast iron (spheroidal graphite cast iron) or forged steel; the middle layer is made of C: 1.5 to 3.0% by mass. High carbon materials are preferred.

首先，說明限定本發明的熱軋用複合輥子的外層(外層材)的組成分的理由。此外，在以下的說明當中針對於質量%單純記載成%。 First, the reason for limiting the composition of the outer layer (outer layer material) of the hot-rolled composite roll of the present invention will be explained. In the following description, mass% is simply described as%.

C：2.0~3.0%     C: 2.0 ~ 3.0%    

C是會發生固溶而使基質硬度增加，並且具有與碳化物形成元素結合而形成硬質碳化物，來提昇輥子外層材的耐磨損性之作用。隨著C含量的多寡，共晶碳化物量將會改變。共晶碳化物是會影響輥軋的使用特性。因此，如果C含量低於2.0%的話，共晶碳化物量將會不足，將會增加輥軋時的摩擦力，導致輥軋變得不穩定，並且固溶在基質組織中的C量太低，因而導致耐熱間轉動疲勞性變差。另一方面，如果C含量高於3.0%的話，碳化物變粗大化，共晶碳化物量將會過度增加，導致輥子外層材太過硬質而容易脆化，將會促進疲勞龜裂的發生和成長，使得耐疲勞性變差。因此，將C含量限定在2.0~3.0%的範圍。更好是在2.1~2.8%。 C is a solid solution that increases the hardness of the substrate, and has the effect of combining with carbide forming elements to form hard carbides to improve the wear resistance of the outer layer of the roller. With the amount of C content, the amount of eutectic carbide will change. Eutectic carbides can affect the use characteristics of rolling. Therefore, if the C content is less than 2.0%, the amount of eutectic carbide will be insufficient, which will increase the friction during rolling, causing rolling to become unstable, and the amount of C dissolved in the matrix structure will be too low. As a result, the thermal fatigue resistance deteriorates. On the other hand, if the C content is higher than 3.0%, the carbides become coarse and the amount of eutectic carbides will increase excessively, which will cause the outer layer of the roller to be too hard and easily embrittle, which will promote the occurrence and growth of fatigue cracks. , Making the fatigue resistance worse. Therefore, the C content is limited to the range of 2.0 to 3.0%. Better is 2.1 ~ 2.8%.

Si：0.2~1.0%     Si: 0.2 ~ 1.0%    

Si具有脫氧劑的作用，並且是用來提昇熔融金屬液的 鑄造性之元素。為了獲得這種效果，含量必須是0.2%以上。另一方面，即使含量高於1.0%，效果已趨飽和，無法獲得與含量相應的效果，經濟性變差，有時候也會導致基質組織脆化。因此，將Si含量限定在0.2~1.0%。更好是在0.3~0.7%。 Si functions as a deoxidizer and is an element for improving the castability of molten metal. In order to obtain this effect, the content must be 0.2% or more. On the other hand, even if the content is higher than 1.0%, the effect has become saturated, the effect corresponding to the content cannot be obtained, the economy is deteriorated, and sometimes the matrix tissue is brittle. Therefore, the Si content is limited to 0.2 to 1.0%. It is even better at 0.3 ~ 0.7%.

Mn：0.2~1.0%     Mn: 0.2 ~ 1.0%    

Mn是可將S變成MnS而予以固定下來，具有可使S變得無害化的作用，並且一部分的Mn會固溶在基質組織，是具有提昇淬火硬化性的效果之元素。為了獲得這種效果，Mn含量必須是0.2%以上。另一方面，即使Mn含量高於1.0%，效果已趨飽和，無法獲得與含量相應的效果，有時候也會導致材質脆化。因此，將Mn含量限定在0.2~1.0%。更好是在0.3~0.8%。 Mn is an element that can be fixed by changing S into MnS and has the effect of making S harmless. In addition, a part of Mn is solid-dissolved in the matrix structure, and is an element having an effect of improving hardenability. To obtain this effect, the Mn content must be 0.2% or more. On the other hand, even if the Mn content is higher than 1.0%, the effect has become saturated, and the effect corresponding to the content cannot be obtained, and sometimes the material becomes brittle. Therefore, the Mn content is limited to 0.2 to 1.0%. More preferably, it is between 0.3 and 0.8%.

Cr：4.0~7.0%     Cr: 4.0 ~ 7.0%    

Cr會與C結合而主要是形成共晶碳化物，而可提昇耐磨損性，並且在輥軋時可降低與鋼板的摩擦力，可減輕輥子的表面損傷，是具有可使輥軋趨於穩定化的作用之元素。為了獲得這種效果，Cr含量必須是在4.0%以上。另一方面，如果Cr含量高於7.0%的話，粗大的共晶碳化物將會增加，因而導致耐疲勞性變差。因此，將Cr含量限定在4.0~7.0%的範圍。更好是在4.3~6.5%。 Cr combines with C and mainly forms eutectic carbides, which can improve wear resistance, and can reduce friction with the steel plate during rolling, can reduce surface damage of the roller, and can make the rolling tend to Stabilizing effect element. In order to obtain this effect, the Cr content must be 4.0% or more. On the other hand, if the Cr content is higher than 7.0%, coarse eutectic carbides will increase, resulting in poor fatigue resistance. Therefore, the Cr content is limited to the range of 4.0 to 7.0%. It is even better at 4.3 ~ 6.5%.

Mo：3.0~6.5%     Mo: 3.0 ~ 6.5%    

Mo會與C結合而形成硬質的碳化物，是用來提昇耐磨損性的元素。此外，Mo可固溶在V、Nb與C結合之硬質的MC型碳化物中而可強化碳化物，並且也會固溶在共晶碳化物中，而使得這些碳化物的抗破壞性增加。經由這樣的作用，Mo係可提昇輥子外層材的耐磨損性、耐疲勞性。為了獲得這種效果，Mo含量必須是在3.0%以上。另一方面，Mo含量高於6.5%的話，將會生成以Mo為主體的硬脆性碳化物，導致耐熱間轉動疲勞性變差，耐疲勞性也變差。因此，將Mo含量限定在3.0~6.5%的範圍。更好是在3.5~6.0%。 Mo combines with C to form hard carbides, and is an element used to improve wear resistance. In addition, Mo can be solid-dissolved in hard MC-type carbides in which V, Nb, and C are combined to strengthen carbides, and can also be solid-dissolved in eutectic carbides, thereby increasing the damage resistance of these carbides. Through this action, the Mo system can improve the wear resistance and fatigue resistance of the outer layer of the roller. To obtain this effect, the Mo content must be 3.0% or more. On the other hand, if the Mo content is higher than 6.5%, hard and brittle carbides mainly composed of Mo will be generated, resulting in deterioration of thermal fatigue resistance and fatigue resistance. Therefore, the Mo content is limited to the range of 3.0 to 6.5%. It is even better at 3.5 ~ 6.0%.

V：5.0~7.5%     V: 5.0 ~ 7.5%    

V是用來使得輥子兼具有耐磨損性與耐疲勞性，是本發明中的重要元素。V係可形成極硬質的碳化物(MC型碳化物)而可提昇耐磨損性，並且具有可將共晶碳化物分斷而有效地使其分散地晶析出來的作用，可提昇耐熱間轉動疲勞性，是可顯著地提昇輥子外層材的耐疲勞性之元素。這種效果是在V含量為5.0%以上時變明顯。另一方面，如果V含量高於7.5%的話，將會使MC型碳化物變得粗大化，因而導致輥軋用輥子的各種特性變得不穩定。因此，將V含量限定在5.0~7.5%的範圍。更好是在5.2~7.0%。 V is used to make the roller have both abrasion resistance and fatigue resistance, and is an important element in the present invention. V series can form extremely hard carbides (MC-type carbides) to improve wear resistance, and it can break eutectic carbides and effectively disperse and crystallize them, which can improve the heat resistance. Rotation fatigue is an element that can significantly improve the fatigue resistance of the outer layer of the roller. This effect becomes apparent when the V content is 5.0% or more. On the other hand, if the V content is higher than 7.5%, MC-type carbides will be coarsened, and various characteristics of the roll for rolling will become unstable. Therefore, the V content is limited to the range of 5.0 to 7.5%. It is better at 5.2 ~ 7.0%.

Nb：0.5~3.0%     Nb: 0.5 ~ 3.0%    

Nb是可經由：固溶於MC型碳化物中來強化MC型碳化物，而使MC型碳化物的抗破壞性增加的作用，來提昇耐磨損性，尤其是提昇耐疲勞性。Nb與Mo都是藉由固溶於碳化物中來使得耐磨損性與耐疲勞性的提昇更為顯著。此外，Nb可促進共晶碳化物的分斷，具有可抑制共晶碳化物的破壞之作用，是可提昇輥子外層材的耐疲勞性之元素。此外，Nb也兼具有：可抑制MC型碳化物在離心鑄造時偏析出來的作用。這種效果是在Nb含量為0.5%以上時變明顯。另一方面，如果Nb含量高於3.0%的話，將會促進熔融金屬液中的MC型碳化物的成長，導致耐熱間轉動疲勞性惡化。因此，將Nb含量限定在0.5~3.0%的範圍。更好是在0.8~1.5%。 Nb can strengthen MC-type carbides by solid-solving in MC-type carbides and increase the damage resistance of MC-type carbides to improve wear resistance, especially fatigue resistance. Both Nb and Mo make the improvement of wear resistance and fatigue resistance more significant by solid solution in carbide. In addition, Nb promotes the breaking of eutectic carbides, has the effect of suppressing the destruction of eutectic carbides, and is an element that can improve the fatigue resistance of the outer layer of the roller. In addition, Nb also has the effect of suppressing segregation of MC-type carbides during centrifugal casting. This effect becomes apparent when the Nb content is 0.5% or more. On the other hand, if the Nb content is higher than 3.0%, the growth of MC-type carbides in the molten metal liquid will be promoted, and the thermal fatigue resistance will deteriorate. Therefore, the Nb content is limited to the range of 0.5 to 3.0%. More preferably, it is between 0.8 and 1.5%.

Ni：0.05~3.0%     Ni: 0.05 ~ 3.0%    

Ni是可固溶於基質中，而可降低在熱處理中之沃斯田鐵的變態溫度，是可提昇基質的淬火硬化性之元素。為了獲得這種效果，Ni含量必須是在0.05%以上。另一方面，如果Ni含量高於3.0%的話，沃斯田鐵的變態溫度變得太低，而且淬火硬化性也被提昇，因而，在熱處理後很容易有沃斯田鐵殘留下來。如果有沃斯田鐵殘留下來的話，在熱軋中容易發生龜裂等的現象，將會導致耐熱間轉動疲勞性變差。因此，將Ni含量限定在0.05~3.0%的範圍。此外，基於所謂的「即使熱處理中的冷卻速度太慢， 依然可使得基質組織的結晶粒徑保持微細化」之作業上的容易性的考量，更好是在0.2~3.0%。 Ni is a solid solution in the matrix, and can reduce the abnormal temperature of Vosted iron during heat treatment, and is an element that can improve the quench hardenability of the matrix. To obtain this effect, the Ni content must be above 0.05%. On the other hand, if the Ni content is higher than 3.0%, the transformation temperature of Vosstian iron becomes too low, and the hardenability is also improved. Therefore, Vosstian iron is likely to remain after heat treatment. If the Wastfield iron is left, cracks and the like are likely to occur during hot rolling, which will result in poor rotation fatigue resistance between heat resistance. Therefore, the Ni content is limited to the range of 0.05 to 3.0%. In addition, based on the easiness consideration of the operation of "so that the crystal grain size of the matrix structure can be kept fine even if the cooling rate during the heat treatment is too slow", it is more preferably 0.2 to 3.0%.

Co：0.2~5.0%     Co: 0.2 ~ 5.0%    

Co是會固溶於基質中而特別是在高溫中可強化基質而具有提昇耐疲勞性的作用之元素。為了獲得這種效果，Co含量必須是在0.2%以上。另一方面，如果Co含量高於5.0%的話，效果已趨飽和，無法獲得與含量相應的效果，經濟性變差。因此，將Co含量限定在0.2~5.0%的範圍。更好是在0.5~3.0%。 Co is an element that is solid-dissolved in the matrix, and can strengthen the matrix especially at high temperatures, and has the effect of improving fatigue resistance. In order to obtain this effect, the Co content must be 0.2% or more. On the other hand, if the Co content is higher than 5.0%, the effect becomes saturated, and an effect according to the content cannot be obtained, resulting in poor economic efficiency. Therefore, the Co content is limited to the range of 0.2 to 5.0%. More preferably, it is between 0.5 and 3.0%.

W：0.5~5.0%     W: 0.5 ~ 5.0%    

W是會固溶於基質中而特別是在高溫中可強化基質而具有提昇耐疲勞性的作用之元素，而且會形成M2C或M6C系的碳化物，可提昇耐磨損性。為了獲得這種效果，W含量必須是在0.5%以上。另一方面，W含量超過5.0%的話，不僅效果已趨飽和，也會形成粗大的M2C或M6C系的碳化物，導致耐熱間轉動疲勞性變差。因此，將W含量限定在0.5~5.0%的範圍。更好是在1.0~3.5%。 W is an element that is solid-dissolved in the matrix, and can strengthen the matrix especially at high temperatures, and has the effect of improving fatigue resistance. It also forms M 2 C or M 6 C-based carbides, which can improve wear resistance. In order to obtain this effect, the W content must be 0.5% or more. On the other hand, if the W content exceeds 5.0%, not only the effect will become saturated, but also coarse M 2 C or M 6 C-based carbides will be formed, resulting in poor rotation fatigue resistance during heat resistance. Therefore, the W content is limited to the range of 0.5 to 5.0%. More preferably, it is between 1.0 and 3.5%.

本發明是在上述範圍內含有：C、Cr、Mo、V、Nb、Ni、W，並且必須調整其含量來符合下列的數式(1)的關係。 The present invention contains C, Cr, Mo, V, Nb, Ni, and W in the above range, and its content must be adjusted to meet the relationship of the following formula (1).

0.05≦(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)≦4.0 數式(1) 0.05 ≦ (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) ≦ 4.0 Equation (1)

此處的%C、%V、%Nb、%Cr、%Mo、%W、%Ni是表示：各元素的含量(質量%)。 Here,% C,% V,% Nb,% Cr,% Mo,% W, and% Ni indicate the content (mass%) of each element.

藉由將(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)中的各元素含量，調整成符合上述數式(1)的關係，可顯著地增加：折損滾動數，耐熱間轉動疲勞性將會顯著地提昇。(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)是用來提昇耐熱間轉動疲勞性的驅動力的重要因素，如果落在上述數式(1)的範圍外的話，耐熱間轉動疲勞性將會惡化。V、Cr、Mo、Nb、W是容易生成碳化物的元素，(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)是表示：固溶於基質中的碳量。因此，(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)就是固溶於基質中的碳量與Ni量的總和，藉由將這個數值調整在適正的範圍的話，可獲得：基質中的龜裂的傳播速度較慢之熱軋疲勞壽命優異的輥子外層材。因此，在本發明中，乃將(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)予以調整成符合上述數式(1)的關係。 By adjusting the content of each element in (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni), it is adjusted to meet the above formula ( 1) The relationship can be significantly increased: the rolling number is broken, and the rotation fatigue resistance between heat resistance will be significantly improved. (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) is an important factor for driving force for improving the rotation fatigue resistance between heat resistance, If it falls outside the range of the above formula (1), the thermal fatigue resistance will deteriorate. V, Cr, Mo, Nb, and W are elements that easily form carbides. (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) means: solid The amount of carbon dissolved in the matrix. Therefore, (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) is the sum of the amount of carbon dissolved in the matrix and the amount of Ni By adjusting this value to a proper range, it is possible to obtain a roll outer layer having excellent hot rolling fatigue life with a slow propagation speed of cracks in the matrix. Therefore, in the present invention, (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063-% W × 0.033) + (% Ni) is adjusted to conform to the above formula (1) The relationship.

上述成分以外的其餘部分是Fe以及不可避免的雜質。 The balance other than the above components is Fe and unavoidable impurities.

又，在本發明中，基質組織的85%以上是回 火麻田散鐵及回火變韌鐵組織的至少其中一種組織，且回火麻田散鐵或回火變韌鐵的短徑是落在0.5~3.0μm的範圍為宜。殘留沃斯田鐵和波來鐵組織的百分率太多的話，耐熱間轉動疲勞性將會變差，因此，在基質組織中，回火麻田散鐵及變韌鐵組織的至少其中一種組織的含量是85%以上為宜，基於耐熱間轉動疲勞性的觀點考量，含量是90%以上更好。此外，其餘部分係可舉出：殘留沃斯田鐵及波來鐵的至少其中一種。此外，為了使得基質組織的85%以上都是回火麻田散鐵及變韌鐵的至少其中一種，只要先加熱到500~570℃並且加以保持之後，然後，藉由進行冷卻工序的反覆次數的多寡來進行控制即可。 In the present invention, more than 85% of the matrix structure is at least one of tempered Asada loose iron and tempered and toughened iron structure, and the short diameter of the tempered Asada loose iron or tempered and toughened iron falls on A range of 0.5 to 3.0 μm is suitable. If the percentage of the residual Vostian iron and Plei iron structure is too large, the rotation fatigue resistance between heat resistance will be deteriorated. Therefore, in the matrix structure, the content of at least one of tempered Asada loose iron and toughened iron structure is contained. It is preferably 85% or more, and based on the viewpoint of thermal fatigue resistance, the content is preferably 90% or more. In addition, the remaining part may include at least one of a residual Vosstian iron and a boron iron. In addition, in order to make more than 85% of the matrix structure be at least one of tempered Asada loose iron and toughened iron, as long as it is heated to 500-570 ° C and maintained, then, the number of repeated cooling steps is performed. How much to control.

又，如果是回火麻田散鐵或回火變韌鐵的短徑小於0.5μm的這種成分系的話，變態溫度太低，即使反覆進行回火，也難以降低殘留沃斯田鐵的數量，在進行熱軋途中有可能發生起因於殘留沃斯田鐵的龜裂現象，耐熱間轉動疲勞性將會變差。此外，如果回火麻田散鐵或回火變韌鐵的短徑大於3.0μm的話，基質組織的龜裂傳播速度很快，耐熱間轉動疲勞性將會變差。因此，將基質組織的回火麻田散鐵或回火變韌鐵的短徑限定在0.5~3.0μm的範圍為宜。基於耐熱間轉動疲勞性的觀點考量，是限定在0.5~2.0μm的範圍更好。又，為了獲得這種範圍的短徑，只要控制組成分以及冷卻速度，來使得基質的變態溫度落在200~400℃的範圍內即可。 In addition, if it is a component system of tempered Asada loose iron or tempered toughened iron with a short diameter of less than 0.5 μm, the abnormal temperature is too low, and even if it is repeatedly tempered, it is difficult to reduce the amount of residual Vostian iron. During hot rolling, cracking may occur due to the residual Vostian iron, and the rotation fatigue resistance between heat resistance will be deteriorated. In addition, if the short diameter of tempered Asada loose iron or tempered toughened iron is greater than 3.0 μm, the crack propagation speed of the matrix structure is fast, and the rotation fatigue resistance between heat resistance will be deteriorated. Therefore, it is preferable to limit the short diameter of the tempered Mata loose iron or the tempered toughened iron to 0.5 to 3.0 μm. From the viewpoint of thermal fatigue resistance, it is more preferable to limit it to the range of 0.5 to 2.0 μm. In order to obtain the short diameter in this range, it is only necessary to control the composition and cooling rate so that the abnormal temperature of the substrate falls within the range of 200 to 400 ° C.

其次，說明本發明的熱軋用複合輥子之合宜 的製造方法。 Next, a suitable manufacturing method of the hot-rolled composite roll of the present invention will be described.

在本發明中，輥子外層材的製造方法，最好是利用公知的離心鑄造法或連續澆鑄堆積法之類的鑄造法來進行製造。此外，在本發明中，當然是不限定只有這些方法而已。 In the present invention, the method for manufacturing the outer layer of the roller is preferably manufactured by a casting method such as a known centrifugal casting method or a continuous casting deposition method. It is needless to say that these methods are not limited in the present invention.

利用離心鑄造法來進行鑄造輥子外層材的話，首先，是在旋轉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，直到既定的厚度為止，而該鑄模的內面則是披覆著厚度1~5mm之以鋯石等作為主材質的耐火物，並且進行離心鑄造。此時，鑄模的迴轉數，是設定在可使得加諸在輥子外表面的重力倍數落在120~220G的範圍內為宜。並且，如果是要形成中間層的話，則是在輥子外層材的凝固途中或者完全凝固之後，一邊旋轉鑄模一邊注入中間層組成分的熔融金屬液來進行離心鑄造為宜。外層或中間層完全凝固之後，停止鑄模的旋轉，將鑄模豎立起來，讓內層材進行靜置鑄造，因而製作成複合輥子為宜。如此一來，輥子外層材的內面側將會再熔解，而成為外層與內層、或者外層與中間層、中間層與內層融合一體化的複合輥子。 When the outer layer of the roller is cast by the centrifugal casting method, first, a molten metal liquid having the composition of the outer layer of the roller is injected into a rotating mold to a predetermined thickness, and the inner surface of the mold is coated. Centrifugal casting is performed on a refractory material having a thickness of 1 to 5 mm and using zircon as a main material. At this time, the number of rotations of the mold is preferably set so that the multiple of gravity applied to the outer surface of the roller falls within the range of 120 ~ 220G. In addition, if the intermediate layer is to be formed, it is preferable to perform the centrifugal casting by injecting the molten metal of the intermediate layer composition while rotating the mold while the outer layer of the roller is being solidified or completely solidified. After the outer layer or the middle layer is completely solidified, the rotation of the casting mold is stopped, the casting mold is erected, and the inner layer material is subjected to static casting, so it is appropriate to make a composite roller. In this way, the inner side of the outer layer of the roller will be melted again, and become a composite roller that is integrated with the outer layer and the inner layer, or the outer layer and the middle layer, and the middle layer and the inner layer.

此外，進行靜置鑄造的內層，是使用鑄造性與機械性質優異的球狀石墨鑄鐵、芋蟲(毛毛蟲的幼蟲)狀石墨鑄鐵(CV鑄鐵)等為宜。離心鑄造製的輥子，因為是外層與內層形成一體融合，因此外層材的成分會有1~8%左右混入到內層。含在外層材內的Cr、V等的碳化物形成 元素混入到內層的話，會使內層脆弱化。因此，必須將外層成分混入到內層的混入率控制成低於6%為宜。 In addition, as the inner layer to be subjected to the stationary casting, a spheroidal graphite cast iron excellent in castability and mechanical properties, a taro (caterpillar larva) -shaped graphite cast iron (CV cast iron), or the like is preferably used. The centrifugal cast roller is integrated with the outer layer and the inner layer, so about 1 ~ 8% of the ingredients of the outer layer material are mixed into the inner layer. If carbide-forming elements such as Cr and V contained in the outer layer material are mixed into the inner layer, the inner layer is weakened. Therefore, it is necessary to control the mixing ratio of the outer layer components to the inner layer to be less than 6%.

又，如果要形成中間層的話，中間層材是使用石墨鋼、高碳鋼、亞共晶鑄鐵等為宜。中間層與外層同樣地一體融合，外層成分將會在10~95%的範圍內，混入到中間層。因此，基於減少外層成分混入內層的混入量的觀點考量，儘可能在事前就降低混入中間層之外層成分的混入量的作法是很重要。 In addition, if an intermediate layer is to be formed, it is preferable to use graphite steel, high carbon steel, hypoeutectic cast iron, or the like as the intermediate layer material. The middle layer is integrated with the outer layer in the same way, and the outer layer components will be mixed into the middle layer within the range of 10 ~ 95%. Therefore, from the viewpoint of reducing the amount of mixing of the outer layer components into the inner layer, it is important to reduce the amount of mixing into the outer layer components of the middle layer as much as possible in advance.

本發明的熱軋用複合輥子，在鑄造後是實施熱處理為宜。熱處理是進行下列工序為宜。亦即，先加熱到950~1100℃後進行空冷或吹風空冷的工序；以及再度加熱到500~570℃並加以保持之後，進行兩次以上的冷卻工序。此時，可配合不同的組成分來調整冷卻速度，以使變態溫度落在200~400℃的範圍內，如此一來，就可獲得前述之較佳的短徑大小。此外，再加熱到500~570℃並加以保持之後，依據反覆進行的冷卻工序的次數的不同，基質組織中的回火麻田散鐵及回火變韌鐵的至少其中一種的量將會改變，因此，只要將冷卻工序的反覆次數，設定成：基質組織的85%以上將會是回火麻田散鐵及回火變韌鐵的至少其中一種即可。此外，本發明的熱軋用複合輥子的合宜硬度是79~88HS(蕭氏硬度)，更好的硬度是80~86HS。如果硬度低於80HS的話，耐磨損性會惡化，相反地，硬度高於86HS的話，將難以利用研磨車削方式將熱軋中形成在熱軋用輥子表面的龜裂予以除去。為了能 夠穩定地確保這種硬度，必須調整鑄造後的熱處理溫度、熱處理時間。 The hot-rolled composite roll of the present invention is preferably heat-treated after casting. The heat treatment is preferably performed in the following steps. That is, the process of heating to 950 to 1100 ° C and then air-cooling or blowing air-cooling is performed; and the process of heating to 500 to 570 ° C and maintaining it again is performed twice or more. At this time, the cooling rate can be adjusted in accordance with different compositions so that the abnormal temperature falls within the range of 200 ~ 400 ° C. In this way, the aforementioned preferred short diameter size can be obtained. In addition, after reheating to 500 to 570 ° C and maintaining it, the amount of at least one of tempered Asada loose iron and tempered toughened iron in the matrix structure will change depending on the number of repeated cooling steps. Therefore, as long as the number of repetitions of the cooling process is set, at least 85% of the matrix structure will be at least one of tempered Asada iron and tempered iron. In addition, a suitable hardness of the composite roll for hot rolling of the present invention is 79 to 88HS (Shore hardness), and a more preferable hardness is 80 to 86HS. If the hardness is lower than 80HS, the abrasion resistance is deteriorated. On the contrary, if the hardness is higher than 86HS, it is difficult to remove cracks formed on the surface of the hot rolling roll during hot rolling by grinding and turning. In order to secure such hardness stably, it is necessary to adjust the heat treatment temperature and heat treatment time after casting.

[實施例]     [Example]    

利用高頻感應加熱爐熔製出：表1所示的輥子外層材組成分的熔融金屬液，利用離心鑄造法鑄造成環狀試驗材(環狀輥子；外徑：250mm 、寬度：65mm、厚度：55mm)。此外，澆鑄溫度設定在1450~1530℃，離心力是設定在：讓環狀輥子材的外周部成為重力倍數之180G。鑄造後，以淬火硬化溫度：1070℃進行再加熱，進行空冷之後，進行淬火硬化處理，而回火處理則是以溫度：530~570℃，並可使得殘留沃斯田鐵量低於10%(以體積%計)的方式，依成分的不同而實施兩次或三次，並且將硬度調整到78~86HS。從製得的環狀試驗材身上採取出：硬度試驗片、熱間轉動疲勞試驗片以及EBSD測定用試驗片，實施了硬度試驗、熱間轉動疲勞試驗以及組織觀察試驗。 The high-frequency induction heating furnace was used to melt the molten metal liquid of the roller outer layer composition shown in Table 1, and cast it into a ring-shaped test material (ring-shaped roller; outer diameter: 250 mm) by a centrifugal casting method. , Width: 65mm, thickness: 55mm). In addition, the casting temperature was set to 1450-1530 ° C, and the centrifugal force was set to make the outer peripheral portion of the ring-shaped roller material 180 G of the multiple of gravity. After casting, it is reheated at quenching temperature: 1070 ° C, and after air cooling, it is quenched and hardened, while tempering is performed at temperature: 530 ~ 570 ° C, and the amount of residual Vostian iron can be less than 10% (using Volume%), two or three times depending on the composition, and the hardness is adjusted to 78 ~ 86HS. From the obtained annular test material, a hardness test piece, a thermal rotation fatigue test piece, and an EBSD measurement test piece were taken, and a hardness test, a thermal rotation fatigue test, and a microstructure observation test were performed.

針對於製得的硬度試驗片，依據日本工業規 格JIS Z 2244的規定，使用維氏硬度計(試驗力：50kgf(490N))來測定維氏硬度HV50，再根據日本工業規格JIS換算表，換算成蕭氏硬度HS。此外，測定點是設成各10點，將最高值和最低值去除之後，計算出平均值，將其視為該試驗材的硬度。 For the prepared hardness test piece, the Vickers hardness HV50 was measured using a Vickers hardness tester (testing force: 50kgf (490N)) according to the Japanese Industrial Standard JIS Z 2244, and then converted according to the Japanese Industrial Standard JIS conversion table. Into Shore hardness HS. In addition, the measurement points were set to 10 points each, the highest value and the lowest value were removed, and then the average value was calculated, and this was regarded as the hardness of the test material.

熱間轉動疲勞試驗方法，則是如下所述。從製得的環狀試驗材的身上採取出熱間轉動疲勞試驗片(外徑60mm ，厚度10mm，有做倒角加工)。在熱間轉動疲勞試驗片身上，係如第1圖所示，在外周面上的兩個地方(分開180°的位置上)，使用直徑0.20mm 的焊線，利用放電加工(焊線切割)法，導入兩個凹口(深度t：1.2mm，周方向長度L：0.8mm)。熱間轉動疲勞試驗，係如第1圖所示般地，是以讓試驗片與對手材的兩個圓盤進行打滑轉動的方式來實施的。將試驗片1以冷卻水2一邊進行水冷，一邊使其以迴轉數為700rpm的方式進行旋轉，將利用高頻感應加熱線圈3加熱到800℃後的對手片(材質：S45C，外徑：190mm ，寬度：15mm、C1倒角)4以980N的荷重，一邊接觸於正在旋轉中的該試驗片1，一邊以9%的打滑率，使該對手片進行轉動。並且持續使其進行轉動，直到被導入熱間轉動疲勞試驗片1外周面上的兩個凹口5折損為止，分別求出各凹口折損時的轉動迴轉數，並且將其平均值當作熱軋疲勞壽命。將熱軋疲勞壽命超過35萬轉的情況，評判為熱軋疲勞壽命非常優異。 The thermal rotation fatigue test method is as follows. Take the thermal fatigue test piece (outer diameter 60mm) from the ring-shaped test material. , Thickness 10mm, with chamfering). As shown in Figure 1 on the thermal fatigue test piece, a diameter of 0.20mm was used at two places on the outer peripheral surface (at a position separated by 180 °). In the welding wire, two notches (depth t: 1.2 mm, circumferential length L: 0.8 mm) were introduced by an electric discharge machining (welding wire cutting) method. The thermal-rotation fatigue test was carried out by sliding the test piece and the two discs of the opponent as shown in FIG. 1. The test piece 1 was cooled with cooling water 2 while being rotated at a rotation speed of 700 rpm, and the opponent piece (material: S45C, outer diameter: 190mm) heated to 800 ° C by a high-frequency induction heating coil 3 was used. , Width: 15mm, C1 chamfer) 4 With a load of 980N, while contacting the test piece 1 being rotated, the opponent piece was rotated at a slip rate of 9%. And continue to rotate until the two notches 5 on the outer peripheral surface of the thermal fatigue test piece 1 are broken, and calculate the number of rotations when each notch is broken, and use the average value as the heat Rolling fatigue life. When the hot rolling fatigue life exceeds 350,000 revolutions, it is judged that the hot rolling fatigue life is very excellent.

組織觀察，是先從環狀輥子材的外表面起算 之10mm內部的任意位置內，採取出10×10×5mm(5mm是在環圈的厚度方向上)的組織觀察試驗片，並且對於10×10mm的面進行鏡面研磨，再以硝酸蝕刻液(5體積%硝酸+乙醇)進行10秒左右的腐蝕處理，然後使用光學顯微鏡觀察金屬組織。 The structure observation is to take a 10 × 10 × 5mm (5mm is in the thickness direction of the ring) from any position inside the 10mm from the outer surface of the annular roller material, and for the 10 × A 10 mm surface was mirror-polished, and then subjected to an etching treatment with a nitric acid etching solution (5 vol% nitric acid + ethanol) for about 10 seconds, and then the metal structure was observed using an optical microscope.

回火麻田散鐵或回火變韌鐵的短徑(短軸長度)的測定方法，是先從製得的環狀輥子材的外表面起算10mm內部的任意位置，採取出供進行測定的EBSD測定試驗片(5mm×10mm×5mm)，並且對於5mm×10mm的面進行鏡面研磨，利用EBSD測定而求得。是以加速電壓為15kV，步進量為0.1μm的條件，針對10000μm2以上的領域進行了EBSD測定。使用所測得的資料，如第2圖所示，在與相鄰的測定點之間的方位差為15°以上之處畫上境界線，將被境界線所圍繞的領域視為一個結晶，在測定面上對於長徑為10μm以上之20個結晶的短徑進行測定，並且算出其平均值。 The method for measuring the short diameter (short-axis length) of tempered Asada loose iron or tempered toughened iron is to first obtain an EBSD for measurement from any position within 10 mm from the outer surface of the obtained annular roller material. A test piece (5 mm × 10 mm × 5 mm) was measured, and a 5 mm × 10 mm surface was mirror-polished, and obtained by EBSD measurement. The EBSD measurement was performed on an area of 10000 μm 2 or more under the conditions of an acceleration voltage of 15 kV and a step amount of 0.1 μm. Using the measured data, as shown in Figure 2, draw a boundary line where the azimuth difference from the adjacent measurement point is 15 ° or more, and consider the area surrounded by the boundary line as a crystal. The short diameter of 20 crystals having a long diameter of 10 μm or more was measured on the measurement surface, and the average value was calculated.

將所獲得的結果標示於表2。 The obtained results are shown in Table 2.

本發明例都顯示出：熱軋疲勞壽命顯著增加，都具有超過35萬轉以上的優異的熱軋疲勞壽命。此外，組織觀察的結果，可以確認出本發明例的每一個例子都是：基質組織的85%以上是回火麻田散鐵及回火變韌鐵組織的其中至少一種。 The examples of the present invention all show that the hot rolling fatigue life is significantly increased, and all have excellent hot rolling fatigue life in excess of 350,000 revolutions. In addition, as a result of the structure observation, it can be confirmed that each of the examples of the present invention is that at least 85% of the matrix structure is at least one of tempered Asada loose iron and tempered and toughened iron structure.

因此，根據本發明，係可製造出：龜裂的傳播速度顯著的降低之熱軋用複合輥子。其結果，也可獲得：可減少表面粗糙和缺損之類的因為進行熱軋而產生的輥子表面損傷，而可達成延長連續輥軋的距離和提昇輥子壽命之效果。 Therefore, according to the present invention, a composite roll for hot rolling in which the propagation speed of cracks is significantly reduced can be manufactured. As a result, it is possible to reduce the surface damage of the roller caused by hot rolling such as surface roughness and defects, and to achieve the effects of extending the continuous rolling distance and improving the life of the roller.

Claims (2)

一種熱軋用輥子外層材的特徵為：其組成分以質量%計，含有C：2.0~3.0%、Si：0.2~1.0%、Mn：0.2~1.0%、Cr：4.0~7.0%、Mo：3.0~6.5%、V：5.0~7.5%、Nb：0.5~3.0%、Ni：0.05~3.0%、Co：0.2~5.0%、W：0.5~5.0%，並且C、Cr、Mo、V、Nb、Ni、W的含量，係符合下列數式(1)的關係，其餘部分是Fe以及不可避免的雜質，基質組織的85%以上是回火麻田散鐵組織及回火變韌鐵組織之其中至少一種組織，回火麻田散鐵或回火變韌鐵的短徑是0.5~3.0μm，0.05≦(%C-%V×0.177-%Nb×0.129-%Cr×0.099-%Mo×0.063-%W×0.033)+(%Ni)≦4.0 數式(1)此處的%C、%V、%Nb、%Cr、%Mo、%W、%Ni是表示各元素的含量(質量%)。     The outer layer of a hot rolling roll is characterized by its composition in terms of mass%, containing C: 2.0 to 3.0%, Si: 0.2 to 1.0%, Mn: 0.2 to 1.0%, Cr: 4.0 to 7.0%, and Mo: 3.0 to 6.5%, V: 5.0 to 7.5%, Nb: 0.5 to 3.0%, Ni: 0.05 to 3.0%, Co: 0.2 to 5.0%, W: 0.5 to 5.0%, and C, Cr, Mo, V, Nb The contents of Ni, Ni, and W are in accordance with the following formula (1). The rest is Fe and unavoidable impurities. More than 85% of the matrix structure is tempered Asada loose iron structure and tempered toughened iron structure. At least one structure, the short diameter of tempered Asada loose iron or tempered toughened iron is 0.5 ~ 3.0μm, 0.05 ≦ (% C-% V × 0.177-% Nb × 0.129-% Cr × 0.099-% Mo × 0.063- % W × 0.033) + (% Ni) ≦ 4.0 Equation (1) Here,% C,% V,% Nb,% Cr,% Mo,% W, and% Ni indicate the content of each element (% by mass) .     一種熱軋用複合輥子，其係外層與內層融合一體化而成的熱軋用複合輥子，前述外層是由申請專利範圍第1項所述的熱軋用輥子外層材所形成的。     A hot-rolling composite roll is a hot-rolling composite roll in which an outer layer and an inner layer are integrated. The outer layer is formed by the outer layer material of the hot-rolling roll described in the first item of the scope of patent application.    
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