JP2004162104A - Roll external layer material for hot rolling and composite roll for hot rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roll external layer material for hot rolling excellent in resistances to wear, surface roughening, sand burning, and thermal impact; and a composite roll for hot rolling using the same. <P>SOLUTION: The external layer material comprises, in terms of mass%, 2.6-3.5% C, 1.0-2.5% Si, 0.2-1.5% Mn, 0.8-2.7% Cr, 1.0-3.0% Mo, 2.0-7.0% Ni, 1.3-2.5% V, 0.1-0.8% Nb, 0.020-0.2% B, at least either lower than 0.05% Ti or 0.1% or lower Al, and the balance being Fe and unavoidable impurities, provided that the contents of C, Cr, Nb, and V satisfy 2.0≤C-(0.24V+0.13Nb)≤3.0, Cr/C<1.0, and 3.0≤Cr+V≤4.5 [wherein C, V, Nb, and Cr respectively satisfy their contents (mass%) described above]. The material may further contain 0.1-4.0% Co. <P>COPYRIGHT: (C)2004,JPO

Description

【００５４】
【表２】

【００５５】
本発明例は、いずれも耐摩耗性に優れ、かつ焼付きや肌荒れの発生がなく、また、亀裂深さも浅く、極めて優れた耐摩耗性、耐焼付き性、耐肌荒れ性および耐熱衝撃性を兼備したロール外層材となっている。
一方、本発明の範囲から外れる比較例は、耐摩耗性、耐肌荒れ性、耐焼付き性、および耐熱衝撃性の少なくとも１つ以上が著しく低下している。
【００５６】
Ｎｂ含有量が本発明範囲を高く外れる比較例（リング材Ｎｏ． Ｉ）では、肌荒れが著しくなり、また亀裂深さが深く、耐肌荒れ性、 耐熱衝撃性が劣化している。また、Ｎｂ無添加、Ａｌ、Ｔｉのいずれも含有しない比較例（リング材Ｎｏ． Ｊ）では、肌荒れが発生し、亀裂深さも深く、耐肌荒れ性、耐熱衝撃性が低下している。また、Ｍｏ、Ｖ含有量、（Ｃｒ＋Ｖ）量が本発明範囲を高く外れ、Ｎｂ、Ｂを含有しない比較例（リング材Ｎｏ． Ｋ）では、著しい肌荒れ、焼付きが発生し、亀裂深さも深く、耐肌荒れ性、耐焼付き性、および耐熱衝撃性が低下している。Ｖ含有量が少なく、Ｗを含有する比較例（リング材Ｎｏ． Ｌ）では、摩耗量が増加し耐摩耗性が低下するとともに、肌荒れが発生し耐肌荒れ性が低下している。Ｗを含有し、Ｃｒ、Ｃｒ／Ｃ、（Ｃｒ＋Ｖ）量が本発明範囲を高く外れる比較例（リング材Ｎｏ． Ｍ）では、著しい肌荒れ、焼付きが発生し、亀裂深さも深く、耐肌荒れ性、耐焼付き性、および耐熱衝撃性が低下している。Ｗを含有し、Ｖ含有量、（Ｃｒ＋Ｖ）量が本発明範囲を低く外れ、Ｂ、Ａｌ、Ｔｉのいずれも含有しない比較例（リング材Ｎｏ． Ｎ）では、摩耗量が増加し耐摩耗性が低下し、肌荒れが発生し、亀裂深さが深く、耐肌荒れ性、耐熱衝撃性が低下している。Ｍｏ含有量が本発明範囲より低く外れ、有効Ｃ量が本発明範囲から高く外れ、Ａｌ、Ｔｉのいずれも含有しない比較例（リング材Ｎｏ． Ｏ）では、摩耗量が増加し耐摩耗性が低下し、肌荒れが発生し、亀裂深さが深く、耐肌荒れ性、耐熱衝撃性が低下している。なお、従来例（リング材Ｎｏ．ＮｉＧ）は耐焼付き性、耐熱衝撃性に優れるが耐摩耗性が著しく劣っている。
（実施例２）
製品胴径６８５ ｍｍ、胴長２３８０ｍｍの複合ロールを以下の手順で製造した。
【００５７】
遠心力１４０ Ｇで回転する鋳型内に、外層として肉厚１２０ｍｍ になるように、外層材溶湯を鋳込んだ。外層が凝固した後に鋳型の回転を停止し、鋳型を立てて内層材（ 球状黒鉛鋳鉄）を鋳造することで、外層−内層を一体化させ、外層の表面温度が８０℃以下になるまで冷却した後、鋳型を解体し、外層−内層からなる複合ロールとした。
【００５８】
得られた複合ロールは、４００ 〜５００ ℃に３０時間加熱したのち徐冷する熱処理（焼戻し処理）を実施し、外層の硬さを８０〜８３Ｈｓとした。
熱処理後、ロール胴端部から外層の化学組成分析用試験材、組織観察用試験片を採取した。なお、内層についてはロール軸端の中心部から化学組成分析用試料を採取した。各複合ロールの外層、内層の化学組成を表３に示す。
【００５９】
得られた複合ロールを、熱間仕上圧延ミルのＦ７スタンドの作業ロールとして投入し、炭素鋼１００ 本の試験圧延を実施した。なお、その中の１本で絞り圧延を再現し、焼付き状況を比較した。
【００６０】
【表３】

【００６１】
本発明例（複合ロールＮｏ．１）は、従来ロールであるＮｉＧ 鋳鉄ロールの約１．６ 倍の極めて良好な耐摩耗性と耐肌荒れ性を有することが確認された。また、絞り圧延において焼付きは発生しなかった。
【００６２】
【発明の効果】
本発明によれば、鋼板の熱間圧延の後段圧延スタンド用ロールとして、優れた耐摩耗性、耐焼付き性、耐肌荒れ性および耐熱衝撃性を兼備した複合ロールが安価に製造でき、産業上格段の効果を奏する。また、本発明の複合ロールは、鋼板の熱間圧延において絞り事故の多発する、後段圧延スタンド用ロールとして安定して使用できる。また、本発明の複合ロールは、優れた耐焼付き性、耐肌荒れ性および耐摩耗性が要求される鋼管圧延用ロールとしても適用できる。
【図面の簡単な説明】
【図１】（ａ）十点平均粗さ（Ｒｚ ）と有効Ｃ量との関係、（ｂ）亀裂深さと有効Ｃ量との関係を示すグラフである。
【図２】（ａ）摩耗量、十点平均粗さ（Ｒｚ ）と（Ｃｒ＋Ｖ）量の関係、（ｂ）亀裂深さと（Ｃｒ＋Ｖ）量の関係を示すグラフである。
【図３】焼付き試験の概要を示す概略説明図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a composite roll for hot rolling, and in particular, is excellent in abrasion resistance, seizure resistance, surface roughening resistance, and thermal shock resistance, and is suitable for a hot rolling finish mill or a seamless steel pipe forming. The present invention relates to a composite roll for cold rolling.
[0002]
[Prior art]
In recent years, the hot rolling technology of steel sheets and steel pipes has been remarkably advanced, and accordingly, there has been a strong demand for improving the properties of the hot rolling rolls used, particularly the wear resistance. In response to such demands for improved wear resistance, a high-performance roll (hereinafter referred to as HSS) having an outer layer composition similar to that of a high-speed tool steel and precipitating hard carbide to significantly improve wear resistance. System roll) has been developed and put into practical use.
[0003]
On the other hand, in rolling stands and mills in which the material to be rolled is subjected to drawing rolling accidents and seizure of the material to be rolled, hot rolling is performed by incorporating a Ni-grain cast iron roll containing graphite and having excellent seizure resistance. Have been. The inclusion of graphite in the hot-rolling roll is effective in preventing seizure because graphite is rich in lubricity. However, the conventional Ni-grain cast iron roll has a problem in that the wear resistance is inferior and the roll life is short. On the other hand, a high-speed steel roll excellent in wear resistance has a problem in terms of accident resistance, such as a coarse thermal shock crack being generated due to a drawing accident or seizure. For example, a high-speed steel roll cannot be used stably in a hot-rolling finishing post stand of a steel sheet having a high frequency of squeeze rolling accidents, and a large amount of Ni-glen cast iron rolls are still used.
[0004]
To solve such a problem, for example, Patent Document 1 proposes a roll for hot rolling in which 1.0 to 5.0% of V is added to Ni grain cast iron to improve wear resistance. I have. In addition, Patent Document 2 discloses that 2.0 to 8.0% of V is added to Ni grain cast iron, and 0.2 to 10% of MC type carbide appears in addition to 0.5 to 5% of graphite. Rolls for hot rolling have been proposed which improve wear resistance. Further, Patent Literature 3 includes 1.5 to 10% in total of 2 to 10% of Cr, 0.1 to 10% of W, and one or two of V and Nb, and contains graphite. A high-speed cast iron material having the same has been proposed.
[0005]
In addition, in the case of steel pipe rolling as well as in the case of steel plate rolling, there is a strong demand for improvements in seizure resistance and wear resistance to hot rolling rolls.
In recent years, in order to improve the quality and efficient production of rolled products, an increase in a rolling speed and an increase in a continuous rolling amount have been aimed at, and the use environment of hot rolling rolls has become increasingly severe. In addition, due to the high alloying of the material to be rolled and the strict requirements for the surface quality of the rolled product, there is a demand for a hot rolling work roll which is excellent in abrasion resistance and seizure resistance and also excellent in surface roughening resistance.
[0006]
For example, Patent Document 4 proposes a hot-rolling roll in which the contents of Nb and W are controlled to suppress gravitational segregation of carbides and to suppress occurrence of surface roughness. Patent Document 5 discloses a wear-resistant hot-rolling roll in which the total content of Cr, V, and Nb is limited to 3% or less, and 2% or more of graphite is crystallized to suppress the occurrence of surface roughness. Proposed.
[0007]
[Patent Document 1]
JP-A-1-287248
[Patent Document 2]
JP-A-6-335712
[Patent Document 3]
JP-A-6-256889
[Patent Document 4]
JP 2001-20335 A
[Patent Document 5]
JP 2001-181780 A
[0008]
[Problems to be solved by the invention]
However, the rolls for hot rolling manufactured by the techniques described in Patent Literatures 4 and 5 have low thermal shock resistance and exhibit the required abrasion resistance, seizure resistance, rough surface resistance and thermal shock resistance. It was impossible to be satisfied at the same time.
The present invention advantageously solves the above-mentioned problems of the prior art, and is excellent in both abrasion resistance, seizure resistance, surface roughening resistance, and thermal shock resistance, and is an outer layer material for hot rolling and a composite for hot rolling. The purpose is to propose a role.
[0009]
[Means for Solving the Problems]
The present inventors have intensively studied various factors affecting the abrasion resistance, seizure resistance, surface roughness resistance, and thermal shock resistance of a hot rolling roll in order to achieve the above object.
It has been well known that wear resistance is improved by adding a large amount of V, Nb, Mo, Cr and W, and that the wear resistance is improved in the order of V>Nb>Mo> Cr, W. Have been. However, according to the study of the present inventors, when Cr or W is increased for the purpose of improving the wear resistance, the surface roughness becomes more remarkable. If Cr and W are increased simultaneously with V (Nb), seizure resistance and thermal shock resistance deteriorate. This is probably because the eutectic carbide formed of Cr or W causes roughening or seizure or promotes the propagation of thermal shock cracks.
[0010]
As described above, Cr and W have a small effect of improving abrasion resistance as compared with V, Nb and Mo, and have a tendency to promote roughening, seizure and thermal shock cracking. Have found that it is preferable that the content of Cr should be minimized in a hot-rolling roll and that W should not be added. It is to be noted that the use of Cr in the minimum necessary content and no addition of W is effective for promoting graphitization, and contributes to the improvement of the surface roughness resistance and the seizure resistance.
[0011]
According to the study of the present inventors, V must be contained in an amount of 1.3% by mass or more in order to secure the minimum required wear resistance as a hot rolling roll. However, when V is contained in an amount of 1.3% by mass or more, coarse MC carbides are crystallized. The coarse MC carbide remains on the roll surface in a convex shape in hot rolling, and induces roughening of the surface. The present inventors have further studied a method for suppressing crystallization of coarse MC carbides and have found that it is preferable to add Nb simultaneously with V. Nb forms Nb carbides, and MC carbides are crystallized from the nuclei. Therefore, the coarsening of the MC carbide is suppressed to a certain level or less.
[0012]
In addition, the present inventors have conceived to reduce the effective C amount (= C- (0.24V + 0.13Nb)) as a method for reducing eutectic carbides in order to improve the surface roughness resistance. The remaining C amount (effective C amount) consumed for the formation of MC carbides by V and Nb contributes to the formation of eutectic carbides and graphite. If the effective C content is reduced, the amount of eutectic carbides is reduced, and it is considered that the rough surface resistance is improved. However, the graphite which is effective in seizure resistance and thermal shock resistance is also reduced.
[0013]
Therefore, the present inventors can satisfactorily adjust the effective C content to 2.0% or more and 3.0% or less to achieve excellent seizure resistance, rough surface resistance and thermal shock resistance. I thought.
According to the study of the present inventors, in addition to V and Nb, by strictly controlling the effective C amount and further containing Al or Ti, a generation nucleus of Nb carbide is formed. It has also been found that MC carbide grows with finely dispersed Nb carbide as a nucleus and that coarsening of MC carbide is further suppressed. However, it has also been found that, even when Nb, Al, and Ti are contained, V must be limited to 2.5% by mass or less in order to suppress skin roughness.
[0014]
In addition, the present inventors strictly adjusted the effective C amount in addition to V and Nb, and further contained B in addition to Al or Ti, thereby promoting the branching of graphite. It has also been found that thermal shock resistance is improved because cracks due to thermal shock are branched and dispersed along graphite.
Further, the present inventors have proposed to prevent an increase in the amount of eutectic carbide and a decrease in thermal shock resistance and seizure resistance due to a decrease in graphite, or to prevent seizure caused by concentration of Cr in a matrix or carbide. It was also found that it was necessary to adjust Cr / C to less than 1.0 in order to prevent the occurrence of cracks. It has also been found that in order to achieve both abrasion resistance and skin roughness resistance, it is necessary to adjust the total amount of Cr and V to a range of 3.0 to 4.5% by mass.
[0015]
First, the results of basic experiments performed by the present inventors will be described.
In mass%, 2.2 to 3.9% C-1.5 to 1.9% Si-0.5 to 0.6% Mn-4.3 to 4.4% Ni-1.7 to 1. 8% Cr-1.9 to 2.0% Mo-1.9 to 3.2% V-0.3 to 0.4% Nb-0.03 to 0.04% Ti-0.03 to 0. Effectively, a Y-type keel block having a thickness of 35 mm is prepared by melting a molten metal mainly containing C and V containing 04% B and the balance of Fe, and tempering at 400 to 500 ° C. The test material was changed in the amount of C.
[0016]
Test specimens were collected from these test materials and subjected to seizure tests, wear tests, and thermal shock tests. Further, in mass%, 3.1 to 3.4% C-1.6 to 1.8% Si-0.5 to 0.6% Mn-4.4% Ni-1.8% Cr-1. 9 to 2.0% Mo-1.9 to 2.0% V-0.3% Nb, or 0.03% of B, and the remaining Fe melt (effective C content: 2.8) , 2.6, 2.9) were melted and similarly used as test materials, and a test was performed.
[0017]
As shown in Fig. 3, the seizure test was performed by heating a high frequency heating coil to 900 ° C and rotating at 150 rpm to a disk-shaped counterpart material (material: SUS410, size: 190mmφ) with a 25mm thickness plate test. The piece was pressed for 10 s under a load of 100 kgf. After the test, the surface of the plate-shaped test piece was observed, and the case where seizure (sticking) of the mating material was observed on the surface was regarded as seizure, and the mating material was worn without seizing (sticking). In the case, there was no seizure.
[0018]
The abrasion test was performed by a two-disc sliding wear method of a mating material (material: S45C, size: 190 mmφ) and a test piece (size: 60 mmφ). The mating member was heated to 800 ° C. while rotating at a rotation speed of 700 rpm, and rolled for a total of 240 minutes while being pressed against a test piece and a mating member at a slip rate of 10% under a load of 100 kg. The amount of water was adjusted such that the surface temperature of the test piece (test surface) was 420 ° C. while cooling the test piece with water.
[0019]
After the test, the abrasion loss (abrasion amount) of the test piece was measured. Further, the surface roughness of the test piece surface is visually observed, and a large portion of the rough surface is measured for a length of 10 mm in the peripheral direction of the test piece using a stylus type roughness meter in accordance with JIS B 0601-1994. A roughness curve was determined, and a ten-point average roughness Rz was determined.
In the thermal shock test, a disk-shaped counterpart material (material: S45C, size: 190 mmφ) heated to 820 ° C. by a high-frequency heating coil and rotated at 150 rpm was applied to a 25 mm-thick plate-shaped test piece at 100 kgf for 10 s. The plate-shaped test piece was rapidly heated by being press-contacted, and was cooled with water simultaneously with unloading, and a thermal shock was applied to the plate-shaped test piece. After the test, it was cut at two locations where a large crack in the opening was present, and the cross section was observed to measure the maximum crack depth.
[0020]
FIG. 1 shows the obtained results in relation to the effective C amount: {C− (0.24 V + 0.13 Nb)}. In addition, Cr, C, V, and Nb are contents (mass%) of each element.
From FIG. 1A, it can be seen that when the effective C amount exceeds 3.0%, the roughness (Rz: μm) significantly increases, and significant skin roughness occurs. If the effective C amount is less than 2.0%, seizure occurs. That is, by limiting the effective C amount to 2.0 to 3.0%, a roll for hot rolling having both seizure resistance and surface roughness resistance can be obtained.
[0021]
In addition, from FIG. 1 (a), even within the range of the effective C amount, when the V amount becomes higher than 3.1 mass%, 3.2 mass%, and 3.0 mass% (marked with □), it becomes remarkable. It can be seen that rough skin occurs. Also, even within the range of the effective C amount, when neither Al nor Ti is contained, remarkable skin roughness occurs. In addition, when B is not included (marked with “△”), image sticking also occurs.
[0022]
FIG. 1B shows that when the effective C amount is out of the range of 2.0 to 3.0%, the thermal crack depth becomes extremely deep, and the thermal shock resistance deteriorates. Further, even when the effective C content is in the range of 2.0 to 3.0%, when the V content exceeds 3.0% by mass or less than 2.0% by mass, the thermal crack depth is remarkable. Has increased. Further, even within the range of the effective C amount, when neither Al nor Ti is contained, or further when Al, Ti and B are not contained (marked by Δ), the thermal crack depth is remarkably increased.
[0023]
As described above, even when the effective C amount is within the predetermined range, the rough skin resistance may deteriorate, and the present inventors have further studied. In order to obtain a hot-rolling work roll having excellent wear resistance, excellent surface roughness resistance, excellent seizure resistance and excellent thermal shock resistance, the effective carbon content is 2.0 to 3.0%. It has been found that after adjusting to the range, the total content of Cr and V (Cr + V) must be further adjusted within the range of 3.0 to 4.5% by mass. Cr forms a hard eutectic carbide to improve wear resistance, but as the Cr content increases, the eutectic carbide increases, and the surface roughness resistance and thermal shock resistance deteriorate. Further, V is extremely useful for improving the wear resistance, but when the amount of V is increased, the MC carbides become coarse and the skin becomes rough. Therefore, it is effective to balance the amount of Cr and the amount of V within a suitable range in order to achieve both surface roughness resistance, thermal shock resistance, and wear resistance.
[0024]
Next, basic experimental results for obtaining such knowledge will be described.
In mass%, 3.1 to 3.4% C-1.5 to 1.8% Si-0.4 to 0.5% Mn-4.6 to 4.8% Ni-1.6 to 3. 1% Cr-2.0 to 2.4% Mo-1.2 to 3.9% V-0.3 to 0.4% Nb-0.05 to 0.09% Al-0.05 to 0. A molten metal containing 06% B-remaining Fe and having mainly changed Cr and V contents was melted to produce a Y-type keel block having a thickness of 35 mm. Then, these keel blocks were tempered at 400 to 500 ° C. to obtain test materials. In addition, the effective C amount of the test material was 2.21 to 2.95%. Specimens were collected from these test materials and subjected to a wear test and a thermal shock test.
[0025]
The wear test was carried out by a two-disc sliding wear method of a mating material (material: S45C, size: 190 mmφ) and a test piece (size: 60 mmφ). The mating member was heated to 800 ° C. while rotating at a rotation speed of 700 rpm, and rolled for a total of 240 minutes while being pressed against a test piece and a mating member with a load of 100 kgf with a slip ratio of 10%. The amount of water was adjusted such that the surface temperature of the test piece (test surface) was 420 ° C. while cooling the test piece with water.
[0026]
After the test, the abrasion loss (abrasion amount) of the test piece was measured. Further, the surface roughness of the test piece surface is visually observed, and a large portion of the rough surface is measured for a length of 10 mm in the peripheral direction of the test piece using a stylus type roughness meter in accordance with JIS B 0601-1994. A roughness curve was determined, and a ten-point average roughness Rz was determined.
In the thermal shock test, a disk-shaped counterpart material (material: S45C, size: 190 mmφ) heated to 820 ° C. by a high-frequency heating coil and rotated at 150 rpm was applied to a 25 mm-thick plate-shaped test piece under a load of 100 kgf. The plate-shaped test piece was rapidly heated for 10 s, rapidly heated, cooled with water simultaneously with unloading, and a thermal shock was applied to the plate-shaped test piece. After the test, it was cut at two positions where a large crack having an opening was present, and the cross section was observed to measure the maximum crack depth.
[0027]
FIG. 2 shows the obtained results in relation to (Cr + V). Note that Cr and V are the contents (% by mass) of the respective elements.
From FIG. 2A, it can be seen that when (Cr + V) is less than 3.0, the amount of wear increases and the wear resistance decreases. When (Cr + V) exceeds 4.5, the surface roughness (Rz) increases, and the surface roughness resistance deteriorates. FIG. 2B shows that when (Cr + V) exceeds 4.5, the crack depth due to thermal shock increases, and the thermal shock resistance deteriorates. From the above, the present inventors set the total of the Cr content and the V content (Cr + V) to 3.0 to 4.0 in order to improve both the wear resistance, the rough surface resistance, and the thermal shock resistance. 5 was found to be necessary. It should be noted that when neither Al nor Ti is contained, rough surface occurs, the thermal crack depth is large, and both the rough surface resistance and the thermal shock resistance are deteriorated.
[0028]
The present invention has been completed based on the above findings, with further investigations.
That is, the present invention relates to a roll outer layer material used for an outer layer of a composite roll for hot rolling, in which, by mass%, C: 2.6 to 3.5%, Si: 1.0 to 2.5%, Mn: 0.2-1.5%, Cr: 0.8-2.7%, Mo: 1.0-3.0%, Ni: 2.0-7.0%, V: 1.3- 2.5%, Nb: 0.1 to 0.8%, B: 0.020 to 0.2%, and the contents of C, Cr, Nb and V are expressed by the following formulas (1) to (3).
2.0 ≦ C− (0.24 × V + 0.13 × Nb) ≦ 3.0 (1)
Cr / C <1.0 (2)
3.0 ≦ Cr + V ≦ 4.5 (3)
(Here, C, V, Nb, Cr: Content of each element (% by mass))
And a composition comprising one or two selected from Ti: less than 0.05% and Al: 0.1% or less, with the balance being Fe and unavoidable impurities. It is a roll outer layer material for hot rolling. In the present invention, in addition to the above composition, it is preferable to further contain Co: 0.1 to 4.0% by mass%.
[0029]
Further, the present invention is a composite roll for hot rolling, in which an outer layer and an inner layer are welded and integrated, wherein the outer layer is, by mass%, C: 2.6 to 3.5%, and Si: 1.0 to 1.0%. 2.5%, Mn: 0.2 to 1.5%, Cr: 0.8 to 2.7%, Mo: 1.0 to 3.0%, Ni: 2.0 to 7.0%, V 1.3 to 2.5%, Nb: 0.1 to 0.8%, B: 0.020 to 0.2%, and the contents of C, Cr, Nb, and V are the above (1) to It satisfies the formula (3), and further contains one or two selected from Ti: less than 0.05% and Al: 0.1% or less, and has a composition consisting of the balance of Fe and unavoidable impurities. In the present invention, the outer layer further contains Co: 0.1 to 4.0% by mass in addition to the composition. It is preferred.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reasons for limiting the composition of the outer layer (outer layer material) of the composite roll for hot rolling of the present invention will be described. In addition, the mass% in the composition is simply described as%.
C: 2.6 to 3.5%
C combines with V, Nb, Cr, and Mo and is an element essential for forming a hard carbide for improving the abrasion resistance of the roll, and secures crystallization of graphite, seizure resistance, and thermal shock resistance. In the present invention, the content is required to be 2.6% or more. On the other hand, when the content exceeds 3.5%, a large amount of eutectic carbides appears, and the MC type carbides become coarse and the surface roughening resistance decreases. For this reason, C was limited to the range of 2.6 to 3.5%. In addition, preferably, it is 2.8 to 3.3%.
[0031]
Si: 1.0 to 2.5%
Si is an element that acts as a deoxidizing agent, increases the activity of C, and facilitates crystallization of graphite. In the present invention, Si needs to be contained in an amount of 1.0% or more. On the other hand, if the content exceeds 2.5%, coarsening of graphite and coarsening of the structure occurs, and the surface roughening resistance and abrasion resistance of the roll are significantly reduced. For these reasons, Si is limited to the range of 1.0 to 2.5%.
[0032]
Mn: 0.2-1.5%
Mn is effective for fixing S in molten steel as MnS 2 and harmless and stabilizing S, which inhibits wear resistance. In addition, there is also an effect of improving hardenability and increasing hardness. In order to obtain such an effect, the content of 0.2% or more is required. However, if the content exceeds 1.5%, segregation occurs at the solidification interface and the material becomes brittle. For this reason, Mn was contained in the range of 0.2 to 1.5%. Incidentally, the content is preferably 0.3 to 1.0%.
[0033]
Cr: 0.8 to 2.7%
Cr is an element that increases the amount of eutectic carbide and hardens it, and has the effect of suppressing carbide breakage during roll rolling and improving wear resistance when contained together with Mo. In order to obtain such an effect, a content of 0.8% or more is required. On the other hand, when the content exceeds 2.7%, eutectic carbides increase and the surface roughening resistance decreases, and the amount of graphite decreases, and seizure resistance and thermal shock resistance also decrease. For this reason, Cr was limited to 0.8 to 2.7%.
[0034]
Mo: 1.0 to 3.0%
Mo has the effect of strengthening carbides and matrix without excessively increasing the amount of eutectic carbides, and has the effect of improving wear resistance while maintaining excellent surface roughness resistance. In particular, by containing Nb in combination, the hard MC type carbide is strengthened and has an important effect of remarkably improving the abrasion resistance. % Or more is required. On the other hand, when the content exceeds 3.0%, a large amount of hard and brittle carbide mainly composed of Mo is formed, and the surface roughness resistance and the thermal shock resistance are deteriorated. For this reason, Mo was limited to 1.0 to 3.0%. In addition, preferably, it is 1.2 to 2.7%.
[0035]
Ni: 2.0 to 7.0%
Ni has the effect of improving the hardenability, increasing the hardness of the material, and improving the wear resistance. Ni also has the effect of promoting crystallization of graphite. Such an effect is observed at a content of 2.0% or more. However, when the content exceeds 7.0%, austenite is remarkably stabilized, the amount of retained austenite increases, and the seizure resistance decreases. For this reason, Ni is limited to the range of 2.0 to 7.0%. In addition, it is preferably 3.0 to 6.0%.
[0036]
V: 1.3 to 2.5%
V is an element that forms a hard MC-type carbide and has an effect of improving wear resistance. In the present invention, in order to obtain a certain level or more of abrasion resistance, the content of 1.3% or more is required. On the other hand, if it exceeds 2.5%, MC type carbides become coarse and rough skin occurs. Further, there are also adverse effects such as the occurrence of seizure and deterioration of thermal shock resistance. For this reason, V was limited to the range of 1.3 to 2.5%.
[0037]
Nb: 0.1 to 0.8%
Nb is an element having a function of strengthening the carbide by forming a solid solution in the MC-type carbide. In particular, when Nb is contained in combination with a predetermined range of Cr, Mo, and V, the carbide is significantly strengthened and the wear resistance is improved. Has an important effect of improving significantly. In addition, when only V is contained, the MC type carbide grows in a feather shape, the structure becomes coarse, and the rough surface of the roll is induced. However, by containing Nb and V in combination, the MC type carbide becomes feathered. By adding Ti and / or Al in combination, oxides, nitrides, carbides, etc. of Ti and / or Al become crystallization nuclei of NbC 2 and finely disperse NbC 2. Next, there is also an effect that MC-type carbides are finely dispersed with NbC 2 as a nucleus, thereby suppressing roughening of the skin. In order to obtain such an effect, the content needs to be 0.1% or more. If Nb is less than 0.1%, segregation and coarsening of MC type carbide occur. On the other hand, when the content exceeds 0.8%, the MC-type carbide coarsens into a dendrite shape, so that the skin becomes rougher. Further, when manufactured by a centrifugal casting method, segregation of MC type carbide occurs. For these reasons, Nb is limited to the range of 0.1 to 0.8%. In addition, from the viewpoint of MC type carbide coarsening, Nb is preferably set to 0.1 to 0.5%.
[0038]
B: 0.020 to 0.2%
B has the effect of finely dispersing graphite and has the effect of improving seizure resistance and thermal shock resistance. Such an effect is recognized at a content of 0.020% or more in the coexistence of Al and / or Ti. However, when the content exceeds 0.2%, carbides become brittle, wear resistance is reduced, and graphite is reduced. The amount also decreases. For this reason, B was limited to the range of 0.020 to 0.2%. In addition, it is preferably 0.02 to 0.10%.
[0039]
One or two selected from Ti: less than 0.05% and Al: 0.1% or less
Both Ti and Al have the important effects of promoting graphitization, promoting the formation of the graphite into a branched shape, and improving seizure resistance and thermal shock resistance. In addition, it has an effect of finely dispersing MC carbides by being a core of Nb carbides. Such an effect is remarkably recognized when the content of Ti is 0.005% or more and the content of Al is 0.003% or more. On the other hand, when Ti is contained in an amount of 0.05% or more, fine MC-type carbides are densely formed, and a large rough surface is generated at the portion. Further, when Al is contained in excess of 0.1%, the fluidity of the molten metal is reduced and casting defects are liable to occur. For this reason, Ti was limited to less than 0.05% and Al was limited to 0.1% or less. When neither Al nor Ti is contained, seizure resistance and thermal shock resistance are remarkably deteriorated, and at the same time, MC type carbides are coarsened and remarkable surface roughness occurs. In addition, it is preferable to set Ti to 0.01 to 0.04%. Moreover, it is preferable that Al is 0.01 to 0.07%.
[0040]
Further, in the present invention, after being within the above component range, the following formulas (1) to (3) are further obtained.
2.0 ≦ C− (0.24 × V + 0.13 × Nb) ≦ 3.0 (1)
Cr / C <1.0 (2)
3.0 ≦ Cr + V ≦ 4.5 (3)
(Here, C, V, Nb, Cr: Content of each element (% by mass))
It is important to adjust the content of each component so as to satisfy the following. As a result, a roll outer layer (outer layer material) for hot rolling work having excellent wear resistance, surface roughness resistance, seizure resistance and thermal shock resistance is obtained.
[0041]
2.0 ≦ C− (0.24V + 0.13Nb) ≦ 3.0% (1)
When the effective C amount is less than 2.0, the amount of graphite is remarkably reduced, and the seizure resistance and the thermal shock resistance are deteriorated. On the other hand, if the effective C content exceeds 3.0%, the eutectic carbides excessively increase, causing significant surface roughness, deteriorating the surface roughness resistance, and deteriorating the thermal shock resistance. For this reason, the effective C amount was limited to 2.0 or more and 3.0 or less. When the V content exceeds 2.1%, the effective C content is preferably set to 2.2 to 2.9.
[0042]
Note that (0.24V + 0.13Nb) means the amount of C consumed by the V and Nb to form the MC type carbide, and {C- (0.24V + 0.13Nb)} means improvement in seizure resistance and heat resistance. This is a value indicating the amount of C remaining which contributes to the production of graphite which is advantageous for improving impact resistance and eutectic carbide which affects abrasion resistance and surface roughness resistance.
Cr / C <1.0 (2)
When Cr / C is 1.0 or more, that is, when the Cr content is not less than the C content, eutectic carbides are excessively generated, the amount of graphite is significantly reduced, and seizure is likely to occur. The thermal shock resistance also deteriorates significantly. Therefore, in the present invention, Cr / C is limited to less than 1.0.
[0043]
3.0 ≦ Cr + V ≦ 4.5 (3)
Cr and V are elements that greatly affect the rough surface resistance, the thermal shock resistance, and the wear resistance. In the present invention, (Cr + V) is adjusted so as to satisfy the expression (3). If (Cr + V) is less than 3.0, the amount of wear increases significantly and the wear resistance decreases. On the other hand, when it exceeds 4.5, the surface roughness becomes remarkably large and the thermal shock resistance is deteriorated. For this reason, in the present invention, (Cr + V) is limited to the range of 3.0 to 4.5. In addition, when importance is attached to the rough surface resistance and thermal shock resistance, it is preferable that Cr + V has a composition close to 3.0, and when importance is attached to the wear resistance, it is preferable that Cr + V has a composition close to 4.5.
[0044]
By adjusting the composition so as to satisfy the above-mentioned component ranges and all of the above formulas (1), (2) and (3), the wear resistance, the seizure resistance, the rough surface resistance and the thermal shock resistance can be simultaneously achieved. Can be improved.
The roll outer layer material (outer layer) of the present invention may further contain Co: 0.1 to 4.0% in addition to the above composition.
[0045]
Co: 0.1 to 4.0%
Co is distributed to the matrix, has an effect of increasing the solid solution amount of the alloy element in the matrix, strengthening the matrix, and suppressing the generation of coarse drawing cracks, and can be contained as necessary. In order to obtain such an effect, the content is preferably 0.1% or more. On the other hand, if the content exceeds 4.0%, the effect is saturated, an effect corresponding to the content cannot be expected, and it is economically disadvantageous because it is an expensive element. Therefore, it is preferable that Co is limited to the range of 0.1 to 4.0%.
[0046]
By adjusting the composition in the above-described range, a roll outer layer material (outer layer) having excellent wear resistance, surface roughness resistance, seizure resistance and thermal shock resistance can be obtained. In order to further improve seizure resistance and thermal shock resistance within the above composition range, it is preferable to generate more graphite. It is preferable to inoculate Si with a Si inoculant such as Fe-Si or Ca-Si. The amount of Si added by inoculation is preferably 0.5 to 1.0% by mass. When the Si inoculant contains a graphite spheroidizing element such as REM or Mg, the branching of graphite is inhibited and the amount of graphite is reduced, resulting in deterioration of seizure resistance and thermal shock resistance.
[0047]
In the present invention, the method for producing the roll outer layer material is not particularly limited, but it is preferable from the viewpoint of the production cost that the molten metal having the above-described composition be formed into a roll outer layer material having a predetermined shape by centrifugal casting. In this case, it is preferable that the rotation of the mold is stopped and the inner layer material is statically cast during or after solidification of the outer layer material of the roll to form a composite roll. As a result, the inner surface side of the roll outer layer material is redissolved and the outer layer and the inner layer are welded and integrated to form a composite roll.
[0048]
The inner layer to be subjected to stationary casting is preferably made of spheroidal graphite cast iron, worm-like graphite cast iron or graphite steel having excellent castability and mechanical properties. Further, an intermediate layer made of graphite steel or high carbon steel may be provided between the outer layer and the inner layer. When the roll is manufactured by the centrifugal casting method, the intermediate layer may be subjected to the centrifugal casting following the centrifugal casting of the outer layer.
Although the above description has been mainly directed to hot rolls for steel sheets, the present invention is not limited to composite rolls for hot rolling steel sheets, It goes without saying that there is no problem if applied to a role. In the case of manufacturing a sleep type roll for rolling a steel pipe, the outer layer may be subjected to centrifugal casting, followed by centrifugal casting using spheroidal graphite cast iron or high carbon steel as an inner layer material.
[0049]
【Example】
(Example 1)
After melting the molten metal having the composition shown in Table 1 and inoculating it with Ca-Si, a ring-shaped test material (outer diameter: 250 mmφ, wall thickness: 80 mm) was cast by a centrifugal casting method. The casting temperature was 1450 ° C., and the centrifugal force was 160 G as a multiple of gravity. After casting, the test material was tempered at 400 to 500 ° C. The hardness after tempering was Hs 77 to 86. In addition, Ni grain cast iron was used as a conventional example.
[0050]
Test specimens were collected from these ring-shaped test materials, and were subjected to a wear test, a seizure test, and a thermal shock test.
(1) Wear test
A test piece (size: 60 mmφ) was sampled from the ring-shaped test material, and an abrasion test was performed on the mating material (material: S45C, size: 190 mmφ) using a two-disk sliding wear method. While rotating the test piece at 700 rpm, the counterpart material is heated to 800 ° C., the test piece is water-cooled, the slip ratio of the test piece and the counterpart material is set to 10%, and the test piece is pressed for 150 min under a load of 100 kgf (980 N). Rolled for a while. After the test, the abrasion loss (abrasion amount) of the test piece was measured. Further, the surface roughness of the test piece surface is visually observed, and a part of the large surface roughness over a length of 10 mm in the peripheral direction of the test piece is used in accordance with JIS B 0601-1994 using a stylus type roughness meter. Then, a roughness curve was determined, and a ten-point average roughness Rz was determined.
(2) Seizure test
A test piece (plate having a thickness of 25 mm) was sampled from the ring-shaped test material, and a seizure test was performed using a tester having a method shown in FIG. A test piece (25 mm thick plate) was heated to 900 ° C. by a high-frequency heating coil and rotated at 150 rpm for 10 seconds with a disk-shaped mating member (material: SUS410, size: 190 mmφ) under a load of 100 kgf (980 N). We pressed for a while. If the mating material (metal) has burrs on the surface of the test piece after the test, "seizure"(x); if there is no burrs and the surface is worn, "no seizure" (o) The seizure resistance was evaluated.
(3) Thermal shock test
A 25 mm-thick plate-shaped test piece was sampled from the ring-shaped test material, and a disk-shaped counterpart material (material: S45C, size: 190 mmφ) was used in a tester having the configuration shown in FIG.
[0051]
A disk-shaped mating member (material: S45C, size: 190 mmφ) heated to 820 ° C. by a high-frequency heating coil and rotated at 150 rpm is pressed against a 25-mm-thick plate-shaped test specimen under a load of 100 kgf for 10 s. The plate-shaped test piece was rapidly heated, cooled with water simultaneously with unloading, and a thermal shock was applied to the plate-shaped test piece. After the test, a penetrant test was carried out. The test piece was cut at two places where the developer had a large amount of bleeding, the cross section was observed, the maximum depth of the crack was measured, and the thermal shock resistance was evaluated as the crack depth.
[0052]
Table 2 shows the obtained results.
[0053]
[Table 1]

[0054]
[Table 2]

[0055]
All of the examples of the present invention are excellent in abrasion resistance, have no occurrence of seizure and rough surface, and have a shallow crack depth, and have extremely excellent abrasion resistance, seizure resistance, rough surface resistance and thermal shock resistance. Roll outer layer material.
On the other hand, in Comparative Examples outside the scope of the present invention, at least one or more of abrasion resistance, surface roughness resistance, seizure resistance, and thermal shock resistance are significantly reduced.
[0056]
In the comparative example (ring material No. I) in which the Nb content is outside the range of the present invention, the surface roughness is remarkable, the crack depth is deep, the surface roughness resistance and the thermal shock resistance are deteriorated. Moreover, in the comparative example (ring material No. J) which does not contain Nb and does not contain any of Al and Ti, surface roughening occurs, the crack depth is deep, and the surface roughening resistance and the thermal shock resistance are reduced. In addition, the Mo, V content and (Cr + V) content deviated from the range of the present invention to a high degree, and in the comparative example (ring material No. K) containing no Nb and B, remarkable roughening and seizure occurred, and the crack depth was deep. , Rough surface resistance, seizure resistance, and thermal shock resistance are reduced. In the comparative example (ring material No. L) having a low V content and containing W, the wear amount is increased and the wear resistance is reduced, and the surface roughness is generated and the skin roughness resistance is reduced. In a comparative example (ring material No. M) containing W and having a Cr, Cr / C, and (Cr + V) amount outside the range of the present invention, remarkable surface roughness and seizure occur, crack depth is large, and surface roughness resistance is high. , Seizure resistance and thermal shock resistance are reduced. In the comparative example (ring material No. N) containing W, the V content and the (Cr + V) content deviating from the range of the present invention, and containing neither B, Al nor Ti, the wear amount increases and the wear resistance is increased. And the surface roughness is reduced, the crack depth is deep, and the surface roughness resistance and thermal shock resistance are reduced. In the comparative example (ring material No. O) in which the Mo content is lower than the range of the present invention, the effective C content is higher than the range of the present invention, and neither Al nor Ti is contained, the wear amount is increased and the wear resistance is increased. The surface roughness is reduced, the surface is roughened, the crack depth is deep, and the surface roughness resistance and thermal shock resistance are reduced. The conventional example (ring material No. NiG) is excellent in seizure resistance and thermal shock resistance, but is extremely inferior in wear resistance.
(Example 2)
A composite roll having a product body diameter of 685 mm and a body length of 2380 mm was manufactured by the following procedure.
[0057]
An outer layer material melt was cast into a mold rotating at a centrifugal force of 140 G so that the outer layer had a thickness of 120 mm. After the outer layer was solidified, the rotation of the mold was stopped, the mold was erected and the inner layer material (spheroidal graphite cast iron) was cast, thereby integrating the outer layer and the inner layer, and cooling until the surface temperature of the outer layer became 80 ° C. or less. Thereafter, the mold was disassembled to obtain a composite roll composed of an outer layer and an inner layer.
[0058]
The obtained composite roll was subjected to a heat treatment (tempering treatment) in which the composite roll was heated to 400 to 500 ° C. for 30 hours and then gradually cooled, and the hardness of the outer layer was set to 80 to 83 Hs.
After the heat treatment, a test material for chemical composition analysis of the outer layer and a test piece for structure observation were collected from the end of the roll body. For the inner layer, a sample for chemical composition analysis was collected from the center of the roll shaft end. Table 3 shows the chemical composition of the outer layer and inner layer of each composite roll.
[0059]
The obtained composite roll was thrown in as a work roll of an F7 stand of a hot finish rolling mill, and 100 carbon steels were subjected to test rolling. In addition, reduction rolling was reproduced by one of them, and the state of seizure was compared.
[0060]
[Table 3]

[0061]
It was confirmed that the present invention example (composite roll No. 1) had extremely good abrasion resistance and rough surface resistance about 1.6 times that of the conventional NiG cast iron roll. Further, no seizure occurred in the reduction rolling.
[0062]
【The invention's effect】
According to the present invention, a composite roll having both excellent wear resistance, seizure resistance, surface roughness resistance and thermal shock resistance can be manufactured at low cost as a roll for a subsequent rolling stand for hot rolling of a steel sheet. Has the effect of Further, the composite roll of the present invention can be used stably as a roll for a post-rolling stand, in which frequent drawing accidents occur during hot rolling of a steel sheet. Further, the composite roll of the present invention can also be applied as a roll for rolling a steel pipe, which is required to have excellent seizure resistance, surface roughening resistance and wear resistance.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between (a) a ten-point average roughness (Rz) and an effective C amount, and (b) a relationship between a crack depth and an effective C amount.
FIG. 2 is a graph showing (a) the relationship between the amount of wear, ten-point average roughness (Rz) and the amount of (Cr + V), and (b) the relationship between the crack depth and the amount of (Cr + V).
FIG. 3 is a schematic explanatory view showing an outline of a seizure test.

Claims (4)

It is a roll outer layer material used for the outer layer of the composite roll for hot rolling.
C: 2.6 to 3.5%, Si: 1.0 to 2.5%,
Mn: 0.2 to 1.5%, Cr: 0.8 to 2.7%,
Mo: 1.0 to 3.0%, Ni: 2.0 to 7.0%,
V: 1.3 to 2.5%, Nb: 0.1 to 0.8%,
B: 0.020 to 0.2%
And the contents of C, Cr, Nb and V satisfy the following formulas (1) to (3), and are selected from Ti: less than 0.05% and Al: 0.1% or less. An outer layer material for a roll for hot rolling, characterized in that it contains one or two kinds and has a composition consisting of a balance of Fe and unavoidable impurities.
2.0 ≦ C− (0.24 × V + 0.13 × Nb) ≦ 3.0 (1)
Cr / C <1.0 (2)
3.0 ≦ Cr + V ≦ 4.5 (3)
Here, C, V, Nb, Cr: content of each element (% by mass) The roll outer layer material for hot rolling according to claim 1, further comprising Co: 0.1 to 4.0% by mass in addition to the composition. A composite roll for hot rolling in which an outer layer and an inner layer are welded and integrated, wherein the outer layer is, by mass%,
C: 2.6 to 3.5%, Si: 1.0 to 2.5%,
Mn: 0.2 to 1.5%, Cr: 0.8 to 2.7%,
Mo: 1.0 to 3.0%, Ni: 2.0 to 7.0%,
V: 1.3 to 2.5%, Nb: 0.1 to 0.8%,
B: 0.020 to 0.2%
And the contents of C, Cr, Nb and V satisfy the following formulas (1) to (3), and are selected from Ti: less than 0.05% and Al: 0.1% or less. A composite roll for hot rolling, characterized in that it contains one or two kinds and has a composition consisting of a balance of Fe and unavoidable impurities.
2.0 ≦ C− (0.24 × V + 0.13 × Nb) ≦ 3.0 (1)
Cr / C <1.0 (2)
3.0 ≦ Cr + V ≦ 4.5 (3)
Here, C, V, Nb, Cr: content of each element (% by mass) The composite roll for hot rolling according to claim 3, wherein the outer layer further contains Co: 0.1 to 4.0% by mass in addition to the composition.

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