阅读说明：本技术 通过离心铸造法制造的轧制用复合辊及其制造方法 (Composite roll for rolling produced by centrifugal casting method and method for producing same ) 是由 上宫田和则 石川晋也 绀野裕司 于 2020-03-25 设计创作，主要内容包括：提供具有与高速铸铁辊相当的优异的耐磨损性、耐表面粗糙性,并且具有与高合金麻口铸铁辊相当的抗事故性的通过离心铸造法制造的轧制用复合辊。外层的化学成分以质量比计为C：1.5～3.5％、Si：0.3～3.0％、Mn：0.1～3.0％、Ni：1.0～6.0％、Cr：1.5～6.0％、Mo：0.1～2.5％、V：2.0～6.0％、Nb：0.1～3.0％、B：0.001～0.2％、N：0.005～0.070％、余量：Fe和不可避免的杂质,外层的化学组成满足式(1),并且,具有以面积比计为5～30％的M-(3)C型碳化物,辊表面的外层肖氏硬度(A)满足式(2),辊表面的残余应力(B)满足式(3),2×Ni+0.5×Cr+Mo＞10.0(1)、Hs75≤A≤Hs85(2)、100MPa≤B≤350MPa(3)。(Provided is a composite roll for rolling, which is produced by a centrifugal casting method and has excellent wear resistance and surface roughness resistance comparable to high-speed cast iron rolls and accident resistance comparable to high-alloy pitted cast iron rolls. The outer layer comprises the following chemical components in percentage by mass: 1.5-3.5%, Si: 0.3-3.0%, Mn: 0.1 to 3.0%, Ni: 1.0-6.0%, Cr: 1.5-6.0%, Mo: 0.1-2.5%, V: 2.0-6.0%, Nb: 0.1-3.0%, B: 0.001-0.2%, N: 0.005-0.070%, and the balance: fe and unavoidable impurities, the chemical composition of the outer layer satisfying formula (1), and the surface area ratio of M being 5-30% 3 C-type carbide, wherein the Shore hardness (A) of the outer layer of the surface of the roller meets the formula (2), the residual stress (B) of the surface of the roller meets the formula (3), 2 xNi +0.5 xCr + Mo is more than 10.0(1), Hs75 is more than or equal to A and less than or equal to Hs85(2), and B is more than or equal to 100MPa and less than or equal to 350MPa (3).)

1. A composite roll for rolling manufactured by a centrifugal casting method, characterized by having an outer layer,

the chemical components of the outer layer are calculated according to mass ratio

C：1.5～3.5％、

Si：0.3～3.0％、

Mn：0.1～3.0％、

Ni：1.0～6.0％、

Cr：1.5～6.0％、

Mo：0.1～2.5％、

V：2.0～6.0％、

Nb：0.1～3.0％、

B：0.001～0.2％、

N：0.005～0.070％、

And the balance: fe and inevitable impurities, and the balance of the Fe and the inevitable impurities,

the outer layer has a chemical composition satisfying the following formula (1), and has an M content of 5 to 30% by area₃A carbide of the type C, a carbon-containing compound,

the Shore hardness (A) of the outer layer of the roll surface satisfies the following formula (2),

the residual stress (B) of the roll surface satisfies the following formula (3),

2×Ni+0.5×Cr+Mo＞10.0 (1)

Hs75≤A≤Hs85 (2)

100MPa≤B≤350MPa (3)。

2. the composite roll for rolling produced by centrifugal casting according to claim 1, wherein the chemical component further contains a chemical component in a mass ratio in the outer layer

Ti：0.005～0.3％、

W：0.01～2.0％、

Co：0.01～2.0％、

S: 0.3% or less of 1 or more.

3. A method of manufacturing a composite roll for rolling manufactured by centrifugal casting according to claim 1 or 2,

in the heat treatment performed after casting by the centrifugal casting method, tempering is performed without quenching, and the tempering is performed at a tempering temperature of 400 ℃ or higher and 550 ℃ or lower.

Technical Field

(cross-reference to related applications)

The present application claims priority based on Japanese application No. 2019-071305 filed on 4/3 in 2019, the contents of which are incorporated herein by reference.

The present invention relates to a clad roll for rolling produced by a centrifugal casting method used in a hot strip mill in a hot rolling process, and a method for producing the same.

Background

The clad roll for rolling used in a hot strip mill for hot rolling is required to have excellent wear resistance, surface roughness resistance, crack resistance and accident resistance in the outer layer that comes into contact with the steel sheet during rolling. In recent years, there has been an increasing demand for improving the thickness accuracy and surface quality of hot-rolled steel sheets, and particularly, rolling rolls having high wear resistance have been demanded, and high-speed cast iron rolls are widely used in the front stage of hot finishing mills for producing thin steel sheets. However, in the latter stage of the hot finishing mill, since the rolled material is overlapped and sandwiched between the upper and lower rolls while moving between the rolling mills due to the thin plate thickness, so-called seizure accident is liable to occur, and high-alloy pitted iron rolls have been mainly used.

In such a snap accident, cracks occur on the outer surface of the roll, but if the cracks are left and the roll is continuously used, the cracks may be accelerated, causing roll breakage called roll breakage or peeling. In addition, when a seizure accident occurs, the roll surface must be ground to remove cracks, and therefore if the cracks are deep, the roll wear also increases. Therefore, there is a demand for an outer layer for a rolling roll having less damage due to cracking and excellent accident resistance (crack resistance) even when a rolling accident occurs, and a composite rolling roll having the outer layer.

In order to satisfy the requirements for a roll having both accident resistance and wear resistance, patent document 1 discloses a hot rolling roll outer layer material having excellent seizure resistance, which is characterized by having a composition comprising: contains, in mass%, C: 1.8-3.5%, Si: 0.2-2%, Mn: 0.2-2%, Cr: 4-15%, Mo: 2-10%, V: 3-10%, further comprising P: 0.1-0.6%, B: 0.05-5%, and the balance of Fe and inevitable impurities. Patent document 1 describes that the heat treatment after casting is preferably a quenching treatment in which the casting is quenched by heating at 800 to 1080 ℃ and further a tempering treatment is performed 1 or more times at 300 to 600 ℃. However, the roll described in patent document 1 has a problem that it is segregated at grain boundaries and becomes brittle because the P content is too high, and the following technical problems are found: due to the existence of M₂C type carbide, M₇C₃Since the carbide type is a eutectic carbide mainly, when a seizure accident occurs during rolling, deep cracks are likely to occur on the surface of the outer layer of the roll, as compared with the case of a high-alloy nodular cast iron roll. Further, the following technical problems have been found: since the value of the residual stress of the outer layer of the roll surface tends to become excessive, the crack propagation speed is high and the risk of bursting is high.

In addition, patent documents2 discloses a composite roll for rolling, which is characterized in that the composite roll has a structure formed by welding and integrating an outer layer and an intermediate layer made of centrifugally cast Fe-based alloy and an inner layer made of nodular cast iron; the outer layer has the following composition: the alloy material contains, by mass, 1-3% of C, 0.3-3% of Si, 0.1-3% of Mn, 0.5-5% of Ni, 1-7% of Cr, 2.2-8% of Mo, 4-7% of V, 0.005-0.15% of N, 0.05-0.2% of B, and the balance Fe and inevitable impurities; the intermediate layer contains 0.025 to 0.15 mass% of B, the B content of the intermediate layer is 40 to 80% of the B content of the outer layer, and the total content of carbide-forming elements of the intermediate layer is 40 to 90% of the total content of carbide-forming elements of the outer layer. Patent document 2 describes that after casting, quenching treatment is performed as necessary, and tempering treatment is performed 1 or more times. The tempering temperature is preferably 480-580 ℃. However, the following technical problems have been found: in the roller described in patent document 2, M is provided₂C type carbide, M₇C₃Since the carbide type is a eutectic carbide mainly, when a seizure accident occurs during rolling, deep cracks are likely to occur on the surface of the outer layer of the roll, as compared with the case of a high-alloy nodular cast iron roll. Further, the following technical problems are found: since the value of the residual stress of the outer layer of the roll surface tends to become excessive, the crack propagation speed is high and the risk of bursting is high.

Further, patent document 3 discloses a composite roll for rolling, which is produced by a centrifugal casting method and has an outer layer, wherein the outer layer is C: 2.2% -3.01%, Si: 1.0-3.0%, Mn: 0.3% -2.0%, Ni: 3.0-7.0%, Cr: 0.5% -2.5%, Mo: 1.0% -3.0%, V: 2.5% -5.0%, Nb: greater than 0 and 0.5% or less, the remainder: fe and inevitable impurities, satisfying the condition (a): Nb%/V% < 0.1, condition (b): 2.1 XC% +1.2 XC% -Cr% +0.5 Mo% + (V% + Nb%/2) less than or equal to 13.0%. Patent document 3 describes that the treatment with gammatization heat at 850 ℃ or higher, quenching and tempering can be performed. However, the following technical problems have been found: the roll described in patent document 3 has significantly deteriorated wear resistance as compared with a high-speed roll, and when a seizure accident or the like occurs during rolling, a deep crack is likely to occur on the surface of the outer layer of the roll as compared with the case of a high-alloy nodular cast iron roll. Further, the following technical problems are found: since the value of the residual stress of the outer layer of the roll surface tends to become excessive, the crack propagation speed is high and the risk of bursting is high.

Further, patent document 4 discloses a hot-rolling composite roll manufactured by a centrifugal casting method, which includes an outer layer made of cast iron having a structure containing 0.3 to 10% of a graphite phase on an area basis and a chemical composition as follows: the composition contains C: 2.5% -3.5%, Si: 1.3% -2.4%, Mn: 0.2% -1.5%, Ni: 3.5% -5.0%, Cr: 0.8% -1.5%, Mo: 2.5% -5.0%, V: 1.8% -4.0%, Nb: 0.2 to 1.5 percent, and the balance of Fe and inevitable impurities, and the mass ratio of Nb to V is 0.1 to 0.7, the mass ratio of Mo to V is 0.7 to 2.5, V +1.2 is more than or equal to 2.5, and Nb is less than or equal to 5.5. Patent document 4 discloses that the compressive residual stress of the outer layer on the discard diameter is 150 to 500 MPa; in order to obtain the compressive residual stress, tempering treatment at 450 to 550 ℃ is performed 1 or more times after casting. However, the roller described in patent document 4 has the following technical problems: since the addition amount of Mo is too large, the composition of M₂Since eutectic carbide mainly composed of C-type carbide is formed, when a seizure accident or the like occurs during rolling, deep cracks are likely to occur on the surface of the outer layer of the roll as compared with the case of a high-alloy nodular cast iron roll. Further, it is found that the outer layer residual stress value on the roll surface tends to be too large, and therefore, the crack propagation speed is high, and the risk of cracking is high.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4483585

Patent document 2: international publication No. 2018/147370

Patent document 3: japanese patent No. 6313844

Patent document 4: japanese patent No. 5768947

Disclosure of Invention

Problems to be solved by the invention

However, it is found that the rolls described in patent documents 1 to 4 have a technical problem that deep cracks are likely to occur on the surface of the outer layer of the roll when a steel jam or the like occurs during rolling, as compared with the case of a high-alloy pitted cast iron roll. Further, it is found that the outer layer residual stress value on the roll surface tends to be too large, and therefore, the crack propagation speed is high, and the risk of cracking is high.

In view of these circumstances, an object of the present invention is to provide a composite roll for rolling produced by a centrifugal casting method, which has excellent wear resistance and surface roughening resistance comparable to those of a high-speed cast iron roll, and has accident resistance comparable to those of a high-alloy pitted cast iron roll, and a method for producing the same.

Means for solving the problems

In order to achieve the object, according to the present invention, there is provided a composite roll for rolling manufactured by a centrifugal casting method, characterized by having an outer layer,

the chemical components of the outer layer are calculated according to mass ratio

C：1.5～3.5％、

Si：0.3～3.0％、

Mn：0.1～3.0％、

Ni：1.0～6.0％、

Cr：1.5～6.0％、

Mo：0.1～2.5％、

V：2.0～6.0％、

Nb：0.1～3.0％、

B：0.001～0.2％、

N：0.005～0.070％、

And the balance: fe and inevitable impurities, and the balance of the Fe and the inevitable impurities,

the outer layer has a chemical composition satisfying the following formula (1), and has an M content of 5 to 30% by area₃A carbide of the type C, a carbon-containing compound,

the Shore hardness (A) of the outer layer of the roll surface satisfies the following formula (2),

the residual stress (B) of the roll surface satisfies the following formula (3),

2×Ni+0.5×Cr+Mo＞10.0 (1)

Hs75≤A≤Hs85 (2)

100MPa≤B≤350MPa (3)。

in the outer layer, the chemical component further contains a component in mass ratio

Ti：0.005～0.3％、

W：0.01～2.0％、

Co：0.01～2.0％、

S: 0.3% or less of 1 or more.

In addition, from another aspect, the present invention provides a method for manufacturing a composite roll for rolling by centrifugal casting, wherein the method is characterized in that a tempering treatment is performed without performing a quenching treatment in a heat treatment performed after casting by centrifugal casting, and the tempering treatment is performed at a tempering temperature of 400 ℃ or higher and 550 ℃ or lower.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, in a composite roll for rolling produced by a centrifugal casting method, which is composed of an outer layer having wear resistance superior to that of a conventional high-alloy nodular cast iron roll, when a crack is generated in the outer layer surface during rolling, the problem of breakage such as peeling caused by the progress of the crack can be suppressed. That is, the composite roll for rolling manufactured by the centrifugal casting method can have wear resistance and surface roughening resistance comparable to those of a high-speed cast iron roll and accident resistance comparable to those of a high-alloy cast iron roll. The composite roll for rolling produced by the centrifugal casting method of the present invention is suitable for use in a hot strip mill, particularly a post-stage rolling mill for finish hot rolling in which operational stability is sought.

Drawings

Fig. 1 is a schematic cross-sectional view of a composite roll for rolling produced by a centrifugal casting method according to an embodiment.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and are not described again.

Fig. 1 is a schematic cross-sectional view of a composite roll for rolling 10 produced by a centrifugal casting method according to an embodiment of the present invention. As shown in fig. 1, the composite roll for rolling of the present invention manufactured by the centrifugal casting method has an outer layer 1 for rolling. Further, the outer layer 1 has an intermediate layer 2 and an inner layer (axial core material) 3 on the inner side. As the inner layer material constituting the inner layer (core material) 3, there can be exemplified: as the intermediate layer material constituting the intermediate layer 2, a material having toughness such as high-grade cast iron or nodular cast iron can be exemplified: nickel-chromium wear-resistant cast iron and graphite steel.

The outer layer 1 by centrifugal casting is formed of an Fe-based alloy as follows: the alloy material contains, by mass, 1.5-3.5% of C, 0.3-3.0% of Si, 0.1-3.0% of Mn, 1.0-6.0% of Ni, 1.5-6.0% of Cr, 0.1-2.5% of Mo, 2.0-6.0% of V, 0.1-3.0% of Nb, 0.001-0.2% of B, 0.005-0.070% of N, and the balance of Fe and inevitable impurities.

The structure of the outer layer 1 is composed of (a) MC type carbide, (b) eutectic carbide, (c) matrix, (d) other components, and (b) eutectic carbide having an area ratio of 5-30% of M₃Type C carbide. In addition, except for M₃In addition to C-type carbide, M may be contained₂C type carbide, M₆C-type carbide and M₇C₃Type carbide, but M₂C type carbide, M₆C-type carbide and M₇C₃Type carbides need not be present. Further, the structure of the outer layer may also contain graphite, but graphite need not be present.

(reasons for defining Components)

The reason why the chemical composition of the outer layer of the present invention is limited will be explained below. In the following, the symbol "%" represents "% by mass" unless otherwise specified.

C：1.5～3.5％

C mainly combines with Fe, Cr, Mo, Nb, V, W, etc. to form various hard carbides. In addition, graphite is sometimes formed in some cases. Further, the solid solution is dissolved in the matrix to form pearlite, bainite, martensite, and the like. The larger the content, the more effective the improvement of wear resistance, but when it exceeds 3.5%, coarse carbides and graphite are formed, which causes deterioration of toughness and surface roughness. If the content is less than 1.5%, the amount of carbide is small, and it is difficult to secure hardness, resulting in deterioration of wear resistance. Therefore, the range is set to 1.5 to 3.5%. A more preferable range is 2.0 to 3.0%.

Si：0.3～3.0％

Si is required to suppress the generation of oxide defects by deoxidation of molten steel. In addition, it has the effect of improving the fluidity of molten steel to prevent casting defects. In addition, in high-alloy nodular cast iron and the like, an element is necessary for promoting the precipitation of graphite crystals when the graphite crystals are precipitated. Therefore, the content is 0.3% or more. However, if it exceeds 3.0%, the toughness is lowered, which causes the crack resistance to be lowered. Therefore, the range is set to 0.3 to 3.0%. A more preferable range is 0.6 to 2.7%.

Mn：0.1～3.0％

Mn is added for deoxidation and desulfurization. In addition, Mn combines with S to form MnS. MnS has a lubricating effect, and therefore has an effect of preventing sintering of a material to be rolled. Therefore, it is preferable to contain MnS in a range without side effects. When Mn is less than 0.1%, these effects are insufficient; when the content exceeds 3.0%, the toughness is lowered. Therefore, the range is set to 0.1 to 3.0%. More preferably, the content is in the range of 0.5 to 1.5%.

Ni：1.0～6.0％

Ni has an effect of improving the hardenability of the matrix, and is an element that effectively strengthens the matrix by preventing pearlite formation and promoting bainitization during cooling, and therefore needs to be contained by 1.0% or more. However, if the content exceeds 6.0%, the retained austenite amount becomes too large, it becomes difficult to secure hardness, and deformation or the like may occur during use of hot rolling. Therefore, the range is 1.0 to 6.0%, and a more preferable range is 2.0 to 5.5%.

Cr：1.5～6.0％

Cr is added for the purpose of improving hardenability, improving hardness, improving temper softening resistance, stabilizing carbide hardness, and the like. However, if it exceeds 6.0%, the amount of eutectic carbide becomes too large and the toughness decreases, so the upper limit is set to 6.0%. On the other hand, if the content is less than 1.5%, the above-mentioned effects cannot be obtained. Therefore, the range is set to 1.5 to 6.0%. More preferably in the range of 1.55 to 5.0%.

Mo：0.1～2.5％

Mo mainly combines with C to form hard carbide, contributes to improvement of wear resistance, and improves hardenability of the matrix, and therefore, it is necessary to contain 0.1% or more as the minimum. On the other hand, if it exceeds 2.5%, M, which is one of the objects of the present invention₃The amount of crystal precipitation of the type C carbide decreases. Therefore, the range is set to 0.1 to 2.5%. More preferably, the content is in the range of 0.5 to 2.45%.

V：2.0～6.0％

V is an important element particularly for improving wear resistance. That is, V is an important element that bonds with C to form high-hardness MC carbide that greatly contributes to wear resistance. When the content is less than 2.0%, the amount of MC carbide is insufficient and the improvement of wear resistance is insufficient; if the content exceeds 6.0%, a region in which low-density MC carbide is crystallized alone in the form of primary crystals is formed, and if the MC carbide is manufactured by the centrifugal casting method, the density of the MC carbide is lower than that of molten steel, and therefore, significant gravity segregation occurs. Therefore, the range is set to 2.0 to 6.0%. More preferably, the content is in the range of 3.0 to 5.0%.

Nb：0.1～3.0％

Nb is hardly dissolved in the matrix, and most of Nb forms high-hardness MC carbide, thereby improving wear resistance. In particular, the MC carbide formed by adding Nb has a smaller difference in density from molten steel than the MC carbide formed by adding V, and therefore has an effect of reducing gravity segregation caused by centrifugal casting. When the content of Nb is less than 0.1%, the effect is insufficient; when the content exceeds 3.0%, the MC carbide becomes coarse, and the toughness is lowered. Therefore, the range is set to 0.1 to 3.0%.

B：0.001～0.2％

B is solid-dissolved in carbide and forms a carboride. The carborides have a lubricating effect and have an effect of preventing sintering of the material to be rolled. When the content of B is less than 0.001%, the effect is insufficient; when the content exceeds 0.2%, the toughness is lowered. Therefore, the range is set to 0.001 to 0.2%.

N：0.005～0.070％

N has the effect of refining carbides, combining with V to form nitrides (VN) or carbonitrides (VCN). When the content is less than 0.005%, the refining effect of the carbide is insufficient; when the content exceeds 0.070%, excessive nitride (VN) or carbonitride (VCN) is formed, and the toughness is lowered, so that it is necessary to suppress the content to 0.070% or less. Therefore, the range is set to 0.005 to 0.070%.

As described above, the basic component of the outer layer of the present invention may be appropriately selected from the basic components described above and further contain the following chemical components as other chemical components according to the size of the roll to be applied, the required use characteristics of the roll, and the like.

Ti：0.005～0.3％

The composite roll for rolling produced by the centrifugal casting method of the present invention may contain Ti in addition to the above-described essential elements. Ti is expected to outgas N and O and form TiCN or TiC to become the nuclei of MC carbide. When the Ti content is less than 0.005%, the effect thereof cannot be expected; if the content exceeds 0.3%, the viscosity of molten steel increases, and the risk of casting defects increases. Therefore, when Ti is added, the range is set to 0.005 to 0.3%. More preferably, the content is in the range of 0.01 to 0.2%.

W：0.01～2.0％

The composite roll for rolling produced by the centrifugal casting method of the present invention may contain W in addition to the above-described essential elements. W is solid-dissolved in the matrix like Mo to reinforce the matrix, and is combined with C to form M₂C、M₆Hard eutectic carbide such as C contributes to improvement of wear resistance. In order to strengthen the matrix, the minimum content is 0.01% or more, and when it exceeds 2.0%, coarse eutectic carbides are formed, and the toughness is lowered. Therefore, when W is added, the range is set to 0.01 to 2.0%. It should be noted that, in the following description,the choice of whether or not to add W is, for example, added when the amount of eutectic carbide is increased to improve wear resistance, and the effect is greater.

Co：0.01～2.0％

The composite roll for rolling according to the present invention produced by centrifugal casting may contain Co in addition to the above-described essential elements. Most of Co is dissolved in the matrix to strengthen the matrix. Therefore, it has an effect of improving hardness and strength at high temperature. When the content is less than 0.01%, the effect is insufficient; if the content exceeds 2.0%, the effect is saturated, and therefore, from the viewpoint of economy, the content is 2.0% or less. Therefore, when Co is added, the range is set to 0.01 to 2.0%. The choice of whether or not to add Co is effective when, for example, it is required to improve wear resistance and increase the amount of eutectic carbide is difficult.

S: less than 0.3%

In general, S is an element that is inevitably mixed into the raw material to some extent, but as described above, it forms MnS to have a lubricating effect, and thus has an effect of preventing sintering of the rolled material. On the other hand, the content in excess may embrittle the material, so that it is preferably limited to 0.3% or less.

Inevitable impurities

The composition of the outer layer of the composite roll for rolling produced by the centrifugal casting method of the present invention is such that the balance is substantially Fe and inevitable impurities, in addition to the above elements. Among the inevitable impurities, P deteriorates toughness, and therefore is preferably limited to 0.1% or less. Further, as other inevitable elements, elements such as Cu, Sb, Sn, Zr, Al, Te, Ce, and the like may be contained within a range not impairing the characteristics of the outer layer. The total amount of inevitable impurities is preferably 0.6% or less so as not to impair the characteristics of the outer layer.

(relational expression relating to chemical composition)

In addition, with respect to the chemical composition (chemical composition) of the outer layer of the composite roll for rolling produced by the centrifugal casting method of the present invention, it is necessary that the following formula (1) is satisfied with respect to the content (%) of Ni, Cr and Mo particularly when V, Nb, Mo and Cr are added as hard carbide forming elements in the present invention.

2×Ni+0.5×Cr+Mo＞10.0(1)

The outer layer of the composite roll for rolling manufactured by the centrifugal casting method is characterized by having M of 5-30% in area ratio as an element constituting a microstructure₃C carbide, and is characterized in that the tempering treatment is performed without performing the quenching treatment, and the tempering treatment is performed at a tempering temperature of 400 ℃ or higher and 550 ℃ or lower. Under these conditions, it has been very difficult to stably control the Shore hardness (Hs) of the outer layer of the roll surface to 75 to 85 in the conventional art.

The present invention has found that the outer layer has M of 5 to 30% by area ratio as an element constituting the microstructure₃And C carbide, and tempering without quenching, the tempering being performed at a tempering temperature of 400 ℃ to 550 ℃, and under such conditions, the chemical composition (chemical composition) of the outer layer of the clad roll for rolling produced by centrifugal casting according to the present invention satisfies formula (1), and thereby the Shore hardness (Hs) of the outer layer on the surface of the clad roll for rolling produced by centrifugal casting can be stably controlled within a range of 75 to 85. This makes it possible to provide a roller having both high abrasion resistance and high accident resistance (crack resistance).

(Heat treatment after casting by centrifugal casting method)

The present inventors have found that, although the composite roll for rolling produced by the centrifugal casting method of the present invention is produced by a general centrifugal casting method, it is preferable to perform a tempering treatment without performing a quenching treatment with respect to a heat treatment performed after casting in the centrifugal casting method. It has also been found that the tempering treatment is preferably performed at a tempering temperature of 400 ℃ or higher and 550 ℃ or lower. The following findings were obtained: the hardness of the outer layer surface is maintained at a Shore hardness equivalent to that of a high-speed cast iron roll, and the residual stress value of the outer layer surface of the body is suppressed to a level equivalent to that of a high-alloy pockmarked cast iron roll by performing a tempering treatment at a tempering temperature of 400 ℃ to 550 ℃ without performing a quenching treatment in which the Fe matrix is rapidly cooled to a region where the Fe matrix is transformed into austenite.

As described above, the shore hardness (a) of the outer layer of the clad roll for rolling produced by the centrifugal casting method of the present invention satisfies the following formula (2) by performing the tempering treatment without performing the quenching treatment and setting the tempering temperature to 400 ℃ or more and 550 ℃ or less. Further, the residual stress (B) of the outer layer surface of the composite rolling roll for rolling produced by the centrifugal casting method of the present invention satisfies the following formula (3).

Hs75≤A≤Hs85 (2)

100MPa≤B≤350MPa (3)

(M₃Content of C-based carbide

In addition, the outer layer of the composite roll for rolling manufactured by the centrifugal casting method of the present invention is required to contain 5 to 30% of M in terms of area ratio₃Type C carbide. The present inventors have studied the use of centrifugal casting rolls for hot rolling and found that, in a composite roll for rolling produced by a centrifugal casting method and having wear resistance equivalent to that of a high-speed roll, M is present at a predetermined ratio in the microstructure constituent elements of the outer layer in order to impart accident resistance equivalent to that of a high-alloy nodular cast iron roll₃Type C carbides are effective. M present in the outer layer₃When the amount of the type C carbide is less than 5% by area ratio, wear resistance is deteriorated and it is difficult to secure accident resistance comparable to a high-alloy pitted iron roll. In addition, M₃When the amount of C type carbide exceeds 30% by area ratio, M₃The crystals of C-type carbide are coarse and rather the accident resistance is deteriorated, so M is used₃The amount of C-type carbide is limited to 5 to 30% by area ratio.

(Effect)

As described above, in the composite roll for rolling produced by the centrifugal casting method of the present invention, the chemical composition of the outer layer is set to the predetermined composition and the above formula (1) is satisfied, and M is further contained in an amount of 5 to 30% by area₃The C-type carbide has a Shore hardness satisfying the above formula (2), and the residual stress is suppressed to satisfy the above formula (3). Thereby, excellent resistance equivalent to that of a high-speed cast iron roll is achievedA composite roll for rolling produced by centrifugal casting, which has wear resistance, surface roughness resistance and accident resistance comparable to those of a high-alloy pitted cast iron roll.

Although the embodiment of the present invention has been described above, the present invention is not limited to the illustrated embodiment. It is obvious that those skilled in the art can conceive various modifications or variations within the scope of the idea described in the claims, and these are also within the technical scope of the present invention.

Examples

Composite rolls having chemical compositions shown in Table 1, namely, Nos. 1 to 16 (inventive examples) and 17 to 28 (comparative examples) were produced by centrifugal casting to form composite rolls for hot finish rolling mill rolling having an inner layer diameter of 600mm, a roll outer diameter of 800mm, an outer layer thickness of 100mm and a body length of 2400 mm. The melting temperature was 1550 ℃ and the casting temperature was set at a freezing point +90 ℃. After casting, tempering heat treatment was performed at the tempering temperature described in table 1.

In table 1, underlined portions indicate that the chemical components of the outer layer are out of the predetermined ranges described in the above embodiment, that the chemical components do not satisfy the formula (1), and that the tempering temperature is out of the predetermined ranges. In addition, regarding the Shore hardness of the outer layer surface in Table 1, the symbol "O" indicates that it is within the scope of the present invention (Hs: 75 to 85) and "X" indicates that it is outside the scope of the present invention; regarding the residual stress of the outer layer surface, the symbol "O" indicates that the stress is within the range of the present invention (100MPa to 350MPa), and "X" indicates that the stress is outside the range of the present invention. In addition, with respect to M₃The C carbide area ratio is indicated by the symbol O within the range of the present invention (area ratio: 5 to 30%) and X is indicated outside the range of the present invention.

[ Table 1]

Then, the Shore hardness of the surface of the outer layer of the main body of the composite roll was measured to determine whether or not a Shore hardness (Hs: 75 to 85) comparable to that of a high-speed cast iron roll could be secured. In addition, the residue on the surface of the outer layer of the subject was measured by X-rayAnd (4) inspecting the stress value, namely whether the stress value is 100-350 MPa equivalent to that of the high-alloy pitted cast iron roll. Further, M in the tissue of the test piece collected from the roller body was measured₃And (3) inspecting whether the area ratio of the C-type carbide is in the range of 5-30%. For M₃Determination of the area ratio of C-type carbides requires identification of M₃Type C carbide and other eutectic carbides (M)₂C type carbide, M₆C type carbide, M₇C₃Type carbide, etc.), so only M is extracted by photographing using the element mapping function of EPMA (electron probe microanalyzer)₃Images of C-type carbide (magnification: 100 times), and M in the images was measured by image analysis software₃Area ratio of C-type carbide.

As a result, it was confirmed that, in the rolls of invention examples nos. 1 to 16 in which the chemical components of the outer layer were within the predetermined ranges described in the above embodiments and the conditions relating to the above formula (1) and the tempering temperature were within the ranges of the present invention, when cracks were generated on the outer layer surface during rolling, the conditions that the rate of crack propagation could be suppressed to a level comparable to that of a high-alloy millstone roll, that is, the shore hardness (Hs: 75 to 85) and the residual stress value (100MPa to 350MPa) of the main outer layer surface were satisfied. It was confirmed that the condition for providing wear resistance equivalent to that of a high-speed roll and providing accident resistance equivalent to that of a high-alloy nodular cast iron roll, that is, the condition for satisfying M in the microstructure constituent elements of the outer layer₃The area ratio of C-type carbide is 5-30%.

On the other hand, it was confirmed that the chemical composition of the outer layer was not within the predetermined range described in the above embodiment, and that the conditions relating to the above formula (1) and the tempering temperature were not within the range of the present invention, and in the rolls of comparative examples 17 to 28, cracks were generated in the outer layer surface during rolling, and they did not satisfy: the aggravating speed of the crack can be inhibited to the level equivalent to that of a high-alloy pitted cast iron roller, namely the Shore hardness (Hs: 75-85) and the residual stress value (100 MPa-350 MPa) of the outer layer surface of the main body are not met; the condition for providing the abrasion resistance equivalent to that of a high-speed roll and the accident resistance equivalent to that of a high-alloy nodular cast iron roll is not satisfied, namely, the microstructure of the outer layer is not satisfiedM in the constituent elements₃The area ratio of C-type carbide is 5-30%.

From the results of the above-described examples, it is understood that in the composite roll for rolling produced by the centrifugal casting method, the chemical composition of the outer layer is within a predetermined range and the chemical composition is limited to satisfy the above formula (1), and M is contained in an amount of 5 to 30% by area₃The C-type carbide has a structure such that the shore hardness and residual stress of the roll surface can be set to values within desired ranges, and a composite roll for rolling produced by centrifugal casting having excellent wear resistance and surface roughening resistance comparable to a high-speed cast iron roll and accident resistance comparable to a high-alloy pitted cast iron roll is realized.

Industrial applicability

The present invention is applicable to a clad roll for rolling produced by a centrifugal casting method used in a hot strip mill in a hot rolling process, and a method for producing the same.

Description of the reference numerals

1 outer layer

2 intermediate layer

3 inner layer (axle core material)

10 composite roll for rolling manufactured by centrifugal casting method