JP2024027590A - Hot rolling roll outer layer material and hot rolling composite roll - Google Patents

Abstract

An object of the present invention is to provide an outer layer material for a hot rolling roll and a composite roll for hot rolling which have better seizure resistance and slip resistance than conventional ones. [Solution] In mass %, C: 1.2 to 2.5%, Si: 0.15 to 2.50%, Mn: 0.15 to 2.50%, Ni: 0.2 to 8.0 %, Cr: 1.5-10.0%, Mo: 3.5-12.0%, V: 2.0-7.5%, W: 0.1-6.0%, P: 0. 01 to 0.04%, S: 0.001 to 0.010%, the balance consists of Fe and unavoidable impurities, and the content of C, Cr, Mo, V, and W satisfies a specific formula. , carbides with a particle size of 1 μm or more are present in an area ratio of 8.0 to 20.0%, and the Shore hardness at 20°C is 75.0HS or more and 85.0HS or less and the Shore hardness at 600°C is A hot rolling roll outer layer material having a diameter of 45.0HS or more and 50.0HS or less. [Selection diagram] None

Description

The present invention relates to a hot rolling roll outer layer material and a hot rolling composite roll, and particularly to a hot rolling roll outer layer material and a hot rolling composite roll suitable for application to a stand after rough rolling of steel plates. Regarding.

In recent years, the demand for high-quality steel sheets has increased, and there has been a need to improve hot rolling technology for steel sheets. Therefore, there is a strong demand for improvements in the properties of hot rolling rolls used in hot rolling equipment, specifically improvements in wear resistance, seizure resistance, slip resistance, and the like. To improve wear resistance, HiCr cast steel rolls incorporate Cr-based _M7C3 carbides, and _high -speed steel rolls, which are a type of tool steel, contain carbide-forming elements such as V, Cr, Mo, and W. However, a high-speed roll incorporating a large amount of hard carbide such as V-based MC carbide, Mo, W-based M ₂ C carbide, and Cr-based M ₇ C ₃ carbide (M represents a metal element that forms a carbide) is used. ing. However, when a large amount of carbide is introduced to improve wear resistance, the hardness and wear resistance are high, so the surface roughness of the roll is reduced, and the coefficient of friction during rolling is reduced, resulting in slippage. It is more likely to occur. On the other hand, when the coefficient of friction during rolling increases, seizure occurs, which is a phenomenon in which a part of the rolled material is transferred to the roll material, and the quality of the rolled product deteriorates after the occurrence of seizure.

Various techniques have been disclosed to solve such problems. For example, in Patent Document 1, the chemical components of the outer layer are C: 1.0 to 3.0%, Si: 0.2% by mass ratio. ~2.0%, Mn: 0.2~2.0%, V: 3.0~10.0%, Cr: 3.0~10.0% and one or two of Mo and W. .0 to 10.0%, or further contains one or two of Ni: 0.2 to 5.0% or Co: 0.2 to 10.0%, with the remainder being Fe and inescapable A composite roll for hot rolling has been proposed which is characterized by comprising impurities. The company claims that this results in a composite roll for hot rolling that can ensure a high and stable coefficient of friction with rolled steel by crystallizing a large amount of hard, fine, and granular MC type carbides.

Furthermore, in Patent Document 2, in mass %, C: 0.8 to 4.0%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, Cr: 3.0 ~15%, V: 3.0 ~ 15%, one or both of Mo and W: ≧2%, and Mo + 0.5W: ≧6.1%, or further, Ni: 0.2 ~ 5%, Co: 0.5 to 10%, Nb: 0.50 to 5.0%, and one or more of Al, Ti, and Zr: ≦0.5%, and the metal structure is A composite roll for hot rolling has been proposed, which includes an outer layer material having a carbide content of 5 to 30% and an average gap between adjacent carbides of 20 μm or less. The company claims that this will result in a composite roll for hot rolling that has improved slip resistance and seizure resistance by dispersing the appropriate amount of granular carbides in fine particles and reducing the adjacent gaps between each carbide.

Patent Document 3 describes, in mass%, C: 0.90 to 1.40%, Si: 0.50 to 1.50%, Mn: 0.50 to 1.50%, Ni: 0.5 to 2 .0%, Cr: 9.0 to 16.0%, Mo: 1.00 to 3.00%, Al: 0.010 to 0.030%, and V: 0.05 to 0.0%. 50%, Ti: 0.05 to 0.50%, Nb: 0.02 to 0.20%, and (1) formula: 8≦Cr/C≦14, ( 2) formula: 3.0≦12.3C+0.55Cr-15.2≦7.0, and (3) formula: 26.0≦15.5C+Cr, and the molten metal composition consists of Fe and inevitable impurities. A work roll for a hot rolling rough rolling stand has been proposed in which an outer shell layer made of cast steel and a shaft core material made of ductile cast iron cast inside the outer shell layer are integrated via an intermediate layer. There is. Accordingly, by adding appropriate amounts of C and Cr and controlling the amount of M ₇ C ₃ carbide, a work roll for a hot rolling rough rolling stand can be obtained that can achieve both wear resistance and slip resistance.

Japanese Patent Application Publication No. 2002-346613 Japanese Patent Application Publication No. 2004-255457 JP2020-63485A

However, as the demand for high-quality steel sheets increases and the hot rolling technology for steel sheets improves, the properties required for hot rolling rolls become increasingly strict, with wear resistance being particularly required. . Therefore, if a roll is designed to meet requirements for wear resistance, it will tend to slip, and conversely, if the coefficient of friction is increased to prevent slip, it will tend to seize, increasing the frequency of roll troubles. The conventional hot rolling rolls described in Patent Documents 1 to 3 do not have sufficient seizure resistance and slip resistance.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an outer layer material for a hot rolling roll and a hot rolling composite roll having excellent seizure resistance and slip resistance, which solve the above problems.

The present inventor investigated in detail the relationship among the base structure, carbide, hardness, coefficient of friction, and chemical components of a hot rolling roll. As a result, they found that seizure resistance and slip resistance can be improved by optimizing the chemical components so that the area ratio of carbides and high-temperature hardness fall within a specific range.
The present invention was completed based on these findings and further studies. That is, the gist of the present invention is as follows.
[1] In mass%,
C: 1.2-2.5%,
Si: 0.15-2.50%,
Mn: 0.15-2.50%,
Ni: 0.2-8.0%,
Cr: 1.5-10.0%,
Mo: 3.5-12.0%,
V: 2.0-7.5%,
W: 0.1-6.0%,
P: 0.01-0.04%,
Contains S: 0.001 to 0.010%,
The remainder consists of Fe and unavoidable impurities, and the content of C, Cr, Mo, V, and W satisfies the following formulas (1) and (2), and the area ratio of carbides with a grain size of 1 μm or more is 8.0 to 20.0%, and the Shore hardness at 20°C is 75.0HS or more and 85.0HS or less, and the Shore hardness at 600°C is 45.0HS or more and 50.0HS or less. Roll outer layer material for rolling.
20.0≦[%C]×([%V]+[%Cr]+[%Mo]+[%W])≦35.0 (1)
1.00≦[%C]×((0.177×[%V])/(0.099×[%Cr]+0.063×[%Mo]+0.033×[%W]))≦3 .00 (2)
Here, in formulas (1) and (2), [%C], [%Cr], [%Mo], [%V], and [%W] represent the content (mass%) of each element. .
[2] A composite roll for hot rolling having two layers, an outer layer and an inner layer, or three layers, an outer layer, an intermediate layer, and an inner layer, wherein the outer layer is in mass%,
C: 1.2-2.5%,
Si: 0.15-2.50%,
Mn: 0.15-2.50%,
Ni: 0.2-8.0%,
Cr: 1.5-10.0%,
Mo: 3.5-12.0%,
V: 2.0-7.5%,
W: 0.1-6.0%,
P: 0.01-0.04%,
Contains S: 0.001 to 0.010%,
The remainder consists of Fe and unavoidable impurities, and the content of C, Cr, Mo, V, and W satisfies the following formulas (1) and (2), and the area ratio of carbides with a grain size of 1 μm or more is 8.0 to 20.0%, and the Shore hardness at 20°C is 75.0HS or more and 85.0HS or less, and the Shore hardness at 600°C is 45.0HS or more and 50.0HS or less. Composite roll for rolling.
20.0≦[%C]×([%V]+[%Cr]+[%Mo]+[%W])≦35.0 (1)
1.00≦[%C]×((0.177×[%V])/(0.099×[%Cr]+0.063×[%Mo]+0.033×[%W]))≦3 .00 (2)
Here, in formulas (1) and (2), [%C], [%Cr], [%Mo], [%V], and [%W] represent the content (mass%) of each element. .

According to the present invention, it is possible to provide a hot rolling roll outer layer material and a hot rolling composite roll having excellent seizure resistance and slip resistance. As a result, the time loss due to interruption of rolling due to occurrence of roll troubles is reduced, thereby improving the rolling efficiency of the hot rolling rolls, which also has the effect of improving the productivity of hot rolled steel sheets.

FIG. 2 is an explanatory diagram schematically showing the configuration of a testing machine used in a hot rolling wear test and a test piece for a hot rolling wear test.

The reasons for limiting the composition of the outer layer material of the hot rolling roll of the present invention will be explained. In addition, hereinafter, mass % is simply written as % unless otherwise specified.

C: 1.2-2.5%
C combines with V, Cr, Mo, W, etc. to form hard carbides and contributes to improving wear resistance. It also solidly dissolves in the base to increase hardness. If C is less than 1.2%, the amount of carbide is insufficient and excellent wear resistance cannot be obtained. In addition, since the hardness is low, plastic flow occurs and the coefficient of friction increases, making it easier to seize. On the other hand, if C exceeds 2.5%, carbides are excessively produced, resulting in a decrease in roughness resistance and crack resistance. Furthermore, when the hardness increases, the surface roughness of the roll decreases, and the coefficient of friction decreases, causing slipping. Therefore, C was limited to 1.2% or more and 2.5% or less. Note that the content of C is preferably 1.5% or more and 2.2% or less.

Si: 0.15-2.50%
Si acts as a deoxidizing agent in the molten metal, improves the fluidity of the molten metal, and has the effect of preventing casting defects. If Si is less than 0.15%, the deoxidizing effect will be insufficient. On the other hand, even if Si exceeds 2.50%, the effect is saturated. Therefore, Si was limited to 0.15% or more and 2.50% or less. Note that the Si content is preferably 0.30% or more and 1.50% or less.

Mn: 0.15-2.50%
Mn has the effect of deoxidizing the molten metal and fixing S, which has an adverse effect, as MnS. If Mn is less than 0.15%, the effect of its addition is insufficient. On the other hand, even if Mn exceeds 2.50%, the effect is saturated. Therefore, Mn was limited to 0.15% or more and 2.50% or less. Note that the Mn content is preferably 0.30% or more and 1.50% or less.

Ni: 0.2-8.0%
Ni has the effect of improving the hardenability of the base and improving the hardness of the base. If Ni is less than 0.2%, the effect will hardly be exhibited. On the other hand, if Ni exceeds 8.0%, austenite tends to remain, resulting in a decrease in hardness. Therefore, Ni was limited to 0.2% or more and 8.0% or less. Note that the Ni content is preferably 1.0% or more and 4.0% or less.

Cr: 1.5-10.0%
Cr is a carbide-forming element and combines with C to form M ₇ C ₃ carbide. Since it is a hard carbide, it has the effect of improving wear resistance. If the Cr content is less than 1.5%, the amount of M ₇ C ₃ carbide is insufficient, resulting in a decrease in wear resistance. On the other hand, when Cr exceeds 10.0%, coarse M ₇ C ₃ carbides are generated, which actually deteriorates the wear resistance. Therefore, Cr was limited to 1.5% or more and 10.0% or less. Note that the Cr content is preferably 3.0% or more and 7.0% or less.

Mo: 3.5-12.0%
Mo is a carbide-forming element and combines with C to form M ₂ C carbide. Since it is a hard carbide, it has the effect of improving wear resistance. If Mo is less than 3.5%, these effects are insufficient. On the other hand, when Mo exceeds 12.0%, coarse M ₂ C carbides are generated, resulting in a decrease in toughness. Therefore, Mo was limited to 3.5% or more and 12.0% or less. Note that the Mo content is preferably 5.5% or more and 9.5% or less.

V: 2.0-7.5%
V is a carbide-forming element and combines with C to form MC carbide. MC carbide has a Vickers hardness Hv of 2800 and is one of the hardest carbides. When V is less than 2.0%, the amount of crystallization and precipitation of MC carbides is insufficient, resulting in poor wear resistance. On the other hand, when V exceeds 7.5%, VC carbide, which has a lower specific gravity than the molten iron, concentrates inside the outer layer due to the centrifugal force during centrifugal casting, causing segregation. Therefore, V was limited to 2.0% or more and 7.5% or less. Note that the V content is preferably 3.0% or more and 6.5% or less.

W: 0.1-6.0%
W is a carbide-forming element, and combines with C to form a hard carbide such as hard M ₂ C, which increases the hardness of the outer layer and has the effect of improving wear resistance. If W is less than 0.1%, the effect is insufficient and wear resistance deteriorates. On the other hand, when W exceeds 6.0%, coarse M ₂ C carbides are generated, and the wear resistance is rather deteriorated. Therefore, W was limited to 0.1% or more and 6.0% or less. Note that the W content is preferably 1.0% or more and 4.0% or less.

P: 0.01-0.04%
It has been thought that P is mixed in during the manufacturing process and deteriorates mechanical properties, but as a result of intensive studies by the inventors, it has become clear that the inclusion of a small amount of P has the effect of improving hardness and wear resistance. I made it. If P is less than 0.01%, the effect will not be sufficient, while if P is more than 0.04%, mechanical properties will deteriorate. Therefore, P was limited to 0.01% or more and 0.04% or less. Note that the P content is preferably 0.02% or more and 0.03% or less.

S: 0.001-0.010%
S is normally treated as a harmful element in iron-based alloys and its content is limited to a certain amount or less, but within that range, MnS has the effect of a lubricant. On the other hand, if the content is high, the material becomes brittle. Therefore, S was limited to 0.001% or more and 0.010% or less. Note that the S content is preferably 0.002% or more and 0.006% or less.

Unavoidable Impurities The remainder other than the above-mentioned components consists of Fe and unavoidable impurities.

Further, the present invention is characterized in that the contents of C, Cr, Mo, V, and W are within the above ranges, and in addition, the following formula (1) and the following formula (2) are satisfied.
20.0≦[%C]×([%V]+[%Cr]+[%Mo]+[%W])≦35.0 (1)
1.00≦[%C]×((0.177×[%V])/(0.099×[%Cr]+0.063×[%Mo]+0.033×[%W]))≦3 .00 (2)
Here, in formulas (1) and (2), [%C], [%Cr], [%Mo], [%V], and [%W] represent the content (mass%) of each element. .

Regarding [%C] × ([%V] + [%Cr] + [%Mo] + [%W]), this parameter indicates the relationship between carbon and carbide-forming elements, and satisfies (1) above. By adjusting in this manner, the amount of carbide and the C content in the matrix are optimized, the hardness is improved, and the wear resistance is thereby improved. If the value of [%C] x ([%V] + [%Cr] + [%Mo] + [%W]) is less than 20.0, the amount of carbide is insufficient or the C content in the base is low. Therefore, sufficient hardness cannot be obtained and wear resistance decreases. Additionally, plastic flow tends to occur during rolling, making the steel material more likely to seize. On the other hand, when it exceeds 35.0, the amount of carbides increases or the C content in the matrix increases, so that more than sufficient hardness is obtained. Therefore, as the surface roughness of the rolls during rolling becomes smaller, the coefficient of friction becomes lower, making slips more likely to occur. Therefore, the value of [%C]×([%V]+[%Cr]+[%Mo]+[%W]) was limited to 20.0 or more and 35.0 or less. Furthermore, preferably it is 25.0 or more and 30.0 or less.

For [%C] × ((0.177 × [%V]) / (0.099 × [%Cr] + 0.063 × [%Mo] + 0.033 × [%W])), this parameter is It represents the ratio of the amount of MC carbide and (the amount of M ₂ C carbide + the amount of M ₇ C ₃ carbide), and by adjusting it to satisfy the above (2), the proportion of each carbide amount is optimized and the It becomes possible for the coefficient of friction to take a value that does not cause seizure or slippage. The value of [%C] × ((0.177 × [%V]) / (0.099 × [%Cr] + 0.063 × [%Mo] + 0.033 × [%W])) is 1.00 If it is less than 20%, the proportion of M ₂ C and M ₇ C ₃ carbides increases. Since these crystallize widely in a planar shape, the roll surface becomes flat, the surface roughness becomes small, and the coefficient of friction during rolling becomes small, making slips more likely to occur. On the other hand, when it exceeds 3.00, the proportion of MC carbide increases. This is a fine granular carbide, and as the number of protrusions on the roll surface increases, the coefficient of friction during rolling increases, making seizure more likely. Therefore, the value of [%C] × ((0.177 × [%V]) / (0.099 × [%Cr] + 0.063 × [%Mo] + 0.033 × [%W])) is It was limited to 1.00 or more and 3.00 or less. Furthermore, preferably it is 1.20 or more and 2.00 or less.
Next, the reasons for limiting the structure of the hot rolling roll outer layer material of the present invention will be explained.

The hot rolling roll outer layer material of the present invention has a composition within the above-mentioned range, and is characterized by having a structure in which carbides with a grain size of 1 μm or more exist in an area ratio of 8.0 to 20.0%. . The carbides are MC carbide, M ₂ C carbide, and M ₇ C ₃ carbide crystallized during solidification.
Here, the base is preferably martensite or bainite. Various studies have been conducted on carbides, but most of them are related to wear resistance. As a result of intensive studies by the inventors, in order to make the amount of each carbide an appropriate ratio, carbides having a composition within the above range and having a particle size of 1 μm or more exist in an area ratio of 8.0 to 20.0%. It has been discovered that by limiting the structure to the structure, seizure resistance and slip resistance can be greatly improved. By focusing not only on the hardness of each carbide but also on its morphology, and adjusting the amount of granular and fine MC carbides and the amount and ratio of planarly crystallized M ₂ C and M ₇ C ₃ carbides, the It is thought that the friction coefficient value can be controlled, and the seizure resistance and slip resistance are improved accordingly.
Next, a preferred method for manufacturing the hot rolling roll outer layer material and hot rolling composite roll of the present invention will be described.

In the present invention, centrifugal casting, continuous overlay casting, and the like are preferred as methods for manufacturing the roll outer layer material, but from the viewpoint of manufacturing costs, centrifugal casting is more preferred. Note that the present invention is not limited to these manufacturing methods.

When the roll outer layer material is cast by a centrifugal casting method, the composite roll for hot rolling of the present invention consists of a centrifugally cast outer layer and an inner layer welded and integrated with the outer layer. Note that an intermediate layer may be arranged between the outer layer and the inner layer. That is, instead of the inner layer welded and integrated with the outer layer, there may be an intermediate layer welded and integrated with the outer layer, and an inner layer welded and integrated with the intermediate layer. Note that the inner layer is preferably manufactured by a static casting method.

For the inner layer manufactured by the static casting method, it is preferable to use spheroidal graphite cast iron, caterpillar graphite cast iron (CV cast iron), etc., which have excellent castability and mechanical properties. In centrifugal casting rolls, the outer layer and inner layer are welded together, and the components of the outer layer material mix into the inner layer. When carbide-forming elements such as Cr and V contained in the outer layer material mix into the inner layer, the inner layer becomes brittle. For this reason, it is preferable to suppress the mixing rate of the outer layer material components into the inner layer as much as possible.

Moreover, when forming an intermediate layer, it is preferable to use graphite steel, high carbon steel, hypoeutectic cast iron, etc. as the intermediate layer material. The intermediate layer and the outer layer are welded together, and the components of the outer layer material are mixed into the intermediate layer. In order to suppress the mixing rate of the outer layer material components into the inner layer, it is preferable to suppress the mixing rate of the outer layer material into the intermediate layer as much as possible.

The composite roll for hot rolling of the present invention is preferably subjected to heat treatment after casting. The heat treatment included heating to 900 to 1100°C and quenching by air cooling or blast air cooling, and further heating and holding so that the tempering parameter P described in the formula (3) below was within the range of 10000 to 20000. It is preferable to perform tempering treatment, which is followed by cooling, two or more times. At this time, the above-described structure can be obtained by changing the quenching temperature, tempering parameters, and number of times of tempering within the stated ranges depending on the components.
P=T(log(t)+A) (3)
Here, T is the tempering temperature (K), t is the tempering time (h), and A is a constant. (A=20 is used in the present invention)

The preferred hardness of the composite roll for hot rolling of the present invention is 75.0HS to 85.0HS in Shore hardness at 20°C, and 45.0HS to 50.0HS in Shore hardness at 600°C. . If the 20°C shore hardness is less than 75.0 HS, wear resistance will deteriorate, while if the hardness exceeds 85.0 HS, cracks formed on the surface of the hot rolling roll during hot rolling will be removed by grinding. becomes difficult. Further, the roll surface temperature during hot rolling is around 600°C, and if the Shore hardness at 600°C is less than 45.0 HS, plastic flow occurs and the steel material tends to seize on the roll surface. On the other hand, when the hardness exceeds 50.0 HS, the roll hardness is too high and slips are likely to occur during rolling. Such hardness can be stably ensured by heat-treating a roll containing the components of the present invention so that the tempering parameter P falls within the range of 10,000 to 20,000.

The present invention will be explained in more detail with reference to the following examples, but the present invention is not limited to these examples.

In the chemical composition of the hot rolling roll outer layer material shown in Table 1 (the remainder is Fe and unavoidable impurities), No. Each sample material of Examples 1 to 8 of the present invention and No. Each sample material of Comparative Examples 9 to 20 was heated to 1450 to 1550°C, melted, and cast into a Y-shaped keel block mold (cuboid part: thickness 35 mm, width 230 mm, height 120 mm). After cooling, the ingot was taken out and quenched at 900° C. to 1100° C., and then tempered three times by heating and holding and then cooling so that the tempering parameter P was within the range of 10,000 to 20,000. Thereafter, the structure was observed, the hardness was measured, and the friction coefficient was measured using a hot rolling wear tester. Note that the specimen for microstructural observation and hardness measurement was taken from the center of the wall thickness.

The Vickers hardness HV of each sample cut from the ingots of the inventive example and the comparative example was measured at 5 points each at 20°C and 600°C using a Vickers hardness meter (testing force: 1 kgf), and the average value was calculated. . The high temperature (at 600° C.) Vickers measurement was based on JIS Z2252 "High temperature Vickers hardness test method." Diamond was used as the indenter, and a Nikon QM-2 (simultaneous heating of the indenter and test piece) testing machine was used, the test atmosphere was an argon gas atmosphere, the heating rate was 20°C/min, and the load holding time was 10 sec. I conducted an experiment. The obtained Vickers hardness was converted into Shore hardness using the calculation formula of JIS B 7731.

The friction coefficient measurement method using a hot rolling wear tester was as follows. Hot rolling wear test pieces (outer diameter 60 mmφ, width 10 mm, with C1 chamfer) were collected from the obtained ingots of each invention example and each comparative example. The wear test was carried out using a two-disc sliding rolling method between a test piece and a counterpart piece, as shown in FIG. The test piece 1 was cooled with cooling water 2 and rotated at 76 rpm, and a mating piece (outer diameter 190 mmφ, width 15 mm, C1 chamfer) 4 heated to 1000°C with a high frequency induction heating coil 3 was placed on the rotating test piece 1. A load of 180 N was applied in the load direction 7, and the test pieces were rolled while being in contact with each other. The rotation direction 5 of the test piece and the rotation direction 6 of the mating piece are rotation directions in which the tangents at the contact points of the test piece 1 and the mating piece 4 are in the same direction. The friction coefficient was measured by conducting the test for 300 minutes, replacing the mating piece with a new one every 60 minutes, and conducting the test five times in total. The torque and load during the test were measured, and the friction coefficient was calculated from the following equation (4).
μ=T/P×L (4)
Here, μ is the friction coefficient, T is the torque (kgf·m), P is the load (kgf), and L is the radius of the test piece (m).

The above test assumes continuous operation of hot rolling, so the mating piece is heated to 1000°C, and the friction coefficient and seizure status are evaluated after 300 minutes. The presence or absence of seizure was visually confirmed on the surface of the test piece after 300 minutes, and those with transfer of the material of the other piece were evaluated as having seizure, and those with no transfer were evaluated as no seizure.

The hot rolling wear test (hereinafter also referred to as wear test) method was as follows. As in the friction coefficient measurement test, hot rolling wear test pieces (outer diameter 60 mmφ, width 10 mm, with C1 chamfer) were collected from the obtained ingots of each invention example and each comparative example. The wear test was carried out using a two-disc sliding rolling method using a test piece 1 and a mating piece 4, as shown in FIG. The test piece 1 was cooled with cooling water 2 and rotated at 700 rpm, and a mating piece (outer diameter 190 mmφ, width 15 mm, C1 chamfer) 4 heated to 800°C with a high frequency induction heating coil 3 was placed on the rotating test piece 1. A load of 686 N was applied in the load direction 7, and the test pieces were rolled while being in contact with each other. The rotation direction 5 of the test piece and the rotation direction 6 of the mating piece are rotation directions in which the tangents at the contact points of the test piece 1 and the mating piece 4 are in the same direction. The wear test was carried out for 135 minutes, and the test piece was replaced with a new one every 45 minutes (31,500 revolutions of the test piece), and the test was performed a total of 3 times (94,500 revolutions of the test piece). The amount of wear was measured.

For each sample after heat treatment, the structure was observed using a digital microscope after mirror polishing and corrosion with nital solution. Photographs were taken in a field of view where more than 200 eutectic cells could be seen within the field of view. Further, using an image analysis tool (ImageJ), a photograph at a measurement magnification of 200 times was subjected to binarization processing. Since there is a difference in brightness between the base structure and the carbide in the photograph, by performing binarization processing, it is possible to classify the base structure and the carbide and calculate the area. Five images of each sample were photographed, and the average value of the area ratio of carbide was calculated. Here, the area ratio of carbides is the area ratio of carbides having a particle size of 1 μm or more. The particle size of the carbide was determined by measuring the diameter of the carbide from a digital microscope image taken at a magnification of 500 times, and this was defined as the particle size of the carbide. For rod-shaped carbides, the length of the short side was taken as the particle size of the carbide. In addition, when the shape of the carbide was elliptical or the like, the minimum diameter was taken as the particle size.

The results obtained are shown in Table 2.

Regarding the friction coefficient in Table 2, values in the range of 0.15 to 0.30 were considered acceptable, and values less than 0.15 or greater than 0.30 were judged as failure. If the friction coefficient is less than 0.15, it is considered that the slip resistance is not sufficient because the friction coefficient during the test is small. Moreover, when it was larger than 0.30, the friction coefficient during the test was high, and seizure occurred. It is thought that by adjusting the high temperature hardness of the base and the ratio of each carbide amount, the friction coefficient during the test was within an appropriate range, and the seizure resistance and slip resistance were improved. Further, the amount of wear in the invention example is 0.50 g or less, whereas the comparative sample No. 1 has a friction coefficient greater than 0.30. 16 to 20 exceeds 0.50 g. Furthermore, Sample No. of Comparative Example contains Cr in excess of the specified component. In No. 11 as well, the amount of wear exceeds 0.50 g. It is thought that the wear resistance was improved due to the friction coefficient being below the upper limit and the appropriate component composition.

Therefore, according to the present invention, it is possible to manufacture a hot rolling roll outer layer material and a composite roll having excellent seizure resistance and slip resistance. As a result, the rolling efficiency of hot rolling rolls is improved by reducing time loss during rolling interruptions due to roll troubles such as poor roll biting due to slips and rough skin such as slip marks on the rolled material. Accordingly, the effect of improving the productivity of hot-rolled steel sheets can also be obtained.

1: Test piece 2: Cooling water 3: High frequency induction heating coil 4: Opposite piece 5: Rotation direction of test piece 6: Rotation direction of counterpart piece 7: Direction of load

Claims (2)

In mass%,
C: 1.2-2.5%,
Si: 0.15-2.50%,
Mn: 0.15-2.50%,
Ni: 0.2-8.0%,
Cr: 1.5-10.0%,
Mo: 3.5-12.0%,
V: 2.0-7.5%,
W: 0.1-6.0%,
P: 0.01-0.04%,
Contains S: 0.001 to 0.010%,
The remainder consists of Fe and unavoidable impurities, and the content of C, Cr, Mo, V, and W satisfies the following formulas (1) and (2), and the area ratio of carbides with a grain size of 1 μm or more is 8.0 to 20.0%, and the Shore hardness at 20°C is 75.0HS or more and 85.0HS or less, and the Shore hardness at 600°C is 45.0HS or more and 50.0HS or less. Roll outer layer material for rolling.
20.0≦[%C]×([%V]+[%Cr]+[%Mo]+[%W])≦35.0 (1)
1.00≦[%C]×((0.177×[%V])/(0.099×[%Cr]+0.063×[%Mo]+0.033×[%W]))≦3 .00 (2)
Here, in formulas (1) and (2), [%C], [%Cr], [%Mo], [%V], and [%W] represent the content (mass%) of each element. . A composite roll for hot rolling having two layers, an outer layer and an inner layer, or three layers, an outer layer, an intermediate layer, and an inner layer, wherein the outer layer is in mass%,
C: 1.2-2.5%,
Si: 0.15-2.50%,
Mn: 0.15-2.50%,
Ni: 0.2-8.0%,
Cr: 1.5-10.0%,
Mo: 3.5-12.0%,
V: 2.0-7.5%,
W: 0.1-6.0%,
P: 0.01-0.04%,
Contains S: 0.001 to 0.010%,
The remainder consists of Fe and unavoidable impurities, and the content of C, Cr, Mo, V, and W satisfies the following formulas (1) and (2), and the area ratio of carbides with a grain size of 1 μm or more is 8.0 to 20.0%, and the Shore hardness at 20°C is 75.0HS or more and 85.0HS or less, and the Shore hardness at 600°C is 45.0HS or more and 50.0HS or less. Composite roll for rolling.
20.0≦[%C]×([%V]+[%Cr]+[%Mo]+[%W])≦35.0 (1)
1.00≦[%C]×((0.177×[%V])/(0.099×[%Cr]+0.063×[%Mo]+0.033×[%W]))≦3 .00 (2)
Here, in formulas (1) and (2), [%C], [%Cr], [%Mo], [%V], and [%W] represent the content (mass%) of each element. .

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