JPH1161321A - Outer layer material for hot rolling roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an outer layer material for a hot rolling roll, capable of improving the quality of a rolled stock at the time of hot rolling and excellent in wear resistance and surface roughing resistance. SOLUTION: This material has a composition which consists of, by weight, 1.5-3.0% C, 0.3-2.0% Si, 0.3-1.5% Mn, 1.0-4.0% Cr, 3.0-12.0% Mo, 3.0-12.0% W, 1.0-5.0% V, <=5.0% Nb, <=1.0% Ni, and the balance essentially Fe with inevitable impurities and in which either or both of the value of (Mo+W)/Cr and the value of (Mo+W)/(V+Nb) is regulated to 4.0-10.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a roll outer layer material for hot rolling.

[0002]

2. Description of the Related Art Conventionally, high chromium cast iron and high alloy grain cast iron have been used as hot rolling rolls. High chromium cast iron contains 20-40% by area ratio of M ₇ C ₃ type carbide is excellent in wear resistance, poor resistance to cracking, the trouble rolling, there are problems such as a crack occurs to a considerable extent . On the other hand, high-alloy grain cast iron contains 20 to 40% of M ₃ C-type carbides and crystallizes graphite, so that there is little seizure of the material to be rolled and cracks occur even in the event of a rolling accident. It has the characteristic of relatively little progress, and it has been widely used, but its wear resistance is not sufficient. In recent years, the required level of abrasion resistance has advanced, and roll materials having more excellent abrasion resistance are disclosed in, for example, JP-A-1-96355 and JP-A-2-96355.
-88745, WO88 / 07594 WIPO International Publication and
A hot-rolling roll made of a high-carbon high-speed steel material, as disclosed in WO91 / 19824 WIPO International Publication, is used. These high speed rolls are Cr, Mo,
Contains a few percent of W, V, Co, etc., and has a structure composed mainly of hard MC-type carbides and crystallized from M ₆ C-type and M ₂ C-type carbides. doing. But,
In order to emphasize wear resistance, many hard MC type carbides are dispersed, but due to the large difference in hardness between the carbide and the matrix, preferential wear of the matrix is caused by rolling, and the carbides protrude to the surface, There is a problem that the skin is easily roughened due to an increase in the coefficient of friction, an increase in the rolling load, a deterioration in seizure resistance, or a dropout of protruding carbide. In order to improve the seizure resistance, a high-speed material in which graphite is crystallized in the structure is disclosed in JP-A-1-287248, JP-A-7-6030 and JP-A-8-209299. Have been. Rolls made of these materials have improved seizure resistance, but their abrasion and crack resistance still do not exceed those of conventional high-speed steel.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems which occur in the high-speed steel roll for hot rolling.
It is an object of the present invention to provide a roll outer layer material for hot rolling that is capable of improving the quality of a rolled material in hot rolling and has excellent wear resistance and surface roughness resistance.

[0004]

In order to solve the above-mentioned problems and to provide a material excellent in abrasion resistance and surface roughening resistance, which is a major feature of a high-speed hot-rolling high-speed roll, the inventors of the present invention. , first, minimizing the M ₇ C ₃ type carbide carbide hardness be considered to be a cause of the wear resistance of the degradation due to low along with causing degradation of crack resistance and crack developed along grain boundaries I thought it was necessary. The inventor then considers that MC-type carbides, which are indispensable for securing wear resistance but are considered to form fine protrusions due to the wear of the matrix and reduce the surface roughening resistance, do not deteriorate the wear resistance. Considered reducing in range. Instead, it was considered effective to actively crystallize rod-like or needle-like carbides, which are considered to make the roll surface smooth and uneven, and to further refine the crystallized carbides. According to the above policies and measures, the contents of Cr, Mo, W, V, Nb and carbon, which are carbide forming elements, and the
M ₇ C ₃ type, M ₆ C-type, M ₂ C type, MC-type or consider area ratio in detail carbide, hardness, wear coefficient, wear amount, such as to measure the surface roughness after abrasion test As a result of intensive research, the present invention has been completed.

That is, the outer layer material of the hot rolling roll of the present invention comprises 1.5 to 3.0% by weight of C, 0.3 to 2.0% by weight of Si,
0.3-1.5 wt%, Cr 1.0-4.0 wt%, Mo 3.0
~ 12.0 wt%, W is 3.0 ~ 12.0 wt%, V is 1.0 ~ 5.0
% Of Nb, 5.0% by weight or less of Ni, 1.0% by weight or less of Ni, and the balance substantially consists of Fe and non-impurities.
The first feature is that one or both of the value of (W) / Cr and the value of (Mo + W) / (V + Nb) are in the range of 4.0 to 10.0. Further, in addition to the first feature, the outer layer material for a hot rolling roll according to the present invention contains 0.01 to 2.5% by weight of one or more components selected from Ti, Zr, and Hf. Features.

According to the roll outer layer material for hot rolling of the present invention having the above characteristics, Mo and W can be appropriately contained so that MC
Instead type carbides, fine rod-like or needle-like M ₆ C-type,
By crystallizing a large amount of M ₂ C-type carbide, wear resistance,
The rough surface resistance can be improved without deteriorating the crack resistance. Therefore, according to the hot-rolling roll using the outer layer material, compared to the conventional high-speed rolls, particularly excellent surface roughness, abrasion resistance, crack resistance, etc., performance is not inferior to conventionally known high-speed rolls. .

In the present invention, the content of C is 1.5 to 3.0.
% By weight. C combines with Cr, Mo, W, V, Nb, etc.
Crystallizes and precipitates carbides to improve wear resistance. 1.5
If the amount is less than 10% by weight, the amount of carbide generated is small and sufficient wear resistance cannot be obtained. If the content exceeds 3.0% by weight, the amount of carbides is too large, and the toughness is reduced.

The content of Si is 0.3 to 2.0% by weight. Si
Is necessary for deoxidation of the molten metal and good castability. 2.
If it exceeds 0% by weight, the remaining amount becomes brittle, which is not preferable.

The content of Mn is 0.3 to 1.5% by weight. Mn
Add 0.3% by weight or more for deoxidation and desulfurization of molten metal. Further, Mn has an effect of improving the hardenability and the abrasion resistance, but if it exceeds 1.5% by weight, the toughness of the material is lowered, which is not preferable.

The content of Cr is 1.0 to 4.0% by weight. Cr
Is added in an amount of 1.0% by weight or more to improve the hardenability by forming a solid solution in the matrix and to form carbide. But,
If it exceeds 4.0% by weight, a large amount of carbides such as M ₇ C ₃ crystallize out, causing a problem of deterioration of wear resistance and deterioration of crack resistance. Preferably it is less than 3.0%.

The content of Mo is 3.0-12.0% by weight. Mo
Is dissolved in the matrix to increase the high temperature hardness of the matrix,
Alternatively, a needle-like M ₆ C-type or M ₂ C-type carbide is formed, which is effective in improving the surface roughness resistance. If Mo is less than 3.0% by weight, the area ratio of these carbides is small, and the effect cannot be expected. If the content exceeds 12.0% by weight, carbides are excessively crystallized, and the toughness is lowered, which is not preferable.

The content of W is 3.0-12.0% by weight. W
Like Mo, it combines with C to form M ₆ C-type or M ₂ C-type carbides, which has the effect of ensuring wear resistance and improving the surface roughening resistance due to the form of the carbides. In addition, it has a solid solution in the matrix and has the effect of improving the high-temperature softening resistance. 3.0% by weight
If the amount is less than 12%, these effects are not obtained. If the amount is more than 12% by weight, the toughness of the material is reduced, which is not preferable.

The content of V is set to 1.0 to 5.0% by weight. V
Combines with C to form MC type carbide with high hardness and is indispensable for improvement of wear resistance. If it is less than 1.0% by weight, the effect cannot be expected. On the other hand, if it exceeds 5.0% by weight, MC
The area ratio of the type carbide is increased, and asperity is generated on the surface by rolling, causing an increase in the coefficient of friction and rough surface,
Not preferred.

The content of Nb is 5.0% by weight or less. Nb, like V, forms a hard MC-type carbide, and its addition is effective in improving wear resistance. However, the carbide morphology causes an increase in the coefficient of friction. Nb and V form MC-type carbides, but NbC has a higher specific gravity than VC and a small difference in specific gravity from the molten metal, and therefore has an effect of preventing segregation, particularly in the case of manufacturing by centrifugal casting. Therefore, it is preferable to add Nb instead of V. However, if the content exceeds 5.0% by weight, oxidation of the molten metal becomes severe, and it becomes difficult to perform melt casting in the atmosphere, which is not preferable.

The content of Ni is set to 1.0% by weight or less. Ni is preferably contained in a small amount in order to improve the hardenability, but if it exceeds 2.0% by weight, the amount of retained austenite becomes excessive, which causes problems such as a decrease in hardness and transformation cracking. Preferably, it is 0.5% or less.

Ti, Zr, and Hf all have the effect of suppressing segregation of carbides and of causing fine crystallization and precipitation of carbides. In the present invention, rod-like or needle-like carbides such as M ₆ C type and M ₂ C type are crystallized to improve the surface roughness resistance.
When the M ₆ C type or M ₂ C type carbide is coarse, crack resistance,
It is not preferable in terms of toughness and the like. In particular, when the content of Mo and W is large, one or more types of Ti, Zr, and Hf are used in an amount of 0.01 to 2.5% by weight.
By containing it, the M ₆ C-type or M ₂ C-type carbide can be made finer, and it is effective in preventing crack resistance and toughness from being deteriorated.

In the roll outer layer material for hot rolling of the present invention, one or both of the value of (Mo + W) / Cr and the value of (Mo + W) / (V + Nb) fall within the range of 4.0 to 10.0. Like that. When the value is less than 4.0, the amount of crystallization of M ₆ C-type and M ₂ C-type carbides is small, as is clear from the examples described later, and the effect of improving the surface roughness is small. When the value of (Mo + W) / Cr is less than 4.0, M ₇ C ₃
The main component is the Cr carbide of the mold, and the crack resistance deteriorates. That is, one or both of the value of (Mo + W) / Cr and the value of (Mo + W) / (V + Nb) are limited to the range of 4.0 to 10.0, whereby M ₆ C type and M _{2 are} contained in the tissue. the area ratio of C-type carbides 9-20%, it is preferable that the area ratio of MC type carbide and M ₇ C ₃ -type carbide and 5% or less, respectively. on the other hand,
If the value of (Mo + W) / (V + Nb) is less than 4.0, a large amount of MC-type carbides crystallize, causing problems such as an increase in friction coefficient, deterioration of seizure resistance, and deterioration of surface roughness resistance. If this value exceeds 10.0, M ₆ C-type and M ₂ C-type carbides become excessive, and the addition of Ti, Zr, Hf makes the carbides finer, and even if the carbides are refined, the crack resistance deteriorates, and the toughness decreases. Absent.

The hot-rolling roll having an outer layer material according to the present invention is preferably a composite roll having high toughness inside. In this case, a continuous casting method in which a steel core material is continuously cast. Alternatively, after the outer layer material is cast, the inner layer material is cast by a centrifugal casting method. Further, the roll material manufactured as described above is subjected to a quenching and tempering treatment to form a matrix having appropriate hardness and toughness. The outer layer material of the roll of the present invention can be applied to any roll used in a hot state, such as a roll for strip steel rolling and a roll for pipe production, in addition to the outer layer material for the hot rolled finishing work roll.

[0019]

EXAMPLES Rolls for hot rolling were manufactured using the outer layers of the hot rolling rolls of the present invention shown in No. 1 to No. 8 in Table 1. For the outer layer materials of No. 1 to No. 6, rolls were manufactured by a continuous casting method. In the case of the continuous casting method, a roll was manufactured by continuously casting a molten metal of the material of the present invention indicated by No. 1 to No. 6 on the outer periphery of a core material made of a rolled steel material. Also N
Rolls were manufactured by centrifugal casting for the outer layer materials of o.7 and No.8. In the case of centrifugal casting, No. 7 and N
Rolls were manufactured by casting a melt of the material shown in o.8 under centrifugal conditions to form a hollow outer layer, and then casting a graphite steel melt or a ductile cast iron melt as an inner layer material. Each of the obtained rolls was subjected to a quenching / tempering treatment so that the hardness of the roll surface became 80 to 90 in Shore hardness (Hs). As a comparative example, for materials shown in No. 9 to No. 13 having a high-speed component that is not included in the scope of the present invention,
Similarly, rolls were manufactured by a continuous casting method or a centrifugal casting method. Also, as another comparative example, a roll was manufactured for a high alloy gray cast iron material and a high chromium cast iron material, and a comparison was made. Table 1 shows the components of each material. The underlined component values and the like in Table 1 indicate that the component values are out of the range and conditions in the present invention.

[0020]

[Table 1]

The structure of the outer layer of the manufactured roll was analyzed by EPMA surface analysis and image analysis to obtain M ₇ C ₃ type carbide, M ₂ C type and M ₆ C type carbide.
The area ratio of the carbide was measured for each of three types of carbides, i.e., type carbide and MC type carbide. Similarly, the kinetic friction coefficient, abrasion loss, surface roughness after the abrasion test, crack resistance, and Shore hardness were measured. The wear friction test was performed under the following conditions. That is, the test method is a pin-on-disk method, the test piece temperature is 300 ° C, and the load is 5
kg / cm ² , speed 100 m / min, sliding distance 20000 m.
The heat crack resistance was evaluated by raising the temperature of a φ20 × 30 mm test piece to a predetermined temperature, maintaining the temperature, rapidly cooling in water, and measuring the thermal shock temperature difference (° C.) at the time when the crack was formed. Table 2 shows the results.

[0022]

[Table 2]

Roll outer layer materials for hot rolling of Examples No. 1 to N
o.8 shows that, as shown in Table 2, the area ratio of M ₂ C type and M ₆ C type carbide is 9.7 to 16.8%, MC type carbide is 0.5 to 4.3%, and M ₇ C ₃ type carbide The rate is 0.4-3.0%.
That is, compared to the comparative examples and the like, the amount of M ₂ C-type and M ₆ C-type carbides is large, and the amount of MC-type carbides and M ₇ C ₃ -type carbides is small. As a result, in Examples No. 1 to No. 8, the surface roughness after the wear test was reduced.
Ra 1.3 to 2.9 μm, which indicates that the Ra is improved as compared with Comparative Examples No. 9 to No. 13. On the other hand, Examples No. 1 to No. 8
As is clear from Table 2, the abrasion loss and heat crack resistance of
The comparative examples No. 9 to No. 13 which are equivalent to the conventional high-speed rolls are almost the same or more, and are good. In addition, Examples No. 1 to No. 8 of the present invention show abrasion resistance, surface roughening resistance (surface roughness), crack resistance, etc., even when compared with conventional high-alloy grain cast iron and high chromium cast iron. It can be seen that all the characteristics are excellent.

In Examples No. 6 and No. 8 of the present invention, at least one component of Ti, Zr and Hf was added.
In comparison with Examples No. 1 and No. 2 which did not add any of r and Hf and had the same carbide area ratio, Examples No. 6 and N
In o.8, the surface roughness was small but small, and the heat crack resistance was high, indicating that the effect of reducing the size of the carbides appeared.

Examples No. 7 and No. 8 of the present invention and Comparative Example No. 1
3 is manufactured by the centrifugal casting method, but has a slightly inferior abrasion resistance as compared with the outer layer material manufactured by the continuous casting method having the same carbide area ratio as them. This is due to a difference in cooling rate during solidification of the outer layer, and the cooling rate in centrifugal casting is slower than that in the continuous casting method, and carbides are coarsened.

As shown in the above examples, the roll outer layer material of the present invention has the same abrasion resistance as the conventional high-speed roll material, but also has excellent skin roughness resistance. The roll basic unit in hot rolling is affected not only by the amount of wear of the roll material, but also by the degree of roughening and the increase or decrease in the amount of rework due to the degree of thermal crack depth. Therefore, the roll outer layer material of the present invention is excellent in rough surface resistance, abrasion resistance and heat crack resistance, so that it is possible to reduce the basic unit of roll and improve the rolling quality. In addition, the roll outer layer material for hot rolling of the present invention is, in addition to a work roll for hot rolling finishing, a roll for steel pipe rolling and a roll for strip steel rolling, particularly a roll for hot rolling in which the rough surface resistance of the roll is required. High suitability for

[0027]

According to the roll outer layer material for hot rolling according to the first aspect, while maintaining good wear resistance and heat crack resistance in hot rolling, very good rough surface resistance is exhibited. can do. Since the surface roughening resistance is better than that of the conventional high-speed roll material, it is possible to further reduce the basic unit of roll and to improve the quality of the rolled product as compared with the conventional high-speed roll material. According to the hot-rolling roll outer layer material of the second aspect, in addition to the effect of the configuration of the first aspect, the carbide can be made finer, and the wear resistance and the heat crack resistance are improved. , Toughness can be further improved.

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[Procedure amendment]

[Submission date] September 11, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Roll outer layer material for hot rolling

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a roll outer layer material for hot rolling.

[0002]

2. Description of the Related Art Conventionally, high chromium cast iron and high alloy grain cast iron have been used as hot rolling rolls. High chromium cast iron contains 20-40% by area ratio of M ₇ C ₃ type carbide is excellent in wear resistance, poor resistance to cracking, the trouble rolling, there are problems such as a crack occurs to a considerable extent . On the other hand, high-alloy grain cast iron contains 20 to 40% of M ₃ C-type carbides and crystallizes graphite, so that there is little seizure of the material to be rolled and cracks occur even in the event of a rolling accident. It has the characteristic of relatively little progress, and it has been widely used, but its wear resistance is not sufficient. In recent years, the required level of abrasion resistance has advanced, and roll materials having more excellent abrasion resistance are disclosed in, for example, JP-A-1-96355 and JP-A-2-96355.
-88745, WO88 / 07594 WIPO International Publication and
A hot-rolling roll made of a high-carbon high-speed steel material, as disclosed in WO91 / 19824 WIPO International Publication, is used. These high speed rolls are Cr, Mo,
Contains a few percent of W, V, Co, etc., and has a structure composed mainly of hard MC-type carbides and crystallized from M ₆ C-type and M ₂ C-type carbides. doing. But,
In order to emphasize wear resistance, many hard MC type carbides are dispersed, but due to the large difference in hardness between the carbide and the matrix, preferential wear of the matrix is caused by rolling, and the carbides protrude to the surface, There is a problem that the skin is easily roughened due to an increase in the coefficient of friction, an increase in the rolling load, a deterioration in seizure resistance, or a dropout of protruding carbide. In order to improve the seizure resistance, a high-speed material in which graphite is crystallized in the structure is disclosed in JP-A-1-287248, JP-A-7-6030 and JP-A-8-209299. Have been. Rolls made of these materials have improved seizure resistance, but their abrasion and crack resistance still do not exceed those of conventional high-speed steel.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems which occur in the high-speed steel roll for hot rolling.
It is an object of the present invention to provide a roll outer layer material for hot rolling that is capable of improving the quality of a rolled material in hot rolling and has excellent wear resistance and surface roughness resistance.

[0004]

In order to solve the above-mentioned problems and to provide a material excellent in abrasion resistance and surface roughening resistance, which is a major feature of a high-speed hot-rolling high-speed roll, the inventors of the present invention. , first, minimizing the M ₇ C ₃ type carbide carbide hardness be considered to be a cause of the wear resistance of the degradation due to low along with causing degradation of crack resistance and crack developed along grain boundaries I thought it was necessary. The inventor then considers that MC-type carbides, which are indispensable for securing wear resistance but are considered to form fine protrusions due to the wear of the matrix and reduce the surface roughening resistance, do not deteriorate the wear resistance. Considered reducing in range. Instead, it was considered effective to actively crystallize rod-like or needle-like carbides, which are considered to make the roll surface smooth and uneven, and to further refine the crystallized carbides. According to the above policies and measures, the contents of Cr, Mo, W, V, Nb and carbon, which are carbide forming elements, and the
M ₇ C ₃ type, M ₆ C-type, M ₂ C type, MC-type or consider area ratio in detail carbide, hardness, wear coefficient, wear amount, such as to measure the surface roughness after abrasion test As a result of intensive research, the present invention has been completed.

That is, the outer layer material of the hot rolling roll of the present invention comprises 1.5 to 3.0% by weight of C, 0.3 to 2.0% by weight of Si,
0.3-1.5 wt%, Cr 1.0-4.0 wt%, Mo 3.0
~ 12.0 wt%, W is 3.0 ~ 12.0 wt%, V is 1.0 ~ 5.0
% Of Nb, 5.0% by weight or less of Ni, 1.0% by weight or less of Ni, and the balance substantially consists of Fe and non-impurities.
The first feature is that one or both of the value of (W) / Cr and the value of (Mo + W) / (V + Nb) are in the range of 4.0 to 10.0. Further, in addition to the first feature, the outer layer material for a hot rolling roll according to the present invention contains 0.01 to 2.5% by weight of one or more components selected from Ti, Zr, and Hf. Features.

According to the roll outer layer material for hot rolling of the present invention having the above characteristics, Mo and W can be appropriately contained so that MC
Instead type carbides, fine rod-like or needle-like M ₆ C-type,
By crystallizing a large amount of M ₂ C-type carbide, wear resistance,
The rough surface resistance can be improved without deteriorating the crack resistance. Therefore, according to the hot-rolling roll using the outer layer material, compared to the conventional high-speed rolls, particularly excellent surface roughness, abrasion resistance, crack resistance, etc., performance is not inferior to conventionally known high-speed rolls. .

In the present invention, the content of C is 1.5 to 3.0.
% By weight. C combines with Cr, Mo, W, V, Nb, etc.
Crystallizes and precipitates carbides to improve wear resistance. 1.5
If the amount is less than 10% by weight, the amount of carbide generated is small and sufficient wear resistance cannot be obtained. If the content exceeds 3.0% by weight, the amount of carbides is too large, and the toughness is reduced.

The content of Si is 0.3 to 2.0% by weight. Si
Is necessary for deoxidation of the molten metal and good castability. 2.
If it exceeds 0% by weight, the remaining amount becomes brittle, which is not preferable.

The content of Mn is 0.3 to 1.5% by weight. Mn
Add 0.3% by weight or more for deoxidation and desulfurization of molten metal. Further, Mn has an effect of improving the hardenability and the abrasion resistance, but if it exceeds 1.5% by weight, the toughness of the material is lowered, which is not preferable.

The content of Cr is 1.0 to 4.0% by weight. Cr
Is added in an amount of 1.0% by weight or more to improve the hardenability by forming a solid solution in the matrix and to form carbide. But,
If it exceeds 4.0% by weight, a large amount of carbides such as M ₇ C ₃ crystallize out, causing a problem of deterioration of wear resistance and deterioration of crack resistance. Preferably it is less than 3.0%.

The content of Mo is 3.0-12.0% by weight. Mo
Is dissolved in the matrix to increase the high temperature hardness of the matrix,
Alternatively, a needle-like M ₆ C-type or M ₂ C-type carbide is formed, which is effective in improving the surface roughness resistance. If Mo is less than 3.0% by weight, the area ratio of these carbides is small, and the effect cannot be expected. If the content exceeds 12.0% by weight, carbides are excessively crystallized, and the toughness is lowered, which is not preferable.

The content of W is 3.0-12.0% by weight. W
Like Mo, it combines with C to form M ₆ C-type or M ₂ C-type carbides, which has the effect of ensuring wear resistance and improving the surface roughening resistance due to the form of the carbides. In addition, it has a solid solution in the matrix and has the effect of improving the high-temperature softening resistance. 3.0% by weight
If the amount is less than 12%, these effects are not obtained. If the amount is more than 12% by weight, the toughness of the material is reduced, which is not preferable.

The content of V is set to 1.0 to 5.0% by weight. V
Combines with C to form MC type carbide with high hardness and is indispensable for improvement of wear resistance. If it is less than 1.0% by weight, the effect cannot be expected. On the other hand, if it exceeds 5.0% by weight, MC
The area ratio of the type carbide is increased, and asperity is generated on the surface by rolling, causing an increase in the coefficient of friction and rough surface,
Not preferred.

The content of Nb is 5.0% by weight or less. Nb, like V, forms a hard MC-type carbide, and its addition is effective in improving wear resistance. However, the carbide morphology causes an increase in the coefficient of friction. Nb and V form MC-type carbides, but NbC has a higher specific gravity than VC and a small difference in specific gravity from the molten metal, and therefore has an effect of preventing segregation, particularly in the case of manufacturing by centrifugal casting. Therefore, it is preferable to add Nb instead of V. However, if the content exceeds 5.0% by weight, oxidation of the molten metal becomes severe, and it becomes difficult to perform melt casting in the atmosphere, which is not preferable.

The content of Ni is set to 1.0% by weight or less. Ni is preferably contained in a small amount in order to improve the hardenability, but if it exceeds 2.0% by weight, the amount of retained austenite becomes excessive, which causes problems such as a decrease in hardness and transformation cracking. Preferably, it is 0.5% or less.

Ti, Zr, and Hf all have the effect of suppressing segregation of carbides and of causing fine crystallization and precipitation of carbides. In the present invention, rod-like or needle-like carbides such as M ₆ C type and M ₂ C type are crystallized to improve the surface roughness resistance.
When the M ₆ C type or M ₂ C type carbide is coarse, crack resistance,
It is not preferable in terms of toughness and the like. In particular, when the content of Mo and W is large, one or more types of Ti, Zr, and Hf are used in an amount of 0.01 to 2.5% by weight.
By containing it, the M ₆ C-type or M ₂ C-type carbide can be made finer, and it is effective in preventing crack resistance and toughness from being deteriorated.

In the roll outer layer material for hot rolling of the present invention, one or both of the value of (Mo + W) / Cr and the value of (Mo + W) / (V + Nb) fall within the range of 4.0 to 10.0. Like that. When the value is less than 4.0, the amount of crystallization of M ₆ C-type and M ₂ C-type carbides is small, as is clear from the examples described later, and the effect of improving the surface roughness is small. When the value of (Mo + W) / Cr is less than 4.0, M ₇ C ₃
The main component is the Cr carbide of the mold, and the crack resistance deteriorates. That is, one or both of the value of (Mo + W) / Cr and the value of (Mo + W) / (V + Nb) are limited to the range of 4.0 to 10.0, whereby M ₆ C type and M _{2 are} contained in the tissue. the area ratio of C-type carbides 9-20%, it is preferable that the area ratio of MC type carbide and M ₇ C ₃ -type carbide and 5% or less, respectively. on the other hand,
If the value of (Mo + W) / (V + Nb) is less than 4.0, a large amount of MC-type carbides crystallize, causing problems such as an increase in friction coefficient, deterioration of seizure resistance, and deterioration of surface roughness resistance. If this value exceeds 10.0, M ₆ C-type and M ₂ C-type carbides become excessive, and the addition of Ti, Zr, Hf makes the carbides finer, and even if the carbides are refined, the crack resistance deteriorates, and the toughness decreases. Absent.

The hot-rolling roll having the outer layer material of the present invention is preferably a composite roll having high toughness inside. In this case, the molten metal of the outer layer material and the steel core material are melted.
It is cast by a method of attaching and integrating, or a centrifugal casting method of casting an inner layer material after casting an outer layer material. Further, the roll material manufactured as described above is subjected to a quenching and tempering treatment to form a matrix having appropriate hardness and toughness. The outer layer material of the roll of the present invention can be applied to any roll used in a hot state, such as a roll for strip steel rolling and a roll for pipe production, in addition to the outer layer material for the hot rolled finishing work roll.

[0019]

EXAMPLES Rolls for hot rolling were manufactured using the outer layers of the hot rolling rolls of the present invention shown in No. 1 to No. 8 in Table 1. For the outer layers of No.1 to No.6, the molten metal of the outer layers
A roll was manufactured by welding and integrating the steel core material . The rolls of No. 7 and No. 8 outer layers were manufactured by centrifugal casting. In the case of the centrifugal casting method,
Rolls were produced by casting a molten metal of the materials No. 7 and No. 8 under centrifugal conditions to form a hollow outer layer, and then casting a molten graphite steel or a molten ductile iron as an inner layer material. Each of the obtained rolls was subjected to a quenching / tempering treatment so that the hardness of the roll surface became 80 to 90 in Shore hardness (Hs). As a comparative example, the materials shown in No. 9 to No. 13 having a high-speed component, which are not included in the scope of the present invention, were similarly welded and integrated with the molten metal of the outer layer material and the steel-based core material.
It was manufactured rolls by causing the method or a centrifugal casting method.
Also, as another comparative example, a roll was manufactured for a high alloy gray cast iron material and a high chromium cast iron material, and a comparison was made.
Table 1 shows the components of each material. The underlined component values and the like in Table 1 indicate that the component values are out of the range and conditions in the present invention.

[0020]

[Table 1]

The structure of the outer layer of the manufactured roll was analyzed by EPMA surface analysis and image analysis to obtain M ₇ C ₃ type carbide, M ₂ C type and M ₆ C type carbide.
The area ratio of the carbide was measured for each of three types of carbides, i.e., type carbide and MC type carbide. Similarly, the kinetic friction coefficient, abrasion loss, surface roughness after the abrasion test, crack resistance, and Shore hardness were measured. The wear friction test was performed under the following conditions. That is, the test method is a pin-on-disk method, the test piece temperature is 300 ° C, and the load is 5
kg / cm ² , speed 100 m / min, sliding distance 20000 m.
The heat crack resistance was evaluated by raising the temperature of a φ20 × 30 mm test piece to a predetermined temperature, maintaining the temperature, rapidly cooling in water, and measuring the thermal shock temperature difference (° C.) at the time when the crack was formed. Table 2 shows the results.

[0022]

[Table 2]

Roll outer layer materials for hot rolling of Examples No. 1 to N
o.8 shows that, as shown in Table 2, the area ratio of M ₂ C type and M ₆ C type carbide is 9.7 to 16.8%, MC type carbide is 0.5 to 4.3%, and M ₇ C ₃ type carbide The rate is 0.4-3.0%.
That is, compared to the comparative examples and the like, the amount of M ₂ C-type and M ₆ C-type carbides is large, and the amount of MC-type carbides and M ₇ C ₃ -type carbides is small. As a result, in Examples No. 1 to No. 8, the surface roughness after the wear test was reduced.
Ra 1.3 to 2.9 μm, which indicates that the Ra is improved as compared with Comparative Examples No. 9 to No. 13. On the other hand, Examples No. 1 to No. 8
As is clear from Table 2, the abrasion loss and heat crack resistance of
The comparative examples No. 9 to No. 13 which are equivalent to the conventional high-speed rolls are almost the same or more, and are good. In addition, Examples No. 1 to No. 8 of the present invention show abrasion resistance, surface roughening resistance (surface roughness), crack resistance, etc., even when compared with conventional high-alloy grain cast iron and high chromium cast iron. It can be seen that all the characteristics are excellent.

In Examples No. 6 and No. 8 of the present invention, at least one component of Ti, Zr and Hf was added.
In comparison with Examples No. 1 and No. 2 which did not add any of r and Hf and had the same carbide area ratio, Examples No. 6 and N
In o.8, the surface roughness was small but small, and the heat crack resistance was high, indicating that the effect of reducing the size of the carbides appeared.

Examples No. 7 and No. 8 of the present invention and Comparative Example No. 1
3 is manufactured by the centrifugal casting method, but the molten metal of the outer layer having the same carbide area ratio as these and the steel core material are welded together.
The wear resistance is slightly inferior to the outer layer material manufactured by embedding. This is due to the difference in the cooling rate during outer layer solidification, and the cooling rate is low in centrifugal casting, and the carbides are coarsened.

As shown in the above examples, the roll outer layer material of the present invention has the same abrasion resistance as the conventional high-speed roll material, but also has excellent skin roughness resistance. The roll basic unit in hot rolling is affected not only by the amount of wear of the roll material, but also by the degree of roughening and the increase or decrease in the amount of rework due to the degree of thermal crack depth. Therefore, the roll outer layer material of the present invention is excellent in rough surface resistance, abrasion resistance and heat crack resistance, so that it is possible to reduce the basic unit of roll and improve the rolling quality. In addition, the roll outer layer material for hot rolling of the present invention is, in addition to a work roll for hot rolling finishing, a roll for steel pipe rolling and a roll for strip steel rolling, particularly a roll for hot rolling in which the rough surface resistance of the roll is required. High suitability for

[0027]

According to the roll outer layer material for hot rolling according to the first aspect, while maintaining good wear resistance and heat crack resistance in hot rolling, very good rough surface resistance is exhibited. can do. Since the surface roughening resistance is better than that of the conventional high-speed roll material, it is possible to further reduce the basic unit of roll and to improve the quality of the rolled product as compared with the conventional high-speed roll material. According to the hot-rolling roll outer layer material of the second aspect, in addition to the effect of the configuration of the first aspect, the carbide can be made finer, and the wear resistance and the heat crack resistance are improved. , Toughness can be further improved.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toru Niwa 403 Yoshimi Otsu-ku, Himeji-shi, Hyogo Pref.

Claims (2)

[Claims] C: 1.5 to 3.0% by weight Si: 0.3 to 2.0% by weight Mn: 0.3 to 1.5% by weight Cr: 1.0 to 4.0% by weight Mo: 3.0 to 12.0% by weight W: 3.0 to 12.0% by weight V: 1.0 -5.0% by weight Nb: 5.0% by weight or less Ni: 1.0% by weight or less, the balance being substantially composed of Fe and non-impurities, the value of (Mo + W) / Cr and (Mo +
W) / (V + Nb) any one or both of the values are in the range of 4.0 to 10.0. 2. The roll outer layer material for hot rolling according to claim 1, wherein one or more components selected from Ti, Zr and Hf are contained in an amount of 0.01 to 2.5% by weight.