JP2005264322A - External layer material of roll for hot rolling and composite roll for hot rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external layer material of a roll for hot rolling combining wear resistance, surface roughening resistance and seizure resistance. <P>SOLUTION: The external layer material of a roll has a composition containing, by mass, 1.8 to 3.5% C, 0.2 to 2.0% Si, 0.2 to 2.0% Mn, 4 to 15% Cr, 2 to 10% Mo and 3 to 10% V, and further containing 0.1 to 0.6% P and 0.05 to 0.5% B, and the balance Fe with inevitable impurities. Further, the external layer material may contains one or two kinds of metals selected from ≤3% Nb and ≤5% W, or ≤5% Ni, or ≤2% Co, or one or two kinds of metals selected from ≤0.1% Al and ≤0.1% Ti. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a composite roll for hot rolling, and in particular, to a composite roll for hot rolling suitable for a post-stand of a steel sheet after hot rolling.

  In recent years, the progress of hot rolling technology for steel sheets has been remarkable, and accordingly, there has been a strong demand for improvement of the properties of hot rolling rolls used, particularly improvement of wear resistance. In response to such demands for improving wear resistance, the outer layer composition is similar to that of the high-speed tool steel composition, and hard carbides are precipitated to significantly improve the wear resistance. Is also developed and put into practical use.

  On the other hand, Ni-grain cast iron rolls with excellent seizure resistance are incorporated into rolling stands that tend to cause squeezing of the material to be rolled and seizure of the material to be rolled, for example, a hot-rolling finish post-stage stand, containing graphite. It is. However, conventional Ni grain cast iron rolls have the problem of poor wear resistance and short roll life. On the other hand, a high-speed roll with excellent wear resistance, when a squeeze accident occurs, the steel sheet seizes on the roll or coarse thermal shock cracks are generated on the roll. There was a problem using it on the stand. For this reason, although it is inferior to abrasion resistance in the post-stage stand after hot rolling, it is in a situation where a Ni grain cast iron roll excellent in seizure resistance must be used.

  Under such circumstances, an attempt is made to improve the wear resistance of the Ni grain cast iron roll. For example, in Patent Document 1, 1.0 to 5.0% V is added to Ni grain cast iron to improve the wear resistance. A hot rolling roll has been proposed. Further, in Patent Document 2, when 2.0 to 8.0% V is added to Ni grain cast iron, and 0.2 to 10% MC type carbide appears in addition to 0.5 to 5% graphite, the wear resistance is improved. A hot rolling roll has been proposed.

Patent Document 3 discloses a high-speed cast iron containing graphite containing 2 to 10% Cr, 0.1 to 10% W, and one or two of V and Nb in total, 1.5 to 10%. In the material and Patent Document 4, the total content of Cr, V and Nb is limited to 3% or less, and 2% or more of graphite is crystallized to suppress the occurrence of rough skin. Although rolls have been proposed, these wear-resistant hot rolling rolls are all rolls having graphite.
JP-A-1-287248 JP-A-6-335712 JP-A-6-256889 JP 2001-181780 A

In steel rolling, increasing the rolling speed and increasing the amount of continuous rolling are aimed at improving the quality and efficient production of rolled products, and the usage environment of hot rolling rolls has become increasingly severe. Furthermore, there is a demand for a hot rolling work roll that has excellent surface roughness resistance and seizure resistance due to high alloying of the material to be rolled and stricter surface quality requirements of the rolled product.
Since the roll for hot rolling manufactured by the technique described in Patent Literature 1 to Patent Literature 4 contains graphite, it is superior in seizure resistance compared to a general high-speed roll, There was a problem that the abrasion resistance and rough skin resistance were inferior.

  The present invention advantageously solves such problems of the prior art, is excellent in both wear resistance and rough skin resistance, and has excellent seizure resistance comparable to that of a Ni-glen cast iron roll. And it aims at proposing the composite roll for hot rolling.

  In order to achieve the above-described problems, the present inventors first conducted a detailed structural investigation on the seizing portion of the high-speed roll that encountered a squeeze accident. As a result, at the interface between the baked steel sheet and the roll, a phase is formed in which the steel sheet that is the material to be rolled, the roll material, and the scale (black skin) formed on the surface of the steel sheet are fused. It was found that the surface of the roll became extremely hot due to the heat generated by friction caused by machining. From this, even if the present inventors have formed a phase in which the steel sheet and the roll material are fused due to heat generation due to a squeeze accident, for example, if the roll surface can be prevented from peeling off and sticking to the roll, I was able to prevent the occurrence of In order to prevent the roll surface from peeling and seizing, the idea has been reached that the roll composition should be such that the roll surface can be melted and peeled off by frictional heat in the event of a squeeze accident.

  Based on the above-mentioned idea, the present inventors further examined various factors affecting the lowering of the melting point of the roll material based on the high-speed roll composition having wear resistance and rough skin resistance. As a result, by using a roll composition containing appropriate amounts of P and B, a low melting point compound phase is formed, and the seizure resistance of the hot rolling roll is remarkably improved, and the wear resistance and rough skin resistance are It was found that there was no deterioration.

The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
(1) In mass%, C: 1.8-3.5%, Si: 0.2-2%, Mn: 0.2-2%, Cr: 4-15%, Mo: 2-10%, V: 3-10% Furthermore, a roll outer layer material for hot rolling excellent in seizure resistance, characterized in that it contains P: 0.1 to 0.6%, B: 0.05 to 0.5%, and has a composition composed of the remaining Fe and inevitable impurities.
(2) In (1), in addition to the above composition, the composition further contains, by mass%, one or two selected from Nb: 3% or less and W: 5% or less. Roll outer layer material for hot rolling.
(3) A roll outer layer material for hot rolling characterized in that, in (1) or (2), in addition to the above composition, the composition further contains, by mass%, Ni: 5% or less.
(4) The roll outer layer material for hot rolling according to any one of (1) to (3), wherein in addition to the above composition, the composition further contains, by mass%, Co: 2% or less.
(5) In any one of (1) to (4), in addition to the above-described composition, the composition further contains one or two selected from Al: 0.1% or less and Ti: 0.1% or less by mass%. A roll outer layer material for hot rolling, characterized in that it has a composition to be used.
(6) A composite roll for hot rolling in which an outer layer and an inner layer are integrated by welding, wherein the outer layer is in mass%, C: 1.8 to 3.5%, Si: 0.2 to 2%, Mn: 0.2 to 2%, Cr: 4 to 15%, Mo: 2 to 10%, V: 3 to 10%, P: 0.1 to 0.6%, B: 0.05 to 0.5%, balance Fe and inevitable A composite roll for hot rolling excellent in seizure resistance, characterized by having a composition comprising impurities.
(7) In (6), in addition to the above composition, the composition further contains, by mass%, one or two selected from Nb: 3% or less and W: 5% or less. A composite roll for hot rolling.
(8) A composite roll for hot rolling according to (6) or (7), wherein, in addition to the above composition, the composition further comprises Ni: 5% or less by mass%.
(9) The composite roll for hot rolling according to any one of (6) to (8), further containing, in addition to the above composition, Co: 2% or less by mass%.
(10) In any one of (6) to (9), in addition to the above composition, the composition further contains one or two selected from Al: 0.1% or less and Ti: 0.1% or less by mass%. A composite roll for hot rolling characterized by having a composition to be used.

  According to the present invention, as a roll for a hot stage after-rolling of a steel sheet, a composite roll for hot rolling that combines excellent wear resistance and rough skin resistance and further excellent seizure resistance can be manufactured at low cost. There are remarkable effects in the industry.

The reason for limiting the composition of the outer layer (outer layer material) of the composite roll for hot rolling of the present invention will be described. The mass% in the composition is simply referred to as%.
C: 1.8-3.5%
C increases base hardness and combines with V, Nb, Cr, Mo, etc. to form hard carbide, and together with P, B, forms a low melting eutectic compound, and wear resistance of rolls. It is an element effective for improving the rough skin resistance and the seizure resistance, and in the present invention, it needs to contain 1.8% or more. On the other hand, if the content exceeds 3.5%, a large amount of eutectic carbide appears, the MC type carbide becomes coarse, and the rough skin resistance decreases. For this reason, C was limited to the range of 1.8 to 3.5%.

Si: 0.2-2%
Si is an element that acts as a deoxidizing agent, and also has an effect of improving the flowability of hot water, so that it is necessary to contain 0.2% or more in the present invention. On the other hand, even if the content exceeds 2%, the above-described effect is saturated, an effect commensurate with the content cannot be expected, and this is economically disadvantageous. For this reason, Si was limited to the range of 0.2 to 2%.

Mn: 0.2-2%
Mn fixes S as MnS and has the effect of detoxifying S that impairs wear resistance, and also has the effect of improving hardenability and increasing the hardness of the material to improve wear resistance. Such an effect is recognized when the content is 0.2% or more. On the other hand, when the content exceeds 2%, segregation becomes remarkable and the material becomes brittle. For this reason, Mn was limited to the range of 0.2 to 2%.

Cr: 4-15%
Cr is an element that produces hard eutectic carbide together with Mo and improves wear resistance and skin roughness resistance, and has the effect of not lowering the melting point of the low melting eutectic compound phase of P and B more than necessary. In the present invention, the content of 4% or more is required. On the other hand, if it exceeds 15%, the seizure resistance is lowered. For this reason, Cr was limited to the range of 4 to 15%.

Mo: 2-10%
When Mo is contained together with Cr or V and Nb, Mo has an effect of generating a tougher hard carbide and significantly improving the wear resistance. In order to obtain such an effect, the present invention needs to contain 2% or more. However, if it exceeds 10%, the amount of carbide becomes excessive and the material becomes brittle. For this reason, Mo was limited to the range of 2 to 10%. In addition, Preferably it is 3 to 7%.

V: 3-10%
V forms a hard MC carbide and has the effect of significantly improving the wear resistance. In order to ensure a certain level or more of wear resistance as a high wear-resistant roll, the present invention needs to contain 3% or more. However, if the content exceeds 10%, the viscosity of the molten metal is increased and casting defects are likely to be generated, which is a problem in producing a healthy roll. For this reason, in this invention, V was limited to the range of 3 to 10%. In addition, Preferably, it is 3 to 7%.

P: 0.1-0.6%
P is an important element in the present invention, and improves the seizure resistance by forming a M—C—P system eutectic compound (M is a metal) having a low melting point. Such an effect is recognized when the content is 0.1% or more in the combined addition with B. On the other hand, if the content exceeds 0.6%, the material becomes brittle. For this reason, in this invention, P was limited to 0.1 to 0.6% of range. In addition, Preferably it is 0.2 to 0.5%.

B: 0.05-0.5%
B is an important element together with P in the present invention, and improves the seizure resistance by forming a MC— (P, B) eutectic compound (M is a metal) having a low melting point. By containing B together with P, there is an important effect of forming a large amount of a low melting point eutectic compound phase as compared with containing P alone. Such an effect is recognized by adding 0.05% or more of B together with P. On the other hand, if the content exceeds 0.5%, the material becomes brittle. For this reason, in the present invention, B is limited to a range of 0.05 to 0.5%. In addition, Preferably it is 0.1 to 0.3%.

In addition to the basic components described above, one or two selected from Nb and W, or one or two selected from Ni, Co, Al, Ti, as required It can be selected alone or in combination.
1 or 2 types selected from Nb: 3% or less, W: 5% or less
Nb and W are both elements that improve the wear resistance, and can be selected as necessary to contain one or two kinds.

  Nb improves the wear resistance and further the rough skin resistance through the action of making MC type carbide finely granulated and solid-dissolving in MC type carbide to strengthen MC type carbide. Such an effect becomes remarkable when the content is 0.05% or more. However, when the content exceeds 3%, the MC type carbide is coarsened, promotes segregation of the carbide, and deteriorates rough skin resistance. For this reason, it is preferable to limit Nb to 3% or less.

  W improves wear resistance through the formation of hard carbides. Such an effect is recognized with a content of 0.05% or more. However, when the content exceeds 5%, segregation of carbides is promoted, and the rough skin resistance is deteriorated. For this reason, it is preferable to limit W to 5% or less. In addition, when manufacturing this roll by a centrifugal casting method, since W has the effect | action which promotes segregation, it is more preferable to limit to less than 2%.

Ni: 5% or less
Ni is an element having an effect of improving hardenability and increasing the hardness of the material, and Ni is preferably contained when there is a possibility that desired hardness cannot be ensured by ordinary quenching. Such an effect becomes remarkable when the content is 0.05% or more. However, when the content exceeds 5%, austenite is stabilized, the amount of retained austenite is increased, the hardness is decreased, and the wear resistance is decreased. For this reason, in the present invention, Ni is preferably limited to 5.0% or less. In addition, More preferably, it is 0.2 to 4%.

Co: 2% or less
Co is an element that has a function of improving the heat resistance of the base by being dissolved in the base and can be contained if necessary. Such an effect becomes remarkable when the content is 0.05% or more. However, when the content exceeds 2%, the hardenability is lowered and the hardness may be lowered. For this reason, it is preferable to limit Co to 2% or less. From the viewpoint of ensuring hardenability, when Co is contained in an amount of 0.5% or more, it is desirable to contain Ni in an amount of 0.1% or more.

One or two selected from Al: 0.1% or less, Ti: 0.1% or less
Both Al and Ti are elements that form crystallization nuclei of MC carbides and improve the rough skin resistance through the effect of particulate dispersion of MC type carbides, and can be selected and contained as necessary. Such an effect becomes remarkable when the content of each of Al and Ti is 0.01% or more, but the content of each of Al and Ti exceeding 0.1% decreases the fluidity of the molten metal and increases the risk of occurrence of casting defects. . For this reason, it is preferable to limit to Al: 0.1% or less and Ti: 0.1% or less, respectively.

In the outer layer material of the present invention, the balance other than the above components is Fe and inevitable impurities. As unavoidable impurities, N: 0.1% or less and S: 0.03% or less are acceptable. In the case of normal dissolution, N is mixed in an amount of about 0.1% or less, but this level of mixing does not affect the effect of the present invention.
Below, the preferable manufacturing method of the composite roll for hot rolling of this invention is demonstrated.

In the present invention, the method for producing the roll outer layer material is not particularly limited, but a centrifugal casting method, a continuous build-up casting method, and the like are preferable, but a centrifugal casting method is more preferable from the viewpoint of manufacturing cost.
When casting the roll outer layer material by the centrifugal casting method, it is preferable that after the roll outer layer material is solidified or completely solidified, the rotation of the mold is stopped and the inner layer material is statically cast to form a composite roll. Thereby, the inner surface side of the roll outer layer material is redissolved, and a composite roll is obtained in which the outer layer and the inner layer are welded and integrated.

As the inner layer to be statically cast, it is preferable to use spheroidal graphite cast iron, worm-like graphite cast iron, graphite steel or the like having excellent castability and mechanical properties. An intermediate layer made of graphite steel or high carbon steel may be provided between the outer layer and the inner layer. When rolls are manufactured by centrifugal casting, the intermediate layer may be centrifugally cast following the centrifugal casting of the outer layer.
The composite roll for hot rolling of the present invention is preferably subjected to heat treatment after casting. The heat treatment is preferably a quenching treatment in which heating is performed at 800 ° C. to 1080 ° C. and quenching, and further a treatment in which a tempering treatment is performed at 300 to 600 ° C. at least once. If the heating temperature for quenching is less than 800 ° C., the heating temperature is too low to ensure hardness. On the other hand, when the heating temperature is higher than 1080 ° C., the low melting point eutectic compound of P and B is melted to increase microporosity defects. For this reason, it is preferable that quenching heating temperature shall be the temperature of the range of 800-1080 degreeC. The preferred hardness is 70 to 90 Hs.

  The molten metal having the composition shown in Table 1 was melted in a high-frequency melting furnace, and a ring-shaped test piece (outer diameter: 250 mmφ, wall thickness: 70 mm) corresponding to the roll outer layer material was cast by a centrifugal casting method. The casting temperature was 1450-1500 ° C., and the centrifugal force was 160 G as a multiple of gravity. After casting, quenching and tempering were performed under the conditions shown in Table 2. The hardness after tempering was Hs 78-84. Ni-grain cast iron (test material No. NIG) and high-speed roll material (test material No. HSS) were used as conventional examples.

A test piece was collected from the obtained ring-shaped test material, and subjected to an abrasion test and a seizure test. The test method was as follows.
(1) Abrasion test Take a test piece (outer diameter: 60mmφ, thickness: 10mm) from a ring-shaped test material, and the other material (material: S45C, size: 190mmφ, thickness: 15mm) and test piece 2 A wear test was carried out by the disc sliding wear method. While rotating the test piece at a rotation speed of 700 rpm, the mating material is heated to 820 ° C, the test piece is cooled with water, the sliding rate between the test piece and the mating material is 10%, and the load is 100 kgf (980 N) for 30 min The rolling wear test was performed three times. After the test, the wear loss (wear amount) of the test piece was measured. The wear resistance was evaluated by the wear ratio, that is, the ratio to the wear amount of Ni grain cast iron (= (wear amount of NIG) / (wear amount of test piece)). When this numerical value is large, it means that the wear resistance is excellent. For example, test piece No. HSS shows wear resistance of 4.9 times that of NIG.
(2) Seizure Test A test piece (25 mm thick plate) was taken from the ring-shaped test material, and a seizure test was performed with a tester of the system shown in FIG. A disk-shaped mating material (material: SUS410, size: 190 mmφ, wall thickness: 15 mm) that is heated to 900 ° C. and rotated by a high-frequency induction heating coil was pressed onto the test piece for 20 s at a load of 100 kgf (980 N). . The rotational speed of the mating material was 175 rpm. “If there is seizure” (×) when the specimen is seized on the surface of the test specimen after the test, “No seizure” (○) if there is no seizure and the surface is worn. As a result, the seizure resistance was evaluated.

  The obtained results are shown in Table 2.

  Each of the inventive examples has wear resistance several times that of the conventional example (test material No. NIG), and no seizure occurs as in the conventional example (test material No. HSS). That is, the example of the present invention is a roll outer layer material excellent in both wear resistance and seizure resistance. On the other hand, in comparative examples that are outside the scope of the present invention, either or all of the wear resistance and seizure resistance are lowered.

It is explanatory drawing which illustrates the outline | summary of the testing machine used for the seizure test typically.

Claims (10)

% By mass
C: 1.8-3.5%, Si: 0.2-2%,
Mn: 0.2-2%, Cr: 4-15%,
Mo: 2-10%, V: 3-10%
Including,
P: 0.1-0.6%, B: 0.05-0.5%
And a roll outer layer material for hot rolling excellent in seizure resistance, characterized by having a composition comprising balance Fe and inevitable impurities.   2. The composition according to claim 1, wherein in addition to the composition, the composition further comprises one or two selected from Nb: 3% or less and W: 5% or less by mass%. Roll outer layer material for hot rolling.   The roll outer layer material for hot rolling according to claim 1 or 2, further comprising a composition containing Ni: 5% or less by mass% in addition to the composition.   The roll outer layer material for hot rolling according to any one of claims 1 to 3, wherein in addition to the composition, the composition further contains, by mass%, Co: 2% or less.   The composition according to any one of claims 1 to 4, wherein in addition to the composition, the composition further contains one or two selected from Al: 0.1% or less and Ti: 0.1% or less by mass%. The roll outer layer material for hot rolling according to any one of the above. It is a composite roll for hot rolling formed by welding and integrating the outer layer and the inner layer, and the outer layer is in mass%,
C: 1.8-3.5%, Si: 0.2-2%,
Mn: 0.2-2%, Cr: 4-15%,
Mo: 2-10%, V: 3-10%
Including,
P: 0.1-0.6%, B: 0.05-0.5%
And a composite roll for hot rolling excellent in seizure resistance, characterized by having a composition comprising the balance Fe and inevitable impurities.   The composition according to claim 6, further comprising, in addition to the composition, at least 1% or 2 types selected from Nb: 3% or less and W: 5% or less in terms of mass%. Composite roll for hot rolling.   The composite roll for hot rolling according to claim 6 or 7, wherein in addition to the composition, the composition further contains, by mass%, Ni: 5% or less.   The composite roll for hot rolling according to any one of claims 6 to 8, wherein in addition to the composition, the composition further contains, by mass%, Co: 2% or less.   The composition according to any one of claims 6 to 9, wherein in addition to the composition, the composition further contains one or two kinds selected from Al: 0.1% or less and Ti: 0.1% or less by mass%. A composite roll for hot rolling according to any one of the above.