JP2003105483A - Composite roll for hot rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new composite roll for hot rolling which is obtained by using a high alloy grain cast iron having a new componential composition, and has remarkably improved wear resistance without deteriorating its seizure resistance and accident resistance characteristic of a roll made of the high alloy grain cast iron. SOLUTION: In the composite roll for hot rolling, at least the barrel part consists of an external layer and an internal layer. The external layer has a componential composition containing, by weight, 2.0 to 4.0% C, 0.5 to 2.0% Si, 0.2 to 2.0% Mn, 2.0 to 6.0% Ni, 1.0 to 4.0% Cr, 0.3 to 4.0% Mo, 0.1 to 2.0% V and 0.1 to 1.0% Ti, and 0.2 to 2.5% of one or more kinds selected from W, Nb, B and rare earth elements, and the balance substantially Fe.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composite roll for hot rolling.

[0002]

2. Description of the Related Art Conventionally, a composite roll having a high alloy grain cast iron as an outer layer has been used as a finishing post-roll for, for example, hot strip rolling. In general, a roll made of high-alloy grain cast iron has excellent seizure resistance, and even if a drawing accident occurs, seizure of the rolled material is small, and cracks are not generated or propagated. On the other hand, recently, as a material that meets the demand for improving the wear resistance of hot rolling rolls, application of a high-speed material containing Cr, Mo, W, V, Co, and the like in a few wt% is progressing.

[0003]

However, in the case of a hot rolling roll using the above HSS material as the outer layer of the roll,
Although it has a great effect on the improvement of wear resistance, there is a problem that the rolled material is easily seized when a drawing accident occurs, cracks are easily generated and propagated, and damage is increased. Therefore, the present applicant previously filed Japanese Patent Application No. 2000-48444.
In, a new component composition was provided for the high alloy grain cast iron that constitutes the outer layer material of the composite roll, and a composite roll for hot rolling with improved wear resistance was provided. However, the component composition of the high alloy grain cast iron used in the outer layer of the roll of Japanese Patent Application No. 2000-48444 is a composite roll having a high alloy grain cast iron having a different component composition in the outer layer. It is also necessary to develop a roll that has characteristics equal to or better than that of a roll.

Therefore, the present invention relates to a roll using a high alloy grain cast iron having a new composition of components, which does not impair the seizure resistance and accident resistance of the high alloy grain cast iron roll. Another object of the present invention is to provide a new composite roll for hot rolling that has significantly improved wear resistance.

[0005]

A hot-rolling composite roll of the present invention for solving the above-mentioned problems is a hot-rolling composite roll in which at least a roll body comprises an outer layer and an inner layer,
The composition of the outer layer is% by weight, and C: 2.0 to 4.0.
%, Si: 0.5 to 2.0%, Mn: 0.2 to 2.0
%, Ni: 2.0 to 6.0%, Cr: 1.0 to 4.0
%, Mo: 0.3 to 4.0%, V: 0.1 to 2.0%,
Ti: 0.1 to 1.0%, and 0.2 to 2.5% of at least one of W, Nb, B, and rare earth elements, and the balance being substantially Fe. It is characterized by 1. In addition to the first characteristic, the composite roll for hot rolling of the present invention has an area ratio of 25 to 45 in the outer layer structure.
% Cementite and 2-6% graphite are dispersed, and fine carbides are dispersed in the matrix of the outer layer.
It is a feature of. In addition to the first or second characteristic, the composite roll for hot rolling of the present invention is formed by welding and integrating the molten metal of the outer layer material and the molten metal of the inner layer material made of ductile cast iron by centrifugal casting. Is the third feature.

According to the first feature of the present invention, V and Ti are added to the high alloy grain material composed of the respective components C to Mo in the indicated content range, and W, W, N
By adding at least one of b, B and rare earth elements in the indicated range, the primary crystallized cementite is hardened, and hard fine carbide is crystallized or precipitated in the matrix, and fine It is possible to increase the crystallization of spheroidal graphite. This makes it possible to provide a new composite roll for hot rolling which has improved seizure resistance and accident resistance while maintaining the excellent seizure resistance and accident resistance of conventional high alloy grain materials. According to the second feature of the present invention,
In addition to the function and effect of the first characteristic, 25
Good wear resistance can be exhibited by cementite having an area ratio of ~ 45% and fine carbides dispersed in the matrix, and high alloy grain material by crystallizing and dispersing 2-6% of graphite. Excellent seizure resistance can be maintained. Further, according to the third feature, in addition to the effect of the first or second feature, the outer layer material having excellent seizure resistance, accident resistance, and wear resistance is different from the ductile cast iron as the inner layer material. By forming a composite roll by welding and unifying by means of centrifugal casting method, it is possible to add further toughness to the hot rolling composite roll, and it is also applied to the finishing post-stage roll for hot sheet rolling. Became possible.

Regarding the composite roll for hot rolling of the present invention,
The reason for limiting the content range of each component element in the component composition of the outer layer will be described below. In addition, all component compositions are shown by weight%.

The content of C is 2.0 to 4.0%. C
Is an element necessary for forming hard carbide to contribute to improvement of wear resistance and to crystallize graphite to enhance seizure resistance. If the content is less than 2.0%, the amount of carbide will be insufficient and graphite will not crystallize, while if it exceeds 4.0%, the amount of carbide will increase and the toughness will decrease. The C content is more preferably 2.8 to 3.5%.

The Si content is 0.5 to 2.0%.
Si is an element that promotes graphitization, and has an effect of improving castability. If the content is less than 0.5%, a sufficient effect cannot be obtained, while if it exceeds 2.0%, the toughness and mechanical properties deteriorate. The content of Si is more preferably 0.6
It is good to be set to 1.2%.

The Mn content is 0.2 to 2.0%.
Mn has a deoxidizing effect, and if its content is less than 0.2%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 2.0%, toughness decreases and graphitization is hindered. The Mn content is more preferably 0.5 to 1.2%.

The Ni content is 2.0 to 6.0%.
Ni is effective for crystallization of graphite and strengthening of matrix structure. If the content is less than 2.0%, a sufficient effect cannot be obtained, while if it exceeds 6.0%, the austenite is too stable,
It leads to lower hardness and toughness. The Ni content is more preferably 3.0 to 5.0%.

The content of Cr is 1.0 to 4.0%.
Cr is one of the main elements constituting the carbide that improves wear resistance, and is also an element that is essential for improving the matrix hardness. If the content is less than 1.0%, the amount of carbide formed is insufficient, so the hardness decreases, and if it exceeds 4.0%, the amount of carbide increases, the toughness decreases, and graphitization is impeded. C
The content of r is more preferably 1.5 to 3.0%.

The content of Mo is 0.3 to 4.0%.
Mo is an element effective in improving the wear resistance because it forms a solid solution in the matrix structure to strengthen the matrix. If it is less than 0.3%, the effect cannot be obtained, while if it exceeds 4.0%, a plate-like M ₂
C-type carbides crystallize, leading to a decrease in toughness and a decrease in surface roughening resistance. The content of Mo is more preferably 0.5.
It is good to be set to 2.0%.

The V content is 0.1 to 2.0%. V
Crystallizes or precipitates MC type carbides. Further, it has an effect of making a solid solution in the primary crystallized cementite and hardening the cementite. If the total content is less than 0.1%, those effects cannot be obtained. On the other hand, if it exceeds 2.0%, coarse primary carbides are crystallized and the amount of crystallized graphite is reduced, resulting in resistance to surface roughening and seizure resistance. Deteriorates sex. The V content is more preferably 0.2 to 0.7%.

The Ti content is 0.1 to 1.0%.
Ti partially combines with carbon to form TiC, and when used in combination with V and Cr, wear resistance and toughness are further improved. Further, by including Ti, the amount of crystallized graphite can be increased. If the total content is less than 0.1%, those effects cannot be obtained, while if it exceeds 1.0%, the toughness is deteriorated. The Ti content is more preferably 0.2-0.
7% is recommended.

W, Nb, B and rare earth elements are at least 1
0.2 to 2.5% of seeds or more is contained in total. W and Nb
Where W is M ₂ C type carbide and M ₆ C type carbide,
Nb crystallizes or precipitates MC type carbides. Further, it has an effect of making a solid solution in the primary crystallized cementite and hardening the cementite. If the total amount of W and Nb is less than 0.2%, these effects cannot be obtained, while both elements of W and Nb are 1.
If it exceeds 0%, coarse primary carbides are crystallized and the amount of crystallized graphite is reduced, resulting in deterioration of the rough skin resistance and seizure resistance.
B binds to oxygen in the molten metal and exhibits a deoxidizing effect. In addition, it has the effect of refining the solidified structure centered on the generated oxide and the effect of increasing the hardenability due to B dissolved in the matrix. Therefore, in the case of a large mass casting such as a rolling roll,
Although it may be difficult to increase the cooling rate in some cases, the improvement of the hardenability makes it easier to obtain a good hardened structure. The rare earth element has an effect of making graphite fine and spherical, and improving mechanical properties. If it is less than 0.01%, such an effect is not sufficient, while if it exceeds 0.5%, the material becomes brittle. Preferably, W + Nb is 0.2 to 2.0% by weight, and B + rare earth element is 0.02 to 0.5%. The rare earth elements include Ce, La, Nd, and Pr.
A mixed misch metal (it is difficult to separate each element) can be used.

By making the composition of the outer layer material within the above range, 25 to 45% by area ratio of cementite and 2 to 6% of graphite in the structure and fine carbides are crystallized and precipitated in the matrix. Can be dispersed.

The composite roll for hot rolling of the present invention can be manufactured by fusion-melting the melt of the outer layer material having the above-described composition and the melt of the inner layer material made of ductile cast iron by centrifugal casting.

In the composite roll for hot rolling of the present invention, after the inner layer material is welded and integrated with the outer layer material by the centrifugal casting method to cast, the retained austenite transformation and the strain relief heat treatment for removing the residual stress are performed. There is a need to do. This heat treatment is carried out by heating and holding at 400 to 600 ° C. in the as-cast state and then slowly cooling.

The composite roll for hot rolling of the present invention is suitable, for example, as a post-finishing roll for hot strip rolling.

[0021]

EXAMPLES Examples 1 to 5 of the composite roll for hot rolling according to the present invention are set as Comparative Examples 1 to 4, and the composition of each component of the outer layer is shown in Table 1. The balance of the component composition consists essentially of Fe. In the chemical composition of the outer layer of Comparative Examples 1 to 4, V, T
i is not contained, and none of W, Nb, B, and rare earths is contained.

[0022]

[Table 1]

An outer layer material having the components shown in Table 1 and an inner layer material made of general ductile cast iron were centrifugally cast into a composite roll having a body diameter of 350 mm and a body length of 600 mm. The obtained casting roll was subjected to strain relief heat treatment for transformation of residual austenite and removal of residual stress. In the structure of the outer layer portion of each roll after the heat treatment obtained, in the range of the optical microscope was not able to detect the structural difference between the example and the comparative example, but in the electron microscope in each tissue of the example, the primary crystal It was confirmed that V was solid-dissolved in the cementite and that very fine carbide was uniformly dispersed in the matrix.

In order to evaluate the materials of these Examples and Comparative Examples, samples were taken and the Shore hardness, texture, friction and wear test,
A seizure test was performed. The results are shown in Table 2.

[0025]

[Table 2]

The above evaluation is based on EPMA surface analysis and image.
The carbide area ratio was measured by analysis. Also try friction and wear
The test was carried out using the following pin-on-disc method to determine the friction coefficient and wear reduction.
It was measured. The seizure test is based on the Falex method below
The load and the seizure torque were measured. <Frictional wear test>           Test method: Pin-on-disk method           Test piece temperature: 300 ℃           Load: 5kg / cm^Two           Rotation speed: 100m / min           Sliding distance: 20000m <Baking test>           Test method: Falex method (KF type seizure tester)           Test piece size: φ6.35 × 32L           Counterpart material (V block): SUS304           Rotation speed: 290 rpm

As is clear from Table 2, in the seizure test, the rolls of Examples 1 to 5 and the rolls of Comparative Examples 1 to 4 have almost the same performance. On the other hand, in the wear reduction in the friction wear test, it can be seen that the roll of the example has a significantly smaller wear reduction than the roll of the comparative example. That is, in the present invention, by adding V and Ti in the range shown, and by adding at least one or more of W, Nb, B and rare earth elements in the range shown,
It can be seen that improvement in wear resistance can be expected while maintaining excellent seizure resistance and accident resistance of conventional high alloy grain materials.

[0028]

According to the composite roll for hot rolling described in claim 1, the present invention has the above-mentioned constitution and operation, and the high alloy grain composed of the components C to Mo shown therein. Addition of V and Ti to the material within the indicated content range, and W, N
By adding at least one of b, B, and rare earths in the indicated range, the primary crystallized cementite is hardened, and hard fine carbides are crystallized or precipitated in the matrix, and the fine grained It is possible to increase the crystallization of spheroidal graphite. Therefore, this makes it possible to provide a new composite roll for hot rolling with improved wear resistance while retaining the excellent seizure resistance and accident resistance of conventional high alloy grain materials. It can also be applied to the rolls for the subsequent stage of hot-rolled sheet rolling, and it is possible to improve the quality of hot-rolled products and achieve high productivity of rolling work. Further, according to the hot rolling composite roll of claim 2, in addition to the effect of the configuration of claim 1, there is actually 25
Good wear resistance can be exhibited by cementite existing in an area ratio of ~ 45% and fine carbides dispersed in the matrix, and by crystallizing and dispersing 2-6% of graphite, It is possible to maintain the excellent seizure resistance of the high alloy grain material. Further, according to the composite roll for hot rolling of claim 3, in addition to the effect of the configuration of claim 1 or 2, an outer layer material excellent in seizure resistance, accident resistance, and wear resistance is obtained. On the other hand, by using ductile cast iron as the inner layer material to form a composite roll by welding and integration by the centrifugal casting method, it is possible to further impart toughness to the composite roll for hot rolling, and for hot thin plate rolling. Can be more favorably applied to the finishing second-stage roll.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takaaki Takagi             403 Yoshimi, Otsu-ku, Himeji City, Hyogo Prefecture             Himeji Nishi Factory F-term (reference) 4E016 CA08 DA03 EA03 EA23 FA02

Claims (3)

[Claims] 1. A composite roll for hot rolling in which at least a roll body is composed of an outer layer and an inner layer, wherein the composition of the outer layer is% by weight, and C: 2.0 to 4.0% Si: 0.0. 5 to 2.0% Mn: 0.2 to 2.0% Ni: 2.0 to 6.0% Cr: 1.0 to 4.0% Mo: 0.3 to 4.0% V: 0.0. 1 to 2.0% Ti: 0.1 to 1.0% and 0.2 to 2.5% of at least one of W, Nb, B and rare earth elements, and the balance substantially Fe. A composite roll for hot rolling. 2. An outer layer structure comprising 25-45% of cementite and 2-6% of graphite dispersed in an area ratio, and fine carbides dispersed in a matrix of the outer layer. Item 1. A composite roll for hot rolling according to Item 1. 3. The composite roll for hot rolling according to claim 1, wherein the melt of the outer layer material and the melt of the inner layer material made of ductile cast iron are welded and integrated by a centrifugal casting method.