JP2002273506A - Work roll for cold rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a work roll for cold rolling which is made by continuous burn on and padding and has wear resistance, roughness resistance holdability of a roll surface during rolling and grindavility in combination. SOLUTION: This work roll for cold rolling is constituted by forming an outer layer by a continuous tinkering and padding method on the circumference of a core material consisting of cast steel or forged steel. The chemical components of the outer layer consist, by mass%, 0.8 to 2.0% C, 0.2 to 2.0% Si, 0.2 to 2.0 to 2.0% Mn, 4.0 to 10.0% Cr, 1.0 to 6.0% Mo, 0.5 to 3.0% V, 0.5 to 3.0% W and the balance Fe and inevitable component and further consist of 0.1 to 1.0 Cbal of the following formula. Further, the work rolls contains 0.02 to 0.05%>=1 kind of Ti, B and Mg in the outer layer: Cbal=C-(0.060Cr+0.063Mo+0.033W+0.235V).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work roll for cold rolling used for cold rolling of steel.

[0002]

2. Description of the Related Art Conventionally, as a work roll for cold rolling of iron and steel, a so-called forging roll in which a steel ingot of a single material is manufactured by an electro-slag remelting method and then subjected to a quenching and tempering heat treatment through a forging process. Used a lot. However, in the conventional forging roll, as an actual roll, mainly abrasion resistance, grindability, crack resistance at the time of a rolling trouble, and the like are generated, which is still insufficient and has a problem. As a technique for solving such a problem, for example, Japanese Patent Application Laid-Open
The outline of this technique disclosed in Japanese Patent Application Laid-Open No. 1-302777 is that a continuous casting overlay method is adopted in place of the conventional manufacturing method of electro-slag remelting and forging, and the solidification rate is increased. By making the crystal grain size of the crystallized carbide finer by appropriate control, the roughness maintenance of the roll surface during rolling is remarkably improved, and the Cbal of C, which is a chemical component, is defined in a certain range, so that the grindability is further improved. It is to improve.

[0003]

As described above, as described above,
According to the technology described in JP-A-1-302777, the roughness retention and the grindability of the roll surface during rolling are significantly improved as compared with the conventional technology, and the performance of the actual roll can be significantly improved. However, Japanese Patent Application Laid-Open No.
In the technology described in Japanese Patent No. 2777, for example, when rolling a material having a high required surface quality or using it in a rolling mill in which rolling conditions are more severe, further wear resistance and roughness retention are required. And grindability is desired. In view of the above problems of the prior art, an object of the present invention is to provide a work roll for cold rolling having abrasion resistance even in severe rolling conditions, resistance to roughness of the roll surface during rolling, and grindability. To provide.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, the present inventors have found that wear resistance is maintained even in rolling under severe rolling conditions, and that the surface roughness of the roll during rolling is maintained. It is possible to manufacture a cold rolled work roll having good grindability and grindability. The gist of the invention is as follows. (1) An outer layer is formed around a core material made of cast steel or forged steel by a continuous casting overlay method, wherein the chemical composition of the outer layer material is% by weight, C: 0.8 to 2.0%, Si: 0.2-
2.0%, Mn: 0.2-2.0%, Cr: 4.0-1
0.0%, Mo: 1.0-6.0%, V: 0.5-3.
0%, W: 0.5 to 3.0%, the balance being Fe and unavoidable components, and Cbal of the following formula being 0.1
1.0 or more of Ti, B, and Mg in the outer layer.
A work roll for cold rolling, characterized in that the work roll contains 0.50% to 0.50%. Cbal = C- (0.060Cr + 0.06
3Mo + 0.033W + 0.235V)

(2) The work roll for cold rolling according to the above (1), wherein the outer layer further contains Ni: 0.1 to 5.0% by mass% as a chemical component. (3) The outer layer surface has a Vickers hardness of 750 or more;
The work roll for cold rolling according to the above (1) or (2), having a compressive residual stress of 0 MPa or less.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the components of the outer layer are described below. C is an important element for obtaining hardness. If the C content is less than 0.8%, the crystallization of carbides effective for improving durability is small, and furthermore, C dissolved in the matrix is insufficient, and sufficient base hardness cannot be obtained even by quenching. At the same time, high alloying becomes difficult. on the other hand,
If the content exceeds 2.0%, carbides become coarse and the amount of crystallization becomes excessive, so that the uniformity required for a work roll for cold rolling cannot be maintained, and particularly, scratches such as uneven grinding or small scratches during grinding. Therefore, the upper limit was set to 2.0%.

Si and Mn both have a deoxidizing effect and are effective elements at the same time in view of the fluidity of the molten metal.
% Or less contained in general high-speed steel. However, if the content is 0.2% or more, the effect is exhibited, so the lower limit is set. Ni has an effect of improving hardenability. In particular, when a large curing depth is required for a roll having a large diameter or the like, it may be added according to the requirement. However, if the content exceeds 5.0%, the retained austenite becomes excessive and high hardness cannot be obtained, so the upper limit is set to 5.0%. If it is 0.1% or more, the lower limit is set for achieving the effect.

[0008] Cr combines with C to form a hard carbide of M ₇ C ₃ type at crystal grain boundaries, thereby improving wear resistance and forming a strong cast structure which is less likely to plastically flow during rolling.
However, if the added amount is small, the effect cannot be sufficiently secured, while if too large, the carbides are coarsened and develop into a network, and the homogeneity and grindability of the structure are impaired and the toughness is reduced. Therefore, an appropriate range is 4.0% or more.
0% or less. Mo is a hard M ₂ C-type or M ₆ C-type carbide similar to Cr, and is an element that strongly contributes to the secondary hardening when tempering is performed at a high temperature. 1.
If it is less than 0%, precipitation as carbides is insufficient.
However, if the content exceeds 6.0%, coarse carbides having a network shape are formed. Therefore, the appropriate range is set to 1.0% or more and 6.0% or less.

V is an element useful for forming extremely hard and granular MC-based carbides and improving wear resistance. However, if it is less than 0.5%, the effect is small,
If the content exceeds 3.0%, MC-based carbides cause scratches and impair the grindability.
It was set to not less than 3.0%. The addition of Ti, B, and Mg serves as nuclei for crystallization of crystallized carbides, particularly MC carbides, and disperses them in crystal grains, and further forms M ₇ C ₃ type, M ₂ C type, or M ₆ C type carbides. Has a synergistic effect with the action of casting the crystal grains surrounded by the above-described continuous casting method, which will be described later, and has an action of stably reducing the size. Thus, Ti, B, Mg
Is the greatest feature of the present invention. If the addition amount is less than 0.02%, a sufficient effect cannot be obtained. On the other hand, since these elements have a strong tendency to oxidize,
If it exceeds 0.50%, it is undesirable to promote the generation of oxidized inclusions.

[0010] The value of Cbal is important for balancing the carbide and the matrix structure in the material in which the carbide exists, and particularly for controlling the solid solution C in the matrix. In the material of the present invention, an appropriate amount of the above-mentioned hard carbide is crystallized, and the value is set to 0.1 to 1.0 in order to secure the base hardness by quenching. 0.1
If it is less than 3, the solid solution of C in the base structure is so small that hardness cannot be obtained. On the other hand, if it exceeds 1.0, carbides increase and grindability is impaired. Since W produces hard carbides like Cr and Mo, it is effective to add or replace with these elements in a range of 3.0% or less. The effect is exerted when 0.5% or more is added.

As described above, the present invention is characterized in that the use of hard crystallized carbide is one of the most important features in order to improve the wear resistance.
50 or more. Carbide is MC type by V or Cr
・ M ₇ C ₃ type, M ₂ C type or M ₆ by Mo ・ W
Type C was mainly used. In detail, in the case of conventional rolls, Shore hardness was used as a control index using high residual stress, but in order to secure and improve the durability of abrasion resistance, roughness retention, and dent resistance, push-in type Vickers hardness, one of the representative hardnesses of
The durability was improved by setting it to 50 or more, preferably 800 or more.

Particularly, in order to improve accident resistance, tempering was performed at a high temperature, and a low compressive residual stress of 700 MPa or less was obtained on the outer layer surface. As a result, the Shore hardness, which is a rebound type hardness affected by residual stress and the like in addition to the properties of the material itself, which has conventionally been generally used as a management index, does not need to be as high as 95 or more as in the conventional roll. For example, if the Vickers hardness is 90 or less, if the Vickers hardness is not less than the above value, the durability is sufficiently improved, and the accident resistance is also provided. Further, if the roughness of the roll surface during rolling can be maintained within a predetermined range, the rolling operation is stable, and the rolling operation can be continuously performed for a long time, so that the operability can be improved.

Therefore, the roll material of the present invention was cast as a surface material of the outer layer by a continuous casting method, and the roll surface roughness retention during rolling was remarkably improved. This is achieved by controlling the cast structure, which has a strong relationship with the surface roughness, to be dense by the high solidification rate of the continuous casting method.
That is, the casting by the continuous casting method of the present invention and the T
The synergistic effect of the addition of i, B, and Mg makes it possible to stably achieve a dense casting structure with a small crystal grain size surrounded by the eutectic carbide, thereby stabilizing the rolling operation and the roll surface roughness during rolling. And a beautiful rolled material surface can be obtained.

[0014]

EXAMPLES Examples of the present invention will be described below together with conventional materials and comparative materials. (Example 1) As an example of the present invention, the material No. 1 of the present invention shown in Table 1 was used. No. 1 to 10, conventional material No. 11-13, comparative material N
o. Microstructures of 14 to 17 were investigated and compared.
First, the test piece was melted in a high-frequency induction furnace, and then the molten metal was cooled to a diameter of 10 so that the solidification rate was equivalent to that of an actual roll.
0mm, 300mm height sand mold, then 10
A quenching treatment from 00 ° C. and a tempering treatment at 500 to 550 ° C. were performed to produce various test pieces for microstructure examination. The amount of crystallized carbide, the crystal grain size, the distribution of carbide in the crystal grains, and the hardness were measured from each of the manufactured test pieces using an image analyzer. Table 1 shows the results.

[0015]

[Table 1]

First, the grain size of the present invention, which greatly affects the wear resistance, the retention of roughness of the roll surface during rolling, and the grindability, is smaller than that of the conventional material having a grain size of about 50 μm. , Ti, B, Mg at least one of 0.02 to 0.2.
It is clear that the crystal grain size of the material of the present invention containing 50% is reduced by 20 to 30% when the crystal grain size is 40 μm or less, and a dense structure is obtained. In addition, the dispersion of the carbide in the crystal grains was also sufficient. On the other hand, Ti, B, M shown as comparative materials
The content of g is in the same range as the material of the present invention, but a sufficient amount of carbide cannot be obtained with a low C material in which the amount of C is smaller than that of the material of the present invention. In addition, the dispersion of the carbide in the crystal grains, which is one of the features of the present invention, was insufficient. As a result of the above lab test, the operation and effect of the material of the present invention were sufficiently confirmed. Next, an actual rolling roll was manufactured. This will be described below.

(Embodiment 2) As an embodiment of the present invention, Table 2
The outer layer is made of the chemical components shown in the above, and the body diameter φ550 mm, the body length 15
A composite work roll for cold rolling of 00 mm and a total length of 3500 mm was cast. After casting, subjected to soft annealing, after rough processing,
A tempering treatment was performed for the purpose of separating carbides. afterwards,
Quenching was performed by progressive induction heating and water quenching at a surface temperature of 950 to 1100 ° C. Furthermore, tempering is 450 ~
Performed at 600 ° C. A test piece was taken from a part of the rolling roll, and the amount of crystallized carbide, the crystal grain size, the distribution of carbide in the crystal grain, and the hardness were also measured using an image analyzer in the same manner as in the lab test. Was measured. Table 3 shows the results. As is clear from the table, the results with the actual machine roll, that is, the amount of crystallized carbides, the crystal grain size, the distribution of carbides in the crystal grains, and further the hardness, etc. are all the same as the results of the lab test of the present invention described above. The same good result was shown, and the operation and effect of the material of the present invention could be confirmed on the actual roll.

[0018]

[Table 2]

[0019]

[Table 3]

Table 3 shows the results of actual rolls subjected to actual cold rolling. As is evident from the results shown in Table 3, the grinding work before use of the rolls was performed for the first-stage rolling mill having a relatively large required surface roughness, for the successively smaller middle-stage rolling mill, and for the second-stage rolling mill. This was possible without harmful scratches under the conditions. Furthermore, in the case of actual cold rolling, the conventional forging roll was unable to secure the required surface roughness after rolling a product of about 500 tons, and the rolling operation was interrupted and the roll was replaced. The roll could be continuously rolled to 3000 tons or more without lowering the roughness.

Further, Japanese Patent Application Laid-Open No.
With regard to the roll described in JP-A-302777, particularly when rolling a product of strict quality, it was not sufficiently satisfactory, for example, for a subsequent rolling mill, etc. It became possible to use it, and productivity in the rolling operation was remarkably improved. In addition, there was no generation of cracks when encountering an accident during rolling, and the typical wear resistance of the roll was improved to at least six times that of a conventional forged roll.

[0022]

As described above, the rolling roll of the present invention has an appropriate amount of crystallized carbide, a small crystal grain size, and carbides dispersed and distributed in the crystal grains. When used for rolling materials with high surface quality or used in rolling mills where rolling conditions are more severe, it must have both excellent wear resistance, roughness retention of the roll surface during rolling, and grindability. This greatly contributes to improving the productivity of cold rolling.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI theme coat ゛ (reference) C22C 38/58 C22C 38/58 F term (reference) 4E016 CA04 CA09 EA03 EA22 EA23 FA01

Claims (3)

[Claims] 1. Around a core material made of cast steel or forged steel,
An outer layer is formed by a continuous casting overlaying method, and the chemical composition of the outer layer material is% by weight: C: 0.8 to 2.0%, Si: 0.2 to 2.0%, Mn: 0 0.2 to 2.0%, Cr: 4.0 to 10.0%, Mo: 1.0 to 6.0%, V: 0.5 to 3.0%, W: 0.5 to 3.0% %, The balance being Fe and an unavoidable component, and Cbal of the following formula being 0.1 to 1.0 in a cold-rolling work roll, wherein Ti, B,
A work roll for cold rolling, comprising 0.02 to 0.50% of at least one kind of Mg. Cbal = C- (0.060Cr + 0.063Mo +
0.033W + 0.235V) 2. The chemical composition of the outer layer further comprises:
The work roll for cold rolling according to claim 1, wherein the content of Ni is 0.1 to 5.0%. 3. The work roll for cold rolling according to claim 1, wherein the outer layer surface has a Vickers hardness of 750 or more and a compressive residual stress of 700 MPa or less.