JP2002336904A - Method for manufacturing composite work roll for cold rolling and work roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a composite work roll for cold rolling and the roll for realizing the increase of the diameter in use, that is, the increase of an outer layer of the composite work roll having a limit to thickening of the outer layer for preventing the break of a core material at quenching, prolonging the life of the composite work roll for rolling and reducing the manufacturing cost of a steel product. SOLUTION: In the manufacturing method for the composite work roll for cold rolling, which is manufactured by performing low frequency gradual induction heating and water quenching after forming the outer layer consisting of high-speed steel base material around the core material consisting of cast steel or forged steel by continuous cladding by tinkering, this manufacturing method of the composite work roll for cold rolling and this work roll are characterized by that a depth range where the core material is heated to not lower than the deformation point A1 of the core material at the low frequency gradual induction heating is taken as the thickness of the outer layer to <=0.7 of the radius of the work roll and, after that, the water quenching is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a composite roll has been known as a work roll for cold rolling of iron and steel, and the roll is provided with sufficient abrasion resistance and severe scratch resistance under severe rolling conditions. The outer layer material is generally given a high hardness of 90 or more in Shore hardness by a low frequency progressive induction heating / water quenching method. However, in such a composite work roll, a large compressive residual stress is generated in the outer layer that is hardened and transformed and expanded by the quenching, and a large tensile stress is generated in the core material as the inner layer material so as to balance the residual stress.
If the tensile stress generated in the core material is excessive, the core material may break during quenching. As a technique for solving this, for example, Japanese Patent Application Laid-Open No. 5-169112 is disclosed. The outline of this technique is to prevent the core material from breaking during the quenching by providing a material having an elongation of 10% or more to the core material serving as the inner layer material of the composite roll.

[0003]

The prolongation of the life of the composite work roll for cold rolling greatly contributes to a reduction in the manufacturing cost of the steel product rolled by the roll. For this purpose, not only can the life of the roll be extended by improving the abrasion resistance and scratch resistance of the roll itself, but also the use diameter of the roll can be increased, that is, the outer layer thickness at the time of manufacturing the composite work roll can be increased. This is an extremely effective measure. However, the tensile stress generated in the core material due to the transformation expansion during the quenching becomes more severe as the outer layer becomes thicker, and the core material disclosed in JP-A-5-169112 has a tensile stress of 10% or more. Just by providing a material with elongation,
There was a limit to the thickening. As the limit amount, the outer layer thickness was limited to 40 mm in the case of a work roll having a ratio of 0.20 to the radius of the composite work roll, for example, a work roll having a radius of 200 mm.

[0004] In view of the above-mentioned problems of the prior art, an object of the present invention is to use a composite work roll in which the thickness of the outer layer is limited in order to prevent breakage of the core material during quenching as described above. Increased diameter, that is, increased outer layer thickness,
An object of the present invention is to provide a method and a roll for manufacturing a composite work roll for cold rolling, which can extend the life of the composite work roll for rolling and significantly reduce the cost of manufacturing steel products.

[0005]

SUMMARY OF THE INVENTION The present invention is to achieve the above-mentioned object, and the gist of the invention is as follows. (1) After forming an outer layer made of a high-speed material around a core material made of cast steel or forged steel by a continuous casting overlay method,
In the low-frequency progressive induction heating and cold method for producing a rolling composite work roll that is manufactured by performing water quenching, when the low-frequency progressive induction heating, the depth range, which is heated above the A ₁ transformation point of the core material layer A thickness of not less than 0.7 and a radius of the work roll of 0.7 or less, followed by water quenching.

(2) In a composite work roll for cold rolling manufactured by forming an outer layer made of a high-speed material around the core material by continuous casting and overlaying, and then performing low frequency progressive induction heating and water quenching. , low time-frequency progressive induction heating, the depth range, which is heated above the a ₁ transformation point of the core material and less 0.7 of the radius of the work roll than the thickness of the outer layer, for cold rolling comprising subsequently subjected to water quenching A composite work role,
The chemical composition of the outer layer is represented by mass%, C: 0.9 to 1.5%,
Si: 0.2 to 2.5%, Mn: 0.2 to 2.5%, C
r: 4.0 to 10.0%, Mo: 2.0 to 8.0%,
V: A composite work roll for cold rolling, characterized in that it contains 0.5 to 5.0% and the balance is Fe and inevitable impurities. (3) The outer layer is further in mass%, Ni: 0.2 to 5%,
The composite work roll for cold rolling according to the above (2), characterized in that it contains at least one member selected from the group consisting of W: 0.2 to 5% and Co: 0.2 to 5.0%.

Hereinafter, the present invention will be described in detail. The present inventors have variously set the material of the core material and the chemical composition of the outer layer as means for suppressing the tensile stress in the core material during quenching, which increases with the increase in the thickness of the outer layer. Was performed. As a result, as a core material before low-frequency progressive induction heating, use of a material having an elongation of 15% or more, or giving the core material an elongation of 15% or more, and water quenching the center of the core material, not cause transformation expansion during cooling, i.e., at a low-frequency progressive induction heating, the depth range, which is heated above the a ₁ transformation point by more than 0.7 of the radius of the work roll than the thickness of the outer layer, water quenching The risk of core material breakage at the time is extremely low, the work roll has a thick wall having a radius ratio of 0.2 to 0.4, and has a Shore hardness of 90.
A method for manufacturing a composite work roll for cold rolling and a composite work roll that enable the above are completed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a core material of the present invention will be described. In the composite work roll for cold rolling according to the present invention, a high-speed material having excellent wear resistance is used as an outer layer material described later, and the high-speed material is a hard-to-cut material. Therefore, before low-frequency progressive induction heating and water quenching, it is necessary to perform softening annealing to facilitate machining to an actual roll shape. By performing this softening annealing, the core material is also softened, and the strength and elongation are impaired. Even after the above-mentioned soft annealing, it is possible to secure an elongation of 15% by selecting a steel having a C content of 0.5% or less as a core material.
As a specific example of the application of the core material, carbon steel for machine structure is mentioned as an example.

[0009] On the other hand, the above core material may have insufficient strength to be applied to a mill having a large rolling stress such as bending. In that case, at least one of Cr, Mo, and Ni
It is sufficient to select a low alloy steel containing an appropriate amount of the seed or more as a core material. The preferable ranges are respectively Cr: 0.5 to
3.0%, Mo: 0.1 to 5.0%, Ni: 0.1 to
5.0%. In any case, if the amount is less than the above lower limit, the effect of the addition cannot be obtained. Conversely, if the amount exceeds the upper limit, quenching properties become too good and cracks are generated during heat treatment. Specific examples of the core material include, for example, cast steel disclosed in Japanese Patent Publication No. 7-61489,
It is better to use high strength steel such as forged steel. S as an example
CM materials and SNCM materials are suitable.

[0010] However, when the high-strength steel is selected as the core material, in the state where the softening annealing is performed,
An elongation of 15% or more cannot be obtained, and it is difficult to increase the thickness of the outer layer for the above-described reason. In this case, it is preferable to secure the elongation of 15% or more by performing the following preliminary heat treatment before quenching. 900-1200 ° C as the preliminary heat treatment
From the high temperature to 300 to 400 ° C. is subjected to blast cooling at a cooling rate of −5 ° C./min or more, and then tempering is performed once or several times at a temperature of 650 to 750 ° C. In the preliminary heat treatment, when the heating temperature exceeds 1200 ° C., the structure becomes coarse and brittle.

On the other hand, if the temperature is lower than 900 ° C., the diffusion is insufficient and the heat treatment effect cannot be obtained. Therefore, the optimal heating temperature was set to 900 to 1200 ° C. The cooling rate is -5 ° C / min to obtain a fine structure.
The above cooling rate is required, and blast cooling is suitable as the method. In the above-mentioned several times of tempering, when the heating temperature exceeds 750 ° C., the strength is greatly reduced. On the other hand, when the temperature is 650 ° C. or less, the effect of tempering cannot be obtained. 650-750 ° C
Is preferred.

Next, the outer layer material of the present invention will be described.
The main reason for selection is that the outer layer material of the present invention has a high hardness required for a cold rolled composite work roll, and that it can withstand low frequency induction heating and water quenching for imparting the high hardness. Basically, for example, JP-A-5-271867, JP-A-11-25400
The high-speed material disclosed in Japanese Patent Publication No. 7 is preferable, and the component system of the outer layer material is preferably in the following range.

The reasons for limiting the chemical components are described below. C is an important element for obtaining hardness. If the C content is less than 0.9%, the amount of C dissolved in the matrix becomes insufficient, so that sufficient matrix hardness cannot be obtained, and at the same time, high alloying becomes difficult. However, if the content exceeds 1.5%, carbides become coarse and the strength decreases, so the upper limit was made 1.5%. Si is added for the purpose of deoxidation. 0.2%
If it is less than 2.5%, the effect is insufficient, and if it exceeds 2.5%, the toughness is reduced.
%.

Mn is added for the purpose of deoxidation and desulfurization. If it is less than 0.2%, the effect is insufficient,
If it exceeds 2.5%, the toughness is reduced, so the range is set to 0.2 to 2.5%. Cr is easily bonded to C and M
Constituting ₇ C ₃ -based carbides, it is an element necessary for securing wear resistance. However, if it is too small, sufficient wear resistance cannot be secured, while if it is too large, carbides become coarse and develop into a net shape. Tends to decrease toughness. The optimal range is
It is 4.0 or more and 10.0% or less.

Mo is an element capable of obtaining a hard carbide and strongly contributing to the secondary hardening when tempering at a high temperature. If it is less than 2.0%, precipitation as carbides is insufficient. However, if the content exceeds 8.0%, a net-like coarse carbide is formed. Therefore, the optimum range is set to 2.0% or more and 8.0% or less. V is an element that most strongly contributes to wear resistance because it forms MC-based carbide with extremely high hardness. However, if the content is less than 0.5%, the effect is small. On the other hand, if the content is more than 5.0%, the grindability is impaired.

The basic components of the material of the present invention are as described above. However, depending on the size of the roll to which the material is to be applied, the required characteristics of the roll, etc., the above-mentioned chemical component of the present invention may be used as other chemical components. In addition to the above, the following components may be appropriately selected and added. Ni is dissolved in the matrix to stabilize the austenite of the matrix and improve the hardenability. For this reason, a small amount of 0.2% or more is contained, but if it is contained in excess of 5.0%, austenite is excessively stabilized and austenite remains, making it difficult to secure hardness or during rolling use. May be deformed. It should be noted that the presence or absence of the addition of Ni may be determined as appropriate in consideration of, for example, the size, hardness, and the like of a roll to be manufactured.

W is an element effective to obtain a hard carbide similarly to Mo and to be added particularly when wear resistance is required. If the content is less than 0.2%, the effect is insufficient, and if the content exceeds 5.0%, the carbide becomes coarse. Therefore, the appropriate range is set to 0.2% or more and 5.0% or less. Most of Co is dissolved in the matrix and has an effect of improving the hardness and strength of the matrix. 0.2
%, The effect is insufficient, and if it exceeds 5.0%, the effect is saturated.
% Is desirable. Regarding the presence or absence of the addition of Co, for example, the necessity of the addition may be appropriately determined in consideration of, for example, a reduction in the coefficient of friction in use characteristics.

When B is 0.001% or more, quenching properties are enhanced, and a decrease in toughness can be prevented. But,
If it is excessive, the toughness is reduced, so it is necessary to suppress the content to 0.50% or less. Al, Ti, and Zr generate oxides in the molten metal, reduce the oxygen content in the molten metal, improve the soundness of the product, and form a solidified structure because the generated oxide acts as a crystal nucleus. Is effective for miniaturization of
The effect is 0.001%, but if it is contained too much, it becomes an inclusion and remains in the product.
The upper limits are each set to 0.50%.

Cu strengthens the base structure and improves the high-temperature hardness. When the content is less than 0.001%, the effect is not obtained. On the other hand, when the content exceeds 0.50%, the wear resistance and crack resistance are reduced, and the surface properties of the roll are deteriorated. It is good to In the following, various basic ideas in the present invention, analytical calculations and tests were performed,
Now that the feasibility has been confirmed, it will be described in detail below.

First, in the composite work roll for cold rolling according to the present invention, the heating depth at the time of low frequency progressive induction heating and water quenching, and the resulting microstructure and stress distribution inside the roll will be described.
The basic idea will be described with reference to FIGS.
FIG. 3 is a diagram showing a heating depth at the time of quenching of a conventional roll and a structure and a stress distribution inside the roll after quenching.
As shown in FIG. 3 (a), in the conventional low-frequency progressive induction heating method, and all up to the center of the roll being heated to above the A ₁ transformation point. From this heating state, when water quenching is performed, the outer layer portion of the composite roll is rapidly cooled and undergoes a martensitic transformation expansion. The central part of the core material undergoes pearlite transformation expansion.

Here, the outer peripheral portion of the core material (boundary portion of the roll)
The bainite transformation occurs because the heating temperature is higher and the cooling rate is higher than the central part, but the transformation time is later than the martensitic transformation of the outer layer and the pearlite transformation of the core material center, so the transformation expansion occurs first Tensile stress is generated in the bainite transformation region sandwiched between the outer layer and the center of the core material.
This tensile stress increases as the outer layer becomes thicker. For example, when water quenching is performed in the conventional heating state shown in FIG. 3A as described above, the outer layer thickness exceeds the radius ratio of the work roll to 0.2. And the tensile stress generated in the bainite transformation region of the core material, that is, n1 in FIG. 3 (b) becomes excessive, leading to breakage of the core material. For this reason, conventionally, it was impossible to make the thickness of the outer layer 0.2 or more in the radius ratio of the work roll to the work roll.

Here, the present inventors have focused on the fact that the structure and stress distribution inside the composite roll after quenching change depending on the heating depth before quenching. By controlling the heating depth so that transformation expansion does not occur, the tensile stress generated in the bainite region of the inner layer after quenching is reduced, and the elongation of the core material necessary to withstand the generated tensile stress is ensured. Thus, the thickness of the outer layer is increased.

FIG. 2 is a diagram showing the heating depth at the time of quenching of the roll according to the present invention and the structure and stress distribution inside the roll after quenching. For example, as shown in FIG. 2 (a), the so that the heating temperature of the core center before carrying out the water quenching does not exceed A ₁ transformation temperature, i.e., the center site undergo transformation expansion at hardening By controlling such a heating depth, it was possible to reduce the tensile stress n2 generated in the bainite transformation region of the core material as shown in FIG. 2 (b).

The method of setting the heating depth of the roll in the low-frequency progressive induction heating / water quenching is to change the roll moving (down) speed during the low-frequency progressive induction heating / water quenching. Adjustments are possible.
That is, the heating depth can be made shallower as the moving (falling) speed of the roll is higher, and the heating depth can be made deeper as the moving speed is lower. Another method is disclosed in, for example, Japanese Utility Model Publication No. 3-39482, Japanese Utility Model Application Laid-Open No. 62-11 / 1987.
No. 8160, a low-frequency progressive induction heating / water quenching method may be used. In this case, the input power balance between the upper and lower heating coils provided in the low-frequency progressive induction heating / water quenching apparatus may be adjusted. By changing
It is possible to control the heating depth of the roll.

As described above, in the composite roll of the present invention, the correlation between the thickness of the outer layer, the heating depth, and the required elongation of the core before quenching is clarified as the main parameters resulting from the breakage of the core during quenching. I made it. Furthermore, since the three parameters are closely related to each other, an analysis using the finite element method was performed using each of the parameters as parameters to verify the validity of the theory of the present invention. The analysis
FIG. 1 shows the examination results. FIG. 1 is a calculation result showing the correlation between the outer layer thickness ratio, the heating depth, and the required elongation according to the present invention. The outline of the analysis method by the finite element method is described as a solution at that time, using the heating depth (radius ratio) and the outer layer thickness (radius ratio) indicating the straight lines A and B as input conditions on the horizontal axis in FIG. 1
The vertical axis of the graph indicates that the fracture does not occur after quenching, that is, the required elongation of the core material before quenching is obtained as a solution of the calculation result, and the result is shown in FIG.

In FIG. 1, first, a straight line A shows the calculation result when the outer layer thickness (ratio to radius) is 0.15, that is, the conventional outer layer thickness. As is clear from the figure, when the thickness of the outer layer is as small as 0.15, the required elongation of the core material before quenching is such that the core material does not break after quenching even if the heating depth is set to 1.0 as in the prior art. , About 13%. This result shows that, as shown in FIG. 1, the conventional elongation (maximum) of the core material before quenching is 15%. This clearly demonstrates that the quenching could be performed without breaking the core material.

Similarly, the straight line B is the outer layer thickness (ratio to radius).
However, this is the case of 0.2, which has been difficult to implement conventionally, and if the heating depth is 1.0 as in the past, the required elongation of the core material before quenching is about 22%. This value greatly exceeds the conventional elongation (maximum) of the core material before quenching of 15%, and the core material is broken by quenching. Therefore, in the present invention, as described above, the heating depth (radius ratio) is set to 0.7 or less, and the elongation of the core material is given to 15% or more by the preliminary heat treatment. Due to this, during quenching,
The thickness of the outer layer can be increased without breaking the core material.

Here, the lower limit of the heating depth in the present invention will be described. In the rolling roll targeted by the present invention,
Regardless of the thickness of the outer layer, it is necessary that the entire outer layer be sufficiently baked in order to exhibit sufficient wear resistance in the range of the diameter of the composite roll. For this reason,
It is essential that the heating depth during quenching has a depth not less than the minimum outer layer thickness. In the composite roll structure of the present invention, it is generally said that as the outer layer thickness (ratio to radius) increases, the required elongation of the core material before quenching without breakage of the core material after quenching increases. The above analysis will be described below with respect to the results of analysis and study on the upper limit of the outer layer thickness (ratio to radius) of the present invention.

In FIG. 1, the straight line C is a case where the outer layer thickness (ratio to radius) is 0.4, and if the heating depth is 1.0 as in the prior art, the required elongation of the core material before quenching is as follows. It is about 37%. This value exceeds the practical limit of 35% even if the above-mentioned preliminary heat treatment is performed on the core material. Therefore, in the present invention, as described above, since the heating depth (radius ratio) is set to 0.7 or less, the required elongation of the core material before quenching becomes a practically usable level of about 35% or less. It is possible to increase the thickness of the outer layer without breaking.

Next, the straight line D is the case where the outer layer thickness (ratio to radius) is even larger and 0.45. In this case, as described above, the heating depth (ratio to radius) is 0.7 or less and the outer layer thickness is less than 0.7. Even if the heating depth is 0.45, which is the lower limit, the required elongation of the core material before quenching requires a large elongation of about 37% (point A), which is not a practically usable level. On the other hand, in order to reach the practical limit of 35% (point B), the heating depth must be set to 0.3%.
It is necessary to be not more than 7, and in this case, it is not preferable because sufficient baking is not performed at all the outer depths (outer layer thickness: 0.45). Thereby, the upper limit of the outer layer thickness (radius ratio) in the present invention was set to 0.4 (radius ratio). Based on the above various analysis and examination results, the proper elongation of the core material before the low-frequency progressive induction heating and quenching of the present invention is 15% or more, and the appropriate outer layer thickness is set to a radius ratio of 0.2 to 0.4, An appropriate heating depth range was set to a range of the outer layer thickness or more and the radius ratio of 0.7 or less.

In consideration of the fact that the core material is not broken in low frequency progressive induction heating and water quenching,
Reducing cooling by water quenching is certainly one of the effective measures. However, if the cooling is moderated, it may not be possible to achieve a high hardness of 90 or more in Shore hardness required for the work roll for cold rolling, and this is not the intention of the present inventors. It is an object of the present invention to completely transform the outer layer to martensite to a boundary depth so as to obtain a Shore hardness of 90 or more and to control the transformation of the inner layer to prevent the core material from breaking.

Hereinafter, since the above-mentioned various tests could sufficiently confirm the feasibility of the present invention, examples applied to actual rolling rolls will be described.

Examples Table 1 shows No. 1 as an example of the present invention. Nos. 1 to 4 are comparative examples. 5 to 7. Invention Example No. 1 is
As shown in Table 1, a core material S35C and an outer layer material were used, and a work roll material for cold rolling with an outer layer thickness of 0.255 (radius ratio) was manufactured by continuous casting overlaying and then softened. Annealing was performed. Thereafter, a test piece was collected from the end of the work roll material, and the elongation of the core material before quenching was measured. As shown in Table 1, since the elongation of the core material at this time was 21%, low-frequency induction heating and water quenching were carried out to manufacture actual rolls for cold rolling. Incidentally, the method of low-frequency induction heating quenching, heating depth (A ₁ transformation point: the range of about 726 ° C. or higher) heated under heated conditions the atmospheric becomes 0.6 (vs. radius ratio) than the outer layer thickness becomes 135mm Thereafter, normal water quenching was performed, and thereafter, tempering was performed twice at 500 to 550 ° C. The quenching was completed without any breakage on the way, and the hardness after tempering obtained a good result of Shore 93.

Inventive Example No. Nos. 2 to 4 use the core material SCM440 shown in Table 1 and the respective outer layer materials, and have the respective outer layer thicknesses of 0.364, 0.25, 0.3.
83 (outer layer thickness ratio) of the material for the work roll for cold rolling was manufactured by the continuous casting overlay method, and then all were softened and annealed. In this case, in order to secure the elongation of the core material, in all cases, after the above-described softening annealing, about 10
The blast cooling was performed at a surface cooling rate of about −10 ° C./min from 00 ° C., and then tempering was performed twice at about 720 ° C. Thereafter, test pieces were sampled from the end of each work roll material, and the elongation of the core material before quenching was measured. As shown in Table 1, since it was confirmed that the elongation of the core material at this time had a high elongation of 32, 20, and 30%, low-frequency induction heating and water quenching were performed to perform actual cold rolling. Rolls were made. The method of low-frequency induction heating and water quenching is as follows:
The heating depth (A ₁ transformation point: range of about 726 ° C. or more) is heated under heating conditions of 0.7, 0.6, and 0.5 which are larger than the respective outer layer thicknesses, and then normal water quenching is performed. Then, tempering was performed twice at 500 to 550 ° C. On the way,
The quenching was completed without causing any breakage, and the hardness after tempering obtained good results of Shores 94, 93 and 95.

No. Also in the case of the comparative example of No. 5, No. 5 of the above-described example was used. In the same manner as in 2 to 4, the core material SCM shown in Table 1
440 and an outer layer material, and an outer layer thickness of 0.2
After producing a work roll material for cold rolling of 5 (radius ratio) by a continuous casting overlay method, softening annealing was performed. Then, in the above-mentioned Example No. The same preliminary heat treatment as in Examples 2 to 4 was performed, and thereafter, a test piece was collected from the end of the work roll material, and the elongation of the core material before quenching was measured. As shown in Table 1, since the elongation of the core material at this time was 25%, low-frequency induction heating and water quenching were performed to produce actual rolls for cold rolling. However, in the low frequency induction heating / water quenching, as shown in Table 1, the heating depth was not controlled and the conventional method was used (1.0 to radius ratio). A large tensile force was applied to the material, and the core material was broken.

No. Also in the case of the comparative example of No. 6, No. 6 of the above-described example was used. In the same manner as in 2 to 4, the core material SCM shown in Table 1
440 and an outer layer material, and an outer layer thickness of 0.2
After producing a work roll material for cold rolling of 27 (radius ratio) by a continuous casting overlay method, softening annealing was performed. Then, in the above-mentioned Example No. The same preliminary heat treatment as in Example 1 was omitted, and thereafter, a test piece was sampled from the end of the work roll material, and the elongation of the core material before quenching was measured. As shown in Table 1, although the elongation of the core material at this time was 8%, low-frequency induction heating and water quenching were carried out to produce actual rolls for cold rolling. However, in the low frequency induction heating / water quenching, as shown in Table 1, despite the control of the heating depth to 0.6, a large tensile force acts on the core material after the low frequency induction heating / water quenching. The core material was broken.

No. Also in the case of the comparative example of No. 7, No. 7 of the above example was used. In the same manner as in 2 to 4, the core material SCM shown in Table 1
440 and an outer layer material, and an outer layer thickness of 0.4
After producing a work roll material for cold rolling of 5 (radius ratio) by a continuous casting overlay method, softening annealing was performed. Then, in the above-mentioned Example No. The same preliminary heat treatment as in Examples 2 to 4 was performed, and thereafter, a test piece was collected from the end of the work roll material, and the elongation of the core material before quenching was measured. As shown in Table 1, since the elongation of the core material at this time was 24%, low-frequency induction heating and water quenching were carried out to manufacture actual rolls for cold rolling. However, in the low frequency induction heating and water quenching, as shown in Table 1, despite the execution of the preliminary heat treatment and the control of the heating depth at 0.6, the outer layer thickness (radius ratio) was 0.45. Because of the large size, a large tensile force was applied to the core after low-frequency induction heating and water quenching, and the core was broken.

[0037]

[Table 1]

[0038]

As described above, according to the present invention, it is possible to manufacture a composite work roll having an increased effective diameter by increasing the thickness of the outer layer without causing breakage of the core material during quenching. This contributes to the improvement of units and, consequently, the reduction of manufacturing costs of steel products.

[Brief description of the drawings]

FIG. 1 is a calculation result showing a correlation between an outer layer thickness ratio, a heating depth, and a required elongation according to the present invention.

FIG. 2 is a diagram showing a heating depth during quenching of a roll according to the present invention, and a structure and a stress distribution inside the roll after quenching.

FIG. 3 is a diagram showing a heating depth during quenching of a conventional roll, and a structure and stress distribution inside the roll after quenching.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C22C 38/00 301 C22C 38/00 301L 302 302E 38/24 38/24 38/58 38/58 (72) Inventor Takayuki Koya 46-59, Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka New F-term in the Engineering Division, Nippon Steel Corporation 4E016 CA09 DA03 EA02 FA04 FA14 4K042 AA20 BA03 CA04 CA06 CA07 CA08 CA10 CA13 DA01 DB01 DD02

Claims (3)

[Claims] 1. Around a core material made of cast steel or forged steel,
After forming the outer layer made of a high-speed material by continuous casting and overlaying, in a method of manufacturing a composite work roll for cold rolling manufactured by performing low frequency progressive induction heating and water quenching,
At low frequency gradual induction heating, cold to a depth range to be heated above the A ₁ transformation point of the core material and less 0.7 of the radius of the outer layer of thickness above the work rolls, and then characterized by applying water quenching A method for manufacturing a composite work roll for rolling. 2. A composite work roll for cold rolling manufactured by forming an outer layer made of a high-speed material around a core material by continuous casting and overlaying, and then performing low frequency progressive induction heating and water quenching. During the low frequency progressive induction heating, the core material A
_The depth range heated to ₁ transformation point or more is a thickness of the outer layer and 0.7 or less of the radius of the work roll, and then a cold rolled composite work roll subjected to water quenching, wherein the chemical composition of the outer layer is In mass%, C: 0.9 to 1.5%, Si: 0.2 to 2.5%, Mn: 0.2 to 2.5%, Cr: 4.0 to 10.0%, Mo: 2.0-8.0%, V: 0.5-5.0%, The composite work roll for cold rolling characterized by containing, the balance being Fe and unavoidable impurities. 3. The composition according to claim 3, wherein the outer layer further comprises:
The composite work roll for cold rolling according to claim 2, comprising one or more selected from 5%, W: 0.2 to 5%, and Co: 0.2 to 5.0%.