JP3195777B2 - Outer layer material of rolling roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an outer layer material of a rolling roll, and more particularly to an outer layer material of a rolling roll which can be preferably used for a hot rolling roll.

[0002]

2. Description of the Related Art In a rolling roll for hot rolling, a material constituting an outer layer portion is generally required to have rough surface resistance, wear resistance, accident resistance and the like. Examples of roll materials that can meet such demands to some extent include, for example, JP-A-1-96355 and JP-A-2-88745.
High carbon-based high-speed materials, such as those disclosed in Japanese Unexamined Patent Application Publication Nos. WO 88/07594 and WIPO International Publication WO 91/19824, are known. The high-speed material contains Cr, Mo, W, V, etc. in a few percent each, and has good wear resistance at high temperatures.
Suitable as an outer layer material for hot rolling rolls.

[0003]

However, the conventional high-speed steel material has a large thermal crown and a low friction coefficient due to a structure mainly composed of a hard MC-type carbide as compared with a conventional cast iron roll. Due to the large size, there is a problem that the sheet passing property is poor and a drawing accident is apt to occur. Seizure easily occurs due to a drawing accident or the like, and in that case, there is a problem that cracks, particularly deep cracks, easily occur. Because of the above-mentioned problems, it could hardly be used as a finishing stand for hot sheet rolling, particularly a final stand where the sheet thickness is reduced.

Accordingly, the present invention solves the problem when the above-mentioned high-speed material is used as the outer layer material in the rolling roll, and can reduce the thermal crown, reduce the drawing accident, and improve the sheet passing property. An object of the present invention is to provide an outer layer material of a rolling roll that has a large toughness value and hardly causes cracks, and hardly develops even if cracks occur.

[0005]

In order to solve the above-mentioned problems, the outer layer material of the rolling roll according to the present invention is such that the material constituting the outer layer portion of the roll is C: 1.5 to 3.0% by weight, S:
i: 0.2 to 1.5%, Mn: 0.2 to 1.5%, C
r: 3.0 to 5.0 %, Mo: 5.0 to 8.0 %, W:
5.0 to 8.0% V: with containing 3.0 to 6.0%, the balance being substantially Fe, casting and anneal
Once the outer layer material is austenitized,
In the temperature range between the site transformation point and the martensitic transformation point
The austempering and subsequent tempering
Repeated one to several times to obtain carbides in the tissue
Area ratio of M ₇ C ₃ ≦ (M ₂ C + M ₆ C + MC) / 1
0, and (M ₂ C + M ₆ C) / MC ≧ 2 , and the base is 8
It is characterized by having a structure comprising 0% or more of bainite and less than 20% of tempered martensite.

According to the above-mentioned feature of the present invention, by forming a rolling roll using an outer layer material having a component and a structure limited in the above-mentioned feature, reduction of thermal crown while maintaining good wear resistance is achieved. Thus, it is possible to reduce the drawing accident, improve the sheet passing property, and improve the crack resistance. Therefore, according to the rolling roll using the outer layer material of the present invention, it can be sufficiently applied not only as a general hot rolling roll but also as a work roll for a hot thin-rolled finishing stand. In the outer layer material of the present invention, the proportions of the contained components and the carbides are limited as described above to reduce the MC type carbide and the M ₇ C ₃ type carbide, while the M ₂ C type carbide and the M ₆ C type carbide are reduced. By doing so, the coefficient of thermal expansion and the coefficient of friction could be reduced as compared with the conventional outer layer material mainly composed of MC type carbide and M ₇ C ₃ type carbide .
Reduction before SL reduction of thermal expansion coefficient and friction coefficient thermal crown of the rolling rolls, the reduction of aperture accidents, reducing the baking accident,
This leads to improved threadability. In the outer layer material of the present invention,
By setting the amount of bainite in the base structure to 80% or more and the amount of tempered martensite to less than 20%, compared to a conventional outer layer material mainly containing tempered martensite,
The toughness of the material can be improved. Therefore, the fracture toughness value is improved, and the crack generation resistance at the time of a drawing accident or seizure accident is improved, and the crack propagation resistance is greatly improved. Further, by increasing the amount of bainite and reducing the tempered martensite, the residual stress of the material can be reduced, and spalling and delayed fracture at the time of occurrence of an accident can be reduced. Incidentally, there is almost no decrease in hardness due to bainite conversion of the base, and there is little concern about a decrease in wear resistance.

A production example of the outer layer material of the rolling roll of the present invention will be described. First, a material having a predetermined component composition is cast from a general casting temperature, and then softened and annealed to facilitate machining and prevent cracking. After softening annealing, for example, after sufficiently holding at 800 to 1000 ° C.,
The base is made into a pearlite structure by slow cooling. FIG. 1 shows a specific softening annealing work process.

After the soft annealing is completed, necessary machining and the like are performed on the material, and then an austempering process is performed. In the austempering process, first, 1000
After the temperature is sufficiently maintained at １1200 ° C., for example, for 10 to 15 hours, the temperature range between the bainite transformation point (Bs point) and the martensitic transformation point (Ms point) at a rate of 150 ° C. or more per unit time, for example, 300 Cool to a temperature range of 400 to 400 ° C and hold sufficiently in that temperature range, for example, 10 to 15
Hold for hours. And after the austempering process,
The first tempering is performed by sufficiently holding at 500 to 600 ° C., for example, for 10 to 15 hours. Then, if necessary,
The second austempering process is similarly performed in the temperature range between the bainite transformation point and the martensite transformation point,
The second tempering is performed in the same manner. The bainite transformation of the base is completed by one or two austempering processes. If necessary, the third tempering process is performed under general conditions. FIG. 2 shows specific working steps of the austempering process.

The difference between the above-mentioned austempering treatment and the conventional treatment in the present invention is that in the conventional heat treatment of the outer layer material with this type of high-speed steel material, the temperature near or below the Ms point during quenching, for example, 50 to 200. This is a point that the cooling after the first tempering was performed, the cooling was performed to the Ms point or lower, and the process of the next tempering was performed.

The reason for limiting the content range of each component element in the outer layer material of the rolling roll of the present invention will be described below. C
Is 1.5% by weight or more and 3.0% by weight or less. C combines with Cr, Mo, W, and V to form carbides of high hardness, such as M ₇ C ₃ , M ₂ C, M ₆ C, and MC, and enhances the wear resistance of the rolling roll. If the content is less than 1.5% by weight, the amount of carbide generated is insufficient, and the hot wear resistance is insufficient. On the other hand, when the content is 3.0% by weight or more, the amount of carbides increases, and toughness and heat crack resistance decrease. Therefore, the upper limit is set to 3.0% by weight. Preferably 1.6 to 2.4% by weight
And

The content of Si is not less than 0.2% by weight and not more than 1.5%.
% By weight or less. Si is an element necessary for ensuring the fluidity of the molten metal. On the other hand, to improve the toughness of the material, the lower the content, the better. Therefore, the content is set to 0.2 to 1.5% by weight. Preferably, it is 0.4 to 1.0% by weight.

The content of Mn is not less than 0.2% by weight and not more than 1.5%.
% By weight or less. Mn has a function of increasing the curing ability. On the other hand, to improve the toughness of the material, the lower the content, the better. Therefore, the content is set to 0.2 to 1.5% by weight. Preferably 0.
4 to 1.0% by weight.

The content of Cr is 3.0% by weight or more and 8.0% or more.
% By weight or less. Cr partially dissolves in the matrix to strengthen the matrix. On the other hand, it is easy to crystallize a high hardness M ₇ C ₃ type eutectic carbide. When the amount of the M ₇ C ₃ type eutectic carbide increases, cracks easily develop. Therefore, the content of Cr is set to 3.0 to 8.0% by weight. Preferably 3.0 to 5.
0% by weight.

The content of Mo is 4.0% by weight or more.
0% by weight or less. Mo forms an M ₆ C-type or M ₂ C-type composite carbide, increases normal-temperature hardness and high-temperature hardness, and contributes to improvement of wear resistance. It also improves hardenability. If the amount is less than 4.0% by weight, the amount of the M ₆ C-type and M ₂ C-type composite carbides formed will be insufficient, while if it exceeds 12.0% by weight, the amount of carbides will be too large, which is not preferable. Therefore, the content of Mo is set to 4.0 to 12.0% by weight. Preferably 5.
0 to 8.0% by weight.

The content of W is not less than 4.0% by weight and 12.0%.
% By weight or less. W also combines with C to form a composite carbide of mainly M ₆ C type and M ₂ C type,
Increases high temperature hardness and contributes to improvement of wear resistance. It also improves hardenability. If it is less than 4.0% by weight, the above M ₆ C type,
While the amount of the M ₂ C-type complex carbide is insufficient, 1
If it exceeds 2.0% by weight, the amount of carbides becomes too large, which is not preferable. Therefore, the content of W is 4.0 to 12.0% by weight.
And Preferably, it is 5.0 to 8.0% by weight.

The content of V is not less than 3.0% by weight and not more than 8.0% by weight. V is easily associated with C and mainly forms M
It forms C-type carbide and contributes to improvement of wear resistance. If it is too large, the amount of MC-type carbide increases, and the coefficient of friction is increased, which is not preferable. Therefore, the content of V is set to 3.0 to 8.0% by weight. Preferably, it is 3.0 to 6.0% by weight.

The content of Co is 10.0 weight or less (including the case of 0 weight%). Co forms a solid solution in the matrix, increases the hardness of the matrix, increases the solid solution amount of carbide-forming elements such as Cr and Mo in the matrix at a high temperature, lowers the Ms point, facilitates the formation of bainite, and reduces friction. This has the effect of reducing the coefficient and coefficient of thermal expansion and improving crack resistance. 10.0% by weight
Is exceeded, the effect is saturated.
To 10.0% by weight. Preferably, it is 3.0 to 7.0% by weight.

The content of Ti is 0.5% by weight or less (including 0% by weight). Ti has an action of granulating the generated MC type carbide. However, if it exceeds 0.5% by weight, square Ti carbides are crystallized, which has an adverse effect. Therefore T
The content of i is 0 to 0.5 weight percent. Preferably, it is 0.1 to 0.2% by weight.

The basic concept of the present invention regarding carbides is to minimize the amount of crystallization of M ₇ C ₃ type carbides in order to reduce the occurrence of cracks. In order to increase the coefficient and worsen the sheet passing property, it is made to keep it low.
And, instead of these M ₇ C ₃ type carbides and MC carbides, the carbide composition is mainly composed of M ₂ C type carbides and M ₆ C type carbides. The total amount of the carbide is preferably about 15 to 20%.

[0020]

EXAMPLES Examples of the outer layer material of the rolling roll of the present invention will be described below. With the target content shown in FIG.
Nos. 1 to 4 according to the present invention, Each material of Comparative Examples 5 to 6 was cast as an outer layer portion of a rolling roll, and then subjected to softening annealing according to the procedure shown in FIG. 1, and then a test piece was processed from the outer layer portion of the roll. The austempering process was performed on the samples 1 to 4 according to the procedure shown in FIG. In Comparative Examples 5 and 6, ordinary quenching and tempering treatments were performed. FIG. 4 shows the area ratio occupied by each carbide and the area ratio occupied by bainite and tempered martensite in the matrix structure in the structure of each of the obtained test pieces. Next, in order to evaluate the thermal crown and crack resistance of the roll, the thermal expansion coefficient, friction coefficient, compressive strength, and fracture toughness value were measured. The results are shown in FIG.

As shown in FIG. In the case of Nos. 1 to 4, it can be seen that as the carbide ratio, M ₆ C + M ₂ C is sufficiently large, M ₇ C ₃ is sufficiently reduced, and MC is also reduced. As a base organization, 85
% Of bainite and less than 15% of tempered martensite. Also, from FIG.
Each of the material Nos. In the case of Nos. 1 to 4, it was confirmed that a low coefficient of thermal expansion, a low coefficient of friction, and an improvement in fracture toughness were confirmed, and that high hardness was maintained.

[0022]

According to the present invention, the outer layer material of the rolling roll according to the first aspect of the present invention has the MC type by limiting the contained components and the carbide ratio as described in the first aspect. While reducing carbides and M ₇ C ₃ type carbides,
_{Since the amount of 2} C-type carbide and M ₆ C-type carbide is increased, it is possible to sufficiently reduce the coefficient of thermal expansion and the coefficient of friction as compared with the conventional outer layer material mainly composed of MC-type carbide and M ₇ C _3- type carbide. did it. Therefore, by reducing the coefficient of thermal expansion and the coefficient of friction, it was possible to reduce the thermal crown of the rolling roll, reduce the drawing accident, reduce the seizure accident, and improve the sheet passing property. Further, in the outer layer material of the present invention, the amount of bainite in the base structure is set to 80% or more and the amount of tempered martensite is set to less than 20%. The toughness was able to be sufficiently improved. Therefore, by the improvement of the toughness, it is possible to improve the crack generation resistance at the time of the drawing accident and the seizure accident, and to significantly improve the crack propagation resistance. In addition, by increasing the amount of bainite and reducing the tempered martensite, the residual stress of the material can be reduced, and spalling and delayed fracture at the time of occurrence of an accident can be reduced. Of course, there is almost no decrease in hardness due to bainite conversion of the base, and there is little decrease in wear resistance. From the above, by forming a rolling roll using the outer layer material of the present invention, while maintaining good abrasion resistance of the roll, reduction of thermal crown, reduction of drawing accident, improvement of sheet passing property and crack resistance Improvement can be achieved.
Therefore, the rolling roll using the outer layer material of the present invention can be sufficiently applied not only as a general hot rolling roll but also as a work roll for a hot thin plate rolling finishing stand.

[Brief description of the drawings]

FIG. 1 is a view showing an operation process of softening annealing of an outer layer material according to an embodiment of the present invention.

FIG. 2 is a view showing work steps of an austempering process of an outer layer material according to the embodiment of the present invention.

FIG. 3 shows each test piece No. of Example of the present invention. Nos. 1 to 4 and each of the test material Nos. It is a figure which shows the component in 5-6, and its target content.

FIG. 4 shows an area ratio occupied by carbide for each test piece,
It is a figure which shows the area ratio which bainite and tempered martensite occupy in a base structure.

FIG. 5 is a view showing measurement results of a coefficient of thermal expansion, a coefficient of friction, and a toughness value of each test piece.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Kobe 403 Yoshimi, Otsu-ku, Himeji-shi, Hyogo Pref. 176840 (JP, A) JP-A-5-148510 (JP, A) JP-A-1-96355 (JP, A) JP-A-11-61322 (JP, A) JP-A-5-287437 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 B21B 27/00

Claims (1)

(57) [Claims] The material constituting the outer layer portion of the roll is, as weight percent, C: 1.5 to 3.0% Si: 0.2 to 1.5% Mn: 0.2 to 1.5% Cr : 3.0~ 5.0% Mo: 5.0~8.0% W: 5.0~8.0% V: with containing 3.0 to 6.0%, the balance being substantially Fe Consisting of a casting
And the softened and annealed outer layer material is austenitized once
Between the bainite and martensitic transformation points
Austempering in a temperature range of
By repeating the return process once or several times, the set
The area ratio of carbides in the weave is calculated as M ₇ C ₃ ≦ (M ₂ C + M ₆ C +
MC) / 10, and a _{(M 2 C + M 6 C} ) / MC ≧ 2
And, the outer layer material of the rolling roll, characterized in that the base of consisting 80% or more of bainite and less than 20% tempered martensite structure.