JP3116585B2 - Manufacturing method of rolls for hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a roll for hot rolling. More specifically, the present invention relates to, for example, a method for producing a hot rolling roll excellent in wear resistance and accident resistance, which is suitable for use as a work roll of a hot finishing mill for steel materials such as a steel plate. .

[0002]

2. Description of the Related Art In order to cope with the trend toward lower costs and higher grades of hot-rolled products, the amount of rolling per unit roll is increased, that is, the abrasion resistance that enables the rolling schedule to be elastic when manufacturing hot-rolled products. The development and commercialization of rolls with excellent properties are being promoted.

For example, Japanese Patent Application Laid-Open No. 1-96355 or Japanese Patent Application Laid-Open No. 2-88745 discloses an outer layer material made of a high-carbon high-alloy material and a shaft core steel material having excellent toughness.
A method of manufacturing a rolling roll using a composite material welded and integrated by a continuous overlay welding method disclosed in Japanese Patent No. 4903 has been proposed.

In the method proposed in Japanese Patent Application Laid-Open No. 1-96355, the material used as the outer layer material is C: 1.5 to 3.5% (hereinafter "%" unless otherwise specified in the present specification).
Means “% by weight”), Si: 0.3 to 3.0
%, Mn: 0.3 to 1.5%, Ni ≦ 2.0%, Cr: 3.0 to 7.0
%, Mo ≦ 8.0%, V: 3.0 to 12.0%, W: ≦ 20.0%, the balance being Fe and inevitable impurities, and C− (0.06Cr + 0.
033W + 0.063Mo + 0.18V) ≦ 1.0 The alloy used as the outer layer material by the method proposed in JP-A-2-88745 is C: 1.0-3.0%, Si: 0.3-2.0.
%, Mn: 0.3 to 1.5%, Nb ≦ 3.0%, Ni ≦ 1%, Cr: 4
~ 10%, Mo: 3 ~ 10%, V: 2 ~ 10%, W: 3 ~ 10%,
Co: An alloy having a composition of 5 to 10%, the balance being Fe and inevitable impurities. In addition, these proposals relate to the outer layer material of the wear-resistant composite roll by the continuous build-up welding method, and the solidification rate of the composite ingot is 10 mm / min or more.

Japanese Patent Application Laid-Open No. 3-56642 discloses that C:
1.5 to 2.5%, Si: 1.2% or less, Mn: 1.2% or less, Cr:
1.5 to 6.0%, Mo + 0.5W: 1.5 to 5.0%, V: 4.5 to
8.0%, balance Fe and unavoidable impurities and C
=% V × 0.24 + (0.4-1.0)% and 0.3Cr + (Mo + 0.5
V) is made of high-carbon, high-vanadium wear-resistant material that satisfies 2.6% or more. It is rich in toughness in the inside of the body and in the shaft, and has an excellent wear resistance and heat resistance in the surface layer. A method for manufacturing a forging roll has been proposed.

[0006] These rolls are made by dispersing a high-hardness MC-type carbide in a layer used for rolling, thereby forming a conventional Ni-type carbide.
It is characterized in that it has extremely excellent wear resistance of about 5 to 15 times compared to a wear-resistant cast iron roll using a Glen cast iron material or a high chromium cast iron material. Therefore, it is possible to significantly increase the rolling schedule such that the rolling amount per unit roll can be increased to 5 times or more of the conventional rolling roll, and it is possible to directly reduce the rolling cost and to reduce the cost in the steel making process. By consolidating production lots, etc., the production cost of steel materials can be significantly reduced.

[0007]

The rolls for hot rolling, especially the rolls for hot finishing rolling, are usually large mass products having an outer diameter of at least 600 mm and a mass of at least 5,500 kg. On the other hand, the rolling layer is 100 mm in diameter.
This is a tool that is used repeatedly while grinding and removing the surface damage layer a plurality of times until a predetermined disposal diameter is reached.

[0008] Therefore, in addition to the magnitude of the amount of wear and the amount of grinding required by ordinary rolling, the difficulty of forming flaws and the depth of flaws when a rolling trouble occurs, that is, the accident resistance, determine the performance of a rolling roll as a tool. This is the most important characteristic in the final evaluation.

[0009] Generally, the performance of such a roll is expressed by the basic unit of roll (roll consumption mass per t of rolling amount: kg /
t, or roll cost: yen / t). For example, if a conventional Ni-grain cast iron roll is installed after the hot finishing mill, the unit roll at the time of the accident will be the total unit of the roll unit at the time of normal rolling and the unit unit at the time of the accident. The basic unit has reached about 5 to 20% of the basic unit, and how to reduce the basic unit of the roll at the time of an accident was an important technical issue in reducing the total basic unit of the roll.

[0010] The need to reduce the basic unit of a roll at the time of an accident becomes more remarkable in the case of a wear-resistant roll. For example, the basic unit of roll during normal rolling is 1/5
Even if it becomes the following, if deep flaws are easily formed on the roll surface at the time of an accident, the overall roll basic unit will be significantly deteriorated. Normally, wear-resistant rolls contain a large amount of expensive alloying elements such as V, Mo, W or Co and have a large roll outer diameter of 600 mm or more. This is because it becomes significantly larger than the conventional rolling roll.

[0011] Furthermore, the wear-resistant rolling roll is excellent in wear resistance (abrasive wear resistance). Conversely, since the roll grinding property is insufficient, once a deep flaw occurs, the flaw is removed. The cost for the roll diameter is 600m
In addition to the fact that it is larger than m, it is extremely bulky, and significantly impairs productivity.

As described above, although it is an urgent technical problem to improve the accident resistance of the abrasion-resistant roll, the accident resistance of the hot-roll roll, particularly, the sheet breakage which significantly deteriorates the basic unit of the roll, is required.・ A material evaluation test method for crack resistance during drawing trouble (drawing crack resistance) has not been established. Therefore, means for drastically improving the accident resistance has not been studied, and it has been difficult to improve the accident resistance of a hot rolling roll having excellent wear resistance.

Here, an object of the present invention is to provide a hot-rolling roll having a roll outer diameter of not less than 600 mm, which is excellent not only in wear resistance but also in accident resistance in view of the above-mentioned problems of the prior art. It is to provide a manufacturing method of.

[0014]

The present inventor has considered that in order to solve the above-mentioned problems, it is necessary to quickly establish a material evaluation test method regarding the above-described draw crack resistance. By the way, the present inventor investigated in detail the flaws (cracks) generated at the time of drawing in the hot finish rolling mill, and found that those cracks occurred as the same phenomenon as the drawn cracks of the forging steel quenching roll for cold rolling. I found that.
In other words, it was found that the roll surface was subject to rapid heating and quenching (thermal shock) accompanied by a structural change under the conditions of local high pressure when the plate was fractured and squeezed, causing cracks.

[0015] Several methods have been developed so far for evaluating the cracking resistance of a forged steel quenching roll material for cold rolling, and among these methods, friction heat generation is a method that can be carried out relatively easily. By applying the quenching method, it has been found that drawing cracks generated in a work roll of a hot finishing mill can be reproduced.

As shown in FIG. 1, the quenching method of friction heat generation uses a fixed test piece 1 (size: 40 × 60 × 25 mm, test piece surface: 40 mm).
× 60 mm) test piece 2 made of mild steel disk 3 rotated at high speed
(Size: 492 × 30 mm in diameter) is pressed for 15 seconds, rapidly heated by friction and immediately cooled with water by jet injection 4, and the depth of cracks generated by changing the pressing load 5, that is, the amount of thermal shock, is investigated. The present inventor has decided to use the frictional heating rapid cooling method shown in FIG. 1 as a test method for evaluating the accident resistance of a hot rolling roll.

As a result of various studies to solve the above-mentioned problems, the present inventor melted an ingot made of a high-carbon high-vanadium wear-resistant material by an electroslag melting method (ESR method). When manufacturing hot rolling rolls with an outer diameter of 600 mm or more, by limiting the composition of the ingot and the solidification rate during smelting to an appropriate range, the hot rolling roll can be manufactured without impairing wear resistance. Knowing that the accident resistance can be significantly improved, the present invention has been completed.

Here, the gist of the present invention is as follows.
C: more than 1.5% and 2.5% or less, V: 4.5-8.0%, Cr: 1.5
Up to 6.0% and Mo + 0.5 W: Made of high carbon high vanadium wear resistant material containing 1.5% or more and less than 5.0%, and using ingots produced by the ESR method at a solidification rate of 6 mm / min or less. It is a roll for hot rolling characterized by the above-mentioned. Further, from another viewpoint, the present invention relates to C: 1.5 to 2.
In a method for producing a hot rolling roll having a roll outer diameter of, for example, 600 mm or more, using a ingot made of a high-carbon high-vanadium wear-resistant material containing 5% and V: 4.5 to 8.0%, the ingot is melted. Is performed by an electroslag melting method, and the solidification rate of the ingot is set to 6 mm / min or less.

[0019]

Hereinafter, the present invention will be described in detail together with the functions and effects. The reason for limiting the composition of the ingot used in the present invention will be described. In the ingot formed by the electroslag melting method used in the present invention, a large amount of granular and high-hardness MC-type carbide is dispersed to secure wear resistance. In order to form the required amount of such MC type carbides, the C content and the V content are limited to 1.5 to 2.5% and 4.5 to 8.0%, respectively.
C content and V content are less than 1.5% and 4.5%, respectively.
%, The amount of carbides generated is insufficient, and the wear resistance cannot be improved to such an extent that the rolling schedule can be greatly expanded. On the other hand, the C content and the V content are each 2.5%.
If it is more than 8.0%, the homogeneity of the solidified structure of the obtained ingot deteriorates.

Cr, Mo + 0.5W: Cr enhances hardenability and increases high temperature tempering hardness.
Mo dissolves in the matrix or precipitates fine carbides in the matrix
To increase hardenability and temper softening resistance,
In addition, W has almost the same effect as Mo at a content of about 1/2 of the Mo content.
Play. Therefore, in the present invention, Cr, Mo and
And W are added to impart heat resistance.

The alloy elements other than C, V, Cr, Mo and W
The content is determined by the present inventor, for example, in JP-A-3-56642.
The composition of the forging roll for hot rolling proposed from the
i: 1.2% or less, Mn: 1.2% or less, if necessary, Ni:
3.0% or less, Co: 5.0% or less, Nb: 2.0% or less and T
i: One or two selected from the group consisting of 2.0% or less
As described above, the remaining Fe and inevitable impurities can be exemplified. this
The reasons for limiting the numerical values of the compositions of these alloy elements will be briefly described.

Si, Mn: Both Si and Mn can be adjusted for deoxidation, improved fluidity, and quenched.
1.2% or less, similar to ordinary steel, for the purpose of improving
It is desirable to make it.

Ni, Co: Since both Ni and Co form a solid solution in the matrix and are effective in increasing hardenability and heat resistance, it is desirable to add them as necessary.

Nb, Ti: The main component of the element forming the hard and granular MC-type carbide is V. However, Nb or Ti also forms the MC-type carbide similarly to V. It is desirable to add.

Compositions other than those described above are Fe and inevitable impurities. In the present invention, for example, a roll for hot rolling having a roll outer diameter of 600 mm or more is manufactured using an ingot made of a high-carbon high-vanadium-based wear-resistant material having the above composition. And the solidification rate of the ingot
It shall be 6 mm / min or less.

In the present invention, ingot smelting is performed by the ESR method because, for example, in a large-mass ingot which is a raw material of a roll for hot rolling having an outer diameter of 600 mm or more, it is easy to adjust the solidification rate during melting. That's why.

The outer diameter of the hot-rolling roll finally produced by the present invention is usually 600 mm or more.
The outer diameter of the ingot is desirably 600 mm or more. In the present invention, the solidification rate during ingot smelting is limited to 6 mm / min or less. In the present invention, the reason for limiting the solidification rate of the ingot to 6 mm / min or less is that better accident resistance than the conventional Ni-glen cast iron material can be easily obtained. In addition, the solidification speed during ingot smelting is significantly reduced.
It is thought that the lower the solidification rate, the better the accident resistance corresponds to the change in the solidification structure.However, at present, it is difficult to quantitatively grasp the solidification structure of high-carbon, high-vanadium wear-resistant materials. As such, the correlation between solidification rate and accident resistance cannot be explicitly mentioned. However, as a result of examining the relationship between the carbide particle size (μm) and the carbide particle number (mm ^-2 ) for the test materials obtained by the friction heating and quenching test conducted by the inventor, it was found that accident resistance was the same for the test materials. Since the specimens with significantly different properties have significantly different carbide particle size distributions, the smaller the solidification rate, the greater the amount of fine V carbides that precipitate during the solidification process, improving wear resistance and improving accident resistance. It is considered that the crystallization amount of the coarse eutectic carbide to be deteriorated is reduced.

Conventionally, ingots for rolling rolls have been melted by the ESR method in some cases. However, the subject is originally a cold rolling roll material or a low alloy having less than 1.5% C. As a hot rolling roll material having an ingot diameter of 600 mm or more, a high carbon high vanadium-based wear-resistant material was applied only to the extent of a hot rolling roll proposed in Japanese Patent Application Laid-Open No. 3-56642. . In contrast,
In the present invention, not only the wear resistance is simply improved, but also the accident resistance is excellent.For example, in order to obtain a hot-rolling roll having an outer diameter of 600 mm or more, the solidification rate is suppressed to 6 mm / min or less. .

As described above, according to the present invention, a roll for hot rolling having an outer diameter of, for example, 600 mm or more, which is excellent not only in wear resistance but also in accident resistance, can be manufactured, and the rolling schedule is greatly reduced. It is possible not only to reduce the cost of the steel material by enlargement or the like, but also to significantly improve the unit consumption of rolls and productivity. Further, the present invention will be described in detail with reference to examples, but this is an exemplification of the present invention, and the present invention is not limited thereto.

[0030]

Example 1 Tables 1 and 2 show the melting conditions and compositions of various ingots subjected to a frictional heat quenching test conducted by the present inventors. Melting was performed by the ESR method. Table 1
The solidification rate (mm / min) in, strictly indicates the dissolution rate of the ingot in the ESR method, but is substantially the same as the growth rate of the ingot, that is, the solidification rate, and is therefore described as the solidification rate. In addition, test material No. 1 to test material No. 3 shown in Table 2,
And the test material No. 5 is a high-carbon, high-vanadium-based wear-resistant material disclosed by the present inventor in JP-A-3-56642, and the test material Nos. 1 to 3 are almost the same. Because of the composition, by comparing these test materials, it is possible to directly evaluate the influence of melting conditions, particularly the solidification rate, on accident resistance.

A test material was cut out from the surface layer of these ingots, collected, tempered to a hardness of Hs 80 by quenching and tempering, and the pressing load was changed in the range of 100 to 300 kgf. Was subjected to a frictional heat quenching test shown in FIG. Also,
As a comparative material, a test piece was also collected from the surface of a Ni-grain cast iron roll with an outer diameter of 760 mm by the centrifugal casting composite method. did.

The results are shown in a graph in FIG. From the figure, if the solidification rate is 6.0 mm / min or less, the crack depth is 5 mm or less even if the pressing load is 250 kgf, and the crack depth of the conventional Ni-gran cast iron is 250 kgf with the pressing load of 250 kgf.
Considering that it is 10 mm or more, it can be seen that the accident resistance was significantly improved.

[0033]

Example 2 An ingot having the smelting conditions shown in Table 3 and the component composition shown in Table 4 was produced by the ESR method, and a work roll for hot finish rolling having a diameter of 600 mm or more was produced from this ingot.

These work rolls for hot finish rolling are:
Table 5 compares the results of use when installed on rolling mills A and B with those of conventional rolls (Ni-glen cast iron rolls) and high-carbon high-alloy composite rolls.
Are shown together.

From Table 5, it can be seen that the hot-rolling roll manufactured according to the present invention is extremely excellent in accident resistance and has a remarkably improved roll basic unit as compared with a conventional roll or a high-carbon high-alloy composite roll. You can see that there is.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 5]

[0040]

As described in detail above, according to the present invention, a roll for hot rolling which is excellent not only in wear resistance but also in accident resistance can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a procedure of a frictional heat quenching test used in a material evaluation test on accident resistance.

FIG. 2 is a graph showing a result of a frictional heat quenching test in Examples.

[Explanation of symbols]

 1: Test piece 2: Test piece surface 3: Mild steel disc 4: Jet injection 5: Pressing load

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C22C 38/12 C22C 38/12 (56) References JP-A-3-56642 (JP, A) JP-A-6-63743 (JP) JP-A-5-78729 (JP, A) JP-A-3-248703 (JP, A) JP-A-1-96355 (JP, A) JP-A-2-88745 (JP, A) JP 53-80351 (JP, A) JP-A-53-28057 (JP, A) JP-A-53-61524 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 23/10 522 B21B 27/00 C22C 38/00 301 C22C 38/00 302 C22C 38/12

Claims (2)

(57) [Claims] (1) C: more than 1.5% and not more than 2.5% by weight,
V: 4.5-8.0%, Cr: 1.5-6.0% and Mo + 0.5
W: High-carbon high-vanadium wear-resistant material containing 1.5% or more and less than 5.0%, and 6 mm / mi by ESR method
A roll for hot rolling, characterized by using an ingot produced at a solidification rate of n or less. 2. C .: 1.5 to 2.5% by weight and V:
In a method of manufacturing a roll for hot rolling using an ingot made of a high-carbon high-vanadium-based wear-resistant material containing 4.5 to 8.0%, the ingot is melted by an electroslag melting method and the ingot is melted. A method for producing a roll for hot rolling, wherein the solidification speed of the roll is 6 mm / min or less.