JPH06271903A - Roll material for high-performance hot rolling - Google Patents

Abstract

PURPOSE:To produce the roll material for hot rolling which exhibits excellent surface roughening resistance and wear resistance by uniformly dispersing hard particles specified in grain size and inter-particle distance into a metallic matrix such as iron. CONSTITUTION:The hard particle powder having >=0.1mu to <=5mu grain sizes is added into the metallic matrix of iron, nickel, aluminum or cobalt and the mixture is uniformly mixed, is molded to the shape of a roll and is sintered by an HIP method and adjusted in such a manner that the inter-particle distance attains about >=0.3 to <=2 times the grain sizes. A metal carbide, nitride, oxide or boride having >=1100 Vickers hardness is used for the hard particles. As a result, the roll for hot rolling which exhibits the excellent wear resistance and surface roughening resistance is obtd. The production efficiency is improved by decreasing roll exchange frequencies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll material which is used in hot rolling of a thin steel sheet, particularly in a finishing stand, and exhibits excellent surface roughening resistance and abrasion resistance.

[0002]

2. Description of the Related Art A roll used for hot rolling a thin steel sheet has various surface damages such as wear and roughening because its surface is frictional under high temperature and high surface pressure.
Since the surface damage of the roll directly affects the size, shape and surface quality of the product to be rolled, the development of the prevention technique is a very important issue in rolling. Therefore, many roll materials have been developed so far that surface damage hardly occurs. Most of them are related to chemical composition, casting method, or heat treatment method.

From the viewpoint of the metallographic structure according to the present invention, there are few conventional techniques for improving the surface roughening resistance and the abrasion resistance, but for example, JP-A-56-20145 and JP-A-3-3145
-404 publication, etc., respectively, carbide lengths 200-4
A roll material having a diameter of 50 μm and a width of 50 to 100 μm and a primary carbide having an average particle diameter of 5 to 30 μm is disclosed. However, although the needs for improving the wear resistance and surface roughening resistance of rolls are becoming stronger with the progress of rolling technology, the optimal metallographic structure such as the size and distribution of carbides is not clear and the manufacturing technology Since it has not been established, the roll properties of these conventional materials cannot be said to be satisfactory.

It is empirically known that an excellent roll material can be obtained by refining the metal structure. However, since the conventional material roll manufacturing method is mainly a casting method, a fine metal structure is obtained. Is difficult. Therefore, application of the powder metallurgy method is considered as a new method for obtaining a fine structure, and is disclosed in JP-A-4-59901 and the like.
It only specifies the type and size of the raw material powder, not the viewpoint of optimizing the microstructure of the product after sintering.

[0005]

In the present invention, in order to derive a roll material far superior to the conventional one, an optimum material design was attempted from the viewpoint of the surface damage mechanism of the hot rolling roll. That is, the wear of the hot rolling roll is caused by the abrasion of the matrix due to the particles existing on the friction surface.
It is thought that the properties of the hard particles in the tissue strongly control the roll characteristics, since the rough skin is mainly due to the destruction (cracking) and the removal (crack propagation) of hard particles such as carbides in the roll tissue. . Therefore, an object of the present invention is to provide a roll material having excellent wear resistance and rough surface resistance by optimizing the size and distribution of hard particles in the structure.

[0006]

In order to solve the above problems, the present invention is characterized by applying a powder metallurgy method to control the metal structure of a roll material to improve wear resistance and rough surface resistance. To do. That is, the gist of the present invention is as follows. (1) In an iron, nickel, aluminum or cobalt metal matrix, hard particles having a particle size of 0.1 μm or more and 5 μm or less and an interparticle distance of 0.3 times or more of the particle size, 2
A roll material for hot rolling, which has a metallographic structure in which it is uniformly dispersed so as to be double or less. (2) The roll material for hot rolling according to (1) above, wherein the hard particles are metal carbide, nitride, oxide, or boride having a Vickers hardness of 1100 or more. It is in. In addition, a metal matrix here points out the metal base material for hold | maintaining a hard particle.

[0007]

The inventors of the present invention first observed the surface of the hot-rolled roll used for rolling in detail with an electron microscope, and found that the matrix had innumerable abrasion marks, which were interrupted by carbides. However, it became clear that some carbides were cracked due to thermal stress and were about to fall off. Abrasion traces are often found when the matrix is soft and the area is large, and carbide cracks are significant when the size is large. In general, the carbides, which are ceramics, are harder than the metal matrix, so that the matrix wears first. The depth of the abrasion mark is almost the same as the wear depth when the abrasion mark is rubbed enough times to cover the entire area. You can When the matrix undergoes abrasive wear first and carbides are left behind and protrude, high surface pressure concentrates there, and the temperature due to friction also rises, which in turn causes the carbides to break off, or to be consumed by oxidation. By repeating this, wear progresses. Here, when the size of the carbide is small, it is excavated together with the matrix and falls off, and when it is large, stress concentrates on it and the fracture easily occurs, and it falls off in large units. lose. Also, in the latter case where the unit of destruction and dropout is large, the unevenness of the surface becomes large,
It also causes rough skin.

On the other hand, the mechanism of rough skin is the development of rolling fatigue cracks in the presence of thermal fatigue cracks in addition to the above-mentioned ultimate process of wear. Since the propagation direction of this crack is almost parallel to the surface, the surface layer is locally dropped off, and especially when an oxide film is generated on the outermost surface, the dropped portion is conspicuous.
It becomes extremely rough. These fatigue cracks first enter the carbide, and when the carbide size is large and the distribution thereof is rough, the size of the surface layer that falls off is also large.

From the mechanism as described above, it has been clarified that the properties of hard particles such as carbides are dominant in wear resistance and rough skin resistance, and that a fine structure is preferable. However, there is a limit in obtaining a fine structure by a casting method which is a conventional manufacturing method of roll materials. There is a powder metallurgy method as a manufacturing method in which a fine structure can be remarkably obtained as compared with the conventional method and the structure can be easily controlled. And, in this case, as hard particles,
In addition to carbides, nitrides, oxides, borides, etc. can be used. The matrix is preferably a metal such as iron, nickel, aluminum or cobalt which has high strength and toughness and is easily available. The roll material of the present invention can be obtained by sufficiently uniformly mixing these powders, molding them into a roll shape, and applying the HIP method or the like to sintering. At this time, the particle size and mixing ratio of the powder should be adjusted so as to be consistent with the present invention after sintering.

Next, the reasons for limiting the size of these hard particles and the distance between the particles will be described. First, the smaller the hard particle size that is the origin of thermal cracking, the finer the crack size, and the smaller the size of the surface layer that eventually falls off, which is preferable from the viewpoint of resistance to rough skin. However, the size of the abrasive particles that cause wear is 0.1 from the trace of abrasion.
Since the hardness at room temperature is estimated to be around Hv1100, the effect is required only if the size of the hard particles that prevent abrasion is 0.1 μm or more and the hardness is Hv1100 or more. If it is smaller than that, it cannot be a barrier of abrasion and is abraded or cut together with the matrix by the abrasive particles. Therefore, the lower limit of the hard particle size is 0.1 μm.
Thus, from the viewpoint of wear resistance, it seems that a larger hard particle size is preferable, but if it is too large, the surface roughness will be large when it protrudes on the surface, and it will break down due to stress concentration. The upper limit is set to 5 μm from the viewpoint of the surface roughness preferable for the hot-rolling roll, because the unit for increasing the size also becomes large. Also, in terms of skin roughness, a surface roughness exceeding 5 μm is not preferable.

Finally, the interparticle distance was determined as follows from the optimum content of hard particles. That is, it can be easily understood that the wear resistance is inferior when the amount is small, but when the amount is too large, the amount of the matrix that holds the hard particles decreases, so that the particles easily fall off, and the distance between the particles is close. Then, the cracks are connected and the surface layer is likely to drop off. The appropriate area ratio of the particles obtained empirically is 10 to 40%, and the distance between particles when the particles are spherical is 0.3 to 2 times the particle diameter.

[0012]

[Examples] The following experiments were conducted using a hot wear tester using high frequency, which has been conventionally said to be able to well simulate wear and surface roughness of rolling rolls. S45C was used for the counterpart piece corresponding to the rolled material, and current high-chromium cast iron and the present invention materials A, B, and C were used for the test piece corresponding to the roll, and hot wear experiments were conducted under the conditions shown in Table 1. Table 2 shows the types of hard particles, the hardness and the distance between particles, and the types of matrix contained in the test material. Specimen A, B, C are H
The type, particle size and mixing ratio of the powder produced by the IP method and used are shown in the same table. For comparison, a conventional material, high chromium cast iron (HCR) was used, which was manufactured by a casting method.

As an experimental result, the amount of wear is shown in FIG. It can be seen that each of the materials of the present invention exhibits wear resistance twice or more that of the conventional material. Next, FIG. 2 shows the surface roughness profile of the test piece after the experiment as an index of skin roughness. It can be seen that the materials A, B and C of the present invention have smaller roughness than the conventional material HCR and have excellent resistance to roughening.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

As described above, when the material according to the present invention is used for the hot rolling finishing roll of a thin steel sheet, it exhibits excellent wear resistance and rough surface resistance.
The frequency of roll replacement is reduced, which makes it possible to improve production efficiency, reduce the unit consumption of rolls, and improve product quality.

[Brief description of drawings]

FIG. 1 is a result of a hot wear experiment conducted to compare the wear resistance of the roll material of the present invention (A, B, C) and the conventional material (HCR).

FIG. 2 is a surface roughness profile which is also an index of skin roughness.

Claims (2)

[Claims] 1. An iron, nickel, aluminum or cobalt metal matrix having a particle size of 0.1 μm or more,
A roll material for hot rolling having a metal structure in which hard particles of 5 μm or less are uniformly dispersed so that the distance between particles is 0.3 times or more and 2 times or less of the particle diameter. 2. The roll material for hot rolling according to claim 1, wherein the hard particles are a metal carbide, a nitride, an oxide, or a boride having a Vickers hardness of 1100 or more.