JPH05271875A - Wear resistant roll material for hot rolling - Google Patents

Abstract

PURPOSE:To reduce the frequency of the exchange of a roll for finishing in hot rolling by uniformly dispersing >= two kinds of carbides having prescribed grain diameter into a matrix of bainite or the like to regulate its area ratio into a prescribed one and to improve its wear resistance. CONSTITUTION:The objective wear resistant roll for hot rolling is formed of a metallic structure obtd. by uniformly dispersing carbides into a matrix having a bainitic or martensitic structure so as to regulate its area ratio into 5 to 50%. As for the carbides, their grain diameter is regulated to 1 to 50mum, and their kinds are constituted of M2C and M6C (M: Mo, W, V and Nb). The roll using the material is used in a finish stand in hot rolling for a thin steel sheet. Then, it shows excellent wear resistance and surface roughening resistance.

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 wear resistance and surface roughening resistance.

[0002]

2. Description of the Related Art In a roll used for hot rolling a thin steel sheet, the surface of the roll is friction under high temperature and high surface pressure conditions, so that various surface damages such as wear and roughening occur. Since the surface damage of the roll directly affects the size, shape and surface quality of the rolled product, the development of the prevention technique is a very important issue in rolling. Therefore, many roll materials have been developed conventionally. They are chemical constituents,
Most of them are related to casting method or heat treatment.

As conventional techniques for improving wear resistance from the viewpoint of the metallographic structure according to the present invention, there are, for example, JP-A-60-170323 and JP-A-03-404. However, the needs for improving the wear resistance and the surface roughening resistance of the rolls are becoming stronger as the rolling technology progresses, and the roll characteristics are not satisfactory because the size and type of carbides are inappropriate.

[0004]

In the present invention, an optimum carbide design was attempted from the viewpoint of the wear mechanism, using a wear simulation tester for hot rolling rolls. That is, wear of the hot-rolled roll is mainly caused by abrasion by hard particles (scratch), and because it is controlled by the properties and amount of carbides present in the metal structure, the type of carbides,
The purpose was to optimize the size and quantity. Here, the carbide means a primary carbide that is crystallized during solidification.

[0005]

The gist of the present invention for solving the above problems is as follows. A metal structure in which carbides having a grain size of 1 μm or more and 50 μm or less and kinds of M ₂ C and M ₆ C are uniformly dispersed in an area ratio of 5 to 50% in a matrix of bainite or martensite structure. The material of the roll for hot rolling.

The inventors of the present invention firstly observed the surface of the hot-rolled roll used for rolling in detail by an electron microscope, and found that the matrix had numerous scratches (ablation), which were interrupted by carbides. However, it became clear that the coarse carbide was destroyed by thermal stress and was about to fall off. Furthermore, since the depth of the abrasion mark is almost the same as the abrasion depth when the abrasion rubs enough times to cover the entire area, it can be said that this abrasion mechanism is dominated by abrasion. it can.

When the matrix undergoes abrasive wear and the carbides project, high surface pressure concentrates there, and the temperature due to friction also rises, causing the carbides to fracture and fall off. By repeating this, wear progresses. Here, if the size of the carbide is large, stress concentrates, causing fracture and drop, which loses the wear resistance effect and causes rough skin. From the above-mentioned wear mechanism, it is presumed that in order to improve wear resistance, it is effective to disperse more tough and fine carbides uniformly in the matrix at a high temperature of around 500 ° C.

There are various kinds of carbides in steel such as M ₃ C, M ₇ C ₃ , M ₂₃ C ₆ , MC, M ₆ C and M ₂ C, depending on the kind of alloying element M, but the physical properties are different. Not only the values but also the morphology and distribution are different. For example, the softest one is M ₃ C and the hardest and most brittle one is MC.
Further, it is M ₃ C that tends to become a coarse lump, and M ₆ C, M ₂ C, MC, etc. that tend to be finely dispersed. here,
Not only one type of M also forms a solid solution or substitutes with other types, so that carbides having various properties may actually exist. Therefore, if the characteristics of these carbides are known, it is possible to design an ideal wear-resistant roll material by coping with the above-mentioned wear mechanism.

From such a viewpoint, the inventors first set the types of carbides to M ₆ C and M ₂ C types. M is Mo, W,
V, Nb, etc. The form of these carbides is a finely branched dendritic form, or a fine lump form, uniformly dispersed at appropriate intervals. Since the MC type has a fine morphology but is fragile, it is easily broken by thermal stress, and it is presumed that it may drop off and lose its effect or cause rough skin, so it was excluded.

Next, the reasons for limiting the size and amount of these carbides will be described. Since the size of the abrasive grains estimated from the abrasion traces on the roll surface is 1 to 10 μm, the size of the carbide embedded in the matrix to prevent abrasion is not effective. If it is smaller than that, it cannot serve as a barrier of abrasion, and carbide is excavated or cut together with the matrix by the abrasive grains. Therefore, the lower limit of the carbide size is set to 1 μm. The upper limit was set to 50 μm because carbides on the roll surface exceeding 50 μm are likely to crack and fall off to lose the effect.

If the amount of carbides is simply increased, the abrasion resistance is increased, but if the area ratio exceeds 50%, the amount of the matrix holding the carbides is reduced, so that the carbides are liable to drop off. Is less than 5%, the effect is lost, so the upper and lower limits were set.

Finally, as the type of matrix, bainite or martensite, which is excellent in strength and toughness in order to firmly hold the carbide and to increase the scratch resistance by the abrasive grains, is selected, and these are selected.

[0013]

The wear of the hot rolling roll is mainly caused by abrasion with abrasive grains having a size of 1 to 10 μm. Therefore, an appropriate amount of hard carbide of 1 to 50 μm is uniformly dispersed in a tough matrix. By using the material of the invention, the wear resistance can be remarkably improved.

[0014]

[Examples] The following experiments were conducted using a hot wear tester utilizing high frequency, which is conventionally said to be able to well simulate rolling roll wear. S45C was used for the counterpart piece corresponding to the rolled material, and the current high-chromium cast iron and the present invention materials A, B, and C were used for the test piece equivalent to the roll, and hot wear experiments were conducted under the conditions shown in Table 1. Chemical composition of test material (% by weight)
And Vickers hardness Hv (10) are shown in Table 2.
The size of the mating piece is 160 mmφ × 15 mmt, and the size of the test piece is 80 mmφ × 10 mmt.

[0015]

[Table 1]

[0016]

[Table 2]

FIG. 1 shows an example of the roll material of the present invention (A, B,
It is the result of the hot wear experiment performed in order to compare the wear resistance of C) and the example (HCR) of the conventional material. As is clear from FIG. 1, the rolls (A, B, C) of the present invention had very good wear resistance. On the other hand, the conventional HCR has poor wear resistance.

[0018]

When the material of the present invention is used for the hot rolling finishing roll of thin steel sheet, it exhibits excellent wear resistance, so that the frequency of roll replacement is reduced, the production efficiency is improved and the roll unit consumption is reduced. Is possible.

[Brief description of drawings]

 FIG. 1 is a diagram showing the wear resistance of the roll material.

Claims (1)

[Claims] 1. A matrix having a bainite or martensite structure having a particle size of 1 μm or more and 50 μm or less,
An area ratio of carbides of M ₂ C and M ₆ C is 5
A wear-resistant hot-rolling roll material having a metal structure uniformly dispersed so as to be 50% to 50%.