JP2978384B2 - Roll material for hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a roll for steel rolling such as a hot strip mill, and in particular, has excellent wear resistance in hot rolling, and has both crack resistance and rough surface resistance. The present invention relates to a roll material for rolling.

[0002]

2. Description of the Related Art In recent years, this type of roll material has been disclosed in
C2.4- disclosed in JP-A-8-87249.
A wear-resistant cast iron roll material containing 3.5%, V6.1 to 14%, and each alloy element of Cr, Mo, W, and Co was employed to improve wear resistance. Further, in Japanese Unexamined Patent Publication No.
By setting the content to 2.4%, the amount of carbide was limited, and the crack resistance was improved.

[0003]

The most important characteristics required of a roll for rolling include abrasion resistance, crack resistance and surface roughness resistance. If the wear of the roll is small, the accuracy of the thickness of the rolled steel product is improved, and the frequency of changing the roll is reduced, so that the work efficiency is improved. On the other hand, if the crack resistance is insufficient, cracks occur due to heat and mechanical load during use, causing a serious trouble, interrupting the rolling operation, and eventually damaging the rolling equipment. Further, in order to improve the surface quality of a rolled product, a beautiful surface roughness of the roll surface is required. Therefore, it is strongly desired to combine the above-mentioned respective characteristics. With respect to this point,
Both the roll materials disclosed in Japanese Patent No. 87249 and Japanese Patent Application Laid-Open No. WO 91119824A have extremely good wear resistance because the generated carbide itself is hard and the hardness after quenching is high. Further, in Japanese Patent Application Laid-Open No. WO 9119824A, the amount of brittle carbide is limited by limiting C to 1.5 to 2.4%, and the crack resistance is improved.

However, in the case of rolling, especially in a use condition in which the heat load during rolling is large, for example, in the case of performing a large amount of rolling as a work roll for a finishing pre-rolling mill of a hot strip mill, the roll surface is partially minute. Peeling occurred, resulting in rough skin from the starting point. As a result, the roll surface was transferred to the rolled product and the quality of the product was impaired, and the roll had to be replaced in spite of little roll wear. Thus, the quality of the rolled product and the productivity were impaired by the rough surface of the roll.

Accordingly, an object of the present invention is to provide a high-performance rolling material having improved abrasion resistance particularly in hot rolling and having both good crack resistance and rough surface resistance.

[0006]

In order to solve the above-mentioned problems, the rolling material of the present invention has a chemical composition of 0.8 to 2.3% V 3.0 to 9.9% Cr by weight. 3 to 7% Mo, W contains at least one kind of 1% or more and less than 5%,
The balance consists essentially of iron and is C% -0.235V%
The carbon equivalent% represented by the following formula is -1.0 to 0.5% ,
Only the MC type carbide is crystallized on the roll after
A roll material for hot rolling , wherein crystallization of carbides is suppressed .

[0007]

The reason for limiting the C content to the above range of 0.8 to 2.3% is as follows. That is, C is the lower limit 0.8
%, Hard carbides are less crystallized and wear resistance is remarkably deteriorated. On the other hand, if it exceeds the upper limit of 2.3%, the wear resistance is improved, but the amount of carbides increases, and coarse carbides are formed and aggregate at crystal grain boundaries. This causes the oxide film formed on the roll surface to fall off from the roll surface due to thermal fatigue during rolling, resulting in partial peeling and roughening of the surface. The improvement of rough skin resistance, which is the main purpose of the present invention, cannot be expected.

[0008] The V content is the most important factor that determines the form and amount of carbides, and is selected in balance with C. In particular, in the case of the material of the present invention, in addition to forming a fine and minute MC carbide of MC type which is very hard to improve wear resistance, this carbide is directly and preferentially crystallized as primary carbide from the molten metal, It is especially important in controlling the organization. First, if V is less than the lower limit of 3.0%, hard VC carbides are hardly crystallized, and even if crystallized, they are solid-dissolved in the base structure by subsequent heat treatment to become precipitated carbides.
On the other hand, if it exceeds 9.9% of the upper limit, the absolute amount of VC carbide will increase, and the crack resistance and the rough surface resistance will be impaired. Further, in the present invention, the carbon equivalent represented by the formula of C% -0.235V% was introduced as a characteristic value that affects the roll performance due to the change of other carbides and the base structure due to the formation of VC carbide. In the above ranges of the C and V contents,
If the upper limit is more than 0.5%, coarse and brittle carbides other than MC-type carbides, such as M ₂ C, M ₃ C, M ₇ C _{3 and the} like, are aggregated and formed at the crystal grain boundaries. The carbides fall off the roll surface, thereby impairing the rough surface resistance. On the other hand, if the lower limit value is -1.0% or less, the crystallization of the VC carbide is inhibited, and as a result, the wear resistance is reduced.

The reason for limiting Cr to 3 to 7% is as follows. Cr easily bonds with C and forms M ₃ C, M ₂₃ C ₆ and M ₇ C ₃ carbides. Especially hard M ₇ C ₃
Although carbides have been used in the past, they are formed as eutectic carbides at grain boundaries, resulting in rough surfaces and cracks. Therefore, in the roll material of the present invention, in order to suppress and disperse coarse carbides, a minute MC type carbide is formed together with V and a part of the carbide is dissolved in the matrix to impart hardenability as a roll material. The hardness of the base was also increased and the wear resistance was improved. That is, in order to form a hard MC carbide and increase the hardness of the matrix, it is essential to contain 3% or more. On the other hand, the upper limit is, for example, M
_The content must be 7% or less so as not to impair the rough surface resistance and crack resistance due to crystallization of coarse carbides such as ₇ C ₃ and M ₃ C.

It is useful to add appropriate amounts of Mo and W as other main alloy elements to improve the roll performance. All of them are easily bonded to C like Cr, and in the roll material of the present invention, a part forms MC carbides and a part forms a solid solution with the matrix to improve the hardness of the matrix. The effect is remarkable. The lower limit at which this effect is practically recognized is 1% or more. However, since the coarse M ₂ C or M ₃ C carbide is formed more than Cr, the upper limit of the material of the present invention is less than 5% under the use condition of a large heat load, which is the greatest feature, so as not to impair the rough surface resistance. Limited.

[0011] On the other hand, V, Cr, M
Ni or Co, which preferentially forms a solid solution with o and W in the matrix, has an effect of improving hardness and strength at high temperatures and improving roll performance. However, since both Ni and Co are very expensive, it is useful to add 5% or less in view of cost.

Si is a useful element in the melting technique for deoxidizing the molten metal, and it is necessary to contain 0.3% or more. However, if the content exceeds 1.5%, which is the upper limit, the toughness is reduced. Therefore, even if the form and amount of the carbide are appropriate, the base structure is embrittled and the object of the present invention cannot be achieved.

Further, Mn, which is a useful element in the melting technique, is about 0.5%, and P and S impurities may be contained as long as they are about 0.03% or less contained in ordinary castings. Of course, these do not impair the effects of the present invention at all.

[0014]

EXAMPLE As a working example of the present invention, a work roll for a hot strip finishing mill was manufactured. For casting,
The composite roll was prepared by a continuous casting method disclosed in Japanese Patent Application Publication No. 152576 and employing forged steel (SCM440) as a core material. The heat treatment was performed after casting, followed by annealing, quenching and tempering.

Table 1 shows specific chemical components and production quality of the conventional example and the example of the present invention. FIG. 1 is a photograph of a metal microstructure of the roll material of the present invention, and FIG.
This shows a conventional example disclosed in 9119824A. In each of the photographs, the white portions are carbides.
In all of the conventional examples, the amount of coarse carbides is large, and a large amount of carbides aggregated in a network at crystal grain boundaries is recognized. On the other hand, it is clearly confirmed that only the very fine and granular carbides are uniformly dispersed in the material of the present invention shown in FIG. 1 as described above. In addition, as shown in Table 1, the invention materials 1 of the present application,
The amount of the network-like carbides in the crystal grain boundary of No. 2 is extremely small as compared with the conventional example. The amount of the network carbides at the crystal grain boundaries was measured by image analysis from a metallographic micrograph.

[0016]

[Table 1]

[0017]

[Table 2]

The conventional example and the embodiment of the present invention shown in Table 1 were actually used in a hot strip finishing mill, and the results are shown in Table 2. The roll of the present invention has shallow roll cracks caused by troubles such as stoppage of roll rotation due to a motor trip during use, has extremely good wear resistance,
And the rolling durable tonnage until transfer to the rolled material occurs due to the occurrence of the peeling of the oxide film on the roll surface,
Improved rough skin resistance. It is evident that this reduces the frequency of changing rolls and significantly improves the productivity of the rolling operation.

In this embodiment, the material of the present invention is applied as an outer layer material by a continuous casting method using forged steel as a core material. However, the present invention is not limited to this manufacturing method. The same operation and effect can be obtained by using an outer layer material by a method or a single roll material by an ordinary casting method or an electro-slag melting method.

[0020]

By applying the present invention to a roll for steel rolling, it is possible to stably supply a high-performance roll having significantly improved wear resistance and crack resistance, and to have improved surface roughness resistance. The quality of rolled products and the productivity and economics of rolling operations have improved.

[Brief description of the drawings]

FIG. 1 shows a metallographic micrograph (× 100) of a roll material disclosed in the present invention.

FIG. 2 is a metallographic micrograph (× 100) of a roll material disclosed in Japanese Patent Application Laid-Open No. 2-152576.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-180548 (JP, A) JP-A-3-126838 (JP, A) JP-A-2-25205 (JP, A) 80351 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 37/00 B21B 27/00 C22C 38/00 302 C22C 38/24

Claims (1)

(57) [Claims] 1. The chemical component contains at least one of C 0.8 to 2.3% V 3.0 to 9.9% Cr 3 to 7% Mo, W by weight in an amount of 1% or more and less than 5%,
The balance substantially of iron, and a carbon equivalent% represented by the following formula is a -1.0～0.5%, MC-type roll after casting
Crystallizes only carbides and suppresses crystallization of other carbides.
A roll material for hot rolling, characterized in that: Carbon equivalent% = C% −0.235V%