JP3242767B2 - Composite roll for hot rolling with continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to rolls for steel rolling, such as hot strip mills, and has excellent wear resistance especially in hot rolling and also has crack resistance.
The present invention relates to a composite roll for hot rolling by continuous cast overlaying .

[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. Furthermore, in Japanese Unexamined Patent Publication No. WO91119824A proposed by the present applicant, C is set to 1.5 to 2.4.
% Limits the amount of fragile carbides and improves crack resistance.

[0003]

The most important characteristics required for a rolling roll include abrasion resistance and crack 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. In this respect, the roll materials disclosed in JP-A-58-87249 and WO91119824A are all very good in wear resistance because the generated carbide itself is hard and the hardness after quenching is high. On the other hand, if the crack resistance is insufficient, cracks will occur due to heat and mechanical load during use, and the wear of the roll will increase even though the abrasion resistance is good by removing the generated crack, and as a result Decreases performance. JP WO 91198
In No. 24A, the amount of fragile carbide was limited by limiting C to 1.5 to 2.4%, and improvement under ordinary rolling conditions was achieved.

However, when the rolling operation becomes unstable and the rolled product is locally rolled with two or more rolls, generally called "drawing", a part of the product is seized on the roll surface and extremely high heat and A mechanical load was applied, resulting in a deep crack in the roll. As a result, there was an example in which the performance of the roll was significantly reduced.

Accordingly, an object of the present invention is to provide a composite roll for rolling which has improved wear resistance especially in hot rolling and has good crack resistance even in the event of a rolling trouble.

[0006]

In order to solve the above-mentioned problems, the gist of the present invention is to provide a continuous casting method around a steel core material.
For hot rolling of continuous cast overlay with outer layer formed
In the composite roll, the chemical composition of the outer layer is expressed by weight % , and C is 0.8 to 2.3% V 3 to 10% Cr 3 to 7% W 11.02 % to 15% At least one of Mo, Ni, and Co 1% or more and 10%
Less than, with the balance substantially consisting of iron
For between successive Ikake padding made hot rolling a composite roll.

[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. Therefore, the wear resistance is improved, but the brittle carbides increase, so that a deep crack is generated when a mechanical or thermal overload is applied, and the crack resistance of the roll material as a whole is reduced.

[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, while producing a fine, minute and extremely hard MC-type VC carbide to improve wear resistance, the carbide is directly and preferentially crystallized as a primary crystal carbide from the molten metal, It is especially important in controlling the organization. That is, if V is less than the lower limit of 3% in the range of 0.8 to 2.3% of C, hard VC carbides are hardly crystallized, and even if crystallized, solid carbides are dissolved in the base structure by the subsequent heat treatment to form precipitates. It becomes a carbide and cannot achieve the wear resistance targeted by the present invention. On the other hand, if it is 10% or more of the upper limit, carbides increase and the crack resistance and the rough surface resistance are impaired.

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. Particularly hard M ₇ C ₃ carbides have been used in roll materials, but they form as eutectic carbides at crystal 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 or an M ₆ C-type carbide which is difficult to assemble is formed together with V, and a part is solid-dissolved in the base material. The hardenability as a material was given, the hardness of the base was also increased, and the wear resistance was improved. That is, it is indispensable to contain 3% or more in order to form MC type carbide or M ₆ C type carbide which is hard to be dispersed and to increase the hardness of the matrix. On the other hand, the upper limit value must be 7% or less so as not to impair the crack resistance due to crystallization of coarse carbides.

The limitation of W to 11.02 to 15% is a major feature of the present invention, and has an effect of improving crack resistance particularly when a rolling trouble occurs. W is also easily bonded to C and forms MC or M ₆ C-type carbide in the material of the present invention, but a part of it is dissolved in the matrix. Conventionally, as an effect of W, attention has been paid only to the improvement of wear resistance due to crystallization of a carbide such as M ₂ C or M ₆ C and tempering at a high temperature. However, it has been confirmed that the W dissolved in the matrix by the repeated tests of the inventors suppresses the structural change when heated to a high temperature, and has the effect of reducing the thermal contraction and the transformation expansion even in the subsequent cooling. I found it. Therefore, by reducing the structural change (white portion in the figure) of the roll material immediately below the steel sheet seizure portion as shown in FIG. Reduce cracks. If the lower limit is 11.02 % or less, the solid solution of W in the matrix is small, and a practical effect cannot be obtained. If the upper limit is 15% or more, a large amount of carbides such as M ₂ C or M ₆ C will crystallize out, resulting in embrittlement of the roll material as a whole and impairing the overall crack resistance.

As other main alloying elements, Mo, N
Addition of appropriate amounts of i and Co is useful for improving the roll performance. Mo is easily bonded to C like Cr,
Part of the roll material of the present invention is MC or M ₆ C
Formed carbides are formed, and a part thereof forms a solid solution with the matrix, exerts a precipitation hardening effect particularly at a high temperature, improves the hardness of the matrix, and improves the wear resistance especially in hot rolling. On the other hand, Ni or Co, which forms a solid solution with V, Cr, W, and Mo, which are likely to form carbides, has an effect of improving hardness and strength particularly at high temperatures and improving roll performance. The lower limit at which these effects are practically recognized is 1
% Or more. However, since Mo, Ni, and Co are all very expensive, the upper limit is set to 10% in relation to cost.

[0012] In addition, due to the deoxidation of the molten metal, etc.
0.5% each of useful elements Si and Mn
The impurities of P and S may be contained as long as they are about 0.03% or less contained in ordinary castings, and these do not impair the effects of the present invention at all.

[0013]

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 production qualities of the conventional example and the embodiment of the present invention. FIG. 1 shows a metallographic micrograph of the material of the present invention. The conventional examples and examples 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 a shallow crack due to a stoppage of the roll rotation due to a motor trip generated during normal rolling, has extremely good wear resistance, and has a very small crack depth caused by a "drawing" trouble. became. It is evident that the overall roll performance of the new roll, taking into account roll wear due to the removal of cracks in the event of trouble, has been greatly improved and reduced, and the productivity of the rolling operation has been significantly improved.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

By applying the present invention to a roll for steel rolling, it is possible to stably supply a high-performance roll with remarkably improved wear resistance and crack resistance. The productivity and economy in rolling operation 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 cross section of a steel sheet seizure at the time of drawing trouble.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rolled material 2 Roll base material 3 Roll material with changed structure 4 Crack

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tamotsu Kawakami 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works (56) References JP-A-5-230592 (JP, A JP-A-5-169216 (JP, A) JP-A-63-199092 (JP, A) JP-A-5-320819 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 302 B21B 27/00 C22C 38/36

Claims (1)

(57) [Claims] (1) The steel core is surrounded by a continuous casting method.
Composite Roll for Hot Rolling by Continuous Casting Overlay with Layers
In Lumpur, chemical composition of the outer layer by weight%, C 0.8~2.3% V 3~10% Cr 3~7% W 11.02% ~15% Mo, Ni, at least one Co 1% or more and 10%
Less than, with the balance substantially consisting of iron
Continuous Ikake padding made hot rolling composite roll.