JPH10277611A - Composite work roll for high wear resistance cold rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite work roll for cold rolling excellent in wear resistance. SOLUTION: In this composite work roll, an outer layer part consisting of, by weight, 0.9-1.5% C, 0.3-1.0% Si, 0.3-1.0% Mn, 4.0-10.0% Cr, 3.0-8.0% Mo, 0.5-5.0% V and the balance Fe with inevitable impurities is formed on the circumference of the core material which is composed of cast steel by a continuous cladding method by thickering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work roll used for cold rolling of steel.

[0002]

2. Description of the Related Art Conventionally, forged steel containing 5 to 7% Cr has been applied as a work roll for cold rolling of steel. In recent years, Japanese Patent Publication No. 61-11310 or Japanese Patent Publication No.
Mo, such as a roll disclosed in -68588,
The application of so-called semi-high-speed rolls to which small amounts of V, W, etc. are added is expanding.

[0003]

Generally, these conventional work rolls for cold rolling have undergone a complicated process of producing a steel ingot by an electroslag melting method and performing a quenching and tempering heat treatment through a forging process. . In the heat treatment, severe quenching is performed by rapidly cooling from a high temperature using techniques such as progressive induction heating and water quenching in order to secure a high hardness of Hs 90 or more. Conventionally, the electroslag melting method, which has been applied as a casting method for a work roll for cold rolling, has a low solidification rate and tends to coarsen crystal grains or carbides. If the crystal grains and carbides become coarse, quenching cracks will occur during quenching. Therefore, in order to ensure sufficient material strength and elongation, a prior forging step is indispensable. It was suppressed to about 0.9%, and it was necessary to suppress any of the alloys such as Mo, V, and W. Therefore, there is a limit in improving the wear resistance of the roll.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to achieve a finer structure by increasing the solidification rate, to realize a high alloying which was impossible with the prior art, and to achieve excellent wear resistance. It is to secure. In the case of an integrated roll formed from a large ingot, it is difficult to secure a high solidification rate, and by using a composite structure with a small volume of molten metal,
It can be realized more easily. That is, in the composite work roll for high wear resistance cold rolling of the present invention, the outer layer portion has a weight percentage of C: 0.9 to 1.5%, Si: 0.3 to 1.0%,
Mn: 0.3 to 1.0%, Cr: 4.0 to 10.0%,
Mo: 3.0 to 8.0%, V: 0.5 to 5.0%, the balance being Fe and unavoidable impurities, and a core material composed of cast steel or forged steel. . Further, Ni may be contained in the outer layer at 5% or less for the purpose of improving hardenability or strength.

The reason for limiting the components of the outer layer will be described below. C is an important element for obtaining hardness. If the C content is less than 0.9%, the amount of C dissolved in the matrix becomes insufficient, so that sufficient matrix hardness cannot be obtained, and at the same time, high alloying becomes difficult. However, if the content exceeds 1.5%, the carbides become coarse and the strength decreases, so the upper limit was made 1.5%.
Particularly, a preferable range is more than 1.0% and 1.3% or less.

[0006] Si is an element required as a deoxidizing agent, and is required to be 0.3% or more to exhibit its effect, but if it exceeds 1%, it is not preferable because it becomes brittle. Mn is similar to Si,
It is an element necessary as a deoxidizing agent. To exhibit its effect, 0.3% or more is necessary. However, if it exceeds 1%, embrittlement is not preferred. Cr is easily bonded to C and forms an M ₇ C ₃ -based carbide, and is an element necessary for securing wear resistance. However, if the amount is small, sufficient wear resistance cannot be secured. And tends to develop into a net-like shape, resulting in a decrease in toughness. The optimum range is 4% or more and 10% or less.

[0007] Mo is an element that gives a hard carbide and strongly contributes to the secondary hardening when tempering at a high temperature. If it is less than 3%, precipitation as carbide is insufficient. However, if it exceeds 8%, it becomes a net-like coarse carbide. Therefore, the appropriate range is set to 3% or more and 8% or less. In particular, it is preferably in the range of 4% to 6%. V is an element that most strongly contributes to wear resistance because it forms an MC-based carbide with extremely high hardness. But 0.5
If it is less than 5%, the effect is small, and if it exceeds 5%, the grinding property is impaired. Therefore, the range is set to 0.5% or more and 5% or less. In particular, when brilliancy is required, it is preferable to suppress the content to 2% or less from the viewpoint of grindability.

[0008] Ni has the effect of improving the hardenability. When a large curing depth such as a roll having a large diameter is required, it may be added according to the requirement. But 5%
If it exceeds 90%, the residual austenite becomes excessive and a high hardness of Hs 90 or more cannot be obtained, so the upper limit is set to 5%. Since W coarsens carbides, its addition should be avoided in the present invention. Si and Mn are both deoxidizing materials and are indispensable elements from the viewpoint of fluidity of the molten metal, and may be contained in an amount contained in general high-speed steel. These do not have any effect on the effects of the present invention, but the appropriate range is from 0.3% to 1.0%.

[0009] The component system of the roll according to the present invention is designed to have a higher C and higher alloy than conventional rolls in order to improve the wear resistance. If the solidification speed is slow, carbides become coarse. There is a possibility of inducing cracks during quenching. In order to ensure a high solidification rate, a composite structure is one of the effective means. As a means for producing the composite roll, it is preferable to use a continuous casting overlaying method disclosed in Japanese Patent Publication No. 44903/1988 which can obtain a particularly high solidification rate. The continuous casting overlay method is a method in which a molten metal is introduced while being heated by a heating coil so as to form an outer layer in a gap between a steel material serving as a core material and an annular cooling die set therearound, and has a small solidification volume. Therefore, there is a feature that a high solidification rate can be secured.

In order to ensure excellent abrasion resistance and to reliably avoid burning cracks during heat treatment, the crystal grain size in the solidified structure is desirably 150 μm or less. For that purpose, it is desirable that a solidification speed of 15 mm / min or more is secured. In that case, the carbide to be crystallized is also extremely fine, so that the forging step can be omitted. Here, the crystal grain size means a crystal grain size at the time of solidification, and means a region surrounded by a eutectic carbide. FIG. 1 shows the definition of the crystal grain size. The solidification rate obtained by the continuous casting overlay method naturally has a limit, and the limit is at most 30 μm. However, in this crystal grain size range, the grain size and the carbide content are required to avoid quenching cracks during heat treatment. It is desirable that the size is smaller.

Incidentally, the composite work roll for high wear resistance cold rolling according to the present invention has a feature which is greatly different from the conventional cold rolling roll in the outer layer structure.
That is, the M ₆ C-type eutectic carbide exists in a net shape. It is already known that the greater the amount of carbide, the better the wear resistance and seizure resistance. But,
From the viewpoint of ensuring the resistance of the eutectic carbide in the form of net to quenching cracking during quenching, limit the amount of C and alloy so that the eutectic carbide in the form of net does not crystallize during casting, or split the carbide by forging. In addition, measures such as miniaturization have been taken.

[0012]

【Example】

Example 1 Sample materials were melted with each component system shown in Table 1, and normalization was performed. Thereafter, test pieces of φ40 × 100 were cut out and quenched and tempered. During the smelting, the solidification rate was changed by adjusting the thickness of the sand mold to prepare samples having different particle sizes. In Comparative Examples 1 and 2, the amount of C and the amount of alloy are larger than the component ranges of the present invention, and in Comparative Example 3, the crystal grains are coarser than the range of the crystal grain size of the present invention. For the conventional materials 1 and 2, samples were collected from actual rolls. Conventional material is based on electroslag melting method. Conventional material 1 is 5% Cr
The forged steel, conventional material 2 is a semi-high-speed forged steel. Further, the conventional material 1 is a component system in which the M ₆ C-type eutectic carbide does not crystallize. As a characteristic evaluation, a thermal shock test and a cold wear test were performed. In the thermal shock test, after heating and holding at a certain temperature for 30 minutes,
It was immediately dropped into water, quenched, and checked for cracks, and the maximum temperature at which cracks did not occur was determined. In the cold abrasion test, the sample was austenitized at 900 to 1200 ° C., quenched, and tempered at 100 to 600 ° C.
The test was performed using a Nishihara-type abrasion tester after ensuring hardness of s90 or more.

The evaluation results are shown in Table 1 and FIG. In the range of the components and the crystal grain size of the present invention, it was found that all of them had higher wear resistance than the conventional material due to high C and high alloying. Although these have a high C and a high alloy, they have the same thermal shock resistance as the conventional material, and can withstand severe heat treatment without forging. However, as shown in Comparative Examples 1 and 2, when the amount of C or the amount of the alloy is excessive, the carbides are coarsened, so that the thermal shock resistance is greatly reduced, and quenching may occur in the quenching step. Further, as can be seen from Comparative Example 3, even if the structure becomes coarse, the thermal shock resistance decreases.

[0014]

[Table 1]

Embodiment 2 As an embodiment of the present invention, an outer layer material composed of the components shown in Table 2 was continuously welded around a core material made of SCM440 by a cladding method for cold rolling with a body diameter of φ450 and a body length of 1500. A composite work roll was prototyped. Quenching was performed by low frequency progressive induction heating and water quenching. The forging process was omitted. Low frequency progressive induction heating and water quenching are performed at a quenching temperature range of 900 to 1200 ° C, and tempering is 100 to 60
The test was performed twice or more in a temperature range of 0 ° C. In each case, the high C and high alloy components were designed as compared with the conventional roll material, but high hardness could be secured without breaking in severe heat treatment. FIG. 2 shows the hardness distribution of the obtained roll. N
It is understood that the addition of i is effective for improving the hardness depth. When these rolls were used in actual rolling, the conventional 5% Cr
The service life is more than three times that of forged steel rolls and more than twice that of semi-high-speed forged steel rolls, and the frequency of roll replacement is greatly reduced.

[0016]

[Table 2]

[0017]

According to the present invention, a rolling roll having extremely excellent wear resistance can be provided, and the efficiency of rolling can be improved by reducing the frequency of roll replacement.

[Brief description of the drawings]

FIG. 1 is a micrograph (magnification × 100) of a structure for explaining the definition of the crystal grain size in the present invention.

FIG. 2 is a graph showing a relationship among a eutectic carbide area ratio, a thermal shock temperature, and a crystal grain size in Examples.

FIG. 3 is a diagram illustrating a hardness depth of a roll in an example.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsuo Hashimoto 46-59, Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Machinery & Plant Division (72) Inventor Katsushi Hokimoto Tobata-ku, Kitakyushu-shi, Fukuoka Nakahara 46-59 New Nippon Steel Corporation Machinery & Plant Division

Claims (5)

[Claims] C .: 0.9 to 1.5%, Si: 0.3 to 1.0%, Mn: 0.3 to 1.0%, Cr: 4.0 to 10.0% by weight. %, Mo: 3.0 to 8.0%, V: 0.5 to 5.0%, and the remainder is continuously cast around a core material made of cast steel or forged steel with an outer layer portion made of Fe and inevitable impurities. A highly wear-resistant composite work roll for cold rolling, formed by a build-up method. 2. The method according to claim 1, wherein the outer layer further comprises Ni5
% Of a high wear-resistant composite work roll for cold rolling. 3. The outer layer portion according to claim 1, wherein the outer layer portion is composed of a net-like eutectic carbide mainly composed of M ₆ C, granular MC carbide, tempered martensite, and retained austenite, and has a hardness of Hs 90 or more. A composite work roll for cold rolling, which has high wear resistance. 4. The composite work roll for cold rolling according to claim 3, wherein the area ratio of the net-like eutectic carbide is 5% or more. 5. The method according to claim 4, wherein the outer layer portion has a crystal grain size of 1
A highly wear-resistant composite work roll for cold rolling, having a thickness of 50 μm or less.