JPH11254007A - Composite work roll for cold rolling excellent in resistance to accident - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve resistance to accident (spalling) without lowering the wear resistance (hardness) of an outer layer material. SOLUTION: In the composite roll for cold rolling the outer layer material is formed around the core material by a continuous tinkering build-up method. The core material is composed of low-alloy steel containing, by weight, at least 0.3-0.7% C, 0.5-3.0% Cr, 0.1-2.0% Mo and the component of the outer layer material consists of, by weight, 0.9-1.5% C, 4.0-10.0% Cr, 2.0-8.0% Mo, 0.5-5.0% V and the balance Fe with inevitable elements. The compressive residual stress in the outermost layer part of the outer layer is <=60 kgf/mm<2> and also its hardness is Shore hardness of >=90.

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. 7-6
Mo, V, such as a roll disclosed in US Pat.
The application of so-called semi-high-speed rolls to which a small amount of W or the like is added is expanding. By the way, it is known that the compressive residual stress of the roll surface greatly contributes to the surface hardness of the roll. For example, as disclosed in Japanese Patent Application Laid-Open No. 5-169112, it is intentionally high to secure high hardness. It has been proposed to provide a compressive residual stress. In fact, conventional work rolls for cold rolling perform rapid cooling by progressive induction heating and water quenching in order to achieve high hardness of Hs 95 or more, and tempering at a low temperature of 200 ° C. or less so as not to impair the hardness, High compressive force of 70 kgf / mm ² or more remains on the roll surface.

[0003]

Due to the high residual stress of the conventional work roll for cold rolling, intense spalling often occurs during use, and there is a strong demand for improvement in accident resistance.

[0004]

As described in JP-B-7-68588, a conventional work roll for cold rolling performs rapid cooling by progressive induction heating and water quenching to ensure a high hardness of Hs 95 or more. 200 without loss of hardness
Tempering is performed in the low temperature range below ℃. Further, the structure is such that the roll and the shaft are of the same component system, and the material strength inside the body is extremely large. As a result, the compressive residual stress of the roll body was at an extremely high level when it was 70 kgf / mm ² or more. Therefore, intense spalling often occurs due to internal defects or cracks generated on the roll surface during rolling,
There has been a strong demand for improved accident resistance.

Accordingly, the present invention provides a composite structure using a low-alloy steel having a low yield strength as a core material, and further restricts the components of the outer layer so that the hardness is not impaired even when subjected to high-temperature tempering at 500 ° C. or more. , Compressive residual stress is 60kgf /
Thus, it is possible to manufacture a work roll for cold rolling having a low hardness of not more than ² mm and a high hardness having a Shore hardness of 90 or more and having excellent accident resistance.

That is, the work roll for cold rolling excellent in accident resistance of the present invention and the method for producing the same are represented by C:
0.9 to 1.3%, Cr: 4.0 to 9.0%, Mo:
2.0 to 6.0%, V: 0.5 to 5.0%, and the balance is F
e and an outer layer portion composed of unavoidable impurities are formed around the core material made of low alloy steel or carbon steel by continuous casting overlaying, quenching is performed as cast, and 500 to 600
Tempering in a temperature range of ° C., wherein the compressive residual stress on the outer layer surface is 60 kgf / mm ² or less.

In the present invention, the amount of C is increased so as to enable tempering at a high temperature of 500 ° C. or more, and a large amount of Mo effective for secondary curing is contained. In addition, in the steel ingot obtained by the conventional ESR melting method, carbide is coarsened, which causes quenching cracking at the time of quenching.
The addition amount of o was limited to at most 2%. However, in the present invention, the structure is refined by applying the continuous casting method, and high alloying is made possible while suppressing generation of coarse carbides.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the components of the outer layer are 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 1.3%, the carbides become coarse and the strength decreases, so the upper limit was made 1.3%. 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 from 4% to 9%.

Mo is an element from which hard carbides can be obtained and which strongly contributes to secondary hardening when tempering is performed at high temperatures. If it is less than 2%, precipitation as carbide is insufficient. However, if it exceeds 65%, it becomes a net-like coarse carbide, so its appropriate range is set to 2% or more and 6% or less. 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
%, The effect is small, and if it exceeds 5%, the grindability is impaired. Therefore, the range is set to more than 0.5% and 5% or less.

Ni has the effect of improving 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%. Si and Mn are both deoxidizing materials and are indispensable elements from the viewpoint of the fluidity of the molten metal, and contain the amounts contained in general high-speed steel. Has no effect.

A feature of the present invention is that accident resistance is improved by reducing residual stress. Most work rolls for cold rolling by the conventional electroslag melting method have an integral structure. Some attempts have been made to manufacture composite rolls using the electroslag melting method, but the component system of the core material is a high-speed material having 0.8% or more of C and 3% or more of Cr, which are almost the same as the outer layer material. Has been applied. The application of such a material having high yield strength as the core material causes an increase in residual stress. Therefore, in the present invention, at least C: 0.3 to 0.7%,
A low-yield-strength low alloy steel having r: 0.5 to 3.0% and Mo: 0.1 to 2.0% was used as a core material, and the outer layer was formed by a continuous casting overlay method. It is desirable that the C content of the core material is 0.7% or less. More desirably, by limiting the C content of the shaft to 0.5% or less, the residual stress can be reduced to 45 kgf / mm ² or less.

On the other hand, 30 kgf / mm
^Since a strength of ² or more is required, it is not preferable that the C content is less than 0.3%. Here, the continuous casting overlay method of the present invention is shown in FIG. That is, FIG. 1 is a schematic diagram illustrating the continuous casting overlay method according to the present invention. This figure 1
As shown in FIG. 2, a water-cooling mold 7 is provided around a vertically-standing core 1, and a molten metal 9 composed of an outer layer 2 is introduced into a gap between the cores 1 while being heated by a heating coil 6. The solidification and the welding to the core material 1 are sequentially advanced while being pulled out to cast a composite roll. Reference numeral 3 denotes a platform, 4 denotes a preheating coil, 5 denotes a refractory frame, 7 denotes a water-cooled mold, and 8 denotes a nozzle.

[0013] Immediately after casting, after soft annealing, rough processing,
After tempering, progressive induction heating and water quenching were applied.
By performing the tempering at 00 to 600 ° C., the compressive stress remaining on the roll surface could be reduced to 60 kgf / mm ² or less. In the present invention, tempering at a high temperature of 500 to 600 ° C. is made possible by limiting the components of the outer layer. If the tempering temperature is lower than 500 ° C., secondary hardening cannot be obtained, and a Shore hardness of 90 or more cannot be secured.
On the other hand, when the tempering temperature exceeds 600 ° C., the hardness is greatly reduced. The tempering temperature is preferably in the range of 500 to 540 ° C. in order to ensure a hardness of 92 or more in Shore hardness.

[0014]

EXAMPLE As an example of the present invention, a rolled round steel having the components shown in Table 1 was used as a core material, and an outer layer made of the components shown in Table 1 was welded therearound by continuous casting and overlaying. φ55
A composite work roll for cold rolling having a length of 0 mm, a body length of 1500 mm, and a total length of 3500 mm was produced. In Comparative Example 1, when the core material was made of a high alloy, as Comparative Example 2, a material whose outer layer component range was out of the range of the present invention was similarly manufactured by the continuous casting overlay method. Table 1 shows the respective outer layer and core material components. After casting, soft annealing was performed, and after roughing, tempering was performed for the purpose of separating carbide. Thereafter, quenching was performed by progressive induction heating and water quenching. Hardening is 950-1 surface temperature
Tempering was performed at 100 ° C., and tempering was performed three times at 500 to 540 ° C.

FIG. 2 shows a sectional hardness distribution, and FIG. 3 shows a residual stress distribution. In the embodiment according to the present invention, a Shore hardness of 90 or more is secured from the surface to a depth of 50 mm,
The residual stress is also 43.8 kgf / mm ² , which is extremely lower than the residual stress level of the conventional roll, and is expected to prevent spalling. In Comparative Example 2 using a high alloy steel as the core material, a high residual stress of 68.0 kgf / mm ^2, which is equivalent to that of a conventional integrated roll, remains. In the outer layer component, in Comparative Example 2 in which Mo is out of the range of the present invention, when high-temperature tempering at 500 ° C. or more was applied, the secondary hardening action was not obtained, and a Shore hardness of 90 or more could be secured. could not.

[0016]

[Table 1]

[0017]

As described above, according to the present invention, a composite work roll for cold rolling having low residual stress and excellent in accident resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating a continuous casting overlay method according to the present invention.

FIG. 2 is a diagram showing a cross-sectional hardness distribution of a roll in an example.

FIG. 3 is a diagram showing a cross-sectional residual stress distribution of a roll in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core material 2 Outer layer 3 Platform 4 Preheating coil 5 Fireproof frame 6 Heating coil 7 Water-cooled mold 8 Nozzle 9 Molten metal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/24 C22C 38/24 (72) Inventor Mitsuo Hashimoto 46-59 Nakahara, Ota, Tobata-ku, Kitakyushu, Fukuoka Prefecture Nippon Steel Corporation Engineering Business Division (72) Inventor Akira Ito 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Engineering Business Division

Claims (1)

[Claims] 1. A composite roll for cold rolling comprising an outer layer material formed around a core material, wherein the outer layer material is formed around the core material by a continuous casting overlay method, and the core material is expressed in weight%. , At least C: 0.3-0.7%, Cr: 0.5-3.0.
%, Mo: 0.1 to 2.0%, composed of a low alloy steel, and the component of the outer layer material is C: 0.9 to 1.5 by weight%.
%, Cr: 4.0 to 10.0%, Mo: 2.0 to 8.0
%, V: 0.5 to 5.0%, the balance being Fe and unavoidable elements, and the compressive residual stress of the outer layer surface portion is 60 kgf /
mm ² cold rolling composite roll having excellent accident resistance, characterized in that less hardness with it is a Shore hardness of 90 or more