JP2000017341A - Method for quenching work roll for cold rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a work roll for cold rolling in which damage due to crack at the edge parts of a roll in the process of quenching is prevented and having high hardness and high wear resistance. SOLUTION: Around a core material composed of cast steel or forged steel, molten metal for an external layer having components of, by weight, 0.9 to 1.5% C, 0.2 to 1.5% Si, 0.3 to 2.0% Mn, 3.5 to 12.0% Cr, 3.0 to 10.0% Mo, 0.8 to 8.0% V, 1.0 to 10.0% W, and the balance Fe with inevitable elements is built-up by continuous tinkering welding method to form a barrel part, and, after that, the barrel part is subjected to progressive quenching by heating and cooling. In this case, injection of a cooling medium after the heating of the barrel edge parts is started at a point of time in which the edge face temp. of the barrel edge parts is <700 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quenching method for manufacturing a cold rolled work roll having excellent wear resistance and roughness retention used in cold rolling of steel.

[0002]

2. Description of the Related Art Conventionally, as a work roll for cold rolling of steel, forged steel containing 3 to 7% Cr as disclosed in, for example, JP-A-54-159323 has been applied.
After manufacturing the steel ingot by the air melting method and the electroslag melting method, forging processing is performed, and after processing into a certain shape and dimensions,
Hardness was increased by induction heating and quenching to impart wear resistance. Therefore, since the material to be induction hardened is forged at high temperatures, the casting structure is cut off, and the elongation value in the tensile test is as high as 5% or more. There were few problems to do.

[0003] On the other hand, as another manufacturing method, an outer layer made of a high alloy is formed around a tough core material by an overlaying method utilizing an electro-remelting method, a continuous casting overlaying method, or the like, and a composite roll is formed. Japanese Patent Laid-Open No. 4-22010
No. 5 publication.

In the above publication, a method of quenching after forming an outer layer is described in which a surface layer portion of a roll 11 is heated to a predetermined temperature using an induction heating coil 12 as shown in FIG. A progressive induction heating quenching method is disclosed in which cooling water or gas such as air is injected from 13 to gradually quench from the lower part of the body to the upper part of the body while cooling the roll 11.

In this case, usually, the body of the roll 11 is sequentially quenched by the rotation and movement of the roll 11, but in some cases, the induction heating coil 12 and the refrigerant injection cylinder 13 move.

[0006]

In such quenching, the higher the cooling rate during quenching, the higher the hardness is obtained, and the wear resistance is improved.

[0007] However, as the cooling rate is higher, a larger temperature gradient is generated from the surface of the roll to the inside thereof, and the roll may be broken during quenching due to the thermal stress resulting therefrom, resulting in a large loss. In particular, the required function of the work roll for cold rolling targeted by the present invention is required to have a high hardness up to the inside of the roll, so that the cooling rate at the time of quenching is increased, and at the end of the roll during quenching. Many breakage losses have occurred.

An object of the present invention is to provide a work roll for cold rolling that prevents breakage at the end of the roll during quenching and has high hardness and high wear resistance.

[0009]

In order to achieve the above-mentioned object, the present invention relates to a method for producing a steel material comprising a core material made of cast steel or forged steel, in which the components are expressed in terms of% by weight, C0.9-1.5, Si0.2-1. .
5, Mn 0.3 to 2.0, Cr 3.5 to 12.0, Mo
3.0 to 10.0, V0.8 to 8.0, W1.0 to 1
For cold rolling, the molten metal for the outer layer consisting of Fe and unavoidable elements with 0.0 is built up by continuous casting and overlaying to form a body, and then the body is gradually quenched by heating and cooling. In the method for quenching a work roll, the injection of the cooling medium after the heating of the body end is started when the temperature of the end surface of the body end is less than 700 ° C.

In the above quenching method, the components of the molten metal for the outer layer are expressed in terms of% by weight as C 0.9-1.5 and Si 0.2-
1.5, Mn 0.3 to 2.0, Cr 3.5 to 12.0,
Mo 3.0 to 10.0, V 0.8 to 8.0, W 1.0 to
10.0, Ni3.0 or less, and the balance can be composed of Fe and inevitable elements.

Alternatively, the components of the molten metal for the outer layer are
C0.9-1.5, Si0.2-1.5, Mn0.3-
2.0, Cr 3.5-12.0, Mo 3.0-10.
0, V0.8-8.0, W1.0-10.0, Ni3.
0 or less, Co 10.0 or less, and the balance can be made of Fe and unavoidable elements.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. During quenching, the surface is rapidly cooled by heat transfer to the cooling water, while the temperature inside is gradually decreased by heat conduction. For this reason, a large temperature gradient is generated in the surface layer portion, and a thermal stress due to this is generated. This is schematically illustrated with reference to FIG. 1, where the largest tensile stress occurs on the surface. If the strain due to the tensile stress exceeds the elongation at break of the material, the material breaks and the roll breaks.

Generally, the roll material is solidified in a water-cooled mold or a mold during casting. In other words, the cooling proceeds mainly from the roll surface in contact with the mold, so that the crystal grains become coarser and the alloy components are more likely to be deflected toward the inside, and as a result, the mechanical properties (strength, ductility, etc.) of the material are reduced inside the material. It tends to be inferior to the surface as it goes. FIG. 2 shows an example of the relationship between the actual material ductility and the distance from the surface.

Although the thermal stress generated during quenching can be controlled by cooling conditions (such as the amount of cooling water), it is necessary to increase the cooling rate as much as possible in order to increase the hardness and the depth of hardness. It is desirable to perform strong cooling to the vicinity. However, when the progressive induction heating method is used, as shown in FIG. 3, since the inside of the roll having poor mechanical properties is exposed on the body end face 2 of the roll 1,
At the same cooling level as the trunk, breakage will occur. In FIG. 3, reference numeral 3 denotes a shaft of the roll 1.

Therefore, in the present invention, heating of the body end is suppressed,
Heating of the body end at the start of water cooling is suppressed and the end temperature is 700 ° C.
Cool with cooling water at less than. FIG. 4 shows the operation. By setting the initial temperature of water cooling to less than 700 ° C., the generated thermal strain can be suppressed to the material elongation at break of the end face or less, and the breakage can be prevented.

Next, the limitation of the components of the high-speed steel used for the outer layer will be described. C: 0.9-2.5% C improves hardenability, increases matrix hardness,
It forms carbides of high hardness with r, Mo, V, W, and improves wear resistance. If it is less than 0.9%, the amount of carbides is small, and improvement in hardness and wear resistance cannot be expected. On the other hand, if it exceeds 2.5%, the toughness is undesirably reduced.

Si: 0.2-1.5% Si is combined with oxygen in the molten metal as a raw material for powder production, has a deoxidizing effect, and is necessary for producing clean powder.
If it is less than 0.2%, there is no effect, and if it exceeds 1.5%, the effect does not change, so the upper limit is made 1.5%.

Mn: 0.3-2.0% Mn fixes S in the raw material melt for powder production and prevents generation of harmful substances. It also enhances hardenability and contributes to an increase in matrix hardness. Less than 0.3% has no effect.
If it exceeds 2.0%, the effect does not change.

Cr: 3.5 to 12.0% Cr improves the hardenability of the matrix, increases the hardness, and forms carbide to contribute to the improvement of the overall hardness.
If it is less than 3.5%, the effect is not obtained, and if it exceeds 12.0%, the toughness is reduced due to coarsening of the carbide, and the impact resistance is impaired.

Mo: 3.0 to 10.0% Mo enhances the hardenability of the matrix, forms a stable carbide, contributes to the improvement of the overall hardness, and improves the wear resistance. If it is less than 3.0%, there is no effect, and if it exceeds 10%, the effect does not change. Therefore, the upper limit is set to 10.0%.

V: 0.8-8.0% V is an element that combines with carbon to crystallize fine VC carbides with high hardness and has a high effect of improving wear resistance. If it is less than 0.8%, there is no effect, and if it exceeds 8.0%, the amount of solid-dissolved carbide in the matrix is reduced, so that the hardness of the matrix is undesirably lowered.

W: 1.0 to 10.0% W combines with carbon to form a carbide of high hardness and enhances abrasion resistance. However, if it is less than 1.0%, there is no effect, and if it exceeds 10.0%, the carbide is increased. Unfavorably leads to a decrease in toughness and impact resistance.

Although Ni is not an essential component, it has an effect of improving hardenability and increasing matrix hardness. However, when the content exceeds 3.0%, retained austenite increases, which causes a decrease in hardness, which is not preferable.

Co is not an essential component, but has the effect of promoting solid solution of carbon, increasing the hardenability of the matrix, and increasing the matrix hardness. However, if it exceeds 10.0%, the amount of retained austenite increases and the matrix hardness decreases, which is not preferable.

[0025]

Next, the present invention will be described in detail with reference to examples. The roll material used is a composite structure roll having the dimensions shown in Table 2 manufactured by continuously casting a core material of an alloy steel and a high alloy of the outer layer component shown in Table 1 by the overlay method. Heating is axial length 60
This was performed using an induction current having a frequency of 60 Hz with a 0 mm coil. Cooling water is 125 liters of 5% polymer aqueous solution.
Injection was performed through holes with a diameter of 4 mm provided at equal intervals on the cooling ring. While rotating the roll at 30 rpm,
The heating coil and the water-cooling ring were advanced simultaneously from one barrel end to the other. The austenitizing temperature of the roll was 1100 ° C. The heating coil power was adjusted to a predetermined temperature while measuring the surface temperature with a radiation thermometer. At the upper and lower ends of the roll, the heating coil power passing through the end of the roll was adjusted, and the temperature of the end face when the water-cooled ring cooling water arrived was varied.

[0026]

[Table 1]

[0027]

[Table 2]

As is clear from Table 1, in the cold rolling roll of the present invention, the water cooling starting temperature after heating the roll end face at the time of quenching is set to less than 700 ° C. It can be seen that the breakage of the can be reliably prevented.

In order to ensure the cooling of the bottom end, it is also possible to always provide a water cooling nozzle of another system near the end to perform water cooling.

[0030]

As described above, according to the present invention, it is possible to prevent a roll end face from being cracked at the time of progressive induction hardening, and to provide a roll having high hardness and high wear resistance.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a temperature gradient and a thermal stress generation state during quenching.

FIG. 2 is a diagram showing the relationship between the ductility of a material and the distance from the surface.

FIG. 3 is a view schematically showing that a material fragile portion is exposed on a trunk end surface.

FIG. 4 is a diagram showing a relationship between a quenching initial temperature and a generated surface peak stress (strain).

FIG. 5 is a diagram schematically showing an induction heating quenching technique.

[Explanation of symbols]

1: Roll, 2: Body end face, 3: Shaft, 11: Roll, 1
2: Induction heating coil, 13: Cooling injection cylinder

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // C22C 38/00 301 C22C 38/00 301L 302 302Z 38/24 38/24 38/58 38/58 (72) Invention Taku Tanaka 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu-shi Nippon Steel Corporation Engineering Business Headquarters (72) Inventor Kiyoji Otomo 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu City F-term within Nippon Steel Corporation Engineering Business Headquarters (Reference) 4E016 CA09 EA02 EA22 FA03 FA04 4K042 AA20 BA03 CA04 CA06 CA07 CA08 CA10 CA13 CA15 DA01 DB01 DD04 DE07 DF01

Claims (3)

[Claims] 1. Around a core material made of cast steel or forged steel, the components are C 0.9-1.5 and Si 0.2-1.
5, Mn 0.3 to 2.0, Cr 3.5 to 12.0, Mo
3.0 to 10.0, V0.8 to 8.0, W1.0 to 1
For cold rolling, the molten metal for the outer layer consisting of Fe and unavoidable elements with 0.0 is built up by continuous casting and overlaying to form a body, and then the body is gradually quenched by heating and cooling. A method of quenching a work roll for cold rolling, wherein the injection of the cooling medium after the body end is heated is started when the end surface temperature of the body end is less than 700 ° C. 2. The composition of the molten metal for an outer layer in a weight percentage of C0.9
~ 1.5, Si 0.2 ~ 1.5, Mn 0.3 ~ 2.0,
Cr 3.5 to 12.0, Mo 3.0 to 10.0, V0.
2. The method for quenching a work roll for cold rolling according to claim 1, wherein the balance is 8 to 8.0, W 1.0 to 10.0, Ni 3.0 or less, and the balance is Fe and unavoidable elements. 3. The composition of a molten metal for an outer layer in a weight percentage of C0.9.
~ 1.5, Si 0.2 ~ 1.5, Mn 0.3 ~ 2.0,
Cr 3.5 to 12.0, Mo 3.0 to 10.0, V0.
8 to 8.0, W 1.0 to 10.0, Ni 3.0 or less, C
The method for quenching a work roll for cold rolling according to claim 1, wherein the balance is not more than 10.0 and the balance is made of Fe and unavoidable elements.