JPH11310825A - Manufacture of work roll for cold rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing cracking at the end of a roll barrel at the time of quenching after casting in the manufacture of a work roll for cold rolling. SOLUTION: An outer layer is formed by a continuous tinkering padding method around a core material composed of cast steel or forged steel by using a molten metal for the outer layer having a composition 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. Subsequently, by means of refining heat treatment, the Shore hardness of the outer layer and the elongation value by a tensile test are regulated to <=42 and >=0.5%, respectively and then, the Shore hardness of the outer layer is regulated to >=89 by quench-and-temper treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a work roll for cold rolling which is excellent in 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, the material to be induction-quenched is forged at a high temperature, so that the casting structure is divided, and the elongation value in the tensile test is as high as 5% or more. There were few problems to do.

On the other hand, as another manufacturing method, a technique of manufacturing a composite roll by forming an outer layer made of a high alloy around a core material having toughness by a continuous casting overlaying method is disclosed in Japanese Patent Publication No. 5-219.
No. 73. In the components of the outer layer described in the above publication, the amount of C as a main component is 1.5 to
Since it is as large as 3.5%, the carbide is coarsened and the strength is reduced, so that it cannot be used as a roll for cold rolling which is an application of the present invention. In addition, since the roll produced by the continuous casting overlay method has a smaller crystal grain size after casting than the roll produced by each of the above-mentioned methods, it is not forged and is guided in a solidified state as cast. Quench. Therefore, during quenching, there has been a problem that cracks occur in the outer layer from the surface of the quenching start portion.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a sound rolling roll by improving the toughness of an outer layer before induction heating and quenching, preventing cracks on the outer layer surface at the start of quenching occurring during induction heating and quenching. Is to provide.

[0005]

SUMMARY OF THE INVENTION The gist of the invention is as follows: (1) A cold rolling work in which an outer layer is formed around a core material made of cast steel or forged steel by a continuous casting overlay method. A method for producing a roll, comprising:
And 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%, balance of molten metal for outer layer composed of Fe and unavoidable impurities, after forming the outer layer by continuous casting overlay method, then heat treatment The shore hardness of the outer layer is set to 42 or less, the elongation value in a tensile test is set to 0.5% or more, and the shore hardness of the outer layer is set to 89 or more by quenching and tempering. Work roll manufacturing method.

(2) C:
0.9-1.5%, Si: 0.3-1.0%, Mn:
0.3 to 1.0%, Cr: 4.0 to 10.0%, Mo:
3.0 to 8.0%, V: 0.5 to 5.0%, W: 2.0
% Or less, the balance being Fe and inevitable impurities, the method for producing a work roll for cold rolling according to the above (1), wherein (3) C: 0.9-1.
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%, W: 2.0% or less, Ni:
The method for producing a work roll for cold rolling according to the above (1), wherein 5.0% or less, the balance consists of Fe and unavoidable impurities.

(4) As a refining heat treatment performed before quenching,
After holding at 1050 to 1100 ° C for 10 to 20 hours, continuously holding at 900 to 1000 ° C for 10 to 20 hours, air-cooling to room temperature, and then tempering several times at 600 to 700 ° C for 5 to 20 hours. (1)-characterized by the above
(3) The method for producing a work roll for cold rolling according to (3). (5) As the quenching performed after the tempering heat treatment, the roll is rotated at 10 to 50 rpm, heated by induction heating, and shower-cooled, and the cold rolling as described in (1) to (4) above is performed. Manufacturing method of work rolls.

[0008]

The reasons for limiting the components of the outer layer according to the present invention 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, and sufficient matrix hardness cannot be obtained, and at the same time, it becomes difficult to form a high alloy. Moreover, 1.
If it exceeds 5%, the carbides become coarse and the strength decreases, so the upper limit was made 1.5%. Si is an element necessary as a deoxidizing agent, and its effect is required to be 0.3% or more, but if it exceeds 1.0%, it is not preferable because it becomes brittle.

Mn is also an element required as a deoxidizing agent, like Si, and it is necessary to have 0.3% or more to exhibit its effect, but if it exceeds 1.0%, it is not preferable because it becomes brittle. C
r easily combines with C and constitutes 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.

[0010] Mo is an element capable of obtaining a hard carbide and strongly contributing to 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, so the appropriate range is set to 3% or more and 8% or less.
In particular, it is desirable to be 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. However, if it is less than 0.5%, the effect is small, and if it exceeds 5%, the grindability is impaired. Therefore, the range is set to 0.5% or more and 5% or less.

W forms a hard carbide like Mo, and has the effect of improving wear resistance. Further, it has resistance to softening during tempering, and is effective when tempering at high temperatures. However, if the amount of W is too large, the carbide grows to coarsen, and the toughness of the material is reduced or the surface becomes rough during use.
2% or less is desirable. Ni has an effect of improving hardenability. When a large hardening depth is required such as a roll having a large diameter, it may be added according to the demand. However, if it exceeds 5%, the retained austenite becomes excessive and H
Since high hardness of s90 or more cannot be obtained, the upper limit is 5
%.

[0012] The roll material cast by this component is subjected to softening annealing, rough processing, and heat treatment. Then, after performing intermediate processing before quenching, induction heating quenching is performed. In induction hardening, as shown in FIG. 1, the induction heating coil 2 is set at the lower part of the body of the roll body 1, and the roll body 1 is heated by induction heating from below while rotating the roll body 1.
In this method, the quenching process is performed by successively cooling the heated heating section 4 with water using the water cooling nozzle 3. Reference numeral 5 denotes a cooling unit. The quenching start portion at the lower end of the roll body 1 thus quenched has a problem that a vertical crack 6 occurs as shown in FIG.

In order to solve the problem of such vertical cracks,
As a result of various tests and analyses, the inventors found that the hardness of the outer layer was 42
It has been found that when the elongation value in a tensile test is 0.5% or more at HsC or less, the occurrence of cracks on the outer layer surface at the start of quenching can be prevented. FIG. 3 shows the result. That is, FIG. 3 is a diagram showing the range of occurrence of vertical cracks in elongation and hardness in a tensile test taken from the outer layer. According to this figure, when the hardness before quenching is 42 HsC or more and the elongation value obtained by a tensile test of a sample previously taken from the end portion is 0.5% or less, cracks occur on the outer layer surface almost during quenching. However, it was found that cracks could be reliably prevented by setting the hardness at the same position to 42 HsC or less and the elongation value in the tensile test to 0.5% or more.

FIG. 4 shows a method for improving toughness based on such knowledge. That is, FIG. 4 shows the heat pattern under the condition heat treatment before quenching. As shown in this figure, as the tempering heat treatment, first, 1050 to 1100
At 10 ° C. for 10 to 20 hours, and then slowly cooled to 80 ° C.
After cooling to 0 ° C or lower, the temperature is again increased to 900 to 1000 ° C for 10
After holding for ~ 20 hours, air-cool to room temperature and further 600
It has been confirmed that when tempering treatment is performed several times at ~ 700 ° C for 5 to 20 hours, the hardness is improved to 42HsC or less, and the elongation value in a tensile test of the substance is improved to 0.5% or more. In this case, the quenching was performed by rotating the roll by 10 to 50 rpm, heating by induction heating, and shower cooling.

[0015]

(Example 1) A rolled round steel having the components shown in Table 1 was used as a core material, and an outer layer material composed of the components shown in Table 1 was welded to the periphery thereof by continuous casting overlaying to produce a body diameter of φ450 mm. A work roll for cold rolling having a body length of 1900 mm and a total length of 3800 mm was manufactured. After the casting, softening annealing was performed and rough processing was performed, and then heat treatment was performed to separate carbides.
The refining conditions at that time were performed with the heat pattern shown in FIG. After the heat treatment, a tensile test piece was sampled from the roll body near the quenching start part, and a tensile test was performed to check the elongation. As a result, 0.84% was confirmed. Also, when the hardness of the portion located at the quenching start portion of the actual roll material was measured, it was 40 to 41 HsC. This material was subjected to induction heating and water quenching. The main quenching conditions are shown in Table 2. The quenching was performed at a surface temperature of 1100 ° C. ± 10 ° C. At this time, the quenching speed was 0.3 mm / sec, the roll rotation was 30 rpm, and the cooling was performed by a water shower using a cooling nozzle arranged circumferentially below the induction heating coil. At this time, there was no crack in the quenched part and quenching of 1900 mm in material length was successful. After quenching, 500 ~
Tempering was performed twice at 520 ° C. for 10 hours. When the hardness after tempering was measured, the product was processed at 91 to 92 HsC.

[0016]

[Table 1]

[0017]

[Table 2]

(Example 2) A rolled round steel having the components shown in Table 1 was used as a core material, and an outer layer material consisting of the components shown in Table 1 was welded therearound by a continuous casting overlay method.
A work roll for cold rolling having a body length of 1900 mm and a total length of 3800 mm was manufactured. After casting, the same softening annealing as in Example 1 was performed, and after roughing, heat treatment was performed to separate carbides. The refining condition at that time was the same heat pattern as in Example 1. After the tempering heat treatment, a tensile test piece was sampled from the roll body near the quenching start part, and a tensile test was performed to check the elongation. As a result, 0.64% was confirmed. Also, the hardness of the portion located at the quenching start portion of the actual roll material was measured and found to be 41 to 42 HsC. This material was subjected to induction heating and water quenching. The main quenching conditions are shown in Table 2;
The test was performed at a temperature of 10C. The quenching speed at this time is 0.3 m
m / sec, and roll rotation was performed at 30 rpm. Also at this time, there is no crack at the quenched part and the material length is 1900mm
Successfully quenched. After quenching, 1 at 500-520 ° C
Tempering at 0 hours was performed twice. When the hardness after tempering was measured, the product was processed at 90 to 91 HsC.

(Comparative Example 1) A rolled round steel having the components shown in Comparative Example 1 in Table 1 was used as a core material, and an outer layer material having substantially the same components as in the example was welded around the core by continuous casting overlaying. Body diameter φ450mm, body length 1900mm, total length 3800mm
Was manufactured. After casting, soft annealing was performed, and rough processing was performed before induction heating and quenching. At this time, a tensile test piece was sampled from a location near the position of the quenched portion before quenching, and the elongation was measured. In addition, the outer layer surface at the quenching start part has a hardness of 45-4.
7HsC. This material was subjected to induction heating and quenching under the same conditions as in Example 1. As a result, vertical cracks occurred on the outer layer surface from the quenching start portion immediately after water cooling was started.

(Comparative Example 2) A rolled round steel having the components shown in Comparative Example 2 in Table 1 was used as a core material, and an outer layer material having substantially the same components as in the example was welded to the periphery thereof by continuous casting overlaying. Body diameter φ530mm, body length 2000mm, total length 4000mm
Was manufactured. After casting, soft annealing was performed, and rough processing was performed before induction heating and quenching. At this time, a tensile test piece was sampled from a location near the position of the quenched portion before quenching, and the elongation was measured. The outer layer surface at the start of quenching has a hardness of 45 to 4.
7HsC. This material was subjected to induction heating and quenching under the same conditions as in Example 1. As a result, vertical cracks occurred on the outer layer surface from the quenching start portion immediately after water cooling was started.

As described above, cracks in the outer layer surface that occur at the start of quenching are caused by the fact that when the outer layer surface is cooled by a water-cooled shower after heating to a predetermined temperature, the outer layer surface in the cooled portion contracts. Stress occurs. The tensile stress has the largest stress at a temperature at which the elastic region is reached from the plastic region. It was found that the tensile stress increased at the start of quenching, and most cracks occurred at the position where water cooling started.

[0022]

As described above, according to the present invention, cracks in the outer layer could be almost eliminated by induction heating and quenching a roll material cast by the continuous casting overlay method.
Further, the roll for cold rolling manufactured by the method of the present invention achieves abrasion resistance and roughness retention of 2 to 5 times as compared with the conventional roll. Furthermore, the amount of material that can be used at one time can be used about three times that of the conventional roll, and it is possible to greatly improve the productivity, which is an extremely excellent effect.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an induction heating quenching method.

FIG. 2 is a view showing a state of a vertical crack at the lower end of a trunk portion during quenching.

FIG. 3 is a diagram showing a range of occurrence of a vertical crack in elongation and hardness in a tensile test taken from an outer layer.

FIG. 4 is a diagram showing a heat pattern under a refining heat treatment condition before quenching.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Roll main body 2 Induction heating coil 3 Water cooling nozzle 4 Heating part 5 Cooling part 6 Vertical crack

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 37/08 C22C 37/08 Z 38/00 302 38/00 302E 38/24 38/24 38/46 38/46 (72) Inventor Akira Ito 46-59 Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corp. Engineering Business Division

Claims (5)

[Claims] 1. Around a core material made of cast steel or forged steel,
A method for producing a work roll for cold rolling, comprising forming an outer layer by a continuous casting overlaying method, wherein components are expressed by weight% around said core material: 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 After forming the outer layer by continuous casting overlay method, the outer layer molten metal consisting of 5.0%, the balance of Fe and unavoidable impurities, and the heat treatment heat treatment, the outer layer has a Shore hardness of 42 or less, and the elongation value in a tensile test. , The shore hardness of the outer layer is increased to 89 or more by quenching and tempering, thereby producing a work roll for cold rolling. 2. The composition of the molten metal for an outer layer in terms of% by weight: 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%, W: 2.0% or less, the balance being Fe and inevitable impurities. The method for producing a work roll for cold rolling according to claim 1. 3. The components of the molten metal for the outer layer in terms of% by weight: 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%, W: 2.0% or less, Ni: 5.0% or less, the balance being Fe The method for producing a work roll for cold rolling according to claim 1, wherein the method comprises an unavoidable impurity. 4. A refining heat treatment performed before quenching,
After holding at 50 to 1100 ° C for 10 to 20 hours,
The cold rolling according to any one of claims 1 to 3, wherein the steel sheet is kept at 00 to 1000C for 10 to 20 hours, air-cooled to room temperature, and then tempered several times at 600 to 700C for 5 to 20 hours. Method of manufacturing work rolls. 5. The cold rolling as claimed in claim 1, wherein the quenching performed after the tempering heat treatment includes rotating the roll at 10 to 50 rpm, heating by induction heating, and performing shower cooling. Work roll manufacturing method.