JP3110565B2 - Method of manufacturing working roll for cold rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semi-high speed working roll used for cold rolling.

[0002]

2. Description of the Related Art In recent years, with the improvement of the efficiency of the rolling process,
The quality requirements for the working rolls for cold rolling used are becoming increasingly stringent. In particular, in order to withstand continuous operation under severe conditions of high load and high speed, it is important to improve wear resistance as well as accident resistance. Attention has been focused on Seimy high-speed working roll materials for cold rolling, which have high abrasion resistance and are resistant to rolling damage, in which various carbides are precipitated. Since this semi-high-speed working roll material has a strong tendency to segregate, in order to reduce segregation, the electroslag remelting method (hereinafter referred to as E
A special dissolution method called SR method is used.

[0003] In the ESR method, the electrode is melted by Joule heat generated by energization from a solid electrode to a molten slag and dropped under the slag, and the molten metal pool in the mold is directionally solidified to obtain a good skin. This is a method for obtaining an ingot having internal properties. In order to obtain such high quality ingots, it is necessary to control the molten metal pool while maintaining an appropriate slag temperature, electrode feeding speed, voltage, current, slag bath depth, slag composition, fill The plant is operated by appropriately controlling factors such as ratio (electrode diameter / mold diameter).

[0004]

The greatest factor that impairs the soundness of the layer used for semi-high-speed rolls is the appearance of streak-like segregation (reverse V segregation). If this segregation appears at a shallow position below the surface, The effective use diameter of the manufactured roll is reduced. Also, the increased risk of breakage during quenching greatly increases manufacturing difficulties.
However, when manufacturing this roll, applying ESR,
Moreover, even if the above factors are controlled, it is difficult to sufficiently avoid streak-like segregation when the segregation generation tendency is large in composition, and there is a problem that the effective diameter is small and the economic efficiency is poor. . The present invention has been made in view of the above circumstances, and provides a manufacturing method capable of effectively reducing the appearance of streak-like segregation in an ESR ingot to obtain a semi-high-speed cold rolling working roll having a large effective working diameter. It is intended to provide.

[0005]

In order to solve the above-mentioned problems, the present invention relates to a method of the present invention, wherein C: 0.8 to 1.5%, and Si:
1.5% or less, Mn: 1.5% or less, Cr: 2 to 6%,
Mo: 0.7 to 2%, V: 2% or less,
W: A roll containing 2% or less of one or two kinds, and the balance consisting of Fe and unavoidable impurities is applied to the electrode core in the axial direction.
Using a hollow electrode with a hole along
A method of manufacturing by re-melting a lag, wherein
The cross-sectional area of the hollow portion is, with respect to the total cross-sectional area of the electrode including the hollow portion,
It is characterized by having a ratio of 0.04 to 0.9 . Among the inevitable impurities in the roll composition, Si: 0.1
%, Mn: 0.1% or less, P: 0.005% or less,
S: It is desirable that the allowable content is 0.005% or less.

Next, in the second invention , C: 0.
8 to 1.5%, Si: 1.5% or less, Mn: 1.5% or less
Below, it contains 2-6% of Cr and 0.7-2% of Mo.
Furthermore, one or two kinds of V: 2% or less and W: 2% or less are included.
Cold rolling with the balance being Fe and unavoidable impurities
A hole is formed in the electrode core along the axial center direction.
Electroslag remelting using the hollow electrode
Wherein the hollow electrode has a cylindrical shape,
The inner diameter of the electrode is 0.2 to 0.95 with respect to the outer diameter.
And the outer diameter of the electrode is 0.4
比率 0.95. The book
In the invention, among the inevitable impurities in the roll composition, S
i: 0.1% or less, Mn: 0.1% or less, P: 0.00
5% or less, S: 0.005% or less as the allowable content
Is desirable.

[0007]

The working roll material for semi-high speed cold rolling according to the present invention is 1 to 1.5% C, 2 to 6% Cr, 0.7 to 2%.
By adding one or more of V: 2% or less and W: 2% or less to the Cr-Mo steel based on Mo, more excellent various properties as a working roll material for cold rolling were imparted. It is a known roll material. This roll material has a strong tendency to segregate, and a sound ESR ingot without segregation was not obtained even when the ingot was formed by the conventional ESR method. However, in the present invention, the streak-like segregation was achieved by using a hollow electrode. Was found to be reduced. In order to produce an ESR ingot with good internal properties without segregation, it is essential to make the molten metal pool shallow and dish-shaped, and if this becomes deeper, the densification of the solidified structure is hindered and the structure becomes coarse. And streak-like segregation is likely to occur. However, when the ingot is larger than the limit size, it is difficult to make the pool as shallow as not to generate segregation while maintaining good skin.

Considering the influence of the shape of the ESR electrode, for example, when the fill ratio is small, the calorific value at the central portion of the molten slag is large, and a large amount of current flows in the solidified ingot, and the Joule heat also increases. Pools tend to be deep. On the other hand, if the fill ratio is large, heat is generated in the entire molten slag, and the ratio of current flowing to the mold increases, so that the pool tends to be shallow. However, even with the latter method of increasing the fill ratio, it is not easy to make the pool shallow enough to prevent segregation.

Based on these findings, the present invention employs a hollow electrode in the production of an ESR ingot of a semi-high-speed roll having a large segregation tendency, so that the current flowing in the ingot from immediately below the center of the electrode is reduced. In addition, the depth of the molten pool at the center becomes shallow and the pool shape is flattened as a whole, and an ESR ingot with good internal properties and little streak-like segregation can be obtained. Further, in the vicinity of the mold, the amount of electricity increases and the temperature of the slag increases, resulting in a good ingot surface.

The method for producing the electrode of the present invention is not particularly limited. For example, melting, refining,
Ingots made from ingots, hollow ingots, drilled solid ingots, ingots processed into plates and bent and welded, and hollow electrode split materials assembled and welded, etc. A hollow electrode can be obtained. The outer shape of the electrode manufactured in this manner can be a prismatic shape or another irregular shape in addition to the cylindrical shape. The hole formed in the electrode is usually located at the center of the electrode, but is not limited to the one completely located at the center, as long as it is formed at the core which is almost at the center. Good.

Although the shape of the hole is not particularly limited, it is usually formed in a sectional shape similar to the outer wall of the electrode. For example, a circular hole is formed in a columnar electrode, and a square hole is formed in a prismatic electrode. This hole is usually penetrated at both ends of the electrode, but is not necessarily limited to this.
At the beginning or end of the ESR operation, the hole may be closed at one or both ends of the electrode so as to melt the solid part. In addition, the hole is usually formed in a straight hole shape having the same cross-sectional shape along the axial direction, but may have a modified cross-section depending on the axial position, for example, the inner surface shape of the hole in the axial direction. It is also conceivable to have a tapered shape along. Also, although one hole is usually formed in the core of the electrode, a plurality of holes may be formed.

Next, the reason why the relationship between the electrode hole diameter, the electrode outer diameter, the mold inner diameter and the like is limited will be described. Hollow section cross section / (total electrode cross section including hollow section) or pore diameter / electrode outer diameter ratio When the above ratio is less than the lower limit, the influence on the shape change of the molten metal pool is small, and the molten pool is sufficiently flat. No effect of conversion is observed. On the other hand, if the upper limit is exceeded, the electrode length for obtaining the required ingot weight increases, and it becomes difficult to apply the electrode to actual operation. Therefore, the cross-sectional area ratio is 0.04 to 0.9 and the diameter ratio is 0. It was determined in the range of .2～0.95.

Electrode outer diameter / mold inner diameter ratio When the above ratio is less than 0.4, the electrode length for obtaining the required ingot weight increases, and application to actual operation becomes difficult. When the ratio exceeds 0.95, the distance between the mold and the electrode becomes narrow, and the mold and the electrode may come into contact with each other when the mold or the electrode is moved up and down, which may make application to actual operation difficult. The ratio is preferably in the range of 0.4 to 0.95.

[0014]

Embodiments of the present invention will be described below. (Example 1) A test steel having the composition shown in Table 1 was melted by a conventional method, and a cylindrical electrode having a round hole at the center was cast using a core. At the time of casting the electrodes, four types of invention electrodes A to D were prepared by changing the inner diameter / outer diameter ratio of the electrodes as shown in Table 2. A solid electrode cast by a conventional method without using a core was prepared as a reference electrode E.
These electrodes have a shape having substantially the same electrode cross-sectional area (excluding holes), and ESR is set so that the same dissolution rate can be obtained.
Conditions have been set.

Using these ESR electrodes, 800 m
In a m-diameter mold, 50% CaF ₂ -20% CaO-30%
Using a slag of Al ₂ O ₃ (% by weight), 750 kg /
ESR was performed at a dissolution rate of hr. The cross section of the obtained ESR ingot was macro-eroded, the degree of streak-like segregation was observed, and the ingot surface was evaluated. As shown in Table 3, when the conventional solid electrode was used, the ingot surface was poor, and the internal property was streak-like segregation generated at a position at a depth of 68 mm below the surface. On the other hand, in the case of using the hollow electrode, the streak-like segregation was generated from a position deeper than 164 mm from the surface, the ingot surface was improved, and a high quality ESR ingot was obtained.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

As described above, according to the present invention,
When ESR of semi-high speed cold rolling working rolls is performed,
By using a hollow electrode with a specific hollow area cross section, the shape of the molten pool becomes shallow and flattened.
There is an effect that the streak-like segregation generated in the R ingot is driven into the ingot and the effective diameter of the roll is increased.

[Brief description of the drawings]

FIG. 1 is an electrode cross-sectional view showing a modified example of the electrode shape of the present invention.

[Explanation of symbols]

 1 prism electrode 2 segment electrode 3 segment electrode 4 segment electrode

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C22C 38/00 302 C22C 38/00 302E 38/18 38/18 (56) References JP-A-3-122251 (JP, A) JP-A 3-90270 (JP, A) JP-A-60-124442 (JP, A) JP-A-52-149224 (JP, A) JP-A-5-285632 (JP, A) JP-A-6-47520 (JP, A A) JP-A-5-237634 (JP, A) JP-A-5-169112 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 23/10 522 B22D 23/10 531 B21B 27/00 C22C 38/00 301 C22C 38/00 302 C22C 38/18

Claims (2)

(57) [Claims] 1. C .: 0.8 to 1.5% by weight, Si
: 1.5% or less, Mn: 1.5% or less, Cr: 2 to 6
%, Mo: 0.7 to 2%, V: 2% or less, W: 2% or less, and the balance is F
e and cold roll working rolls
A hollow electrode with a hole formed in the electrode core along the axial direction
Using electroslag re-melting
Thus, the cross-sectional area of the hollow portion of the electrode, the electrode including the hollow portion
A method for producing a working roll for cold rolling , comprising a ratio of 0.04 to 0.9 with respect to the total cross-sectional area. 2. C: 0.8 to 1.5% by weight, Si
: 1.5% or less, Mn: 1.5% or less, Cr: 2 to 6
%, Mo: 0.7 to 2%, and V: 2% or less
Bottom, W: contains 1% or less of 2% or less, and the balance is F
e and cold roll working rolls
A hollow electrode with a hole formed in the electrode core along the axial direction
Using electroslag re-melting
Thus, the hollow electrode has a cylindrical shape, and the inside diameter of the electrode is outside.
It consists of a ratio of 0.2 to 0.95 with respect to the diameter.
The ratio of the outer diameter of the electrode to the inner diameter of the mold is 0.4 to 0.95.
Method for producing working roll for cold rolling , characterized by comprising