JPH07305121A - Electrode for remelting electroslag and production of electroslag-remelted steel ingot - Google Patents

Abstract

PURPOSE:To produce an ESR steel ingot having different component areas without increasing the transition range. CONSTITUTION:A contracted part 3a is formed at the boundary part of the different component areas 1, 2 of an ESR electrode 4. This electrode for remelting electroslag is used to produce the ESR steel ingot by making the melting speed in the contracted part 3a smaller than the melting speed in the ordinary diameter part 3b. By this method, since the transition range of this ESR steel ingot is made small and the desired characteristic can be obtd. near the boundary part, the reliability of the product is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for remelting electroslag (hereinafter referred to as "ESR") used for manufacturing a high and low pressure integrated turbine rotor having a heterogeneous region, and an ESR steel ingot using this electrode. The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art Conventionally, in a high-low pressure integrated turbine rotor,
Since the required characteristics differ depending on the high-pressure portion, the medium-pressure portion, and the low-pressure portion, there has been proposed a composition-composite type rotor in which the composition of the material used for each pressure portion is changed according to each characteristic. By the way, a manufacturing method using the ESR method is widely adopted especially from the viewpoint of preventing segregation in a large-sized turbine rotor. However, in order to integrally manufacture the above-described composition composite type rotor, the composition of the rotor is It is necessary to have an ESR electrode whose composition is changed according to the above. Therefore, specifically, ESR electrodes in which steel ingots having different components are joined in the axial direction (Japanese Patent Publication Nos. 52-4254 and 56-14842, etc.)
Alternatively, a method of continuously using electrodes having different components (Japanese Patent Laid-Open No. 23367/56 etc.) has been proposed.

[0003]

However, in any case, the obtained ESR steel ingot may have a wide transition region in which different components are mixed, and the intended properties may not be obtained. There is a problem of poor reliability as a product. On the other hand, an ESR electrode (Japanese Patent Laid-Open No. 60-135536) in which an intermediate portion in which both components are fused in advance is provided between regions having different compositions has also been proposed, but it is necessary to sufficiently reduce the transition region. I haven't arrived. The present invention has been made in view of the above circumstances, and an object thereof is to provide an ESR electrode and an ESR steel ingot manufacturing method capable of effectively reducing a transition region to manufacture a highly reliable product. To do.

[0004]

In order to solve the above problems, the electroslag remelting electrode of the first invention of the present invention comprises two or more different component regions having different chemical components in the axial direction, It is characterized in that a constricted portion is formed at the boundary between these different component regions. In the electroslag remelting electrode of the second invention, the minimum thickness portion of the constricted portion has a cross-sectional area ratio of 0.04 to 0.6 of the normal thickness portion.
It is characterized by being 4 times.

The method for producing an electroslag remelted steel ingot according to the third aspect of the present invention is the first method for remelting electroslag.
Alternatively, the electroslag remelting electrode of the second invention is used, and the dissolution rate of the constricted portion of the electrode is set to be smaller than the dissolution rate of the normally thick portion. The method for producing an electroslag remelted steel ingot according to the fourth aspect of the invention is characterized in that the melting rate of the constricted portion of the electrode is usually 20 to 80% of the melting rate of the thick portion.

The ESR electrode of the present invention is one in which two or more different component regions having different components in the axial direction are joined by, for example, welding or a mechanical method, and is typically used for manufacturing a high and low pressure integrated turbine rotor. Be served. However, the present invention is not limited to the number of different-component regions, usage, and the like. Also,
This electrode has a diameter according to the product to be manufactured. For example, in the manufacture of a large-sized high-low pressure integrated turbine rotor, an electrode having a diameter of 900 to 1350 mm is normally used. However, the electrode thickness is not limited in the present invention.

In the constricted portion of the electrode of the present invention, as shown in the second invention, the minimum thickness portion is preferably 0.04 to 0.64 times the normal thickness portion in terms of sectional area ratio. Further, it is more desirable to set it to 0.04 to 0.25 times. In general, the shape of the electrode is circular in cross section. In other words, in the case of a cylindrical electrode, in other words, the minimum thickness portion of the constricted portion is 0.2 to 0.8 times the normal thickness portion (further 0.2 to 0. It is desirable to set the diameter to 5 times.

Further, it is desirable to form the outer wall surface in a tapered shape from the normal thickness portion to the minimum thickness portion of the constricted portion so that there is no sudden change in thickness, and the inclination angle of the tapered portion is 30. It is desirable to set it to -60 degrees. If this angle is smaller than 30 degrees, the taper portion becomes longer than necessary, and the work of forming the taper becomes troublesome. Further, when the inclination angle is larger than 60 degrees, the change in the cross-sectional area is rapid and it becomes difficult to control the dissolution rate.

When manufacturing an ESR steel ingot using the above electrode, the fill ratio (electrode diameter / steel ingot diameter) is 0.5 to 0.
It is desirable to set it to 8. And the dissolution rate of the electrode is
As shown in the third and fourth aspects of the invention, it is desirable to make the waist portion smaller than the normal thickness portion (desirably 20 to 80%), and further to minimize the minimum thickness portion. Further, the decrease in the dissolution rate may be gradually changed (decreased or increased) in the normal thickness portion before and after the constricted portion so as not to change rapidly.

[0010]

In other words, according to the present invention, the transition region in which different components are mixed can be made as small as possible, and desired characteristics can be obtained even in the vicinity of the boundary between different component regions. Also, when joining materials of different components by welding or the like, the joint area becomes smaller and the work efficiency is improved. Next, the reason for limiting the numerical range in the present invention will be described.

Cross-sectional area ratio: 0.04 to 0.64 times By forming a constricted portion having a small cross-sectional area at the boundary between different component regions, it is possible to reduce the amount of electrode dissolution and the transition region. Become. In order to surely obtain this effect, it is desirable that the cross-sectional area of the minimum thickness part (usually located at the above-mentioned boundary) be 0.64 times or less of the normal thickness part. On the other hand, if the cross-sectional area ratio is less than 0.04 times, not only the above-mentioned action is not improved, but also the strength as an electrode becomes insufficient, so the cross-sectional area ratio is desirable. Further, for the same reason, 0.04 to 0.25 times is more desirable.

Dissolution rate: 20-80% As described above, by providing a constricted portion on the electrode and making the dissolution rate of this constricted portion smaller than that of the normal thickness portion, the molten pool is made shallow and the transition region is made small. it can. In order to obtain the above effect sufficiently, it is desirable that the dissolution rate of the constricted portion is usually 80% or less of the dissolution rate of the thick portion. On the other hand, even if the dissolution rate is less than 20%, the improvement of the action is slight, and further, it takes a long time to dissolve and the work efficiency is lowered, so that it is desirable to set it to 20 to 80%.
For the same reason, it is more desirable to set it in the range of 40 to 70%. Since this dissolution rate is shown as a ratio to the dissolution rate of a normal thick portion, the absolute value is not limited, but, for example, the dissolution rate of a normal thick portion is 8
In the case of 00 to 2000 kg / hr, it is desirable to limit the dissolution rate of the necked portion to 400 to 1600 kg / hr.

Further, as described above, it is desirable to set the fill ratio (electrode diameter / mold diameter) of the electrode within a predetermined range (usually 0.5 to 0.8 in the thick portion). This is because if the fill ratio is less than 0.5, the electrode length must be lengthened to obtain the required amount of dissolution, and the work efficiency decreases, and if it exceeds 0.8, This is because the gap between the mold wall and the electrode becomes small, the work such as slag injection becomes difficult, and the spark phenomenon between the mold wall and the electrode easily occurs.

[0013]

EXAMPLE CrMoV steel ingot 1 and NiC having the composition shown in Table 1
The rMoV steel ingot 2 is melted and forged by a conventional method, and then one end of each is tapered by a taper 1
a and 2a are formed. Next, these tapered portions 1a, 2
Steel ingots were welded to each other so that a was abutted with each other to manufacture an ESR electrode 4 of the present invention having a constricted portion 3a and a normally thick portion 3b. In addition, 3c is an auxiliary electrode. In manufacturing the electrode 4, the tapered portions were welded to each other with a short peripheral length and could be easily performed in a short time.

The ESR electrode 4 usually has a diameter 3350 mm in the thickness portion 3b, a diameter 514 mm in the minimum thickness portion (joint portion) of the constricted portion 3a, and a sectional area ratio of about 0.145. Further, the taper portion 1a had a length of 320 mm and an inclination angle α of about 53 degrees, and the taper portion 2a had a length of 400 mm and an inclination angle β of about 46 degrees. In addition, for comparison, Cr-Mo-
A conventional comparative ESR electrode was prepared by welding the V steel ingot and the Ni-Cr-Mo-V steel ingot as they were. Unlike the ESR electrode of the present invention, this electrode welding work has a long circumference,
It took a long time to work.

[0015]

[Table 1]

Using the above electrode, the dissolution rate of the normal thickness portion is 1600 kg / hr, the minimum thickness portion of the necked portion is the same speed or 1000 kg / hr (62.
5%), electroslag remelting was performed, and the size of the transition region was evaluated by observing the molten pool depth of the ESR steel ingot corresponding to the boundary portion (joint portion) of both steel ingots. The dissolution diagram when the dissolution rate was changed using the electrode of the present invention is as shown in FIG. 2. In order to avoid a rapid change in the dissolution rate, the dissolution rate was usually gradually changed from the thick portion. .

The ESR steel ingots obtained as described above are shown in Table 2.
As shown in FIG. 6, it is understood that when the reference electrode is used, the molten pool is deep and a large transition region is formed. On the other hand, when the ESR electrode of the present invention is used, the melting pool depth is shallow, and particularly when the melting rate of the necked portion is controlled to be small, the melting pool depth is remarkably shallow as shown in FIG. And the reduction of the transition region is clear.

[0018]

[Table 2]

[0019]

As described above, according to the present invention,
It is possible to narrow the transition region where different components are mixed,
It enables the production of large-scale composite ESR steel ingots having a wide range of desired properties. Therefore, by using this ESR steel ingot, it is possible to manufacture a highly reliable product such as a high-low pressure integrated turbine rotor. Further, when preparing the ESR electrode, it is possible to easily join the different composition steel ingots, which also has the effect of improving the work efficiency.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an ESR electrode of the present invention.

FIG. 2 is a dissolution diagram during ESR.

FIG. 3 is an ESR obtained using the electrode of the present invention.
It is a schematic diagram which shows the pool depth of a steel ingot.

[Explanation of symbols]

1 CrMoV steel ingot 2 NiCrMoV
Steel ingot 3a Constriction part 3b Normal thickness part 4 ESR electrode

Claims (4)

[Claims] 1. An electrode for remelting electroslag, which comprises two or more different component regions having different chemical components in the axial direction, and a constriction portion is formed at a boundary portion between these different component regions. 2. The electrode for remelting electroslag according to claim 1, wherein the minimum thickness portion of the constricted portion has a cross-sectional area ratio of 0.04 to 0.64 times the normal thickness portion. 3. When remelting electroslag, the electroslag remelting electrode according to claim 1 or 2 is used, and the dissolution rate of the constricted part of the electrode is usually made smaller than the dissolution rate of the thick part. For producing electroslag remelted steel ingot characterized by: 4. The method for producing an electroslag-remelted steel ingot according to claim 3, wherein the melting rate of the constricted part of the electrode is usually 20 to 80% of the melting rate of the thick part.