JP4884797B2 - Firing-type flux for submerged arc welding, overlay welding method, and turbine rotor - Google Patents

Description

  The present invention relates to a firing flux for submerged arc welding, a build-up welding method using the same, and a turbine rotor, and is particularly useful when applied to a turbine rotor used in a geothermal power plant and a low-pressure turbine rotor used in a thermal power plant. is there.

  As a material for steam turbines used in geothermal power generation, that is, turbine rotors of steam turbines used in an environment containing a large amount of corrosive gas, so-called low alloy steel in which an alloy element is slightly added to iron is widely used. . When a steam turbine made of such low alloy steel is used in a corrosive environment such as in geothermal steam, the turbine rotor will crack due to stress corrosion cracking and corrosion fatigue, making it impossible to continue operation. There is a case.

  Even in steam turbines used for thermal power generation, the temperature on the wake side is low, so condensed moisture and impurities contained in boiler water cause stress corrosion cracking, corrosion fatigue, etc. in the wake pressure low-pressure turbine rotor. There is a case.

  The simplest countermeasure when the operation cannot be continued due to stress corrosion cracking or corrosion fatigue in the turbine rotor is to replace the turbine rotor. However, replacing only the part of the turbine rotor that is damaged results in an economic disadvantage.

  For this reason, it uses for subsequent use by repairing welding about the generation | occurrence | production part of a crack etc. When performing such welding repair, conventionally, it is dealt with by overlay welding using a welding material of the same material or a specific material as the base material (low alloy steel) of the turbine rotor.

As what applied such a welding repair technique to the turbine rotor for geothermal power generation, what is shown, for example in patent document 1 is known. In the welding repair of this patent document 1, the method which uses 12Cr5Ni type | system | group material as a welding material and performs welding repair by 4 steps | paragraphs (2 step | paragraph tempering process) is disclosed.
Table 1 shows an example of chemical components of the welding material.

The impact characteristic required in the specification of the steam turbine rotor for geothermal power generation is, for example, 20 J or more when expressed by the measured value of shock absorption energy at room temperature according to JIS Z2202 (V notch test).
On the other hand, the impact characteristics required in the specifications of the low-pressure turbine rotor are, for example, 54 J or more when expressed in terms of impact absorption energy measured at room temperature according to JIS Z2202 (V notch test).

JP 2004-148346 A

  The welding repair disclosed in Patent Document 1 is usually performed by TIG welding. However, when TIG welding is employed, there is a problem in that the number of welding steps is increased and the cost is increased.

  In addition, as a high-speed welding method with reduced welding man-hours, the submerged arc welding method can be raised, but this welding method has a higher impact characteristic of the weld metal than the case of TIG welding because oxygen is mixed into the weld metal. There was a problem of getting worse.

  In addition, the 12Cr5Ni welding material used for welding repair of the turbine rotor for geothermal power generation can be used for welding repair of the low-pressure turbine rotor in terms of strength, but the specifications of the low-pressure turbine rotor are sufficient in terms of impact characteristics. I was not satisfied.

  The present invention has been made in view of such circumstances, and is a firing flux for submerged arc welding used to form a built-up welded portion having sufficient impact resistance with a small number of welding steps. It aims at providing the overlay welding method and turbine rotor which were used.

In order to solve the above problems, the present invention employs the following means.
Flux according to the present invention is obtained by at least calcining the mixed raw material, in _{mass%, SiO 2: 5~20%,} MgO: 15~20%, Al 2 O 3: 20~30%, CaF 2: 5-20%, manganese oxide: _2-10% in terms of MnO _{value, MgCO 3: 4~10%, ZrO} 2: 2~10%, K 3 AlF 6: 2~10%, 15% or less of metal powder , and CaO: a firing-type flux for submerged arc welding containing 5-20%, the mixed raw material, as a material of the CaO, that contains only calcium oxide as of compounds 5-20% Features.

As the flux for submerged arc welding, there are a melting type and a firing type. Of these, calcined flux (also referred to as “bond flux”) is obtained by adding a small amount of a binder such as water glass to the mixed raw material, kneading and granulating, and then calcining at around 600 ° C. .
Generally, the firing type flux used for submerged arc welding contains CaO for the purpose of stabilizing the weld bead and improving the cleanliness in the metal due to deoxidation and desulfurization effects. The flux normally used for welding contains a metal carbonate such as CaCO _{3 in} the mixed raw material before firing as the raw material of CaO.
On the other hand, in the present invention, a higher deoxidation effect is realized by using calcium oxide (CaO) as a compound instead of CaCO ₃ in the mixed raw material before firing the flux. This high deoxidation effect enables high-speed welding with a small number of welding steps by submerged arc welding, which is a large heat input welding with a large current, while preventing the impact characteristics of the weld metal from being lowered compared to TIG welding. .

  Hereinafter, the reason for limiting the components of the chemical components contained in the firing flux for submerged arc welding according to the present invention will be described. In the following, “%” representing the amount of a component represents% by weight.

₁₎ SiO 2: 5~20%
SiO ₂ gives moderate viscosity and fluidity to the slag and has an action of adjusting the bead shape. When the amount of SiO ₂ is less than 5%, the viscosity of the slag decreases, the fluidity becomes poor, and the beads meander. On the other hand, if the amount of SiO _{2 in the} flux exceeds 20%, the basicity of the flux decreases, the amount of oxygen in the weld metal increases, and the toughness decreases. Therefore, the SiO ₂ amount is 5 to 20%. More preferably, the SiO ₂ amount is 10 to 14%.

2) MgO: 15-20%
MgO is an effective component for increasing the melting point of slag and improving slag peelability. It is also an effective component for increasing the basicity of the flux and reducing the amount of oxygen in the weld metal to improve toughness. If the amount of MgO is less than 15%, the sufficient effect cannot be obtained. On the other hand, if the amount of MgO exceeds 20%, the melting point rises too much and the bead appearance is deteriorated, and slag is often seized on the bead surface. Therefore, the amount of MgO is 15 to 20%. More preferably, the amount of MgO is 17 to 19%.

_{3) Al 2 O 3: 20~30} %
Al ₂ O ₃ has an action of imparting an appropriate viscosity and fluidity to the slag and adjusting the bead shape. If the amount of Al ₂ O ₃ is less than 20%, the viscosity of the slag is lowered and the bead shape is deteriorated. On the other hand, if the amount of Al ₂ O ₃ exceeds 30%, the melting point of the slag increases, the viscosity of the slag increases, and the slag peelability also decreases. Therefore, the amount of Al ₂ O ₃ is 20 to 30%. More preferably, the amount of Al ₂ O ₃ is 22 to 26%.

₄₎ CaF 2: 5~20%
CaF ₂ is an important component for adjusting the fluidity of slag, and since it is a basic component, it has the effect of reducing the amount of oxygen in the weld metal. If the amount of CaF ₂ is less than 5%, a sufficient effect cannot be obtained. On the other hand, if the amount of CaF ₂ exceeds 20%, the arc becomes unstable, the bead waveform becomes rough, and workability is deteriorated. Accordingly, the CaF ₂ content is 5 to 20%. More preferably, the amount of CaF ₂ is 10 to 14%.

5) Manganese oxide: 2 to 10% in terms of MnO
Manganese oxide is effective in adjusting the viscosity of the slag and improving the conformability of the bead. In particular, when overlay welding is performed, it is important to smooth the angle of the bead toe. If the amount of manganese oxide is less than 2% in terms of MnO, the effect cannot be sufficiently obtained. On the other hand, if it exceeds 10%, a pock mark is generated on the surface of the weld slag, and the workability is deteriorated, for example, the slag peelability is lowered. . Accordingly, the manganese oxide is 2 to 10% in terms of MnO. More preferably, the manganese oxide is 3 to 5% in terms of MnO.

6) MgCO ₃ : 4 to 10%
MgCO ₃ is effective for reducing hydrogen penetration into the weld metal during welding. MgCO ₃ is decomposed during welding, CO ₂ is generated, and the hydrogen partial pressure is reduced. If MgCO ₃ is less than 4%, the effect cannot be obtained sufficiently. On the other hand, if it exceeds 10%, gas generation becomes excessive, and a pock mark is generated, thereby deteriorating workability. Therefore, MgCO ₃ is 4 to 10%. More preferably, the amount of MgCO ₃ is 4-7%.

7) ZrO ₂ : 2 to 10%
ZrO ₂ is effective for improving the arc stability and improving the bead gloss and bead waveform. If ZrO ₂ is less than 2%, the effect cannot be obtained sufficiently, while if it exceeds 10%, seizure of slag increases. Therefore, the amount of ZrO ₂ is 2 to 10%. More preferably, the amount of ZrO ₂ is 2 to 5%.

8) K ₃ AlF ₆ : 2 to 10%
K ₃ AlF ₆ is effective in reducing the oxygen content of the weld metal due to its deoxidation effect. Further, there are effects such as improving the stability of the arc and improving the bead shape. If it is less than 2%, the effect cannot be sufficiently obtained. On the other hand, if it exceeds 10%, the arc becomes rough, the bead waveform becomes rough, and workability is deteriorated. Therefore, the amount of K ₃ AlF ₆ is 2 to 10%. More preferably, the amount of K ₃ AlF ₆ is 2 to 5%.

9) CaO: 5 to 20% Calcium oxide in the raw material 5 to 20%
CaO is known to increase the cleanliness of metals due to its strong deoxidation and desulfurization effects when used as a furnace wall material when melting metals. CaO is generally added to the flux used for welding in the form of a metal carbonate such as CaCO ₃ , but the amount of oxygen in the weld metal cannot be sufficiently reduced in this form of metal carbonate. A sufficient effect for improving the toughness of the metal could not be obtained.
Therefore, the present invention is characterized in that CaO is added in the form of calcium oxide as a flux material before firing. By adding this calcium oxide, the amount of oxygen in the weld metal is extremely reduced. Further, CaO is a raw material that increases the basicity of the flux, and the deoxidation effect is further enhanced by the increase in basicity. Therefore, the addition of calcium oxide greatly improves the toughness of the weld metal due to its deoxidation effect. If the amount of calcium oxide is less than 5%, the effect of improving toughness cannot be obtained sufficiently. On the other hand, if it exceeds 20%, bead seizure occurs and the bead appearance deteriorates. Therefore, the amount of calcium oxide (CaO) in the raw material is 5 to 20%. More preferably, the amount of calcium oxide (CaO) in the raw material is 5 to 10%.

10) Metal powder in raw material 15% or less Metal powder is added to the mixed raw material to remove elements that are oxidized and consumed by welding and as a deoxidizer. An appropriate amount of metal Cr, metal Ni, Fe—Mo, or the like is added for the purpose of removing elements that are oxidized and consumed by welding. The deoxidizer improves the toughness of the weld metal and improves the outgassing of the flux. Examples of the deoxidizer include Ti, Al, Si, Mn and the like, or compounds of these elements and Fe (iron). Among these, Ca—Si, which is a compound of Si, is preferable. Only one kind of deoxidizer may be added, or a complex may be added. When the total amount of the metal powder exceeds 15%, workability such as generation of a pock mark is deteriorated. Therefore, the total amount of the metal powder is 15% or less. More preferably, the total amount of metal powder is 5% or less.

In addition, the overlay welding method of the present invention includes a welding step of performing overlay welding on a base material by submerged arc welding using the firing flux for submerged arc welding.
According to this build-up welding method, a build-up weld portion having sufficient impact characteristics can be formed by high speed welding with a small number of welding steps by submerged arc welding which is large heat input welding with a large current.

In the build-up welding method of the present invention, it is preferable to provide a tempering step for heating the build-up weld portion to a predetermined temperature after the welding step.
According to this build-up welding method, the mechanical strength of the build-up welded portion can be improved by adopting the tempering step of heating the build-up welded portion to a predetermined temperature.

In another build-up welding method of the present invention, the build-up welding is performed on a base material to form a first build-up weld portion, and after the first welding step, A first tempering step of heating the first build-up weld portion to a predetermined temperature, and a second embedment weld on the first build-up weld portion to form a second build-up weld portion And a second tempering step of heating the second build-up welded portion to a predetermined temperature after the second weld step, wherein at least the second The welding process is performed by submerged arc welding using the flux according to claim 1 or claim 2.
This build-up welding method is less in harmony with the requirement to make the hardness of the base metal appropriate and the requirement to make the mechanical strength of the build-up weld part appropriate, which had been considered a contradictory requirement in the past. Overlay welding can be performed by high-speed welding with the number of welding steps.

The turbine rotor of the present invention is characterized in that a coating layer formed by any one of the above-described overlay welding methods of the present invention is provided on the surface of a base material formed of low alloy steel.
This turbine rotor has sufficient mechanical strength and is repaired or manufactured at a low cost.

ADVANTAGE OF THE INVENTION According to this invention, the firing type flux for submerged arc welding which makes it possible to perform the submerged arc welding which is high-speed welding with few welding processes, without reducing the impact characteristic of a weld metal can be provided.
Moreover, according to this invention, the build-up welding method which can form the build-up welding part which has sufficient impact characteristics by the high-speed welding of few welding man-hours can be provided. The overlay welding method of the present invention can be suitably used for welding repair and manufacturing of a geothermal power generation turbine rotor and a low-pressure turbine rotor.
Furthermore, according to this invention, the turbine rotor which has sufficient mechanical strength can be provided at low cost. This turbine rotor is suitably used as a geothermal power generation turbine rotor and a low-pressure turbine rotor.

Hereinafter, embodiments of the present invention will be described.
[First Embodiment]
In this embodiment, the composition of the firing flux suitable for submerged arc welding using a 12Cr5Ni-based welding material was examined.

First, after blending a predetermined flux mixed raw material, dry mixing was performed. A small amount of water glass was added to this as a binder and kneaded. Next, the obtained mixture was granulated using an extruder. The granular raw material thus obtained was naturally dried and then fired at about 600 ° C. to obtain a fired flux.
Table 2 shows the component compositions of the calcined fluxes of Examples 1 to 5 according to the present invention and the calcined fluxes of Comparative Examples 1 to 15 for comparison with these. In Table 2, for CaO, CaCO ₃ and metal powder, the component amount in the mixed raw material before firing is shown, and for the other components, the component amount in the flux obtained by firing is shown. Yes.

Submerged arc welding was performed using each of the obtained fluxes and 12Cr · 5Ni-based welding material (same as shown in Table 1), and the welding workability was evaluated. Further, the amount of oxygen in the weld metal and the absorbed energy of the weld metal were measured. The results are shown in Table 3.
In addition, the welding workability was comprehensively judged on peelability, arc stability, and bead shape, and “good” was evaluated as “good” and “bad” as “poor”. The absorbed energy is a measured value of impact absorbed energy at room temperature according to JIS Z2202 (V notch test).

  From the results shown in Table 3, the fluxes of Examples 1 to 5 had good welding workability. The oxygen content in the weld metal was as low as 400 ppm, and the impact characteristics (absorbed energy) were as high as 80 J or more. Therefore, the flux of Example 1 to Example 5 was an excellent flux.

On the other hand, when the fluxes of Comparative Example 1 and Comparative Example _{2 in} which SiO ₂ and ZrO ₂ were reduced were used, welding workability was good because CaCO ₃ was used in the raw material. The amount of oxygen in the metal was as high as 650 ppm or more, and the impact characteristics were inferior.
Further, when the flux of Comparative Example 3 was used, the CaO content in the raw material was below the lower limit of the range of the present invention, so the welding workability was good, but the oxygen content in the weld metal was Exceeding 400 ppm, impact properties were also reduced.
When the flux of Comparative Example 4 was used, the CaO content exceeded the upper limit of the range of the present invention, so the weld metal had extremely low oxygen and good impact characteristics, but the slag was peeled off. The slag seizure occurred and welding workability deteriorated.

When the flux of Comparative Example 5 was used, since the CaF ₂ content exceeded the upper limit of the range of the present invention, the weld metal had low oxygen and good impact characteristics, but the bead waveform became rough, Welding workability has deteriorated, such as the bead shape becoming convex.
When the flux of Comparative Example 6 was used, since the CaF ₂ content was below the lower limit of the range of the present invention, the oxygen content of the weld metal was increased and the impact characteristics were deteriorated. In addition, the welding workability deteriorated, for example, the bead shape deteriorated.
When the flux of Comparative Example 7 was used, since the content of SiO ₂ exceeded the upper limit of the range of the present invention, the welding workability was good, but the oxygen content in the weld metal was high, and the impact characteristics Decreased.

When the flux of Comparative Example 8 was used, since the content of SiO ₂ was below the lower limit of the range of the present invention, the weld metal had low oxygen and good impact characteristics, but the slag viscosity decreased. As a result, fluidity deteriorated and welding workability decreased.
When the flux of Comparative Example 9 is used, since the content of Al ₂ O ₃ is below the lower limit of the range of the present invention, the viscosity of the slag is lowered, the bead shape is deteriorated, and welding workability is lowered. did.
When the flux of Comparative Example 10 is used, the content of Al ₂ O ₃ exceeds the upper limit of the range of the present invention, so that the viscosity becomes too high and the bead shape becomes convex, and the slag peelability is high. Reduced and welding workability decreased.

When the fluxes of Comparative Examples 11 and 12 were used, the amounts of MgO, K ₃ AlF ₆ , and ZrO ₂ were outside the scope of the present invention, so the slag peelability deteriorated and welding workability deteriorated.
When the flux of Comparative Example 13 was used, the MnO content exceeded the upper limit of the range of the present invention, so the slag peelability was poor and the welding workability was reduced.
When the flux of Comparative Example 14 was used, the content of MgCO ₃ exceeded the upper limit of the range of the present invention, and the content of MnO was below the range of the present invention. Workability deteriorated.
When using the flux of Comparative Example 15, the content of ZrO ₂ exceeds the upper limit of the range of the present invention, and the content of MgCO ₃ is below the range of the present invention. Welding workability deteriorated due to increased seizure of slag.

  In addition, in this embodiment, although the case where a 12Cr5Ni type welding material was used as a welding material was examined, this invention is not limited to this. For example, the present invention is applicable even when a welding material having a Cr content of 9 to 13% by weight and a Ni content of 0 to 7% by weight is used.

[Second Embodiment]
Using the firing flux for submerged arc welding of Example 1 and a 12Cr · 5Ni welding material (same as shown in Table 1), the turbine rotor for geothermal power generation having the component composition (unit:% by weight) shown in Table 4 Overlay welding was performed on the material (base material), and various characteristics were examined.

FIG.1 and FIG.2 is a figure which shows the welding test material used by this embodiment, FIG. 1 is a perspective view, FIG. 2 is sectional drawing. This weld test material (turbine rotor) 1 is a model of a real turbine rotor.
In the present embodiment, overlay welding was performed by the following four-stage process (Example 6).

1) Initial prime welding (first welding process):
Overlaying was performed on the base material 2 to a height of about 6 mm by TIG welding to form a first overlaid weld portion 3.
2) First tempering step:
In order to reduce the hardness of the base metal heat-affected zone to 350 Hv or less, heat treatment was performed at 640 ° C. × 10 hours.
3) Post-welding (second welding process):
By submerged arc welding using the flux and the welding material, overlaying was performed up to the target height (about 60 mm) on the first overlay welded part 3 to form the second overlay welded part 4.
4) Second tempering step:
In order to reduce the residual stress of the weld metal and adjust the strength of the weld metal, heat treatment was performed at 580 ° C. for 10 hours.

In addition, for comparison, a weld test material was prepared in which both of the above-described initial build-up welding and post-build-up welding were built up by TIG welding (Comparative Example 16).
Regarding the obtained weld test material 1 (Example 6 and Comparative Example 16), tensile properties (0.2% yield strength, tensile strength), impact properties (absorbed energy), stress corrosion cracking properties (12 in geothermal steam). Monthly test) and welding costs were evaluated.
Table 5 shows the evaluation results of Example 6 and Comparative Example 16 and target values of the turbine rotor for geothermal power generation.
The 0.2% proof stress of tensile properties was measured according to JIS Z2201. The tensile strength of the tensile properties was measured according to JIS Z2201. The absorbed energy of impact characteristics was measured at room temperature according to JIS Z2202 (V notch test). The 12-month test in the geothermal steam of the stress corrosion cracking property was tested by a three-point bending type stress load test method, where ○ indicates that no crack occurred and × indicates that crack occurred. The welding cost is a relative value when the welding cost of Comparative Example 16 is set to 100.
In addition, the measurement values in the upper and lower stages are the respective values obtained by performing the measurement twice.

  From the evaluation results shown in Table 5, the weld test material of this embodiment (Example 6) sufficiently satisfies the target values of tensile properties and impact properties, and the stress corrosion cracking properties are also initially primed welding and subsequent primed welding. Both were found to be equivalent to the weld test material (Comparative Example 16) that was conducted by TIG welding. Moreover, the welding cost of Example 6 is 1/5 compared with the welding cost of Comparative Example 16.

In the welding method (four-stage process) of this embodiment, the strength of the weld metal can be ensured while suppressing the hardness of the heat-affected zone of the base material as low as possible. By applying this method, it is considered that there is an effect as a countermeasure against delayed cracking and SR cracking.
Delayed cracking is a phenomenon in which hydrogen embrittlement occurs due to the fact that hydrogen in the weld metal collects when tensile stress due to welding residual stress acts on the hardened part of the base metal heat-affected zone. SR cracking is a phenomenon in which cracking occurs because the hardened part of the base metal heat-affected zone is exposed to high temperature (SR temperature) in a state where tensile stress due to welding residual stress is applied. For this reason, it is considered that it is effective to reduce the hardness of the heat-affected zone of the base material at the time when the residual stress is low, that is, at the initial build-up time, even for delayed cracking and SR cracking.

[Third Embodiment]
Using the firing flux for submerged arc welding of Example 1 and a 12Cr · 5Ni welding material (same as shown in Table 1), the low-pressure turbine rotor material having the composition (unit:% by weight) shown in Table 6 ( Overlay welding was performed on the base material, and various characteristics were examined.

Since the shape of the weld test material used in the present embodiment is the same as the shape of the weld test material used in the second embodiment, the overlay welding of the present embodiment will be described with reference to FIGS. 1 and 2. To do.
In this embodiment, build-up welding was performed by the following four-stage process (Example 7).

1) Initial prime welding (first welding process):
Overlaying was performed on the base material 2 to a height of about 6 mm by TIG welding to form a first overlaid weld portion 3.
2) First tempering step:
Heat treatment was performed at 580 ° C. for 10 hours in order to reduce the hardness of the base metal heat-affected zone to 350 Hv or less.
3) Post-welding (second welding process):
By submerged arc welding using the flux and the welding material, overlaying was performed up to a target height of about 60 mm on the first overlay welded part 3 to form a second overlay welded part 4.
4) Second tempering step:
In order to reduce the residual stress of the weld metal and adjust the strength of the weld metal, heat treatment was performed at 580 ° C. for 10 hours.

  In addition, since the temperature for suppressing the hardness of the weld heat-affected zone is the same as the temperature for adjusting the strength of the weld metal, it is necessary to apply a four-stage process to the weld overlay on the low-pressure turbine rotor material. Therefore, the first tempering step can be omitted. However, in this embodiment, welding overlaying was performed using a four-stage process as a countermeasure for delayed cracking and SR cracking.

Regarding the obtained weld test material 1 (Example 17) and the low-pressure turbine rotor material (base material 2), tensile properties (0.2% proof stress, tensile strength), impact properties (absorbed energy) and stress corrosion cracking properties ( U-bend test value in alkaline environment) was evaluated.
Table 7 shows the evaluation results of Example 17 and the low-pressure turbine rotor material and the target values of the low-pressure turbine rotor.
The 0.2% proof stress of tensile properties was measured according to JIS Z2201. The tensile strength of the tensile properties was measured according to JIS Z2201. The absorbed energy of impact characteristics was measured at room temperature according to JIS Z2202 (V notch test). The U-bend test for stress corrosion cracking in an alkaline environment was performed using a test piece similar to JIS-G0576 (42% Mg chloride corrosion test method for stainless steel) in a 40% NaOH solution at a test temperature of 120 ° C. The test was performed with no cracks, and the cracks with crosses. The case where no crack was generated was marked with ◯, and the case where a crack was cracked was marked with ×.
In addition, the measurement values in the upper and lower stages are the respective values obtained by performing the measurement twice.

  From the evaluation results shown in Table 7, the weld test material of the present embodiment (Example 7) sufficiently satisfies the target value for the tensile properties of the weld metal, and also satisfies the target value for the impact properties. . Moreover, the stress corrosion cracking property in alkaline aqueous solution was superior to the low-pressure turbine rotor material.

It is a perspective view which shows the welding test material used in 2nd and 3rd embodiment. It is sectional drawing which shows the welding test material used in 2nd and 3rd embodiment.

Explanation of symbols

1 Welding test material (turbine rotor)
2 Base material 3 First build-up weld part 4 Second build-up weld part

Claims (6)

Obtained by firing at least the mixed raw material,
By _{mass%, SiO 2: 5~20%,} MgO: 15~20%, Al 2 O 3: 20~30%, CaF 2: 5~20%, manganese oxide: 2-10% in terms of MnO value, Firing flux for submerged arc welding containing MgCO ₃ : 4 to 10%, ZrO ₂ : 2 to 10%, K ₃ AlF ₆ : 2 to 10%, metal powder 15% or less, and CaO: 5 to 20% Because
The mixed raw material, as a material of the CaO, of submerged arc welding sintering type flux of calcium oxide as a compound only, characterized by containing 5-20%. Obtained by firing at least the mixed raw material,
By _{mass%, SiO 2: 10~14%,} MgO: 17~19%, Al 2 O 3: 22~26%, CaF 2: 10~14%, manganese oxide: 3-5% in terms of MnO value, _{MgCO 3: 4~7%, ZrO 2} : 2~5%, K 3 AlF 6: 2~5%, the metal powder 5%, and CaO: submerged arc welding sintering type flux containing 5-10% Because
The mixed raw material, as a material of the CaO, of submerged arc welding sintering type flux of calcium oxide as a compound only, characterized by containing 5-10%.   3. A build-up welding method comprising a welding step of performing overlay welding on a base material by submerged arc welding using the flux according to claim 1 or 2.   The build-up welding method according to claim 3, further comprising a tempering step of heating the build-up weld portion to a predetermined temperature after the welding step. A first welding step of performing overlay welding on the base material to form a first overlay welding portion;
After the first welding step, a first tempering step of heating the first build-up weld part to a predetermined temperature;
Performing a build-up weld on the first build-up weld portion to form a second build-up weld portion; and
After the second welding step, a second tempering step of heating the second build-up weld part to a predetermined temperature ;
A build-up welding method comprising:
At least the second welding step is performed by submerged arc welding using the flux according to claim 1 or claim 2.   A turbine rotor, wherein a coating layer formed by the overlay welding method according to any one of claims 3 to 5 is provided on a surface of a base material made of low alloy steel.

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