JP2016022503A - Narrow groove tandem submerged arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, in a narrow groove tandem submerged arc welding method of improved 9Cr-1Mo steel, a welding method which is excellent in welding efficiency, satisfactory in a slag peeling efficiency and a bead state, and which can suppress the occurrence of a hot crack of molten metal.SOLUTION: A narrow groove tandem submerged arc welding method uses as a mother material an improved 9Cr-1Mo steel containing C, Si, Mn, P, S, Ni, Cr, Mo, V, Nb, Al, Ti, Zr and N in predetermined quantities, and the remainder being Fe and an inevitable impurity, and a welding wire containing C, Si, Mn, P, S, Ni, Cr, Mo, V, Nb, N and O at predetermined quantities, and the remainder being Fe and an inevitable impurity and having a wire diameter of 4.0 mmφ, uses an AC power source indicating depending characteristics with the combination of said welding wire and a welding flux of a predetermined alkaline degree, and performs the welding under the predetermined conditions of a wire feeding speed Vof the preceding electrode, a wire feeding speed Vof the trailing electrode, a welding speed v, and the deposition quantity per unit length.SELECTED DRAWING: None

Description

  The present invention relates to a submerged arc welding method, and more particularly to a tandem submerged arc welding method in a narrow groove for improved 9Cr-1Mo steel.

  A chemical reaction vessel (reactor) that performs desulfurization and heavy oil decomposition is a pressure vessel used for effective use of heavy oil and efficiency of petroleum refining. Since the reactor is operated at a high temperature and high pressure, ferritic heat resistant steels such as 1.25Cr-0.5Mo, 2.25Cr-1.0Mo, 2.25Cr-1.0Mo-V steel are applied as materials. Is done. At present, 2.25Cr-1.0Mo-V steel is the main material, and its design temperature is generally up to 454 ° C. In recent years, there has been a demand for higher efficiency in the effective use of heavy oil and petroleum refining, and research and development of an improved 9Cr-1Mo steel reactor that can be operated at a design temperature of around 500 ° C has been actively conducted. It is being advanced.

  The improved 9Cr-1Mo steel is steel in which Nb and V are added to the 9Cr-1Mo steel to improve the high temperature strength. For example, SA335Gr. As defined in ASTM (American Society for Testing and Materials) or ASME (American Society of Mechanical Engineers) standards. P91 and SA213Gr. T91 etc. Many of the improved 9Cr-1Mo steels have a track record in the field of boilers for thermal power generation.

  The reactor is a vertical cylindrical pressure vessel having a thickness of 50 mm or more, an inner diameter of 3 to 5 m, a total length of several tens of meters, and a weight of several hundred tons. The body of the reactor is manufactured by machining the end of a ring or forged ring welded by plate winding and circumferentially welding the rings. For this reason, the proportion of the welded portion in the pressure vessel is increased due to the structure, so that there is a strong demand for reduction of welding materials and higher efficiency of welding. In general, there is a method for reducing the weld material by reducing the weld width by narrowing the groove width and reducing the groove angle. In order to improve efficiency, there is a method of performing submerged arc welding from the first layer to the last layer with a tandem electrode. However, since it is a disadvantageous condition for hot cracking during welding, development of a suppression technique has been studied in the past.

For example, Patent Document 1 discloses that when a narrow groove having a groove width of 10 to 25 mm and a groove angle of 15 degrees or less is welded in one layer and one pass by submerged arc welding, 1.6 to 3 is used as a leading electrode. Narrow, characterized in that a 2 mmφ electrode and a 4.0 to 4.8 mmφ electrode are used as the trailing electrode, and the distance between the electrodes is 50 to 150 mm, and welding is performed using a sintered flux. A gap submerged arc welding method is disclosed.
In this welding method, the bead shape ratio (bead depth H / bead width W) is suppressed by setting the distance between the electrodes to 50 to 150 mm by tandem welding. At that time, the wire diameter of the leading electrode is set to 1.6 to 3.2 mmφ, and the wire diameter of the trailing electrode is set to 4.0 to 4.8 mmφ. Thereby, generation | occurrence | production of a hot crack is suppressed.

JP-A-60-177966

However, the conventional techniques have the following problems.
In Patent Document 1, the solid wire for welding described in Examples is mild steel. Here, the welding solid wire composed of the improved 9Cr-1Mo steel and the co-material has a larger Joule heat generation than the welding solid wire composed of the mild steel and the co-material, so that the amount of welding is increased and hot cracking occurs. Increases sensitivity. That is, it is difficult to solve the problem of hot cracking in welding of improved 9Cr-1Mo steel only by the method described in Patent Document 1. Further, there is a risk that the slag formed by the preceding electrode cannot be sufficiently melted by the succeeding electrode, and is not suitable for a place where high quality is required such as circumferential welding of the reactor.

In order to weld thick plates with high efficiency, it is effective to increase the welding heat input, that is, increase the welding current and arc voltage and decrease the welding speed. However, when the welding heat input is increased, the bead shape tends to become a die, especially in a narrow groove, and the risk of occurrence of hot cracking increases. The hot crack that is a problem here is a so-called "hot cracking" that occurs when low melting point compounds such as P, S, Si, and Nb contained in the weld metal segregate between dendrites and austenite grain boundaries during solidification, and weld shrinkage strain is added. It is a solidification crack.
Therefore, as a measure for suppressing hot cracking, it is also effective to suppress the components of the wire, specifically, impurities such as P and S to 100 ppm or less by dissolving with ultra high purity (Extra High Purity). However, ultra-high purity melting is economically difficult because it requires the use of electron beam melting and special furnace wall refractory materials. For this reason, the technique which can suppress generation | occurrence | production of a hot crack even at a general impurity level is calculated | required.

Moreover, the solid wire for welding comprised by the improved 9Cr-1Mo steel and a co-material made into object by this invention is 1.25Cr-0.5Mo, 2.25Cr-1.0Mo, 2.25Cr-1.0Mo-. Compared to each welding solid wire made of V steel and co-material, Joule heat generation is high and the amount of welding is increased, so the hot cracking sensitivity is further increased. Therefore, there is a need for a technique that can suppress the occurrence of hot cracking for the improved 9Cr-1Mo steel.
Further, in tandem submerged arc welding, in addition to improving the welding efficiency, it is also required that the slag peelability and the bead state are good.

  This invention is made | formed in view of the said situation, The subject is in the narrow gap tandem submerged arc welding of improved 9Cr-1Mo steel, while being excellent in welding efficiency, and the state of slag peelability and a bead is favorable. It is to provide a welding method capable of suppressing the occurrence of hot cracks in the weld metal.

As a result of intensive studies, the present inventors have found the following matters.
As a result of earnest research on narrow groove tandem welding, using the base material, welding wire, and welding flux of the components specified in the present invention, the wire feeding speed, welding speed, It was found that the occurrence of hot cracking can be suppressed by defining the amount of welding per unit length calculated by the ratio.

That is, the narrow groove tandem submerged arc welding method according to the present invention has C: 0.08 to 0.12 mass%, Si: 0.20 to 0.50 mass%, Mn: 0.30 to 0.60 mass. %, P: 0.020 mass% or less, S: 0.010 mass% or less, Ni: 0.40 mass% or less, Cr: 8.00 to 9.50 mass%, Mo: 0.85 to 1.05 % By mass, V: 0.18 to 0.25% by mass, Nb: 0.06 to 0.10% by mass, Al: 0.02% by mass or less, Ti: 0.01% by mass or less, Zr: 0.01 Less than mass%, N: 0.030-0.070 mass%, with the balance being Fe and inevitable impurities 9Cr-1Mo steel as a base material, C: 0.03-0.08 mass%, Si: 0.05-0.30 mass%, Mn: 0.50-2.20 mass%, P: 0.015 mass% Below, S: 0.010 mass% or less, Ni: 0.30-1.00 mass%, Cr: 8.00-10.50 mass%, Mo: 0.80-1.20 mass%, V: 0 10 to 0.40 mass%, Nb: 0.020 to 0.080 mass%, N: 0.016 to 0.055 mass%, O: 0.03 mass% or less, with the balance being Fe and inevitable It shows a drooping characteristic by using a welding wire having a wire diameter of 4.0 mmφ and a combination of the welding wire and a welding flux having a basicity of 2.3 to 2.7 represented by the following formula (1). using an AC power source, a wire feed rate _{V L} of the leading electrode 45~90g / min, the trailing electrode wire feed rate _{V T} the 60~110g / min, the welding speed v the 30~55cm / min, units Welding under the condition that the welding amount per length is 2.8 to 3.8 g / cm And features.
Basicity = (CaF ₂ + CaO + MgO + SrO + Na ₂ O + Li ₂ O + 1/2 (MnO + FeO)) / (SiO ₂ +1/2 (Al ₂ O ₃ + TiO ₂ + ZrO ₂ )) (1)
Here, each compound shows content (mass%) of each compound per flux total mass.

According to such a welding method, a narrow groove tandem submerged arc welding method (hereinafter, referred to as a submerged arc welding method or simply a welding method, as appropriate) using a modified 9Cr-1Mo steel as a base material defines a wire component. The creep rupture strength, toughness, oxidation resistance and high temperature strength of the weld metal are improved, and the hot cracking sensitivity of the weld metal is reduced. Also, by defining the wire diameter, the amount of welding becomes appropriate, the welding efficiency is improved, and the hot cracking and toughness deterioration of the weld metal are suppressed.
Further, by defining the basicity of the flux, the toughness of the weld metal is improved, and the bead appearance and bead shape are improved. Moreover, stable welding can be performed by using an AC power source exhibiting drooping characteristics. Furthermore, by regulating the wire feeding speed, welding speed, and welding amount per unit length, the welding efficiency, the bead state and the slag peelability are improved, and the occurrence of hot cracks in the weld metal is suppressed.

  The narrow groove tandem submerged arc welding method of the present invention is an improved 9Cr-1Mo steel welded metal that is excellent in welding efficiency, has a good bead state, and has excellent slag peelability and hot crack resistance. Can be obtained.

It is a front view which shows the state of the leading electrode and the trailing electrode in the welding method of this invention. It is a front view which shows the shape of the welding tip in the welding method of this invention. It is a side view of the welding tip shown in FIG. FIG. 3 is an end view of the tip end side of the welding tip shown in FIG. 2. It is a front view which shows the state of the welding tip in the welding method of this invention. It is a front view which shows the state of the welding tip in the welding method of this invention. It is a front view which shows the state of the welding tip in the welding method of this invention. It is a front view which shows the state of the welding tip in the welding method of this invention. It is a front view which shows the state of the welding tip in the welding method of this invention. It is a front view which shows the state of the welding tip in the welding method of this invention. It is sectional drawing which shows the lamination | stacking state of the test body and weld metal which were used in the Example.

Hereinafter, embodiments of the present invention will be described in detail.
The welding method of the present invention is a narrow groove tandem submerged arc welding method intended for narrow groove welding. The tandem submerged arc welding method refers to, for example, as shown in FIG. 1, a base material 10 made of modified 9Cr-1Mo steel, welding tips 11 a and 11 b in which wires 12 a and 12 b are respectively inserted, and welding not shown. It is a method of welding by arc welding using a flux. That is, in the welding method of the present invention, as shown in FIG. 1, welding is performed with two electrodes, a leading electrode 15a and a trailing electrode 15b. Here, in the present invention, the narrow groove of the base material 10 is defined as a groove having a plate thickness t of 50 mm or more and a groove angle θ of 0 to 5 ° (see FIG. 11). For example, in the test body 20 of FIG. 11 used in the examples described later, the plate thickness t is 250 mm, and the groove angle θ is 4 ° which is 2 ° + 2 °.

The tip shape is a straight tubular shape as shown in FIG. 1, a bend square shape as shown in FIGS. 2 to 4, or FIG. The shape as shown in 3b may be used, and is appropriately selected from the viewpoint of securing wire feedability and feeding position stabilization. In particular, in a bend square bar shaped tip in which the tip end portion 30a is bent within a range that does not hinder wire feeding as shown in FIGS. 2 to 4, the feeding position is stabilized, and as a result, the wire feeding speed is stabilized. .
2 to 10 show the leading electrode or the trailing electrode, which are collectively shown for convenience.

Here, as shown in FIGS. 1, 5 to 7, and FIGS. 8 to 10, the tip / base material distance is a portion where the wires 12a, 12b, and 40 finally protrude from the welding tips 11a, 11b, and 30. This is a vertical distance L between a tip end portion 13a, 13b, 30a and the base material 10.
As shown in FIGS. 1, 5 to 7, and 8 to 10, the tip angle is a line perpendicular to the surface of the base material 10, and the wires 12 a, 12 b, and 40 are finally welded tips 11 a, 11 b, This is an angle formed by the axis at the tip end portions 13a, 13b, and 30a that are portions protruding from 30.
The symbol α is the receding angle at the tip angle, and the symbol β is the advancing angle at the tip angle.
As shown in FIG. 1, the interelectrode distance is a horizontal distance W between the tip of the wire 12a of the leading electrode 15a and the tip of the wire 12b of the trailing electrode 15b.

  The narrow groove tandem submerged arc welding method of the present invention contains a predetermined amount of C, Si, Mn, P, S, Ni, Cr, Mo, V, Nb, Al, Ti, Zr, N, the balance being Fe and Using a modified 9Cr-1Mo steel, which is an inevitable impurity, as a base material, it contains a predetermined amount of C, Si, Mn, P, S, Ni, Cr, Mo, V, Nb, N, and O, the balance being Fe and inevitable A welding wire which is an impurity and has a wire diameter of 4.0 mmφ is used.

Then, the submerged arc welding method uses a combination of the welding wire and a welding flux of a predetermined basicity, and an AC power source that exhibits drooping characteristics, using a wire feeding speed V _L for the leading electrode, and a wire feeding for the trailing electrode. In this method, welding is performed under conditions in which the feeding speed V _T , the welding speed v, and the amount of welding per unit length are predetermined.
Hereinafter, the reasons for limiting the components of the base material and the wire, welding conditions, and the like will be described. In addition, each component content of the base material demonstrated below is with respect to the whole base material, and each component content of a welding wire is with respect to the whole welding wire.

[Chemical composition of base material]
The chemical composition of the base material is C: 0.08 to 0.12% by mass, Si: 0.20 to 0.50% by mass, Mn: 0.30 to 0.60% by mass, P: 0.020% by mass. Hereinafter, S: 0.010 mass% or less, Ni: 0.40 mass% or less, Cr: 8.00 to 9.50 mass%, Mo: 0.85 to 1.05 mass%, V: 0.18 to 0.25% by mass, Nb: 0.06 to 0.10% by mass, Al: 0.02% by mass or less, Ti: 0.01% by mass or less, Zr: 0.01% by mass or less, N: 0.030 It is a modified 9Cr-1Mo steel containing ˜0.070% by mass with the balance being Fe and inevitable impurities.

The present invention is directed to improved 9Cr-1Mo steel as a material to be welded (base material). There are various standards, and improved 9Cr-1Mo steel (hereinafter also referred to as Mod. 9Cr-1Mo steel) is obtained by adding Nb and V to 9Cr-1Mo steel. For example, the ASTM standard or ASME standard The defined SA335Gr. P91 and SA213Gr. There are T10, X10CrMoVNb9-1 defined in EN standards (European standards), and Fire STBA28, Fire STPA28, Fire SCMV28, and Fire SFVAF28 defined in thermal power technical standards.
The components of the base material defined in the present invention are in a range satisfying these standards.

[Chemical composition and size of welding wire]
<C: 0.03-0.08 mass%>
C combines with Cr, Mo, V and Nb to precipitate various carbides, and has the effect of improving the creep rupture strength. However, if the C content is less than 0.03% by mass, sufficient effects cannot be obtained. On the other hand, when C is added excessively, specifically, when the C content exceeds 0.08% by mass, the hot cracking resistance deteriorates. Therefore, C content of a welding wire shall be 0.03-0.08 mass%. The C content is preferably 0.04% by mass or more, more preferably 0.045% by mass or more, from the viewpoint of further improving the effect. Moreover, from a viewpoint of improving a hot cracking resistance more, Preferably it is 0.07 mass% or less, More preferably, it is 0.065 mass% or less.

<Si: 0.05-0.30 mass%>
Si acts as a deoxidizer and has an effect of reducing the amount of oxygen in the weld metal and improving the toughness of the weld metal. However, if the Si content is less than 0.05% by mass, sufficient effects cannot be obtained. On the other hand, Si is a ferrite-forming element, and when added in excess, specifically, if the Si content exceeds 0.30 mass%, δ-ferrite remains in the weld metal and the toughness of the weld metal deteriorates. To do. Therefore, Si content of a welding wire shall be 0.05-0.30 mass%. The Si content is preferably 0.10% by mass or more from the viewpoint of further improving the effect. Moreover, it is preferably 0.25% by mass or less from the viewpoint of further suppressing the deterioration of the toughness of the weld metal.

<Mn: 0.50 to 2.20 mass%, Ni: 0.30 to 1.00 mass%>
Mn acts as a deoxidizer and has the effect of reducing the amount of oxygen in the weld metal and improving toughness. Further, Mn and Ni are austenite-forming elements, and both have the effect of suppressing toughness deterioration due to residual δ-ferrite in the weld metal. However, when the Mn content is less than 0.50% by mass or when the Ni content is less than 0.30% by mass, these effects cannot be obtained and the toughness of the weld metal deteriorates. On the other hand, when the Mn content exceeds 2.20% by mass or when the Ni content exceeds 1.00% by mass, the toughness of the weld metal deteriorates. Therefore, the Mn content of the welding wire is 0.50 to 2.20 mass%, and the Ni content of the welding wire is 0.30 to 1.00 mass%.

The Mn content is preferably 0.80% by mass or more, more preferably 1.10% by mass or more, from the viewpoint of further improving the above effects. Further, from the viewpoint of further suppressing deterioration of the toughness of the weld metal, it is preferably 1.90% by mass or less, more preferably 1.60% by mass or less.
The Ni content is preferably 0.40% by mass or more, more preferably 0.50% by mass or more, from the viewpoint of further improving the above effects. Further, from the viewpoint of further suppressing deterioration of the toughness of the weld metal, it is preferably 0.90% by mass or less, more preferably 0.80% by mass or less.

<Cr: 8.00 to 10.50% by mass>
Cr is the Mod. Targeted for the welding wire used in the present invention. It is a main element of 9Cr-1Mo steel, and an indispensable element for ensuring oxidation resistance and high temperature strength. However, if the Cr content is less than 8.00% by mass, the oxidation resistance and high-temperature strength are insufficient. On the other hand, Cr is a ferrite-forming element, and when it is added in excess, specifically, if the Cr content exceeds 10.50 mass%, δ-ferrite remains and the toughness of the weld metal deteriorates. Therefore, Cr content of a welding wire shall be 8.00-10.50 mass%. Thereby, excellent oxidation resistance and high temperature strength can be obtained. The Cr content is preferably 8.40% by mass or more, more preferably 8.60% by mass or more, from the viewpoint of further improving the effect. Further, from the viewpoint of further suppressing the deterioration of the toughness of the weld metal, it is preferably 9.40% by mass or less, more preferably 9.20% by mass or less.

<Mo: 0.80 to 1.20 mass%>
Mo is a solid solution strengthening element and has an effect of improving the creep rupture strength. However, if the Mo content is less than 0.80% by mass, sufficient creep rupture strength cannot be obtained. On the other hand, since Mo is a ferrite-forming element, if added in excess, specifically, if the Mo content exceeds 1.20% by mass, δ-ferrite remains in the weld metal and the toughness of the weld metal. Deteriorates. Therefore, the Mo content of the welding wire is 0.80 to 1.20 mass%. The Mo content is preferably 0.90% by mass or more from the viewpoint of further improving the above effects. Further, from the viewpoint of further suppressing the deterioration of the toughness of the weld metal, it is preferably 1.10% by mass or less.

<V: 0.10 to 0.40 mass%>
V is a precipitation strengthening element and has the effect of improving the creep rupture strength by being precipitated as carbonitride. However, if the V content is less than 0.10% by mass, sufficient creep rupture strength cannot be obtained. On the other hand, V is also a ferrite-forming element, and when added excessively, specifically, if the V content exceeds 0.40% by mass, δ-ferrite remains in the weld metal and the toughness of the weld metal deteriorates. To do. Therefore, V content of a welding wire shall be 0.10-0.40 mass%. The V content is preferably 0.15% by mass or more, more preferably 0.20% by mass or more, from the viewpoint of further improving the effect. Further, from the viewpoint of further suppressing the deterioration of the toughness of the weld metal, it is preferably 0.35 mass% or less, more preferably 0.30 mass% or less.

<Nb: 0.020 to 0.080 mass%>
Nb is an element that contributes to stabilization of creep rupture strength by precipitation as solid solution strengthening and nitride. However, if the Nb content is less than 0.020% by mass, sufficient creep rupture strength cannot be obtained. On the other hand, Nb is also a ferrite-forming element. When it is added excessively, specifically, if the Nb content exceeds 0.080 mass%, δ-ferrite remains in the weld metal and the toughness of the weld metal deteriorates. To do. Therefore, Nb content of a welding wire shall be 0.020-0.080 mass%. The Nb content is preferably 0.030% by mass or more, more preferably 0.035% by mass or more, from the viewpoint of further improving the above effects. Moreover, from a viewpoint of suppressing the toughness deterioration of a weld metal more, Preferably it is 0.070 mass% or less, More preferably, it is 0.065 mass% or less.

<P: 0.015 mass% or less>
P is an element that enhances hot cracking sensitivity. When P content exceeds 0.015 mass%, hot cracking resistance will deteriorate. Therefore, the P content of the welding wire is regulated to 0.015% by mass or less. The P content is preferably 0.010% by mass or less, more preferably 0.005% by mass or less, from the viewpoint of further suppressing deterioration of hot cracking resistance. The P content is preferably 0% by mass, but substantially 0.003% by mass is the lower limit.

<S: 0.010 mass% or less>
S is an element that enhances hot cracking sensitivity. When S content exceeds 0.010 mass%, hot cracking resistance will deteriorate. Therefore, the S content of the welding wire is regulated to 0.010% by mass or less. The S content is preferably 0.008% by mass or less, more preferably 0.005% by mass or less, from the viewpoint of further suppressing deterioration of hot cracking resistance. The S content is preferably 0% by mass, but substantially 0.003% by mass is the lower limit.

<N: 0.016-0.055 mass%>
N is an element that contributes to stabilization of creep rupture strength by precipitation as a solid solution strengthening and nitride. However, if the N content is less than 0.016% by mass, sufficient creep rupture strength cannot be obtained. On the other hand, when N is added excessively, specifically, when the N content exceeds 0.055% by mass, blowholes are generated. Therefore, N content of a welding wire shall be 0.016-0.055 mass%. The N content is preferably 0.025% by mass or more from the viewpoint of further improving the above effects. Moreover, from a viewpoint of suppressing generation | occurrence | production of a blowhole more, Preferably it is 0.045 mass% or less.

<O: 0.03 mass% or less>
O remains as an oxide in the weld metal and degrades the toughness of the weld metal. Specifically, if the O content exceeds 0.03% by mass, the residual oxide increases and the toughness of the weld metal deteriorates. Therefore, the O content of the welding wire is regulated to 0.03% by mass or less. The O content is preferably 0.02% by mass or less, more preferably 0.015% by mass or less, from the viewpoint of further suppressing the deterioration of the toughness of the weld metal. The O content is preferably 0% by mass, but substantially 0.002% by mass is the lower limit.

<Balance: Fe and inevitable impurities>
The balance of the welding wire components is Fe and inevitable impurities. Examples of inevitable impurities include Cu, As, Sb, and Sn. Cu is contained by copper plating on the wire surface.

<Wire diameter of welding wire>
The diameter of the wire used in the present invention is essential to 4.0 mmφ. In the present invention, the wire diameter is 4.0 mmφ for both the leading and trailing electrodes. When the wire diameter is 3.2 mmφ, a sufficient amount of welding cannot be obtained, and the welding efficiency is sacrificed. On the other hand, at 4.8 mm, since the amount of welding is large, it becomes difficult to control the amount of welding that suppresses hot cracking. Further, at 4.8 mmφ, the layer thickness increases, so that there is a problem that the toughness of the weld metal deteriorates. Therefore, the wire diameter is 4.0 mmφ for both the leading electrode and the trailing electrode.

<Basicity of welding flux>
It is essential that the submerged arc welding flux used in the present invention has a basicity of 2.3 to 2.7. When the basicity is less than 2.3, the amount of oxygen in the weld metal is not sufficiently lowered and the toughness is lowered. On the other hand, when the basicity exceeds 2.7, the bead appearance and bead shape deteriorate. Therefore, the basicity is in the range of 2.3 to 2.7. The basicity is preferably 2.4% by mass or more from the viewpoint of further suppressing the deterioration of the toughness of the weld metal. Moreover, it is 2.6 mass% or less from a viewpoint of suppressing a bead external appearance and bead shape deterioration more.
In addition, the basicity in this invention is based on following formula (1).

Basicity = (CaF ₂ + CaO + MgO + SrO + Na ₂ O + Li ₂ O + 1/2 (MnO + FeO)) / (SiO ₂ +1/2 (Al ₂ O ₃ + TiO ₂ + ZrO ₂ )) (1)
Here, each compound shows content (mass%) of each compound per flux total mass.
In addition, as long as basicity satisfy | fills the said range as a flux used by this invention, other conditions, such as a component, are not prescribed | regulated in particular.

[Welding conditions]
As one of methods for suppressing the occurrence of hot cracking, a method of restricting heat input is taken. However, the welding current and the arc voltage tend to change the energy used for melting the wire depending on the welding environment such as the state of the workpiece and the energization point. That is, even if welding is performed with the same heat input, there may be a difference in the presence or absence of hot cracking. Therefore, the present inventors solved the problem by defining the wire feeding speed, the welding speed, and the amount of welding per unit length.

<Wire feed speed: wire feed rate _{V L} of the leading electrode is 45~90g / min, the trailing electrode wire feed rate _{V T} is 60~110g / min>
If the wire feeding speed of the leading electrode is less than 45 g / min, or the wire feeding speed of the trailing electrode is less than 60 g / min, the welding current is too small and the arc becomes unstable, resulting in poor penetration. On the other hand, if the wire feeding speed of the leading electrode exceeds 90 g / min, or the wire feeding speed of the trailing electrode exceeds 110 g / min, the amount of welding is excessive and hot cracking occurs, and slag peeling Also deteriorates. Thus, the wire feed rate is the leading electrode wire feed speed _{V L} to 45~90g / min, the trailing electrode wire feed speed _{V T} and 60~110g / min.

  The wire feeding speed of the leading electrode is preferably 50 g / min or more, more preferably 55 g / min or more from the viewpoint of further suppressing the occurrence of poor penetration. Moreover, from a viewpoint of suppressing generation | occurrence | production of a hot crack and deterioration of slag peelability more, Preferably it is 85 g / min or less, More preferably, it is 80 g / min or less. The wire feeding speed of the trailing electrode is preferably 65 g / min or more, more preferably 70 g / min or more from the viewpoint of further suppressing the occurrence of poor penetration. Moreover, from a viewpoint of suppressing generation | occurrence | production of a hot crack and deterioration of slag peelability more, Preferably it is 105 g / min or less, More preferably, it is 100 g / min or less.

When comparing the wire feed speed range of the leading electrode and the wire feed speed range of the trailing electrode, the wire feed speed range of the leading electrode is smaller. Here, the amount of weld metal by the leading electrode and the amount of welding metal by the trailing electrode are equally divided by the leading electrode and the trailing electrode, so that the amount of welding metal by the leading electrode is smaller, The bead depth can be reduced and the bead width can be increased. This is advantageous for hot cracking. Therefore, the wire feeding speed is preferably “leading pole V _L <following pole V _T ”.

<Welding speed v: 30 to 55 cm / min>
If the welding speed is less than 30 cm / min, the amount of welding is too large and hot cracking occurs. On the other hand, if the welding speed exceeds 55 cm / min, the molten metal cannot be supplied in time, the bead shape becomes unstable, and fusion failure and slag entrainment occur. Therefore, the welding speed v is set to 30 to 55 cm / min. The welding speed is preferably 35 cm / min or more from the viewpoint of further suppressing the occurrence of hot cracking. Moreover, it is preferably 50 cm / min or less from the viewpoint of bead shape stabilization and prevention of poor fusion and slag entrainment. In addition, the welding speed is a moving speed in the welding direction of the welding tips 11a and 11b of the welding machine as shown in FIG.

<Welding amount per unit length: 2.8 to 3.8 g / cm>
The welding amount per unit length is calculated by “wire feeding speed / welding speed”. That is, the amount of welding per unit length is obtained by the ratio of the wire feeding speed and the welding speed. The wire feeding speed is the sum of the wire feeding speed of the leading electrode and the wire feeding speed of the trailing electrode.
The point of the present invention is to appropriately control the amount of welding per unit length. If the welding amount per unit length is less than 2.8 g / cm, the welding amount is too small and the welding efficiency is deteriorated. On the other hand, when the amount of welding per unit length exceeds 3.8 g / cm, the force accompanying shrinkage increases. Further, since the shape of the bead is close to the shape of a bead, the solidification direction of the weld metal is horizontal toward the center of the bead, and the direction in which the contraction force is applied is perpendicular to the final solidified portion. Therefore, hot cracking is likely to occur. Therefore, the welding amount per unit length is set to 2.8 to 3.8 g / cm. The amount of deposition per unit length is preferably 2.9 g / cm or more, more preferably 3.0 g / cm or more, from the viewpoint of further improving the welding efficiency. Moreover, from a viewpoint of suppressing generation | occurrence | production of a hot crack more, Preferably it is 3.7 g / cm or less, More preferably, it is 3.6 g / cm or less.

<AC welding machine showing drooping characteristics>
The welding current and the arc voltage are adjusted as one means for controlling the wire feeding speed within an appropriate range.
The welding machine used in the present invention is an AC welding machine showing drooping characteristics. The drooping characteristic is a characteristic of a power source that can perform stable welding with little change in current even if the arc length varies. Specifically, when the arc length is increased, the wire feeding speed is temporarily increased, and when the arc length is decreased, the wire feeding speed is decreased. That is, since the power supply characteristic affects the wire feeding speed, the wire feeding speed needs to be managed within the scope of the present invention. In general, the construction conditions are determined by the welding current and the arc voltage, but this is not sufficient, and it has been found that the present invention needs to be managed at the wire feed speed. Even if the welding current is constant, the wire feed speed needs to be used as a parameter because it changes depending on the arc state, wire angle, and the like.
In the present invention, an AC power supply exhibiting drooping characteristics is used.

  As described above, the present invention is suitable for submerged arc welding of improved 9Cr-1Mo steel used in a chemical reaction vessel (reactor) that performs desulfurization and heavy oil decomposition.

Hereinafter, examples that fall within the scope of the present invention will be described in comparison with comparative examples that depart from the scope of the present invention.
Using a base material of chemical components shown in Table 1, ASTM SA335Gr. Three types of modified 9Cr-1Mo steels corresponding to the chemical composition of P91 were prepared. For this improved 9Cr-1Mo steel, as shown in FIG. 11, a 4 ° narrow groove with a plate thickness t of 250 mm, a groove bottom radius of curvature R of 10 mm, and a groove angle θ of 2 ° + 2 ° is machined. A modified 9Cr steel specimen 20 was formed.
Three types of chemical component wires shown in Table 2 were used. The wire diameter is 4.0 mmφ. Further, three kinds of fluxes of particle size, chemical composition and basicity shown in Table 3 were used.

Then, submerged arc welding was performed in the narrow gap of the test body 20 shown in FIG. 11 using the wires shown in Table 2 and the flux shown in Table 3 while changing the wire feeding speed and the welding speed. The wire feed speed was controlled by changing the welding current and welding speed. In the main welding, the weld metal 21 is laminated in the direction of the arrow in the figure.
The welding conditions are as follows. Other conditions are shown in Table 4. In the table, those not satisfying the scope of the present invention are indicated by underlining the numerical values.

<Welding conditions>
Tip / base material distance: leading electrode 25 mm, trailing electrode 30 mm
Tip angle: Leading pole: -5 ° (retraction angle 5 °), trailing pole: 40 ° (advancing angle 40 °)
Distance between electrodes: 20mm
Polarity: AC-AC tandem Power supply characteristics: Drooping characteristics Welding posture: Down Laminating method: 1st layer 1 pass, 1 layer 2 passes thereafter

About the test body 20 which performed this welding, slag peelability, the state of a bead, welding efficiency, and hot crack resistance were evaluated.
<Evaluation of slag peelability>
After completion of welding, the flux adhering to the bead surface was hit with a hammer three times, and the condition for easy peeling was judged as ◯, and the condition for not peeling was judged as x.

<Evaluation of bead state>
In the evaluation of the slag peelability, the surface appearance after peeling the slag is visually confirmed. If there is no weld defect and the bead shape is good, ○, if a weld defect occurs or the bead shape is unstable X was determined.

<Evaluation of welding efficiency>
The welding efficiency was evaluated as ○ when the lamination method can be welded in 2 passes per layer, and × when the amount of welding was reduced and welding was required in 3 passes or more per layer.

<Evaluation of hot cracking resistance>
The macrostructure was observed in cross sections every 50 mm within the range of 300 mm excluding the start and end of the weld bead. In all of the five cross sections, the condition in which no cracks occurred was judged as ◯, and the condition in which cracks occurred was judged as x.
These results are shown in Table 4. In the table, “−” indicates that no evaluation was performed.

As shown in Table 4, Nos. 1 to 7 satisfied the scope of the present invention, and there was no problem in slag peelability, bead state, and welding efficiency, and no hot cracking occurred.
In No. 8, the wire feeding speeds of the leading electrode and the trailing electrode are out of the lower limit of the present invention. In No. 8, since the welding current was small and the wire feed speed was small, the arc was not stable, and poor penetration occurred at the boundary between the groove surface and the bead. Further, the amount of welding per unit length deviated from the lower limit of the present invention. Since the bead state was poor, the welding efficiency and hot crack resistance were not evaluated.
In No. 9, the wire feeding speeds of the leading electrode and the trailing electrode are out of the upper limit of the present invention. Since the welding current was large and the wire feeding speed was large, the amount of welding was too large, causing hot cracks, and the slag peelability also decreased. Further, the amount of welding per unit length deviated from the upper limit of the present invention, and hot cracking occurred. Since the slag peelability was poor, the bead state and welding efficiency were not evaluated.

In No. 10, the welding speed is out of the lower limit of the present invention. Since the welding speed was slow, the amount of welding was too high and hot cracking occurred. Further, the amount of welding per unit length deviated from the upper limit of the present invention, and hot cracking occurred.
In No. 11, the welding speed is outside the upper limit of the present invention. Therefore, the wire feeding is not in time for the welding speed, and the bead width becomes unstable. Since the bead state was poor, the welding efficiency and hot crack resistance were not evaluated.

In Nos. 12, 14, and 15, the amount of welding per unit length is outside the upper limit of the present invention. Therefore, the bead shape was close to that of a mold and hot cracking occurred.
In No. 13, the welding amount per unit length is outside the lower limit of the present invention. Therefore, since the welding amount is small, the number of weldings inside the groove is increased, and the welding efficiency is lowered. In addition, since the welding efficiency was poor, the hot crack resistance was not evaluated.

  Since the present invention is characterized in that the wire feeding speed, welding speed, and welding amount per unit length of the leading electrode and the trailing electrode are defined, comparative examples of other requirements such as wire components are omitted. did. The reasons for limiting other requirements such as wire components are as described in this specification.

  The present invention has been described in detail with reference to the embodiments and examples. However, the gist of the present invention is not limited to the above-described contents, and the scope of right is widely interpreted based on the description of the claims. Must. Needless to say, the contents of the present invention can be widely modified and changed based on the above description.

10 Base material (material to be welded)
11a, 11b, 30 Welding tip 12a, 12b, 40 Welding wire 13a, 13b, 30a Tip tip 15a Leading electrode 15b Trailing electrode 20 Specimen

Claims (1)

C: 0.08 to 0.12 mass%, Si: 0.20 to 0.50 mass%, Mn: 0.30 to 0.60 mass%, P: 0.020 mass% or less, S: 0.010 % By mass or less, Ni: 0.40% by mass or less, Cr: 8.00 to 9.50% by mass, Mo: 0.85 to 1.05% by mass, V: 0.18 to 0.25% by mass, Nb : 0.06-0.10 mass%, Al: 0.02 mass% or less, Ti: 0.01 mass% or less, Zr: 0.01 mass% or less, N: 0.030-0.070 mass% Containing, as a base material, improved 9Cr-1Mo steel containing Fe and the inevitable impurities in the balance,
C: 0.03-0.08 mass%, Si: 0.05-0.30 mass%, Mn: 0.50-2.20 mass%, P: 0.015 mass% or less, S: 0.010 % By mass or less, Ni: 0.30 to 1.00% by mass, Cr: 8.00 to 10.50% by mass, Mo: 0.80 to 1.20% by mass, V: 0.10 to 0.40% by mass %, Nb: 0.020 to 0.080 mass%, N: 0.016 to 0.055 mass%, O: 0.03 mass% or less, the balance being Fe and inevitable impurities, the wire diameter Uses a welding wire of 4.0 mmφ,
A combination of the welding wire and a welding flux having a basicity of 2.3 to 2.7 represented by the following formula (1):
Using an AC power source showing the drooping characteristics, 30～55Cm wire feed rate _{V L} the 45~90g / min of the leading electrode, the trailing electrode wire feed rate _{V T} the 60~110g / min, the welding speed v / Min, a narrow groove tandem submerged arc welding method, wherein welding is performed under the condition that the amount of welding per unit length is 2.8 to 3.8 g / cm.
Basicity = (CaF ₂ + CaO + MgO + SrO + Na ₂ O + Li ₂ O + 1/2 (MnO + FeO)) / (SiO ₂ +1/2 (Al ₂ O ₃ + TiO ₂ + ZrO ₂ )) (1)
Here, each compound shows content (mass%) of each compound per flux total mass.

Images