JP7031271B2 - Flux-cored wire for vertical electrogas arc welding and welding joint manufacturing method - Google Patents

Description

The present invention relates to a flux-filled wire for vertical electrogas arc welding and a method for manufacturing a welded joint using the flux-filled wire for vertical electrogas arc welding.

In general, one-pass large heat input welding of electrogas arc welding enables simpler and more efficient welding than the multi-layer welding method of small to medium heat input. Therefore, it is used for welding welded structures such as ships. The welding heat input is several tens of kJ / mm or more, which is extremely large as compared with the multi-layer welding with a welding heat input of about several kJ / mm. However, in the one-pass large heat input welding, since the welding heat input is large, there is a problem that the cooling rate of the weld metal formed by welding is slow and it becomes difficult to secure the strength of the weld metal. Further, in electrogas arc welding, since it is a one-pass welding, it is not easy to secure the toughness of the weld metal because the structure miniaturization and tempering effect by the subsequent welding beads cannot be expected. As a result, in electrogas arc welding, there is a problem that it is difficult to ensure the safety of the welded joint forming the welded structure. In particular, when the plate thickness is 60 mm or more, the heat input becomes more than 45 kJ / mm in electrogas arc welding, and the problem becomes apparent.

As described above, it is generally difficult to secure both the strength and toughness of the weld metal in high heat input welding.

The technique disclosed in Patent Document 1 secures the strength and toughness of the weld metal even in two-electrode electrogas arc welding with a heat input of more than 50 kJ / mm by adjusting the Ni amount and Mo amount of the flux-cored wire. It proposes a flux-cored wire and a welding method aiming at this. However, this technique is insufficient to improve the toughness of the weld metal because Al is not contained in the weld metal and a fine intragranular transformation structure cannot be obtained.

The techniques disclosed in Patent Document 2 and Patent Document 3 are a method of performing two-electrode electrogas arc welding of a steel plate having a plate thickness of 50 to 80 mm mainly using a flux-cored wire and a solid wire, and welding suitable for the method. It proposes materials. However, these documents do not mention the types of slag agents for flux-cored wires that are effective for ensuring performance, and do not clearly present design guidelines for electrogas arc welding using flux-cored wires.

The technique disclosed in Patent Document 4 proposes to secure the toughness of the weld metal by utilizing a metal fluoride in a 1-pass multi-electrode electrogas arc welding flux-containing wire having a plate thickness of 35 to 100 mm. Is. However, since the flux-cored wire of Patent Document 4 contains 1.0% by mass or more of slag, a large amount of slag is generated during welding, the arc becomes unstable, and welding defects occur.

Japanese Unexamined Patent Publication No. 2008-87045 Japanese Unexamined Patent Publication No. 2005-330578 Japanese Unexamined Patent Publication No. 2005-329460 Japanese Unexamined Patent Publication No. 11-10391

Based on the above background, the present invention is a weld metal having good toughness and strength (yield strength and tensile strength) in an electrogas arc welding method in which a steel plate having a plate thickness of 60 to 80 mm is vertically welded in one pass. It is an object of the present invention to provide a wire having a flux for vertical electrogas arc welding, and a method for manufacturing a welded joint using the wire having a flux for electrogas arc welding.

The gist of the present invention is as follows.
(1) The flux-containing wire for vertical electrogas arc welding according to one aspect of the present invention includes a steel outer skin and a flux, and the flux is used as a slag agent in an amount of% by mass based on the total mass of the flux-containing wire. Na ₂ O: 0.00 to less than 1.00%, NaF: 0.00 to less than 1.00%, CaO: 0.00 to less than 1.00%, CaF ₂ : 0.00 to less than 1.00% , MgO: 0.00 to less than 1.00%, MgF ₂ : 0.00 to less than 1.00%, MnO: 0.00 to less than 1.00%, and MnF ₂ : 0.00 to 1.00% The deoxidizing ability index X represented by the formula (A) is 100 to 200, and the slag agents Na ₂ O, NaF, CaO, CaF ₂ , MgO, MgF ₂ , MnO and MnF ₂ are contained. The total amount Y is 0.10 to less than 1.00%, the product of the deoxidizing ability index X and the total amount Y is 10 to 200, and the flux-filled wire is less than 10%. The flux-containing wire containing iron powder further contains, as an alloy component, C: 0.02 to 0.10% and Si: 0.2 to 0.9% in mass% with respect to the total mass of the flux-containing wire. , Mn: 1.0 to 4.0%, P: 0.03% or less, S: 0.03% or less, Ni: 0.1 to 3.0%, Mo: 0.05 to 1.00%, V: 0.20% or less, Ti: 0.05 to 0.25%, B: 0.0010 to 0.0200%, Al: 0.05 to 0.50%, Mg: 0.01 to 0.50 % And REM: 0 to less than 0.0010%, the balance is Fe and impurities, the Ceq represented by the formula (B) is 0.35 to 0.50%, and iron powder, V. , Cu, Cr, and Nb, one or more of which are contained in the following amounts .
Iron powder: more than 0% and less than 30%, V: 0.005 to 0.20%, Cu: 0.10 to 1.00%, Cr: 0.05 to 0.50%, and Nb: 0.01 to 0.05%
X = 100 × {2.0 × ([Na ₂ O] + [NaF]) + 1.5 × ([CaO] + [CaF ₂ ] + [MgO] + [MgF ₂ ]) + 1.0 × ([MnO]) ] + [MnF ₂ ])} / ([CaO] + [CaF ₂ ] + [MgO] + [MgF ₂ ] + [Na ₂ O] + [NaF] + [MnO] + [MnF ₂ ]) ... (A)
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (B)
However, the chemical formula with [] in the formula (A) indicates the content of the slag agent according to each chemical formula in mass% with respect to the total mass of the flux-filled wire, and the element with [] in the formula (B). Indicates the content of the element in the alloy component according to each element symbol in mass% with respect to the total mass of the flux-filled wire.
(2) The flux-containing wire according to (1) above has Cu: 0.1 to 0.5% and Cr: 0.05 in terms of mass% of the total mass of the flux-containing wire as the alloy component. It may contain one or more of ~ 0.50% and Nb: 0.01 ~ 0.05%.
(3) In the method for manufacturing a welded joint according to another aspect of the present invention, a steel plate is welded using the wire containing a flux for vertical electrogas arc welding according to the above (1) or (2).
(4) In the method for manufacturing a welded joint according to (3) above, the Ceq of the weld metal of the welded joint represented by the formula (C) may be 0.35 to 0.50%.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (C)
However, the element with [] in the formula (C) indicates the content of the element in the weld metal according to each element symbol in the unit mass%.
(5) In the method for manufacturing a welded joint according to (3) or (4) above, the welding is multi-electrode vertical electrogas arc welding, and in the multi-electrode vertical electrogas arc welding, the vertical of all electrodes is said. The flux-cored wire for welding the electrogas arc is the same, the Ceq of the steel plate represented by the formula (D) is 0.30 to 0.40%, and the plate thickness of the steel plate is 60 to 80 mm. May be good.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (D)
However, the element with [] in the formula (D) indicates the content of the element in the steel sheet according to each element symbol in the unit mass%.

According to the method for manufacturing a flux-filled wire for electrogas arc welding of the present invention and a welded joint using the same, the tensile strength (TS) of the weld metal is 570 MPa or more in multi-electrode electrogas arc welding with a plate thickness of 60 to 80 mm. Welding metal with excellent strength and toughness can be stably obtained, with the yield strength (YP) of the weld metal being 460 MPa or more and the -20 ° C charpy absorption energy (vE- ₂₀ ) of the weld metal being 80 J or more. , There are no welding defects, and excellent welding workability can be obtained.

It is a graph which shows the relationship between the slag agent of a flux-cored wire and the oxygen content of a weld metal. It is a schematic diagram which shows the groove shape and the position of each electrode of the Example of this invention. It is a schematic diagram which shows the collection position of the Charpy test piece and the weld metal (WM) tensile test piece of the Example of this invention.

Hereinafter, an example of a preferred embodiment of the present invention will be described in detail.
In the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value. In the present specification, the weld metal means a metal melted and solidified during welding, and the weld heat affected zone (HAZ) means that the structure, metallurgical properties, mechanical properties, etc. change due to the welding heat. It means the part of the base metal that has not been melted. The component of the weld metal is a mixture of the component of the base steel plate (steel plate), which is the material to be welded, and the alloy component of the flux-filled wire for vertical electrogas arc welding (hereinafter abbreviated as "flux-filled wire" or "wire"). Being done. The alloy component of the wire means a component existing as a simple substance or an alloy in the wire. Therefore, elements that form slag agents, arc stabilizers, etc., such as fluorides, oxides, and carbonates, are considered not to be alloy components. This is because the slag agent, the arc stabilizer, and the like are substantially discharged to the outside of the weld metal during welding.

Conventionally, it has been known that reduction of oxygen content and utilization of acicular ferrite are effective for improving the toughness of weld metal. Further, in the prior art, it is said that it is effective to increase the basicity of slag in order to reduce the amount of oxygen in the weld metal. However, even when the basicity of slag is high, the amount of oxygen in the weld metal cannot be reduced if the amount of slag is small. On the other hand, if the amount of slag is increased, the arc becomes unstable during welding, and welding defects occur in the weld metal. Therefore, in the wire according to the present embodiment, both the amount of slag and the basicity of the slag are adjusted, whereby the amount of oxygen in the weld metal can be reduced without affecting the welding workability.

The composition of the wire according to the present embodiment was controlled so that the microstructure of the weld metal was mainly composed of acylical ferrite. Specifically, by incorporating Ti, Al, and B in the alloy component of the wire, the nucleation of acicular ferrite was finely dispersed in the weld metal. According to the studies by the present inventors, when any one of Ti, Al, and B is not contained in the weld metal, the weld metal having a fine structure could not be obtained. Therefore, all of Ti, Al, and B must be contained in the weld metal.

The technical idea of the present invention is shown below.
First, in order to ensure the toughness of the weld metal, the wire configuration was determined so as to control the oxygen content and the microstructure of the weld metal within a preferable range.
The amount of oxygen in the weld metal was controlled by using the slag agent contained in the flux of the wire. Specifically, as a slag agent, one or more of Na ₂ O, NaF, CaO, CaF ₂ , MgO, MgF ₂ , MnO, and MnF ₂ was contained in the flux of the wire.

The above configuration was determined based on the results of the investigation by the present inventors on the relationship between the slag agent of the wire and the oxygen content of the weld metal shown in FIG. According to the findings of the present inventors, the oxygen content of the weld metal is the mass of the deoxidizing ability index X represented by the formula (1) and the metal fluoride and the metal oxide which are the slag agents with respect to the total weight of the wire. It can be arranged by the product (X × Y) with the total amount (total amount of slag agent) Y in%. When X × Y was 50 or less, the oxygen content of the weld metal increased, and when it was 10 or less, the oxygen content of the weld metal was about 0.0600 mass%.
X = 100 × {2.0 × ([Na ₂ O] + [NaF]) + 1.5 × ([CaO] + [CaF ₂ ] + [MgO] + [MgF ₂ ]) + 1.0 × ([MnO]) ] + [MnF ₂ ])} / ([CaO] + [CaF ₂ ] + [MgO] + [MgF ₂ ] + [Na ₂ O] + [NaF] + [MnO] + [MnF ₂ ]) ... (1)
For non-additive substances, zero is substituted in the above equation.
However, the chemical formula with [] in the formula (1) indicates the mass% of the total mass of the flux-cored wire of the slag agent according to each chemical formula.

The deoxidizing ability index X is an index showing the deoxidizing ability of the slag agent when the total amount of slag is the same, and according to the experimental results of the present inventors, the appropriate range was 100 to 200. If the deoxidizing ability index X is less than 100, the required deoxidizing ability cannot be obtained. Considering the upper limit of the total amount Y of the slag agent described later, the deoxidizing ability index X does not exceed 200, so 200 is the upper limit of the deoxidizing ability index X. The lower limit of X is preferably 120.

The appropriate range of the total amount of slag agent Y was 0.10% to less than 1.00%. According to the experimental results of the present inventors, when the total amount Y of the slag agent is less than 0.10%, the amount of slag is insufficient and the amount of oxygen in the weld metal is high. When the total amount Y of the slag agent is 1.00% or more, the amount of slag is too large, so that the arc becomes unstable during welding and welding defects are likely to occur. The preferable lower limit of the total amount of slag agent Y is 0.20%. The preferable upper limit of the total amount Y of the slag agent is 0.80%.

As described above, the amount of oxygen in the weld metal is arranged by XX, and the appropriate range is 10 to 200. When X × Y is less than 10, the deoxidizing ability or amount of slag is insufficient, and the amount of oxygen in the weld metal does not decrease sufficiently. If X × Y exceeds 200, the amount of slag is too large, so that the arc becomes unstable during welding and welding defects occur. The lower limit of X × Y is preferably 50, more preferably 100, and even more preferably 120. The upper limit of X × Y is preferably 180, more preferably 150.

It is not necessary to separately set the upper and lower limit values for each of the above-mentioned slag agents Na ₂ O, NaF, CaO, CaF ₂ , MgO, MgF ₂ , MnO, and MnF ₂ . However, as long as the total amount Y of the slag agent is less than 1.00%, the above-mentioned regulation of the deoxidizing ability index X, the regulation of the total amount of slag agent Y, and the regulation of XXY are satisfied, the slag is satisfied. Considering that the type of the agent is not particularly limited, the values that can be taken for each of the contents of Na ₂ O, NaF, CaO, CaF ₂ , MgO, MgF ₂ , MnO, and MnF ₂ are 0 to less than 1.00%. Become.

Further, in order to suppress the formation of grain boundary ferrite in the weld metal, the alloy component of the wire according to the present embodiment was adjusted so that the Ceq represented by the formula (2) was 0.40 to 0.75. .. As a result, the Ceq of the weld metal is within a suitable range, and both the formation of grain boundary ferrite, which causes a decrease in the toughness of the weld metal, and the over-hardening of the weld metal can be suppressed. However, when Ceq becomes excessive, the weld metal becomes too hard, or microsegregation becomes remarkable, and the toughness deteriorates. Therefore, in order to maximize the effect of B, Mo and B were added in combination. By adding Mo, the hardenable effect of B is promoted. This prevented the Ceq from becoming excessive. If the Ceq of the alloy component of the wire was too low, grain boundary ferrite was formed in the weld metal, and the strength and toughness of the weld metal could not be ensured. When Ceq, which is an alloy component of the wire, is excessive, the hardness of the weld metal becomes excessive, and the toughness of the weld metal cannot be ensured. The lower limit of Ceq of the alloy component of the wire is preferably 0.42, more preferably 0.45. The upper limit of Ceq of the alloy component of the wire is preferably 0.70, more preferably 0.60.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (2)
For elements without additives, zero is substituted into the above equation.
However, the element symbol with [] in the above formula (2) indicates the content of the element in the alloy component according to each element symbol in mass% with respect to the total mass of the flux-filled wire.

Further, the reason for limiting the alloy component of the wire according to the present embodiment will be described. In the following description, "%" in the description of each element means "mass% with respect to the total mass of the flux-cored wire" unless otherwise specified.

(C: 0.02 to 0.10%)
C is an important element that secures the proof stress and tensile strength of the weld metal by solid solution strengthening. If the C content is less than 0.02%, the proof stress and tensile strength of the weld metal cannot be ensured. On the other hand, when the C content exceeds 0.10%, C remains excessively in the weld metal, the proof stress and tensile strength of the weld metal are excessively increased, and the toughness of the weld metal is lowered. In order to stably secure the toughness and proof stress of the weld metal, the C content is preferably 0.03 to 0.08%.

(Si: 0.20 to 0.90%)
Si is a deoxidizing element, and it is necessary to contain 0.20% or more in the wire in order to reduce the amount of O in the weld metal and improve the cleanliness. However, if Si is contained in excess of 0.90%, the toughness of the weld metal is deteriorated, so the upper limit of the Si content is set to 0.90%. Further, in order to stably secure the toughness of the weld metal, the upper limit of the Si content may be 0.70% or 0.50%.

(Mn: 1.0 to 4.0%)
Mn is an element that secures the hardenability of the weld metal and enhances its strength. In order to surely exert the effect, it is necessary to contain 1.0% or more of Mn in the wire. On the other hand, if Mn is contained in excess of 4.0%, the grain boundary embrittlement sensitivity of the weld metal increases and the toughness of the weld metal deteriorates. Therefore, the upper limit of the Mn content is set to 4.0%. In order to increase the strength of the weld metal more stably, the lower limit of the Mn content may be 1.4%, 1.6% or 1.8%. Further, in order to stably secure the toughness of the weld metal, the upper limit of the Mn content may be 3.5% or 3.0%.

(P: 0.030% or less)
Since P is an impurity element and inhibits the toughness of the weld metal, it is necessary to reduce its content as much as possible. However, the P content is 0.030% or less within an allowable range of adverse effects on the toughness of the weld metal. And. The lower limit of the P content is 0%, but it may be 0.0001%, 0.0005%, or 0.001%.

(S: 0.030% or less)
S is also an impurity element, and if it is excessively present in the weld metal, both the toughness and ductility of the weld metal are deteriorated. Therefore, it is preferable to reduce the content as much as possible. The S content shall be 0.030% or less within an acceptable range for adverse effects on the toughness and ductility of the weld metal. The lower limit of the S content is 0%, but it may be 0.0001%, 0.0005%, or 0.001%.

(Ni: 0.10 to 3.00%)
Ni is an element that enhances the strength of the weld metal by improving the hardenability of the weld metal, and further improves the toughness of the weld metal regardless of the structure and composition by solid-dissolving toughness (the action of increasing the toughness by solid-melting). Yes, when it is contained in the wire, it is contained in an amount of 0.10% or more in order to obtain the effect. The higher the Ni content, the more advantageous it is in improving the toughness of the weld metal. However, if the Ni content exceeds 3.00%, the weld crack resistance decreases, so the upper limit of the Ni content is 3.00%. And.

(Mo: 0.05 to 1.00%)
Mo is an element effective for increasing the strength of weld metal. This is because the quenching property of the weld metal is improved by containing Mo. When the Mo content exceeds 1.00%, the weld metal is hardened and the toughness is deteriorated. Therefore, when Mo is contained, the content thereof is set to 1.00% or less. On the other hand, in order to obtain the above-mentioned effect, it is necessary to contain Mo in 0.05% or more. The Mo content is preferably 0.10% or more.

(V: 0.200% or less)
V is an element effective for increasing the strength of the weld metal by enhancing the hardenability of the weld metal, and when it is contained, it is contained in the range of 0.200% or less. If V is contained in excess of 0.200%, carbides are excessively deposited in the weld metal, so that the weld metal is hardened and the toughness of the weld metal is deteriorated. On the other hand, in order to sufficiently obtain the above-mentioned effects, it is preferable to contain 0.010% or more of V.

(Ti: 0.050 to 0.250%)
Ti is effective as a deoxidizing element and has an effect of reducing the amount of O in the weld metal. Further, Ti is also effective for alleviating the adverse effect of N on the toughness by fixing the solid solution N in a small amount remaining in the weld metal. In order to obtain the effect, the wire contains 0.050% or more of Ti. On the other hand, if Ti is contained in an amount of more than 0.250%, there is a high possibility that the toughness of the weld metal is deteriorated due to the formation of excessive precipitates. Generally, Ti is added to the flux as ferrotitanium. The preferable lower limit of the Ti content is 0.100%, and the preferable upper limit of the Ti content is 0.200%.

(B: 0.0010 to 0.0200%)
When B is contained in the weld metal in an appropriate amount, it has an effect of combining with the solid solution N to form BN and reducing the adverse effect on the toughness of the solid solution N. In addition, B also has the effect of increasing the hardenability of the weld metal and contributing to the improvement of strength. In order to obtain the effect, 0.0010% or more of B is contained in the wire. On the other hand, when the B content exceeds 0.0200%, B in the weld metal becomes excessive and forms B compounds such as coarse BN and Fe ₂₃ (C, B) ₆ to deteriorate the toughness of the weld metal. .. The preferable lower limit of the B content is 0.0050%. The preferred upper limit of the B content is 0.0150%.

(Al: 0.05 to 0.50%)
Al is a deoxidizing element, and like Si, it is effective in reducing O in the weld metal and improving the cleanliness. Furthermore, Al is an essential element for the formation of acicular ferrite in the weld metal, and is therefore indispensable for ensuring the toughness of the weld metal. When the Al content is in the proper range, the oxide becomes an Al-containing spinel-type oxide, which may become a nucleus to form acicular ferrite in the weld metal. In order to obtain these effects of Al, 0.05% or more of Al is contained in the wire. If the Al content is less than 0.05%, the deoxidizing power may be insufficient or acicular ferrite may not be produced. When the Al content exceeds 0.50%, Al in the weld metal becomes excessive, the oxide composition becomes Al ₂ O ₃ , and acicular ferrite is not produced. The preferable lower limit of the Al content is 0.08%. The preferable upper limit of the Al content is 0.30%.

(Mg: 0.01-0.50%)
Mg acts as a deoxidizing agent to reduce the amount of oxygen in the weld metal and improve toughness. In order to obtain this effect, it is necessary to contain 0.01% or more of Mn in the wire. On the other hand, when the Al content exceeds 0.50%, blow holes are generated in the welded portion. The preferable range of the Al content is 0.05 to 0.30%.

(REM: 0 to less than 0.0010%)
Since REM is an element that increases the occurrence of spatter, it is necessary to reduce its content as much as possible. Since the smaller the REM is, the more preferable it is, the lower limit is not particularly specified, or may be 0%. However, if it is less than 0.0010%, the content of REM is permissible. Here, "REM" is a general term for a total of 17 elements of Sc, Y, and lanthanoid, and the content of REM refers to the total content of one or more elements of REM.

In addition to the above basic components, the wire according to the present embodiment may contain the following components as an arbitrary alloy component, if necessary. However, since the wire according to the present embodiment does not require an arbitrary alloy component in order to solve the problem, the lower limit of the content of each of these arbitrary alloy components is 0%.

(Cu: 0.10 to 0.50%)
Since Cu has an effect of improving the strength and corrosion resistance of the weld metal, it may be contained if necessary. The lower limit of the Cu content is 0%, but in order to obtain the effect of containing Cu, it is preferable to contain Cu in the wire in an amount of 0.10% or more. More preferably, the Cu content is 0.20% or more. On the other hand, even if Cu is contained in an amount of more than 0.50%, the performance is not improved in proportion to the increase in alloy cost. The upper limit of the Cu content is preferably 1.00% or less, and more preferably 0.50% or less. The Cu content includes not only the amount contained in the steel outer skin of the wire itself or in the flux, but also the amount contained in the wire surface when copper is plated.

(Cr: 0.05 to 0.50%)
Cr is useful for improving the strength by increasing the corrosion resistance and the hardenability, and therefore, it may be contained if necessary. The lower limit of the Cr content is 0%, but in order to obtain the effect of containing Cr, it is preferable to contain Cr in an amount of 0.05% or more. On the other hand, even if Cr is contained in an amount of more than 0.50%, it may be hardened and the toughness may be deteriorated.

(Nb: 0.01-0.05%)
Nb is an element effective for ensuring the tensile strength of the weld metal. This is because when Nb is contained in the wire, fine carbides are formed in the weld metal and precipitation strengthening occurs. The lower limit of the Nb content is 0%, but in order to obtain the effect of Nb, it is preferable to contain 0.01% or more of Nb. On the other hand, even if Nb is contained in an amount of more than 0.05%, coarse precipitates are formed in the weld metal and the toughness is deteriorated, which is not preferable.

The above is the reason for limiting the component composition of the flux-cored wire according to the present embodiment, but the other remaining components are Fe and impurities.
The Fe component includes, for example, Fe of a steel outer skin, iron powder added to the flux, and Fe in the alloy powder. Since iron powder does not have to be contained in the wire according to the present embodiment, the lower limit of its content is 0%. When iron powder is added for adjusting the filling rate, the content is preferably less than 30% in order to ensure the toughness of the weld metal.

The above alloy component is a component existing as a simple substance or an alloy in the wire. As described above, the content of the alloy components does not include the content when those elements are contained in the flux in the form of metal fluoride, metal oxide, metal carbonate or the like.

Further, the effect is the same regardless of whether the alloy component is contained in the steel outer skin or as a metal powder or an alloy powder in the flux. Therefore, both the steel outer skin and the flux can contain an alloy component. When the alloy component is contained in the flux, it does not necessarily have to be a pure substance, and there is no problem even if it is contained in the form of an alloy such as Fe—Ti.

Further, the surface of the wire may be coated with Cu, which is effective for rust prevention, electrical conductivity, and chip wear resistance. In such a case, Cu of about 0.3% is contained as a component of the wire. The flux-cored wire subjected to Cu plating is also included in the range of the wire according to the present embodiment.

Subsequently, the form of the flux-cored wire will be described. Flux-filled wires can be broadly divided into "seamless wires" that do not have slit-shaped gaps in the steel outer skin (so-called seamless shape) and "wires that have seams" that have slit-shaped gaps in the steel outer skin. .. Any cross-sectional structure can be adopted for the wire according to the present embodiment, but in consideration of the manufacturing load, it is preferable to use a "wire having a seam".

Further, in order to improve the feeding property of the wire at the time of welding, a lubricant can be applied to the surface of the wire. The type of lubricant is not particularly limited, and perfluoropolyether oil (PFPE oil), vegetable oil, or the like can be applied.

When the wire form is a tube having a seam on the steel outer skin, moisture in the atmosphere invades into the flux from the seam portion of the outer skin. The possibility of low temperature cracking increases. Therefore, if the period from manufacture to use is long, it is desirable to vacuum-pack the entire wire or store the wire in a container that can be kept dry.

The flux-cored wire according to the present embodiment configured as described above can be manufactured by a normal flux-cored wire manufacturing process. That is, first, a steel strip to be the outer skin and a flux containing a metal fluoride, an alloy component, a metal oxide, a metal carbonate and an arc stabilizer so as to have a predetermined content are prepared, and the steel strip is lengthened. While feeding in the direction, it is formed into an open tube (U-shaped) by a forming roll to form a steel outer skin, and during this forming, flux is supplied from the opening of the open tube, and the opposing edge surfaces of the openings are butt welded. A seamless wire obtained by welding is drawn and annealed during the drawing process or after the wire drawing process is completed to obtain a seamless wire having a desired wire diameter and having a steel outer skin filled with flux. obtain. Further, the wire having a seam is obtained by supplying flux from the opening of the open pipe and then forming a seamless pipe without seam welding and drawing the wire.

Next, a method for manufacturing a welded joint according to another aspect of the present invention will be described. The method for manufacturing a welded joint according to the present embodiment includes a step of welding a steel plate using the flux-cored wire according to the above-described embodiment.

In the method for manufacturing a welded joint according to the present embodiment, the base steel plate (steel plate) of the welded joint is not particularly limited. According to the above-mentioned characteristics of the wire according to the present embodiment, a weld metal having superior yield strength, tensile strength, and low temperature toughness can be obtained regardless of the type of steel plate. On the other hand, in the method for manufacturing a welded joint according to the present embodiment, the steel plate is preferably a thick plate having a tensile strength of 570 MPa class or more and a plate thickness of 60 to 80 mm. In this case, the superiority over the prior art is particularly enhanced. Further, by setting the plate thickness of the steel plate to 60 mm or more, it is possible to prevent the amount of heat input from becoming small, and it is possible to reliably suppress the possibility that the weld metal becomes too hard and the toughness of the weld metal deteriorates. By setting the plate thickness of the steel plate to 80 mm or less, it is possible to prevent an excessive amount of heat input and improve the tensile strength and HAZ toughness of the entire joint.

The Ceq of the steel sheet is preferably 0.30 to 0.40%. In this case, the mechanical properties of the entire joint including the weld heat affected zone (HAZ) can be stabilized. By setting the Ceq of the steel sheet to 0.30% or more, the tensile strength of the entire joint can be further strengthened. By setting the Ceq of the steel sheet to 0.40% or less, it is possible to reliably prevent the lack of HAZ toughness. The Ceq of the steel sheet can be calculated by the following formula (4).
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (4)
For elements without additives, zero shall be substituted into the above equation.
However, the element with [] in the formula (4) indicates the content of the element in the steel plate according to each element symbol in the unit mass%.

In the method for manufacturing a welded joint according to the present embodiment, the Ceq of the obtained weld metal is not particularly limited. On the other hand, by setting the Ceq of the weld metal to 0.35 to 0.50%, both the formation of grain boundary ferrite and the over-curing of the weld metal can be suppressed more effectively. By setting the Ceq of the weld metal to 0.35% or more, it is possible to prevent the formation of grain boundary ferrite in the weld metal and further improve the strength and toughness of the weld metal. By setting the Ceq of the weld metal to 0.50% or less, it is possible to prevent the weld metal from becoming excessively hard and further increase the toughness of the weld metal. The Ceq of the weld metal is preferably 0.38 or more, more preferably 0.40 or more. On the other hand, the Ceq of the weld metal is preferably 0.47 or less, more preferably 0.45 or less. The Ceq of the weld metal can be controlled by appropriately changing the alloy component of the wire, the component of the steel plate, and the welding conditions. The Ceq of the weld metal can be calculated by the following equation (3).
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (3)
For elements without additives, zero shall be substituted into the above equation.
However, the element with [] in the formula (3) indicates the content of the element in the weld metal according to each element symbol in the unit mass%.

In the method for manufacturing a welded joint according to the present embodiment, the type and specific conditions of welding are not particularly limited. According to the above-mentioned characteristics of the wire according to the present embodiment, a weld metal having superior yield strength, tensile strength, and low temperature toughness can be obtained regardless of the type of steel plate. On the other hand, in the method for manufacturing a welded joint according to the present embodiment, it is preferable that the welding is multi-electrode vertical electrogas arc welding. When a steel plate having a plate thickness of 60 mm or more is welded by vertical electrogas arc welding with multiple electrodes, it is possible to prevent an increase in the swing width, stabilize the arc, and further suppress the possibility of fusion failure. Further, when the welding is multi-electrode vertical electrogas arc welding, it is preferable to use the same welding wire for each electrode. By using the same wire for each electrode, the composition of the weld metal can be made uniform in the plate thickness direction, and the mechanical properties of the welded joint can be further stabilized.
In the welding included in the welding joint manufacturing method according to the present embodiment, the shield gas is not particularly limited, but is generally used 100 vol% carbon dioxide gas or a mixed gas of Ar and 3 to 20 vol% CO ₂ . Is preferable. Since these gases are inexpensive, the manufacturing cost of welded joints can be reduced. The wire according to the present embodiment does not significantly increase spatter even when applied to welding using 100 vol% carbon dioxide gas as a shield gas. Therefore, in order to reduce costs, the wire is used for welding in which the shield gas is 100 vol% carbon dioxide gas. When applied, it has a particularly remarkable effect.

Next, the feasibility and effect of the present invention will be described in more detail by way of examples.
As a steel outer skin, C: 0.002 to 0.06%, Si: 0.01 to 0.05%, Mn: 0.20 to 0.45%, P: 0.004 to 0.008%, S: A seam with a wire diameter of 1.6 mm having various component compositions shown in Tables 1-1 to 2-2, using a steel strip containing 0.002 to 0.001% and having a chemical component whose balance is iron and impurities. We made a prototype wire with flux. For components whose content is below the detection limit, the content is shown blank. Using these wires, steel plates P1 to P3 having the components disclosed in Table 3 were welded under the conditions shown in Table 4.

FIG. 2 shows the groove shape and the position of each electrode. Welding is performed under the condition that the groove angle of the groove shape is 20 ° and the distance between the tips of the groove shape is 10 mm, while using SB-60VT (manufactured by Nippon Steel & Sumikin Welding Co., Ltd.) as the backing material. This was done using the welding wires shown in Table 1. The amount of heat input during welding was 46 kJ / mm to 61 kJ / mm.

The components of the weld metal of the welded joint obtained by the above procedure are shown in Tables 5 to 8, and the mechanical properties are shown in Tables 9 to 12. However, when the amount of slag was excessive, high temperature cracking occurred, blowholes occurred, or arc instability occurred, it was impossible to manufacture the joint, so component analysis and mechanical property evaluation were not performed. Analysis of the components of the weld metal was performed by JIS G0321, JIS Z3184. The location where the component was measured was the location where the A1 tensile test piece, which will be described later, was collected. For components whose content is below the detection limit, the content is shown blank. For example, even if the deoxidizing elements Si, Mg, Ti, etc. are contained in the flux-filled wire as alloying elements, they are discharged to the outside of the weld metal as slag during welding and are not detected as components of the weld metal. There is. In such a case, the Mg content of the weld metal is shown blank.

The strength of the weld metal was evaluated by the tensile test and the toughness was evaluated by the Charpy impact test. As shown in FIG. 3, A1 tensile test pieces (round bar) and No. 4 Charpy test pieces (2 mm V notch) conforming to JIS Z3111 (2005) were collected from the weld metal and their mechanical property tests were performed. The tensile strength and Charpy absorption energy of the weld metal were measured. The Sharpy test piece is from the direction perpendicular to the welding line direction, from the front side of the plate thickness to the position 6 mm in the plate thickness center direction (bottom of the table), the position of the plate thickness center (t / 2), and from the back side of the plate thickness. Three pieces were sampled from each of the positions 6 mm in the center direction of the plate thickness (lower back), and a 2 mm V notch was machined in the center of the weld metal. The Charpy impact test was carried out three times under the condition of a test temperature of -20 ° C, and the absorption energy (vE- ₂₀ ) of the weld metal was obtained from this average value at each position of the lower front, t / 2, and lower back. rice field.

The evaluation criteria for the mechanical properties of weld metal are as follows. Regarding the tensile strength, those having a tensile strength (TS) of 570 MPa or more at room temperature were regarded as acceptable. Regarding the yield strength, those having a yield stress (YP) of 460 MPa or more at room temperature were regarded as acceptable. Regarding toughness, those having an absorption energy (vE- ₂₀ ) of the weld metal at each of the front, bottom, t / 2, and bottom back positions of 80 J or more were evaluated as acceptable.

The microstructure of the weld metal was evaluated by the acicular ferrite fraction. After mirror polishing the surface perpendicular to the direction of the weld line, nital corrosion is performed, and four fields are photographed at a magnification of 100 times around the center of the weld metal at the t / 2 position using an optical microscope. The ratio was determined by a point counting method (a method of dividing into a mesh of 30 μm × 30 μm and determining the probability that an acylular ferrite exists at the intersection), and the average value was taken as the cyclic ferrite fraction of the weld metal. The size of one field of view was 900 μm × 900 μm. A weld metal having an acylular ferrite fraction of 85% or more was evaluated as acceptable in terms of the texture of the weld metal.

As is clear from Tables 1 to 12, the welded joints obtained from the wire numbers A01 to A33 have excellent strength (tensile strength and yield strength) and toughness. On the other hand, since the wire numbers B01 to B09, B19, B23 to B25, and B35 to B36 are outside the component range specified in the present invention, welding defects occur and the welded joint can be evaluated. There wasn't. Since the wire numbers B10 to B18, B20 to B22, and B26 to B34 are outside the component range specified in the present invention, the strength or toughness of the weld metal is inferior.

The flux-cored wire for vertical electrogas arc welding according to the present invention has excellent mechanical properties in the weld metal portion when high heat input welding is performed. Therefore, according to the wire containing flux for vertical electrogas arc welding according to the present invention, safety is improved, highly efficient welding is possible, and the construction cost of the welded structure can be dramatically reduced. Will be.

Claims (5)

A flux-cored wire for vertical electrogas arc welding with a steel skin and flux.
The flux is, as a slag agent, by mass% with respect to the total mass of the flux-cored wire.
Na ₂ O: 0.00 to less than 1.00%,
NaF: 0.00 to less than 1.00%,
CaO: 0.00-less than 1.00%,
CaF ₂ : 0.00 to less than 1.00%,
MgO: 0.00 to less than 1.00%,
MgF ₂ : 0.00 to less than 1.00%,
MnO: 0.00 to less than 1.00%, and MnF ₂ : 0.00 to less than 1.00%,
The deoxidizing ability index X represented by the formula (1) is 100 to 200, and the deoxidizing ability index X is 100 to 200.
The total amount Y of the slag agents Na ₂ O, NaF, CaO, CaF ₂ , MgO, MgF ₂ , MnO and MnF ₂ is less than 0.10 to 1.00%.
The product of the deoxidizing ability index X and the total amount Y is 10 to 200.
The flux-cored wire contains 0% or more and less than 30% iron powder.
Further, the flux-cored wire is used as an alloy component in mass% of the total mass of the flux-cored wire.
C: 0.02 to 0.10%,
Si: 0.20 to 0.90%,
Mn: 1.0 to 4.0%,
P: 0.030% or less,
S: 0.030% or less,
Ni: 0.10 to 3.00%,
Mo: 0.05-1.00%,
V: 0.200% or less,
Ti: 0.050 to 0.250%,
B: 0.0010-0.0200%,
Al: 0.05 to 0.50%,
It contains Mg: 0.01 to 0.50% and REM: 0 to less than 0.0010%, and the balance consists of Fe and impurities.
The Ceq represented by the formula (2) is 0.45 to 0.75% .
Contains one or more of iron powder, V, Cu, Cr, and Nb in the following amounts.
A flux-cored wire for vertical electrogas arc welding.
Iron powder: more than 0% and less than 30%,
V: 0.005 to 0.200%,
Cu: 0.10 to 1.00%,
Cr: 0.05 to 0.50%, and
Nb: 0.01-0.05%
X = 100 × {2.0 × ([Na ₂ O] + [NaF]) + 1.5 × ([CaO] + [CaF ₂ ] + [MgO] + [MgF ₂ ]) + 1.0 × ([MnO]) ] + [MnF ₂ ])} / ([CaO] + [CaF ₂ ] + [MgO] + [MgF ₂ ] + [Na ₂ O] + [NaF] + [MnO] + [MnF ₂ ]) ... (1)
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (2)
However, the chemical formula with [] in the formula (1) indicates the content of the slag agent according to each chemical formula in mass% with respect to the total mass of the flux-filled wire, and the element with [] in the formula (2). Indicates the content of the element in the alloy component according to each element symbol in mass% with respect to the total mass of the flux-filled wire. The flux-cored wire , as the alloy component, by mass% with respect to the total mass of the flux-cored wire.
Cu: 0.10 to 0.50%,
Cr: 0.05 to 0.50%, and Nb: 0.01 to 0.05%
The flux-cored wire for vertical electrogas arc welding according to claim 1, wherein the wire contains one or more of the above. A method for manufacturing a welded joint, which comprises welding a steel plate using the flux-cored wire for vertical electrogas arc welding according to claim 1 or 2. The method for manufacturing a welded joint according to claim 3, wherein the Ceq of the weld metal of the welded joint represented by the formula (3) is 0.35 to 0.50%.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (3)
However, the element with [] in the formula (3) indicates the content of the element in the weld metal according to each element symbol in the unit mass%. The welding is multi-electrode vertical electrogas arc welding.
In the multi-electrode vertical electrogas arc welding, the flux-cored wires for the vertical electrogas arc welding of all the electrodes are the same.
The Ceq of the steel sheet represented by the formula (4) is 0.30 to 0.40%.
The method for manufacturing a welded joint according to claim 3 or 4, wherein the thickness of the steel plate is 60 to 80 mm.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 ... Equation (4)
However, the element with [] in the formula (4) indicates the content of the element in the steel sheet according to each element symbol in the unit mass%.

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