JP5387192B2 - Flux-cored wire for gas shield welding - Google Patents

Description

  The present invention relates to a flux-cored wire for gas shielded arc welding filled with a flux having a slag composition that requires CaO and metal fluoride, and has excellent welding workability and toughness in all-position welding. The present invention relates to a flux-cored wire for gas shield welding in which good toughness can be obtained even with a weld metal after performing the above.

In recent years, as the demand for larger and lighter structures has increased, the demand for high tension and high toughness of the steel sheet used has increased. Is required.
In addition, the use of gas shielded arc welding using flux-cored wire is increasing due to its high efficiency compared to welding rods, welding in all positions, and excellent weld bead shape and bead appearance. .

The rutile flux-cored wire has good welding workability and efficiency in all-position welding, but contains a large amount of Ti oxide in the wire and the basicity of the slag is also acidic, so the oxygen content of the weld metal Was high and inferior in toughness. On the other hand, the fluoride wire has a relatively low oxygen content in the weld metal and good toughness is obtained, but the workability of all-position welding is significantly inferior to that of the rutile flux-cored wire.
For this reason, it has been difficult to develop a flux-cored wire that can be welded in all positions and that has good toughness, in response to the demand for high tension and high toughness of the weld metal.

  Further, in the welding of a high-tensile member, PWHT is often performed on the welded part for the purpose of relaxing the residual stress in the welded part, softening the welded heat-affected part, or diffusing and releasing hydrogen in the weld metal. However, since the rutile flux cored wire contains a large amount of inevitable impurities Nb and V in the main raw material Ti oxide, the weld metal formed by the rutile flux cored wire has a high Nb and V content. It is generally known that embrittlement is caused by PWHT.

  Patent Document 1 relates to a rutile flux-cored wire that shows an allowable range of Nb and V amounts in a welding wire that can suppress embrittlement due to PWHT. However, this tolerance is not achievable with commonly used Ti oxides, and in order to achieve this, a special method is used to remove Nb and V from the Ti oxides to increase the purity of the Ti oxides. It is necessary to use an oxide, and there is a problem of high cost. Furthermore, the fundamental problem of the toughness due to the high oxygen content of the weld metal formed by the rutile flux cored wire has not been solved.

Japanese Patent No. 2756084

  The present invention has been made in view of the above problems of the background art, and an object of the present invention is to provide a flux-cored wire that can be welded in all positions and that does not cause embrittlement even in a weld metal subjected to PWHT and can obtain good toughness. And

By using a flux-cored wire filled with a flux having a slag composition that requires CaO and metal fluoride, the present inventors can perform all-position welding and reduce the oxygen content of the weld metal to a rutile flux-cored wire. It has been found that good toughness can be obtained because it can be greatly reduced in comparison. Furthermore, in this slag composition, it is not necessary to use Ti oxide that is essential for rutile flux-cored wires, so that unavoidable impurities Nb and V contained in Ti oxide can be greatly reduced. I found.
The present invention solves the above technical problems, and the requirements of the invention are as follows.

(1) In a flux-cored wire for gas shield welding manufactured by filling a flux inside the steel outer sheath, CaO: 0.3 to 8.0% by mass% with respect to the total mass of the metal, metal fluoride: It contains a slag agent that is essentially 1.0 to 8.0%, and further contains C: 0.03 to 0.30%, Si: 0.2 to 1.5%, and Mn: 0.5 as alloy components. -2.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.002-0.05%, Nb: 0.010% or less, V: 0.010% or less The balance consists of iron, an arc stabilizer, and unavoidable impurities, and X defined by (Equation 1) shown below is 0.20 to 1.2%, and further (Equation 2) shown below. A gas shield welding flask characterized in that the defined Y is regulated to be 0.012% or less. Wire with box.
X = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5
+ [Mo] / 4 + [Cu] / 40 + [Ti] / 30 + 5 × [B] (Formula 1)
Y = [Nb] + [V] / 2 + [Ti] / 20 (Equation 2)
In (Formula 1) and (Formula 2), the elements with [] represent the content (% by mass) of each element.

(2) The flux-cored wire is further in mass% with respect to the total mass of the wire, Ni: 0.1 to 12%, Cr: 0.1 to 4.0%, Mo: 0.1 to 2.0%, Cu: 0.01 to 1.5%, Ti: 0.005 to 0.20%, B: containing 0.001 to 0.015% of one or more, The flux wire for gas shield welding according to (1) above.
(3) The flux-cored wire further contains one or two of Mg: 0.0002 to 3.0% and REM: 0.0002 to 0.01% in mass% with respect to the total mass of the wire. The flux-cored wire for gas shield welding according to (1) or (2) above, characterized in that:

  According to the flux-cored wire of the present invention, all-position welding is possible in welding high-strength steel, and the oxygen content in the welded portion can be greatly reduced as compared with the rutile flux-cored wire, so that the toughness is also excellent. Furthermore, since the weld metal subjected to PWHT does not become brittle and good toughness can be obtained, the industrial effect is extremely large.

It is a figure which shows the cross-sectional shape of the groove | channel in the welding of the Example which confirms the effect of this invention.

Embodiments of the present invention will be described below.
First, the reason for defining the flux-cored wire component of the present invention will be described. % For each component means mass% relative to the total mass of the wire. The flux cored wire of the present invention contains a slag agent and an alloy component.

(Slag agent)
[CaO: 0.3 to 8.0%]
CaO is a high-melting point substance, and by containing CaO as an essential component, the melting point of slag is increased, and vertical welding and upward welding are possible. Further, CaO is an oxide but a strong basic substance, and does not significantly increase the oxygen content of the weld metal even if contained in the wire. In order to raise the melting point of the slag to such an extent that vertical welding and upward welding are possible, 0.3% or more is necessary. However, if the content exceeds 8.0%, the melting point of the slag becomes too high, and the solidification of the slag is accelerated, and the fluidity of the slag cannot be ensured. For this reason, the content of CaO is set to 0.3 to 8.0%. Further, the CaO content is preferably 1.5% or more, and more preferably 2.5% or more. The CaO content is preferably 5.5% or less, and more preferably 4.5% or less.

[Metal fluoride: 1.0-8.0%]
Metal fluorides such as CaF ₂ , NaF, MgF ₂ , SrF ₂ , BaF ₂ and K ₂ ZrF ₆ have the effect of increasing the basicity of the slag and reducing the oxygen content of the weld metal. In addition, it greatly affects the viscosity of the slag and can be combined with CaO to adjust the slag melting point to an appropriate temperature. In order to exhibit these effects, the total mass of the metal fluoride contained in the wire with respect to the total mass of the wire needs to be 1.0% or more, preferably 1.5% or more. More preferably, it is 5% or more. However, if the content exceeds 8.0%, the amount of slag becomes excessive, the arc becomes unstable, and the welding posture deteriorates. The total mass of the metal fluoride with respect to the total mass of the wire is preferably 5.5% or less, and more preferably 5.0% or less.

(Alloy components)
[C: 0.03-0.30%]
C is an element that increases the tensile strength of the weld metal. If the content is low, sufficient weld metal tensile strength cannot be obtained. Therefore, the C content in the welding wire needs to be 0.03% or more. is there. However, if the content exceeds 0.30%, the toughness of the weld metal is deteriorated. For this reason, in the present invention, the C content in the welding wire is 0.03 to 0.30%.

[Si: 0.2 to 1.5%]
Si is a deoxidizing element and increases the cleanliness by reducing the amount of O in the weld metal. Further, the bead appearance and bead shape are improved. In order to obtain these effects, the Si content in the welding wire needs to be 0.2% or more. On the other hand, when the Si content in the welding wire exceeds 1.5% and becomes excessive, a coarse oxide is generated and the toughness of the weld metal is significantly deteriorated. For this reason, in this invention, Si content in a welding wire shall be 0.2 to 1.5%.

[Mn: 0.5 to 2.5%]
Mn improves deoxidation and hardenability of the weld metal. Further, it is an element effective for improving the toughness by refining the structure. In order to obtain these effects, it is necessary to contain 0.5% or more in the welding wire. On the other hand, if the Mn content in the welding wire exceeds 2.5%, residual austenite is excessively generated in the weld metal, which increases the susceptibility to intergranular embrittlement and deteriorates the toughness and strength of the weld metal more than necessary. The weld cracking is likely to occur. For this reason, in this invention, Mn content in a welding wire shall be 0.5 to 2.5%.

[P: 0.02% or less]
P is an impurity element and degrades toughness. In addition, when PWHT is applied to P, brittle P compounds are precipitated at the crystal grain boundaries, so that the toughness is further deteriorated. For this reason, it is necessary to reduce P as much as possible, but if the content in the welding wire is 0.02% or less, an adverse effect on toughness can be tolerated. Therefore, in the present invention, the P content in the welding wire is 0.02%. The following.

[S: 0.02% or less]
S is also an impurity element, and if it is excessively present in the weld metal, it deteriorates both toughness and ductility, so it is preferable to reduce it as much as possible. If the content in the welding wire is 0.02% or less, adverse effects on toughness and ductility can be tolerated. Therefore, in the present invention, the S content in the welding wire is 0.02% or less.

[Al: 0.002 to 0.05%]
Al is a deoxidizing element and, like Si and Mn, reduces the amount of oxygen in the weld metal and is effective in improving cleanliness. In order to exert the effect, it is necessary to contain 0.002% or more of Al in the welding wire. On the other hand, if the welding wire contains more than 0.05% of Al excessively, a coarse oxide is formed in the weld metal, and this coarse oxide significantly deteriorates toughness, which is not preferable. Therefore, in this invention, Al content in a welding wire shall be 0.002-0.05% or less.

[Nb: 0.010% or less]
Nb is a precipitation hardening element, and when it is kept at a high temperature for a long time like PWHT, it is significantly embrittled. When the Nb content in the welding wire is 0.010% or less, there is no embrittlement due to PWHT, and good toughness is obtained. Therefore, in the present invention, the Nb content in the welding wire is limited to 0.010% or less.

[V: 0.010% or less]
V is also a precipitation hardening element like Nb, and when it is kept at a high temperature for a long time like PWHT, it becomes extremely brittle. If the V content in the welding wire is 0.010% or less, there is almost no toughness embrittlement due to PWHT, and good toughness can be obtained. Therefore, in the present invention, the V content in the welding wire is limited to 0.010% or less.

The above is the basic component of the flux-cored wire for gas shield welding of the present invention. The balance is iron, arc stabilizer and inevitable impurities.
As the arc stabilizer, an oxide containing Li, Na, K, Rb, Sr, etc. as known from conventional knowledge can be selected and used. Further, the mass of the arc stabilizer is considered to be appropriately 0.01 to 1.0% or less by mass ratio with respect to the total mass of the wire, and the content within this range is preferable.

  The present invention further provides for the adjustment of specific mechanical properties of the weld metal, optionally further in the wire, one of Ni, Cr, Mo, Cu, Ti, B, Mg and REM. When the seed wire or two or more kinds are contained in the welding wire within the range of the following content, the tensile strength or toughness is affected. The components described below can be contained as required.

[Ni: 0.1 to 12%]
Ni is the only element that can stably improve toughness regardless of the other components and structure of the weld metal by solid solution toughening. In particular, it is an element necessary to ensure toughness with a high-strength weld metal. Yes, it is preferable to contain 0.1% or more. A higher Ni content is advantageous in improving toughness, but if the content in the welding wire exceeds 12%, the effect of improving toughness is saturated. Therefore, in this invention, it is preferable to make Ni content in a welding wire into 0.1 to 12%.

[Cr: 0.1-4.0%]
Cr is an element effective for increasing the strength by enhancing the hardenability. Therefore, when it contains in a welding wire, 0.1% or more is required. On the other hand, if it is contained excessively exceeding 4.0%, bainite and martensite are hardened unevenly and the toughness is remarkably deteriorated. Therefore, in the present invention, the upper limit of the Cr content in the welding wire is 4. It is preferably 0%.

[Mo: 0.1 to 2.0%]
Mo is a hardenability improving element for increasing the tensile strength TS of the weld metal. Moreover, Mo can ensure strength and toughness by increasing tempering resistance. In order to exhibit these effects, it is preferable to contain 0.1% or more of Mo in the wire. On the other hand, if Mo is contained in the welding wire in an amount exceeding 2.0%, coarse precipitates are generated in the weld metal and the toughness of the weld metal is deteriorated. For this reason, in this invention, it is preferable that Mo content in a welding wire shall be 0.1 to 2.0%.

[Cu: 0.01 to 1.5%]
Cu is an element effective for improving the strength, and in order to sufficiently obtain the effect of improving the strength of the weld metal, the content of Cu contained in the wire, and in the case where Cu is plated on the surface, The total content of Cu to be contained and Cu to be plated is preferably 0.01% or more. On the other hand, if the Cu content in the wire exceeds 1.5%, the case where the wire surface is plated or the case where it is contained in the wire is not preferable because the toughness of the weld metal deteriorates. Therefore, in this invention, it is preferable that Cu content in a wire shall be 0.01 to 1.5%.

[Ti: 0.005 to 0.20%]
Ti is effective as a deoxidizing element in the weld metal, and can fix the solid solution N in the weld metal as a nitride to alleviate the adverse effect on the toughness of the solid solution N. In this case, there is an effect of refining the heated austenite grains in the reheat region of the weld metal. Moreover, the weld metal which carried out PWHT can also suppress the toughness fall of a weld metal by containing Ti suitable for the amount of oxygen and nitrogen. In order to exhibit the effect of improving the toughness of the weld metal by the action of Ti, it is preferable to contain 0.005% or more of Ti in the welding wire. On the other hand, when the Ti content in the welding wire exceeds 0.20%, the amount of solute Ti increases, and the toughness deterioration is noticeably caused in the welded metal as-welded and PWHT. For this reason, in this invention, it is preferable to make Ti content in a welding wire into 0.005-0.20%.

[B: 0.001 to 0.015%]
B is an element that enhances the hardenability and contributes to the improvement of the strength of the weld metal, and also has the effect of improving the toughness of the weld metal by forming BN in combination with the solid solution N in the weld metal. In order to exhibit these effects reliably, the B content in the welding wire is preferably 0.001% or more. On the other hand, when the B content in the welding wire exceeds 0.015%, the B in the weld metal becomes excessive and forms coarse B compounds such as BN and Fe ₂₃ (C, B) ₆ to reverse the toughness. It is not preferable because it deteriorates. Therefore, in the present invention, when B is contained in the welding wire, the B content is preferably limited to 0.001 to 0.015%.

In the present invention, in addition to the above components, one or more of Mg and REM can be further contained in the wire within the following range, if necessary.
[Mg: 0.0002 to 3.0%]
Mg is added in the form of metal Mg alone, an alloy with another metal element, and Mg oxide, and has an effect of reducing the oxygen content of the weld metal as a deoxidizer. Further, Mg becomes MgO in the molten pool and affects the viscosity of the slag. In order to obtain the effect of deoxidation, the content of Mg in the wire needs to be 0.0002% or more. On the other hand, if it exceeds 3.0%, the slag viscosity is lowered and welding workability is reduced. Deteriorate. For this reason, in this invention, it is preferable that Mg content in a welding wire shall be 0.0002 to 3.0%.

[REM: 0.0002 to 0.01%]
REM is effective in improving ductility and toughness by changing the structure of sulfide and reducing the size of sulfide and oxide in the weld metal. In order to fully exhibit these effects, the REM content is preferably 0.0002% or more. On the other hand, if REM is contained excessively in excess of 0.01% in the wire, it causes the coarsening of sulfides and oxides, leading to deterioration of ductility and toughness, and deterioration of weld bead shape and weldability. The possibility of For this reason, the upper limit of the REM content in the wire is preferably 0.01% or less.

Further, in the present invention, when the components of C, Si, Mn, Ni, Cr, Mo, Cu, Ti and B are contained within the specified ranges of the respective contents, in order to ensure the tensile strength, X defined by the following (formula 1) is limited to 0.20 to 1.2%. If X is less than 0.20%, the weld metal subjected to PWHT softens more than necessary, so that the strength cannot be maintained. Further, if X exceeds 1.2% and becomes excessive, the toughness of the weld metal deteriorates, which is not preferable.
X = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5
+ [Mo] / 4 + [Cu] / 40 + [Ti] / 30 + 5 × [B] (Formula 1)
In (Formula 1), the elements with [] represent the content (% by mass) of each element.
(Equation 1) limits the content of elements that affect the tensile strength, and the content of each element in (Equation 1) is contained in the flux-cored wire of the present invention as an alloy component. It means the content of each element. Therefore, the element contained in the flux-cored wire of the present invention as a metal oxide or metal fluoride is not an object even if it is the element described in (Formula 1), and the inclusion of each element in (Formula 1) It cannot be added to the quantity.

Further, Nb, V, and Ti are well known as elements that embrittle the weld metal subjected to PWHT, and Y defined by the following (formula 2) is 0 even if the respective contents are within the specified range. If it exceeds 0.12%, embrittlement due to PWHT occurs. For this reason, it is necessary to regulate Y to 0.012% or less.
Y = [Nb] + [V] / 2 + [Ti] / 20 (Equation 2)

The flux-cored wire of the present invention is manufactured by filling a flux into a steel outer shell. For this steel outer shell, a hot rolled steel material or a cold rolled steel material having good workability may be used.
The filling rate of the flux is not particularly limited, but considering the slag amount necessary for obtaining the manufacturability of the wire and stable welding workability, it is preferably in the range of 5.0 to 30% by mass% with respect to the total mass of the wire.

In addition, the flux-cored wire is largely composed of a wire without seam welding (hereinafter referred to as a seamless wire) that is seam-welded at the joint in the manufacturing process, and a wire that is mechanically fastened by caulking (hereinafter referred to as a caulking wire). There are two types, and a seamless wire is preferable, but a caulking wire has no influence on the effect of the present invention. Alternatively, the surface of the seamless wire may be plated with Al or Cu.
Further, the shielding gas to be applied is a shielding gas used for normal MAG welding, such as CO ₂ alone gas, Ar or a mixed gas of He and CO ₂ , and a small amount of O ₂ added to these gases. Either can be used.

Specific contents newly discovered by the present inventors will be described below.
Conventionally, the reason why the fluoride-based flux-cored wire cannot be vertically or upward welded is that the melting point of the slag is low and the molten pool cannot be maintained. The present invention pays attention to CaO, which is a high melting point material, and enables all-position welding by appropriately adjusting the melting point with CaO. Furthermore, CaO is an oxide but a strong basic substance, and even if added to the wire, it does not significantly increase the amount of oxygen in the weld metal and can reduce oxygen in the weld metal more than the rutile flux-cored wire. Therefore, it is excellent in terms of toughness.

Conventionally, Ti oxide has been indispensable to ensure weldability in all positions. However, the Ti oxide contains Nb and V as inevitable impurities, and this has a problem of embrittlement of the weld metal after PWHT.
With the slag composition using CaO of the present invention, all-position welding is possible without using Ti oxide, so Nb and V can be greatly reduced, and even the weld metal after PWHT becomes brittle. Was found to be suppressed. In addition, Nb, V, and the like precipitate in the grains during the PWHT process, so that the intragranular strength is increased, and the intergranular slip preceding the intragranular deformation causes intergranular cracking. It has been found that there is a suppression effect.

The effects of the present invention will be specifically described below with reference to examples.
A steel strip is formed into an open pipe with a forming roll while feeding it in the longitudinal direction. Flux is supplied from the opening of the open pipe in the middle of this forming, and the opposite edge surfaces of the opening are butt-seamed and welded together. A flux-cored wire with a wire diameter of φ1.2 mm was made as a prototype without any (seamless). Some of the wires were caulked flux-cored wires that were mechanically fastened by caulking without seam welding. Tables 1 to 6 show the contents of the slag agent and arc stabilizer of the prototype flux-cored wire, and Tables 7 to 12 show the alloy components.

These prototype wires were welded under the welding conditions shown in Table 13. Welding was performed by processing the groove shown in FIG. 1 on an SM490B steel plate defined in JIS G3106.
For welding workability, arc stability, spatter generation amount, and bead formation state in each of the downward, vertical, and upward welding positions were evaluated. Arc extinction due to arc instability during welding, large amount of spatter generated, clogging of welding torch, gas shield becomes insufficient, pits are generated by entraining the atmosphere, and molten metal is not retained by slag. Those with problems that could not be welded, such as insufficient bead formation due to dripping of molten metal, were judged as bad, and those without were judged as acceptable.

  The mechanical property test evaluated the test body which performed the downward welding. The center part of the test piece in the longitudinal direction of the bead was cut into two parts by a saw, and one side was subjected to PWHT of 620 ° C. × 10 hours. A1 tensile test pieces and No. 4 Charpy test pieces based on JIS Z3111 were sampled from the center of the thickness of each test specimen, and the strength and toughness of the weld metal were evaluated. In addition, the evaluation is intended for weld metals having a tensile strength that may be subjected to PWHT, and both the weld metal as welded and the weld metal subjected to PWHT have a tensile strength TS of 450 or more. In addition, the absorption energy was 27 or more in the Charpy impact test at −30 ° C., and the decrease in the absorption energy obtained by the Charpy impact test after performing PWHT while being welded was 10 J or less. .

The oxygen content of the weld metal was measured by taking an analytical sample from the weld metal that had been welded downward and measuring it by an inert gas dissolution infrared absorption method. The evaluation of the oxygen content is a clear toughness as compared with the oxygen content 600 to 900 ppm by mass of the weld metal obtained when shield gas welding using Ar + 20% CO ₂ gas is performed with a general rutile flux-cored wire. The thing of 400 mass ppm or less in which the improvement of this is seen was set as the pass.
The results are shown in Tables 14-19.

  From the above test results, the flux-cored wire for gas shield welding according to the present invention can be welded in all positions and has a toughness because it can greatly reduce the oxygen content of the weld metal compared to conventional rutile flux-cored wires. Excellent. Furthermore, since the weld metal formed by the flux-cored wire of the present invention does not become brittle even after PWHT and has excellent toughness, the industrial utility value is extremely high.

Claims (3)

In the flux-cored wire for gas shield welding manufactured by filling the flux inside the steel outer shell,
CaO: 0.3 to 8.0%,
_{CaF 2, NaF, MgF 2,} SrF 2, BaF 2, 1 kind or of two or more metal fluorides of K 2 ZrF _6: 1.0~8.0%
Containing slag agent that is essential, and as an alloy component,
C: 0.03-0.30%,
Si: 0.2 to 1.5%
Mn: 0.5 to 2.5%
P: 0.02% or less,
S: 0.02% or less,
Al: 0.002 to 0.05%,
Nb: 0.010% or less,
V: 0.010% or less is contained, the balance consists of iron, an arc stabilizer, and unavoidable impurities, X defined by (Formula 1) shown below is 0.20 to 1.2%, and A flux-cored wire for gas shield welding, characterized in that Y defined by (Equation 2) shown below is regulated to be 0.012% or less.
X = [C] + [Si] / 24 + [Mn] / 6 (Formula 1)
Y = [Nb] + [V] / 2 (Equation 2)
In (Formula 1) and (Formula 2), the elements with [] represent the content (% by mass) of each element. The flux-cored wire is further mass% with respect to the total mass of the wire,
Ni: 0.1 to 12%,
Cr: 0.1 to 4.0%,
Mo: 0.1 to 2.0%,
Cu: 0.01 to 1.5%,
Ti: 0.005 to 0.20%,
B: 0.001 to 0.015%
1 or 2 or more of them, X defined by the following (formula 3) is 0.20 to 1.2%, and further defined by the following (formula 4) Y is characterized by being regulated to be below 0.012%, gas shielded welding flux cored wire according to claim 1.
X = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5
+ [Mo] / 4 + [Cu] / 40 + [Ti] / 30 + 5 × [B] (Formula 3)
Y = [Nb] + [V] / 2 + [Ti] / 20 (Equation 4)
In (Formula 3) and (Formula 4), the element with [] represents the content (% by mass) of each element. The content of elements not contained is 0% by mass. The flux-cored wire is further mass% with respect to the total mass of the wire,
Mg: 0.0002 to 3.0%,
REM: 0.0002 to 0.01%
The flux-cored wire for gas shield welding according to claim 1 or 2, characterized by containing one or two of them.

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