JP2014014833A - Pulse gas shield arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas shield arc welding method for providing weld metal having excellent breaking elongation, by restraining the occurrence of a ductility reduction crack, when welding superhigh tensile steel having tensile strength of 950 MPa or more.SOLUTION: In the pulse gas shield arc welding method, metal fluoride including CaFof 2.0-8.0% and metallic oxide of 0.01-1.2% are included in a flux-cored wire, and are included so that a value of the ratio of the content of the metal fluoride and the metallic oxide becomes 2.0 or more, and inclusion of Fe powder is also limited to be less than 5.0%, and C:0.08-0.20%, Mn:1.0-2.2%, Ni:1.0-9.0% and V:0.05-0.3% are included as an alloy component, and a wire being 0.60-1.40% in Ceq is used, and a pulse current is used as a welding current.

Description

  The present invention relates to a gas shielded arc welding method using a flux-cored wire, and particularly for obtaining a weld metal having excellent strength, toughness, and elongation in welding of ultra-high strength steel having a tensile strength of 950 MPa or more. It relates to a welding method.

  In recent years, the demand for larger and lighter construction machines such as construction cranes and industrial machines has increased, and the steel materials used are super high strength steels such as 950 MPa class steel and 1180 MPa class steel. It is like that. These ultra-high strength steels are used because the weight of the product is reduced and the amount of steel used is reduced, so that the cost of steel and transportation are reduced, and the steel is thinned and the unit weight is reduced. This is because the handling is good and the welding amount is reduced, so that the manufacturing period can be shortened and the construction cost can be reduced.

However, in spite of a very high demand for ultra-high-strength steel, the amount of ultra-high-strength steel of 950 MPa class or higher is still very small when viewed from the total amount.
This is because it is more difficult to obtain a high-strength, high-toughness weld metal that matches the performance of the base steel material when welding ultra-high-strength steel of 950 MPa class or higher. The development of a gas shielded arc welding method is not sufficient.
In the welding of ultra high strength steel, it is necessary to obtain a high alloy weld metal. As a high-alloy welding wire, a flux-cored wire is advantageous in terms of manufacturability, and in particular, it is necessary to develop a gas shield arc welding method for ultra-high strength steel using the flux-cored wire.

Under such circumstances, the following flux-cored wires for gas shielded arc welding have been proposed for the purpose of ensuring the strength and toughness necessary for welding ultra-high strength steel.
In Patent Document 1, Ni, which is effective for securing strength and toughness, and other appropriate amounts of Mo, W, Nb, V and the like are added to ensure the tensile strength and toughness of the weld metal, and further, deoxidation in the wire. By containing appropriate amounts of the elements Si, Mn, Al, Ti, and Mg, the toughness and ductility of the weld metal due to oxygen and diffusible hydrogen in the weld metal during welding are prevented, and the occurrence of cold cracking is prevented. There has been proposed a flux-cored wire.
Further, in Patent Document 2, in welding of high-tensile steel having a tensile strength of 950 MPa or more, in particular, Mg is added to the flux to reduce the amount of diffusible hydrogen in the weld metal, and toughness and low-temperature cracking resistance are achieved. A flux cored wire that can obtain an improved weld metal has been proposed.

JP 2008-093715 A JP 2011-005531 A

Welding Society, “New Edition Welding / Joint Technology” published in 2005, Tokyo, Sangyo Publishing Co., Ltd., page 141

In the welding of ultra-high strength steel of 950 MPa or more, it is required that the weld metal also has an ultra-high tension. However, in the ultra-high-tensile weld metal, there has been a problem that a new ductile drop cracking occurs.
Ductile drop cracking is a phenomenon that occurs when the old γ grain boundaries break in multi-layer welding. Gas shield arc welding of ultra high strength steel is performed by multi-layer welding because it is desirable to limit the heat input per pass. In multi-layer welding, the previously formed weld metal is reheated by the next welding pass. At that time, C and S mainly segregate at the old γ grain boundary, and the embrittled old γ grain boundary is cracked by the heat shrinkage that occurs when it is cooled.

Such ductile drop cracks are not observed in ordinary high-strength steel weld metals, but in ultra-high-strength steel weld metals exceeding 950 MPa, the weld metal is made a high alloy to ensure strength and toughness. Therefore, it has to be a martensite structure, and in such a weld metal, the occurrence of ductile drop cracks becomes significant.
The ductility-decreasing crack is a very small crack, and the stress is concentrated at the crack tip at the time of the tensile test, so that the breakage occurs at an early stage. Therefore, the elongation is particularly low. If the elongation is low, there will be problems such as insufficient bending during production.

In addition, the use of ultra-high-strength steel can reduce the thickness of the steel compared to the conventional steel, while welding with relatively high heat input such that the droplet transfer form becomes spray transfer when the plate thickness is reduced. The strength of the weld metal decreases due to the slow cooling rate of the part. Therefore, in welding thin materials, it is necessary to perform welding with low current and low heat input in order to ensure the strength of the weld metal.
However, in gas shielded arc welding with low current and low heat input, the arc becomes very unstable and the amount of spatter increases significantly. As a result, the generated spatter adheres to the steel sheet, and an operation for removing it occurs. This significantly reduces the work efficiency.

Therefore, in order to use ultra-high strength steel of 950 MPa or more widely, along with the development of a flux-cored welding wire from which a weld metal having excellent strength, toughness and elongation can be obtained, It is necessary to develop a welding method capable of welding with reduced generation.
However, Patent Documents 1 and 2 do not discuss any problems of ductile deterioration cracking and spattering, which are problems in welding high-tensile steels with a tensile strength of 950 MPa or higher, and it is hoped that they will be solved. It is rare.

In Patent Document 1, the ductility of the weld metal is also considered, but referring to Table 5 and the like, the ductility is evaluated by the absorbed energy of the Charpy impact test at −40 ° C., and the amount of oxygen is reduced. The term “ductility” as used herein is used in the same meaning as toughness.
On the other hand, the ductile drop cracking which is a problem in the present invention is a crack due to a local lack of ductility of micro units of the old γ grain boundary as defined in Non-Patent Document 1, for example. The definition is different from the ductility used in. In fact, in the present invention, the ductility evaluation index is the elongation at break in a tensile test performed at room temperature as shown in the examples described later.

  In view of the problems of the background art described above, the present invention provides high strength, high strength by suppressing ductile deterioration cracking in weld metal when, for example, gas shield arc welding of ultrahigh strength steel of 950 MPa or more using a flux-cored wire. An object of the present invention is to provide a gas shielded arc welding method capable of obtaining a welded portion having excellent toughness and elongation and capable of performing welding while suppressing generation of spatter.

Conventionally, no ductile drop cracking occurs at a low strength level, which has not been a problem so far, and therefore no investigation has been made on the suppression of ductile drop cracking.
As a result of various studies for the purpose of suppressing ductility-reducing cracking, the present inventors have obtained the strength and toughness required for a weld metal of 950 MPa or more in a flux-cored wire in which a flux is filled inside a steel outer sheath. Addition of metal fluoride and C, Mn, and V to the wire under specific conditions within the range of flux composition and alloy components necessary to ensure, can suppress the ductile drop cracking and provide excellent elongation at break I found out.
Furthermore, when gas shielded arc welding is performed using such a flux-cored wire, it has been found that if a pulse power source is used for welding, stable droplet transfer can be achieved and spattering can be suppressed.
The gist of the present invention, which has been further studied based on such knowledge, is as follows.

(1) A gas shielded arc welding method using a flux-cored wire,
As the flux-cored wire, in the wire, the metal fluoride containing CaF ₂ is more than 2.0 to 8.0% and the metal oxide is 0.01 to 1.2% by mass% with respect to the total mass of the wire. And the ratio of metal fluoride to metal oxide content (metal fluoride amount / metal oxide amount) is 2.0 or more,
Furthermore, the content of Fe powder added to the flux is limited to less than 5.0%,
As an alloy component,
C: more than 0.08 to 0.20%,
Si: 0.05 to 1.5%,
Mn: 1.0-2.2%
S: 0.02% or less,
P: 0.02% or less,
Al: 0.001 to 0.4%,
Ni: 1.0-9.0%,
V: More than 0.05 to 0.30%
And the balance consists of Fe and inevitable impurities, and the Ceq defined by the following formula 1 is 0.60 to 1.40%,
A pulse gas shielded arc characterized by using a pulse current having a pulse condition of pulse peak current: 350 to 600 A, pulse peak period: 0.5 to 3.0 msec, pulse base current: 30 to 100 A as the welding current. Welding method.
Ceq = [C] +1/24 [Si] +1/6 [Mn] +1/40 [Ni] +
1/5 [Cr] +1/4 [Mo] +1/14 [V] (Formula 1)
However, the element with [] represents 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,
Cu: more than 0.1 to 0.8%,
Cr: 0.1 to 2.5%,
Mo: 0.1 to 2.0%,
Ti: 0.005 to 0.30%,
Nb: 0.01-0.05%
B: 0.0003 to 0.010%
1 or 2 types or more of these are contained, The pulse gas shield arc welding method as described in (1) characterized by the above-mentioned.
(3) The flux-cored wire is further mass% with respect to the total mass of the wire,
Mg: 0.1 to 0.8%
Ca: 0.1 to 0.5%,
REM: 0.002-0.01%
1 or 2 types or more are contained, The pulse gas shielded arc welding method as described in (1) or (2) characterized by the above-mentioned.

(4) The metal fluoride contained in the flux is composed of one or more of CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ containing CaF _2, and the mass ratio of CaF _{2 in} the metal fluoride Is 90% or more, the pulse gas shielded arc welding method according to any one of (1) to (3).
(5) The flux-cored wire further includes one or more of CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO ₃ metal carbonate in less than 0.6% by mass% based on the total mass of the wire. The pulse gas shielded arc welding method according to any one of (1) to (4), wherein:

(6) The pulse gas shielded arc welding method according to any one of (1) to (5), wherein perfluoropolyether oil is applied to the wire surface.

  According to the present invention, particularly in the welding of ultra-high strength steel having a tensile strength of 950 MPa or more, the weld has excellent strength, toughness and elongation by preventing the occurrence of ductile drop cracking and reducing the occurrence of spatter. A gas shielded arc welding method capable of obtaining a metal can be provided.

It is the figure which showed the relationship of the breaking elongation (mark distance 50mm) obtained by the tension test of the round bar tensile test piece of A1, and the amount of metal fluorides / metal oxides. It is the figure which showed the relationship between the elongation at break (mark distance 50mm) obtained by the tensile test of the round bar tensile test piece of A1, and C amount. It is a figure which shows the collection position of the test piece in an Example. It is a figure for demonstrating the form of the oxide in the weld metal after welding using the conventional wire, (a) is a figure by the transmission electron microscope observation photograph of two oxides, (b) These are figures which show the result of having conducted EDS analysis about the surface layer C point of the oxide in each photograph. It is a figure similar to FIG. 4 for demonstrating the form of the oxide in the weld metal after welding using the wire of this invention. It is a figure which shows an example of the result of having observed the inside using the transmission electron microscope about the oxide in the weld metal after welding using the wire of this invention, (a) is an image of an oxide, (b ) Is an EDS analysis map result of oxide, (c) is a distribution of O, and (d) is a diagram showing a distribution of S.

In the welding of steel materials made of ultra high strength steel of 950 MPa or more, the strength of the weld metal to be formed needs to be increased to 950 MPa or more, and the weld metal has a martensite structure. In the weld metal as-welded, the old γ grain boundaries are very coarse, and in addition, the martensite transformation is a non-diffusion transformation, so the γ grain boundaries formed during welding are segregated, impurities It remains in a state including. For this reason, the toughness of the old γ grain boundary of the ultra-high strength weld metal is originally low.
Furthermore, because of the martensitic transformation, C is in a solid solution state. When such a weld metal is reheated during multi-layer welding, C segregates to coarse old γ grain boundaries. Cause significant embrittlement. Similarly, S also segregates to the old γ grain boundary due to reheating during multi-layer welding and causes embrittlement. In that state, the heat shrinkage that occurs during cooling causes cracks in the old γ grain boundaries, resulting in ductile degradation cracks.

  In response to this problem, the present inventors effectively trap C and S in the weld metal subjected to reheating in the grains, and prevent the segregation to the grain boundaries or increase the weld metal elongation. By adding metal fluoride, metal oxide, C, Mn, and V appropriately in the wire, ductile drop cracking can be suppressed even in the case of ultra-high strength weld metal. It was found that the elongation at break can be secured.

An example of such an experiment is shown below.
In the same manner as in the examples described later, the inventors adjusted the wire components and produced a seamless flux-cored wire with a final wire diameter of φ1.2 mm. In the produced wire, the contents of C, Mn, V and the contents of metal fluoride and metal oxide were changed.
When performing butt welding of a 950 MPa class steel sheet using this flux-cored wire, a pulse arc power source was used, and pulsed under a pulse condition of pulse peak current: 450 A, pulse peak period: 1.0 msec, pulse base current: 50 A Gas shield arc welding was performed.
From the obtained weld metal, a No. A1 round bar tensile test piece based on JIS Z3111 (1986) was sampled and subjected to a tensile test at room temperature to evaluate the tensile strength and fracture elongation of the weld metal.

  FIG. 1 shows the relationship between the elongation at break (mark distance: 50 mm) obtained in the tensile test and the amount of metal fluoride / metal oxide in the welding wire. FIG. 2 shows the relationship between the elongation at break (mark distance: 50 mm) obtained in the tensile test and the C content.

From FIG. 1, metal fluoride is added so that the value of metal fluoride amount / metal oxide amount is 2.0 or more, C is more than 0.08%, Mn is 1.0% or more, V It was found that the elongation at break of 12% or more was obtained in the tensile test in the welding using the wire added so that the amount exceeds 0.05%.
Further, as shown in FIG. 2, in the range where the Mn content in the wire is less than 1%, the elongation at break decreases as the C content in the wire increases. On the other hand, when the Mn content in the wire is in the range of 1% or more, the same tendency as when the Mn content is small is shown until the C content is around 0.07%. It increases rapidly with the increase of. It was found that when the C content was 0.08% or more, an excellent breaking elongation of 12% or more was exhibited.

The reason why the above results were obtained is considered as follows.
(I) A metal fluoride is added to the flux in a specific range, and is added so that a specific relationship is established with the metal oxide, so that S is trapped in the oxide during solidification and the amount of solid solution S This is considered to be effective in suppressing the ductile drop cracking by reducing the segregation of S to the old γ grain boundary during reheating.
This inference is based on experimental results as shown in FIGS.

FIG. 4 shows an example of the result of observing with a transmission electron microscope a large number of oxides in the weld metal after welding with a prior art wire, with respect to two oxides 1 and 2 (a ) Is a transmission electron microscope observation photograph of the oxide, and (b) shows the result of EDS analysis of the surface layer C point of the oxide in the photograph. From the results of EDS analysis, almost no S was detected in this example.
On the other hand, FIG. 5 shows welding with the wire of the present invention (that is, a wire to which metal fluoride is added in a specific range and a metal fluoride is added so as to establish a specific relationship with the metal oxide). An example of the later results is shown in the same manner as FIG. 4 for the two oxides A and B. From the result of EDS analysis, in this example, S is detected on the surface layer of the oxide, and it can be seen that it is clearly present.

FIG. 6 shows an example of a result obtained by thinning an oxide in a weld metal welded with the wire of the present invention by ion milling and observing the inside using a transmission electron microscope. ) And EDS element maps inside the oxide shown in (d) clearly show that S is present on the surface of the oxide.
From these results, in the weld metal welded with the wire of the present invention, a large amount of S is taken into the oxide surface layer during the solidification process, so that the solid solution S is greatly reduced and S segregates at the old γ grain boundaries. This is considered to have been effective in suppressing ductile drop cracking.

  (Ii) Further, since Mn in the weld metal has an attractive interaction with C, it is considered to have an effect of suppressing segregation of C to the old γ grain boundary. In addition, V has little segregation during solidification and is relatively uniformly dispersed in the weld metal. Therefore, the composite addition of Mn and V in the weld metal causes the weld metal to be reheated. It is considered that V trapped solute C efficiently within the γ grains and suppressed the segregation of C to the old γ grain boundaries.

  (Iii) Further, the carbide precipitated in the old γ grains can be finely dispersed to contribute to the strength improvement, and the strength difference in the weld metal can be reduced. Further, as C increases, precipitates increase, and the strength difference in the weld metal can be reduced. Therefore, by increasing the C content and adding Mn and V in combination, carbides are finely dispersed and precipitated in the old γ grains, and the entire weld metal is uniformly plastically deformed during processing, resulting in elongation at break. It is thought that there was an effect of improving.

  Moreover, in the above experiment, it was confirmed that the welding can be performed by reducing the generation of spatter under the conditions of the welding current used. As a result of examining the current conditions for reducing the generation of spatter, the pulse power It has also been found that by using it, the spatter amount can be reduced to the same level as that of a solid wire.

The present invention has been made through the above-described studies. The reasons for limiting the technical requirements, which are characteristic of the present invention, will be sequentially described.
First, a flux cored wire used in gas shielded arc welding will be described.
In the description of the wire, “%” means “mass%” unless otherwise specified, and the content of each component is the sum of the mass% of each component in the steel outer sheath and flux with respect to the total mass of the wire. Means the content of the component.

  The flux-cored wire is composed of a steel outer sheath and a flux inserted therein. First, the reason for limitation of the steel outer sheath and the alloy component and metal deoxidation component contained in the flux will be explained. To do.

(C: more than 0.08 to 0.20%)
When the tensile strength of the weld metal is 950 MPa or more, the structure becomes a martensite-based structure. The influence of C on the strength of the martensite structure is large. As the C content in the welding wire increases, the C content in the weld metal also increases, and the strength of the weld metal can be increased.
Furthermore, when Mn and V are added together within the scope of the present invention, carbides are finely dispersed and precipitated in the old γ grains, and the strength difference in the weld metal can be reduced. As a result, the weld metal is uniformly plastically deformed during processing, so that the elongation at break can be improved.
In order to acquire these effects, it is necessary to contain C more than 0.08%. However, if C exceeds 0.20%, the deterioration of toughness becomes remarkable, which is not preferable. Further, in order to stably secure strength and elongation at break, the lower limit of C may be more than 0.09%, more than 0.10%, or more than 0.11%, and the upper limit of C may be 0.18%, It may be 0.16% or 0.14%.

(Si: 0.05-1.5%)
Si is a deoxidizing element and needs to be contained in an amount of 0.05% or more in order to reduce the amount of O in the weld metal and increase the cleanliness. However, if the content exceeds 1.5%, the toughness of the weld metal is deteriorated, so the Si content is set to 0.05 to 1.5%. Further, in order to stably secure the toughness of the weld metal, the lower limit of Si may be 0.2%, 0.3%, or 0.4%, and the upper limit of Si is 1.2%, 1.0% % Or 0.8%.

(Mn: 1.0-2.2%)
Mn has an attractive interaction with C, and is effective in suppressing ductile drop cracking by suppressing segregation of C to the old γ grain boundary. In addition, within the component range of the present invention, the formation of fine carbides in the prior γ grains is promoted, and the strength difference in the weld metal is reduced, thereby improving the elongation at break.
In order to exhibit the effect reliably, it is necessary to contain 1.0% or more. On the other hand, if the content exceeds 2.2%, excessive austenite is generated in the weld metal. In the retained austenite, C is concentrated, and when reheated by welding in that state, excessive carbides are formed where the retained austenite was retained, causing remarkable embrittlement.
For this reason, Mn content shall be 1.0-2.2%. In order to stably secure the effect of improving elongation at break, the lower limit of Mn may be 1.2%, 1.3%, or 1.4%, and the upper limit of Mn is 2.0% or 1%. It may be 8%.

(P: 0.02% or less)
P is an impurity element and needs to be reduced as much as possible in order to inhibit the toughness of the weld metal. However, the P content is set to 0.02% or less as a range in which an adverse effect on toughness can be tolerated. In order to further improve toughness, the upper limit of P may be limited to 0.015% or 0.010%.

(S: 0.02% or less)
S is also an impurity element, which promotes the occurrence of ductile drop cracking. Further, if excessively present, both toughness and ductility are deteriorated, so it is preferable to reduce as much as possible. The S content is set to 0.02% or less as a range in which an adverse effect on toughness and ductility is acceptable. In order to further improve toughness, the upper limit of S may be limited to 0.015%, 0.010%, or 0.008%.

(Al: 0.001 to 0.4%)
Al is a deoxidizing element and, like Si, is effective in reducing O in the weld metal and improving cleanliness, and is contained in an amount of 0.001% or more in order to exhibit the effects. On the other hand, if the content exceeds 0.4%, nitrides and oxides are formed and the toughness of the weld metal is inhibited, so the content is made 0.001 to 0.4%. Further, in order to sufficiently obtain the effect of improving the toughness of the weld metal, the lower limit of Al may be 0.0012% or 0.0015%, and the upper limit of Al is suppressed in order to suppress the formation of coarse oxides. , 0.2%, 0.1%, or 0.08%.

(Ni: 1.0-9.0%)
Ni is the only element that can improve toughness regardless of the structure and components by solid solution toughening (the effect of increasing toughness by solid solution), and in particular, it enhances toughness with a high strength weld metal with a tensile strength of 950 MPa or more. Is an effective element.
In order to obtain the solid solution toughening effect, it is preferable to contain 1.0% or more. A higher Ni content is advantageous in improving toughness, but if the content exceeds 9.0%, the effect is saturated and the manufacturing cost of the welding wire becomes excessive, which is not preferable. . Therefore, the content when Ni is contained is set to 1.0 to 9.0%. In order to ensure that the effect of Ni contributes to improvement of toughness, the lower limit of Ni is preferably set to 1.4%, 1.6%, and 2.1%. Ni is an expensive element, and its upper limit may be limited to 7.0%, 6.0%, or 4.8%.

(V: more than 0.05 to 0.30%)
V has little segregation during welding solidification, exists relatively uniformly in the weld metal, traps solute C when reheated, and suppresses segregation of C to the old γ grain boundary. By doing so, it is effective in suppressing the ductile drop cracking that occurs in the ultra-high strength weld metal. Furthermore, within the component range of the present invention, fine carbides are formed and precipitated in the old γ grains, and the strength difference in the weld metal is reduced, so that the elongation at break is improved.
In order to acquire the effect, it is necessary to make it contain more than 0.05%. The greater the V content, the greater the effect of suppressing ductility-reducing cracking. However, if the content exceeds 0.30%, the effect is saturated and the toughness is deteriorated. In order to enhance the effect of suppressing ductility-reducing cracking, the lower limit of V may be 0.06%, 0.08%, 0.10%, 0.12%, and to suppress toughness deterioration due to V. In addition, the upper limit of V may be limited to 0.28%, 0.25%, and 0.23%.

  The flux-cored wire used in the welding method of the present invention includes Cu, Cr, Mo depending on the strength level of the steel sheet to be welded and the required toughness, in addition to the above basic components as alloy components or metal deoxidation components. , Ti, Nb, or B can be contained alone or in combination.

(Cu: more than 0.1 to 0.8%)
Cu is added to the outer skin surface of the wire and to the flux as a simple substance or an alloy, and suppresses segregation of C into the old γ grains and suppresses ductile deterioration cracking. In order to sufficiently obtain these effects, it is preferable to contain more than 0.1%. On the other hand, if the content exceeds 0.8%, the toughness decreases. Therefore, the content when Cu is contained is set to 0.1 to 0.8%.
In addition, about content of Cu, in addition to the part contained in outer skin itself or a flux, when the copper surface is plated on the wire surface, the part is also included. In order to obtain the effect of Cu more stably, the lower limit may be 0.12%, 0.16%, or 0.18%. Moreover, it is good also considering the upper limit of Cu as 0.6%, 0.5%, or 0.4%.

(Cr: 0.1-2.5%)
Cr is an element effective for increasing strength by enhancing hardenability. In order to acquire the effect, it is good to contain 0.1% or more. On the other hand, if over 2.5% is contained, the bainite and martensite are hardened unevenly and the toughness is deteriorated, so the content when Cr is contained is 0.1 to 2.5%. And In order to obtain the effect of Cr more stably, the lower limit may be set to 0.3% or 0.6%. Further, the upper limit of Cr may be 2.0%, 1.8%, 1.6%, or 1.4%.

(Mo: 0.1-2.0%)
Mo is an element that improves hardenability, forms fine carbides, and is effective in securing tensile strength by precipitation strengthening. In order to exhibit these effects, it is preferable to contain at least 0.1% even in consideration of combined effects with other elements having similar effects. On the other hand, if the content exceeds 2.0% in the welding wire, coarse precipitates are produced and the toughness of the weld metal is deteriorated. 2.0%. In order to obtain the effect of Mo more stably, the lower limit may be 0.2%, 0.3%, or 0.4%. The upper limit of Mo may be 1.8%, 1.6%, 1.4%, or 1.2%.

(Ti: 0.005 to 0.30%)
Ti, like Al, is effective as a deoxidizing element and has the effect of reducing the amount of O in the weld metal. It is also effective for fixing solute N and mitigating the adverse effect on toughness. In order to exert these effects, it is preferable to contain 0.005% or more. However, if the content in the welding wire exceeds 0.30% and becomes excessive, there is a high possibility that toughness deterioration due to the formation of coarse oxides and toughness deterioration due to excessive precipitation strengthening will occur.
For this reason, content in the case of containing Ti in a welding wire shall be 0.005-0.30%. In order to sufficiently obtain the effect of improving the toughness of the weld metal by Ti, the lower limit of Ti may be 0.008%, 0.010%, or 0.015%. The upper limit of Ti is 0.20%, 0 It may be 10% or 0.05%.

(Nb: 0.01-0.05%)
Nb forms fine carbides and is effective in securing tensile strength by precipitation strengthening. In order to obtain these effects, the content is preferably 0.01% or more even in consideration of combined effects with other elements having similar effects. On the other hand, if it exceeds 0.05%, it is not preferable because it is excessively contained in the weld metal and coarse precipitates are formed to deteriorate toughness.
Therefore, in this invention, content when making it contain in a welding wire shall be 0.01-0.05%. In order to obtain the effect of Nb more stably, the lower limit may be set to 0.013% or 0.016%. If necessary, the upper limit of Nb may be 0.04% or 0.035%.

(B: 0.0003 to 0.010%)
When B is contained in an appropriate amount in the weld metal, it has the effect of reducing the adverse effect on the toughness of the solid solution N by combining with the solid solution N and contributing to the improvement of the strength by increasing the hardenability. There is also an effect. In order to obtain these effects, the B content in the welding wire needs to be 0.0003% or more. On the other hand, if the content exceeds 0.010%, B in the weld metal becomes excessive and forms coarse B compounds such as BN and Fe ₂₃ (C, B) ₆ to adversely deteriorate toughness. It is not preferable.
Therefore, when B is contained, the content is set to 0.0003 to 0.010%. In order to obtain the effect of B more stably, the lower limits may be set to 0.0006% and 0.0010%. In order to improve toughness, the upper limit of B may be 0.008%, 0.006%, 0.004%, or 0.003%.

  In the wire, in addition to the above components, for the purpose of adjusting the ductility and toughness of the weld metal, one or more of Mg, Ca, and REM are added as follows, as necessary. It can be contained within the range.

(Mg: 0.1-0.8%)
Mg is a strong deoxidizing element, reduces the amount of O in the weld metal, and improves the ductility and toughness of the weld metal. In order to acquire this effect, it is good to make it contain 0.1% or more. However, if the Mg content in the welding wire exceeds 0.8%, the decrease in toughness due to the formation of coarse oxides in the weld metal cannot be ignored, and the stability of the arc during welding deteriorates, resulting in beading. It also causes the shape to deteriorate.
For this reason, when it contains Mg, the content shall be 0.1-0.8%. In order to obtain the effect of Mg more stably, the lower limit may be 0.2% or 0.3%. In order to ensure the stability of the welding operation, the upper limit of Mg may be set to 0.7% or 0.6%.

(Ca: 0.1-0.5%)
(REM: 0.0002 to 0.01%)
Both Ca and REM are effective in improving ductility and toughness by changing the structure of sulfides and reducing the size of sulfides and oxides in the weld metal. The lower limit content for obtaining the effect is 0.1% for Ca and 0.0002% for REM. On the other hand, excessive content causes coarsening of sulfides and oxides, leading to deterioration of ductility and toughness, and also the possibility of deterioration of weld bead shape and weldability. , Ca is 0.5%, and REM is 0.01%.

(Carbon equivalent Ceq: 0.60 to 1.40%)
The flux-cored wire used in the present invention contains each element as described above as an alloy component or a metal deoxidation component. In order to ensure the tensile strength of the weld metal, the Japanese welding represented by the following (formula 1): The contents of C, Si, Mn, Ni, Cr, Mo, and V are further adjusted so that the carbon equivalent Ceq determined by the association (WES) is 0.60 to 1.40%.
Ceq = [C] +1/24 [Si] +1/6 [Mn] +1/40 [Ni] +
1/5 [Cr] +1/4 [Mo] +1/14 [V] (Formula 1)
However, the elements with [] indicate the content (% by mass) of each element.

  The higher the value of Ceq, the higher the tensile strength is improved because the weld metal is hardened, but on the other hand, the toughness is lowered and the sensitivity to weld cracking is increased. If the Ceq value is less than 0.60%, the target strength of the weld metal of 950 MPa is not satisfied. If the Ceq value exceeds 1.40%, the tensile strength of the weld metal becomes excessive, and the weld metal has toughness. descend. Therefore, the range of Ceq is 0.60 to 1.40%. In order to increase the tensile strength of the weld metal, the lower limit of Ceq may be 0.63%, 0.66%, or 0.70%. In order to reduce the deterioration of the toughness of the weld metal, the upper limit of Ceq may be 1.2%, 1.1%, or 1.0%.

The content of elements contained as the above alloy component or metal deoxidation component does not include the content when these elements are contained as fluoride, metal oxide, or metal carbonate.
Further, these elements are not necessarily pure substances (inevitable impurities can be contained), and there is no problem even if they are contained in the form of an alloy such as Cu-Ni. In addition, since these elements have the same effect regardless of whether they are contained in the steel skin or as a flux, they can be contained in either the steel skin or the flux.

Then, the flux component inserted in the outer skin of a wire is demonstrated.
(Metal fluoride: more than 2.0% to 8.0%)
A total of metal fluorides mainly composed of CaF ₂ is added to the wire in an amount of more than 2.0% to 8.0%. As the metal fluoride, one or more of BaF ₂ , SrF ₂ , and MgF ₂ may be added as necessary.
Metal fluoride is generated in ultra-high-strength weld metal by reducing the amount of dissolved S by trapping S in the oxide during solidification and suppressing segregation of S to the old γ grain boundary during reheating. It is possible to suppress ductile drop cracking. In addition, metal fluoride is effective in reducing the oxygen content of the weld metal, which can be expected to improve the toughness of the weld metal.

In order to obtain these effects, it is necessary to contain more than 2.0% of a metal fluoride containing CaF ₂ as a main component. If the content of metal fluoride is 2.0% or less, these sufficient effects cannot be obtained, and if it exceeds 8.0%, welding fume and slag are excessively generated. It deteriorates remarkably and is not preferable. In order to obtain a large effect of reducing the amount of oxygen, the lower limit of the metal fluoride may be set to 2.2% or more, 2.5% or more, 2.8% or more, and in order to suppress deterioration of welding workability, The upper limit of the metal fluoride may be 7.0% or less, 6.5% or less, or 6.0% or less.

As the metal fluoride, any of CaF ₂ , BaF ₂ , SrF ₂ , and MgF ₂ can be used from the viewpoint of suppressing the ductile drop cracking, but CaF ₂ is the main component from the viewpoint of welding workability. As included. Furthermore, when priority is given to welding workability such as ensuring arc stability and suppressing spatter, it is preferable that the ratio of CaF2 in the metal fluoride to be added is 90% or more.

(Metal oxide: 0.01-1.2%)
As a slag forming agent, one or more of metal oxides of TiO ₂ , SiO ₂ , MgO, and Al ₂ O ₃ are added. These are added as necessary in order to maintain the weld bead shape satisfactorily, and in order to obtain the appropriate effect, it is necessary to add 0.01%. However, if the content of the metal oxide exceeds 1.2%, the oxygen content of the weld metal increases and the toughness is deteriorated.
Therefore, the content of the metal oxide is set to 0.01 to 1.2%. The content of these metal oxides is the total content of TiO ₂ , SiO ₂ , MgO, Al ₂ O _{3 as well as} the total amount of metal oxides contained in binders used for flux granulation. . Moreover, in order to suppress the deterioration of toughness due to the addition of the metal oxide as much as possible, the upper limit of the content of the metal oxide may be set to 1.0%, 0.9%, and 0.8%.

(Amount of metal fluoride / Amount of metal oxide: 2.0 or more)
In order to suppress the ductile drop cracking of ultra-high strength weld metal, in addition to the above-mentioned metal fluoride and metal oxide contents, the metal fluoride content and the metal oxide content expressed in mass%. It is necessary to satisfy the value of the content ratio (metal fluoride amount / metal oxide amount) of 2.0 or more. When the metal fluoride amount / metal oxide amount is less than 2.0, the trapping effect of S on the oxide necessary to suppress the ductile drop cracking disappears.

(Fe powder: less than 5.0%)
Fe powder is added as needed for adjusting the filling rate of the flux-cored wire and improving the welding efficiency (including 0% addition amount). However, the surface layer of Fe powder is oxidized, and adding Fe powder increases the oxygen content of the weld metal and decreases toughness. When the tensile strength is 950 MPa or more, the strength is extremely high, so it is difficult to ensure toughness, and an increase in oxygen due to the addition of Fe powder is not allowed.
Therefore, Fe powder may not be added, but when it is added for adjusting the filling rate, the content is limited to less than 5.0% in order to ensure toughness.

(Metal carbonate: less than 0.6%)
To the flux-cored wire, one or more metal carbonates of CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO ₃ can be further added for the purpose of enhancing arc stability and arc concentration. If added in an amount of at least%, the concentration of arc is too strong and the amount of spatter increases. Therefore, when it contains a metal carbonate, the content shall be less than 0.6% in total.

  Although the above is the reason for limitation regarding the component composition of the flux-cored wire used in the present invention, the other remaining components are Fe and inevitable impurities. The Fe component includes Fe in the steel outer shell, iron powder added in the flux, and Fe in the alloy component.

In addition to the above, an arc stabilizer may be further contained as necessary. Examples of the arc stabilizer include Na and K oxides and fluorides (Na ₂ O, NaF, K ₂ O, KF, K ₂ SiF ₆ , K ₂ ZrF ₆ ), and the content thereof is 0.001 to 0.001. 0.40% is appropriate. Note that the oxides and fluorides exemplified here are not included in the metal oxides and metal fluorides.

Flux-cored wires can be broadly divided into seamless wires that have no slit-like seam in the steel outer shell and wires that have seams with slit-like gaps in the steel outer seam, but any cross-sectional structure is adopted. be able to.
In addition, a method of applying a slippery lubricant to the wire surface to improve the wire feeding property during welding is generally performed. As a lubricant for such a welding wire, perfluoropolyether oil (PFPE oil) which is a fluorine-based lubricating oil can be used.

The flux cored wire used in the present invention can be manufactured by the same manufacturing process as that of a normal flux cored wire manufacturing method.
That is, first, a steel strip to be the outer skin, and a flux containing metal fluoride, an alloy component, a metal oxide, a metal carbonate and an arc stabilizer so as to have predetermined contents are prepared, and the steel strip is elongated. Formed into an open tube (U-shaped) with a forming roll while feeding in the direction to form a steel outer shell. During this forming, flux is supplied from the opening of the open tube, and the opposite edge surfaces of the opening are butt seam welded. The seamless pipe obtained by welding is drawn and annealed during or after the drawing process to obtain a seamless wire having a desired wire diameter. Moreover, it is set as the pipe | tube with a seam without seam welding, and the wire which has a seam is obtained by drawing it.

Next, the welding conditions of gas shield arc welding when welding using the above-described flux cored wire will be described.
In the present invention, metal fluoride is used as the main component of the slag forming agent as described above. With such a wire, the oxygen content of the weld metal can be greatly reduced to improve impact toughness, but on the other hand, the effect of atomization of droplets due to Ti or TiO ₂ contained in solid wire or rutile flux cored wire Therefore, the surface tension of the droplet is improved and the droplet is difficult to be detached from the tip of the wire. In particular, when welding is performed at a low current, the droplet does not detach from the molten pool, and the droplet gradually grows. As a result, a short circuit occurs, and a large droplet is scattered, resulting in large spatter. Arise.
In the present invention, even when welding is performed at a low current, gas shielded arc welding using a pulse power source, that is, pulse gas shielding is performed in order to reduce the spatter amount to the same level as that of a solid wire. Perform arc welding.

Pulsed gas shielded arc welding uses a pulse power supply to generate a pulse current between a wire and a work piece, in which a peak current higher than the average welding current and a base current lower than the average current are periodically repeated. It is a method of energizing and welding.
At the time of welding, the droplet is melted in the molten pool even when the average arc voltage is low by melting the wire in the peak current period and transferring the droplet to the molten pool in the base current period. Since the droplets can be smoothly transferred to the molten pool without being short-circuited, the amount of spatter can be reduced.

  In order to achieve one pulse / one droplet transfer, it is necessary to appropriately adjust the melting energy of the wire. Therefore, as pulse conditions, the inventors have determined that the pulse peak current is 350 to 600 A, the pulse peak period is: It has been found that 0.5 to 3.0 msec and a pulse base current of 30 to 100 A are preferable. The reason for selecting the pulse condition in this way is as follows.

  The pulse peak current greatly affects droplet formation and droplet transferability. If the pulse peak current is less than 350 A, the formation of droplets becomes unstable, the droplets do not become one pulse / one droplet, the amount of spatter increases, and the bead shape becomes poor. On the other hand, if the pulse peak current exceeds 600 A, the arc becomes unstable, the amount of spatter increases, and the bead shape becomes poor. Therefore, the pulse peak current is set to 350 to 600A.

  The pulse base current requires a current value that can hold the arc during the base period. If the pulse base current is less than 30 A, the droplet transfer state becomes unstable, the amount of spatter increases, and the bead shape becomes poor. On the other hand, if the pulse base current exceeds 100 A, the droplets are not detached quickly, the arc becomes unstable, the amount of spatter increases, and the bead shape becomes poor. Therefore, the pulse base current is 30 to 100A.

  The pulse peak period, which represents the length of time that the pulse peak current lasts, is important for the droplet transfer of one pulse per droplet. If the length of the pulse peak period is less than 0.5 msec or more than 3.0 msec, the droplets do not transition to one pulse per droplet, the arc is unstable, the amount of spatter increases, and the bead shape becomes poor. . Therefore, the pulse peak period is set to 0.5 to 3.0 msec.

Other welding conditions are not particularly limited. For example, the shielding gas may be Ar gas or CO ₂ gas alone or a mixed gas thereof. , Ar-5 to 30% CO ₂ is preferable.

Next, the feasibility and effects of the present invention will be described in more detail with reference to examples.
While forming the steel strip in the longitudinal direction, it is formed into an open tube with a forming roll, and flux is supplied from the opening of the open tube during the forming, and the opposite edge surfaces of the opening are butt seam welded to seamless pipe Then, annealing was performed in the course of drawing the piped wire, and a flux-cored wire having a final wire diameter of φ1.2 mm was made as a prototype. In addition, a part of the pipe was a seam-welded pipe and was drawn to produce a flux-cored wire with a wire diameter of φ1.2 mm. [Table 1] and [Table 2] show the component composition of the prototyped flux-cored wire.

Using this flux-cored wire, a steel plate 1 having a tensile strength of 950 MPa or more and a plate thickness of 19 mm is abutted with a root gap of 12 mm and a groove angle of 45 ° as shown in FIG. Arc welding was performed. At that time, pulse gas shield arc welding or DC gas shield arc welding was carried out under the welding conditions shown in [Table 3-1] to [Table 3-4] using a pulse power source for some and a DC power source for others. .
In addition, although SM490A was used for the steel plate 1 and the backing metal 2, two or more layers and 3 mm or more of the grooved surface of the steel plate 1 and the surface of the backing metal 2 using a flux-cored wire to be tested. Battering was performed and used.

As shown in FIG. 3, A1 tensile test piece (round bar) 5 and No. 4 Charpy test piece (2 mmV notch) 4 in accordance with JIS Z3111 were sampled from the obtained weld metal 3 and tested for their mechanical properties. The yield strength, tensile strength, elongation at break and Charpy absorbed energy of the weld metal were measured.
Further, the amount of spatter generated during welding was measured in accordance with WES2807 “Method for measuring total spatter amount of MAG welding” of the Japan Welding Association standard.

The measurement results and evaluation results of the obtained mechanical properties are shown in [Table 4-1] to [Table 4-4].
The mechanical properties were evaluated as acceptable if the tensile strength was 950 MPa or more, the breaking elongation was 12% or more, and the toughness was a Charpy impact test at −40 ° C. and the absorbed energy was 27 J or more. As for the amount of spatter, the amount collected was good at 0.5 g / min or less.

As shown in the test results of [Table 4-1] to [Table 4-4], welding numbers A1 to A10, B1 to B10, C1 to C10, D1 to D10, E1 to E10, and F1 that are examples of the present invention. ˜F10 and G1 to G10 were all excellent in strength, elongation and toughness, and generated less spatter and passed.
On the other hand, welding numbers A11 to A16, B11 to B16, C11 to C16, D11 to D16, E11 to E16, F11 to F16, and G11 to G16, which are comparative examples, do not satisfy the pulse welding conditions defined in the present invention. The amount of spatter was increased, and the characteristics could not be evaluated due to poor welding workability.
In addition, wire numbers H1 to M1, which are also comparative examples, do not satisfy the requirements specified in the present invention for the flux composition and alloy components, and therefore cannot satisfy the strength, elongation, and toughness. It became.

Weld numbers A11, B11, C11, D11, E11, F11, and G11 can be evaluated because the pulse peak current is lower than the range of the present invention, the droplet transfer state becomes unstable, the spatter amount is large, and the bead shape is poor. I failed.
For welding numbers A12, B12, C12, D12, E12, F12, and G12, the pulse peak current is higher than the range of the present invention, so the arc becomes unstable, the amount of spatter is large, and the bead shape is also poor, so it cannot be evaluated and rejected. It became.
The welding numbers A13, B13, C13, D13, E13, F13, and G13 are rejected because the pulse peak period is below the range of the present invention, the arc becomes unstable, the amount of spatter is large, and the bead shape is also poor and cannot be evaluated. became.

Welding numbers A14, B14, C14, D14, E14, F14, and G14 are unacceptable because the pulse peak period exceeds the range of the present invention, the arc becomes unstable, the amount of spatter is large, and the bead shape is also poor. became.
Welding numbers A15, B15, C15, D15, E15, F15, and G15 can be evaluated because the pulse base current is lower than the range of the present invention, the droplet transfer state becomes unstable, the spatter amount is large, and the bead shape is poor. I failed.
For welding numbers A16, B16, C16, D16, E16, F16, and G16, the pulse base current is higher than the range of the present invention, so the arc becomes unstable and the amount of spatter is large. It became.

Since the number of fluoride contained in the wire was less than the range of the present invention, the welding number H1 failed to suppress the ductile drop cracking, resulting in a low value of elongation at break and a low value of toughness.
In weld number I1, since the ratio of metal fluoride / metal oxide was smaller than the range of the present invention, ductile deterioration cracking could not be suppressed, and the elongation was low and it was rejected.
Since welding number J1 had less C than the range of this invention, tensile strength became a low value and it failed.
Since welding number K1 had less Mn than the range of this invention, elongation became a low value and it failed. Moreover, since the welding number L1 had more Mn than the range of this invention, elongation became a low value and it failed.
Since welding number M1 had less V than the range of this invention, it could not suppress a ductile fall crack, but became low and became unsatisfactory.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Backing metal 3 Weld bead 4 2mmV notch Charpy impact test piece 5 Round bar tensile test piece

Claims (6)

A gas shielded arc welding method using a flux-cored wire,
As the flux-cored wire, in the wire, the metal fluoride containing CaF ₂ is more than 2.0 to 8.0% and the metal oxide is 0.01 to 1.2% by mass% with respect to the total mass of the wire. And the ratio of metal fluoride to metal oxide content (metal fluoride amount / metal oxide amount) is 2.0 or more,
Furthermore, the content of Fe powder added to the flux is limited to less than 5.0%,
As an alloy component,
C: more than 0.08 to 0.20%,
Si: 0.05 to 1.5%,
Mn: 1.0-2.2%
S: 0.02% or less,
P: 0.02% or less,
Al: 0.001 to 0.4%,
Ni: 1.0-9.0%,
V: More than 0.05 to 0.30%
And the balance consists of Fe and inevitable impurities, and the Ceq defined by the following formula 1 is 0.60 to 1.40%,
A pulse gas shielded arc characterized by using a pulse current having a pulse condition of pulse peak current: 350 to 600 A, pulse peak period: 0.5 to 3.0 msec, pulse base current: 30 to 100 A as the welding current. Welding method.
Ceq = [C] +1/24 [Si] +1/6 [Mn] +1/40 [Ni] +
1/5 [Cr] +1/4 [Mo] +1/14 [V] (Formula 1)
However, the element with [] represents the content (% by mass) of each element. The flux-cored wire is further mass% with respect to the total mass of the wire,
Cu: more than 0.1 to 0.8%,
Cr: 0.1 to 2.5%,
Mo: 0.1 to 2.0%,
Ti: 0.005 to 0.30%,
Nb: 0.01-0.05%
B: 0.0003 to 0.010%
2 or more types of these are contained, The pulse gas shield arc welding method of Claim 1 characterized by the above-mentioned. The flux-cored wire is further mass% with respect to the total mass of the wire,
Mg: 0.1 to 0.8%
Ca: 0.1 to 0.5%,
REM: 0.002-0.01%
1 or 2 types of these are contained, The pulse gas shielded arc welding method of Claim 1 or 2 characterized by the above-mentioned. The metal fluoride contained in the flux is composed of one or more of CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ containing CaF _2, and the mass ratio of CaF _{2 in} the metal fluoride is 90%. It is the above, The pulse gas shield arc welding method of any one of Claims 1-3 characterized by the above-mentioned. The flux-cored wire further contains one or more of CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO ₃ metal carbonates in less than 0.6% by mass% with respect to the total mass of the wire. The pulse gas shield arc welding method according to any one of claims 1 to 4, wherein the pulse gas shield arc welding method is provided.   6. The pulse gas shielded arc welding method according to claim 1, wherein perfluoropolyether oil is applied to the wire surface.