JP6365063B2 - High toughness flux shielded wire for gas shielded arc welding with excellent vertical welding workability - Google Patents

Description

  The present invention relates to a flux-cored wire for gas shielded arc welding (hereinafter sometimes simply referred to as a wire) in which a steel outer sheath is filled with flux, and in particular, has excellent workability in vertical welding, and The present invention relates to a flux-cored wire from which a high toughness weld metal can be obtained.

  Flux-cored wires are widely used in industry as welding materials that enable highly efficient gas shielded arc welding. As a typical wire, there is a rutile flux-cored wire using a Ti oxide such as rutile as a main slag forming material. This rutile wire has excellent welding workability, and has a feature that welding can be easily performed in various welding postures such as downward and vertical. However, since this wire contains a large amount of Ti oxide in the wire, the basicity of the slag is lowered. For this reason, the oxygen content of the weld metal tends to be high, and it is often difficult to ensure the toughness of the weld metal in, for example, welding of high-strength steel or low-temperature steel.

Therefore, as a wire that can cope with various welding postures and secure the toughness of the weld metal, a flux that uses oxides such as CaO, MgO, SrO, BaO and fluorides such as CaF ₂ as a main component instead of rutile. Cored wires have been proposed. For example, in Patent Literature 1 by the present inventors, CaO, CaF ₂ , MgO, MgF ₂ , SrO, SrF ₂ , BaO, BaF _{2 and the} like are contained as flux components, thereby improving the toughness of the weld metal, and A wire that enables all-position welding is disclosed. Further, Patent Document 2 discloses a wire that enables a downward and vertical posture using an oxide such as BaF ₂ , iron oxide, Mn oxide, and Zr oxide, and obtains a tough weld metal. Has been.

Japanese Patent No. 4834191 JP 2008-119748 A

For example, in the vertical improvement welding in which the corner portions 2 of the steel plates 1 and 1 combined as shown in FIG. 1 are welded, the cross-sectional shape of the weld metal 3 tends to be a convex shape as shown in FIG.
When the shape of the weld metal is convex, it becomes easy to cause poor fusion at the toe ends 4 and 4 of the weld metal when welding subsequent passes. To avoid poor fusion, the weld metal can be removed with a grinder or the like. It is necessary to grind and smooth the surface of the weld metal 3 as shown in FIG. However, performing such work is a major obstacle from the viewpoint of welding construction efficiency.

  In the study by the present inventors, by using a flux-cored wire whose main flux component is an oxide such as CaO and fluoride, vertical welding can be carried out without causing the weld metal to sag, and Although a tough weld metal can be obtained, it has been recognized that the weld metal has a convex shape. Patent Documents 1 and 2 do not particularly mention such a problem.

  Therefore, in view of such problems, the present invention provides a high-toughness weld metal, and a flux-filled gas shielded arc welding that can make the shape of the weld metal not a convex shape but a smooth shape in vertical welding. It is an object to provide a wire.

  The present inventors searched for a new flux component to be contained in the flux-cored wire in order to solve the above-described problems. In the process, it was found that it is effective to contain both MnO and CaO in the wire in order to obtain a smooth weld metal shape. The gist of the present invention made based on this study is as follows.

[1] A flux-cored wire for gas shielded arc welding formed by filling a steel outer shell with flux, which satisfies the following conditions (a) to (d) simultaneously: Wire.
(A) MnO is contained by 1.0% or more and 6.0% or less by mass% with respect to the total mass of the wire.
(B) CaO is contained by 1.0% or more and 6.0% or less by mass% with respect to the total mass of the wire.
(C) The total content of MnO and CaO is 4.0% or more by mass% with respect to the total mass of the wire.
( D ) The value of Pcm defined by the following formula (1) is in the range of 0.15% or more and 0.40% or less, and the total mass of P and S is 0. Be limited to 040% or less.
Pcm = N (C) + N (Si) / 30 + N (Mn) / 20 + N (Cu) / 20 + N (Ni) / 60 + N (Cr) / 20
+ N (Mo) / 15 + N (V) / 10 + 5N (B) (1)
Here, N (X): mass% of element X with respect to the total mass of the wire.
( E ) The balance is Fe, an arc stabilizer, and inevitable impurities.
[2] Further, one or more of MgF ₂ , CaF ₂ , SrF ₂ , and BaF ₂ are contained, and the total content is 5.0% or less by mass% with respect to the total mass of the wire. The flux-cored wire for gas shielded arc welding according to the above [1], which is characterized by the above.
[3] Further, one or more of Mn oxides other than Si oxide, Al oxide, Ti oxide, B oxide, Zr oxide, Fe oxide, and MnO are contained, The flux-cored wire for gas shielded arc welding according to the above [1] or [2], wherein the total is 4.0% or less by mass% with respect to the total mass of the wire.
[4] Further, one or more of Al, Ti, Mg, Zr, Ca, Ce, and La in the metal state are contained, and the total content is 2.0% or less with respect to the total mass of the wire. The flux-cored wire for gas shielded arc welding according to any one of the above [1] to [3], wherein
[5] Further, one or more of MgCO _3, CaCO ₃ , SrCO ₃ , BaCO ₃ , and MnCO ₃ are contained, and the total content is 4.0% or less by mass% based on the total mass of the wire. In addition, when one or two of CaCO ₃ and MnCO ₃ are contained, the amount of CaO and MnO generated by thermal decomposition of CaCO ₃ and MnCO ₃ is added to the amount of CaO and MnO contained in the flux-cored wire. the total amount obtained by adding the, CaO, in an amount not to exceed the upper limit of the content of each of _MnO, according to any one of [1] to [4], wherein the Rukoto is contained CaCO 3, MnCO ₃ Flux-cored wire for gas shielded arc welding.
[6] In addition, MgO, SrO, is contained in one or more of BaO, the total content of Ri der 3.2% or less by mass% with respect to total mass of the wire, and, MgCO the flux cored wire ₃ , when one or more of SrCO ₃ and BaCO ₃ are contained , the total amount obtained by adding the amounts of MgO, SrO, and BaO generated by thermal decomposition of MgCO ₃ , SrCO ₃ , and BaCO ₃ is 3.2. gas shielded arc welding flux cored wire according to any one of [1] to [5], wherein the Rukoto is contained in an amount not in excess of mass%.
[7] The flux for gas shielded arc welding according to any one of the above [1] to [6], wherein Nb is contained in a range of 0.1% or less by mass% relative to the total mass of the wire. Cored wire.
[8] The flux-cored wire for gas shielded arc welding according to any one of [1] to [7], wherein the steel outer shell has no slit-like gap.
[9] The flux-cored wire for gas shielded arc welding according to any one of [1] to [7], wherein the steel outer shell has a slit-like gap.

  According to the present invention, a high-toughness weld metal can be obtained, and a flux-cored wire that can make the surface shape of the weld metal not a convex shape but a smooth shape in vertical welding can be provided.

It is a figure for demonstrating the point of vertical improvement progress welding. It is a figure which shows the example whose cross-sectional shape of a weld metal is convex shape. It is a figure which shows an example of the desirable cross-sectional shape of a weld metal. It is a figure for demonstrating the dce value which is a parameter | index which evaluates the cross-sectional shape of a weld metal. It is a figure which shows the influence which content of MnO has on a dce value. It is a figure explaining the manufacturing process of a flux cored wire. It is a figure which shows the groove shape for evaluating the defect of a weld metal, oxygen amount, Charpy impact value, and hardness. It is a figure explaining the hardness measurement position of a weld metal. It is a figure which shows an example of the cut cross section of a wire.

  In Patent Document 1, all-position welding is enabled by using CaO to increase the melting point of slag. However, with the flux-cored wire, vertical welding is possible, but it has been recognized that the weld metal has a convex shape as shown in FIG. If the shape of the weld metal is a convex shape, the work for smoothing is required as described above, which is a serious problem in terms of welding work efficiency.

Therefore, the present inventors investigated the influence of oxides other than CaO on the shape of the weld metal formed by vertical welding in a flux-cored wire containing an oxide such as CaO.
In the shape evaluation of weld metal in vertical welding, since there is no measurement method that is generally widely used, the present inventors examined a measurement method that can evaluate the shape of the weld metal, and used the following method. Devised.
That is, as shown in FIG. 4, the corner portion 2 formed by the steel plates 1 and 1 arranged at an angle of 90 ° is used as a groove to perform the vertical improvement welding, and both toe ends 4 of the obtained weld metal 3 are obtained. The distance between the line A connecting the line 4 and the convex vertex 5 of the weld metal 3 and the line B parallel to the line A is dce, and this dce value is measured from the cross section of the weld metal. The shape of the metal was evaluated.

The oxide added to the wire as a flux component mainly has the effect of forming a slag to envelop the weld metal and maintaining a good shape of the weld metal. Attention has been focused on experiments to investigate the relationship between the content of various oxides and the dce value. In the process, it was found that MnO is particularly effective in eliminating the convex shape of the weld metal.
Hereinafter, an example of an experimental result in which such knowledge is obtained will be shown. In the following description, “%” means “mass%” unless otherwise specified, and the content of each component means mass% relative to the total mass of the wire.

In FIG. 5, MnO: 0.4 to 6.9%, CaO: 3.7%, CaF ₂ : 0.9%, Si oxide: 0.5%, Ti oxide: 0.3% are flux components. 1 shows the relationship between the dce value of the weld metal and the MnO content when the joint shown in FIG.

  As shown in FIG. 5, when the MnO content is 1.0% or more and 6.0% or less, the dce value is greatly reduced to 2.0 or less, the convex shape of the weld metal is suppressed, and the smooth shape It can be seen that a weld metal is obtained. The reason why such a result was obtained is not necessarily clear, but it is estimated that the interfacial tension between the molten metal and molten slag and the wettability between the molten slag and the base steel sheet at the toe are affected. doing.

The present invention has been made as a result of the above studies, and the reasons for limiting the technical requirements and preferred aspects of the flux-cored wire of the present invention will be sequentially described below.
First, the flux component and other components filled in the steel outer shell will be described.

First, the reason for the inclusion of MnO will be described.
MnO has the effect of forming a smooth weld metal shape as described above, and is added to the flux for that purpose. When the content of MnO is less than 1.0%, the content is too small, and the weld metal may have a convex shape in vertical welding. On the other hand, if the content exceeds 6.0%, the arc may become unstable and the molten pool may vibrate vigorously. For this reason, it becomes difficult to obtain a smooth weld metal shape, and it tends to be a convex weld metal shape. For the above reasons, MnO is defined as 1.0% or more and 6.0% or less. Moreover, when the content of MnO is 1.6% or more and 5.5% or less, the effect of smoothing the weld metal shape is clear and preferable. Furthermore, when the content is limited to 2.6% or more and 5.0% or less, the effect of smoothing the shape of the weld metal is manifested particularly clearly, which is still more preferable. MnO is a basic substance and does not significantly increase the amount of weld metal oxygen even if it is contained in the wire. For this reason, the toughness of the weld metal is very good.

Subsequently, the reason for the CaO content will be described.
CaO is a basic substance like MnO, and does not significantly increase the amount of weld metal oxygen even if contained in the wire. In vertical welding, it is extremely important to hold the molten pool with slag, and the melting point of the slag needs to be high. Since CaO is a high melting point substance, it is effective for raising the melting point of slag with MnO.

  When the content of CaO is less than 1.0%, the content is too small, and in vertical welding, the molten pool drips during welding, making welding impossible. On the other hand, if the content exceeds 6.0%, the melting point of the slag is too high, so that the solidification of the slag is accelerated and the fluidity of the slag cannot be ensured, so that slag is likely to occur. For these reasons, CaO is defined as 1.0% or more and 6.0% or less. Further, the content of CaO may be limited to 1.7% to 5.5%, or 2.2% to 4.9% as necessary.

  The total content of MnO and CaO is preferably 4.0% or more. Further, CaO and MnO do not need to be contained in the wire as simple oxides, and there is no problem even if they are contained in a complex oxide such as CaO · MnO. In this case, for CaO and MnO, only the mass of the corresponding part is calculated as the content.

The alloy elements contained in the wire include various elements such as C, Si, Mn, P, S, Cu, Ni, Cr, Mo, V, and B. The content of these elements is represented by the following formula (1). It is necessary that the defined Pcm value is in the range of 0.15% or more and 0.40% or less, and the total mass of P and S is limited to 0.040% or less in terms of mass% based on the total mass of the wire. It is.
Pcm = N (C) + N (Si) / 30 + N (Mn) / 20 + N (Cu) / 20 + N (Ni) / 60 + N (Cr) / 20
+ N (Mo) / 15 + N (V) / 10 + 5N (B) (1)
Here, N (X): mass% of element X with respect to the total mass of the wire.
Formula (1) is a formula that is widely known as Pcm (see Welding Society: “Introduction to Welding and Joining Technology”, Sangyo Publishing, Tokyo, (1998) p. 118) and evaluates the hardenability of weld metal. It is an expression that can be done.

When the Pcm value is less than 0.15%, the hardenability of the weld metal is too low, and a coarse structure such as grain boundary ferrite is generated, and the toughness of the weld metal is deteriorated. On the other hand, when the Pcm value exceeds 0.40%, the weld metal becomes too hard and a hardened structure such as martensite is mainly used, and the toughness of the weld metal is deteriorated. For this reason, in order to ensure the toughness requested | required of a weld metal, it is essential that Pcm value is the range of 0.15% or more and 0.40% or less.
In addition, since the hardenability of the weld metal is discussed in Formula (1), elements contained as oxides, fluorides, and carbonates are out of scope.

  Further, the total content of P and S in the wire needs to be limited to 0.04% or less from the viewpoint of avoiding hot cracking of the weld metal and ensuring toughness. However, excessively reducing P and S is not practical from an industrial viewpoint because the production load increases, and the total content of P and S does not need to be reduced to 0.001% or less.

  The above is the basic outline of the present invention, but additional requirements for making the wire of the present invention higher performance will be described below.

_{First, MgF 2, CaF 2, SrF} 2, describes the addition of BaF _2.
Since these fluorides exhibit an effect of reducing the amount of diffusible hydrogen in the welded joint, one or more of them can be contained in the wire of the present invention. However, if the content exceeds 5.0%, the amount of fume generation increases, and the welding work environment tends to be adversely affected. For this reason, the total mass of one or more of MgF ₂ , CaF ₂ , SrF ₂ , and BaF ₂ is defined as 5.0% or less. Moreover, when using the wire of this invention in the welding work site which intends to reduce the amount of fumes generated, the total mass of one or more of MgF ₂ , CaF ₂ , SrF ₂ , and BaF ₂ is 3.0. % Or less, and when the wire of the present invention is used in a welding work site where the amount of generated fume is particularly concerned, the total mass of one or more of MgF ₂ , CaF ₂ , SrF ₂ , and BaF ₂ is 1 More preferably, it is less than 0.0%. In order to clearly obtain the effect of reducing diffusible hydrogen, the total content of one or more of MgF ₂ , CaF ₂ , SrF ₂ , and BaF ₂ is preferably 0.2% or more.

Subsequently, Mn oxides excluding Si oxide, Al oxide, Ti oxide, B oxide, Zr oxide, Fe oxide, and MnO will be described.
It is known that when these oxides are contained in the slag, the amount of oxygen in the weld metal increases and the toughness of the weld metal may deteriorate. Therefore, from the viewpoint of ensuring the toughness of the weld metal, the content of these oxides is preferably suppressed as low as possible. However, these oxides have an effect of facilitating slag peeling because the uniformity of the foreskin is enhanced when the slag encloses the weld metal.

  Therefore, the inventors experimentally searched for a range in which the content of these oxides does not adversely affect the toughness of the weld metal. As a result, if the total mass of Mn oxide excluding Si oxide, Al oxide, Ti oxide, B oxide, Zr oxide, Fe oxide, and MnO is 4.0% or less, the toughness of the weld metal It has been found that deterioration can be suppressed within a practical range and good slag releasability is ensured. For the above reasons, the total mass when one or more of Mn oxides excluding Si oxide, Al oxide, Ti oxide, B oxide, Zr oxide, Fe oxide, and MnO is contained. Is limited to 4.0% or less. In order to clearly obtain the effect of improving the slag peelability, the total mass of these oxides is preferably 0.2% or more. If necessary, the total content of these oxides can be limited to 2.8% or less, or 1.0% or less.

In the case where the oxide is a composite oxide, for example, in Al ₂ O ₃ .SiO ₂ , the Al ₂ O ₃ portion is Al oxide and the SiO ₂ portion is Si oxide. The total mass is calculated by calculating the mass of the part concerned, Si oxide is converted to SiO ₂ , Al oxide is converted to Al ₂ O ₃ , Ti oxide is converted to TiO ₂ , and B oxide is B ₂ O ₃ equivalent value, Zr oxide is ZrO ₂ equivalent value, Fe oxide is FeO equivalent value, and Mn oxide excluding MnO is MnO ₂ equivalent value.

Subsequently, Al, Ti, Mg, Zr, Ca, Ce, and La as deoxidizing elements will be described.
Metallic Al, Ti, Mg, Zr, Ca, Ce and La all have a strong deoxidizing action and are known to be effective elements for reducing oxygen in weld metals. The total value of the content of one kind or two kinds or more can be added within a range of 2.0% or less. In order to express this deoxidation effect clearly, the total content of Al, Ti, Mg, Zr, Ca, Ce, and La is preferably 0.2% or more. On the other hand, if the total amount of Al, Ti, Mg, Zr, Ca, Ce, and La exceeds 2.0%, an extreme hard structure such as the MA structure is formed, and the toughness of the weld metal deteriorates. To do. For this reason, the total content of Al, Ti, Mg, Zr, Ca, Ce, and La in the metal state is determined to be 2.0% or less.

  These metal elements do not necessarily need to be contained as pure metals (inevitable impurities can be contained), and there is no problem even if they are contained in the form of an alloy such as Al—Mg. Here, since it is premised on a deoxidation reaction during welding, Al, Ti, Mg, Zr, Ca, Ce, and La contained as oxides, fluorides, and carbonates are not included.

Subsequently, CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ will be described as carbonates.
The wire of the present invention can contain one or more of CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ as carbonates. These carbonates are pyrolyzed by arc heat to generate carbon dioxide from the inside of the wire. Thereby, the detachment of the droplet formed at the wire tip during welding is facilitated, and there is an effect of making the droplet fine.
In order to clearly obtain this effect, the total content of CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ is preferably 0.2% or more. On the other hand, if the total content of one or more of CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ exceeds 4.0%, carbon dioxide is excessively generated and formed at the wire tip. On the contrary, the spatter amount increases because the droplets are blown off. For this reason, the upper limit of the total content of CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ is set to 4.0% or less.

Note that CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ are substances containing CaO, MgO, BaO, SrO, and MnO, as shown in the following formulas (2) to (6). When CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ are contained, CaO, MgO, BaO, SrO, and MnO generated by thermal decomposition are the above-mentioned CaO, MnO, and MgO described below, It is added to each content of BaO and SrO. Therefore, it is necessary to contain these carbonates so that the respective contents of CaO and MnO after addition and the total contents of MgO, BaO and SrO after addition do not exceed the specified upper limit contents, respectively. There is.
CaCO ₃ → CaO + CO ₂ Formula (2)
MgCO ₃ → MgO + CO ₂ Formula (3)
BaCO ₃ → BaO + CO ₂ Formula (4)
SrCO ₃ → SrO + CO ₂ Formula (5)
MnCO ₃ → MnO + CO ₂ Formula (6)

Subsequently, MgO, SrO, and BaO will be described.
The wire of the present invention can contain MgO, SrO, and BaO as oxides other than the oxides listed above. Since these have the function of reducing the viscosity of the slag, the slag can be easily discharged from the molten pool. When MgO, SrO, and BaO are contained, the slag does not stay in the molten pool, and the slag flows quickly to the rear in the welding direction, so that the welder can more easily confirm the position of the molten pool. . However, if these contents are too large, the viscosity of the slag is remarkably lowered, the molten pool cannot be maintained by vertical welding, and welding is likely to be impossible. Therefore, the total content of MgO, SrO, BaO is 3.2% or less. It was. In order to exhibit the effects of MgO, SrO, and BaO, the total content of these elements is preferably 0.1% or more.

Next, the effect of Nb will be described.
The weld metal using the wire of the present invention is generally multi-layer welding, and a softened part may be generated in a part of the weld metal due to the influence of welding heat in the subsequent pass. In order to suppress this softening, Nb can be contained in the wire. In order to clearly obtain this effect, the Nb content is preferably 0.01% or more. On the other hand, if the Nb content exceeds 0.1%, a hardened structure such as an MA structure is excessively generated, and the toughness of the weld metal deteriorates. For this reason, the Nb content is set to 0.1% or less.

Subsequently, other components filled in the steel outer shell will be described.
Even in the wire of the present invention, it is not limited at all to contain iron powder and an arc stabilizer that are generally used in the past, and by including those components in the outer skin as necessary, The function of the flux-cored wire can be further enhanced. These components are described below.

  It is well known that when iron powder is contained in the flux, the welding efficiency is improved and the arc stability is improved. However, since iron powder tends to break during wire drawing when iron powder is added in excess, the content when added is preferably 5.0% or less.

  As the arc stabilizer, generally used oxides, fluorides, carbonates and the like containing Li, Na, K, and Rb are appropriately selected, and are 0.001% or more and 1.0% or less. It can be contained in a range.

  Some of the alloy components and metal deoxidation components described above can be contained in the steel outer sheath, but since these components are determined by the entire wire, they are contained in either the flux component or the steel outer sheath. Even if there is no problem, the content of the entire wire is important.

  Next, the form of the steel outer sheath of the wire will be described. For flux-cored wires, there are two types of wires: one with a steel outer seam welded without a slit gap in the steel outer shell and one with a slit outer gap in the steel outer joint without welding. Can be separated. The wire of the present invention contains a substance that easily absorbs moisture, such as CaO or fluoride, in the flux, and if there is a gap in the steel outer shell, it causes moisture absorption. It is useful from the viewpoint of preventing moisture absorption and stabilizing the quality of the welding wire.

  Of course, it is possible to use a wire having a slit-like gap in the steel outer shell, but in that case, it is preferable to pack in a sealed container until just before use to suppress moisture absorption of the flux. Furthermore, from the viewpoint of reducing diffusible hydrogen, the lubricating oil applied to the wire surface is preferably an oil containing no hydrogen content such as perfluoropolyether. There is no problem even if it is applied to the wire of the invention.

The flux cored wire used in the present embodiment 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 an outer skin and a flux prepared so as to have a predetermined content of metal oxide, metal fluoride, alloy component, metal carbonate and arc stabilizer are prepared. While feeding the steel strip in the longitudinal direction, it is formed into an open tube (U-shaped) with a forming roll to form a steel outer shell. During this forming, flux is supplied from the opening of the open tube, and the opposing edge surface of the opening is Butt seam welding. A wire without a gap obtained by welding is drawn, annealed in the middle of the drawing or after the drawing process is completed, has a desired wire diameter, and has a slit shape in which a flux is filled in the steel outer shell. Get a wire with no gaps (seamless). Further, a wire having a slit-like gap (having a seam) is obtained by supplying a flux from an opening of an open pipe, then forming a pipe with a gap without seam welding, and drawing it.

Here, the form of the seamless wire, particularly the cross-sectional structure, will be described with reference to FIGS. 9 (a) to 9 (c). Fig.9 (a)-FIG.9 (c) are figures which show the cross section of a wire.
A cross section obtained by cutting a wire without slit-like gaps made by butt seam welding looks like FIG. If this cross section is polished and etched, welding marks are observed, but if not etched, no welding marks are observed. Therefore, it may be called seamless. It is described as “seamless type” in the “New Edition Introduction to Welding and Joining Technology” (2008) Sangyo Shuppan, p.111, edited by the Japan Welding Society. Even if there is a gap as shown in FIGS. 9B and 9C, a wire having no slit-like gap can be obtained even after brazing or brazing after bracing. It is done. In FIGS. 9B and 9C, the wire that is not brazed is a wire having a slit-like gap as shown.

  Although there is no special restriction regarding the diameter of the wire of the present invention, it is preferable to set it in the range of 1.2 mm to 1.6 mm in view of both welding efficiency and wire productivity. Further, the total mass of the flux filled in the steel outer shell is preferably 6.0% or more and 18.0% or less in terms of mass% with respect to the total mass of the wire.

Hereinafter, effects of the present invention and comparative examples will be verified using examples.
A steel sheet for steel skin having the components shown in Table 1 is formed into a U-shape as shown in FIG. 6, and at this stage, flux is filled into the U-groove of the steel sheet from above, and then the U-shaped steel sheet is converted into an O-shape. It was formed into a tubular wire blank. In the case of a wire having a slit-like gap, the wire tube was finished into a trial wire having a diameter of 1.2 mmφ through a wire drawing process. For wires without slit-like gaps, wire is drawn after the process of removing the slit-like gaps in the steel sheath that causes moisture absorption of the flux by welding the seam of the steel sheath of the wire base tube. A finished wire having a diameter of 1.2 mmφ was prepared.

Tables 5, 7, 9, 11, 13, 15, 17, 19, and 21 show the flux compositions of the prototyped wires.
In each table, the wires No. 1 to No. 9 in Table 5 verify the effect of MnO. The wires No. 10 to No. 18 in Table 7 verify the effect of CaO. Table 9 Wire No. 19 to Wire No. 30 verify the Pcm value, Nb content, and P and S contents determined from the wire components.

The wires No. 31 to No. 48 in Table 11 verify the effects of MgF ₂ , CaF ₂ , SrF ₂ , and BaF _2. The wires No. 49 to No. 71 in Table 13 are Si-oxidized. The content of Mn oxides except for oxides, Al oxides, Ti oxides, B oxides, Zr oxides, Fe oxides, and MnO was verified.

Wire numbers 72 to 93 in Table 15 verify the contents of Al, Ti, Mg, Zr, Ca, Ce, and La contained as deoxidizing elements. Wire numbers 94 to 111 in Table 17 verify the contents of CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ .
The wire numbers 112 to 123 in Table 19 verify the contents of MgO 2 _, SrO, and BaO. The wire number 124 in Table 21 verifies the effect of adding the above-mentioned contained substances in combination. The wire numbers 125 to 149 in Table 23 verify the effects of eliminating the steel outer slit.

The following tests were conducted using the above-described prototyped wires to evaluate the performance of the wires.
In the first test, evaluation was made on whether or not the test-made wire can be welded in the vertical direction, the amount of spatter generated, the smoothness of the weld metal shape, and the slag peelability. The first test was conducted by vertical improvement welding under the conditions of the vertical posture shown in Table 3. The steel material used in the first test was a 10 mm thick steel plate having the components shown in Table 2, and this was assembled and used at an angle of 90 ° as shown in FIG.

  Whether or not vertical improvement welding is possible was determined by whether or not a welding length of 500 mm was stably obtained by the welding shown in FIG. Spatter generated during the welding was collected, the weight of the spatter was measured, and the amount of spatter generated per minute of arc time was evaluated. After welding, the slag covering the weld metal was peeled off, and the time required for slag peeling was measured. After peeling the slag, a cross section of the weld metal was cut out, and the smoothness of the weld metal was measured as shown in FIG.

The wire that passed the first test proceeded to the second test, and in the second test, the presence or absence of welding defects and the oxygen content, toughness, and hardness distribution of the welding genus were evaluated. The second test was conducted by vertical improvement welding under the conditions of the vertical posture shown in Table 3. In the second test, a steel plate having a groove shown in FIG. 7 was used, and welding was performed until a surplus was formed on the surface of the steel by multi-layer welding, and the welding length was 500 mm.
The welded joint produced in the second test was subjected to a nondestructive test by X-ray inspection and evaluated for the presence or absence of weld defects. After the X-ray inspection, a pin sample was collected from the weld metal for oxygen analysis, and a 10 mm full-size V-notch Charpy test piece defined in JIS Z 2242 was further collected for testing. The notch of the Charpy specimen was processed in the center of the weld metal. Further, a cross section of the weld metal was cut out, and the Vickers hardness of the weld metal was measured at intervals of 2 mm at a position 7 mm below the steel plate surface as shown in FIG. The load used for the hardness measurement is 98N. The difference between the maximum value and the minimum value of the obtained Vickers hardness was evaluated as the homogeneity of the hardness distribution.

Further, as a third test, the amount of fumes generated during welding and the amount of diffusible hydrogen were measured. The amount of fumes generated during welding was measured according to JIS Z 3930. The amount of diffusible hydrogen was measured according to JIS Z 3118. In the third test, the downward posture conditions shown in Table 3 were used, and evaluation was performed by downward welding.
The acceptance criteria for the first to third tests are listed in Table 4.

Next, the evaluation result of the test using the prototyped wire is shown.
Table 6 shows the results of verifying the MnO content using the wires in Table 5.
Good results were obtained with wire numbers 1 to 7 whose components were adjusted within the scope of the present invention and passed. In particular, wire Nos. 2 to 6 having a MnO content of 1.6% or more and 5.5% or less had a clear and preferable result of smoothing the weld metal shape. Furthermore, wire Nos. 3 to 5 having a MnO content of 2.6% or more and 5.0% or less were even more preferable results in which the effect of smoothing the shape of the weld metal was clearly manifested. On the other hand, wire numbers 8 and 9 whose MnO content deviated from the scope of the present invention were rejected because a smooth weld metal shape was not obtained.

Table 8 shows the results of verifying the CaO content using the wires in Table 7.
Good results were obtained with wire numbers 10 to 16 whose components were adjusted within the scope of the present invention and passed. On the other hand, wire No. 17 in which the CaO content deviated from the scope of the present invention was not capable of standing up welding, and wire No. 18 was rejected because slag entrainment occurred.

Table 10 shows the results of verifying the Pcm value, the Nb content, and the total content of P and S as indicators of the alloy element content using the wires in Table 9.
Good results were obtained with wire numbers 19 to 26 whose components were adjusted within the scope of the present invention and passed. The wire numbers 24 to 26, in which Nb is contained within the scope of the present invention, suppresses the softening of the portion of the weld metal that has undergone reheating in the subsequent pass, and therefore the hardness difference in the weld metal is reduced. A weld metal having a homogeneous hardness distribution was obtained. On the other hand, the wire number 27 in which the Nb content deviated from the scope of the present invention was rejected because the toughness of the weld metal deteriorated. Both wire numbers 28 and 29, whose Pcm values deviated from the scope of the present invention, were rejected due to deterioration of the toughness of the weld metal. In addition, the wire number 30 in which the total content of P and S deviated from the scope of the present invention was rejected because cracks were observed in the weld metal and toughness deteriorated.

Table 12 shows the results of verifying the fluoride content using the wires in Table 11.
With wire numbers 31 to 47 whose components were adjusted within the scope of the present invention, good results were obtained and passed. Wire Nos. 32 to 35 containing 0.2% of the total fluoride content within the range of the present invention clearly exhibited the effect of reducing diffusible hydrogen, which was a favorable result. With wire numbers 36 to 47, the total content of fluorides was 0.8% or more within the scope of the present invention, so that the effect of reducing diffusible hydrogen was more clearly manifested, which was a more preferable result. . On the other hand, wire No. 48 in which the total content of fluoride deviated from the scope of the present invention was rejected due to an increase in the amount of fumes generated.

Table 14 shows the results of verifying the content of Mn oxide excluding Si oxide, Al oxide, Ti oxide, B oxide, Zr oxide, Fe oxide, and MnO using the wires in Table 13.
Good results were obtained with wire numbers 49 to 70 whose components were adjusted within the scope of the present invention and passed. In particular, the wire number in which the total content of Mn oxide excluding Si oxide, Al oxide, Ti oxide, B oxide, Zr oxide, Fe oxide and MnO is 0.2% or more within the scope of the present invention. In the case of No. 50 to No. 70, the slag peelability was improved. On the other hand, wire No. 71 in which these oxides deviated from the scope of the present invention was rejected because the oxygen of the weld metal was high and the toughness of the weld metal deteriorated.

Table 16 shows the results of verifying the contents of Al, Ti, Mg, Zr, Ca, Ce, and La, which are deoxidizing elements, using the wires in Table 15.
Good results were obtained with wire numbers 72 to 92 whose components were adjusted within the scope of the present invention and passed. In particular, when the total content of Al, Ti, Mg, Zr, Ca, Ce, and La is 0.2% or more within the range of the present invention, the wire numbers 74 to 92 reduce the oxygen of the weld metal, It was a favorable result that the toughness was further improved. On the other hand, wire number 93, in which the total content of these deoxidizing metal elements deviated from the scope of the present invention, was rejected because the toughness of the weld metal deteriorated.

Table 18 shows the results of verifying the contents of CaCO ₃ , MgCO _3, SrCO ₃ , BaCO ₃ , and MnCO ₃ using the wires in Table 17.
Good results were obtained with wire numbers 94 to 110 whose components were adjusted within the scope of the present invention and passed. In particular, wire Nos. 95 to 110 having a total content of 0.2% or more within the range of the present invention reduced the amount of spatter generated, which was a more preferable result. On the other hand, the wire No. 111 in which the total content of these carbonates deviated from the scope of the present invention was rejected due to an increase in the amount of spatter generated.

Table 20 shows the results of verifying the contents of MgO 2 _, SrO, and BaO using the wires in Table 19.
Good results were obtained with wire numbers 112 to 122 whose components were adjusted within the scope of the present invention and passed. In particular _, with wire numbers 113 to 122, in which the total content of MgO 2 _, SrO, and BaO is 0.2% or more, the weld pool can be more easily observed during welding, and the work load on the welding operator can be reduced. Was confirmed. On the other hand, when the total content of MgO 2 _, SrO and BaO deviated from the scope of the present invention, wire No. 123 was not able to be welded and was rejected.

  In the case of wire number 124 in Table 21, the case where the above-mentioned contained substances were contained in combination was verified. The results are shown in Table 22. Since all substances were contained within the scope of the present invention, the test results were good and passed.

  Table 24 shows the results of verifying the effect of the slit-shaped gaps in the steel outer sheath using the wire numbers 125 to 149 in Table 23. Eliminating the slit-like gaps in the steel outer shell further reduced the diffusible hydrogen and gave more favorable results. Wire numbers 125 to 149 all passed. In particular, the numbers of diffusible hydrogen were particularly reduced in wire numbers 134 to 149, where the effect of eliminating the inclusion of fluoride and the elimination of slit-like gaps in the steel outer shell was reduced, which was a more preferable result. The wires in Table 23 were tested for the purpose of verifying the effect of the slit-shaped gaps in the steel outer shell on the amount of diffusible hydrogen, so tests other than the amount of diffusible hydrogen were omitted.

  As described above, it has been clarified that the flux-cored wire of the present invention has a smooth weld metal shape that can be easily obtained by standing-up advance welding, thereby greatly reducing the risk of weld defects. Moreover, it is judged that the toughness of the weld metal is good and the safety of the weld metal is very high. In addition, it was confirmed that diffusible hydrogen can be reduced when fluoride is contained, and this effect is more clearly manifested by eliminating the slits in the steel shell. From the above results, the flux-cored wire of the present invention provides great industrial value.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Corner | angular part of combined steel plate 3 Weld metal 4 The toe part of the weld metal formed by vertical welding 5 The convex vertex of the weld metal formed by vertical welding A The toe part of both ends of weld metal Line B connecting the projection vertex of the weld metal and parallel to line A dce Distance between lines A and B (mm)

Claims (9)

A flux-cored wire for gas shielded arc welding, in which a steel sheath is filled with a flux, wherein the following conditions (a) to (d) are satisfied simultaneously:
(A) MnO is contained by 1.0% or more and 6.0% or less by mass% with respect to the total mass of the wire.
(B) CaO is contained by 1.0% or more and 6.0% or less by mass% with respect to the total mass of the wire.
(C) The total content of MnO and CaO is 4.0% or more by mass% with respect to the total mass of the wire.
( D ) The value of Pcm defined by the following formula (1) is in the range of 0.15% or more and 0.40% or less, and the total mass of P and S is 0. Be limited to 040% or less.
Pcm = N (C) + N (Si) / 30 + N (Mn) / 20 + N (Cu) / 20 + N (Ni) / 60 + N (Cr) / 20
+ N (Mo) / 15 + N (V) / 10 + 5N (B) (1)
Here, N (X): mass% of element X with respect to the total mass of the wire.
( E ) The balance is Fe, an arc stabilizer, and inevitable impurities.
Further, one or more of MgF ₂ , CaF ₂ , SrF ₂ , and BaF ₂ are contained, and the total content is 5.0% or less by mass% with respect to the total mass of the wire. The flux-cored wire for gas shielded arc welding according to claim 1.   Further, one or more of Mn oxides other than Si oxide, Al oxide, Ti oxide, B oxide, Zr oxide, Fe oxide, and MnO are contained, and the total content is wire. The flux-cored wire for gas shielded arc welding according to claim 1 or 2, wherein the mass% with respect to the total mass is 4.0% or less.   Further, one or more of Al, Ti, Mg, Zr, Ca, Ce, and La in the metal state are contained, and the total content is 2.0% or less with respect to the total mass of the wire. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 3. _{Furthermore, MgCO 3, CaCO 3, SrCO} 3, BaCO 3, 1 or more kinds of MnCO ₃ is contained state, and are total 4.0% or less by mass% with respect to total mass of the wire of the content, and When one or two of CaCO ₃ and MnCO ₃ are contained, the amount of CaO and MnO generated by thermal decomposition of CaCO ₃ and MnCO ₃ is added to the amount of CaO and MnO contained in the flux-cored wire . the total amount, CaO, in an amount not to exceed the upper limit of the content of each of _MnO, gas shielded arc according to any one of claims 1 to 4, characterized in Rukoto is contained CaCO 3, MnCO ₃ Flux-cored wire for welding.
Further, MgO, SrO, is contained in one or more of BaO, the total content of Ri der 3.2% or less by mass% with respect to total mass of the wire, and, MgCO ₃ in the flux cored wire, SrCO ₃ , when one or more of BaCO ₃ are contained , the total amount of MgO ₃ , SrCO ₃ , BaCO ₃ generated by thermal decomposition of MgCO ₃ , SrCO ₃ , BaCO ₃ is 3.2% by mass. gas shielded arc welding flux cored wire according to any one of claims 1 to 5, wherein Rukoto is contained in an amount not in excess.   Furthermore, Nb is contained in the range of 0.1% or less by the mass% with respect to the total mass of a wire, The flux cored wire for gas shielded arc welding of any one of Claims 1-6 characterized by the above-mentioned.   The flux cored wire for gas shielded arc welding according to any one of claims 1 to 7, wherein the steel outer shell has no slit-like gap.   The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 7, wherein the steel outer shell has a slit-like gap.