JP2005279768A - Flux cored wire for welding and weld joint for steel structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance crack resistance and weldability of stainless steel and also to improve fatigue strength and crack resistance in manufacturing a large structure such as a ship and a bridge by lowering martensitic transformation temperature of weld metal and reducing or eliminating residual tensile stress. <P>SOLUTION: In the flux cored wire in which a flux powder is filled inside a tubular metallic jacket made of stainless steel, the flux cored wire to use is designed to contain 6.5-25 mass % flux powder in the wire weight, wherein the quantity of metallic powder in the flux powder is 0.3-10 mass % in the wire weight, and wherein 3.5-15 mass % metal other than the powder in the wire weight is contained together with the flux powder inside the metallic jacket. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The invention of this application relates to a welded flux-cored wire and a welded joint for steel structures. More specifically, the invention of this application is intended to improve the crack resistance and welding workability of steel materials including stainless steel, reduce martensite transformation temperature of weld metal, reduce or eliminate tensile residual stress, The present invention relates to a flux-cored wire for welding that can improve fatigue strength and crack resistance when manufacturing large structures such as bridges, and a welded joint using the same. Here, stainless steel typically refers to steel types represented by JISG4304 “Hot-rolled stainless steel plates and steel strips” and JISG4305 “Cold-rolled stainless steel plates and steel strips” and their sub-steel types. It is not limited to standards. In terms of composition, stainless steel refers to a steel material having 10.5% by mass or more of chromium, and generally 32% by mass or less of chromium.

  Flux-cored wires are widely used for various steel materials such as carbon steel, stainless steel, Ni and Ni alloys, and it is easy to obtain a smooth weld bead shape that avoids stress concentration at the toe due to the action of the flux contained. It is a welding material.

  In the case of flux-cored wire with a pipe-shaped metal sheath made of stainless steel, it has high efficiency and good workability even in all-position welding compared to normal welding, and defects such as poor fusion, undercut and crack Since a weld metal that does not generate slag has been obtained, it is widely used and its usage is increasing. However, in general, it is said that the quality of the weld metal is inferior to that of TIG welding, etc. and may not be applied to important structures. In some rare cases, hot cracking may occur depending on the type of steel.

  In addition, for large steel structures such as ships, offshore structures, penstock, and bridges, it is required to increase the strength of steel used for the purpose of increasing the size and accompanying weight reduction. As materials used for these structures, so-called low alloy steel materials containing less than 3.0% by mass of various alloy elements such as Cr, Ni, and Mo are used, and the tensile strength level of these materials is 400 to 1000 MPa.

  In response to the demand for higher strength, when using a low-strength steel material with a high strength, the fatigue strength of the high-strength steel is the same as the material strength of the base material. Although it rises with an increase, fatigue strength is not improved even when the material strength is increased in a welded joint (for example, see Non-Patent Document 1).

  For this reason, conventionally, the fatigue strength of welded joints of high-strength steel materials is the same as that of low-strength steels. Therefore, in structures that employ joints joined by fillet welding, etc., design strength can be maintained even when high-strength steel materials are used. There was a problem that it could not be raised. The reasons why fatigue strength does not improve in welded joints include the presence of tensile residual stress and stress concentration at the toe.

  Against this background, conventionally, as a method of improving the fatigue strength of welded joints in large steel structures such as ships, offshore structures, penstocks, bridges, etc., martensitic transformation is performed in the cooling process after welding of weld metal produced by welding. Has been proposed, and a method of applying compressive stress has been proposed by causing the material to expand more than the start of the martensitic transformation at room temperature (see, for example, Patent Documents 1 and 2).

When this concept is applied to a flux-cored wire, the start temperature of martensitic transformation in the weld metal becomes lower, and the effect of improving fatigue strength is seen by expanding more than the start of the martensitic transformation at room temperature. In some cases, there is a problem that hot cracking occurs.
Outline of National Conference of Japan Welding Society NO.52, 1993, P.256-257 Japanese Patent No. 3350726 JP 2002-361485 A

  Therefore, the invention of this application eliminates the conventional problems from the above circumstances, and in the flux-cored wire having a pipe-shaped metal shell made of stainless steel, the welding workability is good, and the undercut or the like Providing flux-cored wires with no cracks and good crack resistance. Furthermore, in welding in large steel structures such as ships, marine structures, penstocks and bridges, crack resistance is good. It is an object of the present invention to provide a flux-cored wire that can improve the fatigue strength of a welded joint, and to provide a welded joint for a steel structure by welding using these wires.

  This application provides the following invention to solve the above-mentioned problems.

  [1] In a flux-cored wire for welding in which flux powder is filled in a pipe-shaped metal shell made of stainless steel, the amount of the flux powder is 6.5 to 25% by mass with respect to the wire weight, and the flux The amount of metal powder in the powder is 0.3 to 10% by mass with respect to the wire weight, and 3.5 to 15% by mass with respect to the wire weight in the metal skin together with the flux powder. A flux-cored wire for welding, which contains a metal other than powder.

  [2] A flux-cored wire for welding, wherein the total deposited metal formed by the welding wire contains 0.13 mass% or less of C, 21 mass% or less of Cr, and 4.0 or more and 20.0 mass% or less of Ni.

[3] In any one of the above-mentioned flux-cored wires for welding, the main component other than the metal powder in the flux powder is 50% to 80% TiO ₂ , 5 to 30% SiO ₂ in mass% with respect to the whole non-metal powder. 0.5 to 7% Al ₂ O ₃ , F in 1 to 10% fluorine compound, alkali metal oxide converted to 1 to 10% oxide, alkaline earth metal converted to 5% or less oxide A flux-cored wire for welding, characterized in that it is an oxide and ZrO ₂ of 8% or less.

  [4] In a welded joint for steel structures formed by welding steel using the above welding material, the weld metal of the welded joint undergoes martensitic transformation in the cooling process after welding, and the martensite is at room temperature. A welded joint for a steel structure, wherein the welded metal is in a state of expansion from the start of transformation.

  [5] A welded joint for steel structures formed by welding steel using the above welding material, wherein the martensitic transformation start temperature of the weld metal of the welded joint is 50 ° C or higher and 360 ° C or lower. A welded joint for steel structures.

[6] In a welded joint for steel structures formed by welding steel using the above welding materials, the contents of C, Cr, Ni, Si, Mn, Mo and Nb of the weld metal of the welded joint are as follows: A welded joint for steel structures, which is an iron alloy satisfying the formula (1).
50 ≦ 719-795 × C (mass%) − 23.7 × Cr (mass%) − 26.5 × Ni (mass%) − 35.55 × Si (mass%) − 13.25 × Mn (mass%) ) -23.7 × Mo (mass%)-11.85 × Nb (mass%) ≦ 360 (1)
[7] In a welded joint for steel structures formed by welding steel using the above welding material, the weld metal of the welded joint is 0.15 mass% C or less, 19.0 mass% Cr or less. 0 to 18.0 mass% Ni, 0.2 to 5.0 mass% Si, 0.4 to 9.0 mass% Mn, and / or 4.0 mass% or less Mo, 3.0 mass% Hereinafter, a welded joint for steel structure, comprising at least one of Nb and the balance being substantially made of Fe.

  According to the invention of this application as described above, the crack resistance and welding workability of stainless steel can be improved, and the martensitic transformation temperature of the weld metal can be lowered to reduce or eliminate the tensile residual stress. This makes it possible to improve fatigue strength and crack resistance when manufacturing large structures such as ships and bridges.

  The invention of the present application having the above-described features occurs rarely in a flux-cored wire having a pipe-shaped metal shell made of stainless steel, which is obtained from the results of intensive studies by the inventors. The cause of hot cracking is not only due to impurities contained in all fluxes other than metal and metal, but also due to minute segregation of the weld metal due to slight variations in the metal shell of the metal flux powder to be included. Based on knowledge.

  For this reason, in 1st invention of this application, as shown in FIG. 1 as a structure of the wire for welding, by restrict | limiting the total flux amount with respect to a wire weight to 6.5-25 mass%, in flux powder | flour. Hot cracking due to the amount of impurities contained is prevented, the amount of metal powder in the flux powder is similarly regulated to 0.3 to 10% by mass, and 3.5 to 15% by mass with respect to the wire weight in the metal shell By containing a metal other than the above powder, microsegregation of the weld metal caused by the metal flux powder is prevented.

  The impurities in the flux material used can be reduced if it is costly, but it is not economical. When using a flux material of a level that is normally available, if it exceeds 25% by mass with respect to the wire weight, hot cracking due to impurities contained in the flux cannot be completely prevented, and if it is less than 6.5% by mass The deoxidizer, arc stabilizer, slag forming agent, etc. necessary as flux in the flux-cored wire are insufficient, and good welding cannot be performed.

  The amount of the metal powder in the flux-cored wire may be reduced to such an extent that fine segregation that causes cracking does not occur, and this value was found to be 10% by mass or less with respect to the wire weight. If this value is exceeded, there is a risk of microsegregation in the weld metal. However, if it is less than 0.3% by mass, a deoxidizer necessary as a flux in the flux-cored wire is insufficient and a sound weld metal cannot be obtained.

  Also, the addition of metal other than powder of 3.5 to 15% by weight with respect to the wire weight helps maintain a stable welding arc and smoothly transfer droplets, reduce spatter generation, poor fusion, The occurrence of defects such as cuts can be reduced, and a good bead shape can be obtained.

  In a flux-cored wire for welding consisting of a metal shell and an inner flux, reducing the amount of flux and metal contained in the wire will increase the amount of the metal sheath relatively, reducing impurities from the flux and microsegregation. Although the effect is seen in preventing this, the stability of the welding arc is deteriorated and stable welding cannot be performed. For this reason, a normal flux-cored wire contains metal powder as a balance agent in addition to the purpose of adjusting the components of the weld metal.

  The molten state during gas shielded arc welding using these flux-cored wires is that the arc is generated from the metal shell, the metal shell melts faster than the internal flux, and the inner flux remains as a flux column.

  This flux column becomes longer as the amount of internal flux increases, causing spatter and undercut due to arc instability.

  In the invention of this application, the metal powder is characterized by using a metal other than the powder such as a wire which has relatively few impurities and is stable in composition, so that the amount of the encapsulated flux is minimized. To do.

  When the weight of the metal other than the powder with respect to the weight of the unit length of the wire is set to 3.5 to 15% by mass, the arc is stabilized, undercut and spatter hardly occur, and the occurrence of cracks can be prevented. If it is less than 3.5% by mass, the balance relationship between the metal shell and the amount of encapsulated flux will be lost, the arc will become unstable, and undercut and spatter will easily occur and stable welding will not be possible. If it exceeds 15% by mass, the amount of inclusion flux is limited, and the required amount of non-metallic flux such as arc stabilizer is reduced. For this reason, the arc state is deteriorated, and undercut and spatter are likely to occur, and stable welding cannot be performed.

  As the metal other than the powder, wire rods having various cross-sectional shapes such as polygons and circles can be used.

  FIG. 2 shows an example of the cross-sectional shape of the above-described flux-cored wire of the invention of this application.

In FIG. 2, each symbol is
1: Flux-cored wire for welding 2: Metal skin (hoop)
2a: Lapping part 3: Inner flux (metal powder and non-metal powder)
4: A metal other than powder is shown.

  For the welding flux-cored wire of the invention, the total deposited metal formed contains 0.13% by mass or less C, 21% by mass or less Cr, 4.0% or more and 20.0% by mass or less Ni. It is preferable.

As for the flux, the main component of the non-metal flux, by mass% to the whole non-metal flux, 50-80% of TiO _2, 5 to 30% of SiO _2, 0.5 to 7% of Al ₂ O ₃ F in 1 to 10% fluorine compound, alkali metal oxide converted to 1 to 10% oxide, alkaline earth metal oxide converted to 5% or less oxide, 8% or less ZrO ₂ If it is.

  If the amount of internal flux is less than 6.5% by mass with respect to the wire weight, the slag necessary to obtain a sound and smooth weld bead shape is not formed. If the amount exceeds 25% by mass, the amount of slag increases. Passing and fluxed wire molding becomes difficult.

  If the amount of non-metallic flux in the flux is less than 20% by mass with respect to the total flux, the slag necessary to obtain a sound and smooth weld bead shape is not formed. May become stable and cause defects such as undercut.

TiO ₂ is a component that adjusts the melting point and viscosity of slag to smooth the shape of the toe end of the bead. If it is less than 50%, the effect is not sufficient, and if it exceeds 80%, the melting point and viscosity become too high, and the bead shape Becomes worse.

SiO _{2 is} also a component that adjusts the melting point and viscosity of slag and smooths the shape of the toe end of the bead, just like TiO _{2. If} less than 5%, the effect is not sufficient, and if it exceeds 7%, the melting point and viscosity increase. Too much bead shape.

Al ₂ O _{3 is} also a component that adjusts the melting point and viscosity of slag and smooths the shape of the toe end of the bead in the same way as TiO _{2. If} less than 0.5%, the effect is not sufficient. Viscosity becomes too high and the bead shape gets worse.

  F is a component that increases the fluidity of the slag and reduces impurity elements such as oxygen in the weld metal. If less than 1%, the effect is not sufficient. It becomes stable and the bead shape gets worse.

Here, the fluorine compound is LiF, NaF, CaF ₂ , MgF ₂ , BaF ₂ , K ₂ ZrF ₆ , K ₂ SiF ₆ , Na ₃ AlF _6, etc., and any of these fluorides may be used in the present invention, The amount of F in these fluorides should just be 1 to 10% by mass% with respect to the whole nonmetallic powder.

  Alkali metal oxide is a component that stabilizes the arc and increases the fluidity of the slag. If it is less than 1%, the effect is not sufficient, and if it exceeds 10%, the fluidity is improved and the bead shape is deteriorated.

The alkali metal oxides in terms of _{oxides, K 2 O · Al 2 O} 3 · 6SiO 2 in _{K 2 O, Li 2 O ·} Al 2 O 3 · 8SiO 2 in Li ₂ O, Na ₂ O · The values include not only Na ₂ O in SiO ₂ but also potassium in K ₂ SiF ₆ and lithium in LiCO ₃ converted to oxides. -10% may be sufficient.

  Alkaline earth metal oxide is a component that increases the fluidity of the slag and reduces impurity elements such as oxygen in the weld metal. If it exceeds 5%, the fluidity becomes too good and the arc becomes unstable and the bead shape. Becomes worse.

Alkaline earth metal oxides converted to oxides include oxides such as MgO, decomposition of carbonates such as CaCO ₃ , and composite compounds such as CaO · SiO ₂ , 2MgO · 2Al ₂ O ₃ · 5SiO ₂ And the values obtained by converting Ca and Ba of CaF ₂ and BaF ₂ into oxides are included, and the total of these may be 5% or less in terms of mass% with respect to the entire non-metallic powder.

ZrO ₂ is a component that adjusts the melting point and viscosity of the slag and smoothes the shape of the bead toe as in SiO _2, and if it exceeds 8%, the melting point and viscosity become too high and the bead shape deteriorates.

  Furthermore, the weld metal produced by welding using this flux cored wire undergoes martensitic transformation in the cooling process after welding, and is in a state of expanding more than the start of the martensitic transformation at room temperature, thereby reducing the compressive stress. As an imparting method, the invention of this application also proposes limiting the chemical component of the weld metal to the range of the following formula (1).

50 ≦ 719-795 × C (mass%)-23.7 × Cr (mass%)
-26.5 x Ni (mass%) -35.55 x Si (mass%)
-13.25 × Mn (mass%)-23.7 × Mo (mass%)
-11.85 × Nb (mass%) ≦ 360 (1)
Further, as described above, when the operating temperature is near room temperature, the amount of expansion due to martensitic transformation of the weld metal can be increased by setting the martensitic transformation start temperature of the weld metal to 50 ° C. or more and 360 ° C. or less. In addition, the state in which the amount of expansion is large is near room temperature, and at the end of the cooling process of the weld metal, the weld metal is in a state of expanding more than at the start of martensitic transformation.

  For this reason, the expansion reduces the amount of shrinkage in the cooling process to prevent weld cracking, and further introduces compressive residual stress to reduce the expansion residual stress generated in the cooling process of the weld metal. FIG. 3 shows the transformation characteristics of the weld metal according to the invention of this application in comparison with the conventional one.

  The martensitic transformation start temperature can be changed by adjusting the contents of C, Cr, Ni, Si, Mn, Mo and Nb in the weld metal. The invention of this application is a weld metal comprising C 0.15 mass% or less, Cr 19.0 mass% or less, Ni 3.0 to 18.0 mass%, Si 0.2 to 5.0 mass%, Mn 0.4 to 9.0 mass%, And / or it is characterized by containing at least one of Mo in an amount of 4.0 wt% or less and Nb of 3.0 wt% or less.

  Here, the content of C is preferably less in order to ensure weldability and reduce the hardness of martensite, and in order not to cause weld cracking, 0.15% by mass or less is necessary, and 0.10% by mass or less. It is preferable to do this.

  The martensitic transformation start temperature can be changed by adjusting the contents of C, Cr, Ni, Si, Mn, Mo and Nb. Of these elements, Cr and Ni increase the content. However, since the workability in the manufacturing process is not significantly affected, it is preferable to adjust the martensitic transformation start temperature by increasing the Cr and Ni contents.

  The reason why the Cr content is 19.0% by mass or less is that when the content exceeds 19.0% by mass, a ferrite structure appears in the structure of the weld metal, the transformation expansion decreases, and the joint fatigue strength decreases.

  In addition, the Ni content is regulated to 3.0 to 18.0% by mass, and if it is less than 3.0% by mass, the weld metal's mechanical properties, particularly toughness, etc., are set to make the martensitic transformation start temperature of the weld metal less than 360 ° C. It is necessary to contain a large amount of other components that deteriorate. Moreover, since Ni is an expensive element and it is not economically preferable to add a large amount, the upper limit of the Ni content is set to 18.0% by mass.

  In order to obtain the above-mentioned weld metal, the chemical composition of the total deposited metal formed only by the welding material is such that C is 0.13 mass% or less, Cr is 21.0 mass% or less, and Ni is 4.0 to 20.0 mass%. preferable.

  Next, Si is contained in an amount of 0.2 to 5.0 mass%, Mn is 0.4 to 9.0 mass%, Mo is 4.0 wt% or less, and Nb is 3.0 mass% or less.

  Here, the Si content is set to 0.2 to 5.0 mass%, since Si is added as a deoxidizer, 0.2 mass% is necessary, and if it exceeds 5.0 mass%, the mechanical properties of the weld metal, particularly toughness This is because of the decrease.

  Similarly, the Mn content is set to 0.4 to 9.0% by mass, since Mn is added as a deoxidizer, 0.4% by mass or more is necessary, and if it exceeds 9.0% by mass, the mechanical properties of the weld metal, This is because the toughness is particularly lowered.

  Mo and Nb can be added for the purpose of imparting corrosion resistance to the weld. However, if the Mo content exceeds 4.0% by mass, the mechanical properties of the weld metal, particularly toughness, will decrease. Since it is an expensive element and it is economically undesirable to add it in a large amount, the Mo content is set to 4.0% by mass or less.

  If the content of Nb exceeds 3.0% by mass, the mechanical properties of the weld metal, particularly toughness, will decrease, and Nb is an expensive element and it is economically undesirable to add a large amount. The content was 3.0% by mass or less.

  Therefore, an example will be shown below and will be described in more detail. Of course, the invention is not limited by the following examples.

  Tables 1 and 2 show the metal sheath components used for the flux-cored wires and the metal components other than the encapsulated powder.

表３には試験に用いた鋼板の成分を示した。

Table 3 shows the components of the steel sheet used in the test.

以上のフラックス入りワイヤを用いて溶接を行い、その特長を比較例とともに評価した。

Welding was performed using the above-mentioned flux-cored wires, and the features were evaluated together with comparative examples.

  First, Table 4 shows the total weld metal components, welding workability, and crack test results of the flux-cored wire. In the crack test, B5 in Table 3 was used for the steel plate.

  Tables 5 and 6 show the components other than the metal in the flux contained wire, the Ms point, the welding workability, and the crack test result inclusion flux. In the cracking test, B1 in Table 3 was used as a steel plate.

  Table 7 shows the components, Ms point, and fatigue strength of the welded joint made of flux-cored wire.

なお、図４にはＪＩＳ−Ｚ−３１５３（１９９３）Ｔ形溶接割れ試験を参考にしたＴ形溶接割れ試験要領を示した。具体的には、２つの鋼板Ｐ１，Ｐ２を１ｍｍのギャップＧを設けてＴ形にタック溶接した後、拘束ビードＢ２を溶接し、速やかに試験Ｂ１を溶接する。その後、試験ビードＢ１及びクレータ部の割れ長さを染色浸透探傷試験方法により求めて２つの割れ率［（ビード部割れ長さ／全ビード長さ）×１００]および［（クレータ部割れ長さ／クレータの長さ）×１００］を算出した。なお、溶接条件は、電流２００〜２１０Ａ、電圧２９〜３０Ｖ、試験ビードの溶接速度３００ｍｍ／ｍｉｎ、拘束ビードの溶接速度２５０ｍｍ／ｍｉｎとした。その結果は表４〜６に示されている。

FIG. 4 shows the T-type weld crack test procedure with reference to the JIS-Z-3153 (1993) T-type weld crack test. Specifically, two steel plates P1 and P2 are tack-welded in a T shape with a gap G of 1 mm, then a restraining bead B2 is welded, and test B1 is quickly welded. Thereafter, the crack lengths of the test bead B1 and the crater part were determined by a dye penetration test method, and two crack rates [(bead part crack length / total bead length) × 100] and [(crater part crack length / Crater length) × 100] was calculated. The welding conditions were as follows: current 200 to 210 A, voltage 29 to 30 V, test bead welding speed 300 mm / min, and constraining bead welding speed 250 mm / min. The results are shown in Tables 4-6.

  FIG. 5 illustrates the shape of the weld joint.

FIG. 6 shows a fatigue test piece (unit: mm) taken from a load non-transmission type cross welded joint and a corner-turned welded joint prepared in accordance with JIS Z 2273. The welding conditions were a current of 200 to 210 A, a voltage of 29 to 30 V, a test bead welding speed of 300 mm / min, and the fatigue test was a 9.8 × 10 ⁵ N servo pulse fatigue test. The steel plate and wire combinations and joint shapes used are shown in Table 7 along with the fatigue properties obtained.

In the above results, with respect to welding workability, current 200 to 210 A, voltage 29 to 30 V, welding speed 300 mm / min in the direction extending in the longitudinal direction of the plate on the surface of the steel plate B4 of Table 3 having dimensions 12 × 100 × 250 mm. The bead is formed with the glass, and the arc state (arc strength, continuity, etc.), slag state (slag hullability, peelability), and bead shape are judged visually, etc. ^-, △, it was evaluated in five stages of ×.

Undercuts were better with the presence or absence of occurrence and with a smaller depth when present, and those with no undercut were marked with ◎. Hereinafter, the evaluation was made in the order of ◎, ○, ○ ⁻ , Δ, and × in the order of goodness.

Further, the spatter generation status was evaluated in five stages of ◎, ○, ○ ^- , △, and × from the size and number of spatters generated. Specifically, the spatter deposition amount per 150 mm of the weld bead central portion is 0-1: ◎, 2-5: ○, 6-10: ○ ^- , 11-25: Δ, 26 or more: × Was used as an evaluation standard.

Furthermore, the five-point evaluation of ◎, ○, ○ ^- , △, × is made in order of 5 points, 4 points, 3 points, 2 points, 1 point, and the total evaluation points of each item are summed up as a total evaluation point of welding workability. did. The results are shown in Tables 4-6.

  Regarding the flux-cored wire of the invention of this application, first of all, from the test results in Table 4, the welding workability and crack resistance are improved in any of the four types of steel types 308, 309, 316, and 310. It turns out that it is excellent.

  In Table 5, if the test results of symbols 13 and 14, 15 and 16, 17 to 19, 20 to 22, 23 and 24, and 25 and 26, which are substantially the same components, are compared, the invention of this application is It can be seen that the welding workability and crack resistance are excellent.

Further, with respect to the flux-cored wire, it can be seen from the test results in Table 7 that the 2 million times fatigue strength of the welded joint according to the invention of this application exceeds 200 MPa and is superior to the comparative example. Among them, the fatigue strength of welded joints (symbols F, G, H) that start martensitic transformation at low temperatures according to the above-mentioned Patent No. 3350726 and Japanese Patent Laid-Open No. 2002-361485 proposed by the inventors Although it is low compared with the present invention product of the application, it can be seen that both exceed 170 MPa and are far superior to less than 100 MPa of other comparative examples (symbols I and J).

It is the figure which showed the structure outline | summary of the flux cored wire for welding of invention of this application. It is the figure which illustrated the outline of composition of the flux cored wire for welding of the invention of this application as a section shape. It is the figure which illustrated the outline of the cooling curve of a weld metal. It is the figure which illustrated the point of the T type weld crack test. (A) (b) (c) (d) is the perspective view which illustrated the shape of the welding joint, respectively. (A) and (b) are the top view and front view which illustrated the shape of the fatigue test piece.

Explanation of symbols

1: Flux-cored wire for welding 2: Metal skin (hoop)
2a: Lapping part 3: Inner flux (metal powder and non-metal powder)
4: Metal other than powder P1, P2: Base material (Table 3 B2)
B1: Test bead B2: Restraint bead G: Gap (1mm)

Claims (7)

  In the flux-cored wire for welding in which flux powder is filled in a pipe-shaped metal shell made of stainless steel, the amount of the flux powder is 6.5 to 25% by mass with respect to the weight of the wire, The amount of the metal powder is 0.3 to 10% by mass with respect to the wire weight, and other than the powder of 3.5 to 15% by mass with respect to the wire weight in the metal skin together with the flux powder. A flux-cored wire for welding characterized by containing a metal.   The total weld metal formed by the flux-cored wire for welding contains 0.13 mass% or less of C, 21 mass% or less of Cr, and 4.0 or more and 20.0 mass% or less of Ni. Flux-cored wire for welding. In the flux-cored wire for welding according to claims 1 and 2, the main component other than the metal powder in the flux powder is 50% to 80% TiO ₂ , 5 to 30% SiO ₂ in mass% with respect to the whole non-metal powder, 0.5 to 7% Al ₂ O ₃ , F in 1 to 10% fluorine compound, alkali metal oxide converted to 1 to 10% oxide, alkaline earth metal converted to 5% or less oxide A flux-cored wire for welding, characterized in that it is an oxide and ZrO ₂ of 8% or less.   A welded joint for a steel structure formed by welding a steel material using the flux-cored wire for welding according to any one of claims 1 to 3, wherein the weld metal of the welded joint is in a cooling process after welding. A welded joint for a steel structure, which is a weld metal that undergoes martensitic transformation and is in a state of being expanded at room temperature more than at the start of the martensitic transformation.   A welded joint for steel structure formed by welding a steel material using the flux cored wire for welding according to any one of claims 1 to 3, wherein a martensitic transformation start temperature of the weld metal of the welded joint is 50. A welded joint for steel structures, characterized by having a temperature of ℃ to 360 ℃. A welded joint for steel structures formed by welding steel using the flux-cored wire for welding according to any one of claims 1 to 3, wherein C, Cr, Ni, Si of the weld metal of the welded joint , Mn, Mo, and Nb are iron alloys that satisfy the following formula (1).
50 ≦ 719-795 × C (mass%) − 23.7 × Cr (mass%) − 26.5 × Ni (mass%) − 35.55 × Si (mass%) − 13.25 × Mn (mass%) ) -23.7 × Mo (mass%)-11.85 × Nb (mass%) ≦ 360 (1) A welded joint for a steel structure formed by welding a steel material using the welding flux-cored wire according to any one of claims 1 to 3, wherein a weld metal of the welded joint is 0.15 mass% C or less. 19.0 mass% Cr or less, 3.0 to 18.0 mass% Ni, 0.2 to 5.0 mass% Si, 0.4 to 9.0 mass% Mn, and / or A welded joint for steel structures, comprising at least one of at least one of Mo and 3.0% by mass or less Nb, and the balance being substantially made of Fe.

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