JP2007136547A - Method for producing metallic flux cored wire with little slag and welded joint having high fatigue strength - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a wire having remarkably little slag formation compared with gas shielded arc welding using conventional metallic flux cored wire, and also for producing welded joints having high fatigue strength. <P>SOLUTION: The wire is for the gas shielded arc welding of a steel plate having a thickness of 1.0-5.0 mm and a strength of 440-980 MPa. The wire contains, by mass% based on the whole wire, 0.001-0.20% C exclusive of SiC, 0.6-1.2% SiC, 0.05-1.2% Si exclusive of SiC and SiO<SB>2</SB>, 0.2-3.0% Mn, ≤0.03% P, ≤0.02% S, and 0.05-0.40% in total of one or more of SiO<SB>2</SB>, Al<SB>2</SB>O<SB>3</SB>, Na<SB>2</SB>O and K<SB>2</SB>O, the balance being iron and unavoidable impurities, with the proviso that SiC and one or more of SiO<SB>2</SB>, Al<SB>2</SB>O<SB>3</SB>, Na<SB>2</SB>O and K<SB>2</SB>O are contained at least as the flux in a steel sheath. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to arc welding used for arc welding joints in the automotive field, and in particular, by reducing the amount of slag on the surface of the weld bead generated when welding using a metal-based flux-cored wire. The present invention relates to a metal-based flux-cored wire that enables the use of a metal-based flux-cored wire instead of a solid wire, and a technique for welding.

  An arc welded joint in the automotive field is manufactured using a solid wire that generates a small amount of slag during welding for the painting process after the end of welding. This is because when the welded portion is covered with slag, coating is performed from the top of the slag, causing a problem in the adhesion between the coating film and the welded portion.

  On the other hand, with the increasing awareness of environmental issues, the automobile field is also promoting weight reduction from the viewpoint of improving fuel efficiency. For this reason, a steel material with higher strength tends to be used and the plate thickness tends to be reduced, but a major problem at this time is the fatigue strength of the weld. That is, even when a high strength steel material is used, the fatigue strength of the welded portion does not increase in proportion to the steel material strength, and there is a problem that the merit of using the high strength steel material is lost when designing with fatigue strength.

  As one means for solving such a problem, a method of improving the fatigue strength by designing a component so as to lower the transformation temperature of the welding material and reducing the residual stress of the welded portion has been proposed (Patent Document). 1 and 2; hereinafter, such a welding material is referred to as a high fatigue strength welding material). This method does not require any particular new manufacturing process, and can be said to be an efficient method by which high fatigue strength is obtained simply by replacing the conventional welding material.

  However, conventional high-fatigue strength welding materials have been manufactured and used for each application of solid wires that are designed to contain a large amount of expensive alloy elements. It is economically undesirable to apply this welding material (welding wire). Therefore, it is necessary to limit the application of the expensive high fatigue strength welding material only to the portion where fatigue is a problem and to reduce the wire consumption as much as possible. In other words, the solid wire used in the production of a conventional high fatigue strength welded joint cannot be adjusted by changing only the flux in the same steel sheath (pipe) like a metal flux-cored wire. For this reason, there is a problem that once the material for solid wire production is prepared, the composition design cannot be changed after that, and when the wire consumption is low or the variety is used in small quantities, the economic efficiency of solid wire is rather flux. It becomes inferior to the incoming wire.

  On the other hand, there is a flux-cored wire as a high fatigue strength welding material capable of economically realizing a high fatigue strength or a high strength weld metal even when the wire consumption is small. However, the flux-cored wire for ordinary arc welding is filled with a flux component in the steel outer sheath in addition to the alloy component in order to maintain good welding workability and wire workability. Therefore, when this is applied to the automobile field and an arc welded joint is manufactured, the amount of slag in the welded portion increases, resulting in a problem that the paintability of the welded portion after welding deteriorates. This problem can be solved by newly investing in the slag removal process after welding, but this case is not preferable because an increase in cost for capital investment is inevitable.

  Various techniques for reducing the amount of slag in welding using a flux-cored wire have been proposed so far. For example, for a wire to be welded using a mixed gas of an inert gas and carbon dioxide gas, C: 0.08% or less, Si: 0.7-1.5%, Mn: 1.0 to 3.0%, flux filling rate is 10 to 30%, Al is 0.3 wt% or less, and arc stabilizer is 0.005 wt% or less in terms of alkali metal In addition, a welding wire in which alkaline earth metal fluoride is regulated to 0.2 wt% or less and Ti is regulated to 0.005 wt% or less, and by using this wire, the amount of slag generated when horizontal fillet welding is suppressed, A metal-based flux-cored wire that provides a flat bead shape has been proposed (see, for example, Patent Document 3). However, although the amount of generated slag is smaller than the amount of slag of a normal flux-cored wire, this invention is not a technique that can suppress the slag amount to a level that can be compared with a solid wire.

  There is also a technique for suppressing the flux filling rate to be low and increasing the ratio of the steel outer shell (see, for example, Patent Documents 4, 5, and 6). That is, this method is a technique for bringing the cross-sectional structure of the flux-cored wire as close as possible to the solid wire. Considering that the amount of slag generated by a solid wire is small, it will be possible to reduce the amount of slag by using this technique. However, this method reduces the amount of flux in the wire with respect to the total mass of the wire, making it difficult to adjust the component design of the entire wire simply by adjusting the flux component without changing the steel outer sheath. Cannot fully enjoy the economic benefits of.

  Moreover, the wire which fills the flux which uses a graphite as an essential component as an arc stabilizer within the range of 5-25% by a wire cross-sectional area ratio is disclosed (for example, refer patent document 7). In this flux-cored wire, the ratio of the flux (particles) to the entire wire is about 12%, and the flux (powder) contains about 1% of graphite as an arc stabilizer. Therefore, the graphite content with respect to the entire wire is about 0.12%. In addition, the flux (powder) contains Ti, Mn, etc. as an Fe alloy as an arc stabilizer or deoxidizer other than graphite, and does not contain any metal oxide, thereby generating slag during welding. The amount is reduced. However, when the flux is reduced to such an extent that an oxide is not substantially added, in a metal-based flux-cored wire containing a weld metal alloy element that requires high fatigue strength or high strength as a flux, the oxide is formed of the flux. It is an indispensable component for maintaining the workability of the grains and the flux-cored wire, and there is a problem in terms of wire production when these are not added. In general, in a flux-cored wire, a flux to be filled is granulated, and mica or the like serving as a lubricant is attached to the surface of the flux-cored wire to reduce resistance during wire drawing.

  Therefore, both the paintability and fatigue strength of welded parts can be achieved by reducing the amount of slag generated by devising the metal-based flux component and ensuring the content of alloying elements, without relying on a low flux filling rate. Therefore, a technique for producing a welded joint excellent in the above has been desired.

JP 11-138290 A JP 2004-1075 A JP 2000-197991 A JP 2001-179488 A JP 2001-287087 A JP 2003-94196 A Japanese Patent Publication No. 51-1659

  In view of these problems of the prior art, the present invention is a wire for gas shielded arc welding of a steel plate having a plate thickness of 1.0 to 5.0 mm and a strength of 440 to 908 MPa, Good operability and productivity in manufacturing, especially in the preparation and granulation process of flack and wire drawing process, slag generation during welding is much smaller than conventional metal-based flux-cored wires, and excellent fatigue strength It is an object of the present invention to provide a welding wire from which a welded joint can be obtained and a method for producing a welded joint using this wire.

  From the above viewpoint, the present inventors have paid attention to the relationship between the flux component and the amount of slag generation, and have intensively studied the relationship and the slag reduction method. And it discovered that the amount of slag could be reduced remarkably compared with the conventional metal type flux cored wire by controlling a flux ingredient. This invention is made | formed by such a research, The summary is as follows.

(1) A wire for gas shielded arc welding of a steel plate having a plate thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa, and is a mass% of the whole wire, and C other than SiC: 0.01 to 0.20%, SiC: 0.6 to 1.2%, Si other than SiC and SiO ₂ : 0.05 to 1.2%, Mn: 0.2 to 3.0% , P: 0.03% or less, S: 0.02% or less, and further, one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O are added in total to 0.05 containing 0.4%, the balance being iron and unavoidable impurities, and the SiC, and the _{SiO 2, Al 2 O 3,} Na 2 O and _{K 2} O 1 or two or more of the least flux Slag generation amount characterized by being contained in steel hull Less metal-based flux cored wire.

(2) The metal-based flux-cored wire contains, in mass% of the whole wire, and further contains graphite: 0.02% or more in the steel outer shell as at least the flux, and is defined by the following (1) The total amount of the graphite and the C-converted value of SiC is 0.6% or less, and the metal-based flux-cored wire with a small slag generation amount according to (1) above.
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.

  (3) In the metal-based flux-cored wire, in mass% of the entire wire, Ni: 0.5 to 5.0%, Cr: 0.1 to 2.0%, Mo: 0.1 to 2 0.0% and Cu: 0.1 to 0.5% of a metal-based flux-cored wire containing 0.5 to 6.0% in total of one or more of one or more of the above (characterized in that ( A metal-based flux-cored wire with a small amount of slag as described in 1) or (2).

(4) A wire for welding an automotive steel plate having a plate thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa, and is a mass% of the whole wire, and C other than SiC: 0.01 -0.20%, SiC: 0.05-0.6%, Si other than SiC and SiO2: 0.05-1.2%, Mn: 0.2-3.0%, P: 0 0.03% or less, S: 0.02% or less, Ni: 0.5-5.0%, Cr: 0.1-2.0%, Mo: 0.1-2.0%, and Cu: 0.1 to 0.5% of one or more of 1.0 to 6.0% in total, and further SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O containing 0.05 to 0.4% one or two or more in total, the balance being iron and unavoidable impurities, and the SiC, and the SiO _{, Al 2 O 3, Na 2} O and K _{2 O} of one or more the metal-based flux cored wire is small amount of formation of slag, characterized in that it contains in the steel sheath at least as a flux.

(5) The metal-based flux-cored wire contains, in mass% of the entire wire, and further contains graphite: 0.02% or more in the steel outer shell as at least the flux, and is defined by the following (1) The total amount of the C-converted values of the graphite and the SiC is 0.35% or less, and the metal-based flux-cored wire with a small amount of slag generation according to the above (4).
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.

  (6) Any of (1) to (5) above, wherein the metal-based flux-cored wire further contains B: 0.001 to 0.015% by mass% of the entire wire. A metal-based flux-cored wire with a small amount of slag generation described in 1.

  (7) The metal-based flux-cored wire contains 0.005% to 0.3% in total of one or more of Nb, V, and Ti in mass% of the entire wire. The metal flux cored wire with a small amount of slag generation according to any one of (1) to (6).

  (8) In the metal-based flux-cored wire, an arc stabilizer other than an oxide-based material is contained in the outer shell made of steel at a mass% of the entire wire, and at least 0.05 to 0.5% as the flux. The metal-based flux-cored wire with a small amount of slag generation according to any one of the above (1) to (7).

(9) C% other than SiC: 0.01% to 0.20%, SiC: 0.6% to 1.2%, Si other than SiC and SiO ₂ : 0.05% to 1.2% by mass% of the entire wire %, Mn: contains 0.2 to 3.0%, P: 0.03% or less, S: limited to 0.02% or less, _{further, SiO 2, Al 2 O 3} , Na 2 O and K 1 type or 2 types or more of ₂ O are contained in total 0.05 to 0.4%, the balance is made of iron and inevitable impurities, and the SiC, and the SiO ₂ , Al ₂ O ₃ , Na ₂ O One or more of K ₂ O and at least one metal flux cored wire contained in the steel outer sheath as a flux has a plate thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa. It is characterized by gas-shield arc welding of steel plates The method for manufacturing a slag generation amount is small high fatigue strength welded joint that.

(10) The metal-based flux-cored wire contains, in mass% of the whole wire, and further contains graphite: 0.02% or more in the steel outer shell as at least the flux, and is defined by the following (1) The total amount of graphite and the C-converted value of SiC is 0.6% or less, The method for producing a high fatigue strength welded joint according to (9), wherein the amount of slag generation is small.
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.

  (11) In the metal-based flux-cored wire, in mass% of the entire wire, Ni: 0.5 to 5.0%, Cr: 0.1 to 2.0%, Mo: 0.1 to 2 0.0% and Cu: 0.1 to 0.5% of a metal-based flux-cored wire containing 0.5 to 6.0% in total of one or more of one or more of the above (characterized in that ( The method for producing a high fatigue strength welded joint according to 9) or (10) with a small amount of slag generation.

(12) By mass% of the whole wire, C other than SiC: 0.01 to 0.20%, SiC: 0.05 to 0.6%, Si other than SiC and SiO ₂ : 0.05 to 1.2 %, Mn: 0.2-3.0%, P: 0.03% or less, S: 0.02% or less, Ni: 0.5-5.0%, Cr: 0.0. 1 to 2.0%, Mo: 0.1 to 2.0%, and Cu: 0.1 to 0.5%, or a total of 1.0 to 6.0%. Furthermore, it contains 0.05 to 0.4% in total of one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O, and the balance consists of iron and inevitable impurities, and SiC, and, on the _{SiO 2, Al 2 O 3,} Na 2 O and _{K 2} O 1 kind or 2 or more is a steel within the outer skin at least as flux High fatigue with low slag generation, characterized by gas-shield arc welding a steel plate having a thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa using a metal-based flux-cored wire having A method for producing a strength welded joint.

(13) The metal-based flux-cored wire contains, in mass% of the whole wire, and further contains graphite: 0.02% or more in the steel outer shell as at least the flux, and is defined by the following (1) The method for producing a high fatigue strength welded joint according to (12), wherein the total amount of the graphite and the C-converted value of SiC is 0.35% or less.
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.

  (14) Any of (9) to (13) above, wherein the metal-based flux-cored wire further contains B: 0.001 to 0.015% by mass% of the entire wire. The manufacturing method of the high fatigue strength welded joint with few slag production | generation amounts to description.

  (15) The metal-based flux-cored wire contains 0.005 to 0.3% in total of one or more of Nb, V, and Ti in mass% of the entire wire. The manufacturing method of the high fatigue strength welded joint with little amount of slag production | generation in any one of said (9)-(14) to do.

  (16) In the metal-based flux-cored wire, an arc stabilizer other than an oxide is contained in a mass% of the whole wire, and further 0.05 to 0.5% is contained in the steel outer sheath as at least the flux. The method for producing a high fatigue strength welded joint according to any one of (9) to (15), wherein the slag generation amount is small.

(17) The slag as described in any one of (9) to (16) above, wherein the shielding gas is a shielding gas containing 3 to 25% of CO ₂ and the balance being Ar gas and inevitable impurities. A method for producing a high fatigue strength welded joint with a small amount.

(18) The method for producing a high fatigue strength welded joint according to (17), wherein the shield gas further includes a shield gas containing 4% or less of O ₂ gas.

  According to the present invention, the amount of slag generated in a welded portion can be significantly reduced as compared with the case of arc welding using a conventional metal-based flux-cored wire, and the amount of slag can be reduced to the same level as when using a solid wire. It becomes possible. As a result, the welded joint produced according to the present invention can provide a welded joint with good paintability without performing the slag removal process that impairs the paintability of the welded portion, so that the productivity of the automobile manufacturing process by welding can be improved. It can be maintained well. Further, according to the present invention, the fatigue strength of a welded joint can be markedly improved economically by using a metal-based flux-cored wire containing an alloy element like a solid wire. Therefore, the technical significance in the industry such as the automobile field according to the present invention is enormous.

  The present invention is described in detail below.

  An arc welded joint in the automobile field enters a painting process after the end of welding, and a problem in that case is slag present on the surface of the weld bead. In order to ensure adhesion between the coating film and the joint surface, it is desirable to reduce slag as much as possible. Therefore, solid wire has been used in the prior art.

  Generally, a solid wire generates much less slag than a flux-cored wire, and therefore, as long as the solid wire is used, it can be coated well without particularly undergoing a slag removal step. However, in welding materials used to make high fatigue strength welded joints, applicable joint components are limited, so wire consumption is small, and it is necessary to adjust the components for each application, so solid wires are economical. The problem that it is inferior to a flux-cored wire from a viewpoint arises. In other words, the component design of the solid wire is limited by the material component, but in the case of flux-cored wire, the degree of freedom in component design is large by changing the component of the flux without changing the steel outer sheath. The flux-cored wire is more advantageous from the viewpoint of economy.

  Conventionally, a metal-based flux-cored wire containing a large amount of metal powder as a flux is known compared to a normal flux-cored wire. A normal flux-cored wire has a good bead shape and ensures a predetermined amount of slag component in the flux so that it can be welded in all positions. In contrast, the metal-based flux-cored wire has less slag components due to the greater amount of metal powder, making it difficult to weld in all positions, but it is possible to suppress slag generation. However, even with a conventional metal-based flux-cored wire, the amount of slag generated in the weld cannot be reduced to the same level as that of a solid wire during gas shielded arc welding.

When the composition of the slag generated during gas shielded arc welding using a flux-cored wire is analyzed, most of them are oxides such as SiO ₂ , MnO, Al ₂ O ₃ , and Fe ₂ O ₃ . This tendency does not change even in the case of a metal flux-cored wire in which an alloy element such as Ni, Cr, or Mo is added to the flux. Therefore, in order to reduce the amount of slag generation when performing gas shielded arc welding using a metal-based flux-cored wire to the level of a solid wire, it is necessary to reduce the generation of oxide in the weld.

However, oxides such as SiO ₂ , MnO, Al ₂ O ₃ , and Fe ₂ O ₃ in the metal-based flux-cored wire are represented by, for example, mica mainly composed of SiO ₂ and Al ₂ O ₃ , It acts as a lubricant that suppresses the resistance between the steel sheath and the flux during wire drawing and prevents troubles such as breakage. In addition, since these oxides have a role of improving the weld bead shape, it is not preferable to reduce the slag in the dark from the viewpoint of reducing the slag and maintaining the wire processability and the bead shape.

  That is, as a method for reducing the amount of slag generated in the welded portion, the method for reducing the oxide content in the flux of the metal-based flux-cored wire has a limit in terms of wire production and welding quality. Therefore, the inventors examined a method for releasing the oxide in the flux from the weld metal in a form other than slag during welding as another method for reducing the amount of slag generated in the weld. did.

In the prior art disclosed in Patent Documents 3, 4, 5, and 6, slag materials such as SiO ₂ , K ₂ O, Na ₂ O, and Al ₂ O _{3 that} have the greatest influence among slag generation sources are reduced. In addition, if slag reduction is carried out within the prior art, the problem of efficiency deterioration in wire production due to insufficient lubricant will not be solved. Therefore, within the range of the prior art, in order to suppress the amount of slag generation, it has been necessary to rely on a technique for reducing the flux filling rate.

  From the above background, the inventors have studied various metal flux components, and finally applied SiC as the flux of the metal flux cored wire to utilize the lubricating action and deoxidation action of SiC. By doing so, the present inventors have found a method for reducing the amount of slag generated during welding without impairing the wire workability.

  When SiC is applied as the flux of the metal-based flux-cored wire, there is a concern about an increase in the amount of C and Si in the weld metal due to C and Si in SiC. Generally, if the amount of C in the weld metal increases, the disadvantages of joint properties such as weld cracking problems, hardenability problems, and toughness problems increase. Therefore, except when welding high-C steel materials such as rails. C is not consciously added to the welding wire. Therefore, the amount of C in a normal weld metal is usually designed to be 0.2%, and in some cases, not to reach 0.1%. Moreover, when the amount of Si in the weld metal increases, there is a possibility that mechanical properties such as a decrease in toughness of the welded portion deteriorate.

  Therefore, the present inventors first examined the increase in the C content and Si content of the weld due to SiC in the flux and the effect on the mechanical properties of the welded joint.

  FIG. 1 shows the relationship between the SiC content (mass% with respect to the entire wire) in the flux of the metal-based flux-cored wire, and the C content and Si content in the weld metal in the weld metal test.

  In addition, the steel outer sheath in the metal-based flux-cored wire uses C containing 0.05% with respect to the total mass of the wire and Si containing 0.2% with respect to the total mass of the wire. Contained.

From the relationship between the SiC content in the flux (mass% with respect to the entire wire) in the metal-based flux-cored wire shown in FIG. 1 and the C content in the weld metal in the weld metal test (●), for example, SiC is contained in the flux. Even if about 1.2% is added, the C content in the weld metal is about 0.2%, and the amount of C is such that the problem of deterioration of the mechanical properties of the welded joint does not occur. The reason why the C content in the weld metal does not increase even if SiC is added to the weld metal in this way is that the C in the SiC added to the weld metal and slag is combined with oxygen and becomes CO or CO ₂ . This is considered to be due to the release from the weld metal and slag into the atmosphere.

  On the other hand, from the relationship between the SiC content (mass% with respect to the whole wire) in the flux in the metal-based flux-cored wire shown in FIG. 1 and the Si content in the weld metal in the weld metal test (O), SiC in the flux When the content exceeds 1.2%, the Si content in the deposited metal exceeds 1.0%, and there is a concern about deterioration of mechanical properties such as toughness of the weld metal.

From the above results, when the SiC content in the flux is 1.2% or less, C in SiC does not become CO or CO ₂ and C in the weld metal does not become excessive, but in SiC Si increases the Si content of the weld metal, and there is concern about the problem of deterioration of the mechanical properties of the weld due to the Si content. Therefore, in the present invention, in the metal-based flux-cored wire, at least the SiC content contained as the flux prevents deterioration of the mechanical properties of the weld metal due to an increase in the Si content of the weld metal due to Si in the SiC. Therefore, the upper limit of the content needs to be 1.2%.

  Next, to what extent can the oxides in the flux be reduced without impairing the wire processability by replacing the oxide in the flux of the metal-based flux-cored wire with SiC? It was investigated.

  FIG. 2 is a conceptual diagram showing the relationship between the SiC content in a metal-based flux-cored wire and the minimum amount of oxide in the wire that can maintain wire workability under the conditions of the SiC content and the amount of slag generated during welding. It is.

  In FIG. 2, the solid line is a curve showing the relationship between the SiC content in the wire and the amount of slag generated when welding with this wire. Moreover, the minimum oxide amount that can maintain the wire workability when the oxide content in the wire is reduced under the condition of the SiC content in the wire indicated by the broken line on the horizontal axis is shown. From these relationships, by increasing the SiC content in the metal-based flux-cored wire, the oxide content in the wire can be reduced while maintaining wire processability. Furthermore, the amount of slag generation at the time of welding can be reduced by the reduction of the oxide content in the wire and the deoxidation action of slag (oxide) by C in SiC.

  According to FIG. 2, under the condition that the amount of SiC in the wire is small, the amount of slag generation during welding (solid line) and the minimum amount of oxide (dashed line) for maintaining wire workability are almost the same, and there is a one-to-one relationship. It is in. On the other hand, under conditions where the amount of SiC added in the wire is large, the amount of slag generation during welding (solid line) is smaller than the minimum amount of oxide in the wire (dashed line) that can maintain wire workability. For example, in FIG. 2, when the SiC content in the wire is A%, the oxide in the wire can be reduced to B% without impairing the wire processability, and welding is performed by welding using this wire. The amount of slag generated in the portion can be reduced to a lower C% than the oxide amount B% in the wire.

  On the other hand, when the SiC content in the wire to which no SiC is added is 0%, the minimum amount of oxide that can reduce the oxide in the wire without impairing the wire processability is limited to D%. The amount of slag generation increases to almost the same level as the amount of oxide in the wire.

In FIG. 2, the reason why the amount of SiC added in the wire increases and the amount of slag generated during welding (solid line) becomes smaller than the minimum amount of oxide in the wire (dashed line) that can maintain wire workability is as follows. Can be considered. That is, when the amount of SiC added in the wire increases, oxygen in the slag (oxide) generated during welding combines with C in SiC to produce CO or CO _2, and out of the weld metal and slag. This is because the deoxidation reaction is promoted.

  In the present invention, by including SiC in the flux filled in the steel outer sheath of the metal-based flux-cored wire, the SiC lubrication action and the deoxidation action of C in the SiC are utilized, and the wire workability is not impaired. The effect of reducing the oxide in the wire and deoxidizing the generated slag is obtained, and the amount of slag generated during welding can be greatly reduced as compared with the conventional case.

  The metal-based flux-cored wire of the present invention can reduce the amount of slag generation in the welded part and improve the paintability of the welded part as solid wire, so that the solid wire applied to the conventional high strength and high fatigue strength joints It can be replaced with metal flux cored wire. Conventional solid wires for high-strength and high-fatigue strength joints must be manufactured by designing the content of the alloy element according to the required level of strength and fatigue strength, so the manufacturing cost is a disadvantage However, the metal-based flux-cored wire of the present invention expands the degree of freedom of wire component design by adjusting the content of alloy elements in the flux filled in the steel outer sheath, and at low cost, low slag, high strength and high fatigue. A strength joint can be realized.

  Next, the reason for limiting each component composition of the metal-based flux-cored wire will be described.

  The basic component system of the metal-based flux-cored wire of the present invention is roughly divided into two types: a high SiC component system and a low SiC component system. The design philosophy is that SiC having lubricity and deacidification is an essential component as the main element C source for reducing the transformation start temperature of the weld metal in common with these component systems, and the high SiC component system has a high SiC content. The low SiC component system has a low SiC content and contains one or more alloy elements of Ni, Cr, Mo and Cu for reducing the transformation start temperature. It reduces the amount of slag generated in the weld zone without impairing the wire workability, and makes it possible to produce a welded joint with excellent paintability and high fatigue strength.

  In addition, C other than SiC, for example, C mainly contained in the steel outer shell SiC also contributes to the reduction of the transformation start temperature. In the present invention, however, SiC contained in the flux filled in the steel outer shell starts transformation. As an essential component for temperature reduction, C other than SiC is added for other purposes such as workability of a steel outer shell, as will be described later.

  In addition, in the metal-based flux-cored wire, the C component in the conventional solid wire is changed to include SiC, which is effective for wire workability, low slag, and high fatigue strength, as a flux that fills the steel outer sheath. Compared to the above, the degree of freedom in designing the wire component is high, and the manufacturing cost can be reduced.

  Further, in the high SiC component system, the alloy elements of Ni, Cr, Mo and Cu are not essential components, but in the low SiC component system, in order to reduce the transformation start temperature of the weld metal in the same manner as the C source, Ni It is necessary to contain one or more of Cr, Mo and Cu.

  In general, since SiC is relatively inexpensive compared to alloy elements of Ni, Cr, Mo and Cu, a high SiC component system is advantageous from the viewpoint of wire manufacturing cost, but due to a high amount of C. The toughness of the weld metal tends to be low. On the other hand, the low SiC component system is disadvantageous from the viewpoint of wire manufacturing cost, but mechanical properties such as toughness of the weld metal can be improved by adding Ni. Since mechanical characteristics such as toughness required for a welded joint depend on the use environment, the wire component system may be selected while comparing the joint required characteristics with the manufacturing cost.

  The reason for limiting the component composition of the high SiC component system and the low SiC component system of the metal flux cored wire of the present invention will be described below.

The “%” shown below means “mass%” unless otherwise specified.
First, the reason for limiting the basic components common to the high SiC component system and the low SiC component system will be described.

(C other than SiC (required))
C other than SiC is contained mainly in the steel outer sheath in the metal-based flux-cored wire, and contained for the purpose of preventing disconnection in the wire drawing process during wire manufacture. C other than SiC also has the effect of reducing the transformation temperature of the weld metal, but in the present invention, the content of SiC in the flux filled in the steel outer shell is adjusted according to the component system, and the weld metal The transformation temperature can be sufficiently reduced. In order to obtain an effect of preventing disconnection in the wire drawing step by C in the steel outer shell, the lower limit of the C content other than SiC needs to be 0.01%. On the other hand, if C is excessively added to the steel outer shell, it will harden during drawing and cause breakage, so the upper limit of the C content other than SiC is set to 0.20%.

  In addition, when iron powder is filled in the steel outer shell as a flux, C in the iron powder is included as C other than SiC. Therefore, from the point of reducing the hardening in wire drawing caused by C in the steel outer shell, the iron content in which the C content in the steel outer shell is 0.15% and the remaining C amount is added as a flux. It is desirable to supplement with the C content.

(Si other than SiC and SiO ₂ (essential))
In order to obtain the deoxidation effect of the weld metal during arc welding, the lower limit of the content of Si other than SiC and SiO ₂ is set to 0.05%. In addition, since Si has an action for improving the compatibility between the molten pool and the steel plate and obtaining a good bead shape, in order to obtain the bead shape improvement effect in addition to the deoxidation effect, the lower limit of the Si content Is preferably 0.1%. On the other hand, if Si other than SiC and SiO ₂ is added excessively, the weld metal is hardened, which is not preferable from the viewpoint of joint characteristics, so the upper limit of its content was set to 1.2%.

(Mn (required))
Mn is an element necessary for ensuring the strength of the weld metal. If the content is lower than 0.2%, it becomes difficult to ensure the strength of the weld metal. Therefore, the lower limit of the Mn content is set to 0.2%. On the other hand, if the Mn content is excessively high, the toughness of the weld metal is deteriorated, so the upper limit of the Mn content is set to 3.0%.

(P, S)
P and S are unavoidable impurity elements of the weld metal, and in the present invention, when these elements are present in the weld metal in a large amount, the toughness deteriorates, so the upper limit of the P and S content is 0.03%, 0.02%.

_{(SiO 2, Al 2 O 3} , Na 2 O, K 2 O ( Required))
The SiO ₂ , Al ₂ O ₃ , Na ₂ O, and K ₂ O contained in the flux are usually called slag materials. These act as a binder when granulating the metal flux component before the production of the metal flux cored wire, and after drawing the metal flux component into the steel outer sheath, the wire is drawn to a predetermined wire diameter. In this process, it acts as a lubricant that reduces the resistance between the inner surface of the steel skin and the metal flux. In the present invention, by containing SiC having a lubricating action, the workability in the wire drawing step can be ensured even if the slag material that is these oxides is reduced as compared with the conventional case. However, if the total amount of one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O is less than 0.05%, it becomes difficult to maintain the workability and the wire quality. In order to cause problems in production efficiency, the lower limit of the total amount is set to 0.05%. On the other hand, when the total amount of one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O exceeds 0.40%, the amount of slag generated in the welded portion increases, and the paintability is increased. Since the problem of deterioration occurs, the upper limit of the total amount is set to 0.40%.

The above is the reason for limiting the basic components common to the high SiC component system and the low SiC component system in the present invention.
Next, the reasons for limiting the basic component and the selection component of the high SiC component system will be described.

(High SiC component SiC (required))
In the high SiC component system, SiC which is a main element C source for reducing the transformation start temperature of the weld metal and has lubricity and deacidification is an essential component.

  In the high SiC component system, the effect of reducing the transformation start temperature of the weld metal can be sufficiently obtained by setting the content of SiC in the flux filled in the steel outer shell to 0.6% or more. Similarly, improvement in joint fatigue strength can be expected without containing alloy elements of Ni, Cr, Mo, and Cu, which have the effect of reducing the transformation start temperature of the weld metal. The high SiC component system can realize improved joint fatigue strength without containing expensive alloy elements of Ni, Cr, Mo, and Cu, so it is more economical than the low SiC component system that requires these alloy elements. There is merit in terms of sex.

  When the SiC content in the flux is less than 0.6%, the transformation start temperature of the weld metal is sufficiently reduced and the joint fatigue strength is sufficiently improved unless the alloy elements of Ni, Cr, Mo, and Cu are contained. Therefore, the lower limit of the SiC content in the flux is set to 0.6%. On the other hand, when the SiC content in the flux exceeds 1.2%, the toughness and impact characteristics of the welded portion cannot be ensured by increasing the Si content in the weld metal as shown in FIG. There is a fear. Further, an increase in the SiC content in the flux is not preferable because problems such as a problem of hardening of the weld metal and a problem that the austenite structure increases and the transformation point temperature becomes high and improvement of joint fatigue strength cannot be expected. For this reason, the upper limit of the SiC content in the flux was limited to 1.2%.

  This high SiC component system requires graphite and / or one or more of Ni, Cr, Mo and Cu in order to further improve wire workability and low slag or high fatigue strength. Can be added accordingly.

(High SiC component graphite (selection))
In the high SiC component system of the present invention, the graphite contributes to reduce the transformation start temperature of the weld metal as a C source and has the effect of improving the joint fatigue strength, as well as the steel outer shell during wire drawing. It works to reduce resistance to flux and improve wire workability. For this reason, it is preferable to contain 0.02% or more of graphite in the flux in order to improve the wire processability, lower slag, and improve the joint high fatigue strength by using these actions. Preferably it is 0.05% or more. In the present invention, the upper limit of the graphite content in the flux does not need to be specified in particular. However, when graphite is contained in the wire together with SiC, C in the weld metal is increased in the same manner as SiC described above. This causes the austenite structure to increase and the transformation point to increase, and also causes problems of hardening of the weld metal, toughness and weld cracking. Therefore, the C conversion of graphite and SiC defined by the above formula (1) The total amount of values is preferably in the range of 0.6% or less.

  In addition, since graphite has a fine particle size, it is easily scattered when blended with other fluxes and mixed. For this reason, in order to reduce the amount of graphite scattering when blended into the flux and mixed, when SiC is contained in the wire together with SiC, the C-converted value of SiC and graphite defined by the above formula (1) It is desirable to limit the ratio of the graphite content to the total amount of 60% or less.

(One or more of Ni, Cr, Mo and Cu of high SiC component system (selection))
In the high SiC component system of the present invention, Ni, Cr, Mo and Cu have the effect of reducing the transformation start temperature of the weld metal in the same manner as C. Therefore, in order to further improve the joint fatigue strength, Ni, Cr and Mo And 1 type (s) or 2 or more types of Cu can be contained. These alloying elements can be added from either or both of the steel outer shell and the flux.

  Ni is an element that lowers the transformation start temperature of the weld metal and is effective for improving joint fatigue strength, and also improves joint characteristics such as strength and toughness. When Ni is contained, the lower limit of the Ni content is preferably set to 0.5% as the minimum amount at which the effect of improving fatigue strength can be sufficiently expected. As for the upper limit of the Ni content when Ni is contained, in the high SiC component system, since the C content in SiC contained in the flux is sufficiently high, the effect of reducing the transformation start temperature of the weld metal is sufficiently obtained. When the Ni content exceeds 5.0%, the interaction with C contained in the weld metal in a large amount causes the weld metal to be transformed into bainite or martensite that transforms at a low temperature, and cooling is completed while remaining austenite. Since there is a possibility that improvement in fatigue strength cannot be expected, the upper limit of the Ni content is preferably 5.0%.

  Cr and Mo are elements having an effect of reducing the transformation start temperature of the weld metal and increasing the strength and hardenability. In particular, Cr and Mo are more effective than Ni in improving the strength of the weld metal and ensuring hardenability. Therefore, using this effect, the weld metal is transformed into a structure having a low transformation temperature such as martensite, and the weld joint In order to further improve the fatigue strength, the Cr and Mo contents are preferably set to 0.1% or more. On the other hand, since Cr and Mo are less effective in improving the toughness of the weld metal than Ni, if excessively contained, the toughness of the weld metal may decrease, so the upper limit of the Cr and Mo content is 2 0.0% is preferable.

  Cu, like Cr and Mo, is an element that has the effect of reducing the transformation start temperature of the weld metal, improving the strength, and ensuring hardenability. Cu may also be plated on the surface of the wire to ensure normal electrical conductivity. In order to obtain the effect of improving the strength and hardenability of the weld metal by Cu and the effect of ensuring electric conductivity, the lower limit of the Cu content is preferably set to 0.1%. However, if Cu is excessively added to the weld metal, there is a risk of causing Cu cracks in the weld metal, so the upper limit of the Cu content is preferably 0.5%.

  In addition, in the high SiC component system, when the total addition amount of one or more of Ni, Cr, Mo and Cu is less than 0.5%, the transformation start temperature is not sufficiently reduced, and the fatigue strength is increased. Since the effect cannot be expected, the lower limit of the total content is set to 0.5%. On the other hand, in the high SiC component system, since the SiC content is high, the effect of reducing the transformation start temperature is sufficiently obtained by C in the SiC, and if the total content exceeds 6.0% and is excessively contained, Since the weld metal does not transform into a bainite or martensite that transforms at a low temperature in the cooling process after welding and remains in the austenite structure, it is difficult to improve the joint fatigue strength. For this reason, it is preferable to make the upper limit of content of the said total content 6.0%.

  Next, the basic component and the selection component of the low SiC component system in the present invention will be described.

(Low SiC component based SiC (required))
The low SiC component system, like the high SiC component system, is a main element C source that lowers the transformation start temperature of the weld metal and requires SiC having lubricity and deacidification, but reduces the SiC content. As in C, the fatigue strength of the joint is improved by containing an appropriate amount of one or more of Ni, Cr, Mo and Cu having the effect of reducing the transformation start temperature of the weld metal. The low SiC component system has a lower SiC content than the high SiC component system, so there is little decrease in toughness due to the C content of the weld metal, improving joint fatigue strength, and maintaining good weld metal toughness. can do.

  In the low SiC component system, when the SiC content in the flux filled in the steel outer shell is less than 0.05%, the wire workability is improved by the lubrication and deoxidation of SiC, and the slag amount is reduced. Is not enough. Further, if the SiC content is less than 0.05%, the effect of reducing the transformation start temperature of the weld metal cannot be sufficiently obtained, so the total content of one or more of Ni, Cr, Mo and Cu is contained. This is not preferable because the amount needs to be increased and the wire manufacturing cost is increased. For this reason, the minimum of the addition amount of SiC in a flux was made into 0.05%. On the other hand, when the SiC content in the flux exceeds 0.6%, it is transformed into bainite or martensite where the weld metal transforms at low temperature due to the alloy elements of Ni, Cr, Mo, Cu in the weld metal. The upper limit of the SiC content was set to 0.6% because an austenite structure was not formed and fatigue strength improvement could not be expected.

  The low SiC component system in the present invention requires the addition of one or more of Ni, Cr, Mo, and Cu. The addition of these elements also has the purpose of reducing the transformation start temperature of the weld metal and increasing the fatigue strength, and thus functions in the same manner as the addition of SiC.

(One or more of Ni, Cr, Mo and Cu of low SiC component system (essential))
In the low SiC component system, since the SiC content is as low as 0.6% or less, the transformation start of the weld metal is started in the same manner as C in order to reduce the transformation start temperature of the weld metal and sufficiently improve the joint fatigue strength. It is necessary to contain an appropriate amount of one or more of Ni, Cr, Mo and Cu having a temperature reducing action. These alloy elements can be added from either or both of the steel outer shell and the flux.

  Ni is an element that lowers the transformation start temperature of the weld metal and is effective for improving joint fatigue strength, and also improves joint characteristics such as strength and toughness. When Ni is contained, the lower limit of the Ni content needs to be 0.5% as the minimum amount at which the effect of improving joint fatigue strength can be sufficiently expected in a low SiC component system. As for the upper limit of the Ni content, the effect of reducing the transformation start temperature of the weld metal is sufficiently obtained. When the Ni content exceeds 5.0%, the interaction with C contained in the weld metal allows the cooling to end while the austenite remains austenite without transformation to bainite or martensite where the weld metal transforms at low temperatures. Therefore, the upper limit of the Ni content is set to 5.0%.

  Cr and Mo are elements having an effect of reducing the transformation start temperature of the weld metal and increasing the strength and hardenability. In particular, Cr and Mo are more effective than Ni in improving the strength of the weld metal and ensuring hardenability. Therefore, using this effect, the weld metal is transformed into a structure having a low transformation temperature such as martensite, and the weld joint In order to further improve the fatigue strength, the content of Cr and Mo needs to be 0.1% or more. On the other hand, since Cr and Mo are less effective in improving the toughness of the weld metal than Ni, if excessively contained, the toughness of the weld metal may decrease, so the upper limit of the Cr and Mo content is 2 0.0%.

  Cu, like Cr and Mo, is an element that has the effect of reducing the transformation start temperature of the weld metal, improving the strength, and ensuring hardenability. Cu may also be plated on the surface of the wire to ensure normal electrical conductivity. In order to obtain the effect of improving the strength and hardenability of the weld metal by Cu and the effect of ensuring the electrical conductivity, the lower limit of the Cu content needs to be 0.1%. However, if Cu is excessively added to the weld metal, there is a risk of causing Cu cracks in the weld metal, so the upper limit of the Cu content is set to 0.5%.

  In addition, since the SiC content is low in the low SiC component system, when the total addition amount of one or more of Ni, Cr, Mo and Cu is less than 1.0%, the transformation start temperature is sufficiently reduced. Since the effect of increasing fatigue strength cannot be expected, the lower limit of the total content is set to 1.0%. On the other hand, if the total content exceeds 6.0% and is excessively contained, the weld metal does not transform into bainite or martensite that transforms at a low temperature in the cooling process after welding, and remains in an austenitic structure. Therefore, it is difficult to improve the joint fatigue strength. For this reason, it is preferable to make the upper limit of content of the said total content 6.0%.

(Low SiC component graphite (selection))
In the low SiC component system of the present invention, graphite not only contributes to reducing the transformation start temperature of the weld metal as a C source, but also serves to reduce the resistance between the steel outer sheath and the flux during wire drawing. . For this reason, in order to further improve the effects of improving wire processability, reducing slag and improving joint high fatigue strength using these functions, it is preferable to contain 0.02% or more of graphite in the flux. More preferably, it is desirable to contain 0.06% or more.

  In the present invention, the upper limit of the graphite content in the flux does not need to be specified in particular. However, when graphite is contained in the wire together with SiC, C in the weld metal is increased in the same manner as SiC described above. This is because the low SiC component system contains SiC and alloy elements of Ni, Cr, Mo and Cu as essential elements, so the weld metal does not become bainite or martensite which transforms at low temperatures, and becomes an austenitic structure, and the transformation point. And a problem of hardening of the weld metal, toughness and weld cracking occurs, so the total amount of the C-converted values of graphite and SiC defined by the above formula (1) is 0.35% or less. It is preferable to be within the range.

  In addition, since graphite has a fine particle size, it is easily scattered when blended with other fluxes and mixed. For this reason, in order to reduce the amount of graphite scattering when blended into the flux and mixed, when SiC is contained in the wire together with SiC, the C-converted value of SiC and graphite defined by the above formula (1) It is desirable to limit the ratio of the graphite content to the total amount of 60% or less.

  In the present invention, in addition to the high SiC component system and the low SiC component system, component elements can be further contained in the following content ranges for the following purposes.

(B (selection))
B is a hardenable element, which ensures the hardenability of the weld metal, makes the microstructure of the weld metal a stronger structure, and suppresses the formation of a structure that starts transformation at a high temperature and transforms at a lower temperature. Has the effect of making the microstructure. Since the weld metal has a higher oxygen content than steel sheets, B may bind to oxygen and lose its effect. Therefore, the hardenability by B in the weld metal and the tensile strength and fatigue strength by microstructure control. In order to improve the content, the lower limit of the B content is preferably 0.001%. On the other hand, the upper limit of the B addition amount is set to 0.015% because the effect obtained by addition of B does not increase even if an amount exceeding this is added.

(One or more of Nb, V and Ti (selection))
Nb, V, and Ti are all elements that have the function of forming carbides in the weld metal to increase the strength, and by containing a small amount of one or more of Nb, V, and Ti in the weld metal. The joint strength can be improved. If the lower limit of the total content of one or more of Nb, V, and Ti is less than 0.005%, improvement in joint strength cannot be expected so much, so the lower limit of the total content is 0.005%. Is preferable. On the other hand, if the total content exceeds 0.3%, the strength of the weld metal becomes excessive and a problem occurs in joint characteristics. Therefore, the total content upper limit is preferably set to 0.3%. Regarding Ti, in addition to the effect of improving the strength of the weld metal, it has a function of stabilizing the welding arc. Therefore, when Ti is contained, the lower limit of the Ti content is preferably set to 0.003%. desirable.

(Arc stabilizer (selection))
An arc stabilizer is an element which has the effect | action which stabilizes a welding arc by making it contain in the flux with which it fills in the steel outer_layer | skin. Since Na ₂ O, K ₂ O, and the like contained in the flux described above also have a function as an arc stabilizer, these components are contained to the extent that they do not hinder the reduction in the amount of slag generated in the weld of the present invention. It is preferable to do this. Further, the arc stabilizer can function as long as it is a compound of Na, Al, F, such as cryolite (Na ₃ AlF ₆ ), without using an oxide such as Na ₂ O or K ₂ O. Since a stabilizing effect is obtained, it is preferable to contain it as a compound other than an oxide from the viewpoint of reducing the amount of slag generated.

  In order to reduce the amount of slag generated in the weld and to obtain the effect of arc stabilization, the lower limit of the content of the arc stabilizer other than the oxide type is preferably 0.05%. On the other hand, if the content of arc stabilizers other than oxides exceeds 0.5%, the arc stabilizing effect will not change, so the upper limit of the content is preferably 0.5%.

  The above is the reason for limiting the component composition of the metal-based flux-cored wire of the present invention. Next, welding conditions for creating a high fatigue strength joint by welding using this metal flux cored wire will be described.

First, the reason for limiting the shielding gas will be described.
In gas shield welding, generally, a shielding gas containing CO ₂ gas in 100% CO ₂ or Ar gas is used. An object of the present invention is to provide a method for producing a high fatigue strength welded joint with a small amount of slag generation, and considering that most of the slag is an oxide system such as SiO ₂ or MnO, even in shield gas, It is desirable to select one having a low oxygen content. Therefore, in the welding method in the present invention, Ar + 3 to 25% CO ₂ gas is adopted as the shielding gas. In addition, since it is not preferable for the stability of the welding arc to reduce the CO ₂ gas to 0%, it is preferable that the Ar gas contains 3% or more of CO ₂ . Ar gas containing CO ₂ exceeding 25% is almost the same as the case of 100% CO ₂ gas in terms of slag generation, so the upper limit of the CO ₂ content is preferably 25%.

In addition, the O ₂ gas in the shielding gas is an impurity in the present invention because it increases the amount of slag generated in the weld. However, if you are O ₂ gas is present in the Ar gas, since the cost of removing the O ₂ gas is required, in general, towards the shielding gas containing no O ₂ gas, containing O ₂ gas More expensive than shielding gas. Therefore, the present inventors considered that it is industrially significant to clarify the range of the allowable content of O ₂ gas, and decided to set the allowable range. When the O ₂ gas exceeds 4%, an increase in the amount of slag is unavoidable, and therefore the upper limit of the O ₂ gas is preferably 4%.

  Next, the reason for limiting the thickness and strength of the steel sheet will be described.

  The object of the present invention is to provide a method for producing a high fatigue strength welded joint that produces as little slag as a solid wire. In particular, regarding the reduction of the amount of slag, even if the thickness of the steel plate is not limited, the effect can be obtained by using a metal-based flux-cored wire within the scope of the present invention.

  However, in order to achieve sufficient improvement in fatigue strength of welded joints by introducing compressive residual stress into the welded part by transformation expansion of the weld metal using metal-based flux-cored wire, it is necessary to obtain sufficient It is necessary to secure a sufficient binding force. For this reason, in this invention, while limiting the component composition of a metal type flux cored wire as mentioned above, it is necessary to prescribe | regulate the plate | board thickness and intensity | strength of a steel plate.

  The outline of the principle of improving the joint fatigue strength using the transformation expansion of the weld metal is as follows.

  In other words, after the weld metal formed on the weld has solidified, the weld metal starts phase transformation at a relatively low temperature in the process of cooling at room temperature, and the state of compressive stress generated in the weld by the transformation expansion of this weld metal. By maintaining the temperature up to room temperature, the joint fatigue strength can be improved.

However, if the volume expansion is not sufficiently restrained from the steel plate around the weld during the transformation expansion of the weld metal, the compressive stress generated in the weld is reduced. In this case, after that, a tensile stress is generated due to thermal contraction in the process of cooling the weld metal to room temperature, so that the compressive stress is canceled out. As a result, the weld becomes a tensile residual stress state, and the fatigue strength is lowered.
For these reasons, in order to achieve a sufficient improvement in fatigue strength of the welded joint by introducing compressive residual stress into the welded part by transformation expansion of the weld metal using a metal-based flux-cored wire, It is necessary to secure a sufficient binding force from the steel plate.
First, the reason for limiting the thickness of the steel sheet will be described.

(Steel plate thickness)
In the present invention, when the thickness of the steel sheet is less than 1 mm, the depth of penetration with respect to the thickness of the welded portion is increased when a joint is produced using the metal-based flux-cored wire of the present invention. For this reason, when the solidified weld metal undergoes transformation expansion during the cooling process, the expansion of the weld metal from the steel plate around the weld cannot be sufficiently restricted. As a result, the compressive residual stress is introduced into the weld using the transformation expansion of the weld metal, the tensile residual stress cannot be reduced, and it is difficult to improve the fatigue strength. Therefore, in the present invention, in order to maintain the restraining force from the surroundings during the transformation expansion of the weld metal and sufficiently improve the joint fatigue strength by introducing the compressive residual stress of the welded portion, the lower limit of the plate thickness of the steel plate is 1. Set to 0 mm. On the other hand, the improvement in the paintability of the welded joint, which is the object of the present invention, requires thin plate welding applied to the automobile field. In thick plate welding applied in the shipbuilding field, slag exists in the weld bead. However, no big problem occurs. In general, in the automotive field, there is almost no case where the plate thickness exceeds 5 mm, and when the plate thickness increases beyond 5 mm, it becomes difficult for the heat of welding to reach the back surface of the plate, and the heat after the transformation of the weld metal is completed. In the contraction process, tensile stress is generated due to the restraint force strongly from the steel plate around the welded portion, and the effect of improving the joint fatigue strength becomes difficult. Therefore, in this invention, in order to fully obtain the joint fatigue strength improvement effect, the upper limit of the steel plate thickness was set to 5.0 mm.
Next, the reason why the steel plate strength is limited will be described.

(Steel strength)
When the steel plate strength is lower than 440 MPa, when producing a joint using the metal-based flux-cored wire of the present invention, when the solidified weld metal undergoes transformation expansion in the cooling process, the binding force from the steel plate around the welded portion Is not sufficient, and sufficient compressive stress cannot be introduced into the weld. Thereafter, the compressive stress is canceled out by the tensile stress due to the thermal contraction of the weld metal to room temperature. As a result, the tensile residual stress of the welded portion is not reduced, and it is difficult to improve the joint fatigue strength. Therefore, in the present invention, the lower limit of the steel sheet strength of the steel sheet is set to 440 MPa in order to maintain the binding force from the surroundings during transformation expansion of the weld metal and sufficiently improve the joint fatigue strength by introducing the compressive residual stress of the welded portion. did.

  On the other hand, in the present invention, the upper limit of the steel sheet strength is such that the strength of the weld metal formed on the welded portion when the joint is produced using the metal-based flux-cored wire of the present invention does not exceed 980 MPa. The upper limit of the steel plate strength for restraining metal expansion was 980 MPa.

Examples of the present invention will be described below.
As described above, the present invention is a wire for gas shielded arc welding of a steel plate having a plate thickness of 1.0 to 5.0 mm and a strength of 440 to 908 MPa, particularly when manufacturing a welding wire. A welding wire that has good workability and productivity in the flack blending / granulating process and the drawing process, produces a small amount of slag during welding, and has excellent fatigue strength, and a welded joint using this wire An object of the present invention is to provide a manufacturing method of

  In this example, a wire that satisfies the requirements defined by the present invention (invention example) and a wire that deviates from the requirements defined by the present invention (comparative example) are manufactured, and then welding is performed using these wires. It was. In addition, when manufacturing these wires, while evaluating the workability and productivity (graphite scattering amount, drawing processability) in the flux blending and granulating process and the drawing process after filling the steel pipe with the flux The amount of slag generated when steel plates were welded with these wires, and the fatigue strength and toughness of the obtained welded joints were evaluated.

  Table 1-1 and Table 1-2 show the component values of the metal-based flux-cored wires. Table 1-1 and Table 1-2 show the mass% of the components added in the wire, the filling rate, the wire drawability, and the Charpy absorbed energy. Each component is mass% with respect to the total mass of the wire.

  In Table 1-1 and Table 1-2, wires in the 100s in the wire symbol are examples of the present invention and comparative examples of high SiC component wires in the present invention. The wire symbols in the 200s are examples of the present invention and comparative examples of low SiC component wires in the present invention.

  Furthermore, among the 100-th order wires, the 150th and subsequent wires are comparative examples of the high SiC component wire in the present invention. Of the 200 series wires, the 250th and subsequent wires are comparative examples of the low SiC component wires in the present invention.

C in the table indicates C other than SiC, or C other than SiC and graphite (when graphite is added), and Si in the table indicates Si other than SiC and SiO ₂ .

  First, a welded joint was prepared using the wires shown in Table 1-1 and Table 1-2, and then a test piece was collected from the welded portion and a Charpy test was performed. The purpose of the present invention is to improve the paintability and joint fatigue strength by reducing the amount of slag generated in the weld, but since joint toughness is a basic property of welded joints, the Charpy test of the welded joints in advance is used. The toughness of the welded joint of a welded joint welded with two lines of a high SiC component system and a low SiC component system was confirmed.

  The production of the welded joint and the Charpy test were performed in the following procedure.

  First, two 780 MPa class steel plates with a thickness of 3.2 mm were prepared, and the end portions of these steel plates were butt welded with I-grooves to produce a welded joint, and then a 2 mV notch was machined at the center of the weld metal. A Charpy test piece having a thickness of 2.5 mm was prepared by processing. As shown in FIG. 3 of the schematic diagram, the sampling position of the test piece was a Charpy test sampling position S that includes the I groove and the butt weld W. The welding conditions at this time are welding current: 270 A, welding voltage: 26 V, and welding speed: 110 cm / min.

  Using this test piece, a Charpy test was performed at 0 ° C., and the absorbed energy was measured. The Charpy test results are shown in Table 1-2. In addition, about the wire 152 in Table 1-2, since the solidification crack generate | occur | produced in the welded joint, the Charpy test was not able to be performed. Moreover, about the wires 154 and 254, since the disconnection occurred during wire manufacture, the Charpy test was not able to be performed. Table 1-2 shows the evaluation items of the wire drawability at the time of manufacturing the wire, where “◯” indicates that the wire drawing was performed satisfactorily without wire breakage, and “×” indicates the wire drawing. Indicates a wire breakage during drawing.

  Comparing the Charpy absorbed energy of the welded joint in the two types of wire component systems shown in Table 1-1 and Table 1-2, a low SiC component system (wire symbols 200 to 200) within the component composition range defined in the present invention. 204) has higher Charpy absorbed energy than the high SiC component system (wire symbols 100 to 105), but all have joint toughness levels that are practically acceptable.

Next, a method for evaluating workability in the flux blending process during wire production will be described.
As described above, when manufacturing a wire containing SiC and graphite in the wire, graphite is mixed with other fluxes, and when mixed, the graphite is scattered, causing workability and raw material yield to decrease. . The workability in the flux blending process was evaluated by measuring the amount of scattering of the graphite.

  First, the amount of graphite used for preparing the flux is measured. Next, graphite is mixed into a flux and granulated, and then a sample is taken from the granulated flux and the amount of graphite is measured. The amount of scattered graphite was determined from the difference between the measured value of the graphite amount in the flux after granulation and the measured value of the graphite amount before blending and granulation.

  In Table 1-2, the scattering amount of graphite is shown as a ratio with respect to the total amount of C-converted values of graphite and SiC defined by the above formula (1). By reducing the amount of scattered graphite to less than 30%, it is possible to maintain the yield and work of graphite at the time of flux preparation.

  From Table 1-1 and Table 1-2, SiC content is low from the range of this invention among the wires (Wire symbol 102-104,153,201,203-204,252,253) which added the graphite in the wire. The disconnected wires 153 and 253 resulted in a high graphite scattering amount of 34% and 40%, respectively, and there was a problem in terms of workability during wire manufacturing.

  On the other hand, all the wires having the SiC content within the scope of the present invention (wire symbols 102 to 104, 201, 203 to 204, 252) have a relatively low scattering amount of 25% or less, and the flux at the time of wire production The workability in the blending process was excellent.

  Next, a method for measuring the amount of slag generated during welding and the fatigue strength of the welded joint will be described.

  First, the slag generation amount was measured as follows.

  In order to determine the amount of slag generation, a welded joint for collecting a fatigue test piece described below is prepared, and the weight of the joint is first measured. Next, the slag adhering to the surface is removed, and the weight is measured again. And the difference of these weights was calculated and the slag generation amount with respect to the joint was determined. In addition, since the weld bead length of the weld joint for collecting a fatigue test piece was always made constant at 250 mm, the slag generation rates of the respective wires can be relatively compared by comparing the slag generation amounts. The fatigue test specimen was collected from the joint after that. At this time, the welding conditions when the plate thickness is less than 2.0 mm are the welding current: 120 A, the welding voltage: 15 V, the welding speed: 80 cm / min, and the welding conditions when the thickness is 2.0 mm to 3.0 mm: Welding current: 140 A, welding voltage: 15 V, welding speed: 60 cm / min, welding conditions when exceeding 3.0 mm are welding current: 240 A, welding voltage: 24 V, welding speed: 80 cm / min.

  Separately from this example, in order to enable comparison with the solid wire, the amount of slag generation of the solid wire was measured by the same method. As a result, the slag generation amount of the solid wire was 0.09 g when the shield gas was 100% CO2, and 0.05 g when the shield gas was Ar + 20% CO2. Therefore, in this slag amount measuring method, if the amount of slag generation is less than 0.1 g, it can be said that the slag is as low as solid wire.

  Next, a fatigue test was performed by the following procedure using the test piece collected from the welded joint, and the joint fatigue strength was measured.

  Two steel plates were prepared, lap fillet welding was performed, and the amount of slag generated was investigated, and then a fatigue test piece shown in FIG. 4 was collected from the joint. Then, a fatigue load is applied as the arrow direction in FIG. 4 and the fatigue load load direction P, and the stress range where fatigue cracks did not occur even after repeated loading 2 million times is defined as the fatigue strength for the joint. Compared. The stress ratio R was R = 0.1. The steel plate 1 and the steel plate 2 do not necessarily use the same steel plate, and combinations of different strengths and plate thicknesses 3 and 4 were also selected. The value of the stress applied to the test piece was measured by attaching a strain gauge in the vicinity of the weld bead on the upper surface of the steel plate 1.

  First, among the wires in Table 1-1 and Table 1-2, after producing a welded joint under the conditions shown in Table 2-1 using 100th series high SiC component wires, the amount of slag generated in the welded portion And the joint fatigue strength was measured. The results are shown in Table 2-1.

  In the comparative example of test number A8, both the steel plate strength and the steel plate thickness are within the range of the present invention, and the SiC content in the wire component is within the range of the present invention. However, since the total content of the slag material deviated from the scope of the present invention, reduction of the slag amount could not be achieved during welding.

  In the comparative examples of test numbers A9 and A10, both the SiC content of the wire component and the total content of the slag material were out of the scope of the present invention, so that neither the joint fatigue strength improvement nor the slag generation amount during welding could be achieved. It was.

  In the comparative example of test number A11, the SiC content of the wire component was out of the range of the present invention, so that the fatigue strength could not be improved.

  Moreover, about the wire of the comparative example of the wire number 152 shown by Table 1-1 and Table 1-2, since the crack generate | occur | produced when implementing a Charpy test, wire number 154 is wire manufacture. Since the wire was broken in the drawing process, Charpy test, slag generation amount measurement, and fatigue test could not be performed.

  On the other hand, all of the inventive examples of test numbers A1 to A7 in which the wire component is within the scope of the present invention can achieve a slag generation amount at the time of welding of less than 0.1 g, which is a slag generation amount similar to a solid wire, In addition, the joint fatigue strength all satisfies 300 MPa or more.

  Furthermore, among these invention examples, the joints of test numbers A3 to A5 welded using SiC and a wire containing graphite increased the deoxidation action of the molten slag. Reduced.

  In contrast, A8 to A11, which are comparative examples, all had a slag generation amount of 0.1 g or more, and / or the fatigue strength of the welded joint during welding was less than 300 MPa.

  From the above, it was found from the slag generation amount and fatigue strength (high SiC component system) in Table 2-1 that the wire of the present invention can reduce the slag generation amount during welding and can also improve the fatigue strength of the joint. .

  The amount of slag generation and fatigue strength (low SiC component system) in Table 2-2 are examples for the low SiC component system in the present invention. The fatigue strength investigation method and the slag generation amount investigation procedure are as described above.

  In the comparative example of test number B8, since the total content of the slag material in the wire component deviated from the scope of the present invention, the slag generation amount increased to 0.40 g and the slag generation amount increased during welding. Reduction was not achieved.

  Moreover, about the comparative example of B9-B11, since the slag material in a wire is in the range of the present invention, the amount of slag generation is 0.07g, 0.06g, and 0.05g, respectively, and low slag is achieved sufficiently. However, since the alloy component addition amount of SiC and / or Cu, Ni, Cr, and Mo was out of the range of the present invention among the wire components, the fatigue strength was not improved.

  Moreover, the wire number 254 shown in Table 1-1 and Table 1-2 was disconnected in the drawing process at the time of wire manufacture, and the Charpy test, the slag generation amount measurement, and the fatigue test could not be performed.

  On the other hand, in all of the inventive examples of test numbers B1 to B7 in which the wire component is within the scope of the present invention, the amount of slag generated during welding can be less than 0.1 g, which is the amount of slag generated at the same level as solid wire. In addition, the joint fatigue strength also satisfies 300 MPa or more.

  Furthermore, among these inventive examples, the joints of test numbers B2, B4, B6, and B7 welded with SiC and a wire containing graphite were used as a result of the increased deoxidation effect of the molten slag. The amount generated was reduced.

  On the other hand, B8 to B11 as comparative examples had a slag generation amount of 0.1 g or more and / or the fatigue strength of the welded joint during welding was less than 300 MPa.

  From the above, it was found from the amount of slag generation and fatigue strength (low SiC component system) in Table 2-2 that the wire of the present invention can reduce the amount of slag generation during welding and can also improve the fatigue strength of the joint. .

FIG. 1 is a diagram showing the relationship between the SiC content in a flux in a metal-based flux-cored wire, and the C content and Si content in a weld metal in a weld metal test. FIG. 2 is a conceptual diagram showing the relationship between the amount of SiC in the wire and the minimum amount of oxide that can maintain wire workability under the conditions of the SiC content and the amount of slag generated during welding. FIG. 3 is a diagram for explaining a method for producing a welded joint and a method for collecting a Charpy test piece. FIG. 4 is a diagram for explaining a welded joint fatigue test piece and a fatigue load loading direction.

Explanation of symbols

1, 2: Steel plate 3, 4: Plate thickness P: Fatigue load direction S: Charpy test sampling position W: I groove, butt welding

Claims (18)

A wire for gas shield arc welding of a steel plate having a plate thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa, and is a mass% of the whole wire, and C other than SiC: 0.01 ~0.20%, SiC: 0.6~1.2%, SiC and SiO ₂ other than Si: 0.05~1.2%, Mn: contains 0.2 to 3.0%, P: It is limited to 0.03% or less and S: 0.02% or less. Furthermore, one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O are added in a total amount of 0.05 to 0.00. 4% content, the balance being iron and inevitable impurities, and one or more of SiC and SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O are at least a steel outer shell as a flux The amount of slag generated is small Metal-based flux cored wire. In the metal-based flux-cored wire, the graphite contains at least 0.02% or more of graphite as a flux in the steel outer shell, and the graphite defined by the following (1): The total amount of the C conversion value of said SiC is 0.6% or less, The metal type flux cored wire with few slag production | generation amounts of Claim 1 characterized by the above-mentioned.
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.   In the metal-based flux-cored wire, by mass% of the whole wire, Ni: 0.5 to 5.0%, Cr: 0.1 to 2.0%, Mo: 0.1 to 2.0% And a metal-based flux-cored wire containing 0.5 to 6.0% in total of one or more of Cu: 0.1 to 0.5%. Metal-based flux-cored wire with low slag production. A wire for welding a steel plate for automobiles having a plate thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa, and is a mass% of the whole wire, and C other than SiC: 0.01 to 0.00. 20%, SiC: 0.05-0.6%, Si other than SiC and SiO2: 0.05-1.2%, Mn: 0.2-3.0%, P: 0.03% Hereinafter, S is limited to 0.02% or less, Ni: 0.5 to 5.0%, Cr: 0.1 to 2.0%, Mo: 0.1 to 2.0%, and Cu: one or more 0.1% to 0.5% containing 1.0 to 6.0% in total, _addition, SiO _2, Al ₂ O 3, one of Na ₂ O and _{K 2} O or containing 0.05 to 0.4% of two or more in total, the balance being iron and unavoidable impurities, and the SiC, and the _SiO 2, a _{2 O} 3, _Na 2 _O and K _{2 O} of one or more the metal-based flux cored wire is small amount of formation of slag, characterized in that it contains in the steel sheath at least as a flux. In the metal-based flux-cored wire, the graphite contains at least 0.02% or more of graphite as a flux in the steel outer shell, and the graphite defined by the following (1): 5. The metal-based flux-cored wire with a small amount of slag generation according to claim 4, wherein the total amount of C-converted values of SiC is 0.35% or less.
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.   The slag generation amount according to any one of claims 1 to 5, wherein the metal-based flux-cored wire further contains B: 0.001 to 0.015% by mass% of the entire wire. Metal-based flux cored wire with little   The metal-based flux-cored wire contains 0.005 to 0.3% in total of one or more of Nb, V and Ti in a mass% of the whole wire. A metal-based flux-cored wire with a small amount of slag generation according to any one of 1 to 6.   In the metal-based flux-cored wire, an arc stabilizer other than an oxide-based material is contained in the steel outer sheath at a mass% of the entire wire, and further 0.05 to 0.5% as at least the flux. The metal-based flux-cored wire with a small amount of slag generation according to any one of claims 1 to 7. By mass% of the whole wire, C other than SiC: 0.01 to 0.20%, SiC: 0.6 to 1.2%, Si other than SiC and SiO ₂ : 0.05 to 1.2%, Mn : contains 0.2 to 3.0%, P: 0.03% or less, S: limited to 0.02% or less, _{further, SiO 2, Al 2 O 3} , Na ₂ O and _{K 2} O containing 0.05 to 0.4% one or two or more in total, the balance being iron and unavoidable impurities, and the SiC, and the _{SiO 2, Al 2 O 3,} Na 2 O and _{K 2} One or more of O is a steel plate having a thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa using a metal-based flux-cored wire contained in the steel outer shell as a flux at least. Gas shielded arc welding The method for manufacturing a grayed generation amount is small high fatigue strength welded joints. In the metal-based flux-cored wire, the graphite contains at least 0.02% or more of graphite as a flux in the steel outer shell, and the graphite defined by the following (1): The method for producing a high fatigue strength welded joint according to claim 9, wherein a total amount of C-converted values of SiC is 0.6% or less.
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.   In the metal-based flux-cored wire, by mass% of the whole wire, Ni: 0.5 to 5.0%, Cr: 0.1 to 2.0%, Mo: 0.1 to 2.0% And a metal-based flux-cored wire containing 0.5 to 6.0% of one or more of Cu: 0.1 to 0.5% in total. A method for producing a high fatigue strength welded joint with a small amount of slag generation described. In% by weight of the total wire, other than the SiC C: 0.01~0.20%, SiC: 0.05~0.6%, SiC and SiO ₂ other than Si: 0.05 to 1.2%, Mn : 0.2 to 3.0%, P: 0.03% or less, S: 0.02% or less, Ni: 0.5-5.0%, Cr: 0.1-2 1.0%, Mo: 0.1 to 2.0%, and Cu: 0.1 to 0.5%, or a total of 1.0 to 6.0%, Containing one or more of SiO ₂ , Al ₂ O ₃ , Na ₂ O and K ₂ O in a total of 0.05 to 0.4%, the balance consisting of iron and inevitable impurities, and the SiC, and , contained in the _{SiO 2, Al 2 O 3,} Na 2 O and _{K 2} O 1 kind or 2 or more is a steel within the outer skin at least as flux High fatigue strength with low slag generation, characterized in that gas shield arc welding is performed on a steel plate having a thickness of 1.0 to 5.0 mm and a strength of 440 to 980 MPa using a tal-based flux-cored wire A method for producing a welded joint. In the metal-based flux-cored wire, the graphite contains at least 0.02% or more of graphite as a flux in the steel outer shell, and the graphite defined by the following (1): The method for producing a high fatigue strength welded joint according to claim 12, wherein a total amount of C-converted values of SiC is 0.35% or less.
Total amount of C converted value = [graphite] + 0.3 × [SiC] (1)
However, the above [graphite] and [SiC] indicate mass% of graphite and SiC with respect to the whole wire, respectively.   The amount of slag generation according to any one of claims 9 to 13, wherein the metal-based flux-cored wire further contains B: 0.001 to 0.015% by mass% of the entire wire. Method for producing high fatigue strength welded joints with less fatigue.   The metal-based flux-cored wire contains 0.005 to 0.3% in total of one or more of Nb, V and Ti in a mass% of the whole wire. The manufacturing method of the high fatigue strength welded joint with few slag production | generation amounts in any one of 9-14.   In the metal-based flux-cored wire, an arc stabilizer other than an oxide-based material is contained in the steel outer sheath at a mass% of the entire wire, and further 0.05 to 0.5% as at least the flux. The method for producing a high fatigue strength welded joint with a small amount of slag generation according to any one of claims 9 to 15. The high fatigue strength with a small amount of slag according to any one of claims 9 to 16, wherein the shielding gas is a shielding gas containing 3 to 25% of CO ₂ and the balance being Ar gas and inevitable impurities. A method for producing a welded joint. The method for producing a high fatigue strength welded joint according to claim 17, wherein a shielding gas containing 4% or less of O ₂ gas is further used in the shielding gas.

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