KR20090110247A - PURE Ar GAS SHIELDED WELDING MIG FLUX-CORED WIRE AND MIG ARC WELDING METHOD - Google Patents

Abstract

PURPOSE: A pure Ar gas shielded welding MIG flux-cored wire and a MIG arc welding method are provided to improve static tension intensity and the strength by suppressing slag and hume. CONSTITUTION: A steel outer cover is made by charging a flux. The flux contains graphite with 0.16~2.00 mass% per whole wire(13) mass and iron with 20 mass% per whole flux mass. The flux additionally contains one type of wire, selected from a group comprised of Ti and Zr, with 0.03~5.00 mass% per whole wire mass.

Description

MIGR flux cored wire and MIRC arc welding method for pure AR shield gas welding {PURE Ar GAS SHIELDED WELDING MIG FLUX-CORED WIRE AND MIG ARC WELDING METHOD}

The present invention relates to a MIG flux cored wire for pure Ar shield gas welding, which is used to weld MIG arcs to steel materials using pure Ar gas as a shield gas, and a gas shielded arc while unwinding the wire from a welding torch. A MIG arc welding method for welding.

Unlike the case where the base material is an aluminum alloy material, in the gas shielded arc welding of steel materials, it has been considered that the inert gas arc welding method using pure Ar is substantially impossible. The reason for this is considered that when the steel is used as an electrode, electron emission requires an oxide which is energy-low. With pure Ar gas, no oxide is formed on the steel sheet or wire tip surface. Therefore, in general, a mixture of CO ₂ alone or CO ₂ or O ₂ gas in Ar is used as the shield gas. However, if an oxidizing gas such as CO ₂ and O ₂ is present, iron is inevitably oxidized in the molten state and deteriorates its properties. By adding from a wire, deoxidation reaction is caused and it is discharged as slag. In other words, since an oxidizing gas is used, expensive elements that are not necessary for the joint performance are added. In addition, although inexpensive CO ₂ is most commonly used as a shielding gas, it is known as a greenhouse gas, and use should be avoided as much as possible.

On the other hand, welding using pure Ar gas as a shield gas hardly generates slag and fume, which are oxides, in principle, so that the poor coating properties caused by adhesion of slag or the human body due to fume aspiration are caused. With respect to the adverse effect, the improvement effect can be expected.

Thus, pure Ar gas welding is beneficial in many respects, such as no use of greenhouse gases, saving valuable metals, improving the appearance of welds, and improving the sanitary environment of the welding station. In the TIG welding method in which a welding rod is melted by arc heat generated between the electrode and the base material using tungsten, which is a non-consumable electrode, pure Ar gas can be used, but MAG welding method and MIG that generate an arc from the wire itself can be used. Compared with the welding method, since there is no resistance heating effect, there is a drawback that the efficiency is very low.

For example, as a pure Ar-MIG welding method of steel, a special welding wire wound by steel strips of different materials on a steel core is disclosed in Japanese Patent Laid-Open No. 2006-205204. In addition, a similar pure Ar welding method in which an oxidizing gas flows around a pure Ar shield gas using a specially shaped torch is disclosed in Japanese Patent Laid-Open No. 2007-44736. In addition, by using a flux cored wire in which 0.10 to 0.7% by mass of graphite and other appropriate amounts of elements are added, the coating property is improved by reducing the amount of slag, and the martensite transformation temperature is lowered to impart a compressive residual stress. A welding method for improving joint fatigue strength is disclosed in Japanese Patent Laid-Open No. 2006-272405.

However, the welding wire disclosed in Japanese Unexamined Patent Publication No. 2006-205204 is difficult to manufacture, and since its composition also contains a large amount of Ni, Cr, etc., it is very expensive, so its practicality is insufficient. In addition, the welding torch disclosed in Japanese Patent Laid-Open No. 2007-44736 is within the range known in view of the use of an oxidizing gas, and the welding torch has a special shape and thus lacks practicality. In addition, the combination of the shield gas and graphite disclosed in Japanese Patent Laid-Open No. 2006-272405 is undesirable for the environment because it generates a large amount of fume. In addition, since the oxygen is supplied from the shield gas, the slag reduction effect is limited. In addition, the oxygen content of the weld metal is high at several ppm, and the effect of reducing the Ms point is limited. In addition, this Ms point represents the temperature at which austenite begins to transform into martensite during cooling. Moreover, in high carbon steels, there is a drawback that oxides are liable to cause solidification cracks as inclusions.

The present invention has been made in view of these problems, and does not need to use a special torch, does not necessarily use expensive metal resources, and also generates slag and fume without using a greenhouse gas such as CO _2. It is an object of the present invention to provide a MIG flux cored wire and a MIG arc welding method for pure Ar shield gas welding, which can be suppressed and a welded joint having excellent static tensile strength and fatigue strength can be obtained.

The flux cored wire according to the present invention is a flux cored wire used for MIG welding using pure Ar shield gas, and is made by filling flux into a steel sheath, and in the flux, graphite is used as the total mass of the wire. 0.16-2.00 mass% per sugar is contained, and iron content is 20 mass% or more per flux total mass.

It is preferable that the said wire contains 0.03-5.00 mass% of at least 1 sort (s) chosen from the group which consists of Ti and Zr in the said flux per mass of wire.

Moreover, the said wire contains C: 0.16-2.00 mass% per wire total mass, and also Si: 2.00 mass% or less, Mn: 10.00 mass% or less, Al: 1.00 mass% or less, Mg: 1.00 mass% Ni: 3.00 mass% or less, Cr: 3.00 mass% or less, Nb: 3.00 mass% or less, V: 3.00 mass% or less, Mo: 3.00 mass% or less, Cu: 3.00 mass% or less, B: 0.0200 mass% or less At least one selected from the group consisting of rare earth metals (REM): 0.50 mass% or less, F: 0.50 mass% or less, Ca: 0.50 mass% or less, K, Na and Li: total amount of 1.00 mass% or less It is preferable to regulate an impurity to P: 0.030 mass% or less and S: 0.030 mass% or less.

Moreover, as for the said wire, C is preferable in it being 0.45-2.00 mass% per wire total mass.

The MIG arc welding method according to the present invention uses the MIG flux cored wire for pure Ar shield gas welding described above, and uses pure or primary grade Ar of JIS K 1105 as the shield gas. An arc is generated between the base metal of the cathode and MIG welding.

In this case, it is preferable to use a pulse power source as the power source for forming the arc.

Moreover, as said base material, the steel plate whose tensile strength is 490 Mpa or more can be used suitably.

According to the present invention, by using a welding device such as a conventional torch as it is, by appropriately combining the wire composition and the shielding gas, slag and the like without using a greenhouse gas and without necessarily expensive metal resources, The generation of fumes can be suppressed. According to the present invention, a welded joint having high static tensile strength and fatigue strength can be obtained. As a result, pure Ar-MIG welding at low cost and stable for steel materials can be realized.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described concretely with reference to attached drawing. FIG. 1: is a perspective view which shows the MIG welding method which uses the pure water Ar gas of this embodiment as a shield gas. The welding wire 13 is continuously supplied toward the welding torch 1, and the welding wire 13 passes through the central portion of the welding torch 1 and is sent out from the tip of the welding torch 1 toward the base material 21. do. Using the welding wire 13 as an anode and the base material 21 as a cathode, a welding voltage is applied from a power supply device (not shown), and an arc 31 is formed between the welding wire 13 and the base material 21. ) Is formed. By this arc 31, the welding wire 13 and the base material 21 melt, and the molten paper 175 is formed. In this case, as shown in FIG.2 (b), pure Ar gas is supplied as a shield gas in the vicinity of the molten paper 175 formed between the welding wire 13 and the base material 21, and the arc ( 31) and the periphery of the molten pool 175 are blocked from outside air.

By moving the welding wire 13 along the welding line (butt welding of a V groove in FIG. 1), the molten pool 175 solidifies, and the welding bead 173 by the weld metal is formed. Thereby, a welded joint can be obtained.

Next, in this pure Ar gas shield MIG welding, the result of having observed the instability mechanism of the arc 31 in pure Ar gas atmosphere using a high speed camera etc. is demonstrated. 2 (a) and 2 (b) are schematic diagrams showing the behavior thereof. In the pure Ar gas atmosphere, since the endothermic reaction that occurs when the molecules are decomposed when the oxidizing gas is used and the potential hardness inherent in the gas do not occur, the volume of the ordinary solid wire 11 or the flux cored wire 13 is reduced. The distance 15 from the tip of the (droplet) 19 to the arc generation point thereon becomes very large, resulting in an elongated liquid column 17 as shown in Fig. 2A. In addition, the cathode point on the surface of the base material 21 is unstable because oxide is difficult to form, and floats violently with a wide range as an arc generation point. This can be confirmed as a result of the cleaning width formed in the vicinity of the weld bead 173. While the arc 31 is very unstable, the liquid column 17 at the tip of the wire is also thin and long, and is easily affected by the arc, and the liquid column 17 is scattered around by the energy with the movement of the arc point. Violent sputters 171 are generated. Therefore, the welding bead 173 does not become normal, such as meandering, as shown in Fig. 3A, and welding becomes impossible.

About this phenomenon,

(1) An element that is likely to electrically promote arc emission is exposed to an arc generating portion, that is, an anode point.

(2) The energy potential is lowered to supply oxygen from the wire 13 to stabilize the anode and cathode points.

(3) It has a strong deoxidation effect and increases the surface tension of molten iron so that it becomes a spherical droplet 19 rather than a liquid column 17, making it difficult to be influenced by the direction of the arc 31. The above three improve the stability of the arc 31.

As a result of the research by the inventors of the present application, it was found that graphite is effective in order to realize (1). Graphite is a form of carbon and, moreover, inexpensive. As can be seen from the use as gouging rods in the melt, it acts as a powerful arc generator called carbon arc. Since it is stable even at high temperatures, it can be an arc generating point even in gas shield arc welding. Graphite cannot be supplied to the arc 31 in the form of a solid wire 11, and the form of the flux cored wire 13 is essential as shown in FIG. 2 (b).

As means for supplying the oxygen of (2) from the wire 13, it was found that incorporating iron powder into the flux 131 was effective. Specifically, since iron is unstable in the air, oxygen is usually adsorbed or oxidized on the surface. Since iron has a larger surface area per unit mass than the solid form, the amount of oxygen is much higher and forms a stable generation point like the graphite at the arc generation point.

As shown in the bead shape in FIG. 3 (b), it was found that only the arcs 31 stable in the pure Ar atmosphere can be obtained using only (1) and (2). In addition, by adding Ti or Zr as (3), the tip of the wire 13 can be made into a spherical volume 19, and stabilization of the arc 31 and scattering of the sputter 171 can be suppressed. I found something.

When it is possible to weld using pure Ar gas, the formed molten paper 175 has a very small amount of oxygen of 50 ppm or less, so that deoxidation element is not necessarily required. In that case, as much as needed deoxidation element may be added as needed in order to improve the shape of the weld bead 173, for the purpose of adjustment of wettability. The same applies to the improvement of mechanical properties such as strength and toughness. The limitation of each component of the wire 13 which concerns on this invention is explained in full detail below.

`` Graphite: 0.16 to 2.00 mass% per total mass of wire ''

As mentioned above, graphite is added as a flux, and it becomes a stable arc generating source in pure Ar atmosphere. This becomes effective when it is 0.16 mass% or more per total mass of a wire. As a result, it is effective for low sputtering and excellent in the straightness of the welding bead as in the case of general CO ₂ system welding. Preferably it is 0.25 mass% or more, More preferably, it is 0.45 mass% or more, and arc stability, low sputtering property, and linearity will improve. On the other hand, when graphite exceeds 2.00 mass%, an arc force will become excess, a sputter will bundle and hydrogen crack will also bundle. Therefore, 2.00 mass% is made into the upper limit of graphite.

`` Iron: 20% by mass or more per total mass of flux ''

As described above, since iron is fine, oxygen is largely retained on the surface, and coexists with graphite at an arc generation point under a pure Ar environment, thereby becoming an arc generation source. This is effective when it is 20 mass% or more per total mass of flux. Since there is no disadvantage in the case of excess addition, it is not necessary to provide an upper limit, and it is more preferable if it is 40 mass% or more. In addition, iron is defined as a powder having a Fe concentration of 95% by mass or more and a particle size of 500 µm or less.

`` Outer: Formed with pipes of carbon steel strips or seamless steel pipes ''

The structure of the flux cored wire of the present invention is the same as before. The method of manufacturing the wire is a method of spreading flux in the longitudinal direction of the steel strip to be an outer shell, and then pressing both ends of the steel strip as if it is wrapped, forming a circular cross section and drawing a wire, or a seamless seamless diameter. Although there is a method of filling the steel pipe with flux and drawing it, any method may be used in the present invention. In addition, although there is a thing with and without a seam, this may be either. Although there is no need to prescribe any component of an outer shell, it is common to use a mild steel material in terms of cost and freshness. In addition, although the surface may be copper-plated, any of these may be sufficient.

"Ti, Zr: 0.03 to 5.00 mass% each per total mass of wire"

As a means of dramatically improving the arc stability in the pure Ar atmosphere, graphite and iron are used as the flux, but Ti and Zr coexist with them to further increase the stabilizing effect. When these are added in an appropriate amount, the volume at the tip of the wire can be granulated, and shaking can be suppressed. The minimum with which this effect is exhibited is 0.03 mass%. On the other hand, when it adds exceeding 5.00 mass%, Ti or Zr will remain excessive in a weld metal as an interference | inclusion, it will produce a crack, or a volume will become large too much, and an arc destabilizes on the contrary. In addition, as an additive raw material of Ti and Zr, it may be in any form including general ferro titanium, ferro zirconium oxide, titanium oxide, zirconium oxide, metal titanium, metal zirconium oxide, titanium oxygen, potassium titanate, zircon sand and other compounds. none. Moreover, since slag may generate | occur | produce at the time of a shield failure, for prevention, More preferably, it is 1.50 mass% or less.

"C: 0.16-2.00 mass% per total mass of wire"

Since graphite is used as the pure Ar arc stabilizer, the amount of C necessary to increase the strength of the weld metal can basically be sufficiently supplied from graphite. Therefore, the prescribed amount as C is the same as the prescribed amount of graphite. However, since C was added or mixed as a compound, such as SiC, in addition to graphite, it was prescribed | regulated independently. In the case of 0.45 mass% or more, compression residual strain is provided and a joint fatigue strength can also be raised. Adding 0.60% by mass or more can further increase the joint fatigue strength. On the other hand, when C exceeds 2.00 mass%, since a sputter | spatter bundles, the upper limit of C shall be 2.00 mass%.

`` Si: 2.00% by mass or less per total mass of wire ''

In general, welding wire is added with a deoxidizer to suppress oxidation of molten iron. However, since no oxidation occurs in pure Ar-MIG welding, welding is possible even without adding a deoxidizer. Therefore, there is no problem without Si. Moreover, when it adds 0.50 mass% or more, the shape of the bead edge part improves, and it is more preferable. On the other hand, when it exceeds 2.00 mass%, the viscosity of a molten pool will become excessive, and it will become easy to hump at the time of high speed welding. Therefore, the upper limit is 2.00 mass%. Moreover, as an additive raw material of Si, a metal silicon, ferro silicon, silicon manganese, a silica sand, a cali- feldspar, a zircon sand, sodium silicate, etc. are mentioned.

`` Mn: 10.00 mass% or less per total mass of wire ''

Mn, like Si, is also added as a general welding material for deoxidation purposes. However, since no oxidation occurs in pure Ar-MIG welding, welding is possible even without adding a deoxidizer. Therefore, there is no problem without Mn. Moreover, when it adds 0.50 mass% or more, the shape of a bead edge part improves, and it is more preferable. In general, the upper limit of 3.0% by mass may be sufficient in consideration of cost, but it is effective to further add Mn in order to have a function of improving the joint fatigue strength. On the other hand, when it exceeds 10.00 mass%, the viscosity of a molten paper will become excessive and it will become easy to hump at the time of high speed welding. Therefore, the upper limit is 10.00 mass%. Moreover, as an additive raw material of Mn, metal manganese, ferro manganese, silicon manganese, etc. are mentioned.

`` P, S: 0.030 mass% or less per total mass of wire ''

P and S are elements which lower the high temperature crack resistance, and for the purpose of the present invention, there is no special positive addition (no problem even if no addition). Therefore, in consideration of industrial productivity and cost, it is suppressed to 0.030 mass% or less similarly to the conventional wire.

`` Al, Mg: 1.00 mass% or less per total mass of wire ''

Al and Mg are also used as powerful deoxidizers. However, since no oxidation occurs in pure Ar-MIG welding, welding is possible even without adding a deoxidizer. Therefore, there is no problem without Al and Mg. However, when it adds 0.10 mass% or more, there exists an effect which raises an arc force and enlarges a melting depth. On the other hand, when it adds beyond 1.00 mass%, the sputter 171 will increase. Therefore, an upper limit shall be 1.00 mass%, respectively. Moreover, as an additive raw material, metal aluminum, ferro aluminum, metal magnesium, aluminum magnesium, etc. are mentioned.

`` All elements of Ni, Cr, Nb, V, Mo, Cu: 3.00 mass% or less per total mass of wire ''

Ni, Cr, Nb, V, Mo, and Cu have no problem even if they are not added. However, by adding an appropriate amount, Ni, Cr, Nb, V, Mo, and Cu have an effect of lowering the Ms point or securing appropriate strength. In order for these effects to appear, a minimum of 0.05 mass% is required. On the other hand, when it exceeds 3.00 mass%, the viscosity of a molten paper will rise and it will hump at the time of high speed welding. Moreover, since the disadvantage that a crack arises by excess strength arises, it shall be 3.00 mass% or less. Moreover, when Cu is plated on the wire surface, it is set as the ratio containing a plating part.

`` B: 0.0200 mass% or less per total mass of wire ''

Although B has no problem, even if it is no addition, a small amount of addition can lower the Ms point and improve the toughness of the weld metal. This effect requires the addition of 0.0000 mass% or more. On the other hand, addition exceeding 0.0200 mass% produces a crack, so it is referred to as this or less.

`` REM: 0.50 mass% or less per total mass of wire ''

REM is generally composed of La, Ce and the like in the sense of rare earth metal. Although there is no problem even if there is no addition, if it adds 0.01 mass% or more REM, arc stability will improve at the time of MIG welding, and also the oxygen content of a weld metal can be further reduced, and Ms point can be reduced. On the other hand, addition exceeding 0.50 mass% saturates the arc stabilizing effect, and conversely, the volume is opposed, so that the sputtering increases. It also raises costs.

`` Sum of K, Na, Li: 1.00 mass% or less per total mass of wire ''

K, Na, and Li also have no problems even if they are not added. However, by adding appropriate amounts, electron emission is facilitated, and arc stabilization and volume transition are smoothed to reduce the amount of sputter generation. The effect is exhibited by adding 0.001 mass% or more of at least 1 type of elements in total. On the other hand, the addition exceeding 1.00 mass% in total, the effect will be saturated, the arc force will become weak, and the melting depth will become shallow. Therefore, a problem arises such that the molten paper becomes unstable and humps. Therefore, the upper limit is 1.00 mass% in total. Further, K, Na, Li is usually added to the flux feldspar, soda glass, potassium glass mainly containing _{K 2 O, Na 2 O,} Li 2 O as raw materials.

`` F, Ca: 0.50% by mass or less per total mass of wire ''

F and Ca also have no problems even if they are not added. However, by adding an appropriate amount, Ca has a strong deoxidation effect and improves the hardenability of the weld metal. The effect requires at least 0.005 mass% or more. On the other hand, when F or Ca exceeds 0.50 mass%, the viscosity of the molten paper 175 will rise and will be humped at the time of high speed welding. In addition, since the generation amount of sputter increases, F and Ca are made into 0.50 mass% or less, respectively.

The flux rate (charge rate) of the wire of the present invention is not particularly different from the conventional flux cored wire, but is usually 7 to 27% by mass per total mass of the wire. If it is less than 7 mass%, the required amount of the flux elements required for MIG arc welding, such as graphite and iron powder, cannot be secured, and molding processing is also difficult. On the other hand, when it exceeds 27 mass%, an outer skin becomes thin and a disconnection easily arises during drawing, and manufacture is difficult.

As the flux component of the wire of the present invention, in addition to graphite, iron powder, Ti source and Zr source, the following materials may be included. That is, Si source (tactical), Mn source (tactical), Al source (tactical), Mg source (tactical), Ni, Cr, Nb, V, Mo, Cu metal powder or alloy powder, B metal powder, alloy powder, Oxide, REM (La, Ce), K source (tactical), Na source (tactical), Li source (tactical), F member, Ca member, etc. are mentioned. In addition, when mild steel is used as the shell, the components contained in the shell are about C, Mn, Si, P, and S, so that the elements other than them and Mn or Si are added to the flux so as to compensate for the insufficient portion of the shell alone. It is necessary to decide which substance to do.

`` Ar: Class 1 or 2 of JIS K 1105 ''

The expression "pure Ar" in the present invention is not 100% Ar scientifically, but pure Ar as an industrial product. Industrial Ar is prescribed | regulated to JISK1105, 1st grade is 99.999 volume% or more in purity, and 2nd grade is 99.995 volume% or more in purity. Both can be used without a problem as a combination of this welding wire 13 and a welding method. The welding wire can be applied to an Ar gas having a purity of less than that, but adverse effects such as an increase in the amount of fume or sputtering, a decrease in the strength of the metal, or the generation of slag occur.

`` Power supply device: pulse power supply ''

The welding machine is not a problem even if it is a constant voltage characteristic power supply which is generally used for welding a consumable electrode type arc. However, in order to further improve the arc stability in MIG welding, the combination with a pulse welding machine is most recommended. In pure Ar welding, it is inferior to MAG welding using an oxidizing gas with respect to regularity of the volume deviation regarding the humping occurrence. Therefore, the pulse welding method which can provide pinch force by the action of a high electric current always regardless of an average electric current, and can realize regular volume removal is preferable. The pulse setting is not particularly limited, but 0.8 to 5.0 milliseconds are generally used for peak currents of 350 to 600 A, base currents of 30 to 100 A, and between 1 peak (start of start to peak top to end of rise).

`` Steel plate strength 490 MPa or more ''

The greatest effect of the MIG welding method in the pure Ar atmosphere is that no slag is generated in the weld without using valuable metal resources and greenhouse gases added to the welding wire. In order to obtain the advantage, it can be applied universally without requiring any limitation on the base metal. Moreover, the effect of raising the fatigue strength of a welded joint can also be acquired by further limiting the amount of graphite which is one of the components of this wire. The reason why the residual stress occurring in the steel heat affected zone due to transformation expansion of the weld metal can be reduced is that the stress generated on the steel side when the weld metal expands also becomes a compressive stress due to reaction force to the weld metal. For this reason, it can be expected that the higher strength steel plate which can expect a higher reaction force, the larger the improvement of a fatigue characteristic. This is because when the steel strength is low, the reaction force is inevitably lowered, and there is a risk of returning to the tensile stress state again by thermal contraction after the transformation ends. If tensile stress remains, fatigue strength improvement cannot be expected. Therefore, 490 MPa was set as a minimum which can expect fatigue strength improvement. Moreover, it does not need to specifically limit about an upper limit. As for the strength of the thin steel sheet currently used in general, about 1500 MPa is the maximum, if it is a steel plate to this degree, the fatigue strength can be improved by the wire of this invention, and also in terms of a joint tensile strength, Overmatching can be achieved.

<Example>

As the test 1, butt welding as shown in FIG. 1 was performed using the SS400 steel plate of 12 mm of plate | board thickness. The composition of the steel strip for flux cored wire used for this test in Table 1 was shown, and the flux cored wire of the composition shown in Table 2a, 2b, 3a, 3b, 4a, and 4b was manufactured using this as an outer skin. However, Comparative Examples No. 65 and 660,000 are solid wires 11. In addition, each element basically states that it is positively added, and "-" assumes no addition handling. In addition, although P and S are both impurity handling, the analysis value is customarily disclosed. In addition, although content of each element shows the ratio per total mass of a wire, only iron is the ratio per mass of flux. As an implementation condition of the test 1, the shielding gas was made into JISK1105 Class 1 Ar gas, and the wire diameter was 1.2 mm, the wire protrusion length 15 mm, the welding current 280A, and the welding speed 40 cm / min. The polarity was reverse polarity (plus wire and minus base material), and the welding current was made into both a normal DC constant voltage characteristic and a pulse welding machine.

For the evaluation, current and voltage were measured continuously, and the arc instability did not occur once per minute. ◎, the arc instability occurred more than once or four times per minute. When instability occurred and the instability of the arc of 9 times or more per minute (triangle | delta) of the lower limit was made into welding, it was set as x as unwelding. Moreover, in the case of a pulse welding machine, the amount of sputtering was also measured, and 0.5 g / min or less was favorable, (circle), and 0.50 g / min or more and 1.00 g / min or less were made into (circle) and 1.00 g / min or more as x as a large sputter | spatter. In addition, the shape of the weld bead was evaluated for function. Although unstable parts, such as (circle) and a humping tinge, are rare in the edge of a weld bead and are very excellent in linearity, it was made into x as impossible that it was judged that (circle) and a weld bead meandered practically a level which is not a problem. In addition, when the crack of the weld bead was confirmed and there was no crack at all, the case where (circle) and one part cracks were seen per 1m of welding length was evaluated as (triangle | delta) and the case where two or more parts cracks were seen as impossible as x. These evaluation results are shown in Tables 6a, 6b and 7. In Table 6a, 6b, and 7, the result using a DC constant voltage characteristic machine is "P nothing", and the result using a pulse welding machine is shown as "P oil".

Next, as test 2, steel sheets of the composition shown in Table 5 were piled up and fillet-welded as shown in FIG. 4 using the welding wire of evaluation (circle) and (circle) in the conditions using the pulse welding machine of test 1, and the fatigue test was done. . As welding conditions of the test 2, the shielding gas shall be Ar gas of JISK1105 grade 2, the shield gas flow rate shall be 15 liters / minute, the wire diameter is 1.2 mm, the wire protrusion length 15 mm, the welding current 270A, the welding speed 120 It was set to cm / min, and the advance retreat angle of the torch was 0 degrees (perpendicular to the welding line). In the fatigue test, the fatigue test piece 231 shown in FIG. 5 was taken from the welded work, and a double vibration plane bending fatigue test was performed. (Frequency 25 Hz, sine wave stress) The time intensity at 10 ⁷ times was defined as the fatigue strength and compared. Less than 200 MPa does not have a fatigue strength improvement effect, and sets it as (circle) and 200 MPa or more as an effect, and shows the result in Table 6a, 6b, and 7.

Nos. 1 to 53 are examples in which the wire composition satisfies the scope of the present invention containing 0.16 to 2.00% by mass of graphite per mass of wire in the flux and 20% by mass or more of iron per mass of the flux. In pure Ar shield gas, these flux cored wires are stable in arc, have few sputters, and are excellent in linearity of weld beads. As a result, welding with stability such as CO ₂ gas shield welding or Ar + CO ₂ gas shield welding is possible. Also, do not use the CO ₂ gas, which can contribute to the prevention of global warming.

Among Examples, Examples No. 1 to 20, 22 to 35, and 38 to 53 contain 0.03 to 5.00% by mass of at least one selected from the group consisting of Ti and Zr per mass of the wire. In these embodiments, the arc is more stable and more suitable.

Especially, Examples No. 1-20, 23-25, and 27-35 contain C: 0.16-2.00 mass% per wire total mass, and also Si: 2.00 mass% or less, Mn: 10.00 Al: 1.00 mass% or less, Mg: 1.00 mass% or less, Ni: 3.00 mass% or less, Cr: 3.00 mass% or less, Nb: 3.00 mass% or less, V: 3.00 mass% or less, Mo: 3.00 mass % Or less, Cu: 3.00 mass% or less, B: 0.0200 mass% or less, rare earth metal (REM): 0.50 mass% or less, F: 0.50 mass% or less, Ca: 0.50 mass% or less, K, Na and / or Li: At least 1 sort (s) chosen from the group which consists of a total amount of 1.00 mass% or less, and an impurity is a wire regulated to P: 0.030 mass% or less and S: 0.030 mass% or less. In these examples, the shape and crack resistance of the beads are better and more suitable.

Moreover, especially in Example No. 2, 6-8, 10-15, 17, 19, 20, 23-25, and 27-35, the wire which regulated C to 0.45-2.00 mass% per wire total mass to be. In these examples, the joint fatigue strength is high and more suitable.

No. 54-66 is a comparative example.

Comparative Examples Nos. 54 to 58 have a small amount of graphite and correspond to a flux cored wire for general CO ₂ gas shield welding or Ar + CO ₂ gas shield welding. Since there is little graphite, an arc is not stabilized in pure Ar atmosphere, welding bead meanders, sputter | spatter 171 generate | occur | produces in a large quantity, and it is substantially impossible to weld as known conventionally.

In Comparative Example No. 59, the content of graphite and C was excessive, the arc force was too strong, a large amount of sputter occurred, and cracking also occurred.

Comparative Examples Nos. 60 to 62 were satisfied with the amount of graphite, but the iron content in the flux was too small, the arc was unstable, and the weld beads meandered, and a large amount of sputter 171 was generated.

Comparative Example No. 63 is one of commercially available flux cored wires, and the graphite amount and the iron ratio are both too small, the arc is not stabilized at all, the weld bead meanders, and a large amount of sputter is generated. It is impossible to weld.

In Comparative Example No. 64, the content of graphite and C is excessive and the iron content is too low. Again, the arc was unstable, a large amount of sputter occurred, and cracks also occurred.

Comparative Examples No. 65 and 66 are solid wires. In solid wires, neither graphite nor iron could be added while maintaining their shape, so welding in pure Ar atmosphere was impossible.

In addition, when the table does not, but the welding using an Ar 90 volume% + CO ₂ 10 volume% shielding gas, the wire of Example No.30 substrate, and poor stability of the arc fumes are generated in a large amount, and Joint fatigue strength did not improve below 200 MPa. Therefore, it was confirmed that pure Ar shield gas is optimal for this welding wire, and pure Ar gas wire is also suitable for improving joint fatigue strength.

In the present invention, that is, MIG welding using pure Ar, since there is no oxygen source other than the wire component, even if graphite is added in a large amount, the amount of fume is very small and almost no slag is generated. When C is raised to 0.45 mass% or more, the stability of an arc can be improved. In addition, the Ms point decreases as the amount of oxygen in iron decreases. In this means, since the amount of oxygen in the weld metal is very small, a few 10 ppm, the effect of C can be further enhanced, and the Ms point is further lowered to increase the fatigue strength. In addition, there is a secondary effect that hardly causing solidification cracking because there is almost no oxide serving as an inclusion.

1 is a perspective view schematically showing an example of test 1.

2 (a) is a schematic diagram showing a welding state using a conventional welding wire, (b) is a schematic diagram showing a welding state using the welding wire of the present invention.

Figure 3 (a) is a top view and a side view showing the bead shape after performing the pure Ar shield gas MIG welding using a conventional welding wire, (b) is a pure Ar shield gas using the welding wire of the present invention It is a top photograph and a side photograph which show the bead shape after MIG welding.

4 is a side view schematically showing an example of test 2.

5 shows a welded base material as a test piece used in Test 2, (a) is a plan view, and (b) is a side view.

Claims (7)

A flux cored wire used for MIG welding using pure Ar shield gas, which is made by filling a flux in a steel sheath, wherein the flux contains 0.16 to 2.00 mass% of graphite per total mass of wire, and contains iron powder. Flux cored wire containing at least 20% by mass per mass of flux. The method of claim 1, The flux-cored wire which contains 0.03 to 5.00 mass% per mass of wire further at least 1 sort (s) chosen from the group which consists of Ti and Zr in the said flux. The method of claim 1, C: 0.16-2.00 mass% is further contained per wire total mass, Si: 2.00 mass% or less, Mn: 10.00 mass% or less, Al: 1.00 mass% or less, Mg: 1.00 mass% or less, Ni: 3.00 Mass% or less, Cr: 3.00 mass% or less, Nb: 3.00 mass% or less, V: 3.00 mass% or less, Mo: 3.00 mass% or less, Cu: 3.00 mass% or less, B: 0.0200 mass% or less, rare earth metal (REM ): 0.50% by mass or less, F: 0.50% by mass or less, Ca: 0.50% by mass or less, K, Na, and Li: totally at least one selected from the group consisting of 1.00% by mass or less, and as an impurity, Flux cored wire regulated to P: 0.030 mass% or less, S: 0.030 mass% or less. The method of claim 3, wherein Flux cored wire, wherein C is 0.45-2.00 mass% per mass of wire. Using the flux cored wire according to claim 1, using pure or Ar of JIS K 1105 as the shielding gas, using the wire as an anode, an arc is generated between the base metal of the cathode, MIG arc welding method to MIG welding. The method of claim 5, wherein A MIG arc welding method using a pulse power source as a power source for forming the arc. The method of claim 5, wherein The base material is a MIG arc welding method is a steel sheet with a tensile strength of 490 MPa or more.

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