JP5518773B2 - Flux-cored wire for gas shielded arc welding - Google Patents

Description

The present invention relates to a flux-cored wire for gas shielded arc welding used in manufacturing welded structures such as mild steel and 490 N / mm grade ² high-strength steel. This relates to a flux-cored wire for gas shield arc welding (hereinafter referred to as a flux-cored wire) that has improved hot crack resistance, which is a problem in the first pass of welding.

For welding in shipbuilding, TiO ₂ flux cored wire is used, and single-sided joint welding of steel sheets is performed automatically and semi-automatically. FIG. 1 (a) shows the groove shape of a single-sided joint, and FIG. 1 (b) shows an example of the welding situation (in the downward posture). The steel plate 1 is abutted with a groove shape having a groove angle θ and a route interval G, and a ceramic backing material 2 (hereinafter referred to as backing material) is applied to the back surface of the groove to form a back bead 3 by the first layer pass. After that, the joint weld metal 4 is formed by sequentially laminating.

  Welding postures are performed in all orientations, such as downward and vertical, but the first layer pass in single-sided joint welding, particularly in downward orientation, is prone to hot cracking in the center of the bead due to its solidification form. Therefore, the welding current and the welding speed are suppressed, and the groove angle θ and the route interval G of the steel plate 1 are not reduced so much.

  Recently, in order to increase the welding efficiency, when welding speed is increased by increasing the welding current, or by forming a narrow groove shape with a small groove angle θ and route interval G, and welding with a small number of welding passes. However, there is a strong demand for the development of flux-cored wires that are less prone to hot cracking.

  On the other hand, Patent Document 1 and Patent Document 2 propose a flux-cored wire with improved hot cracking resistance by regulating the contents of Sn, B, Bi, and Pb in addition to reducing P and S.

  The applicant previously proposed a flux-cored wire with good hot cracking resistance in which P, S, B, and Bi are reduced in Patent Document 3.

  However, only the reduction of impurities in the flux-cored wire as in the above-described technique does not provide an on-site stable hot crack resistance improvement effect. Especially in a semi-automatic downward posture, the groove angle of the steel sheet is 30-40 ° and the groove shape is narrow, such as a route interval of 3-5 mm, the first layer pass has a welding current of 260 A or more (wire diameter 1.2 mm), welding speed When welding is performed under highly efficient welding conditions of 25 cm / min or more, minute hot cracks may occur in the center of the bead. This is because, as the groove shape is narrower and the welding conditions are higher in current, the arc state and welding speed characteristic of semi-automatic welding are more sensitive to back bead formation. In particular, if the shape of the back bead is non-uniform and a recessed portion is formed on the surface of the bead in the groove, the frequency of occurrence of minute hot cracks increases at that location. Therefore, in order to obtain a stable hot cracking resistance even under high current welding conditions with a groove shape with a narrow groove angle, a flux-cored wire that can be welded to stabilize the arc and form the back bead stably. Is required.

  In addition, P, S contained in the flux-cored wire, and Sn, B, Bi, Pb, which make it easy to generate hot cracks as impurities during solidification, are essential requirements for preventing hot cracks in the first layer pass. However, in all-position welding flux-cored wires, Bi, Pb, and S are components that effectively act on the slag peelability, and B is a component that effectively acts on the impact toughness of the weld metal. Sufficient consideration should be given to the means.

Patent Document 4 proposes a flux-cored wire in which TiO ₂ is lowered and CaO and MgO are contained to increase the basicity of the molten slag and to improve hot cracking resistance by reducing the amount of oxygen. However, metal dripping is likely to occur in an upward or vertical position, and as a flux-cored wire for welding in all positions, there is a tendency to improve the hot cracking resistance and a wide welding condition range and good welding workability can be obtained. is necessary.

JP 2002-137090 A Japanese Patent Laid-Open No. 2003-311476 JP 2006-289404 A Japanese Patent Laid-Open No. 62-151293

  The present invention further improves the hot cracking resistance, which is a problem in the first pass of single-sided joint welding, as well as welding workability such as slag peelability and resistance to metal sag in upward and vertical positions, and the impact of weld metal. An object of the present invention is to provide a flux-cored wire for gas shielded arc welding with good toughness.

The gist of the present invention is that, in a flux cored wire for gas shield arc welding in which a steel outer sheath is filled with flux, C: 0.04 to 0.09%, and Si: 0.3-0.6%, Mn: 2.5-3.1%, provided that Mn / Si: 4.5 or more, Al: 0.1-0.4%, Mg: 0.3-0. _{6%, TiO 2: 5.1~6.5%} , SiO 2: 0.3~0.7%, ZrO 2: 0.1~0.5%, Al 2 O 3: 0.2~0. 5%, the total of Na ₂ O and _{K 2} O: 0.10 to 0.25%, _{however, K 2 O / Na 2 O} : 2.0 or higher, F converted value of the fluorine compounds: 0.03 to 0. 08%, iron powder: 2.0 to 5.0%, P: 0.015% or less, S: 0.010% or less, B: 0.0005% or less, Bi: 0.000 % Or less, FeO converted value of the iron oxide: 0.09% or less, the balance is characterized in that Fe content of the steel sheath, Fe content of the alloy iron and inevitable impurities.

  Further, the present invention provides a flux-cored wire for gas shielded arc welding, which has Cu plating of 0.10 to 0.60 μm on the wire surface.

  According to the flux-cored wire for gas shielded arc welding of the present invention, even when the first layer pass of the groove-shaped single-sided joint welding with a narrow groove angle is performed under high current welding conditions, high-temperature cracking is unlikely to occur, and Since various welding workability and the weld metal impact toughness that should be possessed as the all-position welding wire are good, it is possible to improve the efficiency of welding and improve the quality of the welded portion.

It is the schematic diagram shown in order to demonstrate the groove | channel shape and welding condition of downward single-sided joint welding, (a) is a figure before welding, (b) is a figure which shows the condition after welding.

  The inventors have made various types of flux-cored wires as prototypes, and details of the effects of various components on hot crack resistance in narrow groove single-sided joint welding, welding workability in all-position welding, and impact toughness of weld metal It was examined.

  As a result, in welding in the first layer pass with a narrow groove, if the arc is not stable, or if the molten slag does not follow well and the molten slag precedes the arc point or retracts too much, the welding operator Because the welding speed is changed instantaneously in an attempt to move the arc point to the optimal position for taking out the back bead, the back bead and the bead in the groove have a shape with irregularities in the longitudinal direction, and the dent It has been found that the slag generation state and arc stability are important because small hot cracks are likely to occur in the part.

In addition, C, Si, Mn, Al, Mg, P, S, B, Bi, FeO, welding workability in all-position welding and one-sided as components affecting hot crack resistance in single-sided joint welding and impact performance of weld metal TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ acting as arc stabilizers and Na ₂ O, K ₂ O acting as arc stabilizers to improve welding workability in the first layer pass, and slag forming agents, respectively In order to stabilize the arc by containing an appropriate amount and further stabilizing the wire feedability, stabilizing the electrical conductivity, and reducing the amount of chip wear, the intended purpose was achieved by applying Cu plating to the wire surface. It is.

  The reasons for limiting the components of the flux-cored wire of the present invention will be described below. Hereinafter, the mass% in the composition is simply described as%.

C: 0.04 to 0.09%
If C is less than 0.04%, the strength of the weld metal decreases. On the other hand, if C exceeds 0.09%, the strength of the weld metal becomes too high and the impact toughness decreases.

Si: 0.3-0.6%
In order to ensure the strength and impact toughness of the weld metal, Si is contained in a total of 0.3% or more of the flux and the skin component. If Si is less than 0.3%, the strength and impact toughness of the weld metal decrease. On the other hand, if Si exceeds 0.6%, the impact toughness of the weld metal decreases.

Mn: 2.5-3.1%
Mn is contained in a total of 2.5 to 3.1% of the flux and the outer skin component in order to ensure hot cracking resistance, weld metal strength and impact toughness, in particular to ensure impact toughness of the single-sided joint weld metal. If Mn is less than 2.5%, hot cracking tends to occur. Moreover, the impact toughness of the single-sided joint weld metal is lowered. On the other hand, if Mn exceeds 3.1%, the strength of the weld metal becomes too high.

Mn / Si: 4.5 or more In order to ensure the impact toughness of the weld metal, particularly the single-sided joint weld metal, the ratio Mn / Si of Mn / Si is set to 4.5 or more. When Mn / Si is less than 4.5, the impact toughness of the single-sided joint weld metal decreases.

Al: 0.1 to 0.4%
Al is a total of the flux and the skin component, and is contained by 0.1% or more, thereby reducing the oxygen content of the weld metal and improving the impact toughness of the weld metal. On the other hand, when Al exceeds 0.4%, Si and Mn are yielded in the weld metal, the strength is increased, and the impact toughness is lowered. Moreover, since Al ₂ O ₃ which is a deoxidation product increases excessively in the molten slag, the followability of the molten slag is not stable in narrow groove single-sided joint welding, and irregularities occur in the back bead, resulting in high temperatures in the recesses. Cracks are likely to occur.

Mg: 0.3-0.6%
By containing 0.3% or more of Mg, the oxygen content of the weld metal is reduced and impact toughness is improved. On the other hand, when Mg exceeds 0.6%, MgO which is a deoxidation product is excessively increased in the molten slag, and metal dripping is likely to occur in the vertical posture welding. Further, in the first layer pass of the narrow groove single-sided joint welding, the followability of the molten slag becomes unstable, and irregularities are generated in the back bead, and hot cracks are likely to occur in the concave portions.

TiO _2: 5.1~6.5%
If TiO ₂ is less than 5.1% using rutile, titanium slag, etc. as a raw material, the viscosity of the molten slag is insufficient, and metal dripping is likely to occur in an upward or vertical position, and the bead shape becomes convex. Welding workability as a posture welding wire deteriorates. Moreover, the amount of slag generation is insufficient, and the slag peelability deteriorates in vertical downward welding. On the other hand, if TiO ₂ exceeds 6.5%, the amount of slag generated is too large, and the slag followability becomes unstable in the first layer pass of narrow groove single-sided joint welding, resulting in unevenness in the back bead and high temperature in the recess. Cracks are likely to occur.

SiO _2: 0.3~0.7%
If silica ₂ or less is less than 0.3% using silica sand, zircon sand or the like as a raw material, the slag encapsulation state is poor, and slag peelability, bead shape, and appearance are poor in each position welding. On the other hand, when SiO ₂ exceeds 0.7%, solidification of the molten slag is delayed and metal dripping is likely to occur during upward and vertical posture welding. Further, in the first layer pass of single-sided joint welding, the followability of the molten slag becomes unstable, unevenness is generated in the back bead, and high temperature cracking is likely to occur in the recess.

ZrO ₂ : 0.1 to 0.5%
When ZrO ₂ is less than 0.1% using zircon sand, zircon oxide or the like as a raw material, the metal drooping resistance of vertical position welding and the bead shape of horizontal fillet welding are deteriorated. Further, in the first layer pass of the narrow groove single-sided joint welding, the molten slag is likely to precede, the back bead is not easily generated, and hot cracking is likely to occur. On the other hand, when ZrO ₂ exceeds 0.5%, the slag removability deteriorates.

Al ₂ O ₃ : 0.2 to 0.5%
Al ₂ O ₃ improves the bead shape of vertical improvement welding, but if it is less than 0.2%, the effect is lost, and if it exceeds 0.5%, the slag peelability of the first layer pass of narrow groove single-sided joint welding Deteriorates and the hot cracking resistance also deteriorates.

Total Na ₂ O and _{K 2} O: _0.10~0.25%
If the total content of Na ₂ O and K ₂ O is less than 0.10% using sodium titanate, potash feldspar, etc. as a raw material, the arc state becomes unstable and the bead is prone to dripping during upward or vertical welding. The shape becomes defective. Further, in the first layer pass of the narrow groove single-sided joint welding, the arc state is unstable, so that the followability of the molten slag becomes unstable, and the back bead is uneven, and the recess is likely to be hot. On the other hand, if the total of Na ₂ O and K ₂ O exceeds 0.25%, the fluidity of the molten slag becomes excessive, metal sag is likely to occur during upward and vertical welding, and the slag peelability is also degraded. To do. Furthermore, in the first layer pass of narrow groove single-sided joint welding, the followability of the molten slag is unstable, and high temperature cracking is likely to occur.

K ₂ O / Na ₂ O: 2.0 or more When K ₂ O / Na ₂ O is less than 2.0, the arc is excessively concentrated, the followability of the molten slag becomes unstable, and the back bead has irregularities. This is likely to cause high temperature cracks in the recesses.

F conversion value of fluorine compound: 0.03 to 0.08%
If the F-converted value of a fluorine compound such as sodium fluoride or potassium silicofluoride is less than 0.03%, the arc concentration is weak and metal sag tends to occur during vertical downward welding. In addition, the back bead is hard to come out in the first layer pass of the narrow groove single-sided joint welding, and the flowability of the molten slag is insufficient, the molten slag followability is not stable, and the back bead is uneven and high temperature cracks are generated in the recess. It becomes easy to do. On the other hand, if the F-converted value of the fluorine compound exceeds 0.08%, the arc blowing is too strong, the flowability of the molten slag becomes excessive, the followability of the molten slag is unstable, and the back bead has irregularities. It arises and it becomes easy to generate | occur | produce a hot crack in a recessed part.

Iron powder: 2.0-5.0%
In the flux-cored wire, iron powder has the effect of increasing the welding speed with the arc stabilizer. If the iron powder is less than 2.0%, the arc becomes unstable, and hot cracks are likely to occur along with the irregularities of the bead and the back bead in the narrow groove single-sided joint weld. On the other hand, if it exceeds 5.0%, the spraying of the arc becomes too weak to form a good back bead, and high temperature cracking is likely to occur.

P: 0.015% or less, S: 0.010% or less P and S are components contained as inevitable impurities from the flux raw material and the steel outer shell, but P is selected depending on the selection of the steel outer shell and the flux raw material. Limiting to 0.015% or less and S to 0.010% or less is extremely effective for hot crack resistance.

B: 0.0005% or less, Bi: 0.0005% or less B and Bi are contained as impurities and cause high-temperature cracking in the first layer pass of narrow groove single-sided joint welding. In order to prevent this, it is preferable that B and Bi are small, and the total of the flux and the steel outer skin component is limited to 0.0005% or less.

FeO equivalent value of iron oxide: 0.09% or less Iron oxides such as Fe ₂ O ₃ and FeO inevitably contained in mill scale, hematite and TiO ₂ raw materials have a bead shape in horizontal fillet welding. Although good, the hot crack resistance of the first layer pass of narrow groove single-sided joint welding and the metal dripping resistance of upward and vertical position welding are deteriorated. In addition, the impact toughness of the weld metal is reduced. Therefore, the FeO equivalent value of iron oxide is limited to 0.09% or less.

Cu plating on wire surface: 0.10 to 0.60 μm
Cu plating on the surface of the wire stabilizes the arc by improving the wire feedability and the electrical conductivity at the tip portion, and forms a good bead shape, particularly in the first layer pass of the narrow groove single face joint welding. If the Cu plating thickness on the wire surface is less than 0.10 μm, the long-time welding will deteriorate the electrical conductivity due to wear of the tip and the arc will not stabilize, and the back will be the first layer pass of narrow groove single-sided joint welding. Unevenness is generated in the bead, and hot cracking is likely to occur in the recess. On the other hand, if it exceeds 0.60 μm, precipitation at the final freezing point increases, so that hot cracking is likely to occur.

  The flux-cored wire of the present invention is filled with a flux in a soft steel or alloy steel outer shell having good wire drawing workability after filling the flux, and then a predetermined wire diameter (1.0-1. 6 mm) or manufactured by subjecting the wire surface to Cu plating before reaching a predetermined wire diameter. The cross-sectional structure of the wire is not particularly limited.

The welding shield gas is generally CO ₂ gas, but a mixed gas such as Ar—CO ₂ can also be used.

  Hereinafter, the effect of the present invention will be described in more detail with reference to examples.

  After filling a mild steel pipe having the components shown in Table 1 with flux, the diameter was reduced and various types of seamless-type flux-cored wires having a wire filling rate of 13 to 17% and a wire diameter of 1.2 mm shown in Table 2 were produced. Some of the prototype wires were subjected to Cu plating on the wire surface before reaching a predetermined wire diameter.

Using these prototype wires, a single-sided joint weld specimen having the shape shown in FIG. 1 (steel type: KD36 steel, plate thickness t: 20 mm, width 400 mm, length 500 mm, groove angle θ: 30 °, route interval G: Applying the backing material (Al ₂ O ₃ —SiO ₂ —MgO system) to 5 mm, restraint on the back surface (3 locations), under the welding conditions shown in Table 3, semi-automatic downward posture, high temperature resistance of the first layer pass A cracking test was conducted. The occurrence of hot cracks in the first layer pass was determined by an X-ray transmission test.

Next, it is sequentially laminated by semi-automatic downward welding according to the welding conditions shown in Table 3, and the welding workability is observed, and from the portion where there is no crack in the X-ray transmission test, a tensile test is performed from the center of the plate thickness according to JIS Z3111 after welding A piece (A1) and an impact test piece (No. 4) were collected, and a weld metal tensile test and an impact test were performed. In addition, the tensile test made the tensile strength 520-620 N / mm < ² > favorable. In the impact test, Charpy absorbed energy at 0 ° C. was 47 J or more.

  In addition, SM490B steel with a plate thickness of 12 mm, width of 150 mm, and length of 450 mm is temporarily assembled into a T-shape, and metal sag resistance and slag that are particularly problematic in upward and vertical (upward and downward) posture welding The peelability was evaluated. These results are summarized in Table 4.

  The wire symbols W1 to W8 in Tables 2 and 4 are examples of the present invention, and the wire symbols W9 to W29 are comparative examples. In the wire symbols W1 to W8 according to the present invention, since the components of the flux-cored wire are all appropriate, there is no occurrence of hot cracking that becomes a problem in the first layer pass in single-sided joint welding, and the slag peelability and The tensile strength and absorbed energy of the weld metal were also good results. In addition, the welding workability such as metal sag resistance and slag peelability, which are problems in upward and vertical position welding, was also satisfactory, and the results were extremely satisfactory. The wire symbols W1, W2, W4, W6, and W7 in which Cu plating was applied to the wire surface had an extremely stable arc.

  In the comparative example, the wire symbol W9 had a low C, so the tensile strength of the weld metal was low. Moreover, since there was much Mg, metal dripping generate | occur | produced by the upward and vertical posture welding. Furthermore, in the first layer pass of single-sided joint welding, the followability of the molten slag was unstable, the back bead shape was uneven, and high temperature cracking occurred.

  Since the wire symbol W10 has a large amount of C, the tensile strength of the weld metal was high and the absorbed energy was low. Moreover, since there is much P, the high temperature crack generate | occur | produced in the first layer pass of single-sided joint welding.

  Since the wire symbol W11 has a small amount of Si, the tensile strength and absorbed energy of the weld metal were low. Moreover, since there was much S, the hot crack generate | occur | produced in the first layer pass of the single-sided joint welding.

  Since the wire symbol W12 has a large amount of Si, the absorbed energy of the weld metal was low. Moreover, since there is much B, the high temperature crack generate | occur | produced in the first layer pass of single-sided joint welding.

  Since the wire symbol W13 has a small amount of Mn, hot cracking occurred in the first layer pass of single-sided joint welding. Moreover, the absorbed energy of the weld metal was low.

  Since the wire symbol W14 has a large amount of Mn, the tensile strength of the weld metal was high. Moreover, since there was much iron powder, the spraying of the arc became too weak to form a good back bead and hot cracking occurred.

  Since the wire symbol W15 has a small Mn / Si, the absorbed energy of the weld metal was low.

Since the wire symbol W16 has a small amount of Al, the absorbed energy of the weld metal was low. Further, since the total amount of Na ₂ O and K ₂ O was small, the arc state was unstable, hot cracking occurred in single-sided joint welding, and metal sagging occurred in upward and vertical position welding.

Since the wire symbol W17 has a large amount of Al, the followability of the molten slag is unstable in the first layer pass of single-sided joint welding, the back bead shape is uneven, hot cracking occurs, and the tensile strength of the weld metal is high. Further, since ZrO ₂ is large, the slag removability was poor in each position welding.

Since the wire symbol W18 has a small amount of Mg, the absorbed energy of the weld metal was low. Further, the metal sag occurs in an upward and vertical position welding because Na 2 _O and K _{2 O} Total many of the slag peeling properties were poor. Further, in the first layer pass of single-sided joint welding, the followability of the molten slag was unstable, the back bead shape was uneven, hot cracking occurred, and the slag peelability was poor.

Since the wire symbol W19 has a large amount of Bi, hot cracking occurred in the first layer pass of single-sided joint welding. Further, workability vertical upward advance welding is decreased because Al ₂ O ₃ is less.

In the wire symbol W20, since K ₂ O / Na ₂ O was small, the followability of the molten slag was unstable in the first layer pass of single-sided joint welding, the back bead shape was uneven, and hot cracking occurred.

  With the wire symbol W21, metal dripping occurred in vertical downward welding because the F-converted value of the fluorine compound was small. Also, in the first layer pass of single-sided joint welding, the followability of the molten slag was unstable, the back bead shape was uneven and hot cracking occurred.

  The wire symbol W22 has a large F-converted value of the fluorine compound, so the arc blowing is too strong. In the first pass of single-sided joint welding, the followability of the molten slag is unstable, the back bead shape is uneven, and hot cracking occurs. Occurred.

  Since the wire symbol W23 has less iron powder, the arc is unstable, welding workability in upward and vertical position welding is poor, and the bead and back bead in the narrow groove single-sided joint weld are uneven and high temperature Cracking occurred.

  Since the wire symbol W24 has many FeO equivalent values of iron oxide, metal dripping occurred in upward and vertical posture welding. In addition, hot cracking occurred in narrow groove single-sided joint welding, and the absorbed energy of the weld metal was also low.

Since the wire symbol W25 has a small amount of TiO ₂ , metal sag is generated in upward and vertical position welding, and the bead shape is poor. In vertical downward welding, the slag peelability is also poor. Moreover, since Cu plating on the wire surface was thick, high temperature cracking occurred in narrow groove single-sided joint welding.

The wire symbol W26 has a large amount of TiO ₂ , so the amount of slag generated is too much, the slag peelability is poor and the slag followability becomes unstable in the first layer pass of narrow groove single-sided joint welding, and the back bead becomes uneven and the temperature is high. Cracking occurred. Further, the bead shape and the slag removability since SiO ₂ is small metal sag in an upward and vertical position welding occurred was poor.

The wire symbol W27 has a large amount of SiO ₂ , so metal dripping occurs in upward and vertical position welding and the bead shape is poor, and in the first layer pass of single-sided joint welding, the followability of the molten slag is unstable, The back bead shape was uneven and hot cracking occurred.

Since the wire symbol W28 has a small amount of ZrO ₂ , metal dripping occurred during upward and vertical posture welding, resulting in a poor bead shape. Also, in the first layer pass of single-sided joint welding, the followability of the molten slag was unstable, the back bead shape was uneven and hot cracking occurred.

Since the wire symbol W29 has a large amount of Al ₂ O ₃ , the slag peelability of the first layer pass of the narrow groove single-sided joint welding was poor, and hot cracking also occurred.

1 Steel plate 2 Backing material 3 Back bead 4 Weld metal

Claims (2)

In the flux-cored wire for gas shield arc welding formed by filling the steel outer shell with flux,
C: 0.04 to 0.09%,
Si: 0.3-0.6%
Mn: 2.5 to 3.1%
However, Mn / Si: 4.5 or more,
Al: 0.1 to 0.4%,
Mg: 0.3-0.6%
TiO _2: 5.1~6.5%,
SiO _2: 0.3~0.7%,
ZrO ₂ : 0.1 to 0.5%,
Al ₂ O ₃ : 0.2 to 0.5%,
Total of Na ₂ O and K ₂ O: 0.10 to 0.25%,
_{However, K 2 O / Na 2 O} : 2.0 or more F converted value of the fluorine compounds: from 0.03 to 0.08%,
Containing iron powder: 2.0-5.0%, and
P: 0.015% or less,
S: 0.010% or less,
B: 0.0005% or less,
Bi: 0.0005% or less,
FeO equivalent value of iron oxide: 0.09 or less,
The balance consists of the Fe content of the steel sheath, the Fe content of the alloy iron, and inevitable impurities, and a flux-cored wire for gas shielded arc welding.   The flux-cored wire for gas shielded arc welding according to claim 1, wherein the wire surface has Cu plating of 0.10 to 0.60 μm.

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