KR20090026070A - Flux-cored wire for gas-shielded arc welding - Google Patents

Abstract

Flux cored wire for gas shield arc welding is provided to make weld metal with a superior low temperature toughness as to the large heat input welding. If the content of Mg is [Mg] and the content of Mg0 is [Mg0], Mg0 satisfies the relation of [MgO] + [Mg] x1.66<=2.5 mass % about the content of Mg and Al<= 0.5 mass % are satisfied per whole mass. If the content of Al is [Al] and the content of Al2O3 is [Al2O3], [Al2O3] + [Al] x1 about the content of Al 89: al2O3 is contained in order to satisfy the relation of 1.0 mass % through 0.5.

Description

Flux cored wire for gas shield arc welding {FLUX-CORED WIRE FOR GAS-SHIELDED ARC WELDING}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux cored wire used for gas shielded arc welding of a welded object made of mild steel and tensile strength of 490 MPa class high tensile strength steel, and the flow of molten metal in vertical upward welding. It is possible to perform good welding with high welding current without dropping, and also has excellent high temperature crack resistance at the first layer in single-sided welding, and also has excellent low temperature toughness in high heat input welding. A flux cored wire for gas shielded arc welding, from which metal can be obtained.

Flux cored wire for gas shielded arc welding is mainly used for welding of welded material consisting of mild steel and 490MPa class high tensile steel, and has better bead appearance and welding workability and better welding efficiency than solid wire. In the year, its usage is increasing.

By the way, the flux cored wire for gas shielded arc welding has a higher welding speed than the solid wire, and thus tends to cause high temperature cracking (solidification cracking) in the superlayer forming the back side beads in single side welding. . In addition, since the wire contains a large amount of metal oxides such as rutile, and they cannot rise completely as slag during welding, and remain as metal inclusions in the weld metal, the welding heat input in the high heat input welding such as 30 to 60 kJ / cm − It was difficult to secure a weld metal having good toughness at a low temperature such as 20 ° C. Moreover, in the vertical upward welding, when welding by the same electric current as the downward welding, there existed a tendency for molten metal to flow easily (bead tends to flow down).

The flux cored wire for gas shielded arc welding, which is designed to simultaneously increase the high current in the vertical upward welding, improve the high temperature crack resistance of the superlayer in single-sided welding, and improve the low temperature toughness in the high heat input welding. It has not been proposed conventionally.

Therefore, the subject of this invention is the flux cored wire used for the gas shielded arc welding of the to-be-welded object which consists of mild steel and 490 MPa class high tensile strength steel, and is good welding by solid-state welding current, without dripping of molten metal in a vertical upward welding. Flux core for gas shielded arc welding, which can be carried out and has excellent high temperature cracking resistance in the first layer in single-sided welding, and furthermore, a weld metal excellent in low temperature toughness in high heat input welding with increased deposition amount. To provide the wire.

In order to solve the said subject, this invention seeks the following technical means. That is, a flux cored wire for gas shielded arc welding formed by filling a flux in a mild steel or alloy steel shell, wherein TiO ₂ : 4.5 to 7.0% by mass, Ti: 0.11 to 0.29% by mass, and Mg: 0.30 to 0.70 mass%, C: 0.02 to 0.08 mass%, Si: 0.35 to 0.75 mass%, Mn: 2.20 to 2.85 mass%, and B: 0.002 to 0.010 mass%, and the content of said Mg is [Mg] If the content of MgO is [Mg0], Mg0 satisfies the relationship of [Mg0] + [Mg] x 1.66? 2.5 mass% with respect to the content of Mg.

In the flux-cored wire for gas shielded arc welding, Al ≤ 0.5 mass% is further satisfied per total mass of the wire, the content of Al is referred to as [Al], and the content of Al ₂ O ₃ is set to [Al]. ₂ O ₃ ], it is preferable to contain Al ₂ O ₃ so as to satisfy the relation of [Al ₂ O ₃ ] + [Al] x 1.89: 0.5 to 1.0 mass% with respect to said Al content.

In addition, each content of said Ti, Mg, Al does not contain Ti, Mg, Al which exists as an oxide, respectively.

In the said flux cored wire for gas shielded arc welding, it is preferable to further contain Ni: 0.2-1.0 mass% per wire total mass.

According to the present invention having such a feature, in a flux cored wire used for gas shielded arc welding of a welded object made of mild steel and 490 MPa class high tensile strength steel, good welding with a solid-state welding current without dripping of molten metal in vertical upward welding. Flux core for gas shielded arc welding, which can provide a weld metal excellent in high temperature cracking resistance in the first layer in single-sided welding and furthermore, in a high heat input welding having a higher deposition amount. Drawing wire can be provided.

Hereinafter, the present invention will be described in detail.

In order to solve the above problems, first, the present inventors, and reduce the increase in the amount of slag formed mainly of rutile (TiO ₂₎ for flow of molten metal in the vertical upward welding to prevent the falling. However, although the fall of the molten metal was eliminated by this, the high temperature crack resistance in the initial layer in downward single side welding fell.

Therefore, the cause and countermeasures were reviewed, and the reason why the high temperature cracking was easily caused was found to be due to the increase in the amount of oxygen in the weld metal, and the means for reducing the amount of oxygen while maintaining the amount of slag was examined. .

As a result, TiO ₂ , SiO ₂ from the beginning Instead of adding the required amount of slag generating agent such as the above, by adding an alloy component that turns into a slag component during welding, the amount of oxygen in the weld metal is reduced while improving the high temperature crack resistance while maintaining the slag amount. Usually, although Mn, Si, Al, Ti, Mg, etc. are used as a deoxidizer for a flux cored wire, it turned out that addition of Ti and Mg is effective in this invention.

As for Ti, by reducing the amount of oxygen in the weld metal by acting as a deoxidizer during welding, the high temperature crack resistance at the initial layer in single-sided welding is improved, and the generated TiO ₂ acts as a slag component. The effect of preventing the molten metal from falling off is exhibited. Furthermore, Ti remains slightly in the weld metal, whereby the structure of the weld metal can be refined to improve the low temperature toughness in the high heat input welding.

On the other hand, with respect to the Mg, the effect of reducing the amount of oxygen in the weld metal is large because almost all of it acts as a deoxidizer without remaining in the weld metal, and therefore, the effect of improving the high temperature crack resistance in the first layer in single side welding. Is large. In addition, Mg0 produced by the deoxidation action has an effect of promoting the deoxidation action by changing the equilibrium state of oxygen and the deoxidizer.

In addition, by appropriately defining the contents of Mg, MgO, C, Si, Mn and B, the low-temperature toughness of the weld metal in high heat input welding of about 30 to 60 kJ / cm can be improved.

On the other hand, the flux cored wire for gas shielded arc welding of the present invention is CO ₂ as a shield gas. Using gas. Moreover, the flux content rate is suitable for the range of 10-18 mass% (to the wire total mass).

Next, the reason for limitation of the composition and numerical value of the flux cored wire for gas shielded arc welding of this invention is demonstrated. Each content range is the mass% per wire total mass.

[TiO ₂ : 4.5-7.0 mass%]

TiO ₂ acts as a slag generating agent (slag forming agent). If the content of TiO ₂ is less than 4.5% by mass, the amount of slag that can be supported cannot be ensured so as not to flow down the molten metal in vertical upward welding, and the bead shape becomes poor. On the other hand, when it exceeds 7.0 mass%, the amount of oxygen in a weld metal will increase, the high temperature crack resistance at the top layer in single side welding will fall, and also toughness at low temperature will fall. Therefore, the content of TiO ₂ is 4.5 to 7.0% by weight.

[Ti: 0.11 to 0.29 mass%]

As described above, Ti acts as a deoxidizer to reduce the amount of oxygen in the weld metal, thereby improving the high temperature crack resistance at the initial layer in single-sided welding, and in addition, TiO ₂ generated acts as a slag component and is vertical. It has the effect of preventing the fall of molten metal in upward welding. In addition, Ti remains slightly in the weld metal, thereby making it possible to refine the structure of the weld metal to improve the toughness at low temperatures in the high heat input welding. In order to exhibit such an effect, content of Ti is 0.11 mass% or more. On the other hand, when it exceeds 0.29 mass%, the residual amount in a weld metal will become large too much and toughness will fall with an increase of strength. Therefore, content of Ti is made into 0.11-0.29 mass%. In addition, a more preferable upper limit is 0.20 mass% from a viewpoint of making low temperature toughness favorable.

[Mg: 0.30 to 0.70 mass%]

Mg acts as a deoxidizer, reduces the amount of oxygen in the weld metal, improves high temperature crack resistance at the initial layer in single-sided welding, and improves low temperature toughness of the weld metal. If the content of Mg is less than 0.30% by mass, this effect is not obtained. If the content of Mg is more than 0.70% by mass, the hygroscopic resistance of the wire is lowered and the low temperature crack resistance is lowered. Therefore, content of Mg shall be 0.30-0.70 mass%. In addition, from a viewpoint of making low temperature crack resistance favorable, the upper limit is more preferable 0.50 mass%.

[[MgO] + [Mg] × 1.66 ≤ 2.5 mass%]

When Mg0 is added, oxidation is promoted by the change of redox constant, and Mg0 is a component that can further enhance the effect of deoxidation. However, Mg0 is a component which promotes the fall of molten metal. Therefore, it is necessary to contain content of Mg0 so that the relationship of [Mg0] + [Mg] * 1.66 <= 2.5 mass% with respect to content of the said Mg may be included, More preferably, [MgO] + [ It is good to satisfy the relationship of Mg] × 1.66 ≦ 1.7 mass%. With respect to the content of Mg, the molten metal easily flows out of the content of Mg0 when the value of [MgO] + [Mg] × 1.66 exceeds 2.5% by mass. Moreover, in the lateral welding, since the solidification temperature of slag becomes high, coupling | bonding, such as slag curling, also becomes easy to generate | occur | produce. On the other hand, when Mg is oxidized to MgO, the weight is 1.66 times.

[C: 0.02-0.08 mass%]

C is an element necessary to secure the strength of the weld metal. If the content of C is less than 0.02% by mass, the strength of the weld metal cannot be ensured, and the toughness at low temperature also decreases. On the other hand, when it exceeds 0.08 mass%, the intensity | strength of a weld metal will rise and toughness at low temperature will fall. In addition, low temperature crack resistance also decreases, and the amount of sputter generation also increases. Therefore, content of C is made into 0.02-0.08 mass%.

[Si: 0.35-0.75 mass%]

Si acts as a deoxidizer and has the effect of adjusting the strength of the weld metal, and also has the effect of increasing the viscosity of the molten metal to improve vertical upward weldability. These effects are not acquired when content of Si is less than 0.35 mass%. On the other hand, when it exceeds 0.75 mass%, the strength of a weld metal will become high and toughness at low temperature will fall. In addition, low temperature crack resistance and high temperature crack resistance also decrease. Therefore, content of Si is made into 0.35-0.75 mass%.

[Mn: 2.20-2.85 mass%]

Mn acts as a deoxidizer and has the effect of improving the strength and toughness of the weld metal at low temperatures. If the content of Mn is less than 2.20% by mass, such an effect is not sufficiently exhibited. If the content of Mn is more than 2.85% by mass, the strength of the weld metal is excessively high, the toughness at low temperature is lowered, and low temperature cracking is more likely to occur. Therefore, content of Mn is made into 2.20-2.85 mass%.

[B: 0.002-0.010 mass%]

B has the effect of miniaturizing the grains of the weld metal to improve toughness at low temperatures. If the content of B is less than 0.002% by mass, the toughness improving effect cannot be sufficiently obtained. On the other hand, if the content of B exceeds 0.010% by mass, the high temperature cracking resistance is lowered. Therefore, content of B is made into 0.002-0.010 mass%.

[Al ≦ 0.5 mass%]

Al becomes an oxide during welding, thereby increasing the solidification temperature of the slag, thereby preventing the flow of molten metal in the vertical upward welding. However, Al slightly remains in the weld metal, and if the amount is large, the toughness of the weld metal decreases and the amount of sputter generation increases. Therefore, content of Al needs to be regulated to 0.5 mass% or less.

[[Al ₂ O ₃ ] + [Al] × 1.89: 0.5 to 1.0 mass%]

Al ₂ O ₃ has the effect of raising the solidification temperature of the slag, thereby preventing the flow of molten metal in the vertical upward welding. In the content of Al ₂ O ₃ when the value of [Al ₂ O ₃ ] + [Al] × 1.89 is less than 0.5 mass% with respect to the Al content flow rate, the above anti-dripping effect is not sufficiently exhibited. . On the other hand, in respect to the content of Al, [Al ₂ O _3] + amount of [Al] × 1.89 of Al ₂ O if the value is more than 1.0% by weight _3, and the arc is unstable, that the sputtering amount increases At the same time, the slag becomes too hard and the slag peelability deteriorates. On the other hand, when Al is oxidized to Al ₂ O ₃ , the weight is 1.89 times.

[Ni: 0.2-1.0 mass%]

Ni has the effect of improving the toughness at low temperatures of the weld metal. When content of Ni is less than 0.2 mass%, the said toughness improvement effect is not acquired. On the other hand, even if it adds exceeding 1.0 mass%, the effect of proportional to the addition amount is not obtained with respect to the impact performance at about -40 degreeC, and since the price of Ni as a raw material is high, manufacturing cost also increases. Therefore, content of Ni is made into 0.2-1.0 mass%.

EXAMPLE

Flux cored wire for gas shielded arc welding with a wire diameter of 1.4 mm formed by filling a flux in a sheath of a mild steel (JIS G3141 SPCC) was produced (Examples No. 1 to No. 18, and Comparative Example No. 19 to Comparative Example No. 57). Each wire has a flux content of 14 mass%. The chemical composition of these wires is shown in Table 1, Table 2, and Table 3. Here, as the wire chemistry other than the materials listed in Tables 1 to 3, in addition to the outer shell Fe, metal fluoride (0.05 to 1.50%), alkali metal oxide (0.05 to 1.50%), ZrO ₂ (1.50% or less), and SiO ₂ (0.20-2.00%) and the balance was filled with iron.

Using the wires produced above, the welding conditions shown in Table 4 were: (a) vertical upward welding, (b) downward butt welding according to the heat input to evaluate low temperature toughness, and (c) high temperature cracking. Each welding test was performed for the first-layer welding of the downward butt welding to evaluate the resistance, and (d) the downward butt welding to evaluate the low temperature crack resistance.

In vertical upward welding, fillet welding was performed vertically upward, and the degree of drooping (good or bad bead shape) of molten metal, etc. were evaluated. In the welding current of 180 A and the delta weaving, the good shape of the bead was not a convex shape, and the good was "o", and the poor bead shape was "x". In addition, the good thing which is not a convex shape in a bead shape in 220A and delta weaving was "(circle)-(circle)", The good thing which is not a convex shape in 250A and delta weaving was made into "◎". The evaluation results are shown in Tables 5 and 6.

In downward butt welding, the toughness at low temperature of the weld metal by high heat input welding was evaluated. The Charpy test piece was sampled from the center position in the plate | board thickness direction of a weld part, and the Charpy absorbed energy value in -40 degreeC was measured by the Charpy impact test (test piece size and test method based on JISZ3111). The average value of three Charpy test pieces was taken as -40 degreeC absorption energy. Evaluation was made that "-40" absorption energy exceeds 100J as "(circle)", the thing of the range of 47J-100J was made into "(circle)", and the thing of 47J was made into "x". The evaluation results are shown in Tables 5 and 6.

In the first layer welding (consistency crack test) of the downward butt single side welding, the presence or absence of the high temperature crack was examined by the radiographic test after the welding. Evaluation was made into "(circle)" that there was no high temperature crack in superlayer welding by welding current 230A, and made into "x" that the high temperature crack generate | occur | produced. The evaluation results are shown in Tables 5 and 6. In the downward butt window frame cracking test, the presence or absence of low temperature cracking was examined by an ultrasonic flaw test after welding. Evaluation was made into "(circle)" that there was no low temperature crack, and made into "x" that the low temperature crack generate | occur | produced. The evaluation results are shown in Tables 5 and 6.

As for the results of the comparative examples, in Comparative Examples No. 21 and No. 26, since TiO ₂ exceeded the upper limit, high temperature cracking occurred in the initial layer of single-sided welding, and low-temperature toughness in the high heat input welding was low. . In Comparative Examples No. 35, No. 39, No. 43 and No. 51, since the TiO ₂ was below the lower limit, the bead shape was poor in the convex shape in the vertical upward welding.

Next, in Comparative Examples No. 20 and No. 33, since the Ti exceeded the upper limit, the strength of the weld metal increased and the low temperature toughness in the high heat input welding was low. In Comparative Examples No. 19, No. 23, and No. 28, since Ti was lower than the lower limit, high temperature cracking occurred in the initial layer of single-sided welding, and low-temperature toughness in high heat input welding was low.

Next, in Comparative Examples No. 47, No. 49, and No. 54, low temperature cracks occurred because Mg exceeded the upper limit. In Comparative Examples No. 27 and No. 30, since Mg was lower than the lower limit, high temperature cracking occurred in the initial layer of single-sided welding, and low-temperature toughness in high heat input welding was low. On the other hand, in Comparative Example No. 27, Al and Al ₂ O ₃ were added, and the vertical upward weldability was very good.

Next, in Comparative Examples No. 45 and No. 53, since C exceeded the upper limit, the strength of the weld metal increased and the low temperature toughness in the high heat input welding was low. In addition, low temperature cracks occurred. In Comparative Example No. 29, since C was lower than the lower limit, low-temperature toughness in high heat input welding was low.

Next, in Comparative Examples No. 44 and No. 46, since Si exceeded the upper limit, high temperature cracking occurred in the first layer of single-sided welding, and low-temperature toughness in the high heat input welding was low. In addition, low temperature cracks occurred. In Comparative Example No. 44, since Al ₂ O ₃ and Al were added, the vertical upward weldability was very good. In Comparative Examples No. 24, No. 36, and No. 55, since the Si was less than the lower limit, the bead shape was poor in the convex shape in vertical upward welding. On the other hand, in Comparative Example No. 55, Al ₂ O ₃ was added, but since Si was lower than the lower limit, the bead shape was poor in the convex shape in vertical upward welding.

Next, in Comparative Examples No. 41 and No. 50, since the Mn exceeded the upper limit, the strength of the weld metal was increased, so that the low temperature toughness in the high heat input welding was low, and low temperature cracking occurred. In Comparative Examples No. 25, No. 37, and No. 56, since Mn was lower than the lower limit, low-temperature toughness in high heat input welding was low. On the other hand, in Comparative Example No. 56, Ni was added, but since Mn was below the lower limit, low-temperature toughness in high heat input welding was low.

Next, in Comparative Examples No. 42, No. 48 and No. 57, since B exceeded the upper limit, high temperature cracking occurred in the first layer of single-sided welding. On the other hand, in Comparative Example No. 57, since Ni was added, low-temperature toughness in high heat input welding was good. In Comparative Examples No. 32 and No. 34, since B was lower than the lower limit, low-temperature toughness in high heat input welding was low.

Next, in Comparative Examples No. 22, No. 31, No. 38, No. 40, and No. 52, since the Mg0 exceeded the prescribed value, the bead shape was poor in the convex shape in vertical upward welding. On the other hand, Ni was added in Comparative Example No. 31, and low-temperature toughness in high heat input welding was good. In Comparative Example No. 38, since Al exceeds the upper limit, the amount of sputter generation is large, and since the total amount b of Al and Al ₂ O ₃ exceeds the upper limit, arc stability and slag peelability Was bad.

On the other hand, as shown in Table 5, Example No. 1-Example 18 can perform favorable welding by a solid-state welding electric current, without falling of molten metal in a vertical upward welding, and single-sided welding It was possible to obtain a weld metal having excellent high temperature cracking resistance in the first layer and excellent in low temperature toughness in the high heat input welding with a higher deposition amount. It was also good for low temperature crack resistance.

Claims (3)

Flux cored wire for gas shielded arc welding formed by filling flux into a mild steel or alloy steel shell, per wire mass, TiO ₂ : 4.5-7.0 mass%, Ti: 0.11 to 0.29 mass%, Mg: 0.30 to 0.70 mass%, C: 0.02 to 0.08 mass%, Si: 0.35-0.75 mass%, Mn: 2.20-2.85 mass%, and B: contained 0.002 to 0.010 mass% When the content of Mg is referred to as [Mg] and the content of Mg0 as [Mg0], Mg0 is defined relative to the content of Mg. [MgO] + [Mg] × 1.66 ≦ 2.5 mass% Flux cored wire for gas shielded arc welding that meets The method of claim 1, Satisfies Al≤0.5% by mass per total mass of the wire, Speaking of the content of the Al [Al] la, and the content of _{Al 2 O 3 [Al 2 O} 3], with respect to the content of the Al, [Al ₂ O ₃ ] + [Al] × 1.89: 0.5 to 1.0 mass% Flux cored wire for gas shielded arc welding containing Al ₂ O ₃ to satisfy the relationship of. The method according to claim 1 or 2, Flux cored wire for gas shielded arc welding, which further contains 0.2 to 1.0 mass% of Ni per wire total mass.