JP2008149341A - Flux cored wire for gas-shielded arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flux cored wire for gas-shielded arc welding, a flux cored wire that can obtain a weld metal which secures a strength of ≥620 MPa at 0.2% proof stress (σ<SB>0.2</SB>) and a V Charpy impact value vE<SB>-60</SB>of ≥50J at -60°C and that is most suitable as a welding material of high tensile steel. <P>SOLUTION: The flux cored wire for gas-shielded arc welding contains, by mass% to the total mass of the wire, 0.02-0.15% C, 0.3-1.4% Si, 1.2-3.5% Mn, 0.2-3.4% Ni, 0.02-2.0% Cr, 2.0-6.0% Ti, 0.1-2.2% Mo, and 0.01-1.0% Mg. The TiO<SB>2</SB>content [TiO<SB>2</SB>] and MgO content [MgO] in the flux satisfies the relation of expression (1): [TiO<SB>2</SB>]/[MgO]≥4.7, provided that [TiO<SB>2</SB>] and [MgO] are each the content (mass% to the total mass of the wire) of TiO<SB>2</SB>and MgO contained in the flux. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to TiO ₂ based flux cored wire for gas shielded arc welding formed by filling a (titania-based) flux mainly composed of TiO ₂ in the steel sheath, it is favorable especially weldability In addition, the present invention relates to a flux-cored wire for gas shielded arc welding that can obtain a weld metal exhibiting good toughness and is optimal for welding high-strength steel.

  Ships and offshore structures are constructed by welding high-tensile steel. To build such structures, it is necessary to realize a welding material that exhibits high strength and good toughness (especially low-temperature toughness). It is desired.

  In the fields of covered arc welding and submerged arc welding, welding materials having excellent low-temperature toughness have been developed, but there are problems in terms of work efficiency and welding posture.

On the other hand, gas shielded arc welding using a flux-cored wire is known to have a good bead appearance and excellent welding workability. As the flux cored wire used in such gas shielded arc welding, a titania flux cored wire in which a steel outer sheath is filled with a flux mainly composed of titania (TiO ₂ ) is widely used.

  However, when gas shielded arc welding is performed using a flux-cored wire filled with a titania-based flux, the oxygen concentration in the weld metal tends to be as high as about 500 to 600 ppm, and the low-temperature toughness of the weld metal tends to decrease. There is a problem.

  For these reasons, various welding materials have been developed for flux-cored wires with the aim of achieving both the mechanical properties (particularly, low temperature toughness) of the weld metal and welding workability.

As such a technique, for example, Patent Document 1 uses a titania-based flux mainly composed of TiO ₂ , MgO, and MnO and TiO ₂ / MgO of 1.7 or more, and Co, Cr, C, Mn, Ni, By adjusting the alloy components such as Mo to an appropriate range, good workability and mechanical properties (tensile strength TS: about 790 MPa or more, V Charpy impact value vE- ₃₀ at −30 ° C. is about 100 J or more) It has been proposed that this can be secured.

Patent Document 2 defines an appropriate range of TiO ₂ , MgO, metal fluoride, and alloy components (Si, Mn, Mg, Ni, Cu, Mo, etc.) in a flux-cored wire for gas shielded arc welding. It has been proposed that a satisfactory welding workability and mechanical properties (tensile strength TS: about 830 MPa or more, V Charpy impact value vE- ₄₀ at −40 ° C. of about 108 J or more) can be secured.

Further, in Patent Document 3, in a wire with a basic flux, slag is made of TiO ₂ —CaF ₂ , and Mg, Si, Mn and other metal oxides are added, so that welding workability and mechanical characteristics are improved. It has been shown that KS (Korean National Standard) and AWS (American Welding Association) standards can be satisfied.

On the other hand, in Patent Document 4, as a titania-based flux-cored wire used when welding a steel material having a tensile strength TS of 490 MPa, a welded portion (welded metal) is added by adding SiO ₂ or Al ₂ O ₃ into the flux. It is shown that the residual stress can be reduced and the fatigue strength can be improved.

Further, in Patent Document 5, in a titania-based flux-cored wire applied to gas shielded arc welding, one or more of MgO and FeO, and SiO ₂ and MnO are used in combination with TiO ₂ and added to the flux. Shows that a weld metal with good welding workability and mechanical properties (tensile strength: about 580 MPa or more, V Charpy impact value vE ₀ at 0 ° C. of about 150 J or more) can be obtained.
Japanese Patent Laid-Open No. 3-47695 JP-A-3-294093 JP 2003-154487 A JP 2002-307189 A JP-A-7-314182

The development of various technologies described above has yielded a welded structure with relatively good toughness of the weld metal, but the welded structure has a flux-cored wire that can provide a weld metal with higher strength and toughness. The reality is what is desired. That is, on the strength balance with the high strength steel used as a welding base material (material to be welded), the strength is 0.2% proof stress (σ _0.2 ) and the V Charpy impact value vE ₋ at a low temperature of −60 ° C. at 620 MPa or more. Realization of a weld metal such that ₆₀ can secure 50J or more is desired. However, with the techniques proposed so far, it is a fact that a flux-cored wire for gas shielded arc welding that can obtain such a high strength and high toughness weld metal cannot be realized.

The present invention has been made by paying attention to the above-described circumstances, and the object thereof is to obtain a V Charpy impact value vE _{−60 at} −620 ° C. at a strength of 0.2% proof stress (σ _0.2 ) of 620 MPa or more. Is to provide a flux-cored wire for gas shielded arc welding that is optimal as a welding material for high-strength steel.

The flux-cored wire for gas shielded arc welding according to the present invention capable of achieving the above object is a flux for gas shielded arc welding formed by filling a steel outer sheath with a flux mainly composed of TiO ₂ flux. In the cored wire, in mass% with respect to the total mass of the wire, C: 0.02 to 0.15%, Si: 0.3 to 1.4%, Mn: 1.2 to 3.5%, Ni: 0.2 -3.4%, Cr: 0.02-2.0%, Ti: 2.0-6.0%, Mo: 0.1-2.2% and Mg: 0.01-1.0% In addition to the content, the TiO ₂ content [TiO ₂ ] and the MgO content [MgO] in the flux satisfy the following formula (1).
[TiO ₂ ] / [MgO] ≧ 4.7 (1)
However, [TiO ₂ ] and [MgO] are the contents of TiO ₂ and MgO contained in the flux (mass% with respect to the total mass of the wire).

In the flux-cored wire for gas shielded arc welding of the present invention, the TiO ₂ content [TiO ₂ ] is 4.5 to 6.1%, and the MgO content [MgO] is 0.2 to 1.5%. It is preferable that Moreover, about 10 to 30% is appropriate for the filling rate of the flux.

In the flux-cored wire of the present invention, the chemical component composition of the flux-cored wire as a whole is appropriately adjusted, and the oxygen transferred to the weld metal by setting the ratio of TiO ₂ and MgO in the flux within an appropriate range. The inclusion (oxide) in the weld metal can be reduced by reducing the concentration, and as a result, the toughness of the weld metal having the weld metal having good characteristics as the main constituent part can be remarkably improved.

The inventors of the present invention have made extensive studies to solve the above problems. As a result, it was found that the activity of TiO ₂ with respect to oxygen can be reduced by appropriately adjusting the chemical composition of the flux-cored wire as a whole and adding a predetermined amount of MgO to the flux. As a result, even if the Ti content of the entire wire is increased, the oxygen concentration finally transferred to the weld metal can be reduced, and inclusions (oxides) in the weld metal can be reduced. As a result, it has been found that the toughness of a weld metal having a weld metal having good characteristics as a main constituent part can be remarkably improved, and the present invention has been completed.

  In the flux-cored wire for gas shielded arc welding according to the present invention, it is also important to appropriately specify the content of basic components of C, Si, Mn, Ni, Cr, Ti and Mg (mass% with respect to the total mass of the wire). The reason for limiting the range of the content of these components is as follows. In addition, these components are those in which the content of the entire wire affects the characteristics of the deposited metal, and the same component means the total amount regardless of the form (metal or oxide). For example, Ti and Mg are contained in the form of oxides, but the following contents are values including the amount of metal elements forming oxides.

[C: 0.02 to 0.15%]
C is an important element for ensuring the strength of the weld metal (the weld metal and a part of the base material are fused to form a “weld metal”). In order to secure 620 MPa or more with 0.2% proof stress (σ _0.2 ), the C content needs to be 0.02% or more. However, if the C content is excessive, the strength is excessive and the cold cracking sensitivity is increased, so it should be 0.15% or less. In addition, the minimum with preferable C content is 0.04%, and a preferable upper limit is 0.08%.

[Si: 0.3-1.4%]
Si functions as a deoxidizer and is an effective element for securing the strength of the weld metal and reducing oxygen. In order to exert such effects, the Si content needs to be 0.3% or more. However, if the Si content is excessive and exceeds 1.4%, the viscosity of the deposited metal becomes high and welding workability is lowered. In addition, the minimum with preferable Si content is 0.4%, and a preferable upper limit is 0.9%.

[Mn: 1.2 to 3.5%]
Mn is an element effective for ensuring the strength of the weld metal and reducing oxygen. If the Mn content is less than 1.2%, deoxidation is insufficient and the strength and toughness of the weld metal cannot be secured. On the other hand, when the Mn content exceeds 3.5% and becomes excessive, the strength becomes high and the cold cracking sensitivity becomes high. In addition, the minimum with preferable Mn content is 1.7%, and a preferable upper limit is 2.9%.

[Ni: 0.2 to 3.4%]
Ni is an important element in securing the strength and toughness of the weld metal. When the Ni content is less than 0.2%, sufficient effect of improving toughness is not exhibited, and the hot cracking sensitivity exceeding 3.4% is increased. In addition, the minimum with preferable Ni content is 1.7%, and a preferable upper limit is 2.4%.

[Cr: 0.02 to 2.0%]
Cr is an element useful for ensuring the strength of the weld metal stably. If the Cr content is less than 0.02%, sufficient strength cannot be ensured, and if it exceeds 2.0%, the strength becomes too high and the toughness deteriorates. In addition, the minimum with preferable Cr content is 0.1%, and a preferable upper limit is 0.5%.

[Ti: 2.0 to 6.0%]
Ti is an element having a deoxidizing effect and is an element effective for refining crystal grains. In order to exert these effects, the Ti content needs to be 2.0% or more. However, if the Ti content is excessive, the strength becomes too high, and the amount of slag generated increases, resulting in a decrease in welding workability. In addition, the minimum with preferable Ti content is 3.3%, and a preferable upper limit is 4.0%.

[Mo: 0.1 to 2.2%]
Mo is an important element in securing the strength of the weld metal. If the Mo content is less than 0.1%, sufficient strength cannot be ensured, and if it exceeds 2.2%, it will be remarkably cured and the toughness will be reduced. In addition, the minimum with preferable Mo content is 0.2%, and a preferable upper limit is 1.0%.

[Mg: 0.01 to 1.0%]
Mg has a deoxidation effect, and if the Mg content is less than 0.01%, the deoxidation effect is insufficient and the toughness of the weld metal is lowered. However, if the Mg content becomes excessive and exceeds 1.0%, the amount of fume during welding increases and the welding workability deteriorates. In addition, the minimum with preferable Mg content is 0.1%, and a preferable upper limit is 0.8%.

In the flux-cored wire of the present invention, it is also important that the TiO ₂ content [TiO ₂ ] and the MgO content [MgO] in the flux satisfy the relationship of the following formula (1). The reasons for defining these relationships are as follows.
TiO ₂ /MgO≧4.7 (1)
However, [TiO ₂ ] and [MgO] are the contents of TiO ₂ and MgO contained in the flux (mass% with respect to the total mass of the wire).

In the flux-cored wire of the present invention, by adding MgO to the flux, the TiO ₂ activity in the flux can be reduced, thereby reducing the oxygen concentration in the weld metal. By proceeding with such a phenomenon, inclusions (oxide inclusions) in the weld metal are reduced, and particularly, the low-temperature toughness is good (specifically, the V Charpy impact value vE- ₆₀ at −60 ° C. is 50J or more) can be realized.

The above-described action (oxygen concentration reduction effect) is more effectively exhibited as the MgO content is increased. However, from the viewpoint of welding workability, the effect is worsened against the oxygen reduction effect. From the viewpoint of ensuring at least welding workability, in the present invention, TiO ₂ / MgO needs to be 4.7 or more. However, when the ratio of the content of MgO to TiO ₂ is reduced, the welding workability is good, but the oxygen reduction effect is decreased and the toughness of the weld metal is deteriorated, so that TiO ₂ / MgO is 16.9. It is preferable to make it to the extent. The preferable lower limit of TiO ₂ / MgO is about 8.0.

Flux component in Furakkussu cored wire of the present invention, at least it is intended to include TiO ₂ as a main component, the content of the TiO ₂ ([TiO _2]) also preferably be in an appropriate range. That is, if the TiO ₂ content ([TiO ₂ ]) decreases, the function as a TiO ₂ flux-cored wire (mainly welding workability) becomes difficult to be exhibited, and conversely, if the amount increases, As a result, the oxygen concentration in the weld metal tends to increase. From this point of view, the TiO ₂ content ([TiO ₂ ]) is preferably about 4.5 to 6.1% (ratio to the whole wire). Note that the preferable content of MgO, but will be adjusted to be within the range and above the appropriate range of the addition amount of _{TiO 2 [TiO 2] / [} MgO] is defined, 0.2 About 1.5% is preferable.

In the flux-cored wire of the present invention, if each of the above elements is within the specified range and [TiO ₂ ] / [MgO] is set within the above range, the purpose can be generated. However, in addition to TiO ₂ and MgO, the flux component may also contain other oxides (for example, a fossilizing agent such as Al ₂ O ₃ , SiO ₂ , ZrO ₂ or an arc stabilizer).

  The flux composed of each of the above components is filled in a steel outer shell to constitute a flux-cored wire, but the flux filling rate (hereinafter referred to as “flux filling rate”) should also be in an appropriate range. preferable. The flux filling rate is suitably about 10 to 30%. If the flux filling rate is less than 10%, it becomes difficult to add the necessary alloy elements from the flux alone, and adding these elements from the outer shell increases the cost of the raw materials, and the outer shell strength by adding the alloy elements As a result of this increase, the drawability is degraded. On the other hand, when the flux filling rate exceeds 30%, the outer skin becomes thin, the wire is easily broken, and the drawability is deteriorated. The preferable lower limit of the flux filling rate is about 12%, and the preferable upper limit is about 20%.

The flux filling rate is a value defined by the following formula.
Flux filling rate (% by mass) = {(mass of flux) / (mass of the entire flux-cored wire)} × 100

  In the flux-cored wire of the present invention, the element content with respect to the entire wire is basically affected by the amount of metal elements contained in the oxide in the flux, the content contained in the steel outer shell, and the like. However, due to restrictions such as the amount of oxide and filling rate that can be contained in the flux, and the amount of element that can be contained in the steel outer shell, the amount of metal elements contained in the oxide in the flux and the content contained in the steel outer shell It may be difficult to adjust the element content of the entire wire by the amount alone. In particular, the Ti content in the flux-cored wire of the present invention may be difficult to adjust only by the element content in the oxide or the content in the steel outer shell. In such a case, the Ti content of the entire wire can be adjusted by adding a Ti metal powder to the flux.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[Example 1]
First, a soft steel hoop (steel hull: HT80 containing C: 0.05%, Si: 0.05%, Mn: 0.50%, Ti: 0.02%, the balance: iron and inevitable impurities) Equivalent steel) is bent into a cylindrical shape, filled with a flux containing various oxides (TiO ₂ , MgO, Al ₂ O ₃ , SiO ₂ , ZrO, etc.), then drawn, and the flux filling rate: A flux-cored wire with 13.5% and wire diameter: 1.2 mm was produced. Based on such a configuration, various types of flux-cored wires in which the content of each element as a whole wire is adjusted by using a steel shell with a chemical component adjusted or a metal powder mixed in the flux. Produced. The chemical component composition of each flux-cored wire produced is shown in Table 1 below, and the compounding ratio of the oxide in the flux (mass% with respect to the whole wire) is shown in Table 2 below.

Welding was performed using the prepared flux-cored wires under the following conditions to prepare a weld metal. Tensile test pieces (JIS Z3111 A1) and Charpy impact test pieces (JIS Z3111 A4) were taken from this weld metal, and each test was performed to obtain 0.2% proof stress (σ _0.2 ) and a low temperature of −60 ° C. V Charpy impact value (vE- ₆₀ ) was measured.

[Welding conditions]
Attitude: Downward Shielding gas: 80% Ar + 20% CO ₂
Welding current: 280A
Welding voltage: 31V
Welding speed: 300mm / min
Preheating and interpass temperature: 150 ° C
Heat input: 1.7 kJ / mm
Test steel plate (welding base metal): JIS G 3128 SHY865 (plate thickness: 20 mm)
Groove shape: groove angle 45 ° (V groove), gap 12mm

  In addition, welding (stand-up improvement welding) was performed under the following welding conditions to evaluate welding workability. Evaluation of welding workability is good when standing welding progress is possible and the weld metal surface after welding is smooth (indicated by a circle). Standing improvement can be promoted, but there are large irregularities on the welding metal surface after welding. The case where it occurred was slightly bad (indicated by Δ), and the case where slag and molten metal (droplet) dropped and welding could not be performed was evaluated as bad (indicated by x).

[Welding conditions for welding workability evaluation]
Posture: Standing progress Shield gas: 80% Ar + 20% CO ₂
Welding current: 220A
Welding voltage: 22-24V
Welding speed: 14 cm / min
Groove shape: groove angle 90 ° (V groove)
Weaving width: 7mm

These results (σ _0.2 , vE ₋₆₀ and welding workability) are collectively shown in the following Table 3 (evaluation criteria: σ _0.2 ≧ 620 MPa, pass with vE ₋₆₀ ≧ 50 J). Table 3 also shows the oxygen concentration in the deposited metal determined by the inert gas melting method.

  As is clear from this result, there is a contradictory relationship between strength and toughness, and when the strength is increased, the toughness tends to decrease, but the requirements specified in the present invention are satisfied (Test Nos. 1 to 5). Then, it turns out that the welding metal with favorable both strength and toughness is obtained, and welding workability | operativity is also favorable.

  On the other hand, those lacking any of the requirements defined in the present invention (Test Nos. 6 to 21) are satisfactory in strength, but at least one of toughness and welding workability deteriorates. I understand that.

[Example 2]
Various flux-cored wires were produced in the same manner as in Example 1 except that the blending ratio of various oxides into the flux was changed. The chemical composition of each prepared flux-cored wire is shown in Table 4 below, and the compounding ratio of the oxide in the flux (% by mass with respect to the total mass of the wire) is shown in Table 5 below.

Using each of the flux-cored wires produced, welding was performed under the conditions shown in Example 1 to produce a weld metal, and σ _0.2 , V Charpy impact value (vE _-60 ), and oxygen concentration of the weld metal were measured. The welding workability was also evaluated in the same manner as in Example 1.

These results (σ _0.2 , vE ₋₆₀ , oxygen concentration and welding workability) are collectively shown in the following Table 6 (Evaluation criteria: σ _0.2 ≧ 620 MPa, vE ₋₆₀ ≧ 50 J, passed).

From this result, it can be considered as follows. That is, it can be seen that adding MgO to the titanium-based flux is effective in reducing the oxygen concentration in the deposited metal. Further, when the content of MgO is increased (that is, when TiO ₂ / MgO is decreased), the oxygen concentration in the deposited metal tends to decrease. In particular, when TiO ₂ / MgO is 9.0 or less, the oxygen concentration Is 0.044% or less (440 ppm or less).

On the other hand, when MgO becomes too much (that is, when the TiO ₂ / MgO ratio becomes too small), welding workability deteriorates (Test Nos. 31 to 35). However, it can be seen that when TiO ₂ / MgO is 4.7 or more, good welding workability can be secured.

Therefore, if the TiO ₂ / MgO ratio in the titanium-based flux is controlled to an appropriate range in the flux-cored wire for gas shielded arc welding, the oxygen concentration in the weld metal can be reduced, and the high toughness of the weld metal And good welding workability can be achieved.

Claims (3)

In a flux-cored wire for gas shielded arc welding in which a steel outer sheath is filled with a flux mainly composed of TiO ₂ flux, C: 0.02 to 0.15% by mass% with respect to the total mass of the wire, Si : 0.3-1.4%, Mn: 1.2-3.5%, Ni: 0.2-3.4%, Cr: 0.02-2.0%, Ti: 2.0-6 0.0%, Mo: 0.1-2.2% and Mg: 0.01-1.0%, respectively, and the TiO ₂ content [TiO ₂ ] and MgO content [MgO] in the flux are A flux-cored wire for gas shielded arc welding characterized by satisfying the relationship of the following formula (1).
[TiO ₂ ] / [MgO] ≧ 4.7 (1)
However, [TiO ₂ ] and [MgO] are the contents of TiO ₂ and MgO contained in the flux (mass% with respect to the total mass of the wire). The flux for gas shielded arc welding according to claim 1, wherein the TiO ₂ content [TiO ₂ ] is 4.5 to 6.1% and the MgO content [MgO] is 0.2 to 1.5%. Cored wire. The flux-cored wire for gas shielded arc welding according to claim 1 or 2, wherein a filling rate of the flux is 10 to 30%.