KR100925321B1 - Flux-cored wire for gas-shielded arc welding - Google Patents

Abstract

An object of the present invention is to realize a weld metal that can secure a V Charpy impact value (vE- ₆₀ ) of 50% or more at a 620 MPa or higher and a -60 ° C at 0.2% yield strength (σ _0.2 ) as the strength. It is to provide a flux cored wire for gas shielded arc welding which is optimal as a welding material.

The flux cored wire for gas shielded arc welding of this invention is mass% with respect to the wire total mass, C: 0.02-0.15%, Si: 0.3-1.4%, Mn: 1.2-3.5%, Ni: 0.2-3.4% , Cr: 0.02 to 2.0%, Ti: 2.0 to 6.0%, Mo: 0.1 to 2.2% and Mg: 0.01 to 1.0%, respectively, while the TiO ₂ content [TiO ₂ ] and MgO content [MgO] in the flux were The relationship of the following formula (1) is satisfied.

[TiO ₂ ] / [MgO] ≥ 4.7... (One)

However, [TiO ₂ ] and [MgO] are the contents of TiO ₂ and MgO contained in the flux (mass% relative to the total wire mass).

Flux, Wire, Flux Cored Wire, C, Si, Mn, Ti

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 for gas shielded arc welding, which is formed by filling a TiO ₂ -based (titania-based) flux mainly composed of TiO ₂ in a steel sheath, and particularly exhibits good welding workability and good toughness. The present invention relates to a flux cored wire for gas shielded arc welding, which is capable of obtaining a weld metal and is optimal for welding high tensile steel.

Ships, offshore structures, and the like are constructed by welding high tensile strength steel, but in order to construct such structures, it is required to realize a welding material having high strength and good toughness (especially low temperature toughness).

In the field of coated arc welding and submerged arc welding, a welding material excellent in low temperature toughness has 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 for the flux cored wires used in such gas shielded arc welding, titania-based flux cored wires filled with a flux composed mainly of titania (TiO ₂ ) in a steel jacket are widely used.

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

For this reason, with respect to the flux cored wire, various welding materials have been developed so far, aiming at both the mechanical properties of the weld metal (especially low temperature toughness) and the welding workability.

As such a technique, for example, Patent Literature 1 uses titania-based fluxes containing TiO ₂ , MgO, and MnO as the main components, and TiO ₂ / MgO is 1.7 or more, and Co, Cr, C, Mn, Ni, Mo, and the like. By adjusting the alloy component to an appropriate range, good welding workability and mechanical properties [tensile strength (TS): about 790 MPa or more, V Charpy impact value (vE _{- 30} ) at about -30 ° C are about 100 J or more] can be secured). It is suggested that there is.

In addition, Patent Literature 2 defines a suitable 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 is proposed that welding workability and mechanical properties (tension strength (TS): about 830 MPa or more and V Charpy impact value (vE _-40 ) at -40 ° C of about 108 J or more) can be secured.

In addition, in Patent Document 3, in a basic flux cored wire, slag is made of TiO ₂ -CaF ₂ system, and Mg, Si, Mn, and other metal oxides are added, so that KS (Korean national standard) can be used for welding workability and mechanical properties. And AWS (American Welding Society) are disclosed.

On the other hand, Patent Document 4 is a titania-based flux cored wire used when welding a steel having a tensile strength (TS) of 490 MPa class, and by adding SiO ₂ or Al ₂ O ₃ in the flux, the weld portion (welding metal) remains. It is disclosed that the 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, at least one of MgO and FeO, and SiO ₂ and MnO are added together with TiO ₂ in the flux to perform welding work. It has been shown that a weld metal having both good mechanical properties (tensile strength: about 580 MPa or more and V Charpy impact value (vE ₀ ) at 0 ° C of about 150 J or more) can be obtained.

[Patent Document 1] Japanese Patent Application Laid-Open No. 3-47695

[Patent Document 2] Japanese Patent Application Laid-Open No. 3-294093

[Patent Document 3] Japanese Unexamined Patent Publication No. 2003-154487

[Patent Document 4] Japanese Unexamined Patent Publication No. 2002-307189

[Patent Document 5] Japanese Patent Application Laid-Open No. 7-314182

The development of the above-described techniques has resulted in obtaining a welded structure having a relatively good toughness of the weld metal. However, there is a demand for a flux cored wire capable of obtaining a weld metal having a higher strength and higher toughness. That is, the V Charpy impact value (vE _-60 ) at a low temperature of -60 ° C. is 50 or more at a temperature of 0.2% yield strength (σ _0.2 ) as a strength in terms of strength balance with high tensile strength steel used as a welding base material (being to be welded). The realization of the weld metal which can ensure J or more is calculated | required. However, in the technique proposed so far, it is a fact that the flux cored wire for gas shielded arc welding which can obtain such a high strength and high toughness weld metal cannot be realized.

The present invention has been made in view of the above-described circumstances, and its object is to secure a V Charpy impact value (vE _-60 ) at -60 ° C. of 50% or more at a 0.2% yield strength (σ _0.2 ) as the strength. The present invention provides a flux cored wire for welding gas shielded arc which can be realized as a welding material for high tensile strength steel.

The flux cored wire for gas shielded arc welding which concerns on this invention which could achieve the said objective is the flux cored wire for gas shielded arc welding formed by filling the flux which mainly consists of TiO _{2 type} flux in a steel outer sheath. 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 to 3.4%, Cr: 0.02 to 2.0%, Ti: 2.0 To 6.0%, Mo: 0.1 to 2.2%, and Mg: 0.01 to 1.0%, respectively, and the TiO ₂ content [TiO ₂ ] and MgO content [MgO] in the flux satisfy the relationship of the following formula (1): It is to have the point at that.

[TiO ₂ ] / [MgO] ≥ 4.7... (One)

However, [TiO ₂ ] and [MgO] are the contents of TiO ₂ and MgO contained in the flux (mass% relative to the total wire mass).

In gas shielded arc welding flux cored wire according to the present invention, the TiO ₂ content [TiO _2] is 4.5 to 6.1% and, MgO content of [MgO] is preferably a 0.2 to 1.5%. In addition, the filling rate of the flux is preferably about 10 to 30%.

In the flux cored wire of the present invention, the overall chemical component composition of the flux cored wire is appropriately adjusted, and the ratio of TiO ₂ and MgO in the flux is kept within an appropriate range, thereby reducing the oxygen concentration to be transferred to the deposited metal, thereby depositing the deposited metal. Inclusion (oxide) in the inside can be reduced, and as a result, the toughness of the weld metal which has the weld metal which has favorable characteristics as a main component part can be remarkably improved.

MEANS TO SOLVE THE PROBLEM The present inventors earnestly researched in order to solve the said subject. As a result, it was found that by adjusting the overall chemical composition of the flux cored wire appropriately and adding a predetermined amount of MgO to the flux, the amount of TiO _{2 to} the oxygen can be lowered. As a result, even if the Ti content is increased in the entire wire, the oxygen concentration finally transferred to the weld metal can be reduced, and the inclusions (oxides) in the weld metal can be reduced. As a result, the weld metal having good properties can be used as the main component. The present invention has been completed by discovering that the toughness of a weld metal can be remarkably improved.

In the flux cored wire for gas shielded arc welding according to the present invention, it is also important to appropriately define the content (mass% relative to the total mass of the wire) of the basic components of C, Si, Mn, Ni, Cr, Ti, and Mg. Although it is a requirement, the reason for range limitation of content of these components is as follows. In addition, these components are contents which affect the characteristic of the weld metal as a whole wire, and the same component means the total amount regardless of the form (metal or oxide). For example, although Ti and Mg are contained also as an oxide form, the following content is the value which also included the amount of metal elements which form an oxide.

[C: 0.02 to 0.15%]

C is an important element in securing the strength of the weld metal (the weld metal and a part of the base material are fused to form a "welding metal"). In order to ensure 620 MPa or more at 0.2% yield strength (sigma _0.2 ), it is necessary to make C content into 0.02% or more. However, when the C content is excessive, the strength becomes excessive and the low temperature cracking susceptibility is increased, so it should be 0.15% or less. Moreover, the minimum with preferable C content is 0.04%, and a preferable upper limit is 0.08%.

[Si: 0.3 to 1.4%]

Si functions as a deoxidizer and is an element effective for securing the strength of the weld metal and reducing the oxygen. In order to exhibit such an effect, Si content needs to be 0.3% or more. However, when Si content becomes excess and exceeds 1.4%, the viscosity of a weld metal will become high and welding workability will fall. Moreover, 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 securing the strength of the weld metal and reducing the oxygen. If the Mn content is less than 1.2%, deoxidation will be insufficient, and the strength and toughness of the weld metal will not be secured. On the other hand, when Mn content exceeds 3.5% and becomes excess, intensity | strength will become high and low temperature cracking sensitivity will become high. Moreover, 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 a weld metal. If Ni content is less than 0.2%, sufficient toughness improvement effect will not be exhibited, and if it exceeds 3.4%, high temperature cracking sensitivity will become high. Moreover, 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 stably securing the strength of the weld metal. If Cr content is less than 0.02%, sufficient intensity | strength cannot be ensured, and when Cr content exceeds 2.0%, intensity | strength will become high too much and toughness will deteriorate. Moreover, 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 deoxidation effect and an element effective for refining crystal grains. In order to exhibit these effects, Ti content needs to be 2.0% or more. However, when Ti content becomes excess, intensity | strength will become high too much and slag generation amount will increase and welding workability will fall. Moreover, 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 a weld metal. If the Mo content is less than 0.1%, sufficient strength cannot be secured. If the Mo content is more than 2.2%, the hardness is markedly cured and the toughness is rather lowered. Moreover, 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 when Mg content is less than 0.01%, a deoxidation effect will be insufficient and the toughness of a weld metal will fall. However, when Mg content becomes excess and exceeds 1.0%, the amount of fumes at the time of welding will increase and welding workability will fall. Moreover, 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 following formula (1). The reason for defining this relationship is as follows.

TiO ₂ / MgO ≥ 4.7... (One)

However, [TiO ₂ ] and [MgO] are the contents of TiO ₂ and MgO contained in the flux (mass% relative to the total wire mass).

In the flux cored wire of the present invention, by adding MgO to the flux, the TiO ₂ activity in the flux can be lowered, thereby reducing the oxygen concentration in the deposited metal. By advancing such a phenomenon, inclusions (oxide-based inclusions) in the weld metal can be reduced, and particularly weld metals having good low-temperature toughness (specifically, V Charpy impact value (vE _-60 ) at -60 ° C of 50 J or more) can be realized. It becomes possible.

The above-described action (oxygen concentration reducing effect) is more effectively exhibited as the MgO content increases, but from the viewpoint of welding workability, the effect is deteriorated contrary to the oxygen reducing effect. In view of at least welding workability, in the present invention, TiO ₂ / MgO needs to be 4.7 or more. However, when the ratio of MgO content to TiO ₂ decreases, the welding workability is good, but the oxygen reduction effect is lowered and the toughness of the weld metal deteriorates. Therefore, the TiO ₂ / MgO is preferably up to 16.9. . In addition, a is about 8.0, preferable lower limit of the TiO ₂ / MgO.

Flux component in the flux cored wire of the present invention, but comprising at least as a main component to TiO _2, it is preferable that the content ([TiO _2]) is also a suitable range of the TiO _2. In other words, when the TiO ₂ content ([TiO ₂ ]) decreases, the action (mainly welding workability) as the TiO ₂ flux cored wire becomes difficult to be exhibited. On the contrary, when the amount increases, the welded metal in the weld metal (as a result, welding). The oxygen concentration of the metal) tends to increase. From this point of view, the TiO ₂ content ([TiO ₂ ]) is preferably about 4.5 to 6.1% (ratio relative to the entire wire). In addition, as for the preferable content of MgO, yet within an acceptable range of the addition amount of TiO ₂ addition, the [TiO _2] / [MgO], but it is adjusted to a specified range I, preferably about 0.2 to 1.5%.

In the flux cored wire of the present invention, if the above elements are within the above-mentioned range and [TiO ₂ ] / [MgO] is set within the above range, the object can be generated, but as the flux component, TiO ₂ And other oxides (for example, a preparation agent such as Al ₂ O ₃ , SiO ₂ , ZrO ₂ , and an arc stabilizer) in addition to MgO.

Although the flux which consists of said each component is filled in a steel outer sheath, and a flux cored wire is comprised, it is preferable to make the filling rate of a flux (henceforth "flux filling rate") into the appropriate range. The flux filling rate is preferably about 10 to 30%. If the flux filling rate is less than 10%, it is difficult to add the necessary alloying elements only from the flux, and adding these elements from the skin increases the cost of raw materials and increases the skin strength due to the addition of the alloying elements. It causes the deterioration of freshness. In addition, when the flux filling rate exceeds 30%, the outer skin becomes thin and easily broken, resulting in deterioration of freshness. The minimum with preferable flux filling rate is about 12%, and a preferable upper limit is about 20%.

In addition, the said flux filling rate is a value defined by the following formula.

Flux filling rate (mass%) = {(mass of flux) / (mass of the entire flux cored wire)} × 100

In the flux cored wire of the present invention, the element content of the entire wire is basically influenced by the amount of metal elements contained in the oxide in the flux, the content contained in the steel sheath, and the like. In view of constraints such as the quantity of water, the filling rate, and the amount of elements that can be included in the steel sheath, it is sometimes difficult to adjust the element content of the entire wire only by the content of the metal element in the oxide in the flux or the content contained in the steel sheath. In particular, Ti content in the flux cored wire of this invention may be difficult to adjust only by content of an element in an oxide, or content in a steel outer sheath. In such a case, Ti content can be adjusted with the whole wire by adding the metal powder of Ti in a flux.

Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not restrict | limited by the following example of course, It is implemented by changing suitably in the range which may be suitable for the meaning of the previous and the later. Of course, it is also possible, and they are all included in the technical scope of this invention.

[First Embodiment]

First, C: 0.05%, Si: 0.05%, Mn: 0.50%, Ti: 0.02%, respectively, and the remaining portion: a mild steel hoop (steel sheath: HT80 equivalent steel) composed of iron and unavoidable impurities in a cylindrical shape. While bending, the flux in which various oxides (TiO _{2 ,} MgO, Al ₂ O ₃ , SiO ₂ , ZrO, etc.) were mixed was filled, and then subjected to drawing processing to flux filling rate: 13.5%, wire diameter: A 1.2 mm flux cored wire was produced. Based on such a structure, by using the thing which adjusted the chemical component of a steel outer shell, or using what mixed metal powder in the flux, the various flux cored wire which adjusted each element content on the whole wire was produced. The chemical composition of each produced flux cored wire is shown in Table 1 below, and the blending ratio of the oxide in the flux (mass% relative to the entire wire) is shown in Table 2 below.

Table 1

[Table 2]

Using each produced flux cored wire, welding was performed on the following conditions, and the weld metal was produced. Tensile test pieces (JIS Z3111 A1) and Charpy impact test pieces (JIS Z311l A4) were taken from the weld metal, and each test was carried out to obtain a V Charpy impact value (vE) at 0.2% yield strength (σ _0.2 ) and a low temperature of -60 ° C. _-60 ) was measured.

[Welding condition]

Posture: downward

Shield gas: 80% Ar + 20% CO ₂

Welding Current: 280 A

Welding voltage: 31 V

Welding speed: 300 mm / min

Preheating and pass temperature: 150 ℃

Heat input amount: 1.7 kJ / ㎜

Test steel plate (welding base material): JIS G 3128 SHY865 (plate thickness: 20 mm)

Tip open shape: Tip open angle 45 ° (V-shaped tip open), Gap 12 mm

Moreover, welding (orientation upward welding) was performed on the welding conditions shown below, and welding workability was evaluated. The evaluation of welding workability is good when the orientation can be improved and the weld metal surface after welding is smooth (indicated by ○ mark), and the orientation can be improved. ), The slag and the molten metal (volume) were evaluated as defective (represented by X mark) when the welding cannot be suspended.

[Welding Conditions of Welding Workability Evaluation]

Posture: Upward Advancement

Shield gas: 80% Ar + 20% CO ₂

Welding Current: 220 A

Welding voltage: 22 to 24 V

Welding speed: 14 cm / min

Tip open shape: Tip open angle 90 ° (V-shaped tip open)

Weaving width: 7 mm

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

Table 3

As apparent from these results, there is a contradictory relationship between strength and toughness, and when the strength is increased, the toughness tends to be lowered. It can be seen that a weld metal having both good toughness can be obtained and welding workability is also good.

On the other hand, in omission of any one of the requirements specified in the present invention (Test Nos. 6 to 21), it can be seen that the performance of at least one of toughness and weldability deteriorates even though it is satisfactory in strength.

Second Embodiment

Various flux cored wires were produced in the same manner as in the first embodiment except that the blending ratio of various oxides in the flux was changed. The chemical component composition of each produced flux cored wire is shown in Table 4 below, and the blending ratio (mass% to total wire mass) of the oxide in the flux is shown in Table 5 below.

Table 4

Table 5

Using each produced flux cored wire, welding was performed under the conditions shown in the first example, and a weld metal was produced to measure? _0.2 , V Charpy impact value (vE- ₆₀ ), and oxygen concentration of the weld metal. In addition, welding workability was evaluated in the same manner as in the first embodiment.

These results (σ _0.2 , vE _-60 , oxygen concentration and welding workability) are collectively shown in Table 6 below (evaluation criteria: sigma _0.2 ? 620 MPa, vE _-60 ? 50 J).

Table 6

From this result, it can consider as follows. That is, it turns out that adding MgO in titanium flux is effective in reducing the oxygen concentration in a weld metal. In addition, when the content of MgO is increased (that is, when TiO ₂ / MgO is reduced), the oxygen concentration in the deposited metal tends to be lowered, and 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 is too large (that is, TiO ₂ / MgO ratio of the ground is too small), the welding operability deteriorates (test numbers 31 to 35). However, in TiO ₂ / MgO is 4.7 or more, it can be seen that to secure good welding workability.

Therefore, in the gas-cored arc welding flux cored wire, if the TiO ₂ / MgO ratio in the titanium flux is controlled to be within an appropriate range, the oxygen concentration in the weld metal can be reduced, and the weld metal has high toughness and good quality. It can be seen that the welding workability is compatible.

Claims (4)

Flux cored wire for gas shielded arc welding formed by filling a flux mainly composed of TiO ₂ -based flux in a steel sheath, in mass% of 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 to 3.4%, Cr: 0.02 to 2.0%, Ti: 2.0 to 6.0%, Mo: 0.1 to 2.2% and Mg: 0.01 to 1.0%, respectively, A flux cored wire for gas shielded arc welding, wherein the TiO ₂ content [TiO ₂ ] and the MgO content [MgO] in the flux satisfy the following formula (1). [TiO ₂ ] / [MgO] ≥ 4.7... (One) However, [TiO ₂ ] and [MgO] are the contents of TiO ₂ and MgO contained in the flux (mass% relative to the total wire mass). The flux cored wire 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%. The flux cored wire for gas shielded arc welding according to claim 1, wherein the filling rate of the flux is 10 to 30%. The flux cored wire for gas shielded arc welding according to claim 2, wherein the flux filling rate is 10 to 30%.