JPS60152393A - Composite wire for electrogas arc welding and electrogas arc welding method - Google Patents

Abstract

PURPOSE:To perform high-speed welding without generating pearshap high-temp. cracks with a wire formed by packing a flux in the cavity part enclosed of a tubular sheath made of a mild steel by regulating the content of C in the tubular sheath, the content of Mn in the entire wire and the content of the rare earth and Mg in the flux. CONSTITUTION:A composite wire for electrogas arc welding is formed by packing a flux into the cavity part enclosed of a tubular sheath made of a mild steel. C is incorporated at <=0.06wt% in said sheath and Mn at 1.5-3.5wt% in the entire wire. A rare earth is incorporated into the flux at 0.02-0.2wt% by the entire weight of the wire and Mg at 0.09-0.4wt% therein and the rare earth element in the flux/C content in the entire wire is adjusted to >=1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a composite wire for electrogas arc welding (hereinafter referred to as EGW) that can obtain a weld metal with excellent hot cracking resistance even under high speed and low heat input conditions, and a method using the wire. The present invention relates to the EGW method.

Due to its high welding efficiency, EGWi is often used in shipbuilding and the construction of large structures such as oil tanks, helping to reduce costs. However, when trying to further increase the welding speed in order to further reduce costs and improve the toughness of the welded part, especially from the bond part to the IIA Z part, there is a problem that pear-shaped cracks occur, and there is a limit to increasing the speed. Ta.

By the way, pear-shaped cracks occur due to the segregation of low-melting point impurities in the columnar crystal association area, and the occurrence area is the first
As shown in the figure, it is determined by the correlation between the welding speed and the bead cross-sectional shape factor (see H/W Figure 2). That is, in order to prevent the occurrence of pear-shaped cracks, it is necessary to (1) reduce the welding speed or reduce (21 (H/W).
Reducing the H/W) means making the groove angle obtuse and widening the groove width. However, in all of the above solutions, an increase in heat input is inevitable, so the toughness value of not only the bond area and the HAZ area but also the weld metal decreases, and the welding efficiency decreases, so the advantages of EGW are lost. I end up.

The present invention has been made in view of these circumstances, and provides a composite wire for EGW that makes it possible to perform high-speed, low-heat-input welding without causing pear-shaped hot cracking. The first objective is to provide a welding method that can obtain weld metal with good properties when performing EGW using the wire under high speed and low heat input conditions. This is the second purpose.

The composite wire for EGW of the present invention that achieves the above object is one in which a cavity surrounded by a tubular outer shell made of mild steel is filled with flux, and (a) C: 0 in the outer shell made of mild steel.
(0) Mn in the total wire: 1.5 to 3.5%, and (c) Rare earth metal in the filling flux based on the total weight of the wire. :0.02 to 0.2 valence) Metal M
g: 0.09 to 0.4, respectively, and (e) (rare earth element metal in flux / C maximum in all wires): adjusted to 1 or more), Furthermore, the above EGW
The welding method of the present invention using a wire is such that the current density expressed as (welding current/metal skin cross section flt) is 29
0~500A/mf, [(wire extension)/
(Wire diameter) 2] (hereinafter referred to as L/1)" is 12
The gist lies in that welding is performed with the respective settings set to 25 to 25.

First, the composition of the wire of the present invention will be explained.

(a) C in the mild steel outer skin: 0.06% or less If the amount of C contained in the mild steel outer skin is too large, it will cause explosion of droplets, making the arc unstable, causing deterioration of the workability and spatter. The content needs to be 0.06% or less because it causes slag hold in the surface peed and increases the amount of fume generated, deteriorating the working environment.

(b) Mn in all wires: 1.5 to 3.5% Among the low melting point impurities that cause pear-shaped cracks, Fe5 (melting point 988°C) is particularly representative, but Mn
When an appropriate amount of is added, FeS is reduced to generate MnS, which is dispersed at the grain boundaries or within the grains. As a result, the segregation of low melting point impurities such as FeS is eliminated, and the occurrence of pear-shaped hot cracks is prevented. Furthermore, the addition of Mn makes the crystal grains finer, thereby improving the toughness and strength of the weld metal.

In order to effectively exhibit such an effect, it is necessary to contain Mn with a valence of 1.5 or more. However, if the content exceeds 3.5 yen, the γ phase, which is the primary crystal during solidification, is stabilized, and a large heat input (25 KJ/cm2 even in the case of a small amount) is originally added to the weld zone in EGW. Therefore, M
Conversely, sulfide crystals such as nS grow too much and pear-shaped hot cracks are likely to occur.

Incidentally, examples of the flux raw material blended to add Mn include Fe-Mn%Fe-5i-Mn, metal Mn, and the like. Considering the wire extensibility, Mn in the hoop is desirably 0.6 coefficient 2 or less.

(c) Rare earth metal: Rare earth elements with a ratio of 0.02 to 0.2 relative to the total weight of the wire in the filling flux have a depletion effect and a dephosphorization effect, and react with S+P in the weld metal to form sulfides. and phosphides, which migrate into the slag. As a result, the formation of low melting point impurities such as FeS can be reduced, and segregation of low melting point impurities to grain boundaries can be reduced. Furthermore, the P and S remaining in the weld metal also have a high melting point, Lal! 5stcesζ), this has the effect of preventing the low melting point liquid phase from segregating at the grain boundaries in the final stage of solidification.

In order to effectively exhibit the above effect, it is necessary to add 0.02φ or more of rare earth element metal to the total weight of the wire. However, if the amount added is too large, arc neutrality will be lost, poor penetration will occur, and the rowability will deteriorate, so it must be kept at 2 or less.

Mitshu metal and RE are used as rare earth element gold scrap additive raw materials.
Examples include M-containing Ca-51, among which those containing light rare earth elements such as La and Ca as a main component are desirable.

2) 0.09 to 0.4% Mg is a strong deoxidizing element based on the total weight of the wire in the metal Mg double-filled fusix, and by adjusting the amount added, the amount of oxygen in the weld metal can be controlled. be able to. If the amount of oxygen in the weld metal can be reduced to about 700 ml by which action, the crystal grains at the dendrite grain boundaries of the weld metal can be refined, and the occurrence of pear-shaped hot cracks can be effectively suppressed. It also improves toughness. However, if the above oxygen content decreases too much, the effect of capturing and dispersing S and P as oxides will be lost, a film-like sulfide will be generated, and the cracking resistance will decrease.
m or more. Furthermore, if a large amount of Mg is added to reduce the amount of oxygen, M, which is a high melting point substance, will increase depending on the amount added.
gO is generated and the proportion of MgO in the slag increases. As a result, the sliding resistance of the Cu metal increases and the appearance of the pead deteriorates, so the amount of Mg added is limited from this point of view as well.

For the above reasons, the content of metallic Mg in the filling flux was determined to be 0.09/-0.4% based on the total weight of the wire.

Mg additive raw materials include metal Mg%S1-Mg alloy, N
Examples include i-Mg alloy, Al-Mg alloy, Fe-81-Mg alloy, etc. Among them, AI'-Mg alloy is preferable because a stable arc can be obtained even if the wire extension is made long.

19 (Rare earth metal in flux/C in total wire
amount)=1 or more The solubility of S and 1P in the γ phase, which is the solidified primary crystal of the weld metal, is i-7 of the solubility in the δ phase.

However, since C is an r-phase stabilizing element, when the C content is high, the γ phase increases and the solubility of S and P decreases, which remains in the liquid phase and precipitates at grain boundaries in the final stage of solidification, reducing cracking resistance. decrease. Therefore, it is desirable that the amount of C be small, but since some amount of C is inevitably present, it is necessary to offset this by the effect of adding the rare earth element. That is, by setting the ratio (rare earth metal in flux/C amount in total wire) to 1.0 or more, it is possible to prevent S and P from precipitating at grain boundaries.

The basic formation of the composite wire of the present invention is the above-mentioned throughput, and when EGW is performed using the composite wire, the pear-shaped crack occurrence area is as shown in Figure 3). The permissible range will be expanded.

In addition, the following may be mentioned as composite wire constituents other than those mentioned above.

V: 0.07 to 0.6 inches based on the total weight of the wire has the effect of making the crystal grains finer and stabilizing the δ phase.These factors make the cracking resistance perfect. Therefore, in order to completely prevent pear-shaped hot cracking, it is necessary to
．． It is desirable to add 0.7% or more. On the other hand, if the amount added is too large, (2) acts as an impurity and reduces the toughness of the weld metal 8, so it is recommended to limit it to 0.6 inches or less.

(S i 02 +2T i Ot )/Mg : 1
．． 6 or more Sin and Tie have the effect of keeping the slag glassy and improving the slipperiness with the Cu metal, so it is possible to suppress the increase in the sliding resistance of the Cu metal due to the MgO generation, As a result, deterioration of the bead appearance can be prevented. In order to obtain the above effects, it is desirable to add it to the lux.

Although there is no limit to the slag in which CaF2, etc., which have a large desulfurization effect are added to the flux, and the slag becomes basic, it is desirable to manufacture the slag so as to satisfy the following conditions.

In other words, there is no particular restriction on the cross-sectional structure of the wire, and it may be cylindrical (including open seam and closed seam), apple shape, OW shape, etc., but consideration should be given to preventing wire meandering and application to small diameter wires. In this case, a cylindrical shape is preferable.

By using a composite wire with the above configuration,
Lower heat input without the risk of high-temperature pear-shaped cracking
It is now easier to increase speed.

In order to achieve this effect, we investigated the wire suitable for high-speed, low-heat-input construction and the construction conditions using that wire, and as a result, we achieved the goal by dramatically increasing the melting speed of the wire. .

Regarding the cross-sectional shape of the wire, in order to increase the wire melting rate by exerting the Joule heating effect at the wire extension part, the ratio expressed by (mild steel outer cross-sectional area) / (total wire cross-sectional area) is set to 0. It is desirable to set it as 55-0.69. In other words, if the ratio exceeds 0.69, the proportion of the mild steel outer skin made of a good conductor becomes too small compared to the proportion of the fuselage part, which is a non-conductor, and the electrical resistance decreases and the substantial Current density also decreases. As a result, the amount of Joule heat generated decreases, and the melting rate of the wire also decreases. On the other hand, if the above-mentioned ratio is less than 0.55, the thickness of the metal jacket is too thin, and when the wire is drawn to a small diameter, manufacturing difficulties such as wire breakage and bending of the wire occur.

In addition, when using the above wire, the wire diameter should be 0.9~
It is desirable to set it to 1.6 +n+nφ. That is, the above (
Even if the ratio (cross-sectional area of mild steel sheath/total cross-sectional area of wire) is appropriate, if the wire diameter exceeds 1.6o+mφ, the absolute amount of the metal sheath, which is a highly conductive portion, increases and the current density decreases. As a result, the Joule heating effect is not sufficiently exerted, leading to a decrease in the melting rate, and on the other hand, when the wire diameter is less than 0.9 mmφ, it becomes difficult to manufacture a composite wire.

On the other hand, even if the melting speed is increased, if the weight per unit of wire or the proportion of metal is small, no improvement in the welding speed can be expected as a result. Therefore, it is desirable to increase the amount of weld metal forming elements (10 iron powders and 10 alloy elements) in the filling flux, but on the other hand, it is necessary to include nonmetallic substances as slag forming agents in the flux. In order to secure 4 parts of weld metal formation, it is desirable to adjust the total amount of nonmetallic substances to 0.4 to 3.9% with respect to the total weight of the wire. If the total amount of nonmetallic substances exceeds 3.9, the welding efficiency decreases, making it impossible to expect an increase in welding speed. On the other hand, if it is less than 0.4%, the bead surface cannot be uniformly covered with slag, and the appearance of the bead deteriorates. In addition, the above-mentioned nonmetallic substance is S i02 +
Examples include T + 02 r Ca Or Ca F2.

Furthermore, it is desirable that the bulk specific gravity of the filling flux in the wire finishing state is 4.6 to 6.6. High specific gravity is 6.
When it exceeds 6, the welding current also flows through the metal components in the filling flux, the current density in the metal sheath becomes small, and the Joule heat generation amount decreases. Furthermore, since the filling flux becomes compacted, manufacturing difficulties such as wire breakage occur during wire drawing. On the other hand, if the high ratio is less than 4.6, the filling rate of the four weld metal forming portions decreases and the welding efficiency deteriorates. The bulk specific gravity is adjusted by adjusting the thickness of the mild steel metal shell, flux particle size, flux rate, etc. Furthermore, it is desirable that the amount of iron powder in the flux be 15 or more pieces based on the total weight of the wire. Preferably, the filling flux is granulated in advance with a binder such as water glass, since this prevents the welding current from flowing through the seven sixes, thereby increasing the 71z flow density (described in detail later).

By using a composite wire with the above configuration, it has become possible to perform high-speed, low-heat-input EGW without causing pear-shaped hot cracking.

Next, welding methods, particularly construction conditions, for fully bringing out the characteristics of the composite wire will be described.

Current density expressed as (welding current/metal skin cross-sectional area):
290-500 A/mnF In order to increase the melting rate, it is necessary to increase the current density, but if it is increased to more than 500 A/m♂, the arc becomes unstable, the pead appearance becomes scary, and the penetration becomes shallow. On the other hand, if it is less than 290 A/mm2, the melting rate of the wire is slow and high speed welding cannot be achieved.

L/D2: 12-25 The wire extension is a factor that influences the wire melting rate, and in order to obtain a sufficient Joule heating effect, L/D2
It is necessary to increase the amount by 12 points. However, if L/D2 is too tight, the wire extension becomes too long, causing the wire to meander and the arc to become unstable.
In addition, the welding voltage decreases, resulting in poor appearance and poor penetration, so it is necessary to suppress Φ2 to 25 or less.

In addition, it is recommended to adopt a method of increasing the wire melting rate by 20 to 25 degrees by changing the current polarity to positive polarity, if necessary. It is preferable to use Ar-Co2 or Ar-02 as the shielding gas in order to achieve positive polarity because the arc will be stabilized.

The present invention is constructed as described above, and the soft forged outer skin and the filling flux are specified as yITi, respectively.
In EGW performed using the composite wire, the region where pear-shaped hot cracks occur could be moved back to the side where the H/W value is large and the welding speed is high (upper right side in the figure) as shown in FIG. When performing EGW using the composite wire, welding conditions were specified as described above, so high speed and low heat input of EGW could be achieved without generating pear-shaped hot cracking. As a result, welding costs could be reduced. Furthermore, by achieving high speed and low heat input, it was possible to improve the toughness from the bond part to the HAZ part.

Although the present invention is mainly applied to vertical EGW, it also exhibits crack prevention results in horizontal EGW and electroslag welding.

Next, examples of the present invention will be described.

Using a composite wire with the components and compositions shown in Table 1 (a) and (b), a CO2 flow rate of 30 /j /sin was used, and a power supply with thyristor type DC constant voltage characteristics (reverse polarity) was used, and the plate thickness was 2.
EGW of 5mm HT50 material was performed. Furthermore, wire A~
Wires I and PT represent comparative examples, wires J-N represent reference examples, and wires U-Z represent examples, respectively.

Wire A had a high carbon content of 0.01% in the mild steel outer sheath, which caused frequent spatter, poor workability, reduced welding efficiency, and caused slag hold, which worsened the bead appearance. Wire B has M n ff (1.3
8, which inhibited the dispersion of sulfides and coarsened the crystal grains, resulting in pear-shaped cracks.

Wire C has a high Mn content of 3.87% in the entire wire, so the primary γ phase is stabilized, and the sulfide that cannot be completely dissolved in the γ phase and remains in the columnar crystal association grows too large and becomes pear. A mold crack occurred. Wire D did not exhibit pear-shaped cracking prevention effect 1 because the rare earth element content was as low as 0.005%. Wire E had a high rare earth element content of 0.24%, so the arc concentration was lost, poor penetration occurred, and workability deteriorated. Wire F had a low ratio of rare earth element/total C content of 0.58, so the influence of carbon on cracking could not be offset, and pear-shaped cracking occurred. Wire G is metal M
Since the g amount is as low as 0.06, the deoxidizing effect is not exhibited and oxygen 1
The effect of grain refinement due to lowering the grain size was weakened, and pear-shaped cracks occurred. The amount of oxygen at this time was 900 pIll11. In wire H, the gold scrap Mg bond was too high at 0.51 mm, so the proportion of Mg0 (high melting point substance) in the slag increased, the sliding resistance of the Cu metal increased, and the appearance of the bead deteriorated. Since Wire I did not contain any rare earth elements, the occurrence of pear-shaped cracks could not be prevented.

On the other hand, wire J-N is a reference example of the present invention, and wire J is (cross-sectional area of mild steel outer skin/total cross-sectional area of wire)
Since the ratio shown by is too thick, the electrical resistance as a wire decreases, and the current density also decreases, so that the Joule heating effect is not fully exhibited. As a result, the melting rate of the wire became low and the welding speed decreased slightly. Since the total amount of non-metallic substances in the wire was too small at 0.29%, the amount of slag was insufficient and the bead surface could not be coated sufficiently uniformly, resulting in poor appearance of the bead. In wire L, the total amount of the four non-gold substances in the slack was 4.35q6, which was too large, so the metal components were relatively insufficient, the welding efficiency decreased, and a sufficient welding speed could not be obtained. In wire M, the bulk specific gravity of the filling flux was too low, so the welding efficiency decreased and the welding speed decreased slightly. In Wire N, since the bulk specific gravity of the filling flux was too high, the welding current also flowed through the flux, reducing the current density, diluting the Joule heating effect, and making the wire more likely to break.

On the other hand, wires I~S are comparative examples whose welding conditions do not satisfy the present invention, and wire P has a current density of 550 A.
/mm2, which was too high, made the arc unstable, deteriorated the bead appearance, and caused poor penetration. Wire Q had a low current density of 270 A/mm2, so the wire melting rate was low. The wire R has a ratio L/D2 of 2.
9, which was too large, caused wire meandering, arc instability, voltage drop, etc., resulting in poor bead appearance and poor penetration. Since the wire S had a low L/D2 of 9, that is, the wire extension was short and small, a sufficient Joule heating effect could not be obtained and the welding speed was reduced.

In addition, the wire T has a large wire diameter of 2.0 mmφ, and the ratio shown by (soft j (cross-sectional area of the outer skin made of 1/total area of the wire)) is normal, so the absolute ( 1t increased, the IL flow density decreased, and a sufficient Joule heating effect could not be obtained.As a result, the welding speed decreased.

On the other hand, Wire U-Z satisfies the present invention in both the component composition of the composite wire and the welding conditions, and it not only does not cause pear-shaped cracks, but also has good welding workability and bead appearance, and produces a sound weld metal. I was able to get it.

[Brief explanation of drawings]

Fig. 1 is a graph showing the crack occurrence area when EGW is performed using a conventional composite wire, Fig. 2 is a cross-sectional view explaining H/W, and Fig. 3 is a graph showing the crack occurrence area when EGW is performed using the composite wire according to the present invention. EG is a graph showing the crack occurrence area when vV is performed.

Claims (2)

[Claims] (1) In a composite wire for electrogas arc welding in which a cavity surrounded by a mild steel tubular sheath is filled with flux, C: C in the mild steel sheath: 0.06 cracks (meaning weight attack, the same applies hereinafter) or less (b) Mn in the total wire: 1.5 to 3.5%, and (c) Rare earth element metal: 0.02 to 0.2%) metal in the filling flux based on the total weight of the wire. M
g: 0.09 to 0.4, and (e) rare earth metal in flux/C in total wire.
Composite wire for electrogas arc welding characterized by having a sensitivity of 1 or more. (2) An electrogas arc welding method using a composite wire for electrogas arc welding in which a cavity surrounded by a tubular outer skin made of mild steel is filled with flux, wherein (a) C in the outer skin made of mild steel: 0.06 % or less (b) Mn in the total wire: 1.5 to 3.5%, and (c) Rare earth element metal: 0.02 to 0.2 strips based on the total wire weight in the filling flux. ) Metal M
Composite wire for electrogas arc welding, containing g:0.09 to 0.4H, and (e) (rare earth element gold JfA in flux/C amount in total wire) = 1 or more. using a current density of 290 to 500 A/mrrP expressed as (welding current/cross-sectional area of mild steel outer skin). An electrogas arc welding method characterized in that welding is performed by setting [(wire extension)/(wire diameter) 2] to 12 to 25, respectively.