JPS6252679B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite wire for electrogas arc welding (hereinafter referred to as EGW) that can obtain weld metal with excellent hot cracking resistance even under high-speed, low-heat-input conditions, and an EGW performed using the wire.
It is about the method. Due to its high welding efficiency, EGW 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 HAZ part, there was a problem that pear-shaped cracking occurred, and there was a limit to increasing the speed. . By the way, pear-shaped cracks occur due to the segregation of low-melting point impurities in columnar crystal aggregates, and the area where they occur is determined by the welding speed and the bead cross-sectional shape factor (H/W 2), as shown in Figure 1. (see figure). In other words, in order to prevent the occurrence of pear-shaped cracks, (1) reduce the welding speed or (2) (H/
W) needs to be lowered. Note that reducing (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 unavoidable, 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.
The advantages of EGW will be lost. 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 purpose 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 purpose. The composite wire for EGW of the present invention that has achieved the above object is one in which the cavity surrounded by the mild steel tubular sheath is filled with flux. meaning,
The same applies hereafter) Below (b) Mn in the whole wire: 1.5 to 3.5%, and in the filling flux, based on the total weight of the wire (c) Rare earth element metal: 0.02 to 0.2% (d) Metal Mg: 0.09 ~0.4%, respectively, and (e) (Rare earth element metal in flux/C amount in total wire): The gist is that it is adjusted to 1 or more, and furthermore, the above
The welding method of the present invention using EGW wire has a current density of 290 to 500 A/ ^mm2 , expressed as (welding current/metal skin cross-sectional area), [(wire extension)/(wire diameter) ² ]( The gist lies in that welding is performed with L/D ² (hereinafter referred to as L/D 2) set at 12 to 25, respectively. First, the composition of the wire of the present invention will be explained. (b) C in the mild steel outer shell: 0.06% or less If the amount of C contained in the mild steel outer shell is too large, it will cause the droplets to explode and the arc to become unstable.
It causes deterioration of workability, spatter generation, and slag hold on the surface bead.
Since it increases the amount of fume generated and worsens the working environment, the content needs to be 0.06% or less. (b) Mn in all wires: 1.5 to 3.5% FeS (melting point 988°C) is a particularly typical low melting point impurity that causes pear-shaped cracks, but an appropriate amount of Mn should be added. and FeS are reduced to generate MnS, which is dispersed at grain boundaries or within 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. Also, 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 in an amount of 1.5% or more. However, if the MnS content exceeds 3.5%, the γ phase, which is the primary crystal during solidification, is stabilized, and in EGW, a large heat input (25 KJ/cm at the least) is added to the weld zone. On the other hand, sulfide crystals such as sulfide crystals grow too much and pear-shaped hot cracks are likely to occur. The flux raw materials used to add Mn are as follows:
Examples include Fe-Mn, Fe-Si-Mn, and metal Mn. Considering wire drawability, the Mn content in the hoop is preferably 0.6% or less. (c) Rare earth metal: 0.02 to 0.2% of the total wire weight in the filling flux Rare earth elements have desulfurization and dephosphorization effects, and react with S and P in the weld metal to form sulfides and phosphides. is generated and transferred into the slag. As a result, the generation of low melting point impurities such as FeS can be reduced, and the segregation of low melting point impurities to grain boundaries can be reduced. Furthermore, the P and S remaining in the weld metal are also replaced by high melting point La ₂ S ₃ and CeS.
This has the effect of preventing the low melting point liquid phase from segregating at grain boundaries in the final stage of solidification. In order to effectively exhibit the above effect, it is necessary to add 0.02 of the rare earth metal in the flux to the total weight of the wire.
It is necessary to add more than %. However, if the amount added is too large, the arc will not be concentrated, resulting in poor penetration and poor workability.
Must be kept below 0.2%. Examples of raw materials to which rare earth metals are added include Mitsushi Metal and REM-containing Ca-Si, among which La and
It is desirable that the main component is a light rare earth element such as Ca. (d) Mg metal: 0.09 to 0.4% based on the total weight of the wire in the filling flux Mg is a strong deoxidizing element, and the amount of oxygen in the weld metal can be controlled by adjusting the amount added. This action reduces the amount of oxygen in the weld metal.
If it can be lowered to about 700 ppm, the crystal grains at the dendrite grain boundaries of the weld metal can be made finer, the occurrence of pear-shaped hot cracking can be effectively suppressed, and the toughness can also be improved. However, if the above oxygen amount decreases too much, S and P
It is necessary to keep the content above 300 ppm because the effect of trapping and dispersing oxides as oxides is lost and film-like sulfides are generated, reducing cracking resistance. If a large amount of Mg is added to reduce the amount of oxygen, MgO, which is a high melting point substance, will be generated depending on the amount added, and the proportion of MgO in the slag will increase. As a result, the sliding resistance of the Cu metal increases and the appearance of the bead deteriorates, so the amount of Mg added is also limited from this point of view. For the above reasons, metals in the filling flux
Mg content is 0.09 to 0.4 relative to the total weight of the wire
%. Examples of Mg-added raw materials include metal Mg, Si-Mg alloy, Ni-Mg alloy, Al-Mg alloy, Fe-Si-Mg alloy, etc. Among them, Al-Mg alloy is suitable for long wire extensions. This is desirable because a stable arc can be obtained. (e) (Rare earth metal in flux/C amount in total wire): 1 or more The solubility of S and P in the γ phase, which is the solidified primary crystal of the weld metal, is 1/3 to 1/4 of the solubility in the δ phase. It is. However, since C is a γ-phase stabilizing element, when the C content is high, the γ phase increases, reducing the solubility of S and P, 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 structure of the composite wire of the present invention is as described above, and when EGW is performed using the composite wire, the pear-shaped crack occurrence area is as shown in FIG.
The permissible range of W value and welding speed is expanded. In addition, the following may be mentioned as composite wire constituents other than those mentioned above. V: 0.07 to 0.6% based on the total weight of the wire V has the effect of refining crystal grains and stabilizing the δ phase, thereby making the cracking resistance more perfect. Therefore, in order to more completely prevent pear-shaped hot cracking, it is desirable to add 0.07% or more to the total weight of the wire. On the other hand, if the amount added is too large, V
acts as an impurity and reduces the toughness of the weld metal, so it is recommended to limit it to 0.6% or less.
(SiO ₂ + 2TiO ₂ )/Mg: 1.6 or more SiO ₂ and TiO ₂ have the effect of keeping the slag glassy and improving the slipperiness with the Cu metal.
It is possible to suppress the increase in the sliding resistance of the Cu metal due to the generation of MgO, and in turn, it is possible to prevent the bead appearance from deteriorating. In order to obtain the above effect, it is desirable to add SiO ₂ and/or TiO ₂ to the flux so that the ratio [(SiO ₂ +2TiO ₂ )/Mg] is 1.6 or more. It is also recommended to add _CaF2, etc., which has a strong desulfurization effect, to the flux, or to add a slag forming agent that makes the slag basic. In addition, although there are no particular limitations regarding the manufacturing conditions for the composite wire of the present invention, it is desirable to manufacture the composite wire so as to satisfy the following conditions. In other words, there are no particular restrictions on the cross-sectional structure of the wire, and it may be cylindrical (including oven seam and closed seam), apple shape, OW type, 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 having the above configuration, it has become easier to achieve lower heat input and higher speed without risking the occurrence of high-temperature pear-shaped cracks. In order to achieve this effect, we investigated the wire suitable for high-speed, low-heat-input construction and the construction conditions for using the wire, and as a result, we achieved the purpose 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 heat effect at the wire extension part, the ratio expressed by (mild steel outer cross-sectional area) / (total wire cross-sectional area) is set to 0.55. It is desirable to set it to ~0.69.
That is, if the ratio exceeds 0.69, the proportion of the mild steel outer skin, which is a good conductor, becomes too large compared to the proportion of the flux portion, which is a non-conductor, resulting in a decrease in electrical resistance and a decrease in substantial current density. As a result, the amount of generated Joule heat is reduced, and the melting rate of the wire is also reduced. On the other hand, if the above-mentioned ratio is less than 0.55, the thickness of the metal sheath is too thin, and manufacturing difficulties such as wire breakage and bending of the wire occur when the wire is drawn to a small diameter. When using the above wire, please check the wire diameter.
It is desirable to set it as 0.9-1.6mmφ. In other words, even if the ratio shown above (cross-sectional area of mild steel skin/total cross-sectional area of wire) is appropriate, if the wire diameter exceeds 1.6 mmφ, the absolute amount of the metal skin, which is a highly conductive part, increases and the current density decreases. do. As a result, the Joule heat 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 components (iron powder + alloying elements) in the filling flux as much as possible.
On the other hand, it is necessary to include nonmetallic substances in the flux as slag forming agents, etc., so in order to secure the amount of weld metal forming agent, the total amount of nonmetallic substances should be 0.4 to 3.9% of the total weight of the wire. It is desirable to adjust the 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. Incidentally, examples of the non-metallic substance include SiO ₂ , TiO ₂ , CaO, CaF ₂ and the like. Furthermore, it is desirable that the bulk specific gravity of the filling flux in the finished state of the wire is 4.6 to 6.6. When the bulk specific gravity exceeds 6.6, the welding current also flows through the metal components in the filling flux, the current density in the metal sheath becomes smaller, and the amount of heat generated by the unit decreases. Furthermore, since the filling flux is in a compacted state, manufacturing difficulties such as wire breakage during wire drawing occur. On the other hand, the bulk ratio is 4.6
If it is less than 20%, the filling rate of the weld metal parts will decrease and the welding efficiency will deteriorate. The bulk ratio is adjusted by adjusting the thickness of the mild steel metal shell, flux particle size, flux rate, etc. Further, it is desirable that the amount of iron powder in the flux be 15% or more 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 flux, thereby increasing the current density (described in detail later). By using the composite wire with the above configuration, high speed and low heat input can be achieved without causing pear-shaped hot cracking.
It became possible to perform EGW. 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 to 500 A/mm ² To increase the melting rate, it is necessary to increase the current density, but if you increase it beyond 500 A/mm ² , the arc will It becomes unstable, the bead appearance deteriorates, and penetration becomes shallow. On the other hand, if it is less than 290 A/mm ² , the melting speed of the wire becomes slow and high-speed welding cannot be achieved. L/D ² :12-25 The wire extension is a factor that influences the wire melting rate, and in order to obtain a sufficient Joule heat effect, it is necessary to set L/D ² to 12 or more. However, if L/D ² becomes too large, the wire extension becomes too long, causing the wire to meander and the arc to become unstable, and the welding voltage to drop, resulting in poor appearance and poor penetration ^. must be kept below 25. In addition, it is recommended to adopt a method of increasing the wire melting rate by 20 to 25% by changing the current polarity to positive polarity, if necessary. It is preferable to use Ar--CO ₂ or Ar--O ₂ as the shielding gas in order to achieve positive polarity, since this stabilizes the arc. The present invention is constructed as described above, and since the mild steel outer shell and the filling flux are specified as described above, the area where pear-shaped hot cracking occurs in EGW using the composite wire is as shown in FIG. It was possible to retreat to the side where the H/W value was large and the welding speed was high (upper right side in the figure). When performing EGW using the composite wire, welding conditions were specified as described above, so we were able to achieve high speed and low heat input in EGW without generating pear-shaped hot cracking, and as a result, welding We were able to reduce costs. Furthermore, by achieving high speed and low heat input, we were able to improve the toughness from the bond area to the HAZ area. Although the present invention is mainly applied to vertical EGW, it also exhibits the effect of preventing cracking 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 plate thickness of 25 mm was used at a CO ₂ flow rate of 30/min with a thyristor type DC constant voltage characteristic (reverse polarity) power source.
EGW of HT50 material was carried out. Note that wires A to I and P to T are comparative examples, wires J to N are reference examples, and wires U to Z are examples, respectively.

【table】

[Table] Wire A had a high C content of 0.09% 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 is one of all wires.
Since the Mn content was as low as 1.38, dispersion of sulfides was inhibited and the crystal grains became coarse, resulting in pear-shaped cracks. Wire C has a high Mn content of 3.87% in the total wire, so the primary γ phase is stabilized, and the sulfide that remains in the columnar crystal association grows too large without being completely dissolved in the γ phase, resulting in pear-shaped cracking. There has occurred. Wire D contains rare earth elements.
Since the content was as low as 0.005%, the effect of preventing pear-shaped cracking was not exhibited. Wire E contains 0.24% rare earth elements.
As a result, the concentration of the arc was lost, poor penetration occurred, and workability deteriorated. Wire F is
Because the ratio of rare earth elements/total C content was as low as 0.58, the effect of carbon on cracking could not be offset, and pear-shaped cracking occurred. Wire G had a low metal Mg content of 0.06, so the deoxidizing effect was not exhibited, and the crystal grain refinement effect due to the decrease in oxygen content was weakened, resulting in pear-shaped cracking. The amount of oxygen at this time was 900 ppm. In wire H, the metal Mg content was too high at 0.51%, so the proportion of MgO (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, wires J to N are reference examples of the present invention, and wire J has a too large ratio (cross-sectional area of mild steel outer skin/total cross-sectional area of the wire), so the electrical resistance as a wire decreases. Moreover, the current density also decreases, and the Joule heat 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 wire K 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 bead appearance. For wire L, the total amount of nonmetallic substances in the flux was too high at 4.35%, so the metal component was relatively insufficient, resulting in a decrease in welding efficiency and a sufficient welding speed. For 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 heat effect, and making the wire more likely to break. On the other hand, wires P to S are comparative examples whose welding conditions do not satisfy the present invention, and wire P has a current density as high as 550 A/mm ² , which makes the arc unstable and the bead appearance deteriorates. In addition, poor penetration occurred. Wire Q had a low current density of 270 A/mm ² , so the wire melting rate was low. Wire R is L/
Since the ratio indicated by ^D2 was 29, which was too high, wire meandering, arc instability, voltage drop, etc. occurred, resulting in poor bead appearance and poor penetration. Since the wire S had a low L/D ² of 9, that is, the wire extension was short and small, a sufficient Joule heat 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 (cross-sectional area of mild steel outer skin/total cross-sectional area of wire) is normal, so the absolute amount of the outer skin of mild steel is large, and the current The density decreased and it was not possible to obtain a sufficient Joule heat effect. As a result, the welding speed decreased. On the other hand, wires U to Z satisfy the present invention in terms of both the composition of the composite wire and the welding conditions, and not only do pear-shaped cracks not occur, but welding workability and bead appearance are also good, resulting in sound weld metal. I was able to get it.

[Brief explanation of the drawing]

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 the H/W value, and Fig. 3 is a graph showing the crack occurrence area when EGW is performed using the composite wire according to the present invention. It is a graph showing the crack occurrence area when performing.

Claims (1)

[Scope of Claims] 1. A composite wire for electrogas arc welding in which a cavity surrounded by a tubular outer shell made of mild steel is filled with flux, (a) C: 0.06% (meaning % by weight) in the outer shell made of mild steel;
The same applies hereafter) Below (b) Mn in the whole wire: 1.5 to 3.5%, and in the filling flux, based on the total weight of the wire (c) Rare earth element metal: 0.02 to 0.2% (d) Metal Mg: 0.09 A composite wire for electrogas arc welding, characterized in that the amount of C is adjusted to 1 or more, and (e) the amount of rare earth metal in the flux/the amount of C in the total wire is adjusted to 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 shell made of mild steel is filled with flux, which method comprises: (a) C: 0.06% or less in the outer shell made of mild steel; ) Mn in the total wire: 1.5 to 3.5%, and the filling flux contains (c) rare earth metal: 0.02 to 0.2%, and (d) metal Mg: 0.09 to 0.4%, respectively, based on the total weight of the wire. (e) (Rare earth metal in flux/C content in total wire): Using a composite wire for electrogas arc welding adjusted to 1 or more, (welding current/mild steel outer skin cross-sectional area) The current density expressed is 290~500A/ ^mm2 ,
[(Wire extension)/(Wire diameter)
² ) An electrogas arc welding method characterized in that welding is carried out by setting 12 to 25.