JP5001595B2 - Solid wire - Google Patents

Description

  The present invention relates to a solid wire used for arc welding, and more particularly to a carbon steel solid wire that can be applied to arc welding of a thin plate.

  In recent years, there has been a strong demand for improving fuel efficiency of automobiles from the viewpoint of environmental problems. In order to cope with this, attempts are being made to reduce the plate thickness and reduce the weight by replacing the conventional steel plate with a tensile strength of 300 MPa or less with a high strength steel plate with a tensile strength of 400 MPa or more.

  Here, when the plate thickness is reduced, there is almost no problem in the spot welding method, but in the arc welding method, the steel sheet is melted by the arc heat and a so-called burn-out is likely to occur.

  Strengthening of steel sheets is generally achieved by controlling the cooling during rolling and increasing the amount of elements added to the steel sheet. However, increasing the amount of elements added to the steel sheet increases the viscosity of the molten pool during arc welding. The so-called undercut in which the conformability deteriorates and the weld toe portion loses the thickness is likely to occur.

  Further, in terms of welding, if the welding speed is increased in order to improve the welding efficiency, an arc precedes the molten pool, and the arc tends to directly contact the molten surface, so that the melting is likely to occur. Moreover, even if it does not lead to melting-down, when it is melted to the back side of the plate material being welded (this is also referred to as a back wave), hot cracking is very likely to occur.

  For example, Patent Document 1 discloses that a wire having a diameter of 0.9 mm or less with a specified electrical resistivity is used to reduce the heat input per welding amount, thereby making it difficult to melt (that is, improving the burn-off resistance). ) Is stated.

Further, for example, Patent Document 2 defines Si + Mn and Si × (Si + Mn) of a wire, and further contains a very small amount (3 to 7%) of O ₂ gas in Ar, thereby improving the burn-off resistance. Is described. This technology is due to a synergistic effect of the effect of reducing the heat input per welding amount by appropriately increasing the electrical resistivity of the wire and the effect of reducing the penetration depth by increasing the Ar ratio of the shielding gas. Is.

  Further, for example, Patent Document 3 and Patent Document 4 describe that a special welding power supply tip having a ceramic attached to the tip is used. This reduces the heat input per welding amount by increasing the electrical resistance heat generated between the energization point at the tip of the welding power supply tip and the arc generation point, thereby improving the burn-off resistance and reducing the current. Therefore, the occurrence of undercut is suppressed (that is, the undercut resistance is improved).

Further, for example, in Patent Document 5, Ar and CO ₂ are used as shielding gases, and a large amount (5.5 to 15%) of O ₂ is mixed with the gas to change the convection direction of the molten pool, thereby improving the resistance. It describes that the undercut property is improved.

In addition, it has been known from the past that empirical vertical welding can improve the resistance to melting and undercut, but the welding posture is limited and the downward angle is excessive. If so, there is a problem in that control is difficult because drooping of beads and a large amount of spatter are generated.
JP 2001-96392 A Japanese Patent No. 2922814 JP-A-9-94667 Japanese Patent No. 3345883 JP 2005-254284 A

  However, a thin wire as described in Patent Document 1 has a problem that it is easy to buckle because it is thin, and the welding workability is poor because the feeding stability of the wire is poor. Moreover, since the cost of such a thin wire becomes high, there is a problem that the cost of welding is increased.

  In addition, the single wire described in Patent Document 2 cannot solve the problem of poor burn-through resistance. In addition, when the ratio of Ar in the shielding gas is increased in this way, the cost of the shielding gas is increased, leading to an increase in welding costs.

  On the other hand, since a special welding power feed tip as described in Patent Literature 3 and Patent Literature 4 is used, the cost of the tip increases, leading to an increase in welding cost.

  And in the arc welding method of patent document 5, since the cost of shielding gas becomes high because special shielding gas is used, there is a problem that it leads to cost increase of welding, and since there is a large amount of oxygen, slag and A large amount of spatter is generated. The presence of slag and spatter leads to deterioration of the paintability of the welded part. Furthermore, there is a problem that inclusions increase due to a significant increase in the amount of oxygen contained in the weld metal and hot cracking is likely to occur (that is, the crack resistance is poor).

  In addition to the above-described problems, in order to perform general-purpose general thin plate welding, the weld metal has a hardness equal to or higher than that of the base metal, does not cause brittle fracture, and performs welding smoothly. It is required to have good feed stability.

  The present invention has been made in view of the above-mentioned problems, and is excellent in wire feeding stability, anti-melting-out resistance, undercut resistance, and crack resistance while minimizing an increase in welding costs, and is provided with slag and spatter. An object of the present invention is to provide a solid wire that has a weld metal hardness that is less than or equal to that of the base metal and does not cause brittle fracture.

  The solid wire according to the present invention that has solved the above problems is a solid wire used for arc welding, and C is 0.005 to 0.060 mass%, and Si is 0.60 to 1.00 mass%. , Mn 1.10-1.65 mass%, S 0.045-0.090 mass%, O 0.0015-0.0100 mass%, and the total of the contents of C and S 0.125% by mass or less, P is contained at 0.017% by mass or less, and the balance is Fe and impurities. The impurities are Ti 0.15% by mass or less, B is 0.0050% by mass or less, N 0.0075 mass% or less, and Cr, Ni, Al, Nb, V, Zr, La, and Ce are each contained at 0.20 mass% or less.

The solid wire according to the present invention can greatly reduce the viscosity and surface tension of the molten pool by limiting the contents of C, Si, Mn, S, and O to a specific range, and at the time of arc welding A molten pool can be formed deeply. Thereby, the barrier effect | action which relieve | moderates arc force can be obtained, and since it becomes possible to reduce the penetration depth, the burn-off resistance can be improved.
In addition, since the solid wire according to the present invention significantly reduces the viscosity and surface tension of the molten pool, even if undercut occurs, the weld metal melted in the molten pool is affected by gravity. Since it flows into the cut portion, undercut can be eliminated before the welded portion solidifies (that is, the undercut resistance can be improved).
And the solid wire which concerns on this invention makes it hard to generate | occur | produce slag and a spatter by optimizing the content of S and the content of O, C content, S content, C and S content The crack resistance can be improved by optimizing the total amount of P, the content of P and the total amount of C and S.
Furthermore, the solid wire according to the present invention can further prevent the viscosity and surface tension of the molten pool from being increased by containing a specific type of impurities in a specific range. Can be further prevented from becoming shallow. Therefore, the barrier action to relieve the arc force can be obtained more reliably, and the penetration depth can be reduced, improving the burn-off resistance and undercut resistance, and generating more spatter and slag. Can be difficult. In particular, cracking resistance can be further improved by regulating B below a specific content, and embrittlement of the weld metal can be prevented by regulating N below a specific content. The soundness of the welded portion can be further improved.

In the solid wire according to the present invention, the total content of O and N is preferably limited to 0.0110% by mass or less. Moreover, it is preferable that the solid wire which concerns on this invention contains Mo at 0.30 mass% or less.
As described above, the solid wire according to the present invention can prevent the viscosity of the molten pool from becoming too low by regulating the total content of O and N to a specific content or less. Undercut resistance can be improved.
And since the solid wire which concerns on this invention can prevent that the viscosity and surface tension of a molten pool become high by controlling Mo below specific content, a molten pool becomes shallow at the time of arc welding. Can be prevented. As a result, a barrier action to alleviate the arc force can be reliably obtained, and the penetration depth can be reduced, so that the burn-off resistance and the undercut resistance are improved, and spatter is hardly generated. be able to.

The solid wire according to the present invention preferably has a total of 0.5 to 30 ppm of at least one element selected from K, Li, Na, and Ca on the surface of the solid wire.
Since the solid wire according to the present invention has at least one element selected from such a group applied or adhered to the surface of the solid wire, it can be easily emitted by having it in the specific range described above. Acts as an arc stabilizer in welding using Ar and an oxidizing gas (such as O ₂ or CO ₂ ). Therefore, a change in arc length can be suppressed, and the burn-through resistance can be further improved.

The solid wire according to the present invention preferably has 0.01 to 1.00 g / 10 kg of MoS ₂ on the surface of the solid wire.
The solid wire according to the present invention has a specific range as described above by applying or adhering MoS ₂ to the surface thereof, thereby reducing the instantaneous fusion at the energization point and reducing the resistance. Wire feeding stability can be improved.

The surface of the solid wire according to the present invention may be coated with copper plating.
By covering the solid wire according to the present invention with copper plating, the rust resistance is improved, the wear resistance of the current-carrying tip is improved, the productivity is improved by the effect of improving the wire drawing at the time of wire production, and the associated low cost. Can be achieved.

  According to the solid wire according to the present invention, the wire feed stability, anti-melting-out resistance, undercut resistance, and crack resistance are excellent while minimizing the welding cost increase, and slag and spatter are hardly generated. And it has the hardness of the weld metal equivalent to or higher than that of the base material, and can make it difficult to cause brittle fracture.

Next, the best mode for carrying out the solid wire according to the present invention will be described in detail.
The present inventors pay attention to the behavior of the molten pool and the weld metal during the above-described vertical downward welding, and do not depend on the posture such as horizontal welding, downward welding, lateral welding, upward welding, and vertical improvement welding. In addition, if the weld pool and the weld metal were able to obtain the same behavior as described above, it was considered that arc welding could be performed more suitably, and intensive research was conducted.

  First, the principle of the solid wire according to the present invention which has been completed by the present inventors will be described with reference to FIG. FIG. 1 is a diagram schematically showing a state of arc welding, (a) is a diagram schematically showing a state of performing arc welding using a conventional solid wire, and (b) is a diagram. It is a figure which shows typically a mode that arc welding is performed using the solid wire which concerns on this invention.

As shown in FIG. 1A, in the arc welding using the conventional solid wire 31, the viscosity and surface tension of the molten pool 6 are large. Therefore, since the push-up P ₁ of the molten pool 6 by arc force and surface tension becomes large with respect to gravity P _2, is lowered by gravity P ₂ of the molten pool 6 itself is reduced. That is, the depth L ₁ of the molten pool 6 of an arc immediately below is small, the penetration depth L ₂ increases.
Further, the resistance heat generation of the so-called protruding portion A and the droplet 4 formed at the tip from the tip 2 / solid wire 31 energization point (mainly the tip of the tip 2) to the generation point of the arc 5 becomes low.

Therefore, as shown in FIG. 1 (b), the inventors of the present invention are that the weld pool moves from the rear of the arc to the position immediately below the arc by gravity during vertical downward welding, that is, always deep under the arc. It has been found that the molten pool is formed and the barrier action to alleviate the arc force works, so that the molten pool becomes difficult to be burned out (improved burn-off resistance). In addition, even if an undercut occurs instantaneously, the lowering action of the molten pool due to gravity works greatly, and the weld metal of the molten pool flows into the undercut portion, so that the undercut disappears during solidification (undercut resistance) Improved).
This is the viscosity of the molten pool 6 formed welded rearwardly from immediately below the arc 5, to decrease the surface tension, the P ₂ by P ₁ decreases prevails, causing dropped the molten pool 6 to the arc 5 immediately below. Thus, increasing the depth L ₁ of the molten pool 6 just below the arc 5, by defending the action of the arc power, it is by reducing the depth of penetration L _2.

As a result of diligent research, the inventors have increased the electrical resistance of the solid wire itself, thereby increasing the resistance heat generation of the protruding portion and the droplet itself, thereby increasing the temperature and reducing the melting due to arc heat. By reducing the heat input and optimizing the composition of the solid wire, the viscosity and surface tension of the molten pool are greatly reduced, and the gravity action acting on the molten pool is fully extracted, so that it is not vertical down welding It has been found that the above-described mechanism can be realized even with this attitude.
In addition, at the research stage, the viscosity of the molten pool is increased by increasing the oxygen by means such as increasing the oxygen content of the gas components known in the art and reducing the strong deoxidation components such as Si and Mn contained as solid wire components. When the surface tension is lowered, problems such as a large amount of slag, blowholes, bead shape deterioration, and increased spatter frequently occur.

The present inventors have also made the S and O contents appropriate as means for improving this problem, making it difficult to generate slag and spatter, and maintaining the bead shape and the viscosity and surface of the molten pool. It has also been found that the tension can be significantly reduced.
Further, it is generally known that when S is contained at a high concentration, hot cracking is likely to occur. The present inventors appropriately regulate the content of a predetermined element such as the content of C, the content of P, the content of S, and the total content of C and S, in particular, FIG. It was also found that even when S is contained at a high concentration, it is possible to prevent high-temperature cracking by appropriately regulating the C content (improvement in crack resistance). In addition, FIG. 2 is a figure for demonstrating the range of the appropriate content of C and S performed in order to complete the solid wire of this invention.
Based on this knowledge, the present inventors have completed a solid wire according to the present invention suitable for arc welding.

In the solid wire according to the present invention, C is 0.005 to 0.060 mass%, Si is 0.60 to 1.00 mass%, Mn is 1.10 to 1.65 mass%, and S is 0.045 to 0.055 mass%. 0.090% by mass, O is 0.0015 to 0.0100% by mass, and the total content of C and S is 0.125% by mass or less, P is 0.017% by mass or less, The balance consists of Fe and impurities.
Hereinafter, the reason why numerical values are limited in the solid wire of the present invention will be described.

(C: 0.005-0.060 mass%)
C has a deoxidizing action and has an effect of increasing the strength of the weld metal. Thin plate welding does not require multi-layer welding, so there is no need to consider strength reduction due to reheating. From low-added 300MPa or less mild steel to 590MPa class high-tensile steel (high-tensile steel) even at low additions. A strength equal to or higher than that of the base material can be obtained.
However, if the C content is reduced to less than 0.005% by mass, the strength can be applied only to mild steel and the versatility is lost. Therefore, C needs to be contained by 0.005% by mass or more.
On the other hand, when the content of C increases, as described above, the crack resistance is remarkably deteriorated. In addition, the explosion of CO near the arc increases not only spatter generation but also fume generation. Furthermore, since deoxidation becomes excessive, oxygen in the molten pool is reduced, and the viscosity and surface tension of the molten pool are increased. For this reason, the barrier action to alleviate the arc force is reduced, and the burn-out resistance and undercut resistance are likely to be inferior. Therefore, in consideration of ensuring cracking resistance, C must be contained at 0.060% by mass or less, and is preferably contained at 0.050% by mass or less. As will be described later, the upper limit value of C may be further reduced depending on the S content.

(Si: 0.60 to 1.00% by mass)
Si is necessary for securing strength, but has an effect of increasing the electrical resistance of the solid wire. If it is less than 0.60% by mass, the strength is lowered, and the strength is not applicable except for mild steel. Further, since the electric resistance of the solid wire becomes too small, the current value per feeding amount increases. As a result, the heat input is increased, so that the burn-out resistance and the undercut resistance are likely to be inferior. Therefore, Si needs to be contained at 0.60% by mass or more.
On the other hand, when the Si content exceeds 1.00% by mass, deoxidation becomes excessive, oxygen in the molten pool is reduced, and the viscosity and surface tension of the molten pool are increased. For this reason, the barrier action to alleviate the arc force is reduced, and the burn-out resistance and undercut resistance are likely to be inferior. Further, if Si is excessive, the weld metal becomes brittle and the soundness of the welded portion may be lost. Therefore, Si needs to be 1.00 mass% or less.

(Mn: 1.10 to 1.65% by mass)
While Mn is also necessary for securing strength, it has the effect of increasing the electrical resistance of the solid wire. If the Mn content is less than 1.10% by mass, the strength decreases, and the strength cannot be applied to anything other than mild steel. Further, since the electric resistance of the solid wire becomes too small, the current value per feeding amount increases. As a result, the heat input is increased, so that the burn-out resistance and the undercut resistance are likely to be inferior. Moreover, when there is too little Mn, a weld metal will become brittle and there exists a possibility that the soundness of a welded part may be lost. Therefore, it is necessary to contain Mn 1.10% by mass or more.
On the other hand, when the Mn content exceeds 1.65% by mass, deoxidation becomes excessive, oxygen in the molten pool is decreased, and the viscosity and surface tension of the molten pool are increased. As a result, the weld metal in the molten pool is less likely to fall directly under the arc, so that the barrier action for reducing the arc force is reduced, and the burn-off resistance and undercut resistance are likely to be inferior. In addition, a lot of slag is generated, so that the paintability is deteriorated. Therefore, Mn needs to be contained at 1.65% by mass or less.

(S: 0.045 to 0.090 mass%)
S is one of the most important elements in the present invention, and has the effect of reducing the viscosity and surface tension of the molten pool. By containing S in an appropriate content, even when the arc precedes the molten pool, it becomes easy to obtain a barrier action that relaxes the arc force by the molten pool with low viscosity and surface tension. Dropping ability and undercut resistance can be improved. In order to obtain such an effect, it is necessary to contain 0.045% by mass or more of S.
On the other hand, if the S content exceeds 0.090% by mass, the surface tension of the droplet formed not only at the molten pool but also at the tip of the solid wire is greatly reduced, and the droplet cannot maintain a spherical shape. Moreover, even if a long arc length is provided in combination with the molten pool formed to have an excessive thickness, a short circuit is caused, resulting in a great increase in spatter. Moreover, even if other elements are adjusted, the crack resistance cannot be improved, and high-temperature cracks tend to occur remarkably when the steel is melted to the back side. Furthermore, the viscosity of the molten pool is excessively lowered, and the bead tends to sag due to the action of gravity, and the bead is hardly formed on the upper plate side of the lap fillet weld, so that the undercut resistance tends to be inferior. Furthermore, the weld metal may become brittle and the soundness of the welded portion may be lost. Therefore, S needs to be contained at 0.090% by mass or less. In addition, it is more desirable to contain S at 0.073 mass% or less from a viewpoint of improving undercut resistance and a viewpoint of improving toughness (that is, preventing embrittlement of the weld metal).

(O: 0.0015 to 0.0100 mass%)
Addition of an appropriate amount of O together with S is effective in improving the burn-off resistance and undercut resistance, since the viscosity and surface tension of the molten pool can be lowered appropriately. In order to exhibit such an effect, it is necessary to contain 0.0015% by mass or more of O.
On the other hand, if the solid wire O content exceeds 0.0100% by mass, the decrease in viscosity and surface tension of the molten pool due to high oxygenation becomes excessive, resulting in an increase in spatter, a large amount of slag, and inclusions. Deterioration of crack resistance due to increase occurs. Although the burn-through resistance is unlikely to be inferior, the viscosity of the molten pool decreases excessively, so that the bead tends to sag due to the action of gravity, and it becomes difficult to form a bead on the upper plate side of the lap fillet weld, resulting in undercut resistance. It tends to be inferior. Further, the weld metal becomes brittle and the soundness of the welded portion may be lost. Therefore, it is necessary to contain O at 0.0100 mass% or less. Depending on the N content described below, it may be desirable to further lower the upper limit of O, as will be described later.
In order to make the solid wire contain O in the above-described content, the O content of the wire is increased by relaxing the conditions of deoxidation treatment at the time of melting, or annealing is performed when the solid wire is drawn. To cause oxidation in the vicinity of the surface and leave it to concentrate O on the surface.

(Total content of C and S: 0.125% by mass or less)
Both C and S are elements that degrade crack resistance, and each has an upper limit. However, when the total content of these elements exceeds 0.125% by mass, each of C and S is the upper limit described above. Even if it is contained below, the crack resistance tends to be poor. Therefore, in order to improve crack resistance, the total content of C and S needs to be 0.125% by mass or less.

(P: 0.017 mass% or less)
P, like C, is reduced as much as possible in order to significantly degrade the crack resistance. In JIS Z3312, the content of P is allowed to 0.030% by mass, but in the present invention, the content of S is increased, so the content of P is relatively lowered to prevent cracking. It is necessary to make inferior. In particular, when the P content exceeds 0.017% by mass, hot cracking tends to occur remarkably when the steel is melted to the back side. Therefore, P needs to be contained at 0.017% by mass or less.

(The balance is Fe and impurities)
And the remainder of the solid wire of this invention consists of Fe and an impurity.
Impurities are 0.15% by mass or less for Ti, 0.0050% by mass or less for B, 0.0075% by mass or less for N, and Cr, Ni, Al, Nb, V, Zr, La, and Ce are each 0. It is good to contain at 20 mass% or less.
By containing Cr, Ni, Al, Ti, Nb, V, Zr, La, and Ce, the viscosity and surface tension of the molten pool are increased. As a result, the metal melted in the molten pool is less likely to fall directly under the arc, reducing the barrier action to relieve the arc force, not only inferior in resistance to burn-off and undercut, but also more spatter. appear.
In addition, since elements other than Ni are oxidized, a lot of slag is generated, and paintability is deteriorated.
If B is contained in an amount exceeding 0.0050% by mass, the crack resistance is remarkably deteriorated. If N exceeds 0.0075 mass%, the weld metal becomes brittle and the soundness such as hardness of the welded portion may be lost.
Therefore, it is desirable that the above-mentioned impurities be as small as possible, but if it is within the above-mentioned range, it is allowed to be contained in the solid wire of the present invention. More preferably, Cr and Ni are 0.05 mass% or less, Ti is 0.05 mass% or less, Al, Nb, V, Zr, La, and Ce are 0.01 mass% or less, and B is 0.00%. It is 0030 mass% or less. Even if impurities are positively added in these ranges, there is no advantage for the purpose of the present invention, and it can be said that the present invention is within the scope of the present invention.

  The solid wire according to the present invention desirably limits the total content of O and N to 0.0110% by mass or less, and more preferably contains Mo at 0.30% by mass or less. .

(Total content of O and N: 0.0110 mass% or less)
When the total content of O and N exceeds 0.0110% by mass, there is no problem with respect to the burn-off resistance, but the viscosity of the molten pool is excessively lowered. Beads are hardly formed on the upper plate side of fillet welds, and the undercut resistance tends to be poor. Therefore, the total amount of O and N is preferably 0.0110% by mass or less.

(Mo: 0.30 mass% or less)
Mo can increase the strength of the weld metal. Although there is no lower limit at which this effect is effective, the above-described effect can be remarkably obtained by containing 0.05% by mass or more.
On the other hand, if the Mo content exceeds 0.30% by mass, the viscosity and surface tension of the molten pool increase. As a result, the weld metal in the molten pool is less likely to fall directly under the arc, so that the barrier action for reducing the arc force is reduced, and the burn-off resistance and undercut resistance are likely to be inferior. Also, a lot of spatter is generated. Therefore, it is desirable to contain Mo at 0.30 mass% or less.

Further, the solid wire of the present invention preferably contains a total of 0.5 to 30 ppm of at least one element selected from K, Li, Na, and Ca on the surface of the solid wire. The solid wire of the present invention more preferably contains 0.01 to 1.00 g / 10 kg of MoS ₂ on the surface of the solid wire.

(A total of 0.5 to 30 ppm of at least one element selected from K, Li, Na, and Ca on the surface of the solid wire)
There is no problem even if K, Li, Na, and Ca are not contained. However, in welding using Ar and an oxidizing gas (O ₂ , CO ₂ ), these elements have an action of acting as an arc stabilizer. If these elements are in the vicinity of the surface of the droplet, electron emission is facilitated and effective for stabilizing the arc. When the arc becomes unstable, the arc length changes and the arc force also fluctuates. As a result, the burn-off resistance tends to be inferior, so that the arc is desirably as stable as possible. The stabilization of the arc can be obtained by applying or containing at least one of the above-mentioned elements that act as an arc stabilizer, and the content thereof should contain any element of 0.5 ppm or more. Can be obtained significantly.
However, when the above element is contained in an amount exceeding 30 ppm, not only the effect of stabilizing the arc is saturated, but also the lubricity of the surface of the solid wire is impaired and the feeding stability may be lowered. Therefore, this is the upper limit from a practical viewpoint.
These are melted and difficult to add. As a means for applying the above-mentioned element to the surface of the solid wire, (a) For example, a wire drawing lubricant containing K, Li, Na, Ca such as potassium carbonate, lithium carbonate, sodium carbonate, calcium carbonate during the wire drawing step is used. Used, left on the surface of the solid wire, (b) for example, immersed in a solution containing K, Li, Na, Ca, and then annealed, and diffused into the grain boundary or grain in the surface of the solid wire, (c) For example, copper plating is performed using a potassium cyanide or sodium cyanate solution. (D) Further, for example, an oil containing K, Li, Na, or Ca ions is applied as a feed lubricating oil to be applied in the vicinity of the surface. be able to.

(MoS ₂ is 0.01 to 1.00 g / 10 kg on the surface of the solid wire)
When MoS ₂ is present on the surface of the solid wire, instantaneous fusion at the energization point is reduced and resistance is reduced, so that the feeding stability of the solid wire is improved. If the feeding stability of the solid wire is unstable, the arc length also becomes unstable, and the arc force also fluctuates. As a result, the burn-through resistance tends to be inferior, and it is desirable that the feeding stability of the solid wire be as stable as possible. When MoS ₂ is applied, the burn-through resistance can be improved, and the effect becomes effective by applying MoS ₂ to the surface of 0.01 g / 10 kg or more.
On the other hand, even if MoS ₂ is applied to the surface in excess of 1.00 g / 10 kg, MoS ₂ is likely to be deposited and clogged in the feed liner and the current-carrying tip, and on the contrary, the lubricity is impaired. However, the feeding stability may be reduced. Therefore, the content of MoS ₂ applied (contained) on the surface of the solid wire is desirably 1.00 g / 10 kg or less.
In addition, as a method for applying MoS _{2 to} a solid wire, there is a method in which this is mixed with the drawing lubricant in the wire drawing process and left to the final diameter, or mixed with the lubricating oil to be applied at the finished diameter.

(Copper plating)
The solid wire according to the present invention may be coated with copper plating.
For general solid wire, the surface of the wire is coated with copper plating to improve rust resistance, maintain the wear resistance of the current-carrying tip, and improve the wire drawability during production of solid wire It is possible to improve performance and reduce costs.
In addition, when the surface of a strand is not coat | covered with copper plating, the electrical resistance in an electricity supply part rises. Due to the heat generation effect at this time, the temperature at which the solid wire reaches the arc generation point becomes high, and the solid wire is easily melted. Since the welding power source provides a current sufficient to melt the solid wire to be fed, the current can be lowered in the solid wire that is easily melted, and the heat input can be lowered if the amount of melting is constant. For this reason, the penetration depth can be further reduced, and the arc force can also be reduced. Thereby, the undercut resistance can be improved.

Next, the solid wire of the present invention will be described in detail by comparing an example that satisfies the requirements of the present invention with a comparative example that does not satisfy the requirements of the present invention.
A solid wire having a diameter of φ1.2 mm having the composition components shown in Tables 1 to 3 was prepared, (1) burn-off resistance, (2) undercut resistance, (3) hardness of the weld metal, and (4) crack resistance. The evaluation items were as follows: (5) Spatter generation amount, (6) Feed stability, (7) Slag encapsulation rate, and (8) Charpy absorbed energy. In addition, the evaluation method of the evaluation item of (1)-(8) is as follows. In Tables 1 to 3, the units of C, Si, Mn, P, S, Cr, Ni, Al, Ti, Nb, V, Zr, La, Ce, B, N, O, and Mo are mass%. The unit of K, Na, Li, and Ca is ppm, and the unit of MoS ₂ is g / 10 kg.

(1) Burn-off resistance FIG. 3 is a diagram for explaining the overlap fillet welding test and the definition of the depth of undercut.
As shown in FIG. 3, a carbon steel plate having a plate thickness of 2.0 mm and a tensile strength of 520 MPa was used as a lap joint with a root gap of 0.5 mm and an overlap margin of 4 mm, and lap welding was performed at a horizontal posture and a welding speed of 80 cm / min. The composition of the shielding gas at that time was Ar 80% + CO ₂ 20%, the polarity was negative, and the protruding length of the solid wire was 15 mm. The current was changed in increments of 5 A, and the solid wire feed rate at the maximum current value at which no burn-out occurred was taken as the limit feed rate (m / min) and used for evaluation of burn-off resistance. Here, the reason why the burn-through resistance was not evaluated by the current value is that the relationship between the current value and the feeding speed varies depending on the composition of the solid wire. The voltage value is adjusted every time the changed current value is changed so that the value at which the arc is determined to be most stable (optimum determination value) is taken. In this way, when the welding amount is constant, the penetration becomes shallower as the limit feeding speed increases, so that the burn-out resistance is excellent.
For evaluation of the burn-through resistance, a material with a critical feed rate of 5.60 m / min or more and less than 6.50 m / min is evaluated as good (◯), and a material with a speed of 6.50 m / min or more is evaluated as excellent (◎). evaluated. On the other hand, those having a limit feeding speed of less than 5.60 m / min were evaluated as not good (x). In addition, the thing which is favorable ((circle)) and excellent ((double-circle)) was set as the pass, and the thing (x) which is not favorable was set as the rejection.

(2) Undercut resistance In response to the result of the test of (1), the current value was set to (current value of limit feeding speed −30 A), and the voltage was set to (optimum judgment value +2 V) for welding. A cross-sectional macro photograph (magnification 10 times) of the bead was taken, and the undercut depth of the weld toe portion was measured from the cross-sectional macro photograph (in Tables 4 to 6, “undercut depth” (Mm) "). As shown in FIG. 3, both the upper plate side and the lower plate side were measured, and the maximum value was taken as the evaluation value.
The undercut resistance was evaluated as good (◯) when the above-mentioned maximum value exceeded 0.50 mm or less and 0.20 mm, and further evaluated as excellent (◎) when the maximum value was 0.20 mm or less. On the other hand, the above-mentioned maximum value exceeding 0.50 mm was evaluated as not good (x). In addition, the thing which is favorable ((circle)) and excellent ((double-circle)) was set as the pass, and the thing (x) which is not favorable was set as the rejection.

(3) Hardness of weld metal Vickers hardness at the center of the cross section of the weld metal of the lap joint welded with the current value set to (current value of limit feed rate-10A) in response to the test result of (1) (load 1 kgf (1N)) was measured three points, and the average was taken as the hardness of the weld metal (HV).
For the evaluation of the hardness of the weld metal, a Vickers hardness of 160 HV or higher was evaluated as good (◯) and a Vickers hardness of less than 160 HV was evaluated as poor (×) from the general view that it was equal to or higher than that of the base metal. In addition, the thing which is favorable ((circle)) was set as the pass, and the thing (x) which is not favorable was made into the rejection.

(4) Crack resistance In response to the result of the test of (1), a welding length of 100 mm was welded 10 times at the current value of the critical feed rate and the critical feed rate, and all X-ray transmission tests were conducted. In Tables 4 to 6, it is shown as “crack”.
As for the evaluation of cracking resistance, as a result of the X-ray transmission test, those that were not cracked and were all sound were evaluated as “No” (good (◯)), and those that were cracked were evaluated as “Yes” (not good ( X)). In addition, the thing which is favorable ((circle)) was set as the pass, and the thing (x) which is not favorable was made into the rejection.
In addition, as a result of investigating all the cracks, as shown in FIG. 4, the crack generation form was a vertical crack almost at the center of the bead width. Moreover, as a result of observing the fracture surface, it was found that the hot crack was a solidification crack. In addition, FIG. 4 is a figure for demonstrating the crack used as the evaluation object in evaluation of crack resistance.

(5) Spatter generation amount Welding is performed at a current of 200 A by bead-on-plate welding and a voltage set to an arc length of 2 mm by enlarged projection near the arc, and the generated spatter is collected in a collection box. The weight was measured.
The sputter generation amount is evaluated as good (◯) when the spatter generation amount exceeds 1.30 g / min and is equal to or less than 1.50 g / min, and excellent when it is 1.30 g / min or less (◎). It was evaluated. On the other hand, the case where the amount of spatter generated exceeded 1.50 g / min was evaluated as not good (x). In addition, the thing which is favorable ((circle)) and excellent ((double-circle)) was set as the pass, and the thing (x) which is not favorable was set as the rejection.

(6) Feeding stability By bead-on-plate welding, welding was performed for 1 hour at a voltage of a solid wire feeding speed of 6.00 m / min and an arc length of 2 mm, and the stability was subjected to sensory evaluation.
Evaluation of feeding stability is evaluated as excellent (◎) when there is no fluctuation in the feeding speed, and although there is some fluctuation in feeding speed, it is good that there is no practical problem (○) It was evaluated. On the other hand, what was judged to be unsatisfactory (x) was evaluated as being unsatisfactory in use because there was much fluctuation in the feeding speed and the arc became unstable. In addition, the thing which is excellent ((double-circle)) and favorable ((circle)) was set as the pass, and the thing (x) which is not favorable was made into the rejection.

(7) Slag encapsulation rate In the electrodeposition coating carried out after welding, the area ratio of slag generated on the beads was measured in order to evaluate the risk that the coating would peel off due to peeling of the slag. .
Evaluation of the encapsulation rate of the slag is evaluated as excellent (）) when the ratio of the total area of the slag to the surface area of the bead is 4.0% or less, and exceeds 4.0% and is 5.0% or less. The case was evaluated as good (◯). On the other hand, the case where this ratio exceeded 5.0% was evaluated as not good (x). In addition, the thing which is excellent ((double-circle)) and favorable ((circle)) was set as the pass, and the thing (x) which is not favorable was made into the rejection.

(8) Charpy absorbed energy JIS Z3312 “Magnet welded solid wire for mild steel and high-strength steel” was used to evaluate the impact performance of the welded portion, that is, whether or not the weld metal in the welded portion is brittle. The Charpy absorbed energy was measured based on this. The test temperature was 0 ° C. and three tests were performed and the average value was used for evaluation.
In the evaluation of Charpy absorbed energy, the most commonly used index of 27J or more and less than 47J was evaluated as good (◯), and the value of 47J or more was evaluated as excellent (）). On the other hand, those having Charpy absorbed energy of less than 27 J were judged to be embrittled metals and evaluated as not good (x). In addition, the thing which is favorable ((circle)) and excellent ((double-circle)) was set as the pass, and the thing (x) which is not favorable was set as the rejection.
The evaluation results of the evaluation items (1) to (8) are shown in Tables 4 to 6.

  No. Nos. 1 to 56 and 88 to 91 show that the component composition of the solid wire satisfies the requirements of the present invention, so that the limit feed speed (melt-off resistance), the undercut resistance, the weld metal hardness, and the amount of spatter generated Good evaluation results were obtained for all evaluation items of solid wire feeding stability, slag encapsulation rate, and Charpy absorbed energy (impact performance) (Examples; remarks column in Tables 4, 5 and 6) reference).

  On the other hand, no. 57-87, 92, and 93, because the composition of the solid wire did not satisfy the requirements of the present invention, an unsatisfactory evaluation result was obtained in any of the above-described evaluation items (Comparative Example; Table). (See 5 and 6 remarks column). Specifically, it is as follows.

No. In No. 57, since the C content was too small, the hardness of the weld metal was insufficient. That is, the strength of the welded portion is insufficient and cannot be used for general purposes.
No. No. 58 was excessively deoxidized because the C content was excessive, the limit feeding speed was small, and the depth of the undercut was deep. That is, the burn-through resistance and the undercut resistance were not good. In addition, the amount of spatter generated was large, and solidification cracking occurred, so the crack resistance was not good.

No. In No. 59, since the Si content was too small, the hardness of the weld metal was insufficient. That is, the strength of the welded portion is insufficient and cannot be used for general purposes. Further, since the electric resistance of the solid wire is low, the current value per feeding amount is high. For this reason, heat input and arc force are increased, so that overflow and undercut are likely to occur, and the overflow resistance and undercut resistance are not good.
No. In No. 60, since the Si content was excessive, deoxidation was excessive, and the anti-melt-off resistance and undercut resistance were not good. Further, Charpy absorbed energy was not good and embrittlement of the weld metal was observed.

No. In 61 and 62, since the Mn content was too small, the hardness of the weld metal was insufficient. That is, the strength of the welded portion is insufficient and cannot be used for general purposes. Further, since the electric resistance of the solid wire is low, the current value per feeding amount is high. For this reason, heat input and arc force are increased, so that overflow and undercut are likely to occur, and the overflow resistance and undercut resistance are not good. Further, Charpy absorbed energy was not good and embrittlement of the weld metal was observed.
No. No. 63 was excessively deoxidized because the Mn content was excessive, and the burn-off resistance and undercut resistance were not good. Moreover, since many slags also generate | occur | produced, the encapsulation rate of slag became high. This means that the paintability is deteriorated.
No. No. 64 is an excess of the Mn content, the sum of the C and S contents, and the N content. Since the Mn content was excessive, deoxidation was excessive, and the resistance to erosion and undercut resistance were not good. Since much slag was generated, the encapsulation rate of slag increased. Although the respective contents of C and S satisfy the requirements of the present invention, solidification cracking occurred because the total amount of C and S exceeded the upper limit. That is, the crack resistance was not good. Further, since N is excessive, Charpy absorbed energy is not good and embrittlement of the weld metal is recognized.

No. In No. 65, since the P content was excessive, solidification cracking occurred. That is, the crack resistance was not good.
No. In No. 66, since the P content was excessive, solidification cracking occurred. That is, the crack resistance was not good. Further, since the S content was too small, the viscosity and surface tension of the molten pool did not fall to an appropriate range, and a barrier action to alleviate the arc force of the arc preceding the molten pool could not be obtained. Therefore, the burn-through resistance and the undercut resistance were not good.
No. In No. 67, since the content of S was too small, the viscosity and surface tension of the molten pool did not fall to an appropriate range. For this reason, it was not possible to obtain a barrier action to alleviate the arc force caused by the molten pool, resulting in poor melt-off resistance and undercut resistance.
No. In No. 68, the content of S and the total content of C and S were excessive, so that solidification cracking occurred. That is, the crack resistance was not good. Furthermore, the viscosity and surface tension of the droplets became too small, and the droplets and the molten pool were easily short-circuited, resulting in a very large amount of spatter. Charpy absorbed energy was not good and embrittlement of the weld metal was observed. Although the burn-off resistance was good, the molten pool was likely to sag due to gravity, the undercut on the upper plate side was likely to occur, and the undercut resistance was not good.

No. In 69, the C content, the Si content, the S content, and the total of the C and S contents are all excessive. Solidification cracks occurred and the crack resistance was not good. Further, the burn-through resistance and undercut resistance were inferior, and the amount of spatter generated was large. Furthermore, Charpy absorbed energy was not good and embrittlement of the weld metal was observed.
No. Although 70, 71, and 72 satisfy the requirements of the present invention for each of C and S, solidification cracking occurred because the total content of C and S was higher than the upper limit defined in the present invention. Therefore, the crack resistance was not good.
No. 73, although each of the contents of C and S satisfies the requirements of the present invention, the total of the contents of C and S is higher than the upper limit specified in the present invention, and the contents of O and N Since the total was higher than the upper limit specified in the present invention, solidification cracking occurred. Therefore, the crack resistance was not good.

No. In No. 74, since the Cr content was excessive, the viscosity and surface tension of the molten pool became excessive, and the burn-off resistance and undercut resistance were not good. Moreover, since many slags generate | occur | produced, the encapsulation rate of slag became high. A large amount of spatter was generated.
No. In No. 75, since the Ni content was excessive, the viscosity and surface tension of the molten pool became excessive, and the burn-off resistance and the undercut resistance were not good. Also, the amount of spatter generated was large.

  No. 76, 77, 78, 79, 80, 81, 82 have excessive contents of Al, Ti, Nb, V, Zr, La, Ce, respectively, and the viscosity and surface tension of the molten pool became excessive. The results showed poor resistance to burn-through and undercut resistance. Moreover, a lot of slag was generated, and the encapsulation rate of slag increased. Furthermore, the amount of spatter generated was also large.

No. No. 83 had an excessive content of B, so that solidification cracking occurred and the crack resistance was not good.
No. No. 84 had excessive N content, so no pore defects occurred, but the weld metal became brittle.
No. In No. 85, since the content of O was too small, the viscosity and surface tension of the molten pool did not fall to an appropriate range, and a barrier action to alleviate the arc force by the molten pool could not be obtained. Cutability was not good.
No. In 86, the O content was excessive, and the total content of O and N was excessive, so that inclusions increased and cracking occurred. That is, the crack resistance was not good. Moreover, since the viscosity and surface tension of the molten pool became too small and the droplets and the molten pool were easily short-circuited, the amount of spatter generated was very large. Charpy absorbed energy was not good and embrittlement of the weld metal was observed. Although the burn-off resistance was good, the molten pool was liable to sag due to gravity, and an undercut on the upper plate side was likely to occur. That is, the undercut resistance was not good. Moreover, there was much slag and the encapsulation rate of slag was also high. That is, it was suggested that the paintability is inferior.
No. In No. 87, since the Mo content was excessive, the viscosity and surface tension of the molten pool became excessive, resulting in poor drop-off resistance and undercut resistance. Also, the amount of spatter generated was large.

No. 92 is a kind of solid wire distributed in the market, but the Si content and the S content are less than the requirements of the present invention, and the P content is more than the requirements of the present invention. It has become. Since the Si content is insufficient, the hardness of the weld metal is not good. Therefore, it is suggested that the strength of the welded portion is insufficient and cannot be used for general purposes. Further, since the electric resistance of the solid wire is low, the current value per feeding amount is high, and heat input and arc force are increased. In addition, because the S content is too low, the viscosity and surface tension of the molten pool do not fall to the proper range, and coupled with the failure to obtain a barrier action to relieve the arc force caused by the molten pool, It was easy to occur. That is, the result was that the burn-through resistance and the undercut resistance were not good. Furthermore, since the P content was excessive, cracking occurred and the crack resistance was not good.
No. 93 is also a kind of solid wire distributed in the market, but the content of C, Mn, B, Mo is excessive than the requirement of the present invention, and the content of S is less than the requirement of the present invention. It has become. Since the C content and the B content were excessive, crack welding occurred and cracks occurred (crack resistance was low). In addition, the content of C, Mn, and Mo is excessive, and the content of S is excessively low, so the viscosity and surface tension of the molten pool are remarkably increased, and the resistance to burn-off and undercut resistance are not good. became. In addition, the amount of spatter generated increased. Furthermore, since the Mn content was high, a lot of slag was generated, and the encapsulation rate of slag was increased. That is, it was suggested that the paintability is inferior.

(A) is a figure explaining the molten pool and penetration depth at the time of arc welding in the case of using the conventional solid wire, (b) at the time of arc welding in the case of using the solid wire of the present invention It is a figure explaining the molten pool and penetration depth. It is a figure for demonstrating the range of the appropriate content of C and S performed in order to complete the solid wire of this invention. It is a figure for demonstrating the description of a lap fillet weld test, and the definition of the depth of an undercut. It is a figure for demonstrating the crack used as evaluation object in evaluation of crack resistance.

Claims (6)

A solid wire used for arc welding,
0.005 to 0.060 mass% for C, 0.60 to 1.00 mass% for Si, 1.10 to 1.65 mass% for Mn, 0.045 to 0.090 mass% for S, and O for O 0.0015 to 0.0100 mass%, and the total content of C and S is 0.125 mass% or less, P is 0.017 mass% or less, and the balance is Fe and impurities, The impurities are 0.15 mass% or less for Ti, 0.0050 mass% or less for B, 0.0075 mass% or less for N, and Cr, Ni, Al, Nb, V, Zr, La, and Ce are A solid wire containing 0.20% by mass or less.   2. The solid wire according to claim 1, wherein the total content of O and N is limited to 0.0110 mass% or less.   3. The solid wire according to claim 1, wherein Mo is contained in an amount of 0.30% by mass or less.   The surface of the solid wire has a total of at least one element selected from K, Li, Na, and Ca in a range of 0.5 to 30 ppm. Solid wire as described in The solid wire according to any one of claims 1 to 4, wherein the surface of the solid wire has 0.01 to 1.00 g / 10 kg of MoS ₂ .   The solid wire according to any one of claims 1 to 5, wherein the surface is coated with copper plating.

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