JP4979278B2 - Solid wire for gas shielded arc welding - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a solid wire for gas shielded arc welding used when gas shielded arc welding is performed on thin mild steel and high-tensile steel plate having a thickness of 0.6 to 10 mm such as steel plates for automobiles.

  In recent years, welded structures by gas shielded arc welding have been required to achieve even higher quality production, as well as thorough labor saving and higher efficiency. For example, in the automobile industry, full automation of welding using a welding robot is promoted, and in the current mass production line, construction is carried out at a welding speed of about 1.0 m / min. Welding work is desired.

  On the other hand, the above-mentioned thin plate structure has become a major technical issue to deal with global environmental problems. Especially in the automobile industry, from the viewpoint of weight reduction with the aim of improving fuel efficiency, it is an urgent need to use gauges that use high-tensile steel plates. It has become. However, while the load stress on the weld zone increases, the fatigue strength of the weld zone does not increase compared to the smooth base metal, and can only be as high as that of conventional mild steel. I can't show it.

  Further, when welding is performed at a high speed exceeding 1.3 m / min for the purpose of further improving the welding efficiency using a conventional filler material, irregular beads such as undercut and humping are likely to occur. In addition, due to variations in workpiece press accuracy, the root interval of the fillet welded portion is likely to fluctuate. If high-speed welding is performed with the gap exceeding 1.0 mm, welding defects such as burnout and hole opening may occur. Cheap. Therefore, there is a strong demand for a welding material that can form a stable bead even in high-speed welding, and at the same time, can obtain a wide bead width that can bridge the root gap.

  As a conventional solid wire for gas shield arc welding of a thin plate having a thickness of 6 mm or less, there is one described in Patent Document 1. The solid wire described in Patent Document 1 is C: 0.02 for the purpose of improving welding workability and welding quality when a thin plate having a thickness of 6 mm is welded at a high speed of 1.0 m / min or more. To 0.10 mass%, Si: 0.8 to 1.2 mass%, Mn: 1.0 to 1.8 mass%, P: 0.020 mass% or less, S: 0.020 to 0.100 mass% %, Al: 0.005 mass% or less, O: 0.0070 mass% or less, N: 0.00790 mass% or less, and the Mn / Si ratio is 1.2 to 1.8, with the balance being Fe And a composition comprising inevitable impurities. In the technique described in Patent Document 1, a large amount of S is added to adjust the interfacial tension of the molten metal to improve the bead formation during high-speed welding.

  Also, if high-speed welding is performed on a thin steel plate base material using conventional welding materials, the bead tends to have a convex shape even if it does not become an irregular bead, and fatigue strength decreases due to stress concentration at the toe end of the bead. It's easy to do. Therefore, the welding speed must be reduced as compared with the conventional welding. In order to further expand the application of high-tensile steel sheets in these structures, a welding material that can provide high fatigue strength as a welded structure and at the same time does not reduce the welding efficiency is required.

  Conventionally, as a means for improving joint fatigue strength characteristics, the application of a welding material capable of applying a compressive stress to a welded portion has attracted attention. Specifically, attention is focused on the martensite transformation start temperature (hereinafter referred to as Ms point). There is a method of reducing the residual stress by lowering the Ms point and utilizing transformation expansion at a low temperature. Patent Document 2 proposes a welding material in which the Ms point is adjusted to 250 to 170 ° C. by defining C, Cr, Ni, Si, Mn, Mo, Nb and the like in a predetermined composition. .

JP-A-5-305476 JP-A-11-138290

  However, the conventional techniques described above have the following problems. S added to the solid wire described in Patent Document 1 is an element that greatly changes the interfacial tension and molten metal flow of the molten metal, and enables high-speed welding depending on the amount of addition. However, S is an element that promotes hot cracking, and the tendency is remarkable in a weld metal made of a filler metal added in an amount of 0.02% or more. In particular, when high-speed welding of 1.0 m / min or more is performed in a state where the route interval varies and the gap exceeds 1.0 mm, there is a problem that high-temperature cracking is very likely to occur.

  Further, S not only causes hot cracking, but the sulfide is coarsened with the addition of S, thereby reducing the strength and toughness of the material. Sulfur free-cutting steel (JIS G4804), which is cutting steel, has improved machinability by adding a large amount of S (SUM24L S: 0.26 to 0.35 mass%). However, the presence of S is extremely harmful in weld metals that require a certain degree of mechanical performance such as strength and toughness, and it is common to suppress the addition amount to 0.03% or less as much as possible. For this reason, the solid wire described in Patent Document 1 described above has a problem in that the strength and toughness are inferior to those of a normal wire, including extremely high hot cracking sensitivity.

  In addition, in the welding material described in Patent Document 2, a large amount of expensive alloy elements such as Cr and Ni are added, and in the case of a solid wire, the wire drawing is poor and welding is extremely expensive. Become a material. In addition, since the weld metal has a high viscosity, there is a problem that the applicability of an actual welding line such as high speed required in thin plate welding and an increase in the amount of spatter generated due to difficult transfer of droplets is poor.

  The present invention has been made in view of such problems. In welding thin steel plates having a thickness of 0.6 to 10 mm, bead formation is stable even in high-speed welding of 1.0 m / min or more, and hot cracking occurs. An object of the present invention is to provide a solid wire for gas shielded arc welding capable of obtaining a welded joint having low sensitivity and excellent fatigue strength, tensile strength and toughness.

The solid wire for gas shielded arc welding according to the first invention of the present application is a solid wire for gas shielded arc welding of mild steel and high-tensile steel plate having a thickness of 0.6 to 10 mm. 03 to 0.15% by mass, Si: 0.50 to 1.50% by mass, Mn: 1.00 to 3.00% by mass and S: 0.040 to 0.150% by mass, and Ti : 0.01 to 0.20 mass%, Zr: 0.01 to 0.20 mass%, La: 0.01 to 0.05 mass%, and Ce: 0.01 to 0.05 mass% It contains at least one selected element, and the balance consists of Fe and inevitable impurities. P is controlled to 0.025% by mass or less of the inevitable impurities, and the Mn content in the wire is set to [Mn ](mass% ), Ti content in the wire [Ti] (mass%), Zr content in the wire [Zr] (mass%), La content in the wire [La] (mass%), When the Ce content is [Ce] (mass%) and the S content in the wire is [S] (mass%), the value of A given by the following formula 1 is 100 or more.

In the present invention, since the S content is 0.040 to 0.150 mass% per the total mass of the wire, it is possible to reduce the flow rate of the molten metal to the rear and promote the hot water flow in the width direction. it can. Further, since the Mn content is 1.00 to 3.00 mass%, MnS is crystallized to increase the eutectic temperature, and the hot cracking sensitivity is reduced. Further, since it contains an appropriate amount of at least one element selected from the group consisting of Ti, Zr, La, and Ce that easily forms sulfides, sulfides containing these elements with a high melting point are generated, and S Is dispersed in the matrix phase. Thereby, it can prevent that a sulfide produces | generates in a grain boundary. Furthermore, since the value of A given by Equation 1 is 100 or more, bead formation in high-speed welding is stable, high-temperature cracking susceptibility is reduced, and fatigue strength is excellent even when high-tensile steel plates are welded. A welded joint is obtained.

  This solid wire can have a Mn content of 1.50% by mass or more. Thereby, hot cracking sensitivity can be reduced significantly.

Further, since the S content above 0.040 wt%, it is possible to improve the bead-forming in high speed welding, improving the fatigue strength.

The solid wire for gas shielded arc welding according to the second invention of the present application is C: 0.02 to 0.15 mass%, Si: 0.50 to 1.50 mass%, Mn: 1.00 based on the total mass of the wire. To 3.00 mass%, P: 0.025 mass% or less, S: 0.040 to 0.150 mass%, Nb: 0.005 to 0.5 mass%, V: 0.005 to 0.5 wt%, Al: 0.155 to 0.5 wt%, Cr: 0.005 to 0.5 mass%, Ni: 0.005 to 0.5 wt%, and B: 0.0010 to It contains at least one selected from the group consisting of 0.0100% by mass, and the balance is Fe and inevitable impurities.

  In the present invention, by appropriately adjusting the amount of addition of S and other alloy elements, bead formation is stabilized even at high speed welding, and at the same time, the high temperature cracking susceptibility is low, and fatigue strength, tensile strength and toughness are high in high strength steel plates Therefore, an excellent welded joint can be obtained.

  The gas shielded arc welding method according to the third invention of the present application is characterized in that the above-described solid wire for gas shielded arc welding is used and a high-tensile steel plate having a thickness of 0.6 to 10 mm is welded.

  In the present invention, since the above-described solid wire for gas shielded arc welding is used, even if a high-tensile steel plate having a thickness of 0.6 to 10 mm is welded, the bead shape in high-speed welding is stabilized and the temperature is high. It is possible to obtain a welded joint having low cracking sensitivity and excellent fatigue strength.

  According to the present invention, a beautiful bead having a small slag and a wide width can be formed, and the electrodeposition coating property of the bead is excellent. In particular, in the welding of a thin steel plate having a thickness of 0.6 to 10 mm, this effect becomes remarkable in high-speed welding of 1.0 m / min or more. In thin high-speed welding, the bead shape is stabilized and the fatigue strength is improved. An excellent welded joint can be obtained. Moreover, the hot cracking sensitivity is low, and appropriate strength and toughness can be ensured.

  The inventors of the present invention have conducted extensive experimental research to solve the above problems, and as a result, formed irregular beads in the welding of thin steel sheets having a thickness of 0.6 to 10 mm or less, high-temperature cracking due to S, and fatigue strength of weld metal. It has been found that the following phenomena have occurred with respect to the decrease and the decrease in strength and toughness.

  On the surface of the weld pool of a normal weld bead, molten metal is sucked from the high temperature portion to the rear low temperature portion, and the strength is proportional to the surface tension gradient based on the temperature difference and the molten pool length. In high-speed welding at 1.0 m / min or more, since the molten pool extends long in the weld line direction, the flow rate of the molten metal becomes extremely large, which is a factor in forming irregular beads such as undercut and humping.

  Although the original solidification temperature range in the weld metal is relatively narrow, S increases the solidification temperature range even when a small amount is added. At this time, with the solidification of the matrix phase, S is concentrated in the residual melt between dendrites, and sulfide is crystallized by eutectic solidification of the residual melt at the end of solidification. The Fe—FeS eutectic temperature is very low compared to the melting point of iron. When such a low-melting-point liquid phase and compound segregate at the grain boundary in the final stage of solidification, hot cracks are generated.

  Further, S not only causes hot cracking, but also sulfides are coarsened with the addition of S, thereby reducing the elongation toughness of the material. A steel plate with improved machinability by adding a large amount of S (SUM24L S: 0.26 to 0.35% by mass), such as sulfur free cutting steel (JIS G4804), which is usually cutting steel. However, in a weld metal that requires a certain degree of mechanical performance such as elongation and toughness, the presence of S is extremely harmful, and it is common to suppress the addition amount to S: 0.03% or less as much as possible.

  Furthermore, the fatigue limit of high-strength steel welded joints may be lower than the fatigue limit of the smooth material that is the base material, and this is mainly due to local stress concentration occurring at the weld toe of the welded joint. It is known that there is. FIG. 1 is a view showing a bead toe portion of a joint welded by overlap fillet. The joint shown in FIG. 1 is obtained by welding a base material (lower plate) 1a and a base material (upper plate) 1b in a posture aiming obliquely downward. The inventors of the present invention strongly depend on the portion where the surface of the base material 1a and the surface of the weld bead 2 shown in FIG. 1 intersect, that is, the shape of the bead toe, and the bead toe radius ρ is 0. It was found that the fatigue strength of the welded joint is improved by making it larger than 3 mm. However, when high-speed welding is performed using a high-strength steel plate, the bead tends to be convex, so that the bead toe radius ρ becomes small, and the inherent fatigue strength of the high-strength steel plate cannot be exhibited.

  On the other hand, S is an element that reduces the surface tension of the molten metal and changes the surface tension gradient based on the temperature difference. Therefore, the inventors of the present application have succeeded in reducing the flow rate of the molten metal to the rear and promoting the hot water flow in the width direction by adjusting the addition amount of S and other elements. The present inventors have found a component system capable of obtaining a bead that hardly causes undercutting and humping even in welding. Specifically, by setting the S content per total mass of the wire to 0.020 to 0.150 mass%, the flow rate of the molten metal to the rear is reduced and the hot water flow in the width direction is promoted. Can do. Thereby, bead toe radius (rho) shown in FIG. 1 can be 0.3 mm or more, and the fatigue strength in the welded joint which welded the high-tensile steel plate at high speed can be improved.

  As described above, the addition of S increases the hot cracking sensitivity. In order to reduce the hot cracking susceptibility due to S, the eutectic temperature is increased, and an element having a strong affinity with S is added to form a compound having a high melting point, so that S can be dispersed in the matrix phase. That's fine. Specifically, by setting the Mn content per total mass of the wire to 1.00 to 3.00% by mass, MnS crystallizes and the eutectic temperature can be increased. In addition, by adding an appropriate amount of at least one of Ti, Zr, La, and Ce, which are elements having a high tendency to form sulfides, a high melting point compound containing S is generated. Can be dispersed. As a result, almost no sulfide is generated in the grain boundary.

  Furthermore, the Mn content in the wire is [Mn] (mass%), the Ti content in the wire is [Ti] (mass%), the Zr content in the wire is [Zr] (mass%), When the La content is [La] (mass%), the Ce content in the wire is [Ce] (mass%), and the S content in the wire is [S] (mass%), When the amount of each alloy component added is adjusted so that A is 100 or more, the bead shape is stabilized and the high temperature cracking property is lowered. can get.

  In consideration of these findings, the present inventors have optimized the addition amount of S and other alloy elements, so that in gas shield arc welding of a high-tensile steel sheet having a thickness of 0.6 to 10 mm, A solid wire for gas shielded arc welding according to the first invention of the present application was completed, which can provide a welded joint that can stably form beads even when speed welding is performed, has low hot cracking susceptibility, and excellent fatigue strength.

  On the other hand, as described above, the hot cracking susceptibility increases with the addition of S. The method for reducing the hot cracking susceptibility is first to suppress the formation of the low melting point compound FeS, which is the main cause of causing the hot cracking. In this method, an element having high affinity with S is added, the eutectic temperature is increased, and the formed sulfide is dispersed in the matrix phase, thereby suppressing the formation of the low melting point compound FeS. Second, by adding elements with high hardenability, the crystal grains formed by solidification are refined, and by increasing the surface area of the grain boundaries, FeS is uniformly dispersed and segregation is suppressed, There are methods to reduce hot cracking susceptibility. From the above, it has been found that it is necessary to find an effective addition amount of these elements in order to reduce the hot cracking susceptibility.

In consideration of these findings, the inventors have adjusted the addition amount of S and other alloy elements to stabilize bead formation even in high-speed welding, and at the same time have low hot cracking susceptibility, and high strength steel sheets have fatigue strength. This completes the solid wire for gas shielded arc welding according to the second invention of the present application, which can obtain a welded joint excellent in tensile strength and toughness.
(1) By regulating the amount of S to 0.020 to 0.150 mass%, the flow rate of molten metal in the rear direction is reduced, and at the same time, the hot water flow in the width direction is promoted.
(2) By limiting Mn to 1.00 to 3.00 mass%, MnS is crystallized and the eutectic temperature is raised to reduce crack sensitivity.
(3) Nb: 0.005 to 0.50 mass%, V: 0.005 to 0.5 mass%, Al: 0.010 to 0.5 mass%, Cr: 0.005 to 0.5 mass% , Ni: 0.005 to 0.5 mass%, B: Inclusion of one or more of 0.001 to 0.010 mass% to increase hardenability and refine crystal grains . By adding appropriate amounts of these elements, the structure formed by solidification is refined and the surface area of the grain boundaries is increased, thereby suppressing the segregation of the FeS liquid phase that becomes the starting point of cracks formed at the grain boundaries and dendritic interfaces. Disperses and reduces hot cracking susceptibility. In addition, the toughness is improved by the grain refinement effect, and there is an effect of reducing the hot cracking susceptibility by relaxing the concentration of solidification strain in the FeS liquid phase due to expansion and contraction during welding.
(4) Since the additive element of (3) is an element that does not easily form slag, the addition of an appropriate amount reduces the hot cracking susceptibility without impairing the characteristic that a beautiful bead with less slag can be formed. It is possible to ensure moderate strength and toughness.

  Hereinafter, the reasons for adding components and limiting the composition of the welding wire according to the present invention will be described. First, the reason for adding each component and the reason for limiting the numerical value in the solid wire for gas shielded arc welding of the first invention of the present application will be described.

“C: 0.03 to 0.15 mass%”
Carbon (C) is an element necessary for ensuring the strength of the weld metal, and is also an element effective for promoting deoxidation. However, when the C content per total mass of the wire is less than 0.03% by mass, the strength of the weld metal is insufficient. On the other hand, when the C content exceeds 0.15% by mass, the toughness of the weld metal decreases and the hot cracking sensitivity increases. Therefore, the C content is 0.03 to 0.15 mass% per the total mass of the wire.

“Si: 0.50 to 1.50 mass%”
Silicon (Si) is an element that strongly promotes deoxidation, is an element necessary for improving the strength of steel, and is an element that further improves the familiarity of beads. However, when the Si content per total mass of the wire is less than 0.50% by mass, these effects cannot be obtained. On the other hand, when the Si content exceeds 1.50% by mass, the drop detachability deteriorates and the toughness of the weld metal deteriorates. Therefore, the Si content is 0.50 to 1.50 mass% per the total mass of the wire.

“Mn: 1.00 to 3.00 mass%”
Manganese (Mn) is not only an element effective for promoting deoxidation together with Si, but also an element for improving the mechanical properties of the weld metal. In addition, MnS is crystallized to increase the eutectic temperature and to reduce hot cracking sensitivity. However, when the Mn content per total mass of the wire is less than 1.00% by mass, the hot cracking sensitivity is increased. On the other hand, if the Mn content exceeds 3.00% by mass, the content in the weld metal becomes excessive, and the toughness deteriorates on the contrary. Therefore, the Mn content is 1.00 to 3.00 mass% per the total mass of the wire. In addition, it is preferable that Mn content shall be 1.50 mass% or more.

“S: 0.020 to 0.150 mass%”
Sulfur (S) has the effect of reducing the surface tension of the molten metal, and when added in an appropriate amount, improves the familiarity between the bead and the base material at the toe end of the bead and also improves the fatigue strength of the welded joint. be able to. However, when the S content per total mass of the wire is less than 0.020% by mass, these effects cannot be obtained. On the other hand, if the S content exceeds 0.150% by mass, hot cracking is likely to occur even if the addition amount of other elements is adjusted. Therefore, the S content is 0.020 to 0.150 mass% per the total mass of the wire. In addition, it is preferable that S content shall be 0.040 mass% or more, More preferably, it is 0.060 mass% or more.

“Ti: 0.01 to 0.20 mass%, Zr: 0.01 to 0.20 mass%, La: 0.01 to 0.05 mass%, and Ce: 0.01 to 0.05 mass%. At least one element selected from the group "
Titanium (Ti), zirconium (Zr), lanthanum (La), and selenium (Ce) are elements that easily combine with S to form a high-melting sulfide. Among these elements, at least one element is selected. By adding an appropriate amount, S can be dispersed in the matrix phase. However, if the content of each element is less than 0.01% by mass with respect to the total mass of the wire, the above-described effects cannot be obtained even if they are added in combination. On the other hand, if the Ti content or the Zr content exceeds 0.20% by mass, the droplets become large and the transition is disturbed, and the slag amount becomes excessive, resulting in a decrease in welding workability. Therefore, when adding Ti and / or Zr, the content thereof is set to 0.01 to 0.20% by mass with respect to the total mass of the wire. On the other hand, if the La content or Ce content exceeds 0.05% by mass, the sulfide becomes coarse and the yield at the time of steelmaking decreases, leading to an increase in cost. Therefore, when adding La and / or Ce, the content thereof is set to 0.01 to 0.05 mass% with respect to the total mass of the wire.

“P: 0.025 mass% or less”
Although phosphorus (P) is mixed as an inevitable impurity in steel, P is an element that increases the hot cracking susceptibility, and its content is desirably kept low. However, there is no problem if the P content per the total mass of the wire is 0.025% by mass or less. Therefore, the P content is regulated to 0.025% by mass or less per the total mass of the wire.

"A: 100 or more"
In the present invention, the value of A given by the following formula 3 is set to 100 or more. In the following formula 3, [Mn] is the Mn content (mass%) in the wire, [Ti] is the Ti content (mass%) in the wire, and [Zr] is the Zr content (mass%) in the wire. , [La] is the La content (mass%) in the wire, [Ce] is the Ce content (mass%) in the wire, and [S] is the S content (mass%) in the wire. When the value of A is less than 100, the hot cracking sensitivity is increased. On the other hand, by adjusting the Mn content, Ti content, Zr content, La content, Ce content and S content per total mass of the wire so that the value of A is 100 or more, MnS is crystallized. The eutectic temperature can be increased, and the low-melting liquid phase and the compound are prevented from segregating at the grain boundary in the final stage of solidification, and the high-melting sulfide containing Ti, Zr, La or Ce is added. Can be generated. As a result, the hot cracking susceptibility can be greatly reduced. In addition, each coefficient in following Numerical formula 3 is prescribed | regulated based on the result of the crack test, and it is thought that the sulfide formation tendency of each element contributes greatly to these values.

  In addition to the above-mentioned P, inevitable impurities contained in the solid wire of the present invention include Cu, Al, Ni, Cr, Mo, and B.

  Next, the reason for adding each component and the reason for limiting the numerical value in the solid wire for gas shielded arc welding of the second invention of the present application will be described.

“C: 0.02 to 0.15 mass%”
C is an element necessary for ensuring the strength of the weld metal, and is also an effective element as a deoxidizing element. If the C content is less than 0.02% by mass, the strength of the weld metal is insufficient. On the other hand, when C exceeds 0.15% by mass, the toughness of the weld metal is lowered and at the same time the hot cracking sensitivity is increased. Further, excessive addition of C deteriorates the droplet detachability and at the same time generates a large amount of spatter, resulting in poor welding workability and a large amount of slag. Therefore, the C content is specified to be 0.02 to 0.15% by mass.

“Si: 0.50 to 1.50 mass%”
Si is also a strong deoxidizing element, and at the same time, an element necessary for improving the strength of steel. Si is an element that improves the conformability of beads. If Si is less than 0.50 mass%, this action is insufficient, the conformability of the bead shape is deteriorated, the toe shape is deteriorated, and stress concentration is likely to occur. As a result, the fatigue strength decreases. Desirably, the Si content is 0.60% or more. On the other hand, when the Si content exceeds 1.50% by mass, the viscosity of the molten pool becomes excessive, and it becomes easy to hum during high-speed welding. Further, excessive addition of Si deteriorates the droplet detachability and at the same time generates a large amount of spatter, so that the welding workability is deteriorated and a large amount of slag is generated. More preferably, Si content is 1.20 mass% or less.

“Mn: 1.00 to 3.00 mass%”
Mn is not only an element useful as a deoxidizing element together with Si, but also an element that improves the mechanical properties of the weld metal. In addition, MnS is crystallized, the eutectic temperature is increased, and the hot cracking susceptibility is reduced. When Mn is less than 1.00% by mass, the sensitivity to hot cracking is increased, and sufficient strength of the weld metal cannot be obtained. On the other hand, when Mn exceeds 3.00 mass%, the viscosity of the molten pool becomes excessive, and it becomes easy to hum during high-speed welding, and a large amount of slag is generated. Therefore, Mn is specified to be 1.00 to 3.00 mass%. A more preferable range is that Mn is 1.00 to 2.00% by mass.

“P: 0.025 mass% or less”
P is an element that increases the hot cracking susceptibility. Moreover, even if an alloying element is added, a P compound having a high melting point cannot be produced, so it is desirable to keep it as low as possible. However, there is no problem if the P content is 0.025 mass% or less.

“S: 0.020 to 0.150 mass%”
S has the effect of reducing the surface tension of the molten metal, and by adding an appropriate amount, the compatibility with the base material at the bead toe is improved and the fatigue strength is also improved. However, the addition of a large amount of S without a special element shown below coarsens sulfides formed in the crystal grains and in the grain boundaries, and decreases strength and toughness. The above effect can be obtained by adding S in an amount of 0.020% by mass or more. On the other hand, if S exceeds 0.150 mass%, even if other elements are adjusted, the risk of hot cracking is increased, and the strength and toughness are remarkably reduced. Therefore, S is 0.020 to 0.150 mass. %. A more preferable range of S is 0.040 to 0.150 mass%. A more preferable range of S is 0.050 to 0.150% by mass.

“Nb: 0.005 to 0.50 mass%”
Since Nb has a high affinity with S, it is likely to be a sulfide, and by adding an appropriate amount, Nb has an effect of suppressing the formation of FeS causing hot cracking. Further, since Nb is an element that improves hardenability, it has the effect of refining crystal grains, reducing high-temperature cracking susceptibility, and ensuring appropriate strength and toughness. However, when Nb is less than 0.005% by mass, the effect of reducing the hot cracking susceptibility and the effect of securing appropriate strength and toughness cannot be obtained, and the hot cracking susceptibility increases. A more preferable range of Nb is 0.02% by mass or more. On the other hand, if Nb exceeds 0.50% by mass, the effect becomes saturated, segregates at the grain boundaries and dendrite boundaries during solidification, and conversely increases the hot cracking susceptibility. Further, excessive addition of Nb increases the manufacturing cost of the wire, increases the viscosity of the molten pool, causes humping during high-speed welding, and increases the amount of spatter generated.

“V: 0.005 to 0.5 mass%, Al: 0.010 to 0.5 mass%, Cr: 0.005 to 0.5 mass%, Ni: 0.005 to 0.5 mass%”
V, Al, Cr, and Ni are elements that improve the hardenability. Therefore, by adding them, the crystal grains of the weld metal formed by welding are refined, and have the effect of ensuring appropriate strength and toughness, and hot cracking. Reduce sensitivity. These effects are required to be at least 0.005% by mass for V, Cr and Ni, and 0.010% by mass for Al. A more preferable range is 0.02% by mass or more for V, Cr, and Ni, and 0.030% by mass or more for Al. On the other hand, if these elements exceed 0.5% by mass, the manufacturing cost of the wire becomes excessive, the viscosity of the molten pool increases, and humping occurs during high-speed welding, resulting in an increase in the amount of spatter generated.

“B: 0.001 to 0.010 mass%”
Since B is an element that improves hardenability, it has the effect of refining the crystal grains of the weld metal formed by welding to ensure adequate strength and toughness, and the effect of reducing hot cracking susceptibility. There is. In order to obtain this B addition effect, 0.001 mass% or more of B needs to be added. On the other hand, when B is added in excess of 0.010% by mass, the hot cracking sensitivity is increased, so B is made 0.010% by mass or less. Therefore, B is specified to be 0.001 to 0.010 mass%.

"Welding method according to the present invention"
The solid wires of the first and second inventions of the present application are for gas shielded arc welding of thin steel plates having a thickness of 0.6 to 10 mm. The following welding methods and welding conditions are recommended. As a gas shield arc welding method applied to welding, any welding method such as CO ₂ , MAG, MIG, TIG and the like may be used. The welding conditions, for example, welding conditions such as output or current and welding speed may be selected according to the type of processing machine used, the thickness and shape of the workpiece, and the like. Moreover, it is more effective when MAG pulse welding, MIG pulse welding, and TIG pulse welding are performed. What is necessary is just to select a suitable welded joint according to the site | parts to join, such as a butt | joint and a lap joint, and this invention is applicable to any joint.

"Pulse welding machine"
A combination with a pulse welder is recommended to achieve high-speed weldability, arc stability and low fume in thin plate welding. The setting of the pulse is not particularly limited, but the peak current is 350 A to 600 A, the base current is 30 A to 100 A, and 1 peak (from the rising start to the peak steady period to the end of falling) is 0.8 to 5 0.0 ms is commonly used. Also in the present invention, welding can be performed under such conditions.

“Thin steel plate with a thickness of 0.6 to 10 mm”
When the plate thickness is less than 0.6 mm, penetration and melting of the plate due to the arc force occur, so that arc welding with a normal reverse polarity is difficult. On the other hand, when the plate thickness exceeds 10 mm, the restraining force increases, so that distortion due to thermal expansion and contraction on the weld metal is excessively loaded, and the cooling rate of the molten pool increases, resulting in the risk of hot cracking. Becomes higher. In addition, the viscosity of the molten pool formed by the wire of the present invention is low, and when the large leg length is one pass by T-shaped horizontal fillet welding, the upper leg length droops, which is not suitable. Therefore, the preferable range of the thickness of the steel plate to be welded is 0.6 to 10 mm. The strength of the steel sheet to be welded can be applied from a normal mild steel class steel plate to a high-tensile steel plate, but there is no particular limitation on the upper limit of the steel strength.

  Hereinafter, the effect of the Example of this invention is demonstrated compared with the comparative example which remove | deviates from the scope of the present invention. First, a first embodiment of the first invention of the present application will be described.

  In this example, a solid wire having the composition shown in Table 1 below was used to perform gas shielded arc welding, bead formation during high-speed welding, mechanical properties of the weld metal, bead toe radius ρ, hot cracking. The sensitivity and welding workability were evaluated. The balance in the composition of each solid wire shown in Table 1 below is Fe and inevitable impurities.

Next, an evaluation method for each item will be described. The mechanical properties of the weld metal were evaluated by a tensile test method for a butt weld joint specified in JIS-Z3121 and an impact test method for a welded joint specified in JIS-Z3128. At that time, the case where the tensile strength is 560 N / mm ² or more and the absorbed energy in the Charpy impact test is 100 J or more at a test temperature of −20 ° C., the tensile strength is less than 560 N / mm ² or the absorbed energy in the Charpy impact test Is less than 100 J at a test temperature of −20 ° C.

The bead formation during high-speed welding is as follows: a lap joint of a high-strength steel sheet having a composition shown in Table 2 with a thickness of 2.3 mm, a root gap of 1.0 mm, a welding current of 200 to 300 A, and a shielding gas MAG pulse welding was performed using a mixed gas of Ar 80 vol% -CO ₂ 20 vol% as the welding speed of 1.3 to 1.5 m / min. As a result, undercut, humping, melt-down and hole opening did not occur, and those that could bridge the gap across the entire weld line were marked with ○, and undercut, humping, melt-down or hole-opening defects occurred did.

Further, the welding workability was evaluated by observing the arc stability and droplet transfer regularity with a high-speed camera and the amount of spatter scattered. The welding conditions at that time were a welding current of 200 to 300 A, a mixed gas of Ar 80 volume% -CO ₂ 20 volume% as a shielding gas, and MAG welding without pulse. The case where the arc was stable, the droplet transfer regularity was high, and the amount of spatter was small was evaluated as “◯”, and the case where even one of arc stability, droplet transfer regularity and spatter amount was inferior was rated as “x”.

  Furthermore, the hot cracking susceptibility of the weld metal was evaluated based on the results of the fishbone cracking test and the crater cracking test. First, the method of the fishbone crack test will be described. FIG. 2A is a cross-sectional view showing a sampling position of a test piece, and FIG. 2B is a plan view showing a method for producing a test piece for a fishbone cracking test. As shown in FIG. 2 (a), the base material 11 is 20 mm thick mild steel SM490A and the backing material 13 made of mild steel SM490A, and the groove shape is V-shaped with an angle of 45 °. did. Then, the welded joint was reduced in thickness by mechanical grinding until the thickness became 5 mm, and a test piece 14 for a fishbone crack test having a length of 175 mm, a width of 250 mm, and a thickness of 5 mm was produced.

  Next, as shown in FIG. 2B, slits 15 were formed at equal intervals on both ends of the long side of the test piece 14. At this time, the length of the slit 15 is increased from one short side toward the other short side, and the amount of thermal deformation (thermal strain) received by the molten metal corresponding to each slit length is continuous. To change. That is, the amount of thermal deformation is large on one short side where the length of the slit 15 is short, and the amount of thermal deformation is small on the other short side where the length of the slit 15 is long. The test piece 14 was placed on a copper plate 16 having a length of 750 mm, a width of 500 mm, and a thickness of 25 mm, and test plate carriage traveling type TIG welding was performed under the conditions shown in Table 3 below. At this time, a stationary arc is generated at the shallow end of the plate for about 5 seconds to sufficiently melt the end of the plate, thereby thermally deforming the end of the plate. (Hot cracking) was generated. Thereafter, welding was performed with the welding direction 17 being directed from the edge of the plate where the cracks occurred toward the deep side of the slit. And hot crack resistance was evaluated by how much the crack which generate | occur | produced in the start part of the test piece 14 progressed. The length of the crack corresponds to the amount of thermal deformation described above, that is, the sensitivity to hot cracking. Specifically, a color check is performed after welding, the crack length generated in the bead 12 is measured, the ratio of the crack length to the test piece length is obtained, and the case where the crack rate is 5% or less is The case where it exceeded 5% was set as x.

In addition, the crater cracking test was performed using mild steel SM490A, using a mixed gas of Ar 80 volume% -CO ₂ 20 volume% as a shielding gas on a groove groove having a groove angle of 90 ° and a depth of 5 mm. By using MAG welding with a pulse of 200 to 300 A, three weld beads having a length of about 70 mm were intermittently formed under the same conditions, and the total crack length on the surface of each weld crater portion was measured. And the ratio of the length of the crack with respect to the weld crater length or the diameter of a weld crater was calculated | required, and the average value of three weld craters was made into the parameter | index. As a result, the case where the cracking rate was 15% or less was rated as ◯, and the case where it exceeded 15% was rated as x.

The bead toe radius ρ was measured as a means for conveniently evaluating the fatigue strength of the welded joint. As the bead toe radius ρ is larger, the stress concentration is reduced and the fatigue strength is improved. Specifically, a lap joint of a high-strength steel sheet having a thickness of 2.9 mm having the composition shown in Table 2 above is used with 80 volume% Ar-20 volume% CO ₂ as the shielding gas, and an average welding current of 200 to 300 A. MAG welding with pulses was performed by automatic overlapped fillet welding with a welding speed of 1.3 to 1.5 m / min. Thereafter, the bead toe radius ρ shown in FIG. 1 was measured, and the case where the bead toe radius ρ was 0.3 mm or more was evaluated as ◯, and the case where it was less than 0.3 mm was evaluated as x. The above evaluation results are summarized in Table 4 below.

  As shown in Table 4 above, Example No. which is within the scope of the present invention. 1 to No. Twenty solid wires gave excellent results in all evaluations. On the other hand, Comparative Example No. deviating from the scope of the present invention. 21-No. The 40 solid wires had insufficient bead formation during high-speed welding, mechanical properties of the weld metal, bead toe radius ρ, hot cracking susceptibility or welding workability. Specifically, Comparative Example No. Since the solid wire No. 21 had a C content less than the range of the present invention, the strength of the weld metal was insufficient. On the other hand, Comparative Example No. The 22 solid wire has a C content exceeding the range of the present invention, so that the weld metal lacks the toughness, and further, the value of A is smaller than the range of the present invention, thereby increasing the hot cracking susceptibility. did.

  Comparative Example No. Since the solid wire of No. 23 has a Si content lower than the range of the present invention, the strength of the weld metal is insufficient, the bead formability during high-speed welding deteriorates, and the bead toe radius ρ is also small. It was. On the other hand, Comparative Example No. In the 24 solid wire, since the Si content exceeded the range of the present invention, the toughness of the weld metal was insufficient, the droplets became coarse, and the spatter increased. Further, Comparative Example No. The 25 solid wire had a Mn content lower than the range of the present invention, and the value of A was also smaller than the range of the present invention. On the other hand, Comparative Example No. Since the solid wire of No. 26 had a Mn content exceeding the range of the present invention, the toughness of the weld metal was insufficient.

  Furthermore, Comparative Example No. Since the solid content of No. 27 exceeded the range of the present invention, the P cracking susceptibility increased. Furthermore, Comparative Example No. Since the 28 solid wire has a lower S content than the range of the present invention, the hot cracking susceptibility is low, but the bead forming property of the high-speed welder is inferior and the bead toe radius ρ is also small. On the other hand, Comparative Example No. In 29 solid wires, the S content exceeds the range of the present invention, and the value of A is also smaller than the range of the present invention, so that the content of other elements is within the range of the present invention. The hot cracking susceptibility was high. Furthermore, Comparative Example No. 30, no. 32, no. 34 and no. Since the value of A was smaller than the range of the present invention, the 35 solid wires were highly susceptible to hot cracking.

  Furthermore, Comparative Example No. In the solid wire No. 31, since the Ti content exceeded the range of the present invention, the droplets became coarse, the spatter amount increased, and the slag was also large. Similarly, Comparative Example No. Since the solid wire No. 33 had a Zr content exceeding the range of the present invention, the droplets became coarse, the amount of spatter increased, and the slag was also large. Furthermore, Comparative Example No. 36, no. 37 and no. The 38 solid wire was not added with any element of Ti, Zr, La, and Ce, and the value of A was smaller than the range of the present invention, so the hot cracking susceptibility was high. Furthermore, no. 39 and no. The 40 solid wire was not added with any element of Ti, Zr, La and Ce, and further, the S content exceeded the range of the present invention, so the hot cracking susceptibility was high.

  Next, a second embodiment of the second invention of the present application will be described. In this example, using wires having the composition shown in Table 5 below, bead formation during high-speed welding, mechanical performance of weld metal, bead toe radius ρ, paintability, hot cracking susceptibility and welding operation Sex was evaluated. The balance in the composition of each solid wire shown in Table 5 below is Fe and inevitable impurities.

  Next, an evaluation method for each item will be described.

"Mechanical properties of weld metal"
The mechanical properties of the weld metal were evaluated by a tensile test method for a butt weld joint specified in JIS-Z3121 and an impact test method for a welded joint specified in JIS-Z3128. At that time, when the tensile strength is 560 N / mm ² or more and the absorbed energy in the Charpy impact test is 100 J or more at a test temperature of −20 ° C., the tensile strength is less than 560 N / mm ² or the absorbed energy in the Charpy impact test is The case where the test temperature was less than 100 J at −20 ° C. was evaluated as x.

“Bead formation during high-speed welding”
The bead formation during high-speed welding is as follows. In a lap joint of a high-strength steel sheet having a thickness of 2.9 mm having the composition shown in Table 6, the root interval is 1.0 mm, the welding current is 250 A, and Ar 80% -CO ₂ 20 is used as a shielding gas. MAG pulse welding was performed at a welding speed of 1.5 m / min. As a result, no defect such as undercut, humping, burn-through, and hole opening occurred, and a gap that could be bridged across the entire weld line was marked with ◯, and those with these defects marked with x.

"Welding workability"
Welding workability was evaluated by observing arc stability and regularity of droplet transfer with a high-speed camera, and evaluating the amount of spatter scattered. The welding conditions at that time were a welding current of 250 A, a mixed gas of Ar 80% -CO ₂ 20% as a shielding gas, a welding speed of 1.0 m / min, and MAG welding without pulses. And, when the arc was stable, the droplet transfer regularity was high, and the amount of spatter was small, ○, and at least one of the arc stability, the droplet transfer regularity, and the amount of sputter was inferior. .

"Paintability"
The paintability was determined by the slag area formed on the surface of the bead after welding to determine the risk of the paint being peeled off due to the slag peeling in the electrodeposition coating process after welding. The welding conditions at that time were MAG welding without pulses, with a welding current of 250 A, a mixed gas of Ar 80% -CO ₂ 20% as a shielding gas, a welding speed of 1.0 m / min. And the thing whose slag area is less than 10% with respect to a bead surface area was made into (circle), and 10% or more was made into x.

"Fishbone cracking test"
The high temperature cracking susceptibility of the weld metal was evaluated by this fishbone cracking test and a crater cracking test described later.

  The sampling position of the test piece is as shown in FIG. As shown in FIG. 2 (a), the base material 11 is a 20 mm thick soft steel SM490A and a backing material 13 made of the soft steel SM490A, and the groove shape is a butt-weld with an angle of 45 °. did. Then, the welded joint was reduced in thickness by mechanical grinding until the thickness became 5 mm, and a test piece 14 for a fishbone crack test having a length of 175 mm, a width of 250 mm, and a thickness of 5 mm was produced.

  As shown in FIG. 2B, slits 15 were processed at equal intervals on both ends of the long side of the test piece 14. At this time, the length of the slit 15 is increased from one short side to the other short side, and the amount of heat change (thermal strain) received by the weld metal corresponding to each slit length is continuous. To change. That is, the amount of thermal deformation is large on one short side where the length of the slit 15 is short, and the amount of thermal deformation is small on the other short side where the length of the slit 15 is long. The test piece 14 was placed on a copper plate 16 having a length of 750 mm, a width of 500 mm, and a thickness of 25 mm, and TIG welding of a test plate carriage traveling vehicle type was performed under the conditions shown in Table 7 below. At this time, a stationary arc is generated at the shallow end of the plate for about 5 seconds to sufficiently melt the end of the plate, thereby thermally changing the end of the plate, and solidification cracking (hot cracking) due to shrinkage solidification strain generated in the cooling process. ) Was generated. Thereafter, welding was performed with the welding direction 17 being directed from the edge of the plate where the cracks occurred toward the deep side of the slit. And hot crack resistance was evaluated by how much the crack which generate | occur | produced in the start part of the test piece 14 progressed. This crack length corresponds to the aforementioned amount of thermal deformation, that is, the hot cracking sensitivity. Specifically, a color check is performed after welding, the crack length generated in the bead 12 is measured, the ratio of the crack length to the test piece length is obtained, and the case where the crack rate is 5% or less is The case where it exceeded 5% was set as x.

"Crater crack test"
Using mild steel SM490A, three weld beads having a length of about 70 mm are intermittently formed on the V-groove groove (groove angle 90 °, depth 5 mm) by mag welding under the same conditions. The total crack length measured on the surface of each weld crater part was measured, the ratio with respect to the weld crater length (diameter) was calculated | required, and the average value of three weld craters was made into the thing of 15% or less as the pass.

"Bead toe radius ρ"
The bead toe radius ρ was measured as a means for conveniently evaluating the fatigue strength of the welded joint. As the bead toe radius ρ is larger, the stress concentration is reduced and the fatigue strength is improved. Specifically, a lap joint of a high-strength steel sheet having a thickness of 2.9 mm having the composition shown in Table 6 above, a mixed gas of Ar 80% -CO ₂ 20% as a shielding gas, and a welding current of 250 A is used. MAG pulse welding was performed by horizontal lap welding at a welding speed of 1.5 m / min. Thereafter, the bead toe radius ρ shown in FIG. 1 was measured. The above evaluation results are summarized in Table 8 below.

  As a result, in Examples 1 to 25, the composition of the welding wire was within the scope of the present invention, and all the evaluation results were excellent. On the other hand, Comparative Examples 26 to 50 are out of the scope of the present invention, and bead formation at high speed welding, mechanical performance of weld metal, bead toe radius ρ, hot cracking susceptibility, paintability, welding It was insufficient in terms of workability.

  As shown in Table 8 above, Example No. which is within the scope of the present invention. 1 to No. With the 25 solid wires, excellent results were obtained in all evaluation items. On the other hand, Comparative Example No. deviating from the scope of the present invention. 26 thru | or No. The 50 solid wires had insufficient bead formation during high-speed welding, mechanical properties of weld metal, bead toe radius ρ, paintability, hot cracking susceptibility or welding workability.

  Comparative Example No. Nos. 26 to 30 are not added with Cr, Ni, Nb, V, Al, or B, or even if added, they are lower than the specified range of the present invention. Insufficient strength and toughness. Comparative Example No. Since 31 has a high C, the toughness of the weld metal is insufficient, and at the same time, the hot cracking susceptibility increases. In addition, the droplets become coarse and spatter increases, and a large amount of slag is generated, resulting in poor paintability. Comparative Example No. Since No. 32 has a high Mn, the toughness of the weld metal is insufficient, and at the same time, humping occurs during high-speed welding, and normal beads are not formed. In addition, a large amount of slag is generated and the paintability is poor. Comparative Example No. Since No. 33 is high in Si, the toughness of the weld metal is insufficient, and at the same time, the droplets become coarse and spatter increases. In addition, a large amount of slag is generated and the paintability is poor. Comparative Example No. Since 34 is high in P, it is highly susceptible to hot cracking.

  Comparative Example No. Since 35 to 36 have low S, the hot cracking susceptibility is low, but the bead formability during high-speed welding is poor, and the bead toe radius is also small. Comparative Example No. Since Nos. 37 to 40 are high in Cr, Ni, V, and Al, the cost is high and humping occurs in high-speed welding. In addition, the droplets became larger and a lot of spatter was generated. Comparative Example No. Since No. 41 has high Nb, it has high hot cracking sensitivity and high cost, and humping occurred in high-speed welding. In addition, the droplets became larger and a lot of spatter was generated. Comparative Example No. 42 has a high B and high hot cracking sensitivity. Comparative Example No. Since No. 43 has high B and V, it has high hot cracking susceptibility and high cost, and humping occurred in high-speed welding. Also, the droplets increased and a lot of spatter occurred.

  Comparative Example No. Since No. 44 has high Si and low Mn, the strength of the weld metal was insufficient, and at the same time, the droplets became coarse and spatter increased. Further, high speed welding causes humping, a large amount of slag is generated, paintability is inferior, and high temperature cracking sensitivity is high. Comparative Example No. 45 is high in S, and the strength and toughness of the weld metal are insufficient, and at the same time, the hot cracking sensitivity is high. Comparative Example No. No. 46 has low C and Mn, so the strength of the weld metal is insufficient, and at the same time, the hot cracking susceptibility is high. Comparative Example No. 47 is high in C and low in Si, so that the weld metal lacks the toughness and at the same time the hot cracking susceptibility increases. Also, the familiarity of the beads deteriorated, the bead toe radius decreased, the droplets became coarse, the spatter increased, a large amount of slag was generated, and the paintability was inferior. Comparative Example No. No. 48 has low Si and high P, so that the weld metal has insufficient strength, and at the same time, the bead fit becomes worse, the bead toe radius becomes smaller, and the hot cracking susceptibility is also higher.

  Comparative Example No. No. 49 had high C and Mn, so the strength of the weld metal was excessive and the toughness was poor. In addition, humping occurred during high-speed welding, normal beads were not formed, droplets became coarse, spatter increased, a large amount of slag was generated, paintability was inferior, and hot cracking susceptibility was high. Comparative Example No. No. 50 had a low C and a high P, so that the strength of the weld metal was insufficient and at the same time the hot cracking susceptibility was high.

It is a figure which shows the bead toe part of the joint by which overlap fillet welding was carried out. (A) is sectional drawing which shows the sampling position of a test piece, (b) is a top view which shows the preparation methods of the test piece of a fishbone crack test.

Explanation of symbols

1a, 1b, 11; base material 2, 12; weld bead 13; backing material 14; test piece 15; slit 16; copper plate 17;

Claims (4)

C: 0.03 to 0.15 mass%, Si: 0.50 to 1.50 mass%, Mn: 1.00 to 3.00 mass%, and S: 0.040 to 0.150, based on the total mass of the wire. In addition, Ti: 0.01 to 0.20 mass%, Zr: 0.01 to 0.20 mass%, La: 0.01 to 0.05 mass%, and Ce: 0.01 to Containing at least one element selected from the group consisting of 0.05% by mass, the balance consisting of Fe and inevitable impurities, and restricting P among the inevitable impurities to 0.025% by mass or less, Mn content in the wire is [Mn] (mass%), Ti content in the wire is [Ti] (mass%), Zr content in the wire is [Zr] (mass%), La content in the wire The amount is [La] (mass%), and the Ce content in the wire is [Ce] ( The S content amounts%) and in the wire [S] when the (mass%), a solid wire for gas shielded arc welding, wherein the value of A given by the following equation is 100 or more.

Mn content is 1.50 mass% or more, The solid wire for gas shielded arc welding of Claim 1 characterized by the above-mentioned. C: 0.02 to 0.15 mass%, Si: 0.50 to 1.50 mass%, Mn: 1.00 to 3.00 mass%, P: 0.025 mass% or less with respect to the total mass of the wire , S: 0.040 to contain 0.150 wt%, further, Nb: 0.005 to 0.5 mass%, V: 0.005 to 0.5 mass%, Al: 0.155 to 0. At least one selected from the group consisting of 5% by mass, Cr: 0.005 to 0.5% by mass, Ni: 0.005 to 0.5% by mass, and B: 0.0010 to 0.0100% by mass A solid wire for gas shielded arc welding, wherein the balance is Fe and inevitable impurities. A gas shielded arc welding method using the solid wire according to any one of claims 1 to 3 and welding mild steel and high-tensile steel plate having a thickness of 0.6 to 10 mm.

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