JP2009178737A - Solid wire for carbon dioxide shielded arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid wire for carbon dioxide shielded arc welding, the solid wire that enables sufficient penetration to be obtained even in a narrow groove execution and that enables weld metal to be obtained which is superior in mechanical performance such as strength and toughness. <P>SOLUTION: The solid wire contains, by mass%, 0.03-0.10% C, 0.67-1.00% Si, 1.81-2.50% Mn, 0.006-0.018% S, 0.100-0.150% Ti, 0.0015-0.0070% B, and ≤0.10-0.45% Cu having solder content, with parameters P<SB>BS</SB>and P<SB>MT</SB>satisfying P<SB>BS</SB>≤10 and P<SB>MT</SB>≤32, controlling ≤0.020% P, ≤0.04% Nb, ≤0.04% V, ≤0.04% Al, with the balance being Fe and inevitable impurities, wherein P<SB>BS</SB>=[B]×[S]×10<SP>5</SP>and P<SB>MT</SB>=[Mn]×[Ti]×10<SP>2</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a solid wire for carbon dioxide welding used in carbon dioxide shielded arc welding of mild steel or 490 to 520 N / mm grade ² high strength steel, and is particularly capable of high-efficiency welding and good mechanical performance. TECHNICAL FIELD The present invention relates to a solid wire for carbon dioxide shielded arc welding that can obtain a simple weld metal.

Recently, in the field of building steel frames, gas shielded arc welding using CO ₂ as a shielding gas is mainly used because of its high efficiency. Previously, this gas shielded arc welding method was mostly a semi-automatic welding method by hand. However, automatic welding by a robot was aimed at reducing costs by saving labor and further improving welding efficiency by unattended operation at night or on holidays. Has also become popular. On the other hand, in terms of welding quality, in order to improve the performance of welded joints with an emphasis on improving earthquake resistance, the upper limit control of heat input and interpass temperature during welding was made in the 1997 JASS 6 revision and the 1999 Building Standards Law revision. Was stipulated. In response to this trend, the welding wire also has a maximum heat input of 40 kJ / cm for a 490 N / mm grade ² carbon steel plate and a maximum heat input of 30 kJ / for a 520 N / mm grade ² carbon steel plate up to 350 ° C. between passes. A wire with a high heat input and a high inter-pass temperature was developed as being acceptable up to a temperature of cm and an inter-pass temperature of 250 ° C., and in 1999, JIS was established as 540 N / mm ² class = YGW18. Since then, to date, 540 N / mm class ² wires, which can obtain superior mechanical performance at a higher heat input and higher inter-pass temperature than the conventional wires, have been rapidly spread. In addition, this 540 N / mm class ² wire has been widely used in semi-automatic welding where it is difficult to control heat input and interpass temperature, but recently, 540 N / mm class ² wire has also been applied to fully automatic welding by robot welding. There has been a lot to be done.

  As conventional carbon dioxide welding high current / high pass temperature compatible wires, the wires described in Patent Documents 1 to 16 are known. These wires generally contain more deoxidizing components such as Si, Mn, and Ti than conventional wires, and Mo, B, Cr, Al, Nb, V, Ni, etc. are added as necessary. Yes. As a result, the hardenability of the steel is increased, and the strength is increased by combining the improvement of toughness by crystal grain refinement and the effects of precipitation hardening and solid solution hardening.

However, the fact is that these conventional wires are not designed in consideration of use for welding by robots. Conventional high current / high pass temperature compatible wires have the disadvantages of excessive slag generation and poor peelability. Since the slag is insulative, the accumulated slag impedes arc stability and directly causes defects such as insufficient penetration and slag winding. Furthermore, if the slag does not peel off to any extent, even if the welding robot tries to re-arc while shifting the start position, an arc start error will continue, and the welding robot will determine an error and stop. Welding robots show the greatest advantage by being unmanned, but if slag accumulates in a short time and causes arc instability, manual slag removal work is frequently required, The advantages such as the need to remove the slag from the arc start portion in order to recover from the arc start mistake cannot be exhibited. Therefore, in order to solve this problem, it has necessary and sufficient mechanical performance for 490 N / mm grade ² steel under the conditions of maximum heat input 40 kJ / cm and maximum interpass temperature 350 ° C., and the amount of slag generated is small and peeling Therefore, a highly efficient welding wire having a high continuous lamination height is desired.

  In response to this demand, the wires described in Patent Documents 17 to 19 have been developed as wires with improved slag peelability. Further, Patent Documents 20 and 21 disclose wires in which the amount of slag generation is reduced along with the improvement of slag peelability.

JP-A-10-230387 Japanese Patent Laid-Open No. 11-90678 JP 2000-317678 A JP 2001-287086 A JP 2002-321087 A JP 2002-346789 A JP 2002-79395 A JP 2002-103082 A JP 2003-119550 A JP 2003-136281 A JP 2004-195543 A JP 2004-202572 A JP 2004-237361 A JP 2004-98143 A Japanese Patent Laid-Open No. 11-239892 JP 2004-237333 A JP 2006-88187 A JP 2006-305605 A JP 2006-150437 A JP 2004-122170 A JP 2006-26643 A

  However, the recent progress in robot welding technology is remarkable. For this reason, a narrow groove with a groove angle of 30 ° is realized. That is, conventionally, the groove angle is 35 ° as standard, but by reducing the number of passes and shortening the welding time by reducing the groove area, reducing the amount of welding wire used, reducing thermal strain, and reducing the temperature rise between passes. For the purpose of improving the mechanical performance of weld metal such as strength and toughness, it is possible to realize a narrow groove of about 30 °. As described above, since the torch nozzle easily interferes with the groove surface when the groove angle becomes small, the distance from the tip end to the groove bottom surface, that is, the so-called wire protrusion length is inevitably increased, and the arc force It has been found that poor penetration due to lowering tends to occur. Further, since the protruding length is increased, the gas shielding property is deteriorated, and nitrogen is mixed into the weld metal from the atmosphere, so that the toughness tends to be lowered.

  Conventionally, there is no disclosure of a technique for preventing poor penetration from the surface of the welding wire. In addition, there is no welding wire having excellent mechanical performance such as strength and toughness while realizing the conventional excellent slag peelability and minimization of the amount of slag. Therefore, there is a demand for the development of an optimum welding wire that prevents penetration failure and has excellent mechanical performance and can also be applied to narrow groove construction by multi-layer welding by a robot.

  The present invention has been made in view of such problems, and is capable of achieving sufficient penetration even in narrow groove construction, and a solid for carbon dioxide welding that provides a weld metal having excellent mechanical properties such as strength and toughness. The object is to provide a wire.

The solid wire for carbon dioxide welding according to the present invention includes C: 0.03 to 0.10% by mass, Si: 0.67 to 1.00% by mass, Mn: 1.81 to 2.50% by mass, S: 0.006 to 0.018% by mass, Ti: 0.100 to 0.150% by mass, B: 0.0015 to 0.0070% by mass, Cu content including plating: 0.10 to 0.45% by mass or less And the parameters P _BS and P _MT represented by the following formulas 1 and 2 satisfy P _BS ≦ 10 and P _MT ≦ 32, P: 0.020 mass% or less, Nb: 0.04 mass% or less V: 0.04% by mass or less, Al: 0.04% by mass or less, and remaining Fe and inevitable impurities.

The solid wire for carbon dioxide welding contains at least one selected from the group consisting of Mo: 0.25% by mass or less, Cr: 0.25% by mass or less, and Ni: 0.25% by mass or less. Is preferred. Further, it is preferable that MoS ₂ is present on the wire surface in an amount of 0.01 to 1.00 g per 10 kg of the wire.

  As a result of studies on the relationship between the wire protrusion length, the droplet transfer form, and the penetration depth, the present inventors have elucidated the following events. When the wire feed amount is constant, the longer the protrusion length, the higher the electrical resistance between the wire tip and the current-carrying point in the chip, and the easier it is to melt due to the temperature rise. On the other hand, the welding voltage rises. Under conditions where the welding current is decreased and the welding voltage is increased, the droplet that melts at the tip of the wire and falls to the weld zone has a small arc reaction force and a long transition space (arc length). Prone to transition. The directivity of the arc becomes weaker, and the area of the concentric droplet drop area centered on the wire increases. In addition, the transition period becomes longer, the arc force applied to the base material becomes weaker, and the penetration depth becomes smaller. In order to avoid this phenomenon, it is most effective to prevent complete globule droplet transfer, and it is necessary for the present inventors to suppress factors that cause the droplet to grow greatly. I found it. Ti has the greatest effect on the size of the droplet. The smaller the Ti content in the wire, the more the droplet growth is suppressed and the short-circuit transition is achieved, and the concentration of the arc is increased. The area of the zone is reduced and the penetration depth is increased.

  FIG. 1 is a graph showing the relationship between the Ti content, the wire protrusion length, and the penetration depth, with the wire protrusion length (mm) on the horizontal axis and the penetration depth (mm) on the vertical axis. is there. However, the wire feed rate is 10 m / min. As shown in FIG. 1, the longer the wire protrusion length, the smaller the penetration depth. However, when the wire protrusion length is the same, the smaller the Ti content, the greater the penetration depth. It is shown.

  Moreover, Ti oxide is a slag source, and the problems caused by slag deposition can be reduced by reducing the amount of Ti as compared with the prior art.

  On the other hand, Ti has a strong affinity with nitrogen, and has an effect of preventing the occurrence of blowholes by combining with nitrogen at the time of shielding failure and preventing metal embrittlement. Reducing Ti causes the problem of blowholes and metal embrittlement, so that the improvement of the penetration depth due to the decrease of Ti and the problem of blowholes and metal embrittlement are offset. In addition, the contents of Mn and B were optimized.

  Below, the reason for adding components and the reason for limiting the composition of the solid wire for carbon dioxide welding of the present invention will be described.

“C: 0.03 to 0.10% by mass”
C is an important additive element for securing the strength, but if it is less than 0.03% by mass, the required strength cannot be secured at the time of large heat input and high pass temperature welding. For this reason, C is 0.03 mass% or more, desirably 0.05 mass% or more. On the other hand, when C is added excessively, hot cracking tends to occur. If C is added excessively, the amount of spatter generated by the CO explosion phenomenon in the arc atmosphere also increases, and the arc stability deteriorates. Furthermore, when there is much C content, the intensity | strength of a weld metal will become excessive and toughness will fall conversely. If the C content exceeds 0.10% by mass, these effects become significant, so the upper limit is set to 0.10% by mass.

“Si: 0.67 to 1.00% by mass”
Si is mainly added to ensure strength and prevent pore defects due to deoxidation. Moreover, although addition of Si increases the amount of slag, slag peelability improves. These effects are effective when the Si content is 0.67% by mass or more. When the Si content is less than 0.67% by mass, the slag peelability is poor and the arc becomes unstable. A more preferable lower limit value of Si is 0.75% by mass. On the other hand, when Si is added excessively exceeding 1.00 mass%, the amount of slag becomes excessive, the arc stability deteriorates, and the toughness value decreases. For this reason, the upper limit of Si is set to 1.00% by mass.

“Mn: 1.81 to 2.50 mass%”
Mn has the effect of deoxidizing the weld metal, and also has the effect of increasing the strength of the weld metal and obtaining a highly tough weld metal. In robot systems equipped with a function to cope with narrow gaps, the maximum wire protrusion length is set long, and blowholes and toughness are liable to deteriorate due to shielding failure. Therefore, a relatively large amount of Mn is added as a robot wire. Can be prevented. For this purpose, it is necessary to add at least 1.81% by mass or more of Mn content. On the other hand, when the Mn content exceeds 2.50% by mass, the amount of slag increases and the slag peelability decreases. As a result, arc stability also deteriorates. As will be described later, depending on the relationship with the amount of Ti, the upper limit value of Mn is further suppressed.

“S: 0.006 to 0.018 mass%”
The addition of S lowers the surface tension of the molten pool and has the effect of reducing the physical unevenness during solidification and smoothing the surface of the weld metal. Thereby, slag peelability can be improved. If S is less than 0.006% by mass, this effect does not appear, and arc stability deteriorates due to poor peelability. On the other hand, even if S is added in an amount exceeding 0.018% by mass, the effect of improving the surface shape of the weld metal is saturated and hot cracking is likely to occur. Moreover, the form of slag is granulated, preventing melting by arc, causing partial arc instability and reducing toughness. Therefore, the upper limit of S is 0.018% by mass. As will be described later, the upper limit value of S is further suppressed by the relationship with the B amount.

“Ti: 0.100 to 0.150 mass%”
Ti has an effect of improving arc stability in a high current castle. In general, there are many wires to which Ti is added at about 0.20 mass%. One of the characteristics of the composition of the wire of the present invention is that the Ti content is lower than the general one. When Ti is less than 0.100% by mass, the arc stability deteriorates and the amount of spatter generated increases. Therefore, it is necessary to add 0.100% by mass or more of Ti. On the other hand, when the Ti content is increased, the penetration depth is reduced due to the above-described variation of the droplet transfer form, and poor penetration tends to occur when the wire protrusion length is long. If the Ti content exceeds 0.150 mass%, complete globule droplet transfer occurs and poor penetration occurs, so the upper limit is set to 0.150 mass%. As will be described later, depending on the relationship with the Mn content, the upper limit of the Ti content is further suppressed. In the case of robot welding, the optimum voltage and welding speed can always be set optimally, so that the arc stability does not deteriorate even when the Ti content is low.

“B: 0.0015 to 0.0070 mass%”
B has the effect of improving the strength and toughness by refining the crystal grains of the weld metal with a small amount of addition. When the B content is less than 0.0015% by mass, the effect of improving the strength and toughness of the weld metal does not appear, and these mechanical properties are insufficient. For this reason, B sets 0.0015 mass% as a lower limit. On the other hand, when B is added excessively exceeding 0.0070 mass%, hot cracking tends to occur. Therefore, the B content has an upper limit of 0.0070% by mass. In addition, the upper limit of B content is further suppressed by the relationship with the amount of S.

“Cu: 0.10 to 0.45 mass%”
When Cu is added excessively, it becomes easy to generate hot cracks, and the properties of the slag are changed to deteriorate the peelability. As a result, arc stability is degraded. There is no need to positively add Cu to the wire element, and what is added as a Cu component in the copper plating applied to the wire surface in order to improve the electrical conductivity, rust resistance, wire drawing and design. It is almost. When the plating amount is less than or equal to the amount converted to Cu of 0.10% by mass, the thickness of the plating film is too thin, the electrical conductivity is poor, arc instability occurs, and spatter increases. On the other hand, if the Cu content exceeds 0.45 mass%, hot cracking and slag peelability become problems, so the upper limit value of Cu is 0.45 mass%. In addition, Cu is taken as the value which added the thing contained in a wire, and a copper plating part.

“P _BS ≦ 10 (P _BS = [B] × [S] × 10 ⁵ )”
Both B and S are elements that cause hot cracking. In addition to defining the contents of B and S independently, it is necessary to prevent hot cracking by regulating both elements in relation to each other. In other words, high-temperature cracking is likely to occur in narrow groove welding, so it is necessary to pay more attention to prevention of cracking than before, and these contents are mutually related in addition to regulating the contents of B and S independently. It is necessary to regulate with

FIG. 2 is a graph showing the relationship between the occurrence of cracks and these S and B contents, with the S content on the horizontal axis and the B content on the vertical axis. As shown in FIG. 2, as a result of the experimental study by the inventors of the present application, in the range of P _BS > 10, both B and S are in the specified range in the present invention, and both elements are in a high content range, It was found that it occurred. Therefore, when the correlation parameter _{P BS} is defined as [B] × [S] × 10 5, it is necessary to the _{P BS} 10 or less.

“ _PMT ≦ 32 ( _PMT = [Mn] × [Ti] × 10 ² )”
Mn and Ti are the main generation elements of slag, and in addition to defining the contents of Mn and Ti independently, it is necessary to prevent the occurrence of excessive slag by regulating both elements in correlation with each other. .

FIG. 3 is a graph showing the relationship between the slag amount and these Mn and Ti contents with the Mn content on the horizontal axis and the Ti content on the vertical axis. As shown in FIG. 3, in the range of P _MT > 32, both Mn and Ti are within the specified range of the present invention, and both elements have a high content, so the amount of slag generated is large and the slag peelability is poor. Therefore, the inventors of the present application have found that the stability of the arc deteriorates. Moreover, when the amount of slag increases, it is necessary to frequently remove slag, and the operation efficiency is lowered. Therefore, when the correlation parameter _PMT is defined as [Mn] × [Ti] × 10 ² , it is necessary to set the _PMT to 32 or less.

“P: 0.020 mass% or less”
P is one of the main elements that cause hot cracking, and there is no need to add P actively. Therefore, the upper limit value of P is set to 0.020% by mass as an upper limit value at which hot cracking does not cause a problem.

“Nb: 0.04 mass% or less, V: 0.04 mass% or less, Al: 0.04 mass% or less”
Nb, V, and Al reduce the toughness of the weld metal under low heat input welding conditions. For this reason, it should be avoided that these elements are positively added, and the upper limit value of these elements is set to 0.04 mass% as the upper limit of the allowable range in which toughness deterioration can be ignored.

“Mo: 0.25 mass% or less, Cr: 0.25 mass% or less, and Ni: 0.25 mass% or less”
Mo, Cr, and Ni are preferably added positively in order to improve the hardenability of the weld metal and increase the strength. These Mo, Cr, and Ni can maintain moderate strength even at higher heat input and interpass temperature. The addition of these elements is not particularly required to have a lower limit, but the effect becomes remarkable when 0.05% by mass or more is added. On the other hand, if these elements are added in an amount exceeding 0.25 mass%, the microstructure of the weld metal becomes martensite and the toughness decreases. Therefore, when these elements are added, the content is 0.25% by mass or less.

“MoS _{2 on} wire surface: 0.01 to 1.00 g per 10 kg of wire”
Wire feedability has a great influence on slag peelability. When the wire feed is stabilized, the formation of the molten pool is also stabilized, the thickness of the generated slag becomes uniform, and the heat shrinkage strain acts uniformly, so that the entire surface is easily peeled. MoS _{2 on the} surface of the wire reduces fusion at the feeding point between the chip and the wire, leading to an improvement in wire feedability. As a conventional means for improving the wire feedability, there is a method of excessive oxidation along the grain boundary on the surface of the wire, but this method has a drawback that the amount of O becomes excessive and the amount of slag increases. On the other hand, application of MoS ₂ does not increase the amount of slag as compared with other feedability improving means, and is therefore suitable as the wire feedability improving means for the wire of the present invention. This effect is effective with the adhesion of 0.01 g or more of MoS ₂ per 10 kg of wire. On the other hand, when MoS ₂ is deposited exceeding 1.00 g per 10 kg of wire, deposition in the feeding system starts, and conversely, feeding failure due to clogging of MoS ₂ occurs, affecting the slag properties. This will reduce the peelability. As a result, arc stability is degraded. Accordingly, it is preferable that 0.01 to 1.00 g of MoS ₂ be present on the wire surface per 10 kg of the wire.

  Hereinafter, in order to explain the effect of the present invention, the results of performing a welding test on the wire of the example that falls within the scope of the present invention and the wire of the comparative example that falls outside the scope of the present invention will be described. 4 (a) to 4 (c) are diagrams showing a welded specimen shape and a groove shape. 4A is an enlarged sectional view showing the groove portion, FIG. 4B is a front view of the test body, and FIG. 4C is a side view. The diaphragm 1 is disposed with its surface vertical, the round steel pipe 3 is disposed with its axis horizontal, and the end surface of the round steel pipe 3 is opposed to the diaphragm 1. The end face of the round steel pipe 3 is chamfered, and a lave groove is formed between the round steel pipe 3 and the diaphragm 1. A cylindrical backing metal 2 is disposed on the inner surface of the round steel pipe 3. The groove was circumferentially welded with a welding torch 4.

  Table 1 below shows the welding conditions. Table 2 below shows combinations of the diaphragm 1, the steel pipe 3, and the backing metal 2, and Table 3 shows the composition (mass%) of the diaphragm 1, the steel pipe 3, and the backing metal 2. The weld specimen shown in FIG. 4 was welded using a commercially available steel building construction robot welding system under the welding conditions shown in Table 1. The diaphragm 1 and the steel pipe 3 are blast furnace materials, whereas the backing metal 2 is a commercially available electric furnace material, and the backing metal 2 has a remarkably high nitrogen content and poor weldability. The groove angle is generally 35 ° and the root gap is 7 mm. In this welding test, narrow groove construction with a groove angle of 30 ° and a root gap of 5 mm is adopted. Then, the slag peelability after completion of welding was calculated by digital image processing, the amount of slag was measured, and a tensile test and a Charpy impact test were performed as indicators of the strength and toughness of the weld metal. The stability of the arc during welding and the amount of spatter generated were also recorded. Furthermore, the presence or absence of insufficient penetration and the occurrence of hot cracking was examined by an ultrasonic flaw detection test.

  Table 4 below shows the wire compositions (mass%) of Examples and Comparative Examples. Table 5 below shows the test results of the welding test. In the composition of Table 4, “<0. ***” indicates that the analysis result of the composition is less than the lower limit value of general analysis accuracy, which is industrially contained. There is nothing.

  The evaluation method of each characteristic shown in Table 5 is as follows. About the slag peelability evaluation method, the peelability and the slag amount were measured only under condition 1 (see Table 2) where the steel pipe was thin. In addition, it has confirmed that the welding wire whose slag peelability was favorable on condition 1 is also favorable on condition 2. When the welding start point entered the welding of the final pass, 100 mm front and back, a total of 200 mm, were photographed centered on the point returned 90 ° from the wire (see FIGS. 4B and 4C). Next, the bead appearance photograph was binarized into (a) a part where the slag naturally peeled and (b) a part where the slag was adhered, and the distribution was obtained. The total of each pixel was calculated by image analysis software, and the slag peeling rate (%) was obtained by (a) / ((a) + (b)) × 100. Those having a slag peel rate of 15% or more were judged to have good slag peelability.

  Next, with regard to the amount of slag, all slag was collected and weighed, including those that spontaneously peeled off after bead appearance photography. A slag amount of 12 g or less was determined to be good.

The weld metal tensile test and Charpy impact test were conducted under conditions 2 (see Table 2) with JIS Z3111 A2 (parallel part diameter 6 mm) and standard test piece (10 mm square) shown in FIGS. 5 and 6 respectively. More samples were collected and used for testing. Note that the tensile test was performed at 20 ° C. at room temperature, and the Charpy impact test was performed at 0 ° C. and the average of three samples was evaluated. The tensile strength was 490 N / mm ² or more, and the average Charpy impact test was 70 J or more.

  The arc stability was determined by sensory evaluation during welding. In particular, it was judged that the slag did not disturb the generation of the arc and was not disturbed. In addition, the case where the disturbance of the arc resulting from the wire feeding failure occurred was also rejected.

  The amount of spatter generated is the weight measured by collecting spatter adhering to the shield nozzle after welding in Condition 1 (see Table 2). A spatter generation amount of 6 g or less was determined to be good.

  As shown in Table 5, in Examples 1 to 18 of the present invention, the composition range of each component is within the range defined in claims 1 to 3 of the present invention, so slag peelability, slag amount, welding Metal strength, toughness, arc stability, low spattering, penetration performance, and crack resistance are all good, and excellent welding workability and excellent mechanical properties of the weld metal are obtained.

On the other hand, Comparative Examples 19 to 50 are out of the scope of the present invention, but Comparative Example 19 has an insufficient amount of C and lacks the strength of the weld metal. In Comparative Example 20, C was excessive, hot cracks were generated in the weld metal, the strength was excessive, and the toughness was reduced. Moreover, since there was much spatter and arc stability was bad, continuous weldability also deteriorated. In Comparative Example 21, the amount of Si was too small, the strength of the weld metal was insufficient, the slag peelability was poor, the slag was obstructed and the arc became unstable, and the continuous weldability deteriorated. In addition, blow holes were generated due to insufficient deoxidation. In Comparative Example 22, Si was excessive, the toughness of the weld metal was insufficient, the amount of slag was excessive and obstructed, the arc became unstable, and the continuous weldability deteriorated. In Comparative Example 23, Mn was insufficient, toughness was low, and blow holes were generated due to insufficient deoxidation. In Comparative Example 24, Mn was excessive, the amount of slag was large, and the peelability was poor. Moreover, the arc became unstable due to the slag and the continuous weldability deteriorated. In Comparative Example 25, Ti was excessive, the amount of spatter was large, the arc stability was poor, and the shield nozzle was easily clogged, so that the continuous weldability deteriorated. In Comparative Examples 26 and 27, Ti was excessive, and the droplet transfer was a complete globule transfer, so that poor penetration occurred frequently. In Comparative Example 28, each component of Mn and Ti satisfied the specified range, but because the parameter _PMT was too large, the amount of slag was large and the peelability was poor. In addition, the slag was an obstacle, the arc became unstable, and the continuous weldability deteriorated. In Comparative Example 29, S was too small, the slag peelability was poor, the slag became an obstacle and the arc became unstable, and the continuous weldability deteriorated. In Comparative Example 30, S was excessive, the toughness was low, and hot cracking occurred. Although the slag has good releasability, the adhered slag is granulated, and the thickness is increased to impair the stability of the arc. As a result, continuous weldability deteriorated.

In Comparative Example 31, each component of S and B satisfied the specified range of the present invention, but because the parameter _PBS was too large, crack resistance was impaired and cracking occurred. In Comparative Example 32, P was excessive, the toughness was low, and hot cracking occurred. In Comparative Example 33, the amount of Cu was too small and the copper plating layer was thin, resulting in poor energization, frequent frequent fusion, destabilization of the arc, and increased spatter. In Comparative Example 34, Cu was excessive, high-temperature cracking occurred and slag peelability was poor, the slag became an obstacle and the arc became unstable, and the continuous weldability deteriorated. In Comparative Example 35, B was insufficient and the strength and toughness were insufficient. In Comparative Example 36, B was excessive and hot cracking occurred.

In Comparative Example 37, each element of Mn, Ti, B, and S independently satisfies the specified range of the present invention, but the parameters P _MT and P _BS exceed the specified range of the present invention. For this reason, there was much slag amount and slag peelability was also bad. Moreover, the arc became unstable due to the slag, the continuous weldability deteriorated, and hot cracking also occurred. In Comparative Examples 38 to 40, Nb, V, and Al were excessive and the toughness was lowered. In Comparative Examples 41 to 43, Mo, Cr, and Ni were excessive and the strength was improved, but this strength was excessive and the toughness was decreased. In Comparative Example 44, the adhesion amount of MoS ₂ was excessive, and MoS ₂ was deposited and clogged in the feeding system such as a conduit liner, and the wire feeding became very unstable. As a result, the arc stability was impaired, the slag distribution became non-uniform and adversely affected, and the slag peelability was reduced. As a result, the slag was in the way and the continuous weldability deteriorated.

  In Comparative Example 45, Ti is excessive, S is excessive, and B is not added. For this reason, since migration of the solution became complete globule due to excessive Ti, poor penetration occurred frequently. Furthermore, since S was too small, slag peelability was also bad. Moreover, the arc became unstable due to the slag and the continuous weldability deteriorated. Furthermore, since B was not added, strength and toughness were insufficient. In Comparative Example 46, Ti is excessive and S and Mn are excessive. Since the droplet transfer became complete globule transfer due to excessive Ti, poor penetration occurred frequently. Furthermore, since S was too small, the peelability was also poor. The arc became unstable due to the slag and the continuous weldability deteriorated. Since Mn was too small, strength and toughness were insufficient, and blow holes were also generated due to insufficient deoxidation. In Comparative Example 47, C is excessive, Mn is insufficient, and Ti and B are not added. For this reason, the strength and toughness were insufficient due to the lack of Mn and the addition of B, and blow holes were also generated due to insufficient deoxidation. Hot cracking occurred due to the excess of C, and furthermore, spatter was extremely large in synergy with addition of Ti, and the arc stability was poor.

In Comparative Example 48, Ti, P _MT , and Mo are excessive, and Si and S are insufficient. For this reason, since the droplet transfer became complete globule transfer due to excessive Ti, poor penetration occurred frequently. Furthermore, since there was too little Si and S, the slag peelability was also bad. The arc became unstable due to the slag and the continuous weldability deteriorated. Moreover, the toughness was insufficient due to excess Mo. Further, blowholes were generated due to insufficient deoxidation due to insufficient Si. In Comparative Example 49, Si and S are excessive, Ti is insufficient, and B is not added. The addition of B decreased the toughness and the strength. Since Si and S were excessive, the amount of slag was large and granulated to impair arc stability. As a result, continuous weldability deteriorated. Moreover, spatter frequently occurred due to lack of Ti. Due to the excess of S, hot cracking also occurred. In Comparative Example 50, Si is insufficient, B is excessive, and _PBS is too large. Due to the lack of Si, the strength of the weld metal was insufficient, the slag removability was poor, the slag was obstructed and the arc became unstable, and the continuous weldability deteriorated. Blow holes also occurred due to insufficient deoxidation due to insufficient Si. Moreover, since _PBS was too large, hot cracking also occurred.

It is a figure which shows the influence which Ti amount and wire protrusion length in a wire component have on the penetration depth. It is a figure which shows the range of B and S in this claim. It is a figure which shows the range of Mn and Ti in this claim. It is a figure which shows a welding test body shape and a groove shape. This is the sampling position of the weld metal tensile test piece. This is the sampling position of the weld metal Charpy impact test piece.

Explanation of symbols

1 Diaphragm 2 Backing Metal 3 Round Steel Pipe 4 Torch

Claims (3)

C: 0.03 to 0.10% by mass, Si: 0.67 to 1.00% by mass, Mn: 1.81 to 2.50% by mass, S: 0.006 to 0.018% by mass, Ti: 0.100 to 0.150 mass%, B: 0.0015 to 0.0070 wt%, including plating min Cu: 0.10 to contain 0.45 wt% or less, the parameter _{P BS} represented by the following formula And P _MT satisfies P _BS ≦ 10 and P _MT ≦ 32, P: 0.020 mass% or less, Nb: 0.04 mass% or less, V: 0.04 mass% or less, Al: 0.04 mass solid wire carbon dioxide gas welding, wherein the% restricted to the following, the balance Fe and unavoidable impurities.
P _BS = [B] × [S] × 10 ⁵
P _MT = [Mn] × [Ti] × 10 ² It contains at least 1 sort (s) selected from the group which consists of Mo: 0.25 mass% or less, Cr: 0.25 mass% or less, and Ni: 0.25 mass% or less. Solid wire for carbon dioxide welding. The solid wire for carbon dioxide gas welding according to claim 1 or 2, wherein 0.01 to 1.00 g of MoS ₂ is present on the wire surface per 10 kg of the wire.

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