JP2008302406A - Solid wire for carbon dioxide gas-shielded arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid wire for carbon dioxide gas-shielded arc welding having high practicality as a 540 N/mm<SP>2</SP>class wire (=YGW18), which obtains a weld zone having excellent strength and toughness, and has suitable slag peelability at a suitable slag amount. <P>SOLUTION: The solid wire has a composition comprising 0.020 to 0.070% C, 0.70 to 1.10% Si, 1.50 to 1.74% Mn, 0.005 to 0.018% P, ≤0.010% S, 0.18 to 0.30% Ti, 0.0015 to 0.0060% B, ≤0.08% Mo, ≤0.0100% O and ≤0.45% Cu (if the circumferential face is provided with copper plating, the content of the plating is included), and the balance Fe with inevitable impurities, and, if a parameter X<SB>W</SB>(%) is defined by X<SB>W</SB>=C+Si/24+Mn/6+B×30 based on the contents of C, Si, Mn and B, the X<SB>W</SB>is in the range of 0.380 to 0.600. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a solid wire for carbon dioxide shielded arc welding, which can provide a weld metal with high efficiency and excellent mechanical performance when mild steel or 490 to 520 N / mm grade ² high strength steel is subjected to carbon dioxide shielded arc welding. .

Recently, in the field of building steel frames, gas shielded arc welding using carbon dioxide (CO ₂ ) as a shielding gas has been mainly used because of its high efficiency. In order to improve the performance of welded joints with a focus on improving seismic resistance in terms of welding quality, the building construction standard specification JASS6 was revised in 1996, and the building standards law was revised in 1999. Management was prescribed. In response to this trend, the welding wire can accept a maximum heat input of 40 kJ / cm for a 490 N / mm grade ² steel sheet and a pass-to-pass temperature of 350 ° C., or a maximum heat input of 30 kJ / cm for a 520 N / mm grade ² steel sheet. , A wire with a high heat input and a high interpass temperature was developed that allowed an interpass temperature of up to 250 ° C. In 1999, it was converted to JIS as 540 N / mm ² class. Since then, 540 N / mm class ² wires, which can obtain superior mechanical performance even at higher heat input and higher inter-pass temperatures than those of conventional wires, have rapidly spread. In particular, unlike robot welding, in the field of manual semi-automatic welding where it is difficult to control heat input and temperature between passes, the widespread use of 540 N / mm class ² wire, which has a wide allowable range of heat management, is remarkable.

  Conventionally developed high-current / high-pass temperature wires for carbon dioxide welding have been disclosed in Patent Documents 1 to 13.

  These are generally characterized by containing more deoxidizing components such as Si, Mn, and Ti than conventional wires, and adding Mo, B, Cr, Al, Nb, V, Ni, etc. as necessary. It is. As a result, the hardenability of the steel is enhanced, and the strength is enhanced by combining the improvement of toughness by refining crystal grains with the effects of precipitation hardening and solid solution hardening. This type of wire is more effective for a steel plate having a larger groove width and a higher plate thickness at which the interpass temperature is higher.

Japanese Patent Laid-Open No. 10-230387 JP-A-11-90678 JP 2001-287086 A JP 2002-321087 A JP 2002-346789 JP 2002-79395 A JP 2002-103082 A JP 2003-119550 A JP 2003-136281 A JP 2004-202572 A JP 2004-237361 A JP 2004-98143 A JP 2006-289395 A

When inter-pass temperature control was introduced to the steel building industry, when it reaches the specified temperature, a waiting time is generated until cooling, and even if slag accumulates, slag is removed with a tool such as a chipper. I was able to. For this reason, the 540 N / mm ² class carbon dioxide welding high-current / high-pass temperature compatible wire that has been developed so far has not taken into account the slag peelability. However, in recent years, a method has been developed in which a single welder is in charge of many welded joints at the same time, and when the specified temperature is reached, the welding is moved to another welded joint and the front joint is cooled during that time. Has become popular. When the waiting time almost disappears in this way, a large amount of slag generation and poor peelability of the wire for high current / high-pass temperature, which has not been considered as a problem until now, have begun to be recognized as a major problem that reduces efficiency. It was. Therefore, in order to solve this problem, sufficient mechanical performance for 490 N / mm grade ² steel under conditions of maximum heat input of 40 kJ / cm and maximum pass temperature of 350 ° C, or maximum heat input of 30 kJ / cm and maximum pass There is a need for a high-efficiency welding wire that has the necessary and sufficient mechanical performance for 520 N / mm grade ² steel under the condition of a temperature of 250 ° C. and that has the added performance of good slag peelability. It has been developed.

Recently, however, new demands are being made with the spread of 540 N / mm class ² wires.

As described above, the high heat input high-pass temperature compatible wire is more effective as the steel plate has a larger thickness. For this reason, in the case of a relatively thin plate thickness of 20 mm or less where both heat input and interpass temperature do not increase so much, 490 N / mm class ² = YGWII, which has been used for a long time, is considered necessary and sufficient from the viewpoint of cost. When the plate thickness is thick, it was properly used as 540N / mm class ² = YGW18, but recently, replacement is troublesome, and the cost of wire is 490N / mm due to the spread of 540N / mm class ² wire. ^{As a} matter of course, 540N / mm class ² wire is also applied to thin steel sheets due to the fact that the difference from class ² has been reduced, and that building structure designers have been increasing the direction of increasing strength in terms of improving earthquake resistance. Has come to apply. However, this causes two problems.

The first problem is that, since the groove area is small, the heat input may only rise to about 25 kJ / cm, and the number of passes is small, so the temperature between passes will only rise to about 200 ° C before welding. Will finish. In other words, it becomes a condition of excessive cooling rate with low heat input and low pass temperature, and the conventional 540 N / mm class ² wire is not refined as a ferrite structure, but causes a transformation to a bainite structure or a martensite structure. On the contrary, the toughness is lowered.

  The second problem is that the base metal dilution rate of the backing gold is relatively increased due to the small groove area, which is easily affected by the composition. At present, low-quality steel sheets with low nitrogen and high nitrogen content are often used for backing metal, and the toughness is reduced by increasing the nitrogen content in the weld metal.

  Furthermore, with regard to slag removability, in robot welding, it is a preferable condition that slag removability is good, whereas in semi-automatic welding by hand, excessive slag removability is vigorous when slag peels. This is a problem because it is easy to fly and get into the eyes of workers.

  It has also been found that there is a problem with excessively reducing the amount of slag. Semi-automatic welding has a large difference in skills among individual workers. Welders with low skills use extremely high welding currents, perform excessive weaving, or increase the amount of welding per pass. Due to the cause, the shielding property of the molten pool may be deteriorated, and pore defects such as blowholes may be generated. For this reason, if the amount of slag is reduced excessively, the molten pool is not protected by the slag, exposed to the gas atmosphere, the shielding performance is lowered, and the pore defect resistance is further deteriorated. . For this reason, it becomes easy to receive not only a skill difference but the influence of the wind to a molten pool.

  Based on such a background, development of a welding wire that can achieve the following conditions is desired.

(1) Basic mechanical properties as a 540 N / mm class ² wire (= YGW18) suitable for use in carbon dioxide shielded arc welding of mild steel or 490 to 520 N / mm class ² high strength steel .

  (2) The strength and toughness of the welded portion are good without being affected by the composition of the backing material, not only when the plate thickness is thick, but also when it is thin.

  (3) For semi-automatic welding, the slag removability is moderated from the viewpoint of welding efficiency (higher efficiency as the peelability is better) and safety (safer as the peelability is worse).

  (4) The amount of slag is made moderate so as not to have a large effect on the performance of the weld metal due to differences in the skills of semi-automatic welding or slight fluctuations in the air flow. The mechanical performance becomes more stable as the amount of slag increases, and the efficiency becomes higher as the amount of slag decreases.

The inventor of the present application has made improvements on the basis of the conventional 540 N / mm class ² wire, and has completed a solid wire for carbon dioxide shielded arc welding that can achieve the above object.

The present invention has been made in view of such problems, and has a high practicality as a 540 N / mm ^second grade wire (= YGW18), and can provide a welded portion having excellent strength and toughness. An object of the present invention is to provide a solid wire for carbon dioxide shielded arc welding having a moderate amount of slag removability.

The solid wire for carbon dioxide shielded arc welding according to the present invention is C: 0.020 to 0.070 mass%, Si: 0.70 to 1.10 mass%, Mn: 1.50 to 1.74 mass%, P: 0.005 to 0.018 mass%, S: 0.010 mass% or less, Ti: 0.18 to 0.30 mass%, B: 0.0015 to 0.0060 mass%, Mo: 0.08 % By mass or less, O: 0.0100% by mass or less, Cu (in the case of having a copper plating on the peripheral surface, including this plating content): 0.45% by mass or less, the balance Fe and inevitable impurities, When the parameter X _W (mass%) is defined as X _W = C + Si / 24 + Mn / 6 + B × 30 based on the contents of C, Si, Mn and B, X _W is 0.380 to 0.600. It is characterized by that.

In this solid wire for carbon dioxide welding, Nb: 0.08 mass% or less, V: 0.08 mass% or less, Al: 0.08 mass% or less, Cr: 0.50 mass% or less, and Ni: 0 One or more elements selected from the group consisting of .50% by mass or less can be contained. In this case, the parameter _XW is further added with the contents of Ni, Mo, V, Nb and Al (elements not included are set to 0), and X _W (mass%) = C + Si / 24 + Mn / 6 + B × If you define as 30 + Ni / 20 + Cr / 20 + Mo / 4 + V / 14 + Nb / 14 + Al / 20, the parameter _{X W} is 0.380 to 0.600.

Further, 0.01 to 1.00 g of MoS ₂ can be present on the wire surface per 10 kg of the wire.

According to the present invention, a welded portion having excellent strength and toughness can be formed, the amount of slag and slag peelability are appropriate, and carbon dioxide shielded arc welding having excellent characteristics as a 540 N / mm ^second grade wire (= YGW18). A solid wire can be obtained.

The inventors of the present invention have conducted research on a welding slag of a 540 N / mm class ² wire (= YGW18), and have clarified influential factors on the characteristics. That is, the amount of weld slag produced has the strongest relationship with the amount of Mn, Ti, and O among the strong deoxidation components, and the amount of slag produced increases with the increase of these contents. Further, when poor quality backing metal is used during thin plate welding, the nitrogen content decreases the toughness of the weld metal, but the more Ti, the more the TiN is fixed, contributing to the improvement of the toughness. In other words, if the amount of Ti is small, toughness tends to deteriorate in the case of a thin plate. On the other hand, when Ti decreases excessively, the droplet transfer changes from a large globule transfer to a small short-circuit transfer, the scattering distance is long, and a large amount of spatter is generated. If it is a robot, it will not be a problem so much, but semi-automatic welding is a very big problem, and it is necessary to frequently clean the torch nozzle, so that the welding efficiency is lowered. In addition, a significant decrease in slag tends to cause shielding failure.

  Slag detachability is strong between the interfacial energy between the slag / welded metal in the molten state, the strength of the slag itself after solidification, the unevenness of the surface of the weld metal, that is, the physical height difference, and the frequency of the formation of the heights There is a relationship, and the increase in Mn and Ti and the decrease in P lower the slag peelability. On the other hand, based on these findings, excessive pursuit of technology to reduce slag generation and improve peelability leads to instability of mechanical performance such as strength and toughness, reduced safety during welding due to peeled slag, welding Disadvantages such as occurrence of hot cracking of metal are likely to occur.

  Mo is well-known as an element that can increase the strength of weld metal. Even in the JIS Z3312 YGW18 standard, addition is permitted with an upper limit of 0.40 mass% or less. Under the interpass temperature condition, the weld metal becomes excessively quenched due to the addition of Mo. In addition, when Mo is added in combination with a rough backing metal having a high nitrogen content, the weld metal has a remarkable low toughness. Therefore, although the margin of mechanical performance on the thick plate side is reduced, as a wire that can obtain high toughness from a thin plate having a thickness of about 12 mm to a thick plate having a thickness of about 80 mm, it is preferable that Mo be as little as possible. The addition was found to be desirable.

  It has also been found that as a factor other than the other wire components, when the wire feeding becomes unstable, the formation of the molten pool is disturbed, the thickness of the generated slag becomes uneven, and the slag peelability is deteriorated.

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

“C: 0.020 to 0.070 mass%”
C is an important additive element for securing the strength, but if it is less than 0.020% by mass, the required strength cannot be secured under the high heat input and high pass temperature welding conditions during thick plate welding. Desirably, it is 0.040 mass% or more. On the other hand, when C is added excessively, hot cracking tends to occur. Further, the amount of spatter generated by the CO explosion phenomenon in the arc atmosphere also increases, and the arc stability deteriorates. Low heat input during thin plate welding. Under low-pass temperature welding conditions, the strength becomes excessive and the toughness decreases. If the amount exceeds 0.070% by mass, these effects become significant, so the upper limit is made 0.070% by mass. Desirably, it is 0.060 mass% or less.

“Si: 0.70 to 1.10 mass%”
Si is mainly added to ensure strength and prevent pore defects due to deoxidation. When added in a large amount, the amount of slag increases, but there is an effect of improving the slag removability, and these effects are effective at 0.70% by mass or more. If it is less than this, the peelability is poor, and the efficiency is lowered and the arc becomes unstable. A more preferred lower limit is 0.85% by mass. On the other hand, when Si is excessively added exceeding 1.10% by mass, the amount of slag becomes excessive, the arc stability deteriorates, and the toughness decreases. Peelability becomes excessive and safety during semi-automatic welding is also reduced. Therefore, 1.10 mass% is made the upper limit of Si.

“Mn: 1.50 to 1.74 mass%”
Mn has the effects of obtaining deoxidation, increasing strength, and high toughness. Many general heat input wires contain a large amount of Mn. On the other hand, Mn increases the amount of slag produced and degrades the peelability. If it is less than 1.50% by mass, the toughness and the strength during thick plate welding are insufficient. Since the amount of slag is too small, a welder with insufficient skill may lead to insufficient shielding and insufficient performance of the weld metal. Slag peelability becomes excessive, and safety during semi-automatic welding is also reduced. Therefore, 1.50 mass% is taken as the lower limit of Mn. On the other hand, addition exceeding 1.74% by mass results in deterioration in arc stability and efficiency due to increase in slag value and decrease in peelability. In addition, the strength becomes excessive in the low heat input and low pass temperature welding conditions during thin plate welding, and the toughness is reduced. Therefore, 1.74 mass% is made the upper limit of Mn. More desirably, it is 1.70 mass% or less.

“Ti: 0.18 to 0.30 mass%”
Ti is a main component that improves the migration and stability of large droplets in a high current region and forms a slag film. If it is less than 0.18% by mass, in the case of a wire with a diameter of 1.4 mm used for semi-automatic welding, the arc stability is significantly deteriorated in a high current region of 400 A or more, and the amount of spatter generated increases, so that the removal work. Efficiency decreases. In addition, the amount of slag is insufficient, and a welder with insufficient skill may lead to insufficient shielding and insufficient performance of the weld metal. It is also susceptible to wind. Slag peelability becomes excessive, and safety during semi-automatic welding is also reduced. On the other hand, if added over 0.30% by mass, the amount of slag is excessively increased, resulting in deterioration of arc stability and efficiency due to increase in slag amount and decrease in peelability. Therefore, the upper limit is made 0.30% by mass or less. Desirably, it is 0.23 mass% or less.

“Mo: 0.08 mass% or less”
Mo generally improves hardenability and increases the strength of the weld metal, but on the other hand, the thinner the plate, the lower the toughness due to excess strength. Further, the combination with a bad backing metal with a high nitrogen content makes the toughness remarkably remarkable. Therefore, it is preferable that Mo is as little as possible as a wire to obtain high toughness from a thin plate having a thickness of about 12 mm to a thick plate having a thickness of about 80 mm, and it is desirable that no additive be added. However, the allowable upper limit as an impurity is 0.08% by mass. More preferably, it is less than 0.01% by mass.

“P: 0.005 to 0.018 mass%”
The addition of P has the effect of reducing the surface tension of the molten pool and reducing the physical unevenness during solidification to make it smooth. Thereby, there exists an improvement effect of slag peelability. When P is less than 0.005% by mass, this effect does not appear, and the efficiency is lowered and the arc becomes unstable due to poor peelability. Therefore, the lower limit of P is 0.005% by mass or more. On the other hand, addition exceeding P: 0.018% by mass results in excessive peeling, and the safety during semi-automatic welding decreases. Furthermore, hot cracks are likely to occur in the weld metal. Toughness is also reduced. Therefore, the upper limit of P is P: 0.018% by mass.

“S: 0.010 mass% or less”
S, like P, reduces the surface tension of the molten pool, reduces the physical unevenness during solidification and smoothes it, and can improve the slag peelability. While improving and reducing safety, the disadvantage of reduced toughness is significant. For this reason, in the present invention, S is not actively added but is an impurity element. If S is contained in a large amount, hot cracking also occurs. If S is suppressed to 0.010% by mass or less as an impurity, these defects do not occur, so 0.010% by mass is the upper limit. In addition, Preferably, desulfurization at the time of melting is strengthened, and S is limited to 0.006% by mass or less.

“B: 0.0015 to 0.0060 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. Although there is Y additive-free YGW18 wire, it is indispensable to add B particularly in order to improve toughness in consideration of nitrogen content from a high nitrogen backing metal in a relatively thin plate. If B is less than 0.0015% by mass, the effect of improving the toughness and particularly the strength at the time of application of a thick plate does not appear and is insufficient. On the other hand, when it is added excessively exceeding 0.0060% by mass, the toughness is reduced due to the excessive strength when the thin plate is applied. Moreover, it becomes easy to generate | occur | produce a hot crack. Therefore, this is the upper limit. More preferably, it is 0.0035 mass% or less.

“O: 0.0100 mass% or less”
Slag is an oxide. Therefore, as the amount of O increases, the amount of slag produced by the chemical reaction also increases. As a result, the efficiency decreases due to the increase in removal work as the arc stability deteriorates. In addition, the increase in inclusions causes toughness deterioration, and high temperature cracking is likely to occur. Since there is usually no problem if it is 0.0100% by mass or less, O is restricted to 0.0100% by mass or less. The distribution of O, that is, the position of the wire, such as the bulk and surface, is irrelevant and is a total.

“Cu: 0.45 mass% or less”
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 meaning to positively add as an element wire, and the amount of copper plating applied for improving the electrical conductivity, rust resistance, wire drawing and design is almost all. If it exceeds 0.45% by mass, hot cracking and slag peelability become problems, so the upper limit is 0.45% by mass. In addition, Cu is not only contained in the wire itself, but in a wire plated with copper on the peripheral surface, the Cu content is also included.

“Nb, V, Al: 0.08% by mass or less for each, Cr, Ni: 0.50% by mass or less for each”
Nb, V, Al, Cr, and Ni add a small amount to refine crystal grains and improve toughness. However, if Nb, V, and Al are added in excess of 0.08 mass%, and Cr and Ni are added in excess of 0.50 mass%, the amount of slag increases and the peelability decreases, and the efficiency decreases due to the increase in removal work. And the arc becomes unstable. Furthermore, weld metal also brings about low toughness due to excessive strength when a thin plate is applied. Accordingly, Nb, V, and Al have an upper limit of 0.08% by mass, and Cr and Ni have an upper limit of 0.50% by mass. In addition, about Nb, V, and Al, 0.020 mass% is made into an upper limit as a more preferable range. As for Cr and Ni, the upper limit is more preferably 0.10% by mass.

“Parameter X _W (mass%); 0.380 to 0.600”
However, the parameter X _W is defined by the following equation.

In the case of the wire of claim 1 which does not contain a selective component:
X _W = C + Si / 24 + Mn / 6 + B × 30
In the case of the wire of claim 2 comprising a selected component:
X _W = C + Si / 24 + Mn / 6 + B × 30 + Ni / 20 + Cr / 20 + Mo / 4 + V / 14 + Nb / 14 + Al / 20

This parameter _XW is a variable uniquely found to represent the hardenability of the B-added weld metal, and is calculated from the welding wire component. As for operation, if each element of C, Si, Mn, B, Ni, Cr, Mo, V, Nb, and Al constituting the equation is positively added or detected regardless of impurities, it is included in the calculation and analyzed in reverse If the amount is considered to be substantially no addition below the lower limit, it is excluded as 0. It shows that the hardenability of the obtained weld metal is so low that parameter _XW is small. If the parameter X _W is less than 0.380 wt%, the high heat input and high interpass temperature conditions during particularly thick plate applied with toughness, strength is insufficient. Therefore, the lower limit value of the parameter _{X W} is a 0.380 wt%. On the other hand, results in the parameter X _W exceeds 0.600 mass%, the hardenability excessively, upon application to the low heat input and low interpass temperature conditions of the thin plate, a low toughness due to excessive strength conversely. For this reason, the parameter X _W (mass%) is set to 0.380 to 0.600.

“MoS _{2 on} wire surface: 0.01 to 1.00 g per 10 kg of wire”
Wire feedability also has a significant effect 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 off. 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. Existing wire surface of the wire feedability improved means according to a method of over-oxidation along the grain boundaries, such as oxygen amount becomes excessive there is a drawback of increasing slag volume, MoS ₂ coating means than other means Since there is no fear of increasing the amount of slag, etc., it is suitable as a means for improving the wire feedability of the wire of the present invention. This effect is effective with an adhesion of 0.01 g or more per 10 kg of wire. On the other hand, if more than 1.00 g per 10 kg of wire is deposited, deposition in the feeding system begins, and conversely, feeding failure due to clogging occurs, affecting the slag properties and reducing the peelability. Become. As a result, arc stability is degraded. Accordingly, the upper limit of MoS _{2 on} the wire surface is 1.00 g per 10 kg of wire.

  A steel column skin plate / beam flange joint was simulated, and welding was performed by a so-called semi-automatic welding method under the welding conditions shown in Table 1 using a weld specimen having a groove shape shown in FIG. The welding place was outdoors and was an environment where a stable wind of 0.5 to 0.8 m / sec was blowing. Tables 2 and 3 below show the components of the column material, beam material, and backing metal used. The column material and beam material are manufactured by a blast furnace manufacturer, whereas the backing metal is manufactured by a commercial electric furnace manufacturer, which has a remarkably high nitrogen content and poor weldability. In addition, the restraint board attached in order to prevent distortion with a non-welded body uses the same material as the column material with a plate thickness of 25 mm.

  Then, the slag peelability after welding is calculated by digital image processing (Test 1), the slag amount is measured (Test 2), and the tensile test and Charpy impact test (Test 3) are used as indicators of the strength and toughness of the weld metal. Carried out. In addition, the arc stability during welding (Test 4) and the amount of spatter generated (Test 5) were also recorded. Furthermore, the occurrence of cracks was examined by an ultrasonic deep wound test (Test 6). Inventive wire components and comparative components, and their welding test results are shown in Table 4 below. In addition, “<0. ***” in the chemical components in Table 4 indicates that the value is less than the general lower limit of analysis, and is not contained industrially.

  Next, the slag peelability evaluation method of Test 1 will be described. The evaluation of peelability and slag amount was measured only under condition 1 where the plate thickness of the beam material was thin. In addition, it has confirmed that the welding wire which was favorable in the conditions 1 is also favorable in the conditions 2. Natural peelability was evaluated as a quantitative evaluation method. After the welding was completed, the bead appearance was photographed when the steel plate surface temperature at the general interpass temperature measurement position shown in FIGS. 1 (A), 1 (B), and (C) was cooled to 250 ° C. 1A is a plan view, FIG. 1B is a front view, and FIG. 1C is a perspective view. Reference numeral 1 denotes a column skin plate, reference numeral 2 denotes a beam flange, reference numeral 3 denotes a restraint plate, reference numeral 4 denotes an end tab, and reference numeral 5 denotes a backing metal.

  Next, the bead appearance photograph is binarized into (a) a portion where the slag is naturally peeled and (b) a portion where the slag remains adhered. The total of each pixel was calculated by image analysis software, and the slag peeling rate (mass%) was obtained by (a) / ((a) + (b)) × 100. The lower limit of the slag peeling rate was determined to be 5% by mass from the viewpoint of high efficiency, and the upper limit of 15% by mass was determined to be good from the viewpoint of ensuring safety.

  Next, regarding the slag amount of Test 2, all the slag was collected and weighed, including the one that naturally separated after the bead appearance photography. From the viewpoint of mechanical performance stability, the lower limit was determined to be 5 g, and from the viewpoint of high efficiency, the upper limit was determined to be 8 g.

Next, the tensile test and the Charpy impact test of the weld metal in Test 3 are shown in FIGS. 2 and 3 for JISZ3111 A2 (parallel part diameter 6 mm) and standard test piece (10 mm square) under conditions 1 and 2, respectively. The sample was taken from the position and used for the test. Note that the tensile test was performed at 20 ° C. at room temperature, and the Charby impact test was performed at 0 ° C. with an average of 3 samples. The tensile strength was 490 N / mm ² or more, and the average Charlie impact test was 70 J or more.

  The arc stability in Test 4 is based on sensory evaluation during welding. Especially when the slag did not disturb the generation of the arc and it did not disturb, or the droplet transfer was disturbed and a large amount of spatter was not generated. The case was judged good. 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 in Test 5 is obtained by collecting the spatter attached to the shield nozzle after welding in Condition 1 and measuring the weight. A spatter generation amount of 12 g or less was determined to be good.

  Table 1 below shows welding conditions, Table 2 shows combinations of steel plates, and Table 3 shows chemical compositions (mass%) of steel plates and backing metal.

Table 4 below shows the composition of each wire (mass%, MoS ₂ only unit is g / wire 10 kg), and Table 5 shows the test results. As shown in Tables 4 and 5, Example No. 1 to 20 are examples of the present invention, and the content of each component is within the scope of the present invention, so slag peelability, slag amount, weld metal strength, toughness, arc stability, low spattering, and crack resistance. The weld metal has a good mechanical property and has stable mechanical properties irrespective of the welding workability and the plate thickness.

On the other hand, Comparative Example No. 21 to 50 are outside the scope of the present invention. Comparative Example No. No. 21 had too little C, and the strength of the weld metal was insufficient during thick plate welding. Comparative Example No. In No. 22, C was excessive, high-temperature cracking occurred in the weld metal, excessive strength and low toughness at the time of thin plate welding, a lot of spatter, arc stability was poor and clogging of the shield nozzle was likely to occur, and continuous weldability deteriorated. Comparative Example No. In No. 23, Si was insufficient, the strength of the weld metal was insufficient at the time of thick plate welding, the slag peelability was poor, the slag was obstructed and the arc became unstable, and the continuous weldability deteriorated. Comparative Example No. In No. 24, 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. Furthermore, the slag peelability was excessive and the scattered slag was dangerous from the safety aspect.

  Comparative Example No. No. 25 had a small amount of Ti, a large amount of spatter was generated, the arc stability was poor, and clogging of the shield nozzle was likely to occur, so that the continuous weldability deteriorated. In addition to the nitrogen flowing in from the backing metal, the amount of slag was too small, so the shielding property of the molten pool was poor, and the toughness decreased due to the inclusion of nitrogen in the atmosphere. Moreover, the slag peelability was excessive and the scattered slag was dangerous from the safety aspect. Comparative Example No. No. 26 had excessive Ti, a large amount of slag, and poor peelability. The arc became unstable due to the slag and the continuous weldability deteriorated. Comparative Example No. In No. 27, Mn was too small and the tensile strength of the weld metal at the time of thick plate welding was low. Since the amount of slag was too small, the shielding property of the molten pool was poor, and the toughness was reduced by the inclusion of nitrogen in the atmosphere. Moreover, the slag peelability was excessive and the scattered slag was dangerous from the safety aspect.

  Comparative Example No. No. 28 had excessive Mn, a large amount of slag, and poor peelability. The arc became unstable due to the slag and the continuous weldability deteriorated. Low toughness with excessive strength during thin plate welding. Comparative Example No. In No. 29, Mo was excessive and toughness deteriorated due to excessive strength during thin plate welding. Comparative Example No. In No. 30, Mo was further excessive, and toughness deteriorated due to excessive strength not only during thin plate welding but also during thick plate welding. Comparative Example No. Nos. 31 and 32 had excessive S, low toughness and hot cracking. Moreover, the slag peelability was excessive and the scattered slag was dangerous from the safety aspect. Comparative Example No. In 33, O was excessive and the amount of slag increased. Degradation of continuous weldability due to loss of arc stability. Inclusions in the weld metal became excessive, causing high temperature cracks and toughness.

  Comparative Example No. In P, P was too small, the slag peelability was poor, the slag was obstructed and the arc became unstable, and the continuous weldability deteriorated. Comparative Example No. In 35, P was excessive, and the toughness was low and hot cracking occurred. The slag peelability was excessive and the scattered slag was dangerous for safety. Comparative Example No. In No. 36, Cu was excessive, hot cracks were generated, and slag peelability was poor, and the slag was obstructed and the arc became unstable, resulting in deterioration of continuous weldability. Comparative Example No. No. 37 had insufficient B, and toughness was insufficient regardless of the strength and thickness of the thick plate welding. Comparative Example No. In No. 38, B was excessive and hot cracking occurred. In addition, toughness deteriorated due to excessive strength during thin plate welding. Comparative Example No. 39 to No. No. 43 had excessive amounts of Nb, V, Al, Cr and Ni, respectively, and the amount of slag increased and the peelability also decreased. The arc became unstable due to the slag and the continuous weldability deteriorated. The strength became excessive during thin plate welding, and the toughness decreased.

Comparative Example No. No. 44 had an excessive MoS ₂ adhesion amount, 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 had an adverse effect, and the peelability was reduced. The amount of spatter also increased. Comparative Example No. 45 is excessive in Mn and O. The amount of slag increased and the peelability decreased remarkably, the slag became obstructive and the arc became unstable, and the continuous weldability deteriorated. Oxides in the weld metal became inclusions, resulting in reduced toughness and cracking. Comparative Example No. 46 is too Si, and Mo and B are excess. Due to the lack of Si, the slag peelability was poor, the slag was obstructed and the arc became unstable, and the continuous weldability deteriorated. Since B was excessive, hot cracking occurred. Furthermore, since Mo and B are excessive, the toughness deteriorates due to excessive strength during thin plate welding. Comparative Example No. 47 is excessive in C, Mn, and S. Due to the excess of Mn, the amount of slag increased and the peelability decreased, and the arc became unstable due to the slag being disturbed, and the continuous weldability deteriorated. Hot cracking occurred because C and S were high. The toughness was low due to excessive strength and excessive S due to excessive C and Mn. A large amount of spatter was generated due to excess C.

Comparative Example No. No. 48 is excessive in Ti, Mn, Mo, S, and B, and the parameter _XW is too large. Therefore, the increase in slag amount and the decrease in peelability are remarkable, the slag becomes obstructive and the arc becomes unstable, and the continuous weldability deteriorates. . Excessive hardenability and extremely high strength resulted in excessive strength and decreased toughness not only during thin plate welding but also during thick plate welding. Hot cracking also occurred because S and B were high. Comparative Example No. 49 is an example of a JIS Z3312 YGW11 standard wire called a 490 MPa class, which is S excessive and B insufficient. The toughness was insufficient and the strength was insufficient when welding thick plates. The slag peelability was excessive and the scattered slag was dangerous for safety. Comparative Example No. 50 is excessive Mn and Mo. The amount of slag increased and the peelability decreased remarkably, the slag became obstructive and the arc became unstable, and the continuous weldability deteriorated. The toughness deteriorated due to excessive strength during thin plate welding. Comparative Example No. 51 Although the content of each element satisfies the provisions, X _W is insufficient. Due to the lack of hardenability, the toughness was insufficient, and the strength was insufficient when welding thick plates. Comparative Example No. 52 is No. 52. This is a typical example of JIS Z3312 YGW11 standard wire called 490 MPa class as in 49, and S is excessive and B is insufficient. The toughness was insufficient and the strength was insufficient during thick plate welding. The slag peelability was excessive and the scattered slag was dangerous for safety. Comparative Example No. 53 content of each element but shall satisfy, X _W is excessive. Since the hardenability was excessive, the toughness deteriorated due to excessive strength during thin plate welding.

It is a figure which shows a welding test body shape and a groove shape. It is a figure which shows the extraction | collection position of a weld metal tensile test piece. It is a figure which shows the collection position of a weld metal Charpy impact test piece.

Explanation of symbols

1: pillar skin plate 2: beam flange 3: restraint plate 4: end tab 5: backing metal

Claims (3)

C: 0.020 to 0.070 mass%, Si: 0.70 to 1.10 mass%, Mn: 1.50 to 1.74 mass%, P: 0.005 to 0.018 mass%, S: 0.010 mass% or less, Ti: 0.18 to 0.30 mass%, B: 0.0015 to 0.0060 mass%, Mo: 0.08 mass% or less, O: 0.0100 mass% or less, Cu (If the peripheral surface has copper plating, this plating content is included): 0.45% by mass or less, balance Fe and unavoidable impurities, parameter X _W (% by mass), C, Si, Mn and when defined by _{X W = C + Si / 24} + Mn / 6 + B × 30 based on the content of B, solid wire for carbon dioxide shielded arc welding, wherein _{X W} is 0.380 to 0.600. Further, from the group consisting of Nb: 0.08 mass% or less, V: 0.08 mass% or less, Al: 0.08 mass% or less, Cr: 0.50 mass% or less, and Ni: 0.50 mass% or less. It contains one or more selected elements, and the parameter X _W (mass%) further includes the contents of Ni, Mo, V, Nb and Al (elements not contained are set to 0), and X _{W = C + Si / 24 +} Mn / 6 + B × 30 + Ni / 20 + Cr / 20 + Mo / 4 + V / 14 + Nb / 14 + Al / 20 If you define as, claimed in claim 1, characterized in that the parameter _{X W} is 0.380 to 0.600 Solid wire for carbon dioxide shielded arc welding. 3. The solid wire for carbon dioxide shielded arc welding according to claim 1, wherein 0.01 to 1.00 g of MoS ₂ is present on the surface of the wire per 10 kg of the wire.

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