JP2009291802A - Low hydrogen covered electrode for welder using dc power source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low hydrogen covered electrode for a welder using DC power source, capable of obtaining a welded structure whose weld metal is excellent in crack resistance and low temperature toughness when welding high-tensile steel having a 0.2% proof stress of ≥830 MPa. <P>SOLUTION: The electrode includes, by mass% to the total mass of the electrode, 0.05-0.15% C, 0.3-2.5% Si, 0.5-2.5% Mn, 1.0-5.0% Ni, >0.30% and ≤0.80% Ti, 0.002-0.08% Al, 0.02-0.20% Cr, and the balance Fe, an arc stabilizing agent, a slag generating agent, a binder, and inevitable impurities. The slag generating agent includes, by mass% to the total mass of a coating flux, at least 30-60% metal carbonate and 11-23% metal fluoride. The coating ratio that is expressed by the ratio of the mass of the coating flux to the total mass of the electrode is 25-45 mass%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is a low hydrogen dedicated to a DC power source welding machine used when manufacturing a steel structure that requires both high strength with a 0.2% proof stress of 820 MPa or more (equivalent to a tensile strength of 900 MPa or more) and low temperature toughness. The present invention relates to a system coated arc welding rod.

  In recent years, with the increase in size of welded structures and the harsh use environment, required characteristics for welded parts have become severe. For this reason, low hydrogen coated arc welding rods for high-strength steel not only require both high strength and high toughness and good welding workability, but also reduce diffusible hydrogen and ensure all-position weldability. It is also necessary to ensure the joint bending characteristics. For this reason, if the chemical composition of the raw material varies in the manufacturing stage of the welding material, or if the storage and welding conditions of the welding material are inappropriate, the designed joint performance cannot be ensured. Thus, compared with the welding material for low-strength steel, the welding method for high-strength steel must manage a manufacturing method and welding conditions correctly.

  On the other hand, when welding is performed overseas, welding is often performed using a DC welding power source instead of the mainstream AC welding power source in Japan. In this case, there are phenomena peculiar to DC welding, such as magnetic arc blowing that makes the arc unstable and defects and gas components tend to be involved, and the yield of alloying elements tends to fluctuate compared to AC welding. It occurs. This phenomenon peculiar to direct current welding cannot be ignored in the welding material design particularly in a high-strength welding rod whose joint characteristics are easily affected by fluctuations in welding conditions. Therefore, the development of a coated arc welding rod that can ensure the required characteristics stably even in DC welding has been an issue.

  Until now, a welding rod specialized for DC welding power source has not been developed yet. However, as a technique for achieving both high strength and high toughness, which is a problem of the present invention, Patent Document 1 discloses a high tensile strength of 590 MPa or higher. In order to obtain a weld metal having both strength and high toughness, a technique for improving toughness by adding Mg to the coating material or limiting the particle size of Mg is disclosed. Moreover, in patent document 2, as a coated arc welding rod for high-tensile steel materials having a tensile strength of 880 to 1180 MPa, the relationship between the tensile strength of the steel materials and the alloy elements in the weld metal is defined by a formula, thereby welding metal Techniques for improving the crack resistance and toughness of steel are disclosed.

Japanese Patent No. 3026899 Japanese Patent No. 3354460

  However, in the invention described in Patent Document 1, since the arc becomes unstable due to magnetic blowing or the like when DC welding is performed, resulting in an increase in welding defects and oxygen content, the coated arc welding rod that satisfies the required characteristics even in DC welding. Is insufficient.

  In addition, in the invention described in Patent Document 2, the toughness is insufficient even for AC welding, and the arc becomes unstable when DC welding is performed, so that the toughness is further deteriorated and a defect may occur. .

  Therefore, the present invention advantageously solves the above-mentioned problems peculiar to DC welding, and is a welded structure excellent in crack resistance and low-temperature toughness of weld metal in welding of high-tensile steel having a 0.2% proof stress of 830 MPa or more. It is an object of the present invention to provide a low hydrogen-based coated arc welding rod for a DC power source welding machine.

  In the welding of high-strength steel having a 0.2% proof stress of 830 MPa or more, the present inventors have solved the problems peculiar to direct current welding while achieving both high crack resistance and low temperature toughness of the weld metal. The hydrogen-coated arc welding rod has been studied earnestly. As a result, by adding an appropriate amount of Ti, the arc can be stabilized even in DC welding, and defects can be reduced and the amount of oxygen in the weld metal can be reduced, which results in good weldability and high toughness weld metal. I found out that It was also found that the toughness of the weld metal can be improved and the amount of diffusible hydrogen can be reduced by adjusting the amount of Mg added and the particle size.

  The present invention has been newly made based on such new findings, and the gist thereof is as follows.

  (1) Mass% with respect to the total mass of the coated arc welding rod, C: 0.05 to 0.15%, Si: 0.3 to 2.5%, Mn: 0.5 to 2.5%, Ni: 1 0.0 to 5.0%, Ti: more than 0.30% to 0.80% or less, Al: 0.002 to 0.08%, Cr: 0.02 to 0.20%, P: 0.02% Hereinafter, S: 0.01% or less, N: 0.005% or less, O: 0.005% or less, with the balance being Fe, an arc stabilizer, a slag generator, a binder, and inevitable impurities The slag-forming agent contains at least metal carbonate and metal fluoride in mass% with respect to the total mass of the coating agent, including 30 to 60% metal carbonate and 11 to 23% metal fluoride. Low water for a DC power welding machine, characterized in that the coverage expressed by the coating mass relative to the mass is 25 to 45 mass% System covered electrode.

  (2) Further, the above-mentioned (1), characterized in that the total content of one or more of Mo, Nb, and V is 1.0 to 3.0% by mass% with respect to the total mass of the coated arc welding rod. A low hydrogen-based coated arc welding rod for a DC power source welding machine as described in 1.

  (3) The above-mentioned coating agent contains 0.2 to 2.0% by mass of Mg having an average particle size limited to 120 to 250 μm with respect to the total mass of the coated arc welding rod. ) Or a low hydrogen-based coated arc welding rod for a DC power source welding machine according to (2).

  As described above in detail, in the low hydrogen-based coated arc welding rod, the composition and covering ratio of the coating agent and the entire welding rod are regulated, so that it is excellent for high strength weld metal with 0.2% proof stress of 830 MPa or more. Toughness is obtained. Therefore, the reliability of the welded joint for various steel structures can be greatly improved.

The present invention provides a low hydrogen-based coating for a DC power source welding machine capable of obtaining a welded structure excellent in crack resistance and low-temperature toughness of weld metal in welding of high-tensile steel having a 0.2% proof stress of 830 MPa or more. It relates to arc welding rods.
The reason for component limitation in the low hydrogen-based coated arc welding rod for DC power supply welding machine of the present invention will be described in detail below.

[Welding bar as a whole]
In this invention, it is necessary to adjust each component of the said low hydrogen type | system | group covering arc welding rod for DC power supply welding machines as the whole welding rod. In this case, the amount of each component of the entire welding rod is an amount expressed by the following equation in consideration of the following coverage A (%), taking the case of Ti as an example.
[Ti of welding rod] (mass%) = [Ti in core wire] × (100−A) / 100
+ [Ti in coating] x A / 100
Ti is the most important element in a welding rod for DC welding because it is effective as a deoxidizer and affects the stability of the arc.

  FIG. 1 is a graph showing the relationship between the Ti content relative to the total mass of the welding rod and the number of defects per 1 m of weld bead. When Ti in the entire welding rod is 0.30 mass% or less, the number of defects per 1 m of beads in DC welding increases as shown in FIG. When the Ti content decreases, the arc length increases and the arc is easily affected by magnetism, and the inclusion of nitrogen seems to cause the increase in the number of defects. Moreover, when such a magnetic blow occurs, not only nitrogen but the oxygen content rate in a weld metal will increase, and toughness will fall. On the other hand, in FIG. 1, even if it exceeds 0.80 mass%, the number of defects increases, but this is not due to magnetic blowing of the arc but because the coating tends to dry crack. Thus, when the Ti content in the weld metal increases, the number of defects increases. Considering these, the range of Ti content is set to be more than 0.30 mass% to 0.80 mass% or less. Furthermore, since Ti adversely affects Charpy absorbed energy, when considering the toughness of the weld metal, a more preferable range of Ti content is more than 0.30 mass% to 0.60 mass% or less.

  When C is 0.05% by mass or less, pores are easily generated in the weld metal due to insufficient deoxidation, and sufficient solid solution strengthening cannot be obtained, resulting in insufficient strength of the weld metal. On the other hand, if it exceeds 0.15% by mass, martensite is generated to deteriorate toughness and crack resistance is inferior, so the range of the C content of the welding rod is set to 0.05 to 0.15% by mass.

  The Si of the welding rod is intended for deoxidation of the weld metal, but is also necessary for ensuring welding workability. When the content of the entire welding rod is less than 0.3% by mass, pores are likely to be generated in the metal after melting due to insufficient deoxidation, and the welding workability in an elevational posture is deteriorated. On the other hand, if it exceeds 2.5% by mass, the toughness of the weld metal decreases, so the range of the Si content of the welding rod is set to 0.3 to 2.5% by mass.

  Mn is important as a deoxidizer like Si, and at least 0.5% by mass must be contained in the entire welding rod, but if it exceeds 2.5% by mass, it becomes a mixed structure of upper bainite and martensite, Since the toughness is deteriorated, the range of the Mn content of the welding rod is set to 0.5 to 2.5% by mass. Furthermore, if the Mn content is 1.4% or less, segregation during solidification is reduced, and an effect of improving toughness can be obtained. Therefore, the more preferable range of the Mn content is 0.5 to 1.4% by mass.

  Ni is a target high-strength weld metal, and when Ni in the entire welding rod is less than 1.0% by mass, it is difficult to obtain high toughness. On the other hand, if it exceeds 5.0 mass%, the grain boundary of the weld metal becomes brittle, grain boundary fracture occurs, and the toughness decreases, so the range of Ni content of the welding rod is 1.0 to 5.0 mass%. It was.

Al is effective as a part of a strong deoxidizer and must be contained in an amount of 0.002% or more. However, if it exceeds 0.08% by mass in the entire welding rod, Al ₂ O in the deoxidation product. _{Since 3} remains in the metal after melting and the amount of oxygen increases, the toughness deteriorates, so the range of the Al content in the welding rod is set to 0.002 to 0.08 mass% or less.

  Cr is an element necessary for ensuring the strength of the joint and must be contained at least 0.02% by mass in the entire welding rod. However, if it exceeds 0.20% by mass, the toughness is deteriorated. The range of Cr content was set to 0.02 to 0.20 mass%.

[Impurity elements]
P and S are segregated at the final solidified portion during welding and the toughness is lowered. Although it is desirable to reduce the P and S of the welding rod as much as possible, the manufacturing cost of the core increases as the number decreases. For this reason, the amount of P and S of a welding rod was made into 0.02 mass% and 0.01 mass% or less as a range with little influence on the low-temperature toughness fall of a weld metal, respectively.

  N is effective in improving the toughness of the weld metal if the content in the rod after melting is reduced. N in the weld metal is mixed from N in the welding rod in addition to being mixed from the atmosphere during welding. Therefore, it is desirable to keep N in the welding rod as low as possible, but it is necessary to carefully select raw materials in order to keep N low, and as a result, the manufacturing cost increases. For this reason, N content rate of a welding rod was made into 0.005 mass% or less as a range with few bad influences on the low temperature toughness of a weld metal.

If the content of O is high in the rod after melting, it reacts with the deoxidizer or alloying agent in the coating during welding to reduce its yield, causing variations in the performance of the weld metal. Interstitial flowers are produced in the metal and cause toughness reduction. For this reason, O content rate of the welding rod was made into 0.005 mass% or less as a range where the stable weld metal component is obtained.
In addition, Si, Mn, Ti, Al, and the like contained in the welding rod are contained in a pure metal or alloy state (for example, Fe—Si, Fe—Mn, Mn—Si, TiC, Al—Mg, etc.). May be.

  In addition, although it does not prescribe | regulate especially as a core wire used for this invention welding rod, it is desirable that it is the range defined by JISG3523.

  The types and optimum addition rates of elements contained in the welding rod of the present invention are as described above, and the object of the present invention is achieved as long as the above requirements are satisfied.

  Furthermore, if necessary, the strength of the weld metal can be increased by containing one or more of Mo, Nb, and V in a total amount of 1.0 to 3.0% by mass. Each of these components is contained in the steel core wire, or added to the coating agent in the form of metal powder or alloy powder with other metals.

[Coating agent]
The metal carbonate of the coating agent refers to CaCO ₃ , MgCO ₃ , BaCO _3, etc., and has a function of decomposing with arc heat to generate gas and protecting the arc atmosphere from the atmosphere. If the total of one or more of them is less than 30% by mass in the coating agent, the shielding gas is insufficient, and a large amount of nitrogen and hydrogen in the atmosphere dissolves in the weld metal, leading to deterioration of toughness and crack resistance. . Moreover, when it exceeds 60 mass% in a coating material, an arc will become unstable, a bead shape will deteriorate, and the peelability of slag will also deteriorate, Therefore It was set as the range of 30-60 mass% in a coating material.

Metal fluoride refers to CaF ₂ , MgF ₂ , AlF _3, etc., which are added to adjust the fluidity of the molten slag. If the total of one or more of them is less than 11% by mass in the coating agent, the molten slag is added. The viscosity of the slag is insufficient, the encapsulation of the slag is deteriorated, and the bead shape is also deteriorated. If the amount exceeds 23% by mass in the coating agent, the shape of the coated cylinder becomes incomplete and the stability of the arc deteriorates, so the range of 11 to 23% by mass in the coating agent was set.

  As the components of the coating agent, each of the above components is an essential component, but the other components are mainly composed of a deoxidizer, an alloy agent, an arc stabilizer, a slag generator, and a binder. The deoxidizer may be a deoxidizer such as Fe-Si, Fe-Mn, or Mn. Alloying agents refer to Mo, Nb, V, etc., and are added as necessary for the purpose of increasing the strength of the weld metal, improving heat resistance, fire resistance, and the like. These are added in the form of alloy powders with iron and other metals in addition to the respective metal powders. The arc stabilizer and slag forming agent refer to iron, alkali components, rutile and the like. As the binder, potassium silicate, sodium silicate and the like are indicated.

  Furthermore, in order to increase the low temperature toughness of the weld metal more effectively, it is preferable to contain 0.2 to 2.0% by mass of Mg having an average particle size limited to 120 to 250 μm. FIG. 2 is a graph showing the relationship between the average particle diameter of Mg and the impact absorption energy of the weld metal. Mg can reduce the amount of oxygen while minimizing an increase in the amount of diffusible hydrogen in the weld metal, and can reduce variations in the toughness of the weld metal. When the average particle size is less than 120 μm, the contribution to stabilization of toughness expected by the present invention is small, and the Charpy absorbed energy at −40 ° C. is below the acceptable range as shown in FIG. This is because the smaller the particle size, the easier it is for Mg to oxidize during high temperature drying, which is carried out to reduce the amount of diffusible hydrogen, and Mg does not perform its original function. When the average particle size exceeds 250 μm, weld metal performance is good and a sound weld metal can be obtained, but there is a problem in flux fluidity at the time of coating, which may hinder productivity. If the amount of Mg added is less than 0.2% by mass, a sufficient deoxidation effect cannot be obtained. On the other hand, if the amount added exceeds 2.0% by mass, the arc during welding becomes unstable, and spatter increases and the viscosity of the slag increases. Since the slag peelability deteriorates, the Mg addition range is set to 0.2 to 2.0 mass%.

[Coverage]
It is necessary to coat | cover the coating material of the said composition around a steel core wire so that the coverage represented by the coating material mass with respect to the welding rod total mass may be 25-45 mass%. If the coverage is less than 25% by mass, the function as a protective cylinder becomes insufficient, resulting in insufficient shielding, N in the weld metal increases, toughness decreases, spatter increases, and the amount of generated slag is insufficient. This is because the bead appearance deteriorates. On the other hand, if it exceeds 45% by mass, the amount of slag increases so that defects such as slag entrainment are likely to occur, and it becomes difficult to carry the rod when applied to a welded joint with a narrow groove width. .

  Examples of the present invention will be described below. In this embodiment, a core wire having the chemical components shown in Table 1 (the balance is Fe and inevitable impurities) and a coating agent having the chemical components shown in Table 2 are used to coat the outer periphery of the core wire diameter of 4.0 mm. The coating agent was applied to produce a coated arc welding rod. The balance of the coating material is composed of Fe, an arc agent, a slag forming agent, a binder and inevitable impurities. In addition, components such as Si, Mn, Ti, and Al contained in the welding rod were used in a pure metal or alloy state such as Fe—Si, Fe—Mn, and Mn—Si as necessary. Table 2 shows the content ratio of the components with respect to the entire welding rod.

  Using each of the obtained coated arc welding rods, X welding was performed on a steel plate having a thickness of 25 mm as a test base material, and arc welding was performed. The welding power source uses a DC power source, the polarity is electrode plus (DCEP), the welding conditions are welding current 150A, welding heat input 30kJ / cm, preheating / pass-to-pass temperature 100-200 ° C, and the welded joint is in an upright position. The sample was prepared, and a tensile test and a 2 mmV notch impact test at a test temperature of −40 ° C. were performed. We also investigated welding workability and oxygen content of the weld metal. The survey results are shown in Table 3. In addition, the amount of oxygen made less than 0.03 mass% the (circle) mark, and 0.03 mass% or more made the x mark.

  E1 to E15 all satisfied the requirements of the present invention, showed good values for both strength and toughness, and had good welding workability.

  The welding rods E21 to E34 show comparative examples. In welding rods E21 and E22, Al and Si in the welding rod each exceeded the upper limit, and the toughness was low. In the welding rod E23, since the metal carbonate and Ti in the welding rod exceed the upper limit, the welding workability is poor, the strength is too high, and the toughness is low. In welding rod E24, metal fluoride and Mn in the welding rod were removed, so that welding workability was poor and toughness was lowered. In the welding rod E25, the metal carbonate was below the lower limit, and the welding workability was poor. The welding rod E26 had poor welding workability because the metal fluoride exceeded the upper limit, and Ni in the welding rod was lower than the lower limit, resulting in low toughness. The welding rod E27 was inferior in welding workability because Mg in the coating exceeded the upper limit. In the welding rods E28 and E29, Cr and Ni in the welding rod exceeded the upper limit, respectively, and the toughness was low. The welding rod E30 had many pores and low toughness because O exceeded the upper limit. The welding rod E31 had a covering rate lower than the lower limit and N exceeded the upper limit, so that the welding workability was poor, and nitrogen in the weld metal increased and the toughness was low. Since the total amount of Mo, Nb, and V exceeded the upper limit, the welding rod E32 had low toughness. As for the welding rod E33, since C exceeded the condition, cracks occurred and the toughness was low. Some of the welding rods E34 had P and S of the core wires used exceeding the upper limit, and the low temperature toughness was remarkably low as compared with the welding rods of the present invention.

It is a figure which shows the relationship between Ti content rate with respect to the welding rod total mass, and the number of defects per 1 m of welding beads. It is a figure which shows the relationship between the average particle diameter of Mg, and the impact absorption energy of a weld metal.

Claims (3)

In mass% with respect to the total mass of the coated arc welding rod,
C: 0.05 to 0.15%,
Si: 0.3 to 2.5%,
Mn: 0.5 to 2.5%
Ni: 1.0-5.0%,
Ti: more than 0.30% to 0.80% or less,
Al: 0.002 to 0.08%,
Cr: 0.02 to 0.20%,
P: 0.02% or less,
S: 0.01% or less,
N: 0.005% or less,
O 2: 0.005% or less, the balance consisting of Fe, an arc stabilizer, a slag generator, a binder and inevitable impurities, and the slag generator contains at least a metal carbonate and a metal fluoride, In mass% of the total mass of the coating
Metal carbonate: 30-60%
Metal fluoride: 11-23%
A low hydrogen-based coated arc welding rod for a DC power supply welding machine, characterized in that the coating ratio is 25 to 45% by mass with respect to the total mass of the welding rod.   The direct current according to claim 1, further comprising one or more of Mo, Nb, and V in a total mass of 1.0 to 3.0% by mass% with respect to the total mass of the coated arc welding rod. Low hydrogen coated arc welding rod for power welding machines.   In the said coating agent, 0.2-2.0 mass% of Mg with which the average particle diameter was restrict | limited to 120-250 micrometers was contained with respect to the covering arc welding rod total mass, It is characterized by the above-mentioned. A low hydrogen-based coated arc welding rod for a DC power source welding machine as described.

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