JP5726708B2 - Submerged arc welding method for low temperature steel - Google Patents

Description

  The present invention relates to a submerged arc welding method for low-temperature steel used for welding LPG storage tanks, low-temperature equipment, steel structures for cold regions, and the like, and more particularly, weld metal having excellent mechanical performance even under high-speed welding conditions. Further, the present invention relates to a submerged arc welding method for low-temperature steel that can obtain a bead shape and welding workability.

  Submerged arc welding is applied in a wide range of fields such as pipe making, steel frames, bridges, vehicles, etc. because it provides highly efficient and stable welding workability and mechanical performance of weld metal. In recent years, with the development of the energy industry, low-temperature steel is widely used, and the usage rate is increasing year by year. Therefore, in submerged arc welding, further improvement in quality is required to improve productivity and secure safety and durability in construction using low-temperature steel. There is a great demand for high toughness of weld metal.

  Conventionally, in submerged arc welding of low-temperature steel, a melt-type flux and a fired-type flux are used as a flux, and a solid wire is mainly used as a wire in accordance with the component of the flux. The melt-type flux is a material in which various mineral raw materials are melted at a high temperature of 1500 ° C. or higher and pulverized into a powder after cooling, has low moisture absorption, and can reduce the amount of diffusible hydrogen in the weld metal. It is characterized by easy storage. On the other hand, the calcining flux is granulated by adding water glass or the like to various raw materials and calcined at about 550 ° C., and has an excellent feature that the chemical components of the weld metal can be freely adjusted. There is a drawback that it is easy to do.

  For submerged arc welding of low-temperature steel, in particular, a melt-type flux is often applied in order to increase the toughness, speed, and stable quality of the weld metal. However, since the molten flux cannot freely adjust the chemical composition of the weld metal, in order to increase the toughness of the weld metal, the basicity must be increased and the oxygen content of the weld metal must be reduced. However, simply increasing the basicity has a limit of increasing toughness, and a normal bead shape and good welding workability cannot be obtained. Therefore, in order to adjust the chemical components of the weld metal and increase the toughness, it is necessary to include alloy components such as Ni, Mn, and Mo in the solid wire. However, an increase in the amount of alloy components of the wire leads to an increase in strength of the wire itself, and work hardening is added at the time of wire drawing in manufacturing a welding wire, and the wire is further cured. Since the hardening of the wire causes die wear and wire breakage, the manufacture becomes difficult. Therefore, in general, heat treatment is performed in the middle of wire drawing to reduce the strength of the wire. However, when the alloy component is large, the transformation temperature of the wire is lowered, so when softening by annealing treatment, it takes a long time. Must be maintained. In addition, when softening is performed by a high-temperature normalizing treatment, the structure is easily transformed into a high-strength structure. Therefore, in order to soften the wire, it is necessary to set the heat treatment temperature to be low, and to maintain and gradually cool for a long time, so the productivity becomes very poor.

  Further, when welding is performed using a high-strength solid wire, it is difficult to correct the wire, and the center deviation from the center of the groove tends to occur, and a good bead cannot be obtained. Thus, when a high-strength solid wire is used, there is a problem that productivity and weldability are lowered.

  Thus, various flux cored wires for submerged arc welding have been developed. However, in order to obtain a high toughness weld metal, it is necessary to reduce the oxygen content of the weld metal, and welding of low-temperature steel tends to cause low-temperature cracking (hydrogen cracking), so the flux-cored wire is reduced in hydrogen. Therefore, it has been difficult to apply with conventional flux-cored wires.

  In consideration of weldability such as solid wire productivity and wire feedability, a low-strength wire with few alloy components was used, and a calcined flux (bond flux) that can adjust the amount of alloy components added was applied. A welding method has also been proposed. However, calcination type flux has a slower melting rate than fusion type flux, so it is difficult to apply it to high-speed welding, it is easy to absorb moisture, and there is some variation in toughness of weld metal, bead shape There are problems such as slightly convex shape. As described above, the firing flux has a problem that it is difficult to obtain good welding workability in high-speed welding.

  Considering these points, we have developed submerged arc welding melt fluxes that provide good weld metal mechanical performance and welding workability, and submerged arc welding wires with good wire productivity and weldability. Has been tried.

For example, Japanese Patent Application Laid-Open No. 6-285679 (Patent Document 1) discloses a melt-type flux that improves welding workability and low-temperature toughness in high-speed submerged arc welding. However, the disclosed technique of this document has a problem that the amount of oxygen in the weld metal is high because the SiO ₂ flux component is high, which is insufficient for the demand for high toughness. Further, in the disclosed technology of the same document, the flux component MgO is high, so the softening and melting point of the flux is high, protrusions are easily generated on the bead surface, the wave is rough, and the slag peelability and bead appearance are poor. There is a problem of becoming.

Japanese Patent Application Laid-Open No. 8-187593 (Patent Document 2) discloses a melt-type flux in which welding workability is improved by adjusting the particle size of the flux and toughness is improved by reducing the oxygen content of the weld metal. However, in the disclosed technique of this document, only a small amount of the flux component Al ₂ O ₃ is added. Al ₂ O ₃ is very important component in order to obtain good slag removability and bead appearance, and because there is also the effect of making the arc stability better, Al ₂ O ₃ addition amount described in Patent Document 2 Then, there is a problem that those effects cannot be obtained sufficiently.

  Japanese Patent Laying-Open No. 2006-142377 (Patent Document 3) discloses a composite wire for submerged arc welding with a low tensile strength of the wire, and is intended to improve wire productivity and feedability. Is disclosed. However, this flux-cored wire is a flux-cored wire having a seam in the wire cross-sectional shape, and therefore tends to absorb moisture in the atmosphere. Therefore, it is not sufficient to reduce the moisture content of the flux, and there is a problem that the amount of diffusible hydrogen in the weld metal increases and low temperature cracks are likely to occur after welding.

JP-A-48-85443 (Patent Document 4) contains a highly basic slag forming component in the flux to be filled, and is used in combination with a neutral flux or a weakly basic flux. A composite wire for submerged arc welding that provides a weld metal with high welding workability and high toughness is disclosed. However, in the disclosed technique of this document, since the flux to be filled contains a large amount of a slag forming component such as CaF ₂ , the alloy component is insufficient, and the demand for higher toughness of the weld metal is met. There is a problem that it is insufficient.

  Japanese Patent Laid-Open No. 49-103858 (Patent Document 5) discloses a high toughness composite wire for submerged arc welding, which is intended to increase the toughness of weld metal and improve welding workability. It is disclosed. However, the wire described in Patent Document 5 has not been sufficiently studied for the wire component and the filling flux component, and further improved performance while achieving both high toughness of the weld metal and good welding workability. There is a problem that it is not enough to plan.

  In addition, the present applicant has proposed a flux cored wire and a welding method for submerged arc welding of low temperature steel in Japanese Patent Application Laid-Open No. 2010-125509 (Patent Document 6). However, since an arc stabilizer such as an alkali metal compound is hardly added to the flux-cored wire and the melt-type flux component described in Patent Document 6, a stable and good welding workability can be obtained under high-speed welding conditions. There was a problem that could not.

JP-A-6-285679 JP-A-8-187593 JP 2006-142377 A Japanese Patent Laid-Open No. 48-85443 JP-A 49-103858 JP 2010-125509 A

  Therefore, the present invention has been devised in view of the above-described problems, and the object of the present invention is to provide a weld metal having excellent welding performance and excellent mechanical performance even under high-speed welding conditions. It aims at providing the submerged arc welding method of the steel for low temperature obtained.

  In order to solve the above-mentioned problems, the present inventors have studied in detail the chemical component of the flux-cored wire, the total hydrogen amount of the wire, the chemical component of the molten flux to be combined, and the like. As a result, by limiting the chemical composition of the flux-cored wire and the total hydrogen content of the wire, and further limiting the chemical composition of the molten flux to be combined, a high-toughness weld metal can be produced in high-speed submerged arc welding of low-temperature steel. It has been found that a good weld workability and bead shape can be obtained, a diffusible hydrogen content of the weld metal is low, and a high-quality weld with no weld defects can be obtained.

That is, the gist of the present invention is the total mass of the wire percent of the flux cored wire, the sum of both the filled flux and the steel sheath, C: 0.03~0.15%, Si: 0.08~0. 6%, Mn: 1.2~3.2%, Ni: 0.5~3.5%, Mo: contains 0.03 to 0.6%, and the filled flux, CaF _2: 2 to 12 %, CO ₂ min of metal carbonate: 0.05 to 0.7%, total of one or more of Na ₂ O converted value, K ₂ O converted value and Li ₂ O converted value of alkali metal compound: Contains 0.02 to 0.2%, the balance consists of Fe in steel outer shell, Fe in alloy powder, iron powder and inevitable impurities, and the total hydrogen content of the wire is 50ppm or less. and the wire, in _{mass%, SiO 2: 8~25%,} Al 2 O 3: 25~40%, MgO: 0 5~8.0%, MnO: 5.5~11%, CaO: 5~20%, CaF 2: 25~45%, 1 or more kinds of the sum of alkali metal oxides: 0.1-3 The submerged arc welding method for low-temperature steel is characterized in that welding is performed in combination with a molten flux containing 0.0% and the balance being FeO and 2.9% or less in total of FeO and inevitable impurities.

  According to the submerged arc welding method for low temperature steel of the present invention, in high speed submerged arc welding of low temperature steel, a high toughness weld metal with low oxygen content and nitrogen content in the weld metal can be obtained. Since workability and bead shape are obtained and the amount of diffusible hydrogen in the weld metal can be reduced, it is possible to obtain a high-quality weld with no weld defects.

It is a figure which shows the groove shape of the multilayer pile-welding test board used in the Example of this invention. It is a schematic diagram of the welding method in the Example of this invention. It is a schematic diagram of the groove shape and welding method of the test plate for horizontal fillet welding used in the examples of the present invention.

  In order to solve the above-mentioned problems, the present inventors combine the chemical composition of the wire, the chemical composition of the filling flux, the total amount of hydrogen of the wire, and the wire in the total of the steel sheath of the flux-cored wire and the filling flux. We have intensively studied the chemical components of the molten flux.

  In order to increase the toughness of the weld metal, it is most important to optimize the crystal grain structure by adding the oxygen balance and alloying elements of the weld metal. Therefore, the present inventors first studied the application of a flux-cored wire that can freely adjust the necessary alloy components without increasing the strength of the wire itself.

About the chemical component of the flux cored wire, in order to ensure the intensity | strength and toughness of a weld metal, the quantity of C, Si, Mn, Ni, and Mo was adjusted. In addition, in order to ensure toughness at low temperatures, the amounts of C, Si, Mn and CaF ₂ were adjusted to reduce the amount of oxygen in the weld metal, and an appropriate amount of metal carbonate was added to reduce the amount of nitrogen in the weld metal. Furthermore, the amount of diffusible hydrogen was reduced by reducing the total amount of hydrogen in the wire.

  In addition, the flux combined with the flux-cored wire is also important for increasing the speed and increasing the toughness of the weld metal. Therefore, a melt-type flux is used as the flux, thereby enabling high-speed welding.

Further, in order to maintain good weld metal mechanical performance without impairing the welding workability, it is essential to increase the amount of Al ₂ O ₃ added. Al ₂ O ₃ is a very important component for obtaining good slag peelability and bead appearance. Furthermore, it has been found that a bead shape can be secured in high-speed welding by adding an appropriate amount of MnO. It was possible to obtain good slag peelability and bead appearance by increasing the amount of Al ₂ O ₃ added and the appropriate amount of MnO, but it was difficult to maintain a stable arc state for long-time high-speed welding. Met. Therefore, an appropriate amount of alkali metal oxide was added to ensure a stable arc state.

  However, with respect to the addition of the alkali metal oxide, the improvement effect cannot be obtained simply by adding it to the melt type flux. This is because, when added in a large amount, the gloss of the bead surface is lost, the bead appearance is deteriorated, and the maximum addition amount of the alkali metal oxide is limited. Therefore, in order to maintain a stable arc state in high-speed welding, it is necessary to add a certain amount of alkali metal oxide or more, so it cannot be improved only by adding the alkali metal oxide to the molten flux. I understood that.

  Therefore, a new finding has been the addition of an alkali metal compound to the filling flux of the wire. The addition of the wire to the filling flux can only be added in a small amount compared to the melt type flux, but in the case of submerged arc welding, the alkali metal compound added to the filling flux in the wire is directly added to the arc atmosphere or the molten pool. Therefore, the arc state tended to be remarkably stabilized even when added in a small amount.

  From the above, by limiting the chemical composition of the flux cored wire, the chemical composition of the filling flux, and the total hydrogen content of the wire, and further limiting the chemical composition of the molten flux to be combined, high-speed submerged arc welding of low temperature steel In addition to obtaining a weld metal with high toughness, it was found that good welding workability and bead shape can be obtained, the diffusible hydrogen content of the weld metal is low, and a high-quality weld with no weld defects can be obtained. .

  The present invention has been made on the basis of such knowledge, and the details of the submerged arc welding method for low temperature steel according to the present invention will be further described below.

  In submerged arc welding, prior to welding, a granular flux is dispersed in advance along the welding line, and a welding wire is continuously fed into the flux, between the welding wire and the base metal. This is a welding method performed by generating an arc. In the present invention, a low temperature steel is welded by combining a flux cored wire and a molten flux as described below. Examples of the low temperature steel include aluminum killed steel, low temperature high strength steel, 2.5% Ni steel, and the like, but are not limited thereto.

First, the chemical component of the flux-cored wire used in the present invention, the chemical component of the filling flux filled in the wire, and the reason for limiting the total hydrogen amount of the wire will be described. In the following description, the chemical component of the wire and the chemical component of the filling flux are expressed as a total mass% of the wire, which is a ratio with respect to the total mass of the wire. . Further, where the term chemical composition of the wire (hereinafter, simply referred to as the wire component.) Refers to the chemical components of the sum of those contained to both in the filled flux and the steel sheath.

  C of the wire component is an important element for securing the strength of the weld metal by solid solution strengthening, and has a deoxidation effect that reacts with oxygen in the arc to reduce the arc atmosphere and the amount of oxygen in the weld metal. If the C content of the wire component is less than 0.03%, the effect of securing the strength is insufficient, and the deoxidation effect is insufficient and the toughness is also reduced. On the other hand, if the C of the wire component exceeds 0.15%, the amount of C of the weld metal increases, so that the structure is mainly composed of martensite, the strength becomes too high, and the toughness decreases. Therefore, C of the wire component is set to 0.03 to 0.15%.

  The wire component Si is an element important for improving the strength and toughness of the weld metal, and is combined with oxygen during welding to become a slag component, and has the effect of reducing the oxygen content of the weld metal. When the wire component Si is less than 0.08%, the strength of the weld metal is lowered, and the amount of oxygen is increased to lower the toughness. On the other hand, if the wire component Si exceeds 0.6%, the weld metal matrix is strengthened by solid solution, but the ferrite crystal grains are coarsened, so the toughness is remarkably lowered. Therefore, Si of the wire component is set to 0.08 to 0.6%.

  Mn, which is a wire component, is an effective component for improving the hardenability and enhancing the strength and toughness of the weld metal. If the Mn of the wire component is less than 1.2%, the hardenability is insufficient and the strength and toughness are lowered. On the other hand, if Mn of the wire component exceeds 3.2%, the hardenability becomes excessive, the strength of the weld metal becomes too high, and the toughness decreases. Therefore, the Mn of the wire component is set to 1.2 to 3.2%.

  The wire component Ni is an effective component for improving the toughness of the weld metal. If Ni of the wire component is less than 0.5%, the effect cannot be sufficiently obtained and the toughness is lowered. On the other hand, when the wire component Ni exceeds 3.5%, since Ni is an austenite stabilizing element, the austenite grain size is increased to deteriorate the toughness of the weld metal. Therefore, Ni of the wire component is set to 0.5 to 3.5%.

  Mo of the wire component is an effective component for ensuring the strength of the weld metal. If Mo of the wire component is less than 0.03%, the effect cannot be sufficiently obtained and the strength is lowered. On the other hand, if Mo of the wire component exceeds 0.6%, an intermetallic compound is generated in the weld metal, the weld metal is remarkably hardened, and the toughness is lowered. Therefore, Mo of the wire component is set to 0.03 to 0.6%.

The filling flux CaF ₂ is an important element for improving the toughness of the weld metal, and has the effect of reducing the oxygen partial pressure in the arc atmosphere during welding and reducing the oxygen content of the weld metal. If the filling flux CaF ₂ is less than 2%, the amount of oxygen in the weld metal increases and the toughness decreases. On the other hand, when the filling flux CaF ₂ exceeds 12%, the arc becomes unstable and the slag component in the wire increases, so that the amount of welding decreases and the welding efficiency decreases. Therefore, the CaF ₂ of the filling flux is ₂ to 12%.

Filling flux metal carbonate is an important element for improving the toughness of weld metal. During welding, metal carbonate decomposes and CO or CO ₂ gas lowers the nitrogen partial pressure in the arc atmosphere. There is an effect of reducing the amount. If the CO ₂ content of the metal carbonate of the filling flux is less than 0.05%, the amount of nitrogen in the weld metal increases and the toughness decreases. On the other hand, when the CO ₂ content of the metal carbonate of the filling flux exceeds 0.7%, pock marks, undercuts, and further blow holes are likely to occur on the surface of the weld bead. Therefore, the CO ₂ content of the metal carbonate of the filling flux is set to 0.05 to 0.7%.

The metal carbonates _can be used _{CaCO 3, BaCO 3, MgCO 3} , MnCO 3.

The alkali metal compound of the filling flux is an extremely important component for obtaining a stable arc state in high-speed welding. Terms of Na ₂ O values of the alkali metal compounds, K in one or less than 2 or more total 0.02% ₂ O conversion value and Li ₂ O conversion value, unstable its effects arc not sufficiently obtained It becomes. On the other hand, if the total of one or more of Na ₂ O converted value, K ₂ O converted value and Li ₂ O converted value of the alkali metal compound exceeds 0.2%, the bead surface is lost in gloss and the bead appearance. Deteriorates and the amount of welding fume generated increases significantly. Accordingly, the total of one or more of the alkali metal compound Na ₂ O equivalent, K ₂ O equivalent and Li ₂ O equivalent is 0.02 to 0.2%.

  Here, the alkali metal compound is a solid component of water glass made of sodium silicate or potassium silicate, fluorine compounds such as sodium fluoride, lithium fluoride and potassium silicate fluoride, potassium feldspar, lithium titanate, etc. It refers to complex compounds.

  As the total amount of hydrogen contained in the flux-cored wire increases, the amount of hydrogen gas increases during welding, and welding defects such as blow holes, pits, and pock marks are more likely to occur. Moreover, since the amount of diffusible hydrogen in the weld metal increases as the total amount of hydrogen in the flux-cored wire increases, cold cracking easily occurs. Therefore, in order to prevent welding defects and cold cracks, the total hydrogen content of the wire needs to be 50 ppm or less.

  In addition, it is preferable that P and S as inevitable impurities are as low as possible in order to form a low melting point compound and reduce toughness.

  Next, chemical components of the molten flux will be described. In the following description, the chemical component of the molten flux is expressed by mass%, which is a ratio with respect to the total mass of the molten flux, and description relating to the mass% is simply described as%.

SiO ₂ is an important component for forming a good weld bead, but if it is excessive, the amount of oxygen in the weld metal increases and the toughness deteriorates. If the SiO ₂ content is less than 8%, the fit of the bead end becomes worse, the slag removability deteriorates, and undercut is likely to occur particularly in high-speed welding. On the other hand, if SiO ₂ exceeds 25%, the oxygen content of the weld metal increases and the toughness deteriorates. Thus, SiO ₂ is set to 8-25%.

Al ₂ O ₃ is a very important component for obtaining good slag peelability and bead appearance in high-speed welding. Al ₂ O ₃ also has an effect of improving the arc stability. If Al ₂ O ₃ is less than 25%, those effects cannot be obtained sufficiently. On the other hand, if Al ₃ O ₃ exceeds 40%, it becomes a convex bead and the slag peelability becomes poor. Accordingly, Al ₂ O ₃ is set to 25% to 40%.

  MgO has the effect of improving the fire resistance and basicity of the slag. When MgO is less than 0.5%, the basicity of the flux is lowered, the amount of oxygen in the weld metal is increased, and the toughness is deteriorated. On the other hand, if MgO exceeds 8.0%, the softening and melting point of the flux becomes high, and protrusions are likely to be generated on the bead surface, and the corrugation becomes rough, resulting in poor slag peelability and bead appearance. Therefore, MgO is made 0.5 to 8.0%.

  MnO is an effective component for adjusting the viscosity, fluidity and melting point of slag. If MnO is less than 5.5%, the viscosity of the slag is lowered and the fluidity is deteriorated, and bead meandering and undercut are likely to occur particularly in high-speed welding. On the other hand, if MnO exceeds 11%, the viscosity of the slag becomes too high and the slag is entrapped and seized easily, and the slag peelability deteriorates. Therefore, MnO is set to 5.5 to 11%.

  CaO is an important component for adjusting the melting point and fluidity of the slag. If CaO is less than 5%, the fit of the bead heel ends is poor and the bead appearance is poor, and undercut is likely to occur in high-speed welding. On the other hand, if CaO exceeds 20%, the slag fluidity is poor, the bead height is uneven, and the slag peelability is also poor. Therefore, CaO is 5 to 20%.

CaF ₂ is effective in improving toughness, but since the melting point is low, if it is excessive, the smoothness of the beads is impaired. If CaF ₂ is less than 25%, the effect of improving toughness is not sufficient, whereas if CaF ₂ exceeds 45%, the bead appearance is poor. Therefore, CaF ₂ is set to 25% to 45%.

  Alkali metal oxide is a very important component for obtaining a stable arc state in high-speed welding. If the total of one or more alkali metal oxides is less than 0.1%, the effect cannot be sufficiently obtained. On the other hand, if the total of one or more of the alkali metal oxides exceeds 3.0%, the gloss of the bead surface is lost, the appearance is deteriorated, and the generation amount of welding fume is remarkably increased. Therefore, the alkali metal oxide is 0.1 to 3.0%.

As the alkali metal oxides as referred to herein, Na ₂ O, K ₂ O, can be used in combination with one or more of Li ₂ O.

  Others are inevitable impurities such as iron oxide (FeO, etc.) and P, S, etc. Both P and S are preferably as low as possible because they produce low melting point compounds and reduce toughness.

  The flux-cored wire used in the present invention has a structure in which a steel outer shell is formed into a pipe shape and filled with a filling flux. The types of wires can be broadly classified into seamless wires penetrating the steel outer shell and wires having a seam in the steel outer shell. Among these, the seamless wire that penetrates the steel outer sheath can be heat-treated by annealing in a temperature range of 650 to 1000 ° C. for the purpose of reducing the total hydrogen content of the wire, and also absorbs moisture after production. Therefore, it is more preferable because the amount of diffusible hydrogen can be reduced and the low temperature cracking resistance can be easily improved. In addition, a wire having a seam in the steel outer shell needs to select a flux having a low hydrogen content in order to improve cold cracking resistance.

  Further, the outer diameter of the flux-cored wire is preferably set to 1.0 to 4.0 mm in order to perform welding capable of improving stable arc, wire feedability, and welding efficiency.

  Further, the flux filling rate of the filling flux is preferably 10 to 25%. When the flux filling rate is less than 10%, the alloy components necessary for the intended increase in toughness are insufficient and sufficient mechanical performance cannot be obtained. On the other hand, if the flux filling rate exceeds 25%, breakage occurs frequently at the time of wire production, and the productivity deteriorates. Further, when the flux filling rate increases, the oxygen amount of the filling flux increases and the oxygen amount of the weld metal also increases, so that the toughness decreases. The flux filling rate can be adjusted by adding iron powder to the filling flux.

  In addition, the alloying components in the filling flux are adjusted to the blending components within each limited range in consideration of the steel outer shell components and their contents, and contain flux according to the components of various steel materials (base materials). It can be a wire.

  Further, in order to reduce the oxygen content of the weld metal, it is desirable that the main component of the filling flux is metal powder, and oxides or the like that become slag forming agents are not added as much as possible.

  In addition, the particle size composition of the molten flux is 1.4 × 0.21 mm in consideration of shielding properties of the molten metal from the atmosphere and outgassing, and the flux having a particle size of less than 0.21 mm is 12% or less. Is preferred.

  Hereinafter, the effect of the present invention will be described in more detail with reference to examples.

  Various flux-cored wires shown in Table 2 were made using the steel outer sheath shown in Table 1, and a submerged arc welding test was performed by combining the various flux-cored wires and molten fluxes of various components shown in Table 3. In this welding test, in order to evaluate the mechanical performance of the weld metal in multi-layer welding, a steel plate having a plate thickness of 25 mm shown in Table 4 was formed with a groove angle of 30 ° and a groove interval of 13 mm as shown in FIG. It processed into the shape and the welding test was implemented on the welding conditions shown in Table 5, and the 2 wire 1 electrode system shown in FIG. Further, in this welding test, in order to evaluate welding workability, a steel plate having a thickness of 25 mm shown in Table 4 was assembled into a T-shape as shown in FIG. A welding test with a welding length of 1 m was carried out by a 2-wire 1-electrode system under the welding conditions shown in FIG.

  In the flux-cored wires shown in Table 2, F1 to F3 steel outer skins shown in Table 1 were used. The F1 steel pipe was subjected to vibration filling with a flux, and then reduced in diameter and annealed to form a strand. The steel strip of F2 was formed into a U-shape in a molding process, filled with flux, formed into an O-shape, welded to the seam portion, and then reduced in diameter and annealed to form a strand. The steel strip of F3 was formed into a U shape in a molding process and filled with flux, and after forming into a wrap mold, the diameter was reduced to form a strand. Furthermore, those strands were drawn to a diameter of 2.0 mm. The total hydrogen amount of the wire was measured by an inert gas melting method for a 2.0 mm diameter wire in accordance with JIS Z 2614.

  The melt type flux shown in Table 3 was prepared by melting various mineral raw materials at a high temperature of 1500 ° C. or higher, pulverizing them into powder after cooling, and adjusting the particle size to 1.4 × 0.21 mm. .

  Each prototype flux-cored wire and combined fusion type flux was evaluated based on the amount of diffusible hydrogen in the weld metal, the appearance and shape of the bead after horizontal fillet welding, the presence or absence of slag peelability and the presence of undercut, and weld defects after multi-layer welding This was done by examining the presence / absence, the oxygen content and nitrogen content of the weld metal, the tensile strength and the toughness.

  The amount of diffusible hydrogen in the weld metal was measured in accordance with JIS Z 3118 with various combinations of flux-cored wires shown in Table 2 and molten fluxes of various components shown in Table 3 shown in Table 7. The evaluation of the amount of diffusible hydrogen was 6 (ml / 100 g) or less.

  Weld defects in multi-layer welding were investigated by an X-ray transmission test.

  The mechanical performance evaluation of the weld metal was performed by collecting Charpy impact test pieces (JIS Z2242 V notch test pieces) and tensile test pieces (JIS Z2241 No. 10) around 7 mm below the steel plate surface of the multi-layer welded test specimen. A mechanical test was performed. The toughness was evaluated by a Charpy impact test at −60 ° C., and the average of three repetitions was evaluated for each combination. The absorbed energy in the Charpy impact test was 100 J or more. The tensile strength was evaluated as good as 550 MPa or more. These survey results are summarized in Table 7.

  Test symbols T1 to T10 in Table 7 are examples of the present invention, and test symbols T11 to T24 are comparative examples. The test symbols T1 to T10, which are examples of the present invention, have low diffusible hydrogen amounts in the horizontal fillet welding because the wire symbols W1 to W10 and the combined flux symbols MF1 to MF10 satisfy the constituent requirements of the present invention. The welding workability was good, the multi-layer welded part was free of defects, and the mechanical performance of the weld metal was excellent.

The test symbol T11 in the comparative example has a low C in the wire symbol W14, so that the oxygen content of the weld metal is large, the absorbed energy is low, the tensile strength is low, and the arc is unstable because CaF ₂ is high. . Moreover, since MnO of the combined flux symbol MF17 is high, the slag releasability is poor, and slag entrainment defects occur in multi-layer welding.

Test symbol T12 has a low tensile strength of the weld metal because the Mo of the wire symbol W16 is low, and further, the CO ₂ content of the metal carbonate BaCO ₃ is low, so the amount of nitrogen in the weld metal is high and the absorbed energy is low. Met. Further, since the total of Na ₂ O, K ₂ O and Li ₂ O, which are alkali metal oxides of the combined flux symbol MF21, is high, the gloss of the bead surface is lost and the appearance is deteriorated.

  In the test symbol T13, since the Ni of the wire symbol W20 was high, the absorbed energy of the weld metal was low.

Test symbol T14 had low bead appearance and slag peelability due to the low SiO _{2 of} flux symbol MF11, and undercut occurred. Furthermore, since CaF ₂ is low, the absorbed energy of the weld metal was low.

The test symbol T15 is a wire with seam wire W11, so the total hydrogen amount of the wire is high, the diffusible hydrogen amount of the weld metal is high, and the weld metal is cracked in the X-ray transmission test after multi-layer welding. A blowhole was generated. Moreover, since Si was high, the ferrite crystal grains became coarse and the absorbed energy was low. Furthermore, since the CaF _{2 of} the combined flux symbol MF20 was high, the bead shape was poor.

  In the test symbol T16, since the Si of the wire symbol W17 is low, the tensile strength of the weld metal is low, the amount of oxygen is large, and the absorbed energy is low. Further, since the CaO of the combined flux symbol MF19 was low, the bead appearance was poor and undercutting occurred.

In the test symbol T17, the amount of oxygen in the weld metal was large and the absorbed energy was low because the SiO _{2 of the} flux symbol MF12 was high. Moreover, since no alkali metal oxide was added, the arc became unstable.

In the test symbol T18, since the Mn of the wire symbol W12 is low, the tensile strength and absorbed energy of the weld metal are low, and the CO ₂ content of the metal carbonate CaCO ₃ is high. A cut occurred, and a blowhole was generated inside the weld metal in the X-ray transmission test after multi-layer welding. Moreover, since CaO of the combined flux symbol MF18 was high, the bead appearance and slag peelability were poor.

  In the test symbol T19, since the Ni of the wire symbol W18 was low, the absorbed energy of the weld metal was low. Moreover, since MgO of the combined flux symbol MF15 was high, the bead appearance and slag peelability were poor.

The test symbol T20 has a high C for the wire symbol W15, so the strength of the weld metal is high and the absorbed energy is low, and the total of Na ₂ O converted value and K ₂ O converted value of the alkali metal compound is high. The gloss was lost and the appearance deteriorated. Further, since Al ₂ O ₃ of the combined flux symbol MF14 was high, the bead shape and slag peelability were poor.

  Test symbol T21 had high Mn of wire symbol W19, so the strength of the weld metal was high and the absorbed energy was low.

In the test symbol T22, since the CaF _{2 of the} wire symbol W13 is low, the amount of oxygen in the weld metal is large and the absorbed energy is low, and the arc becomes unstable because the Na ₂ O equivalent value of the alkali metal compound is low. Further, since the MnO of the combined flux symbol MF16 was low, the bead meandered and undercut occurred.

  Test symbol T23 had a high strength of the weld metal because the Mo of the wire symbol W21 was high, and the absorbed energy was low.

The test symbol T24 has a low arc energy because the Al ₂ O ₃ flux symbol MF13 is low, the slag peelability and the bead appearance are poor, and since the MgO is low, the oxygen content of the weld metal is large and the absorbed energy is low. Met.

1 Welding tip 2 Wire

Claims (1)

In total wire weight percent of the flux cored wire, the sum of both the filled flux and the steel sheath,
C: 0.03-0.15%,
Si: 0.08 to 0.6%,
Mn: 1.2 to 3.2%
Ni: 0.5 to 3.5%,
Mo: 0.03-0.6%
And in the filling flux,
CaF ₂ : 2 to 12%,
Metal carbonate CO ₂ min: 0.05-0.7%,
Total of one or more of alkali metal compounds in terms of Na ₂ O, K ₂ O and Li ₂ O: 0.02 to 0.2%
And the balance consists of Fe in the steel sheath, Fe in the alloy powder, iron powder and inevitable impurities, and the flux-cored wire for submerged arc welding in which the total hydrogen content of the wire is 50 ppm or less,
% By mass
SiO _2: 8~25%,
Al ₂ O ₃ : 25 to 40%,
MgO: 0.5 to 8.0%,
MnO: 5.5-11%,
CaO: 5 to 20%,
CaF ₂ : 25 to 45%,
Total of one or more alkali metal oxides: 0.1 to 3.0%
A low-merging steel submerged arc welding method characterized by comprising welding in combination with a molten flux containing a balance of FeO and unavoidable impurities of 2.9% or less .

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