JP5339871B2 - Flux-cored wire for submerged arc welding of low temperature steel and welding method. - Google Patents

Description

  The present invention relates to a flux cored wire and a welding method for submerged arc welding of low temperature steel used for welding of LPG storage tanks, low temperature equipment, steel structures for cold districts, etc., and particularly excellent in high-speed welding conditions. The present invention relates to a flux-cored wire and a welding method for submerged arc welding of low-temperature steel capable of obtaining high-performance weld metal, bead shape, and welding workability.

  Submerged arc welding is applied in a wide range of fields such as pipe making, steel frames, bridges, and vehicles because it provides highly efficient and stable welding workability and mechanical properties 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, as a wire for submerged arc welding of low-temperature steel, a solid wire containing an alloy component such as Ni, Mn, and Mo is mainly used for the purpose of increasing the toughness of the weld metal. However, when the alloy component amount of the wire is increased to increase the toughness of the weld metal, the wire itself has high strength, and work hardening is added and the wire is further hardened during the wire drawing process for manufacturing the welding wire. When the wire is cured, die wear and wire breakage increase, making manufacturing difficult. Therefore, in general, heat treatment is performed in the middle of wire drawing to reduce the strength of the wire, but when the alloy component is large, the transformation temperature of the wire is lowered. Retention is required. 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, the heat treatment temperature is set low, and it is necessary to hold and anneal slowly for a long time, so the productivity is very poor.

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

  Therefore, various flux-cored wires have been developed. 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 has low-temperature cracking (hydrogen cracking). Since it is easy to generate | occur | produce, it is necessary to make a flux cored wire low, and application with the conventional flux cored wire was difficult.

  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. There is also a welding method, but the firing type flux is slower than the melting type flux, so it is difficult to apply it to high-speed welding, and it is easy to absorb moisture and there is some variation in the toughness of the weld metal. In addition, there is a problem that it is difficult to obtain good welding workability in high-speed welding, such as a slightly convex bead shape.

  Considering these points, attempts have been made to develop a wire and a welding method for submerged arc welding, which can obtain a weld metal having good wire productivity and weldability and high toughness.

  For example, a composite wire for submerged arc welding with a low tensile strength of the wire is disclosed in Patent Document 1, and the productivity and feedability of the wire are improved. However, in this flux-cored wire, the amount of oxygen in the wire is reduced. Since it is high, the amount of oxygen in the weld metal increases and good low temperature toughness cannot be obtained. Furthermore, since the wire cross-sectional shape is a flux-cored wire having a seam, it absorbs moisture in the atmosphere. Therefore, it is not sufficient to reduce the moisture content of the flux, and the amount of diffusible hydrogen in the weld metal increases and low temperature cracks are likely to occur after welding.

  Patent Document 2 includes a weld metal having good welding workability and high toughness by containing a highly basic slag forming component in a flux to be filled and using it in combination with a neutral flux or a weakly basic flux. A composite wire for submerged arc welding is disclosed. However, since Si, Mn, Mo, and Ni are added to the wire hoop material, the tensile strength of the wire itself is high, the wire feedability is inferior, and the flux to be filled contains a large amount of slag forming components. Therefore, the alloy components are insufficient, which is insufficient for the demand for higher toughness of the weld metal.

  Further, a high-toughness composite wire for submerged arc welding is disclosed in Patent Document 3, which aims to increase the toughness of the weld metal and improve the workability of the weld metal. It is impossible to achieve both high toughness and good welding workability.

  Further, although a large-diameter seamless flux-cored wire for large heat input submerged arc welding of low-temperature steel is disclosed in Patent Document 4, the wire component described in Patent Document 4 cannot obtain good weld metal toughness. In addition, even if the alloy component of the steel material applied to the outer sheath of the wire is low, the wire diameter is as thick as 4.5 to 10 mm, so that the rigidity of the wire itself is increased, and the wire feedability deteriorates and the groove of the welded portion However, since it can be applied only to a wide construction method, there is a problem that the use range is limited and the production efficiency is lowered.

Furthermore, a composite wire for submerged arc welding is disclosed in Patent Document 5, which aims to increase the toughness of weld metal and improve welding workability. However, since a large amount of Mn is added to the wire component, welding is performed. The strength of the metal becomes excessively high and cracking is likely to occur, and since oxides such as SiO ₂ and TiO ₂ are contained in the wire component, the oxygen content of the weld metal increases and the toughness deteriorates. There is a problem, and it is not possible to achieve both high toughness of weld metal and good welding workability.

JP 2006-142377 A Japanese Patent Laid-Open No. 48-85443 JP-A 49-103858 JP 61-242791 A JP 62-61798 A

  An object of the present invention is to provide a flux cored wire and a welding method for submerged arc welding of low-temperature steel that can obtain a weld metal with excellent welding performance and excellent mechanical performance even under high-speed welding conditions. To do.

  The gist of the present invention is as follows.

(1) in the total wire weight percent of the flux cored wire, the sum of both the filled flux and the steel sheath, C: 0.02~0.30%, Si: 0.08~0.6%, Mn: It contains 1.2 to 3.4%, Ni: 0.5 to 3.5%, Mo: 0.03 to 0.8%, and the filling flux includes C: 0.01 to 0.27% , CaF ₂ : 2 to 15%, metal carbonate CO ₂ content: 0.05 to 0.7%, the balance consists of Fe and inevitable impurities, the total hydrogen content of the wire is 50 ppm or less, A flux-cored wire for submerged arc welding of low-temperature steel, characterized in that the steel outer sheath comprising 10-30% of the flux filling rate of the filling flux in the components is seamless.

(2) in _{mass%, SiO 2: 8~25%,} Al 2 O 3: 30~50%, MgO: 0.5~5.0%, MnO: 0.5~5.0%, CaO: 5 -20%, CaF ₂ : 25 to 50%, Li ₂ O: 0.1 to 5.0%, and the others are 3.9% or less of iron oxide and molten flux that is an inevitable impurity (1) A submerged arc welding method for low-temperature steel, comprising welding in combination with the flux-cored wire for submerged arc welding described in 1.

  According to the low-merging steel submerged arc welding wire and welding method of the present invention, the high-speed submerged arc welding of low-temperature steel facilitates the production of a wire containing a large amount of alloy components, and oxygen and nitrogen in the weld metal. A high-quality weld with no welding defects can be obtained because a weld metal with a low amount and high toughness can be obtained, a good welding workability and bead shape can be obtained, and the amount of diffusible hydrogen in the weld metal can be reduced. Can be obtained.

  In order to solve the above-mentioned problems, the inventors of the present invention have prepared a wire component that is the sum of the steel sheath and the filling flux of the flux-cored wire, the filling flux component, the total hydrogen amount of the wire, the flux filling rate, and the melting combined with the wire. We have intensively studied the chemical composition of the mold flux.

  For increasing 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 examined the application of a flux-cored wire that can freely adjust the necessary alloy components without increasing the strength of the wire itself.

First, in the wire component, Mg and Al, which are strong deoxidizers, were applied to control the amount of oxygen in the weld metal. However, as Mg is known as a hydrogen storage alloy, the amount of hydrogen in the Mg raw material itself is large. For this reason, the amount of diffusible hydrogen in the weld metal increased and cold cracking occurred. Further, Mg undergoes a reaction of Mg + 2H ₂ O → Mg (OH) ₂ + H ₂ during welding to generate hydrogen gas, so that a large amount of blow holes, pits and pock marks are generated. Furthermore, since Al produces a large amount of coarse Al oxide in the weld metal, the coarse oxide was the starting point of fracture in the acicular ferrite main structure of the low-temperature steel, and the toughness was significantly reduced.

  From the above, the oxygen content control of the weld metal could be easily adjusted by containing a small amount of Mg and Al in the wire, but welding of cold cracks, blowholes, pits, pock marks, etc. Application was difficult due to the occurrence of defects, the strength and toughness of the weld metal. Therefore, the addition of C was newly found as a strong deoxidizer to replace Mg and Al. However, in order to make the deoxidation effect work significantly, a tendency was found that the effect of increasing the C content of the flux was greater than the increase of the C content of the steel shell. This is because, in the case of submerged arc welding, since the welding current is high, C added to the steel outer shell tends to be oxidized and consumed before being combined with oxygen in the molten metal. Therefore, in order to maintain C up to the molten pool without oxidative consumption before the deoxidation of the weld metal, C is added to the filling flux. When C is added to the steel sheath and the oxygen content of the weld metal is controlled, it is necessary to add a large amount in consideration of oxidation consumption of C. If a large amount is added, the tensile strength of the wire itself increases. Productivity, wire feedability and welding workability were inferior.

  It became possible to obtain weld metal with excellent mechanical performance by adjusting the wire component and flux filling rate, applying low hydrogen raw materials, etc., but further, by eliminating the seam in the steel outer shell, , Annealing can be performed, the amount of hydrogen in the wire can be further reduced, and pickling treatment and plating treatment can also be performed, so the wire surface state can be cleaned and rust resistance can be improved. As a result, wire feedability is improved and welding workability can be improved.

  However, in the process of manufacturing a flux-cored wire without a seam in the steel outer skin, nitrogen is mixed in the wire and hermetically sealed, resulting in a problem that the amount of nitrogen in the weld metal increases and the toughness decreases. did. Therefore, as a result of manufacturing while filling with inert gas such as argon gas or helium gas so that nitrogen is not mixed in the wire, the effect of reducing the nitrogen content of the weld metal was obtained, but the manufacturing cost became very high. In addition, since the flux filled by blowing the gas flows in the wire, the filling rate varies, the welding workability deteriorates, and the toughness and strength of the weld metal increase. there were.

Because of the above, it was difficult to reduce the amount of nitrogen in the wire during the manufacturing process, and as a result of investigating techniques to prevent nitrogen from being mixed into the weld metal during welding even if the amount of nitrogen in the wire is high When metal carbonate was added to the filling flux, the effect of reducing the amount of nitrogen in the weld metal was obtained. In this method, the metal carbonate is decomposed by arc heat during welding, and CO or CO ₂ is generated to lower the nitrogen partial pressure in the arc, thereby reducing the nitrogen content in the weld metal.

In addition, the chemical composition of the flux is also important for increasing the speed and increasing the toughness of the weld metal, and has a great influence. Therefore, by applying a melt type flux, high-speed welding became possible, and the bead shape was flat and a beautiful appearance with fine waves was obtained. However, in order to increase the toughness of the weld metal, it is necessary to increase the basicity of the flux, and as a result of increasing the addition amount of basic mineral raw materials, the toughness of the weld metal has improved, but conversely, the slag peelability, The bead appearance and arc stability deteriorated. Generally, it is known that welding workability is inferior when the basicity of the flux is increased, and it is impossible to achieve both good welding workability and weld metal mechanical performance simply by increasing the basicity. Therefore, the addition of Al ₂ O ₃ was newly found in order to maintain good weld metal mechanical performance and obtain excellent welding workability. Al ₂ O ₃ is an extremely important component for obtaining good slag releasability and bead appearance, and also has an effect of improving arc stability. Further, since Al ₂ O ₃ is a neutral oxide, it has been clarified that the oxygen content of the weld metal does not increase even if the addition amount is increased somewhat. Thereby, it became possible to further improve the weld metal mechanical performance and welding workability in high-speed welding by optimizing the chemical composition of the flux including Al ₂ O ₃ .

  From the above results, by limiting the chemical composition of the flux-cored wire, the total amount of hydrogen in the wire, and the flux filling rate, and limiting the chemical composition of the molten flux to be combined, high toughness in high-speed submerged arc welding of low-temperature steel It was found that a weld metal having a high quality can be obtained, a good weld workability and a bead shape can be obtained, a diffusible hydrogen content of the weld metal is low, and there is no weld defect.

  The reasons for limiting the composition of the flux-cored wire for submerged arc welding according to the present invention will be described below. In addition, the following% shows the mass%.

C in the entire flux-cored wire is an important element for ensuring the strength of the weld metal by solid solution strengthening, and has an effect of reacting with oxygen in the arc and reducing the arc atmosphere and the amount of oxygen in the weld metal. Total both the steel sheath and the filled flux (hereinafter. Referred wire component) in the C is less than 0.02%, the effect of deoxidation and ensuring the strength are insufficient, also decreases toughness. On the other hand, if it exceeds 0.30%, C of the weld metal becomes high, so that it becomes a structure mainly composed of martensite, the strength is high, and the toughness is lowered. Therefore, C of the wire component is set to 0.02 to 0.30%.

  Moreover, in order to make the deoxidation effect by C work significantly, the effect of increasing the C of the filling flux is greater than that of increasing the C of the steel outer sheath, so the C of the filling flux is 0.01 to 0.00. 27%. When C of the filling flux is less than 0.01%, a sufficient deoxidizing effect cannot be obtained and the toughness is deteriorated. On the other hand, if it exceeds 0.27%, deoxidation becomes excessive, the strength of the weld metal is increased, and the toughness is deteriorated.

  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. If the wire component Si is less than 0.08%, the strength of the weld metal is low, the amount of oxygen increases, and the toughness decreases. On the other hand, if it exceeds 0.6%, the weld metal matrix is strengthened by solid solution, but the ferrite crystal grains are coarsened, so that the toughness is remarkably lowered. Therefore, Si of the wire component is set to 0.08 to 0.6%.

  Mn of the wire component is an effective component for improving the hardenability and increasing the strength. If the Mn of the wire component is less than 1.2%, the hardenability is insufficient and the strength is lowered. On the other hand, if it exceeds 3.4%, the hardenability becomes excessive, the strength of the weld metal increases, and the toughness decreases. Therefore, the Mn of the wire component is set to 1.2 to 3.4%.

  The wire component Ni aims to ensure the strength and toughness of the weld metal. When the wire component Ni is less than 0.5%, the strength is low and the toughness is lowered. On the other hand, if it exceeds 3.5%, since Ni is an austenite stabilizing element, the austenite grain size is coarsened and the toughness of the weld metal is deteriorated. Therefore, Ni of the wire component is set to 0.5 to 3.5%.

  The purpose of the wire component Mo is to ensure the strength of the weld metal. If the wire component Mo is less than 0.03%, the strength is low. On the other hand, if it exceeds 0.8%, an intermetallic compound is generated in the weld metal, the weld metal is hardened significantly, and the toughness is lowered. Therefore, Mo of the wire component is set to 0.03 to 0.8%.

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, if it exceeds 15%, the arc becomes unstable and the slag component in the wire increases, so the amount of welding decreases and the welding efficiency decreases. Therefore, the CaF ₂ of the filling flux is ₂ to 15%.

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 partial pressure of nitrogen 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, if it exceeds 0.7%, welding defects such as pock marks, pits, and undercuts 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 carbonate may be used _{CaCO 3, BaCO 3, MgCO 3} , MnCO 3.

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

  The flux filling rate of the filling flux in the component is 10 to 30%. 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 it exceeds 30%, the seam part is welded after molding to eliminate the seam when producing a seamless flux-cored wire, but the flux easily enters the seam part at the time of welding, a welding defect occurs, and the productivity deteriorates. . Further, when the flux filling rate increases, the oxygen content of the filling flux increases and the oxygen content of the weld metal also increases, so that the toughness decreases.

  The alloying component in the filling flux is a flux-cored wire corresponding to the components of various steel materials (base materials) by adjusting the compounding components within each limited range in consideration of the components of the steel outer shell and its content. can do.

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 that no oxide or the like that becomes a slag forming agent is added.
The balance of the components described above is Fe and unavoidable impurities, and the balance of Fe is Fe in the steel outer shell, Fe in the alloy powder, and iron powder.

  Next, the component composition of the melt type flux to be combined will be described.

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 it is less than 8%, the fit of the bead end becomes worse, the slag peelability deteriorates, and undercutting also occurs particularly in high-speed welding. On the other hand, if it exceeds 25%, the oxygen content of the weld metal increases and the toughness deteriorates, so the content is made 8 to 25%.

Al ₂ O ₃ is a very important component for obtaining good slag peelability and bead appearance in high-speed welding, and also has an effect of improving arc stability. If the content is less than 30%, the effect cannot be obtained. On the other hand, if it exceeds 50%, it becomes a convex bead and the slag peelability becomes poor, so the content is made 30 to 50%.

  MgO has the effect of improving the fire resistance and basicity of the slag. If the content is less than 0.5%, the basicity of the flux becomes low, the amount of oxygen in the weld metal increases, and the toughness deteriorates. On the other hand, if it exceeds 5.0%, the softening and melting point of the flux becomes high, the generation of protrusions and the wavyness on the bead surface become rough, and the slag peelability and bead appearance become poor. Therefore, the content of MgO is set to 0.5 to 5.0%.

  MnO is an effective component for adjusting the viscosity, fluidity and melting point of slag. If the content is less than 0.5%, the viscosity of the slag is lowered and the fluidity is deteriorated. Therefore, bead meandering and undercut occur particularly in high-speed welding. On the other hand, if it exceeds 5.0%, the viscosity of the slag becomes too high, slag entrainment and seizure occur, and the slag peelability deteriorates. Therefore, the content of MnO is set to 0.5 to 5.0%.

  CaO is an important component for adjusting the melting point and fluidity of the slag. If it is less than 5%, the fit of the bead heel end is poor, the bead appearance is poor, and undercutting occurs at high speed welding. On the other hand, if it exceeds 20%, the slag fluidity becomes poor, the bead height is non-uniform and the slag peelability becomes poor, so the content is made 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 it is less than 25%, there is no effect of improving toughness, and if it exceeds 50%, the bead appearance becomes poor, so its content is made 25 to 50%.

Li ₂ O is an effective component for improving the bead shape, and lowers the melting temperature and viscosity of the molten slag to improve the bead shape. In addition, the bead width is uniform because the hot water flow of the bead is stabilized. If the content is less than 0.1%, the effect cannot be obtained. On the other hand, if it exceeds 5.0%, fine irregularities occur on the bead surface and the bead appearance deteriorates, so the content is made 0.1 to 5.0%.

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

Others are iron oxides (FeO, etc.) and inevitable impurities such as P, S, etc., and the others show (FeO and inevitable impurities) 3.9% or less. Both inevitable impurities P and S are preferably as low as possible because they both generate a low melting point compound and reduce toughness.

  The flux cored wire for submerged arc welding and the submerged arc welding method for low-temperature steel according to the present invention have a wire outer diameter of 1 for combining in order to achieve stable arc, wire feedability, and welding efficiency improvement. It is preferable to set it as 0.0-4.0 mm.

  In addition, this wire has a seamless cross-sectional shape (hereinafter referred to as seamless) in the steel outer shell, so it has excellent moisture absorption performance and can be annealed during the manufacturing process, so that the diffusion of weld metal The amount of reactive hydrogen can be reduced as much as possible. With a normal seamed flux-cored wire that is formed from steel strip and does not weld the seam, the filling flux is easy to absorb moisture, and it cannot be annealed during the manufacturing process, so the amount of diffusible hydrogen in the weld metal Tend to be more. The reason why this seamed flux-cored wire cannot be annealed during the manufacturing process is that there is a slight gap in the seam, so if annealing is performed, the alloying agent in the filled flux is oxidized and the metal carbonate is decomposed. Since it becomes an oxide, the amount of oxygen in the weld metal increases and the predetermined quenching characteristics cannot be obtained, and the amount of nitrogen increases and the strength and toughness of the weld metal decrease. It is. A seamed flux-cored wire has an asymmetrical wire cross-section, and the wire itself tends to twist and easily shifts from the center of the groove during welding, but a seamless wire has a concentric wire cross-section and is symmetric in all directions. It is possible to obtain a wire that is easy to handle and hardly twists.

  In addition, seamless wire can be pickled and plated during the manufacturing process, so the wire surface can be cleaned and rust resistance can be improved. Welding workability can be improved.

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

  Various types of flux-cored wires shown in Table 2 were made using the steel outer sheath shown in Table 1, and combined with molten fluxes of various components shown in Table 3 to evaluate the weld metal mechanical performance of multi-layer welding. 4 is processed into a groove shape 3 with a groove angle of 30 ° and a root interval of 13 mm as shown in FIG. 1, and the wire 2 is connected to the welding conditions shown in Table 5 and the welding tip 1 shown in FIG. A welding test was carried out by a two-wire one-electrode system in which two wires were set. In addition, the welding workability evaluation was performed by horizontal fillet welding. A steel plate having a thickness of 25 mm shown in Table 4 was assembled into a T shape as shown in FIG. 3 and the wire 2 was set on the welding tip 1. A welding test with a welding length of 1 m was carried out by a 2-wire 1-electrode system under welding conditions.

  In the case of F1 steel pipes, the flux-cored wires shown in Table 2 were subjected to vibration filling with flux, and then reduced in diameter and annealed to form strands. 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 a high-frequency heating method using a thermal conductivity method for a 2.0 mm diameter wire.

  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 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 peeling and undercuts, and the weld defects after multi-layer welding. Existence and absence, oxygen content and nitrogen content of weld metal, tensile strength and toughness were investigated.

  The amount of diffusible hydrogen in the weld metal was measured in accordance with JIS Z 3118 by measuring various flux-cored wires shown in Table 2 and melt fluxes of various components shown in Table 3 with the combinations shown in Table 7 and 6 ml / 100 g The following were considered good.

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

  For mechanical performance evaluation of weld metal, mechanical test was conducted by collecting Charpy impact test piece (JIS Z2204 No. 4) and tensile test piece (JIS Z 2201 A1 No.) centering on 7mm below the steel plate surface of the multi-layer welded specimen. Carried out. The toughness was evaluated by a Charpy impact test at −60 ° C., and evaluated by the average of 3 repetitions. The absorbed energy in the Charpy impact test was 100 J or more. The evaluation of the tensile strength was good at 560 MPa or more. These survey results are summarized in Table 7.

  As is clear from Table 7, the test symbols T1 to T10, which are examples of the present invention, have low diffusible hydrogen amounts 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 in horizontal fillet welding was good, the multi-layer weld was free from defects, and the mechanical performance of the weld metal was excellent, which was a very satisfactory result.

On the other hand, the test symbol T11, which is a comparative example, has a high flux filling rate of the wire symbol W13, so that the amount of oxygen in the weld metal is large, the absorbed energy is low, and the arc is unstable because CaF ₂ is high. It became. Further, since the SiO _{2 of} the combined flux symbol MF14 was low, the bead appearance and slag peelability were poor, and undercutting occurred.

  In the test symbol T12, since C in the filling flux of the wire symbol W14 is low, the oxygen content of the weld metal is large and the absorbed energy is low, and furthermore, Mo is low, so the tensile strength is low. Further, since the CaO of the combined flux symbol MF16 is low, the bead appearance is poor and undercutting occurs.

  Test symbol T13 had a high weld metal strength and low absorbed energy because C in the filled flux of wire symbol W15 was high. Moreover, since MnO of the combined flux symbol MF17 was low, the bead meandered and undercut occurred.

  Since the Mn of the wire symbol W20 is high in the test symbol T14, the strength of the weld metal is high and the absorbed energy is low.

  Since the test symbol T15 is a wire with seam of the wire symbol W11, the total amount of hydrogen in the wire is high and the amount of diffusible hydrogen in the weld metal is high. Cracks occurred. Moreover, since Si was high, the ferrite crystal grains became coarse and the absorbed energy was low. Furthermore, since the combined flux symbol MF15 had high MgO, the bead appearance and slag peelability were poor.

Test symbol T16 had a high amount of oxygen in the weld metal due to the high SiO _{2 of} flux symbol MF12, and the absorbed energy was low. Further, since the Al ₂ O ₃ low, the arc is unstable, the slag removability and the bead appearance was poor.

In the test symbol T17, since the Si of the wire symbol W18 was low, the tensile strength of the weld metal was low, the amount of oxygen was large, and the absorbed energy was low. Further, since Li ₂ O in the flux code MF21 in combination is large, the bead appearance was poor.

In the test symbol T18, the Mn of the wire symbol W19 is low, so that the tensile strength of the weld metal is low, and further, the CO ₂ content of the metal carbonate CaCO ₃ is low, so the amount of nitrogen in the weld metal is high and the absorbed energy is high. It was low. Further, since Li ₂ O in the flux code MF22 in combination is not contained, the bead shape was poor.

The test symbol T19 has a low flux filling rate of the wire symbol W12, so that the tensile strength and absorbed energy are low, and further, the CO ₂ content of CaCO ₃ that is a metal carbonate is high. Welding defects such as pits and undercuts occurred, and blow holes were generated in the weld metal in the X-ray transmission test after multi-layer welding. Moreover, since Al ₂ O ₃ of the combined flux symbol MF11 was high, the bead shape and slag peelability were poor.

  In test symbol T20, the MgO of flux symbol MF13 was low, so the amount of oxygen in the weld metal was large and the absorbed energy was low. Moreover, since MnO is high, the slag releasability was poor, and slag entrainment defects occurred in multi-layer welding.

  In the test symbol T21, since the Ni of the wire symbol W22 is high, the absorbed energy of the weld metal was low.

  In test symbol T22, since the total (wire component) C of wire symbol W16 was low, the tensile strength of the weld metal was low, the amount of oxygen increased, and the absorbed energy was low. Further, since the CaO of the combined flux symbol MF18 was high, the bead appearance and slag peelability were poor.

In test symbol T23, the total C of wire symbol W17 was high, so the strength of the weld metal was high and the absorbed energy was low. Further, since high CaF ₂ in the flux code MF20 in combination, bead shape was poor.

  The test symbol T24 had high Mo of the wire symbol W23, so the strength of the weld metal was high and the absorbed energy was low.

In test symbol T25, the CaF _{2 of} wire symbol W24 was low, so the amount of oxygen in the weld metal was large and the absorbed energy was low.

  In the test symbol T26, the Ni of the wire symbol W21 was low, so the tensile strength and absorbed energy of the weld metal were low.

Since the test symbol T27 has a low CaF _{2 of the} flux symbol MF19, the absorbed energy of the weld metal was low.

It is a figure which shows the groove shape of the flat joint multilayer build-up test plate used in the Example of this invention. It is a figure which shows the model of the welding method in the Example of this invention. It is a figure which shows the groove shape of the test plate for horizontal fillet welding used in the Example of this invention, and the model of the welding method.

Explanation of symbols

1 Welding tip 2 Wire 3 Groove shape

Claims (2)

In total wire weight percent of the flux cored wire, the sum of both the filled flux and the steel sheath, C: 0.02~0.30%, Si: 0.08~0.6%, Mn: 1.2 -3.4%, Ni: 0.5-3.5%, Mo: 0.03-0.8%, and the filling flux contains C: 0.01-0.27%, CaF ₂ : 2 to 15%, CO ₂ content of metal carbonate: 0.05 to 0.7%, the balance consists of Fe and inevitable impurities, the total hydrogen content of the wire is 50ppm or less, A flux cored wire for submerged arc welding of low-temperature steel, characterized in that the steel outer shell having a flux filling rate of 10 to 30% is seamless. By _{mass%, SiO 2: 8~25%,} Al 2 O 3: 30~50%, MgO: 0.5~5.0%, MnO: 0.5~5.0%, CaO: 5~20% And CaF ₂ : 25 to 50%, Li ₂ O: 0.1 to 5.0%, and the others are 3.9% or less of iron oxide and inevitable impurities, a molten flux, and A submerged arc welding method for low temperature steel, characterized by welding in combination with a flux cored wire for submerged arc welding.

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