JP5136466B2 - Flux-cored wire for welding high-strength steel and method for producing the same - Google Patents

Description

  The present invention relates to a flux-cored wire for welding high strength steel used in high strength steel having a yield strength of 690 MPa or more in construction machinery, offshore structures, etc., and in particular, high strength steel capable of all-position welding and having excellent crack resistance. The present invention relates to a flux-cored wire for welding and a manufacturing method thereof.

  Welding of high-strength steel, which is mainly used in construction machinery and offshore structures, employs covered arc welding rods with excellent impact toughness, submerged arc welding, and gas shielded arc welding using solid wire. . Among them, a gas shielded arc welding method using a covered arc welding rod or a solid wire is generally applied to a member that requires posture welding such as vertical, upward, and horizontal.

  However, the coated arc welding rod has low welding efficiency, and the gas shielded arc welding method using solid wire also requires high current welding because it requires low current welding to prevent metal dripping in posture welding. Welding is difficult.

  On the other hand, gas shield arc welding using a flux-cored wire is mostly applied to general orientation welding of low strength steel having a proof stress of less than 690 MPa.

  In gas shielded arc welding using flux-cored wire, the high melting point slag agent added to the wire at the time of welding solidifies and retains it before the weld metal. Therefore, it is possible to perform high-current welding with high current, that is, high welding.

  However, gas shielded arc welding using a flux cored wire is generally an oxide mainly of slag agent added to the flux cored wire, so it is difficult to obtain impact toughness compared to other welding methods, Since the amount of diffusible hydrogen is higher than that of solid wire due to moisture contained in the flux raw material and moisture absorption during wire storage, it has been difficult to apply it to welding of high-strength steel.

  Various developments have been made so far on flux cored wires for high-strength steel. For example, Patent Documents 1 and 2 disclose metal-based flux cored wires to which no slag agent is added. The main focus is downward welding, and all-position welding requires welding at a low current to prevent metal dripping as in the gas shielded arc welding method using solid wire.

  Patent Documents 3 and 4 also relate to flux cored wires for all positions for high-strength steel by adding metal fluoride or basic oxide to slag agent mainly composed of rutile to reduce the oxygen content of the weld metal. Although flux-cored wires with improved low temperature toughness are disclosed, they are not considered for crack resistance of the weld metal.

  Patent Document 5 discloses a technique for annealing a wire at a predetermined temperature as a method for reducing the amount of hydrogen in the flux-cored wire, but this technique is effective for conventional flux-cored wires. It is not clear whether the present invention is effective even for a flux-cored wire for a proof stress of 690 MPa class. In general, for a 690 MPa-class flux cored wire, it is necessary to add an alloy such as Ni or Mg called a so-called hydrogen storage alloy. The reason for adding these elements is to ensure the strength and toughness of the weld metal, but in the form that the hydrogen present in the flux diffuses out of the wire during wire annealing or stays in the hydrogen storage alloy. Whether the wire remains inside the wire is not clarified in the prior art. Therefore, a high-strength steel welding flux cored wire with improved crack resistance has not been realized within the scope of the prior art.

JP 2006-198630 A JP 2007-144516 A JP 09-253886 A Japanese Patent Laid-Open No. 03-047695 JP 09-57489 A

  The present invention relates to a flux cored wire for high strength steel welding used for high strength steel having a proof stress of 690 MPa or more. High efficiency steel welding flux capable of high efficiency welding in all positions and excellent in crack resistance. An object of the present invention is to provide a corrugated wire and a method for manufacturing the same.

  The gist of the present invention for solving the above problems is as follows.

(1) In a high strength steel welding flux cored wire in which a steel outer sheath is filled with flux,
C: 0.03-0.10%,
Si: 0.25 to 0.7%,
Mn: 1.0 to 3.0%
Ni: 1.0 to 3.5%
B: contains 0.001 to 0.015%,
Cr, Al
Cr: 0.05% or less,
Al: limited to 0.05% or less, and flux
TiO _2: 2.5~7.5%,
SiO ₂ : 0.1 to 0.5%,
ZrO ₂ : 0.2 to 0.9%,
Al2O _3: 0.1~0.4%
The balance is made of Fe, an arc stabilizer, and unavoidable impurities, and the total hydrogen content of the wire is 15 ppm or less. A flux-cored wire for high-strength steel welding.

  (2) Mass% relative to the total mass of the wire, Mo: 0.1 to 1.0%, Nb: 0.01 to 0.05%, V: 0.01 to 0.05%, one or more The flux-cored wire for welding high-strength steel as described in (1) above, characterized by comprising:

  (3) Mass% relative to the total mass of the wire, Ti: 0.1 to 1.0%, Mg: 0.01 to 0.9%, Ca: 0.01 to 0.5%, REM: 0.01 to The flux-cored wire for high-strength steel welding according to (1) or (2) above, containing 0.5% of one or more.

  (4) The steel strip is formed into an open tube with a forming roll while feeding it in the longitudinal direction. Flux is supplied from the opening of the open tube in the middle of forming, and the opposite edge surfaces of the opening are butt welded and welded. When performing diameter reduction and annealing on the tube obtained by the above, the wire is annealed at a temperature of 700 ° C. or more and 1000 ° C. or less after the wire diameter is reduced to 10.0 mm or less. The manufacturing method of the flux cored wire for high-strength steel welding of any one of said (1) thru | or (3).

  According to the flux-cored wire for welding high strength steel of the present invention, high-efficiency welding is possible in all positions in welding of high-strength steel with a yield strength of 690 MPa or more compared to gas shielded arc welding using a coated arc welding rod or solid wire. It is possible to improve the quality of the welded portion and the welding efficiency, such as being excellent in cracking resistance and good low-temperature toughness.

  In the flux-cored wire for all-position welding, the present inventors ensure mechanical performance such as strength and impact toughness including 690 MPa or more as a high-strength steel weld metal and have excellent crack resistance. Various studies were conducted to obtain a wire component.

  As a result, the optimum addition amount of the alloying agent in the slag component for all-position welding mainly composed of rutile is found, and further, as a means for improving crack resistance, by clarifying the conditions of wire annealing, It has been clarified that the total hydrogen amount can be reduced to 15 ppm or less, and it has been found that both can be achieved.

  The reasons for limiting the components of the flux-cored wire for welding high strength steel of the present invention will be described below.

[C: 0.03-0.10 mass%]
C is an important element that ensures the strength of the weld metal by solid solution strengthening. If the C of the steel outer shell and the flux component total (hereinafter referred to as wire component) is less than 0.03% by mass (hereinafter referred to as%), the effect of securing the strength cannot be obtained, and if it exceeds 0.10%. Excessive C yields in the weld metal, yield strength and strength increase excessively, and toughness decreases.

[Si: 0.25 to 0.7%]
Si aims to improve the toughness of the weld metal. If Si of the wire component is less than 0.25%, toughness decreases. On the other hand, when it exceeds 0.7%, the amount of slag generation increases, and slag entrainment defects occur when multi-layer welding is performed. Further, the yield in the weld metal becomes excessive, and the strength increases excessively, so that the toughness decreases.

[Mn: 1.0 to 3.0%]
Mn aims at ensuring the toughness of weld metal and improving the strength and proof stress. If the Mn of the wire component is less than 1.0%, the toughness decreases. On the other hand, if it exceeds 3.0%, the amount of slag generation increases, and slag entrainment defects occur when multi-layer welding is performed. Further, the yield in the weld metal becomes excessive, and the strength increases excessively, so that the toughness decreases.

[Ni: 1.0 to 3.5%]
Ni aims at improving the strength and toughness of the weld metal. If the wire component Ni is less than 1.0%, the effect is insufficient, and if it exceeds 3.5%, the strength increases excessively and the toughness decreases.

[B: 0.001 to 0.015%]
B improves the hardenability of the weld metal by adding a small amount, and improves the strength and low temperature toughness of the weld metal. If B is less than 0.001%, the effect is insufficient, and if it exceeds 0.015%, the strength becomes excessive and the low temperature toughness deteriorates. In addition, since the effect of B can be exhibited by any of a single metal, an alloy, or an oxide, the form when added to the flux is arbitrary.

[Cr: 0.05% or less]
Cr has the effect of improving the strength by forming carbides in the weld metal, but on the other hand, it has the effect of reducing the low temperature toughness, so it is limited to 0.05% or less.

[Al: 0.05% or less]
Al is effective as a deoxidizer that combines with dissolved oxygen in the molten pool, but in the case of relatively low heat input conditions in gas shielded arc welding using a flux-cored wire, Slag levitation tends to be insufficient, and remains as non-metallic inclusions in the weld metal, resulting in a decrease in toughness.

[TiO ₂ : 2.5 to 7.5%]
TiO ₂ is an arc stabilizer and a main component of the slag agent. Encapsulates the weld metal during welding and shields it from the atmosphere, and keeps the bead shape of the weld metal appropriately due to its appropriate viscosity. Affect. If TiO ₂ is less than 2.5%, metal dripping is likely to occur in the vertical improvement welding, and all-position welding is difficult. On the other hand, if it exceeds 7.5%, the amount of slag becomes excessive and slag entrainment occurs, or nonmetallic inclusions increase and toughness decreases.

[SiO ₂ : 0.1 to 0.5%]
SiO ₂ increases the viscosity of the molten slag and improves the slag encapsulation. If SiO ₂ is less than 0.1%, the viscosity of the slag is insufficient and the slag encapsulation is insufficient, and metal dripping occurs in the vertical improvement welding. On the other hand, when it exceeds 0.5%, the viscosity of the molten slag becomes excessive, and the slag peelability and the bead shape become poor.

[ZrO ₂ : 0.2 to 0.9%]
ZrO ₂ has the effect of adjusting the viscosity and solidification temperature of the molten slag and improving the slag encapsulation. If it is less than 0.2%, the effect is insufficient, and metal sag occurs in vertical welding. On the other hand, if it exceeds 0.9%, the bead shape becomes convex, and slag entrainment or poor fusion tends to occur.

[Al ₂ O ₃ : 0.1 to 0.4%]
Al ₂ O ₃ has the effect of adjusting the viscosity and solidification temperature of the molten slag and improving the slag encapsulation, like ZrO ₂ . If it is less than 0.1%, the effect is insufficient, and metal dripping occurs in the vertical improvement welding. On the other hand, if it exceeds 0.4%, the bead shape becomes convex, and slag entrainment or poor fusion tends to occur.

[Total hydrogen content of wire: 15 ppm or less]
The amount of hydrogen in the wire can be measured by an inert gas melting thermal conductivity method or the like. Since hydrogen in the wire serves as a diffusible hydrogen source for the weld metal, it must be reduced as much as possible. If the amount of hydrogen in the wire exceeds 15 ppm, the amount of diffusible hydrogen (JIS Z3118) exceeds 4 ml / 100 g, so that the sensitivity to cold cracking is increased in high strength steel weld metals.

  The total hydrogen content of the wire can be reduced by selecting a filling flux having a low hydrogen content and firing after filling the flux.

[Mo: 0.1 to 1.0%, Nb: 0.01 to 0.05%, V: 0.01 to 0.05%]
Mo, Nb, and V are all intended to improve the yield strength and strength of the weld metal. These are elements to be added to the wire by selecting one or more, but the upper limit of Mo is 1.0%, Nb is 0.05%, and V is 0.05%. If it exceeds, the strength becomes excessive and the toughness decreases.

  In addition, when the Mo content is less than 0.1%, Nb is less than 0.01%, and V is less than 0.01%, the effect of improving the yield strength and strength of the weld metal cannot be obtained.

[Ti: 0.1 to 1.0%, Mg: 0.01 to 0.9%, Ca: 0.01 to 0.5%, REM: 0.01 to 0.5%]
Ti, Mg, Ca, and REM all serve as deoxidizers to reduce oxygen in the weld metal and improve toughness. These elements are selected from one or more elements and added to the wire. The upper limit of Ti is 1.0%, Mg is 0.9%, Ca is 0.5%, and REM is 0.5. Exceeding each specified amount of%, it reacts violently with oxygen in the arc, increasing the generation of spatter and fumes.

  Further, when Ti is less than 0.1%, Mg is less than 0.01%, Ca is less than 0.01%, and REM is less than 0.01%, the oxygen of the weld metal is reduced as a deoxidizer and the effect of improving toughness is achieved. Cannot be obtained.

[There must be no slit-like seams in the steel skin that could cause intrusion into the air]
A flux-cored wire has a structure in which a steel outer shell is molded into a pipe shape and the inside is filled with flux, and the steel outer shell molded in the manufacturing process is welded to form a slit-like seam that has the risk of entering the outside air. It can be roughly divided into a wire having no slit and a slit-like gap without welding. Any cross-sectional structure can be used in the present invention, but a wire without a slit-like joint that has a risk of intrusion into the outside of the steel outer shell can be heat-treated for the purpose of reducing the total amount of hydrogen in the wire. In addition, since there is no moisture absorption after production, it is more desirable for the purpose of reducing the amount of diffusible hydrogen and improving crack resistance.

  In addition, the alloy component in a flux adjusts a compounding component in each limited range in consideration of the component and content of a steel outer shell. By adjusting the alloy components in the flux, it is possible to obtain flux-cored wires according to the components of various high-strength steels (base materials).

  P and S both generate a low melting point compound to lower the grain boundary strength and lower the toughness of the weld metal, so that P is 0.015% or less, S is 0.010% or less, Preferably it is as low as possible. Furthermore, the iron powder can be used to adjust the flux filling rate to 10 to 20%. However, since oxygen is introduced, it is desirable that both the flux filling rate and the iron powder addition amount are low.

In addition, as other components in the wire, steel outer sheath, iron powder added in the flux, and Fe in the alloy components, oxides and fluorides of alkali metals, arc stability of oxides and fluorides of alkaline earth metals As an agent, for example, Na ₂ O, K ₂ O, NaF, K ₂ SiF ₆ , K ₂ ZrF ₆ , Na ₃ AlF ₆ , MgF, Cu on the wire surface effective for rust prevention, electrical conductivity, and chip wear resistance When the plating process is performed, the Cu is included.

  Next, the wire manufacturing method in the present invention will be described.

  In the method for manufacturing a flux-cored wire of the present invention, a steel strip is formed into an open pipe (U-shaped) by a forming roll while feeding a steel strip in the longitudinal direction thereof to form a steel outer shell. After supplying the flux, butt-welding the opposing edge surfaces of the opening, and performing the diameter reduction and annealing on the pipe obtained by welding, after the wire diameter is reduced to 10.0 mm or less, The wire is annealed at a temperature of 700 ° C. or higher and 1000 ° C. or lower. These objects are to reduce the amount of hydrogen in the wire and ensure crack resistance.

  For C-type flux-cored wires with gaps in the seam of the steel outer shell, there is a risk that if the wire is annealed, the gap will expand due to thermal deformation of the steel outer shell, and the contained flux may be oxidized. It is necessary to be careful. On the other hand, if the wire is O-type with no gaps, the joint of the steel outer shell will not open even if annealing is performed, and the flux contained will be blocked from contact with the outside air, so it will be altered such as oxidation and nitridation. There is no.

  So far, even with O-type flux-cored wires, heat treatment has been performed at about 650 ° C., but the amount of hydrogen in flux-cored wires having a tensile strength of 690 MPa class or higher, which is the subject of the present invention, can be reduced. It is not intended. In addition, if annealing is performed at a high temperature exceeding 1000 ° C., the steel outer shell becomes extremely softened, and the risk of the wire breaking in the wire drawing process increases. Therefore, the upper limit of the annealing temperature is set to 1000 ° C.

  In addition, the wire diameter at the time of performing annealing was limited to 10 mm or less. The reason for this is that if a wire with a large diameter exceeding 10 mm is annealed, the amount of air accumulated in the voids in the wire is too large, and this causes the risk of nitriding or oxidizing the flux, and the wire will be altered. Because there is a possibility. In addition, the hydrogen reduction effect by wire annealing is a process in which the hydrogen inside the wire permeates the steel outer shell during the annealing and escapes to the outside of the wire, but the thicker the wire, the longer the hydrogen diffusion distance. However, it is not preferable from the viewpoint of efficiently reducing hydrogen. On the other hand, when the diameter is reduced to a diameter of 10 mm or less as defined in the present invention, the air in the pipe and the air in the flux are pushed backward (opposite to the pipe feed) by the reduced diameter, and the open pipe Since the air is discharged from the opening of the pipe in the state, the amount of air remaining in the pipe is sufficiently reduced to be negligible. The lower limit value of the wire diameter is not particularly defined, but if it is less than 2 mm, productivity is hindered, so it is preferable to perform annealing with a wire diameter of 2 mm or more.

  In addition, even if it uses manufacturing methods other than the wire manufacturing method which this invention discloses, the manufacturing method which can make wire total hydrogen amount 15 ppm or less exists. For example, for a seamless wire, the flux itself is sufficiently annealed before filling the wire with the flux. In this case, after the flux is annealed, if the flux absorbs moisture again, the annealing effect is lost. Therefore, after annealing, it is necessary to strictly manage such as storing the flux in Ar gas. For wires with joints, wire annealing is performed in an Ar gas atmosphere, and thereafter, in order to prevent moisture absorption from the joints, generally, such a method of strict process control increases the wire manufacturing cost. Therefore, when there is no particular circumstance, it is desirable to adopt the wire manufacturing method disclosed in the present invention.

  The diameter of the wire of the present invention can be set to 1.0 to 2.0 mm in diameter to increase the current density during welding and obtain a high deposition rate, but a preferable range is 1.2 to 1.6 mm.

Moreover, it is preferable that the shielding gas at the time of welding is a mixed gas of Ar-5 to 25% CO ₂ in order to reduce the amount of oxygen in the weld metal.

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

A steel-shaped outer shell is molded into a U-shape, filled with fluxes of various components, further molded into an O-shape, and then a seam-shaped seam welded at the seam. A wire with no gap and a wire with a slit-like gap that was not welded were piped and drawn to produce a flux-cored wire with a wire diameter of 1.2 mm shown in Tables 1 and 2. In the present embodiment, the same steel is used for all the prototype flux-cored wires as the steel outer shell. Its components are, by mass, C: 0.03%, Si: 0.25%, Mn; 0.4%, P; 0.003%, S; 0.002%, the balance being iron and inevitable It is an impurity. That is, for this component, a flux-cored wire having the wire components shown in Tables 1 and 2 was manufactured by filling the flux with an insufficient element. However, the present invention is not limited to the case where an alloy element such as Ni is contained only in the flux. Even when an alloy element such as Ni is contained in the steel outer sheath, the component range relative to the total mass of the wire may be within the range of the present invention. Whether an alloy element such as Ni is contained in the steel outer shell or whether the flux is filled should be determined from the viewpoint of the wire manufacturing cost and the like, and can be easily determined by the person concerned.
Each wire is annealed in the middle of wire drawing. However, in the case of annealing a wire having a slit-like gap, in order to prevent the flux in the wire from coming into contact with the air through the gap, an Ar gas atmosphere is used. Annealing was carried out. And after wire manufacture, in order to prevent moisture absorption of a flux, it enclosed with the bag made from vinyl, and stored in the state until just before welding start. In the comparative example wire B18, such annealing and storage are not performed. In general, annealing in an Ar gas shield atmosphere and storage in a plastic bag tend to be expensive, so if it is necessary to prevent this, it is preferable to use a seamless wire.

  The prototype wire was measured by measuring the total amount of hydrogen using a hydrogen analyzer manufactured by HORIBA, Ltd .: EMGA-621, and then using a steel plate specified in JIS G3128 SHY685 to improve the welding process by fillet welding. Evaluation and weld metal test were carried out. Furthermore, a crack test was carried out for the case where the welding workability was good in the case of fillet welding with the vertical improvement. These welding conditions are summarized in Table 3.

  The fillet welding for the vertical improvement was carried out by semi-automatic welding, and after checking the metal sag, spatter generation state, slag peelability and bead shape, five macro sections were collected to check for slag entrainment defects.

  In the weld metal test, a tensile test piece (JIS Z3111 A) and an impact test piece (JIS Z3111-4) were sampled from the center of the thickness of the weld metal and used for the test. In the evaluation of mechanical performance, the 0.2% proof stress was 690 MPa or more, and the absorbed energy at a test temperature of −40 ° C. was 47 J or more.

  The crack test was performed according to the U-shaped weld crack test method (JIS Z3257). About the test body which passed 48 hours after welding, the presence or absence of the generation | occurrence | production of a surface crack and a cross-section crack (5 cross sections) was investigated by the penetration test (JIS Z2343). The results are summarized in Table 4.

  The wire symbols A1 to A13 in Tables 1, 2 and 4 are examples of the present invention, and the wire symbols B1 to B17 are comparative examples. Of these wires, only wire A13 has the total hydrogen content within the scope of the present invention with the wire annealing temperature outside the scope of the present invention. Regarding the wire A13, the reason why the wire A13 was annealed at 800 ° C. in an Ar gas atmosphere before filling the wire with the flux and held in the Ar gas until just before filling, and then annealed in the Ar gas filled in the wire. This is because, in annealing in the air, the flux comes into contact with oxygen and nitrogen, and there is a risk of changing the material of the flux. In general, annealing at such high temperatures is less likely before the flux is wire filled. Except for the wire A13, the flux was annealed in the atmosphere at 200 ° C. to reduce the moisture in the wire. The reason why the wire A13 was further annealed thereafter was to adjust the wire hardness by work hardening during drawing.

  In addition, although the wire annealing temperature exceeded 1000 degreeC, specifically, the wire manufacture at 1050 degreeC was also implemented, since the wire intensity | strength after annealing was very low and a breakage occurred during wire drawing, Table 1 and Table 2 Does not describe examples of such high annealing temperatures.

Wire Symbol A1~A13 an invention example, C, Si, Mn, Ni , B, Cr, Al, TiO 2, SiO 2, ZrO 2, Al 2 O 3 and total amount of hydrogen in an appropriate amount, Mo, Nb The amount of one or more of V and the amount of one or more of Ti, Mg, Ca, and REM are also appropriate, so that the welding workability is good and the proof stress and absorbed energy of the deposited metal are also good. The value was obtained and the results were very satisfactory, such as no cold cracking. Of the present invention, the wire A13 is the same wire component system as the wire A12, and only the wire A13 has sufficient crack resistance because the total hydrogen amount is low although the wire annealing temperature is outside the scope of the present invention. Is shown. As described above, this is because the flux was sufficiently annealed in the Ar gas atmosphere before filling the wire, and thereafter, the flux was kept in the Ar gas to prevent moisture absorption of the flux. In general, such a process increases costs, so whether to reduce the amount of hydrogen by wire annealing, or to anneal the flux before filling, and secure the subsequent holding, consider the impact on the cost of wire production However, a comparison with these can be easily determined by those skilled in the art.

  In the comparative example, the wire symbol B1 has a large amount of spatter due to a large amount of Ti. Further, since C is small, the 0.2% proof stress was low.

Since the wire symbol B2 has a small amount of TiO ₂ , metal dripping occurred. Moreover, since there was much C, 0.2% yield strength was high and the absorbed energy was a low value.

The wire symbol B3 had poor slag removability and bead shape because of a small amount of SiO ₂ . Further, since the amount of Si is small, the absorbed energy is low.

In the wire symbol B4, metal dripping occurred because ZrO ₂ was small. Moreover, since there was much Si, the slag entrainment defect occurred and the absorbed energy was also low.

Wire symbol B5, since SiO ₂ is large slag removability and the bead shape was poor. Moreover, since Mn was small, the absorbed energy was low.

In the wire symbol B6, metal dripping occurred because of a small amount of Al ₂ O ₃ . Moreover, since there was much Mn, the slag entrainment defect occurred, the 0.2% yield strength was high, and the absorbed energy was low.

  The wire symbol B7 has a large amount of spatter due to a large amount of REM. Further, since the amount of Ni is small, the absorbed energy is low.

Since the wire symbol B8 has a large amount of Al ₂ O _{3, the} bead shape is poor, and a slag entrainment defect also occurs. Further, since the Ni content is large, the 0.2% yield strength is high and the absorbed energy is low.

  The wire symbol B9 had a low absorption energy because B was small. In addition, cracking occurred because the total amount of hydrogen was large. The reason why the total amount of hydrogen was large despite wire annealing in an Ar gas atmosphere is considered to be because the wire annealing temperature was outside the scope of the present invention as shown in Table 2. As described above, in order to reduce the total hydrogen amount under the wire annealing conditions outside the scope of the present invention, as in A13 of the present invention example, in order to sufficiently anneal the flux in advance and further avoid moisture absorption of the flux. Strict process control such as storing in Ar gas before wire insertion is required. Since these process controls increase the wire manufacturing cost, it is desirable to employ the wire manufacturing method disclosed in the present invention.

Since the wire symbol B10 has a large amount of ZrO ₂ , the bead shape was poor and slag entrainment defects were also generated. Further, since B was large, the 0.2% proof stress was high and the absorbed energy was low.

  The wire symbol B11 has a large amount of spatter due to a large amount of Ca. Moreover, since Cr is high, the absorbed energy was low.

  The wire symbol B12 had a low absorption energy because of a large amount of Al. Further, cracks occurred because the wire annealing temperature was low and the total amount of hydrogen was large.

The wire symbol B13 had a large amount of spatter due to a large amount of Mg. Moreover, slag inclusion defects because TiO ₂ is large occurs, the absorption energy was also low.

  Since the wire symbol B14 has a large amount of Nb, the 0.2% yield strength was high and the absorbed energy was low. Further, as in Comparative Example B9, although wire annealing was performed in Ar gas, the wire annealing temperature was outside the range of the present invention, so that the total hydrogen amount was large, and cracking occurred.

The wire symbol B15 was poor in slag removability and bead shape because of a small amount of SiO ₂ . Further, since V is large, the 0.2% yield strength was high and the absorbed energy was low.

In the wire symbol B16, metal dripping occurred because of a small amount of TiO ₂ . Moreover, since there was much Mo, the 0.2% yield strength was high and the absorbed energy was low.

  B17 has the same wire component as B16, but the wire diameter during annealing is outside the scope of the present invention. Also, when the flux is annealed before filling, annealing in an 800 ° C. Ar gas atmosphere like the wire A13 is not performed, and annealing at 200 ° C. is performed in the air as in the case of the wires A1 to A12. I just did it. There is a possibility that the moisture in the flux cannot be sufficiently removed during the flux annealing process, and in the wires A1 to A12 of the example of the present invention, the wire annealing was performed under the conditions within the scope of the present invention, so that the reduction in the amount of hydrogen was achieved. However, the wire B17 of the comparative example had a wire diameter outside the scope of the present invention. Therefore, even if the wire annealing temperature is within the range of the present invention, the wire annealing effect cannot be sufficiently exhibited, and the total hydrogen amount is higher than that of the B16 wire as shown in Table 2. As a result, as shown in Table 4, this is an example in which cracks occurred. Furthermore, as shown in Table 4, the Charpy absorbed energy is lower than that of the wire B16 that should have the same component, but this is because the wire diameter during annealing is large, and the atmosphere and flux remaining inside the wire This is thought to be due to a chemical reaction and alteration. It can be understood from the comparative example wire B17 that in order to reduce the amount of hydrogen, the wire is manufactured by the method provided by the present invention, or Ar is used in the flux annealing process as shown by the wire A13 of the present invention example. This means that it is necessary to select either strict annealing control using gas. Generally, hydrogen reduction by Ar gas-based flux annealing tends to increase the wire manufacturing cost due to problems such as process control.Therefore, in the present invention, the wire manufacturing method is not flux annealing conditions, It provides a method for limiting easy-to-manage wire annealing conditions. However, it may be preferable to study not only wire annealing but also hydrogen reduction by flux annealing because of problems such as wire manufacturing equipment conditions. In such a case, a person skilled in the art can easily determine which method is selected.

  The wire B18 is componentally equivalent to the wire B17, but the wire type is C, that is, manufactured by a wire manufacturing process with a joint. And in the thing of the kind of wire C, only one wire annealing was implemented not in Ar gas atmosphere but in air | atmosphere. The annealing temperature at that time was 650 ° C. In this case, it was found that the amount of hydrogen in the wire was 25 ppm, which is twice as high as A13 of the present invention example. Therefore, in order to reduce the amount of hydrogen as in A13 of the present invention example, the wire manufacturing method is made the same as in A13 of the present invention example, or the wire manufacturing method provided by the present invention is carried out. Should. Furthermore, as shown in Table 4, the wire B18 has a low −40 ° C. Charpy characteristic of 18J compared to the wire B17. This is considered to be due to an increase in nitrogen, oxygen, etc. in the flux because there was a seam and atmospheric annealing was performed. Therefore, when air annealing is performed, either a seamless wire manufacturing method is adopted, or when a seamed wire manufacturing method is adopted, annealing is performed in an Ar gas atmosphere. Should. In the present invention, a wire manufacturing method without a seam is provided from the viewpoint of ease of manufacturing management. However, a person skilled in the art can easily determine which one to use.

  From the above test results, the high-strength steel welding flux-cored wire of the present invention and the manufacturing method thereof enable welding of high-strength steel while ensuring excellent crack resistance. It can be concluded that the significance is very great.

Claims (4)

In flux cored wire for welding high strength steel that is made by filling steel outer shell with flux,
In mass% of the total mass of wire
C: 0.03-0.10%,
Si: 0.25 to 0.7%,
Mn: 1.0 to 3.0%
Ni: 1.0 to 3.5%
B: 0.001 to 0.015%
Cr, Al is
Cr: 0.05% or less,
Al: limited to 0.05% or less, and flux
TiO _2: 2.5~7.5%,
SiO ₂ : 0.1 to 0.5%,
ZrO ₂ : 0.2 to 0.9%,
Al ₂ O ₃ : 0.1 to 0.4%
A flux cored wire for high-strength steel welding, characterized in that the balance contains, the balance is made of Fe, an arc stabilizer, and inevitable impurities, and the total hydrogen content of the wire is 15 ppm or less. In mass% of the total mass of the wire
Mo: 0.1 to 1.0%,
Nb: 0.01-0.05%
V: 0.01-0.05%
The flux-cored wire for high-strength steel welding according to claim 1, comprising one or more of the following. In mass% of the total mass of the wire
Ti: 0.1 to 1.0%,
Mg: 0.01 to 0.9%
Ca: 0.01 to 0.5%,
REM: 0.01 to 0.5%
The flux-cored wire for high-strength steel welding according to claim 1 or 2, characterized by containing one or more of the following.   The steel strip is formed into an open tube with a forming roll while feeding it in the longitudinal direction. Flux is supplied from the opening of the open tube in the middle of this forming, and the opposite edge surfaces of the opening are butt welded and obtained by welding. When carrying out the diameter reduction and annealing on the pipe, the wire is annealed at a temperature of 700 ° C. or more and 1000 ° C. or less after the wire diameter is reduced to 10.0 mm or less. Item 4. A method for producing a flux-cored wire for welding high-strength steel according to any one of Items 1 to 3.