JP5387168B2 - Welding wire for high strength steel with flux and manufacturing method thereof - Google Patents

Welding wire for high strength steel with flux and manufacturing method thereof Download PDF

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JP5387168B2
JP5387168B2 JP2009152956A JP2009152956A JP5387168B2 JP 5387168 B2 JP5387168 B2 JP 5387168B2 JP 2009152956 A JP2009152956 A JP 2009152956A JP 2009152956 A JP2009152956 A JP 2009152956A JP 5387168 B2 JP5387168 B2 JP 5387168B2
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flux
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weld metal
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JP2011005531A (en
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修一 中村
俊永 長谷川
竜一 志村
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新日鐵住金株式会社
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Description

  The present invention relates to a welding wire for fluxed high-strength steel filled with a flux containing at least a metal or an alloy inside a steel outer shell, and a method for manufacturing the same, and particularly to applications such as construction machinery and industrial machinery. Welding wire for flux-cored high-strength steel that can reduce both the oxygen content and diffusible hydrogen content of the weld metal to the same level as solid wire when used for welding high-strength steel with a tensile strength of 950 MPa or higher and its production Regarding the method.

  The flux-cored wire here is a seamless wire in which the seam is eliminated by welding the seam of the steel outer shell after filling the flux.

  Flux-cored wires are generally used because of their good workability and workability, but for high-tensile steel welding wires with a tensile strength of 950 MPa or higher, solid wires are used to ensure toughness and to prevent welding cold cracking. Is used. This is because weld metal using flux-cored wire has higher oxygen content and diffusible hydrogen content in the weld metal than weld metal using solid wire. This is because there is a concern about the occurrence of this.

  As for oxygen, a certain amount of oxygen may be required to improve toughness by refining the structure using an intragranular transformation starting from an oxide in a 590-780 MPa class weld metal, but oxygen is generally tough. In particular, in the case of a weld metal having a tensile strength of 950 MPa class or higher, the intragranular transformation hardly occurs in the weld metal, and when oxygen increases, the toughness deteriorates monotonously. For this reason, in order to obtain high toughness with a weld metal of 950 MPa class or higher, it is desired to reduce oxygen.

  Patent Document 1 and Patent Document 2 are disclosed regarding a technique capable of reducing both the oxygen content and the diffusible hydrogen content of a weld metal. Patent Documents 1 and 2 both relate to the use of Mg, which is a strong deoxidizing agent. However, Mg is easy to absorb moisture and cannot fully exhibit the oxygen reduction effect, but also increases the amount of diffusible hydrogen. Reported a problem.

  In Patent Document 1, by adding Mg in a range where Mg does not increase the amount of diffusible hydrogen, the amount of oxygen in the weld metal is reduced, and the increase in the amount of diffusible hydrogen is suppressed, thereby increasing the tensile strength and toughness. We have proposed a welding method that can obtain weld metal with excellent cold cracking resistance. However, this is not a fundamental solution to the hygroscopicity of Mg.

  Patent Document 2 proposes that an organic compound is adhered to the surface of Mg particles to improve moisture absorption resistance and reduce diffusible hydrogen in the weld metal. However, since the organic compound attached to the Mg surface contains hydrogen, the organic compound itself increases diffusible hydrogen, but it is relatively diffuse because it is less than the increase in the amount of diffusible hydrogen due to moisture absorption. Only the amount of reactive hydrogen is reduced.

JP 2001-150186 A JP 11-147196 A

  In view of the above-mentioned problems of the background art, the present invention eliminates the problem of moisture absorption of Mg by examining the average particle diameter of the flux and the manufacturing conditions of the wire, particularly regarding the wire in which flux is added to the flux-cored wire. did. By this, the deoxidation effect inherent in Mg is drawn out, and Mg that has not absorbed moisture has the effect of reducing diffusible hydrogen, and both the oxygen content and the diffusible hydrogen content of the weld metal are found. By making it possible to reduce to the same level as solid wires, the toughness and cold cracking resistance, which were the problems of flux-cored wires, can be made to be comparable to solid wires. Accordingly, an object of the present invention is to provide a welding wire for flux-cored high-tensile steel that can be generally used for high-tensile steel having a tensile strength of 950 MPa or higher and a method for producing the same.

  The present invention solves the above technical problems, and the requirements of the invention are as follows.

(1) In a flux-cored wire in which a flux containing at least a metal or an alloy is filled inside a steel outer sheath, in mass% with respect to the total mass of the wire,
C: 0.04 to 0.30%,
Si: 0.2-2.0%,
Mn: 0.3 to 2.5%
P: 0.02% or less,
S: 0.02% or less,
Al: 0.002 to 0.05%,
Ni: 1.0-12%,
Mg: 0.01-2.0%
And the balance consists of iron and inevitable impurities, the carbon equivalent (Ceq) represented by the following (formula 1) is 0.25 to 1.2%, and the average particle of the flux filled in the flux-cored wire The diameter is 30 to 300 μm , the Mg in the flux is Mg that has not absorbed moisture, the oxygen content of the weld metal is 236 to 348 ppm, the diffusible hydrogen content of the weld metal is 0.7 to 2.0 ml / 100 g weld metal A welding wire for flux-cored high-strength steel, characterized in that there is no slit-like seam in the steel outer skin, which has a risk of intrusion of outside air.
Ceq = [C] + [Mn ] / 6 + [Si] / 24 + [Ni] / 40 · ·· ( Equation 1)
However, elements with [] represent the content (% by mass) of each element.

(2) The flux-cored wire is further in mass% with respect to the total mass of the wire,
Cr: 0.1 to 2.0%,
Mo: 0.1 to 2.0%,
Cu: 0.01 to 1.5%,
V: 0.005-1.0%
Ti: 0.005 to 0.3%,
Nb: 0.005 to 0.1%,
B: 0.001 to 0.015%
Contain one or two or more of the following carbon equivalent represented by (Formula 2) (Ceq) is characterized in 0.25 to 1.2% der Rukoto, according to the above (1) Welding wire for high strength steel with flux.
Ceq = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Mo] / 4
+ [Cr] / 5 + [Cu] / 40 + [Ti] / 30 + [Nb] / 3
+ [V] / 5 + 5 × [B] (Equation 2) However, the element with [] represents the content (% by mass) of each element. The content of elements not contained is 0% by mass.

(3) The flux-cored wire is further in mass% with respect to the total mass of the wire,
Ca: 0.0002 to 0.01%,
REM: 0.0002 to 0.01%
The welding wire for flux-cored high-tensile steel according to (1) or (2) above, comprising one or two of the above.

(4) While forming the steel strip in the longitudinal direction, it is formed into an open tube by a forming roll, and a flux with an average particle size of 30 to 300 μm filling the flux-cored wire is supplied from the opening of the open tube during the forming. , and butt welding the opposite edge surface of the opening, before diameter reduction tubes seamless obtained by welding, the wires 500 ° C. or higher, and annealed under the following annealing temperature 700 ° C., oxygen in the weld metal The flux according to any one of (1) to (3) above , wherein the amount is 236 to 348 ppm and the diffusible hydrogen content of the weld metal is 0.7 to 2.0 ml / 100 g weld metal. Of manufacturing welding wire for high strength steel.

  According to the flux-cored wire of the present invention, in welding high-tensile steel with a tensile strength of 950 MPa or higher, the oxygen content and diffusible hydrogen content of the weld, which was a problem with the flux-cored wire, can be reduced to the same level as a solid wire. Therefore, it becomes possible to obtain a weld metal having high toughness and improved cold cracking resistance. As a result, the flux-cored wire can generally be used for welding high-strength steel of 950 MPa class or higher while maintaining the workability and workability of the flux-cored wire. Very large.

  Embodiments of the present invention will be described below.

  The present invention is a flux-cored wire that contains a steel sheath or a flux-cored wire with a component within a predetermined range, and further adjusts the average particle size of the flux to be filled. In particular, by making the annealing conditions within a predetermined range, the hygroscopicity of Mg was eliminated and the original deoxidation effect of Mg was drawn out. Furthermore, it has been found that Mg having no moisture absorption can reduce diffusible hydrogen, whereby a weld metal having high toughness and improved cold cracking resistance can be obtained.

  First, the reason for defining the flux-cored wire component of the present invention will be described. % For each component means mass%, and the wire component is the total component value of the steel outer shell and the flux combined.

[C: 0.04 to 0.30%]
C is an essential element for increasing the tensile strength of the weld metal, and if the addition amount is small, sufficient weld metal tensile strength cannot be obtained, so 0.04% or more is necessary. However, if it exceeds 0.30% and is added excessively, the toughness of the weld metal is deteriorated, so the addition amount of C is set to 0.04 to 0.30%.

[Si: 0.2-2.0%]
Si is a deoxidizing element, and in order to reduce the amount of O in the weld metal and increase the cleanliness, the Si content in the welding wire needs to be 0.2% or more. On the other hand, if the Si content in the welding wire exceeds 2.0% and becomes excessive, a coarse oxide is generated and the toughness of the weld metal is significantly deteriorated. For this reason, in this invention, Si content in a welding wire shall be 0.2 to 2.0%.

[Mn: 0.3 to 2.5%]
Mn ensures the hardenability of the weld metal and increases the strength. Further, it is an element effective for improving the toughness by refining the structure. In order to obtain these effects, it is necessary to contain 0.3% or more in the welding wire. On the other hand, if the Mn content in the welding wire exceeds 2.5%, the retained austenite is excessively generated in the weld metal, so the susceptibility to grain boundary embrittlement increases and the weld metal deteriorates toughness and weld crack resistance. The possibility of is increased.
For this reason, in this invention, Mn content in a welding wire shall be 0.3-2.5%.

[P: 0.02% or less]
P is an impurity element and needs to be reduced as much as possible in order to inhibit toughness. However, if the content in the welding wire is 0.02% or less, adverse effects on toughness can be tolerated. Therefore, in the present invention, P in the welding wire is acceptable. The content is 0.02% or less.

[S: 0.02% or less]
S is also an impurity element, and if it is excessively present in the weld metal, it deteriorates both toughness and ductility, so it is preferable to reduce it as much as possible.

  If the content in the welding wire is 0.02% or less, adverse effects on toughness and ductility can be tolerated. Therefore, in the present invention, the S content in the welding wire is 0.02% or less.

[Al: 0.002 to 0.05%]
Al is a deoxidizing element and, like Si, is effective in reducing the amount of oxygen in the weld metal and improving cleanliness. In order to exert the effect, it is necessary to contain 0.002% or more in the welding wire. On the other hand, if the content exceeds 0.05% in the welding wire, a coarse oxide is formed in the weld metal, and this coarse oxide significantly deteriorates the toughness, which is not preferable. Therefore, in this invention, Al content in a welding wire shall be 0.002-0.05% or less.

[Ni: 1.0-12%]
Ni is the only element that can stably improve toughness regardless of the other components and structure of the weld metal by solid solution toughening. In particular, it is an element necessary to ensure toughness with a high-strength weld metal. Yes, it is necessary to contain 1.0% or more.

  A higher Ni content is advantageous in improving toughness, but if the content in the welding wire exceeds 12%, the effect of improving toughness is saturated.

Therefore, in the present invention, the Ni content in the welding wire is limited to 1.0 to 12%.
In addition, in order for the effect of Ni to certainly contribute to toughness improvement, 2.5 to 10.0% is more preferable. Furthermore, in order to ensure the toughness at low temperature, 5.1 to 10.0% is more preferable.

[Mg: 0.01 to 2.0%]
Mg is a strong deoxidizing element and has the effect of improving toughness by reducing the amount of oxygen in the weld metal. In order to exhibit the deoxidation effect, it is necessary to add to the flux in a metal or alloy state, not in an oxide or fluoride state. Moreover, since Mg has a high vapor pressure when vaporized in an arc atmosphere, the H 2 partial pressure in the arc atmosphere is reduced, and diffusible hydrogen in the weld metal can be reduced. In order to exhibit these effects, a minimum of 0.01% is necessary. On the other hand, if it exceeds 2.0% and is contained in the welding wire, the arc becomes unstable and the welding workability is hindered. In addition, in order to express a deoxidation effect more reliably, 0.20 to 2.0% is preferable. Furthermore, 0.51 to 2.0% is preferable in order to more reliably reduce the amount of diffusible hydrogen.

  The above are the basic components of the welding wire for flux-cored high strength steel of the present invention. The balance is iron and inevitable impurities.

  The present invention further provides one or more of Cr, Mo, Cu, V, Ti, Nb, and B in the wire as needed for adjustment of specific mechanical properties of the weld metal. Alternatively, when two or more kinds are contained in the welding wire in the range of the following contents, the tensile strength or toughness is affected. The components described below can be added as necessary.

[Cr: 0.1 to 2.0%]
Cr is an element effective for increasing the strength by enhancing the hardenability. Therefore, when it contains in a welding wire, 0.1% or more is required. On the other hand, when the content exceeds 2.0% excessively, bainite and martensite are hardened unevenly and the toughness is remarkably deteriorated. Therefore, in the present invention, the upper limit of the content in the welding wire is set to 2.0. %.

[Mo: 0.1 to 2.0%]
Mo is a hardenability improving element for increasing the tensile strength TS of the weld metal. Moreover, strength and toughness can be ensured by increasing tempering resistance. In order to exert these effects, it is necessary to contain 0.1% or more of Mo in the wire.

  On the other hand, if Mo is contained in the welding wire in an amount exceeding 2.0%, coarse precipitates are generated in the weld metal and the toughness of the weld metal is deteriorated. For this reason, in this invention, Mo content in a welding wire shall be 0.1-2.0%.

[Cu: 0.01 to 1.5%]
Cu is an element effective for improving the strength, and in order to sufficiently obtain the effect of improving the strength of the weld metal, the content of Cu contained in the wire, and in the case where Cu is plated on the surface, The total content of Cu to be contained and Cu to be plated needs to be 0.01% or more.

  On the other hand, if the Cu content in the wire exceeds 1.5%, the case where the wire surface is plated or the case where it is contained in the wire is not preferable because the toughness of the weld metal deteriorates. Therefore, in this invention, it is preferable that Cu content in a wire shall be 0.01 to 1.5%.

[V: 0.005 to 1.0%]
V forms fine carbides and is effective in securing strength by precipitation strengthening. V has the effect of trapping diffusible hydrogen by forming precipitates in the weld metal. In a weld metal having a small amount of diffusible hydrogen as in the present invention, the effect of improving the cold cracking resistance is great even by trapping a small amount of diffusible hydrogen. In order to exhibit these effects, a minimum of 0.005% is necessary. On the other hand, if it exceeds 1.0% and is contained in the welding wire, it is not preferable because it is excessively contained in the weld metal and coarse precipitates are formed to deteriorate toughness.

  Therefore, in the present invention, the content when V is contained in the welding wire is 0.005 to 1.0%.

  In order to surely improve the strength by precipitation strengthening, 0.21 to 1.0% is more preferable. Furthermore, 0.51 to 1.0% is more preferable in order to reliably exhibit the trapping effect of diffusible hydrogen.

[Ti: 0.005 to 0.3%]
Ti is effective as a deoxidizing element in the weld metal, and can fix the solid solution N in the weld metal as a nitride to alleviate the adverse effect on the toughness of the solid solution N. In this case, there is an effect of refining the heated austenite grains in the reheat region of the weld metal. In order to exhibit the effect of improving the toughness of the weld metal by the action of Ti, it is necessary to contain 0.005% or more of Ti in the welding wire. On the other hand, if the Ti content in the welding wire exceeds 0.3% and excessive, there is a great possibility that the formation of coarse oxides in the weld metal and the toughness deterioration due to excessive precipitation of TiN will remarkably occur. It becomes. For this reason, in this invention, Ti content in a welding wire shall be 0.005-0.3%.

[Nb: 0.005 to 0.1%]
Nb is also a ferrite stabilizing element and is effective in reducing retained austenite, and is effective in securing strength by forming fine carbides and strengthening precipitation. In order to exert these effects, it is necessary to make the Nb content in the wire 0.005% or more in consideration of a composite effect with other elements having similar effects. On the other hand, if the Nb content in the wire exceeds 0.1%, it is not preferable because it is excessively contained in the weld metal and coarse precipitates are formed to deteriorate the toughness.

  Therefore, in the present invention, the content when Nb is contained in the welding wire is 0.005 to 0.1%.

[B: 0.001 to 0.015%]
B is an element that enhances the hardenability and contributes to the improvement of the strength of the weld metal, and also has the effect of improving the toughness of the weld metal by forming BN in combination with the solid solution N in the weld metal. In order to exert these effects reliably, the B content in the welding wire needs to be 0.001% or more. On the other hand, if the B content in the welding wire exceeds 0.015%, the B in the weld metal becomes excessive and forms coarse B compounds such as BN and Fe 23 (C, B) 6 to reverse the toughness. It is not preferable because it deteriorates. Therefore, in the present invention, when B is contained in the welding wire, it is preferable to limit the B content to 0.001 to 0.015%.

[One or more of Ca and REM: 0.0002 to 0.01%]
In the present invention, in addition to the above components, for the purpose of adjusting the ductility and toughness of the weld metal, one or more of Ca and REM may be used within the following ranges as necessary. It can be contained.

  Both Ca and REM are effective in improving ductility and toughness by changing the structure of sulfides and reducing the size of sulfides and oxides in the weld metal. In order to fully exhibit these effects, it is preferable that the contents of Ca and REM are both 0.0002% or more. On the other hand, if Ca and REM are excessively contained in excess of 0.01% in the wire, sulfide and oxide are coarsened, ductility and toughness are deteriorated, and weld bead shape is deteriorated. There is also the possibility of deterioration of weldability. For this reason, it is preferable that the upper limit of the content of Ca and REM in the wire is 0.01%.

Next, in order to ensure the target tensile strength TS and toughness in the present invention, when the above components are added within the specified ranges of the respective contents, the following (formula 1) and (formula ) This is a case where the carbon equivalent (Ceq) indicating the quenching hardness of the weld metal shown in 2) becomes the content of each component in the wire within a predetermined range.
Ceq = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 (Formula 1)
However, elements with [] represent the content (% by mass) of each element.
Further, when one or more of Mo, Cr, Cu, Ti, Nb, V and B are contained, the following (formula 2) is followed.
Ceq = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Mo] / 4
+ [Cr] / 5 + [Cu] / 40 + [Ti] / 30 + [Nb] / 3
+ [V] / 5 + 5 × [B] (Equation 2)
However, the elements with [] represent the content (% by mass) of each element, and the content of elements not contained is 0% by mass.

In order to ensure the target tensile strength, the above ( formula ) is based on the contents of C, Mn, Si, Ni, Mo, Cr, Cu, Ti, Nb, V, and B contained in the welding wire. It is necessary to limit the carbon equivalent Ceq, which is an index of quenching hardness obtained in 2 ), to 0.25% or more. When the carbon equivalent Ceq is less than 0.25%, the quenching hardness is insufficient, so that the target tensile strength TS cannot satisfy 950 MPa. The larger the carbon equivalent, the higher the quenching hardness. However, when the carbon equivalent exceeds 1.0%, the toughness of the weld metal deteriorates, which is not preferable. For the above reasons, in the present invention, the carbon equivalent (Ceq) of the welding wire is limited to 0.25 to 1.0%.

  Moreover, in this invention, the average particle diameter of the flux with which a flux cored wire is filled is limited to 30-300 micrometers. The reason for the limitation is described in the specific details newly found.

  Next, the manufacturing method of the welding wire for high strength steel with a flux of this invention is demonstrated. In the method for producing a welding wire for flux-cored high-tensile steel according to the present invention, a steel strip is formed into an open pipe by a forming roll while feeding the steel strip in the longitudinal direction, and a flux is supplied from the opening of the open pipe in the middle of the forming, The edge surfaces facing each other of the openings are butt-welded, and a seamless pipe obtained by welding is annealed at an annealing temperature of 500 ° C. or higher and 700 ° C. or lower.

  Specific contents newly discovered by the present inventors will be described below.

  Conventionally, it has been known that Mg easily absorbs moisture, and the absorbed water molecules cause oxygen and hydrogen in the weld metal to increase. However, since Mg is a strong deoxidizer, the oxygen reduction effect by deoxidation is better than the oxygen increased by the water molecules that have absorbed moisture, so the oxygen content of the weld metal has been reduced. Naturally, the moisture-absorbed Mg cannot sufficiently exhibit the deoxidation effect of Mg. In addition, Mg that has absorbed moisture has a problem of increasing the amount of diffusible hydrogen. In order to solve these problems, a method for removing water molecules absorbed by high-temperature annealing is disclosed, but Mg is very easily oxidized at high temperatures, so Mg is oxidized by the air around Mg, and eventually Oxygen could not be reduced sufficiently.

In the present invention, Mg is added to the flux of the flux-cored wire, and a seam of the steel outer shell is welded to form a seamless pipe, thereby removing water molecules absorbed by high-temperature annealing and oxidizing Mg. It was possible to prevent the deoxidation effect inherent in Mg. Further, since Mg has a high vapor pressure when vaporized in an arc atmosphere, the H 2 partial pressure in the arc atmosphere is reduced, and diffusible hydrogen in the weld metal can be reduced.

  By setting the annealing temperature of the wire to 500 ° C. or higher, water molecules absorbed by Mg can be sufficiently removed. An annealing temperature exceeding 700 ° C. is not preferable because there is no further effect of removing water molecules and the production cost is increased. Also, by setting the average particle size of the flux to 30 to 300 um, the gaps between the fluxes in the wire are sufficiently filled, and there is almost no air around the Mg, preventing oxidation of Mg due to high temperature annealing. It becomes possible. If the average particle size of the flux is too small to be less than 30 um, segregation occurs at the time of flux filling, and the uniformity of the wire component is impaired. On the other hand, if the average particle size of the flux is larger than 300 μm, the gap between the fluxes becomes large and Mg oxidation cannot be prevented.

  The effects of the present invention will be specifically described below with reference to examples.

  While forming the steel strip of the component shown in Table 1-1 into an open pipe with a forming roll while feeding it in the longitudinal direction, from the opening of the open pipe in the middle of the molding, from metal, alloy, deoxidizer or arc stabilizer The powder is granulated into a powder, and the opposite edge surfaces of the opening are butt welded to make the joint seamless, and the wire is first reduced until the internal flux does not move due to transportation work, etc. After that, annealing and secondary diameter reduction were performed, and a flux-cored wire with a wire diameter of φ1.2 mm was made as a prototype. In the present invention, the steel outer shell of the components shown in Table 1-1 (the balance is Fe and inevitable impurities) was used, but the components of the steel outer shell are not particularly limited. Can be used for hulls. Tables 1-2 to 1-5 show the compositions and manufacturing conditions of the trial-made flux cored wires. Of the wire components in Table 1-2 to Table 1-5 (the balance is Fe and inevitable impurities), the alloy components other than the steel outer skin components shown in Table 1-1 were added from the flux.

  Using this wire, a mechanical property test, an oxygen content measurement, a diffusible hydrogen content measurement, and a y-type weld crack test were performed. The results are shown in Tables 2-1 to 2-4.

The mechanical property test is a steel plate having a thickness of 19 mm, the welding conditions are a welding current of 280 A, a voltage of 28 to 30 V, a welding speed of 30 cm / min, the preheating and the interpass temperature are controlled at 100 ° C., Ar + 20% CO 2 gas Welded specimens were produced by a method based on JIS Z3111 (Method for tensile and impact test of weld metal). The welding workability was evaluated at the time of welding. From the weld metal, A1 tensile test piece and No. 4 Charpy test piece based on JIS Z3111 were sampled, and the strength and toughness of the weld metal were evaluated. In addition, the evaluation set the thing whose absorption strength is 47J or more by the Charpy impact test in 0 degreeC with the tensile strength of 950 Mpa or more.

The oxygen content of the weld metal was measured by an inert gas dissolution infrared absorption method. For the evaluation of the oxygen content, an oxygen content of 350 ppm or less, which is equivalent to the oxygen content of the weld metal obtained when shield gas welding using Ar + 20% CO 2 gas was performed with a solid wire, was regarded as acceptable.

  The amount of diffusible hydrogen was measured by a gas chromatograph method in accordance with JIS Z3118 (method for measuring the amount of hydrogen in steel welds). The measured amount of diffusible hydrogen was 2.0 ml / 100 g or less, which is equivalent to that of a solid wire, and passed. The cold cracking resistance of the wire is JIS Z3158 (y-type weld cracking) using a steel sheet with a preheating temperature of 75 ° C., a welding current of 280 A, a voltage of 28 to 30 V, a welding speed of 30 cm / min, a downward posture and a thickness of 25 mm. The test was conducted by a method based on (Test), and the root crack rate of less than 20% was evaluated as acceptable, and 20% or more was evaluated as rejected.

  From the above test results, the welding wire for flux-cored high-strength steel according to the present invention and its manufacturing method show that both the oxygen content and the diffusible hydrogen content of the weld metal welded with the flux-cored wire can be reduced to the same level as the solid wire. This enables the toughness and low-temperature cracking resistance, which were the problems of flux-cored wires, to be comparable to solid wires, so that flux-cored wires can be generally used for high-tensile steel with a tensile strength of 950 MPa or higher. Therefore, the industrial significance of the present invention is very great.

Claims (4)

  1. In a flux-cored wire in which a flux containing at least a metal or an alloy is filled inside a steel outer shell, in mass% with respect to the total mass of the wire,
    C: 0.04 to 0.30%,
    Si: 0.2-2.0%,
    Mn: 0.3 to 2.5%
    P: 0.02% or less,
    S: 0.02% or less,
    Al: 0.002 to 0.05%,
    Ni: 1.0-12%,
    Mg: 0.01-2.0%
    And the balance consists of iron and inevitable impurities, the carbon equivalent (Ceq) represented by the following (formula 1) is 0.25 to 1.2%, and the average particle of the flux filled in the flux-cored wire The diameter is 30 to 300 μm , the Mg in the flux is Mg that has not absorbed moisture, the oxygen content of the weld metal is 236 to 348 ppm, the diffusible hydrogen content of the weld metal is 0.7 to 2.0 ml / 100 g weld metal A welding wire for flux-cored high-strength steel, characterized in that there is no slit-like seam in the steel outer skin, which has a risk of intrusion of outside air.
    Ceq = [C] + [Mn ] / 6 + [Si] / 24 + [Ni] / 40 · ·· ( Equation 1)
    However, elements with [] represent the content (% by mass) of each element.
  2. The flux-cored wire is further mass% with respect to the total mass of the wire,
    Cr: 0.1 to 2.0%,
    Mo: 0.1 to 2.0%,
    Cu: 0.01 to 1.5%,
    V: 0.005-1.0%
    Ti: 0.005 to 0.3%,
    Nb: 0.005 to 0.1%,
    B: 0.001 to 0.015%
    Contain one or two or more of the following carbon equivalent represented by (Formula 2) (Ceq) is characterized in 0.25 to 1.2% der Rukoto, according to claim 1 Welding wire for high strength steel with flux.
    Ceq = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Mo] / 4
    + [Cr] / 5 + [Cu] / 40 + [Ti] / 30 + [Nb] / 3
    + [V] / 5 + 5 × [B] (Equation 2) However, the element with [] represents the content (% by mass) of each element. The content of elements not contained is 0% by mass.
  3. The flux-cored wire is further mass% with respect to the total mass of the wire,
    Ca: 0.0002 to 0.01%,
    REM: 0.0002 to 0.01%
    The welding wire for flux-cored high-strength steel according to claim 1 or 2, characterized by containing one or two of them.
  4. The steel strip is formed into an open tube by a forming roll while feeding the steel strip in the longitudinal direction, and a flux with an average particle size of 30 to 300 μm filled into the flux-cored wire is supplied from the opening of the open tube during the forming, and the opening the opposing edge surface to butt welding, before diameter reduction tubes seamless obtained by welding, the wires 500 ° C. or higher, and annealed under the following annealing temperature 700 ° C., the amount of oxygen in the weld metal 236 The welding for flux-cored high strength steel according to any one of claims 1 to 3 , wherein the weld metal has a diffusible hydrogen content of 0.7 to 2.0 ml / 100 g. Wire manufacturing method.
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