JP4509807B2 - Flux-cored wire for high-tensile steel welding - Google Patents

Description

  The present invention relates to a high-strength steel welding flux-cored wire used for high-tensile steel of 880 MPa or higher in construction machinery, offshore structures, etc., and in particular, welding workability is good and excellent low-temperature toughness is obtained even at high strength. The present invention relates to a flux cored wire for welding high strength steel.

  High-tensile steel is mainly used in construction machinery and offshore structures. Gas welding arc welding is widely used for these welding because of efficiency and convenience, and the welding wires include solid wires and flux-cored wires.

  Various types of solid wires are commercially available that have their components adjusted according to the purpose of use. As conventional techniques, for example, MIG wire for high-tensile steel of 780 MPa or more (see, for example, Patent Document 1) or 880-980 MPa steel. A solid wire has been proposed (see, for example, Patent Document 2). On the other hand, the flux-cored wire is roughly divided into a wire filled with a flux mainly containing a slag component called a slag-based flux-cored wire and a flux mainly containing a metal component called a metal-based flux-cored wire. There are filled wires, which are standardized in JIS Z 3313 and others. When a solid wire is used, the low-temperature toughness can be stably obtained because the amount of oxygen in the weld metal is small. In addition, there are advantages such as deep penetration of the weld metal, very low slag generation, and low fume generation. However, there are disadvantages such as less welding amount than flux-cored wires, and a large amount of spatter generation, which becomes noticeable in welding with a large current.

  Slag flux-cored wires are generally welded with slag as the main component, rutile, stable arc, low spatter generation, large amount of welding, and all-position welding under a wide range of welding conditions. There is an advantage of excellent workability. However, the weld metal has a shallower penetration than solid wire, generates a lot of slag, generates a lot of fumes, and the flux filled in the wire contains a lot of oxide, so the oxygen content of the weld metal increases and low temperature toughness There are drawbacks such as difficult to obtain.

  In the metal-based flux-cored wire, the main component of the filling flux is metal powder, and the greatest feature is that the amount of welding is large. However, since the flux filling rate is generally a high filling rate of 10% or more, there are disadvantages such as a poor penetration of the weld metal and a relatively large amount of slag generation due to oxidation of the metal powder.

  As a technology that incorporates the advantages of both solid wire and flux-cored wire, an appropriate amount of alloying agent and arc stabilizer is added to the flux, and flux-cored wire with a low filling rate of 3 to 10% provides good workability. Attempts have been made to obtain it (see, for example, Patent Document 3). However, with this flux-cored wire, the amount of oxygen in the weld metal increases and good low temperature toughness cannot be obtained. Generally, in order to obtain low temperature toughness in a metal-based flux-cored wire with a flux filling rate of 10% or more, it is possible to add an appropriate amount of an alloying agent, but a flux with a low filling rate of 3 to 10%. In the case of a cored wire, it is difficult to improve the low temperature toughness of the weld metal from the alloy components because the amount of alloying agent is limited.

  On the other hand, in order to improve the low temperature toughness, a technique for reducing the amount of oxygen in the weld metal by adding an appropriate amount of a deoxidizer in the flux is a technique for removing alloying agents, arc stabilizers, Al, Mg, etc. in the flux. There is a metal flux cored wire with a low filling rate of 3 to 10% with a flux filling rate with an acid agent added, and attempts have been made to obtain low temperature toughness of weld metal while maintaining good workability (for example, , See Patent Document 4). However, this flux-cored wire increases the amount of slag generated with the deoxidation reaction of Al, Mg, etc., so it is necessary to remove the slag in the case of multi-layer welding, and welding defects such as a decrease in welding efficiency and slag entrainment May occur.

JP 2000-301379 A JP-A-8-267273 JP 2003-112287 A JP 2003-94196 A

  The present invention reduces the amount of oxygen in the weld metal to the same level as that of solid wire while maintaining good workability such as a small amount of slag generation and spatter generation and a large amount of welding in welding high-tensile steel of 880 MPa or more. And it aims at providing the flux cored wire for high-tensile-strength-steel welding which improves the low-temperature toughness of a weld metal.

  The gist of the present invention is that in a high-strength steel welding flux-cored wire, 0.05% to 0.18% of the total mass% of the simple substance C in the flux filled in the steel outer shell, The total of the flux components is C: 0.07-0.20%, Si: 0.1-1.5%, Mn: 0.3-2.0%, Ni: 1.0-3. 5%, Cr: 0.4 to 0.85%, Mo: 0.4 to 0.85%, V: 0.01 to 0.15%, the balance consisting of Fe and inevitable impurities, The flux filling rate of the flux in the component is 4 to 10%.

  Further, the present invention is a flux cored wire for welding high strength steel, characterized in that the steel outer skin is seamless.

  According to the flux cored wire for high strength steel welding of the present invention, in welding high strength steel of 880 MPa or more, welding efficiency is excellent, slag generation amount and spatter generation amount are small, the arc is stable, and welding workability is good. The quality of the welded portion and the welding efficiency can be improved, for example, the amount of oxygen in the weld metal is low and the low temperature toughness is good.

  In order to solve the above-mentioned problems, the present inventors have made various studies on the wire component and the flux filling rate, which are the total of the steel outer shell and the flux.

As a result, the addition of simple substance C into the flux and the wire contains appropriate amounts of Si, Mn, Ni, Cr, Mo, V, and the flux filling rate is low, resulting in excellent welding efficiency and slag generation. It has also been found that good low temperature toughness can be stably obtained by reducing the amount of spatter generated, good strength, and reducing the amount of oxygen in the weld metal.
The reasons for limiting the components of the flux-cored wire for welding high strength steel of the present invention will be described below.

(Single C in the flux: 0.05 to 0.18% by mass (hereinafter referred to as%))
C in the wire reacts with oxygen in the arc to reduce the amount of oxygen in the weld metal. FIG. 1 shows the relationship between the amount of simple substance C in the wire and the amount of oxygen in the weld metal. As the amount of simple substance C in the wire increases, the amount of oxygen in the weld metal decreases. On the other hand, FIG. 2 shows the relationship between the amount of C in the steel outer shell and the amount of C in the metal powder (high carbon Fe—Mn) and the amount of oxygen in the weld metal. Less oxygen reduction in metal. Therefore, it is effective to add simple substance C to the flux in order to reduce the amount of oxygen in the weld metal.

  If the single C in the flux is less than 0.05%, the deoxidation effect cannot be obtained, and if it exceeds 0.18%, excess C is retained in the weld metal and the toughness is reduced. Further, when deoxidation is performed with the simple substance C, since it is released to the atmosphere as a gas, slag is not generated as in the case where deoxidation is performed with other deoxidizing agents such as Si, Mn, Al, and Mg. Therefore, the slag removal work becomes unnecessary and slag entrainment defects do not occur.

  Also, as described above, when C is added from the steel outer shell and metal powder such as Fe-Mn, effective deoxidation cannot be expected because the yield is easier to weld metal than single C, and the toughness of the weld metal is further reduced. To do.

  The simple substance C referred to in the present invention refers to graphite or coke, and a particle size of 75 μm or less is preferable because reaction with oxygen in the arc is facilitated.

(C of the whole wire: 0.07 to 0.20%)
C is an important element that ensures the strength of the weld metal by solid solution strengthening, and has an effect of reducing oxygen in the arc atmosphere and droplets by reacting with oxygen in the arc. If the C content of the entire wire is less than 0.07%, the effects of deoxidation and ensuring the strength cannot be obtained. Strength becomes excessive and toughness decreases.

(Si: 0.1-1.5%)
Si aims to improve the toughness of the weld metal. If the steel outer shell and flux component total (hereinafter referred to as wire component) Si is less than 0.1%, the toughness is lowered. Moreover, when it exceeds 1.5%, the amount of slag generation increases, and a slag entrainment defect occurs when multi-layer welding is performed. Moreover, since the yield in the weld metal becomes excessive and the strength becomes excessive, the toughness decreases.

(Mn: 0.3-2.0%)
Mn aims to secure the toughness of the weld metal and improve the strength and proof stress. If the Mn of the wire component is less than 0.1%, the toughness decreases. On the other hand, if the content exceeds 2.0%, the amount of slag generated increases, and slag entrainment defects occur when multi-layer welding is performed. Moreover, since the yield in the weld metal becomes excessive and the strength becomes excessive, the toughness decreases.

(Ni: 1.0-3.5%)
Ni is intended to improve 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 becomes excessive and the toughness decreases.

(Cr: 0.4-0.85%)
Cr aims at improving the strength of the weld metal. When the wire component Cr is less than 0.4%, yield strength and strength cannot be obtained, and when it exceeds 0.85%, the strength becomes excessive and the toughness decreases.

(Mo: 0.4-0.85%)
Mo aims at improving the yield strength and strength of the weld metal. If the Mo content of the wire component is less than 0.4%, the desired yield strength and strength cannot be obtained, and if it exceeds 0.85%, the strength becomes excessive and the toughness decreases.

(V: 0.01 to 0.15%)
V aims to improve the strength of the weld metal by precipitating fine nitrocarbides. If V of the wire component is less than 0.01%, the effect is insufficient, and if it exceeds 0.15%, the strength becomes excessive and the toughness decreases.

(Flux filling rate: 4 to 10%)
The flux filling rate excluding the wire component described above is 4 to 10%. When the flux filling rate is less than 4%, molding becomes difficult and productivity is deteriorated. On the other hand, if it exceeds 10%, the amount of slag generation increases and slag entrainment defects tend to occur. In addition, since the amount of iron powder that brings in oxygen increases, the amount of oxygen in the weld metal increases and the toughness decreases even if the deoxidation with the simple substance C is performed. Furthermore, the wire drawability at the time of wire manufacture is inferior, resulting in a decrease in productivity due to wire breakage.

  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-tensile steels (base materials).

  In addition, both P and S are preferably as low as possible because they produce a low melting point compound to lower the grain boundary strength and lower the toughness of the weld metal. Moreover, although iron powder can be used in order to adjust a flux filling rate, since oxygen is brought in, it is desirable that it is less.

  The flux cored wire for high-tensile steel welding of the present invention has a cross-sectional shape that is seamless to the steel outer sheath in order to reduce the amount of diffusible hydrogen as much as possible. It is preferable to apply copper plating to the wire surface because the arc is further stabilized.

  In the method for producing a high-strength steel welding flux cored wire according to the present invention, a steel pipe is vibration-filled with a flux, and then reduced in diameter and annealed to form a strand. Alternatively, the steel strip is molded into a U-shape in the molding process, filled with flux, molded into an O-shape, welded, reduced in diameter, annealed to form a strand, and then plated as necessary. Thus, a product having a predetermined diameter of 0.8 to 2.0 mm is obtained.

The diameter of the high-strength steel welding flux-cored wire of the present invention is preferably 0.8 to 2.0 mm in diameter in order to increase the current density during welding and obtain a high deposition rate. 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.

  Using the steel outer skin shown in Table 1, it is molded into a U-shape in the molding process, filled with flux, molded into an O-shape, welded, reduced in diameter, annealed into a strand, plated, Wires of the wire components shown in Table 2 were drawn to a diameter of 1.2 mm, and various flux-cored wires were prototyped to form spool winding wires.

  After measuring the amount of spatter generated for each prototype wire, a weld metal test was conducted to investigate the presence of weld defects and the mechanical performance.

  The amount of spatter generated is 1 minute of spatter collected by welding 5 times (1 welding time 1.5 min) under the welding conditions shown in Table 3 by bead-on-plate welding using a copper collection box. Converted to quantity. A spatter generation amount of 0.5 g / min or less was considered good.

  The amount of welding was determined from the mass of the steel plate before welding and after removing the slag after welding once (welding time 1 min) under the welding conditions shown in Table 3 by bead-on-plate welding. A welding amount of 70 g / min or more was considered good.

  The weld metal test was performed by multi-layer welding under the welding conditions shown in Table 3 using a steel plate having a thickness of 20 mm shown in Table 4 as a V-shaped groove shape having a groove angle of 45 ° and a root gap of 12 mm. In addition, it welded to the last layer, without removing the slag produced | generated at each pass.

  After the end of welding, an X-ray transmission test was performed to investigate the presence or absence of welding defects. Further, the mechanical properties of the weld metal were obtained by taking a tensile test piece (JIS Z 3111 A1) and an impact test piece (JIS Z 3111 4) from the center of the plate thickness. The mechanical performance was evaluated as acceptable if the 0.2% proof stress was 780 MPa or more, the tensile strength was 880 MPa or more, and the absorbed energy at −20 ° C. was 50 J or more. The results are summarized in Table 5. Table 6 shows the weld metal components.

  In Tables 2, 5, and 6, wire symbols W1 to W9 are examples of the present invention, and wire symbols W10 to W25 are comparative examples.

  The wire symbols W1 to W9, which are examples of the present invention, are suitable because the amount of simple substance C in the flux, the amount of C, Si, Mn, Ni, Cr, Mo and V in the wire are appropriate, and the flux filling rate is also appropriate. The amount generated was small and the amount welded was large. In addition, since the amount of slag generation is small, the X-ray transmission test is also good, 0.2% proof stress and tensile strength of the weld metal are sufficiently obtained, and the absorbed energy is also good because the amount of oxygen in the weld metal is low. The result was very satisfactory.

  In the comparative example, the wire symbol W10 had a low flux filling rate and deteriorated productivity. Therefore, no evaluation was performed.

  Since the wire symbol W11 has a small amount of simple substance C, deoxidation was insufficient and the amount of oxygen in the weld metal increased, so that the absorbed energy was low.

  Since the wire symbol W12 is high in Cr, the tensile strength is excessive and the absorbed energy is low.

  Since the wire symbol W13 had a high V, the tensile strength was excessive and the absorbed energy was low.

  Since the wire symbol W14 had high Mo, the tensile strength was excessive and the absorbed energy was low.

  Since the wire symbol W15 is low in Cr, the 0.2% proof stress and tensile strength decreased. Moreover, since Mn was low, the absorbed energy was low.

  Since the wire symbol W16 used Fe—Mn as the C source of the flux, deoxidation was insufficient, and the amount of oxygen in the weld metal was large and the absorbed energy was low. Further, since a large amount of C was retained in the weld metal, the tensile strength was excessive and the absorbed energy was low.

  Since the wire symbol W17 had a low V, the 0.2% yield strength and tensile strength were low. Moreover, since Si was low, the absorbed energy was low.

  Since the wire symbol W18 is high in Si, the tensile strength is excessive and the absorbed energy is low. Moreover, the amount of slag generation was large, and slag entrainment defects occurred.

  Since the wire symbol W19 is high in Ni, the tensile strength is excessive and the absorbed energy is low.

  The wire symbol W20 had a low absorbed energy because Ni was low.

  Since the wire symbol W21 had high Mn, the tensile strength was excessive and the absorbed energy was low. Moreover, the amount of slag generation was large, and slag entrainment defects occurred.

  Since the wire symbol W22 had low Mo, the 0.2% yield strength and tensile strength were low. Further, since the total C was low, deoxidation was insufficient, the amount of oxygen in the weld metal was increased, and the absorbed energy was low.

  Since the wire symbol W23 has a large amount of simple substance C, since a large amount of C was retained in the weld metal, the tensile strength was excessive and the absorbed energy was low. Moreover, there was much spatter generation amount.

  Since the wire symbol W24 has a high filling rate, a large amount of slag was generated, and slag entrainment defects also occurred. In addition, a large amount of oxygen in the iron powder was mixed in the weld metal, and the absorbed energy was low.

  The wire symbol W25 was a solid wire, and 0.2% proof stress, tensile strength and absorbed energy were good, but the amount of spatter was large and the amount of welding was small.

It is the figure which showed the relationship between the simple substance C amount in a wire, and the oxygen amount in a deposit metal. It is the figure which showed the relationship between the amount of C in the outer skin C and the metal powder, and the amount of oxygen in the weld metal.

Claims (2)

  The flux cored wire for welding high-strength steel with a steel outer shell filled with flux contains 0.05 to 0.18% of the total amount of the single element C in the flux filled in the steel outer shell, and made of steel. The total of the outer sheath and the flux component is C: 0.07 to 0.20%, Si: 0.1 to 1.5%, Mn: 0.3 to 2.0%, Ni: 1.0 in the total mass% of the wire -3.5%, Cr: 0.4-0.85%, Mo: 0.4-0.85%, V: 0.01-0.15%, the balance from Fe and inevitable impurities A flux-cored wire for welding high-strength steel, wherein a flux filling rate of the flux in the components is 4 to 10%.   The high-strength steel welding flux cored wire according to claim 1, wherein the steel outer skin is seamless.

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