JP5146998B2 - Fused flux for submerged arc welding - Google Patents

Description

  The present invention relates to a melt type flux used during submerged arc welding.

  Flux for submerged arc welding forms molten slag during welding to block molten metal from the atmosphere to prevent nitridation and oxidation of the weld metal and to perform metallurgical reaction with molten metal via slag / metal reaction in a short time. It has important functions such as making clean weld metal and forming good beads.

  Strength and toughness are listed as properties required for weld metal, but generally, strength and toughness are contradictory properties, so that it becomes difficult to ensure toughness as the strength increases. In order to cope with this problem, it is known that reduction of the amount of weld metal oxygen is effective, and molten fluxes having various components are disclosed in, for example, Patent Documents 1 to 11. In any literature, proposals have been made from the viewpoint of reducing the oxygen content (or improving the weld metal toughness) by adjusting the basic component and the acidic component in the flux, and securing weldability by adjusting the compounding ratio.

In order to reduce the amount of weld metal oxygen, generally known is a method of reducing the amount of SiO ₂ and increasing the amount of basic components in the flux. For example, Patent Document 5 discloses a technique for reducing the amount of weld metal oxygen by using a low SiO ₂ -high CaF ₂ flux.

On the other hand, in order to perform good welding without welding defects, it is generally necessary to perform welding while keeping the shape of the molten pool constant. In the case of submerged arc welding, since the molten pool is always covered with molten slag, the high-temperature physical properties of the molten slag, particularly the molten slag viscosity, is an important factor for stabilizing the molten pool shape. In high current welding such as submerged arc welding, the molten pool shape is disturbed by the arc pressure. Therefore, the viscosity of the molten slag covering the molten pool is preferably high in order to suppress this disturbance. In this regard, Patent Document 12 discloses a flux excellent in high-speed weldability focusing on slag viscosity.
JP-A-6-31481 JP-A-6-285679 JP 7-256488 A Japanese Patent Laid-Open No. 7-303990 JP-A-8-187593 JP-A-9-85488 Japanese Patent Laid-Open No. 9-262692 Japanese Patent Laid-Open No. 11-277294 JP 2004-154840 A JP 2005-125345 A JP 2005-329462 A JP-A-11-19795

  However, Patent Document 12 does not discuss the amount of weld metal oxygen. This is due to the following reason. As mentioned above, it is necessary to increase the amount of basic components in order to reduce the amount of oxygen in the weld metal. However, because the viscosity of high basic slag is low, the turbulence of the molten pool increases, causing undercuts and slag entrainment. Such a welding defect is likely to occur. That is, there is a reciprocal relationship between the weld metal oxygen content reduction and the weld defect resistance. For this reason, in patent document 12, it is thought that it was specialized in the improvement of only one of the conflicting factors rather than trying to balance both.

  Thus, in the conventional component adjustment based on the flux basicity, it is not easy to balance the reduction in the amount of weld metal oxygen and the resistance to weld defects. In order to achieve both low oxygen and improved weld defect resistance, it is required to strictly control the flux component and the molten slag viscosity. For example, in Patent Document 5, the mutual relationship between a plurality of components is strictly defined. doing. It goes without saying that such a response leads to a decline in productivity.

  In view of this, the present invention provides a molten flux for submerged arc welding that can perform both a reduction in the amount of oxygen in the weld metal and resistance to weld defects by conducting a study from a different viewpoint than the conventional component adjustment based on flux basicity. With the goal.

  In order to reduce the oxygen content of the submerged arc weld metal, the present inventors first considered the influence of the flux composition on the weld metal oxygen content. Specifically, assuming that the flux forms molten slag of the same component, the oxygen distribution equilibrium between the molten slag and the molten metal was estimated thermodynamically, and the effect was considered. The general welding reaction is a non-equilibrium reaction of rapid temperature rise and rapid cooling, but in submerged arc welding, it is in a state of strong stirring due to high temperature and arc pressure. Therefore, the amount of dissolved oxygen in the metal was calculated by thermodynamic equilibrium calculation, assuming that an equilibrium was established between the molten slag / metal, and compared with the measured oxygen amount of the weld metal. As a result, it was found that the calculated amount of dissolved oxygen in the metal and the measured value of the amount of oxygen in the weld metal were correlated, and in order to reduce the amount of oxygen in the weld metal, the flux composition was made a low oxygen potential component system. That is, it was found that it is important to use a component system in which the amount of dissolved oxygen in the metal obtained by slag metal thermodynamic equilibrium calculation is low.

  In addition, the molten slag viscosity was also considered in order to improve the weld defect resistance. As described above, it is effective to increase the slag viscosity to improve the weld defect resistance. However, as a result of various experiments and researches, if the molten slag viscosity is too high even in a low oxygen potential component flux, It was found that the amount of oxygen could not be reduced, and it was found that the molten slag viscosity upper limit (1500 ° C.) capable of reducing the amount of oxygen was less than 1.00 poise. It was also found that the lower limit value of the melt slag viscosity necessary for ensuring the weld defect resistance is 0.1 Poise or more. The reason why it is difficult to reduce oxygen due to the high slag viscosity of the low oxygen potential component flux is not clear, but if the slag viscosity is too high, the stirring force between the molten slag and molten metal during welding will be weakened, resulting in molten slag.・ It is presumed that the mass transfer rate during oxygen distribution between the molten metals is slow.

  Based on the above knowledge, it is possible to achieve both reduced weld metal oxygen content and improved weld defect resistance by setting the flux composition to a low oxygen potential component system and 1500 ° C slag viscosity to 0.1 Poise or more and less than 1.00 Poise. It becomes.

Specifically, it is necessary to improve weld defect resistance, but lowers the SiO ₂ (high viscosity / high oxygen potential component) that increases the amount of weld metal oxygen, and instead reduces the effect of increasing the amount of oxygen and improves the slag viscosity. A large amount of Al ₂ O ₃ (high viscosity / low oxygen potential component) is added. Low oxygen potential component by properly adjusting the CaO-CaF ₂ component balance while preferably suppressing slag fluidity by suppressing an increase in flux melting point due to the addition of a large amount of Al ₂ O ₃ by adding an appropriate amount of CaF ₂ The above-mentioned problem is solved by setting the system at 1500 ° C. and the slag viscosity at 1500 ° C. to 0.1 poise or more and less than 1.00 poise. In addition, it is possible to suppress the occurrence of welding defects resulting from the deterioration of the bead appearance, the undercut, the occurrence of potts marks, and the like.

The present invention thus obtained is as follows.
(1) in _{mass%, SiO 2: 5~20%,} MnO: 1~5%, CaO: 5~40%, CaF 2: 40% or _{less, MgO: 1~10%, Al 2} O 3: 30~ 45%, TiO ₂ : 1 to 4.5%, BaO: 1 to 10%, the balance has a chemical composition consisting of impurities, and the molten slag viscosity at 1500 ° C. is 0.1 Poise or more and less than 1.00 Poise A melt type flux for submerged arc welding characterized by being.

  According to the present invention, the conflicting problems of reducing the amount of weld metal oxygen and improving resistance to weld defects have been solved at the same time, and it has become possible to reduce the amount of weld metal oxygen while preventing weld defects.

  Embodiments of a melt type flux for submerged arc welding according to the present invention will be described below. In the present specification, “%” unless otherwise specified means “mass%”.

1. Chemical composition The chemical composition of the molten flux for submerged arc welding according to the present embodiment will be described below.

₍₁₎ SiO 2: 5~20%
SiO ₂ is an important component constituting slag. SiO ₂ vitrifies the slag and improves the bead appearance. The likely cause welding defects such as inclusion undercut and slag and the amount of SiO ₂ is small. For this reason, 5% or more of SiO ₂ is necessary. On the other hand, SiO ₂ is a component that increases the oxygen potential of the molten slag, and an increase in the amount of SiO ₂ increases the amount of weld metal oxygen, so the upper limit is made 20%. From the viewpoint of stably suppressing welding defects and reducing the amount of weld metal oxygen, it is preferable that the blending amount of SiO ₂ is 7 to 15%.

(2) MnO: 1 to 5%
MnO has the effect of improving the fluidity of the slag and smoothing the bead appearance. Moreover, the effect which improves the yield of Mn to a weld metal is also anticipated. In order to obtain these effects, a blending ratio of 1% or more is necessary. On the other hand, a large amount of MnO increases the oxygen potential of the molten slag to increase the amount of weld metal oxygen and impair the bead appearance, so the upper limit is made 5%. In particular, from the viewpoint of stably achieving both improvement in Mn yield on the weld metal and good bead appearance, it is preferable that the blending amount of MnO is 3.5 to 4.5%.

(3) CaO: 5 to 40%
CaO is a component that lowers the oxygen potential of the molten slag and has the effect of reducing the amount of weld metal oxygen. In order to obtain this effect, 5% or more is necessary. Although a larger amount is preferable for reducing the amount of oxygen, a large amount of addition causes deterioration of slag removability and formation of pock marks due to deterioration of moisture absorption resistance of the flux, thereby impairing weldability. Therefore, the upper limit is made 40%. From the viewpoint of stably achieving both a reduction in the amount of weld metal oxygen and good weldability, the CaO content is preferably 3 to 30%.

(4) CaF ₂ : 40% or less CaF ₂ has the effect of improving the slag fluidity and reducing the amount of weld metal oxygen. However, if blended in a large amount, deterioration of weld defect resistance due to a decrease in slag viscosity occurs, so the blending range is made 40% or less. A preferred blending range is 20 to 35%. Incidentally, if ratio of CaO _(CaF 2 / CaO) in the range of 1.0 to 5.0, particularly preferred from the viewpoint of preventing slag fluidity deterioration due to flux melting point-elevating.

(5) MgO: 1 to 10%
MgO is a component that lowers the oxygen potential of the molten slag and has the effect of reducing the amount of weld metal oxygen. In order to obtain this effect, 1% or more is necessary. On the other hand, if the content exceeds 10%, the melting point of the flux increases, the fluidity of the slag deteriorates and the weldability is impaired, so the upper limit is made 10%. A preferred blending range is 1 to 5%.

_{(6) Al 2 O 3:} 30~45%
Since Al ₂ O ₃ is a component that does not increase the oxygen potential of the molten slag as compared with SiO _2, it has the effect of improving the viscosity without increasing the amount of weld metal oxygen. Addition of less than 30% impairs weld defect resistance due to a decrease in slag viscosity. On the other hand, since the addition of a large amount increases the amount of weld metal oxygen, the upper limit is made 45%. From the viewpoint of stably reducing the amount of weld metal oxygen and suppressing welding defects, it is preferable that the blending amount of Al ₂ O ₃ is 30 to 40%.

₍₇₎ TiO 2: 1~4.5%
TiO ₂ can be added in a small amount to improve slag peelability and improve the yield of Ti to the weld metal. In order to obtain this effect, addition of 1% or more is necessary. On the other hand, the addition of a large amount increases the oxygen potential of the molten slag and increases the amount of weld metal oxygen, so the upper limit is made 4.5%. A preferable blending range is 2 to 4%.

(8) BaO: 1-10%
BaO has the effect of adjusting the melting point of the flux and lowering the oxygen potential of the molten slag to reduce the amount of weld metal oxygen. In order to obtain this effect, 1% or more is added. On the other hand, excessive addition deteriorates the bead shape, so the upper limit is made 10%. A preferred blending range is 1 to 5%.

In addition to the above essential components, FeO, B ₂ O _{3 and the} like are inevitably mixed as impurities during the preparation of the molten flux. Regarding the mixing of these components, if the FeO content is 2.0% or less and the B ₂ O ₃ content is 1.0% or less, the amount of weld metal oxygen and weld defect resistance are not affected.

2. Slag Viscosity at 1500 ° C. The molten flux for submerged arc welding according to the present embodiment has a slag viscosity at 1500 ° C. in the range of 0.1 Poise to 1.00 Poise.

  Slag viscosity is a physical property that affects both the weld metal oxygen content and the weld defect resistance. If the slag viscosity is too low, the weld pool is disturbed by the arc pressure during welding, resulting in weld defects. On the other hand, if the slag viscosity is too high, the slag fluidity is lowered and the stirring force between the molten slag and the molten metal becomes weak. For this reason, the mass transfer rate of oxygen in the oxygen distribution equilibrium between slag metals decreases, and the amount of weld metal oxygen increases. Therefore, the viscosity range is 0.1 Poise to 1.00 Poise. From the standpoint of stably achieving both a reduction in the amount of weld metal oxygen and good weldability, the preferred viscosity range is 0.3 poise to 0.8 poise, more preferably 0.45 poise to 0.65 poise. Thus, since the viscosity range is set from the viewpoint of maintaining the movement speed of oxygen between the slag metals, the flux as in the prior art, for example, from the viewpoint of preventing welding defects like the flux disclosed in Patent Document 5 is used. It is lower than the set viscosity range.

The viscosity may be controlled by adjusting the flux component, and the component adjusted for this purpose is not particularly limited. However, as described above, the high temperature viscosity of the flux according to the present invention is relatively low, and on the other hand, since it contains a relatively large amount of Al ₂ O ₃ that increases the viscosity, the content of the component that decreases the viscosity is within the above range. Therefore, it is preferable to blend them preferentially.

  By changing the mixing ratio of the raw materials, a flux having the chemical components shown in Table 1 was prototyped.

溶接における母材としては、表２の化学成分を示す市販材ＳＭ４００Ｂを用いた。母材の板厚は１６ｍｍであり、ビードオンプレート溶接で溶接長０．６ｍの１層溶接を行った。溶接には表３の化学成分を示す直径４ｍｍのソリッドワイヤを用いて、表４に示す条件で単電極サブマージアーク溶接（使用装置：大阪電気製 形式（型式）：G1-B3-CG）を実施した。

As a base material in welding, a commercially available material SM400B showing chemical components in Table 2 was used. The thickness of the base material was 16 mm, and single layer welding with a weld length of 0.6 m was performed by bead-on-plate welding. For welding, solid electrode with a diameter of 4 mm indicating the chemical composition shown in Table 3 was used, and single electrode submerged arc welding was performed under the conditions shown in Table 4 (Applicable equipment: Osaka Denki model (model): G1-B3-CG). did.

  Table 5 shows the results of 1500 ° C slag viscosity, weld metal oxygen content analysis results, and weld defect resistance. Table 5 also shows the calculated amount of dissolved oxygen in the metal obtained by a slag metal thermodynamic equilibrium calculation assuming a molten slag having the same composition as the flux. The slag metal thermodynamic equilibrium was calculated using general-purpose thermodynamic calculation software (for example, FactStage).

  Here, the amount of weld metal oxygen was determined by analyzing the produced weld bead, and was judged to be inappropriate when an oxygen concentration of 300 ppm or more was measured. For weld defect resistance, check the soundness of the weld bead produced by visual inspection, and comprehensively judge the presence or absence of undercut and the appearance of the bead. Indicated.

  The slag viscosity was measured at a slag temperature of 1500 ° C. using a vibrating piece viscometer. A schematic diagram of the measuring apparatus is shown in FIG. The apparatus is composed of a vibration generator, a vibration piece, a laser displacement meter, an electric furnace, and a control personal computer. The measurement is performed in an atmospheric pressure atmosphere, and the material of the vibrating piece crucible is platinum. The vibration generator uses an industrial vibrator and is electrically driven by a sine generator and an amplifier. The vibrating piece is dipped in a sample that has become a liquid state by heating, and the vibrating piece is suspended around a leaf spring below the vibration generator to vibrate the vibrating piece in a sine wave. When a thin flat plate-like vibrating piece vibrated with a constant driving force is immersed in the liquid, the amplitude is attenuated by the viscous resistance of the liquid. The change in the amplitude is measured by a laser displacement meter with the movement of the mirror fixed to the vibrating bar support rod. The viscosity calculation formula used in this measurement is calculated by applying the following formula (1).

K≡Rm ² / π ・ fa ・ A ²
here,
ρ: Sample density (kg / m ³ )
μ: Liquid viscosity (Pa · s)
Ea: Amplitude in air (m)
E: Amplitude in sample (m
Rm: Mechanical impedance resistance (kg · m / s)
fa: Resonance frequency in air (Hz)
A: Area of vibrating piece (m ² )

In Comparative Example 1, since the amounts of MnO and Al ₂ O ₃ deviated from the scope of the present invention, weldability was deteriorated due to deterioration of the bead appearance. Moreover, although the flux composition has a low calculated value of dissolved oxygen in the metal and a low oxygen potential component system, the weld metal oxygen content could not be reduced because the slag viscosity exceeded the range of the present invention.

In Comparative Example 2, the amount of Al ₂ O ₃ and the slag viscosity did not satisfy the lower limit of the range of the present invention, and undercut occurred due to insufficient slag viscosity, resulting in poor weldability.

In Comparative Example 3, the amount of weld metal oxygen could not be reduced because the amount of SiO ₂ exceeded the upper limit of the range of the present invention.

  In Comparative Example 4, since the amount of MnO exceeded the range of the present invention, the amount of weld metal oxygen could not be reduced.

  In Comparative Example 5, although the amount of weld metal oxygen could be reduced, since the CaO amount exceeded the range of the present invention, a pock mark was generated on the bead surface, and the soundness of the bead was impaired, resulting in a decrease in weldability.

In Comparative Example 6, since the amount of TiO ₂ did not satisfy the upper limit of the range of the present invention, the slag fluidity deteriorated, pock marks were generated, the bead soundness was impaired, and weldability was deteriorated.

In Comparative Example 7, since the amounts of MnO, TiO ₂ and BaO deviated from the scope of the present invention, weldability was deteriorated due to deterioration of the bead appearance.

In Comparative Example 8, the amount of weld metal oxygen could not be reduced sufficiently because the amount of Al ₂ O ₃ exceeded the range of the present invention.

In Comparative Example 9, since the amount of CaF ₂ exceeded the upper limit of the present invention range, the slag viscosity could not satisfy the lower limit of the present invention range. For this reason, undercut occurred due to insufficient slag viscosity, and weldability deteriorated.

  In Comparative Example 10, the flux composition is a low oxygen potential component system with a low calculated amount of dissolved oxygen in the metal, and the flux composition is also within the scope of the present invention, but since the 1500 ° C. slag viscosity exceeds the scope of the present invention, welding is performed. The amount of metal oxygen could not be reduced.

  Compared to the above comparative example, as shown in Invention Examples 11 to 15, in the melt type flux in which the blending ratio and slag viscosity are controlled within the scope of the present invention, the amount of weld metal oxygen was reduced and at the same time improved weld defect resistance was realized. .

It is the schematic of the vibrating piece type viscometer used for the measurement of slag viscosity.

Claims (1)

By _{mass%, SiO 2: 5~20%,} MnO: 1~5%, CaO: 5~40%, CaF 2: 40% or _{less, MgO: 1~10%, Al 2} O 3: 30~45%, TiO ₂ : 1 to 4.5%, BaO: 1 to 10%, the balance has a chemical composition consisting of impurities, and the molten slag viscosity at 1500 ° C. is not less than 0.1 poise and less than 1.00 poise. Characteristic fusion flux for submerged arc welding.

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