JP4783708B2 - Fused flux for submerged arc welding - Google Patents

Description

  The present invention relates to a molten flux for submerged arc welding used in general structures such as pipes, steel frames, bridges, vehicles, and the like, particularly when performing high-speed welding, to form a healthy weld metal without welding defects, Further, the present invention relates to a molten flux for submerged arc welding that can obtain a beautiful bead appearance with good slag peelability.

  Submerged arc welding is applied in a wide range of fields such as pipe making, steel frames, bridges, and vehicles because it provides highly efficient and stable welding workability and performance. In recent years, in submerged arc welding, high-speed welding is required for the purpose of improving welding efficiency and productivity.

  Conventionally, with regard to the development of a melt-type flux for increasing the speed of submerged arc welding, for example, Japanese Patent Laid-Open No. 58-179595 (Patent Document 1) limits the flux component and makes the welding power source have a positive polarity of direct current. Thus, there is a disclosure of a technique for increasing the welding speed and improving the welding efficiency. However, DC positive submerged arc welding produces welding defects compared to AC welding and the reverse polarity of DC power sources, such as overlap, poor penetration, uneven bead width, bead appearance deterioration, and slag peelability deterioration. This is a welding method that is easy and has many unstable elements, and good welding workability cannot be obtained simply by defining the flux composition.

On the other hand, JP-A-59-10495 (Patent Document 2) limits TiO ₂ and ZrO ₂ in the flux composition for the purpose of improving the weld bead shape in high-speed submerged arc welding and improving the slag peelability, There is a disclosure of a technique for improving welding workability. In general, TiO ₂ and ZrO ₂ are known as arc stabilizers and are often contained in a melt-type flux for submerged arc welding, but ZrO ₂ has a high melting point and raises the melting point or softening melting point of the flux. Therefore, it is not suitable for high-speed welding, and good welding workability cannot be obtained.

Japanese Laid-Open Patent Publication No. 4-238694 (Patent Document 3) discloses a technique for improving welding workability in high-speed submerged arc welding by limiting flux components, melting point and viscosity. As an improvement and development of the flux, the influence of basicity and welding workability is investigated, and the melting point and viscosity of the flux are indexed to improve workability in high-speed welding. SiO ₂ , CaO, CaF ₂ The range of the composition limitation is extremely wide, and SiO ₂ , CaO, and CaF ₂ each have completely different welding workability effects. Therefore, in these composition limitation ranges, stable welding workability cannot be obtained.

Furthermore, Japanese Patent Laid-Open No. 2-92497 (Patent Document 4) discloses a technique in which nickel slag and molten flux are mixed to improve welding workability in high-speed submerged arc welding of a spiral steel pipe. Nickel slag is the slag after dissolving and reducing nickel from nickel ore in the refining process of nickel, and the composition is a eutectic composition mainly composed of 50 to 60% by mass of SiO ₂ and 30 to 40% by mass of MgO. It is a stable raw material. However, just mixing this nickel slag and molten flux, nickel slag and molten flux have different particle size configurations and bulk specific gravity, so they cannot be mixed uniformly. Therefore, stable welding workability cannot be obtained.

Japanese Patent Application Laid-Open No. 2003-10995 (Patent Document 5) limits the components of the flux, the viscosity of the molten slag generated by welding, and the solidification temperature of the molten slag, and improves welding workability in high-speed submerged arc welding of inclined portions. There is a disclosure of the technology that has been attempted. In particular, the ratio of TiO ₂ and Al ₂ O ₃ is specified as an important factor for improving the workability of welding. However, in high-speed submerged arc welding of inclined parts, it is necessary only to control the ratio of TiO ₂ and Al ₂ O _3. It is difficult to obtain stable welding workability.
JP 58-179595 A Japanese Patent Laid-Open No. 59-10495 JP-A-4-238694 JP-A-2-92497 JP 2003-10995 A

  The present invention provides a molten flux for submerged arc welding that can form a healthy weld metal free of welding defects in high-speed submerged arc welding, and can obtain a beautiful bead appearance with good slag peelability. With the goal.

The gist of the present invention is as follows:
(1) in mass%, the melt flux for the submerged arc welding containing 35 to 45% and the SiO ₂ 35-45% of _{MnO, MnO 2: 0.1~1.0%,} CaF 2: 1~9% , CaO: 0.1~8%, MgO: 0.5~7%, Al 2 O 3: containing 0.5 to 6% FeO is Ri der 7% or less, other alkali metal oxides and melt flux for the submerged arc welding, wherein unavoidable impurities der Rukoto.
(2) The molten type for submerged arc welding according to (1), wherein the slag of MnO—SiO ₂ melt type flux used for submerged arc welding is used as a melting raw material at 95% by mass or less of the total flux mass. It is in flux.

  According to the molten flux for submerged arc welding of the present invention, a sound weld metal free from welding defects can be formed even in high-speed submerged arc welding, and a beautiful bead appearance with good slag peelability can be obtained. Moreover, since it can be applied to higher-speed submerged arc welding, the welding efficiency and productivity can be remarkably improved. Furthermore, since the molten flux slag for submerged arc welding used for welding can be reused as a raw material for melting and commercialized again, it can greatly contribute to environmental improvement and cost reduction.

The technical idea of the present invention will be described below.
High-speed submerged arc welding is often performed with one electrode or multiple electrodes (1 to 4 electrodes). As the speed increases, the bead appearance and slag peelability deteriorate, the bead width becomes uneven, the penetration is poor, and the fusion is poor. , Welding defects such as overlap, undercut and blowhole are likely to occur.

  Also, in downward inclined welding such as inner surface welding in the manufacturing process of spiral steel pipes, molten metal and molten slag gradually hang down due to gravity and are pushed to the position of the arc generation point, so that concavity is likely to occur, concave beads, undercuts and It tends to overlap. On the other hand, in ascending slope welding such as outer surface welding in the manufacturing process of spiral steel pipes, the molten metal and molten slag move away from the arc generation point position and are pushed back in the welding direction, so that they tend to be convex beads and undercut is likely to occur. .

Therefore, the present inventors diligently studied the flux composition, the flux production method, the welding conditions, and the like in order to improve the above problems. As a result, it has been found that the contents of MnO ₂ and FeO in the flux composition have a very important influence.

In high-speed submerged arc welding, weld defects are likely to occur, and slag peelability deteriorates. Therefore, first, the chemical composition ratio is optimized by improving the component composition based on the conventional fusion flux for high-speed submerged arc welding. As a result, the viscosity, fluidity, and melting point (softening and melting point) of the flux were adjusted, and welding defects could be greatly reduced. However, there is a limit only by controlling the chemical composition ratio of the conventional flux, and the bead width is not uniform, the bead appearance and the slag peelability are not improved. Therefore, the newly found addition of MnO ₂ .

Deterioration of the bead appearance, uneven bead width, and convex bead in high-speed welding can be attributed to the high surface tension of the slag, and the surface tension of the slag must be lowered to improve the bead appearance. It was. It is effective to increase the amount of oxygen as an element to lower the surface tension. Therefore, MnO ₂ is added to the flux, and the amount of oxygen in the molten slag is increased by the decomposition reaction of 2MnO ₂ → 2MnO + O ₂ during welding, and the slag Succeeded in lowering the surface tension. As a result, a uniform and beautiful bead appearance with fine waves was obtained, a smooth bead shape was obtained, and slag peelability was improved.

As a method for increasing the amount of oxygen, it is also effective to increase the amount of SiO _2. However, increasing the amount of SiO ₂ increases the viscosity of the slag, resulting in a convex bead and undercut. Therefore, it was found that MnO ₂ that can increase the amount of oxygen by adding a small amount is extremely effective.

  Furthermore, FeO was reduced in order to improve slag peelability and reduce slag seizure at the end of the bead collar. FeO in the melted flux for submerged arc welding according to the present invention is an impurity, and various melting raw materials often contain FeO as an impurity. Therefore, the final product always contains FeO. Therefore, by using a raw material having a low FeO content, FeO can be greatly reduced, and the slag peelability is improved and the slag seizure at the end of the bead heel is improved.

As a method for reducing FeO, FeO may be reduced by adding an appropriate amount of carbon during dissolution, and Fe may be removed. Since FeO has a smaller standard free energy for oxide formation than SiO ₂ , MnO, CaO, MgO, and Al ₂ O ₃ , FeO is most easily reduced.

Next, an important point of the production method is the method of adding MnO ₂ . In order to remove FeO, reduction reaction dissolution is performed by adding carbon. However, MnO ₂ has a smaller standard free energy for oxide formation than FeO, so if all the melting raw materials are dissolved simultaneously, MnO ₂ is reduced first. , MnO ₂ is hardly left. MnO ₂ is difficult to contain MnO _{2 even} in the final product because oxygen tends to gasify to MnO in normal dissolution. Therefore, in the melt flux for the submerged arc welding of the present invention to dissolve the materials other than MnO ₂ above, after reduction of the FeO by the appropriate amounts of carbon, for example, tapping immediately before, MnO by adding dissolving MnO _{2 2} Can be contained in the final product in the specified amount.

The molten flux for submerged arc welding of the present invention can also reuse the slag of the MnO—SiO ₂ -based molten flux for submerged arc welding used for welding as a melting raw material. The amount of FeO that is slag-out due to the oxidation of steel in the steel plate and welding wire during welding is increasing for slag, but a manufacturing process that removes FeO by carbon reduction in the manufacturing process of molten flux for submerged arc welding is applied. No problem. The welding slag is almost the same MnO-SiO ₂ component composition as the melt flux for submerged arc welding of the present invention, so it can be applied as a stable melting raw material, recycling effect, environmental improvement, cost reduction, etc. It can also make a great social and economic contribution.

This invention is made | formed from the above knowledge, and demonstrates the reason for limitation of the flux component composition in this invention below.
MnO of the flux is the most important component for forming a good bead shape in high-speed submerged arc welding, and is an effective component for adjusting the viscosity, fluidity, and melting point of the slag. If the content is less than 35% by mass (hereinafter referred to as “%”), the viscosity of the slag is lowered and it tends to flow, so that bead meandering and undercutting occur. On the other hand, if it exceeds 45%, the viscosity of the slag becomes high and becomes a convex bead, slag entrainment and seizure occur, and the slag peelability deteriorates. Therefore, the content of MnO is set to 35 to 45%.

Since the flux SiO ₂ is an acidic oxide, it has the effect of reducing the surface tension of the slag, and is an effective component for adjusting the viscosity and melting point of the slag. If the content is less than 35%, the surface tension of the slag cannot be lowered, and the viscosity is insufficient, resulting in concaves, undercuts and overlaps. On the other hand, if it exceeds 45%, the viscosity of the slag becomes too high, and the fit of the heel end portion becomes worse with the convex bead, the slag peelability deteriorates, and the oxygen content in the weld metal increases and the toughness deteriorates. To do. Therefore, the content of SiO ₂ is set to 35 to 45%.

MnO ₂ in the flux is an important component for improving the bead appearance, obtaining a smooth bead shape and good slag releasability, and the oxygen contained in the molten slag by the decomposition reaction of 2MnO ₂ → 2MnO + O ₂ during welding. It is an effective component that increases the amount and lowers the surface tension of the slag. If the content is less than 0.1%, the surface tension of the slag cannot be lowered, resulting in a convex bead, and the slag peelability is deteriorated. On the other hand, if it exceeds 1.0%, the surface tension of the slag is too low and the bead appearance is deteriorated, the bead width becomes non-uniform, and the amount of oxygen in the weld metal is increased to deteriorate toughness. Therefore, the content of MnO ₂ is set to 0.1 to 1.0%.

  FeO of the flux is a component that causes deterioration of slag peelability and slag seizure at the end of the bead collar. Therefore, the content of FeO is set to 7% or less in order to improve the slag peelability and reduce slag seizure at the end of the bead collar.

The CaF ₂ flux is an effective component for improving toughness and adjusting the melting point. If the content is less than 1%, there is no effect of improving toughness, and uneven bead width and poor fusion occur. On the other hand, if it exceeds 9%, concaves and overlaps occur, and the bead appearance deteriorates. Therefore, the content of CaF ₂ is preferably 1 to 9%.

  The flux CaO is an important component for adjusting the melting point and fluidity of the slag. If the content is less than 0.1%, the fit of the bead heel end is poor and undercutting occurs. On the other hand, if it exceeds 8%, the slag fluidity becomes poor, the bead width is non-uniform, and the slag peelability becomes poor, so the content is preferably 0.1 to 8%.

  The MgO flux is an effective component for adjusting the fire resistance and viscosity of the slag. In the case of high-current high-speed welding, it is necessary to increase the slag fire resistance. If the content is less than 0.5%, the slag fire resistance cannot be improved, the bead shape is deteriorated, and the bead width is reduced. It becomes non-uniform. On the other hand, if it exceeds 7%, protrusions are generated on the bead surface, and the appearance is rough with a convex bead, undercut occurs, and the slag removability deteriorates. Therefore, the content of MgO is preferably 0.5 to 7%.

The flux Al ₂ O ₃ has the effect of improving the slag peelability. If the content is less than 0.5%, the slag peelability deteriorates and undercutting occurs. On the other hand, if it exceeds 6%, it becomes a convex bead and the slag removability becomes poor, so the content is preferably 0.5 to 6%.

The slag of MnO—SiO ₂ melt flux used for submerged arc welding is a feedstock having a stable component composition, and is extremely effective for recycling effect, environmental improvement, and cost reduction. If the amount of slag as the melting raw material exceeds 95% of the total flux mass, most of the flux components are determined by the slag components, so that it is impossible to adjust the components and it is impossible to produce a flux with a stable chemical composition. . The MnO—SiO ₂ -based slag component is preferably a component close to the composition of the molten flux for submerged arc welding according to the present invention because it is easy to adjust the components during production.

Hereinafter, the effect of the present invention will be described in more detail with reference to examples.
The fluxes having various chemical compositions shown in Table 1 were experimentally produced, and some of the molten flux slags used in the submerged arc welding and having the compositions shown in Table 2 were used.

  For the welding, steel plates and wires having a chemical thickness of 12 mm shown in Table 3 were used. In the case of double-sided one-pass welding of the I-shaped groove 2 (gap zero) of the joint of the flat plate 1 shown in FIG. 1, one-electrode submerged arc welding was performed under the welding conditions shown in Table 4. In the case of double-sided one-pass welding of the I-shaped groove 4 of the spiral steel pipe 3 shown in FIG. 2, three-electrode submerged arc welding was performed under the welding conditions shown in Table 5. In addition, the melt type flux shown in Table 1 used the particle size adjusted to 12 × 150 mesh after dissolution.

  Welding workability was evaluated by examining the bead appearance, bead shape, slag peelability, slag seizure, slag entrainment, poor fusion, undercut, concave, and overlap. The bead appearance was good if the wavy surface of the bead surface was fine, uniform and beautiful, and the result was ◯.

  As for the bead shape, a good bead shape having uniform bead width and height and having no irregularities was judged as good. The slag peelability was evaluated as good when the slag was easily peeled off by natural peeling and hammering or using a hammer or chisel.

  Regarding slag seizure, after slag peeling, it was judged good if there was no seizure of slag on the bead surface and the end of the bead ridge. The slag entrainment was investigated by an X-ray transmission test. If there was no slag entrainment, it was judged as good. If at least one slag entrainment was confirmed, it was judged as poor.

  The fusion failure was also investigated by an X-ray transmission test. If there was no fusion failure, it was judged as good. If one fusion failure was confirmed, it was judged as poor. Regarding the undercut, it was judged as good when there was no undercut at the end of the bead collar, and it was marked as poor when at least one undercut was confirmed.

  The concave was evaluated as good when no dent was found at the center of the bead surface, and poor when the dent was slightly observed. For the overlap, a case where the wrap width was less than 2 mm was considered good, and a case where the wrap width was more than 2 mm was inferior.

  For mechanical performance evaluation of the weld metal part, a Charpy impact test piece (JIS Z22024) was collected from the center of the weld metal part at the center of the plate thickness, and a mechanical test was performed. The toughness was evaluated by a Charpy impact test at 0 ° C., and the average of three repetitions was evaluated. The Charpy absorbed energy was determined to be good if it was 27 J or more. The results of these surveys are summarized in Table 6.

  As is clear from Table 6, the test symbols T1 to T6, which are examples of the present invention, have good weld metal toughness and good bead appearance because the fluxes F1, F2, F3, and F4 satisfy the constituent requirements of the present invention. The bead shape and slag peelability can be obtained, and a sound weld metal free from welding defects such as slag seizure, slag entrainment, poor fusion, undercut, concave, overlap, etc. can be obtained. Met.

On the other hand, since the test symbol T7 as a comparative example has a high MnO of the flux F5, it becomes a convex bead, slag entrainment and seizure occurred, and the slag peelability deteriorated. Further, since CaF ₂ was high, concaves and overlaps were generated, and the bead appearance was also deteriorated.
In test symbol T8, since MnO of flux F6 was low, bead meandering and undercut occurred, and the bead appearance deteriorated. Further, since CaF ₂ is low, low toughness of the weld metal, bead width uneven, incomplete fusion also occurs.

In test symbol T9, since SiO _{2 of} flux F7 is high, the familiarity of the flange end portion with the convex bead deteriorated, and the slag peelability deteriorated. In addition, the oxygen content in the weld metal increased and the toughness deteriorated. Furthermore, since CaO was high, the bead width became non-uniform.
In the test code T10, since the low SiO ₂ of flux F8, concave, undercut and overlap occurs. Moreover, because of the high Al ₂ O _3, and the slag removability becomes convex bead, bead appearance is deteriorated.

In test symbol T11, since MnO _{2 of} flux F9 was high, the bead appearance deteriorated and the bead width became non-uniform. In addition, the oxygen content in the weld metal increased and the toughness deteriorated. Furthermore, since CaO was low, the familiarity of the bead collar end portion was poor and undercut occurred.
Since the test symbol T12 had a low MnO ₂ in the flux F10, it became a convex bead and the slag peelability deteriorated. Moreover, since MgO was high, protrusions were generated on the bead surface, and the appearance was rough with a convex bead, resulting in undercutting.

In test symbol T13, since the FeO of the flux F11 was high, the slag peelability was deteriorated and slag seizure occurred at the end of the bead collar. Moreover, since MgO was low, the bead shape deteriorated and the bead width became non-uniform.
Since the test symbol T14 had high MnO _{2 of} the flux F12, the bead appearance deteriorated and the bead width became non-uniform. In addition, the oxygen content in the weld metal increased and the toughness deteriorated. Furthermore, since Al ₂ O ₃ is low, the slag peelability deteriorates and an undercut occurs.
In test symbol T15, since the amount of slag used at the time of production of flux F13 was large, MnO ₂ was lowered to form a convex bead, and the slag peelability was deteriorated.

It is a figure which shows the groove shape for 1 electrode submerged arc welding of the flat joint used for the Example of this invention. It is a figure which shows the groove shape for 3 electrode submerged arc welding of the spiral steel pipe used for the Example of this invention.

Claims (2)

In the mass%, a melt type flux for submerged arc welding containing 35 to 45% of MnO and 35 to 45% of SiO ₂ , MnO ₂ : 0.1 to 1.0% , CaF ₂ : 1 to 9%, CaO: _{0.1~8%, MgO: 0.5~7%,} Al 2 O 3: containing 0.5 to 6% FeO is Ri der 7% or less, other than an alkali metal oxide and inevitable impurities melt flux for the submerged arc welding, characterized in Rukoto Oh. Submerged arc welding that the slag MnO-SiO ₂ based melt flux was used was used as the dissolution raw materials to 95 wt% of the total flux mass, characterized in claim 1 the melt flux for the submerged arc welding according.

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