JP4581842B2 - Fused flux for submerged arc welding - Google Patents

Description

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

  As an automatic welding method for a UOE steel pipe or a crude oil tank, a GMAW welding method, a submerged arc welding method, or the like is used. In particular, the submerged arc welding method is often used because a highly efficient and high performance weld metal can be obtained.

As flux used for submerged arc welding, there are bond flux and molten flux. Melt-type flux is made by melting raw materials of various minerals at a high temperature of 1200 ° C or higher, crushing them after cooling, has low hygroscopicity, is easy to handle and store, and can be used for high-speed welding in combination with multi-electrode welding It is frequently used for manufacturing UOE steel pipes.
The bond flux is obtained by adding a small amount of a binder to a raw material and granulating it, followed by baking at about 600 ° C. Although it has the characteristic that the chemical composition of the weld metal can be adjusted relatively freely by adding metal raw materials and deoxidizers to the bond flux, it is highly hygroscopic and difficult to handle, and is not suitable for high-speed welding. There is a problem.

  In any of the fluxes, during welding, the molten metal is shielded from the atmosphere by forming molten slag to prevent nitridation and oxidation of the weld metal, and the metal / slag reaction is used to perform a metallurgical reaction with the molten metal in a short time. It plays important roles such as making clean weld metal and forming good beads.

  As described above, the melt type flux is suitable for high-speed welding of multi-electrodes and has an excellent bead appearance, and is therefore frequently used for the production of high-grade steel pipes such as UOE steel pipes for line pipes. These high-grade steel pipes require high strength and good toughness for the weld metal. Generally, strength and toughness are contradictory properties, and it becomes difficult to ensure toughness as the strength increases. In order to cope with this problem, it is known that reduction of the oxygen content of the weld metal is effective, and molten fluxes having various components have been proposed in, for example, Patent Document 1 to Patent Document 10 and the like. Yes.

In any of the patent documents, proposals are made from the viewpoint of reducing the amount of oxygen (or improving the weld metal toughness) by adjusting the basic component and the acidic component in the flux and ensuring weldability by adjusting the blending ratio. Among these proposals, Patent Documents 1, 3, 8, 9, and 10 specifically show the amount of weld metal oxygen. Among these, Patent Documents 3 and 10 are the ones that most reduce the amount of oxygen.
The amount of weld metal oxygen in the example of Patent Document 10 is reduced to 190 to 270 ppm. In the example of Patent Document 3, oxygen is reduced to 180 to 270 ppm. In another example, the weld metal oxygen content is reduced to approximately 250-300 ppm. That is, these proposals show that the oxygen content of the weld metal is reduced to approximately 300 ppm or less.
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-8-267279 JP-A-9-85488 Japanese Patent Laid-Open No. 9-262692 JP-A-11-19795 Japanese Patent Laid-Open No. 11-277294 Japanese Patent Laid-Open No. 2004-154840

  In each of the above-mentioned patent documents, there is no mention of the strength level of the weld metal, but if it is estimated from the chemical components of the base steel plate and the welding wire used in the examples, the 60 kg class is targeted for the tensile strength. On the other hand, in recent years, development of X100 (tensile strength 75 kg class) and X120 class (tensile strength 95 kg class) as steel pipes for line pipes has been promoted. It is expected that reduction of the amount of metal oxygen will be important.

  Therefore, in the present invention, the amount of oxygen in the weld metal can be reduced more than before (specifically, it is stable at 250 ppm or less at a strength level of 75 kg or higher in tensile strength) and submerged arc welding suitable for the manufacture of UOE steel pipes. An object of the present invention is to provide a melting type flux.

In order to reduce the amount of oxygen in the weld metal by submerged arc welding, the present inventors have considered the influence of the flux component on the amount of oxygen in the weld metal. Specifically, assuming that the flux forms molten slag of the same component, the equilibrium oxygen activity for each slag component was estimated thermodynamically and the effect was considered. As a result, it was found that it is the SiO ₂ content in the flux that dominates the equilibrium oxygen activity, and by reducing the SiO ₂ content more than before, the weld metal with an oxygen content of 250 ppm or less can be stabilized. The present invention has been completed by finding a melt-type flux that can be produced.

Here, the present invention is, in terms of _{mass%, SiO 2: 5~ 13%} , MnO: 1~10%, CaO: 10~30%, CaF 2: 40~50%, MgO: 2~10%, Al 2 _{O 3: 2~20%, TiO 2} : 2~20%, BaO: contains 1 to 10%, UOE total content thereof is more than the tensile strength of 75 kg, characterized in that at least 95% This is a molten flux for submerged arc welding of steel pipes .

Further, it may contain one or more of Na ₂ O: 3% or less, K ₂ O: 3% or less, and B ₂ O ₃ : 1.0% or less.
In conventional proposals and research, the oxygen content of the weld metal is organized by basicity derived from the ratio of the acidic and basic components of the flux. SiO ₂ is handled as an important component as one of the acidic components, but its content is determined in balance with other acidic components. Further, since SiO ₂ is an important component for vitrifying slag, it is generally contained in a relatively large amount of 20 to 40%. The content rate of SiO ₂ in Patent Document 5, which is a proposal for reducing SiO ₂ most in the above-described existing technology, is 13 to 24%. In the present invention, the content of SiO ₂ is set to 5 to 15%, which is remarkably reduced as compared with the prior art.

Further, although the equilibrium oxygen activity with respect to SiO ₂ decreases as SiO ₂ decreases, the equilibrium oxygen activity with respect to MnO increases in a region with little SiO ₂ , so it is necessary to limit the MnO content.

On the other hand, when SiO ₂ is extremely reduced in this way, the bead appearance and slag peelability may be deteriorated, but when CaF ₂ is contained in an amount of 40 to 50%, the bead appearance and slag peelability may be reduced. We found that there was almost no adverse effect. The reason for this is not clear, but when CaF ₂ is contained in an amount of 40% to 50%, the slag is separated into two phases, a phase containing a large amount of CaF ₂ and a phase containing a large amount of other oxides. It is estimated that the change in physical properties of the separated slag alleviated adverse effects on bead properties and the like.

  According to the present invention, it is possible to reduce the oxygen content of the weld metal to 250 ppm or less while preventing generation of welding defects and appearance deterioration of the weld bead even in high-speed welding. In particular, it is a valuable invention from the viewpoint of securing and improving the low temperature toughness of weld metal of high strength line pipes and high frequency bend pipes exceeding the X80 grade.

Next, the reason why the flux composition is limited as described above in the present invention will be described. In the present invention, “%” defining the content of each component in the flux is “% by mass” unless otherwise specified. In addition, since the flux of the present invention is composed of a metal oxide and CaF ₂ except for impurities, the content of each component is the content obtained by converting the metal element content in the flux into a metal oxide, and the fluorine content. Is a content rate in terms of CaF ₂ .

SiO _2: 5~15%
SiO ₂ is an important component constituting slag. SiO ₂ vitrifies the slag and improves the bead appearance. _{On the} other hand, when the amount of SiO ₂ is small, the slag viscosity increases, and undercuts and slag entrainment are likely to occur. For this reason, it is necessary to contain 5% or more of SiO ₂ . On the other hand, SiO ₂ is an acidic component, and an increase in SiO ₂ increases the amount of oxygen in the weld metal. In particular, in order to reduce the oxygen content of the weld metal, which is a target in the present invention, to 250 ppm or less, the content is made 15% or less. A preferable upper limit is less than 15%, a more preferable upper limit is 13%, and a more preferable upper limit is 10% or less.

MnO: 1-10%
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 content of 1% or more is necessary. On the other hand, since MnO is an acidic component and a large amount of compound increases the oxygen content of the weld metal, the upper limit is made 10%. Preferably it is 2.0 to 7.0%.

CaO: 10-30%
CaO is a basic component and has the effect of reducing the oxygen content of the weld metal. A higher content is preferable for reducing the oxygen content, but a larger content deteriorates the slag peelability and facilitates the formation of pock marks through the deterioration of the moisture absorption resistance of the flux. Therefore, the content is made 10 to 30%. Preferably it is 12 to 20%.

CaF ₂ : 40-50%
CaF ₂ is a very effective component for reducing the oxygen content of the weld metal. Prevents deterioration of bead appearance due to SiO ₂ reduction. However, since a slag peelability will be impaired when it contains abundantly, the content rate shall be 40 to 50%. A preferable range is more than 40% and 50% or less.

MgO: 2 to 10%
MgO is a basic component and is added to reduce the oxygen content of the weld metal and adjust the viscosity. In order to obtain this effect, a content of 2% or more is necessary. On the other hand, when the content exceeds 10%, the viscosity becomes too high, and undercuts and slag entrainment are likely to occur, and a pock mark is easily formed due to the moisture absorption resistance deterioration of the flux. Therefore, the upper limit is made 10%. Preferably it is 2.5 to 6.5%.

Al ₂ O ₃ : 2 to 20%
Al ₂ O ₃ is a neutral component and is added for the purpose of adjusting the melting point and viscosity of the slag. If the addition is less than 2%, the bead appearance deteriorates due to insufficient slag viscosity, and the slag peelability also deteriorates. On the other hand, the inclusion of a large amount increases the melting point and viscosity of the slag, and causes the undercut of the bead and slag entrainment to deteriorate the shape. For this reason, the upper limit is set to 20%. Preferably it is 4 to 16%.

TiO ₂ : 2 to 20%
A small amount of TiO ₂ improves the slag peelability and improves the yield of Ti to the weld metal. In order to obtain this effect, it is necessary to contain 2% or more. On the other hand, if a large amount is contained, undercut or slag entrainment occurs due to an increase in slag viscosity, which deteriorates the bead shape. For this reason, the upper limit is set to 20%. A preferred upper limit is 15%, while a preferred lower limit is 2.5%.

BaO: 1-10%
BaO is an effective component that adjusts the melting point of the slag and reduces the oxygen content of the weld metal. In order to acquire this effect, 1% or more needs to be contained. On the other hand, if contained excessively, the bead shape is deteriorated, so the upper limit is made 10%.

In addition to the above components, one or more of Na ₂ O, K ₂ O and B ₂ O ₃ may be contained.
Na ₂ O, K ₂ O: 3% or less Na ₂ O and K ₂ O can be contained for adjusting the viscosity of the slag. In order to obtain this effect, 0.2% or more may be added. On the other hand, since a large amount causes a bead shape deterioration due to an excessive increase in viscosity, the upper limit is made 3%.

B ₂ O ₃ : 1.0% or less B ₂ O ₃ may be contained in order to add boron to the weld metal. Although the content is adjusted according to the amount of boron to be added, it is effective when the content is 0.1% or more and 1.0% or less. If the content is within this range, the oxygen amount and weldability are not significantly affected.

The flux of the present invention contains 95% or more of the total of the above components. The balance is impurities such as FeO. The total of the above components is preferably 97% or more, and more preferably 99% or more.
The flux having such a composition is manufactured by being melted once at 1200 ° C. or higher, and pulverized after cooling and solidification. The particle size of the flux is determined so as to be represented by a mesh corresponding to the maximum and minimum nominal dimensions of the sieve used for sieving (JIS Z 3352 etc.). The particle size of the flux is properly selected depending on the welding conditions to be applied, particularly the applied current.
In the present invention, the welding method itself is not particularly limited as a conventional one.

  Next, the effects of the present invention will be described more specifically with reference to examples.

  By changing the mixing ratio of the raw materials, molten fluxes having various chemical components shown in Table 1 were produced. In this example, since the heat input welding using a large-diameter wire was used, the particle size of the flux was finely crushed. The specific particle size mesh was 20xD.

  As a base material for the welding test, a steel plate having chemical components shown in Table 2 was used. The plate thickness of the steel plate was 16 mm, and a V groove having a groove depth of 6 mm and a groove angle of 70 degrees was produced at the ends of the two steel plates, and one layer welding with a welding length of 1.0 m was performed. The soundness of the produced weld beads was confirmed by visual inspection of the appearance, and the amount of weld metal oxygen was analyzed.

  For welding, a 4 mm diameter solid wire having the chemical composition shown in Table 3 was used, and four-electrode submerged arc welding was performed under the conditions shown in Table 4. A DC power source was used for the leading electrode, and an AC power source was used for the other electrodes.

  Table 5 shows the results of analysis of the amount of weld metal oxygen and the results of visual inspection. Table 5 shows the results of a tensile test of all weld metals and a Charpy test at −30 ° C. for some weld metals. From these results, it can be seen that the melt type flux according to the present invention can be used for the production of a high-grade UOE steel pipe having a strength level of 75 kg or higher.

In all the examples of the present invention, the oxygen amount can be controlled to 250 ppm or less. Further, by limiting the upper limit of SiO ₂ to 13%, the oxygen content of the weld metal is further stably reduced and can be controlled to approximately 200 ppm or less.

In Comparative Example 1, since SiO ₂ exceeds the upper limit of the range of the present invention and does not satisfy the lower limit of CaF ₂ , the oxygen content of the weld metal exceeds 250 ppm.
In Comparative Example 2, the amount of oxygen in the weld metal exceeds 250 ppm because SiO ₂ exceeds the upper limit of the present invention range.

In Comparative Example 3, since MnO exceeds the upper limit of the range of the present invention, the oxygen content of the weld metal exceeds 250 ppm.
In Comparative Example 4, CaO does not satisfy the lower limit of the present invention, and the oxygen content of the weld metal exceeds 250 ppm.

In Comparative Example 5, CaF ₂ exceeds the upper limit of the present invention. For this reason, the slag peelability deteriorated.
In Comparative Examples 6 to 15, the mixing ratio of SiO ₂ , CaF ₂ , CaO, and MnO that has the greatest influence on the amount of oxygen in the weld metal satisfies the present invention, so the amount of oxygen in the weld metal is 250 ppm or less, which is the object of the present invention. Has been reduced. However, since the contents of MgO, Al ₂ O ₃ , TiO _2, and BaO deviate from the scope of the present invention, the appearance of the beads is deteriorated, the slag peelability is reduced, or the undercut occurs.

In contrast to the above comparative example, as shown in Invention Examples 16 , 17, 22, and 23, in the melt type flux whose content is controlled within the scope of the present invention, the amount of oxygen can be reduced and, at the same time, the bead health. Sex was preserved.

Claims (1)

By _{mass%, SiO 2: 5~ 13%} , MnO: 1~10%, CaO: 10~30%, CaF 2: 40~50%, MgO: 2~10%, Al 2 O 3: 2~20% , TiO ₂ : 2 to 20%, BaO: 1 to 10%, and the total content is at least 95%. Melting for submerged arc welding of UOE steel pipe with tensile strength of 75 kg or more Mold flux.