JP3163838B2 - Bond flux for submerged arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bond flux for submerged arc welding, and more particularly to an ultra-low oxygen, which has a low crack sensitivity and excellent fracture toughness for high tensile steel of 80 kgf / mm ² class or higher. The present invention relates to an ultra-low hydrogen bond flux for submerged arc welding.

[0002]

2. Description of the Related Art In recent years, the increase in the size of a welded structure requires not only a higher tensile strength of the steel material itself, but also a further improvement in the performance of the welded portion from the viewpoint of safety and durability. I have. For example, in high-pressure tanks and pressure vessels, improvement research has been promoted to incorporate fracture toughness based on elasto-plastic fracture mechanics into the quality assessment of welds to ensure safety. It is a fracture surface transition temperature (vTrs) by a test, a fracture toughness value at a design temperature (CTOD), and the like.

[0003] When welding a structure made of high-strength steel, hand welding or TIG welding using a covered arc welding rod is often used mainly to secure the toughness of the welded portion. Due to the demand for advanced technology and groove precision, easier and more efficient submerged arc welding of high-efficiency welding employing high heat input is also being advanced.

[0004] The bond flux for submerged arc welding is usually prepared by kneading raw material powders such as a deoxidizer, a slag forming agent, and an arc stabilizer together with a binder component such as water glass.
It is manufactured by heating and drying at a temperature of about 0 ° C. The CO ₂ gas generated by the decomposition of the metal carbonate contained in the raw material lowers the partial pressure of water vapor in the arc atmosphere and reduces the diffusivity in the weld metal. In addition to having the feature of suppressing the amount of hydrogen, it also exhibits excellent performance in moisture absorption resistance.

It has already been confirmed that the amount of moisture in the bond flux affects the amount of diffusible hydrogen in the weld metal, and is closely related to the amount of oxygen that degrades the crack resistance and toughness of the weld metal. . Therefore, when welding high-tensile steel that requires severe performance with respect to crack resistance and toughness, it is necessary to develop a bond flux that can provide a good weld metal regardless of welding conditions and welding environment. There is.

In order to meet such a demand, the present applicant has disclosed a bond flux for high-tensile steel described in Japanese Patent Publication No. 5-21675. This bond flux specifies the type and content of metal carbonates, metal fluorides, metal oxides, etc., as well as the water content and bulk specific gravity, thereby forming an appropriate bead shape without slag entrainment etc. In addition to ensuring the same, the amount of diffusible hydrogen and oxygen in the weld metal is suppressed to improve crack resistance and toughness, and is excellent as a bond flux.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the amount of diffusible hydrogen and oxygen in the weld metal can be further reduced as compared with the bond flux disclosed in the above-mentioned official gazette. An object of the present invention is to provide a bond flux for welding high-tensile steel, which can provide a weld metal with even better toughness.

[0008]

Submerged arc configuration of the welding bonded flux according to the Summary of the Invention The present invention that has solved the above problems, MgO: 23~35% CaO: 5~20 % CaF 2: 18~30% SiO ₂ : 8 to 15% Al ₂ O ₃ : 10 to 18% Metal Ca: 0.2 to 0.8% Metal carbonate: 4 to 8% in terms of CO ₂ , and MgO + CaO + CaF ₂ = 55 to 70 % 1.45 ≦ CaF ₂ / Al ₂ O ₃ ≦ 2.05, and Si: 3% or less Al: 0.5% or less Metallic Ti, Ti alloy and Ti oxide: 0.
5% or less P: 0.015% or less S: 0.015% or less Water: 0.05% or less Each has a gist.

[0009]

SUMMARY OF THE INVENTION Under the above-mentioned problems, the present inventors have developed a submerged arc welding method which provides a weld metal having excellent crack resistance and toughness while maintaining excellent workability for welding high strength steel. In order to develop the bond flux, we studied flux components from various angles. As a result, in a high-strength weld metal composed of martensite or a mixed structure of martensite and bainite, the following (1) to (4)
Have been found to exhibit good fracture toughness.

(1) The amount of oxygen is 200 ppm or less. FIG. 1 is a graph showing the relationship between the oxygen content in the weld metal and the impact resistance (vTrs). FIG. 2 is a graph showing the relationship between the oxygen content of the weld metal and the CTOD value at −20 ° C. As is clear from the graph, a clear correlation is observed between the oxygen content and the vTrs and CTOD values, and excellent fracture toughness can be secured by suppressing the oxygen content in the weld metal to 200 ppm or less. I understand. (2) To reduce the internal strain of the weld metal by suppressing the Ti content to 0.01% or less. (3) The amount of Al must be suppressed to 0.01% or less. (4) The amount of Si should be suppressed to 0.3% or less to prevent the matrix from becoming brittle.

As a result of research on the conditions required for the bond flux to secure the above requirements (1) to (4), it was confirmed that the following conditions were particularly effective. In order to suppress the oxygen content in the weld metal to 200 ppm or less, MgO in the bond flux should be 23% or more and CaO
5% or more, 18% or more of CaF ₂ , MgO + CaO +
CaF ₂ ≧ 55%, metal Ca 0.2% or more, Al 0.5% or less, SiO ₂ 15% or less, Al ₂ O ₃ 1
8% or less, and the CaF ₂ / Al ₂ O ₃ ratio is 1.45 to 1.45%.
Be within the range of 2.05. In order to reduce the Ti content in the weld metal to 0.01% or less, the Ti, Ti alloy and Ti oxide in the bond flux must be suppressed to 0.5% or less in terms of Ti. Al content in the weld metal is suppressed to 0.01% or less.
In order to suppress i to 0.3% or less, the amount of Al in the bond flux should be 0.5% or less and Si should be 3% or less.

In addition, it has been confirmed that the following should be sufficiently considered in order to impart good crack resistance to a high-strength weld metal. In order to increase the hydrogen embrittlement resistance by keeping the diffusible hydrogen amount [H] _D-GC at a very low level of 1 ml / 100 g or less, the metal carbonate in the flux is increased to 4% or more in terms of CO ₂ and 750. The amount of water extracted at ℃ should be less than 0.05%.

A bond flux satisfying the above requirements is used, and the wire to be combined is Al: 0.02%
Hereinafter, it was found that a weld metal having excellent crack resistance and toughness can be obtained by using Ti: 0.01% or less and N: 0.007% or less.

The present invention has been completed as a result of further detailed experiments based on the above findings, and the reason why the component composition of the bond flux is determined in the present invention will be described in detail below.

MgO: 23-35% MgO has an effect of increasing basicity and suppressing oxygen in the weld metal, and is a component indispensable for oxygen reduction. If it is less than 23%, this effect is effective. Is not exhibited. However, if it exceeds 35%, there are disadvantages such as a decrease in slag releasability and a deterioration in bead shape.

CaO: 5 to 20% The effect of increasing the basicity together with MgO and reducing the amount of oxygen is provided. If the content is less than 5%, this effect is not effectively exhibited. However, if it exceeds 20%, the bead appearance deteriorates.

CaF ₂ : 18-30% In addition to the effect of adjusting the melting point of the produced slag, the effect of reducing the oxygen in the weld metal is remarkable, and if it is less than 18%, this effect is not effectively exhibited. However, if it exceeds 30%, the arc becomes unstable, and the bead width and the bead shape become unstable.

Even if MgO, CaO, and CaF ₂ are each within the above range, if their total is less than 55%,
The effect of reducing the oxygen in the weld metal is not sufficiently exhibited.
If it exceeds 0%, the workability deteriorates as described above.

SiO ₂ : 8 to 15% Slag forming agent has an effect of adjusting bead appearance and bead shape. If less than 8%, this effect is not sufficiently exhibited.
On the other hand, if it exceeds 15%, oxygen in the weld metal is increased and the toughness is deteriorated.

Al ₂ O ₃ : 10 to 18% Like SiO _2, it has a function as a slag forming agent, and also functions to enhance the concentration and stability of the arc. These effects are effectively exhibited by containing 10% or more, but if it exceeds 18%, the oxygen in the weld metal is increased and the toughness is deteriorated.

Further, even if CaF ₂ and Al ₂ O ₃ are within the above range, the ratio of CaF ₂ / Al ₂ O ₃ is 1.45 to ₂ .
When it is out of the range of 05, the welding workability is reduced,
The effect of reducing oxygen in the weld metal is not exhibited.

FIG. 3 shows CaF ₂ /
FIG. 4 shows the results of examining the relationship between the Al ₂ O ₃ ratio, the amount of oxygen in the weld metal, and the welding workability. As is clear from this figure, the CaF ₂ / Al ₂ O ₃ ratio was set to 1. 45-
It is understood that by setting the range to 2.05, the oxygen content in the weld metal can be suppressed to a low level without deteriorating the welding workability, thereby providing high toughness.

Metal Ca: 0.2-0.8% It has the effect of deoxidizing to suppress the amount of oxygen in the weld metal. If it is less than 0.2%, this effect is not effectively exhibited. However, if it exceeds 0.8%, the deoxidizing effect is not further improved, but rather an exothermic reaction occurs during firing, which adversely affects productivity. The metal Ca is Ca-S
i, (ReM) -Ca-Si or the like. FIG. 4 is a graph showing the relationship between the amount of Ca in the flux and the amount of oxygen in the weld metal. As is clear from this figure, at least Ca must be added to achieve a sufficient deoxidation effect to improve toughness. It is understood that the content must be 0.2% or more.

Metal carbonate (CO ₂ equivalent): Decomposed by 4-8% welding heat to generate CO ₂ gas, and the effect of lowering the partial pressure of water vapor in the arc atmosphere to lower the amount of diffusible hydrogen in the weld metal. If less than 4%, this effect is not exhibited.
FIG. 5 is a graph showing the relationship between the CO ₂ equivalent content of carbonate in the flux and the amount of diffusible hydrogen in the weld metal, and the above tendency is clearly shown. However, if it exceeds 8%, the slag removability deteriorates, and sometimes a pock mark is formed on the bead, which adversely affects the welding workability. As the metal carbonate, CaCO ₃ or BaCO 3
_Third magnitude is the most common.

Si: 3% or less Although it has a strong deoxidizing effect, if it is too much, the toughness of the weld metal is deteriorated. Therefore, in the present invention which focuses on the improvement of toughness, it is essential to suppress the content to 3% or less. Become. Si is usually added as Fe-Si, Ca-Si or the like.

Al: has a deoxidizing effect of 0.5% or less, but if it is too much, it will remain as aluminum oxide in the weld metal and lose the deoxidizing effect to adversely affect toughness. Therefore, it is regulated to 0.5% or less. FIG. 6 is a graph showing the relationship between the Al content in the flux and the oxygen content in the weld metal. When the Al content exceeds 0.5%, the oxygen content in the weld metal clearly shows a tendency to increase. .

Metal Ti, Ti alloy, Ti oxide: Ti conversion
It has a strong deoxidizing power as low as 0.5% or less of Si (see FIG. 7).
If it is too large, needle-like Ti carbides are formed in the weld metal, and the toughness is deteriorated (see FIG. 8). Therefore, it must be suppressed to 0.5% or less.

P: 0.015% or less, S: 0.015%
Hereafter, it is a harmful impurity in the welding material, and when mixed into the weld metal, causes deterioration of ductility, toughness and crack resistance.
Therefore, the content must be minimized in the flux as well as in the welding wire, and the upper limit of P and S is set to 0.015% at which their harmful effects do not pose a practical problem.

Water content: 0.05% or less When the water content exceeds 0.05%, the amount of diffusible hydrogen in the weld metal is reduced to 1 ml / 100 even when an appropriate amount of carbonate is contained.
g or less, and the crack resistance deteriorates. Therefore, the water content in the flux is suppressed as much as possible, and the water content is reduced to 0.0
It is necessary to keep it to 5% or less. The water content referred to here is 75% from the flux dried at 200 ° C. or higher.
The amount of water extracted at 0 ° C. FIG. 9 is a graph showing the relationship between the amount of moisture in the flux and the amount of diffusible hydrogen in the weld metal. As is clear from this figure, the amount of diffusible hydrogen in the weld metal was reduced to 1 ml / 100 g or less. To keep
It is understood that the amount of water in the flux must be suppressed to 0.05% or less.

The constituents of the flux according to the present invention are as described above. However, in order to maintain better cracking resistance, metals or alloys other than the above, such as Ni, Cr, Mo, and Mn, which are liable to cause solidification segregation, are used. Desirably, it is not substantially contained.

[0031]

EXAMPLES Next, the structure and operation and effect of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and the present invention is applicable to the above and following points. Modifications may be made within the scope of the invention, and all of them are included in the technical scope of the present invention.

Example A submerged arc welding was performed using a wire having a composition shown in Table 1 and a bond flux having a chemical composition shown in Tables 2, 3 and 4, and a welding test was performed. The fluxes shown in Tables 2 to 4 were obtained by adding water glass after mixing the raw materials, granulating and heating and drying at 450 to 550 ° C. for 0.5 to 1.5 hours. Adjusted according to time. Fluxes satisfying the requirements of the present invention are shown in Table 2, and comparative fluxes are shown in Tables 3 and 4.

The welding test was conducted on a 50 mm thick steel plate (80 kg).
f / mm ² grade high strength steel) with X groove, welding condition is 60
Welding was performed at 0A-30V-30cpm, and a tensile test specimen (JIS Z3111 A1), a Charpy impact test specimen (JIS Z3111 A4), and a CTOD specimen were collected from the weld metal according to BS5762 and used for each test. The welding workability was determined by conducting a window-type restraint welding crack test using a test piece having the dimensions shown in FIG. 10 and welding at a preheating / pass-to-pass temperature of 75 ° C., and then visually and ultrasonically inspecting for cracks. Confirmation, welding workability, oxygen content and diffusible hydrogen content of weld metal (JIS Z3118)
Was examined. The results are shown in Table 5 and Tables 6 and 7.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

[Table 5]

[0039]

[Table 6]

[0040]

[Table 7]

From Tables 1 to 7, it can be considered as follows. First, Nos. 1 to 6 in Table 5 are examples satisfying the requirements of the present invention, and all show good workability and good values in strength and toughness. In contrast, Table 6,
Nos. 7 to 30 of No. 7 are comparative examples lacking any of the prescribed requirements defined in the present invention, and do not satisfy workability and toughness.

That is, in No. 7, MgO was as small as 21%,
No. 8 has a small amount of CaO of 3%, and No. 9 has CaF ₂
Is insufficient at 16%, oxygen in the weld metal is not sufficiently reduced, and satisfactory toughness cannot be obtained. No. 10 had too much MgO of 37%, No. 11 had too much CaO of 23%, and No. 12 had too much of CaF ₂ of 33%. There was no.

No. 13 is composed of MgO, CaO and CaF ₂
Is 53%, which is insufficient, so that the toughness cannot be improved, and No. 14 is too large, 73%, resulting in poor workability and needless to be subjected to a physical property test. No. 15 is SiO ₂
The workability was poor due to a shortage of 6%, and the physical property test was stopped. On the other hand, No. 16 has too much SiO ₂ of 17%.
Oxygen in the weld metal is not sufficiently reduced and the toughness is poor.

In No. 17, Al ₂ O ₃ was insufficient at 9%, so the arc was unstable and the workability was poor, so the physical property test was stopped. On the other hand, No. 18 has an excessively _high Al ₂ O ₃ content of 20%, and therefore has a poor toughness. No. 19 is CaF ₂ / Al ₂
O ₃ is as small as 1.35, while No. 20 is 2.15
In all cases, the amount of oxygen is large and the toughness is poor.

No. 21 has no added Ca,
No deoxidizing effect is exhibited and lacks toughness. No. 22 is CO
₂ (carbonate) has a higher amount of diffusible hydrogen in order of 2.0% and less, No.23, because CO ₂ is 9.5% and too high, was discontinued poor physical testing workability. No. 24 has Si of 5.
No. 25 has an excessively high Al content of 0.8%, and No. 26 has an excessively high Ti content of 0.7%.

In No. 27, P is too large as 0.018%, and in No. 28, S is too large as 0.018%.
Both have poor toughness. No. 29 had too much Ni of 5.0%, and No. 30 had too much of Mn of 3.0%. Therefore, solidification segregation occurred in each case, and hydrogen cracking originated therefrom.

[0047]

The present invention is configured as described above. By regulating the composition and moisture content of the bond flux for submerged arc welding, high strength steel such as 80 kgf / mm class ² high strength steel can be obtained. As a target, a weld metal having excellent crack resistance and toughness can be obtained. Therefore, it is possible to contribute to higher toughness of a steel structure using high-tensile steel and higher efficiency of welding.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of oxygen in a weld metal and vTrs.

FIG. 2 is a diagram showing the relationship between the amount of oxygen in a weld metal and CTOD.

FIG. 3 is a diagram showing the relationship between CaF ₂ / Al ₂ O ₃ in a flux, the amount of oxygen in a weld metal, and welding workability.

FIG. 4 is a diagram showing the relationship between the amount of Ca in the flux and the amount of oxygen in the weld metal.

FIG. 5 is a graph showing the relationship between the amount of CO ₂ (carbonate) in the flux and the amount of diffusible hydrogen in the weld metal.

FIG. 6 is a diagram showing the relationship between the amount of Al in the flux and the amount of oxygen in the weld metal.

FIG. 7 is a diagram showing the relationship between the amount of Ti in the flux and the amount of oxygen in the weld metal.

FIG. 8 is a diagram showing the relationship between the amount of Ti in the flux and vTrs.

FIG. 9 is a graph showing the relationship between the amount of water in the flux and the amount of diffusible hydrogen in the weld metal.

FIG. 10 is a view showing the shape of a test plate used for a window-shaped restraint welding crack test.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP 4-57438 (JP, B2) (58) Fields surveyed (Int. Cl. ⁷ , DB name) B23K 35/362

Claims (1)

(57) [Claims] 1. A MgO: 23 to 35% (wt%: hereinafter the _{same) CaO: 5~20% CaF 2:} 18~30% SiO 2: 8~15% Al 2 O 3: 10~18% Metal Ca: 0.2 to 0.8% metal carbonate: contains 4 to 8% in terms of CO ₂ , and satisfies the following condition: MgO + CaO + CaF ₂ = 55 to 70% 1.45 ≦ CaF ₂ / Al ₂ O ₃ ≦ 2.05 Filled, and Si: 3% or less Al: 0.5% or less Metallic Ti, Ti alloy and Ti oxide: 0.1% in terms of Ti.
5% or less P: 0.015% or less S: 0.015% or less Moisture: 0.05% or less Each of the bond fluxes for submerged arc welding, characterized in that: