JPH06328291A - Bond flux for submerged arc welding - Google Patents

Abstract

PURPOSE:To provide a weld metal excellent in the crack resistance and the toughness by specifying the kind and contents of the metallic carbonate, the metallic fluoride, and the metallic oxide, and the contents of Si, Al and Ti. CONSTITUTION:The bond flux for the submerged arc welding having a composition consisting of, by weight, 23-35% MgO, 5-20% CaO, 18-30% CaF2, 0.2-0.8% metallic Ca, and 4-8% in terms of CO2 metallic carbonate is constituted. In this constitution, the relationship of MgO+CaO+CaF2=55-70%, and 1.45<=CaF2/ Al2O3<=2.05 is satisfied. Limitation is made to Si: <=3%, Al: <=0.5%, metallic Ti, Ti alloy and Ti oxide: <=0.5% in terms of Ti, P: <=0.15%, and the water content: <=0.05%. This constitution provides the weld metal having the excellent crack resistance and toughness for the 80kgf/mm<2> high tensile steel or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to bond flux for submerged arc welding, and particularly for ultrahigh oxygen having high crack strength and low fracture susceptibility for high strength steel of 80 kgf / mm ² grade or more, The present invention relates to an ultra-low hydrogen type bond flux for submerged arc welding.

[0002]

2. Description of the Related Art The recent increase in the size of welded structures requires not only high tensile strength of the steel material itself, but also improvement of the performance of the welded portion from the viewpoint of safety and durability. There is. For example, even in high-pressure tanks and pressure vessels, improved research is underway to improve the fracture toughness based on elasto-plastic fracture mechanics in order to ensure the safety of welds. It is a fracture surface transition temperature (vTrs) and a fracture toughness value (CTOD) at a design temperature in the test.

By the way, when welding a structure made of high-strength steel, in order to secure the toughness of the welded portion, hand welding using a covered arc welding rod and TIG welding are mainly used, but these welding methods are used. Since high technology and groove precision are required, the high efficiency heat input welding, which is easier to carry out, and the submerged arc welding is gradually being promoted.

The bond flux for submerged arc welding is generally 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 produced by heating and drying at a temperature of around 0 ° C., and the partial pressure of water vapor in the arc atmosphere is lowered by the CO ₂ gas generated by the decomposition of the metal carbonate contained in the raw material, and the diffusivity in the weld metal is reduced. In addition to having the characteristic of suppressing the amount of hydrogen, it also exhibits excellent performance in moisture absorption resistance.

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

In order to meet such requirements, the present applicant has previously disclosed the bond flux for high-strength 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, so that a proper bead shape can be obtained without causing slag entrainment. This is an excellent bond flux because it is ensured and the amount of diffusible hydrogen and oxygen in the weld metal is suppressed to enhance crack resistance and toughness.

[0007]

The present invention can further reduce the amount of diffusible hydrogen and oxygen in the weld metal as compared with the bond flux as disclosed in the above-mentioned official gazette, whereby crack resistance and An object of the present invention is to provide a bond flux for welding high-strength steel, which can provide a weld metal with even higher 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: 8~15% Al 2 O} 3: 10~18% metal Ca: 0.2 to 0.8% metal carbonate: with containing 4% to 8% in terms of CO _{2, MgO + CaO + CaF 2 =} 55~70 % 1.45 ≦ CaF ₂ / Al ₂ O ₃ ≦ 2.05 is satisfied, and Si: 3% or less Al: 0.5% or less Metal Ti, Ti alloy and Ti oxide: Ti.
5% or less P: 0.015% or less S: 0.015% or less Moisture: 0.05% or less.

[0009]

Under the above problems to be solved, the inventors of the present invention have achieved the workability excellent as welding for high-strength steel while maintaining excellent workability while providing submerged arc welding for providing weld metal excellent in crack resistance and toughness. In order to develop the bond flux of, we conducted research on flux components from various angles. As a result, in the high-strength weld metal composed of martensite or a mixed structure of martensite and bainite, the following (1) to (4)
It has been found that those satisfying the requirement of 1 show 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 impact resistance (vTrs), and 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, there is a clear correlation between the oxygen content and the vTrs and CTOD values, and it is possible to secure excellent fracture toughness by suppressing the oxygen content in the weld metal to 200 ppm or less. I understand. (2) To suppress the internal strain of the weld metal by suppressing the Ti amount to 0.01% or less. (3) Keep the Al content to 0.01% or less. (4) To suppress the embrittlement of the matrix by suppressing the Si content to 0.3% or less.

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

It was also confirmed that the following should be taken into consideration in order to give good crack resistance to the high-strength weld metal. In order to suppress the diffusible hydrogen amount [H] _D-GC to a very low level of 1 ml / 100 g or less and to enhance the hydrogen embrittlement resistance, the metal carbonate in the flux should be 4% or more in terms of CO ₂ and 750 The amount of water extracted at ° C should be 0.05% or less.

Then, using a bond flux satisfying the above requirements, Al: 0.02% as a wire to be combined
It has been 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 the effect of increasing the basicity and suppressing oxygen in the weld metal, and is a component essential for oxygen reduction. If it is less than 23%, this effect is effective. Is not demonstrated to However, if it exceeds 35%, problems such as deterioration of slag releasability and deterioration of bead shape occur.

CaO: 5 to 20% It has the effect of increasing basicity and reducing the amount of oxygen together with MgO, and if it 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 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 each of MgO, CaO and CaF ₂ is within the above range, if the total of them is less than 55%,
Oxygen reduction effect in the weld metal is not fully exerted, while 7
If it exceeds 0%, workability deteriorates as described above.

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

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%, oxygen in the weld metal is increased to deteriorate toughness.

Even if CaF ₂ and Al ₂ O ₃ are in the above ranges, the CaF ₂ / Al ₂ O ₃ ratio is 1.45 to ₂ .
When it is out of the range of 05, the welding workability is lowered,
The effect of reducing oxygen in the weld metal is not exerted.

By the way, FIG. 3 shows CaF ₂ / in the flux.
The results of examining the relationship between the Al ₂ O ₃ ratio, the oxygen content in the weld metal and the welding workability are shown. As is clear from this figure, the CaF ₂ / Al ₂ O ₃ ratio is 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, and thereby high toughness can be provided.

Metal Ca: 0.2 to 0.8% Deoxidizing effect is exerted to suppress the amount of oxygen in the weld metal, and if less than 0.2%, this effect is not exerted effectively. However, even if it exceeds 0.8%, the deoxidizing effect is not further improved, but rather an exothermic reaction occurs during firing, which adversely affects the productivity. 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 is required to improve the toughness by a sufficient deoxidizing effect. It is understood that 0.2% or more must be contained.

Metal carbonate (converted to CO ₂ ): 4-8% Decomposes with welding heat to generate CO ₂ gas, lowers partial pressure of water vapor in arc atmosphere and lowers amount of diffusible hydrogen in weld metal However, if less than 4%, this effect is not exhibited.
FIG. 5 is a graph showing the relationship between the CO ₂ conversion content of carbonate in the flux and the amount of diffusible hydrogen in the weld metal, clearly showing the above tendency. However, if it exceeds 8%, the peeling property of the slag is deteriorated and sometimes a pock mark is formed on the bead, which adversely affects the welding workability. Examples of metal carbonates include CaCO ₃ and BaCO
_3rd grade is the most common.

Si: 3% or less It has a strong deoxidizing action, but if it is too much, it deteriorates the toughness of the weld metal, so in the present invention focused on improving the toughness, it is essential to suppress it to 3% or less. Become. Si is usually added as Fe-Si, Ca-Si or the like.

Al: 0.5% or less It has a deoxidizing effect, but if it is too much, it will remain as aluminum oxide in the weld metal, so that the deoxidizing effect is lost and the toughness is adversely affected. Therefore, it is regulated to 0.5% or less. By the way, FIG. 6 is a graph showing the relationship between the amount of Al in the flux and the amount of oxygen in the weld metal. When the amount of Al exceeds 0.5%, the amount of oxygen in the weld metal clearly shows an increasing tendency. .

Metal Ti, Ti alloy, Ti oxide: Ti conversion
Although it has a strong deoxidizing power like 0.5% or less in Si (see FIG. 7),
If the amount is too large, needle-like Ti carbide is generated in the weld metal and the toughness is deteriorated (see FIG. 8), so it must be suppressed to 0.5% or less.

P: 0.015% or less, S: 0.015%
It is a harmful impurity in the following welding materials, and when mixed in the weld metal, it causes deterioration of ductility, toughness and crack resistance.
Therefore, the content must be suppressed as much as possible not only in the welding wire but also in the flux, and 0.015% at which the harmful effects thereof are not a practical problem was set as the upper limits of P and S.

Moisture content: 0.05% or less When the water content exceeds 0.05%, the diffusible hydrogen content of the weld metal is 1 ml / 100 even when an appropriate amount of carbonate is contained.
It becomes impossible to make it g or less, and the crack resistance deteriorates. Therefore, the moisture content in the flux should be kept as low as possible and the amount of moisture should be reduced to 0.0 by firing at an appropriate temperature and time.
It is necessary to suppress it to 5% or less. The water content referred to here is 75% from the flux dried at 200 ° C or higher.
It is the amount of water extracted at 0 ° C. 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. As is clear from this figure, the amount of diffusible hydrogen in the weld metal should be 1 ml / 100 g or less. To suppress
It can be seen that the amount of water in the flux must be suppressed to 0.05% or less.

The constituent components of the flux according to the present invention are as described above. However, in order to maintain further good crack resistance, metals or alloys other than those mentioned above, such as Ni, Cr, Mo and Mn, which easily cause solidification segregation, are used. It is desirable not to contain it substantially.

[0031]

EXAMPLES Next, the constitution and effects of the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and conforms to the spirit of the preceding and the following. It is also possible to carry out the invention by changing it within the range to be obtained, and all of them are included in the technical scope of the present invention.

Example A submerged arc welding was carried out using a wire having the composition shown in Table 1 and a bond flux having the chemical composition shown in Tables 2, 3 and 4, and a welding test was conducted. The fluxes shown in Tables 2 to 4 are those obtained by adding water glass after blending the raw materials, granulating and heating and drying at 450 to 550 ° C. for 0.5 to 1.5 hours, and the water content mainly depends on the drying temperature. It is 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 carried out on a steel plate with a thickness of 50 mm (80 kg
f / mm ² grade high-strength steel) with X groove formed and welding conditions of 60
Welding was performed at 0A-30V-30cpm, and a CTOD test piece was collected from the weld metal according to a tensile test piece (JIS Z3111 A1), a Charpy impact test piece (JIS Z3111 A4), and BS5762, and used for each test. As for the welding workability, a window-type constrained welding crack test was performed using a test piece having the dimensions shown in FIG. Welding workability, oxygen content of weld metal and diffusible hydrogen content (JIS Z3118)
I checked. 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, the following can be considered. First, Nos. 1 to 6 in Table 5 are examples satisfying the prescribed requirements of the present invention, and all show good workability and good strength and toughness. On the other hand, Table 6,
Nos. 7 to 30 of No. 7 are all comparative examples lacking any of the prescribed requirements defined in the present invention, and workability, toughness and the like cannot be satisfied.

That is, No. 7 has a low MgO content of 21%,
No. 8 has a low CaO content 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. In addition, No. 10 had an excessive MgO content of 37%, No. 11 had an excessive CaO content of 23%, and No. 12 had an excessive CaF ₂ content of 33%. There was no.

No. 13 is MgO, CaO and CaF ₂
The toughness cannot be improved because the total amount is insufficient at 53%, and the workability is poor because No. 14 is too large at 73%, and it is not necessary to perform a physical property test. No. 15 is SiO ₂
The workability was poor and the physical property test was stopped. On the contrary, No. 16 has too much SiO ₂ of 17%,
Oxygen in the weld metal is not sufficiently reduced, resulting in poor toughness.

Since No. 17 had a shortage of Al ₂ O ₃ of 9%, the arc was unstable and the workability was poor, and the physical property test was stopped. On the contrary, in No. 18, Al ₂ O ₃ is too much as 20%, so that the toughness is deteriorated. No. 19 is CaF ₂ / Al ₂
O ₃ is as small as 1.35, while No. 20 is 2.15.
Since they are too large, the amount of oxygen is large and the toughness is poor.

Since No. 21 does not contain Ca,
The deoxidizing effect is not exerted and it lacks toughness. No.22 is CO
_The amount of diffusible hydrogen was high because the content of ₂ (carbonate) was as small as 2.0%, and the workability was poor and the physical property test was stopped because No. 23 had too much CO ₂ of 9.5%. No. 24 has Si of 5.
The toughness is low because the Al content is too high at 0%, the Al content is too high at 0.8%, and the Ti content of No. 26 is too high at 0.7%.

No. 27 has an excessive P of 0.018%, and No. 28 has an excessive S of 0.018%.
Both have poor toughness. No. 29 had too much Ni at 5.0%, and No. 30 had too much Mn at 3.0%. In both cases, solidification segregation occurred, and hydrogen cracking starting from that occurred.

[0047]

EFFECTS OF THE INVENTION The present invention is constituted as described above, and by controlling the composition and water content of the bond flux for submerged arc welding, particularly high strength steel such as 80 kgf / mm ² class high strength steel can be obtained. As a target, a weld metal having excellent crack resistance and toughness can be obtained. Therefore, it can contribute to high toughness of a steel structure using high-strength steel and high efficiency of welding.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing the relationship between CaF ₂ / Al ₂ O ₃ in the flux, the amount of oxygen in the 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 diagram 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 diagram 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 in a window-type restraint weld cracking test.

Claims (1)

[Claims] 1. MgO: 23 to 35% (weight%: same below) CaO: 5 to 20% CaF ₂ : 18 to 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 is contained, and the requirement of MgO + CaO + CaF ₂ = 55 to 70% 1.45 ≦ CaF ₂ / Al ₂ O ₃ ≦ 2.05. Satisfied and Si: 3% or less Al: 0.5% or less Metal Ti, Ti alloy and Ti oxide: 0.
5% or less P: 0.015% or less S: 0.015% or less Moisture content: 0.05% or less, respectively, The bond flux for submerged arc welding characterized by the above-mentioned.