JPH02207996A - Flux cored wire electrode for gas shielded arc welding - Google Patents

Abstract

PURPOSE:To provide the subject wire which is excellent particularly in sea water corrosion resistance and low-temp. toughness and above all, COD characteristic by incorporating respectively prescribed ratios of Cu, Ni, Ti, and B into either or both of a steel sheath and filling flux contg. specific components. CONSTITUTION:The steel sheath contg., by weight %, <=0.06% C, <=0.012% P, <=0.010% S, <=0.0040% N, and <=0.0150% O is prepd. The flux consisting, by the total weight of the wire, of 1 to 10% metal fluoride, 1 to 5% deoxidizing agent, and others including iron power, slag forming agent, arc stabilizer, and unavoidable impurities is filled at 8 to 25% of the total weight of the wire into the cavity enclosed by the above-mentioned steel sheath to constitute the flux-cored wire electrode mentioned above. In this case, 0.1 to 0.6% Cu, 0.2 to 2.5% Ni, 0.01 to 0.3% Ti, and 0.002 to 0.02% B, by the total weight of the wire, are incorporated as essential components into the steel sheath and/or flux. The flux cored wire electrode for gas shielded arc welding having the above-mentioned characteristics is obtd. in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a flux-cored wire for gas-shielded arc welding, which has excellent seawater corrosion resistance and low-temperature toughness, especially CO
D (Crack Opening Displace
+nent) relates to a wire with excellent characteristics.

[Conventional technology] In recent years, the development of energy resources has been moving towards polarization and deepening of the sea, and for this reason, the construction of icebreakers and offshore structures has also become more difficult.
There has been a demand for the development of steel materials and welding materials with excellent low-temperature toughness and seawater corrosion resistance.

Conventionally, the common method for preventing corrosion of steel materials and welded parts for underwater structures has been to apply sufficient coating. However, in places where drift ice exists, such as in the Arctic Ocean, scratches caused by collisions with drift ice occur on the painted surface, and corrosion occurs from these areas, so it cannot be said to be a sufficient anti-corrosion measure. Particularly if the coating is insufficient, corrosion of the entire steel material and local corrosion will occur. Countermeasures can be taken to prevent corrosion of the entire inner steel material, such as increasing the plate thickness, but local corrosion causes stress concentration. This was a major problem as it caused fatigue and other damage. In particular, welded parts are particularly prone to localized corrosion because their chemical composition and thermal history differ from those of the base metal, resulting in differences in corrosion resistance.

Furthermore, in the construction of underwater structures, emphasis has been placed on their seawater corrosion resistance, but as the range of use has recently become more polarized, it is also important to construct structures with excellent COD characteristics in terms of low-temperature toughness, especially brittle fracture. This has become a major demand point.

[Problem to be solved by the invention]

Among the flux-cored wires that have been used in the past, titania-based wires have been used because they have particularly stable arcs, less spatter, and excellent welding workability and bead appearance compared to solid wires.

For example, in JP-A-58-119490, the low-temperature toughness of titania wire is improved by controlling the amount of nitrogen in the steel sheath and iron powder, but the biggest drawback of titania is that Since the amount of oxygen is as high as 500 ppm or more, the performance of the weld metal is poor.

Also, JP-A-46-24124, JP-A-52-1254
As shown in Publication No. 37, low-temperature toughness has been improved by adjusting metal fluoride as the main component, metal carbonate, slag forming agent, and 1-strong deoxidizer; There is no wire that has the properties of both low-temperature toughness and COD properties.

On the other hand, carbon dioxide gas arc welding flux cored wire for weathering steel (JIS Z 3320) uses Cu, Ni,
The range of Cr components is shown, but these are mainly used in building materials,
Cr is used in steel materials used for bridges to improve weather resistance in the atmosphere, and is not preferable for seawater corrosion resistance because it is a component that promotes local corrosion. Further, Cu and Ni alone have not yet been able to significantly improve low-temperature toughness and COD characteristics.

In view of the current situation, it is an object of the present invention to provide a wire that can be used in the construction of marine structures and icebreakers in icy areas, etc., and can yield a weld metal having excellent seawater corrosion resistance and excellent COD characteristics.

[Means to solve the problem]

The gist of the present invention is that the steel outer skin contains C:
0.06% or less, P: 0.012% or less, S:
0.010% or less, N: 0.0040% or less,
O: 0.0150% or less Metal fluoride: 1-1o%, deoxidizer = 1-6%, based on the total weight of the wire, in a cavity surrounded by a steel jacket.

In addition, flux consisting of iron powder, slag forming agent, arc stabilizer, and unavoidable impurities is added to
In a flux-cored wire for gas-shielded arc welding that is filled with 25%, Cu:
0.1-0.6%, Ni: 0.2-2.5%, T
i: 0.01~0.3%, B: 0.002~
A flux-cored wire (hereinafter referred to as wire) for gas shielded arc welding is characterized in that it contains 0.02% as an essential component.

It has been known that it is effective to add appropriate amounts of Ti and B to the weld metal to make its microstructure finer and more uniform in order to improve the COD characteristics of the weld metal. It is also known that the addition of Cu and Cr is effective in improving the seawater corrosion resistance of steel.

Welded joints in steel structures are particularly susceptible to localized corrosion because their chemical composition and thermal history are different from those of the base metal, and if the weld metal undergoes selective corrosion before the base metal, the area Corrosion may progress rapidly depending on the ratio, leading to serious destruction. To prevent this, it is necessary to make the weld metal more electrochemically sensitive than the base metal, and the present inventors have found that the addition of Cu and Ni is particularly effective in preventing local corrosion.

The present invention has been made based on this knowledge, and will be explained in detail below along with its effects.

[For production]

In the wire according to the present invention, the components of the steel sheath are C: 0.06% or less and P: 0.01% based on the total weight of the wire.
2% or less, s: o, oio% or less, N:
It is necessary to use a steel material having an O content of 0.0040% or less and an O content of 0.0150% or less.

That is, in order to obtain a weld metal with high toughness, C in the weld metal must be
However, considering the adhesion of flux, lubricant, etc. to the wire surface, the C content of the steel shell should be 0.06% or less. Also, P, S,
N and O are unavoidable impurities, but P.

S inhibits the hot cracking resistance of weld metal, and N significantly deteriorates toughness, so P is 0.012% or less and S is 0.0%.
It is preferable that N be 10% or less, and N be 0.0040% or less. Furthermore, 0 affects droplet migration during welding, and
The deoxidizing agent lowers the yield of Si, Mn, and Ti in particular, so it should be set at 0.01 to avoid causing fluctuations in these components.
It should be less than 50%.

Furthermore, the wire of the present invention is characterized by the addition of Cu and Nl-TLB to either or both of the steel sheath and the filling flux, which greatly improves the seawater corrosion resistance of the weld metal, and which also has COD characteristics. It is at the point where it has.

In order to prevent local corrosion of welded parts, it is necessary to make the components of the weld metal more electrochemically responsible than those of the base metal, such as Cu, N,
i is a very effective ingredient.

First, C: 0.05%, P: 0.010%, S
:0.008%.

Using a mild steel outer skin material with N: 0.0025% and 0: 0.0120%, CaFt was added to the total weight of the wire.
3.0%, SiO□0.5%, MgOO, 5%,
Fe-3t (40χ5i) 1.0%, Mn2.5
%, Fe-Ti (40χTt) 0.2%, Mg
O, 5%, B (iron powder containing 2% B) 0.4%, NiO
, 3%, CuO~0.9%.

Ten types of flux-cored wires 1.2 mφ containing flux consisting of the remainder iron powder and unavoidable impurities were fabricated. Create a V-groove with a depth of 10 mm using this wire:
0.1%, Sk: 0.3%, Mr: 1.3%, C(1
: 0.4%, Ni: 0.3%, Mo: 0.2% Thickness 25
Welding current 25 OA, arc voltage 27 for IIIl steel material
v, welding heat input 15KJicys, shielding gas (
Welded under the conditions of 80χAr-20χcow) 2i/min,
A test piece with a thickness of 5 IIm was taken from 1ffII11 below the surface and subjected to a rotational immersion test in 3% saline for 3 months.

The results are shown in FIG. The horizontal axis of the figure is Cu in the wire.
The vertical axis is the corrosion loss of weld metal. Corrosion loss is the minimum thickness of the weld metal at the measurement point after the corrosion test, as shown in Figure 3! was measured, and the thickness t of test piece 1 before the test (5 mm
).

Corrosion loss of weld metal without Cu in the wire is 1.5
However, the corrosion weight loss tends to decrease by adding Cu to the wire.

In particular, those with Cu1l of 0.61% or more have a corrosion loss of 0.06% or more.
All showed good seawater corrosion resistance with 4 plates or less. Adding Cu in excess of 0.6% does not significantly improve corrosion resistance, and on the contrary causes embrittlement due to grain boundary segregation.
The amount of addition was limited to 0.1 to 0.6%. It has also been found that the same effect can be obtained by adding Cu only to the plating without adding it to the flux, and that the same effect can be obtained by adding Cu from one or both of the outer skin and filling flux.

Next, although Ni is normally added to improve toughness through solid solution effect in ferrite, it has been found that, like Cu, it is effective in improving seawater corrosion resistance of weld metal.

Figure 2 shows the same outer shell and flux as in the previous stage, but 0% Cu.
We fixed the amount of Ni at 3% and changed the amount of Ni added from O to 3.0% to make prototype wires, and conducted a rotating immersion test to determine the amount of Ni in the wire.
This study investigated the relationship between 1L and corrosion weight loss. The corrosion weight loss of a weld metal that does not contain Ni in the wire is 1.2 mm, whereas the corrosion weight loss is significantly reduced by the addition of Ni. If the amount of Ni in the wire is less than 0.2%, the improvement in seawater corrosion resistance will not be sufficient, and if it is added in excess of 2.5%, not only will no further improvement effect be obtained, but the product will be expensive. , the addition range of Ni to the wire was set to 0.2 to 2.5%. Ni includes metal Ni, Pe-Ni, Ni-M
It may be added as an alloy such as g.

Further, like Cu, Ni may be added to one or both of the outer skin and flux.

Next, the reason for adding Ti and B in addition to the wire will be explained.

Ti forms Ti oxide, refines the microstructure of the weld metal, and is effective in improving toughness, but if it is less than 0.01%, this effect cannot be expected, so the lower limit is set at 0.01%.

Moreover, if it exceeds 0.3%, toughness will be significantly impaired, so the upper limit is set at 0.3%. Ti is other than metal TiO, Fe-T
It may be added as an alloy such as i, or in the form of an oxide such as TiO□, and may be added by reduction using a sclerotic acid.

Since B is a strong deoxidizing carbide-forming element, adding it to the wire promotes crystal nucleation in the weld metal, inhibits the growth of columnar crystals, and results in finer grains. It also has the effect of increasing the hardenability of weld metal, and in order to obtain this effect, the minimum
The amount of B is required to be 2%; if it is less than that, there is no effect, and if it is too much, hot cracking tends to occur in the weld metal, so the upper limit is set to 0.02%. B sources include alloys such as Fe-B and atomized B, as well as B, 0. It can also be added in the form of an oxide, such as, and reduced by a deoxidizing agent.

Incidentally, Ti and B may also be added to one or both of the outer skin and the flux in the same manner as Cu and Ni.

In the present invention, the content of each component was determined as follows based on the above characteristics.

The metal fluoride encapsulates the weld metal as a slag agent, improves the bead shape, and levitates impurities in the molten metal to clean the weld metal and improve toughness. Examples of metal fluorides include CaFz, MgFz, BaF2゜MnF
z, 5rFt, etc. are effective, but when using an alkali metal fluoride, the stability of the arc is improved. 1%
If it is less than 10%, these characteristics will not be fully exhibited, while if it exceeds 10%, the arc will become unstable and the amount of slag produced will be excessive, deteriorating welding workability. Therefore, the metal fluoride should be in a range of 1 to IO%.

As the alkali metal fluoride, K2SiF4. N
aF.

NazSiFi, Na, AIFb, etc. are effective.

On the other hand, when CaFz, which is inexpensive, is used in combination with Ar or the like as a shielding gas, the amount of spatter generated can be reduced even with CaFz alone, so CaF alone can be used as the metal fluoride. However, when COZ gas is used as a shielding gas, it is preferable to use it in combination with an alkali metal fluoride, since the amount of spatter generated increases when using only CaFz.

St, Mn, Al, Mg, etc. are added as deoxidizers, and the amount added is 1 to 6%. If the amount of these deoxidizers added is less than 1%, deoxidation will be insufficient and the weld metal will become porous, resulting in poor X-ray performance.

On the other hand, if it is added in excess of 6%, a large amount of the deoxidizing agent remains in the weld metal, resulting in hardening of the weld metal and a decrease in toughness and cracking resistance. Therefore, in the wire of the present invention, the deoxidizing agent in the flux is in the range of 1 to 6%.

The deoxidizing agent may be added alone or in the form of an iron alloy or alloy.

In addition, iron powder is used for the purpose of increasing the welding speed, and slag forming agent is used to adjust the viscosity of the slag and also has the effect of acting as an arc stabilizer.

^1zOx, Ti0z, MnO, MgO, FeO
, Zr0z and other oxides, CaC0+, LtzCOs
, K2CO2, BaCO3, MgCo, 1゜M n
Carbonates such as COs r S r COz are effective, but carbonates are not preferred because if they are added in excess, carbon in the CO□ gas decomposed in the arc atmosphere will remain in the weld metal and deteriorate the toughness. do not have. Furthermore, oxides and carbonates of alkali metals such as K, Na, and Li are effective as arc stabilizers.

In the present invention, the filling rate of flux is set in the range of 8 to 25% based on the weight of the wire. If it is less than 8%, a sufficient amount of slag forming agent cannot be contained, and welding workability cannot be satisfied. On the other hand, if it exceeds 25%, the amount of slag becomes too large, which deteriorates welding workability and increases troubles such as wire breakage during wire manufacture, which is not preferable.

As the wire sheath, low carbon steel that falls within the composition regulation range is used, but low alloy steel that satisfies the composition regulation range can also be used.

There is no need to limit the cross-sectional shape of the wire, but if the wire has a small diameter of 2 mm or less, a relatively simple cylindrical one is recommended (
, In the case of a large diameter wire of about 2.4 to 3.2 ma+φ, a structure in which the sheath material is folded inside is suitable. Furthermore, it is also effective to perform plating treatment on the surface of seamless wires.

〔Example〕

Welding was carried out using a wire prototyped with the flux composition shown in Table 2, using an outer skin with the components shown in Table 1.
The test results are shown in Table 3.

Second. In Table 3, wire symbols Nα1-15 are examples of wires according to the present invention, and Nα16-24 are comparative examples. Both wires were finished with a diameter of 1.2111 + 1φ, and a rotating immersion test was conducted to investigate seawater corrosion resistance using the same method as described above.The same steel materials were assembled into a 50°V groove and placed vertically with an average heat input of 30 KJ/cm. Welding was carried out and the welding workability and mechanical performance of the welded part were investigated. In the COD test, a COD test piece with a fatigue/puncture mark in the center of the weld metal was prepared based on British Standard B55762-1979, and the COD test was conducted at -50°C. In addition, the shielding gas is 80%Ar -20χCO□
A mixed gas of

The test results were evaluated as good if the COD value was 0.3 mm or more and the corrosion HM was 0.4 mm or less.

As is clear from the test results shown in Table 3, the wires No. 1 to Nα15 of the present invention all have transition temperatures of -70°C or less, and also have a COD value of 0.7°C.
It was confirmed that good performance was obtained because the corrosion loss was also 0.3 mm or less.

On the other hand, the comparative example Nα16.1? , 19.21.24
are Cu, Ni, Ti, which are essential components of the present invention.
Any component of B is out of range, corrosion resistance and CO
D performance cannot be satisfied. Also, Nα20.23
No.2 has good corrosion resistance and COD value, but No.2
0 has a low flux filling rate, resulting in poor welding workability, and 23 has too much metal fluoride, making the metal easy to sag.
Welding workability is poor. Further, in Nα18.22, the outer skin component was outside the scope of the present invention, and although the corrosion resistance was good, no improvement in low temperature toughness and COD value was observed.

Table 1 Returned WO indicates good quality, and × indicates poor quality.

Amount of Cu in Cui X C1) 〔Effect of the invention〕 As explained above, the wire of the present invention has good low temperature toughness.

In particular, it is a wire with extremely excellent COD characteristics and markedly improved seawater corrosion resistance. This is something that cannot be achieved with conventional flux-cored wire for gas-shielded arc welding, and it is particularly effective in the construction of offshore structures and icebreakers in icy areas such as the Arctic Trench.
This will greatly contribute to the development of these industries.

[Brief explanation of the drawing]

Figures 1 and 2 are drawings showing the relationship between the amount of Cu and Ni contained in the wire and the corrosion weight loss in the seawater corrosion resistance test;
FIG. 3 is a side view showing the procedure for measuring corrosion loss in a seawater corrosion resistance test. ■...Test piece representative for corrosion weight loss Patent attorney Masamitsu Akizawa and one other person, 7i2 surface π3 diagram β [''°1 constant @ (5 (maximum thickness of buoyancy) L' test yJ
With the thickness of moxibustion, the customer 0 → 17 Sakae in one beat (p2. On the run, I'l 1j (c> Gunri Doene 3°) 1
Relationship with the case of the person who made the 4B11 amendments to Kokanyo. Address (residence): 2-6-3 Otemachi, Chiyoda-ku, Tokyo.

Claims (1)

[Claims] The component of the steel outer skin is C: 0.06% (weight %: the same below)
Below, P: 0.012% or less, S: 0.010% or less,
N: 0.0040% or less, 0: 0.0150% or less Metal fluoride: 1 to 10%, Deoxidizer: 1 to 6 based on the total weight of the wire %, other iron powder, slag forming agent, arc stabilizer, and unavoidable impurities in a flux-cored wire for gas-shielded arc welding that is filled with 8 to 25% of the total weight of the wire. In one or both fluxes, Cu: 0.1-0.6% Ni: 0.2-2.5% Ti: 0.01-0.3% B: 0.002-0 A flux-cored wire for gas shielded arc welding, characterized in that it contains .02% as an essential component.