JPS6376793A - Bonded flux for three o'clock submerged arc welding - Google Patents

Abstract

PURPOSE:To obtain excellent welding toughness, to prevent pock marks on a bead surface and to improve slag removability by using a specific flux in the case of welding to build a petroleum tank, LPG tank, etc. CONSTITUTION:The respective component ranges of the flux are specified to 2.5-12.5% metal fluoride in terms of F by weight, 0.3-3.0% metal carbonate in terms of CO2, 25-50% Al2O3, 20-40% MgO, where particles larger than 500mum grain size occupy 30-80%, particles smaller than 210mum<=20%, and the bulk density is 0.8-1.3g/cm<3>; furthermore, the value P expressed by the formula is P<=0. (Where, CO2 content: CO2 equiv.% in the flux, F content: F equiv.% in the flux, MgO content: MgO equiv. content in the flux). As a result, the generation of the pock marks on the bead surface is prevented and the excellent slag removability, bead shape and low-temp. toughness are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to pound blacks used for submerged arc welding, and more specifically, for use in horizontal submerged arc welding used in the construction of crude oil tanks, LPG tanks, etc. , relates to a bond flux that can provide excellent toughness and good welding workability.

(Prior Art) In recent years, crude oil tanks, LPG tanks, or LNG tanks have been constructed in various places, and horizontal submerged arc welding of 50 to 60 grade high-strength steel or low-temperature At-killed steel is frequently performed. In addition, in tanks used at low temperatures, such as LPG tanks, strict low-temperature toughness is required for welded parts.

Therefore, bond flux is mainly used for such horizontal welding because it can be easily designed to have high basicity and can easily provide high toughness.

In addition, in such horizontal welding, it is required that the welded part not only have sufficient low-temperature toughness but also bead shape, pot mark resistance, and workability such as slag removability.

That is, lateral welding is welding in a special position in which both ends of the molten pool are located upward, which makes the bead shape more likely to become unstable (and more likely to cause defects).

Particularly in the case of bond flux, the occurrence of pock marks on the bead surface and deterioration of slag removability due to non-uniformity of the bead are major problems.

First, pockmarks are likely to occur on the bead surface. In normal downward welding, the molten slag and molten metal generated in the molten pool solidify from both ends toward the center, but in horizontal welding, , solidification occurs from the top and bottom toward the center.

That is, of the butted base materials to be welded, the molten slag generated on the upper plate side first solidifies from the boundary of the upper plate side base metal, and then solidifies downward.

On the other hand, the gas components in the arc cavity or the gas components generated from the molten pool try to escape upwards, but at this time, because the slag on the upper plate side has solidified, they cannot escape to the outside, and the gas components emit into the metal. It remains at the interface between the gas and the slag and creates pock marks as gas impressions on the bead surface.

Furthermore, the weld metal is also likely to shift in the vertical direction due to fluctuations in the position of the wire tip within the groove, resulting in undercuts, poor bead shapes, poor fusion, and the like. Therefore, the solidified slag also gets stuck in the defective bead shape, making it difficult to peel it off.

In order to solve these problems, for example,
Publication No. 9439 and! Publication No. 55-14166 discloses Ti0z, CaFt, A12os, MgO, Si
Non-melting fluxes have been proposed in which o2, B2O3, CaCOx, etc. are regulated.

These fluxes have excellent welding workability, good Charpy impact values at low temperatures, and COD values (CRACK O
This is the bond flux obtained.

Among these, the bond flux disclosed in Japanese Patent Application Laid-open No. 55-14166 has a large amount of CaF of ■5in2.
It is stated that pock marks are likely to occur when G) SiO2 coexists and ■Co2 amount exceeds 7%.
The amount of O2 is limited to 7% or less.

However, even with these fluxes, the addition balance of gas-generating components and other components must be taken into account (it is not possible to prevent the occurrence of pockmarks), and the slag removability is not sufficient (and welding workability is has significantly deteriorated.

(Problems to be Solved by the Invention) The present invention provides excellent weld metal toughness, prevents pock marks on the bead surface that occur during horizontal welding, and improves slag removability regardless of the bead shape. The purpose is to

(Means for Solving the Problems) The gist of the present invention is that, in a bond flux for horizontal submerged arc welding, metal fluoride is 2.5 to 12.5% by weight in terms of F content based on the entire flux. , metal carbonate group is 0.3 to 30% in terms of C0zt, A2*O
s is 25-50%, 'h1go is 20-35%, and particles with a particle size larger than 500 μm are 30-80%.
%, particles with a particle size smaller than 210 μm account for 20% or less, and the bulk density is 0.8 to 1.35'/m3,
Furthermore, the bond flux for horizontal submerged arc bath welding is characterized in that the value P expressed by the following formula satisfies P≦O.

P = 15. I X (C0Jt)+2.7 X C
F amount) -6,5X (MgO amount) + 115CO2 amount;
CO2 equivalent amount (%) in flux F amount; F equivalent amount (%) in flux MgOi; MgO in flux
Equivalent amount (%) (effect) The present invention will be described in detail below.

The range of each component in the flux of the present invention is specified as follows.

First, fluoride addition is extremely important for transverse welding fluxes. In other words, fluoride is gasified by arc heat in the arc cavity and strengthens the shielding effect of the molten metal, so it contributes to reducing the amount of oxygen and nitrogen in the weld metal, which is extremely advantageous in improving the toughness of the weld metal. .

Furthermore, the fluoride gas is porous and brittle, making it effective in improving slag removability.

Such effects can be obtained when the amount of F in the flux is 2.5% or more.

On the other hand, fluoride is a component that lowers viscosity, and if the amount equivalent to F is added in excess of 12.5%, the fluidity of the generated slag will become excessive, resulting in irregular beads. Undercuts tend to occur on the plate side, and overlaps tend to occur on the lower plate side.

For these reasons, the appropriate range of the amount of fluoride added needs to be 2.5 to 12.5% as F equivalent.

The metal fluorides used in the flux of the present invention are CaF, B
Raw materials such as aF, NaF, AtF3, MgF, etc. are commonly used in the production of bond flux.

Next, CO□ is a necessary component to reduce the amount of diffusible hydrogen in the weld metal. Especially in multi-layer welding where the welding heat input is small, such as horizontal submerged arc welding, the amount of diffusible hydrogen accumulates and hydrogen cracking tends to occur, so it is necessary to add Cot to prevent this. In order to obtain such an effect, it is necessary that the amount of CO2 equivalent in the flux is 0.3% or more.

However, if the amount equivalent to Cot is added in excess of 3.0%,
The size of the arc cavity becomes unstable, and the arc becomes unstable and the arc becomes irregular. For these reasons, the appropriate range of the amount of metal carbonate added is 0.3 to 3
．． It is 0%.

The metal carbonate used in the flux of the present invention is CaC01
, BaC01, MgCOx 1MnCOx, etc. These are the raw materials normally used in the production of bond blacks.

Next, A40. is a necessary component to improve slag removability. That is, addition of a large amount of A/-t Os tends to reduce the amount of slag produced by welding and to make the molten slag glassy.

First, if the amount of slag is small, after welding, there is a tendency for voids to form between the weld metal, the groove and the solidified slag, which will cause the bead to become uneven due to fluctuations in the position of the wire tip within the groove. However, excellent slag removability can be obtained.

Furthermore, since molten slag tends to be glassy, it is more brittle and crumbly than crystalline slag (and the synergistic effect with the porous slag effect caused by fluoride described above makes it possible to create slag that is extremely easy to peel). You can get it.

Such an effect of A40g can be obtained by adding 25% or more, but on the other hand, if the amount exceeds 50%, the viscosity of the produced slag becomes too high (too much, the bead shape becomes triangular bead-like, and furthermore, the bead surface becomes Protruding defects occur, resulting in deterioration of the bead appearance.Furthermore, a large amount of A40s
The addition of slag causes minute slag inclusions in the weld metal. For these reasons, the appropriate range of the amount of Att Ox added is 25 to 50%.

A403 used in the flux of the present invention is a raw material used in the production of ordinary bonded fluxes, such as alumina of AAtOs alone, or compounds such as chamotte and spinel.

Next, MgO is an extremely important component for preventing the formation of pock marks on the bead surface. In other words, higo increases the fire resistance of the flux and reduces the thickness of the molten slag during welding.

When the molten slag is thick, gas generated from flux, etc. is difficult to escape to the outside, and remains at the interface between the metal and slag, resulting in pock marks as gas impressions on the bead surface.
O reduces the thickness of the molten slag, making it easier for gas to escape to the outside (and is effective in preventing pockmarks from occurring).

Furthermore, MgO is effective in increasing the basicity of the flux, suppressing an increase in the amount of oxygen in the weld metal, and obtaining good low-temperature toughness. Furthermore, it is effective in increasing the fire resistance of the flux, preventing drooping of the weld bead, and obtaining a good bead shape. Such an effect of MgO is underestimated when it is added in an amount of 20% or more.

However, if it is added in an amount exceeding 40%, the refractoriness becomes too high, protruding defects occur on the bead surface, and the bead shape becomes poor. For these reasons, the appropriate range of the amount of MgO added is 20 to 40%.

MgO used in the flux of the present invention is a raw material used in the production of ordinary bond fluxes such as magnesia clinker and spinel.

Even if the composition of the flux is defined as described above, good welding workability cannot be obtained unless the physical properties of the flux are further optimized.

First, it is necessary to maintain appropriate air permeability by optimizing the particle size structure of the flux. For this purpose, the particle diameter of the flux must be 30 μm or more.
~80% and particles smaller than 210 μm are 2
It needs to be 0% or less.

In other words, 30% of particles have a particle size larger than 500 μm.
If it is less than that, proper air permeability cannot be maintained. For this reason, gas generated from flux etc. is difficult to pass through the flux, difficult to escape to the outside, and remains at the interface between the metal and slag, resulting in pock marks as gas impressions on the bead surface.

On the other hand, if the particle size of the flux exceeds 80%, the fire resistance of the flux will be excessive, and the flux will not melt smoothly during welding, resulting in irregular beads, and furthermore, the arc cavity will fluctuate. As a result, an undercut occurs at the boundary between the base metal and the weld bead.

Furthermore, even if the proportion of particles larger than 500 μm is in the appropriate range of 30 to 80%, if the proportion of particles smaller than 210 μm exceeds 20%, the air permeability becomes poor and pock marks occur.

Furthermore, even in the flux having the above particle size structure, it is necessary to set the bulk density to 0.8 to 1.3 S'101n". In other words, the bulk density is set to make the air permeability of the flux appropriate, as well as to have a good This is important for obtaining the bead shape.

If the bulk density is less than 0.89/UJk3, the bead cannot be held down by the flux (this results in a sagging bead and deterioration of the bead shape. Also, in repeated use,
It powderizes easily, impairs breathability, and causes pock marks.

On the other hand, when the bulk density exceeds 1.3910 rb3, the bead is pressed down too strongly by the flux, resulting in a slightly triangular bead, and the bead becomes disordered and the bead shape deteriorates. Moreover, the air permeability is further deteriorated and pock marks occur. For these reasons, in the particle size composition of the flux, particles with a particle size larger than 500 μm account for 30 to 50%.
The particles smaller than 210 μm account for 20% or less, and the bulk density is 0.8 to 1.32/3.

The particle size structure and bulk density are adjusted by adjusting the ladder type, amount, etc. of the fixing agent used when granulating the flux, or by a granulation method such as Henschel granulation or dish granulation, or by granulation conditions.

Next, pockmarks are gas impressions caused by some gas remaining at the interface between molten slag and molten metal.
This gas source is generally CO or CO2, F, H2O from the oxidation of C in the steel.

Among these, it should be considered that the amount of HzO in the flux does not differ much in a flux fired at a high temperature such as 530° C. unless the flux absorbs moisture.

Therefore, in the flux of the present invention, the gas source that causes pockmarks is the CO added to the flux.
The main factors are z and F, and their quantities are the problem. That is, C
Not just either ot or F (but the total amount of both increases the susceptibility to pock mark generation.

Further, Cow and F do not have equal influence on the occurrence of pockmarks, and the component that prevents pockmarks is <NfgO as described above. Therefore, in order to prevent the occurrence of pockmarks, it is necessary to
It is important to properly control the ingredients.

Therefore, the number of pockmarks generated per unit length (pieces/m) P
was determined as a function of the amount of CO2, F, and MgO in the flux by multiple regression analysis from the results of experiments conducted with various flux compositions.

That is, P is as shown in the formula below.

p = 15.1 x (Co, amount) + 2.7X (F amount)
-6,5x (MgO amount) + 115CO2 amount: CO2 equivalent amount in flux (%) F amount: F in flux
Equivalent amount (%) MgO amount: Equivalent amount of MgO in flux (
%) In other words, the amount of CO1 for the occurrence of pockmarks,
The coefficients of F amount are +15.1 and +2.7, respectively, and CO
3 indicates that compared to F, pock marks tend to occur 15.1/'2.7 times more easily.

On the other hand, the coefficient of MgO is -6.5, indicating a tendency to reduce pockmarks. That is, it has been shown that pock marks do not occur when P=0, and it has been found that the flux can be designed so that P is 0 or less by adjusting the amounts of co, t, F, and MgO.

In addition to the above-mentioned compositions, Tie, ZrO, etc., which are usually used as flux raw materials depending on the purpose, may also be used.
5ins, metal oxides such as B2O3, Fe-8i,
Fe-At.

Deoxidizing metal powder such as Si, Dog, At, 1Vfn, Ti
, Mo, Ni, etc. can be appropriately selected and added.

The present invention has been described in detail above, and examples will be described below to clarify the effects of the present invention.

(Example) First, a 21λ1 type bond flux of Fl-F21 as shown in Table 1 was prepared. That is, the raw material powder as shown in the flux raw material composition column was granulated using water glass (sodium silicate + potassium silicate) as a fixing agent, and then fired under conditions for 530LXSO to obtain a flux with a particle size of 12Xl 00 mesh.

The content of specific components in the finished flux is shown in the specific component column of Table 1, and the specific value is shown in the specific value column of Table 1.

Among the fluxes in Table 1, Fl-FIO is an example of the present invention, and Fil-F21 is a comparative example for clarifying the effects of the present invention.

First, butt welding was performed using 21 types of horizontal submerged arc welding using each of the fluxes listed in the table.

The test steel plates and test wires (Mn-based steel wires) in this case are shown in Tables 2 and 3, respectively, and the welding conditions are shown in Table 4, FIG. 1, FIG. 2, and FIG. 3.

In FIGS. 1, 2, and 3, l represents the material to be welded. In FIG. 2, 2 is a wire and 3 is a chip.

Moreover, FIG. 3 is a schematic diagram showing the lamination method, and in the figure
is a symbol indicating the order of welding passes.

The welding results are shown in Table 5.

Regarding slag removability, 1st to 3rd pass beads (A) to
The ease of peeling of (c) was investigated. In addition, the bead shape, surface condition of the bead, and presence or absence of pockmarks were examined for the 7th pass bead (G). As for the surface condition, the roughness of coagulation waves was mainly investigated.

In addition, for the impact test, V-notch Charpy test piece 4 (JIS Z31124) was taken from the position shown in Figure 4.
Tests were conducted at 0°C. In addition, in FIG. 4, the distance d from the surface of the material to be welded 10 to the center of the test piece is 7 mm.

Firstly, each flux was subjected to a diffusible hydrogen test using gas chromatography (■S 1003).

The wire used was a 2.0% Mn wire of 4.0φ, and the steel plate was 5lvl-50B. The measurement results after 72 hours are shown in Table 5.

Examples of the present invention, Ya1 to AIO, are due to the effects of the present invention.

Satisfactory results were obtained in all cases, but Comparative Example A1
No. 1-421 had some problems and was not satisfactory.

That is, A11. Ya 13, Bian 15, Ya 16. In both cases, the P value was thicker than O, and pockmarks occurred in both cases. In addition, 413 lacked MgO, A 1 9 had a particle size structure outside of the appropriate range, and A 20 and Ni 21 had bulk densities outside of the appropriate range, causing pock marks.

In addition, Mu12 had an insufficient amount of F, A14 had an insufficient amount of A j4 Oa, and Mu 17 had an insufficient amount of CO□, which resulted in deterioration of the impact value, deterioration of slag removability, and increase in the amount of diffusible hydrogen, respectively. or,
A14 had an excessive amount of MgO, No. 15 had an excessive amount of A 4 Os, and No. 11 had an excessive amount of CO2, resulting in deterioration of the bead shape and the condition of the bead surface.

In addition, 418 had a particle size structure outside of the appropriate range, so it was
In samples No. 0 and No. 21, the bulk density was out of the appropriate range, so the bead shape and surface condition of the bead were deteriorated.

Table 2 Table 3 Table 4 Table 4 (Effects of the Invention) As stated above, the flux of the present invention can prevent the occurrence of pock marks on the bead surface during horizontal submerged arc welding at °C, and has excellent It is possible to obtain good slag removability, bead shape, and low-temperature toughness, and also to reduce the amount of diffusible hydrogen in the weld metal.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view for explaining the groove shape used in the example, Fig. 2 is a cross-sectional view for explaining the wire aiming used in the example, and Fig. 3 is a cross-sectional view for explaining the welding performed in the example. FIG. 4 is a cross-sectional view for explaining the lamination procedure, and FIG. 4 is a cross-sectional view for explaining the sampling position of the test piece in the impact test conducted in the example.

Claims (1)

[Claims] In the bond flux for horizontal submerged arc welding, metal fluorides are 2.5 to 12.5% by weight of the entire flux, converted to F amount, and metal carbonates are CO_2.
In terms of amount, 0.3 to 3.0%, Al_2O_3 is 2
5-50%, MgO is 20-40%, and 50%
30-80% particles with a particle size larger than 0μm, 210μm
Particles having a particle diameter smaller than m account for 20% or less, have a bulk density of 0.8 to 1.3 g/cm^3, and are further characterized in that the value P expressed by the following formula satisfies P≦O. Bond flux for horizontal submerged arc welding. P=15.1×(CO_2 amount)+2.7×(F amount)-6
．． 5 x (MgO amount) + 115CO_2 amount; CO_2 equivalent amount in flux (%) F amount; F equivalent amount in flux (%) MgO amount; MgO equivalent amount in flux (%)