JPH059197B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a fusion type flux for submerged arc welding, and more specifically for use in mild steel, 50 to 60 kg/mm class ² high tensile strength steel used in construction of buildings, bridges, ships, etc. Mainly used for fillet and butt welding,
The present invention provides a melting type flux for submerged arc welding that has excellent slag removability, bead shape, and appearance, has a low amount of diffusible hydrogen, and has high toughness. (Prior Art) Generally, for fillet welding in architecture, bridges, and shipbuilding, the submerged arc welding method is used because it provides a good bead shape and appearance and is highly efficient. Submerged arc fluxes are classified into molten type and fired type, and fused type flux is less likely to absorb moisture than fired type.
It is suitable for fillet welding where it is important to obtain a good bead appearance without surface defects such as pits and pockmarks because there is little segregation of flux components and the appearance of the weld bead is excellent. Among the melting type fluxes, the
The fluxes whose main components are SiO ₂ and MnO shown in Japanese Patent Publication No. 55-42671 have good slag removability and bead shape, which are important in downward fillet welding with small heat input. Under relatively large heat input or long leg welding conditions, it was inevitable that slag would be baked onto the bead surface and that the bead shape would be poor in uniformity and undercuts would easily occur. Furthermore, the flux composition of the SiO ₂ --MnO system is an acid system, and it is essentially difficult to obtain high toughness of the weld metal. In addition, it has been developed as a flux containing a large amount of CaO and CaF, and has excellent toughness and hydrogen cracking resistance.
-81445, etc., but because it contains a large amount of CaO and CaF _two components, the slag removability was not satisfactory. On the other hand, in order to improve the slag removability, it was proposed in JP-A-55-10356 to contain about 20% _TiO2 component.
This method was proposed in Japanese Patent Application Laid-Open No. 14496/1983.
However, when a large amount of TiO ₂ is contained, the slag density increases, and in downward fillet welding, the bead shape becomes a so-called medium-high bead in which only the center part is high, and it cannot be applied to fillet welding, where shape and appearance are important. Normally, in architecture, bridges, or shipbuilding, fillet joint welding and butt joint welding are included in one structure, and welding of joints with mild steel or 60 kg class high-strength steel is also performed, with emphasis on welding workability. Depending on the purpose, different fluxes are used in welded parts of the same structure, depending on the purpose. In other words, SiO ₂ -MnO flux cannot be used in welded parts that require high toughness.
It is necessary to use a neutral or basic flux, and its use is unavoidable despite the fact that it has poor slag removability, poor bead shape, and poor appearance. Poor slag removability requires a process to remove slag adhering to the bead surface, and repairs to defects such as pits and cracks require additional welding, which reduces work efficiency. (Purpose of the Invention) The present invention is suitable for neutral or basic welding, which can provide high toughness of the welded part, but which has the problem of pitting, blowholes, and weld cracking due to the bead shape and high amount of diffusible hydrogen in fillet welding. Good slag removability in downward fillet welding with low flux and relatively low heat input, smooth concave bead shape, and low amount of diffusible hydrogen, so welding defects caused by hydrogen do not occur and the welding is good. To provide an unprecedented fusion type flux for submerged arc welding that has only the advantages of acid flux, which provides a bead appearance but does not have high toughness, and also has no deterioration in welding workability even in high heat input welding. With the goal. (Technical Background of the Invention) When viewed from the viewpoint of flux composition, in the conventional technology, welding workability and toughness can be said to be contradictory performances. Therefore, in trying to obtain a flux that satisfies both performances, we first considered that a certain amount of basic components are essential to ensure high toughness, and investigated the effects of each basic component to be included on welding workability. Ta. We also considered that stabilizing the arc is one of the conditions for obtaining good welding workability. In other words, by maintaining an unbroken arc state, the waves on the bead surface become finer, which in turn weakens the slag entanglement on the bead surface, which can be expected to improve slag removal properties and prevent the formation of pot marks and pits. Of course, it can be considered to be effective. From these points of view, various experiments were conducted to achieve this objective. An experimental example is shown below. As shown in Table 1, the welding workability of various prototype fluxes was determined by the size 4.8φ (symbol W2) of 2% Mn-containing wire specified in JIS Z3311 Type 4.
A 16 mm thick plate (symbol S1) of 50 kg class high-strength steel specified in Type 2 of JIS G3106 was welded at a welding current of 900 A and an arc voltage as shown in Table 2.
The investigation was conducted by performing downward fillet welding under the welding conditions of 37V and welding speed of 35cm/min. For evaluation of toughness, the same type of wire and steel plate as those used for downward fillet welding with a size of 4.0φ (symbol W1) and a plate thickness of 25 mm (symbol S2) were used, and welding was performed as shown in Table 2. The impact value of weld metal welded in multiple layers under welding conditions of 550 A current, 30 V arc voltage, and 40 cm/min welding speed was investigated. The test piece was a No. 4 Shapey test piece specified in JIS Z3112, and the notch was located at the center of the weld metal. The amount of diffusible hydrogen depends on the welding current as shown in Table 2.
Measurement was carried out under the welding conditions of 500 A, arc voltage 33 V, and welding speed 30 cm/min using the glycerin substitution method according to the method for measuring the amount of hydrogen in submerged arc welds specified in JIS Z3116.

【table】

[Table] First, we investigated the necessity of basic components CaO, MgO, and BaO, and the influence of alkali metal compounds by prototyping a molten flux (particle size: 20×D mesh) with the composition shown in Table 3, and testing its performance. investigated. Flux A1 in the table was used as the basic flux in this experiment on the premise that good toughness could be obtained, and its composition contains a large amount of CaO, which is widely used as a basic component and is an inexpensive raw material. , commercially available 60 with low _SiO2 and also a small amount of _TiO2
Kg/mm Close to flux for grade ² steel.

[Table] The values of each component of flux are expressed as numerical values obtained by converting the quantitative values of each element as chemically stable oxides. Regarding F, in the case of molten flux, it is quantified only as F, regardless of the components of the F source such as CaF ₂ , MgF ₂ , AlF _{3 ,} etc., so it is not expressed as CaF ₂ as is conventionally done. The results are shown in Table 4. CaO was reduced based on the components of flux A1, and the equivalent amount was
Slag removability was improved by substituting MgO or BaO. However, the Shapey impact value deteriorates, and in order to obtain the same toughness as the basic flux, SiO ₂ and
It is necessary to further replace part of MnO etc. with MgO or BaO. However, the bead appearance deteriorated and
Occurrence of pockmarks was also observed, and the amount of diffusible hydrogen also increased. On the other hand, by reducing CaO and adding an alkali metal compound like Flux A10, compared to Flux A3, which inevitably contains a very small amount of alkali metal from the flux raw material used, it has improved slag removability, bead appearance, and sharpie impact. It was found that the value was greatly improved and it is a very beneficial ingredient.

[Table] Table 5 shows that F, which is necessary to ensure good toughness but is known to have a negative effect on slag removability and bead shape, showed good performance when added in the previous experiment. In addition, the relationship with alkali metal compounds was investigated.

【table】

[Table] The results are shown in Table 6, and it was found that the relationship between the alkali metal compound and F is extremely important.

[Table] In other words, alkali metal compounds are flux
As with B2 and B4, the effect was hardly seen when the F amount was less than 10%. Also, flux
When the F content was as high as 50% as in B8, the welding arc length became too long and the bead shape became medium to high, similar to flux B4. However, even if the alkali metal content is about 30% of the F content, flux B1
When the amount of F is 1.2%, the amount of diffusible hydrogen is high, as shown in
The impact value is also low, like Flux B9.
It was found that with an amount of 7.0%, a good concave bead could not be formed in the lower fillet, and that there was a limit to the amount of F. Note that the alkali metals K, Na and Li are oxides,
It can be obtained from carbonates or fluorides, and according to the results of separate experiments, K, Na, and Li showed equivalent welding performance. Furthermore, as a result of a separate experiment, SiO ₂ was 35%
Below this level, the slag has low viscosity and high fluidity, making it impossible to obtain a good concave bead in fillet welding. In addition, if the SiO ₂ /MnO ratio is large, the oxygen content of the weld metal becomes high and high toughness cannot be obtained, and even if it is too small, the bead shape is _difficult to become _concave . MnO
It was discovered that there is an appropriate range of ratios. As described above, by replacing CaO with MgO or BaO, adding an alkali metal compound in relation to F, and limiting SiO ₂ , MnO, etc., welding workability such as slag removability and bead shape can be improved. Although we obtained a molten flux that has excellent properties, high toughness, and low hydrogenation, even more excellent slag removal can be achieved by adding an appropriate amount of one or both of PbO and Bi ₂ O ₃ , which are low melting point metal compounds. I was able to get sex. (Structure of the Invention) The present invention is based on the above knowledge, and its most important feature is that the basicity of the flux is neutral, which is so important that it can be said to be essential as a basic component in order to obtain good slag removability. The content of hot CaO is limited to as low as possible. Contains a large amount of MgO or BaO as an ingredient to obtain high toughness instead of CaO. Alkali metal compounds, which are arc stabilizing components and are extremely beneficial for improving slag removability and toughness, are unfavorable for obtaining good slag removability and bead shape, but they reduce the amount of oxygen in the molten metal and reduce diffusion. In order to obtain the desired amount of hydrogen, the effective content ratio of F should be specified. The synergistic effect of these components within a very limited range has resulted in a flux with excellent welding workability and toughness. That is, the gist of the present invention is that in weight %,
_SiO2 : 35%~45%, CaO: 10% or less, F: 1.5~
6%, _Al2O3 : 4-15%, _{TiO2 :} 1-8%,
Total of one or two types of MgO and BaO: 10 to 25
% (total of one or more of K ₂ O, Na ₂ O and Li ₂ O)/F ratio 0.1 to 0.4, SiO ₂ +
A melt-type flux for submerged arc welding characterized by having MnO: 55-70% and SiO ₂ /MnO ratio: 1.4-1.9. And, in order to obtain even better slag removability, there is provided a melt-type flux for submerged arc welding, which further contains 0.005 to 0.2% of one or both of PbO or Bi ₂ O ₃ in total. The components, component amounts, and reasons for limiting the component quantification of the present invention will be explained below. SiO ₂ : 35-45% SiO ₂ is a basic component of flux,
In order to maintain appropriate slag viscosity and fluidity necessary for good bead formation, it is necessary to contain more than 35%. If it is less than 35%, the slag has low viscosity and high fluidity, making it impossible to obtain a good concave bead in fillet welding, and especially under long leg welding conditions, a medium-height bead will result. Also, 45%
If it exceeds 100%, the amount of other essential components to be added will be restricted, making it impossible to obtain the desired flux characteristics. CaO: 10% or less CaO is a strong basic component, and in conventional fluxes it is contained in a large amount in order to obtain high toughness, but in the present invention it must be kept as low as possible, to 10% or less. If it exceeds 10%, slag will firmly adhere to the weld bead surface and removal of the slag will become extremely difficult. F: 1.5 to 6% F is added from metal fluorides such as calcium fluoride, aluminum fluoride, magnesium fluoride, and lead fluoride, and is necessary to reduce the amount of oxygen in the weld metal and obtain high toughness. be. The F content is
If it is less than 1.5%, this effect will be small and the amount of diffusible hydrogen will also increase, making pits, blowholes, and weld cracks more likely to occur. Moreover, when it exceeds 6%, slag viscosity decreases, arc becomes unstable, bead forming ability deteriorates, and slag removability deteriorates like CaO. Al ₂ O ₃ : 4 to 15% Al ₂ O ₃ increases the slag viscosity like the SiO ₂ component without significantly increasing the oxygen content of the weld metal if it is 4% or more, creating a glossy and good fillet bead. Contribute to formation. However, if it exceeds 15%, the slag viscosity becomes too high and pockmarks occur. TiO ₂ : 1-8% TiO ₂ has the effect of improving the toughness by refining the grains of the weld metal, but if it is less than 1%, the effect is not clear, and if it exceeds 8%, the slag removability deteriorates, The fillet bead shape is also difficult to form a good concave shape. Total of one or two types of MgO and BaO: 10~
25% MgO and BaO are strongly basic components CaO
This is a necessary component to maintain appropriate basicity and ensure high toughness without containing MgO and BaO
It has been confirmed through experiments that CaO has almost equivalent performance in terms of flux physical properties and weldability, and if the total amount is less than 10% when used alone or in combination, no effect on improving toughness as a component replacing CaO is observed. %, the slag viscosity increases, which tends to cause pockmarks, and the amount of diffusible hydrogen increases, causing pits, blowholes, and weld cracks. (One type or the sum of two or more of K ₂ O, Na ₂ O and Li ₂ O)/F ratio: 0.1 to 0.4 The alkali metal compound is included as an arc stabilizing component and improves slag removability, bead shape and appearance. In addition to being extremely effective in improving the welding properties, it also functions as a basic component, and by containing it as a substitute for the MgO and BaO components, which cannot be included in large amounts because of the deterioration of welding workability, it improves toughness. This appropriate content is defined in relation to F, which is an arc destabilizing component. If the alkali metal compound is less than 10% of the F content, arc stabilization and toughness improvement cannot be obtained, and if the F content is 40%
If it exceeds this value, welding workability deteriorates, and it becomes difficult to obtain a concave shape, especially in fillet welding. Therefore, (one or two of K ₂ O, Na ₂ O and Li ₂ O)
It is necessary to set the ratio (total of species or more)/F to 0.1 to 0.4. SiO ₂ +MnO: 55-70% If it is less than 55%, the appropriate slag viscosity necessary for bead formation cannot be obtained, and if it exceeds 70%, the same is true, and high toughness cannot be obtained. SiO ₂ /MnO ratio: 1.4 to 1.9 As the SiO ₂ /MnO ratio increases, the amount of oxygen in the weld metal increases, and if it exceeds 1.9, high toughness cannot be obtained.
Furthermore, as the ratio becomes smaller, the slag viscosity decreases and the bead shape deteriorates. In particular, when it is less than 1.4, the amount of diffusible hydrogen increases and pits and blowholes occur. Therefore, it is necessary to set the SiO ₂ /MnO ratio in the range of 1.4 to 1.9 in order to obtain good toughness and welding workability. Total of one or both of PbO or Bi ₂ O ₃ : 0.005
~0.2% is necessary to obtain even better slag removability, but if the content of the low melting point metal in the form of oxide exceeds 0.2%, the toughness will deteriorate significantly and the purpose of the present invention cannot be achieved. Furthermore, if the content is less than 0.005%, there is almost no effect on slag removability. Note that PbO and Bi ₂ O ₃ showed similar effects on improving slag removability and on the tendency to deteriorate toughness. Therefore, it is necessary that at least one of PbO and Bi ₂ O ₃ be in the range of 0.005 to 0.2%. (Example) Next, the effects of the present invention will be described with reference to Examples. Melting flux with the composition shown in Table 7 (particle size:
A 20×D mesh was manufactured and the same test as in the previous experimental example was conducted. As shown in Table 1, welding workability is determined by the size 4.8φ (symbol W2) of 2% Mn-containing wire specified in JIS Z3311 type 4 and JIS Z3106 type 2.
A plate of 16 mm thick (symbol S1) of 50 kg class high tensile strength steel specified in the specifications was welded with a black crust on its surface, at a welding current of 900 A, an arc voltage of 31 V, and a welding speed of 35 as shown in Table 2.
The investigation was conducted by performing downward fillet welding under welding conditions of cm/min. The amount of diffusible hydrogen depends on the welding current as shown in Table 2.
Measurement was carried out under the welding conditions of 500 A, arc voltage 33 V, and welding speed 30 cm/min using the glycerin substitution method according to the method for measuring the amount of hydrogen in submerged arc welds specified in JIS Z3116. For the evaluation of toughness, we used the same type of wire and steel plate as those used for downward fillet welding, with a size of 4.0φ (symbol W1) and a plate thickness of 25 mm (symbol S2), as shown in Table 2. Welding current 550A, arc voltage 30V,
The impact value of weld metal welded in multiple layers at a welding speed of 40 cm/min was investigated. The test piece is JIS Z3112
A No. 4 Shapey test piece was used as specified in the following, and the notch position was at the center of the weld metal. The results of these tests are shown in Table 8, and each comparative flux has its own drawbacks. In other words, flux D1 has very poor toughness because its main components are SiO ₂ and MnO and almost no MgO and BaO. Flux D2 is SiO ₂ ,
Although it satisfies the constituent requirements of the present invention, such as MnO, CaO, and MgO, it is inferior to the present flux in terms of slag removability, bead appearance, and toughness because the alkali metal compound content is small relative to the amount of F. Flux D3
Flux has a high content of CaO and low content of MgO, so the slag removability is particularly poor, and even when the amount of F exceeds the constituent requirements like flux D4, the slag removability is poor, and the bead shape is medium to high and the bead surface is rough. Also,
Flux D5 has good slag removability even if it contains more than 0.2% of PbO and Bi ₂ O ₃ and more than 10% of CaO, but its toughness is extremely poor.
As described above, although the performance of the comparative flux that does not meet the requirements of the present invention is not satisfactory, the flux of the present invention has excellent welding workability and toughness, and has a low amount of diffusible hydrogen.

【table】

[Table] (Effects of the invention) The flux of the present invention has excellent welding workability such as slag removability and bead shape, which are not found in conventional fluxes, and also provides a highly tough weld metal.
Furthermore, due to the low amount of diffusible hydrogen, it is possible to
It is now possible to weld steel types up to 60 kg class high-strength steel with one type of flux, and slag can be easily removed even in fillet welding with long legs, greatly improving welding efficiency and making industrial use possible. The value is extremely large.

Claims (1)

[Claims] 1% by weight: SiO ₂ : 35-45%, CaO: 10% or less, F: 1.5-6%, Al ₂ O ₃ : 4-15%, TiO ₂ :
1 to 8%, a total of one or two of MgO and BaO: 10 to 25%, (K ₂ O, Na ₂ O and
(total of one or more types of Li ₂ O)/F ratio:
0.1~0.4, _SiO2 + MnO: 55~70%, _SiO2 /MnO
A melting type flux for submerged arc welding characterized by a ratio: 1.4 to 1.9. 2% by weight, _SiO2 : 35-45%, CaO: 10% or less, F: 1.5-6% _{, Al2O3} : 4-15%, _TiO2 :
1 to 8%, total of one or two of MgO and BaO: 10 to 25% and one or two of PbO and Bi ₂ O ₃
Total seeds: Contains 0.005-0.2% ( _K2O , _Na2O
and the sum of one or more types of Li ₂ O)/
F ratio: 0.1-0.4, SiO ₂ +MnO: 55-70%, SiO ₂ /
A melt-type flux for submerged arc welding characterized by an MnO ratio of 1.4 to 1.9.