JPS595078B2 - Flux for submerged arc welding - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a flux for submerged arc welding, and more particularly, even when welding a paint-coated steel plate as it is as a base material, defects such as pits and blowholes do not occur in the weld metal part. The present invention relates to a flux for submerged arc welding that has been improved as described above.

5 When welding paint-coated steel plates as they are,
It is known that defects such as pits and blowholes occur in the welded metal parts.

This is because organic compounds such as butyral resin and epoxy resin contained in the paint on the surface of the steel plate are decomposed by the welding heat.
It is thought that this is because gases such as Co, 10H2, O2, and hydrocarbons are generated, which mix into the weld metal and cause bubbles and pores. Therefore, when welding paint-coated steel plates, conventional methods have been adopted in which the paint on the steel plates is removed in advance, but the work of removing the paint from the welding area and its vicinity 15 each time is extremely complicated and time-consuming. This requires a lot of effort for the operator and significantly reduces welding efficiency. From this point of view, research is being conducted on methods to improve the composition of flux for sub-20 merged arc welding so that the above-mentioned defects will not occur even if paint-coated steel sheets are applied as is. As one of the results of this type of research, a method of incorporating hydrated minerals into the flux composition was proposed, and it was found that it was possible to reduce pits on the surface of weld metal as much as possible. However, this Technique 25 can only reduce pits on the surface of the weld metal, but does not have a satisfactory effect of suppressing blowholes that occur inside the weld metal.
It was not possible to completely eliminate welding defects. When the present inventors investigated the cause of this, the following facts were confirmed. In other words, when water-containing minerals are mixed into the flux, the water decomposes and gasifies due to welding heat, promoting agitation of the molten pool, accelerating the dissipation of paint pyrolysis gas, and reducing pits and blowholes. It is being However, paint decomposition gas and water decomposition gas contain a large amount of hydrogen gas, which has a relatively high solubility in molten metal, so it is impossible to completely remove this dissolved hydrogen from the molten pool. cannot be dissipated. However, since hydrogen gas hardly dissolves in the solidified weld metal, a large amount of hydrogen gas is released during the solidification process of the molten metal, but since the bead surface cools faster than the inside, the hydrogen inside the weld metal Gas is trapped inside and appears as a blowhole. This tendency is observed not only in hydrogen gas but also in oxygen gas and nitrogen gas, and it was confirmed that even when there are almost no pits on the bead surface, a large number of blowholes are generated inside the weld metal. Based on the above-mentioned findings, the inventors of the present invention aimed to dissipate not only decomposed gases with low solubility in the molten metal but also gases with high solubility such as hydrogen, oxygen, and nitrogen from the molten metal as much as possible. We believe that if we can do this, we can completely eliminate the pits and blowholes that occur on the surface and inside of the weld metal, and we have been conducting extensive research to find a flux composition that can satisfy this objective.

As a result, by incorporating iron monoxide and deacidifying elements into the flux composition, the deoxidizing reaction is activated and the agitation of the molten pool is facilitated, and by containing dicrystal water and generating decomposition gas, the molten pool In addition to further promoting the stirring of 3 carbons, if dissolved hydrogen and dissolved oxygen in the molten metal are converted into CO and CH with poor solubility and dissipated, the surface of the weld metal will be C. They discovered that it was possible to obtain a sound joint with almost no internal welding defects, and completed the present invention. That is, the composition of the flux for submerged arc welding according to the present invention is as follows: Iron oxide: . '10-20%, titanium oxide: 3
0-55%, deoxidizing element: 10-20%, carbon: 0.1
~0.4%, crystal water: 0.1~0.5%.

The composition of each component constituting the flux of the present invention is as follows. The purpose and reason for limiting the amount to be added will be explained.

(1) Iron oxide and deacidifying elements Iron oxide and deacidifying elements cause active deoxidizing reactions during the welding process as shown in the following formula, agitating the molten pool, and causing gases produced by thermal decomposition of paint. This has the effect of accelerating the dissipation of gas out of the molten metal.

FeO+Mn:Fe+MnO2Fe2O3+3Si:2
Fe+3Si02Fe203+Mn→2Fe0+MnO
However, if the amount of iron oxide added is less than 10%, the stirring effect accompanying the deoxidizing reaction described above is poor, and the effect of preventing pits and blowholes will not be satisfactorily exhibited, while if it exceeds 20% by weight, the viscosity of the slag will decrease. and the arc becomes unstable,
In addition to causing irregularities in the bead shape and biting of slag,
This is not practical because the slag removability deteriorates.

However, if a blending amount in the range of 10 to 20% by weight is adopted, welding workability, bead shape, slag removability, etc. are excellent, and pits and blowholes on the surface and inside of the weld metal can be effectively suppressed. It is most common to use approximately the same amount of deoxidizing elements depending on the amount of iron oxide mixed.
The optimum blending amount differs slightly depending on the type of iron oxide, the amount of oxygen contained in the paint, etc. Therefore, it is not necessarily possible to specify the amount of the deoxidizing element in relation to the amount of iron oxide, but the inventors have confirmed through experiments that it is 10 to 20% by weight of the total composition of the flux. It was optimal to mix them together. Iron oxides that exhibit the above-mentioned effects are FeO and Fe2O3, and are generally used in the form of illuminite, iron sand, mill scale, hematite, etc., which are commonly used as welding materials.

Also, as a deoxidizing element, any metallic element can be used as long as it has a stronger bonding force with oxygen than iron.
Most preferred are Mn, Si, Al, Ti, Nb, etc. ). ) Titanium oxide In the present invention, titanium oxide is the main component of the slag forming agent, and has the effect of imparting appropriate viscosity to the slag, forming appropriate beads, and improving the releasability of the slag.

Is the appropriate amount to be added in the total flux composition 30 to 55% by weight?
The object of the present invention cannot be achieved outside this range. That is, if the titanium oxide content is less than 30% by weight, the viscosity of the slag decreases, the bead shape becomes disordered, and the releasability of the slag significantly decreases. On the other hand, if it exceeds 55% by weight, the melting point and viscosity of the slag will become excessive, resulting in poor fluidity, making it difficult for the bead to spread, resulting in undercuts and slag entrainment, and furthermore, the stirring effect of the molten pool will be reduced. When it becomes scarce, pits and blowholes are more likely to occur. However, when the content is in the range of 30 to 55% by weight, the slag exhibits appropriate viscosity, fluidity, and peelability, and can provide a sufficient stirring effect to the molten pool to prevent pits and blowholes as much as possible. can. The titanium oxide that performs this function may of course be titanium oxide alone, but it is generally used in the form of minerals containing a large amount of titanium oxide, such as illuminite, rutile, titanium slag, reduced illuminite, etc. be done. (3) As mentioned earlier, crystal water and carbon crystal water are decomposed by welding heat to produce hydrogen and oxygen, and as a result of these gases promoting agitation of the molten pool, pits and blowholes occur in the weld metal part. It is believed that this can be prevented as much as possible.

However, when the present inventors conducted an experiment to confirm the relationship between the amount of water added to the flux, the number of pits, and the rate of occurrence of blowholes, the results shown in FIG. 1 were obtained. That is, as is clear from Fig. 1, pitting is almost completely prevented when H2O is added in an amount of 0.3% by weight or more, but blowholes increase as the amount of H2O added increases. There is. The reason for this is that H2 in the cracked gas, as explained earlier,
This is thought to be due to the fact that O2 and the like dissolve well in molten metal but are difficult to dissolve in solidified weld metal. However, when carbon is mixed into the flux, the carbon reacts with the hydrogen and oxygen and is converted into CO and hydrocarbons that are difficult to dissolve in the molten metal, and quickly escape from the molten metal. FIG. 2 shows the experimental results of the present inventors who clarified these relationships for the first time.

That is, Figure 2 is a graph showing the relationship between the amount of crystal water and carbon in the flux and the blowhole generation rate.
0 to 15%, and an X indicates the incidence rate exceeds 15%. Analysis of the results in Figure 2 shows that the carbon content is 0.1
If the amount of carbon is less than 0.4%, the blowhole generation rate cannot be suppressed even if the amount of crystallized water is increased.
If it exceeds this amount, blowholes cannot be suppressed no matter how much the amount of crystallization water is increased or decreased. Also, crystal water is 0.1%
If the carbon content is increased or decreased, it will be difficult to suppress blowholes, and the occurrence of pits will become significant.
．． Although pitting can be effectively prevented if it exceeds 5%,
No matter how much the carbon content is increased or decreased, blowholes cannot be suppressed. That is, as is clear from the second result, in order to effectively suppress the extent of pits and blowholes, the amount of crystallization added should be 0.1 to 0.5% by weight, and the amount of carbon added should be 0.1 to 0.5% by weight. 1
~0.4% by weight (particularly preferably 0.2-0.4% by weight)
) should be set within the range. Further, a more preferable range within this range is a case where the following relationship is satisfied when the carbon content is [C]% and the crystal water content is [H2O]%,
It has been confirmed that when this condition is satisfied, blowholes can be almost completely and reliably prevented.

Crystallization water that exhibits such an additive effect can be added in the form of various hydrated minerals commonly used as welding raw materials, such as talc (containing about 5% crystallization water) and mica (containing about 6% crystallization water). As the carbon, carbon black, charcoal powder, etc., or carbon bonded with Mn, Si, etc. may be used.

Incidentally, fluxes are roughly classified into molten fluxes and sintered fluxes depending on the method of preparation, but one of the characteristics of the present invention is that a specified amount of crystal water is included in the flux composition. It is best to use it as a sintered flux that does not easily release crystal water during the process. The flux for submerged arc welding of the present invention has the above composition, but the key point is that by incorporating appropriate amounts of iron oxide, deoxidizing elements, crystal water, and carbon into the composition,
Even if a paint-coated steel plate is used as the base material, it is possible to almost completely eliminate pits and blowholes that occur not only on the surface of the weld metal but also inside it, resulting in a beautiful and healthy joint on both the inside and outside surfaces. It has become.

Next, examples of the present invention will be shown.

EXAMPLE A flux for submerged arc welding was prepared according to the formulation example shown in Table 1 (water glass with a dry content of about 3% was used as a fixing agent), and a welding test was conducted using this flux A-I.

However, the welding conditions were as follows. Welding wire US-
36 (high Mn wire) 1.61W! φ Base material mild steel (SS4
l) Thickness: 12 mm x Width: 100 x Length: 1000 Wash primer - 20μ Full surface coating Welding position Horizontal fillet welding Welding conditions 260A-32V-40cTL/Mm The results are shown in Table 2.

Combining the flux composition in Table 1 and the welding results in Table 2, the following can be considered.

(a) Fluxes A and B are comparative examples in which all of the fluxes A and B are within the scope of the present invention except that the amount of carbon blended is less than the specified range, but blowholes occur significantly and joint defects cannot be prevented.

(b) Fluxes C, D, and E are examples in which the blended amounts of carbon and crystal water are all within the specified range of the present invention, but they have very few pits and blowholes, and have excellent welding workability, and have no beads. It is beautiful and there are no joint defects.

(c) Flux F is a comparative example containing iron oxide in a larger amount than the specified range, but it is significantly inferior in bead appearance, slag removability, undercut, etc., and cannot withstand use.

(d) Fluxes G, H, and I all have different blending ratios of iron oxide and TiO2 within the specified range of the present invention, but the blended amount of iron oxide is about 13% (Flux H) The best results were obtained when

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the crystallization water content in the flux, the number of pits, and the blowhole generation rate, and Figure 2 is the graph showing the relationship between the crystallization water and carbon content in the flux and the prohole generation rate. This is a graph showing.

Claims (1)

[Claims] 1. Iron oxide: 10-20%, titanium oxide: 30-55%
, deoxidizing element: 10-20%, carbon: 0.1-0.4%
A flux for submerged arc welding, characterized in that it contains 0.1 to 0.5% of crystallized water. 2. The flux according to claim 1, wherein the crystal water is blended as a hydrous mineral such as talc or mica. 3. The flux according to claim 1 or 2, wherein the carbon content is 0.2% or more. 4 Carbon content is [C]%, crystal water content is [H_2O
]%, -0.5[H_2O]+0.3≦[C]
The flux according to claim 1, 2 or 3, which satisfies the formula: ≦-0.5[H_2O]+0.5. 5 Claims 1 to 3 in which the flux is of a sintered type
Or the flux described in Section 4.