JPH0451279B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention is a fusion type flux for submerged arc welding that can be applied from single layer welding of relatively thin steel plates to multilayer welding of thick steel plates, and in particular, in multilayer welding, it has excellent slag release properties within the groove. The present invention relates to a melt-type flux for submerged arc welding that provides a weld metal with good bead appearance and excellent mechanical performance. (Conventional technology) Automatic welding methods for steel plates include submerged arc welding, MIG welding, and CO ₂ welding, but among these, submerged arc welding produces a large amount of welding and deep penetration. It is considered to be an excellent welding method in terms of efficiency and reliability of the joints obtained, and is particularly widely used for welding thick steel plates. By the way, there are two types of flux for submerged arc welding: a fired type and a melted type.The former is made by granulating and firing raw raw materials using a binder such as water glass, and then adding a gas generating source to the flux.
Although it has advantages such as reducing the amount of diffusible hydrogen by reducing the hydrogen partial pressure in the arc and allowing alloying elements to be added from flux, it also has the disadvantages of easy moisture absorption and difficulty in multi-electrode high-speed welding. There are drawbacks. On the other hand, melting type flux melts the raw material and then
It is manufactured by crushing a glass-like solidified product, but since it is usually glass-like, it has the advantage of being difficult to absorb moisture and being suitable for multi-electrode high-speed welding. These are used differently depending on the purpose so that the characteristics of each can be utilized. For example UOE
When welding speed greatly affects the production capacity of the entire factory, such as for pipes, it is necessary to adopt a multi-electrode high-speed welding method, and generally a multi-electrode, double-sided, single-layer welding method using molten flux is applied. has been done. In this case, the characteristics required for the flux are:
Good beads without defects can be obtained even at high speeds, and the mechanical performance of the weld metal is excellent. However, when multi-layer welding is required, such as when welding thick steel plates, the time required for slag removal has a greater effect on the overall efficiency than the actual welding time, resulting in poor slag removal. Flux requires a great deal of time and effort to remove, which is undesirable. As mentioned above, when longitudinal seam welding such as UOE pipe is carried out in a systemized factory, the welding speed has a large effect on productivity, but the shapes of steel frames, bridges, etc. vary, and it is not possible to weld long seams that are close to single parts. Efficiency will be improved if the slag can be reliably removed, the bead shape is good, and welding can be performed without defects. For example, in multi-layer welding, if a flux with poor releasability is used, not only will it take a lot of time and effort to remove the slag, but if the removal is incomplete, the slag left behind will cause poor penetration and slag entrainment. There is a problem in that welding defects such as these are likely to occur. The slag releasability is particularly susceptible to deterioration when the groove angle is narrow, and in the case of a normal X-groove, the slag releasability of the first layer weld, which is the tightest, often becomes a problem. In other words, in the conventional SiO ₂ -MnO and SiO ₂ -MnO-CaO fluxes commonly used for multilayer welding, the groove angle has been widened to 60° or more in order to improve slag removal within the groove. Moreover, in order to prevent deterioration of the bead shape, slow speed and low heat input welding is often used, which cannot be said to be very efficient. As a method to improve slag flaking, SiO ₂
- A method of adding a small amount of PbO to MnO-based flux is proposed in JP-A-53-133543;
This method has the problem of worrying about the effects of Pb on the human body. On the other hand, several proposals have already been made for fluxes that improve slag releasability and can be applied to narrow gap welding. For example, JP-A No. 55-10356,
Publications No. 55-10357 and No. 55-10358, etc., which define the component range of flux,
Although it is designed to enable narrow gap welding, since SiO ₂ is reduced and a large amount of Al ₂ O ₃ is added, there is a problem that the flux melting point is high and it is difficult to form a bead width. When applied to single-layer or multi-layer butt welding, the width is narrower than that of a flux with a large amount of SiO ₂ , and the resulting bead tends to have a high bead height, which is unfavorable in terms of appearance. Here, the following items can be considered as requirements for improving slag removability. (1) There is a large difference between the volumetric shrinkage of the slag and the volumetric shrinkage of the weld metal. (2) The adhesion force between slag and weld metal is small. (3) The cross-sectional shape of the bead is concave and does not mechanically restrain the slag. Regarding (1), it is generally advantageous for the slag to have a larger thermal expansion coefficient, and for this reason it is desirable that the slag separation and solidification temperature be high, but if it is too high, it will be difficult to form a bead width. , must be selected taking this point into consideration. Regarding (2), it is closely related to the interfacial tension between the slag and the weld metal, and as the interfacial energy increases, the adhesion force decreases. Regarding (3), in the case of a convex bead, an undercut occurs at the edge, which mechanically restrains the slag and impedes peelability, so the bead shape must be flat or concave. Since welding conditions are also related to this bead shape, it is of course important to select appropriate conditions. Furthermore, in addition to good slag releasability, the weld metal must have good toughness, and the amount of diffusible hydrogen in the weld metal must be small to prevent cold cracking. . (Problems to be Solved by the Invention) In submerged arc welding, this invention not only provides a good wide bead appearance during single-layer welding, but also provides good slag removability even during multi-layer welding, and also improves the appearance and appearance. The purpose of this study is to propose a molten type flux that also improves the mechanical performance of weld metal. (Means for Solving the Problems) First, the background to the elucidation of this invention will be explained. The inventors melted fluxes with various compositions and investigated the appearance and shape of the bead during single-layer welding, as well as the slag releasability, bead shape, and weld metal properties during multilayer welding within a groove with a relatively small angle. Toughness and other aspects were comprehensively considered. As a result, when the flux contains relatively large amounts of SiO ₂ , TiO ₂ , and MgO, and the SiO ₂ satisfies a certain relationship, the bead width is wide and the flux melts within the groove without making the melting point that high. It has been found that the slag releasability of this material is extremely good, and that the cross-sectional shape of the bead is also flat or concave. At that time, the slag was almost glassy, and a very small amount of TiO ₂ crystalline material was observed by microscopic observation and X-ray observation. It is possible that the amount of shrinkage is increased. From this point of view, it is thought that stable slag releasability can be obtained by making the entire slag crystalline, but this requires increasing TiO ₂ and Al ₂ O ₃ , which results in a decrease in the slag melting point. It was also found that it is better not to increase these values unnecessarily, since this increases the bead width, reduces the bead width, and increases the amount of hydrogen in the flux. In addition, SiO ₂ must be added in a certain amount or more in order to widen the bead width, and from the standpoint of weld metal toughness, MgO must be added a little more.
It was also found that it was necessary to add more than a certain amount of CaO and CaF ₂ to reduce the amount of oxygen in the weld metal. In this way, the prototype flux was able to obtain a good bead during single-layer welding, and had good slag removal properties within the groove during multi-layer welding, but further investigation in relation to the flux particle size showed that It has also been found that beads with better shapes can be obtained with fluxes having a certain particle size condition. This invention is based on the above knowledge. That is, in this invention, _SiO2 : 20 to 30 wt% (hereinafter simply expressed in %) _TiO2 : 13 to 20%, _SiO2 / _TiO2 = 1.0 to 1.55, _Al2O3 : ₂ to 8% MnO: 7 to 15% MgO: 12 to 20% CaO: 5 to 17% CaF ₂ : 5 to 15% and the total of one or two selected from Na ₂ O and K ₂ O: 0.1 to 2.0%. The flux has a particle size of
Less than 5% of the total particles are coarser than 351μm, 74μm
This is a molten flux for submerged arc welding in which finer particles account for 5 to 20% of the total. Moreover, this invention has _SiO2 : 20-30% _TiO2 : 13-20%, and _SiO2 / _TiO2 =1.0-1.55, _Al2O3 : 2-8% MnO: 7-15% _MgO : 12- 20% CaO: 5-17% B ₂ O ₃ : 1.0% or less CaF ₂ : 5-15% and one or two selected from Na ₂ O and K ₂ O Total composition: 0.1-2.0% It is a flux with a particle size of
Less than 5% of the total particles are coarser than 351μm, 74μm
This is a molten flux for submerged arc welding in which finer particles account for 5 to 20% of the total. (Function) First, in this invention, the reason why the component composition is limited to the above range will be explained. SiO ₂ :20-30% SiO ₂ is an important component of flux and has a great effect on bead appearance, weld metal toughness, etc. If the blending amount is less than 20%, the bead width will be difficult to obtain and the bead will be unfavorable in appearance;
%, the amount of oxygen in the weld metal will increase and the toughness will deteriorate, so it is necessary to set it to 20 to 30%. TiO ₂ : 13-20% TiO ₂ has a large effect on the slag releasability within the groove; if it is less than 13%, the slag tends to stick to the bead, while if it exceeds 20%, the slag becomes crystalline all over. The bead width becomes difficult to obtain, and the amount of oxygen in the weld metal increases and the toughness deteriorates.
It should be 12-20%. Furthermore, the reason why the composition conditions for SiO ₂ and TiO ₂ were set to SiO ₂ /TiO ₂ =1.0 to 1.55 is as follows. The value of SiO ₂ /TiO ₂ is a value related to the slag separation property within the groove and the appearance of the bead. If this value is less than 1.0, the bead will become a convex bead with a narrow bead width and a high reinforcement. Slag removability at the bead edge becomes poor. On the other hand, if it is larger than 1.55, the bead appearance will be good, but the slag will be completely vitrified and the releasability within the groove will deteriorate, so SiO ₂ /TiO ₂
The value of must be between 1.0 and 1.55. _Al2 : 2 to 8% _Al2O3 has a large effect on the softening temperature of _the slag, and also effectively contributes to improving the releasability. However, if it is less than 2%, the slag releasability deteriorates, while if it exceeds 8%, the melting point becomes too high and good beads cannot be obtained.
It was set at 8%. MnO: 7 to 15% MnO is a component related to the bead shape and the toughness of the weld metal. If the content is low, the bead tends to become convex, resulting in poor slag releasability, and the yield of Mn in the weld metal decreases, resulting in insufficient hardenability and deterioration of toughness. Therefore, it is necessary to add at least 7%. However, if it is too large, oxygen will increase due to the reduction of MnO and the toughness will deteriorate, so it is necessary to keep it below 15%. MgO: 12-20% MgO is a basic component that reduces the amount of oxygen in the weld metal and improves its toughness.
If it is less than 12%, the effect will be small, while if it is added in excess of 20%, the slag softening temperature will become too high and convex beads will easily form. Therefore, the content was set at 12 to 20%. CaO: 5-17% CaO increases flux basicity and reduces the amount of oxygen in the weld metal, effectively contributing to improving toughness, but if it is less than 5%, no effect can be expected; It must be within the range of 5 to 17%, since pockmarks, commonly called pockmarks, are likely to occur on the bead surface in excess of 5%, and the amount of hydrogen in the flux also increases. _CaF2 : 5 to 15% _CaF2 has the effect of reducing the amount of oxygen in the weld metal, and if it is too small, the effect cannot be expected. Furthermore, CaF ₂ has a strong effect of lowering slag viscosity, and if it is added too much, the fluidity of the slag becomes too large and the releasability within the groove deteriorates. However, for these reasons, it was limited to a range of 5 to 15%. NaO and/or K ₂ O: 0.1 to 2.0% Keeping the arc stable during welding is a basic condition for obtaining a good bead, especially conditions that are stricter than normal welding such as narrow gap welding. These alkali oxides have the effect of greatly improving arc stability during submerged arc welding, even in small amounts, which is an essential requirement in the case of submerged arc welding. However, if the blending amount is less than 0.1%, it will have little effect on improving arc stability, while if it exceeds 2.0%, the moisture content in the flux will increase, resulting in an increase in the amount of hydrogen diffused in the weld metal. Therefore, the blending amount of these components needs to be 0.1 to 2.0%, whether added alone or in combination. B ₂ O ₃ : 1.0% or less B ₂ O ₃ in the flux enables the addition of B to the weld metal through reduction, and is effective in improving the toughness of the Ti-B weld metal. However, if added in excess of 1.0%, hot cracking is likely to occur, so it was decided to add at 1.0% or less. Note that there is no problem with regard to FeO, ZrO ₂ , BaO, etc., which are inevitably mixed in, as long as their total content is 5% or less. Furthermore, according to the inventors' research, it was found that even if the above component range was satisfied, it was not possible to maintain a stable arc and obtain a good bead shape unless the flux particle size was adjusted to an appropriate range. . In other words, if the grain size is coarse, the balance between the escape of the gas generated in the arc and the arc pressure will be poor, causing discontinuous blow-up and making it difficult to obtain a good bead. On the other hand, if there are too many fine particles, it will be difficult for gas to escape, so it will be difficult to obtain a good bead in this case as well. That is, in order to obtain a good bead in both single-layer welding and multi-layer welding, it is necessary that the generated gas escape smoothly and that the arc cavity pressure be maintained almost constantly. In order to achieve this, it is necessary that the flux particles coarser than 351 .mu.m account for 5% or less of the total, and the flux particles finer than 74 .mu.m account for 5 to 20% of the total. (Example) Example 1 Various fluxes adjusted to the compositions shown in Table 1 were combined with 1.8Mn-0.5Mo wire to form a 20mm V-groove with an angle of 70° and a depth of 8mm. Two-electrode submerged arc welding was performed on a JIS SM50B thick steel plate under the conditions shown in Table 2, and the bead shape, welding defects, etc. were investigated. The evaluation results of welding workability and the performance of the weld metal are shown in Table 3. Note that a 2 mm V-notched mechanical impact test piece was taken from a position 2 mm from the outer surface. In addition, welding defect inspection included visual undercut inspection and internal defect inspection using X-ray transmission inspection. Furthermore, all fluxes were subjected to a hydrogen test based on JIS Z 3116, and the results are also listed in Table 3.

【table】

[Table] * Underlined values indicate that the values are outside the appropriate range of this invention.

【table】

[Table] As shown in Table 3, the flux according to the present invention has good slag releasability, good bead shape, no defects, and excellent weld metal toughness, and furthermore, the amount of diffusible hydrogen is 2 c.c. ./100gD.M or less, and the risk of hydrogen cracking was also small. On the other hand, in the comparative flux, there was no particular problem in slag releasability even though the chemical composition and grain size composition were outside the scope of the invention because it was a single layer welding with a V groove. There was something problematic. In other words, there were no major problems with B1 (there are problems with multi-layer welding, as described later), but
In B2, the amount of SiO ₂ is large, so the weld metal toughness is low due to the increase in the amount of oxygen in the weld metal due to the reduction of SiO ₂ . Since B3 had a coarse grain size, the bead shape was too convex and undercuts occurred. Like B1, B4 did not have any major problems in terms of workability when welding a single layer of V-groove, but it contained a lot of MnO.
Since there is little MgO, the toughness of the weld metal is low. B5 had a slightly coarse particle size and tended to form somewhat convex beads, and also had a large amount of CaO, so avatars occurred. With B6, there were too many fine grains, which caused rise-up during welding, resulting in a meandering bead. It was also observed that the bead width tended to be narrower. Example 2 Using the flux shown in Table 1, 1- to 2-electrode submerged arc multilayer welding was performed on a 38 mm thick SM50B plate with an X groove. The wire is Example 1
Similar to 1.80Mn−0.5Mo, a 1.80Mn−0.5Mo system was used. FIG. 1 shows the shape of the X groove. In this case, as shown in FIG. 2, the inner surface was finished in one pass, and the outer surface was welded in five passes using a one-layer, one- to two-pass lamination method. Only the first layer was welded with one electrode to prevent hot cracking. Table 4 shows the welding conditions at this time. Table 5 shows the results of inspecting slag peelability and bead shape during multi-layer welding on the outer surface as inspection items, and inspecting for defects by X-ray inspection after complete lamination.

【table】

【table】

[Table] As is clear from Table 5, the flux of the present invention has good slag releasability and bead shape not only for single-layer inner welding but also for multi-layer outer welding, and is suitable for X-ray inspection. Even after welding, no slag entrainment occurred, and the welding efficiency was very good because the lap between the inner and outer beads was sufficient. On the other hand, with the comparative flux, there was no major problem in internal welding, which is one-layer V-groove welding, and Example 1
The results were almost the same, but there were problems such as poor slag removal within the groove and poor bead shape when welding on the outer surface, which is multilayer welding. All the comparative fluxes had in common that they had poor slag removability, and it took a lot of time to remove the slag stuck to the beads with a pitting hammer or chisel. In other words, in B1, the flux particle size composition was as desired, but the SiO ₂ /TiO ₂ value was outside the appropriate range of this invention, so slag stuck to the bead surface even if the bead shape was good. Peeling was poor. B2 had not only a large amount of SiO ₂ but also a large SiO ₂ /TiO ₂ ratio, and as with B1, the in-groove slag releasability was poor. However, no particular deterioration of the bead shape was observed. In B3, the SiO ₂ /TiO ₂ value is large within the appropriate range, so the slag releasability within the groove is poor, and the particle size composition is 19.4%, which is coarser than 351 μm.
Since the amount of particles finer than 74μm was 4.4%, the bead shape also became convex, making it difficult to determine the target welding position for the next pass. Like B1, B4 had poor slag releasability even though the bead shape was good. Since the chemical compositions of B5 and B6 are outside the appropriate range of the present invention, the slag releasability within the groove is poor, and the powder properties are also off, resulting in beads that are convex or undercut. Example 3 Fluxes A3 and A6 used in Example 1
Using two types of fluxes containing 0.3% B ₂ O ₃ ,
In addition, single-layer V-groove welding was performed under the same welding conditions as in Example 1 and using steel plate wire. The results are shown in Table 6, and the weld metal toughness was further improved compared to the case where B ₂ O ₃ was not present.

[Table] (Effects of the Invention) Thus, according to the flux of the present invention, it goes without saying that a good bead can be obtained in single layer welding, but also a good slag can be obtained in multilayer welding within a groove with a relatively small angle. Since the releasability, bead shape, and appearance are excellent, and the performance of the resulting weld metal is also excellent, it is possible to significantly reduce the number of welding steps compared to conventional methods. Incidentally, the flux of the present invention can of course be applied to high heat input multilayer welding, and its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the X groove shape used in Example 2, and FIG. 2 is an explanatory diagram of the lamination procedure in Example 2.

Claims (1)

[Claims] 1 SiO ₂ : 20 to 30 wt% TiO ₂ : 13 to 20 wt%, and SiO ₂ /TiO ₂ = 1.0 to 1.55, Al ₂ O ₃ : 2 to 8 wt% MnO: 7 to 15 wt% MgO: A flux having a composition of 12 to 20 wt% CaO: 5 to 17 wt% CaF ₂ : 5 to 15 wt% and one or two selected from Na ₂ O and K ₂ O: 0.1 to 2.0 wt%, The particle size is
Less than 5wt% of the total particles are coarser than 351μm,
A molten flux for submerged arc welding, characterized in that particles finer than 74 μm account for 5 to 20 wt% of the total flux. 2 _SiO2 : 20-30wt% _TiO2 : 13-20wt% and _SiO2 / _TiO2 =1.0-1.55, _Al2O3 : _2-8wt % MnO: 7-15wt% MgO: 12-20wt% CaO: A flux with a composition of 5-17wt% B ₂ O ₃ : 1.0wt% or less CaF ₂ : 5-15wt% and one or two selected from Na ₂ O, K ₂ O Total: 0.1-2.0wt% If the particle size is
Less than 5wt% of the total particles are coarser than 351μm,
A molten flux for submerged arc welding, characterized in that particles finer than 74 μm account for 5 to 20 wt% of the total flux.