JPS6129836B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coated arc welding rod, and more particularly to a coated arc welding rod in which the function of the coating as a protective tube is improved, and welding workability and joint performance are enhanced. Various welding methods and welding materials have been proposed to improve welding efficiency and joint performance. However, there are few methods that satisfy both the shortening of the total welding time including post-weld modifications (repair welding) and the joint performance. Particularly when welding using coated arc welding rods such as lime titania or illuminite, high current welding to shorten the welding time will cause the coating to burn and become brittle, resulting in parts of the protective tube being damaged during welding. may fall off. As a result, the function of the covering as a protective tube deteriorates, resulting in insufficient shielding, etc., which not only causes joint defects such as blowholes, but also deteriorates workability. As a result, repair welding becomes necessary, and welding time cannot be shortened. The present inventors focused on the above-mentioned circumstances, and in order to develop a coated arc welding rod that provides excellent welding workability without impairing joint performance, the inventors investigated the composition of the coating material, the physical properties of the coating, etc. We have been conducting research on this. The present invention was completed as a result of such research, and its composition consists of 1 of CaCO ₃ and MgCO ₃
Species or 2 types: 7 to 25% (weight%: same below),
In a coated arc welding rod in which a lime-titania-based or illuminite-based coating material containing 13 to 40% of TiO ₂ and 14 to 33% of SiO ₂ is applied to the outer periphery of a mild steel core wire and fired, the coating material after firing is The bulk density of is 2.1~3.1
The ^gist lies in that it is a coated arc welding rod with excellent resistance to shedding of the coating during welding, which is characterized by a resistance to shedding of the coating during welding. In the present invention, by specifying the composition of the coating material and setting the bulk density of the coating within a specific range after firing, the coating is prevented from falling off during welding, and the original function as a protective tube is maintained. I was able to force it. As a result, high-quality welded joints that do not require repair welding can be obtained with good workability. The basis for setting the numerical range in the present invention will be explained below. CaCO ₃ and/or MgCO ₃ : 7-25% An essential component as a gas generating agent, and the generated gas protects the weld metal from the atmosphere. 7
If it is less than 25%, shielding will be insufficient and joint defects such as blowholes will easily occur, while if it exceeds 25%, the slag viscosity will decrease and the bead shape will deteriorate. Considering these effects, both substances have the same effect, so one may be used alone or in appropriate amounts in combination. Usually lime, dolomite,
It is added as magnesite etc. In addition, other carbonates such as MnCO ₃ and FeCO ₃ do not have a sufficient shielding effect because their decomposition temperatures are low. However, a small amount
There is no problem in using it in combination with CaCO ₃ or MgCO ₃ . _TiO2 : 13 to 40% This is an essential component to give the slag a suitable encapsulation property.If it is less than 13%, the slag encapsulation property deteriorates and the beads become convex. However, if it exceeds 40%, the slag releasability deteriorates significantly, and workability, especially in multilayer welding, becomes extremely poor. Rutile, illuminite, etc. are used as raw materials. SiO ₂ : 14-33% is an important component as a slag viscosity modifier,
If it is less than 14%, the slag encapsulation becomes unstable due to insufficient viscosity, and the bead shape also deteriorates. Also
If it exceeds 33%, the slag becomes glassy and difficult to peel off. The raw materials used are silica sand, talc, mica and other silicates, including SiO ₂ in water glass, which is used as a binder. In the present invention, the above three components are essential components of the coating material, but the following components may be added as necessary. Iron oxide: 3 to 20% in terms of FeO Iron oxide has the effect of improving dissolution into the base metal, and especially in the case of illuminite welding rods, it is necessary to add 3% or more. However, if it is too large, the arc force becomes too strong and undercuts tend to occur, so it must be kept at 20% or less. Illuminite, iron sand, scale, etc. are used as raw materials. Iron powder: 40% or less Increases the amount of deposited metal and increases welding efficiency. However, if it exceeds 40%, the insulation properties of the coating become poor and the bead shape becomes convex, which is not preferable. Note that iron in ferroalloys such as Fe-Mn and Fe-Cr also has the same effect. Alloy powder: 5% or less In order to improve the mechanical properties and corrosion resistance of weld metal, it is extremely difficult to add alloying elements such as Cu, Mo, Ni, Cr, etc. or their iron alloys depending on the target performance. It is effective and is usually added in an amount of 5% or less. The composition of the coating used in the present invention is as described above, but the performance of the coated arc welding rod obtained by applying this coating to the outer periphery of the mild steel core wire and firing it is closely related to the shedding resistance of the coating. have a relationship. That is, as explained earlier, the coating constitutes a protective tube during welding,
It has the effect of stabilizing the arc and increasing the shielding effect, but if the coating falls off during welding, the above effects will be lost. Therefore, we conducted research to improve the shedding resistance of the coating, and found that the shedding resistance is closely related to the bulk density of the coating after firing, and that the bulk density
It has been found that excellent shedding resistance can be ensured by setting the particle size and manufacturing conditions of the coating material raw material so that the particle size is 2.1 g/cm ³ or more. Incidentally, FIG. 1 is a graph showing the relationship between the bulk density of the coating, the number of times the coating falls off during welding, and the bead width in an illuminite-based coated arc welding rod that satisfies the above-mentioned composition. However, in this experiment, a 4.0 mm × 450 mm ^L test rod was used, and downward contact welding was performed on a flat plate at 240 A (AC). The bulk density of the coating was calculated using the following formula. In the formula, K: Bulk density (g/cm ³ ) G: Weight of the welding rod after cutting and removing both ends (g) l: Rod length after cutting and removing both ends of the welding rod (cm) d : Core wire diameter (cm) D: Coating diameter (cm) As is clear from Figure 1, the bulk density is 2.0g/
If the bulk density is less than 2.1 g/cm ³ , the coating will come off significantly, but if the bulk density is 2.1 g/cm ³ or more, there will be no shedding. Note that when using a coated arc welding rod with a diameter of about 4.0 mm, the appropriate current is usually about 140 to 180 A, so as is clear from the experimental data (current: 240 A) in Figure 1, the welding rod of the present invention It is understood that the material exhibits high resistance to falling off even under conditions of high welding current. However, if the bulk density exceeds 3.1 g/cm ³ , the spread of the arc decreases, the bead width becomes narrow, and joint defects such as undercuts are more likely to occur. It should be noted that the above preferred range of bulk density is applicable only when a coating material having the preferred component composition described above is used, and cannot be similarly considered for coating materials having different component compositions. The reason for this is thought to be that the type and blending ratio of the thermally decomposed components in the coating material have an effect on the shedding resistance. The method of adjusting the bulk density of the coating is not particularly limited, but the most common method is a method of adjusting the particle size structure of the coating material raw material. Examples include a method of adjusting the pressure when applying to the outer periphery of the mild steel core wire, a method that combines the above methods, and the like. The present invention is configured as described above, and by specifying the component composition of the coating material and adjusting the bulk density of the coating within a specific range, especially after firing, it is possible to significantly improve the shedding resistance of the coating. It became a matter of fact. As a result, high-speed welding using high current is possible, and the lack of shielding caused by shedding of the coating has been resolved, making it possible to achieve the two major requirements of welding efficiency and joint performance all at once. Next, experimental examples will be given to clarify the structure and effects of the present invention. Experimental example 1 A lime titenia-based coating agent having the composition shown in Table 1 (particle size composition is shown in Table 2) was applied to the outer periphery of a mild steel core wire (4 mm × 450 mm ^l ) at a pressure of 80 Kg/cm 2 and a speed of 80 Kg/cm ^{2 .}
It was coated at 330 m/min and fired at 130°C for 1 hour to produce an arc welding rod. Using each of the obtained welding rods, test plates (material: SM-41, cross-sectional shape: 2nd
Figure) Overlay welding in a downward position (welding current:
240A), and the number of shedding of the coating during welding, welding workability, and X-ray performance of the obtained weld metal were investigated. The results are summarized in Table 1.

【table】

[Table] From Table 1, the following conclusions can be drawn. (1) Because the bulk density of the coating on conventional rods is low, they often fall off during welding, resulting in poor welding workability and poor X-ray performance of the weld metal. Also, because there is too much TiO ₂ , slag peeling is also poor. (2) B-1 and 2 are comparative examples in which the blending ratio of carbonate is outside the specified range; in the case of insufficient carbonate (B-1), good X-ray performance cannot be obtained due to poor shielding; -2) The viscosity of the slag decreases, leading to the slag leading to poor fusion. (3) B-3 and B-4 are comparative examples in which the TiO ₂ blending ratio is outside the specified range, and in the case of insufficient TiO 2 (B-3), the encapsulation of the slag becomes poor and the bead shape becomes convex. On the other hand, if it is too large (B-4), the slag peelability will be poor and workability will be reduced. (4) B-5 and 6 are comparative examples in which the blending ratio of SiO ₂ is outside the specified range, and when it is insufficient (B-5), the viscosity of the slag decreases, leading to slag leading to poor fusion. On the other hand, if the amount is too large (B-6), the slag releasability becomes poor. (5) B-7 and 8 are comparative examples in which the bulk density of the coating is outside the specified range; if it is too low (B-7), the shedding resistance and X-ray performance of the coating cannot be satisfied; on the other hand, if it is too high, (B-7) -8) It is difficult to weld because the spread of the arc is small. (6) Example A that satisfies the requirements of the present invention for these
-1 to 6, the coating did not fall off, the workability was good, and the X-ray performance of the weld metal was also excellent. Experimental Example 2 An illuminite coating material having the composition shown in Table 3 (particle size composition is shown in Table 4) was applied to a mild steel core wire (4.0 mm
〓×450mm ^l ) was coated on the outer periphery under the same conditions as in Experimental Example 1, and baked at 130°C for 1 hour to produce a coated arc welding rod. Using each of the obtained welding rods, multilayer welding (welding current: 240A) was performed on a test plate (material: SM-41, cross-sectional shape: Fig. 3) in a downward position, and the number of times the coating fell off during welding was determined. Welding workability and X-ray performance of the obtained weld metal were investigated. The results are summarized in Table 3.

【table】

[Table] As is clear from Table 3, conventional illuminite welding rods suffer from significant shedding of the coating and have poor welding workability and poor X-ray performance of the deposited metal. Moreover, if even one of the requirements of the present invention is lacking (Comparative Examples D-1 to D-7), any one of the shedding resistance of the coating, the welding workability, and the X-ray performance will deteriorate, making it impossible to achieve the objective. On the other hand, the welding rods (C-1 to C-6) that meet the requirements of the present invention show good results in all of the above three required performances.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the bulk density of the coating and the number of times it falls off, and FIGS. 2 and 3 are diagrams showing the cross-sectional shape of the test plate employed in the experimental example.

Claims (1)

[Claims] 1 One or two of CaCO ₃ and MgCO ₃ : 7 to 25
wt%, _TiO2 : 13-40 wt% and _SiO2 : 14-33
In a coated arc welding rod in which a lime titania-based or illuminite-based coating containing % by weight is applied to the outer periphery of a mild steel core wire and fired, the bulk density of the coating after firing is 2.1 to 3.1 g/ ^cm3 . A coated arc welding rod with excellent coating fall-off resistance during welding.