JPS6129837B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coated arc welding rod for fillet welding, and more particularly to a coated arc welding rod for fillet welding that has an enhanced function as a protective tube and has improved welding workability and joint performance. 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 in welding using a coated arc welding rod specifically for fillet, if high current welding is performed to shorten the welding time, the coating may burn and become brittle, and may fall off during welding. As a result, the function of the coating as a protective tube deteriorates, resulting in insufficient shielding, etc.
Not only do joint defects such as blowholes occur, but the workability deteriorates, and furthermore, the beads become irregular and the isopodity is disturbed. As a result, sufficient joint strength cannot be obtained, or repair welding becomes necessary, and welding efficiency deteriorates. The present inventors focused on the above-mentioned circumstances, and in order to develop a coated arc welding rod for fillet welding that can provide excellent welding workability without impeding joint performance, the inventors have developed a coating material composition and We have been conducting research on the physical properties of the coating. The present invention was completed as a result of such research, and its composition is SiO ₂ :10 to
30% (weight%: same below), _TiO2 : 2-20%,
MgO: 0.5-15%, Mn: 4-15%, Iron powder: 15-50
% is coated on the outer periphery of a mild steel core wire and fired, the coating during welding is characterized by having a bulk density of 2.5 to 3.5 g/cm ³ after firing. The key point lies in the creation of a coated arc welding rod for fillet welding that has excellent drop-off resistance. 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, a high-quality welded joint with excellent isopodality and no defects was obtained with good workability. The basis for setting the numerical range in the present invention will be explained below. SiO ₂ : 10-30% An essential component as a slag viscosity modifier.
If it is less than %, the viscosity of the slag decreases and stable encapsulation cannot be obtained. On the other hand, if it exceeds 30%, the viscosity of the slag becomes too high and the isopod property deteriorates significantly. The raw materials used are silica sand, talc, mica or other silicates, including SiO ₂ in water glass used as a binder. TiO ₂ : 2-20% An important component that determines the encapsulation property of slag, 2%
If it is less than that, the slag coverage is poor and the beads become convex. Moreover, if it exceeds 20%, the amount of slag becomes too large and two-stage beads are likely to be formed. Rutile, illuminite, etc. are used as raw materials. MgO: 0.5-15% Along with the above TiO ₂ , it is an important component that determines the encapsulation properties of slag, and has the effect of smoothing the overall bead shape and increasing the peeling properties of slag, making these functions effective. In order to achieve this, it is necessary to mix 0.5% or more. However, if it exceeds 15%, the isopodality of the bead will deteriorate significantly. As raw materials, talc, olivine sand, magnesia, etc. are used. Mn: 4-15% This is an essential component as a deoxidizing agent. If it is less than 4%, defects such as pits are likely to occur due to insufficient deoxidation, and if it exceeds 15%, pits will also be damaged due to excessive deoxidation. It is more likely to occur. Iron powder: 15-50% It is an important component to increase the amount of deposited metal and improve welding efficiency, and also has the effect of increasing the elongation of the bead, which is necessary as a fillet welding rod. The effect is not fully demonstrated. However, if it exceeds 50%, the bead becomes convex and the joint strength decreases. Usually, iron powder alone is blended, but a portion can also be blended as an iron alloy such as Fe-Mn. In the present invention, the above-mentioned five components are essential components of the coating material, but in addition to these, the following components may be added as necessary. Iron oxide: 10% or less in terms of FeO It has the effect of increasing the apparent amount of slag and improving encapsulation, and is particularly effective when performing high-speed welding. However, if it exceeds 10%, it becomes difficult to remove the slag and welding workability deteriorates. Carbonate: 15% or less CaCO ₃ , MgCO ₃ , BaCO ₃ and the like are exemplified, and these exhibit a shielding effect as a gas generating agent.
Therefore, it is an important component when applied to fillet welding with a large root gap. However, if it exceeds 15%, the viscosity of the slag decreases and the encapsulation properties of the slag become unstable. Organic matter: 5% or less Similar to the above carbonate, it is a gas generating agent and has the effect of increasing the shielding effect. However, if it exceeds 5%, the penetration becomes too deep and undercuts occur. Al ₂ O ₃ : 5% or less This is an effective component as a slag viscosity modifier, but if it exceeds 5%, the isopodity of the bead deteriorates. Alloy powder: 5% or less In order to improve the mechanical properties and corrosion resistance of weld metal, alloying elements such as Cu, Mo, Ni, Cr, etc. are added either singly or in the form of iron alloys, depending on the target performance. is extremely effective and is usually added in a range 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 of the coating material raw material and manufacturing conditions so that the particle size is 2.5 g/cm ³ or more. By the way, Figure 1 is a graph showing the relationship between the bulk density of the coating, the number of times it falls off during welding, and the minimum leg length of the upper leg of the fillet weld line in a coated arc welding rod for fillet welding that satisfies the above-mentioned composition. be. However, in this experiment, a 5.5 mm × 700 mm _L test rod was used, and a T-shaped fillet test piece was heated at 300 A (A.
Gravity welding was performed using C.). 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: Length of the welding rod after cutting and removing both ends (cm) d: Core wire diameter (cm) D: Covering diameter (cm) As is clear from Figure 1, the bulk density is 2.5g/
If the bulk density is less than 2.5 g/cm ³ , the coating will come off significantly, but if the bulk density is 2.5 g/cm ³ or more, the coating will not come off at all. The appropriate current when using a coated arc welding rod with a diameter of about 5.5 mm is usually about 210 to 260 A, so as is clear from the experimental data in Figure 1 (current: 300 A), the welding rod of the present invention It is understood that high drop-off resistance is exhibited even under high welding current conditions. However, if the bulk density exceeds 3.5, it is not preferable that the spread of the arc decreases, the upper leg length decreases, and the isopodality deteriorates. 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 that the viscosity of the slag generated during welding differs.
This is because even if the bulk density is within the preferred range, a good bead shape cannot be formed. 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, particularly 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 becomes possible, and the lack of shielding and deterioration of isopodity caused by shedding of the coating are eliminated, achieving the two major requirements of welding efficiency and joint performance improvement all at once. It became. Next, experimental examples will be given to clarify the structure and effects of the present invention. Experimental example Coating material with the composition shown in Table 1 (particle size composition is shown in Table 2) was applied to a mild steel core wire (5.5 mm × 700 mm _l ).
The coated arc welding rod was applied to the outer periphery of the fillet welding rod at a coating pressure of 80 kg/cm ² and a speed of 330 cm/min and fired at 130° C. for 1 hour to produce a coated arc welding rod for fillet welding. Using each of the obtained welding rods, test plates (material: SM-41, cross-sectional shape: 2nd
The fillet weld line shown in Figure) was gravity welded at a rod ratio of 1.3 and a current of 300A, and the number of times the coating fell off during welding, the minimum upper leg length of the bead, and welding workability were investigated. The results are summarized in Table 1.

【table】

【table】

[Table] From Table 1, the following conclusions can be drawn. (1) Conventional rods tend to fall off during welding due to the low bulk density of the coating, resulting in poor welding workability and joint defects such as undercuts. Also MgO
Because it does not contain , the bead shape is uneven and the slag peelability is also poor. (2) Comparison bars 11 and 12 have SiO ₂ blending ratios outside the specified range; if there is a shortage, beads will precede the slag in 11 and undercuts will occur; if there is an excess, slag viscosity will increase in 12. Too much and the isopodality decreases. (3) Comparison bars 13 and 14 have TiO ₂ content outside the specified range.When there is a shortage, the slag encapsulation properties of 13 decrease and the bead becomes slightly convex, and when there is an excess, the slag becomes slag 14. If the amount becomes too large, a two-stage bead will be formed. (4) Comparison bars 15 and 16 have MgO blending ratios outside of the specified range; in case of insufficient MgO, in 15, the slag encapsulation properties deteriorate, the bead shape becomes disordered, and the slag seizes, resulting in poor peelability. , in the case of excess 16, the isopodity deteriorates. (5) Comparison bars 17 and 18 have Mn content outside the specified range.If Mn is insufficient, pits will occur in 17 due to insufficient deoxidation, and if it is in excess, pits will occur in 18 due to excessive deoxidation. (6) Comparison bar 19 contains too much Fe powder, so the arc spreads small and the bead becomes convex. (7) Comparison bar 20 contains too much Fe oxide, and the slag is baked on, resulting in poor peelability. (8) All of the reference rods 21 to 23 have bulk densities outside the specified range of the coating, and if the bulk density of the coating is insufficient, the coating of both 21 and 22 will fall off during welding, and undercuts will occur. In the case of excess 23, the spread of the arc is small and the bead becomes small. (9) On the other hand, rods 1 to 10 of the present invention all satisfy the requirements of the present invention, the coating does not fall off at all, welding workability is good, and high-quality joints with good isopodity are obtained. can get.

[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 FIG. 2 is an explanatory diagram showing the joint shape adopted in the experimental example.

Claims (1)

[Claims] 1 _SiO2 : 10-30% by weight, _TiO2 : 2-20% by weight, MgO: 0.5-15% by weight, Mn: 4-15% by weight,
A coated arc welding rod in which a coating material containing 15 to 50% by weight of iron powder is applied to the outer periphery of a mild steel core wire and fired, and the bulk density of the coating material after firing is 2.5 to 3.5 g/ ^cm3 . A coated arc welding rod for fillet welding with excellent resistance to shedding of the coating during welding.