JPS5937720B2 - Low hydrogen type coated arc welding rod for fillet welding - 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 exclusively for fillet welding, which is a low-hydrogen type and has an improved function as a protective tube and improved welding workability and joint performance. It is something.

Various welding methods and welding materials have been proposed to improve welding efficiency and joint performance, and many technologies have also been developed for low-hydrogen coated arc welding rods that suppress hydrogen embrittlement.

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 low-hydrogen fillet welding coated arc welding rods, when high current welding is performed to shorten the welding time, the coating burns and becomes brittle, and may fall off during welding. As a result, the function of the coating as a protective tube deteriorates, the arc becomes unstable and workability decreases, and joint defects such as blowholes occur due to insufficient shielding, and even beads become uneven. Legs become disordered. In addition, atmospheric moisture etc. get mixed into the arc atmosphere, impairing the hydrogen embrittlement resistance that is a feature of low-hydrogen welding rods. The present inventors focused on the above-mentioned circumstances, and with the aim of developing a low-hydrogen coated arc welding rod for fillet welding that would provide excellent welding workability without impairing joint performance, the present inventors developed a coating material. We have been conducting research on the component composition and physical properties of the coating.

The present invention was completed as a result of such research, and its composition is SiO2: 10 to 20% (weight %: the same below), TiO2: 5 to 20%, iron powder: 15 to 45%, carbonic acid A coating agent containing salt: 5 to 30% (however, the total carbonate excluding MgCO3 is 10% or less), metal fluoride: 3 to 15%, and deoxidizing metal: 3 to 15% is applied to the outer periphery of the mild steel core wire. A coated arc welding rod for low hydrogen fillet welding that is coated and fired, the bulk density of the coating material after firing being 2.3 to 3.3.
The gist lies in the 1/d&C. 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, it is possible to prevent the coating from falling off during welding and maintain its original function as a protective tube. Ta.

As a result, a high-quality welded joint with excellent isopodality and hydrogen embrittlement resistance was obtained with good workability. The basis for setting the numerical range in the present invention will be explained below.

SiO2: 10-20% An essential component as a slag viscosity modifier;
If it is less than this, the viscosity of the slag decreases and stable encapsulation cannot be obtained.

On the other hand, if it exceeds 20%, the viscosity of the slag becomes too high, and its special characteristics deteriorate significantly. Raw materials include silica sand, talc,
Mica or other silicates are used, including SiO2 in water glass, which is used as a binder. TiO2:
5 to 20% This is an important component that determines the encapsulation of the slag. If it is less than 5%, the slag encapsulation 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. Iron powder: 15-45% It is an important component to increase the amount of deposited metal and improve welding efficiency, and it also has the effect of increasing the elongation of the bead, which is necessary as a fillet welding rod. If it is less than 15%, these effects will be reduced. is not fully demonstrated.

However, if it exceeds 45%, the bead becomes convex and the joint strength decreases. Usually iron powder is used alone, but Fe-Mn
It can also be used in combination with iron alloys such as or Fe-Si. Carbonate: 5 to 30% MgcO3-CacO3 and BacO3 are typical examples, and they exert a shielding effect as a gas generating agent, increasing blowhole resistance and pitting resistance, and preventing contamination with atmospheric moisture, etc. This prevents deterioration of hydrogen embrittlement.

Therefore, it is a particularly important component when used for fillet welding with a large root cap. In order to ensure these effects, it is necessary to mix 5% or more, but if it exceeds 30%, the dissolution becomes deep and undercuts are likely to occur. Among carbonates, MgCO3 is the most suitable, and the sum of other carbonates (CacO3, BacO3, etc.) is 1.
If it exceeds 0%, slag tends to advance and two-stage beads are likely to be formed, so care must be taken. Metal fluoride:
3-15% Metal fluorides include CaF2, AlF3, MgF2
is used and is an essential ingredient as an anti-pore agent.

If it is less than 3%, joint defects such as marks will occur.

However, if it exceeds 15%, the viscosity of the slag becomes too low, resulting in convex beads, which is not preferable. Deoxidizing metal: 3-1
Typical examples include 5%MnlSisTilAlsMg or iron alloys thereof; if it is less than 3%, blowholes and undercuts are likely to occur due to insufficient deoxidation;
On the other hand, if it exceeds 15%, the weld metal becomes hard and crack resistance decreases.

In the present invention, the above-mentioned six components are essential components of the coating material, but the following components may be added as necessary.

MgO: 10% or less is effective in smoothing the bead shape, but if it exceeds 10%, isopodality is significantly impaired.

Al2O3: 5% or less is effective as a viscosity modifier for slag, but if it exceeds 5%, isopodity deteriorates.

Alloy powder: 5% or less In order to improve the mechanical properties and corrosion resistance of weld metal, it is extremely effective to add single alloying elements such as CUsMOsNisCr or iron alloys of these, depending on the target performance. It is added in an amount of 5% or less.

The composition of the coating material used in the present invention is as described above, but the performance of the welding rod of the present invention obtained by applying this coating material to the outer periphery of a 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 an experiment 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 was 2.3 to 3.3 g/d. It has been found that excellent shedding resistance can be ensured by setting the particle size of the coating material raw material, manufacturing conditions, etc. Incidentally, Figure 1 shows 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 in a low-hydrogen coated arc welding rod for fillet welding that satisfies the above-mentioned composition. This is the graph shown. However, in this experiment, 5.5 diameter x 700 mm1
300A (A
．． C. ) gravity welding was performed. The bulk density of the coating was calculated using the following formula. In the formula, K: bulk density (9/Cn
t) G: Rod weight after cutting and removing both ends of the welding rod (9) l: Rod length after cutting and removing both ends of the welding rod (C7rL
) d: Core wire diameter (CTrL) D: Covering diameter ((V7l) As is clear from Figure 1, the bulk density is 2.3 to 3.31
In the cases where the bulk density falls outside of /Crit, the coating falls off significantly, whereas in the cases where the bulk density falls within the above-mentioned preferred range, the coating does not fall off at all.

Note that the appropriate current when using a coated arc welding rod with a diameter of about 5.5 mm is usually about 230 to 270 A, so as is clear from the experimental data (current: 300 A) in Fig. 1, the welding of the present invention It is understood that the rod exhibits high dropout resistance even under extreme conditions of high welding current. Further, within the above-mentioned preferred bulk density range, the leg length of the upper leg portion decreases little, and high isopodality is obtained. It should be noted that the preferred range of bulk density mentioned above is applicable only when a coating material having the above-described preferred component composition is used, and cannot be similarly discussed for coating materials having different component compositions.

The reason for this is that even if the bulk density is within a suitable range, if the component composition differs, the viscosity of the produced slag will differ, making it impossible to form a good bead shape. The method for adjusting the bulk density of the coating is not particularly limited, but the most common methods are: 1) adjusting the particle size structure of the coating material raw material;
2. Method of adjusting the pressure when applying to the outer periphery of the mild steel core wire, 3.
Examples include methods that combine the above 1 and 2. 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 A coating agent having the composition shown in Table 1 (particle size composition is as shown in Table 2) was coated on the outer periphery of a mild steel core wire (5.5nφ x 700m") at a pressure of 60k9/c?il and at a speed of 270m/min. After pre-drying at 50-100°C for 1 hour, drying at 400°C for 1 hour.
A coated arc welding rod for low hydrogen fillet welding was produced by main firing for an hour.

Using each obtained welding rod, a test plate (material: SM-50
)Cross-sectional shape: Figure 2) horizontal fillet weld line with a rod travel ratio of 1.
Gravity welding was carried out in Step 3, 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.

From Table 1, the following can be considered. (1) Comparison bar B-1,
2 indicates that the SiO amount is outside the specified range, and if there is a shortage (
In B-1), slag precedes and undercut occurs,
In the case of excess (B-2), the viscosity of the slag is too high and the isopodity is reduced.

(2) Comparison bars B-3 and B-4 have TiO2 content outside the specified range; in the case of insufficient TiO2 (B-3), the slag coverage is poor and the bead becomes convex; -4) The amount of slag is too large and a two-stage bead is formed in advance.

(3) Comparison bar B-5 contains too much iron powder, so the spread of the arc becomes small and the bead becomes convex.

(4) Comparison bars B-6 and B-7 have a carbonate content outside the specified range. In the case of insufficient carbonate (B-6), pitting occurs due to poor shielding, and in the case of excess (B-7) The penetration becomes deep and an undercut occurs.

Comparison bars B-8 and 9 contain carbonates other than MgCO3 (Ca
cO3 or BaCO3) exceeding 10%, slag leads and becomes a two-stage bead. (5) Comparison bar B-
Nos. 10 and 11 are those in which the amount of metal fluoride is out of the specified range; when it is insufficient (B-10), the pore prevention effect is insufficient and pits occur, and when it is excessive (B-11), the viscosity of the slag is is too high, resulting in a convex bead.

(6) Comparison bars B-12 to B-16 have deoxidizing metal amounts outside the specified range, and in the case of insufficient deoxidizing metals (B-12, 13), blowholes and undercuts occur due to insufficient deoxidizing. In the case of excess (B-14, 15, 16), the cracking resistance of the weld metal is poor.

(7) Comparison bars B-17 and B-18 have coating bulk densities outside of the specified range; if the bulk density is too low (B-18), the coating will fall off and undercuts will occur; if it is too high, the coating will fall off and undercuts will occur. (B
-17) Vertical cracks occur in the coating.

(8) A-1 to 1 that satisfy the requirements of the present invention for these
The No. 0 welding rod does not cause the coating to fall off, provides good workability, and has excellent isopodity of the bead.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1 SiO_2: 10~20% by weight, TiO_2: 5~
20% by weight, iron powder: 15-45% by weight, carbonate: 5-3
0% by weight (however, the total amount of carbonates excluding MgCO_3 is 10% by weight)
% by weight or less), metal fluoride: 3 to 15% by weight, and deoxidizing metal: 3 to 15% by weight, coated on the outer periphery of a mild steel core wire and fired. It is a salt melt rod, and the bulk density of the coating material after firing is 2.3 to 3.
．． A low-hydrogen coated arc welding rod for fillet welding, characterized by having a welding strength of 3 g/cm^3.