JPH04367393A - Low hydrogen type coated electrode - Google Patents

Abstract

PURPOSE:To provide the low hydrogen type coated electrode which allows downward welding even in welding in all positions and allows the enhancement of performance in downward welding of the circumferential butt joint of a pipe in particular. CONSTITUTION:This low hydrogen type coated electrode is constituted by coating the outer periphery of a steel core wire with a coating material contg. 35 to 55% CaCO3, 1 to 4% SrCO3, 1.5 to 4% CaF2, 1 to 5% TiO2, 5 to 12% SiO2, 3 to 9% Si, 1 to 6% Mn, and 15 to 40% Fe, and satisfying the relations 9 to 25 CaCO3/CaF2, and 5 to 22 Fe/CaF2. The effect of an extremely easy performability of the welding operation is obtd. without requiring the welding technique of a high degree if 0.5 to 3% Ti and 0.05 to 0.2% B are further incorporated into this coating material. Further, the toughness of the ferrite structure is increased and the low-temp. toughness is improved even for the additional requirement for the low-temp. toughness if 0.5 to 4.5% Ni is incorporated therein.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-hydrogen coated arc welding rod, and is particularly effective when applied to downward welding of circumferential butt joints of pipes.

0002

[Prior Art] Traditionally, circumferential butt welding at pipeline sites has been carried out in Japan by upward welding using low-hydrogen coated arc welding rods or illuminite coated arc welding rods; In other countries, downward welding is performed using high-cellulose coated arc welding rods. However, when welding high-strength steel pipes, especially on-site welding in cold regions, hydrogen-induced cracking is a major problem, so it is desirable to use a low-hydrogen coated arc welding rod. It was very difficult to weld in advance.

0003

[Problem to be Solved by the Invention] In order to solve this problem, the applicant of the present invention previously proposed Japanese Patent Publication No. 56-21519. However, although the low hydrogen-based coated arc welding rod proposed above has much superior performance compared to previous ones, recently there has been a demand for higher efficiency and harsher performance. This was not necessarily satisfactory, and improvements were required.

That is, in downward welding of circumferential butt joints of pipes, as shown in FIG.
When welding at the position (from 5 o'clock to 6 o'clock), the bead and the base metal may not fit together sufficiently, and rework (such as grinding work) is required.

[0005] The present invention has been made in response to such demands, and is particularly suitable for downward welding of circumferential butt joints of pipes between 4.5 o'clock and 6 o'clock (7.5 o'clock - 6 o'clock). The object of the present invention is to provide a low-hydrogen-based coated arc welding rod that is capable of downward welding not only in position but also in all positions, and that can also be highly efficient.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the inventors of the present invention have developed a method for achieving high efficiency and a specific welding position (4
．． 5:00 to 6:00 and 7.5:00 to 6:00), the present invention was developed as a result of various studies on ways to prevent the bead from becoming poorly compatible with the base material.

[0007] That is, the present invention (first invention)
O3: 35-55%, SrCO3: 1-4%, CaF2
: 1.5~4%, TiO2: 1~5%, SiO2: 5~
12%, Si: 3-9%, Mn: 1-6% and Fe: 1
Contains 5-40% and CaCO3/CaF2:9
~25, Fe/CaF2: The gist of the present invention is a low hydrogen-based coated arc welding rod characterized by coating the outer periphery of a steel core wire with a coating agent satisfying the relationship of 5 to 22.

[0008] Another present invention (second invention) is that CaC
O3: 35-55%, SrCO3: 1-4%, CaF2
: 1.5~4%, TiO2: 1~5%, SiO2: 5~
12%, Si: 3-9%, Mn: 1-6% and Fe: 1
Contains 5 to 40%, furthermore Ti: 0.5 to 3% and B:
Contains 0.05-0.2%, and CaCO3/Ca
The gist of the present invention is a low hydrogen-based coated arc welding rod characterized by coating the outer periphery of a steel core wire with a coating material satisfying the relationships of F2: 9 to 25 and Fe/CaF2: 5 to 22.

[0009] Still another aspect of the invention (third invention) is characterized in that the coating material in the second invention further contains Ni: 0.5 to 4.5%.

The present invention will be explained in more detail below.

[0011]

[Effect]

[0012] Each of the present inventions is a low hydrogen-based coated arc welding rod having the above-mentioned configuration, and according to the first invention, downward welding is possible especially in circumferential butt joints of pipes,
Furthermore, it is possible to provide a low hydrogen-based coated arc welding rod that can also be highly efficient.

On the other hand, the second and third inventions are directed to the aging of welding operators and the increasing demand for easier welding workability and lightening of the load. Arc welding rods have come to be desired, especially in terms of welding workability, arc concentration is necessary to obtain stable penetration, and it is desirable that the bead and base metal fit better than ever before. In light of this, we have developed measures to prevent the bead and base metal from becoming poorly compatible at specific welding positions (4.5 o'clock to 6 o'clock, 7.5 o'clock to 6 o'clock). With this in mind, we conducted various studies to improve arc concentration in all positions and compatibility with the base material, resulting in the completion of this work.

Now, one of the characteristics of the coating material component in the present invention is that Fe is added as an essential component in order to improve efficiency, and the amount of Fe is also the same as that of the low-hydrogen coated arc welding rod proposed above. Much more was added than in the case. but,
Although the addition of Fe was intended to increase efficiency, it was found that the increase in efficiency due to the addition of a large amount of Fe was a factor that adversely affected the compatibility between the bead and the base material.

In order to solve this problem, the present invention takes the following basic measures to dramatically improve the fit between the bead and the base material in all positions.

(a) Reduce the amount of CaF2 added. (b) Increasing the ratio of CaCO3/CaF2. (c) Specifying the Fe/CaF2 ratio. (d) Ti and B were added as necessary. (e) Ni was added when it was desired to further improve impact performance.

Next, the reasons for limiting the components of the coating material in the present invention will be explained.

(CaCO3: 35-55%) CaCO3
is added as a gas generating agent, but if it is less than 35%, the amount of gas generated is small and shielding is insufficient, the viscosity of the slag is reduced, and pits are formed on the bead surface.
The bead does not fit well at the 4 o'clock position. On the other hand, 55
If it exceeds %, the viscosity of the slag will increase significantly, resulting in poor bead compatibility, and the amount of gas generated will increase, resulting in increased spatter. Therefore, the amount of CaCO3 is 35~
The range is 55%.

(SrCO3: 1 to 4%) SrCO3 has the effect of increasing the spread of the crater and improving the conformability of the bead. However, if it is less than 1%, there is no effect, and if it exceeds 4%, the arc becomes unstable, spatter increases, and the slag releasability deteriorates. Therefore, the amount of SrCO3 is set in the range of 1 to 4%.

(CaF2: 1.5-4%) CaF2 has the effect of adjusting the viscosity and fluidity of the slag. However, 1
．． Less than 5% has no effect, and more than 2%
A good bead is formed between 4:00 and 4:00, but when it exceeds 4%, the viscosity of the slag becomes relatively small and the fluidity of the slag increases. At the 6 o'clock position, the bead and base metal do not fit well. Therefore, the amount of CaF2 is set in the range of 1.5 to 4%.

(TiO2: 1-5%, SiO2: 5-1
2%) TiO2 and SiO2 are each added as a slag forming agent, but if TiO2 is less than 1%, the bead will not fit well, and if it exceeds 5%, the fluidity of the slag will increase and Slag easily drips down. Si
If the O2 content is less than 5%, the arc will be weak and the crater will not spread too much, making it difficult for the bead to fit in between the 2 o'clock and 4 o'clock positions.If the O2 content exceeds 12%, the slag will get in the way, especially at the 2 o'clock to 4 o'clock positions. It is easy to get rolled up, making it impossible to obtain a good bead. Therefore, the amount of TiO2 should be in the range of 1 to 5%, and the amount of S
The amount of iO2 is in the range of 5 to 12%. Note that TiO2 may be added as rutile or ilmenite, and SiO2 may be added as silicate or silica sand.

(Si: 3-9%, Mn: 1-6%) Si
, Mn are added as deoxidizing agents, but if they are below the lower limit, they have no effect, and if they exceed the upper limit, excessive deoxidation occurs and pits are generated on the bead surface. In addition, Si is a simple substance or Fe-Si, Si-Mn, Ca-
It can be added in the form of Si, etc. Mn is metal Mn or Fe-
It can be added in the form of Mn, Si-Mn, etc.

(CaCO3/CaF2:9-25)Ca
The CO3/CaF2 ratio has a great effect on slag viscosity and fluidity and is an important factor in all-position downward welding. If this ratio is less than 9, the viscosity of the slag will be relatively small, and workability at the 4.5 o'clock to 6 o'clock (7.5 to 6 o'clock) positions will be poor. The workability at the ~4 o'clock position is better, but if it exceeds 25, the viscosity of the slag increases and the workability at the 4.5 o'clock to 6 o'clock (7.5 to 6 o'clock) position is poor, and the bead and Compatibility with the base material deteriorates. Therefore, the CaCO3/CaF2 ratio should be in the range of 9-25.

(Fe: 15-40%) Fe is added to improve welding efficiency, but if it is less than 15%, the effect will be small, and if it exceeds 40%, the amount of slag forming agent will be relatively small. Slag encapsulation deteriorates. Therefore, the amount of Fe is in the range of 15 to 40%.

(Fe/CaF2: 5-22) As mentioned above, when a relatively large amount of Fe is added to improve the welding efficiency, high efficiency welding becomes possible;
This contributes to poor compatibility between the bead and the base material at the 6 o'clock position and the 7.5 o'clock to 6 o'clock positions. It has been found that in order to prevent this, the Fe/CaF2 ratio should be set to 5 or more. If this ratio is less than 5, the molten metal tends to sag, and the fit between the bead and the base material at the above-mentioned positions is not improved. Moreover, if this ratio exceeds 22, the spread of the crater becomes worse. Therefore, the ratio of Fe/CaF2 is 5-2
The range shall be 2.

(Ti: 0.5-3%) The effect of Ti on welding workability is that it can improve arc concentration and soften the arc, but if it is less than 0.5%, the arc Since the concentration of the stick is poor, it causes poor fusion, and requires skill in operating the stick. If it exceeds 3%, the arc becomes too weak and poor penetration occurs. Therefore, the amount of Ti is set in the range of 0.5 to 3%.

(B: 0.05-0.2%) B is effective for improving the compatibility with the base material, but if it is less than 0.05%, the compatibility with the base material is poor, resulting in insufficient compatibility. This causes the problem and requires skill to operate the stick. Moreover, if it exceeds 0.2%, the arc becomes too weak and poor penetration occurs. Therefore, the amount of B is set in the range of 0.05 to 0.2%.

(Ni: 0.5-4.5%) Ni is effective in strengthening the ferrite structure, but if it is less than 0.5%, the effect cannot be obtained; If it exceeds this value, the arc becomes weaker, droplet migration becomes worse, and poor penetration occurs. Therefore, the amount of Ni is set in the range of 0.5 to 4.5%.

[0029] In order to adjust the mechanical properties of the weld metal, one or more alloy components such as Cr, Mo, Cu, and Nb may be added at the same time.

[0030] Also, in the present invention, water glass is normally used as a binder, but since water glass contains a small amount of components such as Na2O and K2O, it also acts as a slag forming agent and an arc stabilizer. . The cross-sectional area ratio between the coating material and the steel core wire in the present invention is determined as appropriate.

Next, examples of the present invention will be shown.

[0032]

[Example 1] Steel core wire

[Table 1] A test welding rod was prepared by applying a coating having the composition shown in Table 1. Using these test welding rods, a horizontal fixed pipe (10
．． 3mmt×1016mmφ) butt joint (60°V
The workability at each welding position was investigated by welding the groove in a downward direction. The result

[Table 2] Also listed in

As is clear from Table 2, all of the examples of the present invention exhibit excellent weldability in downward welding at any position.

On the other hand, comparative example No. No. 11 has a low amount of CaCO3, so the bead does not fit well at the 3 o'clock (9 o'clock) position, and the CaCO3/CaF2 ratio is small, so the bead does not fit well at the 6 o'clock position.

Comparative Example No. 12 is CaCO3/CaF2
Because the ratio is too large, the bead does not fit well at the 6 o'clock position.

Comparative Example No. No. 13 has a small amount of CaF2, so the ratio of CaCO3/CaF2 and the ratio of Fe/CaF2 becomes too large, resulting in poor slag stability and bead conformability. Furthermore, since the amount of SrCO3 is large, the slag releasability is also poor.

Comparative Example No. 14 is SrCO3 and TiO
2 is low, so the bead does not fit well. Moreover, since the Fe content is high, the slag encapsulation property is poor. In addition, blowholes occurred due to the low Si content.

Comparative Example No. 15 has a low SiO2, so the arc is a little weak, and the Fe/CaF2 ratio is low, so 6
The bead tends to sag at the time position, making it difficult to blend in.

Comparative Example No. 16 has a lot of TiO2, so 3
The slug stability at the 9 o'clock position is poor, and the bead does not fit in well.

Comparative Example No. No. 17 has less CaCO3, so the bead conformability at the 3 o'clock (9 o'clock) and 6 o'clock positions is somewhat poor.

Comparative Example No. No. 18 has a large amount of SiO2, so the slag easily gets in the way, and the Fe/CaF2 ratio is small, so the bead does not conform well at the 3 o'clock (9 o'clock) to 6 o'clock positions.

Comparative Example No. Although No. 19 had good slag stability and bead conformability, pits were generated on the bead surface because there was too much deoxidizing agent.

Comparative Example No. No. 20 has a low SiO2 content, so the arc is a little weak, and the bead conformation at the 3 o'clock (9 o'clock) position is a little bad. In addition, due to high Si content, excessive deoxidation occurs,
Pit occurred on the bead surface.

Comparative Example No. In No. 21, deoxidation was insufficient due to low Mn content, and blowholes occurred.

[0045]

[Example 2] Steel core wire

[Table 3] ,

[Table 4] A test welding rod was prepared by applying a coating having the composition shown in Table 4. Using these test welding rods, a horizontal fixed pipe (12
mmt×1000 mmφ) butt joints (60° V groove) were welded in a downward direction, and the workability and toughness at each welding position were investigated. For the impact test, impact test pieces (10mmt x 10mmw x 50mml,
2V notch) was used. those results

[Table 5] ,

[Table 6] Also listed in

As is clear from Tables 5 and 6, all of the examples of the present invention exhibit particularly excellent welding workability in downward welding at any position.

On the other hand, Comparative Example No. In No. 13, the concentration of the arc is poor due to the small amount of Ti, so the welding operator is required to have advanced welding techniques.

Comparative Example No. Since No. 14 has a small amount of B, it has poor compatibility with the base metal, and requires advanced welding techniques from the welding operator.

Comparative Example No. 15 is CaCO3 and Si
Low O2, high Ti and B, and CaCO3/
Because the ratio of CaF2 was small, the arc became too weak, the crater did not spread, and the slag easily got in the way, resulting in insufficient compatibility with the base metal and poor penetration.

Comparative Example No. 16 is CaF2 and SiO2
Since the CaCO3/CaF2 ratio is large and the ratio of CaCO3/CaF2 is small, the slag interferes and the compatibility with the base material is poor.

Comparative Example No. 17 has a lot of CaCO3,
At the 3 o'clock (9 o'clock) position, the slag tends to get in the way and the bead does not fit well.

Comparative Example No. No. 18 has a small amount of CaF2, so the ratio of CaCO3/CaF2 and the ratio of Fe/CaF2 become too large, resulting in poor slag stability and bead conformability. Moreover, since there is a large amount of SrCO2, the slag removability is also poor.

Comparative Example No. Sample No. 19 contained a large amount of Mn, resulting in excessive deoxidation, and pits were generated on the bead surface.

Comparative Example No. 20 is SrCO3 and Ti
Beads do not conform well due to low O2. Moreover, since the Fe content is high, the slag encapsulation property is poor. In addition, blowholes occurred because the Si content was low.

Comparative Example No. 21 has a too low Fe/CaF2 ratio, so the bead tends to droop at the 6 o'clock position.
Familiarity deteriorates. Further, since the Si content was high, deoxidation was excessive, and pits were generated on the bead surface.

Comparative Example No. No. 22 has a large amount of TiO2, so the slag easily gets in the way, and the bead and base metal do not fit well. In addition, blowholes occurred due to the low Mn content.

Comparative Example No. Sample No. 23 had a large amount of Ni, which weakened the arc and caused poor droplet transfer, resulting in poor penetration.

[0058]

[Effects of the Invention] As detailed above, according to the present invention,
Particularly in downward welding of circumferential butt joints of pipes, it is possible to weld in all positions, especially from 4.5 o'clock to 6 o'clock (7.5 o'clock to 6 o'clock).
Since the bead and base metal are well matched at the position (time),
No rework is required and high efficiency is possible. Furthermore, in addition to these excellent effects, the concentration of the arc and its compatibility with the base metal can be further improved, so that the welding work can be performed very easily without requiring sophisticated welding techniques. On the other hand, in response to further demands for low-temperature toughness,
By strengthening the ferrite structure, it is also possible to improve low-temperature toughness.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing welding positions in downward welding of a circumferential butt joint of a pipe in a clockwise manner.

FIG. 2 is a diagram showing the sampling positions of impact test pieces.

Claims (3)

[Claims] [Claim 1] In weight% (hereinafter the same), CaCO3
:35-55%, SrCO3:1-4%, CaF2:1
．． 5-4%, TiO2: 1-5%, SiO2: 5-12
%, Si: 3-9%, Mn: 1-6% and Fe: 15-
40%, and CaCO3/CaF2:9-2
5. A low hydrogen-based coated arc welding rod, characterized in that a coating agent satisfying the relationship of Fe/CaF2: 5 to 22 is applied to the outer periphery of the steel core wire. [Claim 2] CaCO3: 35-55%, SrCO
3:1-4%, CaF2:1.5-4%, TiO2:1
~5%, SiO2: 5-12%, Si: 3-9%, Mn
:1 to 6% and Fe:15 to 40%, and further contains Ti.
:0.5-3% and B:0.05-0.2%,
and CaCO3/CaF2:9-25, Fe/CaF
A low hydrogen-based coated arc welding rod characterized in that a coating agent satisfying the relationship of 2:5 to 22 is applied to the outer periphery of a steel core wire. Claim 3: The coating further contains Ni: 0.5 to 4.5%.
The low hydrogen-based coated arc welding rod according to claim 2, characterized in that it contains.