JPH0796394A - Low hydrogen type coated electrode - Google Patents

Abstract

PURPOSE:To provide a low hydrogen type coated electrode preventing sagging, etc., of slag even with single layer single pass welding by a weaving procedure and executing welding with a small number of passes. CONSTITUTION:This low hydrogen type coated electrode is formed by coating the outer periphery of a steel core wire with a coating material contg. 1 to 6% Ti oxide contg. >=40% superfine Ti oxides having a grain size of <=0.3mum in a coating rate range of 20 to 30% and regulating the carbon content by the following equation over the entire part of the welding electrode to 0.08 to 0.25%. The carbon content = (the carbon content in the core wire)+{(the carbon content in the coating material)X(coating rate/core wire rate)}, where the coating rate = (the weight of the coating material/the weight of the entire part of the welding electrode)X100%, the core wire rate = (the weight of the core wire/the weight over the entire part of the welding electrode)X100%. As a result, this welding electrode is suitable for down hand welding of particularly the circumferential butt joints of pipes.

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, particularly, to an excellent effect when applied to downward welding of a circumferential butt joint of a pipe.

[0002]

2. Description of the Related Art Conventionally, circumferential butt welding at a pipeline site has been performed in Japan by upward welding using a low-hydrogen coated arc welding rod or an illuminate-based coated arc welding rod. In foreign countries, downward welding using a high-cellulosic coated arc welding rod is performed. But,
Since hydrogen cracking is a major problem in welding high-strength steel pipes, especially in field welding in cold regions, it is desirable to use a low-hydrogen coated arc welding rod. It was very difficult to weld in.

[0003]

In order to solve this problem, the applicant of the present invention has previously proposed JP-A-4-376393. However, the low-hydrogen coated arc welding rod of the above-mentioned proposal has significantly superior performance as compared with those before it, but recently, higher efficiency, severer performance has been required, It was not always satisfactory, and improvements were required.

That is, in order to achieve high efficiency, one-layer one-pass welding in which the number of passes is reduced as much as possible is desired. That is, in the case of 1-layer 2-pass welding, after welding the first bead, before welding the second bead, grind the first bead toe portion in the groove with a grinder or the like to widen the groove. Prevents insufficient penetration. However, since the work takes time, the above steps are not required if the welding is performed in one layer and one pass. Therefore, a low hydrogen system covered arc welding rod capable of performing one layer and one pass has been desired.

However, in the conventional low hydrogen type covered arc welding rod, when weaving is carried out for one-layer one-pass welding, there is a drawback that the slag is liable to droop and the dripping of the weld metal is likely to occur.

Further, in the conventional low hydrogen system coated arc welding rod, if the backside welding is carried out under the conditions of high current and high welding speed in order to carry out high efficiency welding, the slag tends to drip and the weld metal has a concave backing. It had the drawback of becoming a wave bead.

The present invention solves the above-mentioned drawbacks of the prior art and can prevent the slag from sagging even in the one-layer one-pass welding by the weaving process. As a result, the welding process can be performed with a small number of passes. It is intended to provide an arc welding rod.

[0008]

Under the above circumstances, the present inventors first examined a method for preventing slag sag. It was found that the conventional welding rod has a small arc spread and lacks stability in droplet transfer, and as a result, when weaving is performed, the spread of the crater is insufficient and the slag tends to droop. Therefore, various investigations were made on means for securing the spread of the crater, making the arc into a spray, and stabilizing the droplet transfer. As a result, it was found that by adding ultrafine Ti oxide, the protective cylinder was stabilized, that is, the protective cylinder was melted uniformly, the directionality of the arc was stabilized, and the spread of the crater was easily controlled. .

With conventional welding rods, since the work is almost straight and contact welding is performed, the stability of the protective cylinder does not pose a serious problem, but in the weaving work, the welding rod is slightly separated from the base metal. Therefore, it is necessary that the protective cylinder has more uniform meltability, which is considered to be the reason why the conventional welding rod is not suitable for weaving.

[0010] However, although the ultrafine-grained Ti oxide can obtain the above-mentioned effects, on the other hand, the amount of spatter is not sufficiently reduced, and further improvement can be made in terms of spatter removal in the subsequent process and safety during welding. It turned out to be necessary.

Therefore, as a result of studying various components, the present inventors conversely increase the amount of carbon, which is considered to be low in the crack resistance in the conventional low hydrogen type coating agent. It was found that the arc can be stabilized and the amount of spatter generated can be reduced, and the present invention has been completed here.

That is, the present invention is based on the total weight% of the coating agent,
Metal carbonate: 30-50%, metal fluoride: 1.5-4
%, SiO ₂ : 5 to 12%, Ti oxide: 1 to 6% (however,
Contain 40% or more of ultrafine Ti oxide having a particle size of 0.3 μm or less. ), Si: 3 to 9%, Mn: 1 to 6%, F
The coating material containing e: 25 to 50% is applied to the outer circumference of the steel core wire in a coverage of 20 to 35%, and the carbon content of the entire welding rod according to the following formula (1) is 0.08. The gist is a low-hydrogen coated arc welding rod characterized by being regulated to 0.25%. Notation Carbon amount = (carbon amount in core wire) + {(carbon amount in coating material) x (coverage rate / core rate)} (1) where, coverage rate = (weight of coating material / welding rod) Total weight) x 100% Core wire rate = (core wire weight / total weight of welding rod) x 100%

According to another aspect of the present invention, the coating material further comprises N
i: 0.5-4.5%, Mo: 0.1-4.5%, Ti: 0.1
~ 1% or more of 3%, and / or B:
It is characterized by containing 0.05 to 0.2%.

[0014]

The reasons for limiting the components and the coverage in the present invention are as follows.

Metal carbonate: 30 to 50% Metal carbonate is added as a gas generating agent, but if it is less than 30%, the amount of gas generated is small and the shield becomes insufficient and the viscosity of the slag becomes small and pits are formed on the bead surface. To do. On the other hand, if it exceeds 50%, the viscosity of the slag remarkably increases, the familiarity of the bead deteriorates, and the amount of gas generation increases and the generation of spatter increases. Therefore, the amount of metal carbonate is set in the range of 30 to 50%. As the metal carbonate, for example, CaCO ₃ , BaCO ₃ , MgCO ₃ or the like is used.

Metal Fluoride: 1.5 to 4% Metal Fluoride acts to adjust the viscosity and fluidity of the slag. However, if it is less than 1.5%, there is no effect, and if it is more than this, good beads are formed at the position of 2 to 4 o'clock, but if it exceeds 4%, the viscosity of the slag becomes relatively small, and the fluidity of the slag becomes relatively small. Increase, 4.5 to 6 o'clock and 7.5 to
At the 6 o'clock position (see FIG. 1), the bead and base metal become less compatible. Therefore, the amount of metal fluoride is 1.5-4%
The range is. As the metal fluoride, for example, Ca
F ₂ etc. are used.

SiO ₂ : 5 to 12% SiO ₂ has a function of strengthening the arc to secure penetration. However, if it is less than 5%, the arc is weak and the spread of the crater is small. Also, the familiarity of the beads is deteriorated. on the other hand,
When it exceeds 12%, the slag interferes with the position at 2 to 4 o'clock, and it is easy to be involved, so that a good bead cannot be obtained. Therefore, the amount of SiO ₂ is set in the range of 5 to 12%.

Ti oxide: 1 to 6% (however, the particle size is 0.3 μm
40% or more of the following ultrafine Ti oxides should be included.) The Ti oxides have the effect of preventing the sagging of the weld metal even during weaving work by making the arc of the arc uniform by homogenizing the melting of the protective cylinder. There is. For that purpose, it is necessary to contain 1 to 6% of Ti oxide containing 40% or more of ultrafine Ti oxide having a particle size of 0.3 μm or less. If it is less than 1%, the effect cannot be obtained, and the familiarity of the bead is deteriorated. On the other hand, if it exceeds 6%, the fluidity of the slag increases, and the slag hindrance is likely to occur at the 2-4 o'clock position.

Si: 3 to 9%, Mn: 1 to 6% Si and Mn are added as deoxidizing agents, but if each is less than the lower limit value, there is no effect, and if it exceeds the upper limit value, deoxidation becomes excessive. Pits will be generated on the bead surface.
Si is a single substance or Fe-Si, Si-Mn, Ca-Si.
Can be added in the form of Mn, Mn is metallic Mn or Fe-Mn, Si
-Mn or the like can be added.

Fe: 25 to 50% Fe is added to improve the welding efficiency, but 25%
If it is less than 50%, the effect is small, and if it exceeds 50%, the amount of the slag forming agent is relatively small, and the slag encapsulating property is deteriorated. Therefore, the Fe amount is in the range of 25 to 50%. Fe is iron powder, or Fe-Mn, Fe-S
It can be added as Fe component such as i.

Coverage: 20-35% If the coverage is less than 20%, the amount of slag-forming agent decreases, and pits are generated due to insufficient shield. On the other hand, if it exceeds 35%, the amount of the slag-forming agent becomes too much, the slag is disturbed, and good beads cannot be obtained. Therefore, the coverage is set to the range of 20 to 35%.

Carbon amount (value of formula (1)): 0.08 to 0.25% If the carbon amount defined by the following formula (1) is less than 0.08%, the droplets become large and spatter occurs. Increased, also 0.25%
It has been found that the arc becomes too strong when the temperature exceeds the limit, the crater is dug down, the weld metal is easily dropped, and the amount of spatter is slightly increased. Therefore, in the present invention,
The amount of carbon defined by the formula (1) is regulated within the range of 0.08 to 0.25%. It is more preferably 0.12 to 0.20%.

Carbon amount = (carbon amount in core wire) + {(carbon amount in coating material) × (coverage rate / core wire rate)} (1) where, coating rate = (weight of coating material / Welding rod total weight) x 100% Core wire ratio = (core wire weight / welding rod total weight) x 100%

In addition to the above components, if necessary, one or more of the following components may be added to the coating agent in an appropriate amount.

Ni: 0.5-4.5% Ni is effective for strengthening the toughness of the ferrite structure, but if it is less than 0.5%, the effect is not obtained, while on the other hand, it is 4.5.
If it exceeds%, the arc becomes weak and the droplet transferability deteriorates, resulting in poor penetration. Therefore, the amount of Ni is 0.5-
The range is 4.5%.

Mo: 0.1-4.5% Mo is effective for adjusting the strength, but if it is less than 0.1%, the effect cannot be obtained. On the other hand, if it exceeds 4.5%, an impact value is obtained. Deteriorates. Therefore, the Mo amount is set to 0.1 to 4.5%.

Ti: 0.1 to 3% The effect of Ti on the welding workability is that the concentration of the arc can be improved and the arc can be softened. However, if it is less than 0.1%, the concentration of the arc is poor, which causes a defective fusion and requires skill in operating the rod. On the other hand, if it exceeds 3%, the arc becomes too weak, resulting in poor penetration. Therefore, the Ti amount is set in the range of 0.1 to 3%. Incidentally, Ti is added in the form of, for example, Fe-Ti.

B: 0.05 to 0.2% B is effective for improving the compatibility with the base material,
If it is less than 0.05%, the familiarity with the base material is poor, so skill is required in operating the rod. If it exceeds 0.2%, the arc becomes too weak, resulting in defective penetration. Therefore, the amount of B is set in the range of 0.05 to 0.2%. B can be added in the form of B alloy or B oxide.

In order to adjust the mechanical properties of the deposited metal, one or more alloy components such as Cr, Cu and Nb may be added to the coating material or the core wire. The other component composition of the steel core wire is not particularly limited.

In the present invention, water glass is usually used as a viscous agent, but since water glass contains a small amount of components such as Na ₂ O and K ₂ O, it is used as a slag forming agent and an arc stabilizer. Also works. When a DC power source is used, it is preferable that the water glass does not contain K ₂ O because the protective cylinder is more stable.

Next, examples of the present invention will be described.

【Example】

A coating rod having the composition shown in Tables 1 and 3 was applied to the steel core wire in a coating ratio range of 20 to 35% to prepare a trial welding rod. Using these test welding rods, a horizontal fixed pipe (10.3 mmt x 1016 mmφ) butt joint (60 °
V groove) with 1 layer 1 pass welding Welding condition: current 80-2
20A, voltage 18-28V, welding speed 10-25cm / mi
Welding was performed downward at n and the workability at each welding position was investigated. The results are also shown in Table 2.

In the table, No. 1 to No. 10 are all examples of the present invention and showed good results. No welding metal slag, no slag dripping, and little spatter generation.

On the other hand, in Comparative Example No. 11, the amount of metal carbonate was too much, the amount of spatter was increased, and the stability of the slag was lacking. Further, the amount of ultrafine Ti oxide in the Ti oxide was less than 40%, and the weld metal lacked stability (sagging).

In Comparative Example No. 12, the Ti oxide was too much and the slag was disturbed. Further, since the carbon content in the formula (1) is low, spatter frequently occurred. In addition, the amount of metal fluoride was large, the fluidity of the slag increased, and the compatibility with the base material deteriorated.

In Comparative Example No. 13, the amount of SiO ₂ was large and the slag was disturbed. Further, the carbon content in the formula (1) was too high, and the stability of the weld metal deteriorated.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

As described above in detail, according to the low hydrogen type covered arc welding rod of the present invention, the welding electrode 1
Even in the layer 1 pass welding, it is possible to prevent the slag from dripping, and it is possible to achieve construction with a small number of passes. It is also possible to use Uranami.

[Brief description of drawings]

FIG. 1 is an explanatory diagram in which a welding position in a downward welding of a circumferential butt joint of a pipe is represented by a clock type.

Claims (3)

[Claims] 1. A coating material based on the total weight% (hereinafter the same), metal carbonate: 30 to 50%, metal fluoride: 1.5 to 4%, SiO ₂ : 5 to 12%, Ti oxide: 1 ~ 6% (however, containing 40% or more of ultrafine Ti oxide having a particle size of 0.3 µm or less), Si: 3 to 9%, Mn: 1 to 6%, Fe: 25 to 50%, Is applied to the outer circumference of the steel core wire in a coverage of 20 to 35%, and the carbon content of the entire welding rod according to the following formula (1) is 0.08 to 0.25%.
A low-hydrogen coated arc welding rod characterized by being regulated according to. Notation Carbon amount = (carbon amount in core wire) + {(carbon amount in coating material) x (coverage rate / core rate)} (1) where, coverage rate = (weight of coating material / welding rod) Total weight) x 100% Core wire rate = (core wire weight / total weight of welding rod) x 100% 2. The coating material further comprises Ni: 0.5-4.5%,
2. One or more of Mo: 0.1 to 4.5% and Ti: 0.1 to 3% are contained.
The low-hydrogen coated arc welding rod according to 1. 3. The low-hydrogen coated arc welding rod according to claim 1, wherein the coating material further contains B: 0.05 to 0.2%.