JPH07276082A - Low hydrogen type coated electrode - Google Patents

Abstract

PURPOSE:To provide a low hydrogen type coated electrode capable of preventing dry cracking without degrading other performance, such as dislodgment resistance and welding workability even if high-speed coating is executed. CONSTITUTION:The low hydrogen type coated electrode is formed by coating the circumference of a steel core wire with a welding flux compounded with a metal carbonate, metal fluoride, oxide, deoxidizing agent, metallic powder, slipping agent, etc., by using water glass contg. Li2O at a ratio of <=1.20% by total weight of the water glass as a binder, then drying the coating. The grain size constitution of the welding flux is 18 to 28% >=105 to <250mum and 40 to 50% >=6 to <30mum and is confined to <=30% <=250mum and <=9% <6mum. In addition, the ratio of the particles of >=74mum is specified to 30 to 40% and the ratio of the particles of <74mum to 60 to 70%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low hydrogen type coated arc welding rod which is excellent in productivity and has good coating drop resistance, welding workability and moisture absorption resistance.

[0002]

2. Description of the Related Art A low hydrogen type coated arc welding rod is made of CaC.
O _3, metal carbonates such as BaCO _3, metal fluorides such as CaF _2, TiO _2, oxides such as _{SiO 2, ZrO 2, Al 2} O 3, Fe-Si, deoxidizing agents such as Ca-Si, Fe-Mn, Fe
A flux prepared by mixing metal powders such as -Ni and Fe-Ti and a slip agent such as mica and talc was applied around the steel core wire by using a fixing agent, and then schematically shown in FIG. It is generally manufactured by drying in a drying oven.

During the drying process, gas mainly composed of water vapor or hydrogen is generated by the reaction between the adhesive and the metal powder. If these gases are difficult to deviate from the inside of the coating during drying, the coating of This causes cracks and is called dry cracks. When welding with a welding rod with dry cracks,
The coating is chipped and does not form a protective cylinder of normal shape, which causes blowholes and other welding defects. Therefore, in the visual inspection of the product, the welding rod in which the dry crack has occurred is severely selected as a defective product, which is a major cause of a decrease in productivity.

Conventionally, as a method of preventing dry cracking, from the viewpoint of the particle size of the welding flux, JP-A-54-10225 is used.
JP-A-59-1506 discloses drying conditions.
No. 96, JP-A-60-40695 and the like are proposed.

[0005]

Problems to be Solved by the Invention JP-A-54-1022
No. 54 was an epoch-making one which prevented dry cracking by adjusting the particle size of the welding flux without complicated temperature control. However, since then, the coating speed has been increased to improve productivity, for example,
If the rod diameter (core wire diameter) is 5.0 mm, the conventional value is 200 to 300 m.
Attempts have been made to increase the coating speed of 450 m / min to about 450 m / min. The drying time cannot be shortened due to the proposition of the low hydrogen type coated arc welding rod that the coating water content must be kept low when the coating speed is increased, and therefore the speed of the conveyor is maintained at the conventional speed. Or you have to slow it down.

Therefore, as shown in FIG. 2, the degree of overlap of the welding rods on the conveyor becomes larger than in the conventional case, and it becomes difficult to dry the welding rods, and inevitably a higher drying temperature is required. .

Due to such a change in the situation, it has become difficult to suppress the dry cracking only by controlling the particles having the conventional particle diameter. Focusing only on dry cracking, as shown in Japanese Patent Laid-Open No. 54-10225, it can be improved by making the particle size composition coarse, but this is not an effective means because the drop resistance decreases.

At present, when the coating speed is increased, in order to prevent dry cracking, measures are taken such as adjusting the particle size composition of the welding flux in the prior art and controlling the drying conditions more severely. . However, although the temperature control technology has advanced, the drying furnace for welding rods is generally long, and since the welding rods dried at the low drying temperature in the previous stage flow by the conveyor, the temperature must be strictly controlled over the entire length of the furnace. It is difficult to control, and a considerable degree of dry cracking occurs, which is an obstacle to increasing the coating speed. For this reason, the development of a low-hydrogen coated arc welding rod that can prevent dry cracking even when high-speed coating is performed, and has good drop resistance and good welding workability has been awaited.

In order to meet such demands, the present invention is a low hydrogen type coating capable of preventing dry cracking without deteriorating other performances such as drop resistance and welding workability even when high speed coating is performed. It is intended to provide an arc welding rod.

[0010]

In order to solve the above problems, the inventors of the present invention prevent dry cracking without lowering other performances such as drop resistance and welding workability even when high-speed coating is performed. In order to develop a welding rod that can be made, we conducted a thorough study on a more appropriate welding flux particle size composition.

Specifically, as a result of earnest studies on the particle size composition of the welding flux, cracking of the coating due to drying, drop resistance, etc., even if the particles are not so coarse (74 μm or more), the drop resistance is rather high. From the viewpoint of the above, it was found that there is a grain size constitution which can be made finer (less than 74 μm) as compared with the conventional one, and moreover, dry cracking can be greatly suppressed, and the present invention has been made here.

That is, according to the present invention, a welding flux containing a metal carbonate, a metal fluoride, an oxide, a deoxidizer, a metal powder, a slipping agent, etc. is used as a fixing agent and the amount of Li ₂ O is a total weight ratio of water glass. 1. A low hydrogen system coated arc welding rod, which is obtained by applying water glass of 1.20% or less on the periphery of a steel core wire, and then drying, wherein the particle size composition of the welding flux is 105 μm or more and less than 250 μm: 18 Up to 28%, (welding flux total weight ratio, the same below), 6 μm or more and less than 30 μm: 40 to 50%, and 250 μm or more: 3% or less, less than 6 μm: 9% or less, and 74 μm The low-hydrogen coated arc welding rod is characterized in that the above particles are 30 to 40% and particles less than 74 μm are 60 to 70%.

[0013]

The present invention will be described in more detail below. The reason for limiting the grain size composition of the welding flux in the present invention is as follows.

105 μm or more and less than 250 μm: 18 to 28
% Particles smaller than 105 μm are 1 to prevent dry cracking.
It is necessary to be 8% or more, and if less than 18%, dry cracking tends to occur. On the other hand, it is necessary to suppress it to 28% or less in order to obtain good drop resistance. Therefore, 105 μm or more 25
Particles less than 0 μm are in the range of 18-28%.

6 μm or more and less than 30 μm: 40 to 50% In order to obtain good shedding resistance, 40% or more of particles of 6 μm or more and less than 30 μm are necessary, while it is 50% or less to prevent dry cracking. There is a need. Therefore, 6 μm
Particles having a size of 30 μm or more are in the range of 40 to 50%.

250 μm or more: 3% or less If the content of coarse particles of 250 μm or more exceeds 3%, the drop resistance rapidly decreases. Therefore, particles of 250 μm or more are 3
% Or less.

Less than 6 μm: 9% or less Fine particles of less than 6 μm are particles that most affect dry cracking. By suppressing this to 9% or less, dry cracking can be prevented even if the amount of fine particles is increased from the conventional amount (the drop resistance is improved). Therefore, the content of fine particles less than 6 μm is 9% or less.

Particles of 74 μm or more: 30-40% Particles of less than 74 μm : 60-70% Particles of 105 μm or more and less than 250 μm, 6 μm or more and 30 μm
The particle size of particles other than particles smaller than 250 μm and particles smaller than 250 μm and particles smaller than 6 μm has a relatively small effect on dry cracking and falling resistance and is not specified individually, but the total of particles larger than 74 μm When the content is in the range of 30 to 40% (that is, the total amount of particles of less than 74 μm is 60 to 70%), dry cracking hardly occurs, and good drop resistance can be obtained. Therefore, the total number of particles of 74 μm or more is 30-40.
%, Ie the sum of particles less than 74 μm is 60-70
%.

By adopting the grain size constitution as described above, the welding workability also becomes good. With the grain size composition in the direction in which the drop resistance decreases (the grain size composition from the coarseness, especially the contribution of particles of 250 μm or more is large), the particles of the coating are coarse, so the protective tube is likely to be chipped over the entire length of the welding rod, Not well formed. On the other hand, in the case where the dry cracking resistance decreases (the particle size composition from the finer, especially the contribution of particles of less than 6 μm is large), there are many cases where cracks do not reach the coating surface and are hidden inside (in this case, However, if the welding rod, which had been found to have good welding workability, came to the part of the internal crack, the protective cylinder suddenly popped off and became a major obstacle to the welding work. Therefore, the above grain size range is also required in terms of welding workability.

Li ₂ O in water glass : 1.20% or less Li ₂ O content in water glass (ratio to total weight of water glass) is 1.20%
If the content exceeds the limit, after coating, immediately after the coating is put into the primary drying oven as in the normal process (continuous drying), only the coating surface is rapidly dried and a film is formed, and the internal gas cannot escape and dry cracking occurs. Occurs. For this reason, when water glass with a high Li ₂ O content of more than 1.20% is used from the viewpoint of moisture absorption resistance, which will be described later, it should be placed in an appropriate frame in order to improve the ventilation of the welding rod before primary drying. It is necessary to carry out preliminary drying for 1 to 2 hours at room temperature or 12 hours at room temperature and then to the primary drying. The present invention is intended to cope with the improvement of productivity, and the amount of Li ₂ O is 1.2 which enables continuous drying.
It is 0% or less.

Li ₂ O functions to improve the moisture absorption resistance of the coating. Therefore, when extremely good moisture absorption resistance and dry crack resistance are required, the amount of Li ₂ O should be 0.20 to 1.20. % Content is desirable.

In order to further improve the moisture absorption resistance, the other components in the water glass are in the total weight ratio of water glass.
_{SiO 2: 22~28%, Na 2} O: 6~10%, K 2 O:
It is desired to be 4 to 8%, and the drying condition is 470 to 53
40 to 80 minutes at 0 ° C is suitable.

Although the composition of the welding flux is not particularly limited, the following raw materials are used in the low hydrogen type covered arc welding rod. Metal carbonates such as CaCO ₃ and BaCO ₃ : These metal carbonates decompose at high temperatures to generate gas, shielding the arc from the atmosphere and preventing oxidation and nitriding. It also serves as a slag generator. Metal fluorides such as CaF _2: These metal fluorides is a slag basicity, reduce the oxygen in the weld metal. It also works as a slag generator. Oxides such as TiO ₂ , SiO ₂ , ZrO ₂ , SiO ₂ , and Al ₂ O ₃ : These oxides are slag-forming agents and are appropriately adjusted to adjust the viscosity of the slag. Deoxidizing agents such as Fe-Si and Ca-Si: Fe-as deoxidizing agents for low hydrogen type coated arc welding rods that form basic slag
Si is indispensable, and Ca-Si, Mg, etc. may be added for strengthening deoxidation. Metal powders such as Fe-Mn, Fe-Ni, Fe-Ti, and Fe-B: Metal powders are alloy elements that are appropriately added depending on the strength and toughness required of the weld metal, and there are many types. The alloying element may be added in the form of oxide, glass or the like. Sliding agents such as mica and talc: Sliding agents act as lubricants during welding flux coating, and may be added as necessary. Others: In addition to the above, various raw materials may be added in small amounts in order to improve productivity, welding workability, and the like.

The method of adjusting the particle size composition is not particularly limited, but it is convenient to prepare and prepare a few particle size compositions for each raw material.

Next, examples of the present invention will be described.

[0026]

[Examples] Welding flux was produced by mixing each raw material with two or three kinds of grain sizes and blending the individual raw materials so as to have various grain sizes. The welding flux is A:
Mild steel to 490 N / mm ² grade high strength steel, B: low temperature steel,
C: Three types for 780 N / mm ² class high-strength steel. Table 1 shows the composition of the welding flux and the addition amount of water glass used as the fixing agent. A sonic vibration type automatic sieving measuring device was used up to 60 μm for measuring the particle size composition of the welding flux, and a laser diffraction type particle size distribution measuring device was used for measuring smaller particles.

Using a welding machine, these welding fluxes were applied at a coating speed of 200 to 450 m / min and a diameter of 5.0 mm and a length of 40 mm.
It was applied to a 0 mm core wire so that the coating diameter would be 7.8 mm, and then continuously dried under the drying conditions shown in Table 2. The amount of coating is about 1000 kg. Regarding the drying conditions, particularly severe temperature control was not carried out, and the temperature in the furnace fluctuated by about ± 10 ° C with respect to the temperature shown in Table 2.

Table 3 shows the details of the particle size composition of the flux, the coating speed and the secondary drying conditions. For low temperature steel, which is often used for welding thick plates of important structures such as offshore structures,
For 780 N / mm ² grade steel, water glass containing 0.20 or more of Li ₂ O was used to obtain good moisture absorption resistance. Further, for these, in order to suppress the hydrogen content of the weld metal to a lower level, the secondary drying temperature is set higher than that for mild steel to 490 N / mm ² class high strength steel.

After the completion of drying, the dry cracks are as follows: Dry crack ratio (%) = {(Welding rod weight (k
g)) / (total weight of dried welding rod (kg))} × 100, and a dry crack ratio of 0.1% or less was regarded as acceptable.

As for the drop-off resistance, a 5 kg paper box for packing the product is packed with a test welding rod and dropped from a height of 1 m onto a steel plate.
The weight of the coating that had fallen off was measured, and 6.0 g or less was regarded as acceptable.

In the welding workability test, a welding rod selected as a good product was used, a mild steel plate having a plate thickness of 20 mm was assembled into a T-shape, a welding current: 170 A, and a welding speed: 6-8 cm / min. Then, fillet welding was performed to make a determination. Welding workability was rated as good, somewhat poor, and poor, and good was passed.
In this welding workability test, whether or not the protective cylinder was normally formed was observed in detail.

The test results are shown in Table 4. Test Nos. 1 to 4 and Test No. 6 are examples of the present invention, and the occurrence of dry cracks was extremely small, and the drop resistance and welding workability were good.

[0033] In contrast, among Comparative Examples, test No.5 is the case of using water glass Li ₂ O amount exceeds 1.20 percent Li ₂ O added water glass, drying cracking rate 75 % Has been reached. In addition, when a part of the coated welding rod was not continuously dried but pre-dried was added, the dry cracking ratio was as good as 0.08%.

Test No. 7 shows that particles of 250 μm or more are 3.3.
%, The dry cracking rate is good, but the dropout amount is large. Also in the welding workability, since the coating contains a large amount of coarse particles, the protective cylinder tends to be chipped.

Tests No. 8 and No. 9 are examples in which the welding flux was the same and the coating speed was changed. The particle size composition of the welding flux is within the range of JP-A-54-102254, and good results have been obtained at the conventional coating speed (test No. 8). However, test No. 9 for high-speed painting
In this case, since particles with a size of less than 6 μm account for as many as 10.5%, dry cracking occurs. In the welding workability test, it was observed that the protective cylinder sometimes popped off during welding. When the surface of the coating was shaved and examined for confirmation, hidden cracks occurred in various places inside the coating.

In Test No. 10, the number of particles of 150 μm or more and less than 250 μm was as large as 29.5%, and the dropout amount was large. However, since the particles having a size of 250 μm or more are 3% or less, the amount of falling is smaller than that in Test No. 7. The welding workability was also better than that of Test No. 7.

Test No. 11 has a large dry cracking rate when particles having a size of 6 μm or more and less than 30 μm are as large as 50.8%. However, since the number of particles having a size of less than 6 μm was as small as 7.4%, the dry cracking ratio was smaller than that in Test No. 8 and the welding workability was also better than that in Test No. 8.

Test No. 12 shows that particles of 74 μm or more are 29
%, The dry cracking ratio is high. However, since there were no particles of 250 μm or more and few particles of less than 6 μm, the welding workability was judged to be good although there was some deterioration.

Test No. 13 shows that particles of 74 μm or more are 41.
3% is large (less than 74 μm is as small as 58.7%), and the amount of dropout is slightly large. The welding workability was good for the same reason as in Test No.12.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

As described in detail above, according to the present invention,
It is possible to provide a low hydrogen-based coated arc welding rod which has excellent productivity under high-speed coating, and has good drop resistance and welding workability. Of course, it can be applied to low-hydrogen coated arc welding rods for various purposes, and its utility value is extremely high.

[Brief description of drawings]

FIG. 1 is a schematic diagram of drying a welding rod.

FIG. 2 is a schematic diagram showing a state of a welding rod on a conveyor when high-speed coating and low-speed coating are performed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyuki Hara 100-1 Urakawachi Urakawachi, Fujimae City, Kanagawa Prefecture Kobe Steel Works, Fujisawa Works

Claims (2)

[Claims] 1. A welding flux containing a metal carbonate, a metal fluoride, an oxide, a deoxidizer, a metal powder, a sliding agent, etc.,
The amount of Li ₂ O as a fixing agent is 1.20% in the total weight ratio of water glass.
A low hydrogen-based coated arc welding rod which is obtained by applying the following water glass around the steel core wire and then drying, wherein the particle size composition of the welding flux is 105 μm or more and less than 250 μm: 18 to 28%, Welding flux total weight ratio, same below), 6 μm or more and less than 30 μm: 40 to 50%, and 250 μm or more: 3% or less, less than 6 μm: 9% or less, and particles of 74 μm or more: 30 -40%, particles less than 74 μm: 60-70%, a low hydrogen-based coated arc welding rod. 2. Li ₂ O: 0.20 in the total weight ratio of water glass.
The low-hydrogen coated arc welding rod according to claim 1, wherein water glass containing ˜1.20% is used as a fixing agent.