JPS591519B2 - Manufacturing method of ultra-low hydrogen coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a low-hydrogen coated arc welding rod, and more particularly to a method for manufacturing a coated arc welding rod for obtaining a weld metal with good resistance in welding structural steel. It is something.

BACKGROUND ART Conventionally, in welding steel structures, measures have been taken to prevent weld cracks, such as using welding materials with excellent crack resistance or performing preheating.

For example, board thickness 25m? ! In welding 77I class steel of 50 kg/m or more, a low hydrogen welding rod is used and preheating is performed at 75 to 150° C. depending on the atmospheric conditions and the degree of restraint. However, the preheating work that is performed during welding work is complicated, requiring labor and fuel costs, and is not economical in terms of welding costs. There is a need for the development of extremely superior welding rods.

The present inventors have conducted various studies to improve the durability of weld metal, and as proposed in JP-A-53-138947, an appropriate amount of Te can be added to the core wire of a coated arc welding rod, the coating material, or both. It has been found that by adding Be, the amount of diffusible hydrogen in the weld metal is reduced to an extent that could not be expected based on conventional knowledge. Therefore, the present inventors continued to strive to improve the durability of the weld metal, and studied the development of a low-hydrogen coated arc welding rod in which the amount of diffusible hydrogen in the weld metal was even lower. In other words, if the amount of diffusible hydrogen in the weld metal can be further reduced, it will be possible to weld thicker steel plates without preheating and without cracking, as long as they have the same strength.

The main sources of diffusible hydrogen in weld metal are atmospheric moisture dissociating under the arc and penetrating the weld metal, and moisture contained or attached to the coated arc welding rod used and the steel material to be welded. There is hydrogen.

First, in order to further reduce the amount of diffusible hydrogen in the weld metal using a low-hydrogen coated arc welding rod, it is important to reduce the hydrogen source in the core wire or coating itself as much as possible. For this purpose, it is necessary to reduce the hydrogen content in the core wire and the water content on the surface of the core wire, as well as reduce and remove the water content in the coating material. Many attempts have been made to reduce the hydrogen source contained in or attached to coated arc welding rods.

For example, the method of increasing moisture absorption resistance found in Japanese Patent Publication No. 48-34485, or applying various treatments to the coating material,
There are methods to provide moisture absorption resistance, and some methods have been implemented. However, by taking such measures, passive measures such as simply reducing the hygroscopicity of the coated arc welding rod will not reduce the amount of diffusible hydrogen in the weld metal to the extent that cracking can be prevented without preheating. is almost impossible, and it is necessary to minimize the amount of hydrogen source contained in all the raw materials that make up the welding salvage.

In addition, in welding construction of welded structures where it is necessary to completely prevent cracking of welded parts, strict construction management such as re-drying and storage is carried out to prevent the welding rods used there from absorbing moisture.

Therefore, as a performance required of a welding rod to reduce hydrogen, it is necessary to improve moisture absorption resistance, but it is necessary that the hydrogen source contained in the welding rod be extremely small. In order to reduce the amount of hydrogen source contained in the welding rod, it has been attempted to select and use a raw material with a low hydrogen source content, or to use a pre-sintered raw material.

However, when a coating material made of a raw material with low moisture content is used, the coating properties may be poor and the productivity of the welding rod may be reduced. Furthermore, even if raw materials with a small hydrogen source are used in advance, they may come into contact with water added at the same time during kneading of these raw materials and the binder, and react with the water released during preliminary drying of the welding rod. It may be absorbed again as a hydrogen source.

Furthermore, welding rods are dehydrated by drying them in the air at high temperatures, but since the limestone contained in large amounts in the coating material of low-hydrogen welding rods begins to decompose, dehydration at high temperatures in the air is also used. has a limit, and it is not possible to achieve sufficient hydrogen reduction.

That is, the present invention has been made based on this knowledge, and its gist is that one or more of Te and Se is added to either or both of the core wire and the coating material at zero.
002% ≦ (Te, Se) in the core wire + 0.04 x (Te, Se) in the coating agent 0.270. acid agent,
After coating the core wire with a coating material containing the iron in the iron alloy and the binder as the remainder, dehydrogenation treatment is performed at a temperature in the range of 500 to 800 degrees Celsius in an atmosphere containing carbon dioxide gas with a dew point of 5 degrees Celsius or less. The present invention provides a method for producing an ultra-low hydrogen-based coated arc welding rod.

Note that the core wire in the present invention has chemical components other than those described in the claims. l5% or less, S! 0.3% or less, Mn
2.2% or less, PO. O3% or less, SO. O3? Hereinafter, the remainder is composed of Fe, alloying elements other than those mentioned above, and impurities.

The present invention will be explained in detail below.

First, the purpose of adding Te and Se is to reduce diffusible hydrogen by including one or more of these in the core wire or coating material or both in the range shown below.
The goal is to obtain weld metal with good crack resistance.

0.002%≦(Te, Se) in the core wire + 0.04 (Te, Se) in the coating material 0.270, that is, 0.002 to 0.2% when Te and Se are added only to the core wire. , 0.0570 to 5% when added only from the coating material, and any ratio within the range shown above when added from both the core wire and the coating material.

By the way, the reason why the amount added to the core wire is 0.04 times that of the addition to the coating material is as a result of research. This is because it turned out to be equivalent to twice as much.

That is, if one or more of Te and Se is less than 0.002% in either the core wire or the coating material of the welding rod or both,
Diffusible hydrogen in the weld metal cannot be significantly reduced, and the cracking resistance of the weld metal cannot be improved. On the other hand, these elements are 0.0
When the content exceeds 0.02%, the amount of diffusible hydrogen in the weld metal decreases rapidly. However, even if the content exceeds 0.2%, it is not very effective in reducing diffusible hydrogen compared to the addition ratio, and in fact, the slag encapsulation property, arc condition deteriorates, the weld bead deteriorates, and overall welding workability deteriorates. is deteriorating. Therefore, the addition range of Te and Se to either or both of the core wire and coating material of the welding rod produced by the method of the present invention is set to 0.002% (Te, Se) in the core wire + 0.4% coating material. Medium (Te, Se) is set to 0.2%.

Next, the welding rod manufactured by the method of the present invention contains CaCO3, MgCO3, MnCO3, BaCO3, s in the coating material.
It contains 10 to 6070 carbonates such as rcO3.

These carbonates decompose in the arc and generate CO2 gas, which has the effect of shielding weld metal and molten slag from the atmosphere, lowering the hydrogen partial pressure in the arc atmosphere, and generating basic slag.

If the amount added is less than 10%, the melting point of the slag decreases, the encapsulation properties of the slag deteriorate, and good beads cannot be obtained. Furthermore, due to the insufficient amount of gas generated, there is insufficient shielding, which is affected by the atmosphere and causes pits and blowholes, making it unsuitable. On the other hand, if it is added in excess of 60%, the amount of gas generated will be excessive, a large number of pits will be generated, the melting point will rise, and the fluidity of the slag will deteriorate, making it impossible to obtain an appropriate bead waveform and welding. Compatibility with the base material is uneven, resulting in overlap. Therefore, the carbonate addition range in the welding rod to which the method of the present invention is applied is set to 10 to 60%. Further, fluorine compounds such as CaF2, BaF2, MnF2, MgF2, etc. added to the coating material all lower the melting point of the slag and create a slag with good fluidity.

Furthermore, fluorine decomposed in the arc reacts with hydrogen in the molten metal and molten slag, and has the effect of lowering the hydrogen content in the molten metal. The addition range is 1 to 3070, and if it is less than 1%, proper slag fluidity cannot be obtained, the bead shape deteriorates, and pits are likely to occur. On the other hand, if it exceeds 30%, the viscosity of the slag becomes insufficient, making it impossible to obtain good beads. In addition, in the welding rod to which the method of the present invention is applied, a rare earth element (REM) may be added to either or both of the core wire and coating material as necessary to improve arc stability, slag fluidity, and slag flaking. It can also be added to improve the

Note that the rare earth elements (REM) herein refer to Y, Sc, and those belonging to atomic numbers 57 to 71.

The coating material of the welding rod manufactured by the method of the present invention contains a deoxidizing agent, iron in the iron alloy, and a binder as the remainder, and the deoxidizing agent here refers to Zr, Al, Mg, etc. ,S
Single metals such as i, Fe-Al, Fe-Si, Fe-T
Iron alloys such as i, Ni-Mg, Zr-Si, Al-Mg
It refers to each alloy such as. Further, the iron in the iron alloy refers to the iron content contained in the above-mentioned ferro alloy.

Furthermore, the binder refers to a binder component such as water glass typified by sodium silicate. Although not particularly limited, depending on the content of alloying elements in the core wire, alloying elements Mn, Ni, etc. may be used to improve the strength, toughness, heat resistance, and corrosion resistance of the weld metal as necessary.
There is no hindrance to adding a single metal such as Cr or MO or one or more of these iron alloys to the coating material in a total amount of 1570 or less.

In addition, due to the balance with other coating components, arc stabilizers such as iron powder and alkali components with a total content of 4070 or less, TlO2,
It is also possible to appropriately use slag forming agents such as ZrO2 and MgO in a total amount of 20% or less as a coating material component. In the present invention, two coating materials are applied around the core wire.
After coating with an ordinary welding rod coating machine so that the concentration is 0 to 40%, the product is manufactured by performing dehydrogenation treatment as described below in order to remove the hydrogen source.

Welding rods contain various hydrogen sources; metals such as core wires mainly contain atomic hydrogen, and coating materials contain adsorbed water, crystal water, compound water, etc.

Most of these can be removed simply by heating to a high temperature, but in addition to these, there are 0H groups that exist in strong chemical bonds. This 0H is not released simply by heating, but is removed by heating in an atmosphere with an appropriate oxygen potential and low water vapor partial pressure. Carbon dioxide gas is a gas that provides an atmosphere with an oxygen potential most suitable for expelling 0H chemically strongly bonded in the coating material of the welding rod.

Even if a small amount of oxygen gas is mixed with an inert gas such as argon, an oxygen potential comparable to that of carbon dioxide gas can be obtained, but decomposition of carbonates as described below cannot be suppressed. A similar oxygen potential can be obtained with a mixed gas of nitrogen and oxygen like air, but at high temperatures the nitrogen reacts with the ferroalloy in the coating material and the deoxidizing agent to form nitrides, increasing the nitrogen concentration in the weld metal. It is undesirable because it increases the hardness and deteriorates its toughness. Furthermore, the decomposition of limestone, which is mainly used as carbonate in the coating material of low-hydrogen welding rods, is influenced by the partial pressure of carbon dioxide gas in the atmosphere.

For example, carbon dioxide gas is 0.03? Decomposition begins at 450°C under 800°C, and decomposition begins even with 100% carbon dioxide at temperatures above 800°C. Therefore, in order to suppress the decomposition of limestone, the partial pressure of carbon dioxide in the atmosphere should be changed depending on the treatment temperature. When this limestone decomposes, the produced calcium oxide reacts with moisture in the air to become calcium hydroxide, which becomes a hydrogen source in welding. Furthermore, the decomposition reaction of carbonates reduces the coating strength of the welding rod and increases its dropout rate.

Furthermore, the amount of carbon dioxide gas generated during arc welding decreases, worsening the shielding effect, and making it impossible to prevent absorption of moisture, oxygen, and nitrogen from the atmosphere. Therefore, the atmosphere in the dehydrogenation treatment of the present invention needs to contain carbon dioxide gas.

The content of 0H in the coating material is proportional to the square root of the partial pressure of water vapor in the atmosphere, so in order to reduce the content of 0H and the amount of diffusible hydrogen, it is necessary to reduce the partial pressure of water vapor in the atmosphere as much as possible. However, in order to have a low amount of diffusible hydrogen so that no cracking occurs when welding extra-thick steel without preheating, the moisture content in the atmosphere must be below the level corresponding to a dew point of 5°C. There must be. Note that the presence of hydrogen or hydrocarbon gas in the carbon dioxide gas in the atmosphere is not desirable because the hydrogen source in the coating material may not be reduced but may be increased.

The welding rod still contains a considerable amount of moisture even after preliminary drying, so unless sufficiently dried carbon dioxide is introduced from outside and the furnace is completely ventilated, the moisture in the furnace atmosphere will reach the melting point. does not fall below 5°C, and OH in the coating material does not decrease.

In addition, in a directly heated furnace using the combustion heat of fuel as the heat source, care must be taken because the dew point of the atmosphere will not drop due to moisture in the combustion waste gas. If the dehydrogenation temperature is less than 500℃, the removal rate of 0H from the welding rod is extremely slow even in an atmosphere containing carbon dioxide gas with a dew point of 5℃ or less, and the amount of diffusible hydrogen is such that no cracking occurs without preheating. Impossible to drop.

Dehydrogenation treatment at temperatures higher than 800°C removes most of the 0H in the welding rod within a short time, but carbonate in the coating material decomposes even in carbon dioxide gas, causing arc sealing. deterioration of the air quality, leading to the intrusion of air, moisture, etc. from the atmosphere,
Furthermore, the rate of shedding of the coating material increases, the stability of the arc deteriorates, and welding workability deteriorates.

Furthermore, oxidation of iron alloys, deoxidizers, etc. becomes more intense. Therefore, the dehydrogenation treatment in the present invention is carried out at a temperature in the range of 500 to 800°C. The time required for the dehydrogenation treatment of the welding rod may be shorter as the temperature is higher, but a range of 10 minutes to 4 hours is sufficient.

As the heating furnace for the dehydrogenation treatment in the present invention, either a continuous heating furnace or a batch heating furnace can be used as long as the dew point of the atmosphere can be maintained at 5° C. or less.

The effects of the present invention will be illustrated in more detail by way of examples below.

Example Table 1 shows the dehydrogenation treatment conditions, and Table 2 shows the welding rod core wire (4
.

07 nm diameter) and the composition of the coating material.

A1 to A3 in Table 1 are methods of manufacturing the welding rod according to the present invention, and B1 to B5 are comparative methods of manufacturing. Table 3 shows the first
The results of various tests on welding rods under the dehydrogenation treatment conditions shown in the table are shown.

In order to investigate the performance of welding rods made under these various dehydrogenation treatment conditions, 1.1. Weld metal diffusivity hydrogen test (DOc.-A-275-70) by W method, diagonal Y-shaped restraint crack test (ZISZ3l58), welding rod sheathing test, moisture absorption test, and welding workability test were conducted.

In addition,. ．． The diffusible hydrogen test using the W method is a method that uses mercury as a hydrogen scavenging solution, and the welding current is 170A (A.C.) for the diffusible hydrogen test and the diagonal Y-shaped restraint crack test.
The welding was carried out under conditions of a welding heat of 17.0 KJ/CrlL.

The coating removal test was carried out using a 1.5 kg welding rod at 65 x 420 x 29
The coating was placed in a 0111t steel container and rotated for 3 minutes, and the shedding rate of the coating was determined.

In the moisture absorption test, the moisture absorption was determined when the welding rod was left for 24 hours at 30° C. and 80% RH.

By the way, the steel plates used in the diagonal Y-shaped restraint cracking test were HT5O for welding rods g and h, and HT8O for A, b, c, d, e, f, and i, each having a thickness of 751B. The cracking stop temperature was determined. In addition, in the diagonal Y-shaped crack test, those with a crack stop temperature of 20° C. or 0° C. were considered good. In the shedding test, those with a shedding rate of 20% or less were considered good, and in the moisture absorption test, those with a moisture absorption of 0.3% or less were considered good.

The amount of diffusible hydrogen produced by the production method of the present invention was 2.0 d/1009 or less in all cases than that produced by the comparative production method, and cracking stopped at 20°C or 0°C in the diagonal Y-shaped restraint cracking test. On the other hand, when using the comparative manufacturing method, cracking could not be stopped unless the cracking stopping temperature was 125° C. or higher.

By the way, dehydrogenation treatment condition B1 is an atmosphere containing CO2,
Although the dew point was low and the processing time was long, the shedding rate and welding workability were good because the processing temperature was low, but it was not effective in reducing the amount of diffusible hydrogen and moisture absorption.

Furthermore, under dehydrogenation treatment condition B2, the treatment temperature is high, so most of the 0H in the coating material is removed, but the carbonate decomposes and the shedding rate of the coating becomes poor, moisture absorption increases, and the stability of the arc is poor. Welding workability is poor due to poor bead shape, and the arc shielding performance deteriorates, leading to hydrogen intrusion from the welding atmosphere.As a result, it is ineffective in reducing the amount of diffusible hydrogen, and the resistance to Breakability was poor.

Next, under dehydrogenation treatment condition B3, since the treatment temperature was low, it was impossible to sufficiently reduce the amount of diffusible hydrogen, and the cracking resistance was also poor.

Under dehydrogenation treatment condition B4, the atmospheric gas is air and the treatment temperature is high, so the carbonate decomposes and the shedding rate of the coating becomes poor.
Moisture absorption also increases and welding workability is also poor.

Moreover, the decomposition of carbonates deteriorates the arc shielding properties, and the high dew point of the atmosphere generates 0H groups in the coating, resulting in a lower amount of diffusible hydrogen than that produced by normal manufacturing methods. The cracking resistance was also poor. Next, under dehydrogenation condition B5, the carbonate decomposes for the same reason as B4, the shedding rate of the coating, moisture absorption, and welding workability are poor, and the amount of diffusible hydrogen is lower than in the case of B4. Therefore, the increase was smaller than that of B4, but as a result, it was not effective in reducing the amount of diffusible hydrogen, and the cracking resistance was also poor.

The embodiments of the present invention have been explained above using AC welding using a welding rod diameter of 4.01B.
It has been confirmed that there is no significant difference in the results in AC/DC welding of tm, 5.0 mm, etc.

In this way, the present invention makes it possible to significantly reduce the amount of diffusible hydrogen in the weld metal compared to welding rods manufactured by conventional methods, and further improves cracking resistance at the same strength level, making it possible to significantly reduce the amount of diffusible hydrogen in weld metal. It has become possible to construct structures without the need for preheating.

Claims (1)

[Claims] 1. Either or both of the core wire and the coating material have T.
A coating material in which one or more of e and Se is added in the range shown below, and the balance is carbonate 10-60%, fluorine compound 1-30%, deoxidizer, iron in iron alloy, and binder. An ultra-low hydrogen-based coated arc welding rod, which is coated around the core wire and then subjected to dehydrogenation treatment at a temperature in the range of 500 to 800°C in an atmosphere containing carbon dioxide gas with a dew point of 5°C or less. manufacturing method. 0.002%≦(Te, Se) in the core wire + 0.04×(Te, Se) in the coating material≦0.2%