JPS6048280B2 - Manufacturing method of low hydrogen coated arc welding rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a welding rod, which produces a weld metal with excellent crack resistance without deteriorating the adhesion of the welding rod coating.

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, when welding 50 kg/first grade steel with a plate thickness of 25 m 77 l or more, a low hydrogen welding rod is used and preheating is performed to 75 to 150'C depending on atmospheric conditions and the degree of restraint. However, the preheating work that is carried out 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 a welding rod with extremely excellent fragility.

In order to obtain a weld metal with excellent crack resistance that does not cause cracking even when extremely thick steel is welded without preheating, the main condition is to minimize the amount of diffusible hydrogen. The sources of diffusible hydrogen in weld metal are mainly crystal water contained in the welding rod, hydroxyl groups, or hydrogen sources with a higher degree of bonding than these (hereinafter referred to as OH), as well as moisture due to moisture absorption of the coating and the atmosphere during welding. There is moisture contained in it, which is dissociated by arc heat and invades the weld metal. Among these methods, there is a method of improving the moisture absorption resistance of the coating, as described in Japanese Patent Publication No. 48-34485, but this method merely reduces the amount of moisture absorption, and is not a proactive method. It has not been effective in reducing the amount of diffusible hydrogen.

Rather, in order to obtain a weld metal with excellent cracking resistance, it is necessary to reduce crystal water, hydroxyl groups, and highly bonded OH contained in the welding rod coating. By the way, low-hydrogen coated arc welding rods contain carbonates, fluorides, other slag forming agents, deoxidizing agents, ferroalloys, iron powder, paints, etc., along with water glass, in a core wire made of mild steel or alloy steel. It is mixed and coated.

All these feedstocks contain hydrogen sources to varying degrees.

Metals such as core wires, ferroalloys, and iron powder contain hydrogen mainly in atomic form, while carbonates, fluorides, slag forming agents, coating agents, and water glass contain adsorbed water, water of crystallization, hydroxyl groups, and other components. It is contained in the form of 0H, which exists in the chemical structure of However, simply firing the welding rod in air at a high temperature will remove adsorbed water, water of crystallization, and hydroxyl groups, but will not remove OH, which is strongly chemically bonded. Furthermore, when the firing temperature is set to 500°C or higher, a large amount of limestone contained in the coating material decomposes and forms CaCO. →CaO produced by the reaction of CaO+CO2 reacts with moisture in the firing atmosphere or atmospheric moisture during the cooling process after firing, producing Ca(0H). It forms a new source of hydrogen, decomposes limestone, deteriorates arc shielding, and incorporates moisture from the atmosphere during welding.
On the contrary, the amount of diffusible hydrogen increases, and in the end, the amount of diffusible hydrogen cannot be reduced. Moreover, the high temperature firing and the decomposition of limestone further significantly deteriorate the adhesion. Although raw materials with a low hydrogen content are selected and used, hydrogen can also be reduced by using pre-calcined raw materials or the like.

However, when a coating material made of a raw material with low moisture content is used, the coating properties are poor and the productivity of the welding rod is reduced. On the other hand, even if raw materials with a small hydrogen source are used in advance, it is difficult to add them at the same time when kneading these raw materials and the binder. When it comes into contact with water, it further reacts with the water released during pre-drying and is absorbed again as a hydrogen source. In any case, with conventional methods, it is impossible to obtain a coated arc welding rod with excellent crack resistance that does not cause cracks even when extremely thick steel is welded without preheating.

Therefore, in order to make this possible, as mentioned above, it is necessary to prevent the formation of CaO in the limestone in the coating material and reduce the strongly chemically bonded 0H. (It is necessary.

The main sources of this OH are limestone, fluorite, which is the main component of the low hydrogen-based coated arc welding rod coating material, and water glass as a caking agent. (That is, in Figure 1, CaCO: 50%, BaCO3; 7%, CaF2
: 12%, Fe-Si: 14%, Mn: 35%, TiO
. : 6%, iron powder; 7.5%.
O. ;28%. K2; 6.0%, Na2O; 10.0%
So, Na2O/K. The weight ratio of O: 167, 21.2% of water glass was added, and the diameter was 4. c) Tfm) Length 400T
! Un(7) CO coated with a mild steel core wire specified in JIS G3523. CO that prevents the formation of CaO in the limestone in the welding rod coating material fired at various temperatures from 400 to 900°C for 1 hour in an atmosphere with varying mixing ratios of CO and air. These are the test results for determining the concentration. As is clear from this test result, it can be seen that the effect of preventing CaO generation begins to appear at a CO2 content of 2% or higher and a firing temperature of 500°C or higher; however, the higher the firing temperature, the higher the carbon dioxide content. Since a gas concentration atmosphere is required, it is necessary to change the carbon dioxide concentration of the firing atmosphere depending on the firing temperature.

In this case, when the firing temperature is lower than 500° C., the 0H in the coating material (particularly the 0H in the water glass) still maintains its gel-like structure, so naturally a large amount of 0H remains. On the other hand, CO.

Ar, He, N instead. When heated at a temperature of 500°C or higher using an atmosphere of air or a mixture of these gases, the limestone in the coating turns into CaO, the gel-like structure of water glass is destroyed, and only the adhesion of the coating deteriorates. However, a large amount of strongly bound 0H still remains. Moreover, since CaO reacts with moisture to form Ca(0H)2, the amount of diffusible hydrogen increases. Moreover, the adhesion of the coating is significantly deteriorated due to the destruction of the gel structure of water glass and the decomposition and re-reaction of limestone. However, more than 2% C
When fired at a temperature of 500°C or higher in an atmosphere containing O2,
Gelled water glass SiO.

and coating agents limestone (CaCO3) and fluorite (CaF2).
) reacts according to the reaction formula β102+3cac03+CaF2 →3Ca0・CaF2・2Si02+3C02, and the gel-like structure is destroyed and the mineralically stable Cuspidine (3Ca0・CaF2・2
The production of Si02) is promoted, and as this reaction progresses, the 0H contained therein is released outside the system, reducing the amount of 0H in the coating material and significantly reducing the amount of diffusible hydrogen.

When the calcining temperature exceeds 800°C, the limestone in the coating decomposes, and due to the selective reaction of CaCOa → CaO + CO2, Cuspidine is not produced and the water glass is reduced to zero.
H is not reduced.

In addition, the decomposition of lime deteriorates the arc shielding properties, allowing atmospheric moisture to enter during welding, and moisture in the firing atmosphere or sintering. During the cooling process of the welding rod after welding, it reacts with moisture in the atmosphere and forms Ca(0H). is formed, and the amount of diffusible hydrogen is increased by those produced by conventional sintering methods, and at the same time the adhesion of the coating is significantly degraded. The present inventors based on this knowledge, Na.

O and K. O is Na. After coating the core wire with a coating material containing an O/K2O weight ratio of 1 or more, firing is performed at a temperature in the range of 500 to 800°C in an atmosphere containing 2% or more carbon dioxide gas. In Japanese Patent Application No. 55-11738, a low-hydrogen-based Fukuhide arc welding rod was previously proposed, which made it possible to significantly improve the cracking resistance of weld metal. The amount of 0H in the coating material can be determined by, for example, placing the coating of a welding rod in a graphite crucible and heating it at 2100°C.
It is possible to reduce 0H to hydrogen by heating to a certain degree and quantify it by means such as gas chromatography. By the way, the cracking resistance of the weld metal formed by the welding rod obtained by adopting such a manufacturing method is dramatically improved, but on the other hand, the adhesion of the coating is Although various attempts have been made to improve sexual quality, no drastic solution has yet been found.

For this reason, it is currently difficult to prevent the coating from falling off by taking passive measures such as reducing the impact as much as possible during transportation of the packaging materials for welding rods. Therefore, the inventors of the present invention continued to study the possibility of improving the adhesion of the coating by firing at a high temperature of 500 to 800°C.
iO.

and Ka. O, K. It has been found that the adhesion of the coating can be significantly improved by adding water glass having a molar ratio of 2.0 to 2.6 with O. Hectorite is a type of montmorillonite mineral. That is, the present invention applies SiO to a coating material containing 0.1 to 3% hectorite.
After adding and kneading water glass with a molar ratio of 2 and alkaline content of 2.0 to 2.6 and coating the core wire, the mixture is heated at a temperature of 500 to 800°C in an atmosphere containing 2% or more carbon dioxide gas. This is a method for manufacturing a low hydrogen-based coated arc welding rod, which is characterized by firing in a .

In addition, the molar ratio of water glass as used in the present invention is expressed by the following calculation formula.

The present invention will be explained in detail below.

Figure 2 shows CaCO.

;47%, BaCO. 7%, CaF2; 10%, Ti
O2; 13%, Fe-Si; 13%, Mn: 4%, Ni
;3.7%, Cr;0.4%, Fe-MO;1.9%,
Hectorite: Added in a range of 0.94%, molar ratio: 1.
After adding 21% of water glass of 6 (marked with Δ in the figure), 2.3 (marked with O in the figure), and 2.9 (marked with an opening in the figure), respectively, the rod diameter was 4.
0Twt) coated mild steel core wire specified in JIS G3523 with a length of 400TfUrL, CO2 is 20%
These are the test results for the rate of shedding of the coating of welding rods fired at 750°C for 1 hour in an atmosphere of In addition, Fig. 3 shows Ca
CO3; 50%, BaCO3: 6%, CaF2; 15%
, TiO2; 9.5%, Fe-Si; 13%, Mn; 3
．． 5%, Ni; 2.0%, Fe-MO; 1%, Hect.
Light; 0 (Δ mark in the figure), 1.3% (○ mark in the figure), 3
．． After adding 21.4% of each type of water glass with a molar ratio of 1.5 to 2.9, the rod diameter was 4.5% (marked in the figure). Hi, length 400wL (7) JISG3523
Coated and coated mild steel core wire specified in
The results of a test were conducted to determine the shedding rate of the coating of welding rods manufactured by firing at 580° C. for 1 hour in an atmosphere of According to the test results shown in Figures 2 and 3, in order to improve the adhesion of the coating, 0.1% or more of hectorite should be added and the molar ratio of water glass should be 1.6 to 2.6. There is a need.

However, if more than 3% of hectorite is added, the drying rate of the coating will be too fast, and in the drying process following painting,
This will cause coating cracks and significantly reduce manufacturing yield.

(Z area in the figure) Also, perhaps because the amount of hectorite added was excessive, the fluidity of the slag became inappropriate, resulting in poor welding workability.

Moreover, the molar ratio of water glass is 2. If the molar ratio is too low, the drying rate of the coating is slow, and the coating is frequently chipped and cracked during the coating and drying steps, resulting in a significant decrease in production yield.

In addition, in terms of welding workability, the coated tube is weak and the stability of the arc is also poor. (X region in the figure) Furthermore, if the molar ratio of water glass exceeds 2.6, the adhesion of the coating will deteriorate, and the drying speed of the coating will be too fast, resulting in frequent coating cracks and a markedly poor manufacturing yield. I'm going to growl.

(Z area in the figure) Therefore, in the present invention, hectorite is added to the welding rod coating in a range of 0.1 to 3%, and the molar ratio of water glass is 2.0 to 2.6.

Further, in the present invention, CaCO is included in the coating material.

, MgCO. , MnCO. , BaCO, , SrCO. 0.5-60% of one or more carbonates such as CaF. ,B
aF. , MgF2, SrF2, MaF, AlF3 and other fluorides in an amount of 0.5 to 30%, SiO. , MgO
, TiO. , Al2O. , zrO2 and the like can be added in an amount of up to 20%. Also,
Single metals such as Zr, Mg, Al, Mn, and Si, iron alloys such as Fe-Al, Fe-Si, and Fe-Ti, and alloys such as Si-Mn, Zr-Si, and Al-Mg can be used as deoxidizing agents. One or more of these can be added.

In addition, depending on the alloying element content of the core wire, if necessary, alloying elements such as *l'Ni, Cr, and MO may be used to improve the strength, toughness, heat resistance, and corrosion resistance of the weld metal. One or more of these iron alloys can be added to the coating in a total amount of up to 15%.

The coating agent described above is mixed with the water glass mentioned above, and coated around the core wire at a ratio of 20 to 40% of the total weight of the welding rod using a normal welding rod coating machine. After preliminary drying at a temperature of 100 to 350°C,
500-800°C in an atmosphere containing 2% or more carbon dioxide gas
It is fired at a temperature of .

The time required for firing in the production of the welding rod of the present invention may be shorter as the temperature is higher, but it is sufficient if it is in the range of 1 to 4 hours. Further, as the firing furnace, either a continuous heating furnace or a batch type heating furnace can be used. Furthermore, since it is possible to further reduce the amount of diffusible hydrogen when the dew point of the firing atmosphere containing carbon dioxide is 5° C. or lower, it is preferable to control the dew point of the firing atmosphere to 5° C. or lower.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

Example Table 1 shows the firing conditions for the welding rod.

(Note) What is the gas composition of the atmosphere in volume percentage? A1-A4
are the valley firing conditions in the manufacturing method of the present invention.

Under the firing conditions of the welding core wire (4''-diameter) and the coated connecting rod shown in Table 2, B1 to B4 used comparative fungicide compositions,
The welding rod coated with a normal welding coating machine is
Table 3 shows the results of investigating the manufacturing yield during manufacturing under the firing conditions shown in the table and conducting various tests.

The test was a diffusible hydrogen test of weld metal using the l-l-w method (
DOc■-A-275-70), diagonal Y-shaped restraint cracking test (JIS Z3l58), coating shedding test, and welding workability test were conducted, and the manufacturing yield of the welding rod was investigated.

Note that the diffusible hydrogen test using the I-I-W method is a method that uses mercury as a hydrogen scavenging solution, and the diffusible hydrogen test and the diagonal Y-shaped restrained crack test are performed using a welding current of 170 A (A
-C), the welding heat input was 17 KJ/CwL.

By the way, the steel plates used in the diagonal Y-shaped restraint cracking test were welding rods Al, bl, b2 and HT5O, a2, a3, b3, b.
4 is HT6O, a4, a5, b5, b6 are HT8O with various plate thicknesses of 50-MfL, and the crack stop temperature was determined by a diagonal Y-shaped restraint crack test.

In addition, in the diagonal Y-shaped restraint cracking test, those with a crack stop temperature of 20° C. or 0° C. were considered good. In the coating shedding test, a 1.5K9 welding rod is placed in a 65 x 420 x 290 wrIn steel container, and the coating is rotated 100 times for 3 minutes to determine the coating shedding rate, and two items with a shedding rate of 10% or less are considered good. And so.

In addition, the manufacturing yield of welding rods is 97% regardless of the defect content.
% or more was considered good.

In any case, the amount of diffusible hydrogen in the welding rod under the firing conditions of the present invention is 2.0 mt/100 y or less, diagonal 2 Y
In the shape restraint cracking test, cracking stopped at 20°C or 9°C.

On the other hand, under the comparative firing conditions, the amount of diffusible hydrogen was large in all cases, and cracking could not be stopped unless the preheating temperature was 150° C. or higher.

By the way, the comparison firing conditions are CO.

Although the firing time is long in an atmosphere containing hydrogen, the firing temperature is low, so the adhesion of the coating and welding workability are good, but the amount of diffusible hydrogen is large. In addition, the comparative firing conditions were CO.

The firing temperature is also appropriate in an atmosphere containing C.
If the concentration of O was insufficient, certain acid salts decomposed, resulting in poor coating adhesion, poor arc stability, poor bead shape, and poor welding workability. In addition, due to the deterioration of arc shielding, moisture from the atmosphere during welding becomes atomic hydrogen due to arc heat and enters the weld metal, increasing the amount of diffusible hydrogen, resulting in poor cracking resistance and Ta.

Next, comparative firing condition B3 is a 100% CO2 atmosphere, but the firing temperature is high.

Similarly, the carbonate decomposed, the adhesion of the coating was poor, welding workability was poor, and the amount of diffusible hydrogen increased, resulting in poor cracking resistance. Furthermore, comparative firing condition B.

Since the atmosphere is 100% air and the firing temperature is high, B
,,B. The carbonate decomposed in the same manner as in the previous example, the shedding rate of the coating was poor, the welding workability was poor, the amount of diffusible hydrogen was large, and the cracking resistance was poor. In addition, for welding peaks 1 to A5, by combining the firing conditions of the present invention, the coating shedding rate was all 10.
% or less, and there are fewer coating chips, scratches, and cracks during manufacturing.
The manufacturing yield was 97% or more, and the welding workability was also good.

On the other hand, welding rod BL does not contain hectorite,
In addition, because the molar ratio of water glass is low, the drying speed of the coating is slow, resulting in frequent chips, scratches, and cracks in the coating, resulting in poor manufacturing yield.
Moreover, the adhesion of the coating and the welding workability were also poor.

Welding rod B2 has a suitable amount of hectorite added, but since the molar ratio of water glass is low, when combined with the firing conditions of the present invention, the adhesion is good, but the welding workability is poor, and welding rod B2 has a low molar ratio of water glass. As in the previous case, the coating cracked frequently and the manufacturing yield was poor.

Welding rod B3 had an appropriate molar ratio of water glass, but since hectorite was not added, the adhesion of the coating was poor and the manufacturing yield was also somewhat poor.

Although the molar ratio of water glass in weld bar B4 is appropriate, the addition of too much hectorite causes the coating to dry too quickly, resulting in frequent coating cracks, the manufacturing yield is poor, and the physical properties of the slag are poor. This was not good, and welding workability was also poor.

Although welding rod B5 has an appropriate amount of hectorite added,
The adhesion of the coating was poor because the molar ratio of water glass was too high, and the drying rate of the coating was too fast, resulting in frequent cracking of the coating and poor production yield.

Welding rod B6 has an excessive amount of hectorite added and the molar ratio of water glass is also too high, so the adhesion of the coating is poor, and the drying rate of the coating is significantly faster, resulting in more cracking of the coating than in the case of welding rod B4. This occurred frequently, and the manufacturing yield was the worst. Furthermore, welding workability was also poor due to the excessive amount of hectorite added.

Above, in the embodiments of the present invention, the results of AC welding with a rod diameter of 4.0TnnL have been explained, but we have separately explained the results of AC welding with a rod diameter of 3.
．． 277!771) 5.077!771), it has been confirmed that there is no significant difference in the results.

In this way, the amount of diffusible hydrogen in the weld metal produced by the welding rod manufactured based on the manufacturing method of the present invention can be significantly reduced compared to that produced by the welding rod manufactured by the conventional method, resulting in the same strength. The cracking resistance is significantly improved at
It is now possible to turn structures made of extremely thick steel plates without requiring preheating.

Moreover, the adhesion of the coating became even better. This is something that cannot be achieved using conventional methods for manufacturing low-hydrogen coated arc welding rods, and it will greatly contribute to the development of various industries.

[Brief explanation of the drawing]

Figure 1 shows the relationship between firing temperature and carbon dioxide concentration in the firing atmosphere, Figure 2 shows the relationship between the amount of hectorite in the coating and the shedding rate, and Figure 3 shows the relationship between the molar ratio of water glass and FIG. 3 is a diagram showing the relationship between dropout rates.

Claims (1)

[Claims] 1 A coating material containing 0.1 to 3% hectorite is
After adding and kneading water glass with a molar ratio of iO_2 and alkaline component of 2.0 to 2.6 and coating the core wire,
A method for producing a low-hydrogen coated arc welding rod, which comprises firing at a temperature of 500 to 800°C in an atmosphere containing 2% or more carbon dioxide gas.