JPH04313492A - Low hydrogen type coated electrode - Google Patents

Abstract

PURPOSE:To improve welding workability and to obtain weld metal with satisfactory cracking resistance and mechanical property by applying coating flux which is mainly composed of rutile, calcium carbonate and fluorite and has a limited quantity of hydrous ore added on a carbon steel core wire. CONSTITUTION:The composition of the coating flux consists of, by weight, 35-58% rutile, 9-30% calcium carbonate, 1-8% fluorite, 1-4% wollastonite, 1-4% quartz sand, 3-18% Fe-Mn, 0.5-3% Fe-Si, 0.3-2.0% >=1 kind among Al, Mg and Ti and <=0.8 hydrous mineral having <=1% combined water. This coating flux is applied on the carbon steel core wire to form a coated electrode. Moreover, the total quantity of C of the electrode is regulated to <=0.14%. The total quantity of C is expressed by (C%X(alpha/100 in coating flux)+{C quantity % of core wire X(100-alpha)/100}, wherein alpha denotes the coating rate and is expressed by coating flux weight/electrode weight) X100.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a low-hydrogen coated arc welding rod, and more particularly to a low-hydrogen coated arc welding rod that provides excellent welding workability and provides weld metal with good cracking resistance and mechanical properties. It is something.

0002

[Prior Art] Among coated arc welding rods (hereinafter referred to as welding rods), low-hydrogen welding rods whose main components are lime carbonate and fluorite have been known to have excellent weld cracking resistance and It is widely used due to its excellent mechanical properties. On the other hand, compared to illuminite-based welding rods and lime-titania-based welding rods, they have disadvantages in welding workability, such as a lack of arc stability, slow melting speed, poor bead elongation, and convex beads.

On the other hand, MgCO 3 , SiO 2 , MgO
Low-hydrogen welding rods mainly composed of
It has the disadvantage that it is difficult to weld in all positions, including upward. To eliminate such drawbacks, CaCO3
, a welding rod with improved welding workability by blending SiO 2 , TiO 2 , and iron powder as main components
It is disclosed by Japanese Patent No. 9-20467.

However, according to the knowledge of the present inventors, although the welding workability has been considerably improved, it does not fully satisfy the recent strict requirements for mechanical performance and crack resistance. Furthermore, in Japanese Patent Application Laid-Open No. 50-77243, TiO
2. It is disclosed that the amount of welding fume generated is reduced by using a coating material mainly composed of CaCO 3 and SiO 2 , but the effect of reducing the amount of welding fume generated is recognized, but as mentioned above, mechanical Properties, cracking resistance, etc., have not reached the level targeted by the inventors.

Furthermore, the present inventors previously filed Japanese Patent Application No. 2-1
No. 87158 describes an excellent low-hydrogen welding rod that has good welding workability by containing rutile and lime carbonate as its main components and contains hydrated minerals such as mica or talc, and in particular does not cause any pitting on primer-coated steel plates. However, because it contains hydrated minerals such as mica and talc, it does not have sufficient cracking resistance under severe conditions.

Furthermore, in JP-A-2-258194, the present inventors limited the amount of C in the core wire and coating material, and developed a low-hydrogen-based material that has a high melting rate, a small amount of spatter, and good welding workability. A welding rod has been proposed, but although it greatly improves welding workability, it does not have good mechanical properties and crack resistance.

[0007]

[Problems to be Solved by the Invention] It is an object of the present invention to provide a low-hydrogen welding rod that has excellent welding workability and can yield weld metal with good cracking resistance and mechanical properties. .

[0008]

[Means for Solving the Problems] In order to meet the above-mentioned needs, the present invention has investigated various coating material components and core wire components, and has achieved significantly superior welding workability, crack resistance of weld metal, and mechanical properties. It has good properties, and its main points are: rutile: 35 to 58 percent (all percentages below are indicated by weight), carbonate lime: 9 to 30 percent, fluorite: 1 to 8 percent, silica. Stone: 1 to 4%, Silica sand: 1 to 4%, Fe-Mn: 3
to 18%, Fe-Si: 0.5 to 3%, one or more of Al, Mg, Ti: 0.3
It is a coated arc welding rod in which a carbon steel core wire is coated with a coating material containing 2.0% from 1.0% and 0.8% or less of hydrated minerals having 1.0% or more of bound water, and which has the following formula: The total C content of the welding rod expressed is 0.1
A low hydrogen-based coated arc welding rod characterized by a hydrogen content of 4% or less. Total C content of welding rod = (C content percentage in coating material x α/1
00) + {C content percent of core wire x (100-α)/1
00} Here, coverage rate α=(coating material weight/welding rod weight)×10
0

[0009]

[Operation] In view of the above-mentioned circumstances, the inventors of the present invention have conducted extensive research in terms of coating material and core wire composition in order to improve welding workability without deteriorating the performance of weld metal of low hydrogen welding rods. I have been progressing. As a result, as a means to solve these problems, we first decided to use rutile, carbonate lime, and fluorite as the main ingredients to improve welding workability, and to reduce the amount of hydrogen in the weld metal to maintain cracking resistance. To achieve this, it is necessary to suppress the amount of hydrated minerals added and to lower the total C content of the welding rod.Furthermore, to ensure the mechanical properties of the weld metal, the amount of oxygen in the weld metal must be reduced by adding a small amount of strong deoxidizing elements. We have discovered that this is extremely effective. The constituent elements of the present invention will be explained below.

[Rutile] Rutile is used as a slag former, viscosity modifier and arc stabilizer. It is particularly effective in improving the arc transition state of low-hydrogen welding rods. If the amount added is less than 35%, the arc condition will be unstable and the re-arc property will be poor. On the other hand, if it exceeds 58%, the viscosity of the slag increases, and the slag gets entangled with the end of the welding rod during welding, damaging the bead shape. Furthermore, the amount of oxygen in the weld metal increases, resulting in poor mechanical properties.

[Lime carbonate] Lime carbonate adjusts the viscosity of slag, enables welding in all positions, and acts as a gas generating agent, and is effective in obtaining a good quality weld metal without defects. If it is less than 9%, the effect as a gas generating agent is insufficient and pits and blowholes are likely to occur. On the other hand, if it exceeds 30%, the arc becomes weak, the slag encapsulation deteriorates, and the bead shape in the horizontal fillet becomes convex.

[Fluorite] Fluorite is used as a slag former and viscosity modifier. Fluorite is added to the coating to lower the melting point of the slag during welding, creating a fluid slag. In addition, fluorine decomposed in the arc reacts with hydrogen in the molten metal and molten slag, lowering the hydrogen content in the weld metal and creating a weld metal with good crack resistance. If the amount added is less than 1%, appropriate slag fluidity cannot be obtained, the bead shape is poor, pits are generated, and the amount of hydrogen in the weld metal increases, resulting in deterioration of cracking resistance. On the other hand, if it exceeds 8%, the arc condition becomes unstable and the slag releasability deteriorates.

[Wollastonite] Wollastonite is used as an arc stabilizer and slag viscosity modifier. Furthermore, the addition of wollastonite promotes the reaction at the interface between the molten metal and slag during welding, facilitates slag out of oxides in the molten metal, and is effective in obtaining clean weld metal. If the amount added is less than 1%, the effect will not be sufficient, while if it exceeds 4%, the amount of spatter will increase during welding, and
Slag removability deteriorates.

[Silica sand] Silica sand is used as a slag forming agent. If it is less than 1%, sufficient slag viscosity cannot be obtained, and the encapsulation of the slag in downward welding deteriorates, resulting in a convex bead shape. On the other hand, if it exceeds 4%, the viscosity of the slag increases, causing pits to occur and the arc condition during welding to become unstable.

[Fe-Mn] Fe-Mn is effective as a deoxidizing agent and an alloying agent. If it is less than 3%, deoxidation will be insufficient and pits and blowholes will occur. In addition, the mechanical properties of the weld metal deteriorate, and the strength and spread of the arc are impaired, resulting in poor bead shape. On the other hand 18
If the amount exceeds 1%, the deoxidation becomes excessive and pits are generated, and the weld metal is hardened, resulting in deterioration of crack resistance.

[Fe--Si] Fe--Si is used as an effective deoxidizer and viscosity modifier for molten metals. It acts as a deoxidizer during welding, reducing the amount of oxygen in the weld metal, improving mechanical properties, and imparting appropriate viscosity to the molten metal, which is effective in ensuring good welding workability in all positions. If the amount added is less than 0.5%, the effect of reducing the amount of oxygen will not be sufficient and welding workability will also deteriorate. On the other hand, if it exceeds 3%, the crystal grains of the weld metal will become coarse and the toughness will deteriorate.

[Al, Mg, Ti] Welding rods of the type containing a large amount of rutile, such as the welding rod of the present invention, have a lower hydrogen content compared to conventional low-hydrogen welding rods whose main components are lime carbonate and fluorite. The weld metal usually has a high oxygen content and has poor mechanical properties. Therefore, a small amount of a strong deoxidizing agent was added to improve the mechanical properties. For this purpose, Al, Mg, Ti
Addition of one or more of these is very effective. If the amount added is less than 0.3%, the effect of reducing the amount of oxygen will not be sufficient and good mechanical properties will not be obtained. On the other hand, if it exceeds 2%, deoxidation will be excessive and pits will occur, the arc condition will deteriorate, and welding workability will deteriorate. Al, Mg, and Ti can be added not only as individual metals but also as respective alloys and iron alloys.

[Hydrous Minerals] Hydrous minerals usually refer to mica, talc, etc. that have about 3% bound water, and are used to improve paintability when manufacturing welding rods and to improve pit resistance when welding primer-coated steel sheets. It is used for the purpose of enriching the amount of hydrogen in the weld metal. However, the use of hydrated minerals increases the amount of hydrogen and deteriorates the cracking resistance of the weld metal. For this reason, it is necessary to limit the use of low-hydrogen welding rods as much as possible. It was found that cracking resistance could be ensured by reducing the amount of hydrated minerals with bound water of 1.0 percent or more to 0.8 percent or less, so the amount added was limited to 0.8 percent or less.

[Total C content of the welding rod] In order to further improve the cracking resistance of the weld metal, we have found that it is effective to reduce the total C content of the welding rod. In order to investigate the effect of total C amount, rutile: 42%, carbonate lime: 22%, fluorite: 2.5%, wollastonite: 2.5%, silica sand: 3%, Fe-Si: 2%, Mg : 0.7%, mica: 0.5%, Fe-Mn: 10%, and other coating materials made of iron powder and binder, Fe-M with different C contents.
Coatings were prepared in which the amount of C in the coating was varied in six levels by using combinations of n. In addition, the amount of C is 0.03, 0.05
, 0.07, 0.08, 0.11% diameter 40
A welding rod was prepared by coating a core wire of 400 mm in length and 400 mm in length using a conventional method so that the coverage was 35%, followed by drying and firing. Figure 1 uses SM490B steel with a plate thickness of 25 mm, and JIS
These are the results of a U-shaped weld cracking test conducted at a preheating temperature of 50 degrees Celsius according to Z3157.

[0020] In FIG. 1, black circles indicate cases in which cracks occurred, and open circles indicate cases in which cracks did not occur. Total C content of welding rod is 0
．． No cracking occurred in welding rods with a content of 14% or less. Initially, attention was focused on the amount of C only in the core wire, but it has been found that C sources are also contained in the coating material, particularly in Fe-Mn and iron powder, and have a significant effect. For this reason, coating raw materials must be used with great care.

[0021] The welding rod of the present invention has a coating ratio of 25 to 45% around the carbon steel core wire by combining the above solid coating material with a binder such as water glass represented by sodium silicate and potassium silicate. After coating with a regular welding rod coating machine, it is manufactured by baking at 350 to 550 degrees Celsius to remove moisture. In addition to the specified raw materials, alloying elements such as Ni, CrMo, and Cu, iron powder, and the like may be added to the coating material of the welding rod of the present invention, if necessary.

[0022]

EXAMPLES Next, the effects of the present invention will be specifically illustrated by examples. Table 1 shows the welding rod of the present invention, and Table 2 shows the C content of the core wire, coating material composition, and various test results of the welding rod used for comparison.

[Table 1]

[Table 2]

[0023] To produce the welding rod, a core wire with a diameter of 4 mm and a length of 400 mm was coated with a coating agent to a coverage rate of 35% using an ordinary extrusion type coating machine, dried, and baked. . Using this welding rod, a U-shaped weld cracking test was conducted using SM490 steel with a plate thickness of 25 mm at a preheating temperature of 50 degrees Celsius in accordance with JIS Z3157 to check for cracking resistance. A white circle indicates that no cracking occurred, and a black circle indicates that a crack did occur.

[0024] Furthermore, in order to compare the toughness of these bars, an impact test was conducted on the welded metal. That is, JIS Z3
Welding was performed under the conditions of preheating and interpass temperature of 100 degrees Celsius, welding current of 170 A, and welding heat input of 20 kJ/cm based on JIS Z3111, and an impact test of the deposited metal was conducted in accordance with JIS Z3111. Impact test is JI
It was conducted at 0 degrees C according to SZ2242, and absorption energy of 150 J or more was considered good.

Furthermore, welding workability tests were also conducted on these welding rods. Since the welding rods of the present invention have a low total C content and limited hydrated minerals, no cracking occurs even when preheated to 50 degrees Celsius. In addition, the absorbed energy of the weld metals all showed good values of 170 J or more due to the effect of lowering the amount of oxygen by a suitable amount of Fe-Si and a strong deoxidizing agent. Furthermore, all welding rods had excellent welding workability.

On the other hand, welding rods B-6 and B-10 have a total C content of more than 0.14%, and welding rods with a hydrated mineral content of 0.8%.
Welding rods B-4 and B-7 containing more than 1.0% fluorite and welding rod B-5 containing no fluorite cracked in the U-shaped weld cracking test. Welding rod B-2 with a lot of rutile, Welding rod B-5 without strong deoxidizer, Welding rod B without Fe-Si
-7, welding rod B-8 with too much content, and welding rod B-9 with too little Fe-Mn had an absorbed energy of 120 J or less at 0 degrees C.

Furthermore, welding rod B-1 has less rutile, welding rod B-2 has too much rutile, welding rod B-3 has less lime carbonate, and welding rod B-4 has more lime carbonate. Also, welding rod B-5 does not contain fluorite because silica sand is not added, and welding rod B-6 contains too much fluorite and too much strong deoxidizing agent. -7
does not contain Fe-Si, so welding rod B-9 contains Fe-Si.
- Welding rod B-10 has too much Fe-Mn, welding rod B-11 has too much silica sand, and welding rod B-12 has too much wollastonite, so welding workability is poor. It was bad.

[0028]

[Effects of the Invention] As described above, the welding rod of the present invention has better welding workability and better cracking resistance than conventional low hydrogen type welding rods.
Moreover, a weld metal with good mechanical properties can be obtained. This will expand the fields in which welding rods will be used in the future, and will greatly contribute to the development of various industries.

[Brief explanation of the drawing]

[Figure 1] Diagram showing the C content of welding rod core wire, C content in coating material, and U-shaped weld cracking test results.

[Table 1]

[Table 1]

Claims (1)

[Claims] [Claim 1] Rutile: 35 to 58% (
(all percentages below are by weight), carbonate lime: 9 to 30 percent, fluorite: 1 to 8 percent, wollastonite:
1 to 4%, silica sand: 1 to 4%, Fe
- Mn: 3 to 18%, Fe-Si: 0.5 to 3%, one or more of Al, Mg, Ti: 0.3 to 2.0%, and 1.0% or more bond A coated arc welding rod in which a carbon steel core wire is coated with a coating material that limits the content of hydrated minerals to 0.8% or less, and the total C of the welding rod is expressed by the following formula:
A low hydrogen-based coated arc welding rod characterized in that the amount thereof is 0.14% or less. Total C content of welding rod = (C content percentage in coating material x α/1
00) + {C content percent of core wire x (100-α)/1
00} Here, coverage rate α=(coating material weight/welding rod weight)×10
0