JPH08281473A - Low hydrogen type coated arc electrode - Google Patents

Abstract

PURPOSE: To obtain an arc welding electrode having excellent workability and crack resistance by adding a binder to specific ratios of rutile, lime carbonate, fluorite, silica lime, silica sand, Si, Mn, Al, Mg, Ti and V and using the mixture as a coating material for a carbon steel core wire. CONSTITUTION: The binder is added to the coating material contg. 35 to 52wt.% rutile, 9 to 30wt.% lime carbonate, 1 to 8% fluorite, 1 to 5wt.% silica lime, 1 to 10wt.% silica sand, 3 to 15wt.% in total one or two kinds of Si and Mn, 0.1 to 3wt.% in total >=1 kinds among Al, Mg and Ti and 0.1 to 0.7wt.% V and the carbon steel core wire is coated with the mixture thereof. As a result, the use of the rutile the lime carbonate and the fluorite as the essential components is extremely useful for the improvement in the welding workability. The suppression of the amt. of the hydrous ores to be added in order to lower the quantity of the hydrogen in the weld metal and the addition of trace V are extremely effective for the improvement in the crack resistance.

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 more particularly to a low-hydrogen coated arc welding rod having excellent welding workability and good crack resistance.

[0002]

2. Description of the Related Art Conventionally, among coated arc welding rods, low hydrogen type welding rods containing lime carbonate and fluorite as main components have been widely used because they have excellent mechanical properties. On the other hand, compared with the illuminator welding rods and lime titania welding rods, they have drawbacks of welding workability such as lack of arc stability, slow melting rate, bead does not extend, and convex beads.

In order to eliminate such drawbacks, CaCO ₃ ,
A welding rod improved in welding workability by blending SiO ₂ , TiO ₂ , and iron powder as main components is Japanese Patent Publication No. Sho 49-2.
It is disclosed by Japanese Patent No. 0467. However, according to the knowledge of the present inventors, although the welding workability has been considerably improved, it does not satisfy the recent demand for severe crack resistance. Further, in Japanese Patent Laid-Open No. 50-77243, TiO
It discloses that the amount of welding fume generated is reduced by using a coating material containing ₂ , CaCO ₃ , and SiO ₂ as main components. However, although the effect of reducing the amount of welding fumes is recognized, the crack resistance does not reach the target range as described above. Further, in JP-A-4-313492, the inventors of the present invention have proposed a low-hydrogen welding rod which has a limited amount of C in the core wire and the coating material and has good welding workability and mechanical properties. The crackability does not reach the target range.

Several methods have been found as means for preventing or mitigating cracking. Among them, the most commonly used method from the past and the most effective method for welding cracking is the mother. This is a method of preheating or postheating the material. This method, the effect of reducing the cooling rate of the weld zone to reduce the formation of martensite in the structure of the weld zone and the effect of increasing the release time of diffusible hydrogen in the weld zone to suppress hydrogen embrittlement and It has the effect of mitigating the generation of residual stress. Preheating work makes welding difficult and causes a rapid increase in welding costs.Therefore, it is required to develop a covered arc welding rod that does not require a preheating temperature or that can reduce the preheating temperature and that has excellent crack resistance. ing.

As a conventional technique, for example, Japanese Patent Publication No. 59-15.
No. 758 and Japanese Patent Publication No. 60-48280 disclose coated arc welding rods in which the amount of diffusible hydrogen in the welded portion is extremely reduced by firing in a carbon dioxide atmosphere. But this method
Lack of versatility due to the high labor and cost of manufacturing the welding rod.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a low hydrogen type welding rod which is excellent in welding workability and can obtain a weld metal having good crack resistance.

[0007]

Means for Solving the Problems The present invention is to solve the above problems and comprises rutile: 35 to 52% by weight, lime carbonate: 9 to 30% by weight, fluorite: 1 to 8% by weight, wollastonite. : 1
˜5% by weight, silica sand: 1 to 10% by weight, the sum of one or two of Si and Mn: 3 to 15% by weight, Al, Mg,
Total of one or more kinds of Ti: 0.1 to 3% by weight, V: 0.1
A low hydrogen-based coated arc welding rod, characterized in that a carbon steel core wire is coated with a binder added to a coating material containing approximately 0.7% by weight.

[0008]

The present inventors have conducted extensive research to develop a coated arc welding rod which can prevent cold cracking even if the preheating temperature is reduced by means other than the method of reducing the amount of diffusible hydrogen. As a result, conventional C
Focusing on V which is added and used mainly for improving the high temperature strength property in the welding material for r-Mo steel, and by containing a specific amount in the weld metal, fine carbides are generated and carbon in the weld metal is generated. By fixing, carbon in the matrix can be reduced, thereby reducing the crack susceptibility of the weld metal, and by this, the crack resistance of the weld metal can be improved and the strength can be secured. I got it. The present invention has been made based on such knowledge, rutile, lime carbonate, fluorite as the main component from the viewpoint of welding workability improvement, the amount of hydrogen in the weld metal to improve crack resistance. It has been found that it is extremely effective to suppress the addition amount of the hydrous mineral and to add a small amount of V because it decreases. The constituent features of the present invention will be described below.

[Rutile] Rutile is used as a slag generator, viscosity modifier and arc stabilizer. In particular, it is effective for improving the transition state of the arc of the low hydrogen type covered arc welding rod. If the addition amount is less than 35% by weight, the arc state is unstable and the re-arcing property is deteriorated. On the other hand, if it exceeds 52% by weight, the viscosity of the slag increases, and the slag becomes entangled with the welding rod end during welding, impairing the bead shape.

[Lime Carbonate] Lime carbonate adjusts the viscosity of the slag, enables all-position welding, acts as a gas generating agent, and is effective in obtaining a good weld metal without defects. If it is less than 9% by weight, the effect as a gas generating agent is insufficient and pits and blow holes are likely to occur. On the other hand, 3
If it exceeds 0% by weight, the arc becomes weak, the encapsulation of the slag deteriorates, and the bead shape in the horizontal fillet becomes convex.

[Fluorite] Fluorite is used as a slag generator and a viscosity modifier, and lowers the melting point of slag during welding.
Create slag with good fluidity. Further, the fluorine decomposed in the arc reacts with the hydrogen of the molten metal or the molten slag, lowers the hydrogen of the weld metal, and forms a weld metal with good crack resistance. If the amount added is less than 1% by weight, proper fluidity of the slag cannot be obtained, the bead shape is poor, pits are generated, and the hydrogen content of the weld metal is increased to deteriorate the crack resistance. on the other hand,
If it exceeds 8% by weight, the arc state becomes unstable and the slag removability deteriorates.

Wollastonite Wollastonite is used as an arc stabilizer and a viscosity modifier for slag. Furthermore, the addition of wollastonite promotes the reaction at the interface between the molten metal and the slag during welding, facilitates slag out of oxides in the molten metal, and is effective in obtaining a clean weld metal. If the addition amount is less than 1% by weight, the effect is not sufficient. On the other hand, if the addition amount exceeds 5% by weight, the amount of spatter generated during welding increases and the slag removability deteriorates.

[Quartz sand] Quartz sand is used as a slag generator. If it is less than 1% by weight, sufficient slag viscosity cannot be obtained, the slag encapsulation property in downward welding deteriorates, the bead viscosity increases, and pits occur and the arc state during welding becomes unstable. .

[Si, Mn] Si, Mn is used as a deoxidizer and a viscosity modifier for molten metal. As a deoxidizer during welding, it is effective for reducing the oxygen content of the weld metal, improving the mechanical properties, and imparting appropriate viscosity to the molten metal, and ensuring good welding workability in all positions. If the addition amount is less than 3% by weight, deoxidation becomes insufficient and pits and blow holes occur. In addition, the spread of the arc is impaired and the bead shape deteriorates. On the other hand, if it exceeds 15% by weight, deoxidation becomes excessive and pits are generated, the weld metal is hardened, and crack resistance is deteriorated.

[Al, Mg, Ti] A welding rod of a type containing a large amount of rutile, like the welding rod of the present invention, is a conventional low-hydrogen coated arc welding rod containing lime carbonate and fluorite as main components. In comparison, the weld metal has a large amount of oxygen and is generally inferior in mechanical properties. Therefore, add a small amount of strong deoxidizer,
The mechanical properties were improved. For this, Al, M
It is effective to add one or more of g and Ti. If the amount added is less than 0.1% by weight, the effect of reducing the amount of oxygen is not sufficient and good mechanical properties cannot be obtained. On the other hand, if it exceeds 3% by weight, deoxidation becomes excessive, pits are generated, the arc state is deteriorated, and welding workability is deteriorated. Al,
Mg and Ti can be added as their respective alloys and iron alloys in addition to their respective elemental metals.

[V] In order to further improve the crack resistance of the weld metal, it was found that it is effective to add a specific amount of V to the weld metal. To investigate the influence of the appropriate V amount, V: 0 to 1.3% by weight, rutile: 44% by weight, lime carbonate: 20% by weight, fluorite: 2.5% by weight, wollastonite: 2.
5% by weight, silica sand: 4% by weight, Si: 1% by weight, Mn: 7
A coating material composed of wt%, Ti: 0.8 wt%, other iron powder and a binder was prepared.

A core wire having a diameter of 4 mm and a length of 400 mm was coated and coated by a conventional method so that the coverage was 33%, dried and fired to prepare a welding rod. Table 1 shows the results of a U-shaped weld cracking test using a SM490B steel having a plate thickness of 50 mm at a preheating temperature of 50 ° C. according to JIS Z3157. In the table, black circles indicate cracks and white circles indicate no cracks. V content of the coating agent is 0.1
No cracks occurred in the welding rod of 0.7% by weight.

[0018]

[Table 1]

The welding rod of the present invention uses the above-mentioned coating agent with a binder such as sodium silicate or water glass typified by potassium silicate so that the coating rate is about 25 to 45% by weight around the carbon steel core wire. It is manufactured by coating and coating with a conventional welding rod coating machine and then firing at 350 to 550 ° C. to remove water. In addition to the specified raw materials, alloying elements such as Ni, Cr, Mo and Cu, iron powder and the like can be added to the coating material for the welding rod of the present invention, if necessary.

The carbon steel core wire referred to here is JIS
A welding rod core wire corresponding to G3523 can be used, and C: 0.01 to 0.04% by weight, N: 0.001 to 0.005% by weight, and O: 0.00 to improve mechanical performance.
It also indicates a core wire or the like reduced to 1 to 0.01% by weight. Hereinafter, the effects of the present invention will be described more specifically based on Examples.

[0021]

EXAMPLES Tables 2 and 3 show the coating compositions of the welding rods of the present invention and the welding rods used for comparison and the results of various tests.

[0022]

[Table 2]

[0023]

[Table 3]

In producing the welding rod, a diameter of 4 mm,
On a core wire having a length of 400 mm, a coating agent is coated by a normal extrusion coating machine so that the coating rate becomes 33% by weight,
It was dried and baked. In order to test crack resistance with this welding rod, SM490 steel with a plate thickness of 50 mm was used, and JIS Z
According to 3157, a U-shaped weld cracking test was conducted at a preheating temperature of 50 ° C., and the presence or absence of cracking was investigated. The white circles were those without cracks, and the black circles were with cracks. Also,
Welding workability tests of these welding rods were also conducted.

In the welding rod of the present invention, since an appropriate amount of V was added to the coating material, cracking did not occur at a preheating temperature of 50 ° C. in any case. Moreover, all the welding rods had excellent welding workability. Further, the amount of diffusible hydrogen was measured by a gas chromatographic method based on JIS Z3118 “Method for measuring hydrogen amount in steel welded portion”. All the welds of the present invention are 4 to 6 m.
1/100 g, D50 according to JIS Z3212
16 Hydrogen content of 15 m1 / 100 g or less was sufficiently satisfied.

On the other hand, welding rods B-2 and B-6 in which the amount of V in the coating material exceeds 0.7% by weight, welding rod B-1 containing no V in the coating material, and welding containing no fluorite. Stick B-3 is U
Cold cracking occurred in the shape weld cracking test. Furthermore, since welding rod B-4 has too much rutile, welding rod B-5 has little rutile, and welding rod B-6 has little lime carbonate,
Since welding rod B-7 contains too much lime carbonate, welding rod B-3
Does not contain fluorspar, welding rod B-9 contains too much fluorspar, so welding rod B-9 does not contain wollastonite, welding rod B-8 does not contain silica sand. For,
Since welding rod B-1 contains too much Si and Mn, welding rod B-
Since No. 2 did not contain Si, each had poor welding workability.

[0027]

INDUSTRIAL APPLICABILITY As described above, the welding rod of the present invention is a low-hydrogen coated arc welding rod having excellent welding workability and excellent crack resistance as compared with the conventional low-hydrogen welding rod. This will increase the field of use of welding rods in the future and is extremely large in contributing to the development of various industries.

Claims (1)

[Claims] 1. A low-hydrogen coated arc welding rod comprising: rutile: 35-52% by weight, lime carbonate: 9-30% by weight, fluorite: 1-8% by weight, wollastonite: 1-5% by weight, silica sand 1 to 10% by weight, one or two kinds of Si and Mn in total: 3 to 15% by weight, one or more kinds of Al, Mg and Ti in total: 0.1 to 3% by weight, V: 0.1 A low-hydrogen coated arc welding rod, which comprises coating a carbon steel core wire by adding a binder to a coating material containing approximately 0.7% by weight.